An in situ caries model to study demineralisation during fixed orthodontics

OBJECTIVES: To investigate de/remineralization of enamel during the early stages of orthodontic treatment using the in situ caries model. DESIGN: A prospective, longitudinal study, using the in situ caries model. SETTING AND SAMPLE POPULATION: The Department of Orthodontics at the University of Liverpool School of Dentistry. Fifteen orthodontic patients undergoing fixed appliance treatment with extraction of premolar teeth. EXPERIMENTAL VARIABLE: Two enamel samples with pre- formed caries-like lesions were placed bilaterally, in specially constructed holders, on an orthodontic fixed appliance. One sample was bonded with a small bracket base. OUTCOME MEASURE: The parameters of the pre-formed carious lesion, expressed as mineral loss (delta Z), lesion depth (ld), lesion width (lw) and ratio (delta Z/ld) were compared between the bracketed, the non-bracketed and a control sample that had not been placed in the mouth. The difference between brackets place on the dominant (toothbrush hand) side and non-dominant side were also investigated. The correlation between mineral loss and length of time the sample was in the mouth was also analysed. RESULTS: There was considerable individual variation; however, a one-factor repeated analysis of variance showed a significant difference in ratio values between the three groups (p = 0.006). A pairwise comparison showed a significant reduction in ratio value for the non-bracketed sample compared with the control, but not the bracketed sample. There was no significant difference in mineral loss between the dominant and non- dominant sides. There was no linear correlation between the length of time the sample was in the mouth. CONCLUSION: An enamel sample with a pre-formed carious lesion, when placed in the mouth of an orthodontic patient, showed reduced remineralization in the presence of a simulated orthodontic bracket. Consistently effective preventive regimes to prevent demineralization in patients with fixed orthodontic appliances need to be developed. The technique described will be a valuable tool in this process.