Evaluation of the tensile properties of polished and unpolished 3D SLA- and DLP-Printed specimens used for surgical guides fabrication.

Abstract

Introduction: The fundamental mechanical properties of 3D printed surgical guides used in orthodontics represent an important indicator for the accuracy of the insertion of skeletal anchorage devices. The tensile strength of devices printed by stereolithography (SLA) and digital light processing (DLP) methods, respectively, is influenced by factors such as finishing process. Aim of the study: This study illustrates a comparison of the tensile strength in two different types of 3D printed devices (SLA, DLP respectively) undergoing or not a standard process of polishing. Material and methods: Twenty-four specimens obtained according to ASTM D638-14 (Standard Test Method for Tensile Properties of Plastics) were used for the evaluation of tensile strength. Four groups of 6 samples from each category were created: SLA polished, SLA unpolished, DLP polished and DLP unpolished. After removing the support, finishing was performed to obtain smooth surfaces, according to the manufacturer’s recommendation. Type V specimen was used to perform tensile tests in accordance with the standard procedures ASTM D638-14 which recommends at least five specimens to be tested for each sample. One-way analysis of variance (ANOVA) and t-test showed statistically significant results at p < 0.05. SPSSv17 software was used for statistical analysis of the numerical variables, and also descriptive statistics were performed. Results: The measurements included: tensile strength (maximum load), tensile stress at maximum load and tensile strain at maximum load. The maximum load (tensile strength) of the polished specimens was lower, both for the SLA and DLP, with no statistical significance results. Conclusions: The conclusions indicated differences between maximum load and tensile stress at maximum load between polished and unpolished specimens, in both SLA and DLP groups. Althought the polishing process reduces the tensile strenght, the data analysis did not present statistically significant results.