Robert Shaye

Force degradation of orthodontic elastomeric chains—A product comparison study

In the last 20 years, synthetic elastic modules have been introduced to the orthodontist. However, force decay of these materials has been a clinical problem and the purpose of this project was to evaluate the force decay patterns of three commercially available elastomeric products--Ormco Power Chain II, Rocky Mountain Energy Chain, and TP Elast-O Chain--in a simulated oral environment. Thermal-cycled samples experienced less force decay over a 21-day period than samples stored at 37 degrees C. Furthermore, statistical analysis confirmed that there was a highly significant difference (p less than 0.01) between the mean force exerted by short modules and long modules for each material. Overall, modules producing higher initial forces (short modules) underwent less force decay after 21 days than did modules producing lower initial force values (long modules). All materials exerted 216 to 459 grams of force initially. After 21 days of simulated tooth movement, the force exerted by the elastic modules was 70 to 230 grams--a significant reduction (p less than 0.001).

The effect of altered bone metabolism on orthodontic tooth movement.

The purpose of this study was to determine how bone remodeling changes induced by nutritional hyperparathyroidism affect tooth movement through alveolar bone. Twelve beagle dogs, approximately 1 year old, were randomly divided into two groups of six. The controls were fed a standard dog diet (calcium 0.54 percent, phosphorus 0.42 percent). The experimental diet was identical to that fed the controls except for a decrease in the calcium (0.12 percent) to phosphorus (1.20 percent) ratio. At the tenth week of diet administration, following extraction of the lower third premolars, the second and fourth premolars were moved toward each other with a reciprocal elastic force of 100 Gm. Twelve weeks later the animals were killed and the mandibles were prepared for laboratory evaluation, which included Paragon 1301 staining of undecalcified sections, scanning electron microscopy, and a bone ash analysis. Radioimmunoassays during the experiment showed that the test animals had significantly elevated levels of parathyroid hormone, indicating a probable state of hyperparathyroidism. The clinical data revealed more rapid tooth movement in the experimental animals. Laboratory data indicated that the hyperparathyroid animals had significantly decreased bone density, as well as bone remodeling changes consistent with high PTH levels. These findings suggest that, in addition to applied force, tooth movement is dependent upon the state of calcium metabolism in alveolar bone.

Management of cases with upper incisors missing

A problem often confronting the orthodontist is that of missing upper incisors. In evaluation of the individual case, the dicision as to space closure or space regaining and eventual prosthetic reconstruction can be perplexing. Various diagnostic criteria, such as skeletal relation, arch-length analysis, inclination of teeth, and dental esthetics, must be evaluated. On the basis of this diagnostic information, treatment alternative is chosen to correct the malocclusion. The solution may be found in maintaining space, necessitating postorthodontic prosthetic replacement, or closing space and thus avoiding the need for artificial teeth. Four cases are shown to illustrate different approaches to the treatment of patients with upper incisors missing. Other solutions are possible anc correct. Each case must be weighed on its own merits.

Landmark identification accuracy in xeroradiographic cephalometry

Identification accuracy of fourteen cephalometric landmarks was compared between xeroradiographic cephalograms and conventional cephalograms. Four landmarks--point A, upper incisor tip, infradentale, and menton--were more accurately determined on the xeroradiograph, while two landmarks--point B and condylion--were more accurately determined on the conventional cephalogram. Although not conclusively demonstrated in this study, the xeroradiograph does appear to offer more clarity and detail than the conventional cephalogram. Further investigation of this new diagnostic medium will be necessary before its true significance to dentistry can be evaluated.

Interobserver reliability in xeroradiographic cephalometry.

Observer agreement on cephalometric landmarks was compared between xeroradiographs and conventional radiographs of twenty-nine patients. Of fourteen landmarks evaluated, four (condylion, infradentale, Ptm, and ANS) demonstrated clinical significance in favor of the xeroradiograph. In addition, six other landmarks favored the xeroradiograph but not to the degree of statistical significance.