Effect of storage time and framework design on the accuracy of maxillary cobalt-chromium cast removable partial dentures

Abstract

Statement of Problem:Inaccuracies in the fit of palatal major connectors may be related to distortion of the wax pattern due to prolonged storage time and faulty major connector design.Purpose:This in vitro study was carried out to find out the effect of storage time and major connector design on the accuracy of cobalt-chromium cast removable partial dentures (RPDs).Materials and Methods:A brass metal die with a Kennedy Class III, modification 1, the partially edentulous arch was used as a master die. Thirty-six refractory casts were fabricated from the master die. The refractory casts were divided into three groups (Group I: Anterior-posterior palatal bar, Group II: Palatal strap and Group III: Palatal plate) based on the design of maxillary major connector and subdivided into four groups (sub Group A: 01 h, sub Group B: 03 h, Sub Group C: 06 h, and sub Group D: 24 h) based on the storage time. For each group, 12 frameworks were fabricated. The influence of wax pattern storage time and the accuracy of the fit palatal major connector designs on the master die were compared. Casting defects (nodules/incompleteness) of the frameworks were also evaluated before finishing and polishing. Repeated measures analysis of variance was used to analyze the data.Results:The gap discrepancy was least in sub Group A (01 h) followed by sub Group B (03 h) and C (06 h) and most in sub Group D (24 h). Statistically significant differences (P < 0.05 in all locations L1–L5) in the fit of the framework were related to the design of the major connector. The gap discrepancy was least in Group I (anterior-posterior palatal bar) followed by Group II (palatal strap) and most in Group II (palatal plate).Conclusions:It is recommended that the wax patterns for RPD to be invested immediately on completion of the wax procedure. The selection of a major connector design is crucial for an accurate fit of RPD.

Removable partial dentures: The clinical need for innovation

“…10 Traditional RPD design involves the production of stone casts, geometric characterization of the tooth and soft tissues related to the path of insertion, and careful designation of RPD components (major and minor connectors, rests, clasps, and base retention) using a direct waxing method. 3,19 Current digital technologies enable the design of RPD components on 3-dimensional (3D) representations of the patient instead of stone casts by using geometric analysis tools that create designs of micrometer-level accuracy that can be viewed in cross section. The virtual model can then be used to print wax for casting metal frameworks or the direct printing or milling of metal or resin frameworks.…”

Comparison of the Chairside Time and Fitness of Michigan Splints Fabricated With Conventional Method and Digital Method: A Self-Controlled Study

“…The method for quantitative evaluation of fitness in this study was based on PVS replica method described by Parker [14], which was always used in evaluating the fitness of clasp assembly in the field of removable partial denture study [15][16][17]. Then, many 2D measuring instruments including micrometers [18,19], profile projectors [20,21] and stereo microscopes [7,22] were used to measure the space in these studies. These instruments had been tried in this study, but it was difficult to orient the same anatomy position in two replicas and prone to bring error.…”

Evaluation of Anchorage Technique on the Adaption of Partial Denture Framework (Comparative in Vitro Study)

“…The accurate fit of maxillary frameworks with palatal strap major connector was selected to be evaluated in this study as the palatal major connector was indicated to be the most common site for inaccurate fit of RPD as reported by many investigators (2, 8, 19,20,22,23) . A master metal cast fabricated by split mold process using brass material was preferred for laboratory verification in this study, because it was more resistant to abrasion on repeated insertion and removal of the metal frameworks during evaluation procedure (17) .…”

“…Auto polymerized fast set acrylic resin material (Duralay) was used to measure this gap as it has fine grain size that offer fast set, sufficient flow, superior accuracy and rigidity in thin sections that does not distort when being measured with a micrometer caliper (8,22,24) .…”