Principles Of Tooth Preparation PDF

Principles Principles Of Tooth Of Preparation Tooth Preparation Dr.Wayel Mohammed Huraib Dr.Wayel Mohammed Huraib Fixed Prosthodontics-D3 Consultant 15/09/2021 in Prosthodontics Principles Of Tooth Preparation II Mechanical Considerations ...

Principles Principles Of Tooth Of Preparation Tooth Preparation Dr.Wayel Mohammed Huraib Dr.Wayel Mohammed Huraib Fixed Prosthodontics-D3 Consultant 15/09/2021 in Prosthodontics Principles Of Tooth Preparation II Mechanical Considerations  Principles Of Tooth Preparation II Mechanical Considerations The success of fixed prosthodontics relies on adherence to mechanical principles. These principles ensure the restoration's stability and durability.  Principles Of Tooth Preparation II Mechanical Considerations Mechanical considerations can be divided into three categories: 1. Providing retention form. 2. Providing resistance form. 3. Preventing deformation of the restoration.  Principles Of Tooth Preparation II Mechanical Considerations Retention Form The quality of a preparation that prevents the restoration from becoming dislodged by such forces parallel to the path of placement.  Principles Of Tooth Preparation II Mechanical Considerations Retention Form Factors affecting retention form : 1. Magnitude of the dislodging forces. 2. Geometry of the tooth preparation. 3. Roughness of the restoration fitting surface. 4. Materials being cemented. 5. Film thickness of the luting agent.  Principles Of Tooth Preparation II Mechanical Considerations Retention Form 1-Magnitude of the dislodging forces Forces that tend to remove a cemented restoration along its path of placement are small in comparison with those that tend to seat or tilt it. A fixed dental prosthesis can be subjected to such forces by pulling with floss under the connectors or when exceptionally sticky food is eaten.  Principles Of Tooth Preparation II Mechanical Considerations Retention Form 2-Geometry of the tooth preparation Most fixed dental prostheses depend on the geometric form of the preparation rather than on adhesion for retention because most of the traditional cements (e.g., zinc phosphate) are nonadhesive. They do not have a specific adhesion to metal, but they increase the friction between sliding metal parts.  Principles Of Tooth Preparation II Mechanical Considerations Retention Form 2-Geometry of the tooth preparation Taper is defined as the convergence of two opposing external walls of a tooth preparation as viewed in a given plane. The recommended convergence between opposing walls is 6 degrees.  Principles Of Tooth Preparation II Mechanical Considerations Retention Form 2-Geometry of the tooth preparation Surface area If the restoration has a limited path of placement, its retention depends on the length of this path or, more precisely, on the surface area that is in sliding contact. Therefore, crowns with tall axial walls are more retentive than those with short axial walls, and molar crowns are more retentive than premolar crowns of similar taper.  Principles Of Tooth Preparation II Mechanical Considerations Retention Form 2-Geometry of the tooth preparation Surface area Retention form of an excessively tapered preparation can be increased by adding grooves  Principles Of Tooth Preparation II Mechanical Considerations Retention Form 2-Geometry of the tooth preparation Stress concentration Sharp occlusoaxial line angles should be rounded to minimize these stresses, which can precipitate retentive failure  Principles Of Tooth Preparation II Mechanical Considerations Retention Form 2-Geometry of the tooth preparation Type of preparation Different types of preparation have different retentive values. The retention of a complete crown is more than double that of partial coverage restorations.  Principles Of Tooth Preparation II Mechanical Considerations Retention Form 3-Roughness of the surfaces being cemented. When the internal surface of a restoration is very smooth, retentive failure occurs not through the cement but at the cement-restoration interface.  Principles Of Tooth Preparation II Mechanical Considerations Retention Form 4-Materials being cemented Retention is affected by both the type of casting alloy and any core or buildup material that is present on the axial walls of the crown preparation.  Principles Of Tooth Preparation II Mechanical Considerations Retention Form 4-Materials being cemented The cement adhered better to amalgam than to composite resin or cast gold. The base metal alloys are better retained than are less reactive metals with high gold content.  Principles Of Tooth Preparation II Mechanical Considerations FACTORS INFLUENCING THE RETENTION OF A CEMENTED RESTORATION  Principles Of Tooth Preparation II Mechanical Considerations Resistance Form Restoration ability to oppose lateral dislodging forces.  Principles Of Tooth Preparation II Mechanical Considerations Resistance Form Factors affecting resistance form : 1.Magnitude and direction of the dislodging forces. 2.Geometry of the tooth preparation. 3.Physical properties of the luting agent.  Principles Of Tooth Preparation II Mechanical Considerations FACTORS INFLUENCING THE RESISTANCE OF A CEMENTED RESTORATION  Principles Of Tooth Preparation II Mechanical Considerations Preventing Deformation A restoration must have sufficient strength to prevent permanent deformation during function  Principles Of Tooth Preparation II Mechanical Considerations Preventing Deformation Factors affecting deformation : 1.Alloy selection. 2.Adequate tooth reduction. 3.Margin design.  Principles Of Tooth Preparation II Mechanical Considerations Preventing Deformation Adequate tooth reduction A minimum alloy thickness of about 1.5 mm over functional cusps. (buccal in the mandible, lingual in the maxilla). The less stressed nonfunctional cusps can be protected with less metal 1 mm is adequate.  Principles Of Tooth Preparation II Mechanical Considerations Preventing Deformation Margin Design Tooth reduction should provide sufficient room for bulk of metal at the margin to prevent distortion. Principles Of Tooth Preparation III ESTHETIC CONSIDERATIONS  Principles Of Tooth Preparation III Easthetic Considerations Dental restorations should look’s as natural as possible.  Principles Of Tooth Preparation III Easthetic Considerations ESTHETIC CONSIDERATIONS 1.All-Ceramic Restorations. 2.Metal-Ceramic Restorations. 3.Partial-Coverage Restorations.  Principles Of Tooth Preparation III Easthetic Considerations All-Ceramic All-CeramicRestorations. Restorations. Is the most pleasing esthetic restorations. A minimal material thickness of approximately 1 to 1.2 mm is necessary to ensure optimal esthetics.  Principles Of Tooth Preparation III Easthetic Considerations Metal-Ceramic Restorations. A metal-ceramic crown has two layers I- Metal acts as a frame. II- Ceramic, applied over the metal and is responsible for aesthetics.  Principles Of Tooth Preparation III Easthetic Considerations Partial-Coverage Restorations. A metal-ceramic crown has two layers I- Metal acts as a frame. II- Ceramic, applied over the metal and is responsible for aesthetics. Principles Of Tooth Preparation