Light microscopic and SEM findings after orthodontic treatment--analysis of a human specimen

The hard and soft tissue damage caused by orthodontic forces has so far, for obvious ethical reasons, been investigated in animal models primarily. However, the validity of these results as applied to humans remains controversial. The particular value of this study is that the maxilla of a young adult could be analyzed histologically. Thus it was possible to retrospectively study the effects of a routine orthodontic therapy using light microscopy.

The upper jaw of a 24-year-old patient was investigated. He had been in orthodontic treatment with a straight-wire-appliance using superelastic materials for 18 months. Both posterior segments were analyzed in the horizontal plane using the microsection method according to Donath (toluidine blue staining). Both central incisors were analyzed using a scanning electron microscope (SEM). The examination was performed qualitatively and histomorphometrically.

170 lateral root resorptions were found in the nine posterior teeth, while pressure sites and interference areas with the buccal and sinus cortical bone were predominantly affected. However, the extent of root resorption was minimal: mean length 979 +/- 766 microm, mean depth 208 +/- 133 microm. The lateral root erosions presented high repair potential: 55.6% of resorption length, and 28% of the depth were repaired in 76% of all lesions.

The incidence of detected root resorptions seems high at first. However, the prognosis of the affected teeth is not critically impaired, due to the lesions' minor extent (length, depth) and their high repair capacity.