Investigation into the effect of a custom-made jig to enhance guide plane preparation and partial denture framework retention

Abstract

Tooth loss is a common disease and removable partial denture (RPD) is an option to replace ‎missing ‎teeth. One of the major issues of RPDs is reduced retention. Guide plates are RPD ‎components that ‎restrict the path of insertion and improve frictional retention. Dental practitioners ‎have to prepare ‎parallel guide planes on abutment teeth which is difficult to achieve clinically. The ‎invention of a ‎custom cutting guide using computer-aided design and computer-aided ‎manufacture (CAD-CAM) ‎technology by 3Shape TRIOS® software may enhance the accuracy of ‎preparing parallel guide planes, ‎thus improving the RPD retention. The aim of this project was to ‎create a cutting guide using a novel ‎process in CAD-CAM technology and investigate the effect ‎on guide plane preparation and RPD ‎retention. ‎ In this project, a bounded saddle master model was selected and duplicated into 40 printed resin ‎‎models. Four abutment teeth were included in the tests. The upper right second molar (UR7), the ‎‎upper right first premolar (UR4), the upper left second molar (UL7), the upper left first premolar ‎‎(UL4) ‎were utilized. The duplicated models were divided into two groups. In the first group (A), 20 ‎cobalt-‎chromium (Co-Cr) frameworks were fabricated without guide plane preparation for 20 ‎printed models, ‎and the frameworks retention were assessed. In the second group (B), 20 Co-Cr ‎frameworks were ‎designed and fabricated based on prepared guide planes on 20 models. The ‎guide plane preparations ‎of group B were performed using a custom-made jig. The model base ‎was used as a standardised ‎reference for designing the jig and assessing the accuracy of guide ‎plane preparations. The retention of ‎group B frameworks were measured and the accuracy of ‎guide plane preparations were evaluated. ‎ The results showed that the average of maximum load for testing retention of RPD frameworks ‎was ‎‎1.887 ± 2.779 N (N=Newtons) in group A unprepared models and 0.350 ± 0.575 N in group B ‎prepared ‎models. The accuracy assessment of prepared guide planes in group B showed that the ‎‎average angle ‎between the model base and UR7 guide plane was 102⁰ ± 1.21 degrees. ‎The ‎average angle between the ‎model base and UR4 was 93⁰ ± 1.86 degrees. The average angle ‎between the model base and UL4 was ‎‎92⁰ ± 2.03 degrees. The average angle between the ‎model base and UL7 was 103⁰ ± 2.39 degrees. Also, ‎the measurement of parallelism ‎between ‎opposing guide planes on the right and left bounded saddles ‎of prepared guide planes in group B ‎showed that the ‎average angle on the right side between UR7 and ‎UR4 was 15⁰ ± 2.47 degrees, ‎and the ‎average angle on the left side between UL7 and UL4 was 15⁰ ± ‎‎3.36 degrees. Lastly after ‎guide plane preparation in group B, the average of maximum depth tooth ‎reduction on UR7 ‎0.38 ‎‎± 0.09 mm, UR4 ‎0.36 ± 0.09 mm, UL4 ‎0.43 ± 0.14 mm, and UL7 ‎0.42 ‎± 0.11 mm.‎ In conclusion, the resin custom-made Jig that was designed using 3Shape software resulted in ‎non-‎parallel guide planes and divergent guide plane angle which reduced retention of Co-Cr ‎frameworks in ‎group B prepared models compared to group A non-prepared models. Therefore, ‎the chosen design of ‎the jig negatively influenced the accuracy of guide plane preparation and ‎framework retention. ‎