Abstract
We examined the suitability of various cavity preparations for composite resin restoration of a complex cavity developed on the proximal surface of a deciduous molar. Factors contributing to the selection of composite resins and filling method were also examined Artificial deciduous mandibular second molars made of epoxy resin were prepared, then a cavity was made on the gingival wall with a width of 1 or 2 mm and one of three types of margins (straight, flare, reverse-curve). The resulting six types of dental cavities were filled with one of the following composite resins or a combination of two (combination filling) : SOLARE P (paste-type), UnifilⓇLoFlo Plus (flowable-type), and MI Flow (flowable-type). In combination filling, a flowable resin and paste-type resin were filled into the lower and upper layer, respectively. Compression tests of the margin and junction areas of the cavity were performed using a device that applied a compressive load onto the cusp tip. Testing revealed the following.1.Compressive strength was lower in the margin than the junction area, regardless of cavity preparation design, type of composite resin used, and filling method, suggesting a higher risk of fracture in the margin.2.A reverse-curve margin design with the widest possible gingival wall and without causing pulp exposure is desirable for maintaining adequate thickness of the restoration and the dentin margin. This will consequently prevent fracture in the margin region.3.When the cavity margin opens outward, a thin gingival wall is likely to result with low compressive strength.4.When treating a cavity with an outward-opening margin that has developed over a wide area on the proximal surface, it is beneficial to prepare the cavity with sufficient gingival wall width and use composite resins with high compressive strength to prevent fracture in the margin area.5.Use of a flowable resin for the lower layer and conventional paste-type resin for the upper layer provides an effective filling method that improves clinical efficiency and compressive strength.Together, our results suggest that it is important to prepare an appropriate margin and cavity wall width when filling a complex cavity on the proximal surface of a deciduous molar. Furthermore, a selected combination of composite resins has an effect on the prognosis of a restored tooth.
