Study On The Correlation Between Enamel Demineralization And Microflora Changes On The Tooth Surface During Fixed Orthodontic Treatment

Labial or buccal enamel demineralization usually takes place during fixedorthodontic treatment. Many reasons result in this phenomenon, most studies suggest thatthe introduction of fixed appliances into the oral environment is relevant to enameldemineralization. The irregular surfaces of brackets and bands can cause the clean-limitedtooth surfaces and food debris retention, which encourage a lowering of plaque pH and anincreased aciduric bacteria in the presence of carbohydrates, and then lead to the enameldemineralization. The present studies indicate that enamel demineralization is relevant tovarious bacteria, in which Streptococci, Lactobacilli and Actinomycetes are supposed asthe main bacteria.There are some studies suggest that the incidence of the demineralization is increasedafter brackets bonding. We also find that the number of patients with enamel demineralization is increased with the increasing of treatment time by our clinicalobservation. The phenomenon may be related to the microflora change after orthodonticbracket bonding. And it is a matter of fact that some patients do not present obviousdemineralization even though the bad oral hygiene and long orthodontic treatment time.But some patients are easy to present obvious demineralization during orthodontictreatment. Is the susceptibility of demineralization relate with microflora changes on thetooth surface? According to the issue above, the present study was undertaken to observethe microflora change on the tooth surface during fixed orthodontic treatment, and thenfind out the correlation between enamel demineralization and microflora changes on thetooth surface during fixed orthodontic treatment. This study consists of two parts:1) Studyon the microflora change of the tooth surface during fixed orthodontic treatment;2) Studyon the correlation between enamel demineralization and microflora changes on the toothsurface during fixed orthodontic treatment.Part I: Study on the microflora change of the tooth surface during fixedorthodontic treatmentPurpose:To investigate the changes of the quantity and proportion of Streptococcus mutans,Lactobacillus, Actinomyces on the tooth surface before and after brackets bonding, andalso with the increasing of treatment time by our clinical observation. The aim of thisstudy was to analyse the microbial mechanism of enamel demineralization after bracketsbonding during fixed orthodontic treatment.Methods:From the patients undergoing fixed orthodontic treatment in dental hospital of theFourth Military Medical University from August/2011to October/2012,55patients wereselected randomly and divided into the fixed orthodontic treatment group for the study.The patients in the group were without enamel demineralization on maxillary incisors (A3-B3). And20volunteers were selected randomly from patients who visited firstly in thesame department during the same time and divided into the no orthodontic treatmentgroup for the study. According to the time of fixed orthodontic tretment, the patients in the fixed orthodontic treatment group were subdivided into the following three groups:1) thegroup with orthodontic treatment within1year;2) the group with orthodontic treatmenttime from1to2year;3) the group with orthodontic treatment time more than2years.Dental plaque of each patient from upper incisor in the regions gingival to the bracket wasscraped. Streptococcus mutans, Lactobacillus, Actinomyces were isolated and cultured,respectively. For each kind of bacteria, the quantity and proportion in the total bacteriawere calculated. Then the differences of the bacteria were analyzed among the groups.Results:Compared with the no orthodontic treatment group, the quantity and proportion in thetotal bacteria of Streptococcus mutans and Lactobacillus were significantly increased(P<0.05) in all the subgroups of the fixed orthodontic treatment group (with treatmenttime within1year, from1to2year, and more than2years, respectively). But the changedbacteria situation were relatively invariable during the treatment. Compared with the noorthodontic treatment group, there was no significant difference for the quantity andproportion in the total bacteria of Actinomyces (P<0.05) in all the subgroups of the fixedorthodontic treatment group (with treatment time within1year, from1to2year, and morethan2years, respectively).Conclusions:After the fixed appliances are positioned in the patients’ dentition, the quantity andproportion in the total bacteria of Streptococcus mutans and Lactobacillus are increasedsignificantly in the plaque of local surface tooth. But the increasing do not cumulateduring the treatment. It is suggested that microflora of dental plaque will change afterthe fixed appliances used, and get into a kind of balance during the treatment. The changeof microflora may be one of the mechanisms of enamel demineralization during fixedorthodontic treatment.Part II: Study on the correlation between enamel demineralization andmicroflora changes on the tooth surface during fixed orthodontic treatmentPurpose:To investigate the changes of the quantity and percentage of Streptococcus mutans, Lactobacillus, Actinomyces on the tooth surface between the patients with enameldemineralization and without during fixed orthodontic treatment. The aim of this studywas to analyse the microbial mechanism of enamel demineralization after bracketsbonding during fixed orthodontic treatment.Methods:From the patients undergoing fixed orthodontic treatment in the department oforthodontics of the dental hospital of the fourth military medical university in the timefrom August/2011to October/2012,49patients were selected randomly and divided intono demineralization group for the study. The patients in the group were without enameldemineralization on maxillary incisors (A3-B3). And26patients were selected randomlyand divided into demineralization group for the study. Dental plaque of each patient fromupper incisor in the regions gingival to the bracket was scraped. Streptococcus mutans,Lactobacillus, Actinomyces were isolated and cultured, respectively. For each kind ofbacteria, the quantity and percentage in the total bacteria were calculated. The debris indexon the sampled tooth was also investigated. Then the differences of the bacteria and debrisindex between the groups were analyzed.Results:Compared with the patients in the no demineralization group, the quantity and theproportion in the total bacteria of Streptococcus mutans were higher for the patients in thedemineralization group（P<0.05）. No significant differences were found for the quantityand the proportion in the total bacteria of Actinomyces and Lactobacillus between the twogroups（P>0.05）.Conclusions:It is suggested that the increased quantity and proportion in the total bacteria ofStreptococcusmutans may be one of the mechanisms of enamel demineralization duringfixed orthodontic treatment.