Sug-Joon Ahn

Experimental antimicrobial orthodontic adhesives using nanofillers and silver nanoparticles

OBJECTIVES Experimental composite adhesives (ECAs) containing silica nanofillers and silver nanoparticles were compared with two conventional adhesives (composite and resin-modified glass ionomer [RMGI]) to analyze surface characteristics, physical properties and antibacterial activities against cariogenic streptococci. METHODS Surface roughness and surface free energy (SFE) characteristics were measured using confocal laser scanning microscopy and the sessile drop method. Shear bond strength and bond failure interface were analyzed to compare the physical properties. Antimicrobial activities were analyzed by a bacterial adhesion assay, a disk diffusion test, and an optical density measurement of bacterial suspension containing each adhesive. RESULTS ECAs had rougher surfaces than conventional adhesives due to the addition of silver nanoparticles. ECAs had more similar SFE characteristics to composite than to RMGI. Bacterial adhesion to ECAs was less than to conventional adhesives, which was not influenced by saliva coating. Bacterial suspension containing ECAs showed slower bacterial growth than those containing conventional adhesives. There was no significant difference in shear bond strength and bond failure interface between ECAs and conventional adhesives. SIGNIFICANCE This study suggests that ECAs can help prevent enamel demineralization around their surfaces without compromising physical properties.

Survival analysis of orthodontic mini-implants

INTRODUCTION Survival analysis is useful in clinical research because it focuses on comparing the survival distributions and the identification of risk factors. Our aim in this study was to investigate the survival characteristics and risk factors of orthodontic mini-implants with survival analyses. METHODS One hundred forty-one orthodontic patients (treated from October 1, 2000, to November 29, 2007) were included in this survival study. A total of 260 orthodontic mini-implants that had sandblasted (large grit) and acid-etched screw parts were placed between the maxillary second premolar and the first molar. Failures of the implants were recorded as event data, whereas implants that were removed because treatment ended and those that were not removed during the study period were recorded as censored data. A nonparametric life table method was used to visualize the hazard function, and Kaplan-Meier survival curves were generated to identify the variables associated with implant failure. Prognostic variables associated with implant failure were identified with the Cox proportional hazard model. RESULTS Of the 260 implants, 22 failed. The hazard function for implant failure showed that the risk is highest immediately after placement. The survival function showed that the median survival time of orthodontic mini-implants is sufficient for relatively long orthodontic treatments. The Cox proportional hazard model identified that increasing age is a decisive factor for implant survival. CONCLUSIONS The decreasing pattern of the hazard function suggested gradual osseointegration of orthodontic mini-implants. When implants are placed in a young patient, special caution is needed to lessen the increased probability of failure, especially immediately after placement.

Quantitative analysis of adhesion of cariogenic streptococci to orthodontic raw materials

INTRODUCTION Knowledge of adhesion patterns of cariogenic streptococci to orthodontic materials can provide valuable information on the cause of enamel demineralization during orthodontic treatment. The purpose of this study was to investigate the adhesion of 2 cariogenic streptococci strains to 7 orthodontic raw materials (3 light-cured orthodontic adhesives, 3 bracket raw materials, and hydroxyapatite) with respect to bacterial species, incubation time, and saliva coating. METHODS Each material was incubated with unstimulated whole saliva or phosphate-buffered saline solution for 2 hours. Binding assays were then performed by incubating tritium-labeled cariogenic streptococci with each raw material for 3 or 6 hours. RESULTS The degree of adhesion varied by material type. Generally, adhesion of cariogenic streptococci was significantly higher for bonding adhesives than for bracket materials, and adhesion to resin-modified glass ionomer was the highest. A longer incubation time generally increased bacterial adhesion, whereas saliva coating did not significantly influence bacterial adhesion. CONCLUSIONS Bonding adhesives around brackets should be removed carefully during the bonding procedure to avoid enamel decalcification.

Quantitative analysis of the adhesion of cariogenic streptococci to orthodontic metal brackets.

The aim of this study was to analyze the adhesion of cariogenic streptococci to orthodontic metal brackets in terms of the type of bacterial strains, the incubation time, and saliva coating. Two strains of Streptococcus mutans (S. mutans LM7 and S. mutans OMZ65) and two strains of S. sobrinus (S. sobrinus B13 and S. sobrinus 6715) were used. Twenty metal brackets were incubated with either unstimulated whole saliva or phosphate-buffered saline for two hours. The bacterial adhesion assays were then performed by incubating the tritium-labeled streptococci with saliva-coated or noncoated orthodontic brackets for three, six, or nine hours. The results showed a characteristic binding pattern according to the type of bacterial strains used. S. mutans OMZ65 showed the highest amount of adhesion, whereas S. sobrinus B13 showed the lowest amount of adhesion. Generally, an extended incubation time increased the adhesion of cariogenic streptococci, and the amount of adhesion was the highest after nine hours of incubation. The saliva coating did not significantly influence the adhesion of bacteria. However, this saliva-mediated adhesion differed according to incubation time. The saliva coating tended to gradually decrease the adhesion by the extended incubation time, compared with the noncoated controls. This study indicates that each strain of cariogenic streptococci has a characteristic adhesion pattern and the type of bacterial strain, the incubation time, and saliva influenced the adhesion.

Surface characteristics of orthodontic adhesives and effects on streptococcal adhesion

INTRODUCTION In this study, we analyzed the surface roughness (SR) and surface free energy (SFE) characteristics of various orthodontic adhesives and their effects on the adhesion of mutans streptococci (MS). METHODS Three nonfluoride-releasing composites, 1 fluoride-releasing composite, 1 polyacid-modified composite (compomer), and 2 resin-modified glass ionomers (RMGIs) were analyzed with confocal laser scanning microscopy and the sessile drop method. Each material was incubated with whole saliva or phosphate-buffered saline solution. Adhesion assays were then performed by incubating each material with tritium-labeled cariogenic streptococci. RESULTS We found that SFE and its components were significantly different among the adhesives, despite relatively uniform SR. RMGIs showed significantly higher SFE-particularly, dispersive, polar, and acidic characteristics-than did the composites. The compomer had intermediate characteristics between the composites and RMGIs. MS adhered to RMGIs significantly more than to the composites and the compomer, but there was no significant difference among the composites. The longer incubation time increased MS adhesion, whereas saliva coating did not significantly influence MS adhesion. There was a correlation between SFE and MS adhesion. SFE and its dispersive, polar, and acid components significantly influenced MS adhesion irrespective of saliva coating. CONCLUSIONS This study suggests that initial MS adhesion is significantly influenced by SFE characteristics of adhesives rather than SR or saliva coating.

Surface Characteristics of Orthodontic Materials and Their Effects on Adhesion of Mutans streptococci

OBJECTIVE To test the hypothesis that there are no significant differences in the adhesion of mutans streptococci (MS) to various orthodontic materials based on their surface characteristics. MATERIALS AND METHODS Surface roughness (SR) and surface free energy (SFE) characteristics were investigated for nine different orthodontic materials (four orthodontic adhesives, three bracket raw materials, hydroxyapatite blocks, and bovine incisors) using confocal laser scanning microscopy and sessile drop method. Each material, except the bovine incisors, was incubated with whole saliva or phosphate-buffered saline for 2 hours. Adhesion assays were performed by incubating tritium-labeled MS with each material for 3 or 6 hours. RESULTS Orthodontic adhesives had higher SFE characteristics and lower SR than bracket materials. Orthodontic adhesives showed a higher MS retaining capacity than bracket materials, and MS adhesion to resin-modified glass ionomer and hydroxyapatite was highest. Extended incubation time increased MS adhesion, while saliva coating did not significantly influence MS adhesion. SFE, specifically its dispersive and polar components, was positively correlated with MS adhesion, irrespective of saliva coating. CONCLUSIONS The hypothesis is rejected. This study suggests that SFE characteristics play an important role in the initial MS adhesion to orthodontic materials.

Adhesion of oral streptococci to experimental bracket pellicles from glandular saliva.

The aim of this study was to evaluate the functions of bracket pellicles as the binding receptors for Streptococcus mutans and Streptococcus gordonii. Four different types of orthodontic brackets were used: stainless steel, monocrystalline sapphire, polycrystalline alumina, and plastic. The bracket pellicles were formed by incubating orthodontic brackets with fresh submandibular-sublingual saliva or parotid saliva for 2 hours. The pellicles were extracted, and their components were confirmed by gel electrophoresis, immunodetection, and amino acid composition analysis. The roles of the bracket pellicles in the adhesion of oral streptococci were evaluated by incubating tritium-labeled streptococci with pellicle-transfer blots. The results showed that the salivary components adhered selectively according to type of bracket and glandular saliva. The selective adsorption was also proven by the amino acid composition profiles. Among the several salivary proteins, MG2, alpha-amylase, and the acidic proline-rich proteins provided the binding sites for S gordonii. However, none of these proteins in the bracket pellicles contributed to the adhesion of S mutans. These findings suggest that numerous salivary proteins can adhere selectively to the orthodontic brackets, and some of them contribute to the binding of S gordonii.

Cephalometric predictors of long-term stability in the early treatment of Class III malocclusion.

The aim of this study was to examine the differences in the early craniofacial morphology of Class Ill malocclusions. Lateral cephalograms of 45 subjects with a Class III malocclusion and an anterior crossbite in the deciduous or mixed dentition were examined before treatment, after treatment, and during the long-term retention stage. The anterior crossbites of all patients were corrected after a series of orthodontic treatments. After a mean follow-up period of 5.7 years, all the subjects were reevaluated and divided into three groups according to the final occlusal status: good, fair, and poor occlusal stability. Twenty cephalometric variables on the pretreatment lateral cephalograms were analyzed by one-way analysis of variance and discriminant analysis to identify the key determinants for discriminating among the three groups. Among the 20 variables, 11 showed statistical significance. Generally, the subjects with a smaller gonial angle and a more hypodivergent skeletal pattern had good prognosis after the early treatment of Class III malocclusion. When the AB to mandibular plane angle and N-perpendicular to point A were selected in discriminant analysis, the AB to mandibular plane angle was the most significant variable. Discriminant analysis showed a relatively high degree of correct classifications of the patients with early Class III malocclusion. In particular, discriminant analysis showed the highest accuracy (93.3%) when predicting a poor prognosis.

Relationship between the curve of Spee and dentofacial morphology evaluated with a 3-dimensional reconstruction method in Korean adults

INTRODUCTION The purposes of this study were to examine the curve of Spee of the maxillary and mandibular arches by using a 3-dimensional reconstruction method and to determine the relationship between the curve of Spee and dentofacial morphology with multiple regression analysis. METHODS Lateral cephalograms and dental models were evaluated from 18 Korean men and 31 Korean women. The depth of the curve of Spee was measured on the virtual dental models with computer software. Seventeen cephalometric variables related to the lateral cephalograms were analyzed to determine differences in dentofacial morphology. The Pearson correlation analysis and a multiple linear regression analysis were performed to determine the relationship between the curve of Spee as the dependent variable and other cephalometric and dental variables as the independent variables. RESULTS The depth of the curve of Spee in the mandibular arch was significantly related to overbite, overjet, and the sagittal position of the mandible with respect to the anterior cranial base. The curve of Spee was not affected by sex. CONCLUSIONS These results will assist in the determination of the sagittal organization of the teeth as a reference for prosthetic restoration and orthodontic treatment.

Changes of 2-deoxyglucose uptake in the rat auditory pathway after bilateral ablation of the cochlea

It has been reported that the area of decreased glucose metabolism in the FDG-PET of prelingually deaf children correlates significantly with speech performance after cochlear implantation. In this study, we undertook to confirm changes of glucose metabolism in the cerebral cortex using an animal model with age-matching groups to completely exclude the influence of age differences between the deaf and normal-hearing groups. The cochlea was ablated bilaterally at a postnatal 10-14 days in the deaf groups; 3-4 deaf and normal rats were included at each time point at 1, 2, 4 and 8 weeks and 7 months after ablation. After injecting 2-deoxyglucose intraperitoneally, digitalized autoradiographic images were obtained, and analyzed by using two different methods; 3-dimensional voxel-wise statistical analysis and conventional 2-dimensional densitometry. The hypometabolic area analyzed using 3-dimensional analysis and the differences of optical density between normal and deaf as determined by densitometry were widest and most prominent between 4 and 8 weeks after ablation. Differences were not significant before 2 weeks or after 7 months after ablation. This result shows that the hypometabolic area becomes prominent after a critical period and it decreases as the duration of deafness increases. We believe that cross-modal plasticity may be the mechanism of changes in glucose metabolism and that this result reinforced the usefulness of evaluating hypometabolic area using FDG-PET in deaf children.