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Louis Denaud - One of the best experts on this subject based on the ideXlab platform.
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Study on the in-process measurements of the surface roughness of Douglas fir green Veneers with the use of laser profilometer
European Journal of Wood and Wood Products, 2020Co-Authors: Stanisław Stefanowski, Rémy Frayssinhes, Grzegorz Pinkowski, Louis DenaudAbstract:The presented research concerns the use of a laser profilometer to measure the surface roughness of green Douglas fir heartwood Veneers during the peeling process. It investigates the effect of various process parameters on the surface quality. Three experiments were carried out with a single variable factor for each experiment: log centration, soaking temperature and cutting speed. Moreover, the origin of the surface roughness of Douglas fir green Veneers was investigated. The study shows that laser profilometer seems to be a useful equipment in online measurement of surface roughness of green Veneers. Based on the experiment results it was stated that surface roughness of Douglas fir Veneers is characterized by large differentiation depending on the location on the veneer. The performed analysis shows that the surface roughness of Douglas fir green veneer could be improved when using relatively high cutting speed, not too high steaming temperature and logs with a centered core. The presented study shows that the laser profilometer can be effectively applied to the measurement and evaluation of green Veneers during the peeling process and that there is still an area to develop this methodology.
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The influence of veneer thickness and knot proportion on the mechanical properties of laminated veneer lumber (LVL) made from secondary quality hardwood
European Journal of Wood and Wood Products, 2019Co-Authors: Citra Yanto Ciki Purba, Guillaume Pot, Joffrey Viguier, Julien Ruelle, Louis DenaudAbstract:The first objective of this work was to study the influence of veneer quality on the mechanical properties of laminated veneer lumber (LVL) made of secondary quality hardwood. The second objective was to propose an adapted veneer thickness that provides the optimum mechanical properties of LVL, taking the veneer properties into account. Forty-eight LVL panels glued together using polyvinyl acetate (PVAc) were prepared. The quality of fresh Veneers was assessed by measuring veneer knot proportion, lathe check depth and lathe check interval. The static modulus of elasticity (MOE), dynamic MOE, modulus of rupture (MOR) and shear modulus were measured using destructive and non-destructive methods. The 3 mm thick veneer provided the optimum mechanical properties for LVL for both species. The test direction did not have any significant influence on the mechanical properties. In the flatwise direction, the average MOE values obtained were 13.2 GPa for beech LVL and 13.3 GPa for oak LVL, whereas the MOR was 72.0 MPa and 63.4 MPa, respectively. Increasing knot proportion in Veneers results in a decrease in LVL MOE and MOR. Moreover, deeper lathe checks and higher lathe check intervals on veneer surfaces provide lower LVL shear modulus in the edgewise direction for both species. Internal veneer provides LVL with a higher density but weaker mechanical properties due to a higher knot proportion in the internal veneer.
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an innovative method based on grain angle measurement to sort veneer and predict mechanical properties of beech laminated veneer lumber
Construction and Building Materials, 2018Co-Authors: Joffrey Viguier, Christophe Bourgeay, Anti Rohumaa, Guillaume Pot, Louis DenaudAbstract:Abstract This study proposes an innovative model based on local grain angle measurements to predict the modulus of elasticity of LVL made from beech. It includes a Veneers sorting method industrially compatible thanks to its low computational time. For this study 41 LVL panels were prepared from 123 beech sheets of Veneers. Local grain angle was obtained with a two dimensional scanner and veneer density was measured. Several models based on these measurements have been developed and their ability to predict the modulus of elasticity of LVL panels have been compared. The model based only on local grain angle measurements have been proven more efficient than models taking into account the veneer density. The proposed method can be used to sort veneer during the peeling process and grade the production of LVL panels to optimize their mechanical properties even for low-quality veneer.
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The effect of juvenility and veneer thickness on bending strength of Douglas-fir laminated veneer lumber
T.H.E. Journal, 2016Co-Authors: Istie Rahayu, Louis Denaud, Julien Ruelle, Wayan Darmawan, Naresworo Nugroho, Rémy MarchalAbstract:Most of wood industry requires well conformed logs and middle diameter trees to optimize primary processing yields. The raw material, mostly coming from monoculture plantations, contains a considerable proportion of juvenile wood. The objectives of present study were to identify the transition ring between juvenile and mature wood in Douglas-fir and to analyze the effect of juvenility and veneer thickness on bending strength of Douglas-fir laminated veneer lumber (LVL). Microfibril angle (MFA) and tracheid length from five Douglas-fir logs were measured from pith to bark. Veneers peeled with an instrumented lathe to produce LVL. Total of 140 LVL samples were mechanically characterized by measuring modulus of elasticity (MOE) and modulus of rupture (MOR). The results showed that transition rings from juvenile to mature wood at breast height, according to MFA and tracheid length, were at twentieth and twenty-first, respectively. According to analysis of variance, there was a significant effect of juvenility on LVL bending strength. The advantage of using Veneers of mature compare to juvenile wood for LVL was due to an improvement of bending strength in the range of 7–22 %. LVL made of 3 mm Veneers has lower stiffness (2.2 %) compare to LVL made of 5.25 mm Veneers. High correlation between static and dynamic MOE was noted.
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Ten new poplar cultivars provide laminated veneer lumber for structural application
Annals of Forest Science, 2014Co-Authors: Istie Rahayu, Louis Denaud, Rémy MarchalAbstract:Key message Lambro, Brenta, Taro, Alcinde and Soligo are new poplar cultivars suitable for laminated veneer lumber (LVL) for structural purposes. While Lena, Koster, Dvina, Mella and Trichobel must be used with careful veneer material selection to obtain high value of mechanical properties. Context In France, the veneer processing industry uses only a very small number of different poplar cultivars. Aims This paper set out to investigate the potential of laminated veneer lumber made from 14 new cultivars for structural purposes, with a focus on juvenility and veneer thickness effects. Methods The mechanical properties of laminated veneer lumber panels made from each cultivar (114 samples per cultivar) were characterized by measuring their density, modulus of elasticity and modulus of rupture. Results A tight correlation was found between destructive and non-destructivemodulus of elasticity tests (R2=0.90, 1,808 samples). Five cultivars had suitable mechanical properties for structural applications ('Lambro', 'Brenta', 'Taro', 'Alcinde' and 'Soligo'). Five cultivars needed to be used with careful sample selection ('Lena', 'Koster', 'Dvina', 'Mella' and 'Trichobel'), and the final four ('I214', 'A4A', 'Triplo' and 'Polargo') could not be recommended for structural purposes. Conclusion The advantage of using Veneers of mature wood compare to juvenile wood for laminated veneer lumber (LVL) production was due to an improvement of modulus of elasticity and modulus of rupture in the range of 15 to 20 %. The use of thick Veneers (5.25 mm compared to 3 mm) did not appear to be detrimental to laminated veneer lumber mechanical performance.
Ismail Aydin - One of the best experts on this subject based on the ideXlab platform.
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Prediction of the optimum veneer drying temperature for good bonding in plywood manufacturing by means of artificial neural network
Wood Science and Technology, 2014Co-Authors: Sukru Ozsahin, Ismail AydinAbstract:Veneer drying is one of the most important stages in the manufacturing of veneer-based composites such as plywood and laminated veneer lumber. Due to the high drying costs, increased temperatures are being used commonly in plywood industry to reduce the overall drying time and increase capacity. However, high drying temperatures can alter some physical, mechanical and chemical characteristics of wood and cause some drying-related defects. In this study, it was attempted to predict the optimum drying temperature for beech and spruce Veneers via artificial neural network modeling for optimum bonding. Therefore, bonding shear strength values of plywood panels manufactured from beech and spruce Veneers dried at temperatures of 20, 110, 150 and 180 °C were obtained experimentally. Then, the intermediate bond strength values based on veneer drying temperatures were predicted by artificial neural network modeling, and the values not measured experimentally were evaluated. The optimum drying temperature values that yielded the highest bonding strength were obtained as 169 °C for urea formaldehyde and 125 °C for phenol formaldehyde adhesive in beech plywood panels, while 162 °C for urea formaldehyde and 151 °C for phenol formaldehyde in spruce plywood panels.
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surface characteristics of spruce Veneers and shear strength of plywood as a function of log temperature in peeling process
International Journal of Solids and Structures, 2006Co-Authors: Ismail Aydin, Gursel Colakoglu, Salim HizirogluAbstract:The objective of this study was to determine the effect of temperature of spruce (Picea orientalis L.) logs during peeling process on surface roughness, adhesive wettability, colour variation of veneer, and shear strength of plywood made from these veneer sheets. Veneer samples were manufactured from the logs after they were kept for 3 h and 24 h to reach to average temperatures of 52 °C and 32 °C, respectively. A fine stylus method was used for surface roughness evaluation of the veneer produced from two types of the logs and it was found that the samples peeled from the logs with a temperature of 52 °C had significantly better roughness values than those of manufactured from the logs with 32 °C at a 95% confidence level. Wettability of veneer samples was determined with contact angle measurements according to the sessile drop method. Urea formaldehyde (UF) and phenol formaldehyde (PF) resin drops were used in contact angle measurements. Contact angles of PF resin drops on Veneers were similar for each peeling temperature while the contact angles of UF glue resin on Veneers produced from the logs with 32 °C were lower than those of produced from the logs with 52 °C. Small colour difference was measured (indicated by a low ΔE value) on veneer samples depending on the log temperature. The highest shear strength value was determined for the plywood manufactured from Veneers obtained from the logs with 52 °C by using UF glue.
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effects of surface inactivation high temperature drying and preservative treatment on surface roughness and colour of alder and beech wood
Applied Surface Science, 2005Co-Authors: Ismail Aydin, Gursel ColakogluAbstract:Abstract Although extensive research has been conducted in wood surface quality analysis, a unified approach to surface quality characterisation does not exist. Measurements of the variation in surface roughness and surface colour are used widely for the evaluation of wood surface quality. Colour is a basic visual feature for wood and wood-based products. Colour measurement is one of the quality control tests that should be carried out because the colour deviations are spotted easily by the consumers. On the other hand, a common problem faced by plywood manufacturers is panel delamination, for which a major cause is poor quality glue-bonds resulting from rough veneer. Rotary cut Veneers with dimensions of 500 mm × 500 mm × 2 mm manufactured from alder ( Alnus glutinosa subsp . barbata) and beech ( Fagus orientalis Lipsky) logs were used as materials in this study. Veneer sheets were oven-dried in a veneer dryer at 110 °C (normal drying temperature) and 180 °C (high drying temperature) after peeling process. The surfaces of some Veneers were then exposed at indoor laboratory conditions to obtain inactive wood surfaces for glue bonds, and some Veneers were treated with borax, boric acid and ammonium acetate solutions. After these treatments, surface roughness and colour measurements were made on veneer surfaces. High temperature drying process caused a darkening on the surfaces of alder and beech Veneers. Total colour change value (Δ E * ) increased linear with increasing exposure time. Among the treatment solutions, ammonium acetate caused the biggest colour change while treatment with borax caused the lowest changes in Δ E * values. Considerable changes in surface roughness after preservative treatment did not occur on veneer surfaces. Generally, no clear changes were obtained or the values mean roughness profile ( R a ) decreased slightly in R a values after the natural inactivation process.
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activation of wood surfaces for glue bonds by mechanical pre treatment and its effects on some properties of veneer surfaces and plywood panels
Applied Surface Science, 2004Co-Authors: Ismail AydinAbstract:Abstract Some chemical pre-treatments with chemical reagents are widely applied to wood surfaces in order to improve bonding ability, wettability and reactivate wood surfaces for glue–wood bonds. Besides these chemical treatments, some mechanical pre-treatments such as sanding and planing can be applied to get a fresh surface which eliminates bonding problems and improves glue bonding of wood. In this study, 2 mm thick rotary cut Veneers obtained from steamed beech (Fagus orientalis) logs were used as material. Both air-drying and oven-drying methods were used for drying veneer. After drying, the surfaces of some Veneers were sanded with 100 and 180 grit sandpapers. Three-layer-plywood panels were produced from sanded and non-sanded Veneers by using urea formaldehyde and phenol formaldehyde glue resins to evaluate the effects of sanding some mechanical properties of plywood. Changes in pH, surface roughness and adhesive wettability of Veneers were evaluated. Wettability of Veneers was assessed with contact angle measurements according to the sessile drop method. Both veneer and plywood properties investigated in this study improved clearly after the sanding process. Shear and bending strength values of plywood panels manufactured from sanded and non-sanded Veneers were vary depending on glue types and veneer drying methods.
Peter Rechmann - One of the best experts on this subject based on the ideXlab platform.
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Er:YAG laser debonding of porcelain Veneers.
Lasers in surgery and medicine, 2011Co-Authors: Cynthia K. Morford, Natalie C.h. Buu, Beate M.t. Rechmann, Frederick C. Finzen, Arun Sharma, Peter RechmannAbstract:Background and Objectives The removal of porcelain Veneers using Er:YAG lasers has not been previously described in the scientific literature. This study was designed to systematically investigate the efficacy of an Er:YAG laser on veneer debonding, possibly without damage to the underlying tooth, and preservation of the veneer integrity. Study Design/Materials and Methods The Fourier Transform Infrared Spectroscopy was used on 10 flat veneer samples (IPS Empress Esthetic, e.max Press HT) to assess which infrared laser wavelengths transmits through a veneer. Additionally, Fourier Transform Infrared (FTIR) spectra for a bonding cement (RelyX) were obtained. Consequently, Er:YAG laser energy transmission (wavelength 2,940 nm, 10 Hz repetition rate, pulse duration 100 µseconds at 133 mJ/pulse) through different veneer thicknesses was measured. Twenty-four Veneers were bonded to freshly extracted and prepared incisors. The energy necessary for debonding was determined and then the Veneers were debonded with the laser. Time needed for total debonding was measured and possible damage to the underlying tooth structure was assessed by light microscopy. Results While the veneer materials did not show any characteristic water absorption bands in the FTIR, the bonding cement showed a broad H2O/OH absorption band. The Veneers transmitted between 11.5% and 43.7% of the incident Er:YAG energy with Emax transmitting twice the energy as EE at comparable thicknesses. Initial signs of cement ablation occurred at 1.8–4.0 J/cm2 with the fiber tip positioned at a distance of 3–6 mm from the veneer surface and 133 mJ output energy. All 24 bonded Veneers were completely removed with an average removal time of 113 ± 76 seconds. Underlying tooth structure was not damaged. The debonding mainly occurred at the cement/veneer interface. None of the Emax Veneers fractured during debonding, while 36% of the EE did. Conclusion Er:YAG laser irradiation effectively debonds porcelain Veneers while preserving tooth structure. Maintaining veneer integrity possibly depends on the flexure strength of the veneer porcelain. Lasers Surg. Med. 43:965–974, 2011. © 2011 Wiley Periodicals, Inc.
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Er:YAG laser debonding of porcelain Veneers
Lasers in Dentistry XVI, 2010Co-Authors: Natalie C.h. Buu, Cynthia K. Morford, Frederick C. Finzen, Arun Sharma, Peter RechmannAbstract:The removal of porcelain Veneers using Er:YAG lasers has not been previously described in the scientific literature. This study was designed to systematically investigate the efficacy of an Er:YAG laser on veneer debonding without damaging the underlying tooth structure, as well as preserving a new or misplaced veneer. Initially, Fourier Transform Infrared Spectroscopy (FTIR) was used on flat porcelain veneer samples (IPS Empress Esthetic; Ivoclar Vivadent, Amherst, NY) to assess which infrared laser wavelengths are transmitted through the veneer. Additionally, FTIR spectra from a veneer bonding cement (RelyX Veneer Cement A1; 3M ESPE, St. Paul, MN) were obtained. While the veneer material showed no characteristic water absorption bands in the FTIR, the bonding cement has a broad H2O/OH absorption band coinciding with the ER:YAG laser emission wavelength. Consequently Er:YAG laser energy transmission through different veneer thicknesses was measured. The porcelain Veneers transmitted 11 - 18 % of the incident Er:YAG laser energy depending on their thicknesses (Er:YAG laser: LiteTouch by Syneron; wavelength 2,940 nm, 10 Hz repetition rate, pulse duration 100 μs at 133 mJ/pulse; straight sapphire tip 1,100 μm diameter; Syneron, Yokneam, Israel). Initial signs of cement ablation occurred at approximately 1.8 - 4.0 J/cm 2 . This can be achieved by irradiating through the veneer with the fiber tip positioned at a distance of 3-6 mm from the veneer surface, and operating the Er:YAG laser with 133 mJ output energy. All eleven Veneers bonded on extracted anterior incisor teeth were easily removed using the Er:YAG laser. The removal occurred without damaging underlying tooth structure as verified by light microscopic investigation (Incident Light Microscope Olympus B 50, Micropublisher RTV 3.3 MP, Image Pro software, Olympus). The debonding mainly occurred at the cement/veneer interface. When the samples were stored in saline solution for 5 days and/or an air-waterspray was used during irradiation, there was a high chance that the veneer would fractured during debonding. However if samples were not stored in water and only air spray was used, 75% of the Veneers could be removed without any fracture. The use of an Er:YAG laser can be effective in not only debonding porcelain Veneers and preserving tooth structure, but also in maintaining veneer integrity.
Rémy Marchal - One of the best experts on this subject based on the ideXlab platform.
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The effect of juvenility and veneer thickness on bending strength of Douglas-fir laminated veneer lumber
T.H.E. Journal, 2016Co-Authors: Istie Rahayu, Louis Denaud, Julien Ruelle, Wayan Darmawan, Naresworo Nugroho, Rémy MarchalAbstract:Most of wood industry requires well conformed logs and middle diameter trees to optimize primary processing yields. The raw material, mostly coming from monoculture plantations, contains a considerable proportion of juvenile wood. The objectives of present study were to identify the transition ring between juvenile and mature wood in Douglas-fir and to analyze the effect of juvenility and veneer thickness on bending strength of Douglas-fir laminated veneer lumber (LVL). Microfibril angle (MFA) and tracheid length from five Douglas-fir logs were measured from pith to bark. Veneers peeled with an instrumented lathe to produce LVL. Total of 140 LVL samples were mechanically characterized by measuring modulus of elasticity (MOE) and modulus of rupture (MOR). The results showed that transition rings from juvenile to mature wood at breast height, according to MFA and tracheid length, were at twentieth and twenty-first, respectively. According to analysis of variance, there was a significant effect of juvenility on LVL bending strength. The advantage of using Veneers of mature compare to juvenile wood for LVL was due to an improvement of bending strength in the range of 7–22 %. LVL made of 3 mm Veneers has lower stiffness (2.2 %) compare to LVL made of 5.25 mm Veneers. High correlation between static and dynamic MOE was noted.
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The Effect of Jabon Veneer Quality on Laminated Veneer Lumber Glue Bond and Bending Strength
2015Co-Authors: Istie Rahayu, Wayan Darmawan, Naresworo Nugroho, Rémy MarchalAbstract:Jabon ( Anthocephalus cadamba ) is a fast growing wood species widely planted by community in Indonesia. Jabon has large percentage of juvenile wood which affect its veneer quality. This research objective were to determine the effects of wood juvenility and pretreatment on lathe checks, surface roughness and contact angle of the 3.00 mm rotary-cut jabon veneer and to analyze the impact of lathe checks frequency on the LVL glue bond and bending strength. Jabon logs were subjected to boiling in 75 °C water for4 h. Then they were peeled to produce 3.00 mm Veneers in thickness. Frequency, length and depth of lathe checks were measured per 10 cm veneer length by using optical microscope. Laminated veneer lumber (20x20x500) mm3 were made from 7-ply of jabon Veneers by using Poly Vinyl Acetate (PVAc) as adhesive. Glue bond strength and bending strength were measured by UTM Instron. The results showed lathe check (frequency, length and depth), surface roughness and contact angle were influenced by juvenility. Glue bond strength, Modulus of Elasticity (MOE) and Modulus of Rupture (MOR) of jabon LVL decreased as frequency of lathe check increased.
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Ten new poplar cultivars provide laminated veneer lumber for structural application
Annals of Forest Science, 2014Co-Authors: Istie Rahayu, Louis Denaud, Rémy MarchalAbstract:Key message Lambro, Brenta, Taro, Alcinde and Soligo are new poplar cultivars suitable for laminated veneer lumber (LVL) for structural purposes. While Lena, Koster, Dvina, Mella and Trichobel must be used with careful veneer material selection to obtain high value of mechanical properties. Context In France, the veneer processing industry uses only a very small number of different poplar cultivars. Aims This paper set out to investigate the potential of laminated veneer lumber made from 14 new cultivars for structural purposes, with a focus on juvenility and veneer thickness effects. Methods The mechanical properties of laminated veneer lumber panels made from each cultivar (114 samples per cultivar) were characterized by measuring their density, modulus of elasticity and modulus of rupture. Results A tight correlation was found between destructive and non-destructivemodulus of elasticity tests (R2=0.90, 1,808 samples). Five cultivars had suitable mechanical properties for structural applications ('Lambro', 'Brenta', 'Taro', 'Alcinde' and 'Soligo'). Five cultivars needed to be used with careful sample selection ('Lena', 'Koster', 'Dvina', 'Mella' and 'Trichobel'), and the final four ('I214', 'A4A', 'Triplo' and 'Polargo') could not be recommended for structural purposes. Conclusion The advantage of using Veneers of mature wood compare to juvenile wood for laminated veneer lumber (LVL) production was due to an improvement of modulus of elasticity and modulus of rupture in the range of 15 to 20 %. The use of thick Veneers (5.25 mm compared to 3 mm) did not appear to be detrimental to laminated veneer lumber mechanical performance.
Cynthia K. Morford - One of the best experts on this subject based on the ideXlab platform.
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Er:YAG laser debonding of porcelain Veneers.
Lasers in surgery and medicine, 2011Co-Authors: Cynthia K. Morford, Natalie C.h. Buu, Beate M.t. Rechmann, Frederick C. Finzen, Arun Sharma, Peter RechmannAbstract:Background and Objectives The removal of porcelain Veneers using Er:YAG lasers has not been previously described in the scientific literature. This study was designed to systematically investigate the efficacy of an Er:YAG laser on veneer debonding, possibly without damage to the underlying tooth, and preservation of the veneer integrity. Study Design/Materials and Methods The Fourier Transform Infrared Spectroscopy was used on 10 flat veneer samples (IPS Empress Esthetic, e.max Press HT) to assess which infrared laser wavelengths transmits through a veneer. Additionally, Fourier Transform Infrared (FTIR) spectra for a bonding cement (RelyX) were obtained. Consequently, Er:YAG laser energy transmission (wavelength 2,940 nm, 10 Hz repetition rate, pulse duration 100 µseconds at 133 mJ/pulse) through different veneer thicknesses was measured. Twenty-four Veneers were bonded to freshly extracted and prepared incisors. The energy necessary for debonding was determined and then the Veneers were debonded with the laser. Time needed for total debonding was measured and possible damage to the underlying tooth structure was assessed by light microscopy. Results While the veneer materials did not show any characteristic water absorption bands in the FTIR, the bonding cement showed a broad H2O/OH absorption band. The Veneers transmitted between 11.5% and 43.7% of the incident Er:YAG energy with Emax transmitting twice the energy as EE at comparable thicknesses. Initial signs of cement ablation occurred at 1.8–4.0 J/cm2 with the fiber tip positioned at a distance of 3–6 mm from the veneer surface and 133 mJ output energy. All 24 bonded Veneers were completely removed with an average removal time of 113 ± 76 seconds. Underlying tooth structure was not damaged. The debonding mainly occurred at the cement/veneer interface. None of the Emax Veneers fractured during debonding, while 36% of the EE did. Conclusion Er:YAG laser irradiation effectively debonds porcelain Veneers while preserving tooth structure. Maintaining veneer integrity possibly depends on the flexure strength of the veneer porcelain. Lasers Surg. Med. 43:965–974, 2011. © 2011 Wiley Periodicals, Inc.
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Er:YAG laser debonding of porcelain Veneers
Lasers in Dentistry XVI, 2010Co-Authors: Natalie C.h. Buu, Cynthia K. Morford, Frederick C. Finzen, Arun Sharma, Peter RechmannAbstract:The removal of porcelain Veneers using Er:YAG lasers has not been previously described in the scientific literature. This study was designed to systematically investigate the efficacy of an Er:YAG laser on veneer debonding without damaging the underlying tooth structure, as well as preserving a new or misplaced veneer. Initially, Fourier Transform Infrared Spectroscopy (FTIR) was used on flat porcelain veneer samples (IPS Empress Esthetic; Ivoclar Vivadent, Amherst, NY) to assess which infrared laser wavelengths are transmitted through the veneer. Additionally, FTIR spectra from a veneer bonding cement (RelyX Veneer Cement A1; 3M ESPE, St. Paul, MN) were obtained. While the veneer material showed no characteristic water absorption bands in the FTIR, the bonding cement has a broad H2O/OH absorption band coinciding with the ER:YAG laser emission wavelength. Consequently Er:YAG laser energy transmission through different veneer thicknesses was measured. The porcelain Veneers transmitted 11 - 18 % of the incident Er:YAG laser energy depending on their thicknesses (Er:YAG laser: LiteTouch by Syneron; wavelength 2,940 nm, 10 Hz repetition rate, pulse duration 100 μs at 133 mJ/pulse; straight sapphire tip 1,100 μm diameter; Syneron, Yokneam, Israel). Initial signs of cement ablation occurred at approximately 1.8 - 4.0 J/cm 2 . This can be achieved by irradiating through the veneer with the fiber tip positioned at a distance of 3-6 mm from the veneer surface, and operating the Er:YAG laser with 133 mJ output energy. All eleven Veneers bonded on extracted anterior incisor teeth were easily removed using the Er:YAG laser. The removal occurred without damaging underlying tooth structure as verified by light microscopic investigation (Incident Light Microscope Olympus B 50, Micropublisher RTV 3.3 MP, Image Pro software, Olympus). The debonding mainly occurred at the cement/veneer interface. When the samples were stored in saline solution for 5 days and/or an air-waterspray was used during irradiation, there was a high chance that the veneer would fractured during debonding. However if samples were not stored in water and only air spray was used, 75% of the Veneers could be removed without any fracture. The use of an Er:YAG laser can be effective in not only debonding porcelain Veneers and preserving tooth structure, but also in maintaining veneer integrity.
