The influence of the dentin smear layer on adhesion: a self-etching primer vs. a total-etch system.
OBJECTIVE
To determine the effect of dentin smear layers created by various abrasives on the adhesion of a self-etching primer (SE) and total-etch (SB) bonding systems.


METHODS
Polished human dentin disks were further abraded with 0.05 micro m alumina slurry, 240-, 320- or 600-grit abrasive papers, # 245 carbide, # 250.9 F diamond or # 250.9 C diamond burs. Shear bond strength (SBS) was evaluated by single-plane lap shear, after bonding with SE or SB and with a restorative composite. Smear layers were characterized by thickness, using SEM; surface roughness using AFM; and reaction to the conditioners, based on the percentage of open tubules, using SEM.


RESULTS
Overall, SBS was lower when SB was used than when SE was used. SBS decreased with increasing coarseness of the abrasive in the SE group. Among burs, the carbide group had the highest SBS, and 320- and 240-grit papers had SBS close to the carbide group. Surface roughness and smear layer thickness varied strongly with coarseness. After conditioning with SE primer, the tubule openness of specimens abraded by carbide bur did not differ from 240- or 320-grit paper, but did differ from the 600-grit.


CONCLUSIONS
Even though affected by different surface preparation methods, SE yielded higher SBS than SB. The higher SBS and thin smear layer of the carbide bur group, suggests its use when self-etching materials are used in vivo. Overall, the 320-grit abrasive paper surface finish yielded results closer to that of the carbide bur and its use is recommended in vitro as a clinical simulator when using the SE material.
D000537:Aluminum Oxide / Q000737:chemistry; D002244:Carbon / Q000737:chemistry; D003188:Composite Resins / Q000737:chemistry; D001840:Dental Bonding; D045662:Dental Etching / Q000379:methods*; D003804:Dentin / Q000648:ultrastructure*; D017220:Dentin-Bonding Agents / Q000737:chemistry*; D018130:Diamond / Q000737:chemistry; D006801:Humans; D008422:Materials Testing; D018625:Microscopy, Atomic Force; D008855:Microscopy, Electron, Scanning; D012822:Silicon Dioxide / Q000737:chemistry; D016369:Smear Layer; D013314:Stress, Mechanical; D013499:Surface Properties
D003188:Composite Resins; D017220:Dentin-Bonding Agents; D002244:Carbon; D012822:Silicon Dioxide; D018130:Diamond; D000537:Aluminum Oxide