New cavity forms in second deciduous molars which maximize dentin thickness between cavity and pulp chamber.

This study was designed to devise configuratively ideal cavity formations using 49 second deciduous molars, consisting of 25 extracted from the maxilla and 24 from the mandible. A cavity having at least 1 mm subcavitary (below the cavity) dentin thickness at any point of measurement and having an appropriately formed and positioned retention was defined as an ideal cavity. The same methods were used as in our previous study of first deciduous molars. The following results were obtained: 1. In upper second deciduous molars, the subcavitary dentin thickness was thin at the mesiobuccal side of the cavity; it measured 0.9 mm. In lower second deciduous molars, the subcavitary dentin thickness was thin at the mesiobuccal, distolingual sides of the cavity, and central fossa, where the retentional groove was provided; it measured 0.8-0.9 mm. The other measured values exceeded 1.0 mm. All thickness measurements were very close to the values considered as ideal. 2. In upper second deciduous molars, the margins of the cavity were positioned medially to the summits of respective cusps, 1.8-2.0 mm at the buccal side and 1.5 mm at the lingual side. The entire cavity was located lingually. 3. In lower second deciduous molars, the buccal margin of the cavity was positioned 1.7 mm medially to the summit of the distobuccal cusp and 1.2-1.3 mm medially to the summits of the other buccal cusps. The lingual margin was positioned 1.4-1.5 mm medially to the summits of respective cusps. medially to the summits of respective cusps. 4. The buccolingual width of the cavity amounted to 1/3 of the distance between the summits of the buccal and lingual cusps in both upper and lower second deciduous molars. 5. At the mesial side, the depth of cavity was 1.4 mm at the buccal wall and 1.5 mm at the lingual wall in upper second deciduous molars, and 1.4 mm at the buccal wall and 1.6 mm at the lingual wall in lower second deciduous molars. 6. The width of gingival wall in the proximal box measured 1.0 mm in both upper and lower second deciduous molars.