Lasers in Surgery and Medicine 47:602–607 (2015)
The Effect of Transmitted Er:YAG Laser Energy Through A Dental Ceramic on Different Types of Resin Cements Onjen Tak, DDS, PhD,1 Tugrul Sari, DDS, PhD,2 Meral Arslan Malkoc¸, DDS, PhD,3 Subutayhan Altintas, DDS, PhD,4 Aslihan Usumez, DDS, PhD,2 and Norbert Gutknecht, DDS, PhD5 1 Department of Prosthodontics, Faculty of Dentistry, Kocaeli University, Kocaeli, Turkey 2 Department of Prosthodontics, Faculty of Dentistry, Bezmialem Vakif University, Istanbul, Turkey 3 Department of Prosthodontics, Faculty of Dentistry, Inonu University, Malatya, Turkey 4 Department of Prosthodontics, Faculty of Dentistry, Karadeniz Technical University, Trabzon, Turkey 5 Department of Restorative Dentistry, Faculty of Dentistry, RWTH Aachen University, Aachen, Germany
Background and Objective: The laser debonding procedure of adhesively luted all-ceramic restorations is based on the ablation of resin cement due to the transmitted laser energy through the ceramic. The purpose of this study was to determine the effect of Er: YAG laser irradiation transmitted through a dental ceramic on five different resin cements. Materials and Methods: Five different resin cements were evaluated in this study: G-Cem LinkAce, Multilink Automix, Variolink II, Panavia F, and Rely X Unicem U100. Disc shaped resin cement specimens (n ¼ 10) were fabricated for each group. A ceramic disc was placed between the resin cement discs and the tip of the handpiece of Er:YAG laser device. The resin cement discs were irradiated through the ceramic and the volume of the resin cement discs were measured using a micro-CT system before and after Er:YAG laser irradiation. The volume loss of the resin cement discs was calculated and analyzed with one-way ANOVA and Tukey–HSD tests. Results: The highest volume loss was determined in G-Cem (1.1 0.6 mm3) and Multilink (1.3 0.1 mm3) (P < 0.05) groups, and the lowest volume loss was determined in Rely X (0.3 0.07 mm3), Variolink (0.4 0.2 mm3), and Panavia (0.6 0.2 mm3) groups (P < 0.05). All resin cements were affected by the laser irradiation resulting in the volume loss of the cement; however, there are significant differences among different resin cements. Conclusions: All the resin cements tested in this study were effected by the Er:YAG laser irradiation and there were significant differences among the resin cements with regard to ablation volume. Lasers Surg. Med. 47:602–607, 2015. ß 2015 Wiley Periodicals, Inc.
glass-ceramics (IPS e.max Press or CAD, Ivoclar Vivadent) with improved properties such as relatively high strength, translucency, biocompatibility, and adhesive bonding ability, are frequently used in different types of restorations (veneers, inlays, onlays, crowns, and 3-unit anterior fixed partial dentures), ensuring a minimally invasive approach, excellent function and esthetics [1,3,4]. Acidetching and resin luting techniques allow producing restorations with superior esthetic properties and excellent clinical performance [1,5]. Although these advantages, one of the major disadvantages of such adhesively luted ceramics is the difficult removal procedure and it is almost impossible to remove the adhesively cemented all-ceramic restoration in one piece with conventional removal techniques. If necessary, restoration removal is generally performed by cutting– grinding the restoration using rotary burs rather than potentially painful and disturbing manual or automatic crown-bridge removers which are being used by applying impacts to the restoration and meanwhile to the tooth inevitably in the removal direction to disrupt the bonding cement layer and pull out the restoration. However, it is a relatively challenging and time-consuming procedure and also has some risk about damaging underlying tooth structure because of the lack of color contrast among the ceramic–cement–tooth interfaces. In addition, loss of the restoration integrity prevents the reuse of the restoration which could be desirable in case of the misalignment of the restoration during cementation or unexpected early inflammatory pulpal responses. To overcome this problem, the use of pulsed lasers was recently introduced as an
Key words: adhesive cement; debonding; microCT INTRODUCTION In the last decades, many different types of ceramic materials and commercial all-ceramic systems have been developed to satisfy patients’ growing esthetic expectations and are widely used in esthetic dentistry for different indications [1,2]. Particularly, lithium disilicate ß 2015 Wiley Periodicals, Inc.
Conflict of Interest Disclosure: All authors have completed and submitted the ICMJE Form for Disclosure of Potential Conflicts of Interest and none were reported. Correspondence to: Dr. Tugrul Sari, DDS, PhD, Department of Prosthodontics, Bezmialem Vakif University, Faculty of Dentistry, Vatan Caddesi 34093 Fatih, Istanbul, Turkey. E-mail: [email protected] Accepted 22 June 2015 Published online 6 July 2015 in Wiley Online Library (wileyonlinelibrary.com). DOI 10.1002/lsm.22394
EFFECT OF Er:YAG LASER ON RESIN CEMENTS
alternative, more comfortable, safe, and conservative restoration removal method [6]. The laser debonding procedure was first described for debonding orthodontic ceramic brackets by Strobl et al. [7] in 1992. Since then, the use of different lasers such as CO2 [7–12], neodymium-doped yttrium aluminum garnet (Nd:YAG) [13–15], diode [16], Thulium:Ytterbium-Aluminium-Perovskite (Tm:YAP) [17], ytterbium fiber [18], and erbium-doped yttrium aluminum garnet (Er:YAG) [19,20] has been described and evaluated in the literature over the past two decades. However, there are only a few studies published in the literature about removing ceramic restorations such as laminate veneers and crown-bridge restorations using laser irradiation [6,21–27]. It is well known that, Er:YAG (2,940 nm) laser is capable to selectively ablate and remove composite resin material [28,29] while the sound tooth tissue is preserved during the procedure [30], due to the high absorption of the laser in composite resin and the difference between the ablation thresholds of composite resin and sound tooth tissues [6,27]. The debonding mechanism of ceramic restorations using the Er:YAG laser is mostly based on “thermal ablation” and “photoablation” [27]. Although the Er:YAG laser has a water-mediated photomechanical interaction during dental hard tissue ablation, it removes cured composite resin in a slightly different way, involving explosive vaporization followed by a hydrodynamic ejection [31,32]. During the irradiation of composite resin, the instant melting of the organic components creates large expansion forces due to the volume change of the material upon melting [32]. For the removal of a ceramic restoration, initially the Er:YAG laser energy is transmitted through the ceramic, and the resin cement absorbs the transmitted energy, whose amount depends on the ceramic type, thickness, and composition [6,27]. When enough cement is ablated through the ceramic, the restoration slides off the tooth surface in one piece or in parts depending on its pressure resistance [27]. Morford et al. [27] reported that lithium disilicate reinforced ceramic veneers transmitted roughly twice as much Er:YAG laser energy than leucide reinforced ceramic veneers at a comparable veneer thickness. Thus, the removal of the lithium disilicate veneers from the energy transmission perspective requires less initial laser energy. Sari et al. [6] reported different Er:YAG transmission ratios for different restorative ceramics and concluded that lithium disilicate-reinforced ceramic had the highest transmission ratio with 0.5 mm thickness, and feldspathic ceramic had the lowest with 1 mm thickness. Rechmann et al. [21] concluded that lithium disilicate ceramic specimens transmitted the highest percentage of energy (21% and 60%) at any given thickness (1.0, 1.5, 2.0, and 2.5 mm), followed by leucide reinforced ceramic and zirconium dioxide polycrystalline ceramic. In contrast with laser-ceramic interaction research topic, there is still no study published in the scientific literature about the effect of the Er:YAG laser on different types of resin cements. Therefore, the purpose of this study was to evaluate the effect of the transmitted Er:YAG laser energy through lithium disilicate reinforced dental ceramic on five
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different resin cements. It was hypothesized that there were statistically significant differences in the effect of Er:YAG laser on the resin cements tested in the current study. MATERIALS AND METHODS Five different composite resin cements: G-Cem LinkAce (GC Corp., Tokyo, Japan), Multilink N Automix and Variolink II (Ivoclar Vivadent, Schaan, Liechtenstein), Panavia F 2.0 (Kuraray Noritake Dental, Tokyo, Japan), RelyX Unicem U100 (3 M ESPE, St. Paul, MN) were evaluated in this study. Ten disc shaped samples with 0.5 mm thickness and 5 mm diameter were prepared for each group. Preparation of Resin Cement Samples The sample preparation was made as follows: Group 1(GC): In Group 1, a dual-curing self-adhesive resin cement (G-Cem LinkAce) with translucent shade in color was used to fabricate the samples. A 0.5 mm thick polytetrafluoro1 ethylene (Teflon ) plate mold with a 5 mm diameter central hole was used to prepare disc shaped resin cement samples. Two components of the resin cement were mixed using the auto-mixing tip supplied by the manufacturer and the central hole of the Teflon mold was carefully filled with resin cement to avoid entrapment of air porosities within the cement as far as possible. The Teflon plate was sandwiched between 1 mm thick glass plates and then placed on a white-colored sheet. The glass plates have flattened the cement surface, protected it from the oxygen inhibition, and standardized the irradiation distance. The cement was exposed to light through the upper side of the glass plate in contact with the curing light tip (8 mm diameter) for 20 seconds using an LED light source (1,000 mW/cm2; Elipar FreeLight 2; 3 M ESPE, St. Paul, MN). The plates were reversed so that the lower side of the plate was on the top. The cement was once again irradiated for the same irradiation duration. The light intensity of the LED curing unit was measured using a radiometer (Cure Rite Efos, model 8000, range: 0–1,000 mW/cm2; Efos, Inc., Mississauga, ON, Canada) between each sample. No polishing techniques were used to avoid the modification of the surfaces, which could potentially influence the results. Finally, the thicknesses of the samples were measured using a digital caliper (500–784, Mitutoyo Corp., Kawasaki, Japan) and specimens were stored in light-proof boxes at 378C with 100% humidity after the curing procedure to avoid further exposure to light. Group 2 (ML): In Group 2, a self-curing resin cement with light curing option (Multilink N Automix) and transparent shade in color was used to fabricate the samples. The sample preparation was performed using the same procedure described for Group 1. Group 3 (VL): In Group 3, a dual-curing resin cement (Variolink II) with transparent shade in color was used to fabricate the samples. Two component pastes of the cement were mixed with equal portions according to the manufacturer’s instructions and sample preparation process was performed using the same procedure described for Group 1. Group 4 (PF): In Group 4, a dual-curing and fluoridereleasing resin cement (Panavia F2.0) with transparent
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TABLE 1. The Application Parameters of Laser Irradiation Pulse energy
Pulse duration
600 mJ
1,000 ms (VLP)
Frequency
Power output
Energy density
Hand piece
Firing tip
Irradiation duration
2 Hz
1.2 W
45.4 J/cm2
R14 contact
Sapphire, 1.3 mm ø
1s
(light) shade in color, was used to fabricate the samples. Two component pastes of the cement was mixed with equal portions according to the manufacturer’s instructions and samples in this group were prepared using the same procedure described for Group 1. Group 5 (RX): In Group 5, a self-adhesive resin cement (RelyX Unicem U100) with translucent shade in color, was used to fabricate the samples. Two component pastes of the cement were mixed with equal portions according to the manufacturer’s instructions and sample preparation was performed using the same procedure described for Group 1. Ceramic Disc Preparation The ceramic discs, 5 mm in diameter and 1 mm in thickness, were prepared from a lithium-disilicate reinforced glass ceramic computer-aided design/computer-aided manufacturing (CAD/CAM) block (IPS e.max CAD/A2-HT, IvoclarVivadent, Liechtenstein), using a precise cutting machine (Mecatome T1800, Presi, Grenoble, France) and a slow-speed diamond saw (Isomet wafering blades, Buehler, IL) under water cooling. Later the ceramic discs were fired according to the manufacturer’s instructions, using a ceramic furnace (Programat P500/G2, Ivoclar-Vivadent, Liechtenstein) in order to achieve the final crystallization of the ceramic. Finally, the thicknesses and diameters of the samples were measured using a digital caliper (500–784, Mitutoyo Corp., Kawasaki, Japan) to check the sample dimensions. Irradiation Procedure The ceramic disc was placed between the resin cement samples and the tip of the contact handpiece (R14) of an Er:YAG laser device (Lightwalker, Fotona d.d., Ljubljana, Slovenia). A sapphire tip of 1.3 mm in diameter and 8 mm in length was used for the irradiation. The output of the laser device used in this study was set to 600 mJ 2 Hz (1.2 W) and 1,000 ms (VLP ¼ Very Long Pulse) pulse duration (Energy density ¼ 45.4 J/cm2) (Table 1). The output power of the device was checked and confirmed using a laser powermeter (Nova II, Ophir Optronics, Jerusalem, Israel). The resin cement discs were perpendicularly irradiated one by one through the ceramic disc with just two Er:YAG laser pulses without air or water spray. The samples were irradiated while the sapphire tip of the handpiece was at 1 mm distance to the ceramic disc surface with the aid of a custom made handpiece holder. The volume of the resin cement discs was measured using a micro-CT system (SkyScan, Bruker microCT, Kontich, Belgium) before and after the Er:YAG laser irradiation. The decrease in the volume of the resin cement discs was later calculated.
Statistical Analysis The results were statistically analyzed with one-way analysis of variance (ANOVA) and post-hoc Tukey’s honestly significant differences (HSD) tests (SPSS/PC, ver. 10.0, SPSS, Chicago, IL). RESULTS The results of the volume loss measurement of five groups are shown in Table 2. 3D Micro-CT graphs of a specimen before and after Er:YAG laser irradiation are shown in Figure 1A and B. The ablation crater due to Er: YAG laser irradiation can be easily detected in Figure 1B. The differences among the average volume loss values of the groups were statistically significant (ANOVA, P < 0.05). The results of ML (1.3 mm3 0.1 mm3) and GC (1.1 mm3 0.6 mm3) groups were comparable to each other and significantly higher than RX (0.3 mm3 0.07 mm3), VL (0.4 mm3 0.2 mm3), and PF (0.6 mm3 0.2 mm3) groups (Tukey’s HSD, P < 0.05) (Table 2). DISCUSSION The laser debonding procedure of all ceramic restorations is suggested to be a relatively easy and safe technique when compared to conventional techniques. The ceramic materials and dental hard tissues were evaluated by light microscopy after the debonding procedure and it was revealed that the bond between the ceramic restoration and the tooth is disrupted mainly at the ceramic/cement interface, leaving the majority of the inner surface of the ceramic veneer free of resin cement. Additionally, there were no ablation craters or even slight marks of ablation on the tooth surface [6,21,22,27]. Moreover, it was reported that laser debonding procedure does not change the chemical surface composition of dental ceramics [28]. During the debonding process of the all-ceramic restorations, laser energy is transmitted through the ceramic
TABLE 2. The Results of the Volume Loss Measurement of Five Different Resin Cement Materials Average volume loss SD (mm3)
Groups Group Group Group Group Group
1 2 3 4 5
(GC) (ML) (VL) (PF) (RX)
1.1 0.6A 1.3 0.1A 0.4 0.2B 0.6 0.2B 0.3 0.07B
The different superscript letters indicate statistically significant differences.
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Fig. 1. 3D Micro-CT graph of resin cement specimen (A) before and (B) after Er:YAG laser irradiation.
and then the resin cement absorbs the finally transmitted laser energy [27]. The debonding mechanism of all-ceramic restorations using Er:YAG laser is mostly based on thermal ablation and photoablation of the composite resin cement [27]. Explosive vaporization is the ablation mechanism of the cured composite resin, followed by a hydrodynamic ejection [31,32]. Theoretically, in photoinduced thermo-mechanical ablation process, the water in the media or within the material absorbs the energy, vaporizes and rapidly expands, causing subsurface pressure due to the expanding water vapor within the enclosed environment of the irradiated material [20,33]. During
composite resin ablation, the rapid melting of the organic components of resin creates large expansion forces due to the change in volume of the material upon melting [32]. When enough cement is ablated through the ceramic restoration, it slides off the tooth surface in one piece or in parts [27]. It is well known that the Er:YAG laser irradiation is capable of removing composite resin materials [28,29], and therefore, proposed to be used for the removal of all ceramic restorations [6,23–27] while minimizing the inadvertent removal of sound enamel/dentin [30] due to its potential to selectively ablate dental composite. However, there is no
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consensus on laser debonding treatment protocols and different power, pulse energy, and pulse duration parameters were reported in the literature. The settings used in our study (600 mJ 2 Hz [1.2 W], 1,000 ms pulse duration) were chosen and modified in order to simulate the rapid debonding protocol of ceramic brackets described by Mundethu et al. [20]. In the study by Mundethu et al., it was concluded that, Er:YAG laser can cause a photoablative debonding (blow-off process) of the ceramic brackets in just one pulse (in 95% of specimens) [20]. In the current study, the resin cements were irradiated with two laser pulses. We decided to use a long pulse duration since it is known to be less likely to invoke thermomechanical ablation in the enamel [20,33]. It is well known that, with the free-running pulsed laser systems, laser pulses with longer pulse durations results in lower peak power values than the pulses which have the same amount of energy but shorter pulse durations. By the selection of a long pulse duration (1,000 ms) instead of a short pulse duration, it could be possible to keep the ablative effect of laser energy restricted within the cement and ablate only the resin cement layer superficially, without any damage on the underlying hard tissues which need more peak power due to shorter pulse durations and more energy than the composite resins for the ablation. Morford et al. [27] reported, the FTIR spectroscopy of RelyX veneer bonding cement revealed that the cement shows a broad H2O/OH absorption band (wavenumber 3,750–3,640 and 3,600–3,400, respectively). In another study, Rechmann et al. [21] found that the FTIR spectra of the bonding cements (Variolink Veneer, Variolink II, Multilink and SpeedCEM) revealed strong peaks—most likely related to silica and a C═O peak—and demonstrated a broad H2O/OH absorption band (wavenumber 3,750–3,640 and 3,600–3,400, respectively), which coincides with the emission wavelength of an Er:YAG laser. Both of the researchers concluded that all tested bonding cements absorb the Er:YAG laser irradiation, and ablation of the cements is likely to occur when irradiated [21,27]. Further, Rechmann et al. [21] showed that, resin cements mostly require only small amounts of laser energy for deterioration or ablation. They also summarized that, typically all ceramic crowns transmit Er:YAG laser energy and the transmitted energy would be absorbed in the bonding cement resulting in the deterioration of the cement and the debonding of all-ceramic full contour crowns would be possible as a consequence. In the current study, the laser energy of 600 mJ was found sufficient for the ablation of tested resin cements, in accordance with previous studies [21,22,27]. In the current study, five different composite resin cements were used and all tested resin cements were affected by laser irradiation. After the Er:YAG laser irradiation, the ablation areas can be seen clearly in the 3D micro-CT models of the composite resin cements. The dimension of the ablation areas and the volume loss values statistically varied according to the resin cements (GC, ML, VL, PF, and RX) tested. The difference in dimension of the ablation areas and the volume should be originated
from the differences among the chemical compositions of the cements. Further studies are needed to clarify the origin of the differences among different resin cements. In addition, according to the results of this study, it could be hypothesized that different resin cements have their typical ablation thresholds. Instead of volume loss, the ablation threshold of resin cements which is defined as the minimum amount of energy required to start the ablation on the cement–ceramic interface could be much more important for and relevant with the definition of proper debonding procedure which aims to disrupt the resin cement layer without any thermal or mechanical side effect on the underlying hard tissues. The ablation thresholds of different resin cements and possible differences among them should be clarified with further studies as well. This study is one of the pre-clinical pioneer studies that investigates the effect of the Er:YAG laser on composite resin cements through ceramic restorations. The limitations of the current study are that only one ceramic material was used for energy transmission and only five composite resin cements were used for evaluating the interaction with the laser. In addition, the presented study was tested in an in vitro environment. A wider type of ceramic should be used to ensure that all kinds of restorations can be debonded using an Er:YAG laser and multiple resin cements should be tested to allow for the generalization of the results. Furthermore, in generally free-running pulsed commercial laser systems have a ramp-up period during the first ten pulses and the amount of energy seen in the display of the device and actual energy output do not matches. For this reason, first two pulses used in this study could be inconsistent with the settings mentioned before and this situation should be taken into consideration when evaluating the results of this study. CONCLUSIONS Within the limits of this study, the following conclusions were drawn: 1. All composite resin cements were affected by the laser irradiation resulting in the volume loss of the cement. 2. Volume loss varied according to the resin cements tested. Multilink Automix and G-Cem resin cements were statistically more affected by the Er:YAG laser irradiation than the other resin cements tested. REFERENCES 1. Fabbri G, Zarone F, Dellificorelli G, Cannistraro G, De Lorenzi M, Mosca A, Sorrentino R. Clinical evaluation of 860 anterior and posterior lithium disilicate restorations: Retrospective study with a mean follow-up of 3 years and a maximum observational period of 6 years. Int J Periodontics Res Dent 2014;34:165–177. 2. Blatz MB. Long-term clinical success of all-ceramic posterior restorations. Quintessence Int 2002;33:415–426. 3. Gehrt M, Wolfart S, Rafai N, Reich S, Edelhoff D. Clinical results of lithium-disilicate crowns after up to 9 years of service. Clin Oral Invest 2013;17:275–284. 4. Kern M, Sasse M, Wolfart S. Ten-year outcome of three-unit fixed dental prostheses made from monolithic lithiumdi-silicate ceramic. J Am Dent Assoc 2012;143:234–240.
EFFECT OF Er:YAG LASER ON RESIN CEMENTS 5. Dumfahrt H. Porcelain laminate veneers. A retrospective evaluation after 1 to 10 years of service Part 1: Clinical procedure. Int J Prosthodont 1999;12:505–513. 6. Sari T, Tuncel I, Usumez A, Gutknecht N. Transmission of Er: YAG laser through different dental ceramics. Photomed Laser Surg 2014;32:37–41. 7. Strobl K, Bahns TL, Willham L, Bishara SE, Stwalley WC. Laser-aided debonding of orthodontic ceramic brackets. Am J Orthod Dentofac Orthop 1992;101:152–158. 8. Rickabaugh JL, Marangoni RD, McCaffrey KK. Ceramic bracket debonding with the carbon dioxide laser. Am J Orthod Dentofac Orthop 1996;110:388–393. 9. Ma T, Marangoni RD, Flint W. In vitro comparison of debonding force and intrapulpal temperature changes during ceramic orthodontic bracket removal using a carbon dioxide laser. Am J Orthod Dentofac Orthop 1997;111:203–210. 10. Obata A, Tsumura T, Niwa K, Ashizawa Y, Deguchi T, Ito M. Super pulse CO2 laser for bracket bonding and debonding. Eur J Orthod 1999;21:193–198. 11. Iijima M, Yasuda Y, Muguruma T, Mizoguchi I. Effects of CO2 laser debonding of a ceramic bracket on the mechanical properties of enamel. Angle Orthod 2010;80:1029–1035. 12. Tehranchi A, Fekrazad R, Zafar M, Eslami B, Kalhori KA, Gutknecht N. Evaluation of the effects of CO2 laser on debonding of orthodontics porcelain brackets vs. the conventional method. Lasers Med Sci 2011;26:563–567. 13. Tocchio RM, Williams PT, Mayer FJ, Standing KG. Laser debonding of ceramic orthodontic brackets. Am J Orthod Dentofac Orthop 1993;10:155–162. 14. Han X, Liu X, Bai D, Meng Y, Huang L Nd:. YAG laser-aided ceramic brackets debonding: Effects on shear bond strength and enamel surface. Appl Surf Sci 2008;255:613–615. 15. Hayakawa K. Nd:YAG laser for debonding ceramic orthodontic brackets. Am J Orthod Dentofac Orthop 2005;128:638–647. 16. Feldon PJ, Murray PE, Burch JJ, Meister M, Freedman MA. Diode laser debonding of ceramic brackets. Am J Orthod Dentofac Orthop 2010;138:458–462. 17. Dostalova T, Jelinkova H, Sulc J, Nemec M, Jelinek M, Fibrich M, Michalik P, Miyagi M, Seydlova M. Ceramic bracket debonding by Tm:YAP laser irradiation. Photomed Laser Surg 2011;29:477–484. 18. Sarp AS, Gulsoy M. Ceramic bracket debonding with ytterbium fiber laser. Lasers Med Sci 2011;26:577–584. 19. Oztoprak MO, Nalbantgil D, Erdem AS, Tozlu M, Arun T. Debonding of ceramic brackets by a new scanning laser method. Am J Orthod Dentofac Orthop 2010;138:195–200.
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20. Mundethu AR, Gutknecht N, Franzen R. Rapid debonding of polycrystalline ceramic orthodontic brackets with an Er: YAG laser: An in vitro study. Lasers Med Sci 2014;29: 1551–1556. 21. Rechmann P, Buu NCH, Rechmann BMT, Le CQ, Finzen FC, Featherstone JDB. Laser all-ceramic crown removal-A laboratory proof-of-principle study-Phase 1 material characteristics. Lasers Surg Med 2014;46:628–635. 22. Rechmann P, Buu NCH, Rechmann BMT, Finzen FC. Laser all-ceramic crown removal-a laboratory proof-of-principle study-Phase 2 crown debonding time. Lasers Surg Med 2014;46:636–643. 23. Kursoglu P, Gursoy H. Removal of fractured laminate veneers with Er:YAG laser: Report of two cases. Photomed Laser Surg 2013;31:41–43. 24. Cranska JP. Removing all-ceramic restorations with lasers. Dent Today 2013;32:101–104. 25. Oztoprak MO, Tozlu M, Iseri U, Ulkur F, Arun T. Effects of different application durations of scanning laser method on debonding strength of laminate veneers. Lasers Med Sci 2012;27:713–716. 26. Van As G. Laser removal of porcelain veneers. Dent Today 2012;31:84–89. 27. Morford CK, Buu NC, Rechmann BM, Finzen FC, Sharma AB, Rechmann P Er:. YAG laser debonding of porcelain veneers. Lasers Surg Med 2011;43:965–974. 28. Pich O, Franzen R, Gutknecht N, Wolfart S. Laser treatment of dental ceramic/cement layers: Transmitted energy, temperature effects and surface characterization. Lasers Med Sci 2015;30:591–597. 29. Gimbel CB. Hard tissue laser procedures. Dent Clin N Am 2000;44:931–953. 30. Correa-Afonso AM, Palma-Dibb RG, P ecora JD. Composite filling removal with erbium:yttrium-aluminum-garnet laser: Morphological analyses. Lasers Med Sci 2010;25:1–7. 31. Fried D, Zuerlein MJ, Featherstone DB, Seka W, Duhn C, McCormack SM. IR laser ablation of dental enamel: Mechanistic dependence on the primary absorber. Appl Surf Sci 1998;127–129:852–856. 32. Lizarelli RFZ, Moriyama LT, Pelino JEP, Bagnato VS. Ablation rate of morphological aspects of composite resin exposed to Er:YAG laser. J Oral Laser App 2005;5:151–160. 33. Apel C, Franzen R, Meister J, Sarrafzadegan H, Thelen S, Gutknecht N. Influence of the pulse duration of an Er:YAG laser system on the ablation threshold of dental enamel. Lasers Med Sci 2002;17:253–257.
The Effect of Transmitted Er:YAG Laser Energy Through A Dental Ceramic on Different Types of Resin Cements Onjen Tak, DDS, PhD,1 Tugrul Sari, DDS, PhD,2 Meral Arslan Malkoc¸, DDS, PhD,3 Subutayhan Altintas, DDS, PhD,4 Aslihan Usumez, DDS, PhD,2 and Norbert Gutknecht, DDS, PhD5 1 Department of Prosthodontics, Faculty of Dentistry, Kocaeli University, Kocaeli, Turkey 2 Department of Prosthodontics, Faculty of Dentistry, Bezmialem Vakif University, Istanbul, Turkey 3 Department of Prosthodontics, Faculty of Dentistry, Inonu University, Malatya, Turkey 4 Department of Prosthodontics, Faculty of Dentistry, Karadeniz Technical University, Trabzon, Turkey 5 Department of Restorative Dentistry, Faculty of Dentistry, RWTH Aachen University, Aachen, Germany
Background and Objective: The laser debonding procedure of adhesively luted all-ceramic restorations is based on the ablation of resin cement due to the transmitted laser energy through the ceramic. The purpose of this study was to determine the effect of Er: YAG laser irradiation transmitted through a dental ceramic on five different resin cements. Materials and Methods: Five different resin cements were evaluated in this study: G-Cem LinkAce, Multilink Automix, Variolink II, Panavia F, and Rely X Unicem U100. Disc shaped resin cement specimens (n ¼ 10) were fabricated for each group. A ceramic disc was placed between the resin cement discs and the tip of the handpiece of Er:YAG laser device. The resin cement discs were irradiated through the ceramic and the volume of the resin cement discs were measured using a micro-CT system before and after Er:YAG laser irradiation. The volume loss of the resin cement discs was calculated and analyzed with one-way ANOVA and Tukey–HSD tests. Results: The highest volume loss was determined in G-Cem (1.1 0.6 mm3) and Multilink (1.3 0.1 mm3) (P < 0.05) groups, and the lowest volume loss was determined in Rely X (0.3 0.07 mm3), Variolink (0.4 0.2 mm3), and Panavia (0.6 0.2 mm3) groups (P < 0.05). All resin cements were affected by the laser irradiation resulting in the volume loss of the cement; however, there are significant differences among different resin cements. Conclusions: All the resin cements tested in this study were effected by the Er:YAG laser irradiation and there were significant differences among the resin cements with regard to ablation volume. Lasers Surg. Med. 47:602–607, 2015. ß 2015 Wiley Periodicals, Inc.
glass-ceramics (IPS e.max Press or CAD, Ivoclar Vivadent) with improved properties such as relatively high strength, translucency, biocompatibility, and adhesive bonding ability, are frequently used in different types of restorations (veneers, inlays, onlays, crowns, and 3-unit anterior fixed partial dentures), ensuring a minimally invasive approach, excellent function and esthetics [1,3,4]. Acidetching and resin luting techniques allow producing restorations with superior esthetic properties and excellent clinical performance [1,5]. Although these advantages, one of the major disadvantages of such adhesively luted ceramics is the difficult removal procedure and it is almost impossible to remove the adhesively cemented all-ceramic restoration in one piece with conventional removal techniques. If necessary, restoration removal is generally performed by cutting– grinding the restoration using rotary burs rather than potentially painful and disturbing manual or automatic crown-bridge removers which are being used by applying impacts to the restoration and meanwhile to the tooth inevitably in the removal direction to disrupt the bonding cement layer and pull out the restoration. However, it is a relatively challenging and time-consuming procedure and also has some risk about damaging underlying tooth structure because of the lack of color contrast among the ceramic–cement–tooth interfaces. In addition, loss of the restoration integrity prevents the reuse of the restoration which could be desirable in case of the misalignment of the restoration during cementation or unexpected early inflammatory pulpal responses. To overcome this problem, the use of pulsed lasers was recently introduced as an
Key words: adhesive cement; debonding; microCT INTRODUCTION In the last decades, many different types of ceramic materials and commercial all-ceramic systems have been developed to satisfy patients’ growing esthetic expectations and are widely used in esthetic dentistry for different indications [1,2]. Particularly, lithium disilicate ß 2015 Wiley Periodicals, Inc.
Conflict of Interest Disclosure: All authors have completed and submitted the ICMJE Form for Disclosure of Potential Conflicts of Interest and none were reported. Correspondence to: Dr. Tugrul Sari, DDS, PhD, Department of Prosthodontics, Bezmialem Vakif University, Faculty of Dentistry, Vatan Caddesi 34093 Fatih, Istanbul, Turkey. E-mail: [email protected] Accepted 22 June 2015 Published online 6 July 2015 in Wiley Online Library (wileyonlinelibrary.com). DOI 10.1002/lsm.22394
EFFECT OF Er:YAG LASER ON RESIN CEMENTS
alternative, more comfortable, safe, and conservative restoration removal method [6]. The laser debonding procedure was first described for debonding orthodontic ceramic brackets by Strobl et al. [7] in 1992. Since then, the use of different lasers such as CO2 [7–12], neodymium-doped yttrium aluminum garnet (Nd:YAG) [13–15], diode [16], Thulium:Ytterbium-Aluminium-Perovskite (Tm:YAP) [17], ytterbium fiber [18], and erbium-doped yttrium aluminum garnet (Er:YAG) [19,20] has been described and evaluated in the literature over the past two decades. However, there are only a few studies published in the literature about removing ceramic restorations such as laminate veneers and crown-bridge restorations using laser irradiation [6,21–27]. It is well known that, Er:YAG (2,940 nm) laser is capable to selectively ablate and remove composite resin material [28,29] while the sound tooth tissue is preserved during the procedure [30], due to the high absorption of the laser in composite resin and the difference between the ablation thresholds of composite resin and sound tooth tissues [6,27]. The debonding mechanism of ceramic restorations using the Er:YAG laser is mostly based on “thermal ablation” and “photoablation” [27]. Although the Er:YAG laser has a water-mediated photomechanical interaction during dental hard tissue ablation, it removes cured composite resin in a slightly different way, involving explosive vaporization followed by a hydrodynamic ejection [31,32]. During the irradiation of composite resin, the instant melting of the organic components creates large expansion forces due to the volume change of the material upon melting [32]. For the removal of a ceramic restoration, initially the Er:YAG laser energy is transmitted through the ceramic, and the resin cement absorbs the transmitted energy, whose amount depends on the ceramic type, thickness, and composition [6,27]. When enough cement is ablated through the ceramic, the restoration slides off the tooth surface in one piece or in parts depending on its pressure resistance [27]. Morford et al. [27] reported that lithium disilicate reinforced ceramic veneers transmitted roughly twice as much Er:YAG laser energy than leucide reinforced ceramic veneers at a comparable veneer thickness. Thus, the removal of the lithium disilicate veneers from the energy transmission perspective requires less initial laser energy. Sari et al. [6] reported different Er:YAG transmission ratios for different restorative ceramics and concluded that lithium disilicate-reinforced ceramic had the highest transmission ratio with 0.5 mm thickness, and feldspathic ceramic had the lowest with 1 mm thickness. Rechmann et al. [21] concluded that lithium disilicate ceramic specimens transmitted the highest percentage of energy (21% and 60%) at any given thickness (1.0, 1.5, 2.0, and 2.5 mm), followed by leucide reinforced ceramic and zirconium dioxide polycrystalline ceramic. In contrast with laser-ceramic interaction research topic, there is still no study published in the scientific literature about the effect of the Er:YAG laser on different types of resin cements. Therefore, the purpose of this study was to evaluate the effect of the transmitted Er:YAG laser energy through lithium disilicate reinforced dental ceramic on five
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different resin cements. It was hypothesized that there were statistically significant differences in the effect of Er:YAG laser on the resin cements tested in the current study. MATERIALS AND METHODS Five different composite resin cements: G-Cem LinkAce (GC Corp., Tokyo, Japan), Multilink N Automix and Variolink II (Ivoclar Vivadent, Schaan, Liechtenstein), Panavia F 2.0 (Kuraray Noritake Dental, Tokyo, Japan), RelyX Unicem U100 (3 M ESPE, St. Paul, MN) were evaluated in this study. Ten disc shaped samples with 0.5 mm thickness and 5 mm diameter were prepared for each group. Preparation of Resin Cement Samples The sample preparation was made as follows: Group 1(GC): In Group 1, a dual-curing self-adhesive resin cement (G-Cem LinkAce) with translucent shade in color was used to fabricate the samples. A 0.5 mm thick polytetrafluoro1 ethylene (Teflon ) plate mold with a 5 mm diameter central hole was used to prepare disc shaped resin cement samples. Two components of the resin cement were mixed using the auto-mixing tip supplied by the manufacturer and the central hole of the Teflon mold was carefully filled with resin cement to avoid entrapment of air porosities within the cement as far as possible. The Teflon plate was sandwiched between 1 mm thick glass plates and then placed on a white-colored sheet. The glass plates have flattened the cement surface, protected it from the oxygen inhibition, and standardized the irradiation distance. The cement was exposed to light through the upper side of the glass plate in contact with the curing light tip (8 mm diameter) for 20 seconds using an LED light source (1,000 mW/cm2; Elipar FreeLight 2; 3 M ESPE, St. Paul, MN). The plates were reversed so that the lower side of the plate was on the top. The cement was once again irradiated for the same irradiation duration. The light intensity of the LED curing unit was measured using a radiometer (Cure Rite Efos, model 8000, range: 0–1,000 mW/cm2; Efos, Inc., Mississauga, ON, Canada) between each sample. No polishing techniques were used to avoid the modification of the surfaces, which could potentially influence the results. Finally, the thicknesses of the samples were measured using a digital caliper (500–784, Mitutoyo Corp., Kawasaki, Japan) and specimens were stored in light-proof boxes at 378C with 100% humidity after the curing procedure to avoid further exposure to light. Group 2 (ML): In Group 2, a self-curing resin cement with light curing option (Multilink N Automix) and transparent shade in color was used to fabricate the samples. The sample preparation was performed using the same procedure described for Group 1. Group 3 (VL): In Group 3, a dual-curing resin cement (Variolink II) with transparent shade in color was used to fabricate the samples. Two component pastes of the cement were mixed with equal portions according to the manufacturer’s instructions and sample preparation process was performed using the same procedure described for Group 1. Group 4 (PF): In Group 4, a dual-curing and fluoridereleasing resin cement (Panavia F2.0) with transparent
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TABLE 1. The Application Parameters of Laser Irradiation Pulse energy
Pulse duration
600 mJ
1,000 ms (VLP)
Frequency
Power output
Energy density
Hand piece
Firing tip
Irradiation duration
2 Hz
1.2 W
45.4 J/cm2
R14 contact
Sapphire, 1.3 mm ø
1s
(light) shade in color, was used to fabricate the samples. Two component pastes of the cement was mixed with equal portions according to the manufacturer’s instructions and samples in this group were prepared using the same procedure described for Group 1. Group 5 (RX): In Group 5, a self-adhesive resin cement (RelyX Unicem U100) with translucent shade in color, was used to fabricate the samples. Two component pastes of the cement were mixed with equal portions according to the manufacturer’s instructions and sample preparation was performed using the same procedure described for Group 1. Ceramic Disc Preparation The ceramic discs, 5 mm in diameter and 1 mm in thickness, were prepared from a lithium-disilicate reinforced glass ceramic computer-aided design/computer-aided manufacturing (CAD/CAM) block (IPS e.max CAD/A2-HT, IvoclarVivadent, Liechtenstein), using a precise cutting machine (Mecatome T1800, Presi, Grenoble, France) and a slow-speed diamond saw (Isomet wafering blades, Buehler, IL) under water cooling. Later the ceramic discs were fired according to the manufacturer’s instructions, using a ceramic furnace (Programat P500/G2, Ivoclar-Vivadent, Liechtenstein) in order to achieve the final crystallization of the ceramic. Finally, the thicknesses and diameters of the samples were measured using a digital caliper (500–784, Mitutoyo Corp., Kawasaki, Japan) to check the sample dimensions. Irradiation Procedure The ceramic disc was placed between the resin cement samples and the tip of the contact handpiece (R14) of an Er:YAG laser device (Lightwalker, Fotona d.d., Ljubljana, Slovenia). A sapphire tip of 1.3 mm in diameter and 8 mm in length was used for the irradiation. The output of the laser device used in this study was set to 600 mJ 2 Hz (1.2 W) and 1,000 ms (VLP ¼ Very Long Pulse) pulse duration (Energy density ¼ 45.4 J/cm2) (Table 1). The output power of the device was checked and confirmed using a laser powermeter (Nova II, Ophir Optronics, Jerusalem, Israel). The resin cement discs were perpendicularly irradiated one by one through the ceramic disc with just two Er:YAG laser pulses without air or water spray. The samples were irradiated while the sapphire tip of the handpiece was at 1 mm distance to the ceramic disc surface with the aid of a custom made handpiece holder. The volume of the resin cement discs was measured using a micro-CT system (SkyScan, Bruker microCT, Kontich, Belgium) before and after the Er:YAG laser irradiation. The decrease in the volume of the resin cement discs was later calculated.
Statistical Analysis The results were statistically analyzed with one-way analysis of variance (ANOVA) and post-hoc Tukey’s honestly significant differences (HSD) tests (SPSS/PC, ver. 10.0, SPSS, Chicago, IL). RESULTS The results of the volume loss measurement of five groups are shown in Table 2. 3D Micro-CT graphs of a specimen before and after Er:YAG laser irradiation are shown in Figure 1A and B. The ablation crater due to Er: YAG laser irradiation can be easily detected in Figure 1B. The differences among the average volume loss values of the groups were statistically significant (ANOVA, P < 0.05). The results of ML (1.3 mm3 0.1 mm3) and GC (1.1 mm3 0.6 mm3) groups were comparable to each other and significantly higher than RX (0.3 mm3 0.07 mm3), VL (0.4 mm3 0.2 mm3), and PF (0.6 mm3 0.2 mm3) groups (Tukey’s HSD, P < 0.05) (Table 2). DISCUSSION The laser debonding procedure of all ceramic restorations is suggested to be a relatively easy and safe technique when compared to conventional techniques. The ceramic materials and dental hard tissues were evaluated by light microscopy after the debonding procedure and it was revealed that the bond between the ceramic restoration and the tooth is disrupted mainly at the ceramic/cement interface, leaving the majority of the inner surface of the ceramic veneer free of resin cement. Additionally, there were no ablation craters or even slight marks of ablation on the tooth surface [6,21,22,27]. Moreover, it was reported that laser debonding procedure does not change the chemical surface composition of dental ceramics [28]. During the debonding process of the all-ceramic restorations, laser energy is transmitted through the ceramic
TABLE 2. The Results of the Volume Loss Measurement of Five Different Resin Cement Materials Average volume loss SD (mm3)
Groups Group Group Group Group Group
1 2 3 4 5
(GC) (ML) (VL) (PF) (RX)
1.1 0.6A 1.3 0.1A 0.4 0.2B 0.6 0.2B 0.3 0.07B
The different superscript letters indicate statistically significant differences.
EFFECT OF Er:YAG LASER ON RESIN CEMENTS
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Fig. 1. 3D Micro-CT graph of resin cement specimen (A) before and (B) after Er:YAG laser irradiation.
and then the resin cement absorbs the finally transmitted laser energy [27]. The debonding mechanism of all-ceramic restorations using Er:YAG laser is mostly based on thermal ablation and photoablation of the composite resin cement [27]. Explosive vaporization is the ablation mechanism of the cured composite resin, followed by a hydrodynamic ejection [31,32]. Theoretically, in photoinduced thermo-mechanical ablation process, the water in the media or within the material absorbs the energy, vaporizes and rapidly expands, causing subsurface pressure due to the expanding water vapor within the enclosed environment of the irradiated material [20,33]. During
composite resin ablation, the rapid melting of the organic components of resin creates large expansion forces due to the change in volume of the material upon melting [32]. When enough cement is ablated through the ceramic restoration, it slides off the tooth surface in one piece or in parts [27]. It is well known that the Er:YAG laser irradiation is capable of removing composite resin materials [28,29], and therefore, proposed to be used for the removal of all ceramic restorations [6,23–27] while minimizing the inadvertent removal of sound enamel/dentin [30] due to its potential to selectively ablate dental composite. However, there is no
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consensus on laser debonding treatment protocols and different power, pulse energy, and pulse duration parameters were reported in the literature. The settings used in our study (600 mJ 2 Hz [1.2 W], 1,000 ms pulse duration) were chosen and modified in order to simulate the rapid debonding protocol of ceramic brackets described by Mundethu et al. [20]. In the study by Mundethu et al., it was concluded that, Er:YAG laser can cause a photoablative debonding (blow-off process) of the ceramic brackets in just one pulse (in 95% of specimens) [20]. In the current study, the resin cements were irradiated with two laser pulses. We decided to use a long pulse duration since it is known to be less likely to invoke thermomechanical ablation in the enamel [20,33]. It is well known that, with the free-running pulsed laser systems, laser pulses with longer pulse durations results in lower peak power values than the pulses which have the same amount of energy but shorter pulse durations. By the selection of a long pulse duration (1,000 ms) instead of a short pulse duration, it could be possible to keep the ablative effect of laser energy restricted within the cement and ablate only the resin cement layer superficially, without any damage on the underlying hard tissues which need more peak power due to shorter pulse durations and more energy than the composite resins for the ablation. Morford et al. [27] reported, the FTIR spectroscopy of RelyX veneer bonding cement revealed that the cement shows a broad H2O/OH absorption band (wavenumber 3,750–3,640 and 3,600–3,400, respectively). In another study, Rechmann et al. [21] found that the FTIR spectra of the bonding cements (Variolink Veneer, Variolink II, Multilink and SpeedCEM) revealed strong peaks—most likely related to silica and a C═O peak—and demonstrated a broad H2O/OH absorption band (wavenumber 3,750–3,640 and 3,600–3,400, respectively), which coincides with the emission wavelength of an Er:YAG laser. Both of the researchers concluded that all tested bonding cements absorb the Er:YAG laser irradiation, and ablation of the cements is likely to occur when irradiated [21,27]. Further, Rechmann et al. [21] showed that, resin cements mostly require only small amounts of laser energy for deterioration or ablation. They also summarized that, typically all ceramic crowns transmit Er:YAG laser energy and the transmitted energy would be absorbed in the bonding cement resulting in the deterioration of the cement and the debonding of all-ceramic full contour crowns would be possible as a consequence. In the current study, the laser energy of 600 mJ was found sufficient for the ablation of tested resin cements, in accordance with previous studies [21,22,27]. In the current study, five different composite resin cements were used and all tested resin cements were affected by laser irradiation. After the Er:YAG laser irradiation, the ablation areas can be seen clearly in the 3D micro-CT models of the composite resin cements. The dimension of the ablation areas and the volume loss values statistically varied according to the resin cements (GC, ML, VL, PF, and RX) tested. The difference in dimension of the ablation areas and the volume should be originated
from the differences among the chemical compositions of the cements. Further studies are needed to clarify the origin of the differences among different resin cements. In addition, according to the results of this study, it could be hypothesized that different resin cements have their typical ablation thresholds. Instead of volume loss, the ablation threshold of resin cements which is defined as the minimum amount of energy required to start the ablation on the cement–ceramic interface could be much more important for and relevant with the definition of proper debonding procedure which aims to disrupt the resin cement layer without any thermal or mechanical side effect on the underlying hard tissues. The ablation thresholds of different resin cements and possible differences among them should be clarified with further studies as well. This study is one of the pre-clinical pioneer studies that investigates the effect of the Er:YAG laser on composite resin cements through ceramic restorations. The limitations of the current study are that only one ceramic material was used for energy transmission and only five composite resin cements were used for evaluating the interaction with the laser. In addition, the presented study was tested in an in vitro environment. A wider type of ceramic should be used to ensure that all kinds of restorations can be debonded using an Er:YAG laser and multiple resin cements should be tested to allow for the generalization of the results. Furthermore, in generally free-running pulsed commercial laser systems have a ramp-up period during the first ten pulses and the amount of energy seen in the display of the device and actual energy output do not matches. For this reason, first two pulses used in this study could be inconsistent with the settings mentioned before and this situation should be taken into consideration when evaluating the results of this study. CONCLUSIONS Within the limits of this study, the following conclusions were drawn: 1. All composite resin cements were affected by the laser irradiation resulting in the volume loss of the cement. 2. Volume loss varied according to the resin cements tested. Multilink Automix and G-Cem resin cements were statistically more affected by the Er:YAG laser irradiation than the other resin cements tested. REFERENCES 1. Fabbri G, Zarone F, Dellificorelli G, Cannistraro G, De Lorenzi M, Mosca A, Sorrentino R. Clinical evaluation of 860 anterior and posterior lithium disilicate restorations: Retrospective study with a mean follow-up of 3 years and a maximum observational period of 6 years. Int J Periodontics Res Dent 2014;34:165–177. 2. Blatz MB. Long-term clinical success of all-ceramic posterior restorations. Quintessence Int 2002;33:415–426. 3. Gehrt M, Wolfart S, Rafai N, Reich S, Edelhoff D. Clinical results of lithium-disilicate crowns after up to 9 years of service. Clin Oral Invest 2013;17:275–284. 4. Kern M, Sasse M, Wolfart S. Ten-year outcome of three-unit fixed dental prostheses made from monolithic lithiumdi-silicate ceramic. J Am Dent Assoc 2012;143:234–240.
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