In many dental practices the metal-ceramic crown isone of the most widely used fixed restorations. Thishas resulted in part from technologic improvementsin the fabrication of restoration by dental laborato-ries and in part from the growing amount of cos-metic demands that challenge dentists today.

The restoration consists of a complete-coveragecast metal crown (or substructure) that is veneeredwith a layer of fused porcelain to mimic the appear-ance of a natural tooth. The extent of the veneer canvary.

To be successful, a metal-ceramic crown prepara-tion requires considerable tooth reduction whereverthe metal substructure is to be veneered with dentalporcelain. Only with sufficient thickness can thedarker color of the metal substructure be maskedand the veneer duplicate the appearance of a nat-ural tooth. The porcelain veneer must have a certainminimum thickness for esthetics. Consequently,much tooth reduction is necessary, and the metal-ceramic preparation is one of the least conservativeof tooth structures (Fig. 9-1).

Historically, attempts to veneer metal restora-tions with porcelain had several problems. A majorchallenge was the development of an alloy and a ce-ramic material with compatible physical propertiesthat would provide adequate bond strength. In ad-dition, it was initially difficult to obtain a naturalappearance.

The technical aspects of the fabrication of thisrestoration are discussed more in Chapter 24. Fornow, only a brief description is provided. The metalsubstructure is waxed and then cast in a specialmetal-ceramic alloy having a higher fusing rangeand a lower thermal expansion than conventionalgold alloys. After preparatory finishing procedures,this substructure, or framework, is veneered withdental porcelain. The porcelain is fused onto theframework in much the same manner as householdarticles are enameled. Modern dental porcelainsfuse at a temperature of about 960° C (1760° F). Be-cause conventional gold alloys would melt at thistemperature, the special alloys are necessary.

Fig. 9-1.

Recommended minimum dimensions for ametal-ceramic restoration on an anterior tooth (A) and aposterior tooth (B). Note the significant reduction neededcompared to that for a complete cast or partial veneercrown.

I NDICATIONS

The metal-ceramic crown is indicated on teeth thatrequire complete coverage, where significant es-thetic demands are placed on the dentist (e.g., theanterior teeth). It should be recognized, however,that, if esthetic considerations are paramount, anall-ceramic crown (see Chapters 11 and 25) has dis-tinct cosmetic advantages over the metal-ceramicrestoration; nevertheless, the metal-ceramic crownis more durable than the all-ceramic crown and gen-erally has superior marginal fit. Furthermore, it can

216

Chapter 9 The Metal-Ceramic Crown Preparation

serve as a retainer for a fixed partial denture be-cause its metal substructure can accommodate castor soldered connectors. Whereas the all-ceramicrestoration cannot accommodate a rest for a remov-able prosthesis, the metal-ceramic crown may besuccessfully modified to incorporate occlusal andcingulum rests as well as milled proximal and reci-procal guide planes in its metal substructure (seeChapter 21).

Typical indications are similar to those forall-metal complete crowns: extensive tooth destruc-tion as a result of caries, trauma, or existing previ-ous restorations that precludes the use of a moreconservative restoration; the need for superior re-tention and strength; an endodontically treatedtooth in conjunction with a suitable supportingstructure (a post-and-core); and the need to recon-tour axial surfaces or correct minor malinclinations.Within certain limits this restoration can also beused to correct the occlusal plane.

Contraindications for the metal-ceramic crown, asfor all fixed restorations, include patients with ac-tive caries or untreated periodontal disease. Inyoung patients with large pulp chambers, themetal-ceramic crown is also contraindicated be-cause of the high risk of pulp exposure (see Fig.7-4). If at all possible, a more conservative restora-tive option such as a composite resin or porcelainlaminate veneer (see Chapter 25) is preferred.

A metal-ceramic restoration should not be con-sidered whenever a more conservative retainer isfeasible, unless maximum retention is needed-asfor a long-span FPD. If the facial wall is intact, thepractitioner should decide whether it is truly neces-sary to involve all axial surfaces of the tooth in theproposed restoration. Although perhaps technicallymore demanding and time consuming, a more con-servative solution usually can be found to satisfythe patient's needs that may provide superiorlong-term service.

The metal-ceramic restoration combines, to a largedegree, the strength of cast metal with the estheticsof an all-ceramic crown. The underlying principle isto reinforce a brittle, more cosmetically pleasingmaterial through support derived from the strongermetal substructure. Natural appearance can beclosely matched by good technique and if desiredthrough characterization of the restoration with in-ternally or externally applied stains. Retentive qual-

CONTRAINDICATIONS

ADVANTAGES

ities are excellent because all axial walls are in-cluded in the preparation, and it is usually quiteeasy to ensure adequate resistance form duringtooth preparation. The complete-coverage aspect ofthe restoration permits easy correction of axial form.In addition, the required preparation often is muchless demanding than for partial-coverage retainers.Generally, the degree of difficulty of a metal-ceramic preparation is comparable to that of prepar-ing a posterior tooth for a complete cast crown.

DISADVANTAGES

The preparation for a metal-ceramic crown requiressignificant tooth reduction to provide sufficientspace for the restorative materials. To achieve betteresthetics, the facial margin of an anterior restorationis often placed subgingivally, which increases thepotential for periodontal disease. However, asupragingival margin can be used if significantcosmetic concerns do not prohibit it or if the restora-tion incorporates a porcelain labial margin (seeChapter 24).

Compared to an all-ceramic restoration, themetal-ceramic crown may have slightly inferior es-thetics, but it can be used in higher-stress situationsor on teeth that would not provide adequate sup-port for an all-ceramic restoration.

Because of the glasslike nature of the veneeringmaterial, a metal-ceramic crown is subject to brittlefracture (although such failure can usually be attrib-uted to poor design or fabrication of the restoration).A frequent problem is the difficulty of accurate shadeselection and of communicating it to the dental ce-ramist. This is often underestimated by the novice.Since many procedural steps are required for bothmetal casting and porcelain application, laboratorycosts generally place the metal-ceramic restorationamong the more expensive of dental procedures.

PREPARATIONThe recommended sequence of preparation is illus-trated for a maxillary right central incisor (Fig. 9-2);however, the same step-by-step approach can be ap-plied to other teeth (Fig. 9-3). As with all toothpreparations, a systematic and organized approachto tooth reduction will save time.

Armamentarium (Fig. 9-4). The instrumentsneeded to prepare teeth for a metal-ceramic crowninclude:

•

Round-tipped rotary diamonds (regular gritfor bulk reduction, fine grit for finishing) orcarbides

Section 2 Clinical Procedures-Part I

Fig. 9-2.

Preparation of a maxillary incisor for a metal-ceramic crown. A, Heavily restored maxillarycentral incisor. B and C, Rotary instrument aligned with the cervical one third and incisal two thirds togauge correct planes of reduction. D and E, Guiding grooves placed in the two planes. The cervicalgroove is made parallel to the path of withdrawal, which usually coincides with the long axis of thetooth. The incisal depth groove is prepared parallel to the facial contour of the tooth. F and G, Incisalguiding grooves are placed. H, Incisal edge reduction. I to K, Facial reduction accomplished in twoplanes. L, Breaking proximal contact, maintaining a lip of enamel to protect the adjacent tooth from in-advertent damage. M and N, Proximal reduction. O, Placing a 0.5-mm lingual chamfer.

Chapter 9 The Metal-Ceramic Crown Preparation

Fig. 9-2, cont'd.

P, Afootball-shaped diamond is rec-ommended for lingual reductionof anterior teeth. Alternatively, awheel-shaped diamond may beused. Q to S, Finishing the prepa-ration with a fine-grit diamond.T, The completed preparation.

Fig. 9-3.

Preparation of a maxillary premolar for a metal-ceramic crown. A, Depth holes. B, Occlusaldepth cuts. C, Half of the occlusal reduction is completed. D, Occlusal reduction is complete. Guidinggrooves are placed for axial reduction. E and F, Lingual chamfer and facial shoulder are prepared on halfthe tooth. G, Completed preparation.(A to E, Lingual view; F and G, buccal view.)

R

Section 2 Clinical Procedures-Part I

Fig. 9-4.

Armamentarium for the metal-ceramic crownpreparation.

Football- or wheel-shaped diamond (for lin-gual reduction of anterior teeth)Flat-ended, tapered diamond (for shoulderpreparation)Finishing stonesExplorer and periodontal probeHatchet and chisel

The actual sequence of steps can be variedslightly depending on operator preference.

Step-By-Step Procedure. The preparation isdivided into five major steps: guiding grooves, in-cisal or occlusal reduction, labial or buccal reduc-tion in the area to be veneered with porcelain, axialreduction of the proximal and lingual surfaces, andfinal finishing of all prepared surfaces.

Guiding Grooves1. Place three depth grooves (Fig. 9-5), one in

the center of the facial surface and one eachin the approximate locations of the mesiofacial and distofacial line angles (see Fig. 9-2, Ato E). These will be in two planes: the cervicalportion to parallel the long axis of the tooth,the incisal (occlusal) portion to follow thenormal facial contour (see Fig. 9-2, D and E).

2. Perform the facial reduction in the cervicaland incisal planes. The cervical plane will de-termine the path of withdrawal of the com-pleted restoration. The incisal or occlusalplane will provide the space needed for theporcelain veneer; it should be approximately1.3 mm deep to allow for additional reduc-tion during finishing. The incisal groovesusually extend halfway down the facial sur-face, although (depending on the shape of thetooth) they may extend to include the incisaltwo thirds. Cervical grooves are generallymade parallel to the long axis of the tooth.However, they can be adjusted slightly to cre-ate a more desirable path of withdrawal; inparticular, some labial inclination will im-

Fig. 9-5.

Depth grooves in the facial wall are placed intwo directions: incisally, parallel to the tooth contour; cervi-cally, parallel to the path of withdrawal. The groovesshould be 1.3 mm deep.

prove retention on a tooth with little cingu-lum height. On small teeth it may be advis-able to keep the cervical grooves somewhatshallower near the margin.

3. Place three depth grooves (about 1.8 mmdeep) in the incisal edge of an anterior tooth.This will provide the needed reduction of 2mm and allow finishing (see Fig. 9-2, F andG). Verify the depth of these grooves can beverified with a periodontal probe. On poste-rior teeth where the occlusion is to be estab-lished in porcelain, 2 mm of clearance mustexist. If the occlusion is to be established inmetal, the same minimum clearances areneeded as for a complete cast crown. Poste-rior occlusal reduction incorporates a func-tional cusp bevel on the lingual cusp, similarto that for a complete cast crown. When ini-tially positioning the diamond for anteriorteeth, it may be helpful to observe the longaxis of the opposing tooth in the intercuspalposition and to orient the instrument perpen-dicular to that (Fig. 9-6). The grooves mustnot be too deep; otherwise, an overreducedand undulating surface will result.

Incisal (Occlusal) Reduction.

The completedreduction of the incisal edge on an anterior toothshould allow 2 mm for adequate material thicknessto permit translucency in the completed restoration.Posterior teeth generally require less (1.5 mm) be-cause esthetics is not as critical. Caution must beused, however, because excessive occlusal reduc-tion shortens the axial walls and thus is a commoncause of inadequate retention and resistance form in

Chapter 9 The Metal-Ceramic Crown Prepar ation

Fig. 9-6.

A, Depth grooves 1.8 mm deep placed in the incisal edges to ensure adequate and even re-duction. B, Incisal reduction completed on the left central and lateral incisors. Note the angulation of thediamond, perpendicular to the direction of loading by the mandibular anterior teeth.

the completed preparation. This can be particularlyproblematic on anterior teeth (where as a conse-quence of tooth form, most of the retention is de-rived from the proximal walls).

4.

Remove the islands of remaining tooth struc-ture. On anterior teeth, access is usually un-restricted, and the thickest portion of the cutting instrument can be used to maximizecutting efficiency (see Fig. 9-2, H). On poste-rior teeth, the same pattern is followed as inpreparing depth grooves for a complete castcrown (see Chapter 8). This will include theuse of a centric cusp bevel, although addi-tional occlusal reduction will be neededwhere the porcelain is to be applied (see Fig.9-3, A to C.

Labial (Buccal) Reduction. When completed,the reduction of the facial surface should have pro-duced sufficient space to accommodate the metalsubstructure and porcelain veneer. A minimum of 1.2mm is necessary to permit the ceramist to produce arestoration with satisfactory appearance (1.5 mm ispreferable). This requires significant tooth reduction.For comparison, the cervical diameter of a maxillarycentral incisor averages between 6 and 7 mm.

In the cervical area of small teeth, obtaining opti-mal reduction is not always feasible (see Fig. 7-4.)Often a compromise is made with lesser reductionin the area where the cervical shoulder margin isprepared.

5. Remove the remaining tooth structure be-tween depth grooves (see Fig. 9-2,1 to L), cre-ating a shoulder at the cervical margin (Fig.9-7). If a restoration with a narrow subgingi-val metal collar is to be fabricated and suffi-cient sulcular depth is present, place theshoulder approximately 0.5 mm apical to thecrest of the free gingiva at this time. Addi-tional finishing will then result in a marginthat is 0.75 to 1 mm subgingival. Use ade-quate water spray during the entire phase of

B

Fig. 9-7.

A, The cervical shoulder is established as thetooth structure between the depth grooves is removed. Therotary instrument is moved parallel to the intended path ofwithdrawal during this procedure. B, The facial reductionshould be completed in two phases, initially maintainingone half intact for assessment of the adequacy of reduction.Note the two distinct planes of reduction on the facial. Theproximal aspect parallels the cervical reduction on the fa-cial wall. C, Facial reduction completed. A 6-degree taperhas been established between the proximal walls.

preparation, because a significant amount oftooth structure is being removed and copiousirrigation (along with intermittent strokes)will expedite the preparation process. Such acautious approach will prevent unnecessarytrauma to the pulp. The resulting shoulder

A

C

Section 2 Clinical Procedures-Part I

should be approximately 1 mm wide andshould extend well into the proximal embra-sures when viewed from the incisal (occlusal)side (Fig. 9-8). Where access permits, estab-lishing this shoulder from the proximal gin-gival crest toward the middle of the facialwall is preferred. This will minimize place-ment of the initial shoulder preparation tooclose to the epithelial attachment. If the mar-gin is established from facial to proximal, atendency exists to "bury" the instrument andencroach on the epithelial attachment. A con-scious effort to maintain proper margin posi-tion relative to the crest of the free gingiva iscritical (see Fig. 7-49). The location and spe-cific configuration of the facial margin de-pend on several factors: the type of metal-ceramic restoration selected, the cosmeticexpectations of the patient, and operatorpreference.

From a periodontal point of view, a supragingivalmargin is always preferred. Its application is re-stricted, however, because patients often object to avisible metal collar or discolored root surface. Suchobjections are common, even when the gingivalmargin is not visible during normal function, as inpatients with a low lip line. This generally limits the

Fig. 9-8.

A, The facial shoulder preparation should wraparound into the interproximal embrasure and extend atleast 1 mm lingual to the proximal contact. B, The shoulderpreparation extends adequately to the lingual side of theproximal contact. Note that on the mesial (visible) side, thepreparation extends slightly farther than on the distal (cos-metically less critical) side.

use of supragingival margins to posterior teeth (Fig.9-9) and to un-discolored anterior teeth (in whichcase a porcelain labial margin is preferred; see Chap-ter 24). The optimum location of the margin shouldbe carefully determined with the full cooperation ofthe patient. Where a subgingival margin is to beplaced, careful tissue manipulation is essential; oth-erwise, there will be damage that leads to permanentgingival recession and subsequent exposure ofthe metal collar. This is most effectively avoidedthrough meticulous gingival displacement with acord before finishing (Fig. 9-10). The configuration ofthe margin is also finalized at this time (Fig. 9-11).

Axial Reduction of the Proximal and LingualSurfaces. (see Fig. 9-2, M to P). Sufficient toothstructure must be removed to provide a distinct,smooth chamfer of about 0.5 mm width.

6.

Reduce the proximoaxial and linguoaxial sur-faces with the diamond held parallel to the in-tended path of withdrawal of the restoration.These walls should converge slightly fromcervical to incisal or occlusal. A taper of ap-proximately 6 degrees is recommended. Onanterior teeth, a lingual concavity is preparedfor adequate clearance for the restorative ma-terial(s). Typically, 1 mm is required if thecentric contacts in the completed restorationare to be located on metal. When contact is onporcelain, additional reduction will be neces-sary. For anterior teeth, usually only onegroove is placed, in the center of the lingualsurface. For molars, three grooves can beplaced in a manner similar to that describedfor the all-metal complete cast crown.

Fig. 9-9.

Supragingival margins on the maxillary premo-lars. They were possible because of a favorable lip line hid-ing the cervical aspect of these posterior teeth. The subgin-gival margins on the mandibular premolars were preparedonly because of previously existing restorations.

Chapter 9 The Metal-Ceramic Crown Preparation

7. Make a lingual alignment groove by posi-tioning the diamond parallel to the cervicalplane of the facial reduction. When theround-tipped diamond of appropriate sizeand shape is aligned properly, it will be al-most halfway submerged into tooth struc-ture. Verify the alignment of the groove, andcarry the axial reduction from the groovealong the lingual surface into the proximal;maintain the originally selected alignment ofthe diamond at all times.

8. As the lingual chamfer is developed, extendit buccally into the proximal to blend with theinterproximal shoulder placed earlier (Fig.9-12). Alternatively, a facial approach may beused. Although this is slightly more difficultinitially, after some practice it should be easyto eliminate the lingual guiding groove andto perform the proximal and lingual axial re-duction in one step; however, this requiresthat the diamond be held freehand parallel tothe path of withdrawal. The proximal flange

Fig. 9-10.

A, A gingival displacement cord (under tension) is placed in the interproximal sulcus. B, Asecond instrument can be used to prevent it from rebounding from the sulcus after it has been packed.

C

Fig. 9-11.

A, After tissue displacement, the facial margin is extended apically. Caution is needed, be-cause if the diamond inadvertently grabs the cord, it may be ripped out of the sulcus and traumatize theepithelial attachment. B, Note the additional apical extension of the shoulder on the distal aspect. C, Theentire facial shoulder is placed at a level that will be subgingival after the tissue rebounds. D, The facialmargin has been prepared to the level of the previously placed cord.

A B

D

Section 2 Clinical Procedures-Part I

Fig. 9-12.

A lingual chamfer is prepared to allow ade-quate space for metal. A smooth transition from interproxi-mal shoulder to chamfer is essential.

that resulted from the shoulder preparationcan be used as a reference for judging align-ment of the rotary instrument (Fig. 9-13). Theinterproximal margin should not be inadver-tently placed too far gingivally and therebyinfringe on the attachment apparatus. It mustfollow the soft tissue contour (see p. 150). Onposterior teeth, the lingual wall reductionblends into the functional cusp bevel placedduring the occlusal reduction. Anterior teethrequire an additional step: After preparationof the cingulum wall, one or more depthgrooves are placed in the lingual surface.These are approximately 1 mm deep.

9. Use a football-shaped diamond to reducethe lingual surface of anterior teeth (see Fig.9-2, P). It is helpful to stop when half this reduction has been completed to evaluateclearance in the intercuspal position and allexcursions. The remaining intact tooth struc-ture can serve as a reference.

Finishing. The margin must provide distinctresistance to vertical displacement of an explorertip, and it must be smooth and continuous circum-ferentially. (A properly finished margin should feellike smooth glass slab.) All other line angles shouldbe rounded, and the completed preparation shouldhave a satin finish free from obvious diamondscratch marks. Tissue displacement is particularlyhelpful when finishing subgingival margins (Fig.9-14). Sometimes this step is postponed until justbefore impression making after tissue displacement.

10.

Finish the margins with diamonds, hand in-struments, or carbides (see Fig. 9-2, Q andR). All internal line angles should be ra-diused to facilitate the impression-makingand die-pouring steps (see Fig. 9-2, S). The

Fig. 9-13.

A, Proximal reduction of the flange with a fa-cial approach. B, Once sufficient tooth structure has beenremoved, the cervical chamfer is prepared simultaneouslywith the lingual axial surface. After the distolingual prepa-ration has been completed, the mesial chamfer is blendedinto a smooth transition with the shoulder.

Fig. 9-14.

Controlled tissue displacement can be helpfulwhen finishing the margin with a fine-grit diamond or an-other rotary instrument.

finishing steps for the facial margin dependon the design of margin chosen (see Table7-2 and Fig. 9-15). A porcelain labial marginrequires proper support for the porcelain. Ashoulder with a 90-degree cavosurface angleis recommended. This type of shoulder canalso be used for a crown with a conventionalmetal collar and offers the advantage of al-lowing the collar to be kept narrow. How-ever, there is then the risk of leaving unsup-ported enamel. For this reason, the marginis often beveled or sloped to create a moreobtuse cavosurface angle (Fig. 9-16). A

Chapter 9 The Metal-Ceramic Crown Preparation

Fig. 9-17.

The shoulder bevel.

Fig. 9-15.

A, Completed preparation. Note that the tran-sition from incisal to axial walls is rounded, and a distinct90-degree or slightly sloping shoulder has been established.B, Even chamfer width and a smooth transition betweenlingual and axial surfaces. The chamfer is distinct andblends smoothly into the facial shoulder.

Fig. 9-16.

A, 90-degree shoulder. B, 120-degree shoul-der. C, Shoulder bevel.

flat-ended diamond in a low-speed hand-piece creates the 90-degree shoulder. Anyunsupported enamel must be removed sub-sequently by careful planing with a sharpchisel. Care must also be taken to orient therotary instrument as it moves around thetooth if inadvertent undercuts are to beavoided. When a metal-collar design of ce-ramic restoration is planned, the need for a90-degree shoulder is less critical. A slopingshoulder has been advocated to ensure theelimination of unsupported enamel and tominimize marginal gap width (see Chapter7). Such a shoulder (cavosurface angle ofabout 120 degrees) can be accomplishedwith a flat-ended diamond by changing itsalignment, paying particular attention to theconfiguration of the tooth structure cervicalto the margin. Alternatively, a hatchet can beused to plane the margin to the correct an-gulation. Again, be careful to avoid under-cutting the axial wall of the preparationwhere it meets the shoulder during finish-ing. A shoulder-bevel margin is most effec-tively achieved with a flame-shaped carbide

Fig. 9-18.

A, Facial and B, lingual views of metal-ceramic preparations.

bur or hand instrument, depending on thelength of bevel required (Fig. 9-17). Gener-ally a short bevel with a cavosurface angleof 135 degrees is advocated, although longerbevels have been recommended for im-proved marginal fit. Special care must be ex-erted where the bevel meets the interproxi-mal chamfer. The chamfer and bevel shouldbe continuous with each other. Care must betaken not to damage the epithelial attach-ment during beveling; tissue displacementbefore preparation of subgingival bevels isrecommended.

11. After a satisfactory facial margin has beenobtained, round all sharp line angles withinthe preparation (see Fig. 9-2, S). This will facilitate surface wetting and expedite subse-quent procedures (impression making,pouring of casts, waxing, and investing). Afine-grit diamond operating at low speed is

Section 2 Clinical Procedures-Part I

particularly useful. However, where accessallows, a slightly larger tapered diamondmay be preferred because the greater diam-eter of its tip prevents "ditching" of thechamfer. Blend all surfaces together, and re-

Fig. 9-19.

The "wingless" variation does not exhibit thedefined transition from chamfer to shoulder seen in Fig.9-15. Rather, the shoulder gradually narrows toward thelingual side. Interproximally, the same criteria for mini-mum extension of the shoulder apply as for the wing-typeor flange preparation.

move any sharp transitions (see Figs. 9-2, T;9-18; and 9-19).

Evaluation.

Areas often missed during finish-ing are the incisal edges of anterior preparationsand the transition from occlusal to axial wall of pos-terior preparations. The completed chamfer shouldprovide 0.5 mm of space for the restoration at themargin. The chamfer must be smooth and continu-ous, and when evaluated, a distinct resistance tovertical displacement of the tip of an explorer or pe-riodontal probe should be felt. The chamfer shouldbe continuous with the interproximal shoulder orbeveled shoulder. The cavosurface angle of thechamfer should be slightly obtuse or 90 degrees.Under no circumstances should any unsupportedtooth structure remain, especially at the facial mar-gin. Care is also needed to avoid creating an under-cut between the facial and lingual walls. This aspectof the preparation should be thoroughly evaluated.Excessive convergence should also be avoided, be-cause this may lead to pulpal exposure. All residualdebris is removed with thorough irrigation. (Vari-ous examples of metal-ceramic preparations areshown in Figs. 9-20 and 9-21.)

Fig. 9-20.

Metal-ceramic crowns used to restore maxillary incisor teeth.

Chapter 9 The Metal-Ceramic Crown Preparation

B

A, Metal-ceramic preparations on the maxillary premolars in conjunction with more con-servative preparations on the molars. B, Buccal view of the preparations. Note that, by comparison, con-siderable tooth reduction was needed on the premolars to accommodate metal-ceramic restorations.C, Except for the molars, all remaining teeth in this patient have been prepared for metal-ceramicrestorations. Note the subtle variations and modifications of the same underlying theme: wing-typepreparations on the anterior teeth, wingless on the premolars. D, Mandibular arch of the same patient.Many of the smaller mandibular teeth were prepared with wingless restorations. Because of previouslyexisting restorations, excessively heavy shoulderlike chamfers resulted on some of the posterior teeth.

A

C D

Section 2 Clinical Procedures-Part I

Chapter 9 The Metal-Ceramic Crown Preparation