Metal-Ceramic Crown Preparation PDF

PROF. DR. Shaimaa Ahmed Metal-Ceramic Crown Preparation Dr: Shaimaa Ahmed Abo El-Farag Profess. of Fixed prosthodontic department Mansoura University 0  PROF. DR. Shaima...

PROF. DR. Shaimaa Ahmed Metal-Ceramic Crown Preparation Dr: Shaimaa Ahmed Abo El-Farag Profess. of Fixed prosthodontic department Mansoura University 0  PROF. DR. Shaimaa Ahmed Metal-ceramic crown Preparation (Porcelain fused to metal-PFM) Definition: The restoration consists of a complete-coverage cast metal crown (coping, or substructure ) that is veneered with a layer of fused porcelain to give appearance as a natural tooth. The extent of the veneering material varies: If it covers the labial, incisal , and part of the proximal surface , it is called labial ( Facial or partial ) veneered crown. If it covers all the surfaces it called full veneered crown. Facial or partial veneered crown Full veneered crown The coping /framework provide strength and rigidity therefore: o Minimal thickness of gold framework is 0.3-0.5 mm. o Minimal thickness of base metal framework is 0.2mm. For Porcelain: Metal framework The minimal thickness of porcelain is 0.7mm otherwise high opacity & decrease esthetic. The optimum thickness of porcelain is 1mm The maximum thickness of porcelain is 1.5- 2mm otherwise fracture as the porcelain layer away from the framework support will be subjected to tensile stresses & fracture 1  PROF. DR. Shaimaa Ahmed Partial veneered metal-ceramic crown Indications: 1) As a Single crown or bridge retainer where esthetic is important. 2) Extensive destruction of anterior or posterior teeth. 3) Endodontically treated anterior or posterior teeth. 4) Need for recontouring of axial surface 5) In deep bite because all-ceramic cannot withstand high forces. 6) Accommodate a rest of removal prosthesis ( i.e support R.P.D). 7) When partial coverage OR all ceramic is contra-indicated. (short teeth) 8) Teeth require fixed splinting. 9) When jacket crown is contra-indicated. (bad habit / deep bite / parafunctional habits). 10) Where good occlusal surface is required. 11) Increase Caries index and bad oral hygiene. 12) Rampant caries Contraindications: 1. Young patient with large vital pulp. 2. Insufficient bulk of tooth structure (e.g lower centrals, therefore resin bonded restoration can be used). 3. When more conservative restoration can be applied (e.g. ¾ or 7/8). 4. When maximum esthetics is required. 2  PROF. DR. Shaimaa Ahmed Advantages: 1 - It combines, to a large degree, the strength of cast metal crown with the esthetics of an all-ceramic crowns. 2 - It provides better marginal fit than all - ceramic crowns. 3- It is more conservative to tooth structure (lingually & proximally) than all-ceramic crown in the case of partial veneer. 4- Easier preparation than of partial coverage restorations 5- Easy correction of axial contour 6- Retentive qualities are excellent because all axial walls are included in the preparation, and it is usually quite easy to ensure adequate resistance form during tooth preparation. 7- Ease in fabrication than all-ceramic crowns. 8- Long term durability. 9- Compared to all ceramic: ↑ marginal fit stronger can accommodate all types of connectors. can be used to correct the occlusal plane. 10-Can be used for tooth splinting. Disadvantages: 1- Excessive tooth reduction than complete cast crown. 2- To achieve better esthetics the facial margin is often placed subgingivally which increase the potential of periodontal disease. 3- Inferior esthetics than all-ceramic crown but it can be used in higher-stress situations or on teeth that would not provide adequate support for an all-ceramic restoration. 4- Possibility of fracture of the veneering material due to improper metal framework. 5- Expensive dental prosthesis. 6- Difficult shade matching (inferior esthetics than all-ceramic crown) 3  PROF. DR. Shaimaa Ahmed Criteria of ideal tooth preparation to receive Metal-Ceramic restoration: 1) Labial reduction must be prepared in 2 planes. 2) Labial reduction →1-1.5mm with Shoulder F.L Deep chamfer Shoulder with bevel. 3) Incisal (occlusal) reduction →should allow for 2mm of clearance. -To ensure adequate thickness of restoration (strength) -To increase esthetic (translucency) 4) Lingual reduction (cingulum) → chamfer F.L 0.5mm. (partial veneer) 5) Distinct junction (WING OR HALF GROOVE) may exist between both F.L, → shoulder should extend 1mm lingual to proximal contact. 6) Axial reduction→ 6º degree of conversions. 7) In anterior teeth → palatal fossa is prepared with clearance 1mm if centric contact on metal But if centric contact on porcelain → clearance 1.5-2 mm. 4  PROF. DR. Shaimaa Ahmed Wingless variation of tooth preparation: The labial shoulder gradually narrows towards the lingual chamfer → i.e. no distinct transition from shoulder to chamfer (NO WING OR HALF GROOVE). Done in the following cases: 1- Narrow and thin teeth. 2- In young age patient due to large pulp horns to avoid pulp exposure. 3- Proximal caries Preparation: 1- Armamentarium 2- Incisal (occlusal reduction) 3- Labial (buccal reduction) 4- Axial reduction of the Proximal and lingual surface 5- Finishing and evaluation 1- Armamentarium ❖ Round-tipped rotary diamonds (regular grit for bulk reduction, fine grit for finishing) or carbides. ❖ Football- or wheel-shaped diamond (for lingual reduction of anterior teeth) ❖ Flat-ended, tapered diamond (for shoulder preparation) ❖ Finishing stones ❖ Explorer and periodontal probe ❖ Hatchet and chisel 5  PROF. DR. Shaimaa Ahmed 1. Incisal ( occlusal) reduction: a-Incisal reduction guiding grooves In order to achieve the necessary 2mm clearance on the incisal aspect of an anterior tooth, place three depth grooves (about 1.8 mm deep) in the incisal edge of an anterior tooth. ❖ Verify groove depth with a periodontal probe. ❖ Remove the islands of remaining tooth structure. The completed reduction of the incisal edge on an anterior tooth should allow 2 mm of clearance for adequate material thickness to allow translucency in the completed restoration. Direction of the stone should perpendicular to long axis of opposing tooth. Guiding grooves location and direction On a posterior tooth: a-Occlusal reduction guiding groove The same protocol is followed as in preparing depth grooves for a complete cast crown. If posterior occlusion is to be established in metal, the same minimum clearances are needed as for a complete cast crown (1.5 mm for functional and 1 mm for non-functional cusps). If the occlusal surface is to be established in porcelain, clearance must be a minimum of 2 mm. Remove the islands of remaining tooth structure between the depth grooves. This includes the use of a functional cusp bevel 6  PROF. DR. Shaimaa Ahmed Occlusal guiding grooves Centric cusp bevel on posterior teeth 2. Facial reduction: Using tapered, flat tipped diamond, Place three depth grooves, one in the center of the facial surface and one each in the approximate locations of the mesiofacial and distofacial line angles. These are placed in two planes: The cervical portion parallels the long axis of the tooth (i.e., the path of placement), and the incisal (occlusal) portion follows the normal facial contour. Facial reduction should be uniform and approximately 1.3 mm deep, in the understanding that some additional reduction 0.2 will occur during finishing. (finally, 1.5 mm is preferable). The incisal portion of the facial grooves usually extends half to two thirds of the way down the facial surface, depending on the shape of the tooth. Remove the tooth structure that remains between the depth grooves, creating a shoulder margin at the cervical margin. 7  PROF. DR. Shaimaa Ahmed The cervical shoulder is established as the tooth structure between the depth grooves is removed. The rotary instrument is moved parallel to the intended path of withdrawal during this procedure. ❖ Location of the facial margin Supragingival margin ❖ Location of the anterior facial margin is Subgingival margin Steps of Facial reduction Subgingival margin of anterior facial margin ❖ If a restoration with a narrow metal collar is to be fabricated and sufficient sulcular depth is present, place subgingival shoulder approximately 0.5 mm apical to the crest of the free gingiva at this time. Additional finishing then result in 0.75 to 1 mm subgingival. 3. Lingual reduction: Fossa: 1. A guiding groove is placed on the lingual surface 2. Half the lingual surface is reduced. Clearance is verified before reduction of the other half 8  PROF. DR. Shaimaa Ahmed 3. Use a football shaped diamond to reduce the lingual concavity to obtain clearance with the opposing teeth. 1mm → if centric contact on meta1, 0.5-2 mm → if centric contact on porcelain Lingual concavity reduction Cingulum 1. Make a depth groove in the center of the cingulum 0.3 mm→ parallel to the cervical plane of labial reduction. 2. Carry the axial reduction from the groove along the lingual surface into the proximal using tapered diamond with round end to create chamfer finish line of 0.5 mm → allow 6º taper incisally or occlusally 3. On posterior teeth, occlusally, the lingual wall reduction blends into the functional cusp bevel placed during the occlusal reduction lingual wall reduction on posterior tooth 4. Proximal reduction; ❖ As the lingual chamfer margin is developed, extend it buccally into the proximal area to blend with the interproximal shoulder margin that was placed earlier ❖ Long needle diamond is used to complete access through the proximal areas → to avoid injury of adjacent teeth. ❖ To ensure esthetics, the facial shoulder margin preparation should wrap around into the interproximal embrasure and extend at least 1 mm lingual to the proximal contact. 9  PROF. DR. Shaimaa Ahmed Extension of buccal and lingual reductions through proximal surface (Wing or half groove) Preparation design Distinct junction may exist between both finish lines → shoulder should extend 1mm lingual to proximal contact. Wing Preparation design Wingless variation of tooth preparation: The labial shoulder gradually narrow towards the lingual chamfer → i.e no distinct transition from shoulder to chamfer (NO WING OR HALF GROOVE). Done in the following cases: 1. Narrow and thin teeth. 2. In young age patient due to large pulp horns to avoid pulp exposure. (provided that patient is indicated for FPD). 3. Proximal caries Wingless tooth preparation 10  PROF. DR. Shaimaa Ahmed 5. Finishing the preparation: The margin must provide distinct resistance to vertical displacement of the tip of a periodontal probe or an explorer, and it must be smooth and continuous circumferentially All other line angles should be rounded, and the completed preparation should have a satin finish The finishing steps for the facial margin depend on the design of margin chosen A, Depth holes. B, Occlusal depth cuts. C, Completed occlusal reduction. D,Lingual chamfer margin E, facial shoulder margin F,Completed preparation Shoulder with bevel Recommended minimum dimensions for a metal- ceramic restoration. 11  PROF. DR. Shaimaa Ahmed Different types of labial F.L used for veneered restoration: 1) 90º shoulder: Advantage → provide bulk for restoration (Structural durability). Disadvantages not conservative placed subgingival. 2) Shoulder with bevel: (USED IN CASE OF GOLD ALLOYS) Advantages bulk of restoration. remove unsupported enamel allow finishing of metal (better margin fit) 12  PROF. DR. Shaimaa Ahmed Disadvantages not conservative placed subgingival 3) All porcelain labial margin crown (Shoulder porcelain) All ceramic margins can be fabricated using special type of porcelain called shoulder porcelain → which eliminate metal collar at the Facio-gingival margin therefore ↑ esthetic. The wax pattern is cut back 1mm cervically shorter than finish line Advantages: High esthetic gingival biocompatible Disadvantages. Technique sensitive less margin adaptation 13  PROF. DR. Shaimaa Ahmed References 1. Rosenstiel S, Land M, Fujimoto J. Contemporary Fixed Prosthodontics 5.th Ed, 2016. Mosby, Inc. Best Wishes 14