Study the precision of fixed partial dentures of Co-Cr alloys cast over 3D printed prototypes

Abstract

Purpose: of this paper is to investigate the accuracy of Co-Cr dental bridges, manufactured using 3D printed cast patterns. Design/methodology/approach: Four-unit dental bridges are fabricated from the alloys i-Alloy and Biosil-f by lost-wax process. The polymeric cast patterns are 3D printed with different layer’s thickness (13 μm, 35 μm and 50 μm). Two 3D printers are used: stereolithographic “Rapidshape D30” and ink-jet “Solidscape 66+”. The geometrical and fitting accuracy as well as the surface roughness are investigated. Findings: It is established that Co-Cr bridges, casted from 3D printed patterns with 50 μm layer thickness, characterize with the largest dimensions – 3.30%-9.14% larger than those of the base model. Decreasing the layer thickness leads to dimensional reduction. The dimensions of the bridges, casted on patterns with 13 μm layer thickness, are 0.17%-2.86% smaller compared to the primary model. The average roughness deviation Ra of the surface of Co-Cr bridges, manufactured using 3D printed patterns, is 3-4 times higher in comparison to the bridge-base model. The greater the layer thickness of the patterns, the higher Ra of the bridges. The silicone replica test shows 0.1-0.2 mm irregular gap between the bridge retainers and abutments of the cast patterns and Co-Cr bridges. Research limitations/implications: Highly precise prosthetic constructions, casted from 3D printed patterns, can be produced only if the specific features of the 3D printed objects are taken in consideration. Practical implications: Present research has shown that the lower the thickness of the printed layer of cast patterns, the higher the dimensional accuracy and the lower the surface roughness. Originality/value: The findings in this study will help specialist in dental clinics and laboratories to choose the right equipment and optimal technological regimes for production of cast patterns with high accuracy and low surface roughness for casting of precise dental constructions.

Specifics in Production of Fixed Partial Dentures Using 3D Printed Cast Patterns

“…It is known that the quality of the additively manufactured details depends on the process type, the layer thickness and the position of the object towards the print direction. It was established in our previous research that the surface roughness of the cast patterns, fabricated by stereolithography, is about 2-3 times higher than that of the conventionally cast base model [15]. Decreasing the polymerization layer's thickness leads to decrease of the surface roughness.…”

“…The dimensional accuracy of the cast patterns and bridges, cast of dental alloys, is studied by measurements of the connectors between the bridge retainers and the pontics (a1, a2, a3), the pontics' width (b1, b2) and the bridges' length -L [13][14][15]. Three samples of each group are measured.…”

“…The 3D printing process is characterized by building of the objects layer by layer using polymerization, melting or sintering [8][9][10][11][12]. The quality of the 3D printed details depends on the process type, the layer thickness and the position of the specimen relative to the build direction [1,5,7,10,[12][13][14][15]. Decreasing the thickness of the 3D printing layer results in reduced surface roughness.…”

“…Decreasing the thickness of the 3D printing layer results in reduced surface roughness. However, even after sand blasting, the traces of the layers of the 3D printed pattern can be observed on the surface of the casting [1,[15][16][17]. Therefore, for production of precise castings with high smoothness, it is necessary to use cast patterns, manufactured by stereolithography or multi-jet modelling processes with the possible minimum layer thickness.…”

“…To select the material for the 3D printed cast pattern and the investment material for the casting mold, matching the available printer and the dental alloy; 2. All operations throughout the casting process to be strictly performed in accordance with the materials used and the manufacturer's instructions [1,15,16].…”