J Pharm Bioallied Sci.2011 Jan-Mar;3(1):
170172.doi:10.4103/0975-7406.76505PMCID:PMC3053518Biofunctional
prosthetic system: A new era complete dentureVandana SainiandRuchi
SinglaFaculty of Dentistry, Dr. H.S.J. Dental College, Punjab
University, Chandigarh, India.
E-mail:[email protected] Journal of Pharmacy and
Bioallied SciencesThis is an open-access article distributed under
the terms of the Creative Commons Attribution License, which
permits unrestricted use, distribution, and reproduction in any
medium, provided the original work is properly cited.Sir,This
clinical report describes the prosthetic rehabilitation of an
edentulous patient,who was dissatisfied from her 8-year-old
denture. To give her a better fit, we opted Biofunctional
Prosthetic System (BPS) for the new prosthesis. BPS is the system
designed to work with the body in a biologically harmonious way,
maximizing function, and giving comfort and natural appearance to
the patient. The functional impression technique and simulation of
the jaw movements by the Stratos 200 articulator in BPS ensure that
BPS denture meets most exacting requirements.[1]BPS denture meets
the esthetic demand of patients with its unique Ivoclear teeth,
which replicate anatomy of the natural tooth Ivoclear teeth are
made up of 3 layers of cross-linked acrylic resins that contribute
to a life-like appearance and resistance to wearing. BPS system
uses a controlled heat/pressure polymerization procedure during
which time the exact amount of material flows into the flask to
compensate for shrinkage, which ensures a perfect fit. This
pressure also optimizes the physical properties of the denture.
[2]A 60-year-old edentulous woman with a chief complaint of
compromised function and esthetics was treated in the clinic.
Intraoral examination showed resorbed ridges and masticatory
dysfunction [Figure 1]. An extraoral examination revealed flattened
mandibular plane. She was wearing dentures with attrited teeth and
worn out denture base. A significant loss of vertical dimension
affected the temporomandibular joint. Hence, a BPS denture was
planned to give her a better fitted prosthesis.The BPS recommends
impression making similar in principle to the mucostatic method
that minimally compresses tissues, using a combination of
irreversible hydrocolloids of varying densities together in the
same impression.[3] Low-density impression material (syringe Acc
Gel) was syringed into the vestibular area and the occlusal centric
tray was loaded with high-density hydrocolloid and inserted into
the patients mouth to get the initial vertical dimension [Figure
2]. This vertical dimension was used for mounting the casts
obtained from initial impressions, taken with Accu-trays (different
from conventional denture trays) with an extra flange to cover the
vestibular areas and extended distal part to cover the
retromandibular pad area more efficiently [Figure 3]. Custom trays
were made on the primary casts. The Gnathometer M tracing device
was attached to the casts, which facilitates the clinical
procedures of secondary impression making, face-bow record and jaw
registration [Figure 4].The secondary impression was taken with
zinc oxide eugenol impression paste [Figure 5]. Casts were poured
and a wax-up denture was made for the trial [Figure 6]. After
checking the fit and occlussal relations, the denture was sent to
the laboratory. Dentures were cured with injection molding
technique [Figure 7] using Ivocap high-impact plus denture base
material.[4] Necessary adjustments were done and the dentures were
delivered to the patient.The patient was recalled after 6 months
and examined. There was no occlusal disharmony or sore spots. The
patient was very much satisfied with her new prosthesis and she
showed her gratification for the comfortable prosthesis and a
younger look.AcknowledgmentsWe are grateful to Mr. Chauhan, Dental
Technician, Chauhan Dental Lab, Sec-32, Chandigarh, India, for his
laboratory work.References1.Available from: BPS Dentures
smilebydesign_in Best Dentist In Delhi[Last cited in
2010]2.Available
from:http://www.familydentalhealthcentre.com/completedenture[Last
cited in 2010]3.Roraff AR, Stansbury BE. Errors caused by
dimensional change in mounting materials.J Prosthet
Dent.1972;28:24752.[PubMed: 4558968]4.Patel BN. Acrylic removable
prosthesis- an integral part of modern Day
Dentistry.Famdent.2005;6:624.Figures and TablesFigure 1
Resorbed ridgesFigure 2
Occlussal centric tray loaded with impression for recording
initial vertical dimensionFigure 3
Biofunctional prosthetic system impression traysFigure 4
Bite registration through Gnathometer MFigure 5
Secondary impression-making with zinc oxide eugenol pasteFigure
6
Wax-up trial for the patientFigure 7
Acrylized denture
Articles fromJournal of Pharmacy & Bioallied Sciencesare
provided here courtesy ofMedknow PublicationsJoint Vibration
Analysis in Routine Restorative DentistryWritten by Mark W.
Montgomery, DMDFriday, 10 September 2010 12:46INTRODUCTIONClinical
ConsiderationsThe urgency for taking the temporomandibular joint
(TMJ) condition into account is the pervasiveness of
occlusion-related disease and the recent advances in restorative
and prosthetic systems. Clinical best practices would include the
screening and diagnosis of the temporomandibular condition in the
evaluation and treatment of the occlusion-related diseases such as
abfractions, wear, mobility, periodontal damage, fractured teeth,
and abnormal parafunctional muscle activity.During routine
dentistry, in the vast majority of dental practices, 2
oversimplified assumptions are made that then determine the course
of occlusion, mastication, and dental anatomy decisions for the
patient. These assumptions are: (1) that the asymptomatic TMJ is
either healthy, or as healthy as can be expected for this patient,
and (2) that maximum intercuspal position (MIP) is the most stable
position in which to reference the patients dental care.
Figure 1.Preoperative photo.Figure 2.Deprogramming appliance (in
anterior contact only).
Figure 3.Stabilized bite registration for Joint Vibration
Analysis (JVA) (BioRESEARCH) testing.Figure 4.Maximum intercuspal
position versus stable condylar position on the articulator.
Figures 5a and 5b.Preoperative JVA with disc derangement.
Figures 6a and 6b.Before and after JVA.
Figure 7.Before and after case photos.
These 2 assumptions are commonly adopted as the default scenario
for dental care for several reasons. Namely, the clinical
manifestations of TMJ derangements are often encountered at a later
or more chronic stage that does not lend itself easily to diagnosis
and/or treatment. Many of these later-stage, chronic disc
derangements are often asymptomatic before and after routine dental
care. Furthermore, most of these later-stage TMJ derangements are
not correctable withroutinedentistry.Also, the MIP is seemingly the
most easily determined position of the interface between the
maxilla and mandible due to patient accommodation and preference of
interdigitated teeth. Additionally, the facet-to-facet
interdigitation of the teeth is routinely utilized to relate the
maxillary teeth to the mandibular teeth on laboratory models of the
patients dentition.Relying on either or both of these assumptions
creates or perpetuates the existing conditions, pathologies, and
the position of the mandibular condyles and their respective disc
and ligament apparatus. This perpetuation of the current status
puts even the most limited restoration in jeopardy of early failure
or worsening of the patients condition.While the majority of
patients without reported symptoms will accommodate or continue to
accommodate to this condition/position of the condyles, the glaring
signs of occlusal disease and pathology are staring the
practitioner in the face. These signs are primarily being treated
symptomatically or ignored, rather than systematically evaluated
and treated at the source of the problem.This situation is
frustrating for dentists, as they often feel that they dont have
the opportunity or urgency of symptoms to be able to take control
of the problems. Additionally, there has been a challenge to
integrate the concepts of occlusion with the condylar position.
Many dentists have studied with various occlusion camps only to
become confused regarding the relevance of the condylar position or
which condylar position is correct. This debate has continued for
years as to the best way to define and establish what a normal
condylar position is. As a result, the only established norms for
occlusion have relied on the systems created to produce successful
clinical results and idealistic concepts that are perpetuated in
texts and academia.Consequently, dentists end up discussing their
philosophy of occlusion without regard to routine objective
measurements that could establish the relative health or normality
of the stomatognathic system.This situation is also frustrating for
patients, as they are at a loss as to what is normal for them. How
much deterioration of their dentition is acceptable? Why, when they
return to the dentist year after year, is something wrong, every
time? And which of their symptoms are important enough to report to
their dentist? They often end up years down the road with thousands
of dollars of dentistry done only to discover that their wear
and/or pain continues, and their condition is never truly under
control, despite their best intentions and investment.Technological
Implications ofJoint Vibration Analysis
Lou Shuman, DMDDr. Peter Dawson wrote, on page 3 of his latest
text Functional Occlusion: From TMJ to Smile Design, that all
occlusal analysis begins with the TM joints. The temporomandibular
joint (TMJ) is widely considered to be the skeletal base of the
stomatognathic system. As dentists, we understand that TMJ
stability is critical to a stable and predictable occlusion. It has
become clear that a key component of the stomatognathic health is
the interplay among the teeth, muscles, and the TMJs. Without a
pair of stable TMJs, a stable occlusion is next to impossible, and
this has a direct and obvious impact on the success or failure of
our restorative, cosmetic, and orthodontic treatments. Without a
clear objective and detailed assessment of TMJ function, we cannot
predict the future success (or failure) of our dental treatments,
nor can we determine if subsequent TMJ pathologies previously
existed, or were the result of our dental work.We need a tool that
can alert us to subclinical pathology before we begin treatment,
one that can quickly and accurately assess TMJ function (or
dysfunction) and compare it to previous screenings to see if our
patients TMJs are improving, stable, or getting worse. We also need
a tool that can immediately assess the impact of our treatments on
TMJ function. A suitable device for screening, assessment of
pathology progression, and treatment outcome analysis has been hard
to find.The TMJ has been the subject of much confusion because the
quick and inexpensive methods of screening for TMJ pathology are
either subjective and unreliable (auscultation, palpation, patient
report, and Doppler); or they are expensive, invasive, and provided
only static images of the joint with no information on the dynamic
function of these unique joints (computed tomography scans, cone
beam tomography, magnetic resonance imaging). In fact, the most
recent research from the British Institute of Radiology indicates
that the interobserver agreement on MRI scans is fair at
best.1Enter Joint Vibration Analysis (JVA) (BioRESEARCH). The JVA
system brings objectivity and predictability to the assessment of
TMJ function and stability. Normal TMJs have smooth,
well-lubricated surfaces in a proper biomechanical relationship and
produce almost no vibration. But surface changes, such as those
caused by degeneration, tears, or displacements of the disk,
generally produce friction and vibration. Different disorders can
produce different vibration patterns or signatures. PC-assisted
vibration analyses helps identify these patterns and helps you
distinguish among various TM disorders.JVA provides a fast,
noninvasive, and repeatable measurement of TMJ function to aid in
the diagnosis of TMJ condition. Understanding TMJ function is vital
any time you are changing the vertical, lateral, or the
anterior/posterior position of the mandible. Common dental
treatments can change mandibular position. In addition to TMD
treatment, orthodontics, prosthodontics, restorative, and sleep
dentistry can all benefit from JVA testing.A JVA recording takes 10
seconds of patient time, and less than 2 minutes of staff time. In
less than 5 minutes, your staff can be trained to take accurate,
repeatable data. Simply searching JVA 60-second instructional video
on youtube.com will give you an idea of how fast and easy it is to
get this data on every one of your patients.
Reference1. Butzke KW, Batista Chaves KD, Dias da Silveira HE,
Dias da Silveira HL. Evaluation of the reproducibility in the
interpretation of magnetic resonance images of the
temporomandibular joint.Dentomaxillofac Radiol.
2010;39:157-161.
Fortunately, we currently are in a new place of discussion
regarding the diagnosis and possible therapies for occlusal,
masticatory, and temporomandibular care. With an objective test for
TMJ condition, better treatment plans can be devised for occlusal
disease.This new place where we are is directly related to the
development and usage of biometric technology that gives the doctor
objective data from which to make decisions and measured documented
treatment results.The past attempts to record and/or measure the
condylar position and condition included axiopath recordings of
joint position and border movements, transcranial and tomographic
radiography with objective and subjective interpretation,
comparison of condylar position on articulators with multiple jaw
position bite recordings, magnetic resonance imaging (MRI) and
functional MRI scans, computed tomography (CT) and cone beam CT
scans, contrast arthrography, computerized mandibular positions
based on transcutaneous electrical nerve stimulation pulsed muscle
contractions irrespective of the condylar position, face-bow
mounted casts on various articulators referenced to numerous
closure paths from speech to swallowing, from controlled
manipulation to deprogrammed patient closure. At best, these
methods were expensive and time consuming; and at worst, these
techniques were dependent on the clinicians experience and
subjective analysis.The current biometric standard with the Joint
Vibration Analysis (JVA), a system of equipment and software
manufactured by BioRESEARCH(bioresearchinc.com), allows the dentist
to easily and objectively measure the condition of the condyles
quickly, affordably, and irrespective of treatment philosophy. The
mandate from the ADA, as stated in 1990 and 1992, calls upon the
dentist to document, assess, note, describe, evaluate, and record
the presence, location, loudness, timing, consistency, and quality
of joint vibrations. This mandate then encourages us to consider
biometrics that will accomplish this effectively and affordably
with high levels of sensitivity and specificity. The JVA system
achieves this standard and creates a 21st-century documentation of
objective information that will afford the treating dentist the
ability to diagnose the patients condition and monitor the patient
throughout preventive or therapeutic care. By establishing
objective measurements of the condylar condition, the dentist can
evaluate the effect of future events such as injury, accident, or
therapy. The doctor can also begin to correlate the condylar
condition with other data, such as bite force analysis (with
T-Scan) and/or electromyography (BioPAK [BioRESEARCH]) measurements
of the muscles of mastication. In addition this JVA system can be
overlaid on data regarding mastication analysis (BioPAK), range of
motion, and mandibular position.CASE REPORTA patient presented to
our office with severe occlusal-related disease. Examination
revealed abfractions, anterior wear into the dentin, and
periodontal attachment loss. The patient desired a long-term
restorative solution that would include aesthetic enhancement of
the smile (Figure 1).The case was designed with a mock-up of the
anterior smile zone, followed by a determination that the envelope
of function would be well controlled without having to restore the
vertical dimension. The development of the anterior envelope of
function was accomplished by first deprogramming the avoidance
pattern muscle engrams with an anterior contact (only) appliance.
In the deprogrammed patient, the mandibular position is determined
by an anterior contact composite ball bite (open-bite centric).
This open-bite registration is then tested with the JVA and
compared to the preoperative JVA. By testing the stability of the
TMJs at the time of bite registration, we can be confident that our
diagnostic wax-up will be designed not only to the desired
aesthetic result, but also that the provisionals and final
restoration will be accomplished with the condyles in a more smooth
and stable position (Figures 2 and 3).The patients preoperative
casts and mock-up casts were mounted, and cross mounted, at the
most stable condylar position allowing for the desired smile design
and functional anterior zone. This mounting with the apex of force
centric open-bite registration can then be studied on the
articulator for a comparison of the condylar position with the
condylar position that is associated with the preoperative MIP
interdigitation (Figure 4).Commonly, the cases that have
avoidance-related anterior wear and muscle engrams also show a
condylar position discrepancy between the MIP condylar position and
the stabilized mandibular restorative position. These small
dislocations of the condyle in the MIP are frequently associated
with disc movement and subtle changes in the morphology of the
posterior band of the meniscus. This increases the frequency of
inflammation in the joint and the likelihood that the patient will
suffer a partial- or full-disc displacement, along with the
associated popping and possible retrodiscal impingement and pain
(Figures 5a and 5b).The condyle position discrepancy between
stable/normal and the MIP dislocation can be in almost any
direction and position. The clinical manifestation of this
discrepancy is usually referred to as a slide, or as a closure
interference. Rarely does this dental slide actually show up as the
condyle being on the disc and downward and forward on the eminence.
Rather, the abnormal MIP condyle is pulled downward and away from
the disc and eminence, thus destabilizing the disc and allowing for
the disc movement that is observed on the JVA.JVA Practice
Management Ramifications
Amy MorganIf part of your practices vision is to implement the
very latest technologies and cutting-edge clinical skills to
enhance your patients experience, Joint Vibrational Analysis (JVA)
(BioRESEARCH) can be a very significant addition. Using JVA as a
tool for diagnosing and educating your patients in a holistic
approach to their overall oral health and well-being by addressing
temporomandibular Joint diesease prior to treatment is
essential.The initial investment in the equipment necessary to
perform JVA is approximately $10,000. This includes the training
needed to incorporate it into the practice. In our interviews with
various practitioners, all have reported increased case acceptance,
increased fabrication of appliances, decreased restorative remakes,
and an increased number of referrals (from both patients and
specialists); translating into a significant potential return on
investment. The more passive or qualitative returns include more
predictability in results, becoming another tool to exceed patients
expectations and confidence in the treatment results.The most
impacted team members are the chairside assistants (and possibly
the hygienists, depending on its incorporation into the periodic
examination schedule). Team members are trained in-office. This
helps to promote immediate comfort in utilizing this new tool in
the real environment. The learning curve for the team can be fairly
rapid. We have reports that clinical team members can learn the
mechanics of the instrument within 10 minutes! These new skills are
very empowering and can enhance each clinical job description, thus
providing opportunities for improvement and growth.Lets not forget
the educational impact on the dentist as well! An extensive 3-day
course provides the initial training for the doctor in
interpretation of the data. Continued training online and or
additional off-site provide opportunities for the doctor and team
to finish certification on JVA.The impact on the practice is
usually minimal regarding scheduling. Simply incorporating it into
your new patient evaluation as an additional screening tool is a
common approach. Patients of record can be exposed to JVA during
your periodic or status exams. Screening questions about headaches,
tension, joint sounds, or pain are asked and patients with positive
answers are given the JVA quick test (approximately 3 minutes).
Reading and interpretation of this screening either leads to no
further action (negative results), or, if positive indicators
result, the patient is scheduled for further services. Patients are
intrigued by the JVA and feel this technology is yet another sign
of a progressive, high-tech, and comprehensive approach to their
care. This can definitely create a buzz and additional
referrals.For dentists and team members who are passionate about
doing everything possible to improve the health of their patients,
JVA is another option to take to improve your processes and
procedures.
Consequently, we now pay very close attention to any joint
vibration that occurs during the time that the teeth are sliding
into MIP, or in the timeframe just before closure. These are the
early, subclinical vibrations that can be easily treated by
elimination of the closure interferences and/or re-establishing the
normal vertical dimension of occlusion. Certainly, the treatment
plan does not have to include a change in vertical dimension or a
full-mouth rehabilitation; however, it must ensure that the closure
interferences (slides) are eliminated and that any hyperactivity of
the lateral pterygoid muscles related to working or nonworking
interferences be controlled with appropriate occlusal therapy. This
occlusal therapy can include subtractive coronoplasty on the
interferences, but more frequently depends on appropriate additive
coronal enhancement of the anterior and canine teeth.The use of the
JVA during treatment design and provisionalization as well as
postoperatively gives us the assurance that we are not only aware
of any pretreatment problems or red flags, but most importantly,
that in the course of any dentistry that influences tooth contact
or occlusion patterns, we have not made changes that result in a
more unstable TMJ apparatus than we noted before treatment. We
would always like the patient to finish our care better off than
when we first started (Figures 6a to 7).DISCUSSIONRegardless of
other biometrics or treatment philosophy, the JVA provides
objective information to the treating doctor as to the stability or
instability of the TMJ condylar apparatus. This information can be
easily utilized in the decision as to whether (or not) MIP would be
the best choice in making dental treatment plans for the best
long-term patient prognosis. Certainly, an unstable condyle being
present in the attempt to treat occlusal disease would necessitate
the treating doctor to consider and document the effect of his or
her treatment of the dentition on the stomatognathic system,
including the TMJs. In the authors experience, in utilizing the JVA
system in literally hundreds of full-mouth rehabilitations during
the last 11 years, several conditions of the patient bring this
technology to bear.The most enlightening finding from JVA
recordings has been the diagnosis of subclinical problems that
represent early or unstable condyle-disc problems that are not
perceptible with any other technology, especially palpation or
auscultation. This condition shows up as disc movement, joint
laxity, and/or TMJ inflammation. The ability to diagnose this
subclinical condition has revealed that appropriate treatment of
the dentition can result in stabilizing or correcting the problem
in the condyle disc apparatus. This is the missing link in the
conversation of the connection between the occlusion and the TMJ
condition.If problems can be detected before they become permanent
ligament or disc damage, then stabilization through effective
occlusal therapy will afford the patient the best possibility for
long-term health and function
INDIAN DENTAL ACADEMYIndian Dental Academy is the Leader in
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24, 2013ESTHETICS IN COMPLETE DENTURES
ESTHETICS IN COMPLETE DENTURECONTENTSIntroductionReview of
LiteratureDentogenicsDiscussionConclusionBibliography
INTRODUCTIONAn acceptable cosmetic effect in any dental
restoration has always been regarded as important to good
dentistry. A well-made prosthesis will fail if it is deficient in
this respect.Esthetics includes the appreciation and response to
the beautiful in art and nature. Esthetics has been given many
definitions in dentistry but according to Young. It is apparent
that beauty, harmony, naturalness and individuality are major
qualities of esthetics. The dentist must visualize esthetics in
relation to the patient and then translate that visualization into
an acceptable esthetic result. The success of his efforts depends
upon his artistic ability, his powers of observation and his
experience.The selection of anterior teeth for an edentulous
patient is a most important and often difficult problem for the
dentist. He should select teeth which not only embody the proper
form and size, but the most ideal shade as well.The art of
selection of teeth for edentulous patients has been lost in the
maze of tooth guides, folders and pamphlets and the numerous
methods of selection advocated by researchers.An attempt has been
made in this seminar to briefly describe the various methods
advocated in the literature and to reach a practical method.For the
sake of clarity and simplicity, the matter has been dealt with
under the following sub headings.-Introduction-Review of
LiteratureoEvolution of TechniquesoDentogenicsoThe Golden
Proportion-Discussion-Conclusion
REVIEW OF LITERATUREI)Evolution of TechniquesYoung in 1954
described the evolution of various techniques used in the selection
of the anterior tooth mold.Technique 1During the ivory age and
early porcelain period, teeth were selected or created mostly by
dimensional measurements of the denture space and arch size with
little regard to esthetics.Technique 2Technique of Correspondence
and Harmony projected by J.W. White in 1872. By this time, the
temperamental theory was fading out of medicine but white reached
over and suggested that the temperaments called for similarity of
formin faces and teeth.The temperamental theory is a theory of the
fluids of the body, especially the blood, the phlegm and the bile.
It was conceived by Hippocrates in the 5thcentury BC and was used
continuously by the medical profession in diagnosis and treatment
until the nineteenth century, when it gave way to demonstrate
science.Choleric temperament predominance of yellow bile
characterized by anger, irritability, a jaundiced view of life.
Body structures are small and finely textured.Melancholic due to
predominance of black bile and characterized by
depression.Phlegmatic temperament due to abundance of phlegm in
respiratory passages. Alleged to make people stolid, apathetic and
undemonstrative. A physical decline occurs due to phlegm in the
blood.Sanguine temperament attributed to a predominance of blood
and characterized by cheerfulness and optimism. Red complexion,
large body, strong musculature and vigorous action.This was the
introduction of the temperamental theory into dentistry but it was
not widely used till after 1885 when temperamental forms of teeth
were manufactured as named sets.Technique 3The Typical form concept
projected by W.R. Hall in 1887. This was the initiation of the
geometric theory later presented by Williams.The basis of this
classification was two-fold, the major basis was the tooths labial
surface curvatures (transverse and gingivo-incisal), outline form
and neck width.Hall gave the classification of ovoid, tapering and
square.The minor basis was the labio-lingual inclination of the
upper incisors in relation to profile types. This classification
apparently exerted little influence on practice procedure at that
time.Technique 4The temperamental technique was the first technique
of selecting tooth form from the point of view of influence and
universal acceptance. It required several years to associate and
establish dental characteristics of the temperaments and to
incorporate them in manufactured tooth forms, this occurred by
1885.Dentists like Flagg, Laycock, Hutchinson, Kingsley et al and
artists like Madame Schimmelpeinik, spurzheim and Jacques
contributed to the development and acceptance of this
theory.However, only rarely could two dentists agree on exactly
what the theory meant, what it taught and what it required. It had
an intangible quality which could not be defined in any
authoritative way.Technique 5Berrys biometric ratio method
1906.Berry projected in 1903 that the outline form of the inverted
central incisor tooth closely approximated the outline form of the
face. Therefore the outline form of the edentulous face indicated
the outline form of the anterior teeth to be chosen for a denture
patient.Berrys continued investigation into the correlation between
faceform and tooth form resulted in the discovery that the
maxillary central incisor was 1/16ththe width of the face and
1/20thits length. Subsequent research by M.M. House and others
proved the 1/16thwidth ratio but the 1/20thlength ratio which was
frequently not possible to use due to interference by ridge bulk.
Difficulty in practical applications discouraged the use of this
technique.Mavroskoufis et al in 1981 concluded that the inter-alar
nasal width is a reliable guide for selecting the mold of anterior
teeth. The tips of the canines were found to lie on a projection of
two perpendicular lines drawn from the outer surfaces of the nasal
alae.Thus the mesiodistal width of the artificial anterior teeth
should be determined by adding 7mm to the patients nasal width.They
found no relationship between the nasal width and the total/overall
width of the four incisors.The authors advocate that the tips of
the canine be set on a line which passes through the posterior
border of the incisive papilla which proved to be a stable anatomic
land mark.The incisive papilla can also be used as a guide for
arranging the labial surface of the central incisors at 10mm
anterior to the posterior border of the papilla.Kern in 1967
studied various anthropometric parameters of tooth selection by
examining over 6000 skulls. He concluded that:1.The bizygomatic
measurement did not show a high percentage consistency ratio to the
width of the crowns of the maxillary central incisors.2.Nor did the
skull length measurement prove reliable for the determination of
the length of the maxillary central incisor crown.Significantly
consistent ratios were found to occur in:1.The nasiomenton
(internasal and nasofrontal sutures and the chin) measurement and
the length of the maxillary central incisor crown showed a 11:1
ratio in 81 per cent of skulls. However this has little
significance in edentulous patients whose nasiomenton measurements
depends on the degree of mouth opening and the orientation of the
occlusal plane.2.The cranial circumference and the widths of the
maxillary anteriors showed a ratio of 10:1 in 91 percent of skulls.
This has been reported by Sears also.3.93% of skull showed equal or
near equal measurements between the nasal widths, nasal aperture
and the width of the four maxillary incisors.4.The maxillary and
mandibular anterior teeth showed a high percentage ratio of 5:4 in
90% of skulls. Sears also reported similar findings.Technique
6Clapps tabular dimension table method 1910.Teeth were selected
based on the overall dimension of six anterior teeth arranged on
the Bonwill circle and the vertical tooth space available in the
patient.A table with illustrations of molds allowed the dentist to
select and specify the mold to be used by number.
Technique 7Valderramas Molar tooth Basis was projected in 1913.
This method of only historical value used varying measurements
between combinations of cusp points to indicate the size of the
individual and overall tooth measurements. The basic problem with
this technique is that edentulous patients have no
molars.Valderrama also predicted a selection of tooth size on a
1/4thincrement of the size of a Bonwill triangle, determined by
measuring the edentulous mandible.Technique 8Cigrande 1913
advocated the use of the outline form of the fingernail to select
the outline form of the upper central incisor. The size was
modified to meet the requirements of tooth space and other
relationships.Technique 9The Geometric method or Law of
Harmony.Williams Typal form method projected by J. Leon Williams in
1914 is based on the geometric pattern created by the outline form
of the bony face frame the ovoid, square and tapering forms.
William arrived at this classification after extensive
anthropological study and was able to interest a manufacturer. The
Dentists supply company to produce his systematized molds of teeth.
Thus the typal form method or geometric method of anterior tooth
selection gained universal acceptance. However further
investigation by Wright in 1936, Bell in 1978 and Mavroskufis et al
in 1980 invalidate this method of selection. But this method is
probably still the way in which most dentists select anterior
artificial teeth.Technique 10Young proposed the selection of tooth
form by Mold guide sample as the 10thtechnique (in approximate
chronological order).Technique 11Wavrin Instrumental Guide
Technique presented in 1920 was based on Berrys Biometric ratio
method and Williams Typal form teeth but its use was limited to a
single manufacturers product.Technique 12Maxillary Arch outline
form projected by Nelson in 1920. This technique assumed that the
arch outline form was a valid method since it was related to an
individuals anatomy. This was invalidated by changes in arch form
due to resorption.
Technique 13Wrights Photometric method proposed in 1936 was
based on using a photograph of the patient with natural teeth and
establishing a ratio by comparative computation of measurements of
like areas of the face and photograph. The simple unknown
mathematical fomula could be used to select teeth or to create
correct vertical dimension. Minute inaccuracies in measurements
tended to diminish greatly the reliability of the technique so it
has enjoyed little usage.Technique 14The multiple choice method
introduced by Myerson in 1937 was based on a need for a selective
range in labial surface characteristic of transparent labial and
mesial surfaces, varying surface colour tone, and chracterization
of teeth by time and wear. Harmony of tooth size and shape with
face size and shape was associated with this technique.Technique
15Steins coordinated size technique presented in 1940 was based on
the coronal index of 70 to 100 commonly used in prosthetic on 4
model teeth representing the range of maximum frequency of use and
on the common variability in size of individual natural teeth. The
index is the width percent of the length. The variability is 0.5mm
; model size varied from 7.2 to 8.7 mm.Technique 16Anthropometric
Cephalic index method projected by Sears in 1941 was based on the
fact that the width of the upper central incisor could be
determined by dividing either the transverse circumference of the
head by 13 or the bizygomatic width by 3.3. Tooth length was in
proportion to face length.Technique 17Frame Harmony method by the
Justi company in 1949, is based on the fact that the size and
proportions of the teeth are in harmony with the general bony
proportions of the skeleton. The overall tooth size is selected by
a mathematical formula, 1/7ththe total dimension of the upper and
lower edentulous ridges, with the dimensions of the individual
anterior teeth correlated with a developed table of tooth
dimensions to give the indicated over-all dimension. Other
characteristic of tooth form are based on genetics, and the
comparison of such dental qualities of a near relative.Technique
18Bioform technique proposed by the Dentists Supply company in 1950
is based on the geometric outline forms of face and teeth the House
classification for 4 basic and 3 combination typal forms, and
3-dimensional harmony of tooth form and face form. It is associated
with the tabular and mold guide systems. This is currently in
use.Technique 19The Trubyte tooth indicator or Selection Indicator
Instrument method advocated by the Dentists supply company which is
correlated with Williams and Houses Typal form theory and the
Tabular technique.Technique 20House instrumental method of
projecting typal outline and profile silhouettes onto the face by
means of a telescopic projector instrument and silhouette form
plates. This was correlated with designated mold numbers and size
variation. This was proposed by House in 1939 and by the Dentists
Supply company in 1950.Technique 21Automatic instant selector guide
of the Austenal company in 1951 correlated form, size and
appearance in such a manner that only a single reading was required
to select the appropriate tooth mold based on dimensions of denture
space and harmony of face and tooth form.These were the twenty one
techniques detailing the evolution of the selection of anterior
teeth as described by Young in 1954.Then in September 1955 Frush
and Fisher created a revolution in the field of dental esthetics by
the introduction of Dentogenics. In a series of six articles
published between 1955 and 1959 they described various means to
more natural dentures and many tips on how to avoid the denture
look.Krajicek in 1956 proposed methods involving the duplication of
the patients natural teeth either before or after extraction. Klein
(1960), Hayward (1968), Kafandaris and Theodoros (1974) suggested
incorporating the patients natural teeth in the denture. Van Victor
in 1963 proposed the mold guide cast technique.
DENTOGENICSFrush and Fisher in the first, of a series of six
articles, published in 1955 introduced the dental community to
Dentogenic restorations. According to them, there was nothing in
the field of esthetics that had not been considered before. Yet a
vacuum existed and the Denture look prevailed.Dentogenics describes
a denture that is eminently suitable to the wearer in that it adds
to the persons charm, character, dignity or beauty in a fully
expressive smile. Dentogenics then means the art, practice and
techniques used to achieve that esthetic goal in dentistry.The
authors describe the origin of the concept Frush in 1952 met in
Zurich, Switzerland, a master sculptor by the name of Wilhelm Zech
who ground and formed teeth for his dentist father. Zech
experimented with the molding, spacing and arrangement of teeth in
artificial dentures with an artists concept of what belonged in the
mouth of a living human. His work inspired Frush to take anew look
at denture prosthetics and the Swissedent foundation was
established in Los Angeles, California in 1952, from where through
seminars and workshops, the concepts of dentogenics have
disseminated.Frush and Fisher in 1956 advocated sex identity in
dentures by the application of Dentogenics. According to them, the
feminine form is characteristically spherical with a roundness,
smoothness and softness that is typical of women. Whereas the
masculine form is cuboidal, with the hard, muscular, vigorous
appearance which is typical of men.The procedure therefore is to
select a basically Feminine or Masculine mold and then harmonize it
to the individual patient depending upon the personality and age
factors by modifying individual teeth.The authors describe a
procedure they call depth grinding which involves the accentuation
of the third dimensional depth to eliminate the first appearance of
the artificial upper anterior teeth. With a soft stone, the
mesio-labial line angle of the central incisor is ground in a
definite and flat cut, following the same curve as the mesial
contour of the tooth in order to move the deepest visible point of
the tooth further lingually. After this cut has been made, a
careful rounding and smoothing of the sharp angle made by the stone
must be accomplished and a perfect polish must be given to the
ground surface.It is necessary to develop the desired effect in
depth grinding by a consideration of these main factors A flat
thin, narrow tooth is delicate looking and fits delicate women and
involves little depth grinding. Whereas a thick, Bony, big sized
tooth, heavily carved on its labial face is vigorous and is to be
used exclusively for men. This involves rather severe depth
grinding.For the average patient, a healthy women or a less
vigorous man, the depth grinding will be an average between
delicate and vigorous, the feminine or masculine characteristics
being given by other tooth shaping, incisal grinding and the
positioning of the teeth.Depth grinding reduces the width of the
central incisors according to the severity of grinding to be
accomplished. Therefore, to maintain the normal harmony of contrast
in size between the six anterior teeth, a larger sized central
incisor of the same mold should be selected.Again in 1956, Frush
and Fisher discussed another aspect of Dentogenics the personality
of a patient. They stated that the foundation for dentogenic
restorations is the personality of the patient simply because the
basic male or female tooth form is a refinement of that tooth form
which has its inception in the personality factor. Likewise age is
a refinement of the personality factor. They devised the
personality spectrum and explained the precise prosthodontic
application of the otherwise abstract word personality by the 3
divisions of the personality spectrum.1.Delicate meaning fragile,
frail, the opposite of robust.2.Medium pleasing meaning normal,
moderately robust, healthy and of intelligent appearance.3.Vigorous
meaning the opposite of delicate, hard and aggressive in
appearance, the extreme male animal, muscular type almost
primitive, ugly.The personality spectrum can be used in our
artistic endeavour to inject a variety of tooth form and tooth
position, at the comprehensive level of individual patient
personality analysis. A small percentage of patients are delicate,
and a slightly larger percentage are vigorous. The remaining
majority of patients fall into the medium section of the
personality spectrum, but all of these have either vigorous or
delicate tendencies.The use of the dentogenic concept is made
easier by considering the smile as the primary objective
personality trait of the patient. This primary objective
personality trait and the personality spectrum is used for the
selection of the mold category. These fundamental shapes must then
be subjected to the refining procedure of sex and age
modifications.The age factor in dentogenics, considered by Frush
and Fisher in 1957, determines the selection of the shade of the
mold to be used in the denture. Light shades are considered
appropriate for young people and darker shades are considered
esthetic for older people. Also bluish incisal tinges are preferred
for the young and grayish shades for the older. Mold refinement is
done by producing worn incisal edges and cuspid tips, attritional
and abrasional facets, development of diastemata to indicate tooth
loss and subsequent drifting.Thus the dignity of advancing age may
be portrayed in the denture.In 1958, Frush and Fisher propounded
the Dynesthetic interpretation of the dentogenic concept.
Dynesthetics is a compounded word. The prefix dyn is from the Greek
word dynamis meaning power. It implies movement, action, change and
progression in the esthetic phase of prosthodontics. This dynamic
value has been described as making the difference between an
artifact, any object without life-like effect such as a spoon, and
a work of art or visual objects that are alive in meaning such as a
statue.Therefore the application of dynesthetics allows a denture
to be a work of art and have a life-like effect against a denture
lacking artistic treatment and thus remain an artifact.The
dynesthetic techniques are rules which concern the 3 important
divisions of denture fabrication.1.The tooth.2.Its position.3.Its
matrix (visible denture base).The selection and modification of the
tooth according to dentogenics has already been described. The
positioning and denture base considerations are beyond the scope of
this seminar.THE GOLDEN PROPORTIONOf particular interest is the so
called Golden proportion that exists between the perceived widths
of the upper anterior teeth.Lombardi in 1973 and Levin in 1978
demonstrated that the width of the central incisor is in golden
proportion to the width of the lateral incisor. The width of the
lateral incisor to thewidth of the canine is also in golden
proportion as is the width of the canine to the first premolar. The
golden proportion exists when the ratio between a larger part B
(for example) to a smaller part A (for example) is 1.618.
DISCUSSIONA practical approach to the selection of the anterior
teeth is to consider the size, form and color.SIZE:May be
determined from:-Pre extraction records.-Marking the corners of the
mouth on the occlusal rim gives the width of the 6 anterior
teeth.-Marking the inter alar width on the occlusal rim gives the
width of the 6 anterior teeth from cuspid tip to cuspid tip.-Length
may be determined by noticing visibility of the incisal edges and
relating this to lip length and dentogenics.FORM:Inspite of the
body of research that invalidates Williams Typal theory,
clinically, it is observed to provide esthetic results and as
stated by William Observance of this rule will always give you
perfect harmony the harmony of opposition of line.The form may also
be selected considering first the personality of the patient and
then modified according to the sex and age of the patient to
individualize the mold.Pre extraction records may also be of value
in the selection of the form of the anterior teeth.COLOR:Color of
the teeth is to be determined by the skin coloring of the
individual. The color selected should be so inconspicuous so as not
to attract attention to the teeth. The squint test may be helpful
in evaluating colors of the teeth with the complexion of the face.
With the eyelids partially closed to reduce light, the dentist
compares prospective colors of artificial teeth held along the face
of the patient. The color that fades from view first is the one
that is least conspicuous in comparison with the color of the
face.The age of the patient will also effect the color of the
teeth. The general rule is that darker teeth are more appropriate
in older patients and lighter teeth are more harmonious in young
patients.This rule however must be overruled for the patient who
does not smoke and takes food of slight pigmentation and may
continue to have a relatively light tooth body together with the
normal color texture. This is an application of dentogenics to the
color selection.CONCLUSIONThe selection of anterior teeth is an
important part of the esthetic phase of denture fabrication. It is
essential not to be embroiled by the various techniques aimed at
making the task easier. What is necessary is the development of an
esthetic sense by the observation of natural dentitions in response
as well as in function so as to be able to create dentures that are
living things belonging to a human being and not just mere
artifacts that are poor replicas of what has been lost.
BIBLIOGRAPHY1.BELL R.A. : The geometric theory of selection of
artificial teeth : Is it valid ?. JADA 97 : 637, 1978.2.CLAPP G.W.
: How the science of esthetic tooth form selection was made easy.
J. Prosthet. Dent. 5 : 596, 1955.3.Dorlands Illustrated Medical
Dictionary. W.B. Saunders, 28thEd. Pg 1666.4.FENN, LIDELOW, GIMSON
(1989) : Clinical Dental Prosthetics, 3rdEd., Wright.5.FRUSH J.P.
and FISHER R.D. : Introduction to dentogenic restorations. J.
Prosthet. Dent. 5 : 586, 1955.6.FRUSH J.P. and FISHER R.D. : How
dentogenic restorations interpret the sex factor. J. Prosthet.
Dent. 6 : 160, 1956.7.FRUSH J.P. and FISHER R.D. : How dentogenics
interpret the personality factor. J. Prosthet. Dent. 6 : 441,
1956.8.FRUSH J.P. and FISHER R.D. : The age factor in dentogenics.
J. Prosthet. Dent. 7 : 5, 1957.9.FRUSH J.P. and FISHER R.D. : The
dynesthetic interpretation of the dentogenic concept. J. Prosthet.
Dent. 8 : 558, 1958.10.HAYWARD D.E. : Use of natural upper teeth in
complete dentures. J. Prosthet. Dent. 19 : 359, 1968.11.HICKEY
J.C., ZARB G.A., BOLENDER C.L., (1985) : Bouchers prosthodontic
treatment for edentulous patients, 9thEd., Mosby, S.
Louis.12.HEARTWELL C.M. and RAHN A.O. (1986): Syllabus of complete
dentures, 4thEd., Lea and Febiger, Philadelphia.13.KERN B.E. :
Anthropometric parameters of tooth selection. J. Prosthet. Dent. 17
: 431, 1967.14.KAFANDARIS N.M. and THEODOROU T.P. : Complete
denture technique using natural teeth. J. Prosthet. Dent. 33 : 571,
1974.15.KLEIN I.E. : Immediate denture prosthesis. J. Prosthet.
Dent. 10 : 14, 1960.16.KRAJICEK D.D. : Personalized acrylic resin
anterior teeth. J. Prosthet. Dent. 6 : 29, 1956.17.LEVIN E.I. :
Dental esthetics and the Golden proportions. J. Prosthet. Dent 40 :
244, 1978.18.MAVROSKOUFIS F. et. al : The face form as a guide for
the selection of maxillary central incisors. J. Prosthet. Dent. 43
: 501, 1980.19.MAVROSKOUFIS F. et. al : Nasal width and incisive
papilla as guides for the selection and arrangement of maxillary
anterior teeth. J. Prosthet. Dent. 45 : 592, 1981.20.PICARD C.F. :
Complete denture esthetics. J. Prosthet. Dent. 8 : 252,
1958.21.SEARS V.H. : Selection of anterior teeth for artificial
dentures. JADA 23 : 1512, 1936.22.VAN VICTOR A. : The mold guide
cast Its significance in denture esthetics. J. Prosthet. Dent. 13 :
406, 1963.23.WRIGHT W.H. : Selection and arrangement of artificial
teeth for complete dentures. JADA 23 : 2291, 1936.24.YOUNG H.A. :
Selecting the anterior tooth mold. J. Prosthet. Dent. 4 : 748,
1954.
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30, 2013HIGH SPEED CUTTING INSTRUMENTS IN PROSTHODONTICS
HIGH SPEED CUTTING INSTRUMENTS IN PROSTHODONTICSIntroductionIn
order to perform the intricate and detailed procedures associated
with restorative dentistry, the dentist must have a complete
knowledge of the purpose and application of the many instruments
required. During each day of his clinical experience the dentist
operates on vital tissues within the oral cavity where a millimeter
or a fraction there of, is a very significant dimension. A skillful
application of sharp hand and rotary instruments requires ability
and coordination gained only by extensive training.Before the
advent of rotary instruments, removal of tooth tissue was
accomplished with sharp edged chisels, hatchets, and hoes. These
hand instruments possessed a cutting capability, which was used for
clearing away unsupported and undermined enamel resulting from
dental caries. Walls and floors of the cavity were formed by a
planning and lateral scraping action of these sharp edged
instruments. At best, such efforts were crude, time consuming and
often difficult.The first, rotary instruments for cutting tooth
tissue were modified hand instruments. These, drill or bur heads
could be twisted in the fingers to produce a cutting or abrading
action. In 1846 the finger ring was introduced with a drill socket
attached for adapting a series of long bundled burs or drills. This
was the primitive application of the rotary principle. The first
drill having flexible cable drive and the first angle hand piece
were introduced by Charles Merry between 1858 and 1862. In 1871,
Morrison modified and adapted the dental foot engine from the
Singer Sewing machine. This was followed by the introduction of the
electric dental engine utilizing a cable arm in 1883. In 1910 the
endless cord on a jointed arm was made available. The earlier
dental hand pieces were capable of speeds from 4500 to 6000 rpm.In
1940 the use of diamond abrasive paints became widespread. The
diamond point is compared of a number of small diamond particles
bound on a rotary blank.In 1945 Dr. G.V. black, published a report
on the non mechanical preparation of cavities and in doing so
introduced the air abrasive technique. The impact of Dr. Blacks
revolutionary cutting technique on the dental profession was
considerable. This was the first significant break in the long
established traditional method of cavity preparation. The air
abrasive principle utilized particles of aluminium oxide propelled
against the tooth surface by a carbon dioxide stream under the
pressure of 110 psi, and funneled through a tungsten carbide nozzle
with a lumen of 0.018 inch. The penetration of enamel and dentin
was rapid but some what difficult to control.In 1949 Walsh and
Symons published their initial findings relating to the removal of
tooth tissue with diamond points at rotational speeds upto 70,000
rpm. This report indicated the use of lighter forces and a
resulting increased cutting efficiency at these higher speeds.In
early 1950, the ball-bearing hand piece was introduced.In 1963,
following the work of Nelson the first fluid turbine type handpiece
was introduced. This instrument was capable of rotational speeds of
approximately 50,000 rpm and was limited to diamond instruments
operated at one speed only. In 1954, air-driven hand pieces were
developed. A continuous belt-driven contra-angle which utilized a
friction grip chuck and bur was introduced, making possible cutting
speeds of upto 150,000 rpm.By 1957, many dentists were using
rotational speeds upto 3,00,000 rpm. The introduction of
air-bearing hand piece in the early 1950 made possible greater
rotational speeds of approximately 5,00,000 rpm.In 1953, an
ultrasonic method of tooth tissueremoval was also introduced, which
used suitably shaped tips vibrating at frequencies ranging from
2,50,000 to 3,00,000 cycles per seconds.This brief historical back
ground reveals that the profession has been searching for a
suitable method of tooth tissue removal. Only during last 30 years,
this hunt has slowed down still the profession is trying to refine
the procedure and instruments.Review of literatureA search through
literature reveals various methods used in the past for removal of
tooth tissue. The continuous development of newer methods till
1960, indicatesthat the earlier instruments had some disadvantages.
Inspite of the introduction of numerous tooth reduction
instruments, and procedures, the principles and the biologic
objectives have remained the same. These are as follows.1.The
operator should remove the least amount of tooth tissue consistent
with necessary mechanical retention.2.This should be done with the
least barm to the periodontal tissues and the pulp.3.It should be
done with the least discomfort to the patient.4.No pathologic
reactions should be initiated in the pulp.Advantages of high
speeds1.Smaller stones can be used at the increased speeds.2.Less
fatigue results both for the patient and operator.3.Due to high
speed, very light pressure is required.4.Less vibrations are felt
by the patient.5.The chairside time for a given preparation is
considerably reduced.6.Trauma to the pulp is reduced.7.The
efficiency and life of the cutting tools is increased.8.Because of
small tools, control is easy.9.Removal of old amalgam and gold
restorations is easy.Disadvantages of high speeds1.The increased
speed creates increased temperatures in the tooth. Therefore some
method of cooling the tooth more efficiently is required not to
injure the pulp. This necessitates additional equipment.2.When a
dentist changes from the lower speeds, which utilize a pressure in
pounds, to high speeds which need only a pressure in ounces, he
must develop a new technique and retrain himself to a new tactile
sense.3.To operate at high speeds good visibility of the cutting
instrument is necessary to avoid over cutting.4.Due to the ease
with which tooth tissue is removed, caution must be taken not to
injure the proximal enamel of the adjacent healthy tooth and the
gingiva.5.High speeds result in greater wear on the working parts
of the handpiece, necessitating more frequent repairs and
replacements.6.Unless used properly, high speeds have a tendency to
create striations on a tooth surface.7.The ideal preparation for
any type of restoration cannot be accomplished by using high speed
equipment alone. The final exactness and finishing line can best be
established by instruments revolving at moderate speeds.Types of
high speed instrumentsHand piece can be divided into four types
depending upon their speeds as follows.1.Low speed upto 10,000
rpm.2.Intermediate speed 25,000 to 45,000 rpm.3.High speeds 50,000
to 1,00,000 rpm.4.Ultra high speeds 1,00,000 rpm and over.Kilpatric
has further classified the ultra high speed handpiece into three
classes.Type I the gear driven centre-angle handpiece, upto1,25,000
rpm.Type II the belt driven contra-angle handpiece upto 2,00,000
rpm.Type III turbine driven air contra-angle handpiece upto
3,00,000 rpm and higher.Heat generation:Knowledge of the physics
tells us that, whenever there is friction between two surfaces,
heat is generated, which may bring about rise in temperature of
either or both the surfaces. The same applies in the tooth
reduction procedures. Here the rotating cutting tools come in
contact with the tooth surface and the heat is generated.It was not
until 1930 that the workers began to investigate the heat rise in
the dental pulp.There are many factors that influence the rise in
temperature which takes place in cutting operations. The greater
the speed of rotation of the cutting tool, the faster the tool
revolves, the higher the resultant temperature. It has been found
that the temperature rise develops within 10-12 seconds, after the
cutting operation is started. Size of the cutting instrument has an
important bearing on heat generation, since, its diameter affects
the cutting speed at its periphery. Larger the size of the cutting
tool more the host generation.A third factor is the pressure
applied by the dentist during cutting operation. As the pressure
increases, greater will be the rise in temperature.Hudson and
associates in 1954 conducted a study on temperature developed in
dental cutting instruments from their study they have concluded
that,1.The temperatures produced by dental burs in cutting human
dentin ranged from 125F to 275F. Since these temperatures are above
those, said to be tolerated by normal human dentin, it would seem
advisable to use some form of coolant.2.A significant decrease in
time required to accomplish a given operation is apparent, when
high operating speeds are used.3.The amounts of heat transferred to
the tooth from the bur decreases, at speeds above 12000 rpm, since
cutting time at these speeds is reduced and bur temperature
remains.Substantially constant and there is less heat trauma to the
vital structures.Coolants:From the study of Hudson and Sweeney, it
is evident that the temperatures reached during tooth reduction
procedures are above those said to be tolerated by normal human
dentins. This indicates that, some form of coolant must be used,
during the cutting operations, particularly when high speeds are
used.Every means should be employed to keep the temperature down as
much as possible during cutting operations. Coolants must employed
which, to be effective, should be applied at the point of contact
between the cutting instrument and the tooth tissue. There are
three types of coolants usually employed in dental
practice.1.Water.2.Spray of air and water3.Air alone.Peyton has
shown that at speeds ranging from 30000 rpm to 170000 rpm and with
an application of four ounces of pressure, a temperature rise
within the tooth of less than 15C occurred when water or air-water
sprays were employed. He also found that even with a water coolant,
excessive temperatures developed, when large diameter instruments
or excessive pressure were applied with increased operating speeds.
This indicates that the use ofa coolant, does not eliminate the
danger of excessive temperature rise.A reduction in concentration
of the amount of water used during cutting procedure shows the
significant temperature rise of the dental bur.The minimum volume
of water to be applied was estimated at 1.5 ml per minute.The
question whether water in spray form should be used at mouth or
temperature seems to have no significance as far as temperature
rise in the tooth was concerned. Tylman is of the opinion that if
the water reservoir is kept at 100F, it is most comfortable to the
patient, less liable to be harmful to the pulp and still reduces
the heat of friction during cutting.There are certain other
problems associated with the use of the highspeed cutting tools.
Most of the hand pieces are so designed that a spray or stream of
water is directed from the head of the handpiece directly onto the
cutting operation. Where the water strikes the tooth and the
cutting tool directly, full benefit is obtained from the coolant.
Where however, the abrasive on the cutting tool, is on the surface
away from the stream of water, water does not flood the tooth
surface being cut, resulting in excessive temperature rise. The
overcome this difficulty perforated disks have been developed,
which permit the water to go through the openings and lubricate the
disk and tooth on the cutting side. The use of perforated disk
results in less temperature rise. Consequently when disks are non
perforated, and when the stream of water cannot be directed to the
cutting contact areas, they should be used at speeds not exceeding
10,000 rpm.Another advantage of a water coolant lies in the fact
that the tooth debris from the cutting is removed rapidly,
preventing the clogging of the cutting tools. This results in
greater cutting efficiency of the stone. Also, it prolongs the life
and effectiveness of the instrument. It is essential that the water
be in intimate contact with the revolving instrument and the tooth
tissue.To do this more effectively, Nelson recommended the addition
of a wetting agent to the water spray.Because the high speed
technique requires a larger quantity of water as a coolant, there
is the problem of removing this water from the mouth. To have the
dentist stop frequently to allow the patient to spit out the excess
water is time consuming. The customary saliva ejector has
insufficient removal capacity.To solve this problem, Thompson has
suggested a washed field technique.This technique adapts the
suction or vacuum principle. It established and maintains a
powerful but gentle negative pressure of air in the mouth, close to
the field of operation.Accompanying the air stream, is a flow of
isothermal water which is projected copiously onto the operative
field. This water is entrained into the vacuum air stream, which
draws it rapidly across the operative area. The irrigant pulls away
with it tooth cuttings and debris. These are taken into the vacuum
air stream and disposed off in a filter system. A clean, clearly
visible operative field is provided. This technique has the
distinct advantages that it facilitates the use of high speed
instruments, maintains visibility during copious irrigation of the
operative field, reduces operating time, improves the patients well
being and introduces a new concept of cleanliness. Human tissues
are maintained in their natured wet safe pain, trauma and
postoperative complication, which may arise due to ingestion of
tooth debris are reduced.Desiccation of hard and soft tissues is
avoided. Heat is eliminated thus preserved the
tissues.Vibration:Cutting a tooth may be very annoying and
unpleasant to the patient but still not be painful. In pain there
is usually an involvement of the nerve endings, either by trauma or
extreme irritation, resulting in an acute, painful reaction. Most
patients associate the sensation of vibration, noise, pressure and
the slight increase in cutting temperature with the sensation of
pain. Consequently, if the factors of vibration, heat and pressure
are reduced to a minimum, the patient usually experience reduced or
no pain.One mechanical factor that influences vibration is the
dental handpiece, whether it is friction-bearing, ball bearing,
high speed belt driven or turbine ultra speed. When the friction
bearing, conventional type of handpiece is used at a speed of 4500
rpm to 6000 rpm, it is connected by the conventional belt and
pulley system of the dental engine. In this case one may expect a
high order of vibration depending upon the condition of various
mechanical parts, their adjustment and speeds of their
operation.Pulleys that are worn, a worn belt, or an improperly
adjusted belt will cause vibrations that are transmitted down to
the cutting tool. Similarly hand piece which do not hold the
cutting tool properly, which have worm bearing or are out of
adjustment will also cause vibration.The investigations of Walsh
and Symmoss showed that vibration, when applied to tooth, produced
the most unfavorable response when the frequency was between 100
cps and 200 cps. When the frequencies were above 1000 cps, they
were generally beyond the upper threshold of perception of the
average patient. It is the lower frequencies, in the range of 100
200 cps, that are usually developed at the lower speeds, especially
if the equipment is worm and maladjusted.Hudson and Sweeney have
reported the importance of having centricity in the cutting tool.
They found that eccentric burs when rotated at 6000 to 10000 rpm
produced a lower frequency in the range of 100-200 cps, whereas a
true running bur at 10000 rpm produced vibrations in the frequency
range above the upper threshold.Tamner pointed out that only a part
of an eccentric cutting tool is used as it rotates, thus causing
unfavorable impacts and vibrations, which fall into the most
annoying frequency range. The disks and stones that are unmounted
and are screwed onto a mandrel very frequently are eccentric and
therefore should not be used in high speed cutting operations. The
permanently mounted instruments are indicated in preference to
unmounted type.Poorly built burs with blades not evenly cut or
chipped will likewise cause vibration. In using carbide burs, it is
very important the see that none have chipped blades.Correct
adjustment of the belt is important in the reduction on and
elimination of vibration. A belt that is too loose increases the
vibration pattern transmitted directly to the tooth.In the ultra
highspeed hand pieces the metal chuck holding the cutting
instrument often is replaced by a rubber or plastic chuck. This
lessens the vibration transmitted to the cutting instrument and
facilitates the more rapid cutting action.In cutting with a water
turbine handpiece at 45,000 rpm the intensity of vibrations was
well tolerates by the patient.Morrison and Grinnel made the
following observations.The deleterious effects of vibration are two
fold in origin.1.Amplitude.2.Undesirable modulating frequencies.If
we minimize or eliminate these factors, we can then reduce the
undesirable effects of vibration.Amplitude:The wave of vibration
consists of frequency and amplitude.At conventional speeds,
amplitude is greater but frequency is less. At higher speeds the
reverse is true. The greatest harm is caused by the amplitude of
vibration which is the factor, most destructive of instruments and
which causes the most apprehension in the patient and the greatest
fatigue in the dentist.By increasing operating speeds, the
amplitude and its effects are reduced and a more satisfactory
result is attained.Vibration waves are measured in cycles per
second. It has been shown that rotation of approximately 6000 rpm
sets up a vibrational wave of approximately 100 cps. As the rpm is
increased the cps of the fundamental vibration wave are increased
until, at ranges of 100000 rpm, we have a vibration wave of 1600
cps. It has been demonstrated that at wave of vibration of over
1300 cps, vibration is practically imperceptible to the patient.
The reason for this is not fully understood, but there are two
theories for this phenomenon.(1)The Wedensky inhibition phenomenon
frequency increased to a point where vibratory perception
diminishes due to failure to perceive vibration. This is because
Stimulation occurs during Refractory Period of
Recovery.(2)Vibratory perception depends upon the product of the
amount of stimulation (i.e. pressure) multiplied by the frequency
of stimulation necessary for a reaction. This is called Chronaxie.
As the speeds above 1,00,000 rpm, due to light pressure and high
speeds, chronaxie is attained, which is necessary for reaction.Thus
it can be concluded that, the more the rpm, the less the amplitude,
and the greater the frequency. Vibratory perception will be lost in
the ultra highspeed range of 1,00,000 rpm or more.Spread of
pathogenic organisms by Ultra speed cutting procedures:Atmospheric
contamination through the spread of oral organisms particularly
from air turbine action has been a concern of the dental profession
for some time. Dental procedures tend to expose the operator to
infectious diseases. Recent studies suggest that the extent of
aerosol produced by air turbine may increase the normal hazard. A
report involving patients with pulmonary tuberculosis cultures were
demonstrated on all petri dishes exposed during cutting procedures,
with the heaviest concentration being at 2 feet in distances from
the patients mouth. This indicates that the dentist and his
assistant are exposed to a serious health hazard when operating
with an ultra speed exposed instrument on patients having such
pathogens in their oral flora. When a patients history suggests the
existence of tuberculosis, pneumonia, influenza, infections
hepatitis or any infectious diseases including the common cold, a
protective face mask should be worn by both dentist and assistant.
During all ultrahigh speed cutting procedures, protective
eye-glasses should be worm routinely.SUCK-BACK PHENOMENON-The
operation of the turbine is switched off by closing the
compressed-air valve abruptly. Then, owing to its own kinetic
energy, the turbine continues its rotation, so that the turbine
starts operating as an air pump. This causes a negative pressure in
the area of the turbine shaft. The negative pressure sucks air from
the environment that can be contaminated by aerosols of saliva and
blood of the patient.Size of cutting instrument and cutting
speeds:It has been pointed out by Peyton, and Nelson that, the
important factor of increased operating speeds is the instrument
surface speed in fact per minute rather than the revolution per
minute of the instrument.The larger the diameter of the cutting
instrument, the slower the speed required at the spindle. The
specific phase in preparation of an abutment should determine the
size of the cutting instrument and the rpm that should be used.
Employing superspeed for all operations places unnecessary strain
upon the patient and equipment. If the same effect can be
accomplished by using a larger instrument at a lower speed, but
still remaining above the threshold of perception, this should be
done. However, oversized cutting tools should not be used at super
speeds due to the difficulty of instrument control and accuracy of
cutting.VIBRATION SYNDROME :the perception of vibration, pain,
touch and temperature deteriorates. The negative effect of local
vibrations occurs within the range 5-1400 hz, the most harmful
being those below 16 hz. mechanical vibrations arise because the
various machines operating at the dentists workplace contain moving
parts. The main source is vibrating power-driven or air-driven
instruments, such as low- and high-speed handpieces as well as
ultrasonic instruments.The vibrations emitted by these machines
travel directly from the handles to the operators hand. These are
local vibrations.Biologic response of dentin and pulp to high speed
cutting:Dentin:As the contents of the dentinal tubules are in
direct continuity with the odontoblasts, and pulp, cutting or
grinding the dentin causes a reaction in the pulp and this may lead
to changes in the dentin.An early experimental investigation into
the effect of cavity preparation on the dentin and pulp was carried
out by Fish in 1932. He cut cavities in the teeth of dogs and left
the cavities open to the saliva. By sealing dyes into the pulp
chambers of the treated teeth he has shown that one of two
reactions is produced in the dentin.In some cases there was
sclerosis of the cut dentinal tubules which forms a protective some
sealing off the pulp from the injury and underneath this region,
there is a further growth of tubular dentine. These reactions are
produced by the stimulation of the odontoblasts. The other reaction
that resulted was the formation of dead tracts. With this lesion
some or all of the odontoblasts, that are in connection with the
cut tubules die. On the pulpal aspect of these tubules, hyaline
mineralized barrier, secondary dentine is laid down, thereby
sealing the lesion from the pulp.Pulp:The changes in the pulp have
been studied by Langeland and Morslard and Shovelton. They state
that the damage to the pulp is to a large extent due to the heat
generated. They have shown that when precautions are taken to
minimize heat production by using burs rotated slowly in a speed
reducing handpieces, the only evidence of pulp damage was a slight
reduction of the odontoblast layer with the displacement of a small
number of odontoblasts into the dentinal tubules. When speeds upto
5,000 rpm were employed, there was more extensive displacement of
odontoblasts associated with marked vacuolization of the
odontoblast layer, and local hemorrhages may be seen in the pulp.
As the speed was increased, the changes became more severe. When
tooth reduction was done under a stream or spray of water, the
damage to the pulp was markedly reduced.Pulp changes associated
with tooth reduction using the air abrasive technique have been
studied by Kennedy and using ultrasonic technique by Mitchell and
Jenson. The changes in both the cases are similar to those produced
at the speeds of 5,000 rpm.The effects on the pulp of using high
speed rotary instruments such as the air turbine have been
investigated by Marsland and Shovelton. The changes found are no
severe than those produced at lower operating speeds provided that
adequate cooling of the cutting instrument by water jet or
air/water spray is ensured.Alterations in the hard tissues of tooth
cut by air turbines have been observed. The enamel over a wide area
of crown may show minute cracks and the dentin shows altered
staining reactions as a result a local overheating.RECENT
DEVELOPMENT:ANTI-SUCK BACK-Planmeca compact dental units, the
turbine drive air is not shut off abruptly but controlled down by
allowing the driving air to decrease gradually. The software of the
dental unit will keep on supplying the drive air into the turbine
according to carefully chosen parameters. This way there is no
possibility for the build-up of a vacuum effect that would cause
suck-back.Ceramic bearings- no need of lubrication and more
resistant to autoclave sterlization.Use of quartz rods instead of
fibre-optic.Easy-to-use push-button bur releases.Swivel
systems.Titanium handpieces.Smaller head size.ELECTRICAL HIGH SPEED
HANDPIECESadvantages are:More power and torque than air turbine
handpieces.Better bur concentricity.Less vibration and noise.Broad,
controllable speed ranges.Forward/reverse option are available.With
appropriate attachments, one system can be used for restorative,
prosthodontics, prophies and endodontics.Disadvantages are :Heavier
than air turbine.More expensive.Learning curve may be
required.Attachment heads not as small as the small-head air
turbines.May not be able to fully replace the air turbine.Infection
control concerns.DiscussionIt is for more than 125 years, that
rotary instruments have been in use, for tooth reduction
operations, in different forms, from a hand rotary instrument to
ultra sonic instruments, which have the rotational speeds ranging
from very low speeds in case of band rotary instruments to 5,00,000
rpm in case of air bearing hand piece. These remarkable advances in
the instruments have greatly reduced fatigue in the operator
because of the physical case of manipulation and have considerably
increased the comfort to the patient by reducing the actual working
time and pressures required for tooth reduction, thereby minimizing
the factors of heat generation and pain. Though high speed
techniques have been a born to the dental profession, they have
their can limitations. It is interesting to not that, in spite of
considerable improvements in tooth reduction procedures and the
instruments used for the same, the principles and biologic
objectives have not changed.These improved methods of tooth tissue
removal have a potential to damage the healthy teeth and
surrounding structures, if they are used without proper
understanding of their working and if they are used without taking
proper care. Improper handling of these modern equipment may also
be different to the longevity and working capacity of the
instruments themselves.For successful and efficient use of those
cutting tools, certain factors should be given consideration. Heat
that is generated, while the tooth tissue is being removed must be
kept, down to the minimum and at the sametime, whatever heat is
generated, must be eliminated as efficiently and as quickly as
possible by employing coolants, in any one of three forms commonly
used i.e. water, air/water spray or air alone. Simultaneously with
the coolant, if water or air/water spray is used, an efficient
mechanism for remove of the water from the oral cavity must be
employed. Otherwise, the clinical procedure is delayed, if the
patient has to spit out the water, every now and then. By
eliminating the water evacuation equipment, we are losing one of
the advantages of these high speed instruments i.e. reduced working
time for a particular preparation. Use of efficient coolants, not
only eliminate the heat generated, but at the same time, keeps the
operating area clean and free of any debris.High speed cutting
methods have a further advantages in that, they reduce the
annoyance that may be caused to the patient, when low speeds are
used with the modern high speed cutting devices, the vibration
produced is of a frequency that is generally beyond the upper
threshold of perception of the average patient.Pressures that have
to be employed in the use of high speeds are considerably reduced,
in comparison with those needed for low speeds.Thus, when the
factors of pressure, temperature and vibration are kept within the
tolerance limits, the patient comfort is certainly improved.Size of
the cutting tool to be used for particular tooth reduction
procedure is an important consideration, particularly while using
high speeds. Oversized cutting tools should be avoided, as they are
difficult to control and at the same time, the accuracy of tooth
preparation on procedure is also adversely affected.Biologic
reactions of the tooth tissues, particularly dentin and pulp,
should not be over locked, when high speeds are employed for tooth
reduction operation. These responses have been studied by a number
of people and they have shown that, the response are not
significantly different from those, when low speeds are used,
provided, effective coolants are employed.Thus it can be concluded
that, high speed equipments for tooth reduction if used with proper
understanding and due care, provide definite advantages over the
conventional low speed cutting procedures. This fact places the
high speed devices at definitely a higher level as against their
low speed counterparts.Conclusions1.High speed cutting devices, if
used with a thorough understanding of their mechanism and due care
to the biologic integrity of teeth and surrounding structure, are a
boon to dentistry.2.In the process of tooth reduction using high
speeds considerable amount of heat is generated and an effective
coolant is a must for preservation of tooth integrity and patient
comfort.3.Vibration is increased with the increase in speed, but it
is beyond the threshold of prerception of the normal human beings
and hence not harmful.4.Biologic reactions of the dentin and pulp,
to high speed cutting, cannot be overlooked.SummaryA brief history
of rotary instruments has been presented. A critical evaluation of
the high speed cutting devices, as to their advantages,
disadvantages, and precautions to be taken during their use, has
been assessed at length. Biologic reactions of dentin and pulp, to
high speed cutting have been discussed in brief.
ContentsI.IntroductionII.Review of Literaturea.Advantages of
high speedsb.Disadvantages of high speedsc.Types of high speed
instrumentsd.Heat generatione.Coolantsf.Vibrationg.Spread of
pathogenic organismsh.Size of cutting instruments and cutting
speedsi.Biologic responses of dentin and pulp to high speed
cuttingIII.DiscussionIV.ConclusionV.
Summary
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FINISH LINES IN FPDFinish LinesINTRODUCTIONThe ultimate goal in
fixed and removable prosthodontics is the maintenance and
preservation of the remaining dentition. The execution of this goal
can be achieved initially by tooth preparations that are clinically
sound and will increase the longevity of the abutments. Likewise,
proper tooth preparation and contoured restorations that are
periodontically acceptable are of major importance in maintaining
optimal periodontal health, restoration of occlusal harmony, and
stability of the restored dentition. Restoration of teeth is
possible only if sufficient space is created for the application of
the appropriate thickness of material required. Preference for the
shoulder with a bevel preparation allows ample room for the
periodontal tissues and the bulk of the restorative materials
(metal crowns with acrylic resin veneers or porcelain-fused-to
metal). The indications and contraindications for each type of full
coverage preparation will be reviewed.
TYPES OF FINISH LINESOver the years there is often discussion
about the various types of full coverage preparations and their
advantages and disadvantages. There are four types of finishing
lines for full coverage restorations:1.Knife
edge.2.Chamfer.3.Shoulder.4.Beveled shoulder.Knife-Edged
Preparations:A knife-edge, or a feather-edge preparation that is
basically designed so that as the tooth is prepared zero cutting
results at the gingival termination. The dentist employs the rotary
instrument and leans the cutting stone or bur inward by rotating on
that gingivaltermination and cutting mostly at the occlusal end. It
is a process of tipping the rotary instrument occlusally. When
planning the taper of this type of preparations, a number of
problems are observed, especially with a short crowned tooth or on
a tooth with a normal anatomic crown where the preparation ends at
the cementoenamel junction.1.When using ceramometal restorations
and aesthetic considerations are critical, because there is zero
cutting at the gingival termination and aesthetic concerns are of
primary concern and a metal collar is not to be used, then the
resultant slip joint type of crown becomes overcontoured
gingivally. Concomitant with this, the entire contour of the crown
becomes greater, as without overcontouring, color cannot be
achieved in the gingival portion.2.The retention and resistance
form of the preparation is compromised. As the preparation becomes
overtapered, the ability of the crown to be retained on the tooth
structure becomes diminished. As an illustration, altering the
taper from a perfectly parallel preparation to one with a 6-degree
taper, which is considered the ideal because it is achievable,
almost 50 per cent of the retention is lost. With alteration from a
5-degree taper to about 20 degrees, 25 per cent of the retention
remains. Thus, retention is developed on the basis of the luting
strength of the cement. Cement has a crystalline structure, so it
does not fracture at one time. Each time this cement is challenged,
more fracturing of the crystals occur until, finally, enough of the
crystals are fractured to enable the restorations to loosen. Thus,
these overtapered preparations have compromised long-term
retention.3.Another negative aspect of overtapered preparations is
that they develop internal stress wedging. As force is applied into
the ceramometal crown with a conically shaped preparation, it will
act like a wedge. The crown exerts a force on the preparation, even
if cement is in between. All materials have flow, even though they
are solid. That flow is enough to cause wedging of the metal. The
veneering material is strong under compression but is weak under
tension. The internal stress wedging tends to expand the metal
substructure, causing the porcelain veneer to craze and fracture
over a period of time.However, there is a place for a knife-edge
preparation in the dentists armamentarium. This is the type of
preparation that the clinician should utilize with long clinical
crowns found with postperiodontal surgery cases. With a
postperiodontal case, the clinical crown encompasses the anatomic
crown and part of anatomic root structure. If the preparation
extends to the tissue because of old restorations, root caries,
root sensitivity, and aesthetics, very long preparations will be
developed. A shoulder preparation cannot be developed, because once
the practitioner cuts past the junction of the enamel and onto the
cementum, the root may begin to taper severely. Thus, the roots
become narrower, the farther apically the tooth is prepared. In
these compromised cases, if a shoulder is cut, the resultant long,
thin preparation will fracture easily. Interestingly, a knife-edge
preparation when employed with a long clinically crowned tooth is
not a overtapered as on short clinical crowned tooth; therefore,
diminished retention of a normal sized preparation is not a concern
with long preparations.4.Another problem with knife-edged
preparations is the resistance form. Resistance form is the ability
of a crown to withstand displacement from eccentric or lateral
forces. A lateral force is applied when the mandible goes into
eccentric movements. This is a rotational force that tends to
dislodge a crown.5.Three factors reduce the resistance to
dislodgement from rotation.a . The longer preparation the more
resistant to dislodgment.b. The more parallel a preparation, the
more resistant to rotation forces.c.The smaller diameter the crown,
the more resistant to rotation forces.For example, given the same
length and taper, a bicuspid is more resistant to being dislodged
by rotation that a molar. The molar then becomes the liability. In
consequences, in the case of a long-span fixed partial denture
extending from a cuspid to a second molar, cementation wash out
occurs on the molar. Rarely, is it on the anterior tooth, as the
molar has the larger diameter and thus the least resistance to
dislodgment. As a result the management of a large-diameter tooth
requir