Page 398 - IJB-10-3

International Journal of Bioprinting Optimizing 3D-printed mouthguards

been validated. Moreover, the clinical perspective was not In addition to shock absorption, a MG must ensure a
considered. Schewe et al. explored the shock absorption sufficient retention force to avoid dislocation during rapid
of photoinitiators, but did not clarify the specific movement. Previous research indicated that the average
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requirements for designing MGs with a thickness of 2–4 retention force of conventionally fabricated MGs was 6.4 ±
mm. MGs thicker than 4 mm may cause joint discomfort 2.5 N in wet conditions. This value was exceeded only by
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due to the 2–4 mm freeway space in the mouth. Previous D-A70 type of MG samples when without any use. The MG
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studies have not extensively considered the effects of the sample is expected to have more specialized applications
oral environment, such as temperature and humidity. 21,37 for individuals involved in fast-moving contact sports,
Most experiments have been executed at room temperature such as football players and boxers.
and humidity because the conditions follow international According to the evaluation of retention force and RMS,
standards, and are globally applicable. In Tun et al.’s only MG21 samples showed a statistical significance of a
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study, the shock absorption rate of Agilus30 at room larger retention force with a smaller RMS deviation in fatigue
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temperature was 26.9%, but it increased to 65.3% in this tests (Tables 5 and 6). However, previous studies suggest
study. As with Compo50, Agilus50 (A50) showed an that the MG retention force decreases with continued use.
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increased absorption rate from 44.8% at room temperature MGs initially increase or stand the retention force before
and humidity to 63.3% under simulated oral conditions. decreasing it. This may be conducive to the preparation
In contrast, conventional MG materials, ERK and MG21, of MG samples in future clinical applications. Further
demonstrated consistent absorption rates of around 43.5% research is necessary to determine the most appropriate load
and 41.8% at room temperature, and approximately 45.5% preparation for MGs during fatigue tests.
and 44.5% under simulated oral conditions. Our study
demonstrated that additively manufactured material There are some limitations in our study. We excluded
samples had an improvement in shock absorption in a certain values due to similar shock absorption results between
simulated oral environment. the intermediate Shore A hardness number of additively
manufactured material samples. Besides, the unsatisfactory
Both layer design and Shore A hardness affect shock results of the shock absorption tests conducted in MIF-t on
absorption properties. The free-falling steel ball test D-A85 and D-A95 types of material samples removed the
indicated layered design was more influential than hardness need for further durability tests, potentially resulting in a
of materials, as demonstrated by statistical significance data exclusion. Biocompatibility is another consideration.
between hardness-paired material samples (Figure 7). The Agilus series materials have already been applied in several
MIF-t approximation function for single-layer samples medical devices, including stethoscopes and eye gear
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suggested a more complex relationship, with an additional with prescription glasses, and the same type of materials
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peak in growth after A70 samples, encouraging further are being employed in this study. However, little is known
investigation (Figure 9). about the biocompatibility of these materials. Despite these
Our research confirmed that double-layer additively limitations, the findings of this study may contribute to MG
manufactured MG samples were preferred to single-layer enhancement as a medical device in the future.
MG samples, as the single-layer MG samples can be damaged
at fatigue tests. Despite the superior shock absorption 5. Conclusion
ability of single-layer additively manufactured samples, In this study, additively manufactured material samples
their propensity to crack during cycle-loading fatigue tests (except for D-A95) made by Agilus, Vero, and D-ABS
suggests that single-layer designs are not feasible for future performed better in shock absorption than conventional
use. Double-layer additively manufactured MG samples material samples ERK and MG21 in simulated oral
exhibited superior shock absorption than conventionally environments, with additively manufactured single-layer
fabricated MG samples ERK and MG21, except for the type MG samples and specific types of double-layer MG samples
of D-A95 samples. In addition, double-layer additively (D-A50, D-A60, D-A70) demonstrating the same arrival
manufactured materials (D-A50, D-A60, D-A70) had the time of maximum impact force (MIF-t) as conventionally
same MIF-t values as conventional materials. fabricated MGs.
Our research also proved that fabricating inconsistencies Moreover, this study provides insights into the
affected the retention force of conventionally fabricated durability and retention forces of additively manufactured
MG samples. However, additively manufactured MG MG samples, indicating that single-layer additively
samples have manufacturing consistencies, superior shock manufactured MG samples are less durable, but
absorption, and acceptable durability, providing more highlighting the benefits of utilizing hard materials on
consistent, standardized, and reliable safety protection. occlusal surfaces and effective shock absorption capabilities

Volume 10 Issue 3 (2024) 390 doi: 10.36922/ijb.2469