Principles Of Cavity Preparation PDF

‫اَّلل ال هر ْْحَ ِن ال هرِح ِيم‬ ‫بِس ِم هِ‬ ‫ْ‬ ‫َنت‬ ‫كأ َ‬ ‫ه‬ ‫ِ‬ ‫ه‬ ‫ه‬ ‫ِ‬ ‫ِ‬ ‫ك الَ ع ْل َم...

‫اَّلل ال هر ْْحَ ِن ال هرِح ِيم‬ ‫بِس ِم هِ‬ ‫ْ‬ ‫َنت‬ ‫كأ َ‬ ‫ه‬ ‫ِ‬ ‫ه‬ ‫ه‬ ‫ِ‬ ‫ِ‬ ‫ك الَ ع ْل َم لَنَا إال َما َعل ْمتَ نَا إن َ‬ ‫﴿قَالُواْ ُس ْب َحانَ َ‬ ‫يم﴾‬ ‫الْعلِيم ا ْْل ِ‬ ‫ك‬ ‫َ ُ َ ُ‬ ‫صدق هللا العظيم‬ ‫سورة البقرة اآلية (‪)۳۲‬‬ Principles Of Cavity Preparation Dr. Eslam Gabr  The main objectives of cavity preparation are to: 1. Providing access to and allowing removal of the carious tissue 2. Providing clear margin (in a conservative way) where the restoration can end 3. Providing a cavity shape so that under mastication forces, the tooth and/or the restorations do not fracture, and the restoration do not displace 4. Allow esthetic and functional restoring by the restoration  The main objectives of restoring the teeth: 1. To restore the: Integrity, Function, and Appearance of tooth structure 2. To remove and stop the carious tissues.  Principles Of Cavity Preparation Definition: Classification: 1) Biological principles. 2) Mechanical principles. 3) Esthetic principles. I. Biological principles: II. Mechanical principles:  Definition  Definition  Forms of biological principles:  Objectives 1. Pulp protection.  Steps of cavity preparation: 2. Prevention of caries recurrence. 1. Outline form. 3. Aseptic procedure. 2. Resistance & retention forms. 4. Protection of gingival and periodontal 3. Convenience form. tissues. 4. Removal of remaining carious dentin. 5. Finishing of enamel wall. 6. Toilet of the cavity.  Principles Of Cavity Preparation Definition These are number of general and fundamental basics, which must be realized in preparing cavities for the reception of restorative materials. Classification: 1) Biological principles. Definition Steps followed during cavity preparation to minimize irritation of the pulp and preservation the vitality of tooth and protect the supporting structures.  Forms of biological principles: 1. Pulp protection a) Against mechanical irritation: 1. Avoid direct traumatic injury of the pulp. 2. Avoid unnecessary pressure and wrong direction of instruments. 3. Avoid over cutting of dentin and weakening of the tooth structure. 4. Avoid cutting across the recessional lines of the pulp chamber. 5. Avoid Vibration occurs due to eccentricity  Forms of biological principles: 1. Pulp protection a) Against mechanical irritation: 1. Avoid direct traumatic injury of the pulp.  Forms of biological principles: 1. Pulp protection a) Against mechanical irritation: 1. Avoid direct traumatic injury of the pulp.  Forms of biological principles: 1. Pulp protection a) Against mechanical irritation: 2. Avoid unnecessary pressure and wrong direction of instruments. 3. Avoid over cutting of dentin and weakening of the tooth structure.  1. Pulp protection a) Against mechanical irritation: 4. Avoid cutting across the recessional lines of the pulp chamber. These lines represent the lines along which the pulp has receded during the growth of dentin. They are also lines in which usually long pulpal extensions are found. Crossing these lines cause pulp exposure with subsequent pulp irritation.  1. Pulp protection a) Against mechanical irritation: 5. Avoid Vibration occurs due to eccentricity which may lead to: ❑ Patient discomfort. ❑ Cracks in enamel. ❑ Pulp damage.  1. Pulp protection b) Against thermal irritation: 1. Avoid heat generation during cavity preparation by. a) Avoid working without coolant. b) Avoid long time working.  1. Pulp protection c) Against chemical irritation: 1. Avoid using of chemicals and caustics for toilet of the cavity. 2. Avoid using air jet for long time.  2. Prevention of recurrent caries 1. Removal of all carious enamel and dentin. 2. The cavity outline should be extended to include all pits, fissures and areas which prone to caries. 3. Proper extension of cavity margins to self-cleansable areas. 4. Removal of all undermined enamel 5. Proper inclination of CSA suitable with the type of restoration. 6. Avoiding any sharp line angle 7. early detection of caries & topical application of fluorides should be maintained.  2. Prevention of recurrent caries 1. Removal of all carious enamel and dentin.  2. Prevention of recurrent caries 2. The cavity outline should be extended to include all pits, fissures and areas which prone to caries.  2. Prevention of recurrent caries 3. Proper extension of cavity margins to self-cleansable areas. An area of the teeth which by its shape and contour is less likely to retain food debris during normal function Self-cleansable areas. 1. Tips of Cusps 2. Crests of marginal 3. All inclined planes of cusps and ridges 4. Occlusal, incisal, facial and lingual embrasures Self-cleansable areas. 5. Facial or lingual surfaces incisal or occlusal to the height of contour with the exception of pits, if present 6. Axial angles of teeth Non-self-cleansable areas. 1. Pits and Fissures 2. Contact Areas 3. Area of near Approach Non-self-cleansable areas. 4. Gingival Embrasures 5. Facial or Lingual Surfaces Apical to Cervical Ridge  2. Prevention of recurrent caries 4. Removal of all undermined enamel undermined enamel → enamel not supported by sound dentin which may fracture under force leaving marginal ditch that leads to food accumulation and recurrent caries.  2. Prevention of recurrent caries 4. Removal of all undermined enamel ❖ Amalgam restorations with ditching on the margins (arrows).  2. Prevention of recurrent caries 5. CSA A. Proper inclination of CSA suitable with the type of restoration. B. it should be located in areas that are less liable to caries recurrence and less stress bearing.  2. Prevention of recurrent caries 6. Avoiding any sharp line angle  3. Aseptic procedure 1. Using sterile instruments. 2. Application of rubber dam to keep the fields clean and dry. 3. Maintenance of clean, dry and sterile hands (disposable gloves)  4. Protection of gingival and periodontal tissues 1. Avoid over hanged gingival margins of the restoration. 2. Proper matricing during restoration of compound cavities. 3. Proper wedging of the matrix. 4. Controlled cutting to avoid instrument slippage and soft tissue injury. 5. Avoid using irritating chemicals near the gingival margins of the cavity.  4. Protection of gingival and periodontal tissues 1. Avoid over hanged gingival margins of the restoration.  4. Protection of gingival and periodontal tissues 2. Proper matricing during restoration of compound cavities. 3. Proper wedging of the matrix.  4. Protection of gingival and periodontal tissues 4. Controlled cutting to avoid instrument slippage and soft tissue injury. 5. Avoid using irritating chemicals near the gingival margins of the cavity.  II. Mechanical principles Definition Steps should be followed during cavity preparation to preserve the tooth structure integrity and restoration against fracture during force of mastication. Objectives 1. establishment of adequate retention to the restoration against displacement. 2. establishment of adequate resistance against fracture to tooth structure and restoration. 3. Conservation of maximum amount of tooth structure (by avoiding unnecessary cutting of tooth structure).  II. Mechanical principles Steps of cavity preparation According to G.V.Black , the mechanical steps of cavity preparation are: → 1. Outline form. 2. Resistance and retention forms. 3. Convenience form. 4. Removal of remaining carious dentin. 5. Finishing of enamel wall. 6. Toilet of the cavity. N.B.: → If the cavity is too deep, step (4) can be interchanged with step (2) to determine: → The cavity depth. The extent of lesion.  II. Mechanical principles 1. To justify and determine the degree of pulpal involvement 2. To evaluate the amount and strength of remaining sound tooth structure that will affect the resistance and retention features to be selected 3. To select the most suitable restorative technique and the most suitable cavity design matching this technique  1. Outline form Definition The Shape of the boundaries of the completed cavity. External outline form refers to the marginal boundaries Internal outline form refers to the shape of the internal form of the preparation.  Factors affect the outline form 1. The extent of caries or injury. 2. The restorative material to be used. 3. Esthetic considerations: affect the choice of the design of the tooth preparation to maximize the esthetic result of the restoration.  Factors affect the outline form 4. Correcting or improving occlusal relationships (occlusion): also may necessitate altering the tooth preparation to accommodate such changes, even when the involved tooth structure is not faulty (i.e. a cuspal form may need to be altered to effect better occlusal relationships). 5. The desired CSA of the proposed restoration: Restorative materials that need beveled margins require tooth preparation outline form extensions that must anticipate the final cavosurface position and form after the bevels have been placed.  Principles of outline form: 1. All unsupported or weakened (friable) enamel is usually removed. 2. All faults (grooves, pit and fissures) are included. 3. All preparation margins are usually placed in a position that allows. inspection and finishing of the subsequent restoration margins.  Fundamentals of outline form 1. Extension of the carious defect in enamel and its lateral spread in dentin. 2. Defective and retentive pits, fissures and angular grooves which are continuous with cavity outline should be included in the outline 3. The cavity margins should be extended to sound tooth structure without undermined enamel and in a self-cleansable area. 4. All enamel which is weak or undermined by caries must be eliminated. 5. Extension for prevention or cutting for immunity. 6. The outline must be in the form of harmonious sweeping curves, 7. Adjacent cavities, closely approaching to each other, should not be joined into a single cavity  Fundamentals of outline form 8. Cusps and ridges that are severely weakened and subjected to occlusal forces must be reduced and restored with appropriate restoration (cusp capping) 9. Depth penetration into dentin should be kept to a minimum (0.2 to 0.8mm beyond the DEJ) 10. CSA 11. Age considerations 12. oral hygiene and caries susceptibility 13. esthetic versus mechanical demands.  1. Outline form Fundamentals of outline form 1. Extension of the carious defect in enamel and its lateral spread in dentin.  1. Outline form Fundamentals of outline form 1. Extension of the carious defect in enamel and its lateral spread in dentin. ✓ All carious enamel and dentin must be included in the outline, with consideration to the lateral spread of decay at the dentino-enamel junction.  1. Outline form Fundamentals of outline form 2. Defective and retentive pits, fissures and angular grooves which are continuous with cavity outline should be included in the outline because: A. Since they are retentive for food and therefore, subject to caries B. prevent securing of adequate adaptation with restoration at the critical interface.  1. Outline form Fundamentals of outline form 3. The cavity margins should be extended to A. Sound tooth structure B. Area Without undermined enamel C. In a self-cleansable area. D. Should not at stress bearing areas  1. Outline form Fundamentals of outline form 3. The cavity margins should be extended to B. Area Without undermined enamel 4. All enamel which is weak or undermined by caries must be eliminated. ❖ it will break easily under mastication forces leaving a "marginal ditch" since it is brittle and depends on the relative elasticity of the sound dentin for support.. Fundamentals of outline form 1. Outline form 3. The cavity margins should be extended to C. In a self-cleansable area. 5. Extension for prevention or cutting for immunity. Definition: Extension of cavity margins to a self-cleansable area to decrease the possibility of caries recurrence.  1. Outline form Fundamentals of outline form 5. Extension for prevention or cutting for immunity. Factors affecting extension for prevention: 1. The extent of surface involvement in enamel. 2. The lateral spread of caries at DEJ → i.e. Degree of undermining. 3. Esthetic demands necessary the use of special outline with minimal extension. 4. Oral hygiene → The better the oral hygiene, the lesser will be the extension.  1. Outline form Fundamentals of outline form 5. Extension for prevention or cutting for immunity. 5. Patient age → The older the patient, the lesser will be the extension due to tooth attrition. 6. Force of mastication → The more to be ideal, the lesser will be the extension. 7. Restorative material → Different extensions are used with different restorative materials.  1. Outline form Fundamentals of outline form 5. Extension for prevention or cutting for immunity. Adverse effects of extension for prevention: 1. Weakening of the sound tooth structure. 2. Increased irritation to the pulp.  1. Outline form Fundamentals of outline form 6. The outline must be in the form of harmonious sweeping curves, in order to: a) Prevention of recurrent caries. b) Avoid stress concentration areas. c) Better esthetics.  1. Outline form Fundamentals of outline form 7. Adjacent cavities, closely approaching to each other, should not be joined into a single cavity  1. Outline form Fundamentals of outline form 7. Adjacent cavities, Separate spot preparations are preferable. because this preserves the structural continuity and strength of the tooth.  1. Outline form Fundamentals of outline form 7. Adjacent cavities, ❖ This should be especially considered with A. Oblique and transverse ridges B. If two surfaces of the same tooth are involved, as Caries occurring in occlusal fissures and in buccal pit in lower molars. In such case, each lesion should be treated in a separate simple cavity preparation  1. Outline form Fundamentals of outline form 7. Adjacent cavities, closely approaching to each other, should not be joined into a single cavity Unless: If the intervening enamel is ❑ Carious ❑ Undermined ❑ Weak (less than 0.5mm) ❑ Crossed by a deep fissure.  1. Outline form Fundamentals of outline form 7. Adjacent cavities, closely approaching to each other, should not be joined into a single cavity Unless:  1. Outline form Fundamentals of outline form 7. Adjacent cavities,  8. What should be ideal depth of the preparation? ❖ The cavity depth should be at least 1.5 to 2.0 mm vertical from the cavosurface margin to the pulpal floor, to provide adequate bulk for restoration for resistant form ❖ And at least 0.5 mm in dentin below DEJ due to : 1. Enamel is brittle and dentin is elastic, so enamel cannot be used for providing retention and resistance form. So depth of preparation should be increased till elastic dentin is reached 2. Preparation should not end at DEJ. This area is sensitive because of lateral branching of dentinal tubules and cytoplasmic extensions of odontoblasts  1. Outline form Fundamentals of outline form 9. CSA A. Proper inclination of CSA suitable with the type of restoration. B. it should be located in areas that are less liable to caries recurrence and less stress bearing.  1. Outline form Factors modifying the outline form design 1. Age considerations ✓ Old patients having occlusal attrition with shallow grooves and broader proximal contacts are expected to have different outline forms. ✓ Young patient shows increased liability for caries recurrence due to prominent anatomical pits and fissures So, the outline should be well extended to insure all carious lesion and retentive area  1. Outline form Factors modifying the outline form design 1. Age considerations How does age affect outline from? Ans. Because of presence of deep pits and fissures, young teeth are more caries prone, therefore for a young patient, a conventional preparation is indicated. For older patients, a conservative preparation is indicated. In these patients the teeth become less susceptible to caries because of following reasons: a. Attrition of teeth. b. Older patient may follow oral instructions better.  1. Outline form Factors modifying the outline form design 2. Oral hygiene and caries susceptibility ✓ Patients with good oral hygiene, conservative outline form could be performed  1. Outline form Factors modifying the outline form design 2. Oral hygiene and caries susceptibility ✓ Bad oral hygiene, all caries susceptible areas must be included in the cavity outline and the cavity should be extended to area self- cleansable  1. Outline form Factors modifying the outline form design 3. Contact area in proximal cavities:  1. Outline form Factors modifying the outline form design 4. Contact area in proximal cavities:  The bucco-lingual width of the contact area determine the isthmus outline of compound Class II cavities to ensure the cavity outline is located in area self- cleansable, i.e. the embrasures  1. Outline form Factors modifying the outline form design 4. Contact area in proximal cavities: ❖ Proximal, buccal, and lingual contacts: broken by at least 0.5mm When we break the contact? (proximal clearance) ❖ Class II, III, and IV caries always involve a contact with the adjacent tooth, requiring breaking to bring preparation margins into embrasures for easy cleansability (self-cleansable area). ❖ Non-cleansable areas may result in secondary caries due to food stagnation.  Reverse curve ❖ In case of maxillary molars, the contact area is more buccally, i.e.; the lingual embrasures are more than the buccal embrasures ❖ In such cases, extending the bucco- proximal wall into the embrasure lead to excessive cutting of the buccal cusps ❖ To avoid this, a reverse curve ( S- shaped) is made in the buccal proximal wall  Advantages of reverse curve 1. Conservation of tooth structure ( preserve cuspal inclines) 2. Creation of 90 degree cavosurface angle 3. Less display of restorative material ( enhance esthetics) 4. To relieve the contact 5. To place the proximal margins in a selfcleansing area 6. Making the buccal walls follow parallel to the direction of the enamel rods Divergent walls toward the proximal surface change of the contour of the buccal resulting in thin margins for restoration in wall to increase the thickness of the the buccal wall amalgam in the restoration margin (reverse curve)  Isthmus ❖ The junction between the occlusal portion and proximal facial and lingual part of the preparation ❖ The width should be ¼ of the inter- cuspal distance  NB Class I Amalgam Bucco-lingual extension Optimally: width is