Quantitative analysis of intra and peritubular structures of Non-Carious Cervical Lesions (NCCL) dentin-SEM study Introduction-The lost of dental structure because of non carious cervical lesion is one of the most important clinical event discussed in dental literature. The most important etiologic factors related to this type of lesions are: abrasion, erosion and abfraction. According to many authors, this particular lost of dental structures became more interesting and curious when the dentin in regions with NCCL is study microscopically. Objectives-The purpose of this investigation was to study, comparatively, in scanning electronic microscopy (S.E.M.), the dental microstructure of NCCL and lesion-dentin dentin surfaces. The null hypothesis were the following: 1-the methods used for specimens preparations lead to different changes on dentin microstructures; 2-there is no difference between NCCL dentin microstructure and that from lesion-free dentin in the same tooth; 3-ITS can be found both in hypersensitive and non-sensitive dentin. Materials and Method-Dentin samples from buccal and lingual surfaces of 14 extracted human teeth, with NCCL on buccal surface, were used. After extraction the teeth were immediately fixed with Karnovsky. Teeth were than, divided in 2 subgroups, in accordance with specimen's treatment. Samples of region of lesion and their lingual counterpart were, then, post fixed according to appropriated protocol for SEM. The following groups were studied: Group I-specimens sectioned with diamond disc and subdivided in: Group IA-specimens cleaned in ultrasonic bath for 15 minutes; Group IBcleaned in ultrasonic bath 15 minutes, followed by etching with 5%, H 3 PO 4, for 15 seconds. Group II-samples were fractured along the lesions axis and subdivided in: Group IIAultrasonic bath for 30 minutes; Group IIB-etching with 5%, H 3 PO 4, for 15 seconds. Group III-samples also fractured and subdivided in: Group IIIA (control)-without any kind of treatment; Group IIIB-immersion of the specimens in NaOCl to 2%, for 5 minutes. The specimens were dehydrated, critical point dried and coated with gold for in SEM analysis. Results-1-On general, all of methods interfere, in larger or lesser proportion, with the nature of the specimens. On the surface of the lesions, the method that better allowed the visualization and recognition of dentine structures was the ultrasound followed by acid conditioning (Group IB). However, this was the procedure that introduced the greatest changes on dentine structures. In dentine under of the lesion, the best method of specimens preparation was the control group (Group IIIA). 2-Both buccal NCCL and lesion-free lingual surfaces presented similar ITS. 3-No structural differences were found in dentin from hypersensitive and non-sensitive lesions. Conclusions-The methods used for specimens tend to modify the characteristics and relationship of dentin structures. The hypothesis that ITS are specific from NCCL could not be confirmed under the light of method used. Apparently, the ITS c...