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. 2023 Sep 1;18(9):e0285760. doi: 10.1371/journal.pone.0285760

The fracture resistance of 3D-printed versus milled provisional crowns: An in vitro study

Ahmed Othman 1,*, Maximillian Sandmair 1, Vasilios Alevizakos 1, Constantin von See 1
Editor: Mirza Rustum Baig2
PMCID: PMC10473469  PMID: 37656728

Abstract

Background

CAD/CAM has considerably transformed the clinical practice of dentistry. In particular, advanced dental materials produced via digital technologies offer unquestionable benefits, such as ideal mechanical stability, outstanding aesthetics and reliable high precision. Additive manufacturing (AM) technology has promoted new innovations, especially in the field of biomedicine.

Aims

The aim of this study is to analyze the fracture resistance of implant-supported 3D-printed temporary crowns relative to milled crowns by compression testing.

Methods

The study sample included 32 specimens of temporary crowns, which were divided into 16 specimens per group. Each group consisted of eight maxillary central incisor crowns (tooth 11) and eight maxillary molar crowns (tooth 16). The first group (16 specimens) was 3D printed by a mask printer (Varseo, BEGO, Bremen, Germany) with a temporary material (VarseoSmile Temp A3, BEGO, Bremen, Germany). The second group was milled with a millable temporary material (VitaCAD Temp mono-color, Vita, Bad Säckingen, Germany). The two groups were compression tested until failure to estimate their fracture resistance. The loading forces and travel distance until failure were measured. The statistical analysis was performed using SPSS Version 24.0. We performed multiple t tests and considered a significance level of p <0.05.

Results

The mean fracture force of the printed molars was 1189.50 N (±250.85) with a deformation of 1.75 mm (±0.25). The milled molars reached a mean fracture force of 1817.50 N (±258.22) with a deformation of 1.750 mm (±0.20). The printed incisors fractured at 321.63 N (±145.90) with a deformation of 1.94 mm (±0.40), while the milled incisors fractured at 443.38 N (±113.63) with a deformation of 2.26 mm (±0.40). The milled molar group revealed significantly higher mechanical fracture strength than the 3D-printed molar group (P<0.001). However, no significant differences between the 3D-printed incisors and the milled incisors were found (p = 0.084). There was no significant difference in the travel distance until fracture for both the molar group (p = 1.000) and the incisor group (p = 0.129).

Conclusion

Within the limits of this in vitro investigation, printed and milled temporary crowns withstood masticatory forces and were safe for clinical use.

Introduction

Temporary crowns and bridges are used for the immediate restoration of prepared teeth. These temporary materials bridge the period until the final restoration is fabricated and placed [1]. Due to modern technology and patient demands, the need for lifelike dental restorations has expanded dramatically in recent years. As a result, the use of diverse innovative restorative materials with high mechanical qualities is critical for both interim and permanent solutions. Accurate temporary restorations are critical because they protect pulpal tissues, prevent bacterial contamination, and preserve periodontal tissues. Furthermore, it is critical to avoid tooth rotation from its natural position in terms of supraocclusion and infraocclusion and to preseve aesthetics and oral functions, including mastication and speaking [2].

In recent years, developments of revolutionary manufacturing technologies, effective restorative materials, and creative clinical procedures have paved the way for digital dentistry [3]. Intraoral scanners (IOSs) and modern computer-aided design/computer-aided manufacturing (CAD/CAM) techniques, such as milling technologies and 3D printing, have enabled the use of novel metal-free dental materials, allowing them to replace standard metal frameworks and to improve the biomimetic and aesthetic results of restorations [4].

Milled resin-composite crowns made using CAD/CAM have emerged as potential alternatives to metallic restorations in recent years [5]. However, some difficulties, such as milling bar degradation, material waste, and stringent requirements for adequate abutment preparation, must be emphasized. Therefore, three-dimensional printing is a promising, rapid, and cost-efficient method for creating dental prostheses digitally. 3D printing is a sophisticated manufacturing technology that uses computer-aided design digital models to automatically generate personalized 3D objects [6]. Ceramics and resin are among the materials that are used in 3D printing. 3D/4D printing can be integrated with artificial intelligence and machine learning for patient-specific medical technology applications [7]

Recent digital techniques for the fabrication of crowns include digital light processing (DLP) and stereolithography (STL), which provide speedy printing and good precision [8].The DLP approach offers quick printing and excellent accuracy. The item is created according to the CAD design utilizing a resin-filled vat for layer-by-layer photopolymerization on the platform during DLP. Acrylic composites in dental treatment are not new, but 3D printing makes in-office production of intricate parts possible in under 30 minutes, enabling new treatment options [1, 2]. Nevertheless, both conventional and 3D printed materials must fulfill specific mechanical properties to withstand occlusal and masticatory forces [3–12]. To date, 3D-printed materials are used clinically as durable temporary and definitive restorations [13]. The main advantages of CAD/CAM technologies include accuracy, time efficiency, and doability; thus, they are becoming primary health care technologies for solving complex medical problems, making them promising rapid and economical approaches for the digital fabrication of dental prostheses [7]

CAD/CAM technologies provide superior mechanical strength, excellent esthetic and optical characteristics, and trustworthy precision and accuracy, expanding the clinical spectrum and allowing for novel and less invasive restorative solutions [14]

In terms of digital versus conventional workflows, the benefits lie in digital modeling and virtual planning, allowing several procedures to be performed with software and without human contact. The spread of infectious agents, such as COVID-19, can be more easily limited by reducing the number of work steps and procedures that may generate aerosols and environmental contaminants [15]

The main limitations of CAD/CAM technologies include the high initial cost, the lack of color gradients in 3D-printed prostheses, technology failure, and the learning curve.

To fulfill mechanical and chemical requirements, thorough investigations are mandatory prior to in vivo incorporation. Although clinical use cannot be simulated entirely in vitro with a standardized test [16], it is possible to find material-specific properties in vitro, which are essential for its fundamental understanding. Various methods are available for analyzing the mechanical strengths of materials. One of the most commonly used techniques is compression testing [4–6, 9–11, 13]. Compression tests are conducted by loading the test specimen between two plates and then applying a force to the specimen by moving the crossheads together. During the test, the specimen is compressed, and the deformation and applied load are recorded [9]. This testing is used to assess the material’s behavior or reaction under crushing pressures and its plastic flow behavior and ductile fracture limits [10].

As 3D printing resin for temporary crowns has recently been developed, there are limited available data and studies on its mechanical strength [16]. In this study, we aim to analyze the fracture strengths of implant-supported 3D printed temporary crowns relative to milled crowns by compression testing.

We hypothesize that the fracture strengths of the 3D-printed and milled crowns will not show significant differences.

Materials and methods

In the present investigation, 32 specimens were digitally designed using Aadva Software (GC, Tokyo, Japan) (Figs 1 and 2) by estimating the effect size 0.5 with 80% power (alpha = .05, two-tailed). The 3D printer Varseo S (Bego, Bremen, Germany) and the milling unit inLab MC X5 (Sirona, Bensheim, Germany) were used to produce 16 specimens per group from the same digitally designed crowns (Fig 3). Each group consisted of eight maxillary central incisor crowns (tooth 11) and eight maxillary molar crowns (tooth 16).

Fig 1. Virtual planning of tooth crown 11.

Fig 1

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Fig 2. Virtual planning of tooth crown 16.

Fig 2

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Fig 3. 3D printing of provisional crowns with support structures.

Fig 3

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DLP (digital light processing) is an additive technology that was applied for the printed specimens. For 3D printing, a mask printer (Varseo, BEGO, Bremen, Germany) and temporary material (VarseoSmile Temp A3, BEGO, Bremen, Germany) were used. The resin was a light-curing, free-flowing plastic based on methacrylic acid esters for 3D printing.

For the milled crowns, a millable temporary material was used (VitaCAD Temp monocolor, Vita, Bad Säckingen, Germany). The material consisted of a composite made of a highly cross-linked acrylate polymer with a microfiller for milling.

After pretesting for the fitting of both groups, the cement gap was evaluated. The cement gap in the printed group was set digitally at 40 μm. In comparison, the gap was 60 μm in the milled groups to ensure maximum retention [17].

For the 3D printed samples, supports were placed on the occlusal surfaces and incisal edges away from the screw path. Thus, uniform cementation surfaces were guaranteed without abrasive reworking. Their postprocessing was performed according to the manufacturer’s instructions. In summary, an ultrasonic 96% ethanol bath was used to clean the specimens. Then, the specimens were dried with compressed air. Next, the surface was cured using the polymerization unit Otoflash with two cycles of 1500 flashes (Bego, Bremen, Germany).

The crowns were mounted on Ti-base SICvantage CAD/CAM straight implants with an abutment angle of 15° for incisors and 0° for molars (SIC invent AG, Basel, Switzerland).

The test samples were loaded into the universal testing machine z010 (Zwick/Roell, Ulm, Germany).

In order from first to last, we measured the fracture forces between the molar groups, the fracture forces between the incisor groups, the deformations between the molar groups and the deformations between the incisor groups. Thus, it was possible to determine whether the materials differed in fracture resistance or deformation and whether there were differences within tooth regions.

Measurement of the fracture strength

For fracture resistance testing, a load was applied at a cross-head speed of 0.5 mm/min and at the tooth until fracture occurred, according to ISO 11405/2003. The molar specimens were loaded along the implant axis and the incisors at an angle of 45° to simulate the natural teeth position and protrusion forces (Figs 1–3) [18].

The loading forces were recorded in Newtons [N], while the travel distance until failure was measured in millimeters [mm].

Statistical analysis

The statistical analysis was performed using SPSS Version 24.0 (International Business Machines Corporation, New York, USA). A Shapiro‒Wilk test was applied to test the normal distribution of the data, and t tests were performed to compare the two groups. The statistical significance was set at p<0.05.

Results

The test data were normally distributed in all groups. The mean values and standard deviations (M±SD) of the maximum forces and the travel distance for all groups are shown in Table 1.

Table 1. Descriptive statistics for all groups.

Group Maximum Forces (N) Travel Distance (mm)
3D Printed 11 Mean 324.38 1.938
SD 145.010 0.4033
Milled 11 Mean 451.13 2.263
SD 111.716 0.4033
3D Printed 16 Mean 1203.38 1.750
SD 251.861 0.2449
Milled 16 Mean 1850.00 1.750
SD 253.659 0.2000
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The mean fracture strength of the printed molars was 1189.50 N (±250.85) with a deformation of 1.75 mm (±0.25), whereas the milled molars reached a mean fracture strength of 1817.50 N (±258.22) with a deformation of 1.75 mm (±0.20). The printed incisors fractured at 321.63 N (±145.90) with a deformation of 1.94 mm (±0.40), while the milled incisors fractured at 443.38 N (±113.63) with a deformation of 2.26 mm (±0.40) (Figs 4–8).

Fig 4. Main testing for provisional crown 11.

Fig 4

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Fig 8. Testing setup.

Fig 8

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Fig 5. Main testing for provisional crown 16.

Fig 5

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Fig 6. Boxplot force at break.

Fig 6

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Fig 7. Boxplot dL at break.

Fig 7

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The milled molar group revealed significantly higher mechanical fracture strength than the 3D printed molar group (p<0.001). However, no significant differences between the 3D printed incisors and the milled incisors were found (p = 0.084). There were no significant differences in the travel distances until fracture for both the molar group (p = 1.000) and the incisor group (p = 0.129).

All crowns exhibited similar brittle fracture patterns with audible crackling beforehand. After the propagation of an initial occlusal crack, a sudden fracture occurred. The fracture extended downward from the occlusal surface and divided the crown in the middle through the inlet for the abutment.

Discussion

The purpose of this study is to investigate the mechanical performance of 3D-printed and milled temporary crowns. The significance of exact preliminary restorations is widely acknowledged. Furthermore, there is some indication that 3D-printed provisional restorations may be preferable to their CAD/CAM counterparts [19]. The development of provisional 3D-printed restorations promises a simpler manufacturing method and possibly stronger provisional restorations than conventional techniques. Therefore, we compare the fracture resistance levels of 3D printed and milled temporary crowns by compression testing on dental implants in vitro.

The findings show significantly higher fracture strengths for milled molars than for 3D printed molars (p<0.001) but no significant differences in the incisor crowns (p = 0.084). In contrast, the differences in travel distances until failure are not significant for either molars (p = 1.000) or incisors (p = 0.129).

The results in the present study are in line with previously published articles. The meta-analysis of Jain et al. features articles comparing the physical and mechanical properties of 3D-printed provisional crown and FDP resin materials with CAD/CAM milled and conventional provisional resins. The researchers conclude that 3D-printed provisional crown and FDP resin materials have inferior physical properties relative to CAD/CAM milled materials [19]. Furthermore, Ellakany et al. have investigated the mechanical properties of CAD/CAM milled and two different types of 3D-printed, 3-unit IFDPs relative to conventional IFDPs after the thermomechanical aging process. The conclusion of the study is that superior flexural strength, elastic modulus, and hardness are reported for milled IFDPs [20].

If both test groups are considered from a mechanical point of view, the force acting on the molars is perpendicular, which is in contrast to the incisors, where the force acts at an angle of 45° and the tooth surface is negligible. In this case, the incisors are loaded differently than the molars since the crown (force arm) and the acting force form a cross product, which acts as a torque on the rotational axis of the crown. Due to this lever, a greater force acts mechanically on the crown than is indicated on the machine. In the case of the molars, there is no torque because the force acts perpendicularly on the crown.

Screw retained abutments are chosen to ensure consistent test results and reproducibility while remaining true to the clinical reality [21]. The fracture resistance test is chosen because it is a common and standardized test that can be easily compared to the literature [4–6, 9–13]. This test provides comparable and straightforward results. Crown designs are kept consistent within the groups. In vivo, crown designs and layer thickness will differ from this study. Nevertheless, consistent dimensions in vitro are essential for ensuring comparable results of material-specific properties. Although it is not as crucial for permanent restorations, a drawback of the fracture test is that it does not simulate long-term intraoral wear.

Different studies are performed with various crown designs or testing setups [4–6, 9–13]. Consequently, it is difficult to compare the specific fracture values of the milled and 3D printed crowns obtained in the present study to those of other similar publications. For this reason, the resulting values are compared inside the present study. Nonetheless, the relationships of the fracture strengths between materials are compared. In the literature, fracture values for temporary crowns are found, with PMMA and composite-based materials usually having higher values than hand-manufactured chair-side temporary restorations. A study conducted by Karaokutan I. et al. shows that composite-based materials have the highest fracture strength, while conventional chairside temporary restorations have the lowest values [5]. Consistent with the present investigation, a study conducted by Reeponmaha T. et al. shows higher variances in fracture values for 3D-printed crowns than for milled crowns [22]. Further research is needed to provide insight into this matter. Inconsistency and errors during polymerization or differences in positioning between samples on the print platform may lead to higher variances in 3D-printed crowns than in milled crowns [23].

All crowns follow similar brittle fracture patterns with audible crackling beforehand. After the propagation of an initial occlusal crack, a sudden fracture occurs. The fracture extends downward from the occlusal surface and divides the crown in the middle through the inlet for the abutment. Different crown designs and layer thicknesses may change the location and direction of fracture [24].

Very little data exist in the literature regarding the fracture strengths of these modern provisional materials. The results support that the fracture strengths of DLP-based 3D-printed incisor crowns are similar to those of milled crowns. In contrast, milled molar crowns show significantly higher fracture strengths than 3D printed crowns.

The fact that just one system for each manufacturing process is studied is one of the study’s limitations. Furthermore, precision as a criterion of crown accuracy across different production procedures needs further research. DLP-based 3D printing demonstrates good accuracy for the mediodistal and buccolingual widths of dental models. However, the discrepancies in accuracy may be due to thickness and layer shrinking, particularly in the Z-axis. Therefore, further studies are needed to establish guidelines for optimum dimensions for each application while using different manufacturing processes and printing conditions.

Nonetheless, both printed and milled temporary crowns withstand masticatory forces and are safe for clinical use [25]. Further research on 3D-printed materials is needed to determine other chemical and physical properties, such as coloring, during intraoral use. Temporary CAD/CAM restorations allow the clinician to choose an emergence profile that stabilizes the gingiva and prevents severe shrinkage after extractions [26]. The situation worked out in the planning phase can be transferred to the temporary situation. Additionally, aesthetics and function can be tested by the patient.

Conclusion

Within the limitations of the present study, the fracture strength testing shows that milled molar crowns (1817.50 N ±258.22) have significantly higher fracture strengths than 3D printed crowns (1189.50 N ±250.85); however, for incisor crowns, no statistically significant differences are shown in the present study (443.38 N ±113.63 vs. 321.63 N ±145.90). In all cases, for both crown shape and production method, no statistically significant differences are apparent in terms of deformation.

Regarding the results from a clinical point of view, the significant differences between the crowns in terms of fracture strength withstand masticatory forces, making them safe for clinical use.

Clinical significance

3D-printed crowns are considered an alternative for long-term provisional prosthetic restorations.

Supporting information

S1 File

(PDF)

Click here for additional data file. (616.8KB, pdf)

Acknowledgments

The authors acknowledge Dr.med.dent Moritz Wagner for his scientific support.

Data Availability

The data underlying the results presented in the study are available from Danube Private University, Steiner Landstrasse 124, 3500, Krems an der Donau, Austria. https://www.dp-uni.ac.at/de/home

Funding Statement

The author(s) received no specific funding for this work.

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Mirza Rustum Baig

24 Nov 2022

PONE-D-22-19019Comparative mechanical testing of 3D-printed versus milled provisional crowns: An in vitro studyPLOS ONE

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The PLOS Data policy requires authors to make all data underlying the findings described in their manuscript fully available without restriction, with rare exception (please refer to the Data Availability Statement in the manuscript PDF file). The data should be provided as part of the manuscript or its supporting information, or deposited to a public repository. For example, in addition to summary statistics, the data points behind means, medians and variance measures should be available. If there are restrictions on publicly sharing data—e.g. participant privacy or use of data from a third party—those must be specified.

Reviewer #1: Yes

Reviewer #2: Yes

Reviewer #3: No

**********

4. Is the manuscript presented in an intelligible fashion and written in standard English?

PLOS ONE does not copyedit accepted manuscripts, so the language in submitted articles must be clear, correct, and unambiguous. Any typographical or grammatical errors should be corrected at revision, so please note any specific errors here.

Reviewer #1: Yes

Reviewer #2: Yes

Reviewer #3: No

**********

5. Review Comments to the Author

Please use the space provided to explain your answers to the questions above. You may also include additional comments for the author, including concerns about dual publication, research ethics, or publication ethics. (Please upload your review as an attachment if it exceeds 20,000 characters)

Reviewer #1: This study aims to analyze the fracture resistance of implant-supported 3D printed temporary crowns compared to milled crowns by compression testing. And they found that the milled molar group revealed significantly higher mechanical fracture strength than the 3D printed molar group (P<0.001). However, no significant difference between the 3D printed incisors and the milled incisors was found (P=0.084). Some comments.

Title. It is better to replace the “Comparative mechanical testing” in title with more specific testing.

Abstract. If possible, it is better to add brief on the printed and milling technique used. Which materials were used for printing implant crowns.

Introduction.

The introduction is short. It will be better to add details on the Digital techniques of fabrication of crowns. Then explaining more on the 3D printing and milling technologies with indications, advantages and limitations. Some recent literatures are.

https://link.springer.com/chapter/10.1007/978-981-16-7152-4_12

https://www.ncbi.nlm.nih.gov/pmc/articles/PMC7356564/

Method.

Please add on the simple size calculation.

Please discuss more on the results differences between the molars and incisors.

Reviewer #2: Dear Authors,

The aim of this study was to analyze the fracture resistance of implant-supported 3D printed temporary crowns compared to milled crowns by compression testing. As the full-length article, the Introduction section and the Discussion section were too short. Only fracture loads are not enough. Fatigue test and finite element analysis should be contained to be strengthen this manuscript.

Reviewer #3: The abstract need revision. Materials and Methods need to be rewritten again. Discussion need to include comparisons with similar previously published articles. References are not as per journal requirements. Sample size is not justified and very small. What is the power of this study ???. What kind of Force was applied on incisor and molars , how much ???. Conclusion should be revised. What is the mean fracture strength between the group of crowns for incisors and molars ???

**********

6. PLOS authors have the option to publish the peer review history of their article (what does this mean?). If published, this will include your full peer review and any attached files.

If you choose “no”, your identity will remain anonymous but your review may still be made public.

Do you want your identity to be public for this peer review? For information about this choice, including consent withdrawal, please see our Privacy Policy.

Reviewer #1: Yes: Dinesh Rokaya

Reviewer #2: No

Reviewer #3: No

**********

[NOTE: If reviewer comments were submitted as an attachment file, they will be attached to this email and accessible via the submission site. Please log into your account, locate the manuscript record, and check for the action link "View Attachments". If this link does not appear, there are no attachment files.]

While revising your submission, please upload your figure files to the Preflight Analysis and Conversion Engine (PACE) digital diagnostic tool, https://pacev2.apexcovantage.com/. PACE helps ensure that figures meet PLOS requirements. To use PACE, you must first register as a user. Registration is free. Then, login and navigate to the UPLOAD tab, where you will find detailed instructions on how to use the tool. If you encounter any issues or have any questions when using PACE, please email PLOS at figures@plos.org. Please note that Supporting Information files do not need this step.

PLoS One. 2023 Sep 1;18(9):e0285760. doi: 10.1371/journal.pone.0285760.r002

Author response to Decision Letter 0

21 Dec 2022

December 20, 2022

Dear Dr. Mirza Rustum Baig,

Thank you for giving me the opportunity to submit a revised draft of my manuscript titled “Comparative mechanical testing of 3D-printed versus milled provisional crowns: An in vitro study" to the Journal PLOS ONE. We appreciate the time and effort you and the reviewers have dedicated to providing valuable feedback on the manuscript, responded appropriately as noted below, and highlighted the changes within the manuscript.

Reviewer 1:

This study aims to analyze the fracture resistance of implant-supported 3D-printed temporary crowns compared to milled crowns by compression testing. And they found that the milled molar group revealed significantly higher mechanical fracture strength than the 3D-printed molar group (P<0.001). However, no significant difference between the 3D-printed incisors and the milled incisors was found (P=0.084). Some comments.

1. Title. It is better to replace the “Comparative mechanical testing” in the title with more specific testing.

Response: Thank you for your guidance and advice. Done

“The fracture resistance of 3D-printed versus milled provisional crowns: An in vitro study”

2. Abstract. If possible, it is better to add brief on the printed and milling technique used. Which materials were used for printing implant crowns?

Response: Done

“The first group (16 specimens) was 3D printed by a mask printer (Varseo, BEGO, Bremen, Germany) with a temporary material (VarseoSmile Temp A3, BEGO, Bremen, Germany). The second group was milled in which a millable temporary material was used (VitaCAD Temp monocolor, Vita, Bad Säckingen, Germany).”

3. Introduction. The introduction is short. It will be better to add details on the Digital techniques of fabrication of crowns. Then explaining more on the 3D printing and milling technologies with indications, advantages and limitations. Some recent literatures are. https://link.springer.com/chapter/10.1007/978-981-16-7152-4_12

https://www.ncbi.nlm.nih.gov/pmc/articles/PMC7356564/

Response: Done

“Milled resin-composite crowns made using CAD/CAM have emerged as a potential alternative to metallic restorations in recent years [5]. However, some difficulties such as milling bar degradation, material waste, and stringent requirements for adequate abutment preparation must be emphasized. Therefore, three-dimensional printing is a promising, rapid, and cost-efficient method of creating dental prostheses digitally. It is a sophisticated manufacturing technology that use computer-aided design digital models to automatically generate personalized 3D objects [6]. Ceramics and resin are among the materials that be used in 3D printing. Digital light processing (DLP) and stereolithography (STL) provide speedy printing and good precision [7]. The DLP approach offers quick printing and excellent accuracy. The item is created according to the CAD design utilizing a resin-filled vat for layer-by-layer photopolymerization on the platform in the DLP process.”

4. Method. Please add on the sample size calculation.

Response: Done

“In the present investigation, 32 specimens were digitally designed using Aadva Software (GC, Tokyo, Japan) by estimation of the effect size 0.5 with 80% power (alpha = .05, two-tailed).”

5. Please discuss more on the results differences between the molars and incisors.

Response: Done

“If both test groups are considered from a mechanical point of view, the force acting on the molars is perpendicular, in contrast to the incisors, where the force acts at an angle of 45° - the tooth surface is negligible. In this case, the incisors are loaded differently than the molars, since the crown (force arm) and the acting force form a cross product, which acts as a torque on the rotational axis of the crown. Due to this lever, a greater force acts mechanically on the crown than is indicated on the machine. In the case of the molars, there is no torque because the force acts perpendicularly on the crown.”

Reviewer 2:

The aim of this study was to analyze the fracture resistance of implant-supported 3D-printed temporary crowns compared to milled crowns by compression testing.

1. As the full-length article, the Introduction section and the Discussion section were too short.

Response: Done

2. Only fracture loads are not enough.

Response: Thank you for your comment. We agree with you. We used the compression test which is One of the most used techniques. It is used to assess a material's behavior or reaction under crushing pressures, as well as to test a material's plastic flow behavior and ductile fracture limits. Compression tests are conducted by loading the test specimen between two plates and then applying a force to the specimen by moving the crossheads together. During the test, the specimen is compressed, and deformation versus the applied load is recorded. This study aims to analyze the fracture strength of implant-supported 3D-printed temporary crowns compared to milled crowns by compression testing. That would be addressed by measuring; first the fracture forces between the molar groups, Secondly the fracture forces between the incisor groups, Thirdly the deformation between the molar groups, and lastly the deformation between the incisor groups. Thus, it was possible to determine whether the materials differed in fracture resistance or deformation and whether there were differences within tooth regions. We hypothesized that the fracture strength of the 3D-printing method is non-inferior to that of the milling method.

3. Fatigue test and finite element analysis should be contained to strengthen this manuscript.

Response: Thank you for your comment. We agree, a finite element analysis would strengthen this manuscript. But also, without a finite element analysis reader can have clinically relevant and useful information from our manuscript.

Reviewer 3:

1. The abstract need revision.

Response: Sorry for the inconvenience. Done

“Abstract

Aims: This study aims to analyze the fracture resistance of implant-supported 3D-printed temporary crowns compared to milled crowns by compression testing.

Methods: The study sample included 32 specimens of temporary crowns which were divided into 16 specimens per group. Each group consisted of eight maxillary central incisor crowns (tooth 11) and eight maxillary molar crowns (tooth 16). The first group (16 specimens) was 3D printed by a mask printer (Varseo, BEGO, Bremen, Germany) with a temporary material (VarseoSmile Temp A3, BEGO, Bremen, Germany). The second group was milled in which a millable temporary material was used (VitaCAD Temp mono-color, Vita, Bad Säckingen, Germany). The two groups were compression tested until failure to estimate their fracture resistance. The loading forces and travel distance until failure were measured. The statistical analysis was performed using SPSS Version 24.0. We performed multiple t-tests and considered a significance level of p <0.05.

Results: The mean fracture force of the printed molars was 1189.50N (±250.85) with a deformation of 1.75mm (±0.25), whereas the milled molars reached 1817.50N (±258.22) with a deformation of 1.750mm (±0.20). The printed incisors fractured at 321.63N (±145.90) with a deformation of 1.94mm (±0.40) while the milled ones fractured at 443.38N (±113.63) with a deformation of 2.26mm (±0.40). The milled molar group revealed significantly higher mechanical fracture strength than the 3D-printed molar group (P<0.001). However, no significant difference between the 3D-printed incisors and the milled incisors was found (p=0.084). There was no significant difference in the travel distance until fracture for both the molar group (p=1.000) and the incisors (p=0.129). Conclusion: Within the limits of this in-vitro investigation, the printed and milled temporary crowns can both withstand the masticatory forces and are safe for clinical use.”

2. Materials and Methods need to be rewritten again.

Response: Done

3. Discussion need to include comparisons with similar previously published articles.

Response: Done

“The results in the present study are in line with previously published articles. The meta-analysis of Jain et al. compared articles comparing the physical and mechanical properties of 3D-printed provisional crown and FDP resin materials with CAD/CAM milled and conventional provisional resins. They concluded that that 3D-printed provisional crown and FDP resin materials have inferior physical properties compared to CAD/CAM milled ones (23). Furthermore, Ellakany et al. investigated the mechanical properties of CAD/CAM milled and two different types of 3D-printed, 3-unit IFDPs in comparison to the conventional IFDPs after the thermo-mechanical aging process. The conclusion of the study was that superior flexural strength, elastic modulus, and hardness were reported for milled IFDPs (24).”

4. References are not as per journal requirements.

Response: Thank you for the kind information. References style and format were checked to be following journal guidelines.

5. Sample size is not justified and very small. What is the power of this study???.

Response: thank you for your comment. In the present investigation, 32 specimens were digitally designed using Aadva Software (GC, Tokyo, Japan) by estimation of the effect size 0.5 with 80% power (alpha = .05, two-tailed). The 3D printer Varseo S (Bego, Bremen, Germany) and the milling unit inLab MC X5 (Sirona, Bensheim, Germany) were used to produce 16 specimens per group from the same digitally designed crowns. Each group consisted of eight maxillary central incisor crowns (tooth 11) and eight maxillary molar crowns (tooth 16).

6. What kind of Force was applied on incisor and molars, how much ???.

Response: Done

“For fracture resistance testing a load was applied at a cross-head speed of 0.5 mm/min and at the tooth until fracture occurred, according to ISO 11405/2003 (21).”

7. Conclusion should be revised. What is the mean fracture strength between the group of crowns for incisors and molars???

Response: Done

“Within the limitations of the present study, the fracture strength testing showed that milled molars crowns (1817.50N ±258.22) have statistically significantly higher fracture strength compared to 3D printed ones (1189.50N ±250.85), but in case of incisor crowns no statistically significant difference was shown in the present study (443.38N ±113.63 vs. 321.63N ±145.90). In all cases either crown shape and production method no statistically significant differences were shown in terms of deformation.

Regarding the results from a clinical point of view, those significant differences between the crowns in terms of fracture strength both can withstand the masticatory forces and are safe for clinical use.”

Attachment

Submitted filename: Responce to reviewers.docx

Click here for additional data file. (21.3KB, docx)

Decision Letter 1

Mirza Rustum Baig

16 Jan 2023

PONE-D-22-19019R1The fracture resistance of 3D-printed versus milled provisional crowns: An in vitro studyPLOS ONE

Dear Dr. Othman,

Thank you for submitting your manuscript to PLOS ONE. After careful consideration, we feel that it has merit but does not fully meet PLOS ONE’s publication criteria as it currently stands. Therefore, we invite you to submit a revised version of the manuscript that addresses the points raised during the review process.

Please submit your revised manuscript by Mar 02 2023 11:59PM. If you will need more time than this to complete your revisions, please reply to this message or contact the journal office at plosone@plos.org. When you're ready to submit your revision, log on to https://www.editorialmanager.com/pone/ and select the 'Submissions Needing Revision' folder to locate your manuscript file.

Please include the following items when submitting your revised manuscript:

  • A rebuttal letter that responds to each point raised by the academic editor and reviewer(s). You should upload this letter as a separate file labeled 'Response to Reviewers'.

  • A marked-up copy of your manuscript that highlights changes made to the original version. You should upload this as a separate file labeled 'Revised Manuscript with Track Changes'.

  • An unmarked version of your revised paper without tracked changes. You should upload this as a separate file labeled 'Manuscript'.

If you would like to make changes to your financial disclosure, please include your updated statement in your cover letter. Guidelines for resubmitting your figure files are available below the reviewer comments at the end of this letter.

If applicable, we recommend that you deposit your laboratory protocols in protocols.io to enhance the reproducibility of your results. Protocols.io assigns your protocol its own identifier (DOI) so that it can be cited independently in the future. For instructions see: https://journals.plos.org/plosone/s/submission-guidelines#loc-laboratory-protocols. Additionally, PLOS ONE offers an option for publishing peer-reviewed Lab Protocol articles, which describe protocols hosted on protocols.io. Read more information on sharing protocols at https://plos.org/protocols?utm_medium=editorial-email&utm_source=authorletters&utm_campaign=protocols.

We look forward to receiving your revised manuscript.

Kind regards,

Mirza Rustum Baig

Academic Editor

PLOS ONE

[Note: HTML markup is below. Please do not edit.]

Reviewers' comments:

Reviewer's Responses to Questions

Comments to the Author

1. If the authors have adequately addressed your comments raised in a previous round of review and you feel that this manuscript is now acceptable for publication, you may indicate that here to bypass the “Comments to the Author” section, enter your conflict of interest statement in the “Confidential to Editor” section, and submit your "Accept" recommendation.

Reviewer #1: (No Response)

Reviewer #3: All comments have been addressed

Reviewer #4: All comments have been addressed

**********

2. Is the manuscript technically sound, and do the data support the conclusions?

The manuscript must describe a technically sound piece of scientific research with data that supports the conclusions. Experiments must have been conducted rigorously, with appropriate controls, replication, and sample sizes. The conclusions must be drawn appropriately based on the data presented.

Reviewer #1: Yes

Reviewer #3: Partly

Reviewer #4: Partly

**********

3. Has the statistical analysis been performed appropriately and rigorously?

Reviewer #1: Yes

Reviewer #3: I Don't Know

Reviewer #4: Yes

**********

4. Have the authors made all data underlying the findings in their manuscript fully available?

The PLOS Data policy requires authors to make all data underlying the findings described in their manuscript fully available without restriction, with rare exception (please refer to the Data Availability Statement in the manuscript PDF file). The data should be provided as part of the manuscript or its supporting information, or deposited to a public repository. For example, in addition to summary statistics, the data points behind means, medians and variance measures should be available. If there are restrictions on publicly sharing data—e.g. participant privacy or use of data from a third party—those must be specified.

Reviewer #1: No

Reviewer #3: No

Reviewer #4: (No Response)

**********

5. Is the manuscript presented in an intelligible fashion and written in standard English?

PLOS ONE does not copyedit accepted manuscripts, so the language in submitted articles must be clear, correct, and unambiguous. Any typographical or grammatical errors should be corrected at revision, so please note any specific errors here.

Reviewer #1: Yes

Reviewer #3: No

Reviewer #4: Yes

**********

6. Review Comments to the Author

Please use the space provided to explain your answers to the questions above. You may also include additional comments for the author, including concerns about dual publication, research ethics, or publication ethics. (Please upload your review as an attachment if it exceeds 20,000 characters)

Reviewer #1: The authors have not addressed some previous comments.

Introduction. It will be better to add details on the Digital

techniques of fabrication of crowns. Then explaining more on the 3D printing and milling

technologies with indications, advantages and limitations. Some recent literatures are.

https://link.springer.com/chapter/10.1007/978-981-16-7152-4_12

https://www.ncbi.nlm.nih.gov/pmc/articles/PMC7356564/

Reviewer #3: Minor revision includes English language editing, providing complete statistics for assessment.kindly check image quality including resolution, pixels , blurring if any . I would appreciate more pictures from groups. Please add on clinical significance of this study . From my side as of now my queries had been met.

Reviewer #4: Dear Authors,

The topic is interesting but unfortunatelly there are some important lacking. For example; The abstract is poor and not informative. The test groups are inadequate. Because there are different materials for this purpose. Are the crowns include screw hole ore not? How does effect this feature to study? Generally, the information presented are not new, and does not add anything new to the current understanding. This study can't serve important clinical results.

**********

7. PLOS authors have the option to publish the peer review history of their article (what does this mean?). If published, this will include your full peer review and any attached files.

If you choose “no”, your identity will remain anonymous but your review may still be made public.

Do you want your identity to be public for this peer review? For information about this choice, including consent withdrawal, please see our Privacy Policy.

Reviewer #1: No

Reviewer #3: Yes: Prof Dr Hariharan Ramakrishnan

Reviewer #4: No

**********

[NOTE: If reviewer comments were submitted as an attachment file, they will be attached to this email and accessible via the submission site. Please log into your account, locate the manuscript record, and check for the action link "View Attachments". If this link does not appear, there are no attachment files.]

While revising your submission, please upload your figure files to the Preflight Analysis and Conversion Engine (PACE) digital diagnostic tool, https://pacev2.apexcovantage.com/. PACE helps ensure that figures meet PLOS requirements. To use PACE, you must first register as a user. Registration is free. Then, login and navigate to the UPLOAD tab, where you will find detailed instructions on how to use the tool. If you encounter any issues or have any questions when using PACE, please email PLOS at figures@plos.org. Please note that Supporting Information files do not need this step.

PLoS One. 2023 Sep 1;18(9):e0285760. doi: 10.1371/journal.pone.0285760.r004

Author response to Decision Letter 1

21 Feb 2023

15.Feb.2023

Dear Dr. Mirza Rustum Baig,

Thank you for giving me the opportunity to submit a revised draft of my manuscript titled “The fracture resistance of 3D-printed versus milled provisional crowns: An in vitro study" to the Journal PLOS ONE. We appreciate the time and effort you and the reviewers have dedicated to providing valuable feedback on the manuscript, responded appropriately as noted below, and highlighted the changes within the manuscript.

Reviewer 1:

The authors have not addressed some previous comments.

Introduction. It will be better to add details on the Digital techniques of fabrication of crowns. Then explaining more on the 3D printing and milling technologies with indications, advantages and limitations. Some recent literatures are:

https://link.springer.com/chapter/10.1007/978-981-16-7152-4_12

https://www.ncbi.nlm.nih.gov/pmc/articles/PMC7356564/

1. The authors have not addressed some previous comments.

Response: We would like to apologize for any inconvenience. The missing comments have been precisely addressed as much as possible. Thank you for your guidance, advice and understanding.

2. Introduction. It will be better to add details on the Digital techniques of fabrication of crowns. Then explaining more on the 3D printing and milling technologies with indications, advantages and limitations.

Response: Done

“3D/4D printing can be integrated with artificial intelligence and machine learning to apply for patient-specific medical technologies (7). The recent digital techniques of fabrication of crowns includes Digital light processing (DLP) and stereolithography (STL) which provide speedy printing and good precision (8). The main advantages of CAD/CAM technologies includes accuracy, time-efficieny, doability and becoming a main part of healthcare technology solving complex medical problems which are promising for a rapid and economical technology for the digital fabrication of dental prostheses (7) They also provide superior mechanical strength, excellent esthetic and optical characteristics, and trustworthy precision and accuracy, which expand the clinical spectrum and allow for novel and less invasive restorative solutions (14). In terms of digital versus conventional workflow, the benefit lies in digital modeling and virtual planning, allowing several procedures to be performed with software and without human contact. The spread of infectious agents as COVID-19 can be more easily limited by reducing the number of work steps and procedures that can generate aerosols and environmental contaminants (15). The main limitations of CAD/CAM technologies include the high initial cost, the lack of color gradients in 3D-printed prostheses, technology failure, and the learning curve.

Reviewer 3:

Minor revision includes English language editing, providing complete statistics for assessment. kindly check image quality including resolution, pixels , blurring if any . I would appreciate more pictures from groups. Please add on clinical significance of this study. From my side as of now my queries had been met.

1. Minor revision includes English language editing, providing complete statistics for assessment.

Response: The English language editing was controlled by Springer Nature; certificate is attached for your preference. The statistics analysis for your kind assessment are attached as supplementary file.

2. kindly check image quality including resolution, pixels, blurring if any

Response: Done following Preflight Analysis and Conversion Engine (PACE) digital diagnostic tool, https://pacev2.apexcovantage.com/.

3. I would appreciate more pictures from groups.

Response: Done. More pictures were added in the article (Fig.1-3).

4. Please add on clinical significance of this study.

Response: Done. clinical significance was added in the article.

5. From my side as of now my queries had been met.

Response: Thank you for the kind understanding, advice and effort.

Reviewer 4:

The topic is interesting but unfortunately there are some important lacking. For example; The abstract is poor and not informative. The test groups are inadequate. Because there are different materials for this purpose. Are the crowns include screw hole or not? How does effect this feature to study? Generally, the information presented are not new, and does not add anything new to the current understanding. This study can't serve important clinical results.

1. The topic is interesting but unfortunately there are some important lacking. For example; The abstract is poor and not informative.

Response: Done. The abstract was modified to be more informative.

2. The test groups are inadequate. Because there are different materials for this purpose.

Response: Both milled and 3D printed materials must fulfill specific mechanical properties to withstand the occlusal masticatory forces and can be used clinically as durable temporary restorations as well as possibility for definitive restorations production. Both materials are prescribed as long-term temporary which can withstand mechanical forces. Accordingly, testing both materials for evaluating the comparative forces is considered reasonable. Especially that milled crowns are considered the gold-standard. Comparing printed material to the bench-mark milled material might be considered adequate.

3. Are the crowns include screw hole or not? How does effect this feature to study?

Response: They don’t include screw hole. The spacer thicknesses were between 30 and 50 μm were tested for both the anterior and posterior regions. The spacer settings of 40 μm ultimately produced the best results on the abutment, whereupon these were adopted for the anterior and posterior region. However, since for the milled temporaries the default standard settings in the Exocad software of 60 μm had been defined and the findings obtained for the printed temporaries could not be transferred to the milled temporaries. the two materials had to be produced with different spacer thicknesses. Current studies showed that in both 3D printing and milling, the difference between digital milling between the digital setting and the real result are sometimes enormous. differences occur in spacer thicknesses. (Hoang, Lisa N.; Thompson, Geoffrey A.; Cho, Seok-Hwan; Berzins, David W.; Ahn, Kwang Woo (2015): The spacer thickness reproduction for central incisor crown fabrication with combined computer-aided design and 3D printing technology: an in vitro study. In: The Journal of prosthetic dentistry 113 (5), S.398–404. DOI: 10.1016/j.prosdent.2014.11.004).

4. Generally, the information presented are not new, and does not add anything new to the current understanding. This study can't serve important clinical results.

Response: clinical use cannot be simulated entirely in vitro with a standardized test, it is possible to find material-specific properties in vitro, which are essential for its fundamental understanding. Various methods are available to analyze the mechanical strength of materials. One of the most used techniques is compression testing.

Attachment

Submitted filename: Responce to reviewers.docx

Click here for additional data file. (21.1KB, docx)

Decision Letter 2

Mirza Rustum Baig

27 Mar 2023

PONE-D-22-19019R2The fracture resistance of 3D-printed versus milled provisional crowns: An in vitro studyPLOS ONE

Dear Dr. Othman,

Thank you for submitting your manuscript to PLOS ONE. After careful consideration, we feel that it has merit but does not fully meet PLOS ONE’s publication criteria as it currently stands. Therefore, we invite you to submit a revised version of the manuscript that addresses the points raised during the review process.

==============================

Thank you for submitting the revised manuscript with the responses to the reviewers' comments. Please elaborate on the limitations of the study in the 'Discussion' section, including lack thereof fatigue loading tests (chewing simulation) with thermocycling prior to the fracture resistance tests.  ==============================

Please submit your revised manuscript by May 11 2023 11:59PM. If you will need more time than this to complete your revisions, please reply to this message or contact the journal office at plosone@plos.org. When you're ready to submit your revision, log on to https://www.editorialmanager.com/pone/ and select the 'Submissions Needing Revision' folder to locate your manuscript file.

Please include the following items when submitting your revised manuscript:

  • A rebuttal letter that responds to each point raised by the academic editor and reviewer(s). You should upload this letter as a separate file labeled 'Response to Reviewers'.

  • A marked-up copy of your manuscript that highlights changes made to the original version. You should upload this as a separate file labeled 'Revised Manuscript with Track Changes'.

  • An unmarked version of your revised paper without tracked changes. You should upload this as a separate file labeled 'Manuscript'.

If you would like to make changes to your financial disclosure, please include your updated statement in your cover letter. Guidelines for resubmitting your figure files are available below the reviewer comments at the end of this letter.

If applicable, we recommend that you deposit your laboratory protocols in protocols.io to enhance the reproducibility of your results. Protocols.io assigns your protocol its own identifier (DOI) so that it can be cited independently in the future. For instructions see: https://journals.plos.org/plosone/s/submission-guidelines#loc-laboratory-protocols. Additionally, PLOS ONE offers an option for publishing peer-reviewed Lab Protocol articles, which describe protocols hosted on protocols.io. Read more information on sharing protocols at https://plos.org/protocols?utm_medium=editorial-email&utm_source=authorletters&utm_campaign=protocols.

We look forward to receiving your revised manuscript.

Kind regards,

Mirza Rustum Baig

Academic Editor

PLOS ONE

Journal Requirements:

Please review your reference list to ensure that it is complete and correct. If you have cited papers that have been retracted, please include the rationale for doing so in the manuscript text, or remove these references and replace them with relevant current references. Any changes to the reference list should be mentioned in the rebuttal letter that accompanies your revised manuscript. If you need to cite a retracted article, indicate the article’s retracted status in the References list and also include a citation and full reference for the retraction notice.

[Note: HTML markup is below. Please do not edit.]

[NOTE: If reviewer comments were submitted as an attachment file, they will be attached to this email and accessible via the submission site. Please log into your account, locate the manuscript record, and check for the action link "View Attachments". If this link does not appear, there are no attachment files.]

While revising your submission, please upload your figure files to the Preflight Analysis and Conversion Engine (PACE) digital diagnostic tool, https://pacev2.apexcovantage.com/. PACE helps ensure that figures meet PLOS requirements. To use PACE, you must first register as a user. Registration is free. Then, login and navigate to the UPLOAD tab, where you will find detailed instructions on how to use the tool. If you encounter any issues or have any questions when using PACE, please email PLOS at figures@plos.org. Please note that Supporting Information files do not need this step.

PLoS One. 2023 Sep 1;18(9):e0285760. doi: 10.1371/journal.pone.0285760.r006

Author response to Decision Letter 2

29 Mar 2023

28.March.2023

Dear Dr. Mirza Rustum Baig,

Thank you for giving me the opportunity to submit a revised draft of my manuscript titled “The fracture resistance of 3D-printed versus milled provisional crowns: An in vitro study" (PONE-D-22-19019R2) to the Journal PLOS ONE. We appreciate the time and effort you and the reviewers have dedicated to providing valuable feedback on the manuscript, responded appropriately as noted below, and highlighted the changes within the manuscript.

Journal Requirements:

1) ‘’Please review your reference list to ensure that it is complete and correct. If you have cited papers that have been retracted, please include the rationale for doing so in the manuscript text, or remove these references and replace them with relevant current references. Any changes to the reference list should be mentioned in the rebuttal letter that accompanies your revised manuscript. If you need to cite a retracted article, indicate the article’s retracted status in the References list and also include a citation and full reference for the retraction notice’’.

Response: We would like to apologize for any inconvenient it might occur due to incorrect references list. Respectfully find in the manuscript with track changes the modified version of citations following the PLOS reference style outlined by the International Committee of Medical Journal Editors (ICMJE). The reference number 17 was eliminated. Also, reference number 7 was fully corrected. All other references were modified following “Vancouver” style. Thank you.

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Decision Letter 3

Mirza Rustum Baig

2 May 2023

The fracture resistance of 3D-printed versus milled provisional crowns: An in vitro study

PONE-D-22-19019R3

Dear Dr. Othman,

We’re pleased to inform you that your manuscript has been judged scientifically suitable for publication and will be formally accepted for publication once it meets all outstanding technical requirements.

Within one week, you’ll receive an e-mail detailing the required amendments. When these have been addressed, you’ll receive a formal acceptance letter and your manuscript will be scheduled for publication.

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Kind regards,

Mirza Rustum Baig

Academic Editor

PLOS ONE

Additional Editor Comments (optional):

Thank you for your valuable submission. Some amendments were suggested in the 'Discussion' section in the last decision letter sent (by the Editor). Please make sure you address these comments before the final editing of the article is completed.

Reviewers' comments:

Acceptance letter

Mirza Rustum Baig

24 Aug 2023

PONE-D-22-19019R3

The fracture resistance of 3D-printed versus milled provisional crowns: An in vitro study

Dear Dr. Othman:

I'm pleased to inform you that your manuscript has been deemed suitable for publication in PLOS ONE. Congratulations! Your manuscript is now with our production department.

If your institution or institutions have a press office, please let them know about your upcoming paper now to help maximize its impact. If they'll be preparing press materials, please inform our press team within the next 48 hours. Your manuscript will remain under strict press embargo until 2 pm Eastern Time on the date of publication. For more information please contact onepress@plos.org.

If we can help with anything else, please email us at plosone@plos.org.

Thank you for submitting your work to PLOS ONE and supporting open access.

Kind regards,

PLOS ONE Editorial Office Staff

on behalf of

Dr. Mirza Rustum Baig

Academic Editor

PLOS ONE

Associated Data

    This section collects any data citations, data availability statements, or supplementary materials included in this article.

    Supplementary Materials

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    Attachment

    Submitted filename: Response to Reviewers.docx

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    Data Availability Statement

    The data underlying the results presented in the study are available from Danube Private University, Steiner Landstrasse 124, 3500, Krems an der Donau, Austria. https://www.dp-uni.ac.at/de/home

    Articles from PLOS ONE are provided here courtesy of PLOS

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