Factors influencing the dimensional accuracy of additively manufactured dental models: A systematic review of in vitro studies

This study aims to systematically review the literature and evaluate the effect of post-printing factors such as aging, heat, appliance fabrication and storage on the dimensional accuracy of full-arch dental models manufactured by additive manufacturing (AM) technology for the intended use of working model purposes. Three online databases, Medline (Ovid), Scopus and Web of Science were utilised for the data base search. In vitro studies assessing the dimensional accuracy of additively manufactured (AMed) models after being affected by different storage periods, aging methods and appliance fabrication were considered. Studies, between 1994 to March 2023, which analysed full-arch dental casts by AM were included, however studies in language other than English, with only abstracts, or review studies were not considered. Hand searching was done through Google Scholar using the same keywords and reference lists of the selected studies to identify any relevant studies not captured in the database search. Risk of bias for all selected studies was assessed and each study was characterised by the materials and methodologies of model printing, post-processing treatment, measurements of dimensional accuracy before and after post-processing, and conclusions. The systematic search identified and screened 769 different studies after the removal of duplicates. After applying inclusion and exclusion criteria, a total of 30 relevant titles and abstracts were found, yielding six final selections after full-text screening. Four out of the six studies evaluated the effect of both storage and aging on the dimensional accuracy of AMed dental models. The other two studies assessed the dimensional accuracy after the fabrication of thermoformed and vacuum-formed appliances on the AMed dental model. AMed models can be utilised as working models on the condition that specific printing parameters are followed and additional model design features are employed. No definitive conclusions can be drawn on standardised methods to assess the dimensional accuracy of AMed dental models after storage, aging and appliance fabrication. In addition, there is no consensus on specific storage periods for an AMed model. Majority of study designs removed the palatal region to create a horseshoe shaped model, making the results less applicable to a working model scenario requiring the palate for retention purposes. The parameters investigated on AMed models include storage, aging, and appliance fabrication through thermoforming and vacuum-forming. Printing densities of solid models and wall thickness of hollow models were shown to influence the accuracy of AMed models. Dimensional accuracy of AMed models have been shown to be affected during appliance fabrication through thermoforming and vacuum-forming in certain conditions. There is a clear need of standardisation when manufacturing dental models for working model purposes. The current methods investigated in this study lack established protocols to accurately manufacture the AMed models, and effectively store and utilise an AMed dental model for fabrication of orthodontic and prosthodontic appliances.