DOI: https://doi.org/10.21203/rs.3.rs-1808447/v1
Purpose: The repairability of ceramic containing 3D printed materials has not yet been investigated. This study aimed to compare the repair bond strength of permanent resin blocks with composite by applying different intraoral surface treatments after aging in water.
Methods: The study material comprised thirty-five 3D printing cubes, which were aged in 10,000 thermocycles. Surface treatments were applied to the seven groups as A. Negative control (untreated) B. Positive control C. Phosphoric acid D. Er,Cr;YSGG laser E. Sandblasting F. Hydrofluoric acid, and G. Burr abrasion followed by multi-primer and universal bond. The best 1×1×12 mm sticks were tested on a universal testing machine. Data were analyzed using one-way ANOVA and the Duncan test.
Results: The negative control group reached a significantly lower micro tensile bond strength than the laser and sandblasting groups (p≤ 0.05). The repair bond strength of the positive control group didn’t differ significantly from that of the other experimental groups (p=0.374).
Conclusion: The bonding strength of composite resin hasn’t shown a statistically significant difference when different surface treatments were applied to 3D-printed resin. It can be concluded that it is possible to make small repairs of 3D printed permanent restorations with the application of primer and bond.
The application of primer containing silane and MDP increased the bonding of 3D permanent resin with conventional composite resin.
Three-dimensional (3D) printing technology has entered the market as one of the most up-to-date methods in the field of dentistry. It has found an area of use in almost all specialist branches of dentistry and has opened new and different perspectives, not only in patient treatments but also in the education and training of dental practitioners [1–3].
3D printing, in other words, additive manufacturing based on computer-aided design (CAD) digital models, uses digital biomaterials to provide personalized products. There are different printing technologies and different types of resins in this method. The resin is selected appropriate to the target properties of the product to be made. Therefore, new resins are developed both at low cost and appropriate to the desired characteristics [4–6]. 3D printing is mostly used in dentistry to make surgical guides, occlusal splints, working models, removable partial denture frames, full dentures, temporary crowns, and bridges produced with polymer resin material [7]. With the addition of ceramic to the polymer resin printing material, aesthetics, durability, and biocompatibility have been achieved, which allows it to be used in permanent crowns, bridges, veneers, inlays, and onlays.
Even if permanent resins successfully pass mechanical and chemical tests, when the restoration is in the mouth, fracture and chipping may occur for various reasons [8]. When a fracture or material loss occurs in the restoration, replacing the restoration as a whole will not be a practical solution as it will require greater preparation and cause the loss of healthy tooth tissue. At the same time, providing a rapid result at a low cost is extremely advantageous [9, 10].
Several articles in the literature have used composite resin in the repair of CAM-CAD blocks with different content. Although the content is similar in 3D photopolymerized resin, hybrid CAD-CAM blocks, and conventional composite resins, the organic-inorganic matrix type, and the size and geometry of filling particles can affect their bonds. In a study that investigated the effect of different sandblasting particle sizes on the repair of ceramic containing polymer-based CAD-CAM blocks, it was reported that the µTBS results of GC Cerasmart and VITA Enamic blocks were not significantly affected, while the results were significantly changed for LAVA Ultimate block. This showed that the ideal repair protocol for CAD-CAM blocks depended on the content of the material used [11].
Various surface preparations are made to better bond the repair with composite resin to the restoration. These include bur grinding, hydrofluoric acid etching (HF) or phosphoric acid etching, laser conditioning (neodymium-doped yttrium aluminum garnet (Nd:YAG), erbium-doped yttrium aluminum garnet (Er:YAG) or erbium, chromium-doped yttrium, scandium, gallium, and garnet (Er,Cr:YSGG), sandblasting (with 50 µm aluminum oxide (Al2O3) or silica-coated Al2O3), silane coupling agents and porcelain repair kit application, or the combined use of more than one of these techniques [11–14].
Restorations absorb water within the mouth. The material corrodes and the organic and inorganic matrix bonds break. A restoration will age over time as a result of loading with long-term use and there will be material loss on the surface of the restoration [15]. To be able to mimic the intraoral environment, the repair procedures in the current study were applied following an aging process.
The repairability of ceramic containing 3D printed materials has not been investigated to date. Therefore, this study aimed to compare the bond strength of micro-hybrid composite resin by applying different intraoral surface treatments to permanent resin blocks. The null hypothesis of the study was that different surface treatments would not affect the repair micro tensile bond strength of 3D printed resin after aging in water.
In this in vitro study, 35 cubes of 6*6*6* mm3 dimensions were to be produced and were saved in standard tessellation language (STL) format from Thingiverse.com (a popular open-source 3D design repository website) [16]. The design file was imported into the PreForm to be able to produce in large numbers. Stereolithography (SLA) printing technology was used for the 3D printing of the cubes. In the Preform software, the cubes were arranged in such a way that they did not touch each other, and the support contact points were arranged at 0 degrees orientation. To ensure the fastest print time, the samples were lined up in two parallel lines towards the wiper side of the stainless-steel build platform indicated in the PreForm.
The cubes were produced using a 3D printer (Formlabs SLA 3D Printer, Somerville, MA, USA) with photopolymerized resin (Permanent CB Resin, Formlabs, Somerville, MA, USA) by the manufacturer's recommendations. Laser wavelength was 405 nm, layer thickness was 50 µm, and they were printed in 1hr 40 minutes. After printing, the cubes were dipped in Form Wash (Formlabs, Somerville, MA, USA) and soaked in isopropyl alcohol (IPA ≥ 99%) for 3 minutes to remove residual resin, then left to dry for at least 30 minutes. Post-curing was completed in two steps. First, while the supports were still attached to the samples, they were cured in Form Cure (Formlabs, Germany), 390–405 nm, at 60°C for 20 minutes. Then, the supports were removed, and a second 20-minute UV curing cycle was performed with the cubes in a different orientation. Each cube was finally polished with conventional polishing tools (pumic stone and water) used for acrylics and composites. In total, 35 permanent resin cubes were produced [3, 17]. (Fig. 1)
It took approximately 15 minutes to create the design and 1.5 hours for the printing and post-printing procedure. All the samples were kept in distilled water at 37°C for 24 hours and were then aged in 10,000 thermocycles at 55°C (+/-2°C) and 5°C (+/-2°C) 30 sec dwell time and 10 sec transfer time.
The materials used are shown in Table 1. (Table 1)
Materials |
Composition |
Manufacturer |
---|---|---|
Permanent Crown Resin A2 Resin 1Kg (0,7 L) |
Esterification products of 4,4’-isopropylidiphenol, ethoxylated and 2-methylprop-2enoic acid, silanized dental glass, methyl benzoylformate, Diphenyl (2,4,6-trimethyl benzoyl) phosphine oxide. Total content of inorganic fillers (particle size 0.7µm) is 30–50% by mass |
Formlabs, Somerville, MA, USA |
Porcelain Etch |
9% buffered hydrofluoric acid |
Ultradent Products Inc. South Jordan, UT, USA |
Ultra-Etch |
35% orthophosphoric acid |
Ultradent Products Inc. South Jordan, UT, USA |
G-Premio Universal bond |
10-methacryloyloxydecyl dihydrogen phosphate (MDP), 4-MET, MDTP, MEPS, BHT, Acetone dimethacrylate resins, initiators, water |
GC, Tokyo, Japan |
G-ænial Anterior |
UDMA, dimethacrylates, pre-polymerized fillers, silica, strontium, and lanthanide fluoride |
GC, Tokyo, Japan |
G-Multi Primer |
MDP, vinyl silane, phosphoric methacrylate monomer, thiophosphoric ester monomer, methacrylic acid ester, ethyl alchol MDP, MDTP, and γ-MPTS |
GC, Tokyo, Japan |
* The composition of the material is unknown as the company keeps it a trade secret.18,19 |
Surface treatments as in Table 2 were applied to the experimental groups determined after the thermocycle [20, 21]. (Table 2)
Surface Treatment |
Application Procedures |
---|---|
G1: Negative control group |
• No surface application was made. Composite resin were applied |
G2: Positive control group |
• Multi-primer, universal bond and composite resin were applied |
G3: Hydrofluoric acid |
• Hydrofluoric acid etching for 60 second, washed, air dried • Multi-primer, universal bond and composite resin were applied |
G4: Phosphoric acid |
• Phosphoric acid etching for 60 second, washed, air dried • Multi-primer, universal bond and composite resin were applied |
G5: Sandblasting |
• Sandblasting with 50-µm aluminum oxide applied from 10 mm distance, for 10 sec circling motions at 2.5 bar pressure • Multi-primer, universal bond and composite resin were applied |
G6: Er,Cr;YSGG laser |
• Application of Er,Cr;YSGG laser (Waterlase MD, Biolase, California, USA) 2W energy level, for 20 sec, from 10 mm distance, at a 2.78 µm wavelength, 140 µs pulse duration, 10 Hz repetition rate. • Multi-primer, universal bond, and composite resin were applied |
G7: Bur abrasion |
• Roughening with a yellow-banded diamond bur abrasion at 40,000 rpm for 10 sec, in a single direction Multi-primer, universal bond, and composite resin were applied |
Two specimens of each group were separated for Scanning Electron Microscopy (SEM) analysis. The manufacturer's instructions recommend that primer (G-Multi Primer) and a bond (G-Premio Universal bond) be used together in repair cases. [22]. Therefore, for the micro tensile test, a thin layer of G-Multi Primer was spread on the surfaces of 12 specimens from each group with a micro tip applicator except the negative control group. Then was spray dried at maximum pressure for 5 seconds. Processing was continued using a light-curing adhesive. G-Premio Universal bond was applied as a single layer with the microtip applicator and left untouched for 10 secs. It was spray dried at maximum pressure for 5 seconds, then cured with LED light (VALO Cordless, Ultradent Products Inc., South Jordan, UT, USA) for 10 seconds. The light-cured composite was applied three times in two mm layers with specially prepared stainless-steel molds. Same physician carried out all the experiments.
After the specimens were prepared, each specimen block was rotated 90° on its axis to obtain 1.0 mm×1.0 mm×12.0 mm sticks with the aid of a water-cooled diamond saw (Diamond cut-off Wheel MOD15, Struers, Rødovre, Denmark). The tester (Accutom 10, Struers, Rødovre, Denmark) was set at low speed (3000 rpm, feed rate 0,5 mm/min). The 12 best sticks from the center of each block were selected for use (n = 12).
Each stick was attached between parts of the tension device with cyanoacrylate (3M Scotch-Weld Plastic & Rubber Instant Adhesive PR100, USA), then tested at 0.5mm/min crosshead speed on a universal test machine (MOD Dental MIC-101, Esetron Smart Robotechnologies, Ankara, Turkey). Failure loads was measured in Newtons (N). Bond strength was derived from failure load to surface area ratio and recorded in megapascals (MPa). The fractured samples were examined at x40 magnification under a stereomicroscope (SOIF optical instruments, Stereomicroscope, Istanbul, Turkey) to analyze the fracture mode.
The fracture types were classified as follows:
Adhesive failure between the permanent resin and composite interface
Cohesive failure within the permanent resin or composite
Mixed failure between the permanent resin and composite, with more than half the composite on the permanent resin surface.
Specimens prepared for SEM examination. They were examined under ×2,000 and ×20000 magnifications using SEM (FEI, Quanta 650 FEG, Oregon, USA).
Comparisons were made using the mean values of each specimen. The normality of the data was evaluated with the Shapiro-Wilk test and found to be high. This data was analyzed with ANOVA and Duncan's multiple range tests using SPSS Statistics 21 software (IBM Corpn., Armonk, NY, USA).
The negative control group reached a significantly lower micro tensile bond strength than the laser and sandblasting groups (p ≤ 0.05). The repair bond strength of the positive control group showed no significant difference from that of the other experimental groups (p = 0.374). No significant differences in repair bond strengths could be observed within the experimental groups. (Table 3, Fig. 2)
Groups |
n |
Mean |
Std. Deviation |
---|---|---|---|
G1: Negative control group |
12 |
9,48a |
2,46 |
G2: Positive control group |
12 |
14,87ab |
4,34 |
G3: Hydrofluoric acid |
12 |
15,81ab |
8,77 |
G4: Phosphoric acid |
12 |
14,97ab |
10,25 |
G5: Sandblasting |
12 |
18,53b |
12,74 |
G6: Er,Cr;YSGG laser |
12 |
18,70b |
7,74 |
G7: Bur abrasion |
12 |
16,40ab |
7,00 |
Groups with the same letters are not statistically different (p > 0.05). |
100% adhesive failures were observed in all groups.
SEM analysis of the surface treatments demonstrated that the untreated surface of 3D resin had a smoother appearance (Fig. 3B). In the Er,Cr:YSGG irradiation group, ablation, and melting were observed on the 3D resin surfaces (Fig. 3D). Silica-coated alumina particles combined with silane formed a layer in the sandblasting group (Fig. 3E). In the phosphoric acid and bur groups, the organic matrix was seen to have dissolved, and the filler particles were released (Fig. 3C, G). On the HF acid applied surfaces, filler particles were dissolved (Fig. 3F). Inorganic fillers were observed in the phosphoric acid and burs groups, and in the positive control group, to which only the primer was applied (Fig. 3A, C, G).
In this study, the most up-to-date 3D permanent resin was used together with SLA technology. It can be assumed that this technology will be used more in the future, due to the ease of use and reasonable cost. However, as for every material, there is a risk that it may break in the post-treatment period. A material that has the advantages of ease of use in respect of speed of production, form, and cost should be a reasonable form of repair. From this starting point, the effect was evaluated of different intraoral surface treatments on the bonding of the material with composite resin in the repair of small fractures which do not require a complete change of the restoration. Micro tensile bond strength values were not significantly different among the surface treatments (p ≥ 0.05). Therefore, the hypothesis was not rejected.
A strong bond between the restoration material and composite increases the repair capacity of the material. By increasing the contact area on the material surface, the surface procedures are applied to increase the surface energy and wettability [23, 24], and thus a strong micromechanical locking is created between the composite and bonding agent. There are many studies in the literature about the repair and adhesion of CAD-CAM blocks, which have come into current routine clinical practice. To increase adhesion, the focus point is that mechanical and chemical bonding is increased.
Information in literature has proven that roughening with a burr, etching with aluminum oxide and silica-coated particles, laser conditioning, and conditioning with acid, are methods to increase the mechanical bond which will show the best performance in vitro. In addition, for support and chemical bonding, silanization, primer use, and bond use are the chemicals that must be used for substrate conditioning [25, 26].
All the surface processes applied in this study were observed to be at an acceptable level, and except for the negative control group, no significant difference was determined between the groups. The bonding was seen to be significantly increased in the groups applied with sanding and laser compared to the negative control group to which no process was applied. Although the values obtained from the negative control group showed no statistically significant difference compared to the positive control group values, the values of the positive control group, to which primer was applied, were higher.
The roughness of the surface causes the adhesive to flow, creating longer tags and stronger micromechanical locking. The mechanical surface treatments with hydrofluoric acid, phosphoric acid, sandblasting, and Er,Cr;YSGG laser in the current study increased the bond strength.
In a previous study related to the repair of CAD-CAM blocks, the bonding values of groups with no pre-procedure applied to the substrate surface of a conventional methacrylate-based composite were seen to be below the acceptable limit of bonding values [25]. Schwenter et al. found that in the bond between polymer infiltrated ceramic block (VITA Enamic) and 3 different resin composites, there was a significant increase in shear resistance provided by micromechanical bonding with the use of hydrofluoric acid. It was also seen in that study that additional silane application to the surfaces treated with acid increased the bonding. This increase was reported to be due to the chemical bond between silicate and silane [27].
In another study, the use of silane in resin-infused hybrid ceramic block (VITA Enamic) and nanoceramic (Lava Ultimate) CAD-CAM blocks was seen to increase micro tensile bond strength [28]. Ceramic and nanoceramic CAD-CAM blocks were applied with two different primers and/or sanding in another study, and the bond strength of the cement to resin was seen to be significantly greater in the samples of both blocks which had been sandblasted and applied with primer compared to the control group [29]. Barutçigil et al. evaluated other surface roughening methods, and in a study in which the surface of hybrid ceramic blocks (VITA Enamic) was roughened with Er,Cr:YSGG laser, the bonding values obtained from CoJet sandblasting, 50 µm Al2O3 sandblasting, and 10% hydrofluoric acid etching was reported to be similar to those of the laser process [30].
In another study in the repair of different hybrid ceramic CAD-CAM blocks (IPS e.max CAD, Vita Suprinity, Vita Enamic, Lava Ultimate) with different ceramic repair kits, 9% hydrofluoric acid and airborne particle abrasion with 50µm aluminum oxide surface roughening processes were applied to the IPS e.max CAD and Vita Suprinity groups before the application of the repair kits. After the use of the repair kits, the bonding values in all the groups showed no statistically significant difference, and all were found to be successful [10]. The results of these studies reporting that mechanical surface treatment increases the bond strength are similar to the results of the current study.
Na-Kyung examined the repair of 3D temporary resin with traditional bis-acrylic composite and methylmethacrylate monomer by applying different surface roughening processes. The group repaired with bis-acrylic composite without any additional surface treatment showed the highest micro-shear value and the difference from all the other groups was statistically significant. It was also shown that additional mechanical or chemical surface treatments did not increase the shear bond strength in the repair groups of the two different materials [31]. These results aligned with the results of the current study. Different surface roughening treatments in permanent resin does not significantly increase the bond strength when the repair is made with composites containing Bis-GMA.
Chemical surface treatment can also enhance the repair bond strength [32, 33]. The chemical bond between the monomer and filler in composite materials is obtained by an organic silanizing agent called gamma-methacryloxypropyltrimethoxysilane (γ-MPTS) [34]. Conventional silane agents are formed from γ-MPTS, acetic acid, ethanol, and water in one or two-bottle systems. Alkoxy (-OR) groups of γ-MPTS molecules hydrolise to silanol (Si-OH) groups in an acidic environment with water, then by entering a reaction with hydroxyl groups on the silica-based ceramic surface, oxane (Si-O-Si) bonds are formed [32]. By adding 10-methacryloyloxydecyl dihydrogen phosphate (10-MDP) co-polymerized with resin monomers through the hydrophobic methacrylate terminal to both the resin cement and the bonding agent and into metal primers, a chemical bond is constructed between the resin cement and ceramic [35]. In studies by Okutan et al., the bonding strength between previously sandblasted monolithic zirconia ceramics and self-adhesive resin cement was examined by applying and not applying primer containing MDP, and greater bond strength was obtained in the samples applied with primer agent containing MDP [36]. Consistent with the results of the present study, it has been observed that primer with silane and MDP and a separate bond enhances the bond strength.
Taking into consideration that luting cement also has ceramic content, multipurpose primer and bond containing MDP, MDTP, and γ-MPTS were applied to all the experimental groups except the negative control group. The positive control group was defined as the group applied with only primer and bond and no surface treatment. Although the bond strength value obtained by the positive control group was numerically lower than those of the surface treatment applied groups, the difference was not statistically significant. The application of primer (with silane and MDP content) and bond showed sufficient bond strength in repairs.
Güngör et al. examined the effect of surface treatments applied to Lava Ultimate, Vita Enamic, and GC Cerasmart hybrid blocks on bond strength before and after 10,000 thermocycles. It was reported that aging decreased bond strength, and in the group not applied with aging, the highest bond strength was in the group applied with silane following burr abrasion and acid etching [13].
There are yet few studies in literature related to the use of 3D printer technology in the field of dentistry, and the majority of those studies have been related to the testing of the mechanical and physical properties of different types of resin [37].
Adhesive failure occurs when the adhesive separates sooner than the adherents fracture. In the current study, 100% adhesive breakage in the adhesive joint was observed in all the groups. As this is the weakest point of connection between the two materials, this result was expected.
This was an in vitro study, and even though a direct correlation may not be able to be shown with application in a clinical environment, this study can be considered of guide for future studies.
The bonding strength of composite resin has not shown a statistically significant difference when different surface treatments were applied to 3D-printed resin. The application of primer (with silane and MDP content) and universal bond showed sufficient bond strength in repairs, and there was seen to be no need for surface roughening. Under the limitation of this in-vitro study, the small repairs and the modifications of 3D permanent resin restorations were possible with the application of primer and bond. If a large repair is required, renewal of the restoration is recommended.
Conflict of Interests
The authors declare that they have no conflict of interests.
Funding Statement
The authors received no financial support for the research, authorship, and/or publication of this article.
Acknowledgments
The authors would like to thank to Prof. Dr. Yüksel Bek for statistical analysis.
Author Contribution
E.S and G.B.K developed the experimental design. E.S. did the experiment. E.S and G.B.K analyzing the results, wrote the main manuscript text and prepared figures and tables. All authors reviewed the manuscript.
Ethics Approval and Consent to Participate
Not Applicable