Fundamentals in tooth preparation .


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Fundamentals in tooth preparation .

  2. 2. DEFINITION OF TOOTH PREPARATION  Tooth preparation is the mechanical alteration of a defective, injured, or diseased tooth to receive a restorative material that re-establishes a healthy state for the tooth, including esthetic corrections where indicated and normal form and function.
  3. 3. OBJECTIVES OF TOOTH PREPARATION Remove all defects and provide necessary protection to the pulp  (2) extend the restoration as conservatively as possible,  (3) form the tooth preparation so that under the force of mastication the tooth or the restoration or both will not fracture and the restoration will not fracture & the restoration will not displaced, and  (4) allow for the esthetic and functional placement of a restorative material. 
  4. 4. TOOTH PREPARATION TERMINOLOGY Tooth preparation walls  Internal wall –An internal wall is prepared surface that does not extend to external tooth surface.   Axial Wall - An axial wall is an internal wall parallel with the long axis of the tooth  Pulpal Wall- A pulpal wall is an internal wall that is perpendicular to the long axis of the tooth and occlusal of the pulp.
  5. 5.    External Wall- An external wall is a prepared (cut) surface that extends to the external tooth surface. Such a wall takes the name of the tooth surface (or aspect) that the wall is toward . Floor (or Seat)- A floor (or seat) is a prepared wall that is reasonably flat and perpendicular to the occlusal forces that are directed occlusogingivally (generally parallel to the long axis of the tooth Examples are the pulpal and gingival walls.  Enamel Wall- The enamel wall is that portion of a prepared external wall consisting of enamel  Dentinal Wall- The dentinal wall is that portion of a prepared external wall consisting of dentin, in which mechanical retention features may be located.
  6. 6. TOOTH PREPARATION ANGLES Line angle. A line angle is the junction of two planal surfaces of different orientation along a line  An internal line angle is a line angle whose apex points into the tooth  An external line angle is a line angle whose apex points away from the tooth   Point angle – a point angle is the junction of three planal surface of different orietation
  7. 7. CLASSIFICATION OF TOOTH PREPARATION Class I Restoration  All pit rand-fissure restoration are class I and they are assigned to three groups.  Restoration on Occlusal Surface of Premolars & Molars.  Restorations on Occlusal Two Thirds of the Facial and lingual surfaces of Molars.  Restoration on lingual Surface of Maxillary Incisor    class II Restorations. Restorations on Proximal surface of posterior teeth are Class II
  8. 8. Class III Restorations  Restorations on the proximal surface of anterior teeth that do not involve the incisal angle are Class III.  Class IV Restoration Restorations on the proximal surfaces of anterior teeth that do involve the incisal edge are class IV  Class V Restorations  Restoration on the gingival third of the Facial or lingual surface of all teeth( except pit-and-fissure lesions) are Class V  Class VI Restorations Restorations on the incisal edge of anterior teeth or the occlusal cusp height of posterior teeth are class VI 
  9. 9. INITIAL AND FINAL STAGES OF TOOTH PREPARATION Initial tooth preparation stage  Step 1: Outline form and initial depth  Step2 Primary resistance form  Step3 Primary retention form  Step4 Convenience form  Final tooth preparation stage  Step 5 Removal of any remaining infected dentin or old restorative material (or both), if indicated  Step 6: Pulp protection, if indicated  Step 7: Secondary resistance and retention forms  Step 8: Procedures for finishing external walls  Step 9: Final procedure--cleaning, inspecting sealing 
  10. 10. INITIAL TOOTH PREPARATION STAGE  Initial tooth preparation is the extension and initial design of external walls of preparation at a specified limited depth so as to provide access to the caries or defect, reach sound tooth Structure, resist fracture of the tooth restorative material from masticatory forces principally directed with the long axis of the tooth,and retain the restorativc material in the tooth .
  11. 11. STEP 1: OUTLINE FORM AND INITIAL DEPTH Def Establishing the outline form means(1) placing the preparation margins in the positions they will occupy in the final preparation except for Finishing enamel walls and margins and (2) preparing an initial depth of 0.2 to 0.8 mm pulpally of the DEJ Postion or root-surface position 
  12. 12. PRINCIPLES:(1) all friable or weakened enamel should be removed  (2) all faults should be included and  (3) all margins should be in a position to afford good finishing of the margin of the restoration.
  13. 13. FEATURES… 1) Preserving cuspal strength  2) preserving marginal ridge strength  3) Minimizing faciolingual extension  4) using enamelopasty  5) Connecting two close faults or tooth preparation  6) Restricting the depth of the preparation into dentin to a maximum of 0.2mm for pit & fissure caries and 0.2 to 0.8 mm for axial wall of smooth surface caries. 
  14. 14. STEP 2. PRIMARY RESISTANCE FORM Def: Primary Resistance form may be defined as the shape and placement of preparation walls that best enable the restoration and the tooth to withstand, without Fracture, masticatory forces delivered principally in the long axis of the tooth. 
  15. 15. PRINCIPLE__ 1) to use the box shape with a relativity flat floor which helps the tooth resist occlusal loading by virtue of being at right angles to the forces of mastication that are directed in the long axis of the tooth  2) to restrict the extension of the external walls to allow strong cusp and ridge areas to remain with sufficient dentin support  3) to have a slight rounding of internal line angles to reduces stress concentration in tooth structure 
  16. 16.  4) to cap weak cusps and envelope  5) to provide enough thickness of restorative material to prevent its Fracture under load and  6) to bond the material to tooth structure when appropriate.
  17. 17. FEATURES: 1) Relatively flat floors  2) Box shape  3) Inclusion of weakened tooth structure  4) Preservation of cusps & marginal ridges  5) Rounded internal line angles  6) Adequate thickness of restorative material  7) Reduction of cusps for capping when indicated
  18. 18. STEP3: PRIMARY RETENTION FORM  Def:-  Primary Retention form is the shape or form of the conventional preparation that resists displacement or removal of restoration by tipping or lifting forces.
  19. 19. STEP4: CONVENIENCE FORM.  Convenience form is the shape or form of preparation that provide for adequate observation, accessibility and ease of operation in preparing & restorating the tooth.
  20. 20. STEP 5: REMOVAL OF ANY REMAINING ENAMEL PIT OR FISSURE, INFECTED DENTIN, OR OLD RESTORATIVE, IF INDICATED.  Removal of any remaining enamel pit or fissure infected dentin, or old Restorative material is the elimination of any infected carious tooth Structure or faulty restorative material left in the tooth after initial tooth preparation .
  21. 21. ANY REMAINING OLD RESTORATIVE MATERIAL SHOULD BE REMOVED IF ANY OF THE FOLLOWING CONDITIONS ARE PRESENT_- _ 1) The old material may affect negatively the esthetic result of the new restoration.  2) the old material may compromise the amount of anticipated needed retention.  3) Radiographic evidence indicates caries is Under the old material.  4) The tooth pulp was symptomatic preoperatively or  5) The periphery of the remaining old restorative material is not intact. 
  22. 22. STEP 6: PULP PROTECTION, IF INDICATED  The reason for using traditional liner or bases is to protect the pulp or to aid pulpal recovery or both. Other pulpal irritants that affect operative procedure are: 1) Some ingredients of various materials  2) thermal changes conducted through restorative materials,  3) force transmitted through materiel to the dentin  a) Galvanic shock and most importantly  5) The ingress of noxious products & bacteria through microleakage. 
  23. 23. Liners also may provide  1) A barrier that protects the dentin from noxious agents from restorative material oral fluids  2) Initial electrical insulation  3) Some thermal protection  Ex- of bases include zinc phosphate, zinc oxide eugenol calcium hydroxide, polycarboxylate & glass ionomer
  24. 24. STEP 7… SECONDARY RESISTANCE & RETENTION FORMS The secondary retention and resistance form are of two types…  1) Mechanical preparation feature  Retention locks, Grooves & Coves.  Groove Extensions, Skirts  Beveled Enamel Margins.  Pins, Slots, Steps, Amalgampins..  2) treatments of preparation walls with etching, priming &adhesive materials.  Enamel Wall Etching  Dentin Treatment . 
  25. 25. STEP 8: PROCEDURE FOR FINISHING THE EXTERNAL WALLS Finishing the preparation wall is the further development, when indicated, of a specific Cavo surface design & degree of smoothness or roughness that produces the maximum effectiveness of he restorative material being used.  Objectives:  1) create the best marginal seal possible between the restorative material and the tooth strcture.  2)afford a smooth marginal junction and  3) provide maximal strength of the tooth & the restorative material at & near the margin 
  26. 26. FEATURES1) the design of the cavosurface angle &  2) The degree of smoothness or roughness of wall.  . Cavosurface angle of 90° produces maximal. Strength for the amalgam & the tooth. No bevels an placed at the cavosurface margin.  Beveling can serve useful purpose in tooth preparation  1) It produces a strong enamel margin  2) If permits a marginal seal in slightly undersized. Casings. 
  27. 27. STEP. 9: FINAL PROCEDURE: CLEANING, INSPECTING. & SEALING  The usual procedure in cleaning is to free the. Preparation of visible debris with warm water from the syringe & then to remove the visible moisture with a few light surges of air from the air syringe .
  28. 28. THANK YOU