A comparative study of etching enamel by acid and laser

Acid etching is regarded as one of the main means of providing additional retention in aesthetic dentistry. Alternative methods of achieving bonding to tooth tissue which have been proposed include laser etching. Conflicting results on bond strength to enamel have been reported for laser etching. Here the tensile bond strength of composite resin to acid- and laser-etched enamel was measured and the topographical differences between the surfaces were evaluated using the scanning electron microscope. The laser used was a pulsed Nd-YAG laser at 10 pulses per second with a pulse length of 150s, 80mJ pulse^–1, 1.064m wavelength. The results obtained indicate that the bond strength of laser-etched enamel was significantly lower than that of acid-etched enamel. In this study the difference may be attributable to the chromophore used. Variations in the rate of traverse of the laser tip across the surface did not appear to produce significant alterations in the bond strength.     

Effect of Er:YAG laser on enamel acid resistance: morphological and atomic spectrometry analysis

BACKGROUND AND OBJECTIVES: This study evaluated the effect of Er:YAG laser on enamel acid resistance. STUDY DESIGN/MATERIALS AND METHODS: Seventy human enamel slabs were randomly divided into seven groups (n = 10): G1, Er:YAG laser (Key Laser 2, KaVo, Germany) 60 mJ, 2 Hz, 33.3 J/cm2 (handpiece no. 2051, non-contact); G2, Er:YAG laser 80 mJ, 2 Hz, 44.4 J/cm2 (handpiece no. 2051, non-contact); G3, Er:YAG laser 120 mJ, 2 Hz, 66.6 J/cm2 (handpiece no. 2051, non-contact); G4, Er:YAG laser 64 mJ, 2 Hz, 20 J/cm2 (handpiece no. 2055, contact); G5, Er:YAG laser 86.4 mJ, 2 Hz, 26.9 J/cm2 (handpiece no. 2055, contact); G6, Er:YAG laser 135 mJ, 2 Hz, 42.2 J/cm2 (handpiece no. 2055, contact); G7, control. After laser irradiation, samples were submitted to an acid challenge. For both the nos. 2051 and 2055 handpieces, irradiation was performed with a water cooled spray (5.0 ml/minutes). The calcium and phosphorous ions delivered from the tooth surface were quantified by atomic emission spectrometry, and morphological analysis of the enamel surface was performed under scanning electron microscopy. Kruskal-Wallis and multiple comparisons tests were applied to distinguish significant differences among the treatments (alpha = 5%). RESULTS: Groups G1, G2, and G4 presented decreased demineralization. The SEM evaluation revealed different surface alterations as a result of the different energies used. CONCLUSION: Lower energies can decrease enamel solubility without severe alterations of the enamel.     

Microleakage of resin-based sealants after Er:YAG laser conditioning

The aim of this in vitro study was to investigate the effects of Er:YAG laser pretreatment procedures in fissure sealing. The fissures of 90 third molars were prepared in the mesial halves with Er:YAG laser (λ = 2,940 nm, 250 mJ/pulse, 4 Hz, fluence 32 J/cm²) and acid etched. They were randomly assigned to three groups, and the fissures in the distal halves were prepared differently according to the group: acid etching alone, bur and etching or Er:YAG laser alone. The fissures were sealed using Clinpro™ sealant (3M). The extent of microleakage was measured with a digital-image analyzer. The sealants prepared with Er:YAG laser alone displayed greater microleakage than the others (p < 0.05). Er:YAG laser irradiation does not eliminate the need for etching the enamel surface before sealing.     

Adhesion of composite resins to enamel irradiated by the Er:YAG laser: application of the ultrasonic scaler on irradiated surface

BACKGROUND AND OBJECTIVE: The clinical use of the Er:YAG laser in cavity preparation has become widespread. With respect to cavities prepared with the Er:YAG laser, restorations using composite resins and glass ionomer cements are common. The bond strength of current resin bonding systems to ground enamel is 14-30 MPa, whereas the strength to Er:YAG laser-irradiated enamel, regardless of the use or non-use of phosphoric acid etching is less than 10 MPa. STUDY DESIGN/MATERIALS AND METHODS: In this investigation, an ultrasonic scaler was tested as a technique to increase the bond strength of composite resins to the Er:YAG irradiated enamel surface. RESULTS: The application of the ultrasonic scaler significantly increased bond strength. CONCLUSIONS: The tensile bond strength in the groups treated with the ultrasonic scaler exhibited approximately twice the strength observed in groups treated with laser irradiation alone.     

Increased fluoride uptake in human dental specimens treated with diode laser

The hypothesis of this study was the fact that diode lasers can increase the fluoride uptake in dental structures. The main objectives were: (1) to evaluate the effect of diode laser–NaF varnish combination on binding fluoride to dental enamel in an in vitro model and (2) to analyse outer enamel surface changes produced by the laser energy. After NaF enamel varnish and laser irradiation at different levels of energy, specimen surfaces were examined by environmental scanning electron microscopy. The incorporation of F⁻ ion into the dental structure was quantitatively determined by using a fluoride ion-selective electrode. Results showed that the laser treatment significantly increased the binding of fluoride to the enamel surface without damaging it. The amount of F⁻ estimated was 37 ± 7 mg/l to the power of 5 W and 58 ± 12 mg/l to the power of 7 W. These increases were significantly greater than the ones achieved by conventional topical fluoridation. The results were analysed and compared by Kruskal–Wallis and Dunn’s multiple comparison tests, and significant statistical differences were found. These suggest that the NaF varnish–diode laser combination may be a useful option for the effective fluoridation of teeth.     

Comparative evaluation of the effects of Nd:YAG and Er:YAG laser in dentin hypersensitivity treatment

Dentin hypersensitivity (DH) is one of the most common complications that affect patients after periodontal therapy. So far, many investigators have successfully used different types of laser on DH treatment. The aim of this study was to evaluate the comparative effect of Nd:YAG laser and Er:YAG laser on human teeth desensitization. A group of nine patients with a total of 63 chronic hypersensitive teeth were selected. Each one of them should at least have three hypersensitive teeth. These teeth were randomly allocated into three groups. Group 1, Nd:YAG laser (1 W, 15 Hz, 60 s, two times); group 2, Er:YAG laser (100 mJ, 3 Hz, 60 s, two times); and group 3 serves as control group without any treatment. Assessment of pain was performed by a visual analysing scale (VAS) after stimulation of sensitive tooth by using the sharp tip of an explorer. This test was performed before treatment, immediately after that and at 1-, 3- and 6-month intervals after treatment by one blinded examiner. Analysis of VAS score between the three groups at the time of treatment did not show any significant difference (p = 0.506). However, by using repeated-measurement analysis of variance test, significant differences were seen in the three groups between before-treatment VAS score and after treatment (p < 0.0005). This statistically significant difference in the control group demonstrated a placebo effect. However, the effect of using Nd:YAG and Er:YAG lasers was stronger than this placebo effect, so that after removing the effect of the placebo, differences immediately after, 1, 3 and 6 months post treatment between all three groups still were statistically highly significant (p < 0.0005). Compared to the Er:YAG laser group, using Nd:YAG laser resulted in a significant reduction of VAS score at each follow-up examination (p < 0.0005). Although using Nd:YAG and Er:YAG laser in desensitization of hypersensitive teeth showed a placebo effect limited to a short time, results of this study demonstrated that both of these lasers have an acceptable therapeutic effect. The observed effects seemed to last for at least 6 months. It was concluded that Nd:YAG laser is more effective than Er:YAG laser in reduction of patients’ pain.     

Effect of Er,Cr:YSGG laser irradiation on eruption of rat mandibular incisor after disturbance of the enamel organ in the pulp

To investigate the efficacy of Er,Cr:YSGG (erbium,chromium:yttrium scandium gallium garnet) laser irradiation in root canal preparation and to evaluate its effect on eruption of rat incisors after disturbance of the enamel organ in the pulp, 20 canals of lower left incisor teeth were prepared by K-files followed by Er,Cr:YSGG laser irradiation, and 20 canals of right incisors were subjected to K-files only (control). At 1 week after irradiation, both sides of incisors erupted at the same level from the gingival margin. Histological findings showed that laser irradiation produced a slightly larger damage in the pulp than that of control. Scanning electron microscope observation revealed that laser-treated surface revealed a rough, irregular, and very clean surface; there was almost no evidence of debris or smear layer, and dentinal tubules were opened. Adequate power of Er,Cr:YSGG laser irradiation is effective in root canal preparation without disturbance of the eruption.     

The ablation threshold of Er:YAG and Er:YSGG laser radiation in dental enamel

. The scientific investigation of fundamental problems plays a decisive role in understanding the mode of action and the consequences of the use of lasers on biological material. One of these fundamental aspects is the investigation of the ablation threshold of various laser wavelengths in dental enamel. Knowledge of the relationships and influencing factors in the laser ablation of hard tooth tissue constitutes the basis for use in patients and the introduction of new indications. The present paper examines the ablation threshold of an Er:YAG laser (λ=2.94 μm) and an Er:YSGG laser (λ=2.79 μm) in human dental enamel. To this end, 130 enamel samples were taken from wisdom teeth and treated with increasing energy densities of 2–40 J/cm². The sample material was mounted and irradiated on an automated linear micropositioner. Treatment was performed with a pulse duration of τ_P(FWHM)≈150 μs and a pulse repetition rate of 5 Hz for both wavelengths. The repetition rate of the laser and the feed rate of the micropositioner resulted in overlapping of the single pulses. The surface changes were assessed by means of reflected light and scanning electron microscopy. On the basis of the results, it was possible to identify an energy density range as the ablation threshold for both the Er:YAG and the Er:YSGG laser. With the Er:YAG laser, the transition was found in an energy density range of 9–11 J/cm². The range for the Er:YSGG laser was slightly higher at 10–14 J/cm². Paper received 15 May 2001; accepted after revision 14 January 2002. Correspondence to: Dr Christian Apel, Department of Conservative Dentistry, Periodontology and Preventive Dentistry, University of Aachen, Pauwelsstr. 30, D-52074 Aachen, Germany. Tel.: +49 241 8089088; Fax: +49 241 8888468; e-mail: capel@post.klinikum.rwth-aachen.de     

Plasma fluoride and enamel fluorosis

It is postulated that tissue fluid F concentrations are the primary determinants of fluoride effects on bones and developing teeth and that these concentrations are dependent on, or mirrored by, blood plasma F. It has earlier been shown that the plasma F levels are dependent on the dietary F supply as well as on skeletal F concentration. Fasting and post-ingestion or postinjection plasma F levels have been determined in rats on F doses that cause different degrees of enamel fluorosis. The results indicate that temporary peak values rather than elevated fasting values are responsible for the occurrence of enamel fluorosis and that the peak values must approach about 10 M in order to block enamel formation by the ameloblasts. The diagnostic and prognostic importance of plasma F determinations is discussed.     

Comparison of the bond strength of composite resin to Er:YAG laser irradiated human enamel pre-treated with various methods in vitro

BACKGROUND AND OBJECTIVE: We have reported that the application of ultrasonic scalers on the Er:YAG laser-irradiated enamel surface achieved bond strengths of approximately 16 MPa. However, it is reported that a bond strength of 20 MPa is needed to prevent the marginal gaps, so the tensile bond strength (TBS) of composite resin to the Er:YAG laser-irradiated enamel is still insufficient. STUDY DESIGN/MATERIALS AND METHODS: Various methods (phosphoric acid etching, air scaling, ultrasonic scaling, air powder polishing, combination with phosphoric acid etching, and prior mechanical removal methods) were tested as a technique to increase TBS of composite resins to the Er:YAG irradiated enamel. RESULTS: Both the methods of mechanical removal following Er:YAG laser irradiation and the phosphoric acid etching following irradiation and mechanical removal had significant effects on TBS. TBS in the group with acid etching following air powder polishing showed highest value, 22.0 MPa. CONCLUSION: The application of phosphoric acid etching following mechanical removal of Er:YAG laser irradiation was effective to achieve high bond strength.     

Calcium solubility of dental enamel following sub-ablative Er:YAG and Er:YSGG laser irradiation in vitro

BACKGROUND AND OBJECTIVE: The objective of the present study was to investigate the effect of sub-ablative Er:YAG (lambda = 2.94 microm) and Er:YSGG (lambda = 2.79 microm) laser radiation on the acid solubility of dental enamel. The influence of fluoride application prior to laser irradiation was additionally evaluated. STUDY DESIGN/MATERIALS AND METHODS: To this end, 294 enamel specimens were prepared from bovine teeth and divided into 14 groups of 21 specimens each. The enamel samples were irradiated in their groups with the Er:YAG and the Er:YSGG laser, using energy densities of 4, 6, and 8 J/cm(2) in each case. Irradiation was additionally repeated in the same way on specimens, which had previously been immersed in 1% sodium fluoride solution for 15 minutes. One group was left untreated and served as a control group. A further group was not irradiated, but only immersed in the 1% fluoride solution for 15 minutes. The enamel specimens were demineralised for 24 hours in an acetate buffer solution. The calcium content in the demineralisation solution was subsequently determined with the aid of atomic absorption spectrometry. RESULTS: The results indicate a decline in calcium solubility after laser irradiation. Compared to the control group, a 20% lower calcium content was detected in the demineralisation solution after irradiation with the Er:YSGG laser at 8 J/cm(2). The difference between the laser-irradiated groups and the untreated control group was, however, not statistically significant. A significantly lower calcium content was found in the demineralisation solution after fluoridation of the specimens. Additional laser radiation had no further effect on this result. CONCLUSIONS: In summary, it can be stated that, although the erbium laser wavelengths apparently have the potential to increase acid resistance, their application solely for caries prevention would not appear to be sensible under the prevailing conditions.     

Treatment of rhinophyma with Er:YAG laser

BACKGROUND AND OBJECTIVE: Rhinophyma is a benign, disfiguring disorder of the nose which presents the end stage of acne rosacea, and can also occasionally result in nasal airway obstruction. We describe the first series of patients treated with Erbium laser. STUDY DESIGN/MATERIALS AND METHODS: Severe-to-moderate rhinophyma in six patients were treated at our institution between 1995 and 1996, using the Erbium:YAG (Erb:YAG) laser. RESULTS: All patients achieved marked cosmetic improvement, with no complications. Post-operative healing time was seven to fourteen days-significantly shorter than similar other modalities. CONCLUSIONS: The Erbium laser provides very accurate tissue ablation and allows the sculpturing of the hypertrophied areas, offering good cosmetic results, with a very short healing period as shown in our study.     

Bond strengths of brackets bonded to enamel surfaces conditioned with femtosecond and Er:YAG laser systems

The aim of this study was to compare femtosecond and Er:YAG laser systems with regard to enamel demineralization and bracket bond strength. Human-extracted premolars were randomized to three groups (n?=?17) depending on the conditioning treatment used for the buccal surfaces: 37 % orthophosphoric acid, Er:YAG laser etching (MSP mode 120 mJ, 10 Hz, 1.2 W), and femtosecond laser etching (0.4 W, 800 nm, 90 fs/pulse, 1 kHz). Metal brackets were bonded with Transbond XT to the conditioned surfaces and light cured for 20 s. The samples were thermocycled (5000 cycles, 5–55 °C) and subjected to shear bond strength (SBS) testing using a universal testing machine. Failure types were analyzed under an optical stereomicroscope and SEM. The adhesive remnant index (ARI) was evaluated to assess residual adhesive on the enamel surface. The results revealed no significant differences in SBS between the Er:YAG laser (7.2?±?3.3 MPa) and acid etching groups (7.3?±?2.7 MPa; p?<?0.05), whereas a significant difference was observed between the femtosecond laser etching group (3.3?±?1.2 MPa) and the other two groups (p?<?0.01). ARI scores were significantly different among the three groups. The results of our study suggest that laser conditioning with an Er:YAG system results in successful etching, similar to that obtained with acid. The sole use of a femtosecond laser system may not provide an adequate bond strength at the bracket–enamel interface.     

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.     

Factors affecting the rate of post-eruptive maturation of dental enamel

The factors affecting the rate of post-eruptive maturation of dental enamel in Sprague-Dawley rats have been studied, using silver nitrate stain to delineate the hypmineralized areas in molars. Hypomineralization, as measured by the stain, can arise through demineralization, lack of mineralization, or both. Maturation is the net result of the total accumulation of calcium and phosphate in the erupted dental enamel. It was found that the inhibitor of hydroxyapatite crystal growth, disodium ethane-1-hydroxy-1, 1-diphosphonate (EHDP^TM)¹, applied topically to the newly-erupted molars of rats, decreased the rate of post-eruptive maturation of molars. On the other hand, fluoride (a known stimulator of hydroxyapatite crystal growth and inhibitor of demineralization) applied simultaneously with EHDP restored the rate of post-eruptive maturation of the molars to that of a normal control rat. A dentifrice containing 3% EHDP and 0.1% fluoride significantly reduced the progress of caries in rate. Fluoride treatment alone increased the degree of post-eruptive maturation. Also, in a separate experiment, as the mole ration of EHDP to fluoride was decreased from 16 to 0.5 at constant EHDP level, there was a significant increase in the degree of post-eruptive maturation of dental enamel. It is concluded from the results of this study that although EHDP may inhibit the maturation of rat enamel, fluoride prevents this effect when applied simultaneously. The data support the hypothesis that post-eruptive maturation of dental enamel is governed by the sum of two distinct and opposing processes, mineralization and demineralization. The processes can be inhibited singly or together.

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Zusammenfassung Die Faktoren, welche die post-eruptive Reifungsrate von Zahnschmelz bei Sprague-Dawley-Ratten beeinflussen, wurden studiert. Die hypomineralisierten Stellen in den Backenzähnen wurden mittels Silbernitratfärbung dargestellt. Die durch Färbung gemessene Hypomineralisation kann durch Demineralisation, durch Mangel an Mineralisation oder durch beides entstehen. Die Reifung ist das effektive Ergebnis der totalen Akkumulation von Calcium und Phosphat im Schmelz des durchgebrochenen Zahnes. Es wurde festgestellt, daß ein Hemmkörper des Hydroxyapatitkristall-Wachstums, nämlich Disodium Ethan-1-hydroxy-1,1-Diphosphonat (EHDP^TM)¹, bei lokaler Anwendung an frisch durchgestossenen Rattenmolaren deren post-eruptive Reifungsrate herabsetzt. Andererseits bewirkte Fluorid (ein bekannter Stimulator von Hydroxyapatitkristall-Wachstum und ein Hemmkörper der Demineralisation), welches gleichzeitig mit EHDP verabreicht wurde, die Rückkehr der posteruptiven Reifungsrate der Molaren zur Norm. Eine Zahnpaste, welche 3% EHDP und 0,1% Fluorid enthielt, verminderte das Fortschreiten der Karies bei Ratten signifikant. Fluoridbehandlung allein erhöhte das Ausmaß der post-eruptiven Reifung. In einem separaten Ver-EHDP-Gehalt herabgesetzt wurde, konnte ebenfalls eine signifikante Erhöhung im Ausmaß der post-eruptiven Reifung von Zahnschmelz festgestellt werden. Aus den Ergebnissen dieser Untersuchung wird geschlossen, daß, obwohl EHDP die Reifung von Rattenzahnschmelz hemmen kann, diese Wirkung durch gleichzeitig angewandtes Fluorid verhindert wird. Die Befunde erhärten die Hypothese, daß post-eruptive Reifung von Zahnschmelz durch die Summe zweier bestimmter und entgegengesetzter Prozesse, durch Mineralisation und Demineralisation, beherrscht wird. Diese Prozesse können einzeln oder miteinander gehemmt werden.

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Résumé Les facteurs intervenant au cours de la maturation postéruptive de l'émail dentaire, chez les rats Sprague-Dawley, ont été étudiés en utilisant le nitrate d'argent pour la mise en évidence des régions hypominéralisées des molaires. L'hypominéralisation, déterminée par coloration, peut se produire par déminéralisation, défaut de minéralisation ou les deux, à la fois. La maturation résulte de l'accumulation totale de calcium et de phosphate au niveau de l'émail dentaire ayant effectué son éruption. Un inhibiteur de la croissance cristalline de l'hydroxyapatite, le disodium éthane-1-hydroxyle-1, 1-diphosphonate (EHDP^TM)¹, appliqué localement au niveau de molaires de rats, venant de faire leur éruption, diminue la maturation post-éruptive des molaires. D'autre part, le fluor (connu comme stimulant de la croissance cristalline de l'hydroxyleapatite et inhibiteur de la déminéralisation), appliqué simultanément avec l'EHDP, aboutit à une maturation postéruptive des molaires, identique à celle des rats témoins. Un dentifrice, contenant 3% d'EHDP et 0,1% de fluor, réduit la fréquence des caries chez le rat, de façon significative. Le traitement fluoré, appliqué isolément, augmente l'intesité de la maturation post-éruptive. Dans une autre expérience, où le rapport molaire de l'EHDP et du fluor est diminué de 16 à 0,5, à une concentration constante d'EHDP, on note une augmentation significative du degré de maturation postéruptive de l'émail dentaire. Il semble donc que, bien que l'EHDP puisse inhiber la maturation de l'émail de rat, le fluor administré simultanément peut inhiber cet effet. L'hypothèse que la maturation post-éruptive de l'émail dentaire soit contrôlée par deux processus opposés, la minéralisation et la déminéralisation, parait se vérifier. Ces processus peuvent étre inhibés isolément ou simultanément.