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Elrazi College of Medical & Technological Sciences

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dentistry crowns restorative dentistry

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Types Of Crowns Dr. Safaa Amir Heiba BDS, MClincResto, U of K Classification: Crowns are classified into:  According to position: Anterior crowns. Posterior crowns. Classification: Crowns are classified into:  According to material: Metal crowns. Porcelain fused to met...

Types Of Crowns Dr. Safaa Amir Heiba BDS, MClincResto, U of K Classification: Crowns are classified into:  According to position: Anterior crowns. Posterior crowns. Classification: Crowns are classified into:  According to material: Metal crowns. Porcelain fused to metal crowns. All ceramic crowns. Classification: Crowns are classified into:  According to material: Metal crowns. All ceramic crowns. Porcelain fused to metal crowns. Classification: All ceramic crowns are further classified to: 1. Traditional fused porcelain jacket crowns (PJC). 2. Pressed ceramic crowns. 3. Milled ceramic crowns. Classification: 4. Cast crowns. 5. Zirconia cores 6. Reinforced porcelain. 7. Dentin bonded crowns Classification: 1. Traditional fused porcelain jacket crowns (PJC): It is the oldest tooth colored crown. It involves adapting a thin layer of platinum foil over a die, then building an even layer of feldspathic porcelain of 1-2 mm thick on all surfaces which is then fired in a furnace. It is easy to fracture and superseded by the new advanced ceramics. Classification: 2. Pressed ceramic crowns: Produced by pressing ceramic at high temperature and pressure to produce a strong ceramic core. Feldspathic porcelain is then added to the core. Classification: 3. Milled ceramic crowns: Fabricated using computer aided design or computer aided manufacturing (CAD/CAM) systems. A scanned image of the tooth or die is sent to the lab with milling machine which mills the crowns. Classification: 4. Cast crowns: Using a wax pattern on a die, investing and casting in a glass ceramic material i.e Décor. 5. Zirconia cores: Zirconia is an extremely strong material that is dense white in appearance. Classification: 5. Zirconia cores: Zirconia is an extremely strong material that is dense white in appearance. A core of zirconia is built, over it a conventional porcelain is built. Classification: 6. Reinforced porcelain: Alumina is used as substructure on a special plaster, sintered and then glass powder is added to the porous substructure and further fired foe several hours i.e Inceram. Porcelain is added to the surface, finally. Classification: 7. Dentin bonded crowns: Involve the prep of the tooth exposing minimal amount of dentin, thicker than porcelain veneers and cemented acid etching of the enamel and bonding with adhesive. The complete metal crown: The complete cast crown has the best longevity of all fixed restoration. It can be used to rebuild a single tooth or as a retainer for a fixed partial denture. It involves restoring axial as well as occlusal walls. The complete metal crown: The complete metal crown: Although esthetic factors may limit it’s application, the all metal crown should always be offered to patients requiring restorations for badly broken down posterior teeth. The complete metal crown: Advantages:  Has better retention and resistance than a partial crown.  Strength is superior to that of other restorations.  The preparation is more conservative to tooth structure than a metal ceramic or all-ceramic restoration. The complete metal crown: Advantages:  Allows the placement of rests if RPD is part of the treatment.  The restoration permits easy modification of the occlusion, which is often difficult to accomplish. The complete metal crown: Advantages:  Allows the operator to modify axial tooth contour better than partial crowns in cases such as maligned teeth, although adjustment is limited by the periodontal condition. The complete metal crown: Disadvantages:  Less conservative to tooth structure compared to partial crowns which might have adverse effects on the pulp and periodontium (gingival inflammation around the margin of the restoration). The complete metal crown: Disadvantages:  Electric vitality testing is difficult to be done due to the metal conductivity that interferes with the test.  The display of metal might be unacceptable to the patient with a complete cast crown. The complete metal crown: Indications:  Extensively destructed or badly broken down crowns.  In areas of high displacing/occlusal forces.  To be used as a retainer in partial prosthesis specially when dentin is exposed. The complete metal crown: Indications:  The complete cast crown is indicated on endodontically treated teeth. It’s superior strength compensates for both lost tooth structure from a previous restoration or caries and endodontic access. The complete metal crown: Contraindications:  In areas of high esthetic demand.  When a more conservative approach could be achieved specially in areas of intact buccal surface. The complete metal crown: Clinical techniques for preparation of metal crowns: Preparation steps: The clinical procedure to prepare a tooth for a complete cast crown consists of the following steps:  Occlusal guiding grooves.  Occlusal reduction.  Axial alignment grooves.  Axial reduction.  Finishing and evaluation of reduction. The complete metal crown: Preparation steps: Guiding grooves for occlusal reduction: Use of guiding grooves ensures that occlusal reduction follows the anatomic configuration and there for minimizing the loss of tooth structure along with adequate reduction. The complete metal crown: Preparation steps: Guiding grooves for occlusal reduction: Place 1 mm depth holes in the mesial, central and distal pits and connect them so that a channel runs the length of the central groove and extend into mesial and distal marginal ridge. The complete metal crown: Preparation steps: Guiding grooves for occlusal reduction: Correct depth is 0.8 mm for central groove and non-functional cusp, and 1.3 mm for functional cusp (0.2 mm is left for finishing) Measurement is kept by memorizing the diameter of the rotary instrument or by using periodontal probe. The complete metal crown: Preparation steps: Guiding grooves for occlusal reduction: On the non-functional cusp, the groove should parallel the intended cuspal angulation, while on the functional cusp, it should be angled slightly flatter to ensure the additional reduction of the functional cusp. The complete metal crown: Preparation steps: Occlusal reduction: The tooth structure that remains between the grooves is removed with the carbide or the narrow round end tapered diamond bur. Half the occlusal surface is reduced 1st so that the other half can be maintained as a reference. The complete metal crown: Preparation steps: Occlusal reduction: Check that a minimum clearance of 1.5 mm, least 1.0 mm on the non-functional cusps. This can be achieved by:  Reduction gauge.  Dark colored utility wax.  Shimstock. The complete metal crown: Reduction gauge: The complete metal crown: Shimstock: The complete metal crown: Preparation steps: Alignment grooves for axial reduction: Narrow, round end tapered diamond. 3 alignment grooves are placed in each buccal and lingual wall (in the central, mesial transitional line angle wall and distal transitional line angle). The complete metal crown: Preparation steps: Alignment grooves for axial reduction: The shank of the diamond bur should be along the long axis of the tooth so producing convergence that is identical to the taper of the diamond. The tip of the bur in the area of the finish line should enter to half. The complete metal crown: Preparation steps: Alignment grooves for axial reduction: If it goes beyond that, an area of unsupported enamel (gutter) will be produced. The complete metal crown: Preparation steps: Axial reduction: Thin round tipped diamond bur. The remaining tooth structure is removed while the chamfer margin is being placed. Reduce half of the axial surface 1st and leave the other as a reference. The complete metal crown: Preparation steps: Axial reduction: Take care not to injure the adjacent tooth in the interproximal area. How can we protect the neighboring tooth??? The complete metal crown: Preparation steps: Axial reduction: Cut into the proximal area from both sides until a few mm of interproximal island remains (enamel lip technique), then remove contact with a fine needle diamond. The complete metal crown: Preparation steps: Axial reduction: If adjacent proximal surface is damaged it should be polished with white stone, silicon stones and prophylaxis paste. Also fluoride application could be useful to prevent demineralization. The complete metal crown: Preparation steps: Finishing: Fine girt diamond or carbide bur of slightly greater diamond. This could be performed with a high speed handpiece operating at a reduced speed or with a low speed handpiece. The complete metal crown: Preparation steps: Finishing: Roundation of all internal line angles. Smoothen the chamfer finish line, it should be glassy smooth when touched by an explorer. Place a non functional cusp bevel if necessary. Place additional retention features with a tapered carbide bar if necessary ( boxes and grooves). The complete metal crown: Preparation steps: Evaluation: The preparation should be evaluated for: 1- smooth, even, and continuous chamfer FL. 2- a 6° taper. The complete metal crown: Preparation steps: Evaluation: 3- gradual transition between all prepared surfaces. 4- no under cuts should exist. 5-occlusal and proximal clearance are assessed. The complete metal crown: Problems in tooth Preparation : 1- over tapered preparation is a common mistake, this could be corrected by:- Uprighting over tapered axial wall by corrective prep/composite additions. Using boxes, grooves and pinholes. 2- traumatic exposures of the pulp. The complete metal crown: There are couple of methods to evaluate the prep.:  Putty index.  Part reduction of the surface.  Measurements of the reduction burs diameter.  Depth cuts. The complete metal crown: Putty index: The complete metal crown: Putty index: The complete metal crown: Putty index: The complete metal crown: The complete metal crown: Depth cuts: The complete metal crown: Depth cuts: The complete metal crown: Depth cuts: The metal-ceramic crown: The metal-ceramic crown: It’s one of the most widely used fixed restorations in dental practices. It consists of a complete cast metal restoration veneered by fused porcelain to provide better esthetics. The metal-ceramic crown: It involves bonding porcelain to a metal substructure. Metals used could be classified into: 1. Precious: contains gold and platinum content of 25-75%. 2. Semi-precious: contains less gold and platinum. 3. Base metal alloys: basically contain chromium and nickel. The metal-ceramic crown: Cast metal crowns can be fabricated with ceramic veneers or acrylic or composite facings, which are mostly used as temporary restorations. The metal-ceramic crown: Indications:  Complete coverage in high esthetic zone.  Tooth destruction due caries, trauma or failed restoration.  Superior retention and strength.  Endodontically treated tooth with a post and core.  Recontouring or correction of minor axial malinclination.  Correction of the occlusal plane. The metal-ceramic crown: Contraindications:  Active caries and untreated periodontal disease.  Young patients (risk of exposing the wide pulp).  Whenever a more conservative retainer is feasable. The metal-ceramic crown: Advantages:  Combines the strength of cast metal and the esthetics of ceramic restorations.  More retention and more resistance when compared to partial crowns with possibility of occlusal and axial walls Recontouring.  Technically easier then partial crowns. The metal-ceramic crown: Disadvantages:  Less conservative to tooth structure:  The need for more reduction required to accommodate the metal and ceramic.  The need of a subgingival finish line with this type of restoration.  Inferior esthetics compared to all ceramic restoration.  Fracture of porcelain may occur due to it’s brittle nature. The metal-ceramic crown: The metal-ceramic crown: Disadvantages:  Difficult to select porcelain shade due to the underlying metal shadow.  Expensive lab cost. The metal-ceramic crown: Clinical techniques for preparation of metal-ceramic crowns:  The silicon index: Obtained before the start of the reduction, bisectioned into 2 halves to compare the amount of tooth reduction. The metal-ceramic crown: Clinical techniques for preparation of metal-ceramic crowns:  Preparation steps: 1. Occlusal/ incisal guiding grooves and occlusal reduction. 2. Buccal/ labial reduction (will be layered or veneered with porcelain) 3. Axial reduction of proximal and lingual surfaces 4. Finishing and evaluation of reduction. The metal-ceramic crown: Preparation steps: 1. Occlusal/ incisal guiding grooves:  Place three depth orientations grooves (1.8mm deep ) in the incisal edge of an anterior tooth. This will provide the needed reduction of (2mm) & allow finishing, verify the depth with periodontal probe.  In posterior teeth, where the occlusion is to be established in porcelain 1.3-1.7mm of clearance must be existed. The metal-ceramic crown: Preparation steps: 1. Occlusal/ incisal reduction: Reduction of the incisal edge is completed, it should allow 2mm for adequate material thickness to permit translucency in the final restoration. The metal-ceramic crown: Preparation steps: 1. Occlusal/ incisal reduction: The reduction in the incisal edge should be 2mm to permit translucency of the restoration. Posterior teeth require less reduction (1.5mm), because esthetic is not critical. Remove the island of remaining tooth structure. The metal-ceramic crown: Preparation steps: 2. Buccal/ labial reduction (will be layered or veneered with porcelain): The facial surface is divided into 2 imaginary parts; 1/3 cervical and 2/3 incisal. 3 grooves are placed; mesial, distal and at the middle.  Depth of the grooves should be 1.3 mm (0.2 mm left for finishing). The metal-ceramic crown: Preparation steps: 2. Buccal/ labial reduction (will be layered or veneered with porcelain): Cervical grooves and reduction are parallel to the long axis of the tooth and/or the intended path of insertion while incisal grooves are parallel to the facial contour. The inclination of the diamond bur should be perpendicular to the direction of loading of the mandibular anterior teeth. The metal-ceramic crown: Preparation steps: 2. Buccal/ labial reduction (will be layered or veneered with porcelain): The incisal (occlusal) portion should follow the facial contour. And will provide the space needed for porcelain layering (1.3 mm) & allow finishing. The metal-ceramic crown: Preparation steps: 2. Buccal/ labial reduction (will be layered or veneered with porcelain): The shoulder FL is placed 1 mm above the gingival crest, and when finishing the prep; a retraction cord is placed to retract the gingiva and ideally place the FL more apically. The metal-ceramic crown: Preparation steps: 2. Buccal/ labial reduction (will be layered or veneered with porcelain): Proper manipulation of the gingival tissue can prevent gingival recession and exposure of the metal collar. The metal-ceramic crown: The metal-ceramic crown: Preparation steps: 2. Buccal/ labial reduction (will be layered or veneered with porcelain): The shoulder FL should extended well into the proximal embrasures when viewed from incisal (occlual) side. The metal-ceramic crown: Preparation steps: 3. Axial reduction of proximal and lingual surfaces: Sufficient tooth structure must be removed to provide a distinct, smooth chamfer FL of about 0.5 mm in width. Smooth transition between the chamfer and shoulder FL should be provided. The metal-ceramic crown: Preparation steps: 3. Axial reduction of proximal and lingual surfaces: Reduction of the proximoaxial surfaces is done with round-end tapered diamond bur held parallel to the intended path of insertion of the restoration. The metal-ceramic crown: Preparation steps: 3. Axial reduction of proximal and lingual surfaces: On anterior teeth, guiding grooves are placed mesially, distally and at the center of the tooth. The concavity is removed with wheel or football diamond bur, at depth of 1 mm unless centric contacts are prepared in porcelain, they should be placed within the concavity then reduction must be increased. The metal-ceramic crown: Preparation steps: 3. Axial reduction of proximal and lingual surfaces: The interproximal margin should follow the gingival contour. As the lingual chamfer is developed, extend it buccally in to the proximal to blend with the interproximal area. For anterior teeth a foot-ball shaped diamond is used to reduce the lingual surface. The metal-ceramic crown: Preparation steps: 4. Finishing and evaluation of reduction: The margin must provide distinct resistance to vertical displacement of an explorer tip and it must be smooth and continuous circumferentially. The metal-ceramic crown: Preparation steps: 4. Finishing and evaluation of reduction: All angles should be rounded and the prep should have a glassy smooth finish that’s free from diamond bur scratches. A 90° or slightly sloped shoulder FL should be established. Prep. should be of smooth transition between facial and lingual surfaces and smooth finish. The metal-ceramic crown: Preparation steps: 4. Finishing and evaluation of reduction: Chamfer FL should be distinct and blend smoothly with shoulder FL; the transition from facial to proximal should be rounded. The metal-ceramic crown: Preparation steps: 4. Finishing and evaluation of reduction: Under no circumstances should any unsupported tooth structure remain at the facial margin. Care is extremely needed to avoid creating undercuts between facial and lingual walls. The metal-ceramic crown: Preparation steps: 4. Finishing and evaluation of reduction: Excessive convergence should also be avoided because this may lead to pulp exposure. Thorough cleaning and “flushing” of the debris is also needed. The all-ceramic crown: The all-ceramic crown: Since the recent development in dental ceramics, a growing interest in all ceramic restorations is noticed. All ceramic crowns provide high esthetics since there is no metal to block light transmission and the resemblance of natural tooth structure in color & translucency. and increased strength compared to the old PJC; Inceram, Compress II, Procera or Lava. The all-ceramic crown: Advantages of ACC:  Superior esthetics and excellent color matching.  Dimensional stability.  Insolubility in oral fluids.  Tissue tolerance even with subgingival margins, since ceramics are biocompatible material.  High wear resistance.  Low thermal conductivity The all-ceramic crown: MCC VS ACC The all-ceramic crown: Disadvantages of ACC:  Abrasive to antagonists.  Complicated fabrication techniques.  Difficulty to adjust/ polish intraorally.  Low fracture resistance.  Difficulty to repair. The all-ceramic crown: Indications of ACC:  Similar to those for complete cast crown.  Specific indication : where high esthetic is required The all-ceramic crown: Contraindications of ACC:  When more conservative restoration can be used.  When superior strength of metal ceramic crown is needed.  Thin teeth faciolingually.  Unfavorable occlusal load (edge to edge) & parafunctional habits (bruxism). The all-ceramic crown: Contraindications of ACC:  Unable to provide adequate support or an even shoulder circumferentially (fracture, deep cervical caries).  Teeth with constricted neck. The all-ceramic crown: ACC are either: 1. Low strength, etchable glass based ceramics, ex. IPS Impress Esthetic and IPS Impress E-Max and the traditional Feldspathic porcelain. 2. High strength, non etchable ceramics ex. Alumina based ceramics; Procera and zirconia based ceramics ex. Procera zircon. The all-ceramic crown: Clinical techniques for preparation of ACC: Preparation steps are the same as the previous restorations.  Guiding grooves.  Incisal or occulsal reduction.  Labial (buccal) reduction.  Axial reduction of proximal and lingual surfaces.  Finishing and evaluation. The all-ceramic crown: Clinical techniques for preparation of ACC:  Occlusal/ incisal guiding grooves: The all-ceramic crown: Clinical techniques for preparation of ACC:  Occlusal reduction: It should be 2 mm and 0.8 mm axially and 0.2 mm left for finishing, while the labial/facial surface is reduce to 1.5 mm. The recommended FL’s are chamfer or 90° rounded shoulder because they provide bulk of margins and allow the transfer of stresses around these margins, adequately. The all-ceramic crown: Clinical techniques for preparation of ACC:  Preparation margin can be placed supragingivally or equigingivally, unlike MCC, because of ACC better esthetics.  Reduction is made with a flat-end tapered bur.  Lingual surface reduction is made with small wheel/ flame diamond bur.

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