It is very interesting why the dental pulpal pain is induced by the chemical and physical stimulation. However, although this problem has been studing since ever, the sensory mechanism is not yet resolved completely.

  This time, about the outline of sensory mechanism of hypersensitive dentine, I described. First of all, the causes of hypersensitive dentine, secondly the classification and lastly the sensory mechanism including our original research and the other's was presented.

  In the result, a space of approximately 20nm was observed between nerve fibers and odontblastic processes, but no special structures such as gap junctions or synapses were found between them. However, from their morphological relation, the presence of a mechanical stimulant mechanism was hypothesized. There were also findings suggesting the presence of a stimulus transmission mechanism due to some sort of substance transfer between the nerve and the process.

  The purpose of this study was to evaluate the root canal preparation by a) ultrasonic energized filing (Miyahara's method 1.2.3) and b) conventional hand filing (following the standard method with K type hand file, up-down method).

  Extracted and kept in 10% formalin solution, human incisal teeth with (71) were prepared in five different ways ; replica was taken with silicone rubber impression material and then observed under a scanning electron microscope.

   The results were as follows.

  1. With the root canal preparation technique using an ultrasonic device (Miyahara's method 1, 2, 3), the best results were obtained when, in a first step, the ideal pre-curve and working length could be evaluated and when, in a 2nd step, ultrasonic vibrations were applied the first 30～60 seconds.

  2. This ultrasonic filing should be done as smoothly as possible.

  3. With Miyahara's method 2, the files left more marks on the walls of the apex than with methods 1 and 3.

  4. The horizontal view of the hand filed canal wall shows that it is round. However, when prepared with an ultrasonic device, it appears angular or even square.

  5. We found when ultrasonically irrigating a hand filed canal with a smooth broach (square) that the horizontal view had become clearly square.

  6. It appears important to reshape the surface of the canal wall and the apical seat with a hand instrument when filling the root canals, or else to develop a different filling technique.

  On of the reasons of the failure of the maxillary first molars endodontic treatment is due to the treatment of mesiobuccolingual canals.

  The purpose of this study was to examine how cavity preparation should be done in order to have endodontic treatment of the lingual second canal successfully.

  K-type files were inserted in the mesiobuccolingual canal and mesiobuccal canal for measuring the degrees between K-type files and occlusal surface by the use of the extracted teeth of human maxillary first molars.

  The results obtained were as follows ;

  1. K-type file inserted in the mesiobuccal canal had the inclination of 101 degrees from average mesial angle to distal angle and the inclination of 108 degrees from buccal angle to lingual angle.

  2. K-type file inserted in the mesiobuccolingual second canal had the inclination of average 112 degrees toward distal angle and the inclination of 102 degrees toward lingual angle against occlusal surface.

  3. Cavity preparation must be done beyond the transverse ridge.

  In the down town of cities, environmental situation has been unhealthy day by day, for examples, air pollution, water pollution, noise and shock are increased recently.

  Owing to unreasonable rised value of land, the space of dental clinics is becoming smaller and smaller.

  It is poor buffer action against air pollution that the capacity of space has been small in dental clinics.

   In this paper, it is provided the effects of air cleaner to check the contaminants in the air of dental clinic.

  The results are as follows :

  The bacterial colony counts are showed around ninety percent decreased. The collected durst in the air cleaner is showed various form, fibrous, round and fine particles. Their sizes are showed that width is from 0.05μm to 2μm and length is from 1μm to 50～100μm. They contain several elements, sulph, silicon, calcium, phosphor, silver, iron and copper which are come from dental materials.

  It is necessary to set up an air cleaner in dental clinic to prevent allergy or respiratory disease from air pollution and to maintain our health.

  At present, the gutta percha point and the sealer are used at the rate of 70～80% as materials for filling a root canal on the terminal treatment of endodontics.

  The authors developed a new sealer for filling a root canal and comparative tests were performed with the existing sealer on the market.

  Samples were filled in glass tubes and extracted teeth and the sealing ability which is the most important physical property for the sealer to fill a root canal was examined by the test of dye solution permeation.

  As a result of the tests, we have following information,

  1. The Pulp Canal Sealer has poor sealing ability which is different from the report of Grossman L.I,.

  2. The sealing ability of the sealer of eugenol system is poor.

  3. GP sealer the authors developed and Sealapex on the market indicate good value.