J Korean Acad Conserv Dent.  2010 Mar;35(2):125-133. 10.5395/JKACD.2010.35.2.125.

Effect of the exponential curing of composite resin on the microtensile dentin bond strength of adhesives

• Seong SR
• Seo DK
• Lee IB
• Son HH
• Cho BH

• KMID: 2176300
• DOI: http://doi.org/10.5395/JKACD.2010.35.2.125

Abstract

OBJECTIVES
Rapid polymerization of overlying composite resin causes high polymerization shrinkage stress at the adhesive layer. In order to alleviate the shrinkage stress, increasing the light intensity over the first 5 seconds was suggested as an exponential curing mode by an LED light curing unit (Elipar FreeLight2, 3M ESPE). In this study, the effectiveness of the exponential curing mode on reducing stress was evaluated with measuring microtensile bond strength of three adhesives after the overlying composite resin was polymerized with either continuous or exponential curing mode.
METHODS
Scotchbond Multipurpose Plus (MP, 3M ESPE), Single Bond 2 (SB, 3M ESPE), and Adper Prompt (AP, 3M ESPE) were applied onto the flat occlusal dentin of extracted human molar. The overlying hybrid composite (Denfil, Vericom, Korea) was cured under one of two exposing modes of the curing unit. At 48h from bonding, microtensile bond strength was measured at a crosshead speed of 1.0 mm/min. The fractured surfaces were observed under FE-SEM.
RESULTS
There was no statistically significant difference in the microtensile bond strengths of each adhesive between curing methods (Two-way ANOVA, p > 0.05). The microtensile bond strengths of MP and SB were significantly higher than that of AP (p < 0.05). Mixed failures were observed in most of the fractured surfaces, and differences in the failure mode were not observed among groups.
CONCLUSION
The exponential curing method had no beneficial effect on the microtensile dentin bond strengths of three adhesives compared to continuous curing method.

Keyword

Polymerization shrinkage; Exponential curing; Dentin adhesive; Microtensile bond strength; Failure mode

MeSH Terms

Adhesives
Bisphenol A-Glycidyl Methacrylate
Chimera
Dentin
Humans
Light
Molar
Polymerization
Polymers
Resin Cements
Adhesives
Bisphenol A-Glycidyl Methacrylate
Polymers
Resin Cements

Figure

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  Figure 1 SEM micrograph of the bonded interfaces treated with 6 N HCl and 3.5% NaOCl of MP group. No cracks were observed at the junction of the adhesive layer and the hybrid layer or between adhesive layer and composite resin in both continuous curing group (a) and exponential curing group (b).

• 

  Figure 2 The failure mode distribution of tested specimens. C: continuous curing group, E: exponential curing group MP, Scotchbond Multipurpose Plus; AB, All Bond 2; AP, Adper Prompt.

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  Figure 3 SEM micrograph of the dentin surface of a debonded specimen in SB-continuous curing group. (a) Low magnification view (× 100). Adhesive failure and brittle failure pattern was observed. (b) High magnification view (× 1000). The dentinal tubules and fractured resin tags indicate failure at the interface between the adhesive layer and dentin.

• 

  Figure 4 SEM micrograph of the dentin surface of a debonded specimen in SB-continuous curing group. (a) Low magnification view (× 100). Mixed failure mode was observed through the adhesive layer (A), composite resin (R) and hybid layer (H). (b) High magnification view at the area H (× 1000). The dentinal tubules were covered partially by remnants of adhesive.

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