EXTENSION FOR PREVENTION - IS IT RELEVANT TODAY

Extension for prevention has been an integral part of dentistry for ov er 100 years. Because this concept advocated the removal of sound toot h structure, it was not totally accepted at the turn of the century. T he advent of the gold casting catapulted extension for prevention into general acceptance. In 1883, Webb presented a concept of ''prevention of extension of decay''. This concept advocated a proximal cavity pre paration extending toward the buccal and lingual aspects of the tooth so that contact with adjacent teeth would not be at the margins. The s eparation of the margins, along with proper restoration contours, was thought to promote natural cleansing of the embrasures with saliva and fluids in the diet. GV Black's 1891 idea of ''extension for preventio n'' was to provide extension of the preparation to the facial and ling ual line angles in order to bring about ''self-cleansing'' margins via food excursion. Black's concept also included extending preparations through fissures to allow cavosurface margins to be on non-fissured en amel. Black integrated the extension of the proximal margins with his concept of an occlusal isthmus for a Class II amalgam preparation one- third the faciolingual width of the occlusal surface. Challenges to th is concept of extension for prevention were immediate, and, by the 195 0's, narrower, more conservative preparations were seen by a few as be ing more effective in preserving teeth. Not only occlusal width was re assessed, but the need to routinely extend proximal margins to the buc cal and lingual line angles was also questioned. By the mid-1960's and early 1970's a more conservative approach to amalgam preparation was advocated and was being taught in some dental schools. Today, a standa rdized outline form should not be used or taught as a principle of cav ity preparation. In areas where fissure caries has necessitated a prep aration extending into dentin, a composite resin or dental amalgam res toration should be placed, and a fissure sealant should be used to pro tect remaining susceptible fissures from carious attack. This current form of the concept of extension for prevention, which is supported by clinical research, preserves sound tooth structure that, using outdat ed concepts, would have been cut away. Placing proximal margins in sou nd tooth structure that just clears an adjacent tooth is also strongly advocated. Sound enamel margins in certain areas may occasionally be left in contact with adjacent teeth for amalgam preparations. For Clas s II preparations for composite resin, facial or lingual proximal beve ls will usually suffice to separate the margins from the adjacent toot h to allow finishing and polishing at the margins. Preventing unnecess ary extension and allowing sounder tooth structure to remain is one im portant aspect of helping patients to maintain their teeth for their l ifetimes.