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Critical Evaluation of Postprinting Processes and Mechanical Properties in Direct Printed Aligners

1. Introduction

The production of Direct Printed Aligners (DPAs) involves a critical stage known as the postprinting phase. This phase includes the removal of excess resin and subsequent curing of aligners. This postprinting phase is crucial in determining the mechanical properties and overall performance of DPAs.This process is described in the study titled Effects of intraoral aging on mechanical properties of directly printed aligners vs. thermoformed aligners: an in vivo prospective investigation

2. Partial Agreement with Previous Studies

This study observed a partial agreement with previous research on TC-85 resin, with a focus on mechanical properties. However, the DPAs exhibited less favorable mechanical properties, particularly in terms of higher force decay compare with PET-G aligners and smartrack aligners. Despite conducting postprinting polymerization under nitrogen, the lower mechanical properties may indicate incomplete polymerization, compromising both clinical performance and introducing the risk of residual monomers.

3. Health Concerns and Residual Monomers

A study on TC-85 resin DPAs has raised concerns about potential health hazards due to the leaching of UDMA monomer. Residual monomers, if present, may exhibit cytotoxic, mutagenic, and estrogenic effects, leading to allergies and hypersensitivities in patients. This highlights the importance of thorough postprinting processes to minimize the risk of residual monomers.

4. Mechanical Testing Protocols and Comparability

Mechanical testing in this study followed established protocols used in prior research on clear aligners, emphasizing thermoformed aligners. The choice of TC-85, with its glass transition temperature impact, was considered for comparability. It's noteworthy that TC-85's stiffness at body temperature may differ from ambient temperature, potentially affecting clinical performance.

5. Temperature Considerations and Patient Safety

While this testing was conducted at ambient temperature, it's important to consider the potential risks associated with subjecting patients to higher temperatures. The mechanical properties of TC-85 at 80°C, while interesting from a material perspective, may be clinically inconsequential. Patient safety, especially regarding the risk of burns, should be a crucial consideration in aligner manipulation using hot water.

6. Standardization of Production Protocols

With the ongoing evolution of materials for direct printing of aligners, it becomes crucial to establish a standardized production protocol. This is essential for ensuring the quality of in-house end products, addressing the variability introduced by new materials and techniques. Dentists' responsibility for the quality of DPAs emphasizes the need for a standardized approach in this variable and technique-sensitive method.


In conclusion, this study sheds light on the critical postprinting phase, potential health risks associated with residual monomers, and the importance of standardizing production protocols in the evolving landscape of direct printed aligners. These findings contribute to the ongoing discourse on optimizing the production process and ensuring the safety and efficacy of DPAs in clinical practice.

Thermoformed PETG-based in-house aligners (DUR) demonstrated generally favorable mechanical properties compared to DP and INV groups. This included the highest wear resistance, least force decay, and moderate stiffness. As the dental industry witnesses the introduction of new materials and techniques, establishing a standardized production protocol becomes imperative for ensuring the quality of in-house dental aligners.

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