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The enamel surfaces of extracted teeth were studied clinically and with a scanning electron microscope following debonding of orthodontic attachments and subsequent polishing. Excess orthodontic resin was removed with tungsten carbide burs and abrasive discs. Several combinations of polishing agents were evaluated.

The no. 30 fluted tungsten carbide bur appeared to be the most efficient method of removing highly filled resin, and it produced the least amount of scarring. A polishing sequence was developed which used resin points and cups followed by a water slurry of fine pumice and brown and green cups.

This procedure was tested clinically and appeared to return the enamel to an acceptable condition. This procedure is fast, efficient, and comfortable for the patient.

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Five identical samples, each consisting of a fixed appliance, a headgear and a quad-helix for one-half of a dental arch, were immersed in 0.9% sodium chloride for 2 hours, 24 hours and 7 days. A control appliance was subjected to dynamic test conditions in a specially built “oral simulator” under similar test conditions. A significant release of nickel was detected from the quad-helix during the first two hours in static conditions, whereas during the following two periods significantly less nickel was released from the quad-helix than from the other appliances. The fixed appliance with simulated function showed a significantly higher cumulative release of nickel than the similar appliance in static conditions, 44.2 μg (SD 22.8) and 17.1 μg (SD 3.4). The total amounts of chromium released from the fixed appliance were significantly lower than those of nickel. No difference in the release of chromium was seen between the static and dynamic conditions. The results indicate certain differences in the amount and pattern of nickel release from different stainless steel orthodontic appliances in vitro. The release rate of nickel from dynamically loaded fixed appliances was found to be accelerated compared with that released under static conditions. Caution should be exercised when applying the results to the in vivo situation.

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The unique memory property of thermodynamic wire is only partially understood. It is believed to result from the wire's inherent capability to markedly alter its atomic bonding forces as a function of temperature. This shape recovery phenomenon may be the result of a transition in crystal structure that occurs by deformation and cooling. When the transition is reversed, by heating, the structure reverts to its original form and abrupt property changes occur. The purpose of this study was to determine the transition temperature ranges (TTR) of three commercially available thermodynamic archwires and to determine the rate of recovery of the wires when bent to a uniform shape.

A jig was constructed to hold the wires and was suspended in a water bath within a plexiglass box. The temperature of the water bath was gradually increased. A program was written to acquire a single video frame from a running video tape and then allow the operator to graphically overlay the position of each wire specimen.

The results indicate that the TTRs for the three commercially available thermodynamic wires are of similar magnitudes (x̄ = 6.7° C, 6.2° C and 6.7° C). The greatest differences were in the standard deviations (1.3° C, 2.2° C and 3.7° C) which may be a function of manufacturing during alloying of the wire and/or its heat treatment.

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This study was designed to investigate the biomechanical behavior of the periodontium including the periodontal ligament (PDL) in terms of tooth mobility. Tooth mobility was measured in the canines of 10 adolescent patients before and after distal movement. Distal movement of the canines was carried out by use of a calibrated sectional archwire exerting an initial retraction force of 200 g. Tooth mobility was measured immediately before and after canine retraction by use of a noncontact displacement sensor when varying distal forces of 0 to 500 g were applied to the mesial of the canine. Before tooth movement, tooth mobility exhibited a substantial increase in loading with forces ranging from 50 to 150 g. The rate of increase gradually decreased up to 500 g. A nonlinear change in tooth mobility was similarly observed at the end of tooth movement or 24 days after the initiation of movement. Tooth mobility, however, was significantly greater when forces above 200 g were loaded. The periodontal tissues—the PDL and alveolar bone in particular—become more flexible at the end of tooth movement, indicating reduced support by the periodontal tissues. These findings suggest that the elastic nature of the PDL and alveolar bone may decrease substantially at the end of tooth movement.

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This study examined alveolar bone turnover and orthodontic tooth movement after appliance decay. One group of rats (N=54) received orthodontic force (40 g initial activation) while the other (N=36) was sham-treated. Groups of six rats were sacrificed at various times following activation. Tooth movement and appliance decay were monitored cephalometrically, and bone turnover was monitored locally by histomorphometry and phosphatase chemistries and systemically by serum phosphatase and osteocalcin changes. A significant association was found between spring forces assessed by direct measurement and by cephalometric images (R² = 0.784; p=0.02). The cephalometric method indicated appliances were at least 93% deactivated by day 16. Tooth movement continued beyond the point of appliance decay (p<0.001). This was accompanied by a dramatic decline in osteoblast surface (p<0.0001) and an increase in osteoclast surface to control levels (p<0.001). A significant peak in bone formation rate was also noted around appliance decay (p=0.005). Serum acid phosphatase and osteocalcin also increased after appliance decay (p<0.05), but alkaline phosphatase did not. Bone acid phosphatase was characterized by a peak after appliance decay (p=0.0004), but alkaline phosphatase remained depressed (p<0.0001). These data demonstrate that significant amounts of alveolar bone turnover continue for an indeterminant period following appliance decay.

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The remodeling mechanisms of transseptal fibers during and after tooth movement were investigated histologically. An autoradiographic study was conducted to assess the synthetic response. One hundred fifty male Wistar strain growing rats were divided into three groups—one control and two experimental groups. Animals in the experimental groups were subjected to tooth movement with 25 g and 150 g of force. Maxillary first and second molars were separated and retained mechanically.

Transseptal fibers were stretched in proportion to the amount of force applied for up to 2 days. Dynamic remodeling with proliferation of fibroblasts during tooth movement and slow rearrangement during retention periods occurred in both experimental groups. Collagen phagocytosis within the fibroblasts was observed ultrastructually during the experimental periods. The number of silver grains in fibroblasts in the collagen fibers increased 160% the first day and 206% during the first 3 days.

Proliferating fibroblasts remodeled the transseptal fibers through the synthesization and degradation of collagen fibers.

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The method of differential lissajous electromyography (DL-EMG) was applied to investigate the relationship among the integrated EMG activity, timing, and coordination of the bilateral superficial anterior temporal and masseter muscle activities in normal occlusion and Class III malocclusion subjects. In both Class III malocclusion and normal occlusion subjects, the working side muscles showed a higher mean cumulative voltage (MCV) and mean maximum peak voltage (MMPV) compared with the balancing side. In addition, a higher MCV and MMPV of the working side masseter was observed in the normal occlusion group compared with that seen in the Class III group during both right and left side chewing (p<0.01). Discriminant analysis applied to examine the distribution, the size and the shape of DL-EMG pattern further indicated a statistical difference between subject groups (p<0.01). Finally, there was a significantly higher percentage of clockwise DL-EMG pattern-generation in the normal group compared with that seen for Class III subjects (p<0.01). These data indicate that, compared with normal subjects, patients with a Class III malocclusion have a demonstrably abnormal masticatory muscle balance which is well characterized by the DL-EMG method.

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