Non-carious cervical lesions (NCCLs) refer to the loss of a hard tooth structure near the cement-enamel junction, which is not the result of caries. These lesions are wedge or saucer-shaped and vary in depth and width according to the duration, intensity, and frequency of the underlying causes1. The etiology of NCCLs includes parafunctional habits, insufficient tooth brushing, and consumption of highly acidic beverages2. Lesions develop owing to multiple factors. Additionally, the exposure of dentin in the cervical area of the affected teeth is associated with cervical dentin hypersensitivity (CDH)3.

Cervical dentin hypersensitivity is a condition in which exposed dentin causes sharp, short-term pain. The exact etiology is uncertain4, but is thought to be related to open dentin tubules on the surface of the exposed dentin5. The most widely accepted explanation is Brännström's hydrodynamic theory6, which suggests that fluid moving through these tubules stimulates pain receptors in or near the pulp. Blocking tubules reduces the permeability of dentin, and in turn, proportionally reduces the degree of dentin hypersensitivity (DH)7. According to some authors, dental restorations are used as physical barriers to reduce the symptoms caused by exposed dentin in NCCLs. However, this approach may not always be effective. Studies have shown that 20-30% of restored NCCLs were also associated with increased sensitivity to cold stimuli at 6 months8.

Dental restoration is often necessary to manage NCCLs as it helps replace lost tooth tissue and improves sensitivity and esthetics. Additionally, it helps prevent further loss of tooth tissue9. In symptomatic NCCLs, if the dentinal tubules were exposed to the oral environment for prolonged periods, symptoms can persist despite restorative therapy. The primary focus of treatment is to restore the impermeability of tubules by occluding them and controlling the neural elements within the pulp to minimize external stimulation10,11.

Laser therapy has become a widely used method for treating CDH12. There are two ways to treat DH with lasers. High-energy lasers can melt and recrystallize the dentinal tubules to block them. In contrast, low-energy lasers such as diodes can reduce the neurophysiological response and sensitivity of the exposed areas12,13. Diode laser therapy is often used before composite restorations to reduce sensitivity without completely blocking the dentinal tubules, allowing resin tags to form. Different diode laser wavelengths have been studied, including 630 nm for class V composite restorations13, 808 nm for NCCLs composite restorations14, and 940 nm for class II composite restorations before bonding procedures15. These wavelengths have been shown to reduce DH and postoperative sensitivity (POS) more than traditional restoration methods. However, no definitive scientific evidence exists to determine which wavelength is the best option16.

A study assessed the 445 nm blue wavelength diode laser effect on the intra-pulpal temperature of extracted teeth when irradiated at the cervical area. This showed that the parameters were biologically safe for the dental pulp and could potentially be used to treat DH17. However, no studies have been conducted on treating DH prior to composite restoration using the same laser wavelength. Additionally, no in vitro examination has determined the diode laser 445 nm effect on dentin topography.

In laser studies, heterogeneity is observed due to variations in energy density, tip diameter, and devices used16. This is true even when comparing different wavelengths in a single study. This study addresses this issue by using a single-diode laser device (SIROlase Blue) that emits three different laser wavelengths (445 nm, 660 nm, and 970 nm). This allowed us to compare the effects of three wavelengths with the same energy densities18 on the sensitivity changes and dentin topography. Standardization eliminates the variability caused by different parameters, enabling only a comparison of the wavelengths themselves. Furthermore, radiation penetration through dentin depends on several variables, mainly wavelength19.

Considering this gap in the literature, this study was conducted to evaluate the effects of different wavelengths (445 nm17, 660 nm20, and 970 nm21) in treating symptomatic NCCLs. Treatment was administered before composite restoration of the tooth's cervical third following class V cavity preparation over a 6-month follow-up period. Furthermore, an in vitro examination was conducted to compare the effects of irradiation with different diode wavelengths (445 nm, 660 nm, and 970 nm) on dentin topography under SEM. The null hypothesis was that there would be no sensitivity change in symptomatic NCCLs when exposed to 445 nm, 660 nm, and 970 nm diode laser wavelengths prior to composite restoration. Moreover, there would be no change in the dentin topography among the irradiated groups.