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Comparison of Inner Fitness of Crown Prosthesis Manufactured by 3D Printers Based on Lamination Thickness
Int J Clin Prev Dent 2023;19(4):94-98
Published online December 31, 2023;  https://doi.org/10.15236/ijcpd.2023.19.4.94
© 2023 International Journal of Clinical Preventive Dentistry.

Nam-Joong Kim

Department of Dental Technology & Science, Shinhan University, Uijeongbu, Korea
Correspondence to: Nam-Joong Kim
E-mail: wnj120@hanmail.net
https://orcid.org/0000-0001-6334-6402
Received November 28, 2023; Revised December 8, 2023; Accepted December 20, 2023.
This is an Open Access article distributed under the terms of the Creative Commons Attribution Non-Commercial License (http://creativecommons.org/licenses/by-nc/3.0) which permits unrestricted non-commercial use, distribution, and reproduction in any medium, provided the original work is properly cited.
Abstract
Objective: In this study, crowns were manufactured by lamination at three thicknesses of 0.01 mm, 0.05 mm, and 0.10 mm to determine the difference in internal fit of crowns according to lamination thickness using a 3D printer that has been widely used recently. We aim to obtain clinically meaningful results by measuring, comparing, and evaluating the internal fit of crowns printed with different thicknesses.
Methods: The maxillary first molar was selected as the abutment test specimen model. Scan the model with a scanner and design the crown with a dental design program. The designed crown is printed and manufactured with photocurable 3D printing resin. The printed crown is cleaned using an ultrasonic cleaner and cured with a light curing machine. The manufactured crown was scanned and the spacing was measured by fitting the scanned data to the model.
Results: The average value of the overall gap was 0.027 at 0.01, 0.034 at 0.05, and 0.039 at 0.10, with the smallest gap at 0.01, the thinnest stack thickness. The maximum value was 0.061 at 0.10 and the minimum value was 0.011 at 0.01. By measurement location, LM had the smallest gap from 0.01 to 0.032 and the largest from 0.10 to 0.048. The smallest gap was found at Occ, and the gap increased toward the margins.
Conclusion: It was found that the thinner the lamination thickness, the better the internal fit of the dental prosthesis, and the size of the position-specific gap increased from the occlusal surface to the margins. Among them, LM, Occ, and BM had statistically significant differences only at 0.01 and 0.10, LW showed no significant differences, and BW showed no significant differences at 0.05 and 0.10.
Keywords : 3D printer, lamination thickness, inner fitness
Introduction

In recent years, it has become common to use digital methods to produce dental prostheses, and the use of 3D printers to produce prostheses is increasing, along with the use of CAD/CAM and milling to produce prostheses. Among dental prostheses, dental crown prostheses have the disadvantage that the lost wax technique, which melts the existing wax to produce a wax coping, takes a lot of time to produce and the success or failure of the coping depends on the skill of the operator. However, the introduction of digital systems such as CAD/CAM (computer aided design/computer aided manufacturing) in dentistry in the last 30 years has solved many of these problems [1]. This digitalization process has simplified the manufacturing process of dental prostheses, allowing them to be manufactured more quickly and accurately [2].

Now, as digital equipment is becoming more widespread, most of the work is being done by digital equipment to produce prostheses. In particular, as the technology of cam milling processing method has improved, it is possible to produce smooth surfaces, but it is impossible to produce unnecessary material consumption and complex structures, and there are disadvantages such as continuous equipment maintenance costs and large time loss in the process. Therefore, to compensate for the disadvantages of the milling processing method, 3D-printers, which are capable of producing complex structures and require less unnecessary material consumption compared to cutting processing, have been attracting attention [3].

According to a report released by the Ministry of Food and Drug Safety [4] in 2018, Korea’s medical device market is expected to gradually expand and reach $412 billion in 2020, up from $336 billion in 2016. Among them, the 3D-print market has grown more than four times in the last five years, and is expected to grow from $5.16 billion in 2015 to $16.4 billion in 2020, with an average annual growth rate of 26%. In particular, the 3D-print market in the medical and dental fields is expected to grow more than twice from $6.3 billion in 2015 to $1.2 billion in 2020.

When manufacturing dental prostheses, it is important to consider the occlusion, contact relationship with adjacent teeth, and fit of the margins for precision. Currently, when a prosthesis is fabricated using a CAD/CAM system, the tooth is designed using a CAD program after scanning the model or using an oral scanner. Many internal values can be specified and adjusted within the CAD program [1]. In this way, dental prostheses produced by 3D printers are affected by various environments, and differences in the precision of the output appear. Therefore, this study aims to evaluate the difference in internal fit of dental prostheses produced by varying the lamination thickness among various influencing factors of 3D printers.

Materials and Methods

1. Crown abutment model production

The abutment was manufactured by replicating Dentiform’s maxillary first molar abutment model (D51 DP-500A, Nissin Dental, Japan).

2. Abutment model scan

A model of the abutment made with a 3D scanner (E4 scanner, 3shape dental manager, Denmark) was scanned to form the abutment (Figure 1).

Figure 1. Scanner & abutment made by scanning.

3. Design

The shape of tooth No. 16 was designed on the given abutment tooth using the 3shape CAD program (3shape, Copenhagen K, Denmark) (Figure 2).

Figure 2. Designed crown.

4. 3D printing & crown scan

The crown was manufactured by 3D printing with photocurable resin (C&B Hybrid, Arum dentistry, Korea) (Figure 3). Lamination thickness was set to 0.01 mm, 0.05 mm, and 0.10 mm on a 3D printer (Max UV, ASIGA, Australia). The manufactured crown was cleaned using an ultrasonic cleaner (Twin Tornado, MEDIFIVE, Korea) and then cured using a UV lamp (U102H, Graphy, Korea). Afterwards, the manufactured crown was scanned using a 3D scanner.

Figure 3. 3D printer.

5. Measurement and analysis

The inner fit was confirmed by matching the scanned file of the crown with the scanned file of the abutment tooth. The internal measurement areas were lingual margin (LM), lingual wall (LW), occlusal (Occ), buccal wall (BW), and buccal margin (BM) applied by Beuer et al. [5].

The measurement results were obtained using the statistical program SPSS 22.0 Ko (SPSS 22, IBM, USA). One-way ANOVA was performed to compare the means of the experimental results, and multiple comparisons were made using Tukey HSD as a post hoc test. The significance level was set at 0.05.

Results

The dental prostheses were fabricated with three different lamination thicknesses using a 3D printer, and the internal fitness of the dental prostheses at each site was measured, and the results are shown in Table 1.

Table 1 . Comparison of gap by measurement location according to 3D printer lamination thickness (N=10)

Measuring pointLamination thickness M±SDMAXMINp**
LM0.010.032±.0110.0480.014p<0.05
0.05*0.037±.0080.0510.025
0.100.048±.0060.0580.042
LW*0.010.031±.0130.0490.016
0.050.032±.0100.0490.021
0.100.036±.0080.0530.026
Occ0.010.015±.0050.0250.007
0.05*0.021±.0070.0340.011
0.100.024±.0070.0360.016
BW0.010.024±.0100.0400.011
0.05*0.034±.0070.0450.020
0.10*0.040±.0110.0600.025
BM0.010.035±.0140.0520.015
0.05*0.043±.0080.0560.027
0.100.050±.0090.0610.036
Total0.010.027±.0110.0520.007
0.050.034±.0080.0560.011
0.100.039±.0080.0610.016

*No statistically significant difference.

**p-value by one-way ANOVA (Tukey HSD).



First, the average value of the overall gap was 0.027 at 0.01, 0.034 at 0.05, and 0.039 at 0.10, with the smallest gap at 0.01, the thinnest lamination thickness. The maximum value was 0.061 at 0.10 and the minimum value was 0.011 at 0.01. Then, by measurement location, the results were as follows. LM had the smallest variation from 0.01 to 0.032 and the largest variation from 0.10 to 0.048. In LW, 0.01 was the smallest at 0.031 and 0.10 was the largest at 0.036. In Occ, 0.01 is the smallest at 0.015 and 0.10 is the largest at 0.024. The same pattern is seen in the remaining BW and BM, although with a difference in size. From this result, we can see that the gap increases as the stack thickness increases from 0.01 to 0.10, and the maximum and minimum values are the same. By location, the smallest gap is found at Occ, and the gap increases toward the margins.

In the above results, LM, Occ, and BM were only statistically significant at 0.01 and 0.10, LW was not significant at all, and BW was not significant at 0.05 and 0.10.

Discussion

Recently, digital dental technology has already become widespread, and various types of digital dental technology are being used in the field. Therefore, in this study, a crown was manufactured using photocurable 3D printing resin. At this time, we printed three lamination thicknesses of 0.01 mm, 0.05 mm, and 0.10 mm to compare the inner surface fit of the crown.

Recently, as digital dental work has become more common, various studies, including the suitability of digital dental work, are being conducted. In particular, many studies on fit in crown prosthesis are conducted on marginal fit. There are several ways to measure the inner fit of a prosthesis. Methods for measuring fit include the silicon replica technique, which uses silicon to measure the thickness or weight of the silicone filled on the inner surface [6], and the method of cementing the crown prosthesis to the abutment with cement, cutting it, and measuring the cross section [7].

After manufacturing a coronal prosthesis, the adequacy of the margins is an important criterion for completing the prosthesis. If the margins do not fit well, a foreign body sensation may occur and food may be easily deposited, which not only increases the possibility of secondary caries but also causes problems with periodontal management, which can lead to periodontal disease. In addition, inner fit is also an important factor in ensuring that the crown prosthesis fits stably on the abutment tooth. Some believe that even if there is an empty space inside the prosthesis, it is not a big problem because it will be filled with adhesive such as cement. However, if there is an excessive space of adhesive such as cement inside the prosthesis, repetitive loads such as occlusal pressure due to mastication, etc. When transferred to a prosthesis, viscoplastic deformation of the adhesive material occurs, causing stress to concentrate on the tensile surface of the prosthesis, which may cause cracks or fractures in the prosthesis [8].

Therefore, it is very important for the crown prosthesis to fit the abutment tooth accurately. Looking at the existing literature, Sulaiman et al. [9] said that 100 mm is clinically appropriate, and McLean and Von Fraunhofer [10] said that up to 120 mm is acceptable, so the researchers Although there are differences depending on the field, in general, many clinicians seem to have evaluated 120 mm as the appropriate clinically acceptable range.

The results of this study showed that when manufactured with a lamination thickness of 0.01 mm, it was less than 0.052 mm, and when it was laminated with a thickness of 0.10 mm, it was 0.061 mm, which were all within the acceptable standards. In addition, in Park’s study [1], the marginal fitness of metal coping using wax milling was measured to be 0.023 mm for the buccal margin (BM) and 0.020 mm for the lingual margin (LM), and the marginal fitness of metal coping using 3D printing was measured to be 0.029 mm for BM and 0.021 mm for LM. And in Kim’s study [11], the overall average fit of the resin pattern using a 3D printer was <155 µm, excluding the chamfer 3-unit OG (occlusal gap). The knife 2-unit showed a suitability of <100 µm in all measurement areas. Additionally, the MO (margin open) of the chamfer and the MG (margin gap) of the knife showed compliance of <100 µm. The AG (axial gap) was found to be less than 49 µm overall. Therefore, looking at the results of recent fitness tests for digital dental prosthesis production, it was found that most of them showed appropriate fit.

When applied clinically, it may be better to thin the lamination thickness to obtain excellent suitability, but the lamination thickness cannot be unreasonably reduced without considering manufacturing time. Therefore, in the future, it would be good to conduct tests on physical properties such as hardness of crown prosthesis and evaluation of suitability according to lamination thickness considering production time.

Conclusion

This study evaluated the internal fit of dental prostheses made with three different build thicknesses using a 3D printer and found the following results.

The thinner the lamination thickness, the better the internal fit of the dental prosthesis. The size of the position-specific gap was found to increase from the occlusal surface to the margins. Among them, LM, Occ, and BM had statistically significant differences only at 0.01 and 0.10, LW showed no significant differences, and BW showed no significant differences at 0.05 and 0.10.

Based on the above results, it is believed that in the case of fabricating dental prostheses using a 3D printer, it is necessary to select the laminate thickness well to produce excellent dental prostheses with ideal fabrication time and fit.

Acknowledgements

This thesis was researched under the Shinhan University Professor Research Year program in 2022.

Conflict of Interest

No potential conflict of interest relevant to this article was reported.

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