Abstract
Aim :
This study aimed to assess and compare the wear resistance of 3D printable crown and bridge interim resin material with two different 3D printers.
Settings and Design:
In vitro comparative study.
Materials and Methods:
60 specimens were divided into 2 groups and designed using nx12 (Unigraphics) software. This Standard Tessellation Language file was used to print the specimens. Specimens fabricated using Phrozen Sonic Mini 3D printer of LCD software were grouped as Group A (n = 30), and specimens fabricated using Asiga Max 3D printer of DLP software were grouped as Group B (n = 30). Surface micro roughness measurements (Ra) were noted with a profilometer prior to and following toothbrush wear simulation. The collected data were tabulated to facilitate statistical analysis.
Statistical Analysis Used:
Student’s t-test and Mann–Whitney U-test was employed for multiple comparisions.
Results:
The Student’s t-test was employed to compare the mean surface micro-roughness of Group A and Group B specimens before and after toothbrush wear simulation. The test indicated that there was no significant difference.
Conclusion:
Within the scope of this study, both groups underwent wear and were statistically insignificant.
Keywords: Temporary, three-dimensional, wear
INTRODUCTION
Three-dimensional (3D) printing, also called as additive manufacturing or rapid prototyping, was developed in the 1980s and soon adopted in the fields of medicine.[1]
In dentistry, milling – a subtractive manufacturing technique – has become widely used for fabricating dentures. However, milling has notable limitations, including its inability to reproduce complex anatomical features such as undercuts and intaglio surfaces, as well as its restriction to producing one unit at a time. In contrast, additive manufacturing offers several advantages. It is more cost-effective, as it eliminates material waste and tool wear, and it enables the simultaneous production of multiple units with highly intricate geometries. These benefits make 3D printing a promising alternative for dental applications, as noted by Shin et al.[2]
The term “3D printing” refers to a broad category that includes a number of different techniques, such as inkjet printing, stereolithography, liquid crystal display, digital light projection, and fused deposition modeling. DLP’s great resolution, processing speed, and cost-efficiency make it a very attractive technology for dental applications.[3] 3D printing can make use of a wide variety of materials, including ceramics, metals, photopolymers, plastics, polyesters, and polyether ether ketone (PEEK), as stated by Pillai et al.[3]
To endure abrasion from a toothbrush, physical qualities like wear resistance are required. 4 For long-term use of 3D-printed temporary repairs prior to final fabrication, this is of utmost importance.
The degree to which 3D printing materials are polymerized depends on factors such as the amount of print layers, the duration of light exposure, and its intensity. It is necessary to compare the precision of various printers from various software packages because these characteristics vary from one program to another.
According to research by Chimello et al., one of the most common types of wear that affects both natural teeth and dental prostheses is toothbrush abrasion. The front surfaces of teeth and restorations are the most common sites for this kind of wear, which is known as three-body abrasion.[5] The many benefits of additive manufacturing have led to a dramatic increase in its application for the fabrication of temporary crowns and bridges, as reported by Nayyer et al.[6]
An efficient and economical substitute for traditional procedures is the 3D-printed temporary crown, which can be made from digitally scanned data in a matter of minutes. Traditional temporary restorations have a number of drawbacks that these crowns aim to remedy. These include microleakage, the heat produced during polymerization, shrinkage during polymerization, and differences in thermal expansion coefficients between the restoration material and natural enamel.[7] A temporary material for crowns and bridges that can be 3D printed using two separate printers will have its abrasive wear resistance tested and compared in this study. Specimens printed using the Asiga Max and Phrozen Sonic Mini 4K 3D printers do not differ significantly in terms of wear resistance, according to the null hypothesis.
The primary goal of this research was to compare the effects of brushing and wearing down two systems – one using DLP software and the other using LCD software – of 3D printing crown and bridge material that had been made temporarily. The investigation was completed by polishing the samples.
METHODOLOGY
The nx12 (Unigraphics) computer-aided design program was used to create the specimens’ Standard Tessellation Language (STL) file [Figure 1], which had predetermined dimensions of 10 mm in length, 4 mm in breadth, and 2 mm in thickness. The specimens were printed using two separate 3D printers using this STL file. Specimens created using the Asiga Max 3D printer (DLP) were categorized as Group B (n = 30), whereas those created using the Phrozen Sonic Small 3D printer (LCD) were categorized as Group A (n = 30). In order to detect wear resistance, a minimum of 30 samples was needed in each group, and the power was set at 80%, with the statistical significance level at P < 0.05. We 3D printed the crown and bridge using D Tech 3D Accuprint material in shade A2, which is available for purchase.
Figure 1.
Standard Tessellation Language file of 2 mm × 4 mm × 10 mm dimensions
The G code file, which was generated as per the requirements of the printers, was transferred to the printer through an external storage media (USB) device. The d tech 3D Accuprint C and B resin liquid was poured into the resin tank of Asiga and Phrozen Sonic mini 3D printers to fabricate 60 interim specimens, 30 specimens from each printer. The printed specimens were subjected to magnetic stirrer (Remi 1MLH) for cleansing. The cleansed printed specimens were detached from the print bed and subjected to the curing unit (Bre Lux power unit). Post-curing cycle lasted for 6 min. The final thickness was measured using a digital Vernier calipers to ensure specimens were of 10 mm in length, 5 mm in width, and 2 mm in thickness.
We used silicon carbide abrasive paper to polish the specimen for 10 s each on a coarse grit (P120) and a fine grit (P600). Once the specimens were polished, they were rinsed with water and allowed to dry. A contact profilometer (MITUTOYO SJ-310) [Figure 2] was used to evaluate the surface roughness of the specimens in both groups. The profilometer was adjusted using the following settings: A 40° stylus tip angle, a 0.75 µm measurement force, and a cut-off length of 0.8 mm. At the specimen’s center, we measured and recorded the average surface roughness (Ra) values. We used these numbers as our starting point for the surface roughness before we simulated toothbrushing.
Figure 2.
Contact Profilometer (MITUTOYO SJ-310)
Using cylindrical putty molds [Figure 3], die stone templates were created and placed in an eight-compartment brushing simulator [Figure 4]. Each specimen was brushed 10,000 times, at an estimated rate of 30 strokes per day, to simulate 1 year of dental brushing. To make sure the specimen surfaces were covered evenly, a brushing load of 250–300 g was applied at a speed of 30 mm/s while moving in circular motions.
Figure 3.
Specimen mounted on die stone template
Figure 4.
Tooth brush simulator ZM3.8 (SD MECHATRONIK)
The samples were rinsed with distilled water, dried, and then removed from the templates following the simulation. Keeping the same parameters as the first experiment, a contact profilometer was used to measure the surface topography.
To ensure that the acquired roughness data were normal, it was run via Shapiro-Wilk. For this study, we utilized IBM’s Statistical Package for the Social Sciences (SPSS, version 20.0 for Windows, Armonk, New York, USA) software to analyze data and determine sample sizes. To determine whether the surface roughness values increased after being subjected to the tooth brush simulator, a Student’s t-test was used.
RESULTS
The mean surface roughness of Group A before and after brushing is compared in Table 1. Here, a paired t-test was chosen. A statistically significant difference was found (P = 0.001) in the results of the test. In comparison to the mean surface roughness (0.27 µm) with a standard deviation (SD) of 0.11 before the brushing simulation, the mean surface roughness (0.48 µm) with a SD of 0.16 after the simulation was significantly higher for Group A.
Table 1.
Compares the mean surface roughness (Ra) and standard deviation of group A samples prior and following brushing simulation
| Category | Before tooth brush simulation, mean±SD (μm) | After brushing simulation, mean±SD (μm) | P |
|---|---|---|---|
| Group A | 0.27±0.11 | 0.48±0.16 | <0.001 (significant) |
SD: Standard deviation
Group B’s mean surface roughness before and after brushing is compared in Table 2. Group B’s average surface roughness before and after brushing was compared using a paired t-test. A statistically significant difference was found (P = 0.001) in the results of the test. The average surface roughness (0.45 µm) with a SD of 0.15 after tooth brush wear simulation was noticeably higher than the average surface roughness (0.30 µm) with a SD of 0.95 before toothbrush wear simulation in Group A.
Table 2.
Compares the mean surface roughness (Ra) and standard deviation of Group B samples prior and following brushing simulation
| Category | Before tooth brush simulation, mean±SD (μm) | After brushing simulation, mean±SD (μm) | P |
|---|---|---|---|
| Group B | 0.30±0.95 | 0.45±0.15 | <0.001 (significant) |
SD: Standard deviation
Before tooth brush simulation, Table 3 displays the average surface roughness of samples from Group A and Group B. Before the tooth brush wear simulation, Group A had an average Ra value of 0.27 µm and a SD of 0.11. Before brushing, the average Ra value for Group B was 0.30 µm, with a SD of 0.95. Before brushing, the samples in Groups A and B were compared for their mean surface roughness using a Student’s t-test. No statistically significant difference was found.
Table 3.
Presents the mean surface roughness (Ra) and standard deviation of Group A and Group B samples before brushing
| Category | Prior to brushing simulation, mean±SD (μm) |
|---|---|
| Group A | 0.27±0.11 |
| Group B | 0.30±0.95 |
| P | 0.26 (NS) |
NS: Not significant, SD: Standard deviation
After the toothbrush simulation, Table 4 displays the average surface roughness of samples from Group A and Group B. With an SD of 0.16, the mean Ra value following brushing in Group A was 0.48 µm. With SD of 0.15, the mean Ra value following brushing in Group B was 0.45 µm.
Table 4.
Presents the mean surface roughness (Ra) and standard deviation of Group A and Group B specimens following the brushing simulation
| Category | After brushing simulation, mean±SD (μm) |
|---|---|
| Group A | 0.48±0.16 |
| Group B | 0.45±0.15 |
| P | 0.53 (NS) |
NS: Not significant, SD: Standard deviation
To compare the average surface roughness of the brushed samples from Groups A and B, a Student’s t-test was employed. No statistically significant difference was found.
Group A and Group B’s mean surface roughness values before and after the brushing simulation are shown in Bar Diagram 1. Following the brushing simulation, the samples in Group A showed significantly higher mean surface roughness values compared to Group B.
Bar Diagram 1.
The comparison of the mean surface roughness of Group A and Group B samples before and after brushing simulation
DISCUSSION
Temporary restorations play a critical role in the success of dental prosthetic treatments. They serve multiple functions, including diagnostic evaluation, stabilization of occlusion, maintenance of esthetics, facilitation of oral hygiene, and protection of the dental pulp. Key considerations in the design of interim crowns include optimal physical properties, ease of manipulation, and cost-effectiveness.
3D printing technology can fabricate temporary crowns within minutes based on the digitally scanned data, as stated by Tahayeri et al.[7] Acrylic resins and composite resins are chiefly used materials for the production of interim restorations. Acrylic resins are popular because to their inexpensive price and user-friendliness. Traditional acrylic resins have a few problems, though. One is that they generate heat during polymerization. Another is that they shrink during polymerization. Finally, there is microleakage since the resin and natural enamel have different thermal expansion coefficients. In response to these drawbacks, 3D-printed temporary crowns with enhanced processing control and material stability have been developed. According to Pillai S et al., mechanical characteristics and biocompatibility play a crucial role in determining the prosthesis’s long-term clinical performance and success.[3] There are limitations on structural complexity and processing speed, and the setup costs are higher because these processes depend on specialized equipment and materials.[7]
Layers of solid structures can be created using 3D printing resins, which are composed of liquid photosensitive polymers that cure in the light. Making the initial layer on the construction site is the first step. The build platform can move up or down during printing, depending on where the UV light source is located, as explained by Pan et al.[8] Layers are projected onto the build platform or the previously cured layer using a digital projector screen in DLP 3D printing. This process is done through a transparent portion of the resin tank. The construction platform moves vertically until the whole thing is manufactured, as described by Sun et al., after each layer cures.[9]
There are primarily three software options for vat polymerization: SLA, DLP, and LCD. LCD is very comparable to DLP. To avoid the need for a projector, it uses an LED array that, when directed through an LCD screen, exposes whole resin tank layers to ultraviolet radiation. According to Anandakrishnan et al.,[10] print speed is an advantage of DLP and LCD over SLA since they print a full layer at once instead of just one spot.
By comparing DLP and LCD systems in particular, Tsolakis et al.[11] evaluated the efficacy of several 3D printing technologies for the creation of precise dental models. They found that DLP printers were more accurate and reliable than LCD-based systems in terms of both trueness and precision, suggesting that DLP technology is better suited for use in clinical and laboratory settings. There is congruence between these results and the current study’s conclusions that DLP technology is more suitable for dental applications because to its higher abrasion resistance compared to LCD-based printing.
One major issue with restorative materials is wear, particularly in high-stress locations such as full-coverage crowns and veneers. According to Jain et al.[12] and Hu et al.,[13] dental restorations with high wear resistance last longer, look better, and perform better over time.
According to Aker JR (1982),[14] abrasion from toothbrushes and dentifrices is one kind of three-body wear that can happen to any part of the teeth, but it usually shows up on the labial surfaces.
Research on material wear has made use of a variety of brushing simulation cycles. Tanoue et al.[15] used 20,000 brushing cycles and Heintze et al.[16] used 72,000 cycles. Takeuchi et al.[17] and Dindar and Atay[18] used 35,600 and 20,000 cycles, respectively, which differ from the procedure chosen in the present investigation. Heintze et al.[16] used 72,000 cycles, and Tanoue et al.[15] used 20,000 brushing cycles. Research by Goldstein and Lerner[19] determined that 5000 cycles of brushing are equivalent to 6 months, 10,000 cycles to 1 year, and 20,000 cycles to 2 years of clinical teeth brushing wear, respectively. A total of 10,000 cycles were applied to approximate 1 year of brushing, although the current study was not planned as a long-term periodic review. For the purpose of evaluating the wear performance of 3D-printed resins, which are a new class of materials with long-term therapeutic applications, it was decided to simulate a year’s worth of use.
To examine the average difference in surface micro-roughness between the two groups’ samples before and after tooth brush simulation, a Mann–Whitney U-test was employed. The surface roughness of Group A samples was 0.20 µm before and after brushing, with a SD of 0.13. The average difference in surface roughness between the samples in Group B before and after brushing was 0.15 µm, with a SD of 0.11. A statistically significant difference was shown by the test (P = 0.04). Group A samples had a substantially larger mean difference in surface roughness (0.20 µm) compared to group B samples (0.15 µm) in terms of surface micro-roughness.
Light intensity and wavelength are the two most important factors in resin polymerization. Here, the two systems are identical in that they both produce light of about the same intensity and use the same wavelength (405 nm). Light sources and projection techniques may vary, but the fundamental variables controlling polymerization – intensity and wavelength – are almost interchangeable. Hence, it is safe to assume that the two systems will exhibit comparable polymerization tendencies and provide comparable outcomes.
In a chewing simulation, Myagmar et al.[20] compared three distinct intermediate resin materials for their wear resistance and surface roughness. Wear volume losses (mean ± SD, in mm3) of 0.08 ± 0.09 and 0.10 ± 0.01 after 30,000 and 60,000 cycles, respectively, were observed in the 3D-printed resin. Compared to the conventional resin, which showed higher losses of 0.44 ± 0.01 and 0.11 ± 0.01 for the same cycles, the milled resin showed wear losses of 0.21 ± 0.02 and 0.06 ± 0.01. All three materials exhibited notable variations in wear volume, with the 3D-printed resin exhibiting noticeably less wear than the milled and conventional resins at both cycle intervals (P < 0.001).
Three 3D-printed dental materials – 3 Delta Temp, NextDent C and B, and Freeprint Temp – were analyzed for their wear resistance by Kessler et al.[4] We used a DLP 3D printer to additively construct eight samples of each material, and an ACTA machine to simulate three-body wear. Based on the study’s findings, Tetric EvoCeram and 3Delta Temp outperformed the other in terms of wear resistance, with significantly reduced wear rates after 200,000 cycles.
Mayer et al.[21] compared milled polymethyl methacrylate (PMMA) and 3D-printed specimens to determine the two-body wear resistance of resin-based temporary crown and bridge materials. The materials were tested using a chewing simulator. Findings demonstrated that 3D-printed materials had superior wear resistance to milled PMMA, suggesting that 3D-printed resins may provide therapeutic benefits in the areas of performance and longevity.
Park et al.[22] tested sixty specimens for wear resistance. The specimens were made using three different types of resin: Self-cured, milled, and 3D-printed. In a thermocycling environment, each specimen underwent thirty thousand chewing cycles. The results showed that 3D-printed resin had wear resistance that was on par with self-cured and milled resins. Based on these findings, it appears that 3D-printed materials may withstand wear and tear adequately and may even produce stable therapeutic results.
When evaluating the durability of dental restorations, clinical trials are considered to be the most reliable and accurate method. Consistent and reliable results may be compromised by the time and effort required for in vivo investigations, as well as by the large interindividual variability that affects them. There was no statistically significant difference in printer wear, thereby rejecting the null hypothesis of the current investigation.
Because abrasion mechanisms are affected by the interplay of mechanical, chemical, and biological processes, clinical trials are necessary to back up estimates of performance derived from in vitro research about the wear resistance of restorative materials.
The inability to replicate the constant washing activity of saliva that happens in a clinical situation was a limitation of our investigation. To get a final verdict, more wear data and a bigger sample size are needed. Due to varying patient characteristics, in vitro testing cannot be perfectly associated with in vivo studies.
CONCLUSION
The following conclusions were drawn within the scope and limitations of this study:
Specimens fabricated with the Phrozen Sonic Mini 3D printer using LCD technology showed more abrasion after brushing simulation compared to those produced with the Asiga Max 3D printer using DLP technology
Specimens fabricated using the Phrozen Sonic Mini 3D printer (LCD) and the Asiga Max 3D printer (DLP) exhibited signs of abrasion; however, the difference between the two group samples was not statistically significant.
Conflicts of interest
There are no conflicts of interest.
Funding Statement
Nil.
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