Class III cavity preparation in primary anterior teeth: in vitro retention comparison of conventional and modified forms.

Management of mild to moderate caries in primary anterior teeth is still a problem. Presently, class III composite restorations in primary teeth have inadequate retention. The purpose of this in vitro study was to analyze the influence of the design of modified class III cavity preparation on the retention of the restoration when compared to that of the conventional class III preparation. Thirty extracted human primary maxillary central incisors were divided into two groups of 15 teeth each. In one group, the conventional (triangular) class III design was prepared. The second group, the modified class III design, was prepared by adding to the conventional form, 0.5 mm. labial reduction on the labial tooth surface. The dentinal bonding agent, Amalgambond, was applied to 30 teeth according to instructions of manufacturer. The composite resin, Herculite XRV, was inserted into each preparation. All samples were mounted in plastic molds and thermocycled. The samples were tested with Instron testing machine until restoration failure. Results showed that the mean failure load of modified class III restoration group (92.19 +/- 13.6 N) was significantly higher from that of conventional class III preparation group (45.61 +/- 9.8 N) as tested by Student's independent t-test (P < 0.001).