All-Ceramic Crown Preparation PDF

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

PROF. DR. Shaimaa Ahmed All-Ceramic Crown Preparation Dr: Shaimaa Ahmed Abo El-Farag Profess. of Fixed prosthodontic department 0  PROF. DR. Shaimaa Ahmed All-Ceramic Crown Preparation (Complete-Ceramic Crown) All-ceramic restorations (inlays, onlays, veneers, and crowns) can be considered as the most esthetically pleasing prosthodontic restorations: Because: 1. It has no underlying metal to block light transmission. 2. It resembles natural tooth structure better in terms of color and translucency. All-ceramic crowns All-ceramic restorations may be fabricated in several ways. Platinum foil matrix: the original technique (developed more than 100 years ago) for the fabrication of the porcelain jacket crown. Today, several fabrication techniques such as hot-pressing, slip-casting, and milling. Advantages 1. Superior esthetics in comparison with metal-ceramic crowns. Excellent translucency (similar to that of natural tooth structure) No underlying metal to block light transmission Metal-ceramic crown All-ceramic crown 1  PROF. DR. Shaimaa Ahmed 2. Biocompatibility Inert Not release harmful elements Decreased susceptibility to bacterial adhesion healthy gingival tissue 3. Slightly more conservative reduction of the facial surface than is necessary for a metal- ceramic crown because there is lack of reinforcement by a metal. 4. Ability to be formed into precise shapes. 5. A coefficient of thermal expansion similar to that of dentin 6. It has a radiographic contrast similar to that of dentin. Disadvantages 1. Reduced strength because of the absence of a reinforcing metal substructure. 2. It requires more tooth reduction and are less conservative than metal-ceramic (significant tooth reduction is necessary on the proximal and lingual aspects). 3. Marginal adaptation is a matter of concern as difficulties may be associated with obtaining a well-fitting margin when certain techniques are used (i.e., inferior marginal adaptation as compared to metal-ceramic restorations). 4. Proper preparation design is critical for mechanical success. Margin design should result in favorable stress distribution. preparation design The preparation should provide support for the porcelain along its entire incisal edge. 5. Wear on the functional surfaces of natural teeth that oppose porcelain restorations (this also applies to teeth opposed by metal-ceramic restorations). 6. Expensive. 2  PROF. DR. Shaimaa Ahmed Indications 1. It is indicated in areas with a high esthetic requirement, where a more conservative restoration would be inadequate. 2. The tooth should have sufficient coronal structure to support the restoration (particularly in the incisal area) where porcelain thickness must not exceed 2 mm to avoid the brittle failure. 3. Favorable occlusal load (because of the relative weakness of the restoration). In general, the centric contact must be in an area where the porcelain is supported by tooth structure (i.e., in the middle third of the lingual wall). 4. As single crown or retainer for fixed partial denture (using high strength ceramics such as zirconia) 5. Fractured anterior tooth not involving more than one-third of the inciso-gingival length of the tooth. 6. Severely discolored anterior tooth. 7. Malformed / malposed / rotated anterior teeth. Contra-indications 1. When a more conservative restoration can be used. 2. Elevated strength requirements. Although certain ceramics offers additional strength in comparison with the original ceramics, the strongest solution for a molar remains a metal casting, which may be veneered with ceramic material if the molar is visible when the patient smiles. 3. If occlusal loading is unfavorable. 3  PROF. DR. Shaimaa Ahmed Edge to edge relationship because it will produce stress in the incisal area of restoration. Deep bite (opposing teeth occlude on the cervical fifth of the lingual surface). The "half-moon" or "crescent moon" fracture in the labio-cervical area of the restoration is often seen as a result of inadequate preparation length. 4. If it is not possible to provide adequate support or an even shoulder margin width of at least 1 mm circumferentially. Ideally, all-ceramic crowns have occlusal contact in an area that is well supported by the tooth preparation (i.e., the middle third of the lingual wall on an anterior tooth). 5. Teeth with short clinical crowns often do not offer adequate support for all-ceramic crowns. 6. Patient with para-functional habits (e.g., bruxism). 7. Patient with bad oral hygiene. Preparation (Anterior all-ceramic crown) The preparation sequence for a ceramic crown is similar to that for a metal-ceramic crown; the principal difference is the need for a 1-mm-wide circumferential heavy chamfer margin or shoulder with rounded internal angle margin. Armamentarium: - Round-ended, tapered diamonds, regular and coarse grit - Square-ended, tapered diamond, regular grit Anterior all-ceramic crown prep. - Football-shaped diamond - Fine grit finishing diamonds or carbides Incisal Reduction Aim: ❖ Provide adequate room for the restorative material. 4  PROF. DR. Shaimaa Ahmed ❖ The minimum incisal reduction is 1.5 to 2 mm for porcelain in all excursive movements of the mandible. This renders the restoration translucent and cosmetically pleasing, with adequate strength. If the restoration is used for posterior teeth, 2 mm of clearance is needed on all cusps. Place two or three depth grooves (using tapered carbide or a narrow, tapered diamond) in the incisal edge, initially keeping them approximately 1.3 mm deep to allow for additional loss of tooth structure during finishing. The grooves are oriented perpendicular to the long axis of the opposing tooth to provide adequate support for the porcelain crown. Direction of incisal depth groove Complete the incisal reduction, reducing half the incisal edge at a time. Verify on completion that the desired clearance has been achieved. Facial Reduction Instrument: the round-ended, tapered diamond (which results in a heavy chamfer margin). Depth groove is placed in the middle of the facial wall and one each in the mesiofacial and distofacial transitional line angles. It is placed with a cervical component parallel to the proposed path of placement (typically, the long axis of the tooth) and an incisal component parallel to the original external facial contour of the tooth. Depth groove location 5  PROF. DR. Shaimaa Ahmed Tapered diamond direction for facial depth grooves preparation The depth of these grooves should be approximately 0.8 mm to allow for finishing. Reduce the labial or buccal surface with a cervical component parallel to the proposed path of placement (typically, the long axis of the tooth) and an incisal component parallel to the original external facial contour of the tooth. Perform the reduction on half of the facial surface, evaluate its adequacy, and then complete the second half. Extension of the facial reduction through the proximal surfaces. Lingual Reduction After the selected path of placement has been transferred from the cervical wall of the facial preparation, place a depth groove in the middle of the cingulum wall. Extend the margin from the center of the cingulum wall into the proximal aspect, until the lingual margin meets the facial margin. This margin should follow the free gingival crest and should not extend too far subgingivally. 6  PROF. DR. Shaimaa Ahmed Use the wheel or football-shaped diamond for lingual reduction after placing depth grooves approximately 0.8 mm deep. Perform the lingual reduction until clearance in all mandibular excursive movements is 1 mm, to ensure adequate room for the porcelain in all load-bearing areas. lingual reduction Important precaution: i) Over tapering of prepared cingulum→ ↓ retention and resistance. ii) The curved horizontal surface formed at the junction of the prepared fossa & the cingulum should be preserved → to ↓ stresses. ii) When reducing the canine lingual fossa →avoid eliminating the lingual ridge as it divides the surface into 2 concavities → to ↑ rotational resistance. Finishing and Evaluation Finishing A smooth surface finish and continuity of all prepared surfaces will aid most phases of fabrication of the restoration. Smooth transitions from incisal to axial surfaces facilitate. Finish all prepared surfaces and slightly round all line angles. 7  PROF. DR. Shaimaa Ahmed Evaluation of final preparation using index Criteria of All-ceramic crown preparation 8  PROF. DR. Shaimaa Ahmed References 1. Rosenstiel S, Land M, Fujimoto J. Contemporary Fixed Prosthodontics 5.th Ed, 2016. Mosby, Inc. Best Wishes 9