Does chlorhexidine affect the shear bond strengths of orthodontic brackets?

Blue light & chlorhexidine therapies on Streptococcus mutans biofilm and its regrowth on an in vitro orthodontic model

INTRODUCTION

Fixed orthodontic appliances create areas of stagnation for dental biofilms and make it difficult to clean the teeth; therefore, there is a risk of developing incipient caries lesions during the orthodontic treatment. The objective of this study is to determine if the combination of 2 different therapies, phototherapy by blue light (BL) and the antimicrobial 0.12% chlorhexidine (CHX) on enamel, orthodontic brackets, and elastics, would reduce or inhibit mature Streptococcus mutans biofilms and their regrowth on these substrates 24 hours after the application of the treatment; and if this treatment would interfere with bracket adhesion to the enamel.

METHODS

Biofilms of S. mutans UA159 were formed for 5-days over samples composed of a bovine enamel, orthodontic bracket, and orthodontic elastic. Then, the specimens were treated with 0.89% NaCl for 1 minute, BL for 12 minutes (72 J/cm²), 0.12% CHX for 1 minute, and BL for 12 minutes, followed by 0.12% CHX for 1 minute (BL+CHX). Biofilm was evaluated by colonies forming units and dry weight immediately after treatments and 24 hours after treatments (regrowth). The pH of the spent media was measured on the fifth and sixth days. Biofilm formation on the samples after the treatments and regrowth was visually evaluated by confocal laser scanning microscopy. Shear bond strength (SBS) between bracket and enamel was evaluated using a universal testing machine at a crosshead speed of 1 mm/min. After bonding, specimens were thermocycled (500× at 5-55°C), treated, and thermocycled again.

RESULTS

After 5 days of biofilm formation, BL+CHX significantly reduced the bacterial viability on enamel compared with NaCl (P = 0.004) and BL (P = 0.014). For bracket and elastic, all the treatments resulted in similar bacterial viability (P ≥0.081). In the regrowth, CHX and BL+CHX significantly reduced the bacterial viability in the enamel compared with the NaCl (P ≤0.015) and BL (P ≤0.013). For bracket, BL+CHX significantly reduced the bacterial viability compared with NaCl (P = 0.008) and BL (P = 0.009). For the elastic, BL+CHX eliminated the biofilms from the substrate. CHX and BL+CHX significantly reduced the bacterial viability 24 hours after treatment for all substrates (P ≤0.05). The media pH significantly increased when samples were treated with CHX and BL+CHX (P ≤0.001). Confocal laser scanning microscopy images visually showed an abundant quantity of red cells in the samples treated with BL+CHX. There was no difference in the SBS between the treatments (P ≥0.932).

CONCLUSIONS

The association between BL and CHX reduced S. mutans biofilm and its regrowth on an in vitro orthodontic model and did not influence the bonding strength between bracket and enamel.

Effect of high concentration nano-hydroxyapatite serum on shear bond strength of metal brackets following three different enamel surface preparation methods: An in vitro study

OBJECTIVE

White spot lesion (WSL) is one of the most important complications of fixed orthodontic treatment. Many methods have been studied to prevent this problem. This study is aimed to investigate the effect of high concentration nano-hydroxyapatite (nHAP) on shear bond strength (SBS) of metal brackets and Adhesive Remnant Index (ARI) score in different preparation methods.

MATERIAL AND METHODS

Sixty human premolars, which were extracted for orthodontic reasons were included in this in vitro study. The teeth were randomly divided into 4 groups of 15 each: one control group and three nHAP groups. After applying nHAP for 2 to 3 minutes daily for 10 days, the groups 2 to 4 underwent sandblasting using 50μm aluminium oxide and 30 seconds etching, 60 and 30 seconds etching, respectively, and the brackets were then bonded to the teeth. After debonding, SBS and ARI scores were recorded. Data were analysed using the ANOVA test and posthoc test for pairwise comparisons.

RESULTS

No significant difference was observed in SBS between the control group and the nHAP groups. The sandblasted teeth showed significantly higher SBS than the 30 seconds etching after nHAP application (P=0.02). The teeth etched for 60 seconds showed a significantly higher ARI score than the 30 seconds etched teeth with (P=0.003) or without (P<0.001) nHAP application.

CONCLUSIONS

The use of nHAP before bracket bonding can be considered as a caries preventive method since it did not compromise the SBS. Sixty seconds etching is recommended for less likely damage to the enamel after debonding.

Chlorhexidine salt-loaded polyurethane orthodontic chains: in vitro release and antibacterial activity studies

The widespread use of indwelling medical devices has enormously increased the interest in materials incorporating antibiotics and antimicrobial agents as a means to prevent dangerous device-related infections. Recently, chlorhexidine-loaded polyurethane has been proposed as a material suitable for the production of devices which are able to resist microbial contamination. The aim of the present study was to characterize the in vitro release of chlorhexidine from new polymeric orthodontic chains realized with polyurethane loaded with two different chlorhexidine salts: chlorhexidine diacetate or chlorhexidine digluconate. The orthodontic chains constituted of three layers: a middle polyurethane layer loaded with chlorhexidine salt inserted between two layers of unloaded polymer. In vitro release of chlorhexidine diacetate and digluconate from orthodontic chains loaded with 10% or 20% (w/w) chlorhexidine salt was sustained for 42 days and followed Fickian diffusion. The drug diffusion through the polyurethane was found to be dependent not only on chlorhexidine loading, but also on the type of chlorhexidine salt. The antibacterial activity of 0.2% (w/w) chlorhexidine diacetate-loaded orthodontic chain was successfully tested towards clinically isolated biofilm forming ica-positive Staphylococcus epidermidis via agar diffusion test. In conclusion, the chlorhexidine salt-loaded chains could provide an innovative approach in the prevention of oral infections related to the use of orthodontic devices.