Abstract
Objective:The purpose of this study was to compare the accuracy of two working cast fabrication techniques using strain- gauge analysis.Methods:Two working cast fabrication methods were evaluated. Based on a master model, 20 working casts were fabricated by means of an indirect impression technique using polyether after splinting the square transfer copings with acrylic resin. Specimens were assigned to 2 groups (n=10): Group A (GA): type IV dental stone was poured around the abutment analogs in the conventional way; Group B (GB), the dental stone was poured in two stages. Spacers were used over the abutment analogs (rubber tubes) and type IV dental stone was poured around the abutment analogs in the conventional way. After the stone had hardened completely, the spacers were removed and more stone was inserted in the spaces created. Six strain-gauges (Excel Ltd.), positioned in a cast bar, which was dimensionally accurate (perfect fit) to the master model, recorded the microstrains generated by each specimen. Data were analyzed statistically by the variance analysis (ANOVA) and Tukey's test (α= 5%).Results:The microstrain values (με) were (mean±SD): GA: 263.7±109.07με, and GB: 193.73±78.83με.Conclusion:There was no statistical difference between the two methods studied.
Highlights
Failure of passive fit in implant-supported prostheses induces deleterious forces on the implants and their associated components, and can lead to denture failure by fatigue and/or loss of osseointegration[17,20]
To assess the relationship between the relief and the position of the strain-gauge, the data obtained in the present experiment were submitted to ANOVA, after the suppositions of the analysis of variance model were assessed
The clinical relevance of these data are reflected in the fact that the quality of fabrication of prosthetic restorations is related to the quality of the working models obtained
Summary
Failure of passive fit in implant-supported prostheses induces deleterious forces on the implants and their associated components, and can lead to denture failure by fatigue and/or loss of osseointegration[17,20]. It is recognized that absolute passive fit is unattainable[11,19], as the clinical and laboratory variables inherent to rehabilitating treatment itself are obstacles to this[9,7,13]. Et al.[6] (1985) has recommended the splinting technique as the clinical conduct of choice for transferring the intraoral posts to the working model. According to this author, this conduct increases the stability of the transfers both during their removal from the impression and at the moment of fixing the analogs, in addition to having shown more consistent results with regard to precision of the impression[5,14]. Polyether and addition silicone impression materials should be preferred for transfer procedures because they have the lowest distortion values (around 100 μm)[15]
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