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Full Veneer Retainers in Fixed Partial DenturePRESENTED BYDR. SUKHJIT KAUR

Components of FPD

In fixed prosthodontics it is the retainer which provides retention and resistance against horizontal oblique and vertical dislodging forces.Retainer: Any type of device used for stabilization or retention of a prosthesis (GPT-8)Fixed partial denture retainer: The part of a fixed dental prosthesis that unites the abutment(s) to the remainder of the restoration (GPT-8)Extra coronal retainers: That part of a fixed dental prosthesis uniting the abutment to the other elements of a prosthesis that surrounds all or part of the prepared crown (GPT-8) INTRODUCTION

Requirements of an Ideal retainerPrime requirement is mechanical functionto be constructed without injury to pulp & supporting tissuesshould protect and maintain the pulp against thermal and galvanic shock. ability of the retainer to provide safety for the tooth during the lifetime of the restoration establishment of self-cleaning property of the retainer Retainer with least tooth reduction is more advisable Stress should be dispersed to the more receptive areas of the abutment

Uses of retainer

To improve the masticatory efficiency.To establish the contact point to prevent food lodgment.To be useful in correcting malalignment. To close diastema in anterior teeth.To prevent drifting of teeth.

Classification of retainersI. Based on type of preparationA. Intra coronal retainers.Modified class II inlay and MOD onlays.Pinledge retainers.B. Extra coronal retainersFull veneer crown.Partial veneer crowns.C. Radicular retainersDowel crownsRichmond crowns

II. Based on type of materials used in the construction of retainers.Metals e.g. Nickel chrome, Titanium, Cobalt chrome.PorcelainAcrylic resinsComposite resinsCombination of any metal with porcelain or acrylic resin or composite resin.

III. BASED ON TOOTH COVERAGE

1.Major retainers-

-Full veneer crown and partial veneer crowns

2.Minor retainers Inlays and onlays

Indications for multiple retainers

Abutment teeth with short roots.Lack of sufficient bone support.Density of alveolar bone.Excessive length span.Excessive lever arm action because of shape of anterior arch.Distal extension of pontic for increased function.Replacement of a missing cuspid.

TELESCOPIC RETAINERSThis type of retainer is used when the path of insertion of the fixed partial denture does not coincide with the long axis of the abutment tooth. The design involves the fabrication of two copings, one over the other. The internal or primary coping functions to modify the morphology of the tooth. The secondary coping is designed to fit over the primary coping along the new path of insertion.

Selection of retainers

Retainer selection is usually dictated by: 1) age 2) DMF rate 3) edentulous span 4) Periodontal support 5) arch position of the teeth 6) Skeletal relationships 7) Inter occlusal and intra occlusal conditions such as crown length 8) Existing and projected oral hygiene of the patient 9) Vitality of the potential abutment

CRITERIA FOR SELECTING TYPE OF RETAINERS

Alignment of abutment teethIf the abutment teeth are aligned parallel to one another, a full veneer crown can be given. A fixed-fixed bridge can be designed.If the abutment teeth are not aligned parallel to one another, a pin retained crown which need not to be placed along the long axis of the tooth.

AppearanceSometimes full veneer crowns show superior esthetics to partial veneer crowns and sometimes neither type will be completely satisfactory.It is best to retain facial /buccal surface of the natural tooth as they provide the best aesthetics.In cases with inadequate pontic space, full coverage restoration can be designed for better appearance.

The condition of abutment teeth Partial veener crowns are preferred for non carious abutment or abutments with large restoration but intact facial/buccal surface.Endodontically treated teeth may have to be restored with core/post before designing the retainer.

CostAnterior restorations are best restored with all ceramic crowns but they are the most expensive.Metal ceramic crowns could be economically the best replacement for both anterior and posterior teeth.

Preservation of tooth structureBuccal/facial surface should be conserved.Partial veneer crowns are more conservative than full crowns.All ceramic crowns are the least conservative.

EXTRA CORONAL RETAINERS

Full veneer crownsThey are of three typesComplete metal veneer crownsMetal ceramic crownsAll ceramic crowns

Complete cast crown/ full crown/ full cast crown/ complete crown : Complete cast metal crowns can be used where the breakdown of tooth structure is severe. Full veneer crown describes a restoration entirely made of cast metal.

Has the best longevity of all fixed restorations

Advantages 1) Greater retention 2) Greater resistance form 3) Strength 4) Modification of axial tooth contour -special significance when dealing with malaligned teeth -better access to improved oral hygiene.

5) special requirements -when retainers are needed for RPD 6) Easy occlusal modifications - in supra erupted teeth

Disadvantages 1) Extensive removal of tooth structure 2) Adverse effects on soft tissue 3) Vitality tests not feasible 4) Display of metal

IndicationsAny posterior tooth in non-esthetic zone.Short clinical crowns.Fractured tooth.Long edentulous span.Occlusal forces greater than average.Abutment tooth alignment that requires full coverage preparation to achieve adequate retention.Extensive destruction from caries or trauma.Endodontically treated teeth.Necessity for maximum retention and strength.To provide contours to receive a removable appliance.Other recontouring of axial surfaces (minor corrections of mal-inclinations).Correction of occlusal plane.

Contraindications 1) When conservative treatment can be carried out 2) If intact buccal or lingual wall exists 3) If less than maximum retention and resistance are needed 4) High esthetic needs

Rotary instruments used for full veneer preparations:

Shape Use Round end tapered diamond Depth orientation grooves ,Occlusal reduction, Functional cusp bevel Torpedo diamond Axial reduction , Chamfer finish line Short needle Initial interproximal axial reduction in posterior teeth Long needle Initial proximal axial reduction in anterior teeth Small wheel diamond Lingual reduction in anterior teeth

Tapered fissure bur (171L) Seating groove , Proximal groove (posterior teeth) , Smoothing and finishing, Occlusal and incisal bevels Tapered fissure burs (169L & 170L) Initial groove alignment , Angles of proximal boxes , Smoothing and finishing, Occlusal and incisal bevels End cutting bur Conventional shoulder finishing Torpedo bur Axial wall finishing , Chamfer finishing Flame bur Flare and bevel finishing

TOOTH PREPARATION FOR COMPLETE CAST CROWNThe clinical procedure to prepare a tooth for a complete cast crown consists of the following steps:Occlusal guiding groovesOcclusal reductionAxial alignment groovesAxial reductionFinishing and evaluation

PUTTY INDEX AS GUIDE FOR TOOTH REDUCTION

Occlusal guiding grooves: Using a round end tapered diamond and no: 171 bur, depth orientation grooves are made on the triangular ridges and primary developmental grooves. The depth orientation grooves should be 1.3mm deep on functional cusps and 0.8mm deep on non-functional cusps, allowing 0.2 mm for smoothing the preparation. The tooth structures between the orientation grooves are removed following cuspal contours.

Functional cusp bevel is placed using round end tapered diamond and no: 171 bur. The bevel should parallel the inward facing inclines of the cusps of the opposing tooth, at a depth of 1.5 mm usually forming a 45 angle with the axial wall.

Nonfunctional (Noncentric) Cusp Bevel: A minimum of 0.6 mm of clearance at the occlusoaxial line angles of the nonfunctional cusps is needed for adequate strength. Maxillary molars in particular often require an additional reduction bevel in this area to avoid an overcontoured restoration that does not follow normal configuration. Such additional reduction is often unnecessary for mandibular molars, however, because they are lingually inclined and their profile is relatively straight.

Alignment Grooves for Axial Reduction:

Three alignment grooves are placed in each buccal and lingual wall with a narrow, round-end, tapered diamond. One is placed in the center of the wall, and one in each mesial and distal transitional line angle. position of the bur automatically produces a 6 degree convergence between the axial walls.Use a periodontal probe to assess the relative parallelism of the alignment grooves with one another or with the proposed path of withdrawal, of a secondary abutment.Making an impression with irreversible hydrocolloid (alginate) and pouring in rapid-setting stone generates a cast that can be analyzed with a dental surveyor.

Facial and lingual axial reduction is done with a torpedo diamond producing a definite chamfer finish line at the same time. The facial and lingual reduction is carried as far as possible into the interproximal embrasures without nicking the adjacent teeth.

Mesial and distal axial reduction. A short thin tapered diamond is placed against the facial surface of the remaining interproximal tooth structure. Ensure that adequate clearance ( 0.6 mm) exists between the external surface of the proximal chamfer and the adjacent tooth.

Finishing Use a fine-grit diamond or carbide torpedo bur of slightly greater diameter for finishing the chamfer margin. This should be done as smoothly as possible, with the handpiece operating at reduced speed. A properly finished margin should be glassy smooth when touched by the tine of an explorer. Finish all prepared surfaces and slightly round all line angles.

Seating groove is made on the axial surface using no: 171 bur. The groove should be cut to the full diameter and it should extend gingivally to a point 0.5 mm above the chamfer.

The completed preparation is characterized by a smooth, even chamfer; a 6-degree taper; and gradualtransitions between all prepared surfaces.Features of full veneer crown preparation and the function served by each

METAL CERAMIC RESTORATION:

The use of porcelain fused to metal restorations has grown from the development of the first commercially successful porcelain/ gold alloy restoration by Weinstein et al in 1950s. A porcelain-fused to metal crown can serve as a strong and esthetic restoration.

indicationsSingle and multiple restorations for both anterior and posterior teeth.Mandibular anterior teeth where full shoulder preparations are prohibitive. Peg shaped laterals or malformed teeth.Patients with reduced interocclusal clearance.Extensive tooth destruction as a result of caries, trauma or existing previous restorations.Need for superior retention and strength.An endodontically treated tooth with post.Need to recontour axial surfaces or correct minor malocclusions.EstheticsIf porcelain jacket crown is contraindicated.

ContraindicationsLarge pulp chamber because of high risk of pulp exposure.Intact facial wallWhen more conservative retainer is technically feasible. Patients with active caries or untreated periodontal disease

Advantages Superior esthetics as compared to complete cast crowns.

Strength imparted to tooth is superior as compared to partial veneer.

Excellent retentive qualities

Two in one property -because it is a combination -Underlying principle -Natural appearance

Disadvantages:Removal of substantial tooth structure.Subject to fracture because porcelain is brittle.Difficult to obtain accurate occlusion in glazed porcelain.Inferior esthetics compared to porcelain jacket crown.Expensive.Shade selection can be difficult.

POSTERIOR PORCELAIN FUSED TO METAL CROWN PREPARATION

Planar occlusal reduction is done using round and tapered diamond and no: 171 bur. The depth orientation grooves should be 1.5 to 2.0 mm in occlusal areas where porcelain coverage is required. The tooth structures between the orientation grooves are removed following cuspal contours.

Recommended minimum dimensions for a PFM crown

Functional cusp bevel is done using round end tapered diamond and no: 171 bur. The bevel should parallel the inward facing inclines of the cusps of the opposing tooth, at a depth of 1.5 mm usually forming a 45 angle with the axial wall.

Depth orientation grooves for axial reduction A flat end tapered diamond is first aligned with the occlusal portion of the facial surface and three vertical cuts are made to the full diameter of the diamond, fading out at the break where the curvature of the facial surface is the greatest. Two similar grooves parallel to the gingival segment of the facial surface.

Facial reduction, occlusal half: A flat end tapered diamond is used to remove the tooth structure remaining between the orientation grooves in the occlusal portion of the facial surface.

Facial reduction, gingival half: A flat end tapered diamond is used to reduce the gingival segment and extend well into the proximal surface. 1.2 mm to 1.4 mm is the accepted reduction

Proximal axial reduction: Short needle diamond facilitates interproximal reduction without nicking the adjacent tooth. Once separation between the teeth is achieved, the needle diamond is used to plane the proximal axial wall.

Lingual axial reduction: A torpedo diamond is used for lingual axial reduction and to round over the corner created at the line angle with the proximal surfaces.

Axial finishing: All axial surfaces to be veneered with metal are finished using a torpedo finishing bur producing the chamfer finish line. The facial surface and those areas of the proximal surfaces to be veneered with porcelain are smoothened with the flat end tapered bur or no: 171 bur. Lingual to the proximal contact, the transition from the deeper facial reduction to the relatively shallower lingual axial reduction result in a vertical wall or wing of tooth structure.

Shoulder finishing: No: 957 bur is used to finish the shoulder and is planed with a sharp 1.0 m wide chisel. Gingival bevel: Flame shaped diamond and finishing bur are used to produce a narrow bevel, no wider than 0.3 mm.

criteria

PREPARATION FOR ANTERIOR PORCELAIN FUSED TO METAL CROWN

Incisal reduction: Depth grooves are placed (about 1.8mm) in the incisal edge of the anterior tooth that will provide needed reduction of 2mm.

Facial reduction:Depth grooves are placed one at the centre of the facial surface and one each in approximate locations of mesiofacial and distofacial line angles.These grooves will be placed in two planes: Cervical portion - parallel to the long axis of tooth Incisal portion -follow the normal facial contour. The cervical portion will determine the path of withdrawl while incisal portion will provide the space for porcelain veneer.

Finish line:If a restoration with a narrow subgingival metal collar is to be fabricated and sufficient sulcular depth is present, the shoulder is placed 0.75-lmm subgingivally. The resulting shoulder should be 1mm wide and should extend well into the proximal embrasure at least 1 mm lingual to the proximal contact. On the mesial (visible) side, the preparation extends slightly farther than on the distal (cosmetically less critical) side.

Lingual reductionLingual surface is reduced with the diamond held parallel to the intended path of withdrawl. A Cervico Incisal taper of approx 6 is indicated.The lingual concavity is prepared for adequate clearance using a football shaped bur. Typically lmm is required if centric contacts in the completed restoration are to be located in metal where as on porcelain additional clearance is needed.Lingual chamfer is indicated.

Interproximal reduction A short needle diamond is used to begin the proximal axial reduction without touching the adjacent tooth. The axial reduction interproximally is completed by running the flat end tapered diamond labially and torpedo bur lingually.

Winged preparationWingless preparation

Finish line configuation:A porcelain labial margin requires proper support for the porcelain. A shoulder with 900 cavosurface angle is recommended. A sloping shoulder has been advocated to ensure the elimination of unsupported enamel and to minimize the marginal gap width. Such a shoulder of 1200 cavosurface angle can be accomplished by flat end diamond by changing its alignment, paying particular attention to the configuration of tooth structure cervical to the margin. Lingually chamfer and Interproximally shoulder is indicated.

ALL CERAMIC CROWN:The porcelain jacket crown was developed in 1886. In 1965 Mclean and Hughes developed an inner core of aluminous porcelain containing 40% to 50% of alumina crystals to improve material characteristics. Later, platinum foil was included to further improve the porcelain crown. In the 1980s Dicor, a castable ceramic became widely used. Today the latest generation of materials utilizes high strength ceramics with composite materials to reinforce the ceramic. Todays materials include Procera, In-Ceram, Empress I and Empress II.

ALL CERAMIC CROWNSIndications:High esthetic requirementConsiderable proximal cariesIncisal edge reasonably intactEndodontically treated teeth with post and coresFavourable distribution of occlusal load

Contraindications:When superior strength is warranted because of absence of reinforcing metal substructure.Significant caries with insufficient coronal tooth structure for support.Thin teeth faciolingually.Unfavourable distribution of occlusal load.

Advantages:Superior esthetics.Good tissue response even for subgingival margins.Slightly more conservative of facial wall.Disadvantages:Reduced strength compared to metal ceramic crown.Proper preparation extremely critical to ensure mechanical success.Least conservative.Brittle nature of material.Causes wear on the functional surfaces of natural teeth that oppose porcelain restorations.

Tooth preparation for posterior all ceramic crownOcclusal reduction: A large round end tapered diamond is used to place depth orientation grooves on triangular ridges and major grooves. The final occlusal reduction should be 1.5 mm to 2.0 mm deep. Remove the tooth structure remaining between the depth-orientation grooves with the large round-end tapered diamond.

Functional cusp bevel: A minimum of 1.5 mm of clearance is necessary.Facial and lingual axial reduction: The large round end tapered diamond is used to obtain axial reduction ranging from 1.0 to 1.5 mmProximal axial reduction: A short needle diamond and then round end tapered diamond. Depth - 1.0 to 1.5 mmPreparation finishing: round end tapered carbide bur is used to finish the axial surfaces, the functional cusp bevel and chamfer finish line all around. Uniform circular preparation without grooves is preferred. The shoulder preparation should have an angle of 90-120 degrees. Flat chamfers, tangential preparations and bevels are contraindicated.

The features for an all ceramic crown on a posterior tooth and the function served by each

TOOTH PREPARATION FOR ALL CERAM ANTERIOR CROWNS:

Incisal reduction: 2.0 mm deepflat-end tapered diamondLabial reduction: 1.2 to 1.4 mm deepThe rounded shoulder or chamfer should be a minimum of 1.0 mm wide.Lingual reduction done with the small wheel diamond AND the flat-end tapered diamondradial shoulderProximal reduction: is similar to labial and lingual reductions

Tooth reduction for zirconia-based crowns is less than that for PFM or traditional all-ceramic crowns. The reasons are that zirconia is very strong (>1000 MPa) and no opaque layer is required. This is also true regarding other bonded porcelain veneers. The reduction can be kept less than 1mm all around with a chamfer as finish line.

Summary and ConclusionThe objective in selection of retainer whether it involves a single tooth, several teeth or complete restoration of masticatory mechanism, it should restore and maintain function of dental arch. It should be therefore both restorative and preventive.To accomplish this objective preventive as well as therapeutic measures should be utilized. The efficiency in selecting the retainer depends on the intelligent application of mechanical, physiological, hygienic and esthetic principles within the limits of the supporting tissues.