Bonding to Sound vs Caries-Affected Dentin Using Photo- and Dual-Cure Adhesives
Howard E. Strassler, DMD
Say EC, Nakajima M, Senawongse P, Soyman M, Ozer F, Tagami J. Oper Dent.2005;30(1):90-98.
This study aimed to evaluate the microtensile bond strength (µTBS) of photo- and dual-cure adhesives to sound and caries-affected dentin using total- and self-etch techniques. Human third molars with occlusal caries were prepared as previously described by Nakajima and others (1995). Dentin surfaces were bonded with Optibond® Solo Plus (Kerr Corporation, Orange, CA; photo-cure adhesive) or Optibond Solo Plus + Dual-cure activator (dual-cure adhesive) with total- and self-etch technique. Clearfil® AP-X (Kuraray America, Inc, New York, NY) was used for composite buildups. Following storage in distilled water at 37 degrees C for 24 hours, the teeth were sectioned into 0.7-mm thick slices to obtain sound and caries-affected dentin slabs, then trimmed to form hour glass shapes with a 1 mm2 cross-sectional area. The specimens were subjected to microtensile testing using EZ-test (Shimadzu Corporation, Kyoto, Japan) at 1 mm/minute. Data were analyzed using 3-way ANOVA and Student’s t-Test (p<0.05). Bond strengths to sound dentin with photo- and dual-cure adhesives using total- and self-etch techniques were significantly higher than those to caries-affected dentin. Dual-cure adhesive significantly decreased bond strengths both to sound and caries-affected dentin. The total-etch technique showed no beneficial effect on caries-affected dentin compared with the self-etch technique. Scanning electron microscopic observation of the resin-dentin interfaces revealed that hybrid layers in caries-affected dentin were thicker than those observed in sound dentin with photo- and dual-cure adhesives. Resin infiltration into dentinal tubules of caries-affected dentin was hampered by the presence of mineral deposits.
No matter how one assesses the presence or absence of caries, there is no doubt that clinicians place adhesives and restore areas of caries-affected dentin. This study looks at both total- and self-etch systems with photo- and dual-cure adhesives with a composite core material for adhesion on sound dentin and caries-affected dentin. The results of this in vitro study reveal higher bond strengths to sound dentin than caries-affected dentin with all of the tested techniques. Also, the total-etch system was equivalent to the self-etch system on caries-affected dentin. Most importantly, and this research parallels other articles in this respect, the caries-affected dentin had lower tensile bond strengths, most likely as a result of a lack of resin tag hybridization to peritubular dentin. Also, the activator added to Optibond® Solo Plus (Kerr Corporation, Orange, CA) to make it dual-cure caused a significant decrease in bond strength when compared to light-cure only.
Although clinicians usually do not know whether or not the dentin is infected unless certain fusin-based caries disclosing dyes are used, the decrease in adhesion to caries-affected dentin seen in this study and to caries-infected dentin reported in other studies leads to the possible recommendation that one needs to be wary and not expect compromised dentin to have the seal and retention of sound dentin. Also, this study raises the issue that bonding to sound and caries-affected dentin were compromised when dual-cure adhesive was used. This should be kept in mind when restoring teeth, especially when using dual-cure adhesives with dual-cure composite resins used as cores for crowns.
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Howard E. Strassler, DMD