Hardness Of Teeth Research Articles

Field experiments to study the performance of toothed disc mowing mechanisms

Extensive experiments were conducted in the field to examine the performance of toothed discs when mowing a wide range of grass crops. The work was performed using (1) a modular rig fitted with six discs, (2) a two-drum mower fitted with toothed annuli and (3) a five-disc mower-conditioner modified to accommodate toothed discs. Mowing performance was studied over a range of forward speeds from 2 to 12 km/h and at tooth tip speeds up to 80 m/s. Tooth pitch was varied over a range up to 25 mm. Performance was compared with that of commercial drum and disc mowers using conventional blades. The efficacy of mowing was measured by samples of the length of stubble produced and the power consumption of the mowers. Studies were also made of the wear of the disc teeth during mowing. The work has shown that tooth pitch should be between 8 and 10 mm for minimum stubblelength and power consumption, at a typical mowing forward speed of 9 km/h. This results in a bite length for each tooth of 0·5 to 0·6 mm. The optimum tooth form was a 0° rake angle and a 30† clearance angle. The critical speed was in the range of 25 to 35 m/s and that for minimum power was in the range 25 to 30 m/s. A speed of 40 m/s is suggested, however, to achieve effective cutting over a range of crop conditions. Sharp-toothed discs required 65% of the total power of sharp conventional blades and 50% of that with blunt conventional blades. Worn-toothed discs required about 60% of the power of worn conventional blades. Stubble length increased, however, for worn teeth, particularly in laid crops. For stainless and high carbon steel discs a tangential wear volume of 3·6% of the toothvolume was indicated when cutting 10 t (d.b.) of crop. To achieve a minimum wear rate, a tooth hardness of 550 HV is likely to be required. Further development of the toothed-disc mower is required to overcome some problems of soil and crop accumulation at the intersection of co-rotating discs which can cause long stubble at these points.

Study on the Method of Hardness Test and the Distribution of Micro-Vickers Hardness of Human Teeth

Study on the Method of Hardness Test and the Distribution of Micro-Vickers Hardness of Human Teeth

A Study on Rolling Finish of Gear : Plastic Deformations by Rolling Experiment of Rollers

To clarify the deformation mechanism of tooth surface in the rolling finish of gears, it is necessary to grasp the plastic deformation produced by the rolling. the deformation of tooth surface is affected by the face width and the hardness of tooth. In the present study the rolling finish of rollers is experimented under three conditions of specific sliding. The profile of rolled surface and sides, the radial and axial deformations and the hardness below the rolled surface are measured. The deformation of roller becomes steady after about three to six passes but it is affected by the width of roller. The relations among parameters of deformation are clarified.

Dental aspects of patients with cystic fibrosis: a preliminary clinical study

The oral conditions of 42 patients being treated for cystic fibrosis were evaluated. The patients were grouped by age and, in some aspects, were compared with a small control group of their siblings. The patient group had a lowered incidence of plaque and less gingival disease than did the control group in which every person had some amount of plaque or gingival disease. Calculus formation was minimal. The reasons for the finding of minimal plaque in the patient group could be related to several factors, including the life-long use of various antibiotic agents, the chewing of digestive enzyme supplements, the effect of medical management on tooth hardness, and the effect of stained teeth (possible tetracycline deposition) on the plaque microorganisms. It appears that the therapy for cystic fibrosis was beneficial to the periodontal health of these patients. Much further study is needed to understand the interrelationship between an altered oral environment (salivary changes in cystic fibrosis), altered microbial flora (by antibiotics, enzymes) and even altered tooth surfaces (possible tetracycline deposition). Most patients were found to have one or more oral habits. Tooth mobility was associated with tension habits. Patients who had clubbed fingers (indicating pulmonary compromise) and possibly a severe disease process, did not appear to have either stained teeth or the severity of the gingivitis associated with this. The relationship of tetracycline to tooth staining could not be pinpointed.

Effect of thermal high-frequency surface hardening on the hardness and microstructure of bandsaw teeth

Examination of the bandsaw teeth (1) untreated, (2) swaged and (3) treated by thermal high-frequency surface hardening method has shown that their average microhardness is 473 DPN ( 62 Rc) respectively.

Studies on the physical properties of fluorosed enamel—II: Microhardness

The microhardness was measured on thirty teeth collected from Alamosa, Colorado; Colorado Springs, Colorado; Doland, S. Dakota, and Post, Texas, where the water supply contained 1.5, 2.6, 2.9 and 5.0 p.p.m. of fluoride respectively. The average hardness of teeth from each of these areas was compared with the average hardness of teeth from Birmingham, Alabama (0·00–0·03 p.p.m. F in the drinking water). It was found that the teeth from Colorado Springs and from Post were significantly softer than those from Birmingham but that the teeth from the other locations did not differ significantly. The degree of dental fluorosis appeared to be inversely proportional to the Knoop Hardness.

REVIEW OF BOOKS AND ARTICLES

Book reviewed in this article:Klein, Henry. Dental effects of accidentally fluorinated water: I. Dental caries experience in deciduous and permanent teeth of school age children.Klein, Henry. Dental effects of community waters accidentally fluorinated for nineteen years. II. Differences in the extent of caried reduction among the different types of permanent teeth.McKay, F. S. Mss control of caries through the use of domestic water supplies containing fluorine.Phillips, R. W., and Swartz, Marjorie L. Effect of fluorides on hardness of tooth enamel.Proceedings of the Michigan dental caries conference.McClure, F. J. Fluorine in dentin and enamel of sound and carious human teeth.Dreizen, Samuel, and Spies, T. S. Further studies on the association between the products of protein putrefaction and dental caries activity.Blayney, J. R. and Tucker, W. H. The Evanston dental caries study. II. Purpose and mechanism of the study.Rapp, G. W. The mechanism of enzyme action. Oral Surg., Oral Med., & Oral Pathology.