DEPARTMENT OF REVIEWS AND ABSTRACTS

Edited by Dr. J. A. Salzmann New York City

All inquiries regarding information on reviews and abstracts should be directed to the respective authors. Articles OT books for review in this department ShozLld be adCiTeS&& to Dr. J. A. Salzmann, 654 &la&son Ave., New York, New Pork 10021.

Abstracts of papers presented before the Research Section of the American Association of Orthodontists, San Francisco, Calif., May 14, 1968

Comparative Histologic Study of Heavy Intermittent and light Continuous Forces

Thomas Butler, B.A., D.D.S., M.S. Saint Lou&- University, St. LOW’S, MO.

This study compared the histologic effects of light continuous versus heavy intermittent orthodontic forces. Histologic contrasts were made from simul- taneously conducted experiments in the same animal.

Three Macaoa rhesus monkeys were used in the experiments, and three were used as controls. Mandibular first molars were extracted in all animals, and the distal-moving second premolar tooth was the focus of this research.

Heavy intermittent appliances were placed in the right mandibular buccal segments, and light continuous appliances were placed in the left. The light con- tinuous force of 28 grams per square centimeter of root surface was obtained by means of the Begg light-wire appliance in a tipping action. Horizontal elastics were used as the active element. The heavy intermittent force of 200 grams per square centimeter of root surface was delivered in a bodily movement by the edgewise appliance. The active element, a vertical loop with a single helix, was activated 1 mm. at the time of cementation and again after 21 days. The second activation was given to the 42-day experimental animal only.

The six animals were sacrificed in pairs (one control and one experimental) at 48 hours, 21 days, and 42 days. Histologic sections were made of the mandibu- lar second premolars and their supporting structures.

The findings showed tha,t the alveolar boric crest was affected by both types of force, but the light continuous force was more damaging. Only the light con- tinuous force caused root resorption, which was seen in the areas of pressure. The width of immature bone following tooth movement, as interpreted by an

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oral pathologist, was found to be 0.2 to 0.3 mm. The biologic effect of anchorage preparation requires further research.

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The Use of Parathyroid Hormone to Assist Orthodontic Tooth Movement

Anthony A. Gianelly, D.M.D., Ph.D., and Richard M. Schnur, D.D.S. Boston University School of Graduate Dentistry, Boston, Mass.

Fifty units of parathyroid hormone (Lilly) in 0.5 cc. solution were injected along the distal aspect of the left maxillary incisor of each of six rats. Along the distal aspect of the left maxillary incisor of each of six rats in the control group, 0.5 cc. of 0.9 per cent saline solution was injected. Five days later, bands with eyelets on the labial surface were fitted on the incisor teeth of four animals in each group. A 1 ounce force acting to separate the teeth laterally was applied to the maxillary teeth of all animals with bands. On the sixth day, photographs delineating the tooth moveemnt were taken; all animals were sacrificed and the maxillae were processed for histologic examination.

Grossly, the left lateral incisors of rats treated with parathyroid hormone moved significantly farther from the midline than the right lateral maxillary incisors. One the other hand, the maxillary incisors of the control animals moved approximately the same distance from the midline.

Microscopically, evidence of bone resorption was apparent along the alveolar bone of the distal aspect of the maxillary left lateral incisors of those animals treated with parathyroid horomone and not subjected to force aplications. In contrast, the conformation of the periodontium of control animals not subjected to force application appeared normal. Along the alveolar bone of the distal aspect of the teeth subjected to force, bone resorption and partial disorganization of the fibers of the ligament were apparent. Little bone apposition was noted on the tension side of the teeth, possibly because the experimental time was too short to allow appreciable bone formation.

It appears possible to enhance orthodontic tooth movement by the local use of parathyroid hormone. The discreet removal of alveolar bone prior to force application may decrease the resistance to tooth movement, permitting selective tooth movement.

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The Anchorage Factor in Cuspid Retraction

Ira Kreitman, D.D.S., MS. Saint Louis University, St. Louis, MO.

The effect of anchorage preparation in preventing the mesial migration of the buccal segments was evaluated in two ways : (1) from the beginning of treatment