Simulated Nighttime Grinding of 3D Printed Night Guards vs Lab Manufactured Night Guards

Objective: To compare the wear of two different 3D printed resins and a lab manufactured night guard. Methods: Three different materials were tested for their ability to stand up to simulated nighttime grinding. The materials tested were (n=30): Flex: SprintRay Night Guard Flex (SprintRay, Los Angeles, CA), Firm: SprintRay Night Guard Firm (SprintRay, Los Angeles, CA), and NGP: Clear Splint Biocryl 2mm (Great Lakes Orthodontic, Tonawanda, NY). The materials tested were formed into 10mm cubes. Flex and Firm groups were made using the SprintRay Pro55 3D printer, according to manufacturer specifications then polished using silicon carbide grinding papers of 240 and 600 grit with water (Buehler, IL, USA). The NGP group was made with a sheet of 2mm Clear Splint Biocryl plastic placed over a template block in a Biostar V pressure molding machine to replicate the same dimensions as the Flex and Firm groups. The surface roughness of each sample was measured using the Profilometer - Roughness Tester PCE-RT 1200 (PCE Instruments) and marked as initial surface roughness (Ra1). After the wear test, another surface roughness test was measured with the Profilometer and marked as the final surface roughness score (Ra2). In addition, all the specimen of each material were analyzed before and after the test with a 3D laser profilometry TMS-500 Top Map Pro.Surf (Polytec GmbH, Germany). These measurements, prior to the wear test were the initial surface area roughness (Sa1) and the final surface area roughness (Sa2). Enamel antagonists (molars cusps) were prepared from caries-free extracted molars. Four cusps were collected from each tooth. Standardization of the enamel antagonists for shape and size were done by using a diamond bur and high-speed handpiece under water irrigation. The enamel cusps were randomized between three groups. The wear test was performed using a wear simulator developed by the Tufts University School of Engineering. To simulate wear the samples were run through 20,000 cycles roughly equivalent to one-month of normal wear, under a load of 25N. Specimen and antagonists were lubricated with water. Results: The change in roughness/wear (before-after) for each of the three groups (Firm, Flex and NGP) was calculated. Descriptive statistics were calculated for wear, the NGP group showed the highest wear with a mean±SD of -0.94±0.55 for stylus profilometry and -0.92±0.90 for the laser analysis. The Shapiro-Wilk test showed that the data for one of the three groups was not normally distributed; a Kruskal-Wallis test was conducted to assess the difference in wear between the three groups. The Kruskal-Wallis test showed a statistically significant association between group and wear, p<0.0001. The Dunn's test along with the Bonferroni correction used to perform pairwise comparisons showed that there was a statistically significant difference between the Firm and NGP groups (p=0.004 stylus) and (p=0.014 laser) as well as the Flex and NGP groups (p<0.0001). There was no statistically significant difference between the Firm and Flex groups (p=0.612 stylus) and (p=0.443 laser). The statistical significance for within group differences was assessed using the Paired t-test for the Firm and NGP groups, and the Wilcoxon signed-rank test for the Flex group. The within group difference in the NGP group was statistically significant (p=0.0004 stylus) and (p=0.022 laser). Conclusion: Under these in vitro study conditions, Flex and Firm showed more resistance to wear than NGP. There was no statically significant difference between Firm and Flex groups.