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Rotational axes in human incisor teeth
Reviews
and
abstracts
307
The attrition in a majority of teeth was classified as being in the second stage of Broca’s classification ; that is, the cusps were worn down and dentine was exposed. The occlusion of the complete sample was classified as Angle’s Class I. None of the samples studied showed any maxillomandibular dysplasia. At least ten specimens were in perfect normal occlusion. Only 29 out of a total of 636 teeth were crowded, and most of these cases of crowding were considered mild. Only three teeth were considered severely crowded. This includes complete space loss for two lower incisors which were missing and one cuspid which was completely blocked out. The study showed a clinically insignificant incidence of malocclusion in the presence of excessive attrition. 600 W St., N.W. Washington, D. C. 80001
Rotational
Axes
in
Human
Incisor
Teeth
Stephen Miller, D.D.S., M.S. University of Oregon Dental School, Portland,
Ore.
Manually produced tipping forces were applied to the labial crown surfaces of maxillary central incisors. Electronic transducers were employed to measure the instantaneous displacement of two points on the lingual crown surface and the magnitude of force being delivered, Continuous recording with a Sanborn recorder permitted location of the axis within 0.1 mm. More than 1,000 rotational axis positions were calculated at eight force levels ranging from 50 to 500 Gm. Fixed orthodontic appliances were used to tip these same teeth for a period of 28 days. Heavy forces (100 to 200 Gm.) were applied to the left incisors, while light forces (40 to 65 Gm.) were applied to the right ones. Metal tooth markers combined with a radiographic technique, involving the superimposition of lateral head films, were used for the weekly determination of axis position and magnitude of tooth movement. The short-term measurements showed no difference in rotational axis position, whether the applied force was at the gingival area or the incisal edge. Duration of force application (0 to 60 seconds) did not affect the tipping axis. Light forces produced axes of rotation near the cervical area, while the heavier forces provided axes further apically. The long-term effects were more pronounced in that the axes of rotation with heavy forces were even further apically, sometimes beyond the apex. Since these changes were greater than the measurement errors, it is concluded that the heavier forces were sufficient also to deform the alveolar bone. The location of the rotational axis did not vary from the seventh day through the twenty-eighth day. The total tooth movement during the 28 days was the same for the light and heavy forces. 73 Pardo Pointe Claire, Quebec, Canada
and
abstracts
307
The attrition in a majority of teeth was classified as being in the second stage of Broca’s classification ; that is, the cusps were worn down and dentine was exposed. The occlusion of the complete sample was classified as Angle’s Class I. None of the samples studied showed any maxillomandibular dysplasia. At least ten specimens were in perfect normal occlusion. Only 29 out of a total of 636 teeth were crowded, and most of these cases of crowding were considered mild. Only three teeth were considered severely crowded. This includes complete space loss for two lower incisors which were missing and one cuspid which was completely blocked out. The study showed a clinically insignificant incidence of malocclusion in the presence of excessive attrition. 600 W St., N.W. Washington, D. C. 80001
Rotational
Axes
in
Human
Incisor
Teeth
Stephen Miller, D.D.S., M.S. University of Oregon Dental School, Portland,
Ore.
Manually produced tipping forces were applied to the labial crown surfaces of maxillary central incisors. Electronic transducers were employed to measure the instantaneous displacement of two points on the lingual crown surface and the magnitude of force being delivered, Continuous recording with a Sanborn recorder permitted location of the axis within 0.1 mm. More than 1,000 rotational axis positions were calculated at eight force levels ranging from 50 to 500 Gm. Fixed orthodontic appliances were used to tip these same teeth for a period of 28 days. Heavy forces (100 to 200 Gm.) were applied to the left incisors, while light forces (40 to 65 Gm.) were applied to the right ones. Metal tooth markers combined with a radiographic technique, involving the superimposition of lateral head films, were used for the weekly determination of axis position and magnitude of tooth movement. The short-term measurements showed no difference in rotational axis position, whether the applied force was at the gingival area or the incisal edge. Duration of force application (0 to 60 seconds) did not affect the tipping axis. Light forces produced axes of rotation near the cervical area, while the heavier forces provided axes further apically. The long-term effects were more pronounced in that the axes of rotation with heavy forces were even further apically, sometimes beyond the apex. Since these changes were greater than the measurement errors, it is concluded that the heavier forces were sufficient also to deform the alveolar bone. The location of the rotational axis did not vary from the seventh day through the twenty-eighth day. The total tooth movement during the 28 days was the same for the light and heavy forces. 73 Pardo Pointe Claire, Quebec, Canada