Structural Changes in Human Dental Enamel after Subablative Erbium Laser Irradiation and Its Potential Use for Caries Prevention

Abstract

Numerous studies have confirmed the potential of erbium laser irradiation for increasing the acid resistance of dental enamel. The objective of the present paper was to investigate the effect of subablative erbium laser irradiation on the structure and acid resistance of dental enamel by means of confocal laser scanning microscopy (CLSM). To this end, 12 samples of human dental enamel were irradiated with subablative energy densities (Φ) of an Er:YAG (λ = 2.94 µm, Φ = 6 J/cm²) and an Er:YSGG laser (λ = 2.79 µm, Φ = 8 J/cm²). The enamel surfaces of 6 samples were polished prior to irradiation. The remaining 6 samples were left intact (without polishing procedures) and, in the further course of the study, they were subjected to 1-week in situ demineralisation. All irradiated test surfaces were assigned a control surface on the same sample. The changes following laser irradiation and the in situ wearing time were assessed qualitatively using a confocal laser scanning microscope. The irradiation of dental enamel with subablative erbium laser irradiation produces fine cracks in the enamel surface. These cracks act as starting points for acid attack and favour deep demineralisation. These changes reduce or eliminate the positive effect of subablative erbium laser irradiation observed in connection with caries-preventive use. The clinical use of subablative erbium laser irradiation to prevent caries would appear not to make sense under the conditions studied.

The effect of Er,Cr:YSGG irradiation on microtensile bond strength of composite resin restoration

“…Irradiation with erbium lasers promotes loss of carbonate, formation of new hydroxyapatite-like crystals, and consequently more acid-resistant surfaces. 25) Asli et al 26) found that during laser irradiation, the evaporation of organic components may well lead to an increase in Ca, P, Mg contents in the laser-modified dentin, resulting in acquired acid resistance of dentin surface, in turn, affecting the adhesion of dental materials to dental hard tissue. Hossain et al 27) also asserted that acid resistance may be promoted by Er,Cr:YSGG laser irradiation.…”

Laser Technology for Caries Removal

“…Further researches confirmed that the application of USPLs with pulse length of few femtoseconds almost completely avoids thermal damages and the formation of microcracks on irradiated tissues and on surrounding ones (Kruger et al, 1999;Freitas et al, 2010). It must be pointed out that lasers that operate with pulse length of µs can generate the formation of microcracks on irradiated tissue depending on the energy density, and these thermal damages can be responsible for the development of secondary caries (Apel et al, 2005).…”

The role of mesoscopic modelling in understanding the response of dental enamel to mid-infrared radiation

“…Lastly, these results indicate that both CO 2 and Er:YAG lasers may cause unwanted cracking when used to treat the surface of enamel so that it becomes resistant to acid attacks by cariogenic bacteria, a line of treatment currently being investigated by several groups (Apel et al 2005, Tepper et al 2004. The temperatures (400-1000 • C) needed to achieve the intended carbonate loss (Zuerlein et al 1999a) will be more than sufficient to induce cracking through thermal expansion of pore water.…”

“…The temperatures (400-1000 • C) needed to achieve the intended carbonate loss (Zuerlein et al 1999a) will be more than sufficient to induce cracking through thermal expansion of pore water. Unwanted cracking has indeed been reported for enamel surface modification using the Er:YAG laser, but not for the CO 2 laser (Apel et al 2005(Apel et al , 2002b. In using CO 2 lasers to create acid resistant surfaces, researchers often use fluences high enough to induce melting in a thin surface layer, when no cracks would be detected.…”