Fracture resistance of injectable resin composite versus packable resin composite in class II cavities: an in vitro study

Introduction
Restorative materials are constantly evolving due to strong demand for improving the esthetic quality, mechanical properties, and bonding longevity of materials.

Objectives
The aim of the study was to demonstrate that injectable resin composites may bridge the gap between packable resin composites and flowable resin composites.

Material and methods
Fifty extracted maxillary premolars were used in this study, out of which 40 were prepared with small class II box-only cavities and large class II occluso-mesial cavities. Cavities were restored either with injectable resin composite (G-ænial Universal Injectable) or packable resin composite (G-ænial Posterior). Teeth were randomly divided into five groups, with 10 samples in each group. Group 1 (m0c0): negative control, sound unprepared teeth; Group 2 (m1c1): injectable resin composite in small class II (box-only) cavities; Group 3 (m1c2): injectable resin composite in large class II occluso-mesial cavities; Group 4 (m2c1): packable resin composite in small class II box-only cavities; Group 5 (m2c2): packable resin composite in large class II occluso-mesial cavities. Fracture resistance was assessed by a universal testing machine that loaded the teeth axially at marginal ridges of restorations and cuspal inclines. Mode of failure of fractured specimens was analyzed under stereomicroscope whether fractures were restorable or non-restorable.

Results
There were no statistically significant differences between the fracture resistance in all five groups (p > 0.05). Moreover, no statistically significant differences were found between the mode of failure in all five groups (p > 0.05), and they were predominantly restorable.

Conclusions
Teeth restored with injectable resin composite in class II cavities showed comparable fracture resistance to teeth restored with packable resin composite.