Shrinkage vectors in flowable bulk-fill and conventional composites: bulk versus incremental application

• DOI: 10.1007/s00784-020-03412-3
• Publication Date: 2020-07-11T12:02:30Z
• Authors: Dalia Kaisarly; Moataz El Gezawi; Andreas Keßler; Peter Rösch; Karl-Heinz Kunzel...
• Keywords: Dental Materials; 03 medical and health sciences; 0302 clinical medicine; Italy; Materials Testing; Humans; Original Article; X-Ray Microtomography; Dental Caries; Composite Resins; Polymerization

Abstract Objectives Sufficient depth of cure allows bulk-fill composites to be placed with a 4-mm thickness. This study investigated bulk versus incremental application methods by visualizing shrinkage vectors in flowable bulk-fill and conventional composites.

Materials and methods Cylindrical cavities (diameter = 6 mm, depth = 4 mm) were prepared in 24 teeth and then etched and bonded with OptiBond FL (Kerr, Italy). The composites were mixed with 2 wt% radiolucent glass beads. In one group, smart dentin replacement (SDR, Dentsply) was applied in bulk “SDR-bulk” (n = 8). In two groups, SDR and Tetric EvoFlow (Ivoclar Vivadent) were applied in two 2-mm-thick increments: “SDR-incremental” and “EvoFlow-incremental.” Each material application was scanned with a micro-CT before and after light-curing (40 s, 1100 mW/cm2), and the shrinkage vectors were computed via image segmentation. Thereafter, linear polymerization shrinkage, shrinkage stress and gelation time were measured (n = 10).

Results The greatest shrinkage vectors were found in “SDR-bulk” and “SDR-increment2,” and the smallest were found in “SDR-increment1-covered” and “EvoFlow-increment1-covered.” Shrinkage away from and toward the cavity floor was greatest in “SDR-bulk” and “EvoFlow-increment2,” respectively. The mean values of the shrinkage vectors were significantly different between groups (one-way ANOVA, Tamhane’s T2 test, p < 0.05). The linear polymerization shrinkage and shrinkage stress were greatest in Tetric EvoFlow, and the gelation time was greatest in “SDR-bulk.”

Conclusions The bulk application method had greater values of shrinkage vectors and a higher debonding tendency at the cavity floor.

Clinical relevance Incremental application remains the gold standard of composite insertion.