Fractographic Analysis of Dentin-composite Interface After Micro-tensile Bond Test

Objectives: Effects of flowable lining bonded to coronal and cervical dentin on the micro-tensile bond strength and internal fracture after the bond test were evaluated in this study using swept-source optical coherence tomography (SS-OCT).
Methods: Coronal and cervical dentin of human extracted molars was exposed and polished with 600-grit SiC paper to obtain flat surface. Two step self-etch adhesive (Clearfil SE Bond, Kuraray Noritake Dental) was applied to dentin in conjunction with a resin composite AP-X (Kuraray) with or without flowable composite lining (Estelite flow quick, Tokuyama Dental). After the photo curing, the samples from coronal and cervical dentin with and without flowable liner were stored in 37⁰C water for 24 hours, followed by sectioning beam of 1.00 mm² for micro tensile bond test. The micro-tensile bond test were performed with crosshead speed of 1mm/min (n = 43). The debonded specimens were then observed by SS-OCT with the scanning beam perpendicular to the interface. The images of SS-OCT were analyzed using ImageJ to quantify the internal cracks. The area of cracks appeared as white spots and lines within dentin were detected in SS-OCT and defined as crack area. Statistical analysis was performed at a significance level of α = 0.05.
Results: Mann-Whitney's U-test with Bonferroni's correction showed that the micro-tensile bond strength of with flowable composite on cervical dentin was significantly lower than other groups (p<0.05). The groups of cervical dentin exhibited percentage of crack area significantly higher compared to the groups of coronal dentin (p<0.05). Whereas there was no so such significant difference between groups with flowable composite lining and no lining (p>0.05).
Conclusions: The micro-tensile bond strength decreased in the group with flowable lining on cervical dentin. Dentin cracks after the micro-tensile bond test were significantly higher in the groups at cervical dentin.