The Bacterial Inhibitory Effect And Mechanical Property Of Chlorhexidine-added Resin-modified Glass Ionomer

Background:More and more people have accepted orthodontic treatment today, due to improving the patient's dental function, esthetics and self-esteem. However, some studies have reported that there are high risks of enamel decalcification under and around the fixed orthodontic attachment which make tooth cleaning more difficult and lead to an increase in plaque accumulation. Streptococci mutans (S.mutans) and poor oral hygiene are generally considered as the major reasons leading to dental caries. S.mutans produces organic acids primarily, which causes enamel demineralization and dental caries. The number of S.mutans increased during and after the placement of orthodontic appliances. The candidate of antibacterial agent for such application is chlorhexidine, which has been used as an adjunct treatment for dentistry as both collutory and an ingredient in the varnish or toothpastes. The orthodontic cement containing antibacterial agent is an option for decreasing enamel decalcification without patient cooperation. Objectives:This study was to investigate a light cured resin-modified glass-ionomer (RMGICs, Fuji Ortho LC, GC, Japan) combined with different concentration of chlorhexidine on the bacterial inhibitory effect and mechanical property.Methods:1. Bacterial inhibitory property testThe Fuji ORTHO LC (GC Corporation, Tokyo, Japan) was mixed with chlorhexidine (Sigma corporation, USA) at final concentrations of 0%,2.5%,5%,10% w/w. The compound was fabricated into round molds of uniform size and light cured. 21 discs for each group were prepared. Each disc was placed in a plastic tube containing 5ml of sterile distilled water at 37℃.Agar plate diffusion assays were tested for bacterial inhibitory effect. Streptococci mutans (Huaxi, China) was used as the test bacterium.3 discs from each tested group in one agar were placed on the surfaced of preinoculated agar and incubated for 48 hours at 37℃at the test time (Id,7 d,14 d,21 d,28 d,35 d, and 42 d). The growth inhibition zone around each disc was measured.2. Shear bond strength (SBS) test80 extracted caries-free human premolars were collected and stored in 0.1% (wt/vol) thymol. The teeth were randomly assigned to 4 groups (20 per group) according to the adhesive used. And the stainless steel premolar brackets (0.022 MBT, 3M, Unitek. USA) with average base area of 14.1 mm2 were bonded.All the specimens were fixed in acrylic resin then stored in distilled water at 37℃for 24 hours. The shear bond strength of the specimens was tested by a universal testing machine (SANS, MTS system corporation, China) at a crosshead speed of 1 mm/minute. 3. Fractographyic analysisOnce the brackets had been debonded, the enamel surface of each tooth was examined under 20-times magnification to determine the amount of residual adhesive on each tooth. The adhesive remnant index (ARI) scores were recorded according to the original description.4. Statistics analysisThe means±standard deviation (SD) values of shear bond strength and ARI scores for each group were subjected to one-way analysis of variance (ANOVA) and t-test. The ARI scores were also statistically analyzed by Chi-square test.Results:1. Bacterial inhibitory effect:The bacterial inhibitory effect increased as the concentration of chlorhexidine rising. And all discs containing chlorhexidine retained bacterial inhibitory effect over the 42-day testing period. The discs containing 2.5%, 5%,10% chlorhexidine started with zones of growth inhibition of 1.59±0.32, 2.93±0.38, and 5.06±0.42 mm, and ended with 2.14±0.25,4.41±0.49, and 4.82±0.36 mm.2. Shear bond strength:The t-test showed no significant difference (P>0.05) between the 2.5% group,5% group and 10% group, whereas a significant difference with the control group (P<0.05). The mean shear bond strength for control group (9.01MPa) was significantly greater than for 2.5% group (6.52MPa),5% group (4.90MPa) and 10% group (6.40MPa).3. Fractographyic analysis:Chi-square test indicated that there were statistically significant differences among four groups (P<0.05). Conclusions:Chlorhexidine/RMGICs composite material was synthesized. To our observations, the composite material was an appropriate candidate adhesive for preventing occurrence of caries during orthodontic treatment. These findings need further investigation of clinical study, safety, and possible commercial available.