Orthodontic retraction into recent and healed extraction sites. A histologic study.

The aim of this experimental study was to assess the advantages of an early or delayed treatment start after tooth extraction on the basis of hard-tissue findings (density, maturity, osteodynamics) and of soft-tissue responses at the extraction site. Following bilateral extraction of the second incisors, reciprocal space closure was initiated in 3 foxhounds (age: 3.5 years): group 1 (6 teeth) 12 weeks after extraction, group 2 (6 teeth) immediately after extraction. After an 8-week bodily tooth movement period and a 2-month retention period, evaluation was undertaken on the basis of clinical/radiologic and histologic criteria (sequential polychromatic bone marking, light microscopy). Histologic analysis yielded the following findings in group 1 (delayed tooth movement): low bone density at the extraction site with more mature lamellar bone, pronounced horizontal atrophy of the alveolar process with periosteal bone apposition in direction of tooth movement, increased tendency towards gingival invagination. The findings in group 2 were characterized by: higher bone density with less maturity (bundle bone) at the extraction site, broader alveolar process, reduced tendency towards gingival invagination. No qualitative difference between the 2 groups was found with respect to root resorption. The histologic findings therefore indicate that orthodontic retraction into extraction sites should be initiated at an early stage.