Modelo experimental de movimentação dentária induzida com ancoragem esquelética: estudo morfológico

Abstract

Induced tooth movement (MDI) promotes morphological changes, which culminate in cellular responses with the release of inflammatory mediators. These phenomena can be induced by the application of an orthopedic force with a closed nickel-titanium (NiTi) spring in a rat model. Orthodontic mini-implants promote a skeletal anchorage without the undesirable effects of anchorage loss, as occurs with MDI with dental anchorage. In this context, the objective was toanalyze morphological alterations in an experimental model of MDI with skeletal anchorage, using orthodontic mini-implants in two different times. For this, 20 Wistar rats were used, weighing between 180 and 220 grams, divided in two groups with experimental time of 7 and 14 days. In both groups, the animals underwent the installation of a closed NiTi spring, one end of which was fixed around the left upper first molar and the other end attached to the miniimplant. The contralateral hemiarate of both groups was used as control (GC). After the MDI period, the animals were submitted to euthanasia and their hemiarates were removed and fixed in 10% buffered formalin for further EDTA demineralization. Samples were processed for histopathological analysis, and some inflammatory parameters, presence of hyalinization, irregular trabecular surfaces with or without osteoclasts, presence of tissue necrosis and root resorption were evaluated. The tooth movement space was measured using a histological rule (Zeiss®). In addition, the distance between the mesial aspect of the upper left 1st molar and the mini-implant was measured using a digital caliper (Messen®) and between the right upper central incisor palate and the mini-implant. After 7 days of MDI, a reduction in body mass was detected, however, this was recovered after 14 days. As to the measurement of the movement, it was verified that the installation of orthodontic device promoted a reduction of the distance between the upper molar and mini-implant, indicating a movement of this tooth in the mesial sense. When evaluated in percentage, this reduction was (11.08 ± 1.23)% in 7 days and (17.68 ± 1.97)% in 14 days. There was still a significant difference between 7 and 14 days, which corroborated with the histological measurements, which showed that the initial distance changed from (31.06 ± 1.41) μ to (61.71 ± 2.59) μ in 7 days and (74.75 ± 4.94) μ in 14 days. In the histological analysis, it was observed that the MDI promoted periodontal and pulp alterations, in relation to the control group, however there was no difference between the different groups submitted to the movement with skeletal anchorage. MDI with anchorage in mini-implants is efficient, has reproducibility and presented significant mesialization of the upper left molar. The histological changes did not vary between the evaluated times. There was no pulp involvement in MDI at 7 and 14 days.