Evaluation of add-on methods for bis-acryl composite resin interim restorations

Interim restoration materials should allow easy add-on for repair and modification; however, bis-acryl composite resins are reported to have unfavorable performance in this regard.

The purpose of this study was to find a suitably effective add-on method for bis-acryl interim composite resins.

A control group with a new type of bis-acryl material added to the same bis-acryl disks (n=10) was compared to 9 experimental groups (n=20) divided on the basis of their surface conditions: oxygen-inhibited unpolymerized layer preserved; ground; ground and treated with a light-polymerizing bonding agent, with or without a synthetic polyester film (Mylar) cover strip to control oxygen-inhibited unpolymerized layer; with bis-acryl, bis-GMA flowable composite, or poly-methyl methacrylate (PMMA) resins as add-on materials. PMMA specimens added with PMMA resin served as a parallel control group (n=20). Half of the experimental and PMMA control specimens were thermocycled 2000 times at 5 ±2°C and 55 ±2°C. Shear bond strength (SBS) results were then compared using 2-way and 1-way ANOVA and a Tukey honest significant difference (HSD) test (α=.05).

No significant differences were found between SBS of PMMA and those of bis-acryl controls (21.74 and 17.47 MPa, respectively), with all of the experimental groups exhibiting values comparable to the controls and unaffected by thermocycling. The highest SBS (35.58 MPa) was obtained with the bis-GMA-added group, in which the surface was ground and treated with a bonding agent (P<.05). With the bis-acryl resin and bonding agent group, additional light polymerizing significantly increased the SBS from 15.58 to 23.80 MPa (P<.05).

Bis-acryl-based interim material has favorable add-on properties, which are improved by additional surface treatment and use of a flowable composite resin.