Page 394 - IJB-10-3

International Journal of Bioprinting Optimizing 3D-printed mouthguards

lower values for D-A30 and the range between D-A60 and 3.2.1. Assessment of retention force in MG inlayer
D-A70 in MIF. There was a statistical significance in retention force
As described in methods, the arrival time to MIF between each conventionally fabricated MG and each
was denoted as MIF-t. The MIF-t without samples as the double-layer additively manufactured MG sample at
control group was 0.21 ± 0.03 ms; this increased once the any fatigue test stage (P < 0.001). In the comparison of
material sample was implemented. The average MIF-t for retention forces, only MG21 had a statistical significance
conventional materials, ERK and MG21, was 0.58 ± 0.04 that increased retention force throughout the whole fatigue
ms and 0.55 ± 0.04 ms, respectively. There was a statistically tests (P = 0.028); significant increases in retention force
significant difference in MIF-t between single-layer and were also observed from the pre- to post-fatigue test (P =
double-layer additively manufactured samples (P < 0.001), 0.043). In general, all MGs showed an inapparent increase in
except at Shore A hardness of 50 and 60 (P = 0.179 and retention force from the pre-fatigue test to the mid-fatigue
P = 0.975). Single-layer designed samples showed a quintic test (Table 4). During the fatigue test, the retention force
approximation function, which indicated multiple wave in double-layer additively manufactured MG samples was
crests (R² = 0.9037). Double-layer designed samples exhibited found to be increased corresponding to the higher value in
a quartic approximation function with lower values between Shore A hardness of soft-layer materials (A) (Figure 11).
D-A50 and D-A70 (R² = 0.9586) (Figures 8 and 9).
3.2.2. Assessment of morphological changes in MG
3.2. Durability under cycle-loading fatigue test outer layer
All single-layer additively manufactured MG samples had MG outer layer morphological changes were evaluated
cracks on the molar occlusal surface by approximately the using RMS values. There was no statistical significance
1000th cycle. These cracks of the MG’s occlusal surface in RMS values in the pre-mid and mid-post fatigue test
were bitten through by the 5000th cycle; all single-layer
additively manufactured MG samples were discontinued periods for MG samples (conventional, n = 6; double-layer
during the mid-fatigue test (Figure 10). Table 3 shows the additively manufactured, n = 9) (P = 0.159 and P = 0.438,
statistical significance among the three types of MG samples respectively) (Table 5). Compared to pre-mid and pre-post
(conventional, n = 6; single-layer additively manufactured, fatigue tests, the RMS of ERK samples decreased after a
n = 9; double-layer additively manufactured, n = 9) (P < period of cycle-loading fatigue tests. However, the high
0.001). Double-layer additively manufactured MG samples standard deviation among ERK samples made it difficult
and conventionally fabricated MG samples were more to achieve statistical significance. Only MG21 presented
durable than single-layer additively manufactured MG a statistically significant decrease in RMS at the pre-post-
samples. fatigue test stage, and the morphological changes reduced

Figure 7. Maximal impact force (MIF) run chart for single-layer and double-layer additively manufactured samples according to different hardness of
materials. Abbreviations: A, single-layer Agilus or/and Vero composites MG samples; D-A, double-layer MG samples without layer D-ABS, inlayer Agilus,
or/and Vero composites.

Volume 10 Issue 3 (2024) 386 doi: 10.36922/ijb.2469