The dimensional change of cast implant bars after laboratory procedure / 대한치과보철학회지

STATEMENT OF PROBLEMS: The precision of fit between the bearing surfaces of implant abutments and the prosthesis framework has been considered fundamental to implant prosthodontic protocol. PURPOSE: The study aimed to investigate the effect of laboratory procedure on the dimensional accuracy of cast implant bars. MATERIAL AND METHODS: Thirty implant bars were fabricated on a metal master model. The gap distances were measured at the right implant abutment replica-gold cylinder interface after casting procedure. The bar length data of precasting and postcasting state were collected and analyzed. RESULTS: The mean gap distance found after casting was 106.3 micrometer for buccal side, 122.1 micrometer for distal side and 117.1 micrometer for the lingual side. The mean bar length was 17964.7 micrometer at precasting measurement, 17891.6 micrometer at postcasting measurement. The mean change of bar length was - 73.1 micrometer. CONCLUSION: Even though the techniques used in this study strictly followed the guidelines established in the literature, the 30 cast implant bars evaluated all yielded gap distances that were beyond acceptable accuracy. There was a statistically significant difference between precasting and postcasting bar length (P<0.01). There was a decreasing tendency in bar length after casting procedure. It was necessary to correct this dimensional change from laboratory procedure by some corrective methods.

A study for the development of the Korean orthodontic bracket / 대한치과교정학회지

The aim of this study was development of the Straight-Wire Appliance(SWA) suitable for the treatment of Korean. To accomplish the object of this study, Korean adult with normal occlusion were selected with following criteria: 1) no functional abnormality in the craniofacial area, 2) good dental arch form and posterior occlusal relationship, 3) Angle Class I occlusal relationship, 4) no experience of orthodontic, nor prosthodontic treatment, especially, no dental treatment on labial and buccal surfaces of teeth, 5) good facial profile. Impression were taken for upper and lower dental arches of the selected normal occlusion samples and the orthodontic dental stone models were fabricated. 5 well-trained orthodontists had examined the acquired dental stone models to select study samples which satisfy the Six keys to optimal occlusion of Andrews. 155 pairs of dental stone models (92 pairs of Male, 63 of Female) were finally selected. 3 dimensional digitization were performed with the Coordinate Measuring Machine(CMM, MPC802, WEGU-Messtechnik, Germany) and measuring of Angulation, Inclination, In-and-Out, Molar offset angle and Arch form were accomplished with a measuring software to achieve data for the development of SWA. Before the measurement, error study was performed on the 3 dimensional digitization with CMM, and the analysis of reliability of computerized measuring method adapted in this study and conventional manual method presented by Andrews was performed. Results of this study were as follows: 1. Equi-distance digitization with mesh size 0.25 mm, 0.5 mm and 1.0 mm were acceptable in 3 dimensional digitization of dental stone model with the CMM, and the digitization with 1.0 mm mesh size was recommendable in terms of efficiency. 2. Computerized measuring method with 3 dimensional digitization was more reliable than manual measuring method of Andrews. 3. Data were collected for the development of SWA suitable for the morphological characteristics of Korean with the computerized measuring method with 3 dimensional digitization.