Page 388 - IJB-10-3

International Journal of Bioprinting Optimizing 3D-printed mouthguards

1. Introduction most critical ability of MG. These materials are competitive
with those of conventional fabricated materials like EVA
A sports mouthguard (MG) is essential for protecting the and polyolefin (PO). 20,21 It has been demonstrated that
hard and soft tissues of the oral cavity, including teeth and incorporating a hard insert within a conventional material
gums, from impact during athletic activities. The World can significantly enhance the protection capability. 22
Dental Federation emphasizes the importance of custom-
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made sports MGs in preventing trauma. In certain contact While the shock absorption and dispersion properties
sports, such as boxing, MGs usage is mandatory because of additively manufactured MGs have been extensively
they reduce the risk of traumatic dental injuries and brain studied, there is a need for more focused research on their
concussions, as demonstrated by extensive research. 2-8 durability, especially considering the intermittent occlusal
forces during athletic activities. Durability is another
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Despite their importance, creating a comfortable and crucial factor for the long-term, effective, and safe use of
durable MG is a complex challenge. The fabrication process, MGs. The resistance to surface wear and deformation from
particularly the thermoforming phase, often results in continuous use has been evaluated for conventional MG
diminished thickness around the anterior teeth, which materials, but the durability of additively manufactured
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can affect both comfort and protection. Additionally, MGs requires further investigation. Hard occlusal surfaces
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each MG must be tailored to fit comfortably, adding to the in devices such as night guards, which prevent bruxism,
complexity of the design.
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have been shown to improve durability and reduce wear.
The emergence of three-dimensional (3D) digital This study aimed to assess the effectiveness of combining
design and additive manufacturing process, known for its hard and soft materials in additively manufactured MGs
customization, rapid production, and cost-efficiency, has to enhance shock absorption and dispersion properties
attracted substantial interest. Prior studies have validated in simulated oral environments. Additionally, it evaluated
its safety and effectiveness, 10-13 suggesting a promising the durability, retention force, and morphological changes
future for additively manufactured sports MGs. of these MGs, particularly in response to the effects of
In 2020, Li et al. published an extensive exposition intermittent occlusal forces on their surfaces in simulated
of the digital design and manufacturing of sports MGs. oral environments.
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By implementing a semi-digital workflow, Hada et al.
examined how temperature fluctuations affected the 2. Materials and methods
material properties of sports MGs. After investigating 2.1. Samples preparation and digital model design
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various materials, Sousa et al. found that three additively Acrylate-base photoinitiator composites Agilus, Vero,
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manufactured materials—recycled polylactic acid (rPLA), and D-ABS (Stratasys Ltd., Rehovot, Israel) were utilized
polymethyl methacrylate (PMMA), and high-impact (Table 1). Seven types of Agilus and/or Vero composites
polystyrene (HIPS)—outperformed a conventional with Shore A hardness values of 30, 40, 50, 60, 70, 85, and
material, poly-(ethylene vinyl acetate) (EVA) in the 95 were produced under controlled conditions of 20±5℃
shock absorption experiment. A study by Pinho et al. and 50% humidity, denoted as A30, A40, A50, A60, A70,
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demonstrated increased elasticity and resistance in aged A85, and A95, respectively (Table 2). The composites were
sandwich samples.
blended in their liquid state before the printing process.
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The processes are categorized into International Single-layer samples were specified as having a diameter
Organization for Standardization/American Society for of 50 mm and a thickness of 3 mm. Double-layer samples
Testing and Materials (ISO/ASTM) process classes in consist of a 0.5 mm thick hard layer of D-ABS and a 2.5 mm
medical applications of additively manufactured powder thick, soft layer of Agilus or/and Vero composites (A30-
bed fusion, material extrusion, vat photopolymerization, 95), designated as D-A30 through D-A95, respectively
material jetting, binder jetting, sheet lamination, and (Figure 1). Material samples were printed by a J850 Digital
directed energy deposition. The Polyjet process (Stratasys Anatomy 3D printer (Stratasys Ltd., Rehovot, Israel) with
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Ltd., Rehovot, Israel), a revolutionary multi-material a dual-head liquid output. Conventional MG sheets made
jetting process, was widely applied for higher precision and of PO-base material (MG21; CGK, Hiroshima, Japan) and
printing speed, the ability to print multiple materials, and EVA-base material (Erkoflex [ERK]; Erkodent Erich Kopp
hands-free removal of support structure. GmbH, Pfalzgrafenweiler, Germany) were molded for
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comparison. The shock absorption test was conducted on
Materials of acrylate-base photoinitiator composites
(Agilus, Vero, digital poly-(acrylonitrile-butadiene-styrene) 16 samples.
[D-ABS]) are preferred for additively manufactured MGs Materials for additively manufactured MG samples
due to their excellent protection capability, which is the were divided into two groups: single-layer soft samples

Volume 10 Issue 3 (2024) 380 doi: 10.36922/ijb.2469