Abstracts

Introduction

Ceramic restorations have been employed for their innumerous advantages such as color stability, low thermal conductivity, resistance to wear and biocompatibility. However, ceramics without metallic support are prone to crack propagation ⁽¹⁾1Rekow ED, Silva NRFA, Coelho PG, Zhang Y, Guess P, Thompson VP. Performance of dental ceramics: challenges for improvements. J Dent Res 2011;90:937-952.. The feldspathic ceramics used as veneer are commonly affected by shipping, fracture or excessive wear, mainly when supported by zirconia frameworks ⁽²⁾2Della Bona A, Kelly JR. The clinical success of all-ceramic restorations. J Am Dent Assoc 2008;139;8S-13S.. In this way, direct repair with a composite resin appears as an attractive alternative due to the low cost, fast resolution, and preservation of supporting structures ^{( 3}3Raposo LHA, Neiva NA, Silva GR, Carlo HL, Mota AS, Prado CJ, et al.. Ceramic restoration repair: report of two cases. J Appl Oral Sci 2009;17:140-144. ^{, 4}4Kimmich, M, Stappert, C. Intraoral treatment of veneering porcelain chipping of fixed dental restorations: A review and clinical application, J Am Dent Assoc 2013;144:31-44. ^{, 5}5Reston EG, Filho SC, Arossi G, Cogo RB, Rocha CS, Closs LQ. Repairing ceramic restorations: final solution or alternative procedure? Oper Dent 2008;33:461-466. ⁾.

Glass-reinforced ceramics have been also emphasized. Actually, the most popular are the leucite- and the lithium disilicate-reinforced ones. Both may be used to obtain veneers, inlays, onlays and crowns. Monolithic application of these ceramics for crowns has been employed to provide higher resistance than the bi-layer restorations ⁽⁶⁾6Guess PC, Zavanelli RA, Silva NRFA, Bonfante EA, Coelho PG, Thompson VP. Monolithic CAD/CAM lithium disilicate versus veneered Y-TZP crowns: comparison of failure modes and reliability after fatigue. Int J Prosthodont 2010;23:434-442., although fractures and wear may also occur in this type of restoration.

Surface preparation in fractured ceramic must be performed in the repair procedure that involves mechanical or chemical surface preparations to create irregularities on the surface. Bonding components are also required for the adhesion to restorative material. Traditionally, surface treatment for ceramics involves roughening with diamond burs ^{( 7}7Attia A. Influence of surface treatment and cyclic loading on the durability of repaired all-ceramic crowns. J Appl Oral Sci 2010;18:194-200. ^{, 8}8Gourav R, Ariga P, Jain AR, Philip JM. Effect of four different surface treatments on shear bond strength of three porcelain repair systems: An in vitro study. J Conserv Dent 2013;16:208-212. ^{, 9}9Jain S, Parkash H, Gupta S, Bhargava A. To evaluate the effect of various surface treatments on the shear bond strength of three different intraoral ceramic repair systems: An in vitro study. J Indian Prosthodont Soc 2013;13:315-320. ⁾, etching with hydrofluoric acid ^{( 8}8Gourav R, Ariga P, Jain AR, Philip JM. Effect of four different surface treatments on shear bond strength of three porcelain repair systems: An in vitro study. J Conserv Dent 2013;16:208-212. ^{, 10}10Colares RCR, Neri JR, Souza AMB, Pontes KMF, Mendonça JS, Santiago SL. Effect of surface pretreatments on the microtensile bond strength of lithium-disilicate ceramic repaired with composite resin. Braz Dent J 2013;24:349-352. ^{, 11}11Melo RM, Valandro LF, Bottino MA. Microtensile bond strength of a repair composite to leucite-reinforced feldspathic ceramic. Braz Dent J 2007;18:314-319. ^{, 12}12Ozcan M, Valandro LF, Pereira SMB, Amaral R, Bottino MA, Pekkan G. Effect of surface conditioning modalities on the repair bond strength of resin composite to the zirconia core / veneering ceramic complex. J Adhes Dent 2013;15:207-210. ⁾ or tribochemical process based on silica-coated aluminum-oxide particles ^{( 11}11Melo RM, Valandro LF, Bottino MA. Microtensile bond strength of a repair composite to leucite-reinforced feldspathic ceramic. Braz Dent J 2007;18:314-319. ^{, 12}12Ozcan M, Valandro LF, Pereira SMB, Amaral R, Bottino MA, Pekkan G. Effect of surface conditioning modalities on the repair bond strength of resin composite to the zirconia core / veneering ceramic complex. J Adhes Dent 2013;15:207-210. ^{, 13}13Han IH, Kang DW, Chung CH, Choe HC, Son MK. Effect of various intraoral repair systems on the shear bond strength of composite resin to zirconia. J Adv Prosthodont 2013;5:248-255. ^{, 14}14Blum IR, Nikolinakos N, Lynch CD, Wilson NHF, Millar BJ, Jagger DC. An in vitro comparison of four intra-oral ceramic repair systems. Journal of Dentistry 2012;40:906-912. ^{, 15}15Cristoforides P, Amaral R, May LG, Bottino MA, Valandro LF. Composite resin to yttria stabilized tetragonal zirconia polycrystal bonding: comparison of repair methods. Oper Dent 2012; 37:263-271. ^{, 16}16Panah FG, Rezai SMM, Ahmadian L. The influence of ceramic surface treatments on the micro-shear bond strength of composite resin to IPS Empress 2. J Prosthodont 2008;17:409-414. ^{, 17}17Lee SJ, Cheong CW, Wright RF, Chang BM. Bond strength of the porcelain repair system to all-ceramic copings and porcelain. J Prosthodont 2014;23:112-116. ⁾. For restorative material bonding, use of silane is recommended for glasses and porcelains in order to obtain a mesh of siloxane with the silica on the ceramic surface, to improve the bond strength between the ceramic and luting material and to increase the surface energy for adhesive application ⁽¹⁸⁾18Matinlinna JP, Vallittu PK. Bonding of resin composites to etchable ceramic surfaces -can insight review of the chemical aspects on surface conditioning. J Oral Rehabil 2007;34:622-630..

The aim of this study was to evaluate the microtensile bond strength after composite resin repairs in glass-ceramics after different surface treatments. The null hypothesis of the study was that there is no difference among the tested techniques.

Material and Methods

The following ceramics were used in this study: feldspathic ceramic (Vita VM7, Vita Zahnfabrik, Bad Säckingen, Germany), leucite-reinforced glass-ceramic (IPS Empress, Ivoclar Vivadent, Schaan, Liechtenstein), lithium disilicate-reinforced glass ceramic (IPS E.max Press, Ivoclar Vivadent). Twelve blocks (10.0 x 7.0 x 3.0 mm) were obtained for each ceramic and aged in distilled water for 3 months at 37 °C. The bonding surface of all ceramic blocks was abraded for 15 s with 600-grit silicon carbide paper and cleaned using ultrasound for 10 min.

The blocks were randomly divided (n=3) in four groups according surface treatments, as follows: GC (control group) - no surface treatment; GDB: surface wear by 30-µm-grit diamond bur during 20 s under water cooling; GHF: hydrofluoric acid (10%) during 90 s for feldspathic ceramic, 60 s for leucite-reinforced glass-ceramic, and 20 s for lithium disilicate-reinforced glass ceramic; GT: tribochemical process: sandblasting with silica-coated aluminum oxide (45-µm size particles) for 20 s, at a distance of 10 mm, perpendicular to the adhesion surface, under 2.8 bar pressure.

In all ceramic blocks, the surface treated by the different protocols was cleaned with 37% phosphoric acid (Condac 37, FGM Dental Products, Joinvile, SC, Brazil) for 30 s, followed by silane application (Angelus Dental Products, Londrina, PR, Brazil) for 1 min. An adhesive system was used as bonding agent (Adapter Singlebond 2; 3M/ESPE, St. Paul, MN, USA) and light-cured for 20 s using an irradiance of 800 mW/cm (BluePhase LED; Ivoclar Vivadent). Composite resin (Filtek Z350; 3M/ESPE) was used as restorative material by the incremental technique and light-cured for 30 s as previously described until obtaining a 3-mm thickness. A single operator performed the complete repair process.

Samples were submitted to thermocycling process (10,000 cycles, between 5 °C and 55 °C for 30 s in each bath). After the ageing procedure, the specimens were sectioned in serial slabs (1 mm thick) using a diamond-embedded blade under continuous water irrigation (Buehler, Lake Bluff, IL, USA) and subsequently in 1 mm² match-sticks and subjected to the microtensile bond strength (µTBS) evaluation in a universal testing machine (EZ-test, Shimadzu Co., Kyoto, Kansai, Japan) at a crosshead speed of 0.5 mm/min. Data were obtained in MPa. The failure pattern was evaluated by a stereomicroscope (Leica Microsystems, Wetzler, Germany) at 60× magnification and failures were classified as adhesive, mixed or cohesive.

Data were processed using SPSS software (version 20; IBM, Armonk, NY, USA) by two-way ANOVA. Post-hoc tests were calculated using the Tukey's test. All tests were conducted at 95% confidence interval (α=0.05).

Results

Mean values (MPa) and standard deviation for all groups are presented in Table 1. Statistical analysis revealed that for feldspathic ceramic no experimental treatment increased µTBS in comparison with GC. However, the group subjected to tribochemical process had significantly lower results than the other groups (p<0.001), presenting pre-test failures in all sticks. For the leucite-reinforced glass ceramic (IPS Empress), GDB and GT did not differ from GC, while GHF showed lower µTBS values (p<0.001). For the lithium disilicate-reinforced glass ceramic (IPS E.max press), GHF showed significantly higher µTBS values than GC, GBD and GT (p<0.001), which were similar among them. Interaction between the factors (ceramic type and surface treatment) was statistically significant (p<0.001).

Discussion

This study showed that the surface treatment influenced the µTBS of all tested ceramics. Therefore, the null hypothesis was rejected. Additionally, it was observed that the success of surface treatment depends on the ceramic type. For the lithium disilicate-reinforced glass ceramic, the etching with hydrofluoric acid promoted the highest µTBS values, which is in agreement with Colares et al. ⁽¹⁰⁾10Colares RCR, Neri JR, Souza AMB, Pontes KMF, Mendonça JS, Santiago SL. Effect of surface pretreatments on the microtensile bond strength of lithium-disilicate ceramic repaired with composite resin. Braz Dent J 2013;24:349-352.. This ceramic has the lowest vitreous proportion among the ceramics tested in this study. Therefore, it seems that the chemical conditioning is most efficient to infiltrate and remove the vitreous phase, creating irregularities in the surface. For leucite-reinforced glass ceramic, the etching with hydrofluoric acid was the only tested surface treatment that showed lower µTBS compared with control and the other tested groups. Since this ceramic has a higher vitreous proportion in comparison to lithium disilicate, it was suggested that mechanical treatments such as the use of diamond burs are more efficient to create irregularities. The success of tribochemical process for leucite-reinforced glass ceramic, which involves the creation of irregularities by sandblasting with aluminum oxide silica-coated particles and chemical improvement by silica deposition on the ceramic surface, is also in agreement with previous reports ⁽¹⁴⁾14Blum IR, Nikolinakos N, Lynch CD, Wilson NHF, Millar BJ, Jagger DC. An in vitro comparison of four intra-oral ceramic repair systems. Journal of Dentistry 2012;40:906-912..

For the feldspathic ceramic, the tribochemical process was the only tested surface treatment that promoted lower values of µTBS in comparison with other tested groups. In fact, this type of ceramic showed pre-testing failures during the tribochemical process for all samples during the stick preparation, like weak bond strength, which lead to failures previous to the testing method, even during stick preparation or handling them, characterizing a bond strength equal to zero in the results section. This process is characterized by silica deposition on the ceramic surface, used mainly for bonding on crystalline ceramics as zirconia and alumina. Therefore, it may be suggested that silica deposition on feldspathic ceramic has a long-term low stability. Nevertheless, the present results are different from those of Attia ⁽⁷⁾7Attia A. Influence of surface treatment and cyclic loading on the durability of repaired all-ceramic crowns. J Appl Oral Sci 2010;18:194-200. who found that the tribochemical treatment showed similar values of µTBS in relation to diamond bur preparation and also diverge from the study of Melo et al. ⁽¹¹⁾11Melo RM, Valandro LF, Bottino MA. Microtensile bond strength of a repair composite to leucite-reinforced feldspathic ceramic. Braz Dent J 2007;18:314-319. where tribochemical process was similar to etching with hydrofluoric acid. However, it is important to highlight that those studies did not use the ageing process for the bonded interface, as the thermocycling used in this study, which may have caused the interface degradation. As regards the success of other surface treatments (groups GHF and GDB) used in this study to repair feldspathic ceramics, they are in agreement with other studies ^{( 7}7Attia A. Influence of surface treatment and cyclic loading on the durability of repaired all-ceramic crowns. J Appl Oral Sci 2010;18:194-200. ^{, 8}8Gourav R, Ariga P, Jain AR, Philip JM. Effect of four different surface treatments on shear bond strength of three porcelain repair systems: An in vitro study. J Conserv Dent 2013;16:208-212. ^{, 11}11Melo RM, Valandro LF, Bottino MA. Microtensile bond strength of a repair composite to leucite-reinforced feldspathic ceramic. Braz Dent J 2007;18:314-319. ⁾.

These observations for efficacy of mechanical or chemical methods for conditioning depending on the ceramic's type are also supported by the data of control group for all ceramics. The silicone grit paper used in all samples to remove the superficial ceramic layer simulating the repair and also used to standardize the surface roughness probably acts as a mechanical preparation providing roughness on the ceramic surface. In this way, the results of this study showed µTBS values in GC of feldspathic and leucite-reinforced ceramic comparable to those of other mechanical surface treatments. However, for lithium disilicate ceramic the GC was similar to other mechanical treatments, which were significantly lower than HF etching.

The failure patterns observed in this study showed a great prevalence of adhesive failures for all groups, ranging from 85 to 100%. Based on these results, it was not possible to establish a relation of failure pattern with µTBS for the used surface treatments. Other analyses showed that adhesive failures are the most observed for repaired ceramic interfaces ⁽¹⁶⁾16Panah FG, Rezai SMM, Ahmadian L. The influence of ceramic surface treatments on the micro-shear bond strength of composite resin to IPS Empress 2. J Prosthodont 2008;17:409-414., some studies presenting 100% prevailance ^{( 12}12Ozcan M, Valandro LF, Pereira SMB, Amaral R, Bottino MA, Pekkan G. Effect of surface conditioning modalities on the repair bond strength of resin composite to the zirconia core / veneering ceramic complex. J Adhes Dent 2013;15:207-210. ^{, 14}14Blum IR, Nikolinakos N, Lynch CD, Wilson NHF, Millar BJ, Jagger DC. An in vitro comparison of four intra-oral ceramic repair systems. Journal of Dentistry 2012;40:906-912. ⁾. This information may suggest that bond strength of repairs on ceramic surfaces are not comparable to the bulk strength of the materials, thus its clinical prognostic success may be related to application in areas of low occlusal load.

Ceramic fractures may result from several factors, such as inadequate occlusal adjustment, failure in the bonding interface, internal porosities, parafunctional habits, and internal stress from the manufacturing process ^{( 1}1Rekow ED, Silva NRFA, Coelho PG, Zhang Y, Guess P, Thompson VP. Performance of dental ceramics: challenges for improvements. J Dent Res 2011;90:937-952. ⁾. The repair is characterized by a faster and low-cost method if compared to replacement of the entire restoration ^{( 3}3Raposo LHA, Neiva NA, Silva GR, Carlo HL, Mota AS, Prado CJ, et al.. Ceramic restoration repair: report of two cases. J Appl Oral Sci 2009;17:140-144. ^{, 4}4Kimmich, M, Stappert, C. Intraoral treatment of veneering porcelain chipping of fixed dental restorations: A review and clinical application, J Am Dent Assoc 2013;144:31-44. ^{, 5}5Reston EG, Filho SC, Arossi G, Cogo RB, Rocha CS, Closs LQ. Repairing ceramic restorations: final solution or alternative procedure? Oper Dent 2008;33:461-466. ⁾. This study has shown that using the correct surface treatment for each ceramic is the key for success in repair procedure. The methods here employed are traditional treatments used in dental clinic. Roughness with diamond bur might be considered the most practical among them because it does not require any additional precaution or protection of the patient than those traditionally used and does not need the use of other apparatus than the traditional burs. Etching with hydrofluoric acid needs complete rubber dam isolation of the teeth to be applied on, as it is irritating to oral tissues. The tribochemical process also needs rubber dam isolation for protecting the mouth from the sandblasted silica-coated aluminum oxide particles.

Within the limitations of this study, considering the evaluated materials and techniques, it may be concluded that diamond burs can be used as surface treatment for repairs in feldspathic and leucite-reinforced ceramics; hydrofluoric acid etching is indicated for repair of lithium disilicate-reinforced ceramic and tribochemical process in successfully used for repairs of leucite-reinforced ceramic. The success of surface treatment depends on the type of ceramic to which it is applied.

Acknowledgements

The authors would like to thank the Meridional Laboratory, Passo Fundo, RS, Brazil, for the valuable assistance with the sintering process of ceramics.

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