上顎骨の前方拡大の実験的研究 : 骨切り術を応用して

抄録

The correction of severe cases of mandibular protrusion such as are encountered in an underdeveloped maxilla is difficult to achieve by conventional orthodontic approach alone. In the present study, an attempt was made to develope a new method of treating such cases by means of operative orthodontics. A total of 26 adult dogs weighing about 20 kg were served as experimental animal and artificial fracture was made on both sides of the maxilla in the space between the 3rd incisor and cuspid. The fractured space was mechanically widened respectiveiy in one of the following manners. 1) Separate the space by surgeon's hand as wide as possible and keep it in position by applying an acrylic resin splint. This was designated as spaced fixation method. 2) Expand very slowly (0.2 mm per day) over an extended time duration (40 days) the fractured ends by use of a screw expansion plate. Slow expansion method. 3) Expand the fractured ends in the shorter period (in 20 days and by 0.7 mm per day). Rapid expansion method. On 40, 70 and 100days after completion of respective experiment, observation were made on the state of newly formed bones in the extended space and of teeth and surrounding tissue in the anterior maxillary segment, by mesurement of plaster cast and by macroscopic, roentogenographic and pathohistological examinations of the maxilla. Results of the study were summarized as follows. 1) Measurement by the plaster casts showed that the maximum and mean values of space attained by rapid expansion method was respectively 12 mm and 10 mm, by slow expansion method 8.0 mm and 7.5 mm, and by spaced fixation method 4.5 mm and 3.6 mm respectively. 2) The newly formed bones at the fractured space were mainly consisted of uniting callus, and osseous healing was complete about 100 days after fixation of maxilla by rapid expansion method and spaced fixation method. By slow expansion method, however, a marked retardation of osseous healing was shown probably due to an unfavorable effect of constant stimuli given to the blast tissue for too extended time duration. 3) As a general effect of the experimental fracture of maxilla, the tooth pulp was replaced by granulation tissue, and especially in case of slow expansion method, a severe resorption of tooth root due to the inflammatory granulation of alveolar basis was observed. In cases where rapid expansion method and spaced fixation method were applied, however, the tooth root suffered only slight degree of resorption of the dentin and cement substances. 4) Because X-ray observations of the operated maxilla were quite in parallel with those obtained by pathohistological means, X-ray finding may be most advantageous in following the course of bone formation and in judging when is the time of osseous healing. In view of the above, it was concluded that rapid expansion method proved most advantageous in achieving the anterior expansion of maxilla by operative orthodontics.