Experimental Study On Enamel Demineralization Of UsingSelf-etching Adhesives In Orthodontic Bonding

Objective Under a pH cycling experiment, to investigate the effects on enamel demineralization when self-etching adhesives were used to condition the enamel surface before bonding and provide the basis of theory for self–etching adhesives applied in clinical orthodontic bonding frequently.Methods Twenty (ten pairs of) human maxillary and mandibular premolars ,extracted for orthodontic purpose, were used in this study. The samples were randomly divided into two groups: In the control group, teeth were etched with 37% phosphoric acid, the brackets were bonded with composite resin; In the experimental group, the enamel was conditioned with self-etching primer, and the brackets were bonded with TransbondXT. All samples were under the pH cycling experiment each day. In 4 and 8 weeks, demineralization lesions under the orthodontic bracket and the enamel-resin interface were evaluated by eyes, adhesive remnant index scores, the hardness of enamel, the scanning electronic microscope, transmitting light microscope.Results After 4 weeks pH cycling study, randomly selected five samples in experimental group, also in control group. Removing orthodontic brackets at first, observing the residual adhesive remaining on the teeth and taking notes. Cleaned and dried the surface of tooth, observed the zone under the bracket,in control group, the surface of enamel presented gray color, and there was no apparent change on enamel in experimental group. In 8 weeks, the surface of enamel in control group,s sample presented the chalklike spot , and probing felt rough. In experimental group, only slight luster change. The adhesive remnant index was scored after debonding, a comparison of the ARI scores indicated that there was more residual adhesive remaining on the teeth that were treated with conventional acid etching than in the self-etching primer group. The hardness of enamel were measured by microhardness detected(KHN):In 4 weeks, compared with the control group, the KHN of experimental group was higher, but there was no significant difference (P>0.05). In 8 weeks, the KHN of all groups were lower than in 4 weeks, and the experimental group had significantly higher KHN than that in the control group(P<0.01). The present in findings indicate that the demineralization of enamel had serious tendency followed time goes. Besides the demineralization of control group more serious. Scanning electro microscopic examination: In 8 weeks, an irregular but smooth hybrid layer on enamel surface of experimental group, there were shallow hollows. But in control group, a distinct honeycombed structure on enamel surface, the holes were deep and crowed. The...