kumar Dept of Conservative DentistryampEndodontics 8 11 2014 The clinical form of cavity preparation The principles of modern cavity preparation were first defined in 1896 by Dr GV Black a man considered by many to be the father of modern restorative dentistry When his original ID: 1019690
Download Presentation The PPT/PDF document "cavity preparation Dr.Ashok" is the property of its rightful owner. Permission is granted to download and print the materials on this web site for personal, non-commercial use only, and to display it on your personal computer provided you do not modify the materials and that you retain all copyright notices contained in the materials. By downloading content from our website, you accept the terms of this agreement.
1. cavity preparationDr.Ashok kumar,Dept of Conservative Dentistry&Endodontics8- 11- 2014
2. The clinical form of cavity preparationThe principles of modern cavity preparation were first defined in 1896 by Dr. G.V. Black, a man considered by many to be the "father of modern restorative dentistry". When his original sequence of cavity preparation was described, "extension for prevention" of recurrent decay was one of the most important considerations of cavity design.
3. However, the degree of cavity extension is considerably less today, because of the realization that caries, primary or secondary, can be more effectively controlled and prevented by greater emphasis on oral hygiene by the patient
4. Although techniques have been refined and outlines have been modified, Black's Principles are still used as the basic steps in the process of designing and preparing a cavity. The adherence to these principles will facilitate the procedure of cavity preparation and decay removal.
5. The principles as suggested by Dr. Black are1. 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
6. I- Outline form (Margins of the preparation)Obtaining or establishing the outline form means carrying the margin of the cavity to the position it will occupy upon completion of the 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.
7. Many factors govern the outline form of the cavity1- Location and extent of carious lesion.2- Position of pits & fissures dictate outline form.3- Relationship of self cleansable areas to outline form.4- Preservation of healthy and vital tooth structure.5- Restorative material.6- Esthetics.7- Functional requirements of the restoration ,or improving occlusal relationships, even when the involved tooth structure is not faulty.8- The desired cavosurface marginal configuration of the proposed restoration.
8. 1- Location and extent of carious lesion.The cavity preparation must be extended sufficiently to include the entire carious area and the enamel which is not supported by sound dentin.Enamel which is unsupported is subject to fracture. This conservation of tooth structure is of paramount importance for the preservation of esthetics, prevention of irritation to the dental pulp, and the maintenance of the natural relationship between the tooth and the supporting tissues.
9. Conservation of tooth structure is of almost importance and must be considered repeatedly during the design of a cavity preparation.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).
10. 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.
11. Marginal ridges should be encroached upon as minimally as possible in order that their strength is preserved. Occlusal outline of upper and lower molars with marginal ridges parallel to outer tooth surface to preserve enough thickness to these marginal ridges.
12. 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 preventionCavity 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
13. 3- Relationship of self cleansable areas to outline form.The dentist must design the cavity so that all margins are located 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.
14. 4- Preservation of healthy and vital tooth structureHealthy tooth structure should NOT be removed unless justified since tooth structure removed cannot be put back.The dentin surrounding the pulpal horns should be conserved to insulate- and strengthen the restored tooth. The outline is curved and flowing and is constricted as it curves around the cusps.
15. 5- Restorative materialIndividual properties of each material utilized to restore teeth demand certain design factors that must be incorporated into each cavity preparation.Cavity preparations in teeth have been more or less designed to meet the needs of amalgam, with block-shaped cavities, edges with butt joints (The marginal strength (also called "edge-strength") of dental cement and amalgam is relatively weak, so their cavosurface margins must be prepared at an angle of approximately 90° with the tooth surface
16. A restoration that is too shallow, however, has tendency to fracture because amalgam is a material that is quite brittle. Preparations therefore are made so the amalgam will be in the range of 2mm thick
17. Flat walls parallel with or perpendicular to the tooth surface compose the form of these box-like preparations
18. 6- EstheticsIt 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.
19. 7- Functional requirements of the restorationA restoration cannot be considered successful unless it fulfills the functional requirements of the tooth
20. REQUIRED FEATURESGenerally the specific, typical features of establishing proper outline form are:Preserving cuspal strength.Minimizing faciolingual extentions.Preserving marginal ridge strength.Connecting two close faults, cavities, or restorations.Restricting the depth of the preparation into dentin to a maximum of 0.2 mm for pit &fissure caries and 0.2 to 0.8 mm for the axial wall of smooth surface caries.
21. RULES FOR ESTABLISHING OUTLINE FORM FOR PIT &FISSURE TOOTH PREPARATION:1-Extend the preparation margin until sound tooth structure, i.e. all friable &/or weakended enamel should be removed.2-Avoid terminating the margin on extreme eminences such as cusp heights or ridge crests.All margins should be placed in a position to afford proper tooth preparation, restoration placement,& good finishing of the restoration’s margins.
22. All faults should be included. If the extension from a primary groove includes ½ or more of the cusp incline, consideration should be given to capping the cusp. If the extension is 2/3, the cusp-capping procedure is most often the proper procedure
23. 4-Restrict the pulpal depth of the preparation to a maximum of 0.2mm into dentin. To be as conservative as possible, the preparation for a occlusal surface pit&fissure lesion is first prepared to a depth of 1.5mm,as measured at the central fissure
24. 5-When 2 pit &fissure preparations have less than 0.5m of sound tooth structure beween them, they should be joined to eliminate a weakenamel wall between them.
25. 5-When 2 pit &fissure preparations have less than 0.5m of sound tooth structure between them, they should be joined to eliminate a weak enamel wall between them.
26. Rules for establishing outline form for smooth surface lesionSMOOTH-SURFACE LESIONS occur in 2 locations:Proximal surfaces.The gingival portion of the facial and lingual surfaces.
27. When the proximal surface of a tooth is involved and requires restoration, the proximal outline of the cavity preparation is influenced by: -Class II, III & IV smooth surface lesions1. Extent of carious involvement.2. The type of restorative material to be used.3. Area of contact with adjacent tooth/teeth.4. Accessibility of the proximal margins for placement and finishing of the restoration and for subsequent cleansing by the patient.5. Height of the gingival tissue.6. Occlusion with teeth of the opposite arch.
28. On the proximal surface, the facial and lingual outlines for amalgam restorations are parallel to the long axis of the tooth and parallel to each other occluso-gingivally. For the gold inlay, the facial and "lingual outlines diverge as they proceed occlusally from points X & Y to allow withdrawal of the wax pattern.
29.
30. Resistance form:Primary resistance form may be defined as that shape and placement of the preparation walls that best enable both the restoration and the tooth to withstand, with out fracture, masticatory forces delivered principally in the long axis of tooth
31. Principles1- Use the box shape with a relatively flat floor, which helps the tooth resist occlusal loading by virtue of being at right angles to those forces of mastication that are directed in the long axis of the tooth.2- To restrict the extension of the external walls(keep as small as possible) to allow strong cusp and ridge areas to remain with enough dentin support
32. 3- To have a slight rounding of internal line angles to reduce stress concentrations in tooth structure.4- To cap week cusps and envelope enough week tooth structure to resist fracture of the tooth by forces directed both in the long axis and obliquely
33. 5- To provide enough thickness of restorative materials to prevent their fracture under load.6- To bond the material to tooth structure whenever indicated.
34. The factors that contribute to resistance form include:1. Areas included within the outline form.2. Cavity wall angulations.3. Cavity preparation depth.4. Internal line angles.5. Type of restorative material used.
35. 1- Areas included:The more minimal the surface area of the restoration exposed to occlusal stresses, the less liable it will be to deterioration and displacement.Excessive facio-lingual width weakens the cusps and exposes unnecessarily increased surface area of the restoration to stress.
36. 2- Cavity wall angulations.Masticatory forces are directed primarily along the long axis of the teeth. Since the teeth and/restorative materials resist compressive forces best, the cavity preparation should "be designed to minimize tensile and shear stresses.
37. Thus, pulpal and gingival walls should be horizontal or perpendicular to the long axis. The other walls, including the axial, are vertical or parallel to the long axis
38. Cavity walls should be flat and should be directed either parallel or perpendicular to the line of occlusal force. The line of occlusal force is normally parallel to the long axis of the tooth."Cup-shaped" cavity preparations are to be avoided, as they poorly resist dislodging of restorations.
39. Cup shaped cavity(Micro movement of the restoration during occlusal loading leading to cusp flexing & tooth #fracture)
40. 3- Cavity preparation depth.The depth of the pulpal and axial walls must be sufficient for the restorative material to have enough bulk to resist fracture.It is important that the pulpal and axial walls be maintained at their ideal depth just within the dentin if at all possible.
41. At this depth, sufficient dentin remains overlying the pulp to afford it proper protection and enough thickness of amalgam (about 1.5mm) is present to resist fracture under occlusal stresses.
42. 4- Internal line angles.Rounding (coving) internal line angles reduce stress concentration.Line angles such as the pulpo-axial should be slightly rounded to minimize stress concentration in the restoration.
43. 5- Type of restorative material used.The physical properties of the type of restorative material to be used directly influence the amount and type of resistance form to be used in Cavity design.Brittle materials that have low tensile strengths, such as amalgam and cements, require good box form and strict adherence to proper preparation.
44. Resistance to proximal displacement of amalgam restorations is sometimes obtained by placing grooves into the facial and lingual proximal walls at the depth of the axial wall.
45. A dovetail is formed by flaring a portion of a cavity preparation so that it is wider than the isthmus of the preparation and provides mechanicalresistance to proximal displacement of two-surface restorations
46. III- Retention Form:Retention form refers to the features of a cavity preparation that prevents dislodgement of the restoration.
47. Retention forms influenced by the following factors:-1- Relationship of cavity walls to one another:Friction between the restorative material and the walls of the cavity preparation cavity depth and making opposing walls parallel proper box form Walls are not intentionally roughened to increase retention, since normal instrumentation sufficiently rough.
48. 2- Undercut points and grooves:Additional retention may be gained by placing points and grooves in the dentinal walls of the preparationUndercuts are confined to the dentin to avoid undermining the enamel. They are usually placed in the buccal and lingual proximal walls of Class II preparations
49. Incisal and gingival walls of Class V preparations. They are not normally placed in the pulpal or axial walls in order to avoid approaching the pulp.
50. 3- Auxiliary:Dovetails, pins and etching of enamel are additional methods that may be used to enhance retention with certain types of restorative materials.
51. IV- Convenience form:Convenience form means that the dentist must create sufficient access to the lesion to facilitate visibility and instrumentation in the preparation of the cavity and the insertion of a restorative material.
52. This is influenced by:1. Armamentarium to be utilized.2. Location of cavity margins.3. Accessibility for proper caries removal and pulp protection.4. Accessibility for proper restoration placement.5. Type of restoration to be placed.
53. Instruments used:Utilization of rubber dam to effect tissue retraction, together with use of suitably selected burs and instruments for cavity preparation, are determinants for the convenience form required for a specific restorative procedure.
54. V- Removal of remaining carious dentinIn small size cavities, the carious dentin should have been removed during making the cavity extensions.In moderately deep and deep cavities, the carious dentin is peeled off carefully using large spoon excavators, and then scooped out in few and large pieces. Only light pressure in a direction parallel to that of the pulp is utilized. This is continued until a sound dentin floor is reached.
55. The enamel walls of the cavity should be finished free from any undermined enamel, and trimmed to meet the tooth surface at a right cavo-surface angle. This may be done by sharp and regular-edged chisels and hatchets, plane fissure burs, stones, or sand-paper discs. All sharp corners in enamel must be rounded, Planning of Enamel Walls
56. A sharp explorer is then used to check the details of the prepared cavity and to loosen the tooth debris which are then blasted out with warm air.Performing the toilet of the cavity
57.
58. IF“ THE ART OF BEING WISE IS THE ART OF KNOWING WHAT TO OVERLOOK WHAT NOT”Thank you