RESUMO
INTRODUCTION: In the majority of orthodontic premolar extraction cases, the canine retraction phase is the most laborious procedure. This randomized clinical trial aimed to assess the effect of single versus repeated micro-osteoperforations (MOPs) during orthodontic canine retraction. METHODS: In this split-mouth study, two equal groups of 18 patients who required maxillary first premolar extractions and fixed orthodontic therapy were randomly assigned (n=9). In Group I, MOPs were only performed once on one site before retraction, whereas in Group II, MOPs were performed on one site repeatedly once a month for four months. In both groups, the contralateral control sites received no MOPs. The canines were retracted using mini-screws and closed-coil nickel-titanium springs. Using the patients' 3D models, the primary outcome measure at four months was the amount of orthodontic canine distal movement. The amount of anchorage loss (AL), degree of molar rotation (MR) and canine rotation (CR), and degree of canine tipping (CT) were measured as the secondary outcomes. The comparison of mean changes in the primary and secondary outcomes between the groups was done using the independent sample t-test (p<0.05). RESULTS: The rate of canine retraction, degree of CT, and rotation were not significantly different between the two groups (p>0.05). Additionally, there were no statistically significant variations in the maxillary first MR and the degree of AL (p>0.05). CONCLUSIONS: When maxillary canine retraction was performed with a single and repeated regimen of MOPs, comparable levels of distal CR and tipping were observed, along with an identical minimal degree of MR and AL.
RESUMO
OBJECTIVE: To investigate possible adverse effects of orthodontic magnets on the oral mucosa. METHODS: Twenty orthodontic patients, between 14 and 20 years of age, were used. All patients consented to participate in the trial, which ran for six months. Following extraction of the first premolars, samarium-cobalt (SmCo5) orthodontic magnets were used to move the upper right canines into the extraction spaces. The contralateral canines were retracted with elastomeric chain. The orthodontic appliance consisted of direct-bonded standard edgewise fibreglass brackets and molar tubes, and teflon-coated preformed archwires. At regular scheduled visits the following were recorded: the condition of the protective magnet coating; weight loss by the magnets; levels of nickel, iron and chromium ions in unstimulated saliva; viability of recovered oral mucosa cells with trypan blue. DNA fragmentation of the oral mucosa cells was analysed at the start of the trial, after one week, one month, three months and six months with the single cell gel electrophoresis assay (Comet assay). The elemental compositions of five magnets were assessed with energy dispersive X-ray microanalysis. RESULTS: By the third month the magnets had lost their protective resin coats. At six months the magnets had lost 3 per cent of their initial weights. Significant weight loss and raised saliva levels of nickel, iron and chromium ions occurred from the first week. The number of oral mucosa cells with DNA fragmentation increased steadily on both sides of the mouth from the first week. More DNA fragmented cells occurred on the Magnet side than on the Non-magnet side. The trial was discontinued when half of the subjects showed DNA damaged mucosal cells. CONCLUSIONS: Because the protective coating failed after a few weeks, orthodontic magnets are unsuitable for long-term intra-oral use. It is uncertain if the greater cell damage on the Magnet side was due to the corrosion products, proximity to the static magnetic field or both factors.
