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Alaa M. El-Araby*, Ahmed El-Hejazi. Alaa M. El-Araby*, Ahmed El-Hejazi. Dept.of Restorative Dental Sciences. College of Dentistry, King Saud University. Riyadh-KSA.Dept.of Restorative Dental Sciences. College of Dentistry, King Saud University. Riyadh-KSA.

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Results and Discussion Results and Discussion Results and Discussion Results and Discussion

1- Er:YAG laser device produces some thermal explosive changes of dental hard tissues.

2- Linear and circular surface irregularities (Caterpillar-like impressions ) were observed on the lased dentin.

3- No prism structures are evident. with a molten lava-like appearance were produced on the lased enamel.

4- Phosphoric acid etching is essential for surface modification even after laser irradiation.

Topographical characteristics of enamel and dentin after Er:YAG laser ablation versus phosphoric Topographical characteristics of enamel and dentin after Er:YAG laser ablation versus phosphoric acid etching.acid etching.

Topographical characteristics of enamel and dentin after Er:YAG laser ablation versus phosphoric Topographical characteristics of enamel and dentin after Er:YAG laser ablation versus phosphoric acid etching.acid etching.

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A. Typical enamel etching pattern. Etching of prim cores is predominant.B. Lased Enamel treated with phosphoric acid etchant. Enamel prism

are created but not predominant.C. Typical pattern of dentin surface etched with phosphoric acid.

Smear layer is completely removed. Dentinal tubules are completely opened.

D. Lased dentine treated with phosphoric acid.An irregular structure with many microholes was observed on the lased enamel. There is no etching pattern of prism cores. Scaly and rough surfaces were observed. No prism structures are evident. Molten lava-like appearance were produced.

Lased dentine shows irregular and rugged surface aspects with different depths were observed. Smear layer is partially removed. Dentinal tubules are not widely opened.

The SEM examination revealed characteristic micro-irregularities of the lased samples as compared with the conventional prepared samples conditioned with phosphoric acid.Lased dentin surface shows partially evaporated smear layer plus muds. Rare dentinal tubules were opened; linear and circular surface irregularities (Caterpillar-like impressions ) were observed on the dentin this results are in accordance with Cruti et al .4 Jagged outline as well as opened dentinal tubules are the main characteristics of the Er-YAG prepared tooth structure.The lased enamel surfaces were ablated and seemed to be thermally evaporated and to be the scale-like appearance at high magnification.Calcium (Ca) and phosphorus (P) content of lased tooth structure was significantly lower (p < 0.01) than those treated with phosphoric acid etchant. The calcium ratio to phosphorus showed no significant changes between the acid etched specimens and laser irradiated specimens (p > 0.01)

Lasers were first considered for dental use in 1964, researchers have investigated various applications of laser in dentistry. Different studies have evaluated the ruby, CO2, Nd:YAG, Erbium (Er):YAG, excimer, and argon lasers for their effects on hard and soft tissues as well as dental materials. Erbium: yttrium-aluminium-garnet (Er:YAG) laser is the only laser that American Food and Drug administration approved for cavity preparation. Wavelength of Er:YAG (2940 nm) correspond to absorption peak of hydroxyapatite and water.

Er:YAG laser has a cutting mechanism different from other lasers. That is, water molecules in microscopic area on an irradiated dental surface absorb energy immediately after laser irradiation. The pressure produced causes microexplosions and vaporization.The potential of the Er:YAG laser to cut hard dental tissues such as enamel, cementum and bone, without significant thermal or structural damage has attracted attention. Er:YAG laser with a wavelength of 2.94 µm is used for tooth cavity preparations, as well as removing restorative materials.

When Er:YAG laser (2940 nm) is used to prepare cavities, does the bonding procedure require an acid etching step before application of primer and adhesive?

Nine freshly extracted premolars stored in saline solution were used in this study. The specimens were divided into three groups. Group 1 : cut surfaces were irradiated with Er:YAG laser at 200 mJ, 10Hz in SP mode. Group 2 : cut sufaces were conditioned with 37% phosphoric acid gel. Group 3 : laser irradiated surfaces were then conditioned with phosphoric acid gel. The experiment was performed with the Fotona FidelisTM Er:YAG VSP technology dental laser. Laser is applied in contact handpiece with fiber tip with water cooling focused to enamel and dentin. The tooth structure was irradiated with laser beam energy of 200 mJ in contact mode using a very short pulse (VSP) 100 s in length. Frequency was 10 Hz, and each irradiation lasted 10 s.Topographical analysis to enamel and dentin was investigated by SEM and energy-dispersive X-ray analysis (EDX). Scanning electron microscopy ( Jeol, JSM-6360LV- Japan) was operated at 20 kv under low vaccum mode. Uncoated specimens were prepared for EDX analysis. Then these specimens were sputter coated with gold ( Fine Coat, Ion sputter JEL-1100, Jeol-Japan) and viewed in the SEM to observe the appearance of the textured surfaces of different groups.Enamel and dentin calcium (Ca) and phosphorus (P) contents were determined by EDX. Statistical analysis was conducted using one-way nonparametric Analysis of Variance followed by Tukey type nonparametric post hoc test.

The aim of this study was to analyse the surface morphology of enamel and dentin after laser irradiation and compare it to that etched with phosphoric acid, and to determine Calcium (Ca) and phosphorus (P) contents by EDX.

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