Adaptation of cobalt chromium frameworks fabricated by conventional versus selective laser melting techniques: An in vitro and clinical assessment

Abstract

Statement of problem

Three-dimensional (3D) printing of cobalt chromium (Co-Cr) removable partial dentures (RPDs)by selective laser melting (SLM) has been claimed to be less challenging than by conventional casting and provides significant improvements. However, the adaptation and fit of the SLM framework and the optimum build orientation are still unclear.

Purpose

The purpose of this in vitro and clinical study was to evaluate the effect of different build orientations on the adaptation of removable partial denture frameworks fabricated by SLM technology in vitro and to compare the adaptation of the SLM and conventional RPD frameworks clinically.

Material and methods

A master model simulating a maxillary arch of Kennedy class III modification 1 was scanned and duplicated to create a virtual 3D cast and reference cast. Four groups (n=40) of Co-Cr RPD frameworks were fabricated. For the SLM groups, the Co-Cr framework was virtually designed and exported for SLM printing. The SLM printing was done in 3 different build orientations: 0-degree (n=10), 45-degree (n=10), and 90-degree (n=10) groups. Other Co-Cr frameworks were conventionally cast (n=10). All Co-Cr frameworks were scanned and virtually superimposed with the master model using a surface-matching software program. The gap under 9 selected points in the palatal major connectors was analyzed and calculated. A smaller gap indicates more surface adaptation and close contact between the palatal major connector and the master model. The data were analyzed using the Kruskal-Wallis and Dunnett T3 tests (α=.05). Three patients with a partially dentate maxillary arch were enrolled in the clinical part based on inclusion criteria. Two RPD frameworks were provided for each patient (conventional casting and SLM printing). The adaptation of each framework was assessed by measuring the gap between the palatal major connector of the framework and the palate with light-body silicone. The differences in adaptation between the conventional and SLM frameworks were compared by using independent t tests (α=.05).

Results

The in vitro study identified significant differences in the adaptation of the palatal major connector among the 4 groups (P<.001), except for conventional and 0-degree SLM printing (P=.999). The conventional and 0-degree SLM frameworks exhibited the best adaptation, with the lowest gap underneath the palatal major connector of the RPD framework (0.01 ±0.02 mm and 0.01 ±0.01 mm, respectively). In the clinical part of the study, no significant difference was found between the adaptation of SLM and the conventional framework (P=.430)

Conclusions

The adaptation of SLM printing can be maximized with less gap under the palatal major connector of the RPD framework when using the 0-degree build orientation. Co-Cr frameworks produced with SLM printing technology were comparable with conventionally produced frameworks; hence, SLM printed frameworks can be an alternative for clinical applications when optimum SLM parameters are applied.