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Principles of cavity preparations

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Principles of cavity preparations

  1. 1. PRINCIPLES OF CAVITY PREPARATIONS Ass.Prof.DDrr..MMoohhaammeedd AALLssaakkkkaaff CCoonnsseerrvvaattiivvee ddeeppaarrttmmeenntt FFaaccuullttyy ooff ddeennttiissttrryy UUnniivveerrssiittyy ooff AAddeenn 1 L4 كنزارف س 3
  2. 2. PRINCIPLES OF CAVITY PREPARATIONS The 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 was one of the most important considerations of . cavity design 2 Ass.Prof.Dr.Mohamed ALsakkaf
  3. 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 3
  4. 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 4
  5. 5. BIOLOGICAL CONSIDERATION: 'Pulp :protection Avoid over cutting of dentin and ( 1) unnecessary deeping of the cavity because the deeper the cavity the .more irritated pulp Unnecessary application of ( 2) pressure in scooping out soft dentin at the bottom of a deep cavity, only gentle pressure, using . sharp excavators 5
  6. 6. Unnecessary or excessive cutting of enamel, ( 3) in order to expose only a small area of dentin .to irritation .Avoid heat generation( 4) Injudicious use of rotary instruments in ( 5) . removing soft dentin at the bottom Don’t use chemical irritants in performing ( 6) the toilet of the cavity. No cavity sterilization . should be done 6
  7. 7. :STEPS .Obtain the required outline form. 1 .Obtain the required resistance form. 2 .Obtain the required retention form. 3 .Obtain the required convenience form. 4 .Remove any remaining carious dentin. 5 .Finish the enamel wall. 6 Cleanse and medicate the cavity . 7 . preparation 7
  8. 8. Normally, these principles of cavity preparation are followed in the sequence as Outlined above. However , occasionally situations arise when the operator may have to deviate from . this sequence 8
  9. 9. In very deep Lesions, where a pulp expose is feared or when there is gross destruction of the tooth structure because of caries, it is often advisable to remove the carious dentin )Principle #5( resistance and retention from )Principles #2 and #3(, or in extreme cases, even before obtaining the outline form ((.))Principle #1 9
  10. 10. These principles of cavity preparation should be understood on a biomechanical basis . They are concerned with both the biological structure that complement the physical and chemical properties of the restorative .material 10
  11. 11. The basic biological objectives of cavity preparation procedures are the removal of a carious lesion , and the preservation of the optimum amount of remaining healthy tooth structure . Within these parameters the cavity preparation assumes a design that includes the actual carious lesion and the potential f . or it's future occurrence 11
  12. 12. This is reflected by the location of the cavity margins in areas easily cleansable by the patient and readily accessible examination .by the dentist The mechanical factors included in cavity preparation are basically concerned with the retention of the restoration and the .continued vitality and function of the tooth 12
  13. 13. OUTLINE FROM Obtaining or establishing the outline from 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 13
  14. 14. The outline form should follow a gently, sweeping curve, especially on the occlusal surface. Many factors govern the outline .form of the cavity 14
  15. 15. LOCATION AND EXTENT OF THE 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 esthetic, prevention of irritation to the dental pulp, and the maintenance of the natural relationship between the tooth and .the supporting tissues 15
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  17. 17. The areas of tooth with caries susceptibility are usually included in the outline form. This principle is known as "extension for prevention“. The importance of the concept of conservation of tooth structure must be considered. An occlusal outline form on posterior teeth may include the fissured primary (developmental) grooves, and in some cases secondary grooves, as well as buccal and lingual extensions of these . grooves 17
  18. 18. 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 18
  19. 19. RELATIONSHIP OF SELF-CLEANING AREAS TO OUTLINE All cavity preparations normally have their Cavosurface margins located in areas that are self-cleaning or are easily-cleansable by the patient. Recurrent decay is more likely to occur in areas of the tooth that are not cleaned naturally by the action of the lips, .cheek and tongue 19
  20. 20. Therefore, 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, incisal edges and cusp .tips 20
  21. 21. PRESERVATION OF HEALTHY TOOTH STRUCTURE Healthy tooth structure should not be removed unless justified since tooth structure removed cannot be put back. However establishing the margins of cavity preparation sometimes necessitates the removal of some healthy tooth structure. This may conflict with locating the cavity margins in easily-cleansable areas since it necessitates the removal of healthy tooth structure. However compromise can be .reached 21
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  23. 23. RESTORATIVE MATERIAL Individual properties of each material utilized to restore tooth, demand certain design factors that must be incorporated into each cavity preparation. For example , the marginal strength ( also called "edge-strenght") of dental cement and amalgam is relatively weak , so their Cavosurface margins must be prepared at an angle of approximately "90d" with the tooth surf ace to provide maximum edge strength for both .the restorative material and the enamel 23
  24. 24. Placing a bevel and etching the enamel at the Cavosurface angle of composite preparations improves the marginal seal. In some cases, the bevel may also aid in improving the contour and esthetic qualities .of the composite restorations 24
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  26. 26. TOOTH MORPHOLOGY Tooth size and arch position may influence the design of a cavity preparation. Malpositioned and rotated teeth may require unusual outline form because they must be restored where they contact the .adjacent teeth 26
  27. 27. AREAS OF ENAMEL DECALCIFICATION These areas may have to be included in the outline form. Areas of decalcified or chalky enamel are usually included in the outline form. This prevents future marginal breakdown and recurrent caries. The most common areas for decalcified enamel is in the cervical one-third of the crown, and is associated with class five cavity .preparations 27
  28. 28. HOME CARE Lack of patient motivation, salivary and dietary problems may influence the quality of cleaning the tooth. More extension for prevention may be required when these . factors cannot be controlled 28
  29. 29. RESISTANCE FORM Resistance form is the design given to a cavity preparation to help prevent fracture of the restorative martial and the tooth. Resistance form is obtained by giving the cavity "box form" .The factors that contribute : to resistance form include 29
  30. 30. WALL ANGULATION Masticatory forces are directed primary along the long axis of the teeth. Since the teeth and the restorative materials resist compressive forces best, the cavity preparation should be designed to minimize tensile . and shear stresses 30
  31. 31. This is done by preparing the internal walls of the cavity perpendicular or parallel to the direction of the force ,which is along the long axis. 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 31
  32. 32. DEPTH OF THE CAVITY PREPARATION The depth of the pulpal and axial walls must be sufficient for the restorative material to have enough bulk to resist fracture. Placing these walls just within dentin is usually adequate for this purpose. Increasing the width of a cavity will not significantly increase the resistance of the restoration to fracture but it will decrease the strength of .the tooth 32
  33. 33. The restorative material is more likely to fail if the cavity is too shallow rather if it is too .narrow It is important that the pulpal and axial walls be maintained at their ideal depth just .within the dentin if at all possible 33
  34. 34. The contours of the pulpal and axial walls are important in preserving the interadjacent dentin. Ideally the pulpal wall is flat and the axial wall is convex, paralleling the curvature of the surface of the tooth and the dentinoenamel junction. The axial wall should . not be flat or concave 34
  35. 35. INTERNAL LINE ANGLES Well defined internal line angles delineate the walls of the cavity preparation, aid in establishing uniform depth, and contribute to retention form by preventing rotation of restoration. Line angles such as the pulpo-axial should be slightly rounded to minimize stress concentration on the .restoration 35
  36. 36. RESTORATIVE MATERIAL Brittle material that have low tensile strength, such as amalgam and cement, require good box form and strict adherence to proper .preparation Less brittle materials such as composite can be used in shallower or rounded preparation when other means of retention are used in addition to wall friction 36
  37. 37. RETENTION FORM Retention form refers to the features of a cavity preparation that prevent dislodgment of the restoration. Retention form is achieved through: 1) WALL FRICTION: Friction between the restorative material and the walls of the cavity preparation acts to retain all types of restoration. Frictional retention is improved by increasing the area of the walls (cavity depth) and making opposing ).walls parallel (proper box form 37
  38. 38. Consequently, good resistance form also contributes retention form to the cavity by enhancing wall friction. Walls are not intentionally roughened to increase retention, since normal instrumentation leaves the walls sufficiently rough. 2) UNDERCUT POIENTS AND GROOVES: Undercuts are confined to the dentin to avoid . undermining enamel 38
  39. 39. They are usually placed in the facial and lingual walls of occlusal preparation, the buccal and lingual proximal walls of class 2 preparation, and the incisal and gingival walls of class 5 preparation. They are not normally placed in the pulpal or axial walls in order . to avoid approaching the pulp AUXILIARY RETENTION: They are; Dovetails, Grooves, Pins and etching of enamel 39
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  41. 41. CONVENIENCE FORM This means that the dentist must create sufficient access to the lesion to facilitate visibility and instrumentation in preparation of the cavity and insertion of .restorative material Proper convenience form is a requirement for .all operative procedures 41
  42. 42. REMOVAL OF REMAINING CARIOUS DENTIN Cavity preparations are designed to remove carious tooth structure. Preparations that are designed according Blacks principles will automatically include those lesions that have just penetrated the dentin. Moderate or gross amounts of carious tooth structure, however, are not removed by ideal cavity designs and therefore caries removal in these instance becomes a separate and .significant step 42
  43. 43. FINISHING OF THE ENAMEL WALL It is necessary to refine the enamel walls of a cavity preparation to ensure the best possible adaptation between the restorative .material and enamel 43
  44. 44. An other objective of this procedure is the removal of any unsupported enamel which may fracture later, and lead to secondary caries. Adequate planning of all enamel walls will result in a smooth Cavosurface margin which enhances the condensability and adaptability of the restorative material, thereby increasing the strength of the .restoration 44
  45. 45. CLEANSE AND MEDICATE No cavity preparation should be restored that has not been properly cleaned and dried for inspection. It may also be necessary to place certain medicaments in the cavity .preparation 45
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