Effect of Surface Treatments on the Repair of a Hybrid Ceramic through the Microtensile TestAbstract
This study evaluated the microtensile bond strength between a hybrid ceramic and a composite resin under different surface treatments and aging. Hybrid ceramic blocks were divided into five groups based on surface treatment and thermocycling: HF: 5% hydrofluoric acid; HFS: hydrofluoric acid and silane; A110S: sandblasting with aluminum oxide and silicatization; A50: aluminum oxide particle blasting; R: roughening. All samples were cemented to composite resin. After 24-hour storage in distilled water at 37ºC, the blocks were cut into sticks and tested immediately or after 10,000 cycles. Microtensile bond strength was tested using a universal testing machine. Failure modes were visualized and classified as cohesive, adhesive, and predominantly adhesive. Statistical differences were found between groups for surface treatment and thermocycling (p<0.05). Hybrid ceramics showed higher bond strength when etched with hydrofluoric acid and silanized, but bond strength decreased after thermocycling in all groups.
Keywords:
adhesion; composite resins; hybrid ceramic; microtensile bond strength; surface treatment
INTRODUCTION
Fractures and delaminations are the main causes of failure in indirect restorations 1. When minor fractures or chipping are observed, repairs should be performed since they involve a minimally invasive approach that implies the addition of restorative material to the fractured restoration 2. Hence, direct resin composite is considered a suitable material for repairing indirect resin composites or ceramic restorations 3.
Regarding resin composites, the repair of restorations has been widely investigated and successfully reported in clinical studies 4),(5. In addition, in vitro studies have explored methods of repairing all-ceramic restorations 6),(7. In a general view, repair protocols require mechanical treatments (e.g., hydrofluoric acid etching, and sandblasting) followed by chemical surface treatments (e.g., silane application). These surface treatments ensure mechanical interlocking between both repaired and repairing restorative materials 8.
Polymer-infiltrated ceramic network (PICN) is a hybrid indirect material consisting of a porous feldspathic ceramic matrix (86 wt%) infiltrated with a copolymer (urethane dimethacrylate and triethylene glycol dimethacrylate) (14 wt%) (VITA Zahnfabrik H. Rauter GmbH & Co.KG, Germany). Previous literature has shown a survival rate of over 90% for adhesively cemented PICN crowns within 2 years 9. However, minor fractures can occur and require repairs. Since PICN contains both polymer and feldspathic ceramic in its composition, questions have been raised about suitable surface treatment alternatives for this material. Various treatments, such as aluminium oxide particle sandblasting 10),(11),(12 hydrofluoric acid 11),(12, diamond bur 10, and phosphoric acid 11 have been suggested. Nevertheless, there is no consensus regarding the optimal surface treatment for repairing PICN.
Silane is a bifunctional molecule that forms a siloxane network with ceramic surfaces and copolymerizes with resin-based materials, making it the most recommended coupling agent for achieving chemical adhesion when luting dental ceramics 13. However, silane tends to hydrolyze in water, leading to a decrease in bond strength 14. In this sense, long-term aging is paramount when evaluating bonding interfaces. One studied alternative for etching PICN surfaces is sandblasting with silica-coated Al2O3 particles followed by silane application (tribochemical treatment). Nonetheless, it is worth mentioning that these studies often utilize 30-µm particles 10),(11, which may not be readily available in routine dental office settings.
Given the above context, this study aimed to investigate the effect of different surface treatments on the bond strength of PICN to a resin cement. Hydrofluoric acid (HF) etching with and without silane application, tribochemical treatment with 110-µm Al2O3 particles and diamond burs were the chosen protocols. The bond strength was evaluated at baseline and after thermocycling aging. Thus, we intended to confirm or challenge the existing literature by testing the hypotheses that 1 hydrofluoric acid etching would lead to the highest bond strength results and 2 thermocycling aging would decrease the bond strength of all experimental groups.
MATERIALS AND METHODS
This in vitro study evaluated the factors of surface treatment (HF etching, HF etching + silane, tribochemical treatment, or diamond bur) and testing time (baseline or thermocycling aging). The evaluated outcome was microtensile bond strength (µTBS). The study design is depicted at in Figure 1 and the materials used in this study are described in Table I.
Flowchart of experimental procedures for the microtensile test. HF: hydrofluoric acid; S: Silane; SIL: Silicatization; A: Aluminium oxide sandblasting; R: Roughening with drill.
Commercial name, manufacturers, material and chemical composition of materials used in this study.
Bocks of a polymer-infiltrated ceramic network (PICN, Vita Enamic, Vita Zahnfabrick, Bad Säckingen, Germany) were sliced under water cooing with a diamond saw in a cutting machine (Isomet 1000, Buehler, Lake Bluff, USA). The obtained slabs were leveled and polished with #600-grit silicon carbide sandpaper under water cooling in a polishing machine (EcoMet, Buehler, Lake Bluff, Illinois, USA). The final dimensions of the samples were 10 × 8 × 4 mm (N = 48). The samples were ultrasonically cleaned in ethanol for 5 min, air-dried, and randomly divided into four groups (n = 12). Each group was subjected to a surface treatment described in Table II.
Model matrices made of Zetaplus condensation silicone (Zhermack, Italy) in the exact dimensions of the hybrid ceramic specimens (4x4x4mm) were filled with Filtek Z250 XT composite resin (3M ESPE, Brazil) by the incremental technique, and then light-cured by the Bluephase N (Ivoclar Vivadent, Schaan, Liechtenstein) for 40 seconds. A polisher (EcoMet, Buehler, Lake Bluff, Illinois, USA) subsequently burnished the composite resin blocks under water-cooling with #600-grade silicon carbide sandpaper.
The ceramics from each group received different types of surface treatment, as shown in Table II. The ceramics from the HF group had their surface etched with 5% hydrofluoric acid (Condac Porcelana, FGM, Joinville, Brazil) for 60 seconds, followed by water wash and air-jet for 60 seconds and drying with by an air-jet for 20 seconds at a distance of 30 cm. The HFS group received HF application, air-jet drying, and vigorous application using a microbrush of a Monobond N silane bonding agent (Ivoclar Vivadent, Schaan, Liechtenstein) for 60 seconds, followed by jet drying of air for 20 seconds at a distance of 30 cm.
Aluminum oxide particles in the A110S group modified by Rocatec™ plus (3M, MN, USA) silica (Silicate) blasted the material surface (tribochemical treatment) for 10 seconds at a distance of 15 mm and pressure of 2.5 bar, followed by air jet for 20 seconds. Then, a microbrush was used to apply the Monobond N silane bonding agent (Ivoclar Vivadent, Schaan, Liechtenstein) over the material’s surface for 60 seconds, followed by drying with an air-jet for 20 seconds at a distance of 30 cm. The surface treatment in the A50 group was performed by blasting of aluminum oxide particles (Bioart, São Paulo, Brazil) with 50 microns at 2.5 bar pressure for 10 seconds. Finally, a #2134 diamond tip (KG Sorensen, São Paulo, Brazil) was used to roughen the specimen surface in the group (R).
All groups were cemented with Multilink Automix dual-curing resin cement (Ivoclar Vivadent, Schaan, Liechtenstein) with a pressure of 750g applied over the specimens, so the cement film was uniform. A Bluephase N light-curing (Ivoclar Vivadent, Schaan, Liechtenstein) photopolymerized the cement in four different positions around the specimen for 40 seconds each.
After cementation, the samples were stored in an oven (Fanem, Orion Greenhouse 502, São Paulo, Brazil) at 37°C for 24 hours. The generated blocks were taken to a cutting machine (Isomet 1000, Buehler, Lake Bluff, USA) with constant cooling, thereby obtaining specimens with a cross-section of 1 mm2, measured by a digital caliper (Mitutoyo; São Paulo, SP, Brazil). The groups were divided into immediate and aged. The immediate samples were submitted to the μTBS test. The aged samples were exposed to thermal cycling 10,000 cycles in a thermocycler (Biopdi, thermocycler, São Paulo, Brazil), with a temperature ranging from (5 ± 1 ºC) to (55 ± 1 ºC), with 30 seconds of immersion each bath and 2 seconds of water drainage, forming a thermal cycle of 62 seconds. After thermocycling, the specimens were submitted to the μTBS test.
The specimens were end-adhered to a test device (OG01, Odeme; Lucerna, SC, Brazil) with cyanoacrylate (Superbonder, Loctite; Lucerna, SC, Brazil). The µTBS test was performed by a universal testing machine (DL-1000, EMIC; São José dos Pinhais, Brazil) with a speed of 0.5 mm/min and a load cell of 50 kgf.
The failure modes were visualized by an optical stereomicroscope (Carl Zeiss, Discovery V20, Jena, Germany) at 30x magnification. According to the classification of Silva et al. 15 an adhesive failure occurs when the fracture occurs at the adhesive interface and ceramics; predominantly adhesive when the failure occurs in more than 60% of adhesion; ceramic cohesive when there is a ceramic fracture; and finally the resin cohesive, when there is a resin fracture. The type of surface treatment and aging was considered the independent variables (factors), and the µTBS tests, stereomicroscope, and scanning electron microscopy were considered the dependent variables (response). The number of repetitions per group was 4 (n=4), and samples were analyzed in different storage periods. Then, the mean and standard deviation of the µTBS values were obtained, and a 2-factor ANOVA statistical test was performed, followed by Tukey’s
One specimen from each group was visualized by scanning electron microscopy (SEM) analysis (FEI, Phillips, Brno, Czech Republic). The selected specimens were cleaned with 70% alcohol (Alves Santa Cruz Ltda., Guarulhos, SP, Brazil), dried, and coated with a thin layer (12 nm) of gold (EMITECH SC7620, East Sussex, UK) before the analysis in SEM.
RESULTS AND DISCUSSION
Figure 2 shows the failure modes. The HF immediate, A110S immediate, and aged A110S groups were predominantly adhesive failures.
Failure mode distribution for all groups: (HF) Hydrofluoric acid etch, (HF + S) Hydrofluoric acid etch followed by silane application, (SIL + S) Silicatization followed by silane application, (A) Aluminum oxide particles blast, (R) Diamond burr roughening 2134.
Table III and IV display the statistical analysis. There was a statistically significant difference between the groups, with the highest bond strength values observed in the HFS group and the lowest values in the R group. There was a decrease in µTBS values after thermocycling for all groups.
Figure 3 shows the treated specimen’s surface (100/5000x) from each group. The acid etching generated a roughened surface with vitreous portion exposition for the HF and HFS groups. The material surface in A110S and A50 was rough but without vitreous exposure. The roughening did not generate a homogeneous distribution of irregularities over the specimen surface in R.
SEM images (500x) of the ceramic surfaces: a- HF group; b- HFS group; c- A110S; d- A50 group; e- R group.
The present study in vitro aimed to analyze the effect of different surface treatments on the bond strength between a hybrid ceramic and a composite resin. The first hypothesis was accepted, as etching the ceramic surface with 5% HF followed by silane showed the highest bond strength values. The second hypothesis was also accepted, as thermal aging reduced the bond strength values of all tested groups.
The evaluation of microtensile bond strength is already consolidated methods for testing the bond strength between the ceramic/resin assembly 11. Despite the difficulty in obtaining rods with a transferal area of 1mm2 and the stresses that are generated during the cuts, the μTBS test offers advantages such as uniform stress distribution during the test execution 16. In this study, adhesive-type failures were found, predominantly adhesive and cohesive 17. Pre-test failures were not found in this study.
Studies show that aging in water storage does not negatively affect composites with high filler content and high conversion rate 18. In the oral cavity, chemical degradation occurs, including water absorption as well as the release of residual monomers 19, therefore, an aging by thermocycling (5-55ºC) during 10000 cycles was carried out in this study to simulate 1 year clinically 20.
The adhesive strength of a ceramic is related to mechanical interlocking and chemical adhesion on the surface of the restoration 13. Therefore, surface treatment increases surface roughness and consequently increases the wettability of the cementing agent at the adhesive interface 21. In this sense, etching with HF is a potential surface treatment, as the hybrid ceramic has 86% feldspar ceramic and the vitreous part of the surface is dissolved, which can subsequently trigger cracks and even fracture on the surface of the hybrid ceramic 22. Clinically, this factor is of great importance, as biological structures such as the mucosa, gums, and teeth are sensitive to HF corrosion. In this study, the best bond strength values were attributed to the group with acid etching followed by silane application.
As an alternative to etching with HF, we have sandblasting with Al2O3 with 110 µm particles coated with silica, previous studies 21),(23 show that it is a valid treatment for ceramics, although the effect of blasting with particles of different sizes can damage the surface of restorations 24),(25. Within the limits of this study, the hybrid ceramic had superior µTBS compared to the composite when etched with hydrofluoric acid and silanized. There was a significant reduction in µTBS observed in all groups after thermocycling.
CONCLUSION
Within the limits of this study, the hybrid ceramic had superior µTBS compared to the composite when etched with hydrofluoric acid and silanized. There was a significant reduction in µTBS observed in all groups after thermocycling.
ACKNOWLEDGMENT
This study was partly supported by the Sao Paulo Research Foundation (FAPESP; grants 18/05908-4).
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Publication Dates
-
Publication in this collection
24 Mar 2025 -
Date of issue
2025
History
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Received
17 Aug 2024 -
Reviewed
10 Nov 2024 -
Reviewed
31 Dec 2024 -
Accepted
18 Feb 2025
