IMPROVING THE BONDING POTENTIAL
In this context, several researchers and manufacturers have begun developing strategies to improve dental adhesives’ infiltration ability and bonding performance on caries-affected dentin. Possible approaches include the use of a chemical cross-linker prior to application of etch-and-rinse adhesives and cleaning with mildly acidic hypochlorous acid before applying self-etch adhesives.2,3 Applying a chemical cross-linker (glutaraldehyde or grape seed extract) to the etched dentin surface seems to increase the stability of dentin collagen, which may inhibit enzymatic degradation, thereby helping improve the bond’s durability.2 In a laboratory study, the pre-treatment of caries-affected dentin with mildly acidic hypochlorous acid had a positive effect on the micro-tensile bond strength of a subsequently applied self-etch adhesive, presumably by removing gelatinized collagen from the surface.3 None of the pretreatments demonstrated a negative effect on adhesion to normal dentin. In order to eliminate the need for additional components and work steps, 3M focused on developing an adhesive with a new chemical composition designed to improve bonding and sealing caries-affected dentin.
At Piracicaba Dental School (UNICAMP) in Sao Paulo, Brazil, we decided to test the bonding performance of the new 3M™ Scotchbond™ Universal Plus Adhesive to caries-affected dentin. We began by applying the product to prepared samples of caries-affected dentin and sound dentin (as a control) in the etch-and-rinse or self-etch mode. Then the microtensile bond strengths were determined and the dentin-adhesive interfaces were evaluated with the aid of confocal laser scanning microscopy. The results show that the new adhesive delivers reliable bond strength to caries-affected dentin independent of the selected application mode, forms a continuous hybrid layer, and infiltrates deeply into the dentinal tubules to provide the required seal.
Figure 2: Confocal laser scanning microscopic images illustrating the morphological characteristics of 3M™ Scotchbond™ Universal Plus Adhesive (left) and its predecessor 3M™ Scotchbond™ Universal Adhesive (right) bonding to caries-affected dentin after application in etch-and-rinse mode. Scotchbond Universal Plus Adhesive shows a particularly deep diffusion of the resin monomers into the demineralized tissue.
HL = Hybrid layer
RT = resin tags
A = adhesive
RC = resin composite
CAD = caries-affected dentin
(Images courtesy of Dr. Mario De Goes and Dra. Carolina Garfias.)
Figure 3: Confocal laser scanning microscopic images illustrating the morphological characteristics of 3M™ Scotchbond™ Universal Plus Adhesive (left) and its predecessor 3M™ Scotchbond™ Universal Adhesive (right) bonding to caries-affected dentin after application in self-etch mode. Scotchbond Universal Plus Adhesive shows a particularly deep diffusion of the resin monomers in the demineralized tissue.
HL = Hybrid layer
RT = resin tags
A = adhesive
RC = resin composite
CAD = caries-affected dentin
In fact, Scotchbond Universal Plus Adhesive seemed to infiltrate deeper into the inter- and intra-tubular dentinal areas in the sound and caries-affected dentin compared to the control (3M™ Scotchbond™ Universal Adhesive), independent of the application mode, promoting a complete dentin seal in both. This is exactly what is needed to ensure reliable bonding outcomes in minimally invasive dentistry using selective caries removal techniques. The microtensile bond strength was above 30 MPa for both etching modes, which is on the same level as gold standard adhesives like 3M™ Scotchbond™ Multipurpose Adhesive or CLEARFIL™ SE Bond (Kuraray Noritake) on sound dentin, indicating a reliable performance.4
(Images courtesy of Dr. Mario De Goes and Dra. Carolina Garfias.)
