Comparison of the Results of Biostimulation Treatment of Inferior Alveolar Nerve Injury Using Nd:YAG and Diode Lasers With Different Wavelengths.

Intraoral surgical procedures such as sagittal split osteotomy, dental implant placement, and surgical extraction of third molars are widely performed interventions in oral and maxillofacial surgery. Although these operations are generally safe and predictable, they may cause direct or indirect injury to the inferior alveolar nerve, one of the main sensory nerves of the mandible responsible for the innervation of the lower teeth, alveolar bone, gingiva, lower lip, and chin. Damage to this nerve can occur due to mechanical trauma, compression, thermal injury, or stretching during surgery, as well as following facial or mandibular trauma. As a consequence, patients may experience various neurosensory disturbances such as anesthesia, hypoesthesia, paresthesia, or dysesthesia. These conditions often result in discomfort, reduced functional capacity, and psychological distress, affecting both esthetic and functional expectations after surgical recovery. Restoring normal nerve function in such cases remains a major clinical challenge in oral surgery and neuromodulation research. The inferior alveolar nerve follows a delicate anatomical path through the mandibular canal, where it is easily affected by surgical manipulations. Even minor trauma may lead to transient or permanent sensory dysfunction. The pathophysiology of such nerve injuries involves axonal degeneration, demyelination, and subsequent alterations in nerve conduction. Depending on the severity, nerve regeneration may occur spontaneously or may require therapeutic intervention. The degree of recovery depends on the extent of axonal disruption, the inflammatory response in the surrounding tissue, and the capacity of Schwann cells to facilitate remyelination. Traditional treatment approaches for inferior alveolar nerve injury include observation, pharmacological support, surgical decompression, or microsurgical repair. However, outcomes of these methods are often unpredictable, and recovery is slow. Therefore, noninvasive therapeutic modalities that can enhance neuronal healing and accelerate sensory recovery have become an area of increasing interest in modern dentistry and maxillofacial surgery. Among these, the use of laser biostimulation-also known as low-level laser therapy or photobiomodulation-has gained significant attention as a noninvasive, safe, and clinically applicable method to promote nerve regeneration. Laser biostimulation involves the application of light energy at specific wavelengths to biological tissues, leading to a cascade of photochemical and photophysical effects at the cellular level. When absorbed by mitochondrial chromophores, particularly cytochrome c oxidase, the photons increase cellular metabolism, enhance ATP synthesis, stimulate DNA and RNA synthesis, and promote cellular proliferation and differentiation. In neural tissues, this process can lead to activation of Schwann cells, enhancement of neurotrophic factor secretion, reduction of oxidative stress, and modulation of inflammatory mediators, thereby creating a favorable microenvironment for axonal regrowth. Consequently, photobiomodulation represents an advanced therapeutic approach to accelerate neural healing following both iatrogenic and traumatic nerve injuries. Two of the most commonly used laser types for biostimulation in clinical practice are diode and Nd:YAG lasers. Both operate in the near-infrared region of the electromagnetic spectrum but differ in wavelength, absorption characteristics, and depth of tissue penetration. The diode laser emits light typically between 800 and 1000 nanometers, with the 980-nanometer wavelength being one of the most widely used in dentistry. Its energy is well absorbed by melanin and hemoglobin, making it particularly effective in soft-tissue applications, wound healing, pain modulation, and superficial tissue regeneration. The Nd:YAG laser, operating at 1064 nanometers, has a longer wavelength that allows deeper tissue penetration. It is less absorbed by superficial pigments and more effective in reaching submucosal, muscular, and neural tissues. The differences in penetration depth and absorption profiles mean that while diode lasers are efficient for surface-level biostimulation, Nd:YAG lasers are more suited for stimulating deeper anatomical structures such as nerves and bone.

Inferior alveolar nerve injury is one of the most challenging postoperative complications following intraoral surgical procedures and mandibular trauma. The inferior alveolar nerve, which provides sensory innervation to the lower teeth, alveolar bone, and lower lip, is highly susceptible to injury during surgical procedures such as sagittal split osteotomy, dental implant placement, and third molar extraction. Such injuries may lead to neurosensory disturbances, including anesthesia, hypoesthesia, and paresthesia, which significantly affect patients' quality of life, functional comfort, and esthetic satisfaction. Although some nerve injuries recover spontaneously, many cases require active therapeutic intervention to enhance nerve regeneration and restore normal sensory function. Conventional approaches, including pharmacological treatment and microsurgical repair, often have limited effectiveness. Therefore, photobiomodulation therapy has gained attention as a noninvasive, safe, and efficient method for promoting neural regeneration. Photobiomodulation, also known as laser biostimulation or low-level laser therapy, involves the application of monochromatic light at specific wavelengths to biological tissues to stimulate cellular repair and regeneration without causing thermal damage. The absorbed light energy interacts with intracellular chromophores such as cytochrome c oxidase, leading to increased mitochondrial activity, ATP synthesis, and modulation of oxidative metabolism. This cascade enhances cellular proliferation, collagen synthesis, and growth factor release, ultimately supporting nerve tissue repair. In neural tissue, laser irradiation has been observed to stimulate Schwann cell proliferation, promote myelin regeneration, and accelerate axonal growth. Additionally, photobiomodulation exerts anti-inflammatory effects by reducing proinflammatory cytokine levels and modulating oxidative stress, creating an optimal environment for nerve healing. Different laser systems have been used for biostimulation in clinical and experimental studies. Among them, diode and Nd:YAG lasers are two of the most commonly used devices, both emitting light in the near-infrared region but differing in wavelength, penetration depth, and absorption characteristics. The diode laser, operating at approximately 980 nm, is absorbed efficiently by melanin and hemoglobin and is highly effective in soft-tissue applications, wound healing, and superficial neuromodulation. The Nd:YAG laser, with a wavelength of 1064 nm, penetrates more deeply into biological tissues and can reach deeper neural structures. Its energy is less absorbed by superficial pigments, allowing stimulation of submucosal and perineural tissues. These physical and optical differences may influence their biological effects on injured neural tissue. While diode lasers may be advantageous for superficial applications and ease of use, Nd:YAG lasers may provide superior biostimulatory effects for deeper structures such as the inferior alveolar nerve. This study has been designed to investigate and compare the therapeutic effects of Nd:YAG and diode laser biostimulation on inferior alveolar nerve injury resulting from intraoral surgical procedures and mandibular trauma. The hypothesis is that both laser systems will improve neurosensory recovery compared to natural healing, but the Nd:YAG laser may demonstrate superior efficacy due to its greater tissue penetration and direct interaction with deeper nerve structures. A total of 30 participants aged 18 years or older with confirmed inferior alveolar nerve injury will be included. All participants will have experienced nerve damage following procedures such as sagittal split osteotomy, implant placement, or third molar extraction, or due to mandibular trauma. Individuals with systemic diseases affecting nerve healing, history of smoking, or previous laser therapy will be excluded. Participants will be randomly assigned into three equal groups: Group 1 will receive diode laser therapy, Group 2 will receive Nd:YAG laser therapy, and Group 3 will serve as a control group without laser treatment. Randomization will be performed using a sealed-envelope method to ensure allocation concealment, and both participants and evaluators will remain blinded to the treatment assignment. Laser applications will be performed twice a week for three consecutive weeks. In the diode laser group, a 980 nm wavelength laser will be used with parameters of 200 mW power, 10 Hz frequency, and 2 J energy per session. In the Nd:YAG laser group, a 1064 nm wavelength laser will be applied with parameters of 0.5 W power and 10 Hz frequency. In both laser groups, treatment will be performed intraorally and extraorally over the region corresponding to the course of the inferior alveolar nerve. Each session will last one minute per application site, with a total exposure time of two minutes per session. The control group will not receive laser therapy but will be monitored under identical conditions and follow-up intervals. Outcome evaluation will be based on both objective and subjective neurosensory assessments. The primary parameters will be the Two-Point Discrimination (2PD) test and the Visual Analog Scale (VAS) for sensory perception. The Two-Point Discrimination test measures the smallest distance at which a patient can distinguish between two separate points of tactile contact, providing an objective indicator of sensory nerve function. The Visual Analog Scale allows patients to rate the degree of numbness or paresthesia subjectively on a 10-point scale, where 0 represents normal sensation and 10 indicates complete anesthesia. Assessments will be performed at baseline, immediately after the completion of the three-week treatment, and during follow-up visits at one, three, and six months to monitor progressive recovery. Additional parameters such as patient comfort, ease of application, and absence of adverse effects will also be recorded. All laser procedures will be conducted by trained clinicians following safety protocols, including the use of protective eyewear and adherence to standard laser operation guidelines. Throughout the study, potential adverse events such as local irritation, temporary sensitivity, or tissue discomfort will be monitored and documented. A priori power analysis was conducted using the G\*Power 3.1 software to determine the appropriate sample size. Based on previous findings regarding the effect size of laser biostimulation on nerve recovery, and using a t-test for independent means with α = 0.05 and β = 0.80, the minimum number of participants required per group was calculated as 10. Therefore, a total of 30 participants will be included in the study. This sample size is considered sufficient to detect statistically significant differences among groups. The collected data will be statistically analyzed using nonparametric tests appropriate for small sample sizes and non-normally distributed data. Within-group comparisons will be conducted to evaluate changes in sensory function over time, and between-group comparisons will determine the relative efficacy of Nd:YAG and diode laser therapies compared to the control group. The results will be presented as mean ± standard deviation, and a p-value \< 0.05 will be considered statistically significant. It is anticipated that both Nd:YAG and diode laser treatments will enhance neurosensory recovery compared to the control group, reflected by improved 2PD values and reduced VAS scores. Due to its deeper penetration ability, the Nd:YAG laser is expected to demonstrate greater improvement, particularly in patients with nerve injuries located within the mandibular canal. Additionally, patients in both laser groups are expected to report higher satisfaction levels and faster recovery compared to untreated controls. This research will contribute valuable data for developing standardized photobiomodulation protocols in dentistry and oral surgery. Despite widespread clinical use, the parameters for effective laser therapy-such as wavelength, power, exposure duration, and frequency-remain inconsistent in the literature. Establishing scientifically validated treatment protocols will help clinicians optimize therapeutic outcomes and minimize variability in results. Furthermore, the comparative design of this study will provide practical guidance on the selection of laser systems for neurosensory rehabilitation, balancing effectiveness, safety, and ease of application. Beyond its direct clinical implications, this study also carries broader significance for the field of regenerative medicine. Photobiomodulation is a growing area of interest for tissue repair and pain management, and its successful application to neural regeneration could have implications extending beyond dentistry, including neurology and orthopedics. Understanding how different wavelengths and energy densities influence biological responses can guide the development of targeted, wavelength-specific therapeutic approaches. Ethical approval for the study will be obtained from the institutional ethics committee before participant recruitment. All participants will be informed about the study procedures, potential risks, and expected benefits and will provide written informed consent prior to participation. Data confidentiality will be maintained in accordance with institutional and international guidelines. The study will adhere to the principles of the Declaration of Helsinki and Good Clinical Practice standards. Hypothesis, this project seeks to evaluate and compare the effects of Nd:YAG and diode laser biostimulation in the management of inferior alveolar nerve injury after intraoral surgical procedures and trauma. The study combines clinical, biological, and technological perspectives to explore how different laser systems influence nerve regeneration and sensory recovery. It is expected that the findings will provide a foundation for evidence-based use of laser photobiomodulation in managing nerve injuries in the maxillofacial region and potentially other areas of regenerative medicine. The outcomes may help establish an effective, reproducible, and noninvasive therapeutic approach for improving patient recovery, satisfaction, and long-term functional outcomes after oral and maxillofacial surgeries.