Evaluation of dimensional accuracy and degree of polymerization of stereolithography photopolymer resin under different postpolymerization conditions: An in vitro study

Statement of problem. The appropriate postpolymerization of stereolithography (SLA) resins with the least effect on dimensional accuracy and with optimal polymerization is unclear. Purpose. The purpose of this in vitro study was to investigate the dimensional accuracy and degree of polymerization of a photopolymer resin for SLA with different postpolymerizing times and temperatures. Material and methods. Sixty 1.5-mm-thick specimens were made from clear photopolymer resin with a 3D printer to simulate a maxillary complete denture. They were postpolymerized for different periods (15 and 30 minutes) at 3 different temperatures (40 degrees C, 60 degrees C, and 80 degrees C). Both prepolymerization and postpolymerization gap sizes for each specimen were measured at 5 different locations under a stereomicroscope. The tissue surface was scanned before and after polymerization, and the images were superimposed. The deviation was analyzed by using computer-aided design (CAD) software; root mean square estimates (RMSE) and color map data were obtained. Fourier transform infrared spectrometry was used to determine the degree of conversion (DC) of all specimens. The KruskalWallis and Mann-Whitney tests were used to calculate the difference value of the gap sizes (alpha=.05). One-way ANOVA and the Tukey test were used for RMSE and DC (alpha=.05). Results. The smallest average change in gap sizes was found at 15 minutes and 40 degrees C, and the largest change at 30 minutes and 80 degrees C. The lowest RMSE was obtained at 30 minutes and 40 degrees C (P<.05). On the color map, a uniform deposited layer was created at 15 minutes and 40 degrees C and 30 minutes and 40 degrees C. The highest DC was found at 30 minutes and 60 ?C, which differed significantly from 15 minutes and 40 degrees C (P<.05). The lowest degree of polymerization was found at 30 minutes and 40 degrees C. Conclusions. The polymerizing temperature exerted a greater effect than polymerizing time, with lower temperatures leading to improved fit and tissue surface accuracy. The recommended parameters for SLA polymerization are 15 minutes and 40 degrees C. These conditions offered high dimensional accuracy, favorable surface tissue adaptation, and satisfactory DC.

Automated summary

The study aimed to investigate the dimensional accuracy and degree of polymerization of photopolymer resin for stereolithography under different postpolymerizing times and temperatures. Results showed that the smallest average change in gap sizes was observed at 15 minutes and 40 degrees Celsius, while the largest change was seen at 30 minutes and 80 degrees Celsius. The recommended parameters for SLA polymerization are 15 minutes and 40 degrees Celsius.