Influence of the frequency of Er:YAG laser on the bond strength of dental enamel

Er:YAG laser settings for debonding zirconia restorations: An in vitro study

This in vitro study aimed to determine the optimal frequency and energy settings for debonding zirconia restorations using an erbium-doped yttrium aluminum garnet (Er:YAG) laser. A total of 200 zirconia specimens (5 mm × 5 mm × 1.5 mm) were fabricated from two types of materials: (1) 3 mol% yttria oxide stabilized tetragonal zirconia polycrystalline (3Y-TZP) and (2) 5 mol% yttria oxide stabilized tetragonal zirconia polycrystalline (5Y-TZP). The zirconia specimens were bonded to dentin using resin cement (RelyX Ultimate, 3 M) and divided into 20 groups based on their laser treatments (n = 5). Er:YAG laser treatment was applied at various frequencies (10 Hz and 20 Hz) and energies (80 mJ, 100 mJ, 120 mJ, 140 mJ, 160 mJ, 180 mJ, 200 mJ, 220 mJ, 240 mJ, and 260 mJ). The time required to debond the specimens and the temperature changes that dentin underwent during the laser treatment were recorded. The surface morphologies of the debonded dentin and zirconia specimens were observed using scanning electron microscopy (SEM). Additional zirconia specimens were fabricated for 4-point flexural strength testing and surface roughness measurements. Statistical analyses were conducted using three-way analysis of variance (ANOVA) and Student-Newman-Keuls (SNK)-q tests (α = 0.05). The debonding time of each specimen varied between 4.8 and 160.4 s, with an average value of 59.2 s. The dentin temperature change for each specimen ranged from 2.3 to 3.6 °C, with an average value of 2.7 °C. The debonding time was significantly influenced by the zirconia material type and laser energy, but it was not affected by the laser frequency. Among the specimens, those made of 3Y-TZP needed significantly more time for debonding than 5Y-TZP. The optimal energies were 220 mJ for 3Y-TZP and 200 mJ for 5Y-TZP. The laser frequency, laser energy, and type of zirconia material had no effect on the dentin temperature change. Additionally, no surface alternations were observed on the dentin or zirconia materials after laser treatment. The surface roughness and flexural strength of the zirconia materials remained unchanged after laser treatment. In summary, Er:YAG laser treatment effectively and safely removes zirconia restorations without impacting their mechanical properties, with a safe temperature change of less than 5.6 °C. The optimum frequency and energy settings for debonding 3Y-TZP and 5Y-TZP restorations were found to be 10/20 Hz and 220 mJ and 10/20 Hz and 200 mJ, respectively.

An In Vitro Comparison of the Bond Strength of Composite to Superficial and Deep Dentin, Treated With Er:YAG Laser Irradiation or Acid-Etching

Introduction: The aim of this study was to compare the micro-shear bond strength of composite resin on superficial and deep dentin after conditioning with phosphoric acid and Erbium-Doped Yttrium Aluminum Garnet (Er:YAG) laser. Methods: Thirty human molars were selected, roots were removed and crowns were bisected to provide a total of 60 half-crowns. Specimens were ground to expose superficial and deep dentin. Samples were assigned to six groups: (1) AS (acid etching of superficial dentin); (2) AD (acid etching of deep dentin); (3) LS (Er:YAG laser irradiation on superficial dentin); (4) LD (Er:YAG laser irradiation on deep dentin); (5) LAS (Er:YAG laser irradiation on superficial dentin followed by acid etching); (6) LAD (Er:YAG laser irradiation on deep dentin followed by acid etching) The adhesive protocol was performed. Samples were thermocycled and micro-shear bond strength was tested to failure. The data were submitted to statistical analysis with one-way analysis of variance (ANOVA) and Tukey post hoc test. Results: The AS group, demonstrated the greatest amount of micro-shear bond strength. Statistical analysis showed a decrease in bond strength in laser-treated groups which was more significant for deep dentin. Conclusion: Preparation of dentin with laser did not improve bonding to superficial and deep dentin.

Sub ablative Er: YAG laser irradiation on surface roughness of eroded dental enamel

OBJECTIVE

This study evaluated the effects of Er:YAG laser irradiation applied at varying pulse repetition rate on the surface roughness of eroded enamel.

METHODS

Bovine enamel slabs (n = 10) were embedded in polyester resin, ground, and polished. To erosive challenges, specimens were immersed two times per day in 20mL of concentrated orange juice (pH = 3.84) under agitation, during a two-day period. Specimens were randomly assigned to irradiation with the Er:YAG laser (focused mode, pulse energy of 60 mJ and energy density of 3.79 J/cm(2) ) operating at 1, 2, 3, or 4 Hz. The control group was left nonirradiated. Surface roughness measurements were recorded post erosion-like formation and further erosive episodes by a profilometer and observed through atomic force microscopy (AFM).

RESULTS

Analysis of variance revealed that the control group showed the lowest surface roughness, while laser-irradiated substrates did not differ from each other following post erosion-like lesion formation. According to analysis of covariance, at further erosive episodes, the control group demonstrated lower surface roughness (P > 0.05), than any of the irradiated groups (P < 0.05).

CONCLUSIONS

The pulse repetition rate of the Er:YAG laser did not affect roughness of dental enamel eroded. The AFM images showed that the specimens irradiated by the Er:YAG laser at 1 Hz presented a less rough surface than those irradiated at 2, 3, and 4 Hz.

Comparison of microtensile bond strength of a resin composite to enamel conditioned by acid etching and Er,Cr:YSGG laser in human primary teeth

AIM

This study was designed to compare the bond strength of composite resin restorations on the buccal surface of primary human canine after conditioning by conventional acid etching and Er,Cr:YSGG laser.

METHODS

Twenty sound primary canines were cut buccolingually into two halves and each half was randomly placed in Er,Cr:YSGG laser or acid etch group. The samples in the acid etch group were etched with 37% phosphoric acid for 30 s. The samples in the laser group were prepared by Er,Cr:YSGG laser. The G6-Tips and 600 µm diameter were used with a 1.5 W of power output, pulse duration of 140 µs and repetition rate of 20 Hz. The bonding agent was applied on the buccal surface of each sample and layers of resin composite were placed. The samples' bond strengths were evaluated by a microtensile test instrument.

RESULTS

The mean of microtensile bond strength was 18.55±6.41 in the laser group and 24.62±5.56 in acid etch group. Microtensile bond strength achieved by laser conditioning was significantly lower than microtensile bond strength achieved by the conventional acid etching. Statistics To compare the results between the acid etch and laser group, the paired t test was performed (p value<0.001).

CONCLUSION

Conditioning enamel in primary teeth by Er,Cr:YSGG laser, cannot be used as an alternative method for acid etching and cannot substitute this conventional method.

The use of sub-ablative Er:YAG laser irradiation in prevention of dental caries during orthodontic treatment

PURPOSE

This « in-vitro » study had two specific aims: the first, to test using a universal testing machine whether sub-ablative Er:YAG laser irradiation prior to acid etching is effective in orthodontic bracket bonding and secondly using micro-hardness measurements and Scanning Electron Microscopy (SEM) observations to investigate the effectiveness of de-mineralization reduction in enamel treated with sub-ablative Er:YAG laser irradiation followed by fluoride varnish application.

MATERIALS AND METHODS

One hundred and eighty bovine permanent maxillary incisors were selected for shear bond strength testing and microhardness measurements. Sub-ablative Er:YAG laser irradiation was set at a power density of 2.5 J/cm(2), a frequency of 7 Hz and air/water spray. Brackets were bonded with an auto-curing resin paste. The shear bond strength was measured comparing laser irradiated and non-irradiated enamel surface, followed by SEM observation of the bracket-resin-enamel interface. Microhardness measurements were made on enamel samples before treatment, after samples preparation, and after demineralization.

RESULTS

While the adhesion of orthodontic brackets to bovine enamel after sub-ablative Er:YAG laser irradiation and acid etching is comparable to that obtained after conventional acid etching, the effect of laser irradiation associated with topical application of fluoride varnish increases the microhardness of enamel.

CONCLUSION

Sub-ablative Er:YAG laser irradiation before the acid etching doesn't reduce the shear bond whereas when associated with fluoride application it may play a role in caries prevention. Further studies will be necessary to establish the mechanism by which the protective laser activated fluoride effect is achieved.

Shear strength of composite bonded to Er:YAG laser-prepared enamel: an in vitro comparative study

The primary objective of this study is to investigate the adhesion properties between four current generations of bonding systems and enamel surface conditioned by Er:YAG laser, using an energy density comparable to the ablation threshold of enamel. By including an energy density comparable to published adhesion studies, the secondary objective is to compare the adhesion effects of these selected laser conditioning parameters on enamel with other similar published studies.

MATERIAL AND METHODS

Buccal sides of randomly selected human molars (N=117) were prepared and divided into nine experimental groups depending on the generations of bonding system represented by the corresponding number (G4, G5, G6, G7) and the additional laser conditioning on the enamel surface represented by laser etch (LE) and laser etch with a higher pulse energy, followed by acid etch (AE), if required. The bonding resin systems and their specific requirements were applied after the enamel surfaces were laser conditioned following a specific set of laser parameters. Composite posts of 1.6 mm in diameter and approximately 6 mm in length were then restored on each of the sample surfaces. After 48 h, the composite assemblies were tested to failure under compression using a knife edge loading head at a cross head speed of 1 mm/min until the composite cylinders were separated from the surface. The data collected were then analyzed using one-way analysis of variance and SAS software program (9.1, TS1M3).

RESULTS

No significant difference was found among these groups: AE+G4/LEAE+G4, G6/LE+G6, and G7/LE+G7. Significant differences were found in the remaining groups: AE+G5/LEAE+G5, AE+G5/LEAE-H+G5, and LEAE+G5/LEAE-H+G5. The bond strength results were compared among similar published data and possible influences from different laser parameters, bonding systems, and their combined impact on the enamel surface and its adhesion properties were analyzed.

CONCLUSION

Under our specific settings, additional laser conditioning after phosphoric acid etch is beneficial to one generation of bonding resin (G5). There is no significant change or detrimental effect to the other three groups (G4, G6, and G7) of bonding resins with respect to their final bond strength. The published reports of lower bond strength after additional laser conditioning may be related to thermal damage or unfavorable alteration to the enamel surface by excessive laser energy and the chemistry of bonding systems studied. These factors will affect the overall wettability and the subsequent adhesion properties of the enamel surface.

The effect of erbium family laser on tensile bond strength of composite to dentin in comparison with conventional method

The purpose of this study was to evaluate the effect of Er:YAG and Er,Cr:YSGG laser on tensile bond strength of composite resin to dentine in comparison with bur-prepared cavities. Fifteen extracted caries-free human third molars were selected. The teeth were cut at a level below the occlusal pit and fissure plan and randomly divided into three groups. Five cavities were prepared by diamond bur, five cavities prepared by Er:YAG laser, and the other group prepared by Er,Cr:YSGG laser. Then, all the cavities were restored by composite resin. The teeth were sectioned longitudinally with Isomet and the specimens prepared in dumbbelled shape (n = 36). The samples were attached to special jigs, and the tensile bond strength of the three groups was measured by universal testing machine at a speed of 0.5 mm/min. The results of the three groups were analyzed with one-way ANOVA and Tamhane test. The means and standard deviations of tensile bond strength of bur-cut, Er:YAG laser-ablated, and Er,Cr:YSGG laser-ablated dentine were 5.04 ± 0.93, 13.37 ± 3.87, and 4.85 ± 0.93 MPa, respectively. There is little difference in tensile bond strength of composite resin in Er,Cr:YSGG lased-prepared cavities in comparison with bur-prepared cavities, but the Er:YAG laser group showed higher bond strength than the other groups.

Microtensile bond strength of an etch-and-rinse adhesive to enamel and dentin after Er:YAG laser pretreatment with different pulse durations

The purpose of this study is to evaluate microtensile bond strength (μTBS) of an etch-and-rinse adhesive to enamel and dentin after treatment with Er:YAG laser using different pulse durations. Extracted human molars were flattened to obtain enamel or dentin surfaces. The enamel specimens (E) were divided into nine groups and the dentin (D) specimens were divided into seven groups according to the surface treatments (n = 6). E-C: acid was applied according to the manufacturer's instructions and used as control, E-SSP: 120 mJ, 10 Hz, SSP (50 μs), E-SSP-A: 120 mJ,10 Hz, SSP+acid, E-VSP: 120 mJ, 10 Hz, VSP (100 μs), E-VSP-A: 120 mJ, 10 Hz, VSP+acid, E-SP: 120 mJ, 10 Hz, SP (150 μs), E-SP-A:120 mJ,10 Hz, SP+acid, E-LP:120 mJ,10 Hz, LP (300 μs), E-LP-A:120 mJ,10 Hz, LP+acid; D-C: acid was applied and used as control, D-SSP: 80 mJ, 10 Hz, SSP, D-SSP-A: 80 mJ, 10 Hz, SSP+acid, D-VSP: 80 mJ, 10 Hz, VSP, D-VSP-A: 80 mJ, 10 Hz, VSP+acid, D-SP: 80 mJ, 10 Hz, SP, D-SP-A: 80 mJ, 10 Hz, SP+acid. After application of etch-and-rinse adhesive, composite built-ups were created with a nanoceramic composite. Specimens were sectioned into serial 1-mm(2) sticks, and μTBS was measured in five sticks from each tooth randomly selected (n = 30). Failure modes were determined under a stereomicroscope. μTBS test data were analyzed by Welch-ANOVA followed by Dunnett's T3 tests and failure mode distributions were analyzed by Pearson Chi-square test (p = 0.05). μTBS was higher for enamel and dentin after additional acid etching than laser irradiation alone. E-SSP-A group exhibited the highest μTBS for enamel (p < 0.05). The D-SP-A group showed the highest value but the difference was not significant in comparison to D-C (p > 0.05). The μTBS of laser-irradiated but not acid-etched groups decreased when longer pulse durations were used. Laser treatment could enhance or impair the μTBS to enamel and dentin depending on the pulse duration used and additional acid application.

The influence of erbium:yttrium-aluminum-garnet laser ablation with variable pulse width on morphology and microleakage of composite restorations

The objective of this study was to evaluate the influence of various pulse widths with different energy parameters of erbium:yttrium-aluminum-garnet (Er:YAG) laser (2.94 mum) on the morphology and microleakage of cavities restored with composite resin. Identically sized class V cavities were prepared on the buccal surfaces of 54 bovine teeth by high-speed drill (n = 6, control, group 1) and prepared by Er:YAG laser (Fidelis 320A, Fotona, Slovenia) with irradiation parameters of 350 mJ/ 4 Hz or 400 mJ/2 Hz and pulse width: group 2, very short pulse (VSP); group 3, short pulse (SP); group 4, long pulse (LP); group 5, very long pulse (VLP). All cavities were filled with composite resin (Z-250-3 M), stored at 37 degrees C in distilled water, polished after 24 h, and thermally stressed (700 cycles/5-55 degrees C). The teeth were impermeabilized, immersed in 50% silver nitrate solution for 8 h, sectioned longitudinally, and exposed to Photoflood light for 10 min to reveal the stain. The leakage was evaluated under stereomicroscope by three different examiners, in a double-blind fashion, and scored (0-3). The results were analyzed by Kruskal-Wallis test (P > 0.05) and showed that there was no significant differences between the groups tested. Under scanning electron microscopy (SEM) the morphology of the cavities prepared by laser showed irregular enamel margins and dentin internal walls, and a more conservative pattern than that of conventional cavities. The different power settings and pulse widths of Er:YAG laser in cavity preparation had no influence on microleakage of composite resin restorations.

SEM analysis of enamel surface treated by Er:YAG laser: influence of irradiation distance

BACKGROUND

Depending on the distance of laser tip to dental surface a specific morphological pattern should be expected. However, there have been limited reports that correlate the Er:YAG irradiation distance with dental morphology.

PURPOSE

To assess the influence of Er:YAG laser irradiation distance on enamel morphology, by means of scanning electron microscopy (SEM).

METHODS

Sixty human third molars were employed to obtain discs (approximately =1 mm thick) that were randomly assigned to six groups (n=10). Five groups received Er:YAG laser irradiation (80 mJ/2 Hz) for 20 s, according to the irradiation distance: 11, 12, 14, 16, or 17 mm and the control group was treated with 37% phosphoric acid for 15 s. The laser-irradiated discs were bisected. One hemi-disc was separated for superficial analysis without subsequent acid etching, and the other one, received the phosphoric acid for 15 s. Samples were prepared for SEM.

RESULTS

Laser irradiation at 11 and 12 mm provided an evident ablation of enamel, with evident fissures and some fused areas. At 14, 16 and 17 mm the superficial topography was flatter than in the other distances. The subsequent acid etching on the lased-surface partially removed the disorganized tissue.

CONCLUSIONS

Er:YAG laser in defocused mode promoted slight morphological alterations and seems more suitable for enamel conditioning than focused irradiation. The application of phosphoric acid on lased-enamel surface, regardless of the irradiation distance, decreased the superficial irregularities.

Scanning electron microscopic evaluation of enamel and dentin surfaces after Er:YAG laser preparation and laser conditioning

OBJECTIVE

The aim of this study was to observe and evaluate the micro-morphology of enamel and dentin surfaces after Er:YAG laser preparation and conditioning.

BACKGROUND DATA

Information regarding micro-morphologic changes of tooth substance as a result of a change of Er:YAG laser parameters for cavity preparation is limited.

METHODS

Human enamel and dentin surfaces were irradiated with an Er:YAG laser with the following parameters : (1) energy output: 200 mJ, 250 mJ, 300 mJ, 350 mJ, and 400 mJ; (2) repetition rate: 5 Hz and 10 Hz; (3) pulse duration: 100 mus/VSP (very short pulse); (4) 5 and 10 passes over the surface at a distance of 7 mm, speed: 4 mm/s using a non-contact delivery tip; (5) water cooling: 5 mL/min. The hand piece was fixed in a power driven x-y moving table. Subsequently, half of the samples were laser-conditioned at 100 mJ, 10 Hz, 250 mus/SP (short pulse) for enamel, and 80 mJ, 10 Hz, SP for dentin at a distance of 10 mm. Surface morphology and surface alterations were evaluated using scanning electron microscopy (SEM).

RESULTS AND CONCLUSION

SEM evaluation showed the characteristics of Er:YAG-lased enamel and dentin surfaces: irregular enamel surfaces with typical keyhole shaped prisms and rods, and protrusion of dentinal tubules with a cuff-like appearance. Laser conditioning rounded off the sharp edges on the enamel irregularities and dentin surface structures. First signs of vitrification were seen at 250 mJ for enamel samples and 300 mJ for dentin samples. Increase of the pulse repetition rate from 5 Hz to 10 Hz did not result in changes of surface morphology. Laser conditioning did not result in additional vitrification.

Bond strength of self-etching primer to bur cut, Er,Cr:YSGG, and Er:YAG lased dental surfaces

OBJECTIVE

The purpose of this study was to evaluate the tensile bond strength of a self-etching primer system to enamel and dentin surfaces treated with Er:YAG and Er,Cr:YSGG lasers.

BACKGROUND DATA

The recently introduced self-etching primer systems have been shown to adhere better to dental surfaces with thin or no smear layers. Moreover, there have been no previous reports on the bond strength of these adhesives to Er,Cr:YSGG laser-irradiated enamel and dentin, which have been shown to be free of a smear layer.

METHODS

Thirty samples of enamel and thirty of dentin were divided into three groups. The first group of each substrate served as a control with a standardized bur cut, and the other two groups were conditioned with Er:YAG (350 mJ, 10 Hz, 20 J/cm(2) for enamel; 300 mJ, 6 Hz, 17 J/cm(2) for dentin) and Er,Cr:YSGG laser (125 mJ, 20 Hz, 16 J/cm(2) for both substrates). After the bonding procedure, samples were restored with composite resin, and the tensile bond strength test was performed.

RESULTS

The ANOVA two-way analysis and the Tukey test at 5% significance level showed that for enamel and dentin, the bond strength values were statistically higher in Er:YAG-laser treated than in Er,Cr:YSGG-laser treated surfaces (p = 0.0001). However, bond strength means for both laser-irradiated groups were statistically lower than for the bur cut group (Er:YAG: p = 0.0281 and Er,Cr:YSGG: p < 0.0001). SEM observation of laser-irradiated surfaces revealed a roughened aspect and absence of smear layer.

CONCLUSIONS

The self-etching system adhesion was influenced by the type of erbium laser used, and the bond strength was higher in the Er:YAG-laser irradiated than in the Er,Cr:YSGG-laser irradiated surfaces.

Influence of energy and pulse repetition rate of Er:YAG laser on enamel ablation ability and morphological analysis of the laser-irradiated surface

OBJECTIVE

To assess the influence of energy and pulse repetition rate of Er:YAG laser on the enamel ablation ability and substrate morphology.

METHODS

Fifteen crowns of molars were sectioned in four fragments, providing 60 samples, which were ground to flatten the enamel surface. The initial mass was obtained by weighing the fragments. The specimens were hydrated for 1 h, fixed, and a 3-mm-diameter area was delimited. Twelve groups were randomly formed according to the combination of laser energies (200, 250, 300, or 350 mJ) and pulse repetition rates (2, 3, or 4 Hz). The final mass was obtained and mass loss was calculated by the difference between the initial and final mass. The specimens were prepared for SEM. Data were submitted to ANOVA and Scheffé test.

RESULTS

The 4 Hz frequency resulted in higher mass loss and was statistically different from 2 and 3 Hz (p < 0.05). The increase of frequency produced more melted areas, cracks, and unselective and deeper ablation. The 350 mJ energy promoted greater mass loss, similar to 300 mJ.

CONCLUSIONS

The pulse repetition rate influenced more intensively the mass loss and morphological alteration. Among the tested parameters, 350 mJ/3 Hz improved the ability of enamel ablation with less surface morphological alterations.

Spectroscopic characterization of enamel surfaces irradiated with Er:YAG laser

The purpose of this study was to investigate the effect of laser irradiation on the enamel surface spectroscopically. Polished bovine enamel surface was irradiated with an Er:YAG laser apparatus and chemically analyzed using X-ray photoelectron spectroscopy (XPS). XPS detected core electron peaks such as carbon (C 1s) and nitrogen (N 1s), as well as calcium (Ca 2s, Ca 2p, Ca 3s, Ca 3p), phosphorous (P 2s, P 2p), and oxygen (O 1s), from the control enamel surface. After irradiation, XPS revealed that the intensity of C 1s peak slightly decreased while that of N 1s diminished below the detection limit. Detailed C 1s narrow scan spectrum of the Er:YAG laser-irradiated enamel surface showed that C-O/C-N, C = O/-CON=, -COO-, and CO,3(2-) components, attributed to the specific composition of enamel and any common carbon contamination in surplus, relatively decreased. The binding energies of Ca 2p and P 2p, delta (Ca 2p, P 2p), and the Ca/P ratio of lased enamel were found to be different from those of non-lased enamel. It was also shown that Er:YAG laser ablation caused surface alterations to the apatitic inorganic components of tooth tissue.

Influence of Er:YAG laser irradiation distance on the bond strength of a restorative system to enamel

OBJECTIVES

The aim of the present study was to investigate in vitro the effect of Er:YAG laser on bonding to enamel, varying the irradiation distance.

METHOD

Tensile bond strength of an adhesive restorative system to non-irradiated and irradiated enamel surfaces was evaluated. Thirty caries-free human third molars were sectioned in mesio-distal direction and embedded in acrylic resin. Enamel was flattened, and a 3-mm-diameter bonding area was demarcated. Specimens were randomly assigned into six groups: groups I-V were treated with the Er:YAG laser (80 mJ/2 Hz), varying the irradiation distance (11, 12 mm-focused, 14, 16 and 17 mm, respectively), followed by 35% phosphoric acid etching. Control group (VI) received treatment with phosphoric acid alone. Single Bond adhesive system was applied on the conditioned enamel, and composite resin cones, bonded to enamel, were fabricated with Z250. After storage, samples were tested in tensile to failure (50 kgf and 0.5 mm/min).

RESULTS

Means in MPa were: I-9.67 (+/-3.44); II-13.29 (+/-2.65); III-13.33 (+/-2.22); IV-14.87 (+/-3.58); V-16.43 (+/-4.52); VI-22.90 (+/-3.03). ANOVA and Tukey test revealed statistically significant decrease of bond strength in group I (P < 0.05). Groups II-IV presented similar results, as did groups IV and V. Control group (VI) yielded the best overall performance (P < 0.05).

CONCLUSION

Er:YAG laser irradiation adversely affected adhesion to enamel. However, bond strength was influenced by the irradiation distance, thus being stronger with the increase of distance to the target tissue.