Avaliação in vitro da precisão de guias de transferência em próteses parciais removíveis utilizando técnicas convencionais e de impressão 3d: estudo de acurácia

Abstract

The main objective of this diagnostic study was to analyze the accuracy of transfer guides for the preparation of guide planes on abutment teeth of RPDs, using conventional techniques and 3D printing. A total of 10 working models of partially edentulous arches (Kennedy Class III, modification 3) with dental preparations for guide planes on the proximal surfaces (CG=30; DG=30) were analyzed. In these models, guide planes were fabricated, and transfer guides (anterior, isolated, and posterior teeth) were evaluated using conventional and digital methods. The conventional transfer guides were made from a plaster model produced after molding the lower mannequin. The model was taken to the dental surveyor to plan the guide planes on the abutment teeth. The evaluation and reduction of the proximal surface were carried out, and the guide was made with autopolymerizing acrylic resin. The digital guides followed a similar process, starting with a scanned plaster model to generate an STL file. This file was processed in the Dental Wings – DWOS9 software for surveying and designing the guide. The guide was then 3D printed and subjected to post-curing. Based on a questionnaire with dichotomous responses, the retention, stability, and accuracy of preparation of the abutment teeth were evaluated. The normality of the data was assessed using the Shapiro-Wilk test. Fisher´s test was applied to verify the association between techniques and dependent variables (retention and stability). The non-parametric Mann-Whitney test was applied to compare the techniques and the execution time of the procedures. To measure the accuracy between the methods of fabrication of transfer guides (conventional or digital) regarding preparation of guides, sensitivity and specificity tests were used. Considering the retention and stability, no statistically significant association was found between the techniques regarding the anterior, posterior, and isolated guides in anterior, posterior or isolated teeth (p>0.05). The preparation accuracy ranged from 0.80 to 1.00, with the lowest value found for guidance in the anterior tooth (0.80) and the highest value for guidance in the posterior tooth (1.00). Evaluations between examiners comparing the techniques demonstrated that greater precision was found in guides made from molar teeth (n=50; 100%) and in guides from isolated teeth regardless of the face analyzed (n=50; 76%-100%). The working time was significantly longer for the conventional technique in the surveying (p<0.001). Guides made in anterior and posterior teeth using the digital method required longer working time (p<0.001). Regarding the manufacture and processing of the guides, more time was spent to carry out the procedure using the digital technique (p<0.001). Both techniques provided guides with adequate and similar retention and stability. The transfer guides for the preparation of abutment teeth for RPD exhibited very good to excellent accuracy. The digital technique proved to be faster in the surveying but required more work time to manufacturing and processing of the guides.