Weakening of dentin from cracks resulting from laser irradiation

Abstract

Cracking of tooth structure is a frequent mechanism of clinical failure necessitating treatment. Some laser conditions, particularly those without sufficient water cooling, may cause surface cracking of dentin. Surface cracks may serve as initiation sites for the onset of catastrophic fracture under mechanical stress, resulting in failure of the dentin. In this study, the hypothesis that laser initiated cracks result in lower bending strength of dentin was tested. Dentin beam specimens were prepared from human molar teeth, 1.1 × 1.1 × ~9 mm, and divided into groups C (control), W (wet), D (dry) of 12 beams each. In groups W, D, the middle of each beam on one surface (buccal) was irradiated with either a Er-YAG or Q-switched Er-YSGG laser and measured under a microscope, noting the dimensions in the irradiated area and immediately adjacent to irradiated area. Each beam was placed in a mechanical testing machine in a four-point bend jig and tested each with a monotonically increasing load at a displacement rate of 1 mm/min until failure. The bending strengths for groups C, W (Er-YAG laser) and D (Q-switched Er-YSGG laser) were, respectively, 141.6, 114.0, and 90.9 MPa. A one-way ANOVA determined a significant difference between groups C and D, p<0.001. Conclusion The Q-switched Er-YSGG laser without water caused cracks in the surface that significantly decreased the bending strength of dentin.

Screening of CO2 Laser (10.6 μm) Parameters for Prevention of Enamel Erosion

“…This means that if the temperature is not increased only for a short period of time (few microfractions of a second) heat accumulation can happen and cause ablation, melting, or cracking of tissue. 25 Such unwanted effects were also observed here. In addition to the significant increase of enamel resistance to erosion, the laser parameters tested in the present study have shown, under SEM and higher magnification, some surface modification.…”

Degradation in the Fatigue Resistance of Dentin by Bur and Abrasive Air-jet Preparations

“…The apparent subsurface flaw lengths resulting from the bur and abrasive air-jet treatments in this approach are 70 µm and 45 µm, respectively. While smaller than the values documented for laser preparation of dentin (Staninec et al, 2009), they caused a significant reduction in the fatigue resistance. Thus, small flaws introduced during the cutting of dentin are detrimental to its durability.…”

“…An evaluation of the strength of dentin after laser preparations showed that cracks exceeding 100 µm in length were introduced within the dentin under some treatment conditions (Staninec et al, 2009). Thus, flaws introduced with dental burs are potentially too small to see in direct evaluations (i.e., microscopy), but they could cause degradation in strength if they reach an adequate size.…”

On the Mechanics of Fatigue and Fracture in Teeth

“…Tooth fracture is more likely to originate from cracks that initiate and grow within the dentin. Flaws in the form of cracks can be introduced within the dentin during the restorative process as a result of material removal [25,26]. As an alternative, cracks may develop in dentin from incipient flaws as a result of fatigue, particularly in regions of stress concentration posed by the restoration geometry [21].…”