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

Dalia Kaisarly,Karl-Heinz Kunzelmann,Moataz El Gezawi,Andreas Keßler,Peter Rösch

doi:10.1007/s00784-020-03412-3

Abstract

ObjectivesSufficient 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 methodsCylindrical 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).ResultsThe 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.”ConclusionsThe bulk application method had greater values of shrinkage vectors and a higher debonding tendency at the cavity floor.Clinical relevanceIncremental application remains the gold standard of composite insertion.

Highlights

The main drawback of resin-based composites is their shrinkage upon polymerization, leading to shrinkage stresses with possible debonding from the cavity walls, interfacial gap formation, and microleakage [1, 2]
Smart dentin replacement (SDR) was evaluated in a Teflon mold with dimensions of 4 mm × 4 mm × 4 mm to simulate the bulk application (C-factor = 0.5)
SDR and Tetric EvoFlow were applied to the Teflon mold with dimensions of 2 mm × 4 mm × 4 mm (C-factor = 0.33)

Summary

Introduction

The main drawback of resin-based composites is their shrinkage upon polymerization, leading to shrinkage stresses with possible debonding from the cavity walls, interfacial gap formation, and microleakage [1, 2]. The consequences of polymerization shrinkage are usually evaluated only with indirect methods, such as volumetric or linear shrinkage measurements outside a cavity [1, 2] or linear cuspal deflection measurements evaluated inside a cavity [9]. Other indirect measurements of the adverse effects of polymerization shrinkage are interfacial adaptation assessments at the margin of a restoration and bond strength tests [10,11,12].

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