Lasers Med Sci DOI 10.1007/s10103-014-1682-5
Porcelain laminate veneer conditioning for orthodontic bonding: SEM-EDX analysis Sertac Aksakalli & Zehra Ileri & Tevfik Yavuz & Meral Arslan Malkoc & Nilgun Ozturk
Received: 13 December 2013 / Accepted: 17 October 2014 # Springer-Verlag London 2014
Abstract The purpose of this in vitro study was to evaluate and compare the effects of different surface treatments and laser irradiation on the bond strength of brackets bonded to porcelain laminate veneer. Porcelain laminate veneer specimens were embedded in the centers of acrylic resin blocks. Thirty-nine teeth were used for shear bond strength testing and the remaining three (one tooth for each group) were used for evaluation of the debonded bracket interface. Specimens were randomly divided into three groups, each containing 13 specimens. The details of the groups are as follows: Group SB, sandblasting with alumina particles (50 μm); Group HFA, 9.6 % hydrofluoric acid etching; Group ER, erbium-doped yttrium–aluminum–garnet (Er: YAG) irradiation (from 1 mm distance, 2 W, 10 Hz for 10 s). After conditioning, the upper central brackets were bonded to the porcelain surfaces. Porcelain laminate veneers were examined under stereomicroscope for adhesive remnant index and surface damage after debonding. The highest shear bond strength values were obtained with Group HFA (10.8±3.8 MPa) and Group ER (9.3 ±1.5 MPa), whereas Group SB revealed the lowest values. Scanning electron microscopy energy-dispersive X-ray (SEM-EDX) analysis revealed that the silicon level in the porcelain decreased S. Aksakalli (*) Department of Orthodontics, Bezmialem Vakif University, Istanbul, Turkey e-mail: [email protected]
Z. Ileri Department of Orthodontics, Selcuk University, Konya, Turkey T. Yavuz Department of Prosthodontics, Abant Izzet Baysal University, Bolu, Turkey M. A. Malkoc Department of Prosthodontics, Inonu University, Malatya, Turkey N. Ozturk Department of Prosthodontics, Selcuk University, Konya, Turkey
after debonding in all groups. The sandblasting method did not demonstrate any ideal bond strength values; however, the 9.6 % hydrofluoric acid etching and Er: YAG laser did. There were no significant differences among all groups in terms of laminate surface damages. The Er: YAG laser therefore can be selected for ideal bond strength and minimal damage to porcelain laminates. Keywords Laser . Laminate . Orthodontics . Bonding . Dentistry
Introduction There is an increasing demand for orthodontic treatment in adults, and orthodontists are more interested in bonding brackets to porcelain . Until now, different surface treatment methods have been used, including sandblasting (SB) , hydrofluoric acid (HFA) application , and deglazing of the porcelain . There are several advantages and disadvantages of these methods. HFA application can provide adequate shear bond strength (SBS) but HF can be dangerous when it comes into contact with oral soft tissues, and it must be handled carefully . Other surface roughness methods can be assumed for this reason to induce similar or greater surface roughness on porcelains. Another promising technique for the surface treatment of porcelains is laser irradiation. After the introduction of the ruby laser in 1960, different types of lasers have been developed . Some lasers used in orthodontics are erbium-doped yttrium–aluminum– garnet (Er: YAG), neodymium-doped yttrium–aluminum–garnet (Nd: YAG), and erbium-doped yttrium–scandium–gallium–garnet (Er,Cr: YSGG). These kinds of lasers have been used for enamel conditioning to bond brackets and studies of these lasers have revealed good results [6, 7]. However, there is no consensus in the literature regarding the best surface conditioning method to produce optimal bond strength based on the brackets and porcelain or
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porcelain laminate veneers (PLV) used. Therefore, there is still a need to compare surface treatment methods. Er: YAG lasers that are capable of reducing dentinal hypersensitivity, treating caries and periodontal problems, removing restorations, and providing laser-induced etching have been found to be an alternative to acid etching for enamel and dentine surfaces [8, 9]. They can also be used for bleaching and disinfection of the tooth and dental ceramics . There are few studies reporting the effects of lasers on dental ceramics. Pich et al. stated that Er: YAG lasers do not change the chemical surface composition of dental ceramics and can therefore be used for dental ceramics . In a similar study, Topcuoglu et al. stated that Er: YAG laser application did not allow etching on porcelain surfaces . The laser debonding process was initially studied for debonding of orthodontic ceramic brackets . Laser debonding is favorable for ceramics and teeth. It was shown that there was no damage to the tooth from the laser debonding and that the main debonding area was at the ceramic–cement contact area . This kind of application did not differ from the chemical surface compositions of ceramics . The brackets and the materials used for bonding brackets to PLV do not contain any silicon molecules. Measured silicon levels on brackets will define the passage of silicon from PLV to the brackets. So, we can compare the effects of different etching methods on molecular level. In the literature, there is nothing this type of study comparing molecular changes after debonding. Since there is little information about lasers and porcelain surface treatment methods, the objectives of this study were, firstly, to resolve the lack of studies simulating clinical situations in which PLV patients need orthodontic treatment; secondly, to evaluate the SBS of orthodontic brackets to porcelain surfaces after conditioning by Er: YAG laser, sandblasting, and HFA application; thirdly, to determine the mineral composition of debonded bracket interfaces with a scanning electron microscope (SEM) and energy-dispersive X-ray spectrometry (EDX); and lastly, to report any PLV surface damage after debonding all the groups. The null hypothesis was that Er: YAG laser treatment would result in SBS that is comparable to that of air abrasion and acid-etching surface treatment methods.
Materials and methods Forty-two maxillary central incisor teeth extracted for periodontal reasons were used in this study. The teeth were stored in distilled water for a maximum of 1 month. To avoid bacterial growth, the water was changed weekly . The teeth were free of caries, cracks, abrasions, and staining as assessed by visual examination. Thirty-nine teeth were used for SBS testing, and the remaining three (one tooth from each group) were used for SEM and EDX evaluation of the debonded bracket interface. All teeth were sectioned 2 mm below the cementoenamel junction with a slow-speed diamond saw sectioning machine
(IsoMet; Buehler Ltd., Lake Bluff, IL, USA), and the crowns were embedded in autopolymerizing acrylic (Imicryl SC, Imicryl Dis Malz AS, Konya, Turkey) with the labial surfaces facing up. Teeth were prepared with diamond rotary cutting instruments of a veneer preparation set (Freiburger preparation set; Komet Dental, Gebr Brasseler GmbH & Co, Lemgo, Germany). Teeth were prepared freehand by one clinician. The facial surfaces of the teeth were prepared to accommodate veneers of equal thickness. A 0.5-mm facial reduction was performed with an incisal bevel preparation. IPS Empress 2 (Ivoclar Vivadent, Schaan, Liechtenstein) was used for ceramic veneer restorations, and all procedures were performed with IPS Empress 2 materials and protocol. PLVs were luted according to the manufacturer’s instructions. Variolink 2 (Ivoclar Vivadent, Schaan, Liechtenstein) was used for cementation. Photopolymerization was performed with a light-polymerizing unit (Hilux 350; Express Dental Products, Toronto, Canada) for 40 s for mesial, distal, and incisal surfaces. After cementation and bonding brackets, specimens were thermocycled for 1000 cycles between 5 and 55 °C using a dwell time of 30 s. Thirty-nine teeth, 13 for each group, were randomly assigned as follows: In Group SB, the buccal surfaces of the porcelain were sandblasted at 65–70 psi for 10 s with aluminum oxide (GAC International Inc., New York, USA) with a particle size of 50 μm. The sandblasting device (Microetcher II, Danville Engineering, CA, USA) was directed perpendicular to the porcelain surface at a distance of 10 mm. The sandblasted samples were rinsed for 15 s by using an air–water spray to remove all particles from the porcelain surface. To prevent unnecessary sandblasting, acrylic resin with a 4×6-mm hole was placed on the porcelain surface. The upper central brackets (Dentaurum, Ispringen, Germany) were bonded to the porcelain surfaces by a no-mix composite (Unite, 3M Unitek, CA, USA) according to the manufacturer’s instructions by using an index that made bracket slots parallel to the horizontal plane. In Group ER, the porcelain surfaces were irradiated with an Er: YAG laser (Fotona, Ljubljana, Slovenia) with a 2 W power output at a rate of 10 Hz for 10 s. The laser irradiation of all the specimens was performed by the same operator. The laser parameters were as follows: a pulse energy of 200 mJ, power of 2 W, a 100-μs pulse length, pulses per second of 10 Hz, and an energy density of 25.31 J/cm2. Diameter of the tip was 1 mm. The levels for air and water were 90 and 80 %, respectively. The laser was directed perpendicular to the porcelain surface at a distance of 1 mm. To prevent unnecessary irradiation, acrylic resin with a 4×6-mm hole was placed on the porcelain surface. The orthodontic brackets were bonded to the porcelain surfaces using the same method as that for Group SB. In Group HFA, the porcelain surfaces were etched with 9.6 % HFA for 4 min, rinsed for 15 s, and dried with an oil-free air source. Then the brackets were bonded to the porcelain surfaces using the same method as that for Group SB.
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The specimens for each group were stored in distilled water for 24 h at 37 °C. Using an Instron universal testing machine (Instron Corp, MA, USA), bond strengths were calculated in shear mode at a crosshead speed of 0.5 mm/min until fracture occurred. The force decay was recorded for each specimen in Newtons and converted into megapascals (MPa). SBS was determined by dividing the force decay by the bracket base area (base dimensions were provided by Dentaurum Inc.). After debonding, the brackets were examined under magnification with a stereomicroscope (Olympus CX41, ×40, Japan) to determine the amount of resin remaining on the porcelain surface. The adhesive remnant index (ARI) was used to describe the amount of resin . The ARI scoring ranged from 0 to 3 as follows: 0, no adhesive remained on the porcelain surface; 1, less than half of the porcelain bonding site was covered with adhesive; 2, more than half of the porcelain bonding site was covered with adhesive; and 3, the porcelain bonding site was covered entirely with adhesive. Stereomicroscopy was also used to determine the PLV surface damage after debonding. Photographs of post treatment PLV surfaces were taken at ×8 magnification for each group. The images were captured by the stereomicroscope, transferred to a computer, and then analyzed. A score was assigned to each photo using a system similar to that used for enamel surfaces : 0, the laminate surface was free of cracks or tear-outs; 1, the laminate surface showed cracks; 2, the laminate surface showed tear-outs; and 3, the laminate surface showed cracks and tearouts. One specimen from each group was prepared for SEM (Jeol JSM-5600; Jeol Ltd., Tokyo, Japan) and EDX evaluation of the debonded bracket interface. After surface treatment, the specimens were sputter-coated (Polaron SC500 Sputter Coater, VG Microtech, E. Sussex, England) with a gold–palladium alloy under high vacuum, and photomicrographs were obtained. For EDX analysis, the acceleration voltage was set to 15 kV and EDX spectra were collected using count rates of ~1 kcps. Count rates remained constant during the measurements, indicating that neither contamination nor loss of mass occurred. The magnification was ×2000, representing an area of 60×45 μm for analysis. In addition, micrographs of ×5000 magnification were made for the structural investigation of the bracket surfaces. The shear bond strength data of the groups were subjected to a test of normality, the Kolmogorov–Smirnov test. Non-normal distributions were observed, and so a non-parametric test (Kruskal–Wallis) was used to determine the significance between the groups. The Mann–Whitney U test with Bonferroni correction was performed to determine the differences between the groups. The predetermined level of significance (p