Delayed light activation of resin composite affects the bond strength of adhesives under dynamic simulated pulpal pressure

Clinical Oral Investigations - To evaluate the effect of a time delay before the light activation of resin composite on the microtensile bond strength (µTBS) of self-etch adhesives under...     

Ultra-morphological characteristics of dentin surfaces after different preparations and treatments

Using transmission electron microscopy (TEM), this study investigated the characteristics of smear layers after preparation of dentin surfaces using different methods. In addition, this study analyzed, using scanning electron microscopy (SEM), the interactions of smear layers with the various acidic agents used subsequently to treat the dentin surface. Mid-coronal dentin surfaces were prepared according to one of five instrumentation methods: fracture; grinding with carbide bur; grinding with regular-grit diamond bur; grinding with superfine-grit diamond bur; or grinding with 600-grit silicon carbide (SiC) abrasive paper. Then, each prepared dentin surface was further divided into control (no further treatment) or treatment with one of the following agents: phosphoric acid solution (PAS); phosphoric acid gel (PAG); Clearfil SE Bond 2 Primer (SE2); or Scotchbond Universal Adhesive (SBU). Longitudinal ultra-thin sections were made for TEM observations. Dentin discs, representing each surface preparation and treatment method described above, were created, and the morphology was examined by SEM. The TEM results revealed differences in thickness and denseness of the smear layer, according to the different methods of instrumentation used to prepare the dentin surface. The two forms of phosphoric acid completely removed the smear layer in all groups. Agglomerated silica particles were observed on the top of the collagen layer after etching with PAG. For all dentin surfaces, except for that prepared with SiC, SE2 demonstrated better etching efficacy on different smear layers, whereas SBU provided only superficial interaction.     

Effect of topical fluoride application on enamel after in‐office bleaching,as evaluated using a novel hardness tester and a transverse microradiography method

This study evaluated the effect of topical fluoride application on enamel hardness after in‐office bleaching. Twelve human incisors were cut along the long axis, resulting in 24 halves used in four treatment groups (n = 6 in each group): (i) untreated group (C); (ii) in‐office bleaching material (B); (iii) treatment with surface reaction‐type prereacted glass‐ionomer varnish after in‐office bleaching (B+PRG); and (iv) treatment with acidulated phosphate fluoride solution after bleaching (B+F). All specimens were subjected to pH‐cycling for 4 wk. Knoop hardness was measured using a Cariotester. The decalcification of enamel was assessed quantitatively by measuring the integrated mineral loss (ΔIML). Games–Howell analysis was used to assess statistical significance of between‐group differences. The Knoop hardness decreased significantly after bleaching for all groups. In treatment groups B+PRG and B+F, the Knoop hardness returned to the original unbleached values after the first pH cycle and did not change afterwards. In treatment groups C and B there was a gradual decrease in the Knoop hardness until the fourth pH cycle. The integrated mineral loss, ΔIML, was significantly higher in treatment group B+F after 2 wk than in the other treatment groups. After 4 wk, the ΔIML in treatment group B was significantly higher than in treatment group B+PRG. The application of fluoride‐containing materials after bleaching results in recuperation of hardness to levels similar to those of unbleached enamel.     

Effect of air-blowing time and long-term storage on bond strength of universal adhesives to dentin

Objectives

To evaluate the effects of air-blowing time and storage time on microtensile bond strength (μTBS) of universal adhesives to dentin.

Materials and methods

Ninety flat dentin surfaces from extracted human third molars were bonded with three universal adhesives (Clearfil Universal Bond-CU; G-Premio Bond-GP; Scotchbond Universal Adhesives-SB). Bonded dentin surfaces were air-dried for 5 s, 15 s, or 30 s followed by resin composite built-up. Resin-dentin beams were tested with μTBS test after different storage time in distilled water (24 h and 1 year). Data were analyzed by three-way ANOVA and Duncan test at (α = 0.05). Failure mode and resin-dentin interfaces were observed using a scanning electron microscope (SEM). Specific features of fractured beams after μTBS were further observed using SEM at high magnification.

Results

Extension of air-blowing time from 5 s to 30 s increased the 24 h μTBS of CU only. Bond strength of all adhesives significantly decreased after 1-year storage except for CU at 5 s and 30 s of air-blowing time. One-year μTBS were significantly higher when air-blowing times were extended to 15 s for SB and 30 s for CU. Air-blowing time had no influence on GP.

Conclusion

The effect of air-blowing time and storage time on resin-dentin bond was material-dependent.

Clinical relevance

Extended air-blowing time increased the bond strength and bond durability of CU. Extension of air-blowing time to 15 s and 30 s improve the long-term bond strength of SB and CU, respectively.