الفهرس 
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Abstract
Dentinal hypersensitivity treatment represents a real challenge for practicing dentists. Although it is not a lethal condition but it does affect the patient`s quality of life greatly. Dentinal hypersensitivity could affect normal patients due to Attrition, Abrasion, and Erosion causing loss of enamel or deteriorating periodontal condition causing gingival recession. Also genetically affected patients can experience dentinal hypersensitivity due to their genetic condition that can affect either the periodontium causing gingival recession or their tooth structure causing enamel loss and exposure of dentine. Many conventional treatments are available for dentinal hypersensitivity, none of which could fulfil all the needed requirements of the optimum treatment as being painless when applied, consistently effective, not irritating to the pulp, permanently effective, easy to apply, quick acting, and not causing tooth discoloration. Laser therapy has been recently proposed as a treatment for dentinal hypersensitivity. The laser can act on hypersensitive dentine in two ways. The low-level lasers acts on nerve transmission, preventing pain diffusion. By the other side, high-power laser acts on the exposed dentine surface causing a melting effect with crystallization of dentine inorganic component and the coagulation of fluids in the dentinal tubules. The aim of the study is to evaluate the clinical effect of high and low power laser on dentinal hypersensitivity in normal patients and patients suffering from genetic disorders. Also to correlate between the clinical results and the histological effect that the laser can exert on dentine. The current study was conducted in the National Research Center and the National Institute of Laser Enhanced Science, Cairo University This study consists of both an Invitro and an Invivo section which was conducted in compliance with medical research ethical committee of National Research Center, Egypt (Ethical Clearance Number:13049). The invitro study involved 20 dentine discs that were acid etched to simulate the condition of dentinal hyper sensitivity and each divided into 2 areas where one area acted as control and the other received the laser treatment. The 20 discs were equally divided into 2 groups. group A received low level laser protocol. 970-nm diode laser at 0.5W/CW (continuous mode) applied for 30 seconds using 320μm optic fibre. The application is repeated 3 successive times. group B received high level laser therapy protocol. 970-nm diode laser system at 1.5W/CW applied for 5seconds using 320 μm optic fibre. The application is repeated 6 successive times with 20 second break interval after each application. Each disc was examined by Scanning Electron Microscope (SEM) at both control and lased sides to evaluate the closure of the dentinal tubules .The invivo study involved 20 patients each suffering from at least one sensitive tooth. The patients were divided into 4 groups group A: normal patients receiving low level laser protocol. group B: normal patients receiving high level laser protocol. group C: patients suffering from genetic disorder receiving low level laser protocol. group D: patients suffering from genetic disorder receiving high level laser protocol. Patients were assessed for pain response caused by a short blast of cold air 1 second duration at a distance of 0.5cm from each tooth using a Wong-Baker Faces Pain Rating Scale. Pain was assessed pre and directly post-operative during each treatment session then every 2 weeks for 3 month and pain values were recorded in individual patient sheet. Results of the invitro study showed the significant effect of high power laser in narrowing of the dentinal tubules diameter when compared to the control or the low power laser group. The results of the invivo study also showed instant relief of pain in the groups B and D treated with the high power laser protocol that was maintained through the period of follow up. Also the groupsA and C treated with low level laser protocol showed relief of pain but recurrence of pain took place at the first follow up appointment in 95% of the patients so an extra session of treatment was indicated after which pain relief was achieved and maintained throughout the period of follow up. Based on the analysis of the data obtained it was concluded that that 970-nm diode laser can be an effective treatment for dentinal hypersensitivity in both high and low power parameters and it is equally efficient in normal patients and patients suffering from genetic disorders affecting their periodontal condition. High power parameters showed to be more efficient and requires less time of application and histologically proved to have the ability to occlude the dentinal tubules.