Effects of thermoplastic appliance fabrication on the dimensional stability of 3D printed dental models / 대한치과재료학회지

The purpose of this study was to evaluate effects of fabrication of thermoplastic appliance on the dimensional stability of 3D printed dental models. A digital reference model was printed by different printing materials and densities [acrylonitrile butadiene styrene (ABS) and polylactic acid (PLA); 20, 40 and 60%]. Thermoplastic appliances were then fabricated with printed models for three times and models were scanned at three different stated; following the print out, following the fabrication for one time and three times. Tooth and arch measurements were performed to evaluate the accuracy and dimensional stability of printed models after fabrication of thermoplastic appliances. Printed models were not significantly different from the digital reference model regardless of different materials and densities. After the first fabrication of the appliance, most of measurements were decreased in PLA models ranged from 0.05 to 0.24 mm (p<0.05), whereas only a few measurements were decreased in ABS models (p<0.05). After fabrication for three times, measurements were more decreased in PLA models ranged from 0.04 to 0.42 mm (p<0.05) and some measurements were decreased in ABS models ranged from 0.08 to 0.27 mm (p<0.05). ABS models showed relatively good dimensional stability, but the PLA models showed significant dimensional changes even after initial fabrication of the appliance. Repeated fabrication of the appliances increased dimensional changes in printed models, especially printed with PLA.

Dorsal Plate Fixation for Dorsally Displaced Distal Radius Fractures

PURPOSE: The object of this study is to evaluate the clinical and radiographic outcomes of two different kinds of dorsal plating for dorsally displaced distal radius fractures. METHODS: Forty-three patients with dorsal plate fixation for distal radius fracture were retrospectively reviewed. Twenty-four patients were treated with nonlocking dorsal plate (group I) and nineteen patients with locking dorsal plate (group II). Range of motion and Green and O'Brien score were evaluated as clinical results, and radial inclination, radial length, volar tilt at postoperative and last follow up were evaluated as radiographic results. RESULTS: According to AO classification system, there were 18 type A fractures, 4 type B fractures, 21 type C fractures. In group I, the mean flexion and extension were 65.0degrees and 65.3degrees, respectively; ulnar and radial deviation were 25.5degrees and 20.8degrees; pronation and supination were 80.0degrees and 80.4degrees. In group II, the mean flexion and extension were 64.5degrees and 67.3degrees, respectively; ulnar and radial deviation were 30.6degrees and 20.6degrees; pronation and supination were 81.4degrees and 78.6degrees. The mean Green and O'Brien score was 94.4 in group I and 92.2 in group II, and 41 patients had satisfactory result. There was no statistical significant difference in clinical results between the groups. Results of postoperative and last follow-up radiographic analyses for mean radial inclination were 23.9degrees and 24.1degrees in group I, respectively, and 24.2degrees and 24.9degrees in group II; radial length were 9.9 mm and 9.7 mm in group I, and 10.1 mm and 9.2 mm in group II; mean volar tilt were 12.2degrees and 13.1degrees in group I, and 14.8degrees and 13.7degrees in group II. There were no statistical significant changes within radiographic parameters. No extensor tendon rupture was reported. CONCLUSION: Dorsal plate fixation for dorsally displaced distal radius fracture showed satisfactory clinical and radiographic outcomes with low complication rate, regardless of the type of plate.

The Efficacy of Preserved Posterior Cortex in the Treatment of Infected Nonunion of the Tibia

PURPOSE: We studied the efficacy of preserved posterior cortex connecting to adjacent muscle or periosteum during wide debridement in the treatment of infected nonunion of the tibia. MATERIALS AND METHODS: From January 2001 to May 2011, 12 cases of infected nonunion of the tibia with segmental defect larger than 4 cm after wide debridement were selected. The selected cases were categorized according to two groups; group 1 with preserved posterior cortex in the segmental defect site - six cases, group 2 without posterior cortex - six cases. The results were compared by assessing the size of bone defect, the interval between wide debridement and bone reconstruction, bony union time, complications, and clinical results. RESULTS: The mean length of bone defect of group 1 was 7.6 cm (range 4.3-11.0 cm) and that of group 2 was 6.4 cm (range 4.0-12.0 cm). The interval between wide debridement and bone reconstruction was 10.0 weeks (range 5-18 weeks) for group 1, and 12.1 weeks (range 0-24 weeks) for group 2. The time for bony union of group 1 was 6.2 months (range 5-7 months), and that of group 2 was 10.8 months (range 7-18 months). In group 2, there were two cases of fatigue fracture and two cases of docking site nonunion after distraction osteogenesis. CONCLUSION: The preserved posterior cortex after wide debridement of infected nonunion of the tibia helps bony union and reduces the treatment period.