[Effects of saliva contamination on bond strength of resin-resin interfaces]

To estimate the bond strength between different resin composite interfaces, and to evaluate the effect of saliva contamination and management with the contamination on the bond strength.

Two commercial resin composites containing different types of fillers (AP-X: barium-glass; P60: quartz) were tested in this study. The basic composite blocks were made of AP-X. After wet-ground flatted, the experimental groups were divided into three groups according to the surface treatment: (1)Direct bonding group: the bonding surface was rinsed with distilled water for 20 s, then dried with oil-free air for 20 s; (2)Saliva contamination group: the bonding surface was bathed in saliva for 30 min, then distilled water was rinsed for 20 s and dried with oil-free air for 20 s; (3)Saliva contamination and 75% ethanol wiping group: bonding surface bathed in saliva for 30 min, then wipe the surface with 75% ethanol, distilled water rinse for 20 s and dry with oil-free air for 20 s; The control group was made of the basic composite bulks of AP-X directly bonding with composite P60. Cut each resin block into 1 mm×1 mm×14 mm sticks, observing the micro-structures and detecting the micro-tensile strength of the resin composite interfaces. The bonding strength was measured using micro-tensile tester, then calculated and statistically analyzed by one-way ANOVA.

Scanning electronic microscope observation revealed that the control group as well as the direct bonding subgroups, two different resin tags were in good contact with each other. The saliva contamination subgroups had lots of gaps or craters, indicating saliva might have been trapped in the composite buildup and wiping the surface with 75% ethanol had no effect. The micro-tensile bond strength of the control group was (84.07±1.57) MPa and significantly higher than all the other 3 experimental subgroups(P<0.001). In experimental groups, the micro-tensile strength of 3 subgroups was (76.08±2.42) MPa, (70.98±2.33) MPa and (71.08±2.33) MPa, respectively. The saliva contamination subgroup was significant lower than the direct bonding subgroup(P<0.001), but no statistical significance with the ethanol wiping subgroup(P=0.893).

The bond strength of inner polymerization of resin-resin was greater, but decreased after resin composites interfacial bonding. Saliva contamination reduced the tensile bond strength between resin composites surface, wiping the surface with 75% ethanol had no effect.