Development of an in vivo model to investigate the effects of three adhesive removal methods around orthodontic brackets: A pilot study

Abstract

Background Orthodontic treatment has increased significantly over the last two decades, however the prevalence of biofilm related complications in the form of white spot lesions (WSLs) is still unquestionably prevalent. Orthodontic adhesives have been shown to be a critical factor for bacterial attachment and proliferation. With the increasing use of indirect bonding systems, advances in adhesive technology and lack of well-designed clinical trials, there is uncertainty regarding clinical guidelines for the management of excess adhesive around orthodontic brackets.

This study’s primary objectives were to develop a protocol to compare the effects of three removal methods of excess adhesive around enamel-bonded orthodontic brackets on the acidogenicity of the formed biofilm following 96 hours in vivo.

Methods

A prospective study involving participants wearing customised intraoral appliances containing six randomised bovine enamel discs (three on each side) with bonded orthodontic brackets to facilitate intraoral biofilm development.

Validation of pH acidogenicity was initially performed with a Streptoccocus mutans UA159 biofilm formed in vitro on bovine enamel discs containing orthodontic brackets and compared to stainless steel brackets on their own, following a glucose (10% w/v) challenge. The ion dissociation of sterile enamel discs was also tested on the pH assay.

To test the validity of a maxillary double vacuum-formed appliance, a volunteer wore the appliance continuously for four days containing enamel-bonded orthodontic brackets. Ninety-six hours was established as the optimum time for mature biofilm formation.

Eight healthy adult volunteers (age range = 25-39) wore customised maxillary double vacuum-formed appliances containing six bovine enamel discs (three on each side) with bonded orthodontic brackets for 96 hours. The three adhesive removal interventions (bur, no-removal and scaler) were randomised into canine, premolar or molar positions. The appliances were immersed in a sucrose solution (10% w/v) five times a day to facilitate biofilm growth.

pH measurements were done ex vivo on all biofilm bearing discs and control discs (absence of bacteria) following a glucose challenge (10% w/v). Cross sectional microhardness and elastic modulus measurements were obtained at the composite enamel interface and at the internal control (underneath the bracket).

Results

Six volunteers completed the study. There was no difference between adhesive removal methods on final pH after glucose challenge. There was a significantly lower final pH for the discs located at the premolar position (5.3 ± 0.1; p=0.006) and right side of the mouth (5.3 ± 0.1; p=0.009) compared to control discs (7.3 ± 0.2; p<0.001).

There was no significant difference between the interventions for the microhardness and elastic modulus at the enamel-composite interface. There was a significant difference for the microhardness and elastic modulus at the internal control (underneath the bracket) between the scaler, bur and no removal interventions (p≤0.05) and canine, premolar and molar positions (p<0.05).

Conclusion

There is no significant difference between adhesive removal method around orthodontic brackets on the formation of an acidogenic biofilm in low risk individuals. The location in the mouth is highly correlated with creation of a cariogenic biofilm.