A B Carr1, J Master. 1. Ohio State University College of Dentistry, Columbus 43210-1241, USA.
Abstract
PURPOSE: Prosthodontic techniques for implant-supported prostheses continue to evolve in an effort to facilitate treatment and minimize costs. Because research has shown no impression transfer technique to be without error, some clinicians have attempted to control the fit of prosthetic frameworks by reorienting sections of patterns or frameworks intraorally, fabricating a verification cast, and completing the prosthesis to fit such a cast. One manufacturer has attempted to meet both impression-making and verification-cast objectives by providing metallic impression copings (MICS) with extensions that allow contact between the copings for rigid fixation with acrylic resin before impression making. The purpose of this study was to determine the accuracy of casts produced from the MICS transfer process compared with casts produced from sectioned frameworks, where both techniques used a low-polymerization-shrinkage acrylic resin polymer to rigidly join the sections. MATERIALS AND METHODS: Using stainless steel measurement spheres as a reference point on each implant analog, the distances between analogs on the experimental casts were compared with the distances measured on the master cast. Seven casts were produced for each group and measured with a machinist's microscope at a 4-micron level of precision. RESULTS: The results revealed that the MICS transfer exhibited a mean error of 41 microns, which was significantly less than the verification-cast group mean error of 57 microns (p < .01, Student's t test). CONCLUSIONS: Given these results, clinicians can consider the rigid transfer technique as provided in the MICS transfer to be more accurate than the verification technique as outlined in this study.
PURPOSE: Prosthodontic techniques for implant-supported prostheses continue to evolve in an effort to facilitate treatment and minimize costs. Because research has shown no impression transfer technique to be without error, some clinicians have attempted to control the fit of prosthetic frameworks by reorienting sections of patterns or frameworks intraorally, fabricating a verification cast, and completing the prosthesis to fit such a cast. One manufacturer has attempted to meet both impression-making and verification-cast objectives by providing metallic impression copings (MICS) with extensions that allow contact between the copings for rigid fixation with acrylic resin before impression making. The purpose of this study was to determine the accuracy of casts produced from the MICS transfer process compared with casts produced from sectioned frameworks, where both techniques used a low-polymerization-shrinkage acrylic resin polymer to rigidly join the sections. MATERIALS AND METHODS: Using stainless steel measurement spheres as a reference point on each implant analog, the distances between analogs on the experimental casts were compared with the distances measured on the master cast. Seven casts were produced for each group and measured with a machinist's microscope at a 4-micron level of precision. RESULTS: The results revealed that the MICS transfer exhibited a mean error of 41 microns, which was significantly less than the verification-cast group mean error of 57 microns (p < .01, Student's t test). CONCLUSIONS: Given these results, clinicians can consider the rigid transfer technique as provided in the MICS transfer to be more accurate than the verification technique as outlined in this study.