Lasers Med Sci DOI 10.1007/s10103-013-1458-3
ORIGINAL ARTICLE
Shear bond strength of metal brackets to feldspathic porcelain treated by Nd:YAG laser and hydrofluoric acid Mohammad Hashem Hosseini & Farhad Sobouti & Ardavan Etemadi & Nasim Chiniforush & Mahsa shariati
Received: 12 April 2013 / Accepted: 2 October 2013 # Springer-Verlag London 2013
Abstract Adult orthodontic treatment requires bonding orthodontic attachment to dental restorations. Ceramics are commonly used as esthetic restorative materials for the crowns and bridges. The present study evaluated the shear bond strength of metal orthodontic brackets to the feldspathic porcelain surfaces following conditioning by different powers of neodymium-doped yttrium aluminum garnet (Nd:YAG) laser and hydrofluoric acid as a conventional method. Seventy-two glazed porcelain samples were prepared and randomly attributed to six equal groups of 12. In the conventional hydrofluoric (HF) group, the specimens were etched by 9.6 % hydrofluoric acid for 4 min. In laser groups, samples were conditioned by 0.75-, 1-, 1.25-, 1.5-, and 2-W Nd:YAG laser for 10 s. Metal brackets were bonded to porcelain samples and after being stored in distilled water for 24 h, they were subjected to thermocycling for 500 cycles. The debonding was carried out by a Zwick testing machine. The data were statistically analyzed by ANOVA and Tamhane multiple comparisons tests. The mean ± SD of the shear bond strength in the laser group 0.75, 1, 1.25, 1.5, and 2 W and HF group was 2.2±0.9, 4.2±1.1, 4.9±2.4, 7±1.7, 9.6±2.7, and 9.4±2.5, respectively. Together with the increased power of laser, the mean shear bond strength was increased continuously M. H. Hosseini Department of Orthodontics, School of Dentistry, Tehran University of Medical Sciences, Tehran, Iran F. Sobouti (*) Department of Orthodontics, School of Dentistry, Mazandaran University of Medical Sciences, Sari, Iran e-mail: [email protected] A. Etemadi : N. Chiniforush Laser Research Center of Dentistry, School of Dentistry, Tehran University of Medical Sciences, Tehran, Iran M. shariati Department of Orthodontics, School of Dentistry, Islamic Azad University, Tehran, Iran
and no significant differences were found between the HF group and the laser groups with power of 1.5 or 2 W. Also, there was no significant difference between all test groups in ARI scores. There was no significant difference between bond strength of laser groups with power of 1.5 and 2 W and HF-etched group. So, Nd:YAG laser with appropriate parameters can be used as an alternative method for porcelain etching. Keywords Orthodontic bonding . Porcelain treatment . Nd:YAG laser . HF
Introduction Adult orthodontic treatment requires bonding orthodontic attachment to dental restorations. Ceramics are commonly encountered as esthetic restorative materials for crowns and bridges [1]. The orthodontist might not know whether the dental ceramic is feldspathic porcelain, aluminous porcelain, or glass ceramic. It is very common to find feldspathic porcelain in ceramic-fused-to-metal restorations. The physical and chemical properties of the glazed porcelain necessitate a multi step procedure, including deglazing of the porcelain [2] or sandblasting [3], precise isolation, and applying 9.6 % hydrofluoric (HF) acid (HFA) for several minutes [4–6], and then rinsing, drying, and bonding. HF acid has been found to be a harmful and irritating compound for soft tissues [3, 7], also, hydrofluoric acid application is a time-consuming method. Therefore, finding an alternative method for bonding brackets to the porcelain surface has always been of interest in the orthodontic practice. Mechanical roughening of the porcelain surface with diamond burs and sandblasting are reported to provoke crack initiation and surface damage in porcelain. Organosilane-coupling agents are suggested to enhance the bonding of brackets to ceramic because it can act as mediator between the organic and inorganic matrixes of the porcelain [2, 7].
Lasers Med Sci
With the introduction of the ruby laser in 1960 by Maiman [8], its various applications in dentistry have been increased. Different types of laser such as erbium-doped yttrium aluminum garnet (Er:YAG), neodymium-doped yttrium aluminum garnet (Nd:YAG), and Er,Cr:YSGG have been used in orthodontics for enamel conditioning to bond the brackets and they all have shown acceptable results [9–11]. In recent years, CO2 and Er:YAG laser have been used for porcelain conditioning, but destructive effects on the superficial layer of the porcelain have been shown because of the high power and wavelength of these lasers. Li et al. prepared the porcelain surface with of 0.6-, 0.9-, and 1.2-W output power of Nd:YAG laser for bonding and concluded that this type of laser, in combination with light-cure composites, created acceptable bond strength to porcelain [12]. Poosti et al. concluded that etching porcelain surfaces with Nd:YAG laser and 9.6 % hydrofluoric produced no significant difference in the shear bond strength of these methods, Er:YAG with power of 2 and 3 W and surface roughening alone showed significantly lower bond strength than either the Nd:YAG laser or 9.6 % hydrofluoric acid-etching treatment [5]. The aim of this study was to evaluate the shear bond strength of metal brackets to feldspathic porcelain treated with different powers of Nd:YAG laser for determining the best power of this type of laser for etching porcelain surface in orthodontic practice.
Materials and method Seventy-two glazed porcelain samples were produced by duplication of the labial surface of an upper central incisor (10×8 mm). The samples were made of Vita porcelain (Vita, Bad Sackingen, Germany) by the condensing technique and baked under vacuum at 940 °C. The samples were mounted in custom-made PVC cylinders with auto polymerizing acrylic resin (Acropars, Iran). The samples were randomly put under six equal groups of 12 in each. Group 1 (HF group)
Samples were etched by 9.6 % hydrofluoric acid (Ultradent Porcelain Etch, USA) for 4 min, rinsed for 30 s and then dried. Groups 2 to 6 (laser groups) Samples were prepared by 0.75-, 1-, 1.25-, 1.5-, and 2-W output power of Nd:YAG laser (FOTONA, Fidelis, Ljubljana, Slovenia). The irradiation was done by Nd:YAG laser with wavelength of 1,064 nm, fiber of 300 μm, frequency of 10 Hz, and pulse duration of 100 μs (very short pulse) via sweeping motion at approximately 2-mm distance from the surface.
Fig. 1 Bracket bonded to porcelain sample
Organosilane (Silane, Bond Enhancer Corp.) were applied on the etched surface by microbrush according to the instruction of the manufacturer. Then, light-cure adhesive primer (3 M Unitek, California, USA) were applied and cured for 10 s. Finally, the standard edgewise brackets (Dentaurum, Ispringen, Germany) were bonded onto the surface by using light-cure adhesive resin (Transbond XT, 3M Unitek, California, USA) with 40 s for curing time by LED source(Mectron starlight pro GAC, Italy)(Fig. 1). The pressure force during bracket placement was 300 g that is measured by force gauge. After 24 h of sample storage in distilled water at 37 °C and then thermocycling for 500 cycles between 5 and 55 °C using a dwell time of 30 s, the samples were fixed in special jigs and the debonding was performed and measured by Zwick Roell material testing machine (Zwick GmbH, Ulm, Germany) (Fig. 2). Bond strength was determined in shear mode at a crosshead speed of 0.5 mm/min until fracture occurred. The maximum load necessary to debond or initiate bracket fracture was recorded in newtons and then converted into megapascals as a ratio of newtons/bracket surface area (12.68 mm 2). Following debonding, each tooth was examined under ×10 magnification and the site of bond failure recorded together with the adhesive remnant index ARI. This index consists of the following scoring: 1, all resin retained on porcelain with bracket imprint; 2, >90 %
Fig. 2 Sample in Zwick Roell machine
Lasers Med Sci Table 1 Box of 95 % confidence interval measurements and mean value of shear bond strength in six groups 14
12
10
8
6
4
2 0 N=
12
12
Laser .75W
12
12
Laser1.25W Laser1W
Laser1.5W
resin retained on porcelain; 3, >10 but
ORIGINAL ARTICLE
Shear bond strength of metal brackets to feldspathic porcelain treated by Nd:YAG laser and hydrofluoric acid Mohammad Hashem Hosseini & Farhad Sobouti & Ardavan Etemadi & Nasim Chiniforush & Mahsa shariati
Received: 12 April 2013 / Accepted: 2 October 2013 # Springer-Verlag London 2013
Abstract Adult orthodontic treatment requires bonding orthodontic attachment to dental restorations. Ceramics are commonly used as esthetic restorative materials for the crowns and bridges. The present study evaluated the shear bond strength of metal orthodontic brackets to the feldspathic porcelain surfaces following conditioning by different powers of neodymium-doped yttrium aluminum garnet (Nd:YAG) laser and hydrofluoric acid as a conventional method. Seventy-two glazed porcelain samples were prepared and randomly attributed to six equal groups of 12. In the conventional hydrofluoric (HF) group, the specimens were etched by 9.6 % hydrofluoric acid for 4 min. In laser groups, samples were conditioned by 0.75-, 1-, 1.25-, 1.5-, and 2-W Nd:YAG laser for 10 s. Metal brackets were bonded to porcelain samples and after being stored in distilled water for 24 h, they were subjected to thermocycling for 500 cycles. The debonding was carried out by a Zwick testing machine. The data were statistically analyzed by ANOVA and Tamhane multiple comparisons tests. The mean ± SD of the shear bond strength in the laser group 0.75, 1, 1.25, 1.5, and 2 W and HF group was 2.2±0.9, 4.2±1.1, 4.9±2.4, 7±1.7, 9.6±2.7, and 9.4±2.5, respectively. Together with the increased power of laser, the mean shear bond strength was increased continuously M. H. Hosseini Department of Orthodontics, School of Dentistry, Tehran University of Medical Sciences, Tehran, Iran F. Sobouti (*) Department of Orthodontics, School of Dentistry, Mazandaran University of Medical Sciences, Sari, Iran e-mail: [email protected] A. Etemadi : N. Chiniforush Laser Research Center of Dentistry, School of Dentistry, Tehran University of Medical Sciences, Tehran, Iran M. shariati Department of Orthodontics, School of Dentistry, Islamic Azad University, Tehran, Iran
and no significant differences were found between the HF group and the laser groups with power of 1.5 or 2 W. Also, there was no significant difference between all test groups in ARI scores. There was no significant difference between bond strength of laser groups with power of 1.5 and 2 W and HF-etched group. So, Nd:YAG laser with appropriate parameters can be used as an alternative method for porcelain etching. Keywords Orthodontic bonding . Porcelain treatment . Nd:YAG laser . HF
Introduction Adult orthodontic treatment requires bonding orthodontic attachment to dental restorations. Ceramics are commonly encountered as esthetic restorative materials for crowns and bridges [1]. The orthodontist might not know whether the dental ceramic is feldspathic porcelain, aluminous porcelain, or glass ceramic. It is very common to find feldspathic porcelain in ceramic-fused-to-metal restorations. The physical and chemical properties of the glazed porcelain necessitate a multi step procedure, including deglazing of the porcelain [2] or sandblasting [3], precise isolation, and applying 9.6 % hydrofluoric (HF) acid (HFA) for several minutes [4–6], and then rinsing, drying, and bonding. HF acid has been found to be a harmful and irritating compound for soft tissues [3, 7], also, hydrofluoric acid application is a time-consuming method. Therefore, finding an alternative method for bonding brackets to the porcelain surface has always been of interest in the orthodontic practice. Mechanical roughening of the porcelain surface with diamond burs and sandblasting are reported to provoke crack initiation and surface damage in porcelain. Organosilane-coupling agents are suggested to enhance the bonding of brackets to ceramic because it can act as mediator between the organic and inorganic matrixes of the porcelain [2, 7].
Lasers Med Sci
With the introduction of the ruby laser in 1960 by Maiman [8], its various applications in dentistry have been increased. Different types of laser such as erbium-doped yttrium aluminum garnet (Er:YAG), neodymium-doped yttrium aluminum garnet (Nd:YAG), and Er,Cr:YSGG have been used in orthodontics for enamel conditioning to bond the brackets and they all have shown acceptable results [9–11]. In recent years, CO2 and Er:YAG laser have been used for porcelain conditioning, but destructive effects on the superficial layer of the porcelain have been shown because of the high power and wavelength of these lasers. Li et al. prepared the porcelain surface with of 0.6-, 0.9-, and 1.2-W output power of Nd:YAG laser for bonding and concluded that this type of laser, in combination with light-cure composites, created acceptable bond strength to porcelain [12]. Poosti et al. concluded that etching porcelain surfaces with Nd:YAG laser and 9.6 % hydrofluoric produced no significant difference in the shear bond strength of these methods, Er:YAG with power of 2 and 3 W and surface roughening alone showed significantly lower bond strength than either the Nd:YAG laser or 9.6 % hydrofluoric acid-etching treatment [5]. The aim of this study was to evaluate the shear bond strength of metal brackets to feldspathic porcelain treated with different powers of Nd:YAG laser for determining the best power of this type of laser for etching porcelain surface in orthodontic practice.
Materials and method Seventy-two glazed porcelain samples were produced by duplication of the labial surface of an upper central incisor (10×8 mm). The samples were made of Vita porcelain (Vita, Bad Sackingen, Germany) by the condensing technique and baked under vacuum at 940 °C. The samples were mounted in custom-made PVC cylinders with auto polymerizing acrylic resin (Acropars, Iran). The samples were randomly put under six equal groups of 12 in each. Group 1 (HF group)
Samples were etched by 9.6 % hydrofluoric acid (Ultradent Porcelain Etch, USA) for 4 min, rinsed for 30 s and then dried. Groups 2 to 6 (laser groups) Samples were prepared by 0.75-, 1-, 1.25-, 1.5-, and 2-W output power of Nd:YAG laser (FOTONA, Fidelis, Ljubljana, Slovenia). The irradiation was done by Nd:YAG laser with wavelength of 1,064 nm, fiber of 300 μm, frequency of 10 Hz, and pulse duration of 100 μs (very short pulse) via sweeping motion at approximately 2-mm distance from the surface.
Fig. 1 Bracket bonded to porcelain sample
Organosilane (Silane, Bond Enhancer Corp.) were applied on the etched surface by microbrush according to the instruction of the manufacturer. Then, light-cure adhesive primer (3 M Unitek, California, USA) were applied and cured for 10 s. Finally, the standard edgewise brackets (Dentaurum, Ispringen, Germany) were bonded onto the surface by using light-cure adhesive resin (Transbond XT, 3M Unitek, California, USA) with 40 s for curing time by LED source(Mectron starlight pro GAC, Italy)(Fig. 1). The pressure force during bracket placement was 300 g that is measured by force gauge. After 24 h of sample storage in distilled water at 37 °C and then thermocycling for 500 cycles between 5 and 55 °C using a dwell time of 30 s, the samples were fixed in special jigs and the debonding was performed and measured by Zwick Roell material testing machine (Zwick GmbH, Ulm, Germany) (Fig. 2). Bond strength was determined in shear mode at a crosshead speed of 0.5 mm/min until fracture occurred. The maximum load necessary to debond or initiate bracket fracture was recorded in newtons and then converted into megapascals as a ratio of newtons/bracket surface area (12.68 mm 2). Following debonding, each tooth was examined under ×10 magnification and the site of bond failure recorded together with the adhesive remnant index ARI. This index consists of the following scoring: 1, all resin retained on porcelain with bracket imprint; 2, >90 %
Fig. 2 Sample in Zwick Roell machine
Lasers Med Sci Table 1 Box of 95 % confidence interval measurements and mean value of shear bond strength in six groups 14
12
10
8
6
4
2 0 N=
12
12
Laser .75W
12
12
Laser1.25W Laser1W
Laser1.5W
resin retained on porcelain; 3, >10 but
