Abstract
This study aimed to analyze the shear bond strength (SBS) of ceramic orthodontic brackets bonded with two different adhesive systems to intact and eroded teeth. Ceramic brackets were bonded to 72 bovine central incisors divided into four groups, defined by two study factors: enamel condition (control group, kept in artificial saliva; and experimental group, eroded by using immersion cycles in Coke™ for 90 seconds, every six hours for five days), and adhesive system type (Transbond™ XT or Transbond™ Plus Color Change). Polycrystalline ceramic brackets were adhesively fixed on all specimens using the same light curing protocol. SBS was tested using 0.5 mm/min and the failure mode was classified. SBS data was analyzed using two-way ANOVA followed by Tukey test. The adhesive remnant index (ARI) scores were analyzed using Kruskal-Wallis test with Dunn's post-hoc pairwise comparison (α=0.05). Percentages of ARI scores between the groups were compared by Fisher’s exact test. Spearman's correlation coefficient was applied to investigate the correlation between ARI scores and SBS values. Only the adhesive system factor had significant effect on SBS (p=0.014), Transbond™ Plus Color Change showing higher values. No significance was found for enamel condition (p=0.665) or the interaction between adhesive system and enamel condition (p=0.055). ARI scores frequencies differed between groups (p<0.001). The median ARI scores were statistically different for most comparisons among the groups. However, no significant correlation was found between ARI scores and SBS. In conclusion, the type of adhesive system affected the SBS of ceramic brackets to dental enamel, but the enamel condition, intact or eroded, had no significant effect. There was no correlation between ARI scores and SBS values, although eroded enamel tended to retain more adhesive after bracket removal.
Highlights
Bonded brackets are routinely used in fixed orthodontic therapy, being of great importance to achieve adequate bond strength between the bracket and the enamel surface (Cozza et al 2006)
There was no correlation between adhesive remnant index (ARI) scores and shear bond strength (SBS) values, eroded enamel tended to retain more adhesive after bracket removal
scanning electron microscope (SEM) images showed that specimens immersed in artificial saliva did not suffer any erosion, while those immersed in CokeTM showed significant erosion on the enamel surface (Figure 2)
Summary
Bonded brackets are routinely used in fixed orthodontic therapy, being of great importance to achieve adequate bond strength between the bracket and the enamel surface (Cozza et al 2006). Dental erosion comprises an acid-induced wear, characterized by initial softening of the enamel surface, followed by continuous layer-by-layer dissolution of the enamel crystals, leading to a permanent loss of tooth volume (Lussi et al 2011). It is a common problem in modern societies due to the increased consumption of acidic beverages, such as soft drinks, sports drinks, fruit juices, and teas, which present a high potential to provoke dental demineralization (Correr et al 2009). It is a consensus that there is a rising prevalence of dental erosion among children, adolescents, and adults, as a result of the increased consumption of those acid drinks, added to psychosomatic eating disorders and current lifestyles (Gambon et al 2012)
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