Influence of cavity dimension and restoration methods on the cusp deflection of premolars in composite restoration

Objectives The aim of this study was to measure the cusp deflection by polymerization shrinkage during composite restoration for mesio-occluso-distal (MOD) cavities in premolars, and to examine the influence of cavity dimension, C-factor and restoration method on the cusp deflection. Methods Thirty extracted maxillary premolars of similar size were prepared with four different sizes of MOD cavity, and divided into six groups. The width and depth of the pulpal wall of the cavity were as follows: group 1: 1.5 × 1 mm, group 2: 1.5 × 2 mm, group 3: 3 × 1 mm, and groups 4–6: 3 × 2 mm. Groups 1–4 were restored using a bulk filling with a composite. Group 5 was restored incrementally, and group 6 was restored with an indirect composite inlay. Cusp deflections were measured using LVDT transducers. The cusp deflections were compared between groups using ANOVA and Scheffe tests, and a correlation analysis was done. Results The cusp deflections of groups 1–4 were 12.1 (2.2), 17.2 (1.9), 16.2 (0.8) and 26.4 (4.2) μm, respectively. There was a strong positive correlation between the length cubed divided by the thickness cubed of the remaining cusp (L3/T3) and cusp deflection. The C-factor was related to the % flexure (100 × cusp deflection/cavity width). The cusp deflections of groups 5 and 6 were 17.4 (2.0) and 17.9 (1.4) μm, respectively, which were much lower values than those of group 4. Significance : The cusp deflection increased with increasing cavity dimension and C-factor. Use of an incremental filling technique or an indirect composite inlay restoration could reduce the cuspal strain.