Abstract:
The objective of this study was to evaluate the effect of smear layer on dentin
microtensile bond strength (μTBS) and morphology of hybrid layer under SEM and TEM
when two self-etching adhesive systems (Clearfil SE Bond and Clearfil S3 Bond) were
employed. Flat coronal dentin surfaces of one hundred and forty eight extracted human third
molars were produced using either a cylindrical medium grit diamond bur or a cylindrical
carbide bur. Ten teeth treated with diamond burs, and 10 teeth treated with carbide burs, were
sectioned parallel to the flat coronal dentin surface, cracked at the middle and evaluated for
thickness of smear layer under SEM. One hundred and twenty eight teeth were restored with
resin composite with four application techniques of adhesives (following of instruction,
agitation, reapplication and increased time). Restored teeth were divided into three subgroups
for evaluation of μTBS, morphology under SEM & TEM. Eighty teeth (40 teeth treated with
diamond burs and 40 teeth treated with carbide burs) were evaluated μTBS in subgroups. For
evaluation of hybrid layer, thirty two (16 teeth treated with diamond burs and 16 teeth treated
with carbide burs) were examined under SEM in subgroups and sixteen teeth (8 teeth treated
with diamond burs and 8 teeth treated with carbide burs) were examined under TEM in
subgroups. The results demonstrated that the thicknesses of smear layer and irregularity on
dentin surfaces treated with diamond burs were higher than the surfaces with carbide burs
(p≤0.01). For microtensile bond strength test, the effect of the bur was observed. Use of
carbide bur produced higher bond strength than that using a diamond bur within the same
type of adhesive resin. Effect of materials was observed. Clearfil SE Bond demonstrated
higher bond strength than Clearfil S3 Bond for all surfaces. Effect of application techniques
were also demonstrated. Clearfil S3 Bond applied with agitation technique demonstrated
higher bond strength to dentin treated with carbide or diamond burs than the other techniques
(p≤0.05). On surfaces treated with carbide burs, no significant differences of bond strengths
were found among the groups in which an adhesive was applied with increased time,
reapplication or following instruction (p>0.05). On surfaces treated with diamond burs, no
significant differences of bond strengths between the application with following instruction
and increased time groups were found (p>0.05). Clearfil SE Bond produced the highest bond
strength when the adhesive was applied with increasing time on dentin treated with carbide
bur. No significant differences of bond strength among reapplication, agitation and following
instruction technique were found when the adhesive was applied on dentin treated carbide bur
(p>0.05). There were no significant differences of bond strengths to dentin treated with
diamond bur between application with following instruction and agitation (p>0.05) and
between reapplication with agitation and increased time (p>0.05).The difference of hybrid
layer could not be determined under SEM with the thickness of 1-3 μm. Diamond bur
produced thicker hybridized smear layer than carbide bur under TEM.