Miniplates as temporary anchorage in orthodontics : experimental and clinical studies

Since the introduction of temporary skeletal anchorage in orthodontics during the eighties, osteosynthesis miniplates, modified with orthodontic attachments, have been increasingly used. However, no quantitative data about bone reactions around loaded miniplates, and only few prospective clinical studies with small numbers of patients, were found in the literature. Therefore, this project was set up to scientifically emphasize the use of miniplates for orthodontic anchorage with combined experimental and clinical approaches. The specific objectives of the experimental chapters of this thesis were to evaluate if orthodontic loading has an impact on bone reactions around screws supporting miniplates, and to describe the histological components of the bone-screw interface. The clinical chapters aimed to determine patients’, orthodontists’ and surgeons’ perceptions about miniplates, to assess their success rate and to describe the surgical techniques of placement and removal. The experimental study involved eighty miniplates, placed in the jaws of 10 dogs : 2 miniplates per jaw quadrant. After 2 weeks, coil springs applying a 125 g force were placed between the miniplates of an upper quadrant and the controlateral lower quadrant of each dog. The other miniplates were not loaded and were considered controls. Five dogs were sacrificed 7 weeks after implantation and 5 dogs after 29 weeks. Fluorochromes were injected at implantation and at sacrifice. Jaw quadrants were scanned with peripheral Quantitative Computed Tomography. Undecalcified sections were carried out and submitted to microradiographic analysis to assess bone-implant contact and bone volume/total volume. The sections were finally observed under UV light, stained and examined under ordinary light. The success rate in this animal study was 53 % and the proportion of stable miniplates was significantly higher in the maxilla than in the mandible. No significant difference in success rate was found between loaded and nonloaded miniplates. Mobility occurred on average 5 weeks after placement. Bone mineral density was higher around mandibular than around maxillary miniplates, but was not significantly different around loaded and nonloaded miniplates. Bone implant contact and bone volume/total volume did not differ significantly neither between the loaded and the nonloaded screws, nor according to the direction of load, whereas they increased with time. Fifty-six percent of the screws were osseointegrated. Healing reactions showed mainly limited remodelling of lamellar bone. The remaining screws were fibro-integrated. Stability and osseointegration of titanium orthodontic miniplates were thus influenced by the recipient site anatomy, but not by loading. The clinical study focused on ninety-seven consecutive patients treated with miniplates, who completed questionnaires. A total of 200 miniplates were placed by nine oral surgeons, who filled out questionnaires after placement and removal surgeries. The 30 orthodontists treating these patients also completed questionnaires concerning miniplate success, handling complexity, and effectiveness. The success rate obtained in this clinical survey was 92.5 %. Placement surgery, generally performed under local anesthesia, lasted on average 15-30 minutes per plate, and was considered by the surgeons to be very to moderately easy. Patients tolerated the miniplates well : 72 % of patients said they did not mind having the implant and 82 % reported that the surgical experience was better than expected, with little or no pain. The chief complaints were post-surgical swelling, lasting 5 days on average, and cheek irritation. The orthodontists rated these devices as easy to use and simplifying treatment. The removal surgery was shorter and considered easier than the placement surgery. Miniplates were thus well accepted by patients and providers, and were considered a useful tool especially for difficult treatments.