Optimizing Printing Temperature and Post-Curing Time for Enhanced Mechanical Property and Fabrication Reproducibility of 3D-Printed Dental Photopolymer Resins

Abstract

This study aims to evaluate the effects of printing temperature and post-curing duration on double-bond conversion (DBC), mechanical properties, and fabrication reproducibility of three dental photopolymer resins used for fixed dental prostheses (FDPs), denture bases, and direct clear aligners. Specimens were fabricated using stereolithography and masked stereolithography three-dimensional (3D) printers at room temperature (RT, 28 °C) and 50 °C, then subjected to six post-curing durations: 0, 60, 120, 180, 240, and 600 s. DBC was measured using Fourier transform infrared spectroscopy, and tensile strength was measured using tensile testing. Furthermore, fabrication reproducibility for clinical applicability was analyzed using root mean square deviations from 3D scanning. Printing at 50 °C significantly improved the DBC, tensile strength, and fabrication reproducibility of FDP and denture base resins compared to printing at RT, enabling shorter post-curing times (p < 0.001). Clearer aligner resin specimens printed at 50 °C and post-cured for 120 s exhibited the highest fabrication reproducibility (p < 0.001), while tensile strength did not differ significantly from that of RT specimens post-cured for 240 s (p > 0.05). These findings suggest that optimizing printing temperature and post-curing time enhances the mechanical properties and fabrication reproducibility of 3D-printed dental materials.

1. Introduction

Three-dimensional (3D) printing technology has become an innovative approach in dentistry, enabling the rapid and precise fabrication of patient-specific prostheses. Among these techniques, stereolithography (SLA) and masked stereolithography (mSLA) are widely employed to produce various dental appliances, including temporary crowns, denture bases, and clear aligners [1,2,3]. However, the clinical use of photopolymer-based 3D printing remains limited due to insufficient double-bond conversion (DBC), inadequate mechanical strength, and low fabrication reproducibility [4,5]. These limitations are major factors that compromise the clinical reliability of 3D-printed dental prostheses.

To address these challenges, researchers explored various strategies to enhance polymerization efficiency and resin properties. Ultraviolet (UV) irradiation during post-curing increases DBC and improves mechanical performance [6,7,8,9]. In industrial applications, increasing the resin temperature during printing is widely employed to promote monomer mobility and reduce curing time [10,11]; however, scientific evidence regarding the effects of elevated printing temperatures in dentistry remains limited and inconsistent. Some studies report that high-temperature printing improves interlayer bonding and decreases post-curing duration [12], whereas others show that excessive heat may compromise dimensional stability or induce internal stress [9,13]. Therefore, the clinical advantages of high-temperature printing remain inconclusive and require systematic validation.

This study aims to comprehensively evaluate the effects of printing temperature and post-curing duration on three dental photopolymer resins—temporary crown, denture base, and clear aligner materials. Specimens were printed at room temperature (RT, 28 °C) and 50 °C, followed by varying post-curing durations. The DBC, tensile strength, and fabrication reproducibility were analyzed for each resin. The study findings could help determine whether elevating the printing temperature can reduce post-curing duration while maintaining clinically acceptable performance.

2. Materials and Methods

2.1. Pilot Test

Pilot tests were conducted to identify the optimal printing temperature and post-curing time for each resin system. Five temperature conditions (28 °C, 40 °C, 50 °C, 60 °C, and 70 °C) were evaluated under identical experimental settings. The 40 °C condition was excluded because its DBC (%) and mechanical performance were comparable to those at RT, whereas the 70 °C condition caused excessive polymerization shrinkage and dimensional deformation, thereby compromising printing stability [10]. Although the 60 °C condition resulted in mechanical properties similar to those at 50 °C, it showed inconsistent print quality and thermal instability during repeated printing cycles. Consequently, 50 °C was selected as the elevated temperature condition, because it consistently produced high DBC and tensile strength, enhanced resin flowability, and stable printing behavior, making it most suitable for clinically reproducible fabrication. Since the 40 °C condition exhibited polymerization and mechanical behavior similar to those at RT (28 °C), 37 °C—representing physiological temperature—was not further considered, as no meaningful differences were expected within this range. Based on these pilot findings, the final printing temperatures were set at 28 °C (RT) and 50 °C (elevated condition).

2.2. Specimen Preparation

Three types of photopolymer resins were used in this study: temporary crown (ZMD-1000B Temporary; Dentis, Daegu, Republic of Korea), denture base (ZMD-1000B Denture Base; Dentis, Daegu, Republic of Korea), and clear aligner resins (TC-85DAC; Graphy, Seoul, Republic of Korea). Specimens for the temporary crown and denture base groups were fabricated using an SLA 3D printer (Zenith U; Dentis, Daegu, Republic of Korea), whereas the clear aligner specimens were produced with an mSLA printer (Lilivis; Huvitz, Seoul, Republic of Korea). The printing layer thickness was uniformly set to 100 µm for all groups.

To enable temperature-controlled printing, a silicone rubber heater (220 V, 55 W; Woory Electric Heater, Busan, Republic of Korea) was attached to the outer surface of the resin vat. The heater was linked to a digital temperature controller (DH-5562A1-CA; DH Electronics, Busan, Republic of Korea) and monitored in real time using a K-type thermocouple (TT-K-28-SP; ONDI, Gwangmyeong, Republic of Korea) connected to a data logger (midiLOGGER GL240; Graphtec, Yokohama, Japan).

After printing, the temporary crown and denture base specimens were rinsed with 100% isopropyl alcohol to remove uncured resin residue, while the clear aligner resin underwent post-processing via centrifugation following the instructions of the manufacturer.

All specimens were divided into six groups according to post-curing duration (0, 60, 120, 180, 240, and 600 s). The temporary crown and denture base specimens were post-cured using a 385–405 nm LED light-curing unit (Curedden; KwangMyung Daicom, Seoul, Republic of Korea), whereas clear aligner specimens were post-cured with a 395 nm UV LED curing unit (Lilivis Cure; Huvitz, Gyeonggi-do, Republic of Korea). Non-post-cured groups were designated RT-Green and 50 °C-Green, while post-cured groups were labeled RT-Post and 50 °C-Post. All specimens were stored in a light-blocking container until testing to prevent further polymerization.

2.3. Evaluation of Double-Bond Conversion

The DBC (%) was measured using five rectangular specimens measuring 20 × 20 × 15 mm (Figure 1A). Fourier transform infrared spectroscopy was performed with a spectrometer (Nicolet iS10; Thermo Fisher Scientific, Waltham, MA, USA) equipped with a diamond attenuated total reflectance accessory. Before measurement, specimen surfaces were gently polished with silicon carbide abrasive papers of 600–1800 grit to ensure surface uniformity. Spectra were collected over a wavenumber range of 3500–780 cm⁻¹ at a resolution of 0.5 cm⁻¹, with 64 scans obtained per sample. Absorption peaks corresponding to the aliphatic C=C bond (1638 cm⁻¹; baseline: 1650–1624 cm⁻¹) and the carbonyl C=O bond (1716 cm⁻¹; baseline: 1770–1658 cm⁻¹) were analyzed. The DBC (%) was calculated using Equation (1), based on the ratio of the C=C peak area before and after polymerization.

$$\mathrm{D}\mathrm{B}\mathrm{C}\left(\%\right)=\left(1-{\displaystyle \frac{(1638 {\mathrm{c}\mathrm{m}}^{-1}/1716 {\mathrm{c}\mathrm{m}}^{-1})\mathrm{p}\mathrm{o}\mathrm{l}\mathrm{y}\mathrm{m}\mathrm{e}\mathrm{r}\mathrm{i}\mathrm{z}\mathrm{e}\mathrm{d}}{(1638 {\mathrm{c}\mathrm{m}}^{-1}/1716 {\mathrm{c}\mathrm{m}}^{-1})\mathrm{u}\mathrm{n}\mathrm{p}\mathrm{o}\mathrm{l}\mathrm{y}\mathrm{m}\mathrm{e}\mathrm{r}\mathrm{i}\mathrm{z}\mathrm{e}\mathrm{d}}}\right)\times 100,$$

(1)

2.4. Evaluation of Tensile Strength

Tensile testing was performed using dog-bone specimens (n = 5) fabricated in accordance with ASTM D638 [14] and printed in the ZXY orientation (Figure 1B). Each specimen was loaded to failure using a universal testing machine (AGS-X STD; Shimadzu, Kyoto, Japan) operating at a crosshead speed of 5 mm/min. Based on ASTM D638, the recommended crosshead speed ranges from 5 mm/min to 500 mm/min. A speed of 5 mm/min was chosen to maintain a quasi-static strain rate and ensure comparability with previous studies on dental photopolymer resins [10,15]. The tensile strength (MPa) was calculated by dividing the maximum applied load (N) by the cross-sectional area at the gauge section, while the elastic modulus (MPa) and elongation at break (%) were obtained from the corresponding stress–strain curve.

2.5. Evaluation of Fabrication Reproducibility

2.5.1. Temporary Crowns

To evaluate the clinical applicability of the temporary crown resin, a three-unit fixed dental prosthesis (FDP) was digitally designed using the maxillary right first premolar and first molar as abutments, with the second premolar functioning as the pontic. The abutment preparations featured a 1.2 mm chamfer finish line and a 6° convergence angle. A master cast made of Type IV die stone (New Fujirock^®; GC Corp., Tokyo, Japan) was scanned with a desktop scanner (E1; 3Shape, Copenhagen, Denmark) to generate a virtual model. Using computer-aided design (CAD) software (3Shape, Copenhagen, Denmark), the connector cross-sectional area of the pontic was set to 14.00 mm², and the cement space was defined as 30 µm (Figure 1C). The FDP design was exported as a standard tessellation language (STL) file to serve as the CAD reference model (CRM). Five FDPs were printed per group in the XYZ build orientation. Each FDP was then scanned with an intraoral scanner (i700; Medit, Seoul, Republic of Korea) to create CAD test models (CTMs). These CTMs were aligned and superimposed on the CRM, and deviations between the two models were quantified using the root mean square (RMS) method.

2.5.2. Denture Bases

Fabrication reproducibility of denture bases was evaluated using a maxillary edentulous dentiform (402U; Nissin Dental Products Inc., Kyoto, Japan). The dentiform was duplicated with silicone, and Type IV stone (Hi-Koseton; Maruishi Gypsum Co., Osaka, Japan) was poured to create a working cast. The model was scanned (E1; 3Shape, Copenhagen, Denmark) and designed as a complete maxillary denture with a 2.5 mm base thickness using CAD software (Dental Designer; 3Shape, Copenhagen, Denmark) (Figure 1D). The STL file (CRM) was printed to produce five denture bases per group. The intaglio surfaces of the printed denture bases were scanned (E1; 3Shape, Copenhagen, Denmark) to obtain CTMs, which were then superimposed on the CRM to calculate RMS values.

2.5.3. Clear Aligners

Clear aligners were designed from a virtual maxillary typodont model using Medit Design software (Medit, Seoul, Republic of Korea) with a 0.05 mm offset and 0.5 mm thickness (Figure 1E). Five aligner specimens were fabricated per group and digitized using a desktop scanner (E1; 3Shape, Copenhagen, Denmark). To enhance surface capture precision, a thin, uniform layer of scanning spray (Eco Scan Spray; High Dental Korea, Seoul, Republic of Korea) was applied before scanning. The resulting scan data were saved as CTMs and aligned with the CRMs using metrology software (Geomagic Control X; 3D Systems, Rock Hill, SC, USA) to compute the RMS deviation values. The RMS was calculated using Equation (2):

$$RMS={\displaystyle \frac{1}{\sqrt{n}}}·\sqrt{{\sum }_{i=1}^n{{(X}_{1,i}-X_{2,i})}^2},$$

(2)

where n represents the total number of data points, X_1,i denotes the coordinate of the CRM, and X_2,i denotes the coordinate of the CTM. Values approaching 0 indicate higher fabrication reproducibility. Deviations were visualized using a color map ranging from ±200 µm (20 intervals) with a tolerance threshold of ±20 µm (green).

2.6. Statistical Analysis

All statistical analyses were performed using SPSS software (version 23.0; IBM Corp., Armonk, NY, USA). The normality of the data distribution was assessed using the Shapiro–Wilk test. The analyzed parameters included the DBC (%), tensile strength, and fabrication reproducibility (n = 5 per group). Group differences were evaluated using one-way analysis of variance (ANOVA) followed by Tukey’s post hoc test at a significance level of α = 0.05. To further assess the effects of printing temperature and post-curing time, partial η² values were calculated and interpreted according to Cohen’s classification: η² = 0.01 (small effect), η² = 0.06 (medium effect), and η² = 0.14 (large effect). Post hoc power analyses were conducted using G*Power software (version 3.1; Heinrich Heine University, Düsseldorf, Germany) based on the observed partial η² values from one-way ANOVA. All analyses achieved a statistical power (1 − β) > 0.8, suggesting that the sample size (n = 5 per group) was sufficient to detect significant effects.

3. Results

3.1. Results of Double-Bond Conversion

3.1.1. Results of DBC Test for Temporary Crown Resin

The RT-Green group exhibited the lowest DBC, which increased progressively with longer post-curing durations. At the same post-curing duration, specimens printed at 50 °C showed significantly higher DBC than those printed at RT (p < 0.05;

Table 1. Comparison of DBC (%) based on printing temperature and post-processing time.

Resin Type	Printing Temperature	Post- Processing Time (s)	Mean	SD	95% Confidence Interval		Partial η2	F	p
					Lower	Upper
Temporary crown	RT	Green	65.0 A	7.2	56.0	73.9	0.762	15.378	<0.001 *
		60	69.8 A	2.3	67.0	72.6
		120	71.8 A	6.3	64.0	79.7
		180	71.5 A	20.1	46.6	96.5
		240	92.5 B	2.3	89.6	95.4
		600	95.3 B	0.9	94.2	96.4
	50 °C	Green	73.8 A	10.0	61.3	86.2
		60	92.9 B	2.3	90.0	95.7
		120	94.2 B	0.4	93.7	94.6
		180	97.7 B	0.9	96.5	98.9
		240	97.1 B	0.6	96.4	97.9
Denture base	RT	Green	68.2 A	3.7	63.6	72.7	0.748	12.893	<0.001 *
		60	71.6 AB	1.6	69.7	73.6
		120	70.9 AB	1.7	68.8	73.0
		180	70.8 AB	1.3	69.2	72.4
		240	76.7 BC	2.3	73.8	79.5
		600	76.5 BC	5.6	69.6	83.4
	50 °C	Green	79.2 C	2.2	76.5	82.0
		60	82.7 C	0.9	81.5	83.8
		120	82.2 C	2.6	78.9	85.5
		180	82.1 C	3.0	78.4	85.9
		240	80.5 C	2.4	77.5	83.5
Direct clear aligner	RT	Green	86.8 A	0.8	85.9	87.8	0.992	526.463	<0.001 *
		60	95.8 B	0.1	95.6	95.9
		120	96.7 BCD	0.7	95.9	97.5
		180	96.0 B	0.2	95.8	96.3
		240	97.0 DE	0.3	96.7	97.4
		600	100.0 G	0.0	100.0	100.0
	50 °C	Green	85.9 A	0.4	85.3	86.4
		60	96.0 B	0.1	95.8	96.2
		120	97.4 EF	0.7	96.5	98.2
		180	96.4 BC	0.4	95.9	96.9
		240	98.1 F	0.2	97.8	98.4

Abbreviations: DBC, double-bond conversion; s, seconds; SD, standard deviation; RT, room temperature; ANOVA, analysis of variance. * Statistical significance was evaluated using one-way ANOVA (α = 0.05). Different superscript letters (A–F) denote groups that differ significantly according to Tukey’s HSD post hoc test (p < 0.05).

, Figure 2). The 50 °C–Post group after 60 s of post-curing achieved DBC values comparable to those of the RT-Post group after 600 s (p < 0.05). Analysis revealed significant effects of printing temperature and post-curing time on DBC (F = 15.378, p < 0.001), with a large effect size (partial η² = 0.762), indicating that approximately 76% of the variance in polymerization is attributed to the processing parameters.

3.1.2. Results of DBC Test for Denture Base Resin

A similar trend was observed for the denture base resin. Specimens printed at 50 °C exhibited higher DBC than those printed at RT, and the 50 °C-Post group after 60 s of post-curing showed no statistically significant difference from the RT-Post group after 600 s (p > 0.05; Table 1, Figure 2). One-way ANOVA revealed a significant effect of printing temperature and post-curing time on DBC (F = 12.893, p < 0.001), with a large effect size (partial η² = 0.748), indicating that approximately 75% of the variance in polymerization is attributed to the processing parameters.

3.1.3. DBC of Direct Clear Aligner Resin

All groups post-cured for ≥60 s showed increased DBC, with no statistically significant differences between the printing temperature groups (p > 0.05; Table 1, Figure 2). Additionally, no residual monomers were observed in the RT-Post group after 600 s. One-way ANOVA revealed significant effects of printing temperature and post-curing time on DBC (F = 526.463, p < 0.001), with an extremely large effect size (partial η² = 0.992), indicating that nearly all variance in polymerization is attributed to the processing parameters.

3.2. Results of Tensile Test

3.2.1. Results of Tensile Test for Temporary Crown Resin

Specimens post-cured for 0–120 s at RT exhibited the lowest tensile strength (p < 0.001). At identical post-curing durations, specimens printed at 50 °C had significantly higher tensile strength than those printed at RT. The 50 °C-Post group after 60 s of post-curing showed values comparable to or higher than those of the RT-Post group after 600 s (p > 0.05;

Table 2. Tensile properties of the temporary crown resin according to printing temperature and post-curing time.

Resin Type	Printing Temperature	Post- Processing Time (s)	Mean	SD	95% Confidence Interval		Partial η2	F	p
					Lower	Upper
Tensile strength (MPa)	RT	Green	31.8 A	1.4	30.4	33.3	0.910	47.812	<0.001 *
		60	31.3 A	1.8	29.4	33.2
		120	31.3 A	0.9	30.4	32.3
		180	35.6 B	0.9	34.6	36.6
		240	35.5 B	0.7	34.8	36.2
		600	38.7 C	1.6	37.0	40.4
	50 °C	Green	35.9 B	2.2	33.6	38.2
		60	40.5 C	0.6	39.9	41.1
		120	38.9 C	0.6	38.3	39.5
		180	39.6 C	0.5	39.0	40.1
		240	39.0 C	0.9	38.0	40.0
Elongation (%)	RT	Green	13.7E	3.0	9.9	17.5	0.800	17.585	<0.001 *
		60	12.7 E	1.8	10.4	14.9
		120	12.1 DE	1.8	9.8	14.3
		180	10.5 CDE	1.5	8.6	12.3
		240	4.9A	1.7	2.8	7.0
		600	4.7 A	0.9	3.6	5.8
	50 °C	Green	8.9 BCD	1.2	7.4	10.4
		60	7.9 ABC	1.9	5.5	10.3
		120	8.6 BCD	1.5	6.7	10.5
		180	8.5 BC	0.7	7.7	9.4
		240	5.5 AB	0.8	4.5	6.4
Elastic modulus (MPa)	RT	Green	1444.9 A	144.6	1265.4	1624.4	0.953	88.377	<0.001 *
		60	1748.4 B	25.3	1717.0	1779.9
		120	1811.6 B	45.1	1755.6	1867.7
		180	2162.1 C	48.5	2101.9	2222.4
		240	2221.3 CDE	16.7	2200.6	2242.1
		600	2341.9 DEF	103.1	2213.9	2469.9
	50 °C	Green	2176.3 CD	129.6	2015.3	2337.3
		60	2508.4 F	55.9	2439.0	2577.8
		120	2363.2 EF	98.9	2240.3	2486.0
		180	2489.0 F	44.3	2434.0	2544.0
		240	2457.4 F	77.9	2360.7	2554.0

Abbreviations: s, seconds; SD, standard deviation; RT, room temperature; ANOVA, analysis of variance. * Statistical significance was evaluated using one-way ANOVA (α = 0.05). Different superscript letters (A–F) denote groups that differ significantly according to Tukey’s HSD post hoc test (p < 0.05).

, Figure 3).

The elastic modulus increased significantly with higher printing temperature and longer post-curing time (p < 0.001; Table 2). Specimens printed at 50 °C exhibited greater stiffness than those printed at RT, even after short post-curing durations, and the 50 °C-Post group after 60 s showed an elastic modulus comparable to that of the RT-Post group after 600 s. Conversely, elongation at break decreased markedly with longer post-curing times.

Printing temperature and post-curing time significantly affected all mechanical properties of the temporary crown resin (Table 2). Large effect sizes were observed for tensile strength (partial η² = 0.910), elastic modulus (partial η² = 0.800), and elongation at break (partial η² = 0.953).

3.2.2. Results of Tensile Test for Denture Base Resin

Tensile strength increased significantly with higher printing temperature and extended post-curing times (p < 0.001;

Table 3. Tensile properties of the denture base resin according to printing temperature and post-curing time.

Resin Type	Printing Temperature	Post- Processing Time (s)	Mean	SD	95% Confidence Interval		Partial η2	F	p
					Lower	Upper
Tensile strength (MPa)	RT	Green	18.5 A	0.9	17.4	19.7	0.963	50.083	<0.001 *
		60	19.3 AB	1.0	18.1	20.5
		120	19.2 AB	1.2	17.8	20.7
		180	19.5 AB	0.4	19.0	20.0
		240	21.6 BC	1.1	20.2	23.0
		600	21.7 BC	0.8	20.7	22.6
	50 °C	Green	23.8 C	1.3	22.3	25.4
		60	27.7 D	0.3	27.3	28.1
		120	27.9 D	0.5	27.3	28.6
		180	27.9 D	0.5	27.3	28.5
		240	27.9 D	0.4	27.4	28.4
Elongation (%)	RT	Green	14.2 C	3.2	10.3	18.2	0.382	6.055	<0.001 *
		60	10.5 ABC	3.1	6.7	14.3
		120	9.7 ABC	2.1	7.1	12.3
		180	8.2 A	2.7	4.9	11.5
		240	8.5 AB	1.4	6.7	10.3
		600	6.6 A	1.2	5.1	8.2
	50 °C	Green	13.4 BC	2.0	10.9	15.8
		60	10.3 ABC	3.6	5.9	14.7
		120	10.3 ABC	1.6	8.3	12.3
		180	6.7 A	2.0	4.3	9.1
		240	6.3 A	2.2	3.5	9.1
Elastic modulus (MPa)	RT	Green	692.5 A	41.0	641.6	743.4	0.949	81.98	<0.001 *
		60	776.9 A	56.3	707.1	846.8
		120	811.9 A	96.6	691.9	931.8
		180	951.2 B	28.5	915.8	986.6
		240	1022.4 BC	73.8	930.8	1114.1
		600	1081.1 CD	61.9	1004.3	1157.9
	50 °C	Green	1187.9 D	97.4	1067.0	1308.9
		60	1316.7 E	55.7	1247.6	1385.9
		120	1322.5 E	22.6	1294.5	1350.5
		180	1319.0 E	29.6	1282.3	1355.7
		240	1321.5 E	18.5	1298.5	1344.5

Abbreviations: s, seconds; SD, standard deviation; RT, room temperature; ANOVA, analysis of variance. * Statistical significance was evaluated using one-way ANOVA (α = 0.05). Different superscript letters (A–E) denote groups that differ significantly based on Tukey’s HSD post hoc test (p < 0.05).

, Figure 3). Adequate mechanical properties were achieved at 50 °C even after short post-curing durations. The 50 °C-Post group at 60 s exhibited significantly higher tensile strength than that of the RT-Post group at 600 s (p < 0.001). Tensile strength increased significantly with higher printing temperature and longer post-curing times (p < 0.001). Adequate mechanical properties were achieved at 50 °C even after short post-curing durations. The 50 °C-Post group at 60 s exhibited significantly higher tensile strength than that of the RT-Post group at 600 s (p < 0.001). Similarly, the elastic modulus increased significantly with higher printing temperatures and extended post-curing times (p < 0.001; Table 3). Specimens printed at 50 °C exhibited significantly greater stiffness than those printed at RT, even after shorter post-curing durations. The 50 °C-Post group after 60 s showed a significantly higher elastic modulus than that of the RT-Post group after 600 s (p < 0.001). Conversely, elongation at break decreased significantly with longer post-curing (p < 0.001).

Printing temperature and post-curing time significantly affected all mechanical properties of the denture base resin (Table 3). Tensile strength (partial η² = 0.963) and elastic modulus (partial η² = 0.949) exhibited large effect sizes, indicating that over 94% of the variance in these parameters is explained by the processing conditions. In contrast, elongation at break (partial η² = 0.382) showed a moderate effect size.

3.2.3. Results of Tensile Test for Direct Clear Aligner Resin

No significant differences in tensile strength were observed between the RT and 50 °C groups without post-curing (p > 0.05;

Table 4. Tensile properties of the clear aligner resin according to printing temperature and post-curing time.

Resin Type	Printing Temperature	Post- Processing Time (s)	Mean	SD	95% Confidence Interval		Partial η2	F	p
					Lower	Upper
Tensile strength (MPa)	RT	Green	13.6 AB	0.6	12.9	14.4	0.972	154.509	<0.001 *
		60	14.8 B	0.8	13.9	15.8
		120	18.0 C	0.2	17.8	18.3
		180	19.9 D	0.6	19.1	20.7
		240	21.8 F	0.4	21.3	22.4
		600	21.0 DEF	1.0	19.8	22.2
	50 °C	Green	13.4 A	0.7	12.6	14.2
		60	14.8 B	0.5	14.2	15.5
		120	20.9 DEF	0.4	20.0	21.0
		180	21.2 EF	0.3	20.8	21.5
		240	20.2 DE	0.6	19.4	20.9
Elongation (%)	RT	Green	86.9 E	17.2	65.6	108.3	0.637	7.719	<0.001 *
		60	84.4 CDE	2.4	81.4	87.4
		120	76.8 ABCDE	3.9	72.0	81.7
		180	74.0 ABCD	4.8	68.0	79.9
		240	66.5 A	1.5	64.6	68.3
		600	73.4 ABCD	2.1	70.8	76.0
	50 °C	Green	85.9 DE	4.2	80.6	91.1
		60	80.1 BCDE	3.2	76.1	84.0
		120	68.1 AB	2.5	64.9	71.2
		180	67.1 A	1.5	65.3	69.0
		240	72.7 ABC	3.7	68.1	77.3
Elastic modulus (MPa)	RT	Green	427.0 A	50.5	364.2	489.7	0.972	151.697	<0.001 *
		60	757.3 B	65.4	676.1	838.5
		120	1094.9 C	174.6	878.0	1311.7
		180	1301.1 D	114.6	1158.8	1443.4
		240	1663.1 EF	37.1	1617.0	1709.2
		600	1509.9 E	103.8	1381.0	1638.8
	50 °C	Green	554.0 A	19.0	530.4	577.7
		60	1041.4 C	41.9	989.4	1093.5
		120	1538.6 E	77.1	1442.9	1634.3
		180	1728.5 F	48.8	1667.9	1789.1
		240	1493.8 E	34.2	1451.3	1536.3

Abbreviations: s, seconds; SD, standard deviation; RT, room temperature; ANOVA, analysis of variance. * Statistical significance was evaluated using one-way ANOVA (α = 0.05). Different superscript letters (A–F) denote groups that differ significantly based on Tukey’s HSD post hoc test (p < 0.05).

, Figure 3). The RT-Post group at 240 s exhibited the highest tensile strength (21.8 MPa; p < 0.001), which did not differ significantly from that of the 50 °C-Post group at 120 s (20.9 MPa; p > 0.05).

The elastic modulus increased significantly with post-curing duration at both printing temperatures (p < 0.001; Table 4). Specimens printed at 50 °C generally exhibited greater stiffness than those printed at RT, particularly after 120 s of post-curing. Conversely, elongation at break decreased progressively with extended post-curing duration, indicating a trade-off between stiffness and ductility.

Printing temperature and post-curing time significantly affected all mechanical properties of the clear aligner resin (p < 0.001; Table 4). Tensile strength (partial η² = 0.972) and elastic modulus (partial η² = 0.972) exhibited large effect sizes, with processing conditions accounting for over 97% of the variability in strength and stiffness. Elongation at break (partial η² = 0.637) also exhibited a substantial effect size.

3.3. Results of Fabrication Reproducibility

3.3.1. Results of Fabrication Reproducibility for Temporary Crown Resin

RMS analysis revealed that the RT-Green group exhibited the greatest deviation (p < 0.001). Overall, specimens printed at 50 °C exhibited significantly lower RMS values than those printed at RT, except for the RT-Post group at 60 s (p = 0.003;

Table 5. Comparison of RMS values (µm) regarding printing temperature and post-processing time.

Resin Type	Printing Temperature	Post- Processing Time (s)	Mean	SD	95% Confidence Interval		Partial η2	F	p
					Lower	Upper
Temporary crown	RT	Green	65.9 A	8.5	56.9	74.8	0.404	3.206	0.003 *
		60	50.8 B	8.8	41.6	60.0
		120	65.4 A	11.8	52.9	77.8
		180	64.5 AC	9.4	54.6	74.4
		240	55.9 ABC	6.5	49.0	62.7
		600	65.7 A	9.5	55.8	75.6
	50 °C	Green	52.1 B	11.5	40.0	64.2
		60	53.0 B	5.6	47.1	58.9
		120	51.7 B	9.5	41.6	61.7
		180	51.3 B	7.6	43.4	59.2
		240	54.0 BC	7.8	45.9	62.2
Denture base	RT	Green	241.3 D	27.5	207.2	275.4	0.752	13.378	<0.001 *
		60	218.9 CD	22.9	190.5	247.4
		120	173.6 ABC	19.7	149.2	198.0
		180	153.1 AB	23.2	124.3	181.9
		240	162.7 AB	19.8	138.1	187.3
		600	135.5 A	22.2	107.9	163.1
	50 °C	Green	151.7 AB	27.7	117.3	186.2
		60	153.7 AB	21.5	127.0	180.5
		120	167.4 AB	24.8	136.6	198.2
		180	199.1 BCD	20.7	173.5	224.8
		240	241.2 D	20.3	216.0	266.4
Direct clear aligner	RT	Green	179.6 ABCD	27.4	145.5	213.7	0.860	26.942	<0.001 *
		60	231.6 CDE	25.2	200.4	262.9
		120	148.7 AB	18.0	126.3	171.0
		180	203.8 BCD	15.7	184.2	223.3
		240	228.3 CDE	17.8	206.2	250.4
		600	179.2 ABC	31.1	140.5	217.8
	50 °C	Green	235.8 DE	47.9	176.4	295.2
		60	278.6 EF	21.6	251.8	305.5
		120	131.1 A	17.2	109.7	152.4
		180	149.6 AB	33.6	107.9	191.3
		240	334.2 F	12.5	318.7	349.8

Abbreviations: s, seconds; SD, standard deviation; RT, room temperature; ANOVA, analysis of variance; RMS, root mean square. * Statistical significance was evaluated using one-way ANOVA (α = 0.05). Different superscript letters (A–F) denote groups that differ significantly according to Tukey’s HSD post hoc test (p < 0.05).

, Figure 4). Printing temperature and post-curing time significantly affected the RMS values of the temporary crown resin (F = 3.206, p = 0.003), exhibiting a moderate effect size (partial η² = 0.404), with processing parameters accounting for approximately 40% of the variance in surface deviation.

3.3.2. Results of Fabrication Reproducibility for Denture Base Resin

The RT-Post group at 600 s exhibited the lowest RMS value (135.5 µm; p < 0.001; Table 5, Figure 4), indicating the highest fabrication reproducibility. No significant differences were observed between specimens post-cured for ≥120 s at RT and ≤120 s at 50 °C (p > 0.05). Conversely, the RT-Green group (241.3 µm) and the 50 °C-Post group at 240 s (241.2 µm) showed the highest RMS values (p < 0.001). Printing temperature and post-curing time significantly affected the RMS values of the denture base resin (F = 13.378, p < 0.001). The effect size was large (partial η² = 0.752), indicating that over 75% of the variability in surface deviation is explained by the processing conditions.

3.3.3. Results of Fabrication Reproducibility for Direct Clear Aligner Resin

The 50 °C-Post group at 120 s exhibited the lowest RMS value (131.1 µm; p < 0.001), which did not differ significantly from the RT-Post group at 120 s (p > 0.05; Table 5, Figure 4). Conversely, the 50 °C-Post group at 240 s showed the highest RMS value (334.2 µm; p < 0.001), indicating the lowest fabrication reproducibility. Printing temperature and post-curing time significantly affected the RMS values of the clear aligner resin (F = 26.942, p < 0.001). The effect size was large (partial η² = 0.860), with these processing parameters accounting for approximately 86% of the variance in fabrication reproducibility.

4. Discussion

In this study, the influence of printing temperature and post-curing time on the performance of temporary crown, denture base, and clear aligner resins was evaluated. These parameters significantly affect DBC, tensile strength, and fabrication reproducibility. Elevated printing temperature maintains performance despite shorter post-curing durations. Therefore, the null hypothesis was partially rejected.

At 50 °C, temporary crown and denture base resins achieved sufficient DBC with significantly shorter post-curing durations. The 50 °C–Post group reached DBC values at 60 s, comparable to those of the RT–Post group at 600 s, indicating a 90% reduction in post-curing duration. This finding is consistent with that of previous reports showing that elevated temperature increases monomer mobility and subsequently enhances photopolymerization efficiency [16]. Conversely, the clear aligner resin exhibited consistently high DBC across all groups post-cured for ≥60s, regardless of temperature. This behavior may be attributed to its highly photo-reactive formulation [17], indicating that clinically sufficient polymerization can be achieved with relatively shorter post-curing durations. At 50 °C, all resins post-cured exceeded the reported DBC range of conventional dental composites (40–75%) [16,18,19]. While adequate polymerization is essential for ensuring biocompatibility [16,20,21], these findings suggest that high-temperature printing combined with reduced post-curing durations may result in clinically acceptable outcomes.

The large effect sizes observed across all materials underscore the strong influence of processing parameters on photopolymerization. For the temporary crown and denture base resins, partial η² values > 0.7 indicate that a substantial proportion of polymer conversion depends on printing temperature and post-curing duration. These findings align with those of previous studies demonstrating that elevated temperature facilitates monomer mobility, accelerates radical propagation, and increases the DBC (%) [10,16]. In contrast, the clear aligner resin exhibited a large effect size (partial η² = 0.992), suggesting an almost complete dependence of polymerization on these factors. This behavior may be attributed to its relatively low filler content and high transparency, which enhance light penetration.

Tensile testing further confirmed the advantages of elevated printing temperature. The temporary crown and denture base resins exhibited low tensile strength in the RT–Green groups, while the 50 °C–Post group at 60 s showed tensile strength comparable to or exceeding that of the RT–Post group at 600 s, consistent with previous findings [10,12]. Thus, printing at 50 °C may reduce post-curing duration without compromising mechanical performance, supporting its potential application in chairside 3D printing workflows. The clear aligner resin demonstrates low sensitivity to post-curing conditions. While the RT–Post group at 240 s exhibited the highest tensile strength (21.8 MPa), its value did not significantly differ from that of the 50 °C–Post group at 120 s (20.9 MPa). The tensile strength of 3D-printed aligners (~20 MPa) was lower than that of thermoformed materials such as LD30 or Zendura (40–65 MPa) [22,23], though direct comparisons are limited owing to differences in specimen geometry, testing methods, and build orientation. Nevertheless, these findings indicate that adequate strength can be achieved with relatively short post-curing durations, improving clinical efficiency.

Beyond tensile strength, the elastic modulus and elongation at break provide further insight into the mechanical behavior of the 3D-printed resins. The temporary crown and denture base resins exhibited a pronounced increase in elastic modulus with higher printing temperature and longer post-curing duration, reflecting enhanced crosslink density and network rigidity [24,25]. However, this increase in stiffness was accompanied by decreased elongation at break, indicating a trade-off between strength and ductility—a common feature of highly crosslinked photopolymers. The clear aligner resin exhibited relatively lower sensitivity in elastic modulus than that of the other materials, possibly due to its flexible monomer composition designed to withstand repeated deformation under cyclic loading [26,27]. Collectively, these findings indicate that printing temperature and post-curing parameters influence strength and modulate stiffness and flexibility, both of which are critical for clinical applications subjected to repetitive mechanical stress.

Large effect sizes across all tensile tests indicate that printing temperature and post-curing duration are the dominant factors affecting mechanical performance. The temporary crown and denture base resins showed large effect sizes for tensile strength and elastic modulus (partial η² > 0.90), suggesting that >90% of the variance in strength and stiffness is determined by processing parameters. The clear aligner resin exhibited a similarly strong dependence (η² = 0.63–0.97), indicating that temperature-controlled printing and optimized post-curing conditions are essential for achieving an optimal balance between flexibility and rigidity in 3D-printed dental polymers.

RMS analysis revealed that elevated printing temperatures generally reduced deviations and enhanced fabrication reproducibility for temporary crowns and denture bases. FDP specimens printed at 50 °C exhibited lower RMS values than those printed at RT. Reported thresholds for clinically acceptable internal gaps range from 50 to 100 µm [28,29]. However, all groups in this study remained within the clinically acceptable limit of 300 µm, considering mucosal deformation under functional loading [30,31]. At 600 s, the RT–Post group of denture base resin had the lowest RMS value, while the RT–Green and 50 °C–Post groups at 240 s demonstrated the highest deviations. The clear aligner resin exhibited a distinct pattern, with the 50 °C–Post group at 120 s showing the lowest RMS value (131.1 µm) and the 50 °C–Post group at 240 s exhibiting markedly higher deviations (334.2 µm). Studies show that 3D-printed aligners are clinically acceptable within 200 µm [32,33]; in the present study, all groups post-cured for ≥120 s met this criterion. However, prolonged UV exposure may cause polymer shrinkage and stress accumulation [9,13], potentially compromising dimensional accuracy. These findings emphasize the significance of precise control of post-curing duration during clear aligner fabrication.

Most RMS analyses exhibit large effect sizes (partial η² = 0.75–0.86), indicating that printing temperature and post-curing duration strongly influence the dimensional accuracy of all evaluated resins. The high η² values suggest that most of the variance in surface deviation is attributed to these processing parameters. While minor material-specific variations were observed, the overall findings indicate that temperature-optimized 3D printing conditions are critical in enhancing the trueness and reproducibility of printed dental restorations.

Overall, printing at 50 °C enabled shorter post-curing durations while maintaining sufficient DBC, tensile strength, and accuracy. This approach may improve clinical workflows, reduce patient waiting times, and enhance the feasibility of chairside 3D printing. The benefits were most evident for temporary crown and denture base resins, while clear aligners required more precise optimization of post-curing duration.

This study has some limitations, including its in vitro design, small sample size (n = 5 per group), and restriction to specific commercial resins and printing systems. Therefore, future studies should assess a broader range of resin formulations, printers, and long-term performance factors, including water sorption and aging. The variability observed in aligner RMS values also warrants further in vivo validation.

5. Conclusions

The effects of printing temperature and post-curing duration on the mechanical properties and fabrication reproducibility of temporary crown, denture base, and clear aligner resins were assessed. Elevated printing temperature (50 °C) enables sufficient DBC and tensile strength with reduced post-curing durations, particularly enhancing workflow feasibility of temporary crown and denture base resins. However, clear aligner resin is more sensitive to post-curing conditions than to printing temperature, and excessive post-curing adversely affects fabrication accuracy. These findings suggest that chairside 3D printing workflows can be optimized to enhance efficiency and decrease patient waiting times. The limitations of the in vitro design underscore the need for further validation across diverse resin compositions and clinical conditions.