Effect of Dentin Hardness on Ablation Rate with Er:YAG Laser

Abstract

Objective: This study used artificially demineralized bovine dentin to ascertain the effect of hardness of demineralized dentin on ablation rate with the Er:YAG laser. Background Data: Before restoration of carious teeth, it is necessary to ablate any infected dentin that cannot be remineralized due to softening by the invading caries. A correlation has been suggested between the ablation efficiency of the Er:YAG laser and the progression of caries in dentin. To the best of our knowledge, no studies have investigated the relationship between degree of demineralization by dentinal caries and ablation rate with the Er:YAG laser. Materials and Methods: Bovine mandibular anterior tooth roots were used as dentin samples. Each sample was soaked in a demineralizing solution (2 M lactic acid, pH 4.0) for 3 d to obtain demineralized dentin (DD) samples. Another group of samples were prepared without demineralization as a sound dentin (SD) group for comparison. After determining the Knoop hardness number (KHN) of each sample, the dentin surface was ablated with an Er:YAG laser. Tip output and pulse rate were set at 50 mJ and 20 pulses per second (pps), respectively, and the water spray was set at 3.5 mL/min. Ablation width, depth, and volume were measured following irradiation. Results: In the DD group, dentin hardness was 10.4 Ϯ 1.6 KHN at 100 m from the surface. In the sound dentin group, Knoop hardness was 51.0 Ϯ 1.6 KHN cross-sectionally throughout. No differences were observed from the surface to a depth of 2000 m. In the DD group, dentin ablation volume at the superficial demineralized layer was 2888 Ϯ 272 ϫ 10 4 m. In the SD group, dentin ablation volume was 1298 Ϯ 219 m 3 . The relationship between ablation volume and Knoop hardness was defined as Yϭ -40.699x ϩ 3350, revealing a marked negative correlation. Conclusion:The results demonstrate that the ablation volume for demineralized dentin was greater than that for sound dentin. The results suggest that the Er:YAG laser is capable of ablating infected dentin without damaging sound dentin by adjustment of tip output and pulse rate. 395

The Influence of Dentin Demineralization on Morphological Features of Cavities Using Er:YAG Laser

“…Although previous studies [29][30][31] have attempted to determine Er:YAG laser parameters for carious dentin, the literature is scarce and inconclusive about this. Katleen et al 32 claimed that energy output £ 200 mJ should be applied using the Er:YAG laser for caries-affected dentin.…”

“…This also confirms the findings of previous investigations that similar effects of laser parameters were also demonstrated. 29,33 The selected pulse frequency has been also considered the most influential parameter during dentin ablation. 34 Previous studies by Raucci-Neto 35,36 showed that the increase of Er:YAG laser frequency provided greater dentin caries removal, in which a larger amount of tissue was removed during irradiation of demineralized substrate, creating a deeper cavity.…”

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“…The carious dentin has more water content than sound dentin, and this variation between the both substrates was significant enough to affect the gross amount of tissue removed. The relation between the water content of the substrate and the ablation rate was previously observed by Armengol et al (1999), Hibst and Keller (1989), Mercer et al (2003), as well as the higher ablation of demineralized dental tissue (Osuka et al, 2009).…”