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The Journal of the Indian Prosthodontic Society logoLink to The Journal of the Indian Prosthodontic Society
. 2026 Jan 1;26(1):32–42. doi: 10.4103/jips.jips_106_25

Effect of build position on the accuracy and flexural properties of resin model materials for three-dimensional printing technologies

Xiao-Mei Tang 1,2, Na-Yu 1,3, Bin-Ding Bai 1, Peng-Wang 4, Lu-Liu 4, Fa-Bing Tan 1,3,5,✉
PMCID: PMC12912485  PMID: 41476350

Abstract

Aim:

This study aimed to evaluate the effects of build position (rows or columns) on the accuracy and flexural properties of three-dimensional printing resin model materials.

Settings and Design:

This was a comparative experimental study.

Materials and Methods:

Three additive manufacturing technologies – digital light processing (DLP), stereolithography (SLA), and polymer jetting printing (PJP) – were employed to fabricate resin model specimens (2 mm × 2 mm × 25 mm), arranged evenly in 7 rows and 7 columns on the build platform. Dimensional trueness was assessed by measuring deviations in length (X-axis), width (Y-axis), and height (Z-axis) using a digital micrometer. Triplicate printing runs were performed to determine precision, quantified using intraclass correlation coefficient analysis. Flexural properties were evaluated through three-point bending tests.

Statistical Analysis Used:

Data were analyzed using one-way ANOVA followed by Tukey post hoc tests.

Results:

The PJP group exhibited deviations in length (0.18–0.25 mm) and height (0.18–0.22 mm) at several column positions, exceeding 0.1 mm, whereas the DLP and SLA groups showed deviations in all dimensions within 0.1 mm. At different row positions, PJP length (0.20–0.24 mm) and height (0.17–0.22 mm) deviations also exceeded 0.1 mm. Precision in height was lower than in length or width across both rows and columns (P = 0.000). Compared with the DLP and PJP groups, the SLA group demonstrated larger deviations in flexural modulus at column positions (P = 0.003, H = 19.730) and greater variations (95% confidence interval) in flexural strength and modulus at column and row positions.

Conclusion:

Build position had a greater influence on trueness in the PJP group, while precision was lowest for height across all three groups. Furthermore, the flexural strength and modulus of the SLA group varied more significantly with build position. Thus, meticulous selection of the build position is essential to achieve improved accuracy and flexural properties in resin models.

Keywords: Accuracy, build position, flexural properties, resin model material, three-dimensional printing

INTRODUCTION

Gypsum models have traditionally been widely used across multiple fields of dentistry, including orthodontics, restorative dentistry, implantology, and oral and maxillofacial surgery. However, conventional gypsum models present notable clinical drawbacks, such as prolonged fabrication time, susceptibility to environmental degradation, and an increased burden of clinical appointments. These disadvantages compromise both the efficiency of prosthesis fabrication and the long-term preservation of models.[1,2]

With advances in technology and materials, additive manufacturing (AM), or three-dimensional (3D) printing, offers a solution to the limitations of conventional gypsum models through the production of resin models. Currently, most dental resin models are fabricated using liquid resin-based AM technologies, including MultiJet/Polymer jetting printing (PJP), stereolithography (SLA), and digital light processing (DLP). The AM workflow generally consists of three stages: Data processing, manufacturing, and postprocessing.[3,4] Irrespective of whether gypsum models or AM resin models are employed, both must demonstrate high accuracy and adequate flexural properties to meet clinical requirements.

Optimization of parameters in AM is essential to ensure high-quality 3D printing outcomes suitable for clinical application.[5,6] The effects of build orientation,[7,8,9,10] layer thickness,[11] printing technologies,[12,13,14,15] and materials[16,17,18] on the accuracy and mechanical properties of 3D-printed dental models have been extensively studied. Among these factors, determination of the build row and column positions constitutes a critical step in the AM process. Unkovskiy et al.[9] confirmed that build row and column positions influence the accuracy and mechanical properties of 3D-printed resin models; however, their study focused only on a single technology and did not conduct an in-depth evaluation of SLA or extend the analysis to other AM technologies. In addition, the flexural properties of printed resin materials are important determinants of printing strategies, yet this aspect has not been adequately investigated in previous studies.

In summary, existing research provides insufficient evidence to determine the optimal build row and column positions. Therefore, the present study aimed to evaluate the influence of build row and column positions on the accuracy (trueness and precision) and flexural properties (flexural strength and flexural modulus) of three types of 3D-printed resin model materials. If build position is demonstrated to exert a significant effect, the study further aims to quantify the extent of this effect and assess whether it remains within clinically acceptable limits. This study hypothesizes that build position produces clinically acceptable differences in the accuracy and flexural performance of the three types of 3D-printed resin model specimens.

MATERIALS AND METHODS

Preparation of three-dimensional-printed resin model specimens

Construction of resin model specimen data

Based on previous studies, polymer-based dental bar specimens for flexural testing were designed according to DIN EN ISO 4049:2019[19] using Magics software (V21.0.0.263, Materialise Shanghai Co., Ltd., China). Standard model data for bar specimens (dimensions: 2 mm × 2 mm × 25 mm [length × width × height]) were created. Four conical supports and a base (radius: 0.45 mm, total height: 3 mm) were added to the bottom. To differentiate length from width, the number “1” was marked on the base along the Y-axis direction. The final design was exported and saved in Standard Tessellation Language format.

Preparation of resin model specimens

Preparation of digital light processing specimens

Sample size was calculated using G*Power software (version 3.1.9.7, University of Düsseldorf, Düsseldorf, Germany). Based on preliminary experiments with an effect size of 0.6, α-level of 0.05, and power (1− β) of 0.8, a minimum of seven specimens per experimental group was required. Accordingly, a single build platform was designed with a 7 × 7 array configuration, producing 49 specimens per AM technology.[9]

The resin model specimen data were imported into the intelligent marking control software (v1.0; Han’s Laser Technology Industry Group Co., Ltd., China) for layout, with a slice thickness of 50 µm. The compatible model resin material (GV-Model1; Shenzhen Times Pioneer Technology Co., Ltd., China) was printed using a DLP printer (DLP-1080E; Han’s Laser Technology Industry Group Co., Ltd., China). Postprocessing followed the manufacturer’s recommendations: Cleaning in an ultrasonic cleaner with 95% alcohol for 3 min to remove surface resin residues, drying with an air gun, and secondary curing in a UV curing oven (405 nm UV oven, Shanghai Prismlab Electromechanical Technology Co., Ltd., China) for 10 min.[20]

Preparation of stereolithography specimens

The resin model specimen data were imported into Magics software (v21.0.0.263; Materialise Shanghai Co., Ltd., China) for layout, with a slice thickness of 70 µm. The model resin material (RP-405-TZ02Y; Changzhou Pulisheng 3D Technology Co., Ltd., China) was printed using an SLA printer (Prismlab RP-400-T; Shanghai Prismlab Electromechanical Technology Co., Ltd., Shanghai, China). After printing, the specimens underwent the same postprocessing procedures as those applied to the DLP specimens.

Preparation of polymer jetting printing specimens

The resin model specimen data were imported into Objet Studio software (v9.2.11.3626; Stratasys Ltd., Rehovot, Israel) for layout, with a slice thickness of 16 µm. A PJP printer (Eden260VS Dental Advantage; Stratasys Ltd., Rehovot, Israel) was used to print the model resin material (VeroDent MED690; Stratasys Ltd., Rehovot, Israel) together with the support material (Support SUP705B; Stratasys Ltd., Rehovot, Israel). After printing, excess support material was manually removed from the specimen surfaces according to the manufacturer’s protocol. The specimens were then rinsed thoroughly with a high-pressure water jet, immersed in 1% sodium hydroxide solution for 30 min to dissolve residual support material, and rinsed again with the water jet before being air-dried.[20]

The material properties of the printing resins are listed in Table 1, while the manufacturing specifications for the three techniques are presented in Table 2. The specimen configuration and the printed objects are illustrated in Figure 1. All resin specimens in this study were fabricated and subsequently tested by the same experienced operator, strictly following the operating instructions for the equipment and materials. Finally, the resin model specimens obtained from different build positions were stored in a dry, light-shielded container.

Table 1.

Baseline mechanical properties of three tested three-dimensional-printed resin materials

Material classification Main component Tensile strength (MPa) Elongation at break (%) Shore hardness (d) Flexural strength (MPa)
GV-model1 Acrylic acid and its lipid compounds 45–54 8–12 83–85 60–65
RP-405-TZ02Y Polyurethane acrylate oligomer 24–60 9–13 88 60–78
VeroDent MED690 Acrylic resin 54–65 15–25 83–86 80–110
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Table 2.

Production information of the three-dimensional printing technologies and their materials used in this study

3D printing technology Build orientation Build platform size (mm) Slice thickness (μm) Number of plies Material type Main component
DLP 90° 144×81×200 50 560 GV-model1 Acrylic acid and its lipid compounds
SLA 90° 384×216×100 70 400 RP-405-TZ02Y Polyurethane acrylate oligomer
PJP 90° 255×252×200 16 1750 VeroDent MED690 Acrylic resin
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DLP: Digital light processing, SLA: Stereolithography, PJP: Polymer jetting printing, 3D: Three-dimensional

Figure 1.

Figure 1

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Resin model specimen printed using three techniques. Typesetting data: (a) digital light processing (DLP), (b) stereolithography (SLA), (c) polymer jetting printing (PJP). Printed completed specimens: (d) DLP, (e) SLA, (f) PJP

Accuracy analysis

According to ISO 5725-1:2023,[21] the accuracy of dental models is defined in terms of trueness and precision. Trueness reflects the degree of agreement between the measured values of dental resin model specimens and the reference standard values, whereas precision represents the consistency of results obtained from repeated printing of dental resin model specimens.

In this study, resin models were printed in a single batch using three different 3D printing technologies, producing 49 specimens distributed across various build positions for trueness evaluation. Consistent with established methodologies, the length, width, and height of the specimens were measured using a digital micrometer (C/N 293-240-30, Mitutoyo, Tokyo, Japan) with an accuracy of 0.001 mm.[9] The length and width of each specimen were measured three times at both ends and the midpoint, and the mean values were recorded as the measurements for length and width. Similarly, the height of each specimen was determined from three replicate measurements, and the deviation between the mean value and the overall base height (3 mm) was recorded as the height measurement [Figure 2]. Based on previously reported criteria,[9] deviations within ±0.1 mm from the standard value were considered clinically acceptable. These deviations were used to evaluate the influence of build positions on the trueness of resin models fabricated by three different 3D printing technologies.

Figure 2.

Figure 2

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(a-c) Schematic diagram of length (X-axis) and width (Y-axis) measurements, (d) Schematic diagram of height (Z-axis) measurement

For precision evaluation, three resin model specimens were manufactured repeatedly under identical conditions, and their length, width, and height were measured as described above. The intraclass correlation coefficient (ICC) was calculated to evaluate the influence of build position on the precision of the three types of 3D-printed resin model specimens. Higher ICC values indicate greater precision, whereas lower values reflect reduced precision. Following previous literature[22] and the 95% confidence interval (CI) estimated by ICC, four levels of precision (repeatability) were defined: Poor (ICC <0.50), moderate (0.50≤ ICC <0.75), good (0.75≤ ICC <0.90), and excellent (ICC ≥0.90).

Flexural properties testing

After the accuracy experiments, the model specimens produced by the three manufacturing technologies with different build positions were subjected to flexural testing using a universal testing machine (C43.104, MTS Systems, USA). Each specimen was placed on two supporting platforms with a span length of 20 mm (L = 20 mm) arranged parallel to each other [Figure 3]. The loading probe speed was set at 1 mm/min, and data were collected at a frequency of 10 Hz until fracture occurred at the specimen midpoint.[9] The universal testing machine software recorded points selected from the elastic region of the stress–strain curve. In this experiment, F represents the load at a selected point in the elastic region of the stress–strain curve, d represents the specimen deflection at F, L represents the span length, w represents the width, and l represents the length in the following formulas.

Figure 3.

Figure 3

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Schematic representation of the three-point bending test setup

Flexural Strength Formula: Inline graphic

Flexural Modulus Formula: Inline graphic

Statistical analysis

Statistical analysis and ICC calculations were conducted using SPSS software (IBM Statistics, v26.0; IBM Corp., NY, USA). Normality was assessed using the Shapiro–Wilk test, and homogeneity of variance was examined with Levene’s test. If the data were normally distributed and met the assumption of homogeneity of variance, one-way ANOVA was performed at a significance level of α = 0.05. If the overall means were not equal, Tukey’s post hoc test was applied for pairwise comparisons between groups. For data that did not satisfy the assumptions of normality or homogeneity of variance, the Kruskal–Wallis H-test was used.

RESULTS

Accuracy of three types of resin model specimens

The measured length, width, and height values of the three types of 3D-printed resin models at different build positions are shown in Table 3.

Table 3.

Trueness of length, width, and height measurements for three-dimensional-printed resin models at different build positions (rows and columns) (n=7 mm)

Columns DLP
Length
 Width
 Height
Mean±SD 95% CI Mean±SD 95% CI Mean±SD 95% CI
1 1.97±0.01 1.96–1.98 1.95±0.01 1.94–1.95 24.94±0.01 24.92–24.95
2 1.96±0.01 1.95–1.96 1.95±0.01 1.94–1.95 24.99±0.02 24.99–25.01
3 1.98±0.01 1.98–1.99 1.95±0.01 1.95–1.96 25.03±0.02 25.01–25.04
4 1.95±0.01 1.94–1.96 1.95±0.01 1.95–1.96 25.04±0.02 25.02–25.05
5 1.97±0.01 1.97–1.98 1.94±0.01 1.93–1.95 24.98±0.02 24.97–25.00
6 1.95±0.01 1.94–1.96 1.93±0.02 1.92–1.95 24.99±0.03 24.96–25.02
7 1.97±0.00 1.96–1.97 1.93±0.01 1.92–1.94 24.99±0.02 24.98–25.00
F/H F=26.346 H=17.183 F=21.338
P 0.0005** 0.009** 0.0005**
Rows Length
Width
Height
Mean±SD 95% CI Mean±SD 95% CI Mean±SD 95% CI
1 1.96±0.01 1.94–1.97 1.94±0.01 1.94–1.95 24.9±0.03 24.95–25.00
2 1.96±0.02 1.94–1.97 1.93±0.01 1.94–1.95 24.9±0.03 24.95–25.01
3 1.96±0.01 1.95–1.98 1.93±0.01 1.95–1.96 25.0±0.04 24.96–25.03
4 1.97±0.02 1.95–1.98 1.94±0.01 1.95–1.96 25.0±0.04 24.98–25.04
5 1.97±0.01 1.95–1.98 1.95±0.01 1.93–1.95 25.0±0.05 24.96–25.05
6 1.97±0.01 1.95–1.98 1.95±0.01 1.92–1.95 25.0±0.04 24.97–25.04
7 1.97±0.01 1.96–1.98 1.96±0.01 1.92–1.94 25.0±0.03 24.97–25.03
F/H F=1.077 F=5.140 F=0.866
P 0.392# 0.0005** 0.528#
Columns SLA PJP
Length Width Height Length Width Height
Mean±SD 95% CI Mean±SD 95% CI Mean±SD 95% CI Mean±SD 95% CI Mean±SD 95% CI Mean±SD 95% CI
1 1.96±0.00 1.96–1.97 2.02±0.03 1.99–2.05 24.95±0.04 24.91–24.99 1.82±0.01 1.81–1.83 1.93±0.01 1.92–1.94 24.82±0.02 24.48–25.16
2 1.98±0.01 1.97–1.99 2.01±0.02 1.99–2.03 24.98±0.03 24.95–25.01 1.75±0.01 1.75–1.76 1.92±0.01 1.91–1.94 24.82±0.03 24.80–25.39
3 1.99±0.01 1.98–2.00 2.00±0.02 1.99–2.03 24.97±0.02 24.95–24.99 1.79±0.01 1.78–1.79 1.92±0.01 1.91–1.93 24.82±0.02 24.82–25.26
4 2.02±0.01 2.01–2.02 1.99±0.02 1.98–2.01 24.95±0.02 24.93–24.97 1.77±0.04 1.73–1.80 1.93±0.02 1.91–1.95 24.81±0.02 24.91–25.25
5 1.99±0.00 1.98–1.99 1.99±0.02 1.98–2.01 24.95±0.03 24.92–24.98 1.77±0.04 1.73–1.78 1.93±0.02 1.92–1.95 24.79±0.03 24.77–25.11
6 1.97±0.01 1.96–1.98 2.00±0.01 1.99–2.01 24.94±0.03 24.91–24.97 1.75±0.00 1.75–1.75 1.92±0.01 1.91–1.94 24.78±0.03 24.93–25.10
7 1.95±0.02 1.93–1.97 2.00±0.02 1.98–2.02 24.91±0.01 24.91–24.92 1.76±0.00 1.76–1.76 1.93±0.01 1.91–1.94 24.78±0.02 24.89–25.18
F/H H=38.528 F=1.551 H=17.938 H=30.709 F=0.550 F=3.832
P 0.0005** 0.186# 0.006** 0.0005** 0.767# 0.004**
Rows Length Width Height Length Width Height
Mean±SD 95% CI Mean±SD 95% CI Mean±SD 95% CI Mean±SD 95% CI Mean±SD 95% CI Mean±SD 95% CI
1 1.98±0.03 1.95–2.01 1.98±0.01 1.97–1.99 24.95±0.07 24.92–24.98 1.77±0.03 1.74–1.79 1.93±0.01 1.92–1.94 24.83±0.02 24.40–25.05
2 1.98±0.03 1.95–2.00 2.00±0.01 1.99–2.00 24.94±0.07 24.91–24.97 1.77±0.03 1.75–1.80 1.92±0.00 1.92–1.92 24.80±0.03 24.87–25.36
3 1.97±0.02 1.95–2.00 2.02±0.02 2.00–2.04 24.96±0.09 24.94–24.99 1.76±0.03 1.74–1.79 1.92±0.01 1.91–1.93 24.79±0.02 24.92–25.13
4 1.98±0.02 1.96–2.00 2.03±0.01 2.02–2.05 24.96±0.08 24.91–25.01 1.77±0.03 1.75–1.79 1.94±0.01 1.93–1.95 24.82±0.03 24.88–25.30
5 1.98±0.02 1.96–2.00 2.01±0.01 2.00–2.02 24.95±0.07 24.92–24.98 1.76±0.03 1.74–1.79 1.91±0.00 1.90–1.91 24.78±0.03 24.81–25.17
6 1.99±0.02 1.97–2.00 1.99±0.01 1.98–2.00 24.95±0.08 24.92–24.98 1.77±0.03 1.74–1.79 1.94±0.00 1.94–1.94 24.79±0.04 24.90–25.15
7 1.98±0.02 1.96–2.00 1.98±0.01 1.97–1.99 24.95±0.09 24.92–24.98 1.80±0.04 1.76–1.84 1.93±0.02 1.91–1.95 24.81±0.02 24.89–25.19
F/H F=0.224 H=36.484 F=0.386 H=8.308 H=27.728 H=9.607
P 0.967# 0.0005** 0.8848# 0.2168# 0.0005** 0.1428#
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**A highly significant difference at P<0.01, #No significant difference at P>0.05. CI: Confidence interval, SD: Standard deviation, DLP: Digital light processing, SLA: Stereolithography, PJP: Polymer jetting printing

At different column positions, the deviations (defined as the difference between the measured value and the true value, with true values being 2.00 mm for length and width and 25.00 mm for height) in length (0.18–0.25 mm) and height (0.18–0.22 mm) of the PJP group exceeded the specified threshold of ± 0.1 mm. In contrast, the deviations in length, width, and height of the DLP group (0.02–0.05 mm, 0.05–0.07 mm, and 0.01-0.06 mm, respectively) and SLA group (0.01–0.03 mm, 0.00–0.03 mm, and 0.04–0.06 mm, respectively) were all within the specified threshold of ± 0.1 mm.

At different row positions, the deviation ranges of length, width, and height were 0.20–0.24 mm, 0.06–0.09 mm, and 0.17–0.22 mm, respectively, for the PJP group; 0.03–-0.04 mm, 0.04–0.07 mm, and 0.00–0.02 mm, respectively, for the DLP group; and 0.01–0.03 mm, 0.00–0.03 mm, and 0.04–0.06 mm, respectively, for the SLA group.

Regarding precision, the lengths, widths, and heights of three resin model specimens printed three times at different build positions were plotted as line graphs [Figure 4]. The graphs indicate that the variations in length and width of the three printed resin model specimens are relatively consistent across different build positions, whereas the consistency in height is poor.

Figure 4.

Figure 4

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Printing precision across build positions (1–7: Column 1, 8–14: Column 2, etc.). Length (X-axis): (a) digital light processing (DLP), (b) stereolithography (SLA), (c) polymer jetting printing (PJP). Width (Y-axis): (d) DLP, (e) SLA, (f) PJP. Height (Z-axis): (g) DLP, (h) SLA, (i) PJP. DLP: Digital light processing, SLA: Stereolithography, PJP: Polymer jetting printing

The ICC values for the length, width, and height of the three resin model specimens at different build positions are presented in Table 4. The table shows that the ICCs for length, width, and height differ among the three groups. However, overall, the ICC for height is consistently lower than that for length or width across all three groups. Among these, the DLP and PJP groups demonstrated the highest precision in length, followed by width, with height exhibiting the lowest precision. In contrast, the SLA group displayed the highest precision in width, followed by length, with height showing the least precision.

Table 4.

Precision analysis was conducted on the length, width, and height of three different printing technology model specimens, each with three repeated prints (n=49)

Printing technology Dimension ICC P
DLP Length 0.934 0.0005**
Width 0.742 0.0005**
Height 0.630 0.0005**
SLA Length 0.802 0.0005**
Width 0.878 0.0005**
Height 0.386 0.0005**
PJP Length 0.875 0.0005**
Width 0.625 0.0005**
Height 0.437 0.0005**
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**A highly significant difference at P<0.01. ICC: Intraclass correlation coefficient, DLP: Digital light processing, SLA: Stereolithography, PJP: Polymer jetting printing

Flexural properties of three types of resin model specimens

Table 5 presents the flexural strength and modulus of the three types of 3D-printed resin model specimens at different build positions. Table 5 indicates no significant differences (P > 0.05) in flexural strength and modulus among different row positions for all three groups. However, a statistically significant difference (P = 0.003, H = 19.730) was observed in the flexural modulus of the SLA group specimens at different column positions. In addition, compared with the DLP and PJP groups, the SLA group exhibited greater variations (the difference between the upper and lower bounds of the 95% CI) in flexural strength and modulus at different row and column positions [Table 5].

Table 5.

Measurement of bending strength and bending modulus of three types of printed resin model specimens at different build positions (rows and columns) (n=7 MPa)

Columns Flexural strength
 Flexural modulus
DLP
 SLA
 PJP
 DLP
 SLA
 PJP
Mean±SD 95% CI Mean±SD 95% CI Mean±SD 95% CI Mean±SD 95% CI Mean±SD 95% CI Mean±SD 95% CI
1 72.16±3.11 69.28–75.03 96.61±1.97 94.78–98.43 69.62±2.39 67.41–71.83 942.13±77.31 870.63–1013.63 1513.69±143.77 1380.73–1646.65 1113.60±98.66 1022.34–1204.85
2 72.59±1.93 70.81–74.37 95.05±5.82 89.67–100.43 67.06±1.84 65.35–68.76 877.41±37.83 842.42–912.40 1509.63±139.41 1380.70–1638.57 1084.28±45.81 1041.91–1126.65
3 70.96±0.80 70.23–71.70 94.96±3.18 92.02–97.90 68.25±2.30 66.12–70.37 879.26±49.58 833.41–925.12 1513.29±166.82 1359.00–1667.57 1032.04±43.25 992.04–1072.03
4 73.26±1.15 72.20–74.33 95.31±4.80 90.87–99.75 67.01±4.18 63.14–70.88 858.69±51.52 811.04–906.33 1616.27±210.97 1421.16–1811.38 1084.02±97.52 993.83–1174.22
5 74.31±1.73 72.72–75.91 85.73±12.83 73.86–97.60 67.31±3.44 64.13–70.49 877.60±62.68 819.63–935.57 1859.23±365.98 1520.74–2197.71 1065.21±55.94 1013.47–1116.94
6 73.06±1.57 71.61–74.52 91.58±7.51 84.63–98.53 67.23±1.81 65.55–68.90 878.22±32.32 848.33–908.11 1859.12±270.54 1608.91–2109.32 1053.69±116.34 946.10–1161.29
7 72.40±1.65 70.87–73.92 88.26±9.06 79.88–96.64 66.27±1.45 64.92–67.61 854.52±92.30 769.15–939.88 1985.54±215.96 1785.81–2185.81 1028.46±35.22 995.90–1061.04
F/H F=2.246 H=9.355 H=7.966 F=1.561 H=19.730 F=1.120
P 0.057# 0.155# 0.241# 0.183# 0.003** 0.367#
Rows DLP
SLA
PJP
DLP
SLA
PJP
Mean±SD 95% CI Mean±SD 95% CI Mean±SD 95% CI Mean±SD 95% CI Mean±SD 95% CI Mean±SD 95% CI
1 71.90±1.46 70.55–73.25 89.88±10.52 80.15–99.61 65.76±0.76 65.06–65.60 915.66±78.34 870.63–1013.63 1704.57±408.94 1326.36–2082.78 1073.74±100.06 981.20–1166.28
2 73.00±1.70 71.42–74.57 93.75±5.79 88.40–99.11 66.75±1.29 65.57–67.94 913.49±46.93 842.42–912.40 1627.23±231.89 1412.76–1841.69 1046.33±46.44 1003.38–1089.28
3 72.47±1.37 71.20–73.74 91.00±11.77 88.11–101.88 68.81±2.21 66.76–70.85 837.44±54.35 833.41–925.12 1691.06±297.14 1416.25–1965.87 1088.30±83.64 1010.94–1165.66
4 72.26±3.20 69.30–75.22 92.88±8.38 85.13–100.63 66.75±3.54 63.48–70.03 865.65±39.42 811.04–906.33 1704.21±319.26 1408.94–1999.47 1092.19±86.93 1011.79–1172.59
5 73.83±1.64 72.31–75.35 94.42±5.06 89.74–99.10 69.02±2.15 67.03–71.00 882.63±60.42 819.63–935.57 1624.88±292.67 1354.21–1895.56 1053.39±82.99 976.63–1130.15
6 72.43±2.09 70.50–74.36 95.03±4.24 91.12–98.95 67.09±1.66 65.55–68.63 871.00±90.65 848.66–908.11 1695.23±239.72 1473.53–1916.94 1077.90±41.31 1039.69–1116.11
7 72.87±2.03 70.99–74.74 90.53±8.22 82.92–98.13 68.56±4.39 64.50–72.63 881.97±43.06 769.15–939.88 1809.59±266.08 1563.51–2055.68 1029.45±92.57 943.84–1115.06
F/H F=0.679 H=2.197 H=11.485 F=1.381 H=2.147 F=0.608
P 0.668# 0.901# 0.074# 0.245# 0.906# 0.723#
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**A highly significant difference at P<0.01, #No significant difference at P>0.05. CI: Confidence interval, SD: Standard deviation, DLP: Digital light processing, SLA: Stereolithography, PJP: Polymer jetting printing

DISCUSSION

The findings revealed that both the accuracy and flexural properties of the printed resin models were influenced by build position (row vs column). Based on ISO 4049:2019,[19] ISO 20795-1,[23] ISO 6873:2013,[24] and previous studies,[9,25,26,27] the results of this study did not fully meet clinically acceptable standards. Therefore, the null hypothesis is partially rejected.

Clinically, resin models exhibit complex anatomical structures, particularly complete dental arches. Although 3D scanning followed by software best-fit alignment can yield overall displacement measurements (e.g., root mean square error(RMSE)) for the entire dental arch, it remains challenging to independently and accurately evaluate deviations in each segment of the arch. Moreover, the best-fit algorithm for point cloud alignment exhibits an inherent mathematical tendency toward minimization.[20,28] In this study, standardized bar specimens (2 mm × 2 mm × 25 mm) were selected to ensure methodological consistency across different printing groups, thereby guaranteeing the repeatability of measurement results under standardized conditions. Furthermore, in line with a previous study,[9] digital micrometers with a precision of 0.001 mm (1 µ) were employed for sample measurements. The findings and conclusions of this study provide meaningful guidance for evaluating the accuracy and flexural performance of clinical cases, such as complete dental arches, in 3D spatial positioning (X, Y, and Z axes).

This study found that DLP specimens printed in different rows or columns exhibited similar deviations in length and width (i.e., along the X-axis and Y-axis of the build platform). A previous study[29] reported that in the XY plane, printing is performed through layer-by-layer deposition along the Z-axis, whereas in the DLP group, each layer undergoes complete polymerization simultaneously. This fundamental distinction in curing methodology may induce concurrent in-plane contraction within the DLP specimens, leading to measured values for length and width being slightly lower than the actual values. In addition, during the printing process, resin materials may undergo expansion and/or contraction, which also explains the trends of increase or decrease observed in the three types of resin specimens along the X-axis, Y-axis, and Z-axis.[30] Deviations produced by specimens on the XY plane may also be associated with shrinkage during postcuring processes and residual stress accumulation, which can result in deformation or cracking of specimens compared with the true values.[31] The results showed that the ICC was lower in the height direction (DLP: 0.630; SLA: 0.386; PJP: 0.437) than in the length and/or width direction, indicating that Z-axis accuracy was more significantly affected by build position. This finding is consistent with a previous study,[27] which suggested that the primary discrepancy in 3D-printed models lies in the Z-axis plane. This Z-axis deviation may result from the step effect of the layer-by-layer printing technique, which restricts vertical accuracy, surface topography, and isotropic mechanical properties.[31,32]

Many studies[25,32,33] have suggested that differences in dental models within the range of 100 µm to 300 µm are acceptable. In this study, the DLP, SLA, and PJP models at different build positions also exhibited differences within this range. However, the length and height of PJP model specimens at different build positions did not meet the specified requirements within the ±0.1 mm tolerance threshold.

This study adopted evaluation methods from a previous study and classified the precision of the specimens into four levels.[22] The results indicated that the precision of DLP resin model specimens was the highest (particularly in length), followed by SLA resin model specimens, and finally PJP resin model specimens. These findings differ from those reported by Kim et al.,[13] possibly due to variations in specimen types and measurement methods. DLP technology employs a digital light projector to project ultraviolet light, enabling any selected part of the entire X-Y working space to be exposed simultaneously, thereby accelerating the cycle time between layers[34,35] and reducing errors associated with repeated printing. In contrast, SLA technology uses a laser beam to solidify photopolymer materials from a point to a line and subsequently to a surface.[9,36] In this study, each specimen in the DLP group was printed with a total of 560 layers, compared with 400 layers for each specimen in the SLA group and 1750 layers for each specimen in the PJP group. Furthermore, each print job in the PJP group required more than 10 h to complete. The lower printing layer thickness, higher number of layers, and longer printing time may be major factors contributing to the lower trueness and precision observed in the PJP group. Consequently, for cases requiring high-accuracy models, DLP or SLA technologies are recommended as primary options.

According to ISO 4049:2019,[19] dental polymer materials should possess a minimum flexural strength of 80 MPa. In this study, only the SLA group met this requirement. ISO 20795-1[23] specifies that denture base polymers shall have a flexural strength of at least 65 MPa and a flexural modulus of at least 2000 MPa. While all specimens produced by the three AM technologies at different build positions achieved the required strength threshold, none attained the stipulated modulus threshold. At present, international standards exist only for the flexural strength of dental gypsum models (ISO 6873:2013[24]), and there are no established standards for dental 3D printing resin materials. In clinical practice, super-hard artificial stone is typically used for model fabrication, and according to ISO 6873:2013,[24] Type IV gypsum material should have a minimum flexural strength of 35 MPa after being poured for 1 h. Although different specimen sizes were used in this study to test flexural strength, all three groups met the requirements of ISO 6873:2013.[24] Consistent with the findings of de Castro et al.,[8] the bending performance of SLA was significantly affected by build position; however, this study further demonstrated that column position had a greater effect than row position (P < 0.05). Since the SLA group exhibited more pronounced variations in flexural modulus across column positions, DLP or PJP techniques may be considered clinically advantageous when dimensional stability of flexural properties is required, such as for orthodontic models.[25]

This study provides a theoretical basis for parameter optimization in the 3D printing of dental models, enabling clinicians to make evidence-based decisions regarding build position and AM technologies when selecting models for production. It should be noted that this study only evaluated the influence of different build positions (row and column) on the flexural properties of resin model specimens produced by three printing technologies: DLP, SLA, and PJP. Future research should further investigate the effects of build position on other mechanical properties, including the Vickers hardness of 3D-printed resin model specimens. Because identical layer thickness, X-Y resolution, and manufacturing environments could not be applied across all printers, the universality of these findings as an absolute standard for comparing 3D printers is limited. Further studies should also explore the mechanisms by which column position affects the flexural performance (flexural modulus) of SLA group specimens. In addition, ambient parameters such as room temperature and relative humidity were identified as confounding variables that influence experimental outcomes.[37,38] Future studies will incorporate environmental controls to systematically evaluate the effects of these factors.

CONCLUSION

Under the conditions of this experiment, the following conclusions can be drawn:

  1. Compared with the DLP and SLA groups, the deviations in length and height of the PJP group exceeded 0.1 mm (failure to meet the clinically acceptable standard) at different row or column positions, which meant that the build position had a greater influence on the trueness of the PJP group

  2. The precision of the specimen height was lower than that of the length and width in all three technologies, indicating that the stability of the Z-axis in 3D printing remains a challenge

  3. Although row position had no significant influence on the flexural strength and modulus of any group, variations in column position led to notable changes in the flexural modulus of the SLA group. Moreover, the SLA group exhibited greater variations (95% CI) in both flexural strength and modulus across the build positions.

Conflicts of interest

There are no conflicts of interest.

Acknowledgments

The authors thank Chongqing Jingmei Medical Technology Co., Ltd., for kindly supplying 3D printing materials and equipment used in this experiment, as well as technical support.

Funding Statement

This work was supported by the Joint Medical Research Project between Chongqing Science and Technology Bureau and Health Commission (No. 2023MSXM094); Scientific and Technological Research Program of Chongqing Municipal Education Commission, China (No. KJQN 202100439); and the 2023 medical education research project of the medical education branch of the Chinese Medical Association and the National Center for the development of medical education (No. 2023A50).

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