Latib, Yasmin Osman2021-10-072021-10-072020https://hdl.handle.net/10539/31633A research report submitted in partial fulfilment of the requirements for the degree of Master in Dentistry (Prosthodontics), School of Oral Health Sciences to the Faculty of Health Sciences, University of the Witwatersrand, Johannesburg, 2020urpose: The most cost-effective treatment for the replacement of missing teeth is by removable partial dentures, which can either be based entirely in acrylic resin, or be reinforced by a metal framework. Metal frameworks have been traditionally made by the lost wax casting method, which is a lengthy and labour-intensive process. The introduction of computer-aided design and computer-aided manufacture (CAD/CAM) has revolutionised traditional dentistry, where it has been shown to be sufficiently accurate, less labour-intensive and cost-effective. The purpose of this study was to compare the accuracy and comparative costs of two digital workflows that produce resin framework patterns to be cast conventionally with an identical framework manufactured conventionally from a wax pattern. Method and materials: A maxillary master cast was made of a Kennedy Class II modification 3 partially edentulous arch, with appropriate tooth preparations. The same design for the framework was used throughout. From the master cast, 9 casts were made, and their accuracy determined. All measurements of casts and frameworks were made in three dimensions using the Reflex Microscope (Consultantnet Ltd, Cambridge, UK) which measures to an accuracy of 4μm. Six casts were scanned using a D2000 extra-oral scanner (3shape, Denmark). The other three casts were used for the conventional casting technique, by sending normal instructions for the design to a commercial laboratory. The six scanned models were imported into design software (3shape, Denmark, version 2.19.2.0) and a pattern designed on each in accordance with the design. Three digital patterns were milled in a resin burnout block (Yamahachi, Japan) using the Imes-iCoreCoritec350 Pro plus milling unit (Germany) and three were printed with resin burnout (Nextdent, 3S systems, Netherlands) using a 3D printer (Moonray, Sprintray, North America). Each framework and its model was measured using the reflex microscope at pre-determined points on the framework. Thereafter, the milled and printed frameworks, together with their corresponding casts, were conventionally cast and all 9 frameworks were then measured at the pre-determined points. One milled resin framework was miscast. This was a processing error that occurred during the traditional casting method. Results: All resin patterns and all cast frameworks showed intra- and inter-group consistency. The sample size precluded direct statistical conclusions, but no significant differences were found. Duplicate models were accurate and showed minimal differences compared with the master cast. All patterns and all frameworks showed some level of differences to the master cast, but no differences were greater than those reported in the literature as being clinically successful. The maximum overall discrepancy between the cast frameworks was 0.64 mm and at the rest seats, 0.262 mm. The preliminary cost analysis carried out revealed that the total time taken on average, was greater for the conventional technique. Conclusions: Within the limitations of this study, it can be concluded that, given the very small variations in the measurements both within and between the groups of the three different workflows, the use of digitally produced resin patterns prior to their being cast as metal frameworks, is both feasible and well within the accepted limits for clinical acceptability. It is recommended that further economic analyses be carried out, as well as further studies using these digital workflows, to determine the clinical acceptability of the methods.enThesis