Abstract : Dentin hypersensitivity is a serious problem frequently seen in patients. Therefore reliable and sensitive means of measuring pain are essential for selecting better treatments and assessing the efficacy of treatments.

 A verbal rating scale (VRS) is now commonly used as the pain rating scale for dentin hypersensitivity, though several defects have been pointed out. We already reported that a visual analogue scale (VAS) is very effective in the diagnosis of dentin hypersensitivity. So in this study further examination was done about the application of VAS for assessing the efficacy of treatment in dentin hypersensitivity.

 Twenty six teeth of twenty six patients having dentin hypersensitivity were selected at the first oral examination. The levels of sensitivity to cool air blast stimuli, cold water stimuli and tactile stimuli were evaluated with the VAS and the VRS. Then a newly developed solution containing calcium phosphate for the treatment of dentin hypersensitivity was applied to each tooth surface. The levels of sensitivity to the same stimuli were evaluated with the VAS and the VRS again, and the pain scores obtained from the two methods were compaired. The same examination was done after one week.

 The results obtained were as follows.

 1. Changes in the VAS scores correlated well with changes in the VRS scores.

 2. The VAS was more sensitive than the VRS.

 3. There was an obvious difference on the change of pain among the three sorts of stimulation, and this was shown clearly with the VAS.

 These results suggest that the VAS would be a practical and valid method for assessing the efficacy of treatment in dentin hypersensitivity.

Abstract : Opian Carrier Method which is a method of vertical condensation of root canal filling is so performed that after the gutta percha point is softened in flame, it is immersed in eucalyptus oil mixture and vertically condensated in the root canal.

 Opian Gutta was studied and developed as exclusive use for the gutta percha point on 1983, since then it has been clinically used until now.

 Studies on fluidity and conformity and safety to tissue of this root canal filling material were made in the past. In my studies this material has campared with a gutta percha point on the market to examine obturating ability in the apex of root.

 The results suggest that obturating ability of Opian Gutta is excellent.

Abstract : Until today, conventional cleaning and shaping of canal spaces involve the use of hand instruments (reamers or files) with irrigation, and sometimes with the rotary or ultrasonic instruments. But these procedures result in the formation of the endodontic smear layer consisting of dentin shavings, organic tissue remnants and microorganisms. Many types of lasers have been suggested as an aid in root canal preparation.

 In this study, a combined apparatus of the continuous wave CO₂ Laser and the Waterjet Scaler was used to test the ability of this apparatus to clean and shape the canal dentin. The extracted human teeth with necrotic root canal or the vital teeth with periodontal diseases were sectioned longitudinally. Then, the one half was treated by this apparatus, and the other half was used as the control (non-treated). After that, these teeth were fixed, dehydrated and examined by scanning electron microscopy.

 The results demonstrated that this apparatus was capable of removing the pulpal tissue, endodontic smear layer and could occasionally alter dentin walls (opened dentin tubules or melted hydroxyapatite). More research is needed to determine to establish a treating method to prepare canal walls.

Abstract : We have developed a new ultrasonic root canal preparation system which electronically monitors the location of the file tip during all instrumentation procedures.

 For this electronic monitoring, the Root ZX was applied. Because the Root ZX has an effective filter circuit, the large spike noise of the ultrasonic unit can be cut out.

 During enlargement of the canal, the ultrasonic vibration of the file can be stopped at any desired position on the meter display (auto-stop mechanism).

 In extracted human tooth models which can electronically measure the canal length, the characteristic of the device was examined. Pre-and postoperative shapes of the root canals were evaluated using contact-micro-radiography (CMR).

 The auto-stop mechanism worked correctly. Using a weak power and fine files, the straightening, ledge formation, separation of the files were minimal. It was clearly shown that this system minimized the danger of overinstrumentation and could be applied safely in clinics.

Abstract : The electric characteristics of the Sono-Explorer MKⅢ, Neosono MC, and Justy were evaluated in covalent circuits or extracted human tooth models. The results obtained were as follows :

 1. Sono-Explorer MKⅢ

 As the impedance of the load decreased, the frequency of the measuring current of the device increased. This device measures the impedance of the root canal as a change of the frequency of the measuring current. Since the rationale of this device is a single impedance method, it cannot overcome the electrical change in the root canal when an electro-conductive fluid is in the root canal.

 2. Neosono MC

 This device follows the measuring method of the Sono-Explorer MKⅢ. In this device, a change of the frequency is expressed as a distance from the apical foramen.

 3. Justy

 The measuring current of this device has two different frequency rectilinear waves which appear alternatively. These two waves detected from the root canal are separated with digital filters, and two electric potentials are obtained which correspond to two impedances of the root canal. Then, these two potentials are converted to the logarithmic values, and one is subtracted from the other. The result drives the meter.

 Since a subtraction of the logarithm is a logarithm of the quotient, the rationale of the Justy very much resembles that of the Root ZX.

Abstract : The purpose of this study was to evaluate the organic substance dissolving ability of a viscous paste type NaOCl, which was made on an experimental basis.

 A 6% NaOCl paste was prepared by adding an inorganic compound thickener (montmorillonite) to NaOCl solution. A extracted third molar was used for the organic substance dissolving ability survey. The Tooth was cut horizontally at the pulp chamber level to obtain several slices, then the slices were devided to small pieces including the chamber wall by a nipper. Numerous tooth pieces were immersed in NaOCl paste for 5-60 minutes. A 6% NaOCl solution served as a control. After immersion, the specimens were dehydrated and coated with Pt-Pd. The pulp chamber wall of each specimen was observed by a scanning electron microscope.

 Five minutes after the start of immersion in this paste, most pulp remnants on the pulp chamber wall and the superficial layers of the predentin had dissolved. By 10 minutes, the calcospherite immediately below the predentin was partially exposed. By 15 minutes, the predentin was completely dissolved, resulting in full exposure of the calcospherite. The organic substance dissolving ability of the NaOCl paste was a little lower than that of thickener-free NaOCl solution. However, the NaOCl paste is very effective clinically due to the excellent manipulation during mechanical root canal preparation.