Resin Retained Fixed Partial Dentures Introduction Conventional procedures for the preparation of abutment teeth often involve major removal of tooth structure. If coverage is necessary for cosmetic purposes because of caries or pre-existing restorations, this removal of structure is acceptable. However, when the abutment is sound, conventional full coverage procedures seem quite radical. More conservative procedures, such as partial veneer crowns or pin-retained, present limitations in esthetics and retention. Many patients object to these drawbacks and consequently choose removable partial dentures which may not to be used. Recent innovations in the acid-etch technique have led to new alternative to traditional treatment for esthetic and restorative procedure. 1
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Resin Retained Fixed Partial Dentures
Introduction
Conventional procedures for the preparation of abutment teeth often
involve major removal of tooth structure. If coverage is necessary for
cosmetic purposes because of caries or pre-existing restorations, this removal
of structure is acceptable. However, when the abutment is sound,
conventional full coverage procedures seem quite radical. More conservative
procedures, such as partial veneer crowns or pin-retained, present limitations
in esthetics and retention. Many patients object to these drawbacks and
consequently choose removable partial dentures which may not to be used.
Recent innovations in the acid-etch technique have led to new
alternative to traditional treatment for esthetic and restorative procedure.
Review of Literature
J. Ben Stolpa (1975) described a adhesive technique for fixed partial dentures
by using aluminium foil and acrylic resin teeth stabilized by adapting foil
reinforced with acrylic resin to form a matrix. He made Class III cavity
preparation, on mesial surfaces of acrylic resin teeth and on distal surfaces of
abutment teeth. A fresh mix of composite resin applied to the abutment teeth
and Class III cavity preparation of the pontic.
Donald F. Howe and Gerald E. Denehy (1977) they described a technique
which permits the fabrication and attachment of an anterior fixed partial
denture without tooth preparation. The fixed partial denture is attached to the
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lingual surfaces of the abutment teeth utilizing a composite resin and acid
etch enamel.
Comment : since the frame has to be thick enough to prevent flexibility that
may adversely affect the porcelain pontic, a potential for occlusal
interference exists.
Dan Nathanson and Kambiz Moin (1980) they described a technique for
replacement of single anterior tooth. An artificial composite resin tooth
reinforced with orthodontic perforated metal pads is used as a pontic and is
bonded directly to proximal and lingual surfaces of time adjustment teeth
using composite resin and acid etching.
G.J. Livaditis and V.P. Thompson (1982) described a technique for a
retentive mechanism that etches the inner side of the cast fixed partial
denture frameworks. They etched metal ceramometal restoration with 0-5N
nitric acid was then bonded to the enamel surface utilizing the technique for
acid etching enamel. They suggested that improved resin bonded retainers
provide innovative conservative and viable alternatives to traditional fixed
prosthodontics.
J. Robert E. Shleman, Peter C. Moon, Robert F, Branes (1984) during a 32
month period, 39 anterior fixed partial dentures were bonded on 37 patterns.
All used the perforated metal retainer design, from the study they concluded
that minimal tooth preparation enhances the bond strength and can provide
occlusal clearances. The most common clinical failure is the bond to the
enamel which suggested that retainer design should cover the largest possible
surface without placing margins in inaccessible areas.
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Gerald Borrack (1984) the vertical path of insertion is developed so that the
restoration will not be displaced during function. The force is distributed
through wrap around design that includes substantial enamel coverage. This
provides the greatest surface area for bonding and a vertical path of insertion.
He also suggested that the surface to be etched should be cleaned with
an air abrasive with 50µm particle size aluminium oxide after etching the
black alloy surface must be removed by placing the casting in 18%
hydrochloric acid and in ultrasonic cleanser for 10 to 15 minutes.
Jeffery L. Hudgins, Peter C. Moon and Florian J. Knap (1985) they placed 27
particle roughned resin bond F.P.D. during 6 month period. From the study
they concluded that particle roughned metal retainer possesses sufficient
mechanical bond strength for resin bonded system. The weak link in metal to
etched enamel resin bonded system was the resin/etched enamel interface.
They adviced to cover as much surface as feasible when resin bonded
retention etched to enamel.
They also suggested the advantages of particle roughened resin bonded
technique over the etched metal resin bonded procedure as follows:
1) The time consuming and technique sensitive electrochemical etching of
the framework is eliminated which decreases treatment time by the
appointment since the framework is eliminated, which decreases
treatment time by one appointment. Since the framework try in is
obviated.
2) Combination of retentive surface is minimized.
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3) Retentive surface is more easily evaluated.
4) The advantages of the etched metal resin bonded framework technique
over the particle roughened resin bonded procedure are: 1) Pattern
fabrication and investment are less technique, sensitive and 2) smoother
margins are achieved between the metal retainer and tooth structure.
Timothy Brady, Asterious Dockoudakis and Stephen T. Rasmussen (1985)
they compared the retention of the etched metal retainers and perforated
metal retainer, metal disks bonded to prepared tooth specimens and stored in
saline solution for 20 days were measured for shear strength. The etched
disks were capable of withstanding more than four time the breaking load of
the perforated discks. They concluded that etched retainers are superior to the
perforated retainers.
Asterios Doukoudakis, Bernard Cohen and Andreas Tsoutsos (1987)
described a method for etching metal alloys containing beryllium silicon,
boron and all nickel base alloys in following ways:
1) Blast the metal surfaces to be etched with aluminium oxide.
2) Apply a drop of the met-etchgel (containing aqua regia solution) on
metal surfaces and spread with a plastic instrument.
3) Place the framework in warm oven at 150°F for 3 minutes.
4) Remove the framework from the oven and rinse off the gel with tap
water. The met-etchgel is reapplied for 7 to 10 minutes or until the gel
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becomes greenish colour for revarification that the metal has been
etched properly.
5) Rinse the gel with tap water. If the etched surfaces have a dark oxide
film, clean with an 18% solution of hydrochloric acid.
6) Then clean the restoration with distilled water in an ultrasonic cleaner
for 5 minutes.
The advantages of using this method of chemically etching are:
1) This conservative procedure can be performed in two clinical sessions.
2) The etching of the framework can be effectively controlled by the
dentist or laboratory technician and
3) If the metal framework is dislodged it can be cleaned, etched and
reattached during the same appointment.
Comment : Can not etch gold alloys and those with high palladium content.
Mohsen Teleghani, Karl F. Leinfelder and Akram M. Taleghani (1987) they
conducted a study to determine the effectiveness of small undercuts in mesh
patterns on the retention of resin luting agents compared with conventional
etching techniques. The results of the study demonstrated that the cast mesh
surface can serve as an alternative to chemical or electrolyte etching. Another
advantage is the dentists ability to determine the appropriate surface
conditioning of the metal.
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G.F. Priest and H.A. Donatelli (1988) they evaluated 47 patients receiving 58
resin bonded fixed partial dentures for 2 to 51 month periods (perforated
electrolytically and chemical etched retainers) during the evaluation period,
10 prosthesis became dislodged, six restorations were successfully rebounded
and four were remade. Six anterior and four posterior restorations were
dislodged. One restoration containing more than one pontic was dislodged.
They made the following conclusion. Based on retention rates demonstrate in
the study the resin bonded fixed partial denture are indicated as definite
prosthesis. Chemically etched prosthesis offer better retention than
electrolytically etched or perforated prosthesis. Compromises no established
design parameters adversely affect retention, particularly when bonded
enamel is minimal or resistance form is inadequate. Prosthesis location does
not appear to affect retention. Differences seem to exist in retentive strengths
of cementing agents.
J.R. Eshleman. C.E. Janus and C.R. Jones (1988) they suggested designs for
RBFPD’s that provide the best possibly combination of auxiliary retention
and resistance features and resin to enamel bond strength a also suggested
use of data provided by Shillinberg and Grace on average enamel thickness
to as a guide for developing optimal preparations within the confines of the
enamel layers.
Maxillary Anterior Tooth Preparation
The maxillary anterior teeth present a unique problem in RBFPD
design on many anterior teeth, a large percentage of available bonding
surface is also involved in centric and excursive contacts with mandibular
teeth. Consequently, the thickness of the lingual enamel plate of the abutment
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teeth limits the amount of occlusal clearance for the RBFPD retainers that
can be obtained by preparing only these teeth. The available thickness of
enamel is further reduced when the abutment teeth have wear facets.
Additional clearance may be obtained by reducing the incisal edges of the
mandibular teeth. This option is not always viable, however especially when
the incisal edges also exhibit wear. Although etched metal retainers can be
made as thin as 0.2mm the particle roughened retainers should be atleast
0.5mm thick. Additional, it has been shown that photoelastic stresses are
reduced when the retainer castings are 0.6mm thick.
Enamel thickness on the lingual surfaces of six maxillary anterior
teeth is consistently less than 0.5mm at gingival surface. Centric contact 3
mm or less from the cementoenamel junction will require reduction of
opposing dentition to provide adequate (0.5mm) clearance of particle
roughened retainers to leave enamel on the maxillary abutments for bending
the prosthesis patients who have Class II occlusal relationships with a deep
horizontal overlap may be more difficult to treat with a resin bonded
prosthesis in the maxillary region than patients with either a Class I or Class
II occlusion.
The cervical finishing line of retainer should be either 1mm incisal to
the cementoenamel junction or no more than 1.6mm incisal to the free
gingival margin. Because available enamel thickness at this site is
approximately 0.29mm, no more than a light chamfer finishing should be
used. In most instances the casting thickness will exceed the amount of
enamel removed. Therefore, for an optimal periodontal response, the
finishing line should always be placed incisal to the free gingival margin.
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The finishing line on the proximal surface adjacent to the edentulous
space should be placed as far facially as practical without lengthening outline
from the tooth. A shallow groove 0.5mm in depth should be placed slightly
lingual to the labial termination of proximal reduction. The tooth structure
lingual to the groove should be prepared in flat plane terminology cervically
in a knife edge finishing line 1mm from free gingival margin. The proximal
slices on adjacent teeth should have on occlusal divergence in the range of
approximately 6 degrees to 15 degrees. The incisal finishing line should be
lightly chamfered and placed as near to the incisal edge as esthetic
considerations will permit.
The principles of preparation for mandibular anterior teeth are similar
to these for maxillary anterior teeth, with awareness that lingual enamel
thickness for mandibular teeth are from 11 to 50% less than those in
comparable parts of their maxillary counterparts. As the cingulum of
mandibular anterior teeth is usually poorly developed, a positive cingulum
rest seat may be provided to assure correct positioning during bonding.
Posterior tooth preparation
The enamel thickness varies from 1.48mm in the thickest part of
marginal ridge to 0.68mm near the cementoenamel junction. Unless the
abutment teeth are severely tipped in relation to each other, the proximal
slices should be at least 2.5 to 3mm in an occlusogingival dimension. The
proximal slices should have an occlusal divergence of approximately 6 to 15
degrees. A positive rest seat should be prepared in each marginal ridge
adjacent to the edentulous space. The lingual surfaces of mandibular
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posterior teeth are usually prepared in a single plane, terminating cervically
with a knife edge or light chamfer finishing line.
John O. Burgess and James G. McCartney (1989) they compared the load
required to dislodge acid etched resin bonded castings from various tooth
preparations like casting with grooves, one half groove, pins and the labial
extensions. They confirmed the effectiveness of tooth preparation designs to
increase the resistance to lingual displacement of resin-bonded increase the
resistance to lingual displacement of resin bonded retainers. The most
effective proportions involved distinct proximal grooves or labial extension.
Preparations without facial correspond grooves or a single pinhole were
significantly less retentive.
Vincent D. Williams, Keith e. Thayer, Gerald E. Denely, Daniel B. Poyer,
they evaluated ninety-nine anterior and posterior cast metal resin bonded
prosthesis from a 10 year period. The results of 10 years retrospective study
showed that: 1) Caries rate on retainer teeth was minor, 2) The periodontium
did not show a greater incidence of periodontal disease and few prosthesis
needed to remade.
M.H. El Sherif, A. El Messey and M.N. Haithoul (1991) they evaluated the
effects on retention of three metal surface textures : electrochemically etched,
air abraded and particle roughned and four resin luting materials (compson,
conclude, microfill pontic, panavia Ex) by measuring the magnitude of the
force require for the removal of resin bonded fixed partial denture retainers.
The result of study indicate that a retainer surfaces prepared by air abrading
with 250µ aluminium oxide were superior in retention than other and Panavia
Ex material could successfully retain the FPD’s.
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Franklin Garcia Godoy, David A. Kaiser, William F.P. Malone and Gregory
Hubbard (1991) compared the shear bond strength of Panavia Ex and
Compson opaque adhesive resins with electrolytically etched or sandblasted
rexillium and litecast B alloys. They found that panavia resin recorded a
greater bond strength than compson resin with etched and sandblasted
Rexillium III metal. The results of metal etching did not differ from
sandblasting using both panavia and compson resin with sandblasting using
both panavia and compson resins with rexillium III metal. Sandblasting
produced a superior bond strength compared with metal etching using
panavia resin with litecast B metal. Metal etching created a greater bond
strength than sandblasting using compspan resin with litecast B metal.
Dr. N.P. Patil and G.C. Reddy, they concluded that the stress distribution
patterns by fung bridge is quite favourable with less distructive forces on
alveolar bone and there are chances of fracture of bridge post at the pontic
abutment interface under much heavier application of load.
Types of Resin bonded fixed partial denture designs
1) Rochette
2) Maryland
3) Sockwell
4) Virgenia
5) Fung
1) Rochette type
- The Rochette type uses small perforation in the retainer
sections for retention and is best suited for anterior bridges.
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- Care must be exercised in placing the perforations to prevent
weakening the framework. Perforations that are too large or too
closed spaced will invite failure of the metal retainer by fracture.
- The perforations should be approximately 1mm apart and have
a maximum diameter of 1.5mm on tooth side.
- Each hole is countersunk so that the widest diameter is toward
the outside of the retainer.
- When the bridge is bonded with a luting resin, it is
mechanically locked in place by microscopic undercuts in the
etched enamel and the countersunk holes in the retainer.
Advantages of this design are follows:
1) It is easy to see the retentive perforations in the metal.
2) If the bridge must be replaced, the composite resin can be cut away in
the perforations to aid in the removal process.
3) No metal etching is required.
Disadvantages are as follows:
1) The perforations would weaken the retainers if improperly sized or
spaced.
2) The exposed resin is subjected to wear.
3) It is not possible to place perforation in proximal or rest areas.
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Maryland type
- It is reported to have improved bonding strength.
- Instead of perforations, the tooth size of the framework is
electrolytically etched, which produces microscopic undercuts.
- The bridge is attached with a resin luting agent that locks into
microscopic undercuts of both the etched retainer and the
etched enamel.
- It can be used for both anterior and posterior bridges.
- Although this design has been reported stronger, it is more
technique sensitive because the retainers may not be properly
etched or may be contaminated before cementation. Because
the retentive features cannot be seen with the unaided eye of
the etched surface must be examined with a microscopic to