principles of cavity preparation part 1.pdf

Principles of cavity preparation Dr. Ahmed A. Holiel BDS, MSc, PhD Lecturer of Conservative Dentistry Faculty of Dentistry - Alexandria University You can see this carious lower first molar, How can you help this tooth and why?? Definition of Cavity Preparation • Mechanical alteration of a tooth...

Principles of cavity preparation Dr. Ahmed A. Holiel BDS, MSc, PhD Lecturer of Conservative Dentistry Faculty of Dentistry - Alexandria University You can see this carious lower first molar, How can you help this tooth and why?? Definition of Cavity Preparation • Mechanical alteration of a tooth to receive a restorative material which will return the tooth and area to proper form, function, and esthetics • Preparation procedure includes all defective and friable tooth structure Objectives of Cavity Preparation  To remove all defects and give necessary protection to the pulp  To locate the margins of the restorations as conservatively as possible  To form the cavity so that under the masticatory forces the tooth and the restoration will not fracture, and the restoration will not be displaced  To allow for the esthetic and functional placement of a restorative material GV Black’s Classification of Carious Lesions Biological Consideration Mechanical Consideration Esthetic Consideration Biological Principles of Cavity Preparation These principles are concerned with the health and integrity of the remaining tooth tissues. They dictate protection of the pulp and dentin and prevention of caries recurrence These steps followed during cavity preparation to minimize irritation to the vital tooth structures. Forms of Biological Principles: 1. Pulp protection. 2. Prevention of caries recurrence. 3. Aseptic procedure. 4. Protection of gingival and periodontal tissues. Esthetic Principles of Cavity Preparation Factors Affecting Esthetics : 1. Soft tissue management • Finish line formation. • Impression procedure. • The temporary restoration. 2. Tooth reduction 3. Shade selection 4. Color variation 5. Translucency 6. Surface characterization 7. Degree of gloss 8. Tooth form, size and arch position 9. Optical illusion Mechanical Principles of Cavity Preparation The principles as suggested by Dr. Black are: 1. Obtain the required outline form. 2. Obtain the required resistance form. 3. Obtain the required retention form. 4. Obtain the required convenience form. 5. Remove any remaining carious dentin. 6. Finish the enamel wall. 7. Cleanse and medicate the cavity preparation The father of modern restorative dentistry. I- Outline form (Margins of the preparation) • The outline form is referred to the external shape or form of boundaries of the completed cavity. • The outline should encompass the carious lesion and may include portions of caries-susceptible areas on the surface being restored. • The outline form should follow a gently, sweeping curve, especially on the occlusal surface. OUTLINE FORM – Smooth flowing, regular curves. No Sharp angles Angular irregularities in the outline are susceptible to fracture Many factors govern the outline form of the cavity. ➢ Location and extent of carious lesion. ➢ Position of pits & fissures dictate outline form. ➢ Relationship of self cleansable areas to outline form. ➢ Preservation of healthy and vital tooth structure. ➢ Restorative material. ➢ Esthetics. ➢ Functional requirements of the restoration, or improving occlusal relationships, even when the involved tooth structure is not faulty. ➢ The desired Cavo surface marginal configuration of the proposed restoration. 1- Location and extent of carious lesion. • Must extend sufficiently to include the entire carious area • Conservation of tooth structure ➢ Preparing initial depth of 0.2-0.8 mm deep to DEJ ➢ Two separate cavities should not be united unless the separating ridge is less than 0.5mm. (e.g., oblique ridge in upper molars or transverse Ridge in lower 1st premolars). ➢ Unsupported enamel (Undermined Enamel) should be removed during cavity preparation, since it is liable to fracture creating open marginal areas which may lead to secondary decay. An exception to this may be noted at this time. With the introduction of the acid etch technique for composite resins, unsupported enamel is not always removed but may be retained for esthetic reasons. ➢ Marginal ridges should be encroached upon as minimally as possible in order that their strength is preserved. 2- Position of pits & fissures dictate outline form. • The areas of tooth with caries susceptibility are usually included in the outline form. • This principle is known as "extension for prevention". • Cavity preparation should not automatically extend into all the developmental and supplementary grooves, especially if: 1) they are not carious, 2) they are not fissured and are unlikely to become carious. ➢ All non-coalesced pits and fissure should be eliminated ➢ Non-coalesced pits and fissure is imperfect coalescence of enamel, the two end of enamel does not meet and a space remain. ➢ After development of high preventive measures and if the patient with high oral hygiene there is no need to extension for prevention, so we extend our cavity to the limit of caries, then we do saucering to the remaining non carious fissure "enameloplasty“ ➢ Enameloplasty: Is the process of reshaping the enamel surface “rounded or saucered" with suitable rotary instruments, so the area becomes cleanable and finishable , and allow conservative placement of the cavity margins. ✓ Not more than one third of enamel thickness should be removed. 3- Relationship of self cleansable areas to outline form. • Design the cavity so that all margins are in areas easily cleansed by the patient. • These areas are found on smooth surfaces above the height of contour, occlusal cusp inclines, incisal edges and cusp tips. • Naturally, the typical outline form varies with the anatomical form of the individual tooth being operated on. 4- Preservation of healthy and vital tooth structure. • Healthy tooth structure should NOT be removed unless justified since tooth structure removed cannot be put back. • The outline is curved and flowing and is constricted as it curves around the cusps. • The pulpal horns of posterior teeth are located beneath the cusp tips. The dentin surrounding the pulpal horns should be conserved to insulate- and strengthen the restored tooth. 5- Restorative material • Individual properties of each material utilized to restore teeth demand certain design factors that must be incorporated into each cavity preparation. • The physical properties of the restorative material will, therefore, determine the position and configuration of the cavosurface margin. • EX: Amalgam is relatively weak, so their cavosurface margins must be prepared at an angle of approximately 90° with the tooth surface provide maximum edge strength for both the restorative material and the enamel), and undercuts to lock into the cavity. • Placing a bevel and etching the enamel at the cavosurface angle of composite resin preparations improve the marginal seal. In some cases, the bevel may also aid in improving the contour and esthetic qualities of the composite resin restorations. • Cohesive gold restorations require a beveled cavosurface angle in the cavity preparation because the malleting forces needed to place the cohesive gold may fracture enamel rods from the unbeveled cavosurface angle, a beveled margin also allows for the best marginal adaptation and finish. 6- Esthetics. It is important to maximize the conservation of tooth structure, because the natural tooth is the most esthetic. Should esthetics be compromised, then an esthetic material must be used. Extensions consist of: a. Caries and decalcifications b. Enamel unsupported by sound dentin c. Pits d. Major fissures and grooves e. Existing restorations f. Joining two outlines that come close together (i.e., less than 0.5 mm apart) eliminates defective tooth structure and eliminates areas (pits, fissures, etc.) which are susceptible to recurrent caries and facilities oral hygiene procedures. Bucco – lingual extension 1. Optimal isthmus width is ¼ intercuspal distance or less) terminating on smooth surfaces. to preserve the strength and function of the cusps while eliminating susceptible grooves or defective tooth structure 1/4th intercuspal distance Not more than 1 – 1.5 mm Isthmus just wide enough to accept instrumentation (Diameter of bur should be considered) ➢ In a bucco-lingual direction, the cavity is extended just sufficient to eliminate the defective and susceptible tissues. ➢ The lingual and the buccal wall should be parallel to the respective tooth surface (CONVERGED WALLS) Mesio-distal extension 1. If marginal ridge is unsupported or very thin (less than 1.6mm) it should be included, resulting in a Class II preparation. If not included the marginal ridge may fracture. (amalgam will be stronger than the unsupported enamel) 2. Parallel to the contour of the marginal ridge 3. Mesial and distal walls should be made parallel or slightly diverge to preserve a uniform bulk (strength) to the mariginal ridges. any convergence cause unsupported enamel , that will be fractured if subjected to occlusal load because of little amount of dentin supported enamel