Abstract
ObjectivesThe aim of this study was to see the effect of Er:YAG laser irradiation in dentine and compare this with its effect in enamel. The mechanism of crack propagation in dentine was emphasised and its clinical implications were discussed.Materials and methodsCoronal sections of sound enamel and dentine were machined to 50-μm thickness using a FEI-Helios Plasma (FIB). The specimen was irradiated for 30 s with 2.94-μm Er:YAG laser radiation in a moist environment, using a sapphire dental probe tip, with the tip positioned 2 mm away from the sample surface. One of the sections was analysed as a control and not irradiated. Samples were analysed using the Zeiss Xradia 810 Ultra, which allows high spatial resolution, nanoscale 3D imaging using X-ray computed tomography (CT).ResultsDentine: In the peritubular dentine, micro-cracks ran parallel to the tubules whereas in the inter-tubular region, the cracks ran orthogonal to the dentinal tubules. These cracks extended to a mean depth of approximately 10 μm below the surface. On the dentine surface, there was preferential ablation of the less mineralised intertubular dentine, and this resulted in an irregular topography associated with tubules.Enamel: The irradiated enamel surface showed a characteristic ‘rough’ morphology suggesting some preferential ablation along certain microstructure directions. There appears to be very little subsurface damage, with the prismatic structure remaining intact.ConclusionsA possible mechanism is that laser radiation is transmitted down the dentinal tubules causing micro-cracks to form in the dentinal tubule walls that tend to be limited to this region.Clinical relevanceCrack might be a source of fracture as it represents a weak point and subsequently might lead to a failure in restorative dentistry.
Highlights
Dental hard tissues are organised in a three-dimensional and hierarchical manner and exhibit anisotropic mechanical properties [1,2,3]
One each was irradiated with the Er:YAG laser, with the others acting as controls
The following conclusions can be drawn: (1) Laser irradiation of moist enamel with our parameters resulted in a relatively small amount of material removal and no observable sub-surface damage under the conditions used
Summary
Dental hard tissues are organised in a three-dimensional and hierarchical manner and exhibit anisotropic mechanical properties [1,2,3]. Enamel and dentine have heterogeneity of structure, and the variation in structure and mechanical properties may influence the direction of crack progression [4]. Laser radiation of dental hard tissues usually results in the observation of cracks. Previous studies using scanning electron microscope (SEM) imaging explored the presence of cracks formed with high laser powers, CO2 lasers or when irradiated in a dry environment [5, 6], and are not clinically applicable. Yamada et al [7] reported that the irradiation of dentine with a CO2 laser resulted in cracks that were mostly in the peritubular dentine. Burkes et al [8] stated that enamel tissue following Er:YAG laser radiation showed
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