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

• Published in: Clinical oral investigations Vol. 25; no. 3; pp. 1127 - 1139
• Main Authors: Kaisarly, Dalia, El Gezawi, Moataz, Keßler, Andreas, Rösch, Peter, Kunzelmann, Karl-Heinz
• Format: Journal Article
• Language: English
• Published: Berlin/Heidelberg Springer Berlin Heidelberg 01.03.2021; Springer Nature B.V
• Subjects: Composite Resins; Computed tomography; Dental Caries; Dental Materials; Dentin; Dentistry; Gelation; Glass beads; Humans; Image processing; Italy; Materials Testing; Medicine; Original; Original Article; Polymerization; Segmentation; X-Ray Microtomography; Italy; Flowable bulk-fill composite; Bulk application; Incremental application; Shrinkage vectors; Total-etch technique; Medical image registration
• ISSN: 1432-6981; 1436-3771
• DOI: 10.1007/s00784-020-03412-3

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/cm 2 ), 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.