Page 129 - MSAM-4-2

Materials Science in Additive Manufacturing Mouthguards: Disinfection versus properties changes

The calculations followed established procedures and post-UVC), three specimens were analyzed. Each
described in prior studies. Specifically, σ was calculated specimen underwent three indentations using a 490 mN
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f
at the mid-span using the maximum nominal bending load and a holding time of 15 s.
stress, as shown in Equation I: Surface topography was assessed using a fringe
3P L projection phase-shifting method with the Attention 3D
máx
σ = 2bh 2 (I) Topography Module integrated into the Theta Flex optical
f
tensiometer (Biolin Scientific, Sweden). Key surface
Where P is the applied load, L is the span length, b is roughness parameters were measured, including the
the specimen width, and h is the specimen thickness. The r factor (defined as the ratio of the true surface area to the
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flexural modulus, E was determined using the theory of projected area), the average surface roughness (S ), and the
f
a
linear elastic bending beams, according to Equation II: quadratic surface roughness (S ) were determined.
q
PL 3 Wettability was assessed by measuring the static
E (II) contact angle of Milli-Q water at room temperature using
f

I
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the Theta Flex optical tensiometer. For each specimen,
Where I is the moment of inertia of the cross-section, five drops (5 μL each) were deposited, and the contact
and ∆P and ∆μ are the load range and flexural displacement angles were recorded once the air–water–surface interface
range, respectively, within the linear region of the load- reached equilibrium (θ ). Contact angle correction for
a
displacement curve. All results are presented as the mean surface roughness was applied using Wenzel’s equation
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± standard deviation of the mean value. For comparison, (Equation III):
bulk EVA specimens (90 × 10 × 4 mm ), the standard Cosθ = r × cosθ (III)
3
material for mouthguard fabrication, were also tested. a r
Where θ is the corrected angle for a smooth surface, θ
r
a
Given the functional demand placed on mouthguards, is the measured contact angle, and r is the roughness factor
transverse impact tests were conducted to further obtained from the topography analysis. 39
characterize the mechanical resilience of the 3D-printed
parts. Charpy impact tests were performed using V-shaped 3. Results
notched specimens (80 × 10 × 2 mm , with a 1 mm V-notch)
3
in accordance with the ISO 179 standard. These tests 3.1. Chemical characterization
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assessed the energy absorbed during impact to determine FTIR spectroscopy analysis was conducted to identify
the impact resilience of the materials. the characteristic chemical functional groups of each
polymeric filament and to confirm their chemical
Impact testing was conducted at room temperature
(~20℃) using a Ceast 9050 impact machine (Instron, composition (fingerprint). The spectra of each filament
United States) equipped with a 5 J hammer set at a 150° before 3D printing are present in Figure 4.
release angle. For each configuration (tri-layered and The spectra exhibit the expected vibrational bands
bi-layered) and post-processing treatment (dry, pre- characteristic of each polymeric material. For TPU
disinfected, post-Polident, and post-UVC), triplicate (Figure 4A), the following vibrations were identified: C–N
samples were evaluated. Control tests were also conducted stretching at 1220 cm , N–H bending at 1527 cm , and
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on bulk EVA specimens (80 × 10 × 4 mm ). C=O stretching at 1729 cm , associated with the urethane
3
linkage. Additionally, bands centered at 1000 and 1075 cm
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2.5.2. Surface characterization correspond to asymmetric stretching of C–O–C groups
Vickers microhardness testing was conducted to assess from polyether and urethane segments, respectively. 42
the surface mechanical properties of the 3D-printed In the spectrum of HIPS (Figure 4B), a broad band
specimens. Given that disinfection treatments primarily between 3200 and 3000 cm is attributed to aromatic C–H
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affect the outermost polymer chains, it is essential to assess stretching. Vibrations associated with C=C stretching
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the influence of UVC irradiation and Polident immersion in the benzene ring were observed at 1601, 1490,
on surface-level mechanical properties. and 1446 cm , while CH stretching appeared at
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2
Microhardness was measured using Duramin DK 2920 cm . Intense bands at 752 and 693 cm confirm the
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2750 version 0.04 (Eqpolymers, Denmark), equipped with presence of monosubstituted benzene rings, in agreement
a Vickers indenter, in accordance with ISO 6507. For with previous studies. For PMMA (Figure 4C), the
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each material configuration (bi-layered and tri-layer) and stretching frequencies of O–CH , C=O, and CH groups
2
3
treatment condition (dry, pre-disinfected, post-Polident, were observed at 986 cm , 1723 cm , and 2951 cm ,
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Volume 4 Issue 2 (2025) 6 doi: 10.36922/MSAM025130018