Are the properties of 3D printed dental materials affected by nitrogen-rich postpolymerization? A systematic review and meta-analysis

Statement of problem

The vat polymerization-based 3-dimensional (3D) printing of dental materials necessitates a postpolymerization procedure to complete the fabrication of the printed device. A nitrogen-rich postpolymerization (NRPP) environment has been claimed to prevent the formation of an oxygen-inhibited layer, potentially improving material characteristics. However, a consensus on its impact on properties relevant to dental applications is lacking.

Purpose

The purpose of this systematic review and meta-analysis was to synthesize evidence comparing the chemical, physical, mechanical, and biological properties of 3D printed dental materials subjected to NRPP against conventional postpolymerization.

Material and methods

Comprehensive searches were conducted across MEDLINE (via PubMed), Web of Science, Scopus, Open Access Theses and Dissertations, and Google Scholar and using the manual method without language restrictions up to February 2024. Two reviewers screened the literature, assessed the risk of bias (RoB) using the QUality assessment tool for IN vitro studies (QUIN), and independently extracted data from eligible studies. Meta-analysis was undertaken by using a random-effects statistical model with the R-software program, and evidence certainty was rated via the grading of recommendations assessment, development, and evaluation (GRADE) approach.

Results

Of 275 articles, 14 in vitro studies with a medium RoB were included in the systematic review, with 8 eligible for meta-analysis. These studies involved 3D printed occlusal devices, implant guides, denture bases, interim crowns or fixed partial dentures, and orthodontic aligners. No statistically significant standardized mean difference (SMD) in material properties was found between with and without NRPP for water solubility, dimensional accuracy, water sorption, flexural modulus, flexural strength, hardness, or fracture toughness (P>.05). An exception was the degree of surface polymerization, with an SMD of 1.66% (95% CI, 0.56 to 2.76; I²=65%) favoring NRPP. The overall certainty of evidence was graded as low to very low.

Conclusions

NRPP does not significantly alter the physical, chemical, or mechanical properties of 3D printed dental materials except for a higher degree of surface polymerization in unpolished occlusal devices. The overall evidence certainty was rated as low to very low.