Microtensile Bond Strength and Failure Modes of Flowable Composites on Primary Dentin with Application of Different Adhesive Strategies

Abstract

Background: Resin composite is an option for the restoration of primary teeth, and new materials with simplified procedures are increasingly being suggested.

Aims: This study aims to evaluate the microtensile bond strengths and fracture modes of flowable composites on primary dentin with application of different adhesive strategies.

Materials and methods: Sixty extracted noncaries primary molars were abraded from buccal surfaces to expose dentin surface. The teeth were randomly divided into three groups as follows: Group 1, Vertise™ Flow (Kerr) (self-adhering flowable composite); Group 2, G-aenial Universal Flo^® (GC Europe) (used with one-step self-etch system); Group 3, Tetric^® N-Flow (Ivoclar/Vivadent) (used with two-step total etch system). Then, the flowable composites were applied to buccal dentin surfaces with the help of guide mold. Samples were embedded in acrylic blocks and sectioned to form dentin-composite sticks with a surface area of approximately 1 mm². Finally, a total of 180 sticks were obtained to give each group of 60 sticks. Microtensile bond strengths were measured using a universal testing machine (1 mm/min). Fracture modes were evaluated with scanning electron microscopy.

Statistical analysis: Microtensile bond strengths data were analyzed by Kruskal-Wallis nonparametric test.

Results: The microtensile bond strengths of G-aenial (15.5 megapascals [Mpa]) and Tetric (13.0 MPa) were statistically significant higher than Vertise (2.3 MPa). It was recorded that most of fractures in G-aenial was 40% cohesive, Tetric was 53.3% mixed, and Vertise was 83.3% adhesive.

Conclusions: The self-adhering flowable composite Vertise™ Flow had the lowest and G-aenial Universal Flo^® had the highest microtensile bond values.

Keywords: Bond strength; flowable composite; primary dentin; self-adhering.

Figure 1

The results of microtensile bond strength

Figure 2

The distribution of failure modes

Figure 3

As failure modes and typical empty dentin tubules showed in scanning electron microscopy images. (a) Vertise Flow-adhesive failure scanning electron microscopy, ×50. (b) Vertise Flow scanning electron microscopy, ×350. (c) Vertise Flow scanning electron microscopy, ×1200. (d) G-aenial Universal Flo^®-cohesive failure scanning electron microscopy, ×65. (e) G-aenial Universal Flo^® scanning electron microscopy, ×350. (f) G-aenial Universal Flo^® scanning electron microscopy, ×1200. (g) Tetric^® N-Flow-mix failure scanning electron microscopy, ×65. (h) Tetric^® N-Flow scanning electron microscopy, ×350. (i) Tetric^® N-Flow scanning electron microscopy, ×1200. Red arrow: Open dentin tubules. White arrow: Clogged with smear layer of dentinal tubules. Yellow arrow: Material remaining on dentin surface