Edges Of Teeth Research Articles

S112041 高速同期ギヤホーニングによるギヤシェービング工程の廃止([S112-04]伝動装置の基礎と応用(4))

This report outlines that investigation conducted on the OBD stock removal, influence on honing stone breaking by burr of tooth edge, mass productivity and gear noise, in order to eliminate gear shaving process by high-speed synchronous gear honing. As a result of the investigation, it was verified that high-speed honing condition can be decided if the normal base stock removal per work revolution was used. In addition, it has been confirmed that burr of tooth edge have no influence on honing stone breaking and gear accuracy, besides the noise level of this honing gear is same as honing gear which has gear shaving process.

The Prevalence of Tooth Wears Among (18-25) Years Old College Students in Sulaimani City

Non-carious loss of tooth structure is considered the 4th dimension risk factor for
 aesthetic, function and longevity of human dentition after acute trauma, caries and
 periodontal disease The aim of this study was to determine the prevalence and risk
 indicators for tooth wear in (18- 25) years in Sulaimani city. A total of 500 randomly
 selected college students were examined for tooth wear. The data were collected by means
 of a questionnaire about the history of possible causative factors and a clinical
 examination using Smith and Knight’s index on occlusal/incisal, buccal and lingual/palatal
 surfaces. Mild tooth wear (score 1) was present in 63.4%, while only 0.4% had lesions
 extending up to the dentine. There were 36.2% without tooth wear, there is no evidence of
 score 3 or score 4. Incisal edges of both lower and upper teeth were the most affected site
 (75.51%). Occlusal problem was the most common predisposing factor (72.73%). Tooth
 wear defect did not form an urgent problem at 18-25 years aged group, there was only
 minimal enamel loss (63.4%, score 1) that attributed mainly to occlusal problems.

Shearing Mechanics and the Influence of a Flexible Symphysis During Oral Food Processing in Sphenodon (Lepidosauria: Rhynchocephalia)

The New Zealand tuatara, Sphenodon, has a specialized feeding system in which the teeth of the lower jaw close between two upper tooth rows before sliding forward to slice food apart like a draw cut saw. This shearing action is unique amongst living amniotes but has been compared with the chewing power stroke of mammals. We investigated details of the jaw movement using multibody dynamics analysis of an anatomically accurate three-dimensional computer model constructed from computed tomography scans. The model predicts that a flexible symphysis is necessary for changes in the intermandibular angle that permits prooral movement. Models with the greatest symphysial flexibility allow the articulation surface of the articular to follow the quadrate cotyle with the least restriction, and suggest that shearing is accompanied by a long axis rotation of the lower jaws. This promotes precise point loading between the cutting edges of particular teeth, enhancing the effectiveness of the shearing action. Given that Sphenodon is a relatively inactive reptile, we suggest that the link between oral food processing and endothermy has been overstated. Food processing improves feeding efficiency, a consideration of particular importance when food availability is unpredictable. Although this feeding mechanism is today limited to Sphenodon, a survey of fossil rhynchocephalians suggests that it was once more widespread.

Fracture Reasons and Improvements for the Running Gear of Shearers

Running traction mechanism of shearers is adopted as the analysis object in this paper. The finite element models for the elastic contact analysis between the running gears and pin-rails are created. When the gears are running, the variation principles of contact spots, contact force, and internal stress for the gears and pin-rails at the different contact positions are analyzed. The calculation results show that the maximum stress is located at the edges of the gear teeth for the different contact positions. When the teeth are loaded with the repeated large stress, cracks are produced at the tooth edges at first and then are growing. The tooth breakage is produced at last. Gear chamfers using two circulars at the tooth edges can change the location of the maximum stress and the maximum MISES stress can be reduced by 20% or more. Therefore, the fracture problem of gear teeth is solved basically.

Congruency of Stereo Lithographically Produced Surgical Guide Bases Made from the Same CBCT File: A Pilot Study

This is a pilot study evaluating the effect of the algorithms and production processes of four commercial manufacturers of stereolithographically produced surgical guide. A singular Dicom file was used to produce six distinct duplicate dentures, which function as the base for surgical guides. The duplicate dentures were repeatedly fitted (n = 10) into an impression of the occlusal surface of the original scan appliance. The gaps between the incisal edge of teeth #8 and #9 and the corresponding imprints in the vinyl polysiloxane impression were photographed, digitally recorded, and measured in a blinded fashion. Nobel Biocare mean was 0.56 mm (range 0.49-0.65), I-dent mean was 0.57 mm (range 0.31-0.74), Materialise II mean was 1.12 mm (range 0.90-1.40), Blue Sky Bio II mean was 1.13 mm (range 0.93-1.35), Materialise I mean was 1.43 mm (range 1.21-1.86), and Blue Sky Bio I mean was 2.17 mm (range 2.06-2.34). The difference between the fit of the Nobel Biocare and the I-dent guide bases and the guide bases from Materialise and Blue Sky Bio is statistically significant (p < .05). The algorithms and production processes of the different manufactures do influence the congruency outcome of the produced surgical guide bases. Within the limits of this study, we were unable to produce a perfect fit, although some duplicate dentures showed minimal errors. The implications of the discrepancies need further study.

Normal Mouth Opening in an Adult Indian Population

Mouth opening among different population has been shown to vary considerably and its range is specific for a given population. The present study is an attempt to calculate the normal mouth opening in adult Indian population. A total of 894 adults, 463 males and 431 females, in the age range of 21 to 70years were studied. The subjects were asked to open their mouth maximally till no further opening was possible. The distance from the incisal edge of the upper incisor teeth to the incisal edge of the lower incisor teeth was measured using a calibrated fiber ruler. To determine correlation of mouth opening with age a Pearson correlation analysis was performed and statistical significance was tested by the application of t test. The mean maximal mouth opening for males was 51.3mm (SD 8.3) (Range 39-70mm). The mean maximal mouth opening for females was 44.3mm (SD 6.7) (Range 36-56mm). There was significant difference between the mouth opening of male and female in all the age groups with P value <0.05. A linear relationship was observed between the mouth opening and age in both males and females and the mouth opening decreased as the age increased. The mean maximal mouth opening for Indian males is 51.3±8.3mm and for females is 44.3±6.7mm. The mouth opening seems to decrease with age. The mouth opening of females is significantly less than the males in all the age groups.

Supplemental Mesiodens with Facial Talons Cusp-An Unusual Case Report

ABSTRACT Supernumerary tooth is one that is additional to the normal series and can be found in almost any region of the dental arch. Mesiodens is the most common type of supernumerary tooth found in the premaxilla between two central incisors. Talon cusp is a supernumerary structure projecting from the dento-enamel junction to a variable distance towards the incisal edge of an anterior tooth and mostly on the palatal aspect. Only few have been reported on the facial aspect of the teeth. Here we present a case of a ten year old male child with supplemental mesiodens associated with facial talons cusp.

F111004 ギヤドモータ用微小モジュール小形歯車の仕上げ加工技術 : 小形・環境負荷低減・省エネ型歯車仕上げ加工法の開発

Precise micromodule small gears are necessary to realize high-strength low-noise compact geared motors. In the gear manufacturing process, burrs and nicks are generated at the edge or ridgeline of the work gear tooth and they get the gear accuracy worse. Therefore a removal method of burrs and nicks is important. However, it is difficult to remove them from small gears by using usual tools and usual processing devices because the tooth groove of small gears is narrow. In addition, high performance in terms of size, energy consumption, environmental impact, and cost is required for gear manufacturing devices. In order to solve these problems, FRP gear-shaped tool and finishing device for small gears using oscillation have been developed in this research. Experiments are carried out and it is confirmed that the proposed method can remove burrs and nicks from small gears. This finishing device achieves small size, low energy consumption, low environmental impact, and low cost compared with conventional finishing devices. This finishing method has been used already in the gear manufacturing process in the industrial field and it has contributed to higher accuracy and lower defect rate of manufactured gears.

The variation in elastic properties of limpet teeth

ABSTRACTLimpet teeth are an example of a biological short fiber reinforced composite material used for a mechanical function. The local micro-scale elastic properties of limpet teeth were examined by bending FIB fabricated beams of the limpet tooth material using atomic force microscopy (AFM). The elastic modulus values for the limpet tooth material varied from 140 GPa at the tooth posterior edge, through 90 GPa at the tooth core to 120 GPa at the tooth anterior edge. This variation in the elastic modulus of limpet tooth material at the posterior, interior and core regions of the tooth is indicative of a mechanically graded structure and is expected to enhance the durability of limpet teeth during rasping over rock surfaces during feeding.

Relationship between Bruxism and Malocclusion among Preschool Children in Isfahan.

Background and aims Bruxism is defined as a habitual nonfunctional forceful contact between occlusal tooth surfaces. In younger children bruxism may be a consequence of the masticatory neuromuscular system immaturity. The aim of this study was to assess the prevalence of bruxism and investigate the relationship between occlusal factors and bruxism among preschool children. Materials and methods In this cross-sectional survey, 400 3-6-year-old children were selected randomly from different preschools in Isfahan, Iran. The subjects were divided into two groups of bruxers and non-bruxers as determined by the clinical examination and their parents’ reports. The examiner recorded the primary canines (Class I, Class II, and Class III) and molars (mesial step, distal step, flash terminal plane) relationship, existence of anterior and posterior crossbite, open and deep bite. Also, rotated teeth, food impaction, sharp tooth edges, high restorations, extensive tooth caries, and painful teeth (categorized as irritating tooth conditions) were evaluated. The relationship between bruxism and occlusal factors and irritating tooth conditions was evaluated with chi-square test. Results Bruxism was seen in 12.75% of the subjects. Statistically significant relationships existed between bruxism and some occlusal factors, such as flash terminal plane (P = 0.023) and mesial step (P = 0.001) and also, between food impaction, extensive tooth caries, tooth pain, sharp tooth edge and bruxism. Conclusion The results showed significant relationship of bruxism with primary molar relationships and irritating tooth conditions among preschool children.

Precise Modeling of Arc Cylinder-Gears with Tooth Root Fillet

Study on theory of generation processing arc cylinder-gears, machining cutter was designed by the blade fillet and the top tooth edge generating the tooth root fillet of arc cylinder-gears, to build the linear tooth-surface equation of cutter-gear and the position vector of blade fillet curvature center. The linear tooth surface equations and fillet tooth surface equation were derived based on coordinate transformation principle, meshing equation, meshing geometry principle and kinetic theory. The precise 3D model was established. It verifies the feasibility of generation processing the arc cylinder-gears and achieves smooth transition both working and fillet tooth surface of arc cylinder. It provides theoretical basis for tooth contact analysis, tooth bending stress and kinetic analysis, further offers accurate data to numerical control machining and systematically guides the experimental research and practical application.

First record of the genusOnchidoris(Gastropoda: Nudibranchia: Onchidorididae) from the South Atlantic Ocean, with the description of a new species from Brazil

A new species of the genusOnchidorisis described from the south-western Atlantic, on the coast of Brazil, in the States of Rio de Janeiro and São Paulo. To date, the genusOnchidorisis known almost exclusively from the northern hemisphere, especially the Atlantic coast of Europe and the Mediterranean Sea. The single previous record from the southern hemisphere isOnchidoris maugeansis, described from Australia. This is the first record of the family Onchidorididae from the coast of Brazil.Onchidoris brasiliensissp. nov. is very similar toOnchidoris depressa, from England and the northern coast of Spain, but is distinguished by the presence of a triangular protuberance on the edge of the inner lateral radular tooth and a wide closed branchial circle with tubercles inside. Furthermore, the egg mass of O.brasiliensissp. nov. contains a single row of eggs, whereas that ofO. depressahas multiple rows.Onchidoris brasiliensissp. nov. has lecithotrophic development, the first record of this type of development in the genus. There is a relationship betweenO. brasiliensissp. nov. and the bryozoanParasmittina protecta.

Fabrication of Microfluidic Rapid Micromixer

A microfluidic multi-cylindric rapid micromixer is fabricated in the present paper. The key features in the presented MEMS-based microchannel design are (1) micro pump (2) Y-junction type channel (3) cylindric obstacle (4) notch with the edge of sharp teeth. Two different fluids (DI water and red ink) were pumped and injected into Y-type channel, and the fluids were broken-up by a cylindric obstacle in the center of tapered microchannel. The chaotic convection occurs in the mixing channel behind the cylindric obstacle. The mixing index is defined to qualify the mixing efficiency, which demonstrates the outlet notch with sharp teeth along the sidewall plays an important role for mixing effects. The developed micromixer can enhance mixing using the mechanisms of diffusion and convection for wide range of Reynolds number (0.01&lt;Re&lt;100). Parametric studies for volumetric flow rate include the number of cylindric obstacles, the number of notches with sharp-teeth and the width of microchannel. Preliminary results demonstrate that the mixing index reaches the desired effect (&lt;0.1) within 0.08 second when the inlet fluid velocity is 0.49992m/s, i.e. volumetric flow rate is 1200μl /min. The presented device is faster than most of reported micromixers.

Comparison between five commonly used two-dimensional methods of human bite mark overlay production from the dental study casts

The present study was conducted to determine the most accurate bite mark overlay fabrication technique by studying two physical characteristics, i.e., area and rotation of biting edges of anterior teeth of thirty volunteers. The objective of the study was to evaluate the reliability and efficacy of five commonly used methods of human bite mark overlays using two dimensional (2D) digital images of dental study casts as a gold standard, to rank different methods according to statistically based determination of relative accuracy of each method and to determine its feasibility in Forensic science. Overlays were produced from the biting surfaces of six upper and six lower anterior teeth of 30 volunteers using the following five methods: a) hand tracing from study casts, b) hand tracing from wax impressions, c) xerographic method, d) radiopaque impression method and e) 2D computer-based method. Area of the biting edges of the anterior teeth and relative rotation of each anterior tooth were measured and compared. The xerographic method was determined to be the more accurate method with respect to tooth area and rotation. Hand tracing methods, from either wax impressions of teeth or directly from study casts, were determined to be inaccurate and subjective. It is recommended that forensic odontologists discontinue the use of hand tracing overlays in bite mark comparison cases as there is lot of scope for manipulation and observer bias.

Mandibular talon cusp: A rare presentation with the literature review

A talon cusp is a supernumerary structure projecting from the dento-enamel junction to a variable distance towards the incisal edge of an anterior tooth. It consists of enamel, dentine and a variable amount of pulp tissue. Hyperactivity of the enamel organ during morpho-differentiation has been attributed to its formation. It has esthetic and functional concerns. Reports of a mandibular talon cusp are rare in the literature. To the best of our knowledge, only 14 cases have been reported, of which only 2 cases in mandibular left central incisors. We report the second instance of a talon cusp in the lingual aspect of the mandibular left central incisor and the first such report in a patient of Libyan origin. A talon cusp is an odontogenic anomaly, which can cause occlusal interferences, displacement of the affected tooth and speech difficulties. Early diagnosis of a talon cusp helps in selecting the appropriate treatment procedure and to avoid future complications.

Removal Method of Burrs and Pits for Small Gears Using an Oscillation System with a Gear-Shaped Tool Composed of Glass-Fiber-Reinforced Plastic

To improve strength and vibration and noise, it is important to remove the burrs and pits generated at the edges of gear teeth during the gear cutting process. However, as the tooth groove of the small gears in compact geared motors is small, removal of such burrs and pits is difficult due to space constraints. To address this, a gear-shaped tool composed of glass fiber-reinforced plastic (GFRP) has previously been proposed and the effectiveness of the removal process using it has been confirmed. However, in some cases, the method does leave burrs and pits in the position on the pitch circle. Herein, to address this issue, an improved method is proposed which introduces oscillation to the GFRP gear-shaped tool. A theoretical analysis of the sliding velocity at the tool/work-piece interface is also presented. The apparatus for the process was constructed and used to validate the proposed method experimentally.

Smile analysis following orthognathic surgery

Aim: This study compared the different views between orthodontists and oral maxillofacial surgeons, as for smile analysis in patients subjected to orthognathic surgery. Methods: Thirty individuals who had undergone orthognathic surgery and had a minimum postoperative period of 6 months were selected. Posttreatment frontal smile photographs were obtained and examined. Smile features were recorded by 4 professionals (2 orthodontists and 2 surgeons) and the agreement between them was assessed. Results: The subjective analysis of smile as well as the observation of incisal and gingival exposure showed a statistically significant agreement percentage between the two groups. Nevertheless, no agreement was seen between the surgeons, while evaluating the buccal corridor and the parallelism between the incisal edge of antero-superior teeth and the lower lip. Significant agreement percentage (60%) was seen only between the orthodontists regarding the smile arch parallelism. Conclusions: Professionals must be alert as for facial analysis, mainly in terms of smile harmony, so that the orthognathic surgery will satisfactorily reestablish the facial esthetics in all the parameters outlined.

Two new sacoglossan sea slug species (Opisthobranchia, Gastropoda): Ercolania annelyleorum sp. nov. (Limapontioidea) and Elysia asbecki sp. nov. (Plakobranchoidea), with notes on anatomy, histology and biology

Two new sacoglossan species, belonging to the genus Ercolania Trinchese, 1872 (Ercolania annelyleorum sp. nov.) and the genus Elysia Risso, 1818 (Elysia asbecki sp. nov.) are described from Lizard Island, Great Barrier Reef, Australia. Anatomy of both species was reconstructed by analyzing histological serial sections. Radula morphology was investigated by using light microscopy and scanning electron microscopy. Sequence analyses (NeighborNet; sequence divergence) and tree reconstructions showed for both species their distinction from con-generic species, but also two distinct mitochondrial lines in the new Ercolania species. Adults as well as freshly hatched juveniles of E. annelyleorum sp. nov. have been found in clusters of the ulvophycean alga Boodlea sp., which are sucked out by piercing the cell walls with their radular teeth. This new species differs from other, similar transparent, Ercolania species by its pattern of the green branches of the digestive gland and the presence of two distinct red patches, one in the anterior and the other in the posterior third of the dorsal body part. This coloration and furthermore the combination of following characters distinguishes the new species from all other described Ercolania species so far: rhinophores, elliptic in cross section, with one distinct branch of digestive gland running half way up; cerata not inflated; smooth cutting edge of sabot-shaped tooth; two-lobed prostate gland and presence of two allosperm receptacles with no re-opening of the receptaculum seminis to the outside. According to sequence divergence data of CO1, two mitochondrial lines seem to be present in the new species, which are clearly distinct from all other included Ercolania species. Elysia asbecki sp. nov. differs from other Elysia species by its whitish coloration with orange and dark brown dots and a distinct lighter spot in the neck region of the head. The rhinophores exhibit a black and yellow ribbon at the tip. The species has distinct reddish patches at the anterior base of the parapodia (at the conjunction with the head), one along the middle part of the parapodial edge on both sides and very distinct lateral patches at the end of the foot. CO1 sequences clearly distinguish this species from all closely related Elysia species. The food source of Elysia asbecki sp. nov. could not be verified yet. Measurements of photosynthetic activity within these two new species indicate that E. annelyleorum sp. nov. digests chloroplasts immediately after sequestration, whereas Elysia asbecki sp. nov. shows high maximum quantum yield values, similar to E. timida (Risso, 1818) and E. crispata (Mørch, 1863), both known as long term retention forms.

Axial Flux and Eddy-Current Loss in Active Region of a Large-Sized Squirrel-Cage Induction Motor

This paper analyzes the axial flux and the corresponding eddy currents inside the laminated cores of a large-sized squirrel-cage induction motor running under the steady-state operation in order for possible optimum design of large-sized induction motors used in industry. The analysis was based on a complete 3-D numerical model. In the model, the laminated cores were replaced by anisotropic solid bodies, and the eddy currents inside the end portion of the stator frame were modeled with the standard impedance boundary condition. A time-harmonic finite-element analysis based on the magnetic vector potential-electric scalar potential formulation was performed. According to the results, under steady-state no-load, the axial flux, caused mainly by the air-gap fringing flux and the end-winding leakage flux, appears in the end portion of the cores, and decays rapidly toward the middle of the cores. The corresponding planar eddy currents inside the laminations of the stator core are mainly concentrated near the edges of the stator teeth. The eddy-current loss is small, but the distribution of the loss over the laminations is definitely non-uniform.

Method for removing burrs and pits from small gears using a gear-shaped tool composed of glass-fiber-reinforced plastic

Gear characteristics are strongly dependent on the quality of the tooth edge of the gears. Therefore, methods for removing defects such as burrs and pits of gears are very important. Burrs and pits are particularly difficult to remove from small gears due to the small dimensions of the tooth grooves. In addition, the equipment for the removal process should be simple and low in cost. In the present study, a method using a gear-shaped tool made from glass-fiber-reinforced plastic (GFRP) is developed for removing burrs and pits from small gears. A manufacturing method for the GFRP gear-shaped tool is proposed and it was confirmed that a conventional hobbing machine and a carbide hob can easily manufacture such a tool without defects. The ability of the proposed tool to remove burrs and pits is evaluated experimentally and the results demonstrate that the burrs and pits of a work gear can be effectively removed by using the proposed tool with simple equipment based on a lathe. This tool was then applied to the mass production of gears, and it was confirmed that this tool has the durability to remove the burrs of 16,797 work gears.