The purpose of this study was to evaluate the effect of surface treatments on the
shear bond strength between new and old composites. Circular cavities prepared on the
center of acrylic resin mold and the prepared cavities were filled with composite resin.
They randomly assigned into control group and 8 groups according to the difference in
surface treatments of old composites; Control group : no surface treatment, Group 1:
surface treated wtih #120 SiC paper & bonding agent, Group 2: surface treated with
#400 SiC paper & bonding agnet. Group 3: surface treated with #120 SiC paper, 32%
H3PO4 & bonding agent, Group 4: surface treated with #400
SiC paper, 32% H3PO4 & bonding agent, Group 5: surface
treated with #120 SiC paper, primer & bonding agent, Group 6: surface treated with #400
SiC paper, primer & bonding agent, Group 7: surface treated with #120 SiC paper, 32%
H3PO4 primer & bonding agent, Group 8: surface treated
with #400 SiC paper, 32% H3PO4 primer & bonding agent
New composites were applicated on the old composites of experimental groups. The
shear bond strengths for the experimental specimen were mearsured and the results
were analyzed by using one way ANOVA. The observations of surface morphology
after SiC paper roughening and debonded surface morphology after shear bond strength
test were done by SEM.
The results were as follows: 1. Shear bond strengths for specimens roughened with
#120 SiC paper matching with the particle size of coarse diamond bur were significantly
higher than those for the specimens with #400 SiC paper(P<0.05). By SEM, the surface
of the specimens roughened with #120 SiC paper was more irregular than the specimens
with #400 SiC paper.
2. Shear bond strengths for specimens treated with 32%
H3PO4 etchant, primer, bonding resin were significantly
higher than those for specimens treated with 32% H3PO4
and bonding resin(P<0.05).
3. Shear bond strengths for specimens treated with 32%
H3PO4 etchant and bonding resin were significantly higher
than those for specimens treated with only bonding resin(P<0.05). There was no
remarkable change of surface morphology after 32% H3PO4
etching.
4. It was possible to observe mixed fracture patterns (the cohesive fracture of old
composite and the adhesive fracture between old and new composite) in the specimens
roughened with #120 SiC paper, but almost adhesive fracture in the specimens
roughened with #400 SiC paper.
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