96 Reviews and abstracts Am. J. Orthod. Dentofac. Orthop. July 1992

ing patients received conventional retainers. A control group of five persons was similarly followed. The num- ber and distribution of centric and nonworking occlusal contacts were recorded, as well as the relative forces of these contacts. Of the three measurement modalities tested, articulating ribbon proved to be the most reliable method for locating occlusal contacts. Five weeks after debanding, the positioner group had an increase in cert- trie contacts (p = 0.073) and a decrease in nonworking contacts (p = 0.024). The variance of the force of occlusal contacts was found to decrease significantly in the positioner group, while remaining unchanged in the retainer group. These previously unreported findings suggests a more even distribution of occlusal contact forces occurred with positioner therapy.

Cartilage-degrading proteinases in human temporomandibular joint synovial fluid Marie B. Farrar The University of Tennessee, Memphis, Tenn., 1991.

It has been suggested that temporomandibular (TM) disorders are progressive and end ultimately in osteoar- thritis. In arthritis, metalloproteinases are known to be responsible for destruction of cartilage extracellular ma- trix. This study biochemically characterized the TM synovial fluid of patients suffering from various TM disorders.

Synovial flui d "washes" were collected from 8 joints of 7 patients undergoing arthrographic surgery and from 32 joints of 16 patients referred for bilateral arthrog- raphy. Gelatinolytic activity was evaluated using SDS- PAGE with gelatin substrate. Specimens consistently exhibited lytic activity at 70 kDa; this enzyme was characterized as metalloproteinase on the basis of in- hibition/activation studies and identified as 70 kDa ge- latinase. This enzymeis produced by synoviocytes and chondrocytes and degrades gelatin (i.e., denatured col- lagen) and collagen types IV, V, and XI.

Transferrin, as a measure of plasma proteins, was semiquantified densitometrically after SDS-PAGE. Transferrin values, total cell counts, and protein con- centrations correlated highly with each other, as they measure similar cellular processes. These three vari- ables also correlated significantly with disease severity (as graded clinically and/or arthrographically) and with gelatinase activity (as semiquantified densitometri- cally). However, no relationship could be demonstrated between gelatinase activity and disease severity as rated in this study.

These findings implicate metalloproteinases in the joint destruction accompanying TM disorders. They further suggest that TM dysfunction represents a pro-

gressive disorder marked by slow cartilage destruction by metalloproteinases with secondary synovial inflam- mation occurring late in the disease. In addition, they indicate that the disease may be progressing biochem- ically well before macroscopic degeneration is seen.

Cephalometric characteristics of normal bite depth, deep bite, open bite Erwin Lubit New York University College of Deptistry, 1991.

The purpose of this study was to evaluate lateral cephalogram characteristics associated with varying amounts of vertical overbite. Understanding these char- acteristics is important in establishing a diagnosis, choosing among therapeutic modalities, and in under- standing the prognosis of treatment.

Three groups of 20 patients were compared ce- pha!ometrically. One group had normal bite depth, the second had deep bite, and the third had open bite. For each cephalometric characteristic a mean value and a standard deviation were calculated for each group. Then an analysis of variance (ANOVA) was performed to analyze differences among the groups. The most sig- nificant difference among the groups was in the dental measurements. The incisors were significantly more proclined in the open bite group than in the normal or closed bite group.

The effects of extraction and non-extraction treatments on the growth of the lower anterior face height A. Chua College of Dentistry, New York Universitk; New York, 1991.

The effect of orthodontic treatment on the lower anterior face height (Ans-Me) is of fundamental im- portance to the orthodontist. However, the choice be- tween the two main methods of treatment, extraction versus nonextraction is not clear-cut. It is believed that the extraction method decreases Ans-Me, whereas the nonextraction method results in an increase in Ans-Me. This study examined the effects of both methods on Ans-Me for a sample of 174 subjects divided equally between Class I and II malocclusions.

A difficulty of such a study is distinguishing be- tween the composite effects o f growth and treatment- induced changes in growing subjects. Most studies con- trolled for growth by using subjects in the same age group. However, this study controlled for growth by normalizing Ans-Me measurements to the Michigan Growth Standard. With this method, we could compare subjects who differ in terms of the age at which treat-