Comparison of premolar cuspal deflection in bulk or in incremental composite restoration methods.

OBJECTIVES: This study examined the cuspal deflection of maxillary premolars when either a bulk filling or incremental filling technique was employed using a range of composites with different elastic moduli.
METHODS: Four brands of composite materials, Heliomolar (HM, Ivoclar Vivadent, Schaan, Liechtenstein), Heliomolar HB (HH, Ivoclar Vivadent, Schaan, Liechtenstein), Filtec Supreme XT (FS, 3M Dental Product, St Paul, MN, USA), and Renew (RN, Bisco Inc, Schaumburg, IL, USA), as well as three filling techniques, bulk filling, two-layer incremental filling, and three-layer incremental filling methods, were used. One hundred twenty caries-free human premolars were collected and divided into four groups according to the filling material used. Each of these four groups was then subdivided into three groups according to filling method. In group 1, a bulk filling of 0.15 g of each resin was inserted and light-cured with LED light from the occlusal, mesial, and distal surfaces for 60 seconds each. Group 2 was given two horizontal increments, 0.08 g and 0.07 g, with each increment light-cured from the occlusal, mesial, and distal surfaces for 30 seconds each. In group 3, three horizontal increments of 0.05 g were used, each of which was light-cured from the occlusal, mesial, and distal surfaces for 20 seconds each. The cuspal deflection was measured using a customized cuspal deflection measuring machine for 10 minutes after initiating light polymerization. The elastic modulus of each composite resin material was measured using a three-point bending test. Two-way analysis of variance (ANOVA) with a Dunnet test was used to examine the effect of the two variables (curing methods, materials) on the amount of cuspal deflection at the 95% confidence level. In each material, groups 1, 2 and 3 were compared using one-way ANOVA and a Dunnet test at the 95% confidence level. The elastic moduli of HM, HH, FS, and RN were compared using one-way ANOVA and a Tukey test at the 95% confidence level. The relationship between the amount of cuspal deflection in each group and the elastic modulus of the composite was analyzed using a Pearson correlation test.
RESULTS: The amount of cuspal deflection in HH was larger than in the other materials (HM, FS, and RN; p<0.05). There was no significant difference between HM, FS, and RN. The amount of cuspal deflection was greatest in group 1, followed in order by groups 2 and 3 (p<0.05). The amount of cuspal deflection was in the following order: group 1≥2≥3 in HM, and 1>2, 3 in HH, FS, and RN. The elastic modulus was HH>RN>FS>HM (p<0.05). There was a positive correlation between the cuspal deflection and the elastic modulus of the composite.
CONCLUSIONS: The incremental filling techniques reduced the amount of cuspal deflection in all composite groups with different elastic moduli. The amount of cuspal deflection showed a positive correlation with the elastic modulus of the composite.