class 1 cavity Definition: Pit and fissure cavities that involves: 1- Occlusal surface of molars and premolars. 2- Occlusal 2/3 of buccal and lingual surface of molars. 3- Palatal pits in maxillary anterior teeth. 1st: Outline form: There are 2 important guidelines: (1) carious tooth structure should be eliminated (2) margins should be placed on sound tooth structure. Any enamel that has been undermined by the removal of carious dentin should be removed ( the fissure should not extended , instead it would be sealed after the amalgam has been placed). External: 1- Sweeping curves. 2- In upper premolar, buccal wall (convex curved), lingual (Semi- straight). 3- Buccal pit cavity in lower molars - triangular. 4- Buccal pit cavity in upper molars- round. 5- Lingual pit in upper anterior - oval Internal: 1- lingual and buccal wall should be parallel to the respective tooth surface or converge occlusally). 2- Mesial and distal walls should be diverging from pulpal floor to prevent undermining the marginal ridges. 3- pulpal floor should be perpendicular to long axis of the tooth except in lower first premolar, and parallel to occlusal plane in order to: A- to bring force perpendicular to floor. B-Susceptibility to pulp exposure. 4- Preparation should be widened only to obtain enamel margins supported by sound dentin. 5- No sharp angle ( although that , sound tooth structure should not removed so easily for that). 6- Dentine ledge is an option to prevent rotation. 2nd: Resistance form: 1- Cavosurface angle should be 90° (To have sufficient bulk to prevent fracture of amalgam). **Notes: If : Angel >90° - amalgam fracture or restoration fracture. Angel
Posted on: Sat, 24 Aug 2013 20:35:06 +0000
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