Download Rebonding Strength of Resin Composite to Enamel Objective: The

Rebonding Strength of Resin Composite to Enamel
Objective: The objective was to examine the effect of removing the top layer of enamel on the
rebonding strength of resin composite to enamel.
Materials and methods: 50 extracted human molars were divided into five groups and treated
differently (n=10): the first group was left intact as a control group, and in four other groups a surface
(Ø3,6mm) of smooth, flat enamel was exposed by grinding. The enamel was etched (3M Unitek
Etching Gel) for 15s and a small amount of orthodontic adhesive (TransbondXT) was bonded to
measure debonding strength (so-called shear bond strength). Enamel underneath the debonded
adhesive was left as such or ground for different lengths of time (Groups: no grinding (0s), 10s, 20s,
30s), then etched and rebonded. The rebonding strengths were plotted against the grinding time, ie.
amount of enamel loss. The amount of enamel loss in grinding was determined with additional
measuring-samples: 7μm (±2) for 10s-group, 12μm (±1) for 20s-group and 16μm (±3) for 30s-group.
Samples were also imaged using SEM to observe the effect of different treatments on the enamel
surface.
Results: The bond strength to intact enamel was 17.2MPa (±4.9) and the rebonding strength of 0sgroup 14.3MPa (±3.6), 10s-group 16.1MPa (±3.3), 20s-group 16.3MPa (±4.8), and 30s-group 18.0MPa
(±4.3). Although there was trend between the increase of rebonding strength and grinding time
before rebonding (Fig.1.), ANOVA did not show statistical differences between groups (p>0.05). Inside
the groups, the values between first bonding and rebonding strengths differed significantly in 0s
group (p<0.05). In all the groups with ground enamel, the SEM micrographs revealed an enamelsurface that etched well, compared with the debonded sample surface without grinding which still
contained adhesive remnants (Pictures 1-3).
Conclusions: Removal of small amount of enamel refreshed the surface for rebonding. Longer
grinding times showed a trend to improve bond strength further.