Comparative study of shear bond strength between conventional etching and self-etching primer.

Research Abstract

Conventional adhesive systems involved etching, rinsing and priming the enamel surface prior to bonding orthodontic brackets to enamel. In order to facilitate the bonding procedure, reduce the clinical steps and save chairside time, self-etching primers were introduced in orthodontics to simplify the bonding steps and reduce the amount of enamel loss after etching. In an attempt to improve the reliability of bonding and save chairside procedures, APC (adhesive precoated) brackets were developed to simplify the bonding procedures as the manufacturer has eliminated the need to apply adhesive to the bracket base. The aim of this study was to evaluate shear bond strength durability of APCII adhesive system (adhesive precoated brackets) after using two different etching techniques; conventional phosphoric acid etching and etching with Transbond Plus Self-Etching Primer, to examine the site of bond failure with respect to the amount of the adhesive remained on the teeth after debonding and its relationship to the technique of etching and to determine which of the etching techniques gave the optimal bond strength. The study was carried on ninety extracted maxillary premolars collected from orthodontic extraction cases. The teeth were prepared for bonding procedures through polishing the enamel surface and the teeth were divided into two groups (each group containing forty-five teeth) according to the bonding protocols. The first group was bonded using the conventional etching technique. Phosphoric acid was used for etching, Transbond XT primer was applied and APCII brackets were bonded to the teeth. In the second group, Transbond Plus Self-Etching Primer was used for etching and priming the enamel surface in one step and then APCII brackets were bonded as in the first group. Each group was subdivided into three subgroups (each of them containing fifteen teeth) according to the storage time (24 hours, 30 days and 3 months). The shear bond strengths were tested, after each storage time, in a universal testing machine at a crosshead speed of 2 mm / minute and values were calculated in megapascals (MPa). After debonding, the site of bond failure was evaluated to determine the amount of adhesive remained on the teeth and each tooth was given a score according to that developed by Artun and Bergland (1984)(5). The results were statistically analysed and revealed the following: 1- The two etching techniques, phosphoric acid etching and etching with Transbond Plus Self-Etching Primer, gave optimal shear bond strength. 2- For phosphoric acid group, shear bond strength showed no significant difference between 24 hours and 30 days or between 30 days and 3 months while showed significant increase from 24 hours to 3 months. 3- For self-etching primer group, shear bond strength showed no significant difference in relation to time among the stages of testing. 4- There was no significant difference in shear bond strength between the two etching techniques at 24 hours and 30 days, while there was a highly significant difference (p ≤ 0.01) at 3 months, phosphoric acid was significantly higher than self-etching primer. 5- For phosphoric acid group, there was significant difference (p≤ 0.05) in ARI scores between 24 hours and 30 days, while there was no significant difference between 24 hours and 3 months or between 30 days and 3 months. 6- For self-etching primer group, there was no significant difference in ARI scores between 24 hours and 3 months, while there was a highly significant difference (P ≤ 0.01) between 24 hours and 30 days and a very high significant difference (P ≤ 0.001) between 30 days and 3 months. 7- At 24 hours and 3 months, there was a significant difference (p ≤ 0.05) in ARI scores between phosphoric acid etching and self-etching primer, while at 30 days there was a highly significant difference (P ≤ 0.01) in ARI scores between the two etching techniques. 8- For the three storage times, Transbond Plus Self-Etching Primer showed less adhesive remaining on the teeth than that of phosphoric acid etching. 9- At each time, self-etching primer showed a consistent pattern of bond failure (either cohesive at 24 hours and 3 months or at the enamel / adhesive interface at 30 days), while phosphoric acid etching showed variation in the mode of bond failure at the same time (mostly mixed mode of bond failure at 30 days and 3 months and at 24 hours showed cohesive failure and failure at the bracket / adhesive interface). 10- Spearman rank correlation coefficient showed no correlation between shear bond strength and ARI scores when phosphoric acid was used for etching, while showed a significant positive correlation when self-etching primer was used. Conclusions: 1- Transbond Plus Self-Etching Primer can be successfully used for bonding orthodontic brackets as it provided shear bond strength comparable to that of phosphoric acid. 2- The shear bond strength of phosphoric acid increased significantly with time, while the shear bond strength of Transbond Plus Self-Etching Primer showed no significant change as time passed. 3- Transbond Plus Self-Etching Primer showed less adhesive remaining on the teeth than that of phosphoric acid etching.

Research Keywords

Comparative study of shear bond strength between conventional etching and self-etching primer.