Using variable modulus to modify a rack cutter and generate a gear pair

In this paper, two normal imaginary helical rack cutters were first established. One of these cutters is a skewed-rack cutter with an asymmetrical straight edge. The other is a rack cutter with an asymmetric parabolic profile. Second, the gear’s tooth surface of the asymmetric parabolic rack cutter is modified to be barrel-shaped based on a variable modulus. The tooth thickness of the gear is gradually reduced along the face width of the tooth from the middle of the tooth surface. Then the coordinate relationship between the gears’ blanks and the imaginary helical rack cutters was established. Through the differential geometry, crowned and uncrowned helical gear pairs were generated. Because of human factors, when the gear pair is installed, it is easy to cause the gear pair edge contact. It is necessary to add artificial assembly error settings through the tooth contact analysis to investigate the kinematic errors and contact conditions of the crowned and uncrowned helical gear pair. The mathematical models and analysis methods proposed for the crowned imaginary rack cutter using variable modulus should be useful for the design and production of double crowned helical gears with asymmetric parabolic teeth.

Subtypes of early childhood caries predict future caries experience

Objectives: To test whether postulated subtypes of early childhood caries (ECC) are predictive of subsequent caries experience in a population-based cohort of Swedish children. Methods: The study included children aged between 3 and 5 years at study entry with dental records available for at least 5 years of follow-up. Dental record data were retrieved from the Swedish Quality Registry for Caries and Periodontal disease (SKaPa) for the initial and follow-up visits. Participants who had ECC at study entry were assigned to one of five ECC subtypes (termed classes 1 to 5) using latent class modelling of tooth surface-level caries experience. Subsequent experience of caries was assessed using the decayed, missing, and filled surfaces indices (dmfs/DMFS) at follow-up visits, and compared between ECC subtypes using logistic and negative binomial regression modelling. Results: The study included 128,355 children who had 3 or more dental visits spanning at least 5 years post baseline. Of these children, 31,919 had caries at the initial visit. Baseline ECC subtype was associated with differences in subsequent disease experience. As an example, 83% of children who had a severe form of ECC at age 5 went on to have caries in the permanent dentition by the end of the study, compared to 51% of children who were caries-free at age 5 (adjusted odds ratio of 4.9 for new disease at their third follow-up). Conclusions: ECC subtypes assigned at a baseline visit are associated with differences in subsequent caries experience in both primary and permanent teeth. This suggests that the development and future validation of an ECC classification can be used in addition to current prediction tools to help identify children at high risk of developing new caries lesions throughout childhood and adolescence.

The Antiplaque Efficacy and Effectiveness of Activated Charcoal Toothpaste of Elaeis guineensis in Smokers

Plaque on the teeth of smokers comes from cigarette smoke tar that settles on the surface of the teeth and roots of the teeth, causing the tooth surface to become rough and easier to stick with food debris and germs that will react making it easier for plaque to form. This study was aims to determine the safety and effectiveness of removing plaque in palm shell activated charcoal toothpaste with a concentration of 12% calcium carbonate combination of 25%. The content of calcium carbonate as an abrasive against the dental plaque of active smokers. The method used was measurement the plaque index score according to Turesky before and after using toothpaste on 20 panelists of active smokers. The decrease in plaque index in the use of toothpaste by using Wilcoxon's non-parametric statistical test, namely P = 0.000 (Sig <0.05). The results showed that toothpaste in the first week was able to reduce dental plaque by 59% compared to positive control by 45% and without activated charcoal by 34%. Toothpaste and positive control in the second week were able to remove dental plaque by 100%, while toothpaste without activated charcoal and calcium carbonate was only able to remove dental plaque by 68%. It can be concluded that palm shell activated charcoal toothpaste with a concentration of 12% combined with 25% calcium carbonate is safe and effective in removing plaque on the teeth of smokers.Keywords: dental plaque, efficacy, palm shells

Prevention of Caries and Dental Erosion by Fluorides—A Critical Discussion Based on Physico-Chemical Data and Principles

Dental erosion is a common problem in dentistry. It is defined as the loss of tooth mineral by the attack of acids that do not result from caries. From a physico-chemical point of view, the nature of the corroding acids only plays a minor role. A protective effect of fluorides, to prevent caries and dental erosion, is frequently claimed in the literature. The proposed modes of action of fluorides include, for example, the formation of an acid-resistant fluoride-rich surface layer and a fluoride-induced surface hardening of the tooth surface. We performed a comprehensive literature study on the available data on the interaction between fluoride and tooth surfaces (e.g., by toothpastes or mouthwashes). These data are discussed in the light of general chemical considerations on fluoride incorporation and the acid solubility of teeth. The analytical techniques available to address this question are presented and discussed with respect to their capabilities. In summary, the amount of fluoride that is incorporated into teeth is very low (a few µg mm−2), and is unlikely to protect a tooth against an attack by acids, be it from acidic agents (erosion) or from acid-producing cariogenic bacteria.

Prediction and test of stable transmission time of spiral bevel gear during a loss-of-lubrication event in helicopter transmission system

Purpose This paper aims to establish a prediction model of stable transmission time of spiral bevel gear during a loss-of-lubrication event in helicopter transmission system. Design/methodology/approach To observe the temperature change of spiral bevel gear during working condition, a test rig of spiral bevel gear was developed according to the requirements of experiments and carried out verification experiments. Findings The prediction is verified by the test of detecting the temperature of oil pool. The main damage form of helicopter spiral bevel gears under starved lubrication is tooth surface burn. The stable running time under oil-free lubrication is mainly determined by the degree of tooth surface burn control. Originality/value The experimental data of the spiral bevel gear oil-free lubrication process are basically consistent with the simulation prediction results. The results lay a foundation for the working life design of spiral bevel gear in helicopter transmission system under starved lubrication.

Fluorescence-Aided Identification Technique (FIT) Improves Tooth Surface Clean-Up after Debonding of Buccal and Lingual Orthodontic Appliances

The aim of this study was to evaluate the use of fluorescence inducing light to aid the clean-up of tooth surfaces after bracket removal when using buccal or lingual orthodontic appliances. Two full sets of dental arches using extracted human teeth were assembled, with 14 teeth per arch. All teeth were bonded on their buccal and lingual surfaces. After debonding, a single blinded operator performed the tooth surface clean-up, as commonly performed in clinical practice; without the use of fluorescent light (non-FIT) and with two methods using fluorescent light to identify composite remnants on the tooth surfaces (FIT; OPAL and BRACE). Tooth surfaces were scanned before bonding and after clean-up, and the two scans were superimposed using the best-fit method. The results showed that the debonding method, type of tooth and type of tooth surface had a significant effect on the presence of composite remnants, enamel defects, and on debonding time. Contrary to the non-FIT method, there were no composite remnants after clean-up with the use of fluorescence inducing light. Clean-up time was significantly reduced on the buccal surfaces when using the FIT methods. On the lingual surfaces, the FIT methods resulted in larger enamel defects.

Profiling of a shaped worm cutter for shaping gears with non-involute tooth profile

Of the mechanical transmissions used in mechanical engineering, the most common are gears with an involute profile of the teeth flanks. Gears made up of such wheels have a number of advantages, but they also have a number of significant disadvantages. Therefore jne of the current trends is the study of gears with a complex non-involute profile of the teeth flank which have advantages over involute gears in a number of applications, as well as the development of tools for their processing. There are two ways of gear teeth cutting: the copying method and the rolling-in method. The rolling-in method has advantages. The profile of the tool working by the rolling-in method does not depend on the number of teeth of the gear being cut, therefore, the same tool can be used to cut gears with any number of teeth. The accuracy of a gear made by the rolling-in method is significantly higher than the accuracy of a gear made by the copying method. This is primarily due to the continuity of the rolling-in process. When cutting teeth by the rolling method, the tooth surface is formed as a result of processing with a tool, the cutting edges of which are the tooth profile of the mating rack or the tooth profile of the mating gear, and during processing the tool and the workpiece form a mating gear pair. The most common gear cutting tool is the hob cutter. For the machining of gear wheels with a non-involute tooth profile widely used in industry equipment is used. One of the options for a rolling gear cutting tool for shaping gear wheels with a non-involute tooth profile can be a shaped worm cutter. The article describes the method of profiling of the cutting part of shaped hob cutter for machining of gear wheels with normal accuracy. To solve the problem the unified mathematical base – the apparatus of multiparameter mappings of space – the unified structure of mappings for gears and a compact set of unified operators, parameters and functional connections is used.