Biological reaction of alveolar bone to orthodontic tooth movement

Direct and indirect resorption are perceived as reactions to an applied for ce. This is in contrast to the view of orthopedic surgeons, who describe ap position as a reaction to loading of bone. A histomorphometric study of the circumalveolar bone reaction to a force system generating translation of p remolars and molars of five maccaca fascicularis monkeys is described. Thre e force levels (100 cN, 200 cN, and 300 cN) were applied for a period of 11 weeks. Undecalcified serial sections were cut parallel to the occlusal pla ne, and a grid consisting of three concentric outlines of the root intersec ted by six radii was placed on each section. Areas anticipated to be submit ted to different stress / strain distributions were isolated. A-posteriori tests were used in order to separate areas that differed with regard to par ameters reflecting bone turnover. Based on these results, a new hypothesis regarding tissue reaction to orthodontic forces is suggested. Direct resorp tion could be perceived as a result of the lowering of the normal strain fr om the functioning PDL and as such, as a start of remodeling, in the bone b iological sense of the word. Indirect remodeling could be perceived as a st erile inflammation attempting to remove ischemic bone under the hyalinized tissue. At a distance from the alveolus, dense woven bone was observed as a sign of a RAP (regional acceleratory phenomena). The apposition could, acc ording to the new hypothesis, be perceived as a result of the bending of th e alveolar wall produced by the pull from the Sharpey fibers. The above sug gested interpretation of tissue reaction would be shared with bone biologis ts.