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Experimental Oral Carcinogenesis
Published in Samuel Dreizen, Barnet M. Levy, Handbook of Experimental Stomatology, 2020
Samuel Dreizen, Barnet M. Levy
Hamsters were separated into five groups according to preselected sites of application: Group I, lateral border of middle third of the tongue; Group II, lateral border of anterior third of tongue; Group III, midportion of dorsum of tongue; Group IV, tip of tongue; and Group V, undersurface of tongue. The carcinogen was applied to each experimental site after scratching the area with a pulp canal reamer (Number 2 barbed broach) three times a week. The treatment was continued until carcinomas developed. The first neoplastic lesions noted were exclusively in the treated sites. The lingual carcinomas appeared to be responsible for the deaths of the hamsters. In some hamsters in Groups II, IV, and V, relatively large tumors developed in adjacent regions; however, none of these tumors reached the size of those in the various experimental sites on the tongue. The time period from the beginning of the experiment to the deaths of the animals caused by tumors was relatively short in Group I, much longer in Groups II, IV, and V, and very long in Group III, indicating that the lateral border of the middle third of the hamster tongue is the site most sensitive to carcinogenic action and is a predisposed site of lingual carcinomas in the hamster, as it is in man. In summary, lingual carcinomas in various sites of the hamster tongue resulted when the tongue was scratched at a particular experimental site with a pulp canal reamer and DMBA in acetone was applied three times a week. The period of carcinogenesis on the lateral border of the middle third of the tongue was relatively short; the period was longer in the lateral border of the anterior third and under surface and the tip of the tongue, and very long in the midportion of the dorsum of the tongue. Fujita and co-workers thus produced results which mimic the clinical manifestations of human lingual carcinomas and suggest that the use of this kind of experimental animal system could provide a useful model for the study of human lingual carcinoma.
Factors Controlling the Microflora of the Healthy Mouth
Published in Michael J. Hill, Philip D. Marsh, Human Microbial Ecology, 2020
While microbiological sampling of the oral mucosa by, for example, swabbing or direct impression techniques is relatively simple, except for the problem of contamination with saliva, there is no correct or universally accepted way of sampling dental plaque. Dental plaques (Figures 1 and 4) are tenacious aggregates of microorganisms firmly adhering to the teeth and resist removal by rinsing. Plaque contains many different microorganisms, some of them occurring only in low numbers. Many of them are obligate anaerobes which lose their viability if exposed to air. The plaque microflora varies over small areas even on the same tooth surface; therefore, small discrete samples are necessary from defined sites, especially if the intention is to study the microflora in areas of disease activity such as dental caries or various forms of periodontal disease. Clinical characterization of the sites is essential, but is hampered by lack of precise criteria, especially for periodontal diseases. The sampling method of choice depends on the aim of the study and is usually a compromise between conflicting requirements.26,27 On accessible surfaces, plaque may be collected with dental instruments (probes, scalers, curettes) or toothpicks (Figure 8). The surrounding surfaces may be cleaned first to restrict sampling to the desired area. Approximal surfaces may also be sampled using dental floss or abrasive strips between the teeth. Subgingival plaque in periodontal pockets may be sampled with curettes or absorbent paper points, or with capillary tubes following pocket irrigation. Paper point and capillary tube techniques have the disadvantage of mainly sampling the superficial, loosely adhering plaque layer rather than the whole plaque, while on the other hand making repeated sampling less problematic than methods which remove most of the plaque. Access to defmed subgingival areas may be gained during periodontal surgical procedures where a flap of gingival tissue is reflected exposing the plaque on the root surfaces. Special devices have also been designed as tubes through which samples can be taken (with paper points or a barbed broach) from the deepest part of a gingival pocket while bypassing the plaque on the way down. Another function of such a tube can be flushing with oxygen-free gas to protect obligately anaerobic species. Occlusal pits and fissures present a special sampling problem, as even the finest probe or needle only enters the orifice rather than the fissure proper. Studies of fissure plaque, therefore, have utilized various models of artificial or natural fissures carried in the mouth (e.g., in an occlusal filling, Figure 9) during plaque formation, which are removed and split open for sampling.28 Various sampling methods have each their advantages and drawbacks, and when comparing investigations it is important to realize that variations in results may reflect differences in methodology.
The effects of various irrigation protocols on root canal wall adaptation and apical microleakage in primary teeth
Published in Acta Odontologica Scandinavica, 2020
Burcu Nihan Yüksel, Akif Demirel, Meryem Ziya, Kevser Kolçakoğlu, Salih Doğan, Şaziye Sarı
All the teeth are embedded in wax blocks leaving the clinical crowns out. Following the preparation of the access cavity, the tissue residues in the pulp chamber were removed by an excavator and the pulp tissue residues in the canal were removed by a barbed broach. After determining the estimated working length of the specimens by using a file on the periapical radiographs of the samples, and taking this measurement as a reference, the definite working length was determined as 2 mm coronal to the radiologic apex by placing a #15 K-file (G-star Medical Co., Ltd., Guangdong, China) into the root canal. In all groups, each hand-file set was used for only one sample group, and the root canal preparations were made by a single operator, using K-files sized from #15 to #45. During the preparation process, a file with a larger diameter was used after the small file was provided to move freely in the canal, while the irrigation procedures associated with the groups were performed. All the root canals were irrigated with a 27-gauge tip diameter needle attached to 2 ml syringe (Ayset Medical Products, Adana, Turkey) and the needle tip was inserted 2 mm shorter than the working length.
Effects of graphene oxide and graphene oxide quantum dots on the osteogenic differentiation of stem cells from human exfoliated deciduous teeth
Published in Artificial Cells, Nanomedicine, and Biotechnology, 2019
Xin Yang, Qi Zhao, Yijing Chen, Yuanxiang Fu, Shushen Lu, Xinlin Yu, Dongsheng Yu, Wei Zhao
The cells from human exfoliated deciduous teeth were taken from 6- to 10-year-old children whose caries-free deciduous teeth required extraction. Ethics Committee approval was provided by the School of Stomatology, Sun Yat-sen University. Briefly, the teeth were placed in pre-cooled phosphate-buffered saline (PBS, Hyclone, Logan, UT, USA) with 1% penicillin/streptomycin (P/S; Gibco, Thermo Fisher Scientific, Inc., GrandIsland, NY, USA ) and taken to the laboratory within 8 h of extraction. Pulp tissue was extracted with a barbed broach, cut into pieces and digested with 1:1 3 g/l collagenase type I (Sigma-Aldrich, St. Louis, MO, USA) and 4 g/l dispase (Roche, Basel, Switzerland) at 37 °C for 30 min. The pulp cells were then suspended in the primary culture medium, which included Dulbecco’s modified Eagle’s medium (DMEM; Gibco), 20% foetal bovine serum (FBS; Gibco), and 2% penicillin/streptomycin, then cultured in 37 °C and 5% CO2 incubator.
The effect of different irrigation protocols on smear layer removal in root canals of primary teeth: a SEM study
Published in Acta Odontologica Scandinavica, 2019
Akif Demirel, Burcu Nihan Yüksel, Meryem Ziya, Hüsniye Gümüş, Salih Doğan, Şaziye Sari
All teeth were buried in wax blocks leaving the clinical crowns out. Following the preparation of the access cavity, the tissue residues in the pulp chamber were removed by excavators, and the residues in the root canal were removed by a barbed broach (Medin Barbed Broach, Vlachovice, Czech Republic). The estimated working length was determined by using a hand file on the periapical radiographs of the specimens. With reference to this measurement, the correct working length was determined by a #15 K file (G-star Medical Co., Ltd., Guangdong, China) placed 2 mm coronally from the apical foramen. In all groups, each hand file set was used for only one group of samples, and instrumentations were made by the same operator (BNY), starting from the K file #15 to #45. The large diameter hand files were used after the small file could move easily in the root canal during the preparation steps. Instrumentation was done according to the conventional preparation using a pull-back movement. All root canals were irrigated with 27-gauge tip diameter needle attached to 2 ml syringe (Ayset Medical Products, Adana, Turkey) and the needle tip was inserted 2 mm shorter than the working length.