Tooth Form Research Articles

The Tooth Form Deviation Correction of CNC Spiral Bevel Gears Grinding Machine

The influencing factors of machining errors are analyzed aiming at the characteristics of the CNC spiral bevel gears grinding machine. The relation between those factors and machine setting errors is built. The optimization model of nonlinear least square is deduced. According to the mathematics model, an experiment of tooth form deviation correction is done in YK2075 CNC spiral bevel gears grinding machine manufactured by Tianjin No.1 Machine Tool Works. And the mathematics model is verified in the experiment.

Comprehensive Periodontal Therapy: A Statement by the American Academy of Periodontology

Comprehensive Periodontal Therapy: A Statement by the American Academy of Periodontology

Esthetic preferences for the shape of anterior teeth in a posed smile

Although various aspects of smile esthetics have been considered in many studies, few of them have compared laypeople's preferences for an esthetic smile with regard to the shape of the anterior teeth. The aim of this study was to evaluate the effects of the shapes of the maxillary anterior teeth in men and women on the perception of an esthetic smile by different age and sex groups of laypeople. Two pamphlets, each consisting of 9 smile images that differed only in the shapes of the canines and incisors, were shown to 4 groups of judges of different ages and sexes. They were asked to rank feminine and masculine smile images according to their preferences using a 10-cell linear horizontal visual analog scale. Neither in the men's nor in the women's pamphlets were there significant differences between the scores of the 4 groups of judges to the various tooth forms. In both pamphlets, regardless of canine shape, all groups of judges gave significantly different scores to square, square-round, and round incisors so that the median of scores for square incisors was significantly lower than those of the 2 other incisor forms. Sex and age of the laypersons did not affect their esthetic perception of the shapes of the maxillary anterior teeth. Incisor shape was the key determinant of their esthetic preferences; round incisors were the most esthetic. It is recommended to improve smile esthetics by mildly rounding the mesial and distal corners of square incisors.

Frequency and distribution of developmental anomalies in the permanent teeth of a Turkish orthodontic patient population

Background/purpose The aims of this study were to determine the frequency and distribution of developmental anomalies in the permanent teeth of a Turkish orthodontic patient population and determine the relationships between gender and dental anomalies. Materials and methods A retrospective study was performed using pretreatment dental casts, panoramic radiographs, and intraoral photographs of 3165 Turkish orthodontic patients (1940 females and 1225 males) aged 9–25 years. These patients were analyzed for evidence of four types of developmental anomalies (tooth form, number, position, and structural dental anomalies). Descriptive characteristics of these dental anomalies, including gender, jaws, and sides of the jaw were recorded. The Pearson χ 2 test was used for the statistical analysis. Results In 452 (14.3%) of 3165 orthodontic patients, at least one permanent teeth anomaly was detected. Developmental dental anomalies were found in 15.05% of females compared with 13.06% of males. Impacted teeth were the most frequent dental anomaly (4.55%), followed by hypodontia (4.30%), peg-shaped lateral incisors (2.15%), ectopic eruption (1.52%), and hyperdontia (1.30%). Peg-shaped lateral incisors, hypodontia, oligodontia, transposition, transmigrant canines, ectopic eruption of canines, impacted teeth, and amelogenesis imperfecta were more common in females, whereas macrodontia and hyperdontia were more common in males. However, these differences were not statistically significant except for hypodontia and hyperdontia. Conclusion The prevalence of developmental dental anomalies was higher in females than males. Impacted teeth were the most common developmental dental anomaly in this Turkish orthodontic population, followed by hypodontia.

The Smaller Embolomerous Amphibians (Anthracosauria) from the Middle Pennsylvanian (Desmoinesian) Localities at Linton and Five Points Coal Mines, Ohio

The remains of small embolomeres (total midline skull length not exceeding 100 mm) from the Middle Pennsylvanian (Desmoinesian) Linton and Five Points coal mines of southeastern Ohio can be distinguished from those of Leptophractus found at the same localities by the form and size of the teeth. Its well-ossified condition relative to a comparably sized juvenile specimen of the embolomere Archeria indicates a much smaller maximum adult size than that of Leptophractus, the other described embolomere from the Linton Coal Mine. Tooth form and count, shape of the squamosal and surangular crest, and stratigraphic occurrence all support tentative placement in the family Archeriidae.

Three‐dimensional analysis of deciduous maxillary anterior teeth using cone‐beam computed tomography

The recent introduction of cone-beam computed tomography (CBCT) into the medical field has allowed the nondestructive investigation of internal structures at relatively low cost and radiation exposure. The accuracy of CBCT in both two and three dimensions has been demonstrated, and CBCT has been used successfully for craniofacial anatomy. Knowing the anatomical structure of deciduous teeth is essential for clinical dentistry. However, the root structure of deciduous teeth is rarely reported because of the scarcity of intact deciduous teeth without root resorption. The aim of this study was to evaluate the intact root form of deciduous teeth using CBCT. Data from 38 young children was analyzed using an image-analyzing program. The degree of buccal dilacerations was 26.3° for deciduous maxillary central incisors (DMA), 16.5° for deciduous maxillary lateral incisors (DMB), and 17.5° for deciduous maxillary canines (DMC) in about half of the root length. The crown-to-root ratios were 0.52 for DMA, 0.48 for DMB, and 0.52 for DMC. These data will be helpful for understanding the development of dentition, and for clinical dentistry.

Design and Finite Element Analysis on Crown Gear Coupling of High Torque Considering Radial Restriction

In order to meet the requirements of high torque and small center distance of the twin screw pulping extruder, an improved design method of the crown gear coupling (CGC) was studied. Based on the preliminary structural design, the paper selected parameters of tooth form of the crown gear firstly, and according to the contact strength solved the tooth width, then the discussed influences of radius of displacement circle and unilateral thinning amount on tooth thickness, finally through the finite element analysis verified the design results. The results show that under the condition of radial restriction the most effective ways to increase load-bearing capability of the CGC are to improve the tooth stiffness and increase the tooth width, and the increasing of tooth width should consider the tip strength of the crown gear and avoid over-cutting. The CGC design method of the paper can meet the requirements of the twin screw extruder.

Laser Interferometric Measuring Method of Involute Artifact and Stabilization of Measurement

Vibration and noise are serious problems with involute spur and helical gears used, e.g., in drivetrains of vehicles such as automobiles. The gear tooth flank form of micrometer order markedly affects gear vibration and noise; therefore, the tooth flank form quality must be strictly controlled to maximize gear performance. Tooth profile measuring machines used in calibration for form error inspection of involute gears usually use an involute artifact, which itself must be calibrated highly accurately. However, it is typically difficult for current tooth profile measuring machine using contact stylus to calibrate the involute artifact with a high accuracy while satisfying traceability to a national standard. A highly precise and traceable measuring technology for the involute artifact is therefore required. The direct measurement of the involute artifact we propose uses a laser interferometer, whose measurement stability is confirmed in experiments measuring the detailed form of an involute tooth flank.

Development of scanning measurement of tooth flankform of generated face mill hypoid gear pair with reference to the conjugate mating tooth flank form using 2 axes sensor

The three diamensional (3D) scanning measurement method of tooth flank form of generated face mill gear pair is proposed, which is based on the conjugate mating tooth flank form. In this method, deviation sensor is placed at the position which has certain offset from the gear axis and synchronized to the gear rotation. This method realizes the 3D tooth flank form measurement and multi points scanning measurement by using 2 axes sensors. Based upon this proposal of the measurement method, tooth flank form measuring machine was developed and the experimental measurements were carried out. It is confirmed that this method is capable of high speed and high resolution measurement of fine waviness and it has high repeatability. It is confirmed that the proposed method, is capable of 3D scanning tooth form measurement of generated face mill hypoid gear pairs with high repeatability at high speed.

Neutral zone for fabrication of complete dentures in a hemimandibulectomy patient: A case report

The altered anatomy and neuromuscular control makes rehabilitation of an edentulous hemimandibulectomy patient a clinical challenge and denture stability is extremely difficult to achieve. Describes prosthetic rehabilitation of an edentulous hemimandibulectomy patient with complete dentures, incorporating a maxillary posterior occlusal ramp to guide and support the deviated residual mandibular fragment and a neutral zone record to determine the tooth position and final denture form for a stable mandibular denture. A neutral zone record is a useful clinical tool in determining the tooth position and contouring the polished surface of the mandibular denture. It can overcome denture stability difficulties in patients with altered anatomy and neuromuscular control.

Gingival recontouring by provisional implant restoration for optimal emergence profile: report of two cases

PurposeThe emergence profile concept of an implant restoration is one of the most important factors for the esthetics and health of peri-implant soft tissue. This paper reports on two cases of gingival recontouring by the fabrication of a provisional implant restoration to produce an optimal emergence profile of a definitive implant restoration.MethodsAfter the second surgery, a preliminary impression was taken to make a soft tissue working cast. A provisional crown was fabricated on the model. The soft tissue around the implant fixture on the model was trimmed with a laboratory scalpel to produce the scalloped gingival form. Light curing composite resin was added to fill the space between the provisional crown base and trimmed gingiva. After 4 to 6 weeks, the final impression was taken to make a definitive implant restoration, where the soft tissue and tooth form were in harmony with the adjacent tooth.ResultsAt the first insertion of the provisional restoration, gum bleaching revealed gingival pressure. Four to six weeks after placing the provisional restoration, the gum reformed with harmony between the peri-implant gingiva and adjacent dentition.ConclusionsGingival recontouring with a provisional implant restoration is a non-surgical and non-procedure-sensitive method. The implant restoration with the optimal emergence profile is expected to provide superior esthetic and functional results.

Manufacturing Method of Large-Sized Spiral Bevel Gears Using Multi-Tasking Machine Tool with Five Axis Control

Large-sized spiral bevel gears in a Klingelnberg cyclo-palloid system are manufactured using multi-tasking machine tool with five axis control. This manufacturing method has some advantages that realize arbitrarily modification of tooth surface and machining of the part except tooth surface. The pitch circular diameter of the gear treated in this study is more than 1,000 mm. For this study, first the numerical coordinates on the tooth surfaces of the spiral bevel gears are calculated and the tooth profiles are modeled using a 3D-CAD system. Afterwards, the large-sized spiral bevel gears were manufactured based on a CAM process using multi-axis control and multi-tasking machine tool. After rough cutting, the workpiece was heat-treated and it was finished by a swarf cutting using a radius end mill. The real tooth surfaces were measured using a coordinate measuring machine and the tooth flank form errors were detected using the measured coordinates. Moreover, the gears were meshed each other and the tooth contact patterns were investigated. As a result, the validity of this manufacturing method was confirmed.

Functional Impression for Hemimandibulectomy Cases: An Alternative Technique

ABSTRACT The altered cast impression technique is preferred to derive maximum support from the residual ridge in the distal extension partial denture hemimandibulectomy cases. The traditional method is designed primarily for making a secondary impression of the ridge in the functional form to correct a master cast. These functional impression techniques are time-consuming and involve multiple steps. This article describes a new clinical and laboratory technique in impression making. Emphasis is placed on recording the anatomical form of teeth and functional form of the residual ridge in an individual tray using two different impression materials eliminating secondary impression.

Optimizing tooth form with direct posterior composite restorations

Advances in material sciences and technology have provided today's clinicians the strategies to transform the mechanistic approach of operative dentistry into a biologic philosophy. In the last three decades, composite resins have gone from being just an esthetically pleasing way of restoring Class III and Class IV cavities to become the universal material for both anterior and posterior situations as they closely mimic the natural esthetics while restoring the form of the human dentition. In order to enhance their success, clinicians have to rethink their protocol instead of applying the same restorative concepts and principles practiced with metallic restorations. Paralleling the evolution of posterior composite resin materials, cavity designs, restorative techniques and armamentarium have also developed rapidly to successfully employ composite resins in Class II situations. Most of the earlier problems with posterior composites such as poor wear resistance, polymerization shrinkage, postoperative sensitivity, predictable bonding to dentin, etc., have been overcome to a major extent. However, the clinically relevant aspect of achieving tight contacts in Class II situations has challenged clinicians the most. This paper reviews the evolution of techniques and recent developments in achieving predictable contacts with posterior composites. A Medline search was performed for articles on “direct posterior composite contacts.” The keywords used were “contacts and contours of posterior composites.” The reference list of each article was manually checked for additional articles of relevance.

The middle Paleozoic Selachian genus Thrinacodus

ABSTRACT The late Devonian–Carboniferous (D–C) shark Thrinacodus has been known only from highly distinctive teeth since its first description from North America in 1875. The poor quality of illustrations of the type material meant that the thrinacodont tooth form remained unrecognized until the early 1980s when similar teeth were found in D–C boundary beds in Australia. Since then, Thrinacodus taxa have been found globally with a Paleotethyan distribution. Discovery of articulated specimens in the Serpukhovian of Montana could have helped to clarify their phylogenetic relationships and paleobiology of Thrinacodus, but their first formal description has caused taxonomic confusion rather than resolving problems of the thrinacodont taxonomy. A new genus, ThrinacoselacheGrogan and Lund, 2008, was mistakenly erected, the introduction of which is rectified here and supported by taxonomic arguments. A new interpretation of the phylogeny of Thrinacodus is proposed.

Effect of Convex Tooth Flank Form Deviation on the Characteristics of Transmission Error of Gears Considering Elastic Deformation

The transmission error of gears is an important factor for power transmissions, particularly automotive. Consequently, a lot of research has been conducted on the gear transmission. However, in contrast, there remains relatively little research clarifying the characteristics of gear transmission error and its relationship to the tooth flank form. The authors have proposed a general model for tooth meshing between gears. This expresses the transmission error theoretically from a quasi-infinite elastic model, which is composed of springs with stiffness specific to the gears. In this report, the influence of tooth flank form deviation on transmission error is further investigated by using this model. It is shown that the form of the ridge curve of the tooth flank form deviation greatly influences the actual contact ratio at the minimum point of peak-to-peak value of transmission error. The peak-to-peak value of transmission error is affected by the amplitude and the form of the ridge curve.

The effects of boro-tempering heat treatment on microstructural properties of ductile iron

In this study, the effects of boro-tempering heat treatment on microstructural properties of ductile iron were investigated. Test samples with dimensions of 10 × 10 × 55 mm were boronized at 900 °C for 1, 3 and 5 h and then tempered at four different temperatures (250, 300, 350 and 450 °C) for 1 h. Both optical microscopy and scanning electron microscopy were used to reveal the microstructural details of coating and matrix of boro-tempered ductile iron. X-ray diffraction was used to determine the constituents of the coating layer. The boride layer formed on the surface of boro-tempered ductile cast iron is tooth shape form and consisted of FeB and Fe 2B phases. The thickness of boride layer increases as the boronizing time increases and tempering temperature decreases. Tempering temperature is more effective than boronizing time on the matrix structure. Boro-tempering heat treatment reduces the formation of lower and upper ausferritic matrix temperature according to classical austempering. This causes formation of upper ausferritic matrix in the sample when tempered at 300 °C. This is in contrast to general case which is the formation of lower ausferritic matrix via austempering at this temperature.

The heterodonty ofAlbertosaurus sarcophagusandTyrannosaurus rex: biomechanical implications inferred through 3-D modelsThis article is one of a series of papers published in this Special Issue on the themeAlbertosaurus.

The objective of this study is to analyze how different crown morphologies and different root lengths respond to stresses generated by the bite forces of Albertosaurus sarcophagus and Tyrannosaurus rex . Six well-preserved teeth of A. sarcophagus from the Albertosaurus bonebed in Dry Island Park (southern Alberta) were selected to study their biomechanics, and T. rex teeth were included for comparison. The three-dimensional (3-D) models were obtained through computerized tomography (CT) scanning and 3-D digitizing. Finite element analyses were performed in Strand7®. Bite forces for Albertosaurus and Tyrannosaurus were calculated based on cranial and jaw proportions. The results were viewed with the Tresca yield criterion. The ratios of shear stresses observed along the mesio-distal versus labio-lingual axes of all models allows the identification of similar stress distribution patterns in the upper and lower jaws of Albertosaurus and the upper jaws of Tyrannosaurus, with a higher amount of shear along the mesio-distal axis occurring in the mid-maxillary teeth. The dentary teeth of Tyrannosaurus, however, show a different stress distribution pattern, with a higher amount of shear occurring along the labio-lingual axis of the mid-dentary teeth. These differences in jaw mechanics suggest that the function of teeth in the lower jaw of Tyrannosaurus shifted a few positions to compensate different proportions in the dentary that cause the anterior dentary teeth to be aligned with the largest maxillary teeth in Tyrannosaurus. These results suggest that heterodonty in these groups is different and that tooth form and function are sensitive to jaw proportions.

An Unusual Complex Odontoma

Odontoma, complex type is an agglomerate of all the dental tissues that are characterized by normal histodifferentiation but abnormal morphodifferentiation producing little or no resemblance to normal tooth form. They are usually asymptomatic but often associated with eruption disturbances. An interesting case of unusually large complex odontoma that was associated with pain and an impacted as well as missing molar is reported.

Morphology of the larval shell of three oyster species of the genus Crassostrea Sacco, 1897 (Bivalvia: Ostreidae)

In this study we describe the morphology of the larval shell of three oyster species of Crassostrea genus. Two species, C. rhizophorae and C. brasiliana, are native to the Brazilian coast, and C. gigas is an introduced species. Samples of laboratory reared larvae, obtained through artificial fertilisation, were collected at intervals during the cultivation process for analysis using Scanning Electron Microscopy (SEM). Prodissoconch morphology was observed in relation to the presence, position, form and number of teeth in the three larval stages: D-shaped larva, umbo larva and pediveliger. Characteristic of D-shaped larvae of C. rhizophorae was the total absence of teeth in the provinculum area while C. brasiliana and C. gigas had two anterior and two posterior teeth in each valve. In the umbo larval phase, the three species had the same number of teeth in each valve: two posterior and two anterior teeth in the right valve and three posterior and three anterior in the left valve. In the pediveliger stage the three species could be differentiated by the number of anterior teeth of the right valve: C. rhizophorae had two teeth, C. brasiliana one tooth and C. gigas three teeth.