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

verify proper etching (minimum magnification X60).

Sockwell Type

- It incorporates both perforations and etching of metal.

- The perforated type can be etched on the tooth side of metal

retainer to provide microscope undercuts. For added retention.

This is especially important in areas where perforations cannot

be placed.

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- The etched metal type can be improved by adding perforations

to provide both types of retention.

Virginia Type

- Moon and Hudgins et al produced particle roughened retainers

by incorporating salt crystals into the retainer patterns to

produce roughness on the inner surfaces.

- This method is also known as lost salt technique.

- This framework is outlined on the die with a wax pencil and the

area to be bonded is coated first with model spray and then

with lubricant.

- Sieved cubic salt crystal (NaCl), ranging in size from 149 to

250µm are sprinkled over the outlined area.

- The retainer patterns are fabricated from resin leaving 0.5 to

1.0mm wide, crystal free margin amount the outlined area.

- When the resin has polymerized, the patterns are removed from

the cast, cleaned with a solvent and then placed in water in an

ultrasonic cleaner to dissolve the salt crystas.

- This leaves cubic avoids in the surface that are reproduced in

the cast retainer producing retention for the fixed partial

dentures.

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- Subsequent investigation showed that retainer fabricated by this

technique could be 30% to 150% more retentive than retainers

prepared by the electrochemical technique, depending on the

resin used.

Fung Bridge – Introduced by Fung 1998

- It consists of prefabricated pontic with channel inside it.

- The channel permits the placement of bridge post.

Advantages:

- Minimum tooth reduction.

- Reduced appointments and less chair time.

- Esthetically pleasant.

- No expensive equipment.

Disadvantages

- Longevity is questionable.

- Requires occlusal adjustments.

Indication:

- Single tooth replacement.

Contra indications: - Teeth with large pulp chambers.

- Step by step procedure.

1. Try in of fung bridge pontic.

2. Preparation of locking slots on proximal aspect of

abutment tooth on edentulous side.

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3. Try in of bridge post and adjustment of bridge post.

4. Cementation with resin cement.

5. Occlusal adjustments.

Advantages of Resin Bonded Fixed Partial Dentures.

There are many reasons for the almost instant popularity of etched

metal retainer technique. They can all be accounted for, however, by the fact

that the etched metal approach answers nearly all the objections that patient,

dentists and laboratory technicians have to the conventional crowns and

bridge.

1) Minimal Enamel Reduction

- One of the most popular features of the etched metal retainers

is the conservative preparation that they require.

- The amount of enamel that must be removed in preparing a

direct bonded bridge is minimal, until recently this conservative

preparation has been more than just simply on advantage – it

has literally been design requirement.

2) No pulpal involvement

- Because tooth reduction in the etched enamel retainer

technique is minimal there is obviously no pulpal irritation as a

result of preparation. A benefit to all age groups this feature is

particularly important for younger patients.

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- Infact only the conservative nature of these preparations and

complete lack of pulpal involvement allow use to place a

permanent prosthesis in mouth of patients whose pulp would

otherwise be too close to the surface to withstand the normal

rigers of conventional crown and bridge.

- Even in more mature elder patients the etched metal retainer

technique avoids any risk of sensitivity by eliminating

penetration in to dentinal tissue during preparation.

3) Minimal periodontal involvement

- All tooth preparation and the final placement of direct bonded

retainers take place above the gingiva. The supragingival

placement of the gingival border of the retainer is practically

guaranteed by this technique.

- In addition to their supragingival placement, all of the gingival

borders of the prosthesis are cast to a knife edge. These two

features permits easy periodontal maintenance.

4) Simplified impression

- Because the finished prosthesis remains supragingival there is

no need to extend the impression subgingivally. This eliminates

gingival retraction while the impression is made. There is no

need for gingival surgery. There is also no need to pack a

retraction and also it eliminates one of the more vexing aspects

of the conventional crown and bridge procedures.

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5) No analgesia

- The very conservative nature of the preparation requirements

which allow us to finish the preparations entirely within the

borders of the enamel structure, completely precludes the

necessity for any local analgesia. This is certainly a benefit to

the dentists, who save the time in providing regional or local

anesthesia and patients to appropriate that their dentistry can be

performed without the need of needle.

6) Simplified and Accurate esthetics

- Esthetically, a direct bonded retainer is generally an

improvement over a conventional bridge for several reasons.

- First the abutment tooth remains intact.

- There is lack of metal colour along the facial aspect the

abutment.

- The framework do not cover the facial aspect of abutment.

7) Forgiving clinical technique

- Many of the difficulties encountered in conventional crown or

bridge are avoided in the cast alloy direct bonded retainer

technique. For example, there are only three cardinal principles

that must be observed. Provided that these minimal

requirements are met, the techniques themselves are quite

forgiving parallelism, for instance is a concept of very little

value for the direct bonded retainer. The placement of finishing

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time is not nearly as critical for the direct bonded retainer as it

is for a conventional crown or bridge. There is no fear of pulpal

encroachment. All in all the clinical phase of procedure is much

less demanding than with conventional crown and bridge.

8) Forgiving laboratory technique

- There is no need for instance, of waxing and finishing the

retainer to a perfect, precise finish line. There is infact, often no

real finish line at all.

- There are no problems created by ditching the dies because

there is no need for ditching.

- There are no problems arising from adulterating the master

model by trimming away the area that is estimated to represent

the gingival tissue.

- Individual dies are not made for each abutment, because all

dies are usually left together on the model as a single unit. The

advantage is that there is no possibly of slight discrepancies in

their placement when the individual dies are returned to the

model.

- Difficulties with soldering are eliminated because these

frameworks are cast as a unit.

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- All these things considered, the laboratory technique for a

direct bonded retainer is both easier and more forgiving than

that required for a conventional crown or bridge.

9) Less time required for all procedures

- The clinical procedure for direct bonded retainers is usually

less time consuming than that for a conventional bridge.

Usually the saving of time amounts to 50% or more.

- In addition to saving time during the preparation and

impression, direct bonded retainers usually eliminate the need

for temporization. The two major reasons for temporization

with conventional crown or bridge are maintaining the

relationship between the abutment and protecting the denuded

dentinal surface. Neither of these reasons are found with the

direct bonded retainer.

- Usually the preparation for direct bonded retainer do not

change the contact points on adjoining teeth nor do they

substantially change in either the interproximal or occlusal

relationships, there is no reason to expect a sudden shifting of

the abutment teeth. The preparation of the teeth. The

preparation of the teeth for a direct bonded bridge is so minor

that the abutment teeth do not need further protection. There is

infact no denuded after preparation.

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10) Reversibility of procedure

- Because the preparations for a direct bonded retainer are so

minimal the procedure is virtually reversible.

- Accordingly, the reversibility of the procedure gave early

investigations the confidence to begin using direct retainers

clinically.

- If at any time the direct bonded retainer itself should become a

problem, the retainer could simply be removed and the patient

is back to where he started.

11) Advantage of composite resin as luting agent. Although the

insolubility of composite resin cement is only one of its many assets

because this feature allows for wide latitude in the construction of the

appliance within broad limitations when one uses those cements, there is

no longer such a thing as an open margin.

12) Lower cost

- To many patients the greatest single benefit of the direct

bonded retainer is the reduced cost of this appliance.

Disadvantages:

The list of possible disadvantages as associated with direct bonded

retainers are as:

1. The longevity of some of the restorations is not yet known.

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2. Plaque accumulation.

3. Bulky contours.

4. Restricted to single tooth replacement.

Indications:

- The indications for direct bonded techniques are very much the

same as for a conventional crown and bridge with a few

additional considerations.

- The direct bonded technique should be used in preference to a

conventional crown and bridge whenever the conservative

nature of the technique would be an advantage.

1) Replacement of missing teeth.

- Perhaps the most dramatic application of the direct bonded

techniques is the replacement of missing teeth. Before the

direct bonded techniques were developed in order to replace a

missing tooth, a dentist would either fabricate a removable

prosthesis or he would wreak great destruction on the

abutments, in order to secure a permanently cemented

replacement.

- Now not only can missing teeth be replaced with a relatively

simple technique, but in many circumstances it is the only

possible technique.

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- For a young patient, for instance there is not fixed conventional

counter part to the direct bonded techniques.

2) Periodontal splinting

- The more conventional periodontal splints have been extremely

difficult to maintain in the mouth.

- The strength and thinness of the direct bonded cast retainers do

makes the job easier not present a periodontal handicap.

- In this regard they have been as successful as the horizontal and

vertical pin splits, both parallel and non parallel variety.

- The direct retainer are not only easier to apply but they have all

other advantage that have been already be listed.

3) Post-orthodontic Splinting

- Direct bonded cast retainer have also been used for post

orthodontic retention.

- Where indicated, they can replace such traditional removable

retainers as the Hawley retainer.

- Direct bonded cast retainer have the esthetic advantage of not

being visible as are most.

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- The direct retainer only becomes the post orthodontic retainer

of choice for those cases in which retention is expected to be

permanent or of an extremely long duration.

4) Combinations with removal prosthodontics. The direct bonded

techniques have been used to splint weak terminal abutments to stronger

adjacent teeth for reinforcement. In addition, they have been used to bond

stress breakers, cast rest seats, semi precision attachments and precision

attachments to the abutments for removable prosthodontic appliances.

5) Adjusting occlusion

- Direct bonded retainers have been used in many forms for

adjusting the occlusal table.

- One simple appliance used in occlusal rehabilitation is a metal

backing for the lingual canines which is intended to create new

cuspid guidance.

- Some times the framework of an etched metal appliance is

designed so that it can be bonded to rebuild the occlusal surface

of teeth that have been tilted in such a way so that a portion of

their occlusal table is not functioning. On occasion, the occlusal

portion of the alloy has been coated with porcelain for an

improved appearance.

- For post temporomandibular joint therapy, individual wafers of

porcelain fused to bondable alloy have been fabricated to cover

the occlusal surface of existing posterior occlusal surfaces. The

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result is a permanent TMJ prosthetic appliance that has been

achieved at a significantly greater saving of time, tooth and

money than with conventional approach.

6) Strengthening natural teeth

- Cast alloys backings have been used to strengthen incipient

fractures of incisors.

Contraindications:

Presently there are only three contraindications for the direct bonded

techniques:

1) The first is if a patient shows any sensitive to the materials used for

the techniques, including any metal contained in the alloy, sensitivities

to the bonding or fusing materials would also preclude the use of these

techniques.

- Usually a metal sensitivity can be avoided through careful

selection of alloy to be used. Sensitivities to bonding or fusing

material can be avoided as variety of available materials often

makes it possible for a dentist to avoid the altergen while still

using the direct bonded technique.

2) The second contraindication for the use of direct bonded retainer

techniques is insufficient enamel on the abutment teeth for proper

bonding or enamel that does not have caries existing restorations

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sufficient strength to withstand the forces that will be applied.

(Incisors with thin faciolingual dimension abraded teeth).

3) Deep vertical overbite.

Clinical Considerations for the direct bonded retainer:

There are several design considerations that must be kept in mind

when planning a restoration using any of the cast alloy direct bonded

techniques.

The three cardinal requirements are all quite obvious:

1) The framework must be strong enough to withstand the forces that

will be applied to it.

2) The teeth themselves must be strong enough to withstand the

pressures that will be applied to them when the retainer is in place.

3) Making each tooth retentive, it has been referred as the secret of

successful design in direct bonded retainers. This is to say that no

tooth should be able to break free of the retainer after cementation.

This is a requirement for every tooth to be used as abutment.

Factors in cast retention:

1) Surface area: In etched metal frameworks, the total retention of the

case is directly proportional to the surface area that is bonded.

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2) Resistance to torquing: the most important consideration in designing

the shape of metal framework is that it should be able to resist all the

occlusal and torquing forces. Composite cement is exceptionally

strong except for cleavage and peel. Due to the rigidity of the metal

peel is not generally involved with the etched metal restorations.

Cleavage is however, is a problem with composite cement that applies

here. The greatest weakness of the etched metal technique is found

when the cement must withstand cleavage forces. If the case is

designed so that it is not the cement but the metal framework that

withstand the cleavage forces; the cement can easily provide retention

against all remaining forces.

- Even for teeth that are slightly periodontally involved the

design of the metal framework is extremely important in

providing positive resistance against torquing of teeth away

from splint in the facial direction.

- Buccal wraps: Perhaps the easiest way to create positive

resistance to torque is to provide the restoration with a single

path of insertion that is approximately parallel to the long axis

of the teeth. This resistance is generally provided for by the

inclusion of buccal wraps. The buccal wrap is simply an

extension of metal around the buccal surface of the tooth that it

resists any movement of the tooth in buccal direction.

- Retentive slots surprisingly there is a problem with buccal

wraps when the teeth exhibit extensive excessive spacing. Here

the difficulty is that the wraps can be usually obstrusive

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because the interproximal surfaces of teeth are also visible. In

such cases, as well as those involving crowding it is necessary

to provide positive resistance to torquing by creating a single

path of insertion for splint. This is usually can accomplished by

placing small vertical slots in the interproximal surfaces of the

teeth to be splinted.

- Occlusal rests: the greatest forces on the teeth in normal

occlusion are occlusal forces. The forces a pontic in a vertical

direction can be considerable and as the surface area of the

pontics increase, the total amount of force that must be resisted

by framework increases rapidly. The inclusion of a positive

occlusal rest of some sort, which allows the metal framework to

resist these forces eases the stress on cement bond.

- Thickness of metal : Another important consideration in the

framework is the minimum thickness that is required.

- 0.3mm is ideal thickness for every portion of framework.

- Actually 0.3mm is the minimum thickness required on metal

where it is covered with porcelain in order to produce sufficient

rigidity to prevent fracture of the overlying porcelain.

- The areas within the pontic and in areas connecting the pontic

greater strength is necessary and the minimum thickness should

be 1.0mm. another such area is where the framework passes a

proximal line angle, the minimum recommended thickness is

0.6mm.

27

- On other hand, the in such areas as the point where the

opposing tooth occludes on the lingual plate of an anterior

retainer, the major requirement of the metal is more abrasion

resistance than strength. The non precious metals are so hard

that the thickness required at the occlusal contact point is only

0.1mm.

In fabrication of resin retained fixed partial dentures, attention i.e.

detail in all three phases is necessary for predictable success:

1) Preparation of abutment teeth.

2) Design of restoration

3) Bonding of restoration.

1) Preparation of abutment teeth: Whether anterior or posterior teeth are

prepared common principles dictate tooth preparation design.

- A distinct path of insertion must be established, proximal

undercuts must be removed, rest seats to provide resistance

form and a definite and distinct margin must be prepared.

- The amount of reduction is less because the enamel must not be

penetrated. If necessary the opposing teeth can be recontoured

to increase interocclusal clearance. It is essential that there

should be sufficient enamel area for successful bonding and

that the metal retainers encompass enough tooth structure to

resist lateral displacement.

28

Bur selection

- Gingival margins and circumferential preparation are easily

accomplished with a chamfer or round tipped diamond.

- Occlusal and incisal rest seats can be prepared with a diamond

or carbide inverted cone burs.

- Additional retentive features such as slots, grooves or pinholes

can be made with a tapered fissure carbide.

Step-by-step procedure

1) Leave the margins about 1mm for the incisal or occlusal edge and

1mm supragingival if possible.

- Definite lingual ledges will provide resistance form for the

retainers and assist in positive seating during cementation.

Wherever possible to enhance resistance more than half the

circumference of the tooth should be prepared.

2) Make an accurate impression – Marginal fit is a critical for a resin

retained restoration as for a conventional F.P.D.

3) Fabricate a proximal restoration with autopolymerizing acrylic resin.

29

Anterior tooth preparation and frame work design

- In designing an anterior prosthesis the largest possible surface

area of enamel should be used that will not result in

compromise of the esthetics of the abutment teeth.

- The retentive retainers (wings) should extend on one tooth

mesially and distally if a single tooth is replaced.

- If a combination of tooth replacement and splinting is used the

framework may cover a larger number of teeth.

- The gingival margin should be designed so that a slight

supragingival chamfer exists that definite the gingival

extension of the preparation.

- Any undercut enamel is removed at this time.

- The chamfer finish line may also extend incisally through the

distal marginal ridge area.

- The finish line on the proximal surface adjacent to the

edentulous space should be placed as for facially as is practical.

Abutments should have parallel proximal surfaces.

- An optional slot, 0.5mm in depth, prepared with a tapered

carbide bur, may be placed slightly lingual to the labial

termination of the proximal reduction.

30

- The occlusion is assessed to ensure at least 0.5mm of

interocclusal clearance for the metal retainers in the intercuspal

position and throughout the lateral and protrusive excursive

pathways. If inadequate clearance exists, selective

enameloplasty is performed.

- Occasionally additional clearance can be obtained through

reduction of opposing teeth. In presence of wear or attrition on

incisal edges, however, this is not advised.

- A distinct rest seat is then placed in the cingulum area of

abutment tooth. This may consist of ledges similar to those

incorporated in a pin ledge preparation or it can be a notch or

flat plane perpendicular to the long axis of the tooth.

- The objective is to provide resistance to gingival displacement

and to add rigidity to the casting.

- Rest seats are prepared with an inverted cone bur to facilitate

internal refinement.

- The framework is extended labially past the proximal contact

point to prevent torquing forces from dislodging the prosthesis

to the lingual.

- To optimize esthetics the proximal wrap in the anterior region

may be achieved in part through using the metal ceramic

pontic.

31

- Preparation of mandibular anterior teeth is similar to that for

the maxillary incisors. Lingual enamel thickness is 11 to 50

percent less than for maxillary teeth and consequently tooth

preparation must be more conservative, combinations of

periodontal splinting and tooth replacement is commonly used

in the mandibular anterior region.

Posterior tooth preparation and framework design

- The basic framework for the posterior resin retained F.P.D.

consists of three major components. The occlusal rest (for

resistance to gingival displacement) the retentive surface (for

resistance to occlusal displacement) and the proximal wrap (for

resistance to torquing forces).

- A spoon shaped occlusal rest seat is placed in the proximal

marginal ridge area of the abutments adjacent to the edentulous

space. An additional rest seat may be placed on the opposite

side of the tooth.

- To resist occlusal displacement, the restoration is designed to

maximize the bonding area without unnecessarily

compromising periodontal health or esthetics.

- Proximal and lingual walls are reduced to lower their height of

contour to approximately 1mm from the crest of the force

gingiva. The proximal wall are prepared so that parallelism

results without undercuts.

32

- The bonding area can be increased through extension onto the

occlusal surface provided it does not interfere with the

occlusion. Generally a knife edge type of margin is

recommended.

- Resistance to lingual displacement is more easily managed in

the posterior region of the mouth. A single path of insertion

should exist.

- The alloy framework should be designed to engage at least 180

degrees of tooth structure when viewed from the occlusal. This

proximal wrap allows the restoration to resist lateral loading by

engaging the underlying tooth structure. It should not be

possible to remove a properly designed resin bonded F.P.D. in

any direction but parallel to its path of insertion.

- In general, the preparation differs between maxillary and

mandibular molar teeth on the lingual surface only.

- The lingual wall of maxillary tooth may be prepared in a single

plane and the palatal surface of maxillary molars dictates a two

plane reduction due to taper of these centric cusps in the

occlusal two thirds and occlusal function.

Occassionally a combination prosthesis can be used. This type of

F.P.D. includes a resin bonded retainer on one of the abutment teeth and a

conventional cast restoration on the other.

33

Resin to metal bonding:

- In the original design Rochette made six perforations with a

waxing instrument, thus providing mechanical undercuts for

the resin cements.

- A perforated design has a disadvantge of exposing the resin to

oral fluids, which may lead to problems of abrasion of the resin

or microleakage at the resin metal interface.

- A non perforated design avoids this potential problem and can

be highly polished, resulting in improved oral hygiene.

- Presently non perforated retainers are recommended.

Metal resin can be classified as either

I] Mechanical or II] Chemical

Primarily mechanical bonding is subdivided into:

1) Micro mechanical retention which uses etching to create microscopic

porosities and

2) Macro mechanical retention – which relies on visible undercuts

usually with a mesh or pitted metal.

Chemical bonding generally employs tin plating of metal framework

and specific resin adhesives for metal and enamel.

34

Electrolytic etching:

In this procedure microscopic porosity is created in the fitting surface

of a nickel chromium framework by different electrolytic etching.

- The fabrication technique was developed at the university of

Maryland of school dentistry and hence the prosthesis

sometimes referred as the “Maryland bridge”.

Procedure

- Clean the fitting surface of metal restoration with an air

abrasion unit with aluminium oxide.

- Cover the polished surfaces with wax and attach the prosthesis

to an electrolytic etching unit following the manufacturers

instructions.

- A typical etching cycle will be 3 minutes in 10% H2SO4 with a

current of 300 milliamper per square centimeter of casting

surface.

- Clean the etched surface ultrasonically in 18% Hcl and then

wash and air dry it.

- The etched surface must not be handled after this stage.

35

Chemical etching

Procedure:

- A gel consisting of nitric and hydrochloric acid is applied to the

internal surface of the metal framework for approximately 25

minutes.

- As electrolytic etching is extremely sensitive, many authors

believe that chemical etching provides more reliable results due

to procedural simplicity.

Macroscopic retention

In non perforated retainer, porosity cast in the pattern itself rather than

subsequently obtained by etching.

This is done in variety of ways:

- One techniques uses a special pattern to form a meshwork on

the fitting surface and the external lingual surface is waxed to

give a smooth finish that can be highly polished.

- An alternative technique uses water soluble salt crystals

sprinkled onto the die and incorporated into the wax pattern.

The crystals are dissolved away before investing.

- An advantage of both these techniques is that any alloy can be

selected, where as with electrolytic or chemical etching the

alloy usually must be nickel chromium.

36

- Additionally, tryin and bonding of the prosthesis can be

accomplished at the same appointment.

- These surfaces are not likely to be damaged during handling as

are the very fragile etched metal surfaces.

- Disadvantages of the technique include difficulty on adapting

the mesh to create a closely fitting metal framework and a

potentially thicker metal framework than can be obtained with

a etched metal retainer.

- Also, the rate of microleakage along the cast mesh composite

resin interface is significantly greater than along an etched

metal resin inteface.

Procedure:

1) Outline the mesh framework, trim it to the preparation margins and

adapt it to the master cast.

2) Develop the lingual contours, wax the pontic and cutback and sprue

the finished pattern as usual.

3) Soak the cast in cold water to help release the pattern invest it

normally.

4) Cast the framework and prepare the veneering surface in the

conventional way.

37

5) Buildup porcelain, polish the casting and clean the fitting surface with

an air abrasion unit.

6) The restoration is ready for tryin prior to bonding.

Tin plate:

Tin plating is recently introduced procedure that can improve the

strength of adhesive cement to most metals. Precious alloys can be plated

with tin and used as frameworks. For resin retained F.P.D.s. Tin forms

organic complexes with several specific adhesive resin cements that result in

significantly greater bond strength.

Bonding Agents

Composite resins play an important role in the bonding of the metal

framework to etch enamel.

1) Fillwed BisGMA composite resin (Bisphenol A glycidal).

2) TEGDMA (Triethylene glycel dimethacrylate.

3) 4META (4 methacrylyloxethyl trimellitate anhydrite).

4) UDEMA (Urethane dimethacrylate).

1) Filled BisGMA composite resin : A phosphate ester added to the

monomer allows chemical bonding to both the metal and the etched

tooth enamel. The powder contains approximately 75% quartz filler

and is almost insoluble in oral fluids. The material shows excellent

bond strength to non noble metals and tin plated noble metals. It will

no set in presence of oxygen. To ensure a complete cure the

38

manufacturers provides a polyethylene glycol gel, which should be

placed over margins of restoration. This creates oxygen barrier and

can be washed away after the material has set.

Procedure :

1) Clean the teeth with pumice and water isolate them with the rubber

dam and chemically prepare them.

Currently 37% phosphoric acid is used to etch the enamel and

is applied for 30 to 60 seconds.

2) Place the cement on external surface of the prosthesis and completely

seat the restoration.

3) Form pressure should be exerted on the restoration while excess

uncured resin is removed prior to the material completely setting.

4) The restoration should be held in place until resin has polymerized.

39

Summary & Conclusion

Resin bonded fixed partial dentures after the following significant

advantages to the dentist and the patient in properly selected clinical

situations:

1) Tooth preparation is reduced to a minimum.

2) The procedure is reversible.

3) Soft tissue management is simplified.

4) There is less problem with color matching and

5) Reduced cast and simplicity give high patient acceptability.

There are two disadvantages:

1) Bonding procedures are more difficult and time consuming than

conventional luting techniques.

2) Occlusal adjustment at the tryin of the restoration is more difficult

because of the lack of a retentive crowns tooth relationship.

One of the basic principles of tooth preparation for fixed

prosthodontics is conservation of tooth structure. This is the primary

advantage of resin retained fixed partial dentures and a careful patient

selection is an important factor in predetermination of clinical success.

All factors considered, it seems that the use of the cast metal resin

bonded fixed partial denture should be encouraged where sound abutment

teeth exist and only one or two teeth are missing.

40

References

1) Asterios Doukodakis, Benard Cohen and Andreas Tsoutsos : A new

chemical method for etching metal frameworks of the acid etched

prosthesis. J. Prosthet. Dent., 58 (4) : 421-423, 1987.

2) Donald F. Howe and Gerald E. Denehy : Anterior fixed partial denture

utilizing the acid etch technique and a cast metal frame work. J.

Prosthet. Dent., 37 (1) : 28-31, 1977.

3) Dan Nathanson and Kambiz Moin : Metal reinforced anterior tooth

replacement using acid-etch composite resin technique. J. Prosthet.

Dent., 43 (4), 408-412, 1980.

4) Franklin Garcia Godoy, David A. Kaiser, William F.P. Malone and

Gregory Hubbard : Shear bond strength of two resin adhesives for acid-

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6) Gerald Barrock : Recent advances in etched cast restorations. J.

Prosthet. Dent., 52 (5) : 619-626, 1984.

7) G.F. Priest and N.A. Donatelli : A four year clinical evaluation of

resin bonded fixed partial dentures. J. Prosthet. Dent., 59 (5) : 542-546,

1988.

41

8) J. Robert Eshleman, Peter C. Moon, Robert F., Branes : Clinical

evaluation of cast metal resin bonded anterior fixed partial dentures. J.

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12) John O. Burges and James G. McCartney : Anterior retainer design for

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433-436, 1989.

13) M.H. El Sherif, A.El-Messay and M.N. Halhoul : The effects of alloy

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42

15) Resensteil, Land and Fujimoto : Contemporary fixed prosthesis.

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fixed prosthodontics.

17) Sturdvent : The art and science of operative dentistry. 345-346.

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laboratory techniques. Qunitessence Publishing Co., 1989.

19) Tylman : Fixed prosthodontics.

20) Timothy Brady, Astenious Doukodakis and Stephen T. Rasmusten : A

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study.

43