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ePaper created 2017-10-05, 09:25:28 | version 1.38.0
an important factor of this mechanism.8 Examina- tion of tooth necks under a scanning electron mi- croscope (SEM) has shown that affected teeth had eight times as many exposed tubules with a diame- ter twice the size compared with non-sensitive den- tine.8 By demonstrating that the density of sensitive nerve fibres is correlated to pain intensity of a sen- sitive tooth,9 it is also assumed that, in addition to the hydrodynamic theory, other mechanisms, such as nerve stimulation, could be involved. Thus, in- flammation mediators could make nerve endings more sensitive to mild stimuli, which could induce pain.10 Nevertheless, the precise physiological mechanisms underlying dentine hypersensitivity are not clearly understood yet,11, 12 and despite in- tensive research, constant improvement of therapy methods and active substances, reports still show that there is difficulty controlling this painful con- dition.11 Laser treatment of dentine hypersensitivity alone or in combination with conventional treat- ments is a new promising option for rapid and durable pain relief.13 Depending on the laser type and energy settings used, the actual reported ef- fects of laser desensitisation are morphological al- teration of the dentinal structure, for example a closure of the dentinal tubules by melting and reso- lidification of the dentinal structure; laser dehy- dration with protein deposition or deposition of in- soluble salts in the dentinal tubules; as well as bio - stimulation, for example nerve analgesia, induction of sclerosis and secondary dentine formation; and placebo effects. Recently, great effort has also been made to integrate tooth structure-like components into the tooth surface with the help of laser radia- tion.11, 14–17 However, on account of the high temperature increase, these methods are not suitable for clinical application11, 16 and too little is known about the long-term morphological and clinical effects of laser application to recommend the therapy. The aim of our study was to examine the effects of a diode laser with a wavelength of 809 nm in the treatment of dentine hypersensitivity in terms of morphological changes. The ability of this type of laser to close open dentinal tubules, its suitability as a method for dentinal sealing, as well as the induc- tion of recognisable morphological side-effects in the dentinal structure using this laser, were tested in vitro. Furthermore, the effect of laser–fluoride ap- plication was compared with single treatment op- tions, and the acid resistance of the tested treat- ment modalities (fluorides, laser, and laser–fluoride treatment) was evaluated by the method of pH-cy- cling. _Material and methods The samples used were extracted human teeth drawn from a pool of extracted teeth collected for dental research at the University Bonn, Dental Clinic once informed consent had been obtained. Surgical treatment was not linked to research in any way. All experiments were in vitro; hence, there were no po- tential risk factors to human health. Immediately after extraction, the teeth were stored in a sodium chloride solution (0.9 % NaCl, Delta-Pharma) with 0.01 ‰ sodium acid added and kept refrigerated at 5 °C to prevent the teeth drying out and to minimise bacterial and chemical decomposition. Teeth without carious lesions at the tooth neck and root surface (n = 60) were di- vided into four groups of 15 teeth by random se- lection. Every test group had the same number of incisors, canines, premolars and molars from the maxillae and mandible (four maxillary incisors, one maxillary canine, two maxillary premolars, two maxillary molars, one mandibular canine, three mandibular molars and two mandibular third mo- lars). The incisors of the mandibular arch were ex- changed for third molars because the small root surface did not allow preparation of a quadrangle. The experimental surface was located at the vestibular, mesial or distal side of the root surface. Four quadrants were marked in the cervical area (Fig. 1). Enamel and root cementum were completely removed with diamond burs under water-cooling (INTRAmatic LUX 24, KaVo) by one operator to simulate hypersensitive dentine. With removal of a 1 mm layer, we assumed that all dentinal tubules had been totally exposed. The sample surface was smoothed with a Gracey curette (#7-8; Thico- dent) and divided into quadrangles with a dia- mond separating disc (0.5 mm thick) under wa- ter-cooling (INTRAmatic 10 C, KaVo; Fig.1). Groups 3 and 4 underwent a pretreatment (acid etching with 50 % citric acid for 2 minutes, rinsing with distilled water for 30 seconds) to remove the smear layer created by preparation. laser_research Fig. 1_Samples of (a) Incisor, (b) Canini, (c) Premolar and (d) Molar after quadrangle preparation in the tooth neck area. laser 3_2017 3939