ORIGINAL RESEARCH


https://doi.org/10.5005/jp-journals-10019-1433
International Journal of Prosthodontics and Restorative Dentistry
Volume 13 | Issue 4 | Year 2023

Comparative Evaluation of Fitness and Compressive Strength of Temporary Crowns Designed from 3Shape and Exocad Software: An In Vitro Study


Khalid Dhafer Al Hendi

Department of Prosthodontics, Faculty of Dentistry, Najran University, Najran, Saudi Arabia

Corresponding Author: Khalid Dhafer Al Hendi, Department of Prosthodontics, Faculty of Dentistry, Najran University, Najran, Saudi Arabia, Phone: +966567916677, e-mail: kdalhendi@nu.edu.sa

Received: 09 October 2023; Accepted: 08 December 2023; Published on: 30 December 2023

ABSTRACT

Purpose: To evaluate the fitness and compressive strength of temporary crowns designed in 3Shape and Exocad software.

Materials and methods: A sound premolar was scanned by 3Shape intraoral scanner followed by standard tooth preparation, scanning, and matching to obtain the exact crown size of the unprepared premolar. A total of 100 crowns were designed using 3Shape Dental System (3Shape, Copenhagen, Denmark; n = 50) and Exocad (GmbH, Darmstadt, Germany; n = 50) and milled using poly(methyl methacrylate) (PMMA) ViTA computer-aided design (CAD)—temp blocks. The fitness of temporary crown was evaluated by scanning and analyzing the thickness of silicone replica in Geomagic surface matching software. The compressive strength was evaluated by observing the first crack and ultimate failure of the crown using a universal testing machine. The data was recorded and analyzed using Statistical Package for the Social Sciences (SPSS) software. Independent t-tests were used to compare the studied variables.

Results: The results showed a lower but insignificant discrepancy at margins (p = 0.072) in Exocad software (70.23 ± 18.19 µm) compared to 3Shape software (72.21 ± 17.63 µm). The internal fit at different positions (chamfer, axial, angle, and occlusal) was comparatively better with Exocad software than with 3Shape software. Significant difference (p = 0.001) in compressive force required to make the first crack was found in 3Shape-designed crowns (1124.65 ± 170.54 N) and in Exocad-designed crowns 1004.03 ± 146.98 N). Significant difference (p = 0.001) was found in ultimate compressive strength with 3Shape (1731.31 ± 81.43 N) and Exocad (1522.6 ± 142.53 N) prepared crowns.

Conclusion: Marginal fit and internal fit of crowns from both softwares are comparable. Compressive strength of crowns prepared from 3Shape is better than that of Exocad software.

How to cite this article: Al Hendi KD. Comparative Evaluation of Fitness and Compressive Strength of Temporary Crowns Designed from 3Shape and Exocad Software: An In Vitro Study. Int J Prosthodont Restor Dent 2023;13(4):216–221.

Source of support: Nil

Conflict of interest: None

Keywords: 3Shape dental system software, Compressive strength, Exocad software, Marginal fit, Temporary crown

INTRODUCTION

In prosthodontics, temporary crowns are an essential part of the treatment protocol, which are used to protect the prepared tooth until definitive prostheses are given. The temporary crown protects the pulp and periodontal health. It also maintains the position of prepared tooth and protects the occlusion.1 Computer-aided design (CAD) and computer-aided manufacturing (CAM) can be used to fabricate temporary crowns using a digital workflow comprising the entire three-dimensional (3D) ecosystem of machines and software.2,3 Right from data acquisition via the intraoral scanner to designing the crown and milling, it can be performed easily as opposed to the conventional method of the lost-wax technique.4 This digital development has been rampant and significant in the past decade and continues to grow as we progress.5 Conventional methods often require complex procedures like wax pattern, casting which are laborious and time-consuming. They are prone to error and increase the time duration of the treatment.6 On the contrary, digital workflow is hassle-free, definitive, comfortable, and fast along with reduced risk of errors.7 However, this might be associated with increased cost of treatment compared with conventional techniques.8

Digital workflow requires the utilization of different software and machines. These 3D equipment are manufactured by various companies around the world. They often differ in configuration, acquisition process, results, and compatibility factors. Although manufacturers support cross-compatibility, thereby increasing the ease of fabrication with a wide variety of equipment.9 In a complete digital workflow model, the fabrication of crown begins with the digital intraoral scan of the prepared tooth. Then, the files are processed by CAD software to prepare the crown design and CAM machine to mill the final prosthesis. To design the prosthesis, 3Shape and Exocad are the most widely used software. They offer a wide variety of functions and design features to plan a prosthesis.10,11

However, due to variation in software’s program, coding, and scripting, the outcome might be different. This can affect the physical properties of crown manufactured.12,13 The difference in designing software can cause discrepancies in the surface of the crown and the prepared tooth. This can lead to poor fit and affect the compressive strength of the crown. There is a paucity of studies in this arena, and more research is required to evaluate it. Hence, the purpose of the present study was to assess the fitness and compressive strength of temporary crowns designed in the most commonly used software, 3Shape and Exocad. The null hypothesis considered was that no difference would be found in the fitness and compressive strength of temporary crowns designed with the 3Shape and Exocad software.

MATERIALS AND METHODS

This in vitro descriptive study was carried out at faculty of dentistry at Najran University in the year 2022–2023 to evaluate the fitness and compressive strength of temporary crowns designed in 3Shape and Exocad software.

The sample size was determined based on the results of a pilot study and power analysis software (G*Power v3.1.9.2, Heinrich Heine University, Düsseldorf, Germany). Considering the test power to be 90%, type I error of α = 0.05, the sample size was estimated to be 90. To increase the power of the study, a sample size of 100 (50 for each software) was determined to assess the compressive strength. To study the fitness, a sample size of 15 was decided.

The following protocols were followed to design and mill the temporary crowns. A sound first premolar was scanned by a scanner (E3, 3Shape, Copenhagen, Denmark) to obtain a preoperative model. This scan was used to prepare the exact outline of the outer surface of crowns in both software. A standard tooth preparation was done by an experienced prosthodontist in adherence to the principles of tooth preparation. A 2 mm reduction of the occlusal surface, 1.2 mm of buccal and lingual surface, and 1.2 mm deep chamfer at the margins. Reduction was done with 6° taper.14 This prepared tooth was again scanned with the scanner (E3, 3Shape, Copenhagen, Denmark), and the scanned images were matched together to obtain a similar crown resembling the unprepared premolar. A total of 100 crowns were designed using 3Shape Dental System (3Shape, Copenhagen, Denmark; n = 50 and Exocad (GmbH, Darmstadt, Germany; n = 50) (Figs 1 and 2). The designed temporary crowns were saved as standard tessellation language (STL) files and were transferred into milling machine (350i, CORiTEC, Eiterfeld, Germany). The milling unit fabricated all the 100 crowns with poly(methyl methacrylate) (PMMA) block (ViTA CAD-temp, Bad Säckingen, Germany) according to manufacturer’s recommended settings (Figs 3 and 4).15

Fig. 1: Scan model of three-unit temporary dental prosthesis designed in 3Shape software

Fig. 2: Scan model of three-unit temporary dental prosthesis designed in Exocad software

Fig. 3: Three-unit temporary dental prosthesis fabricated using 3Shape software

Fig. 4: Three-unit temporary dental prosthesis fabricated using Exocad software

The internal fitness and the compressive strength of the temporary crown were evaluated. To analyze the fitness of the temporary crown, its internal surface was filled with light body 3M™ Imprint™ 4 VPS Impression Material (3M ESPE, Seefeld, Germany) and seated on the prepared tooth with gentle pressure. Uniform pressure was applied by placing a gauze piece over the crowns and engaging it with a binder clip to hold the occlusal surface and bottom of the crown. The impression material was separated with care from the temporary crown after complete polymerization. The inner crown surface was scanned with and without the impression material, and the STL files were saved (Figs 5 and 6). The standard tessellation language (STL) files were transferred to 3D surface matching software (Geomagic Control X) and superposed to obtain the best-fit orientation. Hypothetical planes passing through the buccolingual and mesiodistal directions were set for all the samples in a similar way. The fitness of the crown was evaluated at margins, chamfer, axial, angle, and occlusal regions.

Fig. 5: Inner surface scan of temporary prosthesis fabricated using 3Shape software

Fig. 6: Inner surface scan of temporary prosthesis fabricated using Exocad software

To evaluate the compressive strength, the samples were subjected to a universal testing machine (Hounsfield H5KS, United Kingdom) by applying a force of 1 mm/minute with a round chisel of 3 mm on the central grove of the crown. The force displayed was recorded at the first crack and ultimate failure of the crown.

The data was recorded and analyzed using Statistical Package for the Social Sciences (SPSS) software (IBM Corp. Released 2011. IBM SPSS Statistics for Windows, Version 20.0. Armonk, New York: IBM Corp.). Independent t-test were used to compare the studied variables. Statistical significance was considered at p < 0.05.

RESULTS

The results showed a lower but insignificant discrepancy at margins (p = 0.072) in Exocad software (70.23 ± 18.19 µm) compared to 3Shape software (72.21 ± 17.63 µm). The internal fit at different positions was comparatively better 3Shape software although the difference was insignificant. Lesser discrepancy was found with Exocad software at different positions compared to 3Shape software (chamfer 49.64 ± 16.84 µm vs 50.92 ± 16.97 µm; axial 71.48 ± 17.83 µm vs 73.31 ± 17.11 µm; angle 105.21 ± 17.4 µm vs 106.45 ± 18.26 µm and occlusal 110.06 ±19.92 µm vs 111.94 ± 21.22 µm), respectively (Table 1).

Table 1: Comparison of marginal and internal discrepancy of temporary crowns in two different software workflows
Fitness Mean ± standard deviation (µm) p-value
3Shape Exocad
Margin 72.21 ± 17.63 70.23 ± 18.19 0.072
Chamfer 50.92 ± 16.97 49.64 ± 16.84 0.098
Axial 73.31 ± 17.11 71.48 ± 17.83 0.147
Angle 106.45 ± 18.26 105.21 ± 17.4 0.082
Occlusal 111.94 ± 21.22 110.06 ± 19.92 0.221

Significant difference (p = 0.001) in compressive force required to make the first crack was found in 3Shape-designed crowns (1124.65 ± 170.54 N) and in Exocad-designed crowns 1004.03 ± 146.98 N). Significant difference (p = 0.001) was found in ultimate compressive strength with 3Shape (1731.31 ± 81.43 N) and Exocad (1522.6 ± 142.53 N) prepared crowns (Table 2).

Table 2: Comparison of mean compressive strength of temporary crowns in two different software workflows
Compressive strength Mean ± standard deviation (N) p-value
3Shape Exocad
First crack 1124.65 ± 170.54 1004.03 ± 146.98 0.001*
Ultimate compressive strength 1731.31 ± 81.43 1522.6 ± 142.53 0.001*

*p-value < 0.05 is significant

DISCUSSION

The difference in equipment and software used in the fabrication of temporary crowns can affect the quality of prosthesis. The purpose of this study was to evaluate the fitness and compressive strength of the temporary crowns prepared from the two most commonly used design software, 3Shape and Exocad. In this study, it was found that the mean discrepancy with Exocad software is less than that of 3Shape software, but it was statistically insignificant. The null hypothesis that there would be no difference in the fitness of temporary crowns designed with the 3Shape and Exocad software was rejected.

Complete digital workflows produce better and increased marginal fit than conventional lab-driven workflows.1618 Scan acquisition process and milling of the crown are the most important steps in fabrication and can greatly influence the final product. Hence, in this study, these two equipment were kept the same, and only the designing software was changed.19,20 The CAD/CAM system uses a milling machine, and the temporary crowns are milled out of PMMA resin blocks using specially designed burs.21 Optimum marginal fit is one of the key criteria for the success of restorations.22 Poor marginal adaptation can lead to periodontal damage, microleakage, dissolution of luting agent, secondary caries, and marginal discoloration.23 A marginal gap of 50–100 µm has been found to be clinically acceptable for CAD/CAM restorations.24

Various methods can be used to evaluate the marginal and internal fit of the prothesis. Methods like cross-sectional microscopy, silicone replication technique, triple scan method, microcomputed tomography and optical coherence tomography have been employed in published literature.25,26 In this study, 3D surface matching software (Geomagic Control X) was used to identify the best-fit alignment and color mapping of the internal surface of the crown. This software has also been used to evaluate the accuracy and adaptation of denture bases and partial denture frameworks.27,28 In a study conducted by Al-Hawwaz and Ibraheem29 to fabricate full contour Zirconia CAD/CAM crowns using different software. They found the lowest marginal gap with InLab SW, followed by Exocad and 3Shape software. The marginal gap seems to be dependent on the kind of scanning device used.30

The null hypothesis was rejected as no difference in the compressive strength of temporary crowns designed with the 3Shape and Exocad software was found. In this study, it was found that the compressive strength of temporary crowns designed in 3Shape software is more than that of Exocad software. This can be attributed to the design and default values of the software. The drill compensation option in 3Shape software matches the crown’s inner surface and the prepared teeth.29,31

Another study32 found that provisional crowns manufactured utilizing CAD/CAM exhibited higher fracture strength than traditionally fabricated monomethacrylate resins after thermomechanical aging. The compressive strength of the temporary crowns fabricated from 3Shape to Exocad software has values in clinically allowable range that can occur in the mouth in normal situations. Around 40 N of force is produced during swallowing, up to 800 N in chewing nuts or other masticatory loads.33 Hence, these crowns can withstand compressive forces. The 3Shape software crowns provide more compressive strength, but that does not mean that they are superior to Exocad software-designed crowns. The properties of the final crown depend upon many factors like scanner precision, software settings, milling machine, etc.31

3Shape is a complete comprehensive scanning, designing, and manufacturing software used to fabricate digital crowns and prosthesis. The software has in-built default settings for marginal gap, space for cement, and thickness of crown. These values can be altered according to preparation angles, undercuts, abutments and patient preferences.11,34 Although the challenges in scanning and designing include implant-supported and full-mouth restorations, software and equipment handling involving a learning curve before confidence in daily practice is achieved.35

The limitation of this study lies in the fact that testing was done under static loading conditions, whereas teeth are exposed to dynamic forces with thermal variations in the oral cavity. Further studies with other software, materials, and test conditions can be done to evaluate the fitness and compressive strength of crowns. Cement space and functional load can also be altered to further evaluate the response.

CONCLUSION

Based on the findings of this in vitro study, it can be concluded that the fitness of temporary crowns prepared from 3Shape to Exocad software is comparable clinically. However, the compressive strength of temporary crowns designed in 3Shape software is more than that of Exocad software.

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