There has been much literature published on the subject of working postures of various operators, which are regarded as being important from human engineering and industrial medicine points of view. However, studies on working postures of the dentist are scanty. In view of the fact that individual dentists assume their own particular postures, the author carried out the present study as part of a series of researches on the occupational and hygienic study of the dentist, conducted for a long time by the Department of Hygiene and Public Dental Health where the author belongs. In the belief that the working posture of a dentist might exert some influence on his spinal column, observations were mode of the occlusal plane angle, inclination of the back of dental chair and position assumed in terms of various treatment spots and contents. As the same time, radiograms were taken of the spinal column and photographs were also taken of various working postures. An artificial spinal column was constructed from these data and careful analyses of changes in the artificial spinal column revealed the following conclusions:
1) Angles of the occlusal plane.
On the average, 27.1° and 23.8° were respectively measured for the treatment of upper and lower jaws in a standing position. In a sitting position, on the other hand, the measured values were 46.6° for the upper and 37.4° for the lower jaw respectively. In either position, the angles were found to be larger in the treatment of the upper jaw.
2) Inclination of the chair back.
On the average, 130.8° and 128.8° were respectively measured for the treatment of upper and lower jaws in a standing position. In a sitting position, on the other hand, the inclinations were 155.8° for the upper and 252.9° for the lower jaw. Here again, upper jaw revealed the tendency of a slight increase over the lower jaw.
3) Treatment positions.
In a standing position, 8.8 o'clock and 9.0 o'clock were measured for the upper and lower jaws respectively. On the other hand, in a sitting position the measured values were 9.8 o'clock and 9.9 o'clock for the upper and lower jaws. In either case, the lower jaw revealed somewhat higher values.
4) As for the lateral curvature of the spinal colum on the part of dentists, those who were above 4° gave an incidence of 52.2%. Distorsion of the spinal column was seen in 87.0% of dentists. The distorsion in many cases was either to the right or in the form of an S and, for this reason, it was thought that unnatural or constrained posture assumed in dental treatment had some bearing on this phenomenon.
5) About 5.9 vertebrae per dentist suffered from the lateral curvature and these were chiefly concentrated around Th, 8 and Th, 9 thoracal vertebrae.
6) The simulation of various movements revealed the following facts. That is, at a standing position the body tended to incline itself forward to the right around the Th, 7 thoracal vertebra, while a distorsion made the cervical region turn to the left. In a sitting position, on the other hand, there was observed a tendency that a backward bending occurred from the Th, 12 thoracal vertebra to the lumbar region.
7) From these findings, it is urged that those conditions should be established which willmaintain the safety of spinal column on the part of dentists engaged in treatment.
8) From a standpoint of health control of dentists, it is thought desirable that some kind of exercises to rotate and extend the spinal column should be routinely performed.

View full abstract

Although there is much published literature on lighting equipment in the dental field, studies on the illumination in this field are scanty. In the present study, the author was concerned with the measurement of illuminative degrees on the surfaces of individual teeth by directly introducing photoconductive cells into the mouth of a subject. Along with the measurement of illumination on the teeth, efforts were also made to find out how much contribution would be made by the dental mirror by way of promoting the dental surface illumination.
For experimental purposes, a complete denture was constructed with 16 photoconductive cells embedded on the distal, lingual and buccal sides 6, labial side of 1, lingual side of 1, occlusal surfaces of 4 5 6 7 distal, lingual and buccal sides of 6, occlusal surfaces of 4 5 6 7. This experimental denture was installed in the mouth, so that indices of the photoconductive cells on the illuminative surfaces would be measured and the indices were subsequently converted numerically by the illuminometer. A subject was instructed to sit in a dental chair and light was projected from three directions: the occlusal surface of the upper jaw (A), the occlusal surface of the lower jaw (C), and midway between the two (B). At the same time, three positions of 20° right of the median line (X), median line (Y) and 20° left of the median line (Z) were established. Therefore, light was be projected from each of these nine directions.
As a result of these comprehensive efforts, the author arrived at the following conclusions.
1) Under direct light at the different positions, the degree of illumination increased in the order of A, B and C with the upper jaw; the highest degree was registered on the labial surface of the central incisors and the lowest was on the distal surface of first molars. The lowest was on the distal surface of the first molars at a position of CX, the latter corresponding to only 0.1% of the former.
2) With the exception of a 19mm dental mirror for the distal surface of the upper and lower first molars, dental mirrors with larger diameter were found to be more efficient. A dental mirror of much larger diameter, devised for the purpose of this study, was quite efficient.
3) All of the commercial dental mirrors failed to come up to the Japanese Industrial Standards in the rate of light reflection.
4) Although a dental mirror of small diameter had a large reflecting rate, mirrors of larger diameter had correspondingly large reflecting rates on the whole.
5) In separating colored rice grains by subjects inexperience with dental mirrors, the 19mm mirror was found less efficient than the 35mm mirror and, when a mirror of smaller diameter was used, more sense of fatigue was complained of. The result was more or less the same with dentists. The illumination of 34000 lux was very efficient. The fact that the 35mm mirror was very efficient was also endorsed by the findings of a flcker test.
6) In a test where Landolt rings were used, the findings were also in favor of the 35mm mirror and 34000 lux. From these facts, it was found that the efficiency differed according to the diameter of dental mirrors and projecting rates.
7) In a group dental examination, it was found that working efficiency and accuracy of the diagnosis were definitely influenced by the diameter of the dental mirrors used.

View full abstract

Generally eye and skin irritation tests havebeen used in examining irritation caused by medicine and cosmetics. However, it is questionable if the results obtained through these irritation tests directly represent levels of irritation in the oral mucosa caused by dentifrice and its confined agents because mucosa tissue and physiological functions of oral mucosa differ from those of eye or skin. Authors have considered another test method, used in the oral cavity, for the irritation of agents combined in dentifrice, and this method appears to be superior to the conventional eye irritation test method.

View full abstract

The in vitro effects of a bacteriolytic enzyme derived from Streptonzyces globisporus strain 1829 on dental plaque, which previously formed on plastic foil attached to the buccal surfaces of maxillary molar tooth in the subject, were evaluated by scanning electron microscopy.
According to the lapse of time (days), the dental plaque became thicker and the plaque bacteria were more densely packed. In early plaque (day 1 or 2) the bacterial constituents in the dental plaque were relatively simple. Cocci and rods predominated in early plaque, and filamentous form bacteria (filaments) appeared occasionally in plaque of day 2. In older plaque (day 7), filaments predominated and occupied most of the area of the plaque surface. A few of these filaments were observed to be coated with cocci and rods giving a “corncob” appearance.
By treatment with the bacteriolytic enzyme, the bacterial cells in early plaque were lysed in situ and formed net-like, honey-comb or sponge-like caves. Bacteria in older plaque did not reveal any alteration by the enzyme, but no cocci and rods were observed in the plaque and the bamboo basket-like structure formed by filaments was partially broken.
It was suggested from the results that the bacteriolytic enzyme might affect the surface structure and bacterial constituent of dental plaque by lysing the enzymesensitive bacteria.

View full abstract

Toothbrushing of an individual with the use of a manual toothbrush is accompanied by manners and customs which are reflected in brushing force and the number of brushing strokes. The percent of plaque removal with a manual toothbrush is generally proportional to the product of brushing force times the number of brushing strokes, and brushing force is regulated by a feedback mechanism from the sensations of the oral mucous and periodontal membrane, and from the muscles and joints of the arm and hand which hold the toothbrush.
Therefore, the difference in individual plaque removal effects is reflected by manners and customs during toothbrushing, and the difficulty or ease of toothbrushing is reflected on the brushing areas.
Thus, it seems that other supplemental procedures are necessary besides toothbrushing with a manual toothbrush. With the use of a manual toothbrush, it would be almost impossible to hope for more effective plaque removal.
Studies were made of 13 men 22-28 years of age having a daily tooth cleaning habit with the rolling method under the following conditions: with the combined use of a manual toothbrush and water jet cleansing devices or water jet cleansing devices only.
The labial, buccal and lingual surfaces of six blocks of the dental arch were brushed for 20 seconds; measurements were made of brushing force, the number of brushing strokes and plaque removal on each surface, and the relations between brushing force and the number of brushing strokes and between plaque removal and brushing force and the number of brushing strokes were studied. The results obtained were as follows:
A. Effects of water jet on brushing force, the number of brushing strokes and plaque removal with a manual toothbrush
1. Effects of a water jet were hardly recognizable on brushing force, the number of brushing strokes and the difficulty or ease of toothbrushing being reflected on the brushing areas.
2. The examinees with a 100% plaque removal showed an indirect relationship between brushing force and the number of brushing strokes with the use of a manual toothbrush only. But such a finding was not obtained with the combined use of a manual toothbrush and a water jet.
In toothbrushing with the combined use of a toothbrush and water jet cleansing devices, the water jet was supplementally effective in plaque removal so long as the water jet was of large volume and intense force. The efficacy would be obtained on the above synergic basis.
3. It is clarified that a water jet changes the plaque removal pattern of manual toothbrushing due to the mechanical force of the water jet without relation to increased brushing force and the number of brushing strokes.
B. Plaque removal by water jet cleansing devices
1. Water jet cleansing devices were less effective than a manual toothbrush in plaque removal.
2. The greater the volume and force of the water jet, the more effective is the plaque removal on each surface of the teeth.
3. The difference among the cleansing areas in plaque removal (the difficulty or ease in removing plaque on the cleansing areas) was not observed with the use of a water jet cleansing devices.
4. Cleansing with a water jet had no relation with the feedback mechanism from the sensations of the mouth, arm and hand.

View full abstract

1) After administration of a fermented milk beverage, the behavior of antibiotic-labeled Lactobacillus casei subsp. casei PSR 3001, with which the beverage was produced, was examined in the mouth under various conditions, using human subjects, male and female, at ages from in their twenties to in their thirties.
In the control group, the bacteria was found to be at 10^5-7 per cc in saliva and at 10^3-5per cc in dental plaque immediately after administration. The bacterial population sharply reduced to the level of 10² per cc in saliva and was virtually eliminated in dental plaque after 24 hours.
In groups with treatment of either tooth brushing before administration or mouth rinsing after administration, no difference could be detected in the pattern of the bacterial behavior. And also, giving sugar-rich foohdstuffs at intervals during the test period did not affect the behavior of the bacteria.
Regardless of the presence or not of dental caries no difference was observed in the behavior of the bacteria following the administration.
In control group, mouth rinsing group, and tooth brushing group, the correlation coefficients for the declining numbers of the bacteria between saliva and dental plaque were calculated to be 0.65, 0.91, and 0.67, respectively, showing a signigcant relationship (P<0.01).
2) Productivity of extracellular polysaccharides and characteristics of sugar fermentation by Lactobacillus casei subsp. casei, a strain used for the production of a fermented milk beverage, was examined in comparison with those of Str. mutans BHT and Str. mutans OMZ 176-1 as control.
When grown in Rogosa's medium containing sucrose, L. casei did not produce any significant amount of either water-soluble or water-insoluble polysaccharides in the culture broth, while large amounts of both polysaccharides could be recovered from Str. mutans culture broth (1, 043mg and 417mg per liter for water-soluble and water-insoluble polysaccharides, respectively).
In ability to ferment polysaccharides, Str. mutans was shown to be able to utilize the watersoluble polysaccharide produced by itself, but not a commercially available dextran. L. casei, on the other hand, could not ferment either type of polysaccharide.
Regarding the acid production from sugars, L. casei consumed glucose effectively to produce acid, the concentration of which reached its maximum after 48 hours, whereas, when grown on sucrose, no acid production was observed until 48 hours, with active production thereafter. With Str. mutans, acid production from both glucose and sucrose proceeded rapidly, and its concentration reached the maximum level within 24 hours.
In a mixed culture of L. casei and Str. mutans, the amount of water-insoluble polysaccharide produced was less than that synthesized by a single culture of Str. mutans.

View full abstract

In school dentistry it is important to understand the incidence of dental caries and the level of treatment and to discover problems in dental care. A dental survey of 458, 040 school children of elementary and junior high schools in Kanagawa Prefecture was made in 1969, and the results were as follows.
1. The DMF possesor rate in elementary school children was generally higher in higher grade children and in females. The DMF possesor rate in junior high school children was also higher in females.
2. The Mean number of DMF teeth per person in elementary school children generally showed a linear increase from lower to higher grades, and it was greater in females and in central geographicol areas. In junior high school children it was greater in females. and in outlying area.
3. The rate of treated teeth in elementary school children generally showed a rapid increase with grade in the first, second, third and fourth grade children, and a slow increase thereafter.
The rate in junior higher school children was higher in females and in central areas.
4. The possesor rate of untreated teeth in elementary school children generally showed an increase with grade; in the three lower grades it showed a rapid increase and a slow one thereafter. The rate in junior high school children also showed a general increase with grade. And it was higher in outlying than in central areas.

View full abstract