Tweed Profile

THETWEED PROFILE

published by

THE CHARLES H. TWEEDINTERNATIONAL FOUNDATION FOR

ORTHODONTIC RESEARCH AND EDUCATION

Volume #62007

CONTENTS

ACKNOWLEDGEMENTS:Cover design by Jasmine Suke and Jack Dale.Cephalometric tracings of a patient treated by Herb Klontz.Beautiful young model, with an ideal Tweed profile, taken from a prominent fashion magazine.

SCIENTIFIC PAPERS

Mechanics Made Understandable— Robert Isaacson

Thirty Years of Faces— C. Edwin Polk

A Critical Review of Class II Severe Malocclusions Treatment: Skeletal, Dentaland Aesthetic Effects — Pierluigi Delogu

Review of the Literature on Post Retention Stability of Mandibular Incisors— Jim Boley

A “Different” Look at Vertical Dimension Control with Tweed-Merrifield Mechanics— Luca Giuliante and Roberto Ursini

An Analysis of Metal Brackets Characteristics— Isabella Lombardi

Premolar and Additional First Molar Extraction: Effects on Soft Tissue in High Angle Class IIDivision 1 Patients — Takemasa Ozaki

CASE REPORTS

Case Report: High Angle Class II Malocclusion Treated with Premolar and Additional FirstMolar Extraction — Elie W. Amm

Case Report: My First Experience with the Tweed Merrifield Philosophy — Luigia Brera

Case Report: My First Experience with the Tweed Merrifield Philosophy— Matteo Beretta

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SCIENTIFICPAPERS

Mechanics is a fundamental of orthodontics and should be well understood by all orthodontists.Unfortunately, this is not the case. The specialty of orthodontics has grown rapidly and its maturationhas lagged behind its application. This is not unique, however, as this sort of evolution is common tomany fields. The only difference is the speed at which it proceeds. First, there are informalpreceptorships where each one teaches one. Then, preceptorships are grouped into schools which areinitially proprietary and soon commercialized. Finally, standards are demanded and evolve and, if a fieldhas a scientific basis, its development proceeds in an orderly fashion with the evolution of accreditedschools and collation of the knowledge base into formal publications. The problem is that the how-to-do-it gets ahead of the rational basis for what is being done and, once in practice, it changes slowly and withgreat difficulty.

No one denies the desirability of knowing and utilizing mechanics, but not many practitionersreally understand mechanics. One major problem has been the lack of well-organized information setout in a didactic manner. Secondly, the problem has been the lack of information on practicalapplications of this information. Personally, I taught all kinds of applications for many years withouttruly understanding them. Finally, when I moved to new geographic locations, it became mandatory forme to offer a rational basis for the appliance designs and wires we were teaching. At that point I made itmy business to read everything available on the subject and ended up pretty confused. Becomingproficient required a long and difficult period of study.

It is apparent that mechanics is a physical science and the physical sciences are far more maturethan the social sciences, with the biological sciences somewhere in between. My first epiphany was todiscover that biomechanics is a merger and needs to be separated for analysis to take place. The bio partis what happens in the body – how the cells and tissues respond to the physical signals we send withappliances. This is very important, but it is not easy to study this question if you do not know whatsignal you sent. The physical displacement of a tooth and the signal sent by an appliance is a result of avery understandable set of force system we create with our appliances.

This means getting the ground rules firmly in place. To start with, it is important to speak thesame language and to define terms. A terminology has arisen in orthodontics that is not identical to whatis used in physics or engineering statics. Center of resistance, force, couple, moment, equilibrium – theseare all the fundamentals. Your motivation comes from understanding, ‘What difference does all of thismake?’

The edgewise appliance was, and continues to be, unique because it provides a series of couplesin all three planes of space. A couple is nothing more than a pair of equal and opposite forces acting on abody in the same plane. The force system of a couple is the sum of the two individual force systemsproduced by the equal and opposite forces of the couple.

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MECHANICS MADE UNDERSTANDABLE

The 2006 L. Levern Merrifield Lecture – A SummaryRobert Isaacson

All existing evidence suggests the probability that the edgewise appliance was empiricallyderived, but in retrospect it is not difficult to see the solid theoretical basis. Once you have seen how anedgewise couple really works, you are the master and able to use it, to modify it and to gain maximumcontrol and efficiency.

Couples are intuitively understood better by some people than others. However, couples haveequilibrium just like a force. The equilibrium of a force is obvious to most people, but the equilibriumof a couple is much more subtle and is obvious to no one. The equilibrium of a couple is not intuitiveand is the source of many of the so-called side effects and unexpected tooth movements seen in patients.

The couple is at the essence of edgewise mechanics and the most non-intuitive part of a couple isits equilibrium. To an orthodontist, equilibrium with a single force is obvious, but with a couple it mightbe a “bit confusing”. Equilibrium requires that the sum of all forces in any plane equal zero.Equilibrium in mechanics is based on Newton’s third law that requires “for every action an equal andopposite reaction” and, consequently, the sum of all the moments in one direction in a couple must equalthe sum of all the moments in the opposite direction.

I am not so arrogant or egotistical as to think I can give you all you need to know in a summarypaper, but I do know you can learn what you need to know, increase your pleasure in practice and avoidunwanted surprises. Start by studying the reference below. It contains everything I know.

REFERENCE

Isaacson RJ, et al. Biomechanics and Appliance Design. Seminars in Orthodontics; 1995:1;1-63.

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When many of us received our specialty training approximately thirty years ago, the way the teeth“fit” after orthodontic treatment was a major concern. Some would have today’s “novice” believe thatthe “fascination” with faces that we are now experiencing is a new phenomenon. Those who suggestthis premise are misinformed.

Why did Tweed start extracting teeth in the mid-late 1930’s? One reason only - THE FACE! Hedid not like the protrusive faces he was creating with non-extraction treatment. He considered 80% ofhis treatment to be a failure because of the protrusive faces that were a direct result of his diagnosticdecisions.

The facial balance, harmony and proportion that a patient has must be 1) improved by orthodontictreatment or 2) preserved by orthodontic treatment. The “complete” orthodontist has always beenconcerned with facial esthetics. This new “buzz word” is really nothing new.

To look at the faces that have been improved/maintained by orthodontic treatment over the course of30 years has been an interesting project. This paper is a brief summary of one practitioner’s attempt tostudy a thirty year effort. A series of faces will be presented.

Figure 2: Patient treated ten years later withextractions

Figure 1: Patient treated approximately thirty yearsago

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THIRTY YEARS OF “FACES”Tweed Foundation Biennial Meeting – October, 2006C. Edwin Polk

Figure 5: Facial esthetics improvement Figure 6: Facial esthetics improvement

Figure 3: Facial esthetics improvement

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Figure 4: Facial esthetics improvement

The first patient (Figure 1) was treated approximately thirty years ago with the extraction of fourpremolars. Note the improvement in the balance and harmony of the lower face. The patient, as ex-pected, has a “better” face at five year recall than at the cessation of treatment.

The next patient (Figure 2) was treated ten years later − again with extractions. The improvement inthe balance and harmony of the face is startling.

The profiles shown in Figures 3 – 6 show improvement in facial esthetics. These photographsreflect a time span of fifteen years in the practice. They exhibit a definite concern for facial esthetics. Inour current world of “clear braces”, “no braces”, self legating brackets, “robo ortho”, etc, etc we mustnever relinquish our concern for balance and harmony of the lower face. None of these magical “new”systems will give the patient balance and harmony of the face as a de facto outcome of treatment. Thebalance and harmony for which we all strive is a result of diagnosis, treatment planning and treatment.Facial balance cannot be ignored for the sake of using a particular “appliance of the day.” Facialbalance and harmony has been, is now, and always will be the goal of the caring, conscientious orth-odontic specialist. Tweed showed the specialty how to achieve it. We must use what we have beentaught for the benefit of our patients. The faces we create are our legacy for future generations oforthodontists.

INTRODUCTION

Class II malocclusions are, without doubt, considered to be a “hard”problem for orthodontists. This is due to the skeletal problems that themalocclusion presents. In the past, dental correction was the most importantobjective of Class II correction and techniques for obtaining large dentalmovements to ensure a Class I occlusal relationship were performed. Severalyears have passed and, particularly in the last two decades, orthodonticobjectives are evaluated more and more by posttreatment function and facialesthetics. Consequently, several studies that have evaluated the achievementof these goals as a result of Class II malocclusion correction have been done.Orthopedic surgical therapies have been developed for improvingorthodontic treatment results of Class II malocclusion treatment.Observation and analysis of treated patients now includes esthetics and

function as well as good occlusion. Several studies 1-2-3-4-7-10-11-13 have demonstrated the clinical results oforthodontic therapy. The research of Delogu et al.6, Pancherz et al.12, and Bolla-Carano et al.1 confirmthat all the aspects of Class II correction should be analyzed in order to help the orthodontist betterunderstand what happens during treatment. In the present study severe Class II malocclusions wereanalyzed for dental results as well as skeletal and esthetic changes. This study sought to give insightinto the limits of Edgewise mechanics. The results of “two phase” treatment were compared with “onephase” permanent dentition treatment.

MATERIALS AND METHODS

55 patients from 9 to 34 years of age were selected (23 male – 32 female). These patients weregleaned from a sample of 1085 patients from orthodontic offices that use Tweed-Merrifield permanentdentition directional force therapy and Phase I treatment with the same concept of controlled force.These severe skeletal Class II malocclusion patients exhibited the following:

• ANB > 6°• OVJ > 5 mm and OVB >5 mm • Class II molar relationship, with at least 4mm distal occlusion on each side. • No surgical treatment

• Only dysmorphic patients. The sample does not include genetic syndromes or congenitaldeformities.

• Class I dentition at the end of treatment

All patients had full orthodontic records pre, during and post therapy: facial and intra oralphotographs, plaster casts, panoramic radiographs and a cephalogram (Figures 1, 2, 3). Cephalometricanalysis of skeletal values was done according to the Tweed Foundation analysis sheet8. Values for

Delogu PierluigiD.D.S. Ort. Ph

Fiorile FaustoD.D.S. Ort.Ph

Napolitano AlfonsoM.D.S. MxF. Surg.

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Gaspa Graziella, D.D.S.

A CRITICAL REVIEW OF CLASS II SEVERE MALOCCLUSION TREATMENT:SKELETAL, DENTAL AND ESTHETIC EFFECTS

Tweed Foundation Biennial Meeting – October, 2006

determining true dental movements were taken from the Gosh and Nanda7 analysis and estheticparameters from Gonzales-Ulloa6 were used (Figure 4).

STATISTICAL ANALYSIS

For each parameter analyzed in this paper the mean of values at the start of treatment, after 12months (only early treatment) and at the end of therapy were calculated. For determining the dispersionaround the mean, the standard deviation was calculated.

In order to “separate” skeletal and esthetic changes induced by therapy, the Student T test wasperformed for every parameter. For 26 patients the same T test was calculated on records made after 12months of therapy.

RESULTS

Statistical results of data observed on cephalograms pre, during and post therapy are shown inTable 1. The statistical difference between the Student T test for pre and posttreatment values issummarized in Table 2. The early treatment values versus permanent dentition treatment values arecompared in Table 3.

Figure 1: PretreatmentCephalogram

Figure 2: Progress Cephalogram

Figure 4: Tracing foranalyzed parametersFigure 3: Posttreatment

Cephalogram

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DISCUSSION

SKELETAL VALUES

The mean of the values shows that correction of sagittal parameters is due to a decrease of SNA(from 81° to 78°) and an increase in SNB from 73.3° to 75° (Graph 1). ANB was corrected (from 6.8°to 3.6°), overjet (from to 8.2mm to 3.8mm), and overbite from 4.8 to 2.8mm. When values of patientstreated early are compared to those treated in the permanent dentition, the mean value of SNB is moresevere at the start in the early treatment sample (71.9° compared to 74.9°).

No significant statistical changes of FMA, FHI and Occlusal Plane angle were found. Thisfinding demonstrates that the forces were good for vertical control of the dentition and impededunfavorable clockwise rotation of the lower third of the face.

Mandibular response had a mean value of 5.5mm at the end of therapy. This value explains theClass II correction that was obtained. The response achieved after 12 months of therapy in the earlytreatment sample was 6.1mm. This finding gives credence to previous studies5 that claim the largestresponse is obtained during treatment (Graph 2). Comparison of mandibular response betweenpermanent dentition and early treatment shows a more favourable mandibular response in the earlytreatment sample (6.06mm to 4.4mm). But – the early treatment sample was in appliances over alonger period of time.

DENTAL VALUES

The maxillary first molar shows slight extrusion after therapy, but the molar does not reallymove distally. The maxillary incisors demonstrated a small lingual inclination as the incisor axis to SNangle decreased from 104.8° to 100.8° (Graph 3). The mandibular first molar moved 4mm mesiallyand 3mm vertically (Graph 4). This change was correlated to the amount of mandibular response and tovertical control of the maxillary dentition. In the early treatment patients the amount of mesial

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Graph 1: Sagittgal values Graph 2: Mandibular response

Table 1: Means pre, during and post therapy of all

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Table 2: T student test statistical significancy (High significant= nn)

movement of the mandibular molar was greater, confirming the larger mandibular response in thissample. Other dental movement values were similar between the two groups.

FACIAL VALUES

The upper lip moved back 1mm. This movement opened the nasolabial angle a mean of only 6°,taking it to 115°. The opening is larger in the early treatment sample (from 108.2 to 115.6°). Z angleincreased (from 63.2° to 69.4°). This was to be expected with the mandibular response and the counterclockwise growth pattern. All these values logically show that applied forces yield quantifiable resultsbecause of good dentition control. The values prove that the solution for a severe Class II malocclusionis a good amount of mandibular response and an upper arch that does not change.

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Table 3: Early treatment vs Permanent dentition treatment results

Graph 3: Upper incisor movement

Graph 4: Lower first molar changes

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CONCLUSIONS

Analysis of the results of this study yield the following conclusions:

• Skeletal values at the end of therapy tend toward a normal range. Positive mandibular response(5.5mm) is a major factor in the correction of a Class II malocclusion.

• Dental movements of the maxillary incisor and the maxillary molar do not show much change.There was only a slight extrusion of the molar (0.7mm) and moderate incisor repositioning.

• The mandibular molar moves mesially 4mm and vertically 3mm.• Esthetic parameters are changed slightly if the nasolabial angle increases. It must remain at a

good value for balanced facial esthetics.• The control of the dentition during therapy was shown to be the primary reason for resolution of

the Class II malocclusion because of the mandibular response which led to achievement ofskeletal and dental objectives.

• Mandibular response in the early treatment patients was greater than it was if treatment wasdone only in the permanent dentition. However the duration of treatment was greater for theearly treatment patients because of the longer treatment times.

REFERENCES

1. Bolla E, Muratore F, Carano A, Bowman SJ.Evaluation of Maxillary Molar Distalization Withthe Distal Jet: A Comparison With Other Contemporary Methods. The Angle Orthodontist: Vol.72, No. 5, pp. 481–494.

2. Bussick TJ, McNamara JA Jr. Dentoalveolar and skeletal changes associated with the pendulumappliance. Am J Orthod Dentofacial Orthop. 2000; 117:333–343.

3. Byloff FK, Darendeliler MA. Distal molar movement using the pendulum appliance. Part 1:clinical and radiological evaluation. Angle Orthod. 1997; 67:4249–260.

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4. Carano A, Testa M. The distal jet for upper molar distalization. J Clin Orthod. 1996; 30:374–380.

5. Delogu P., Fiorile F., Napolitano A. Azione delle forze ortopediche secondo il directional forcesystem nel trattamento intercettivo delle classi II: effetti sulla risposta mandibolare. Doctor Os,16(1), suppl.1, 83-86, gennaio 2005.

6. Delogu P., Fiorile F., Napolitano A., Pazzola F. Critical aesthetic parameters in orthodontictreatment of severe class II malocclusion. Paper winner as “best lecture” in the XVII CongressoInternazionale SIDO. Progress in Orthodontics 2003; 4/II: 74/119.

7. Fortini A, Lupoli M, Giuntoli F, Franchi L. Dentoskeletal effects induced by rapid molardistalization with the first class appliance. Am J Orthod Dentofacial Orthop. 2004; 125:697–705.

8. Gebeck T.R., Merrifield L.L., Analysis: concept and values, Journal of the Charles TweedFoundation, 17: 19-64, 1989.

9. Ghosh J, Nanda RS. Evaluation of an intraoral maxillary molar distalization technique. Am JOrthod Dentofacial Orthop. 1996; 110:639–646.

10. Gianelly AA. Distal movements of maxillary molars. Am J Orthod Dentofacial Orthop. 1998;114:66–72.

11. Hilgers JJ. The pendulum appliance for Class II non-compliance therapy. J Clin Orthod. 1992;26:700–713.

12. Pancherz H. The mechanism of Class II correction in Herbst appliance treatment. Acephalometric investigation. Am J Orthod. 1982; 82:104–113.

13. Zinzinger GS, Wehrbein H, Gross U, Diedrich PR. Molar distalization with pendulumappliances in the mixed dentition: effects on the position of unerupted canines and premolars.Am J Orthod Dentofacial Orthop. 2006 Mar; 129(3):407-17.

Stability of treatment results is one of the four fundamental goals of orthodontic treatment:Dental relapse was a major problem for early practitioners who were faithful followers of Dr. Angle’sphilosophy of adlibidum expansion, i.e. they resolved all tooth size to arch length discrepancies byincreasing arch length.

The next generation of orthodontic pioneers — Tweed, Strang, and Nance — studied theirpatients and others’ patients post retention and concluded that advancing mandibular incisors, lateralexpansion, and/or increase in arch length in the mandibular arch was incompatible with stability. Thesemen led the specialty into an era of minimal expansion in the mandibular arch. They espoused uprightmandibular incisors.

Long term stability remains a major concern for contemporary orthodontists. There has neverbeen and probably will never be what could be considered the “gold standard” prospective, randomizedstudy with matched controls of long term stability. So in this age of evidence based dentistry, it seemswe are left with retrospective studies that help us understand long term postretention stability problems.The study design and the integrity of investigators has to be relied on to eliminate sample selection biasas much as possible.

Most reported samples have been based on the availability of patients with complete pre-treatment, posttreatment, and postretention records and the author’s effort to eliminate bias. Perhaps thebest sample in the literature is one in which every patient was treated in the same manner. Examples ofthis protocol are the two St. Louis University studies of all Class II, Div. 1 patients treated from 1969 to1980. Five attempts were made to contact each patient. Of the 2500 patients, 125 finally made it intothe two studies. This retrieval rate of 1 out of 20 illustrates the difficulty of doing a long termpostretention study.

These two St. Louis studies which compared “borderline” extraction to nonextraction and “clearcut” extraction to nonextraction patients 15 years posttreatment could be the “gold standard” for longterm postretention studies in the existing literature. The long term irregularity index for the foursubsamples was 2.9mm, 3.4mm, 3.2mm and 3.7mm respectively. The mean value for both samples was3.3mm. This value places them in the minimal irregularity (<3.5mm) category. Patients in thesesamples had a satisfactory clinical result.

A search of the American literature for studies on the stability of mandibular incisors wasconducted. Both published papers and unpublished Masters theses have been compiled.

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REVIEW OF THE LITERATURE ON POST RETENTION STABILITY OF MANDIBULAR INCISORS

Tweed Foundation Biennial Meeting – October, 2006Dr. Jim Boley

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Thirty-five (35) studies from numerous universities and individuals are summarized. Onlystudies that used Little’s irregularity index to evaluate the severity of the irregularity were included.Patients had to be free of retention for at least three years. Nearly 2000 patients who had eitherextraction or nonextraction treatment were involved in the studies. The average time posttreatment was12 years. The mean pretreatment irregularity value was 6mm (severe > 6.5mm). Sixty-nine percent(69%) of the samples and subsamples had minimal irregularity (< 3.5mm) postretention. The averageirregularity index for all these studies was approximately 3mm.

Three tables are included that summarize the pertinent aspects of these studies. Table A presentsthe entire sample of 35 studies. Table B presents data for only the extraction samples and Table C forthe nonextraction samples.

This extensive review of the literature should do much to dispel the notion that long termstability is a rare, fortunate accident. Instead, it is just the contrary. A significant majority of the studiesfound satisfactory stability. It is interesting to note that there are several common characteristics of these“satisfactory stable” samples. There was 1) minimal expansion of the mandibular canines and molars,and 2) retraction, or at most, minimal advancement of the mandibular incisors. Of the 16 nonextractionsamples and subsamples that exhibited minimal or near minimal relapse, only two were in the range of3.0mm of AB arch length and/or arch perimeter increase. The average for these measurements was anincrease of only 0.14mm and none of the samples reached 4 or more millimeters. Although thesecommon characteristics cannot guarantee stability, they may be considered prerequisites.

Notably, the poorest stability found in this literature review was for the sample whose selectioncriteria was to have increased arch length at least one millimeter in the mixed dentition. This study byLittle, et al, reported in the May, 1990 AJODO, seems to support the contention that treatment makes adifference. The expansion approach to resolving TSALD by increasing arch length in the mixeddentition resulted in an irregularity index of 6.06mm postretention, while the average IrregularityIndexes for the other 16 nonextraction studies, which exhibited decreases or at most only minimalincreases in arch length/perimeter, was 2.7mm.

The findings of this literature review support the conclusions reached by Blake & Bibby in theirliterature survey, Retention and Stability: A review of the literature, AJODO, September, 1998. Theystated:

“Permanent retention is cited by several authors as the only way to ensure longterm posttreatment stability. However, as trained orthodontists, it is incumbent on us totake a more proactive approach in dealing with the factors associated with relapse. Weshould aim to remove the primary burden of preventing relapse from our patients and

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would be well advised to maintain as treatment the following documented basicprinciples:

1. The patient’s pretreatment lower arch form should be maintained.2. Original lower intercanine width should be maintained as much as possible.3. Mandibular arch length decreases with time.4. Advancing the lower incisors is unstable and should be considered as seriously

compromising lower anterior posttreatment stability.5. Fiberotomy is an effective means of reducing rotational relapse.6. Lower incisor reproximation shows long term improvements in posttreatment stability.”

Table A: Long Term Post Retention Studies

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Table B: Extraction Samples in LT Post Retention Studies

Table C: Non Extraction Samples in Long Term Post Retention Studies

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Summary

“Directional force can be defined as a group of force system thatuses directional control to precisely position the teeth so they arein harmony with the patient’s skeletal and facial patterns. Aprimary objective of directional force mechanotherapy must be tocontrol the vertical dimension during the active phase oforthodontic treatment.1

Good directional force treatment requires cooperation from the patient. He/she hasto wear the high pull head gear (HPHG) throughout the treatment. The main causeof the failure of this type of mechanotherapy is the lack of cooperation by the patient.

In this study the investigators examined an orthodontic force system which makes patientcooperation less difficult while keeping the focus on vertical control, one of the main objectives ofTweed-Merrifield mechanics. Dental and skeletal effects of these “different” mechanics were analyzed ina group of growing patients who presented with class II division 1 or class I protrusive malocclusions.

In order to avoid down and back rotation of the occlusal and the mandibular planes, it is necessaryto support the anterior area of the denture during orthodontictreatment (Figure 1). Extrusion of teeth is a movement whichcan happen easily from the beginning to the end of thetreatment: during denture preparation, (correction of dentalrotations, alignment, levelling of the curve of Spee, mandibularanchorage preparation), denture correction (anterior closing ofspaces, class II mechanics), and during denture completion(use of intermaxillary elastics). (Figure 1) In order, to avoiddown and back rotation of horizontal planes, Merrifield2

introduced two important concepts:

Figure 1: Back rotation of the occlusal andthe madibular planes

A “DIFFERENT” LOOK AT VERTICAL DIMENSION CONTROL WITHTWEED-MERRIFIELD MECHANICSTweed Foundation Biennial Meeting – October, 2006

Luca GiulianteRome, Italy

Roberto UrsiniRome, Italy

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1. Sequential bonding: facilitates less dental movement at one time and allows the clinician tobetter control the vertical reaction of the dental arch.

2. Application of Force: this concept consists of moving the application point of the extraoraltraction from the upper first molar to the anterior denture area. The use of high pull headgear(HPHG), during each phase of orthodontic treatment controls the horizontal planes (palatal,occlusal and mandibular) and therefore facilitates counter clockwise rotation of the lower thirdof the face. This has positive repercussions on facial esthetics (proportion, harmony andbalance). (Figure 2)

For achievement of the optimum orthodontic result, it isnecessary that patients cooperate by wearing the anteriorHPHG during the period of treatment (around 24 months for14 hours for day). This type of cooperation is generallyforthcoming amongst patients who are highly motivated,especially by the presence of a particularly seriousmalocclusion. For the majority of patients however, ourcommon experience is that the level of cooperation with thewearing of headgear diminishes with the passing of time. Poorheadgear wear compromises the achievement of one or more ofthe objectives of treatment: function, stability or esthetics.

Consideration of these concerns has inspired us toinvestigate an alternative orthodontic system of varied forces

that will allow a reduction in the level of cooperation with headgear that is required by the patient,while at the same time maintain a high level of control against undesirable dental reactions so that theideal orthodontic objectives can be achieved.

Description of Mechanotherapy

In place of the HPHG a “second” wire, an .018 x .025 reverse NiTi (Figure 3) is inserted into a 022x .028 tube which is. above the bracket of the first upper molar (Figure 4). This auxiliary arch is tied tothe main archwire at the anterior area (Figures 5, 6).

This auxiliary wire applies a constant intrusive force on the anterior area. The force is not applieddirectly to the teeth. In the posterior area it acts as a second order bend (tip back) that is normallyapplied to the upper first molar. The therapeutic protocol of using this auxiliary wire is different,depending on nonextraction or extraction protocols.

Figure 2: Porportion, harmony andbalance

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1. Nonextraction protocol: The use of anterior verticalelastics (AVE) from maxillary to mandibular hooks facilitates theachievement of denture preparation and of anchorage preparationof the mandibular posterior teeth. The maxillary anterior area isstabilized by the reverse NiTi. This system of force is maintainedfor the duration of treatment: denture correction (class IIcorrection) and denture completion (Figure 7).

2. Extraction protocol: After approximately six months ofcanine retraction with the HPHG anterior space closure is started(Figure 8). During this phase, the constant use of the auxiliarywire tied to the first archwire allows retraction of the anterior teethwithout loss of vertical control. Denture correction and denturecompletion are done with the same force system (auxiliary wire,anterior vertical elastics, class II elastics or cusp seating elastics).

METHODS AND MATERIAL

With this system of force we have treated 20 growing patients(average age:13.2). These patients had all permanent teeth presentand had class II division 1 or class I dentoalveolar biprotrusionmalocclusions (ANB=3.66, std: 2.57), normo/hypo-divergent(FMA: 21,90 std:5.70). The average duration of treatment was 25months.

The goal of this study was to analyze skeletal and dental effects of this system on our sample patientgroup. Cephalograms and tracings of each patient were analyzed at the beginning and at the end oftherapy. The same method of analysis that was used by Gebeck and Merrifield in 19951,2 was chosen to

Figure 3: Second wire

Figure 4: .018x.025 reverse NiTi

Figure 6: Auxiliary arch is tied to mainarchwire

Figure 5: Auxiliary arch is tied tomain archwire

Figure 7: Denture correction andcompletion

evaluate skeletal and dental effects. In addition, three other angular measurements relative to threehorizontal planes (palatal, occlusal and mandibular), were chosen in order to better understand theeffects of this “new” mechanical system on vertical control.

Skeletal values studied were:

· PP-Occ: angle formed between the palatal plane and theocclusal plane;

· PP-MP: angle formed between the palatal plane and themandibular plane;

· Occ-MP: angle formed between the occlusal plane andthe mandibular plane; (Figure 9)

· MR (mandibular response)(Figure 10): measured inmillimetres from projection of x points on theoriginal occlusal plane from both pretreatment andposttreatment cephalograms.

Dental values: (The International tooth numbering system was used)· 16-ptv: the distance in millimeters from the most mesial contact point of the maxillary first

molar to a line perpendicular to the Frankfort plane passing to the most posterior and superiorpoint on the pterigomaxillary fissure (PTV).

· 16-pp: the distance from the tip of the mesiobuccal cusp of the maxillary first molar to thepalatal plane;

· 11-pp: the distance from the tip of the central incisors to the palatal plane; (Figure11)· 46-pm: the distance from the tip of the mesiobuccal cusp of the mandibular first molar to the

mandibular plane;

Figure 8:

Figure 9: Figure 10:

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Figure 11:

Table 1:

Table 2: Vertical Values

· 46-x: the distance from the mesial contact point of themandibular first molar and a line passing by the point x of themandibular symphysis, perpendicular to the occlusal plane ;· 41-pm: measurement of a perpendicular line drawn from the tipof the central incisors to the mandibular plane. (Figure 12)

The statistical model chosen to compare the data was theAnalysis of Variance. Average and standard deviation is registeredfor each value.

RESULTS

The tables show each measurement, in detail. The average value of each measurement beforetreatment, after treatment and the variation between the values before and after treatment was studied.An analysis of the angles of the diagnostic triangle of Tweed (Table 1), confirms a closure of FMA angleand an increase in FMIA, maintenance of IMPA, and an increase in the Z angle.

An analysis of the horizontal planes (Table 2) indicates vertical control of the lower third of the faceduring treatment. The occlusal plane was stable and every other plane closed.

An analysis of the values that reflect the facial height (Table 3), shows a proportional increase inboth values (AFH and PFH) and a maintenance of the value of FHI (ratio)5.

Figure 12:

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To complete the analysis of the results for the skeletal values, note that the values that indicate theanteroposterior position (Table 4) of the lower third of the face reflect a reduction of ANB and anincrease in the SNB angle, therefore a more anterior position of the mandible which is confirmed by thevalue MR (3.90).

DENTAL VALUE ANALYSIS

The “extrusion” of the upper and lower first molars, has been of equal value, while the lowerincisors have been substantially maintained in their initial position. The maxillary incisors have had asmall amount of extrusion. (Table 5)

DISCUSSIONS

The above results confirm a positive reaction of the lower third of the face to this type ofmechanotherapy. In fact, in spite of the high risk of loss of vertical control that can happen during thepreparation of mandibular anchorage and class II correction, the class II correction has beenaccomplished with positive mandibular response (MR: 3.90) and no “vertical expansion” (downwardand backward rotation of the occlusal and mandibular planes).

22

Table 3: Facial Height

Table 4:Antero-Posterior Values

Figure 13: Mandibularincisor and a smallextrusion of the upperincisor

· FMA and all the horizontal planes (Table 2) closed with treatment.· The FHI value remained the same from the beginning to the end of the treatment. The sample

group started with a good relationship between AFH and PFH (FHI: 0.71), and havesubstantially maintained the same relationship (FHI: 0.73).

The Z angle values confirm good facial esthetics. An analysis of the dental values confirms:

· Slight extrusion of maxillary and mandibular molars.· Maintenance of the position of the mandibular incisor and a small

extrusion of the upper incisor (Figure 13).

Some of this vertical molar movement can be attributed to alveolargrowth; but probably the extrusion of the maxillary molar, even though small,can be attributed to the fact that the auxiliary wire has a small extrusive forceon them. However, in spite of this small amount of molar extrusion, thehorizontal planes closed. “The efficacy of orthodontic mechanics isattributed to its ability to integrate with the intramatrix growth process, sothat matrix towards the horizontal development is encouraged.”6

CONCLUSION

In order to stimulate horizontal growth of the mandible and to promote good facial esthetics, it isnecessary to try and prevent all movements that have the tendency to open the mandibular plane and allhorizontal planes. This “vertical expansion” of the lower third of the face, if it happens, is the maincause of unsuccessful treatment according to Gebeck and Merrifield. They affirm, in fact, that this

23

Table 5: Dental Values

24

vertical expansion can be caused by a lack of patient cooperation, i.e. improper wear of the HPHGduring the preparation of mandibular anchorage and during the application of class II mechanics.

The auxiliary wire, instead of HPHG, solves this problem somewhat. As a matter of fact, after thefirst necessary months of HPHG to retract the canines and level the arches, the extraction patient, forthe remaining time in treatment, needs to wear only intraoral elastics. During nonextraction therapy,patient cooperation only involves the use of intraoral elastics.

This study shows that these mechanics work in harmony with growth. During the treatment ofnormodivergent patients, this orthodontic system of forces could be seriously considered. It is not validfor hyperdivergent patients. These patients must wear the HPHG. Without drawing any conclusions,this study could be a first step towards research that might lead to technique simplification while notmoving away from the achievement of ideal objectives. It would be interesting to compare the results ofthis study to those found in an identical sample treated in the conventional way.

REFERENCES

1. Vaden, JL: “Nonsurgical treatment of the patient with vertical discrepancy”, AJODO1998;113:567-82.

2. Merrifield and J.J. Cross: “Directional force system”, AJO 1970;57:435-463.3. Gebeck TR, Merrifield LL: “Orthodontic diagnosis and treatment analysis – concepts and values.

Part I” AJODO 1995;107:434-43.4. Gebeck TR, Merrifield LL: “Orthodontic diagnosis and treatment analysis – concepts and values.

Part II” AJODO 1995;107:541-7.5. Horn A.J. “Facial Height Index” AJODO 1992;102:180-6.6. J.P. Ortial, “La dimensione verticale: evoluzione teorica e pratica in tecnica Tweed-Merrifield” J

Edg, it, 2,37-48.

Isabella Lombardi and Roberta FerroNaples, Italy

INTRODUCTION

Buonocore’s12 introduction of an adhesion system that was used after acid etching of enamel andthe studies of Newman38 have made direct bonding a common clinical practice in orthodontics. Theeffectiveness of this technique is closely dependent upon bond strength. Many factors influence bondstrength: enamel quality, the adhesion system (type and concentration of etching agents, etching time,adhesive type), size and design of the bracket base, bracket composition, etc. There are many studiesreported in the literature about new adhesion systems1,2,3,4,7,8,9,13,16,19,24,25,26,30,35,39,41,44,45,48,49,51 and estheticbrackets4,5,10,11,14,23,24,26,31,39,41. However, in the past twenty five (25) years there are not many studies whichanalyze the characteristics of metal brackets2,6,15,17,18,22,23,24,26,27,29,32,33,34,39,43,46,47,50.

Metal brackets have only mechanical retention and must have bond strength that is able tosupport orthodontic forces and masticatory loads. But, at the same time, metal brackets must be estheticand easily removed at the end of the treatment. The increasing request for a more esthetic metallicappliance has created a reduction in the bracket size. This reduction becomes, then, a variable whichinfluences the bond strength or the ability of the bracket to remain on the tooth. The importance of thedesign and of the dimension of metallic brackets and the necessity to associate a clinically reliable bondstrength with esthetics and lower bracket visibility require bracket manufacturers to continually marketinnovative bracket designs. Additionally, because allergic phenomena are more frequent, the productionof metallic brackets with a lower Nickel content has been required.

In orthodontics, archwires are generally put into the brackets within an hour of initial bonding.The bonding agent might not, at this juncture, be completely polymerized. This assumption can be madebecause most of the laboratory studies of bond strength are done after 24 hours32,39,43,47,50 or 7 days17,26,33.

The purpose of this study was:

1. to compare, using only one adhesive system, the bond strengths of six different metallicbrackets with tensile, shear and torsional tests 15 minutes, 1 hour and 24 hours after bonding;

2. to determine if the bond strengths increase with the passing of time and if these increases aresignificant;

3. to determine the debonding interface.


In this study 270 bovine incisors (deciduous and permanent), 6 metal brackets for the maxillaryright first premolar, and a light-cured composite orthodontic resin (IDEAL Adhesion Systems, GAC)were used. The bovine incisors were extracted from the anterior portion of the bovine mandibles whichwere obtained from a slaughterhouse; the roots were embedded in molds made of autopolymerizing

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SHEAR, TORSIONAL AND TENSILE BOND STRENTHS OF VARIOUS BRACKETBASE DESIGNS (PhD Thesis, University of Naples)

polymethyl methacrylate. Bovine teeth were used because the enamel of bovine incisors hashistochemical characteristics similar to human enamel, therefore, it can be used as a substitute in thebond strength studies 37,40. After polymerization of the polymethyl methacrylate the teeth in the moldswere stored in physiologic saline solution at 4° C in order to avoid dehydration. The metal bracketstested were as follows: Master Series (American Orthodontics, Sheboygan, Wis, USA), Discovery(Dentaurum, Bologna, Italia), Ovation Roth (GAC, Central Islip, NY), Extremo no-Ni (Leone, Firenze,Italia), Optimeshxrt (ORMCO, Glendora, Calif, USA), Tweed SIA (SIA, Rocca d’Evandro (CE), Italia).The metal bracket characteristics are shown in Table I.

Figures A, B, C, D, E, F show the bases of the six brackets photographed under a Intercontinentaltrinocular optic microscope (x40 magnification).

Table I. Characteristics of the 6 maxillary right first premolar brackets.The teeth were randomly assigned to one of 54 treatment groups containing 5teeth per group.

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Figure A. Dentaurum(Discovery)

Figure B. Leone (Extremo no-Ni)

Before the test, the facial surface of each tooth was cleaned for 15 seconds with a pumicepowder/water paste with a rubber cup driven by a slow-speed handpiece. The surface was then rinsedwith abundant water spray for 15 seconds to remove any pumice. Each tooth was subsequently driedwith air spray.

The IDEAL Adhesion System (GAC, Central Islip, NY) was used to bond all brackets to theteeth. Bonding was performed in the standard manner according to the manufacturers’ instructions. Theenamel surface was etched for 20 seconds with 38% phosphoric acid gel. Each tooth was then rinsedwith a water spray for 15 seconds and dried for 15 seconds with the air dryer. The bonding agent wasapplied to the etched enamel surface. A standard dose of resin composite was applied to the bracket baseand the bracket was placed on the sealed enamel surface so that the slot was parallel to the edge of theincisor. Each bracket was then seated with a standard force (300 gr) with a force gauge (Correx Co,Bern, Swiss) for 5 seconds in order to obtain a uniform thickness of composite. Any excess was thenremoved from the periphery of the bracket base with a dental explorer. The composite was cured for 40seconds. The teeth that were to be debonded after 15 minutes and after 1 hour were stored in physiologic

Figure C. AmericanOrthodontics (Master serie)

Figure D. ORMCO (Optimeshxrt)

27

Figure F. Tweed SIAFigure E. GAC (Ovation)

saline solution at room temperature. Those that were to be debonded after 24 hours were stored inphysiologic saline solution in an incubator at 37°.The tests performed were as follows:

· Tensile test: Instron testing machine (Instron universal testing instrument, Model 1011, InstronCorp., Canton, Mass.). Each specimen was placed in the vise in the lower member of theInstron machine so that the tooth surface was perpendicular to the direction of load application.A custom-fabricated tensile debonding instrument, fixed to the cross-member of the Instronmachine, was secured to the mesial and the distal sides of the bracket base. A tensile load wasapplied at a crosshead speed of 2 mm per minute. A computer electronically connected with thetesting machine recorded the results of each test in megaPascals (MPa);

· Shear test: Instron testing machine (Instron universal testing instrument, Model 1011, InstronCorp., Canton, Mass.). Each specimen was placed in the vise in the lower member of theInstron machine so that the tooth surface was parallel to the direction of load application. Acustom-fabricated shear debonding instrument was fixed to the cross-member of the Instronmachine. A shear load was applied at a crosshead speed of 2 mm per minute. A computerelectronically connected with the testing machine recorded the results of each test inMegaPascals (MPa);

· Torsional test: Each specimen was placed in the vise, and a torque meter which contained acustom-fabricated torquing wrench was placed over the bracket. The load was appliedmanually and the maximum torque necessary to debond the bracket was recorded inNewton*metre.

After debonding, the enamel surface was studied to determine the site of bond failure. The sites wereclassified as follows41:

· BA: Bracket-adhesive interface. Adhesive may remain within the bracket’s retention grooves orparticles; however, a continuous layer of adhesive remains on the enamel surface.

· COMB: Combination failure. Failure is noted within the adhesive and at the enamel-adhesiveinterface and/or the bracket –adhesive interface.

· EI: Enamel interface failure. No adhesive is on the enamel surface. All the adhesive is retainedon the bracket base.

· ENAM: Enamel failure. Failure is noted within the enamel surface. Adhesive and enamel arepresent on the bracket base.

· BRF: Intrabracket failure. Failure is within the bracket itself.

RESULTS

Means and standard deviations of the bond strengths were calculated for each group (Tables II,IV and VI). The debonded interfaces were also evaluated (Tables III, V and VII). The diagrams G, H, I,

28

L, M, N show the bond strengths of each type of bracket with tensile, shear and torsional tests afterfifteen (15) minutes, one (1) hour and twenty four (24) hours respectively; the diagrams O, P, Q showthe bond strengths of all of the six brackets with tensile, shear and torsional tests after 15 minutes, 1hour and 24 hours.

The tensile test means and standard deviations (MPa) after 15 minutes, 1 hour and 24 hourswere respectively: 3.54 +/- 1.40, 9.39 +/- 2.94 e 4.83 +/- 2.20 for Discovery; 0.97 +/- 0.36, 1.97 +/-0.82 e 1.12 +/- 0.41 for Extremo no-Ni; 3.54 +/- 1.40, 9.39 +/- 2.94 e 4.83 +/- 2.20 for Master series;1.88 +/- 0.28, 2.59 +/- 0.64 e 3.39 +/- 1.57 for Optimeshxrt; 0.77 +/- 0.39, 1.71 +/- 0.72 e 1.10 +/- 0.52for Ovation; 2.26 +/- 0.79, 2.61 +/- 0.65 e 5.38 +/- 2.39 for Tweed SIA. The location of debondedtooth interfaces did not change with the passing of time. Most failures were found in the bracket-adhesive interface with the exception of some COMB failures and one enamel interface failure.

The shear test means and standard deviations (MPa) after 15 minutes, 1 hour and 24 hours wererespectively: 16.11 +/- 3.93, 16.75 +/- 4.19 e 15.77 +/- 5.33 for Discovery; 15.03 +/- 7.02, 15.48 +/-7.15 e 7.08 +/- 2.68 for Extremo no-Ni; 5.70 +/- 1.79, 8.26 +/- 3.99 e 3.76 +/- 1.84 for Master Series;5.58 +/- 2.36, 5.92 +/- 1.64 e 4.20 +/- 2.03 for Optimeshxrt; 5.09 +/-1.91, 5.95 +/- 2.93 e 5.05 +/- 2.44for Ovation; 16.43 +/- 5.75, 16.98 +/- 5.94 e 16.76 +/- 6.41 for Tweed SIA.

Discovery and Extremo no-Ni underwent combination failures and sometimes bracket-adhesiveinterface failures. Master series, Optimeshxrt and Ovation generally underwent bracket-adhesiveinterface failures. Occasionally, there were combination failures and enamel interface failures. TweedSIA underwent bracket-adhesive interface failure after 15 minutes, combination failure after 1 hour,combination failure and enamel interface failure after 24 hours.

The torsional test means and standard deviations (N*m) after 15 minutes, 1 hour and 24 hourswere respectively: 0.274 +/- 0.040, 0.275 +/- 0.060 e 0.319 +/- 0.107 for Discovery; 0.225 +/- 0.033,0.231 +/- 0.063 e 0.311 +/- 0.058 for Extremo; 0.120 +/-0.028, 0.187 +/- 0.050 e 0.242 +/- 0.036 forMaster Series; 0.087 +/- 0.027, 0.121 +/- 0.034 e 0.148 +/- 0.037 for Optimeshxrt; 0.122 +/- 0.047,0.162 +/- 0.042 e 0.191 +/- 0.072 forOvation; 0.242 +/- 0.031, 0.259 +/- 0.026 e 0.262 +/- 0.035 forTweed SIA.

The brackets generally underwent combination failures and sometimes bracket-adhesiveinterface failures, with the exception of Optimeshxrt, which underwent only bracket-adhesive interfacefailure, and Master series, which underwent combination failure after 15 minutes and 1 hour andbracket-adhesive interface failure after 24 hours.

29

Table III. Evaluation of the debonding interface in the tensile tests

30

Table II. Means and standard deviations of the tensile bond

31

Table V. Evaluation of the debonding interface in the shear tests

Table IV. Means and standard deviations of the shear bond strengths

32

DISCUSSION

Clinically, bond strengths should be able to support orthodontic forces and masticatory loadsand, at the same time, brackets should be debonded without damaging the enamel surface.

A bracket should resist a force of 5kg to 15kg in order to guarantee clinical success21,33,42.Brackets, to be considered reliable, should develop a maximum tensile force of 60-80 kg/cm2 (5.9-7.9MPa) in order to resist the forces of orthodontic treatment24,44. Tensile forces of 50 kg/cm2 (4.9 MPa) areclinically acceptable in vitro. Studies 23,39 of the shear bond strength performed on stainless steel bracketshave found that bond strengths between a range of 12.1 to 20.7 MPa are considered clinically adequate.

When one compares the data found in the literature with this study, only Discovery and TweedSIA develop tensile bond strengths which are clinically acceptable. Discovery develops the maximumtensile force after 1 hour but it is reduced after 24 hours. However, it remains clinically acceptable;Tweed SIA develops a tensile force which is clinically acceptable after 24 hours. Bond strengthincreases are variable with the passing of time: the forces are the same after 15 minutes and after 1 hourwith an increase up to 24 hours for the Master Series, Optimesh xrt and Tweed SIA brackets. There is,however, an increase until 1 hour but a continued decrease until 24 hours for the Discovery, Extremono-Ni and Ovation brackets. The different increases in the tensile bond strength values seem to befunctions of the type of mechanical retention (increasing retention for the single mesh; increasing andthen decreasing retention for the other types of retention). This probably happens because with the singlemesh brackets the penetration of the composite resin in the single mesh bracket increases the mechanicalretention as the composite resin polymerization increases. While with the other brackets, where there is

Table VI. Means and standard deviations of the torsional bond strengths

33

no penetration, the increase of the polymerization “magnifies” the undesirable effect of the compositeresin contraction.

In the shear tests only the Tweed SIA and Discovery brackets developed clinically acceptableforces. Extremo no-Ni, instead, showed values which are clinically acceptable after 15 minutes and 1hour, but it’s shear strength then decreases and is no longer clinically acceptable after 24 hours. All thebrackets, except the Extremo no-Ni, show an increase of the bond strength after 1 hour with a decreaseby 24 hours but the differences are not significant. The uniformity of the shear bond strength values overtime is compatible with the postulate that the superficial section of the bonding medium mechanicallyholds the bracket.

The results of torsional tests confirmed that the values of torque (N*m) for Discovery andExtremo no-Ni after 15 minutes and 1 hour have no significant differences. Both increase until 24hours. Tweed SIA brackets show, instead, values of torque which are practically the same after 15minutes, 1 hour and 24 hours. Master series, Ovation and Optimeshxrt show values lower than the others,but also with increases over time. The major factor involved in torsion strength comes from thegeometry of the base; additionally, the “roughness” plays a fundamental rule. The steady increase of theresistant mechanical values over time is consistent with the fact that the internal layers of compositeundergo a progressive “stiffening” (completion of the polymerization of the internal layers).

Table VII. Evaluation of the debonding interface in the torsional tests.

34

The evaluation of the site of bond failure revealed a certain variability which seemed to beinfluenced more by the type of bracket and the test type, rather than the direction of load application.For example, Optimeshxrt always underwent bracket-adhesive interface failures (BA). In tensile tests thepredominate influence was the direction of the load application with failures in the bracket-adhesiveinterface for all the brackets. In shear tests the data collection was influenced by the type of bracket. Infact Master series, Optimeshxrt and Ovation underwent bracket-adhesive interface failure and Discovery,Extremo no-Ni and Tweed SIA underwent combination failures (COMB). These COMB failures alsoshow a variability with the passage of time. In torsional tests Discovery, Extremo no-Ni, Ovation andTweed SIA underwent combination failures; Optimeshxrt failed at the bracket-adhesive interface. TheMaster series showed a variability with time. The failures were initially combination failures but overtime they became bracket-adhesive interface failures.

During the analysis and interpretation of the results, an important role was played by a series ofspecific characteristics of each base: area, base type, mesh type (wire diameter, size of the aperture,mesh number, free volume between the mesh and the base). The manufacturers furnish only someinformation about these characteristics: notably the area, base type and mesh number. Othercharacteristics of these bases are industrial secrets. It is difficult to confirm our data with that of otherstudies for a multiplicity of reasons. First of all, for the past twenty five years there are not many studiesof this subject reported in the literature. Additionally, there is often a lack of uniformity in 1) themethods used, 2) the specimen preparation or 3) the test type. The literature also confirms discordantopinions about the effects of different retentive designs of bracket bases on the bond strength. McColl33,quoted by Wei Nan Wang, reported that there are no statistically significant differences in the bondstrength between bases with an area between 12.35 and 8.41 mm2; however, with an area between 6.82and 2.38 mm2 there are differences. These data seem to indicate that the bigger the base, the more thebond strength. The bases used in the present study have areas included in this range as well as some thatare larger. This study resulted in the finding that the brackets which fared better in all three tests areDiscovery (10.88 mm2) and Tweed SIA (11.64 mm2). Both have smaller base areas than the other testedbrackets (>12.35 mm2).

Cucu et al15 have tested the bond strength of brackets with 80-100 mesh in both standard andmini base dimension. They have observed that there are no significant differences in the shear bondstrength between brackets with 80 and 100 mesh in either mini or standard dimension and that there areno significant differences between brackets of the same dimensions with meshes of different dimensions,indicating that it is possible to use smaller brackets without adversely impacting the effectiveness of thebonding. Knox et al29 have observed that the bond strengths of the bases of 80-100 mesh aresignificantly higher than those with less than 70. They have postulated that the type of adhesivesignificantly influences the bond strength and that the particular base design could improve thepenetration of the adhesive or of the polymerization light. According to Wei Nan Wang50, the larger themesh dimension, the more bond strength. Bishara et al6 have studied two metallic brackets, one with a

35

single mesh and the other with a double mesh (Victory 3M Uniteck and Ovation GAC) and have foundbond strengths and debonding failures to be the same. The present study found that the brackets with thebest retention are Discovery, produced with MIM technology (laser structured mechanic retention) andTweed SIA (80 mesh), followed by Extremo no-Ni (high roughness surface obtained withelectroerosion). A test of hypothesis and significance on a level of 5% and 1% using a one way Student tdistribution was used to determine if there was a bracket studied which showed the best characteristics.No statistically significant differences were found between Discovery and Tweed, when tensile, shearand torsional mechanical properties were compared. Master series (>100 meshes), Optimeshxrt (>100meshes) and Ovation (double mesh-base) yielded inferior results that were similar.

It is important to observe that in the present study only one type of adhesive was used in anattempt to insure that every variation of the bond strength values would depend on the characteristics(design and dimension) of the considered bases. The adhesive viscosity is a characteristic that influencesthe adhesive penetration into the mesh, it’s presence in the space between the base and the mesh, and inthe mechanical retention and the escape of air. Possibly, the use of a different adhesion system couldhave yielded different results. For example, an adhesive with low viscosity can penetrate better into asmaller mesh. Also, the influence of the filler concentration on the viscosity remains an importantclinical argument.

Other studies have found no statistically significant differences between tensile and sheartests20,46,50. In the present study the test of hypothesis and significance on a level of 5% and 1% using aone way student t distribution was performed. These tests have shown that there are statisticallysignificant differences between the tensile and shear properties of the brackets studied. It is necessary,therefore, to perform all three tests to obtain a complete evaluation of the mechanical properties of thebrackets.

CONCLUSIONS

Based on the results obtained from this study, Discovery and Tweed SIA, and to a lesser extent,Extremo no-Ni, develop bond strengths which are in a range of clinical reliability. Master series,Optimeshxrt and Ovation have bond strengths that are inferior to those reported in the literature. Theretentive characteristics of the base surface determine, to a significant degree, the bond strength.Additionally, the present study points out the importance of performing tensile, shear and torsional teststo obtain a complete analysis of these characteristics.

This study also confirmed that bond strength increases significantly after 24 hours. This is auseful finding. Perhaps, clinicians should initially apply light forces and defer application of heavierforces for at least 24 hours. Additionally, if might be prudent to recommend to patients that “softnourishment” be taken for the first 24 hours after bonding so that masticatory forces do not have agreater tendency to debond the brackets.

36

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42. Proffit WR, Field HW, Nixon Wl. Occlusal forces in normal and long faced adults. J Dent Res1983; 62:566-70.

43. Regan D, van Noort R. Bond strength of two integral bracket base combinations: an in vitrocomparison with foil mesh. Eur J Orthod 1989; 11:144-53.

44. Reynolds IR. A review of direct orthodontic bonding. Br J Orthod 1975;2: 171-8.45. Schaneveldt S., Foley TF. Bond strength comparison of moisture-insensitive primers. Am J Orthod

Dentofacial Orthop 2002; 122:267-73.46. Sharma-Sayal SK, Rossouw PE, Kulkarni GV, Titley KC. The influence of orthodontic bracket

base design on shear bond strength. Am J Orthod Dentofacial Orthop. 2003 Jul;124(1):74-82.47. Siomka LV, Powers JM. In vitro bond strength of treated direct-bonding metal bases. Am J Orthod

1985; 88:133-6.48. Spena R, Della Corte M, Grassia P, Ferro A. Studio comparativo sulla forza di legame di due

combinazioni attacco-composito. Min. Ortognat., 4, 1986.49. Urabe H, Rossouw PE, Titley KC, Yamin C. Combinations of etchants, composite resins, and

bracket systems: an important choice in orthodontic bonding procedures. Angle Orthod 1999; vol.69 no. 3: 267-75.

50. Wei Nan Wang, Chung Hsing Li, Ta Hsiung Chou, Dennis Ding Hwa Wang, Li Hsiang Lin, cheTong Lin. Bond strength of various bracket base designs. Am J Orthod Dentofacial Orthop 2004;125:65-70.

51. Yamada R, Hayakawa T, Kasai K. Effect of using self-etching primer for bonding orthodonticbrackets. Angle Orthod 2002; 72:558-564.

ABSTRACT

Introduction: Angle Class II division 1 patients with a large ANB and severe discrepancies arefrequently found in the Japanese population. In such severe Class II patients, it is difficult to improve theprotrusive profile with only premolar extraction. Additional first-molar extraction (AFME) is aprocedure that can be done after premolar extraction space closure for patients who have a strong needfor further esthetic improvement and who have well-formed third molars.

PURPOSE

This study was performed to determine the effect of premolar and additional first molarextractions (AFME) on soft tissue changes in high angle Class II division 1 patients after closure ofspace created by first premolar extractions. (Figures 1-4)

PREMOLAR AND ADDITIONAL FIRST MOLAR EXTRACTION: EFFECTS ON SOFT TISSUE IN HIGH

ANGLE CLASS II DIVISION 1 PATIENTS

Takemasa Ozaki, D.D.S.

Figure 1: Characteristics of difficult Class IIpatients: high FMA, short mandible, severearch length discrepancy, protrusive profilewith severe over-jet, open bite

Figure 2: Mechanics of maxillary AFME

Figure 3: Mechanics of maxillary AFME stage 2Tweed-Merrifield directional force system

Figure 4: Mechanics of maxillaryAFME stage 3. Maxillary thirdmolars are preserved

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33 AFME patients, 24 of whom had maxillary-only AFME (U-AFME) and 9 of whom had all-four AFME (UL-AFME), (Figures 5, 6) were studied and compared with 43 patients treated with fourpremolar extractions (PRME) as a control group. Lateral cephalograms taken at four points;pretreatment, before AFME, post-treatment and retention, were utilized for statistical analysis using theStudent T-test. Twenty three cephalometric parameters were studied (Figure 7).

Figure 5: Patients Samples Japanese Class II, division 1 patients

Figure 6: Patients Samples Japanese Class II, division 1 patients

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RESULTS

The comparison of the pretreatment characteristics between the AFME group and the PRMEgroup showed that the AFME group consisted of the patients who had more skeletally difficultmalocclusions with high FMA and open bite tendency (Figures 8, 9). Statistical analysis showed thatAFME significantly contributed to maxillary incisor retraction and subsequent soft tissue change as

measured by the Z-angle and LLip-E (Figure 10). Inaddition, the Bivariate correlation analysis revealed that thesoft tissue changes correlated more with maxillary incisorretraction than with mandibular incisor retraction in boththe AFME and the PRME groups (Figures 11-12). Thisfinding suggests that, in Class-II patients, the lower lipposition is most affected by reduction of maxillary incisorproclination.

Figure 7: Twenty three cephalometric

Figure 8: Pretreatment characteristics of AFMEsamples

Figure 9: Pretreatment characteristics of AFME samples. TheAFME group consisted of patients with more skeletallydifficult malocclusions with high FMA angle (37.1°) and anopen bite tendency (FHI:0.62)

Figure 10: LLip- E41

CONCLUSIONS

The AFME approach has been shown to be useful to improve profiles in severe high Angle classII division 1 patients who are “borderline “between premolar extraction only and orthognathic surgerywith premolar extraction. The records of Case #2 give evidence to the validity of additional first molarextractions for the patient with a severe malocclusion (Figures 13-19).

Figure 11: Linear Displacement of Lips and Incisors Figure 12: Bivariate correlation analysis betweensoft tissue changes and incisor movement (TA-TB).

Figure 13: Pretreatment Photographs Figure 14: Pretreatment Photographs

Figure 15: Posttreatment Photographs Figure 16: Posttreatment Photographs42

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Figure 17: Treatment Progression Photographs

Figure 18: Superimpositions Figure 19: Posttreatment Smile Photographs

CASEREPORTS

Introduction

Premolar extraction was, and still is, widely used for correction of tooth arch discrepancy,sagittal discrepancy and profile convexity. However, extraction for vertical control purposes is not wellexplored in the orthodontic literature and the advantage of maxillary molar extraction is underestimated.

The dogma stating that the first molar is the “key of occlusion” leads many clinicians to abideby it in all cases, to the extent that some might finish their patients with additional premolar extractionso that the canine and the first molar contact, in order to correct a residual overjet and class II caninerelationship after four premolar extractions.1,2

When premolar extraction alone does not yield enough space for the correction of excessiveoverjet and class II molar relationship, the clinician will face three options: jaw surgery, class IImechanics or additional extractions. Moving the first molars distally is difficult and requires the patientto wear head gear; also the net space available for anterior retraction is much smaller. Moreover, movingthe first molars distally produces a “wedge effect” and worsens the high angle tendency.3

Merrifield 4 suggested that in class II patients with an anterior deficit larger than 16 mm and withan ANB difference larger than 9°, the maxillary first molars could be considered for extraction after thefour premolar extraction spaces are closed.

Diagnosis and Etiology

The patient was a Lebanese girl aged 12y 11m. She was seeking orthodontic treatment becauseshe was self conscious of her teeth. The clinical examination showed a symmetrical face, incompetentlips with contraction of the mentalis muscle, convex lateral profile, and a retrusive chin (Figure 1).

Analysis of the intra-oral photographs andthe casts (Figure 2), confirmed a class II division1 malocclusion with an overjet of 5mm, and anover bite of 80%. The maxillary midline wasshifted 1mm to the right. The maxillary canineswere in an ectopic blocked out position in thebuccal mucosa due to the lack of space in themaxillary arch. The mandibular tooth archdiscrepancy was 5mm in the anterior area and 2mm in the midarch area. The depth of the curve ofSpee was 2mm.

Figure 1: Pretreatment photographs.

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CASE REPORT: HIGH ANGLE CLASS II MALOCCLUSION TREATED WITH PREMOLARAND ADDITIONAL FIRST MOLAR EXTRACTIONElie W. Amm, DCD, DESInstructor, Department of Orthodontics, School of Dental Medicine,Saint Joseph University.

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Figure 2: Pretreatment dental casts.

Radiographic analysis of the panorex showed incomplete eruption of the mandibular secondmolars and the presence of the third molars at the crown formation stage (Figure 3).

The lateral cephalogram analysisshowed a skeletal class II relationship(ANB=9o) due to a retrognathic mandible(SNB=72o), with a hyperdivergent pattern(FMA=32 o, FHI=.62). The mandibularincisors were significantly proclined(FMIA=47 o, IMPA=101o). The Z angle(66o) indicated a convex profile due to theretrusive chin (Figures 4 and 5). Thecomplete differential diagnostic analysissheet is shown in Table 1.

TREATMENT OBJECTIVES

1. Improve the sagittal skeletal relationship between the maxilla and the mandible: reduce ormaintain the SNA, encourage mandibular anterior growth.

2. Maintain the vertical dimension and control the clockwise rotation of the mandible.3. Reduce the overjet and incisor protrusion.4. Respect all limits of the dentition.5. Improve lip incompetence and harmonize the facial profile.

TREATMENT ALTERNATIVES

Three treatment options wereidentified:

Option 1: Treatment would beconducted with the extraction of thefour first premolars along with classII mechanics, and third molarextractions

Figure 3: Pretreatment panoramic radiograph.

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Figure 5: Pretreatment cephalometric tracing.

Option 2: Treatment with the extraction of the maxillary first premolars and mandibular secondpremolars along with third molars.

Option 3: Extraction of the four first premolars, the maxillary first molars and the mandibular thirdmolars.

Option 3 was selected because it offered the best way to correct the malocclusion, maintain thevertical dimension and improve the facial profile.

TREATMENT PROGRESS

The sequential directional forces system with .022 standard edgewise single brackets was used.The treatment time was 32 months.

Denture preparation: After the extraction of the four first premolars, the maxillary first molarwas banded and the rest of the teeth were bonded sequentially (5, 2, 1). The first archwire was.017x.022 SS. The mandibular arch was bonded sequentially (7, 5, 3, 1), the first wire was .018x.025SS.

After the alignment of the mandibular teeth, the lateral incisors were bonded and the retractionof the mandibular canines was continued with power chains. In the maxillary arch, after the eruption ofthe canines, the bonding was completed and the HPHG J-hook was used to retract them. At this stageall rotations were corrected and both arches were leveled and aligned.

Figure 4: Pretreatmentcephalometric radiograph.

Table 1: Differential Diagnosis

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Denture correction: The mandibular incisors were retracted with an .019x.025 SS closingarchwire. The maxillary space was closed with a .020x.025 SS closing archwire. At this stage, theoverjet and the class II relationship remained uncorrected. The decision was made to extract themaxillary first molars (Figure 6).

Figure 8: Posttreatment cephalometric tracing.Figure 7: Posttreatmentcephalometric radiograph.

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Using the HPHG J-hook headgear, themaxillary canines and premolars were retractedto a class I relationship. The remaining spacewas closed reciprocally using a .020x.025 SSclosing archwire. At this stage, all spaces wereclosed, overjet and overbite corrected, and theclass I relationship was established.

Denture completion: Final spaceclosure and final alignment were done. Theblack triangle between the maxillary centralincisors was corrected with minor stripping toimprove the contact and the esthetics (Figure6).

Denture recovery: A mandibular lingual retainer was bonded from canine to canine. The patientwas given a wraparound retainer and instructed to wear it 24 hours per day for one month and at nighttime thereafter.

TREATMENT RESULTS

The final lateral cephalogram and analysis are shown in figures 7 and 8. There was no forwardmandibular growth, however the sagittal relationship between the maxilla and the mandible improvedfrom an ANB of 9o to 6o and the vertical dimension was controlled with counterclockwise rotation of themandible (FMA from 32o to 29o and the FHI from .062 to .067).

Figure 6:

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The maxillary incisors were retracted and moved backward without tipping (Figures 9 and 10),the overjet was reduced from 5mm to 1mm, and overbite was reduced from 80% to 5% with a mildovercorrection. Maxillary first molar “position” was distalized and intruded. The mandibular incisorswere retracted, and the mandibular molars were uprighted without extrusion (Figures 9 and 10). Thedental and facial changes are evident by comparing the pretreatment and posttreatment dental casts andphotographs (Figures 11 and 12). The final panoramic x-ray showed acceptable root parallelism and nosigns of root resorption (Figure 13). The facial profile became less convex, and lip incompetence wasimproved (Figure 14).

Figure 9: Cephalometric tracingsuperimposition on SN at S.

Figure 10: Maxillarycomposite andmandibular compositesuperimpositions.

Figure 11: Posttreatment photographs.

Figure 12: Posttreatment dental casts.

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Figure 13: Posttreatment panoramic radiograph.

DISCUSSION

Class II mechanics always lead to undesirable vertical reactions in high angle patients. Thedistal movement of the maxillary dentition and the side effect of the class II elastics on the mandibulararch creates a clockwise rotation of the mandible and worsens the class II high angle situation. Toprevent these unwanted results in high FMA patients when premolars have been extracted for intra archdeficit corrections, the clinician must consider maxillary molar extraction to correct the class II dentalrelationship.5

The guidelines given by Merrifield4 can always be a good diagnostic decision tool. For thispatient the anterior deficit was 19mm, the ANB was 9o and the FMA was 32o. These factors made theextraction of four premolars and maxillary first molars a justifiable decision. An additional advantage tothis treatment is that class II mechanics require more patient cooperation than maxillary molarextraction treatment.2 If posttreatment facial balance is to be a reality for patients with average to highFMAs, the following three objectives are proposed by Klontz 6:

Objective 1: Mandibular incisors must be upright over their bony support after treatment. It wouldhave been more desirable if this patient’s mandibular incisors were more upright.

Objective 2: Maxillary anterior tooth position must be controlled. Even though there was nofavorable sagittal mandibular response and the uprighting of the mandibular incisors wasinsufficient, the profile and the lip incompetence were improved. This improvement was due to theretraction and third order control of the maxillary incisors as shown by Ozaki et al.3

Figure 14: Facial lateral profile composite.

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Objective 3: Posterior vertical dimension control: During treatment the FMA decreased from 32o to29o and the FHI increased from .62 to .67, indicating mandibular counterclockwise rotation andgood vertical control.7 This was due to favorable vertical mandibular response on the one hand, andto the vertical control of the mandibular first molars and the maxillary second molars on the otherhand.

One of the most challenging parts of this treatment is the recovery phase; mandibular thirdmolars must be extracted and the evolution and eruption of the maxillary third molars must becontrolled.REFERENCES

1. Janson G, Janson MR, Cruz KS, Henriques JF, de Freitas MR. Unusual orthodontic retreatment. Am JOrthod Dentofacial Orthop. 2003 Apr;123(4):468-75.

2. Amm E. Class II retreatment. Am J Orthod Dentofacial Orthop. 2003 Jul;124(1):17A3. Ozaki T, Ozaki S, Kuroda K. Premolar and Additional First Molar Extraction Effects on Soft Tissue:

Effects on High Angle Class II division 1 Patients. Angle Orthod. 2007;77(2):244-534. Vaden JL, Dale JG, Klontz HA. The Tweed-Merrifield edgewise appliance: philosophy, diagnosis and

treatment in orthodontics. In: Current Principles and Techniques. 2nd ed. Graber T, ed. St Louis, Mo:Mosby; 1994:627–684

5. Ortial PJ. Treatment Planning for Molar Extraction Cases.Vol. 18. Tucson, AZ: Journal of theCharles H. Tweed Foundation;1992:75–82.

6. Klontz HA. Facial balance and harmony: an attainable objective for the patient with a highmandibular plane angle. Am J Orthod Dentofacial Orthop. 1998;114:176–188.

7. Horn AJ. Facial height index. Am J Orthod Dentofacial Orthop.1992;102:180–186.

Figure 1

Introduction

When I think about my first experience with the Tweed-Merrifield Philosophy, a big smile comesand my eyes shine. I was at the beginning of my orthodontic career and everything I did seemed to bedifficult or even impossible, especially when I tried for the first time to bend an .0215 x .0275 with first,second and third order bends. It was very hard for my hands and for my spirit. At the least, practicingwith this technique has taught me to focus on the following:

· Recognize and treat within the dimensions of the dentition· Maximize facial harmony· Understand the skeletal pattern

This is a case report of one of the first patients I treated with the edgewire appliance and the TweedMerrifield philosophy.

Case Report

The patient, S.C., is an 11 year old girl who presents with a class II malocclusion (Figure 1).The skeletal diagnosis is characterized by a dental class II relationship with an orthognathic skeletalpattern. Vertical dimension is normal but the growth pattern is one of posterior rotation. The estheticprofile is categorized by a protrusion of mandibular incisors with respect to facial planes (Figure 2 andTable I).

52

MY FIRST EXPERIENCE WITH THE TWEED-MERRIFIELD PHILOSOPHY

Tweed Foundation Biennial Meeting – October, 2006Dr. ssa LUIGIA BRERAComo, Italy

53

Figure 2 Figure 3

Table I

The craniofacial difficulty is 75 (moderate). The total space analysis deficit is 18.2mm (Figure 3). It isalmost equally distributed between the three areas (Table II), so the total space analysis difficulty is15.2. The total difficulty is 90.7.

The management problems associated with the treatment of this patient are:

• Bialveolar dental protrusion is manifest by the lip incompetence• The skeletal growth pattern seems to reflect posterior condylar rotation without a compensation of the

teeth position• Facial balance is poor.

After review of the records, the treatment plan was to extract the maxillary first premolars andmandibular second premolars. Class II extraction treatment with sequential directional force provides

Figure 4

Table II

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that, after extraction, the surplus space that remains after alignment of the mandibular anterior teeth isclosed by the mesialization of the mandibular first molars. This molar mesialization results in areduction of the posterior area deficit. Class II correction for this patient also required an en massedistalization of the maxillary teeth.

After treatment Hawley appliances were used to guide the recovery. The final dental result isvery good and is characterized by better facial harmony with a reduced gummy smile (Figures 4, 5 andTable III). The time of therapy was 27 months.

Figure 5

Table III

Case Report

The patient, V.M., is an 11 year old boy who presents with a class II malocclusion (Figure 1).The diagnosis is characterized by a class II dental relationship and a class I skeletal pattern. The verticaldimension is hyperdivergent, but the growth pattern seemed normal. The esthetic profile is characterizedby dental and labial protrusion (Figure 2 and Table I).

The craniofacial difficulty is 69 (moderate). The total space analysis shows a 15.2 mm totaldeficit (Figure3 and Table II), but the anterior deficit is 14.2 mm. The total space analysis difficulty is19.2. The total dentition difficulty is 88.22.

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Figure 2

MY FIRST EXPERIENCE WITH THE TWEED-MERRIFIELD PHILOSOPHY

Tweed Foundation Biennial Meeting – October, 2006Dr. Matteo Beretta

Alessandria, Italy

Table I

Figure 3

Figure 1

Figure 5

Figure 4

The Merrifield guidelines suggest the extraction of maxillary and mandibular first premolars fora patient whose anterior deficit is 5 to 15 mm.

When all the extraction spaces have been used to correct the anterior and mid-arch problems, theresulting deficit is absolute and requires a compromised result or the resolution of the problem in themandibular posterior area. Class II correction, must be done in the maxillary posterior area by a step bystep distalization of the maxillary teeth. Anchorage becomes critical. This patient was treated as acritical anchorage patient. Maxillary posterior teeth were distalized 2mm. The correction is satisfactory.The dentition has nice intercupation and facial esthetics is greatly improved (Figure 4).

The final cranial facial analysis shows a class I skeletal relationship and the correction of thedental and aesthetic parameters (Figure 5 and Table III). The time of therapy was 29 months.

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Table II

Table III

Tweed Profile

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