Principles Of Tooth Preparation 2024 PDF

PRINCIPLES OF TOOTH PREPARATION Dr. Francis Ocheng  PRINCIPLES OF TOOTH PREPARATION 4 categories of crowns – All-metal – Metal-ceramic – Ceramic – Composite  PRINCIPLES OF TOOTH PREPARATION Materials for crowns have different requir...

PRINCIPLES OF TOOTH PREPARATION Dr. Francis Ocheng  PRINCIPLES OF TOOTH PREPARATION 4 categories of crowns – All-metal – Metal-ceramic – Ceramic – Composite  PRINCIPLES OF TOOTH PREPARATION Materials for crowns have different requirements in terms of space needed and margin configuration. Tooth preparation, therefore, need to reflect the different requirements for the materials. Preparation of tooth for a cast restoration governed by 5 principles  PRINCIPLES OF TOOTH PREPARATION 1. PRESERVATION OF TOOTH STRUCTURE. 2. RETENTION AND RESISTANCE. 3. STRUCTURAL DURABILITY. 4. MARGINAL INTEGRITY. 5. PRESERVATION OF PERIODONTIUM  PRESERVATION OF TOOTH STRUCTURE Why ? – To avoid weakening the tooth unnecessarily – To avoid compromising the pulp This should never happen to you!  PRESERVATION OF TOOTH STRUCTURE How? – Remove only what you need – Use less destructive alternative  PRESERVATION OF TOOTH STRUCTURE Using less destructive alternative Inlays, onlays versus Crowns  PRESERVATION OF TOOTH STRUCTURE Using less destructive alternative – Partial veneer versus Full veneer crown  PRESERVATION OF TOOTH STRUCTURE Using less destructive alternative – Supra-gingival margin versus sub- gingival.  PRESERVATION OF TOOTH STRUCTURE Using less destructive alternative – Shoulder margin is less conservative than a chamfer margin 1- chamfer 2- Shoulder  PRESERVATION OF TOOTH STRUCTURE Minimize the taper – Excessive taper results in considerable loss of tooth structure  PRESERVATION OF TOOTH STRUCTURE Occlusal reduction – Follow anatomic planes to give uniform thickness in the restoration – Flat preparation results in 1- Insufficient clearance 2- Excessive amount of reduction  PRESERVATION OF TOOTH STRUCTURE Preparation of axial surfaces – Should be as uniform as possible – Path of withdrawal should concide with long axis of the tooth  RETENTION AND RESISTANCE Retention prevents removal of the restoration along the path of insertion or long axis of the tooth preparation. Resistance prevents dislodgement of the restoration by forces directed in an apical or oblique direction and prevents any movement of the restoration under occlusal forces.  RETENTION The essential element of retention is two opposing vertical surfaces of the same preparation. These may be external surfaces such as the buccal and lingual walls of a full veneer crown (sleeve retention).  RETENTION The opposing surfaces can also be internal, such as the buccal and lingual walls of the proximal box of a inlay. An intracoronal restoration resists displacement by wedge retention. Many restorations are a combination of the two types.  RETENTION AND RESISTANCE Retention & Resistance is improved if : 1. Taper is minimal 2. Freedom of displacement is limited. 3. Length is maximized 4. Substitution of internal features 5. Single Path of insertion  RETENTION AND RESISTANCE Maximum retention is achieved when there is only one path of insertion. Preparation with long, near parallel axial walls and grooves, produce such retention  RETENTION AND RESISTANCE Opposite extreme, a short, over-tapered, not-grooved preparation is without retention, because the restoration can be removed along infinite number of paths  TAPER Theoretically, the more nearly parallel the opposing walls of a preparation, the greater is the retention.  TAPER Tooth preparation taper should be kept minimum because of its adverse effect on retention.  TAPER Optimum degree of tooth preparation taper  STRUCTURAL DURABILITY Restoration must withstand the forces of occlusion Tooth preparation must be adequate For structural durability, consideration should given to: 1. Occlusal reduction. 2. Functional cusp bevel. 3. Axial reduction.  STRUCTURAL DURABILITY Occlusal reduction: – Provide adequate clearance for bulk of metal and strength. – For gold alloys- 1.5 mm clearance on the functional cusp. 1mm clearance on the nonfunctional cusp.  Occlusal Reduction The basic inclined plane pattern of the occlusal surface duplicated to produce adequate clearance without over shortening the preparation. A flat occlusal surface may over shorten the preparation. Inadequate Occlusal Reduction Makes the restoration weaker. will not provide adequate space to allow good functional morphology under the anatomical grooves. The restoration easily perforated by finishing procedures or by wear in the mouth.  FUNCTIONAL CUSP BEVEL A wide bevel placed on the functional cusp provides space for an adequate bulk of metal in an area of heavy occlusal contact.  Functional Cusp Bevel Lack of functional cusp bevel may produce several problems: 1. Can cause a thin area or perforation. 2. May result in over contouring and poor occlusion 3. Over inclination of the buccal surface- lessening retention.  AXIAL REDUCTION Important role in securing space for an adequate thickness of the restorative material. Inadequate axial reduction – Result to thin walls restoration- subject to distortion – Result in over contouring the axial surface which could lead to periodontal problems.  MARGINAL INTEGRITY The restoration margin should closely adapt to the cavosurface finish line of the preparation to survive in the oral cavity.  FINISH LINE CONFIGURATION 1. Chamfer 2. Heavy chamfer 3. Shoulder 4. Radial shoulder 5. Shoulder with bevel 6. Knife edge  CHAMFER The preferred gingival finish line for full veneer metal restoration. This finish line exhibit least stress to the underlying cement. It can be cut with round- end tapered diamond. Conservative type when compared with shoulder finish line.  PRESERVATION OF THE PERIODONTIUM The placement of finish lines has a direct bearing on the ease of fabrication and the ultimate success of the restoration. The best results can be expected from margins that are as smooth as possible and are fully exposed to cleansing action.  MARGIN PLACEMENT Whenever possible the finish line should be placed in an area where the margins can be finished by the dentist easily and kept clean by the patient. In addition,finish lines must be placed so that they can be duplicated by the impression without tearing or deformation.  MARGIN PLACEMENT Finish line should be placed in enamel whenever possible. Supra-gingival versus sub-gingival margin. Many situations in which sub-gingival margins are unavoidable. 1. Caries 2. To increase retention 3. Esthetics 4. Extension of previous restoration 5. Trauma.