Research and Education
Additive effects of touch-activated polymerization and extended irradiation time on bonding of light-activated adhesives to root canal dentin

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Abstract

Statement of problem

The bonding of light-activated adhesives to root canal dentin with an additional touch-polymerization activator has been insufficiently examined.

Purpose

The purpose of this in vitro study was to investigate the effect of touch-polymerization activators and extended light-irradiation time on the microtensile bond strength (μTBS) of light-activated adhesives.

Material and methods

Post cavities were prepared in 50 extracted mandibular premolars and bonded using Prime&Bond Universal (PBU); PBU+Self Cure Activator (SCA); Clearfil SE Bond 2 (SEB); SEB+Clearfil DC Activator (DCA); or Clearfil Universal Bond Quick ER (UBQ). After light-irradiation for 10 or 20 seconds, the post cavities were filled with dual-activated resin core materials. Eight beams were prepared per specimen and subjected to the μTBS test. The μTBS data were analyzed by using 3-way ANOVAs with the Bonferroni correction (α=.05).

Results

The 3-way ANOVAs indicated that the use of touch-polymerization activators (SCA and DCA) significantly increased the μTBS of PBU and SEB in both the coronal (P=.015) and apical (P=.001) regions. The extension of light-irradiation time to 20 seconds significantly improved their μTBS in the apical region (P<.001), but not in the coronal region (P=.09). Light-irradiation for 20 seconds increased the μTBS of UBQ significantly in the coronal region (P=.014).

Conclusions

Touch-polymerization activators improved the bond strength of light-activated adhesives to root canal dentin, especially when combined with an extended light-irradiation time.

Section snippets

Material and methods

The study protocol was approved by the dental research ethics committee of Tokyo Medical and Dental University (No. D2013-022-03). Fifty single-rooted human mandibular premolars (length <21 mm), extracted for orthodontic purposes, were collected and stored in a 0.1% thymol solution at 4 °C. After the crowns were removed 2 mm coronal to the cementoenamel junction, the root canals were enlarged with K-files up to size 40, with the working length determined 1 mm from the apical foramen.

Results

The repeated measures ANOVA (Table 2) revealed that the effects of dentin region, bonding system, and light-irradiation time were statistically significantly different (P<.001). The interactions between the bonding systems and the dentin region were also significantly different (P<.001), whereas the interaction between light-irradiation time and both dentin region (P=.111) and bonding system (P=.221) were not. Moreover, the interaction among the 3 factors was also statistically similar (P

Discussion

The results of this study revealed that the addition of a touch-polymerization activator to light-activated adhesives SEB and PBU significantly improved their μTBS to root canal dentin. Hence, the first null hypothesis was rejected. The effect of extended light-irradiation time was significant according to the repeated measures ANOVA, but the 3-way ANOVA for SEB and PBU indicated that the extension significantly affected the bond strengths only in the apical region. Therefore, the second null

Conclusions

Based on the findings of this in vitro study, the following conclusions were drawn:

  • 1.

    The bond strength of light-activated adhesives to root canal dentin may be improved by extending the light-irradiation time and adding a touch-polymerization activator.

  • 2.

    Their effect may be additive, especially in the apical region, but it depends on whether the touch-polymerization activator contains an additional photoinitiator.

CRediT authorship contribution statement

Wahyuni S. Dwiandhany: Conceptualization, Methodology, Investigation, Writing - original draft. Ahmed Abdou: Methodology, Investigation, Formal analysis, Writing - review & editing. Antonin Tichy: Methodology, Writing - review & editing. Kazuhide Yonekura: Methodology, Investigation. Masaomi Ikeda: Validation, Writing - review & editing. Keiichi Hosaka: Conceptualization, Resources. Junji Tagami: Conceptualization, Resources, Supervision. Masatoshi Nakajima: Conceptualization, Methodology,

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  • Cited by (0)

    Supported by the Ministry of Education, Culture, Sports, Science and Technology of Japan (Grant Numbers 17K17125, 18K09571 and 19K10106) and by the Cooperation Program between TMDU and Sony IP&S, Inc scholarship to W.S.D.

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