Actual Tooth Research Articles

Efficacy of gender on the width-length ratio of maxillary anterior teeth in an Egyptian population and establishment of a guideline for esthetical accepted ratio of teeth dimensions to gingival display

Aim: The present study aims to correlate between gender and width-length ratio of maxillary anterior teeth in a sample of Egyptian population and to obtain an optimal esthetical accepted ratio of teeth dimensions to gingival display. Materials and Method: Stone casts were poured from irreversible hydrocolloid impressions of 100 adult Egyptian participants. These casts were used to measure the maximum mesiodistal width, maximum crown length and the width/length ratio for each maxillary anterior tooth. In addition, two frontal photographs were taken for each participant and the visible anterior teeth width, length and width/length ratio were measured. Finally, a sample with gummy smile was selected and the gingival display of the original image was digitally manipulated to create a series of five images with different gingival displays, then these images were subjected to assessment by 50 dentists and 50 laypersons using a numerical rating scale. Results: There was statistically significant difference between female and male group for all teeth width values and W/L ratio of lateral incisor and canine. There was no significant difference between dentists and laypersons perception except for the smile with -4 mm gingival display. Conclusion: Gender affects actual teeth width values as well as actual and apparent W/L ratios of lateral incisor and canine. Laypersons considered 0mm and -2mm gingival display the most attractive situation, on the other hand dentists considered 0 mm gingival display the most attractive one, while all participants agreed that 4mm gingival display is the least attractive one.

Error identification and verification of cycloid gear profile surfaces in precision forming grinding

ABSTRACT This paper presents an error identification method for directly related geometric errors of 4-axis forming grinding machine tool and some processing-induced errors from actual teeth profiles of a machined cycloid gear. Based on the developed 4-axis geometric error model, we build up an overall error model of cycloid gear-tooth profiles by forming grinding, which includes some directly related geometric errors of the machine tool and processing-induced errors. Error separation or identification methods are developed in correspondence with the form grinding process and are verified by some non-cutting identification or measurement techniques, including multi-lateration laser measurement technique and a laser rotary axis calibrator. The experiment results demonstrate that the separated geometric errors based on the machining test approach reach a better accuracy. In order to further improve the machining accuracy of the cycloid gear, two identified geometric errors and tooth-shaped error can be utilised for error compensation in the future.

Contact Analysis of Cycloidal-pin Gear of RV Reducer Under the Influence of Profile Error

Because of the influence of machine tool accuracy, the tooth profile error will occur during the processing of cycloidal gear. In order to evaluate the influence of tooth profile error on the transmission accuracy of cycloidal-pin gear pair, the actual tooth surface coordinate points with tooth profile error are calculated based on the measured tooth profile error of cycloidal gear, and the tooth profile error is obtained by non-uniform rational B-spline curve fitting. Based on the meshing principle, the tooth contact analysis (TCA) of the digitized tooth surface is carried out, and the transmission error curve of cycloidal-pin gear pair under the influence of tooth profile error is obtained.

Full Mouth Rehabilitation Performed Using Customized Broadrick’s Flag to Restore Mandibular Posterior Teeth-A Case Report

Full mouth rehab is an extremely challenging procedure. It needs proper planning and thorough knowledge about the steps involved in the procedure. The patient’s occlusal plane has to be restored in harmony with the tmj and the prosthesis which is to be fabricated. An instrument called the “Occlusal plane analyzer” is used to assist the Prosthodontist in the development of an initial mandibular occlusal plane that is commensurate with the curve of Spee when posterior restorations are designed in diagnostic casts and later as an integral of definitive restorations as well as guidelines for the actual tooth preparations. After complete examination of the reported case, it was planned for full mouth rehabilitation. Pankeymann philosophy was planned to be used for rehabilitation. Bopa being one of the important steps as per the philosophy for restoration of mandibular posterior teeth, it was discussed in detail. The article demonstrates the making and use of a custom made broad rickocclusal plane analyser (bopa) on a semi adjustable articulator to determine the correct orientation of the occlusal plane. Key Words – clear acrylic guide, anterior survey point (A.S.P), posterior survey point (P.S.P), central survey point (C.S.P).

Comparative Measurement of Tooth Length: Actual vs. Orthopantomography and CBCT-Based Measurements

Objective: To compare the reliability of cone beam computed tomography (CBCT) in assessing the tooth length in comparison to orthopantomography (OPG). Material and Methods: Forty patients scheduled for extraction as result of caries or periodontal involvements were randomly selected. Panoramic radiographs and CBCT images were obtained and subsequently patients were subjected for extraction. Teeth with poor prognosis were extracted and stored in 10% formalin. Radiographic teeth measurements were carried out on OPG and CBCT images using a software and the actual tooth length (A-L) measurements were carried out with a digital vernier caliper. The data collected were statistically analyzed for paired “t” test significance of differences and Pearson’s correlation at 5% level of confidence. Results: There was significant difference comparing all three actual tooth length ( A-L) and CBCT- and OPG-measured tooth lengths. A significant positive correlation was observed among all the measurements. Conclusion: CBCT images exhibited accuracy over panoramic images even though the measurements are still significantly different from actual anatomical tooth lengths.

Comparison between Broadrick flag Vs Yurkstas metal occlusal template in the assessment of mandibular Over-erupted teeth

Introduction: An occlusal plane analyzer has long been used to assist an operator in the development of an initial mandibular occlusal plane in diagnostic contour casts and later as an integral part of both the contours of the definitive restorations as guide for the actual tooth preparation. Broadrick and Yurkstas metal occlusal template were devices frequently used to determine the proper occlusal plane. Aim: The aim of this study was to determine which of the two methods. Broadrick flag occlusal plane analyzer or Yurkstas metal occlusal template is more conservative during occlusal plane adjustment. Materials and Methods: Eight diagnostic casts mounted on Hanau semi-adjustable articulator were selected from the casts of patients of undergraduate 6th-year dental students, King Abdulaziz University. Diagnostic maxillary cast was mounted according to arbitrary ear-bow and the mandibular casts were mounted according to centric relation records. First, Broadrick occlusal plane analyzer was secured to the upper member of the articulator. The anterior and posterior survey points were drawn. From the intersection point, the anteroposterior curve was drawn on the buccal surfaces of the canine, premolar, and molar. The distance from these lines to the cusp tip was measured through mesiobuccal, midbuccal, and distobuccal areas. Yurkstas metallic occlusal plane was used in the second method. The articulating paper horseshoe was placed between the occlusal table of the stone teeth and the metallic template, and the articulator was closed and taped several times, a die marking indicating the first over-erupted teeth. Then the highlighted area was reduced to 1 mm. The procedure was repeated until a uniform touch of the template over the mandibular teeth was maintained. Finally, the amount of reduction was collected. Conclusion: Producing curve of Spee is more conservative while using Yurkstas metallic occlusal plane.

Development and Validation of 3D Finite Element Models for Prediction of Orthodontic Tooth Movement.

Objectives The aim of this study was to develop and validate three-dimensional (3D) finite element modeling for prediction of orthodontic tooth movement. Materials and Methods Two orthodontic patients were enrolled in this study. Computed tomography (CT) was captured 2 times. The first time was at T0 immediately before canine retraction. The second time was at T4 precisely at 4 months after canine retraction. Alginate impressions were taken at 1 month intervals (T0–T4) and scanned using a digital scanner. CT data and scanned models were used to construct 3D models. The two measured parameters were clinical tooth movement and calculated stress at three points on the canine root. The calculated stress was determined by the finite element method (FEM). The clinical tooth movement was measured from the differences in the measurement points on the superimposed model. Data from the first patient were used to analyze the tooth movement pattern and develop a mathematical formula for the second patient. Calculated orthodontic tooth movement of the second patient was compared to the clinical outcome. Results Differences between the calculated tooth movement and clinical tooth movement ranged from 0.003 to 0.085 mm or 0.36 to 8.96%. The calculated tooth movement and clinical tooth movement at all reference points of all time periods appeared at a similar level. Differences between the calculated and clinical tooth movements were less than 0.1 mm. Conclusion Three-dimensional FEM simulation of orthodontic tooth movement was achieved by combining data from the CT and digital model. The outcome of the tooth movement obtained from FEM was found to be similar to the actual clinical tooth movement.

Crown therapy in young individuals with amelogenesis imperfecta: Long term follow-up of a randomized controlled trial

ObjectivesAmelogenesis imperfecta (AI) is a rare, genetically determined defect in enamel mineralization. Several problems are associated with AI: hypersensitivity, wear, restorations requiring replacement, gingivitis, aesthetic problems, and social avoidance. We conducted a randomized controlled trial of crown therapy in young individuals with AI showing excellent results. This study reports results from a long-term-follow-up with focus on quality, longevity and adverse events. MethodsThe RCT included 27 patients (aged 11–22 years) with severe AI in need of crown therapy and used a split-mouth technique. After placing 119 Procera® crowns and 108 IPS e.max Press crowns following randomization, we assessed longevity, quality, adverse events, and tooth sensitivity and calculated survival rates and success rates. ResultsWe followed the original 227 crowns for 4.3–7.4 years (mean 5.5 ± 0.8). In all, 79% (193) crowns were followed for at least 5 years. The survival rate was 99.6% and the success rate, 94.7%; 95% of the crowns had excellent or acceptable quality. Due to suboptimal marginal integrity, 4% of the crowns required adjustment. Sensitivity problems decreased after crown therapy (p < 0.001). All adverse events occurred in patients aged 19–23 years and involved apical periodontitis (3% of teeth); all but two events were related to dental trauma in the actual tooth. ConclusionsCeramic crown therapy in adolescents and young adults with severe forms of AI show excellent survival and success rates and longevity with few adverse events. Clinical significanceCeramic crown therapy can be recommended for adolescents and young adults with severe forms of amelogenesis imperfecta.

Residents' journal review

Residents' journal review

A new digitized reverse correction method for hypoid gears based on a one-dimensional probe

In order to improve the tooth surface geometric accuracy and transmission quality of hypoid gears, a new digitized reverse correction method is proposed based on the measurement data from a one-dimensional probe. The minimization of tooth surface geometrical deviations is realized from the perspective of mathematical analysis and reverse engineering. Combining the analysis of complex tooth surface generation principles and the measurement mechanism of one-dimensional probes, the mathematical relationship between the theoretical designed tooth surface, the actual machined tooth surface and the deviation tooth surface is established, the mapping relation between machine-tool settings and tooth surface deviations is derived, and the essential connection between the accurate calculation of tooth surface deviations and the reverse correction method of machine-tool settings is revealed. Furthermore, a reverse correction model of machine-tool settings is built, a reverse correction strategy is planned, and the minimization of tooth surface deviations is achieved by means of the method of numerical iterative reverse solution. On this basis, a digitized reverse correction system for hypoid gears is developed by the organic combination of numerical control generation, accurate measurement, computer numerical processing, and digitized correction. Finally, the correctness and practicability of the digitized reverse correction method are proved through a reverse correction experiment. The experimental results show that the tooth surface geometric deviations meet the engineering requirements after two trial cuts and one correction.

Analysis of the golden proportion and width/height ratios of maxillary anterior teeth in Arab and Kurdish populations

Statement of problemDentists providing anterior restorations are guided by the principles of anatomic tooth dimension. Dental biometrics should consider ethnicity to produce a more comprehensive evaluation. PurposeThe purpose of this clinical study was to analyze the anatomic crowns of maxillary central incisors (CI), lateral incisors (LI), and canines (C) with respect to the golden proportion (GP) and width/height (W/H) ratio in Kurdish and Arab populations. Material and methodsMaxillary gypsum casts were obtained from 100 participants (50 from a Kurdish and 50 from an Arab population). Standardized digital photographs of each cast were recorded. The apparent and actual anterior tooth dimensions were determined by ImageJ software for the calculation of the GP and W/H ratio. Data were statistically analyzed using ANOVA to investigate ethnic, sex, and arch side differences. The chi-square test was used to explore the GP, and the 1-sample t test was used to test the ideal W/H ratio (α=.05). ResultsThe GP was found in both the Kurdish and Arab groups in the LI/CI mean (0.62, 0.63), but not in the C/LI mean (0.69, 0.73). No difference due to sex was detected in the LI/CI in either ethnic group, but Kurdish men had significantly larger C/LI than women (0.73, 0.66, P=.006) and larger right-side LI/CI than left (0.63, 0.60, P=.049). The W/H ratio was higher than the predicted ideal ratio of 80% (range, 88% to 90%). The LI W/H ratio in Arabs was significantly larger than in Kurds (90.3% versus 82.7%, respectively; P<.001). ConclusionsThe GP was found to exist between the apparent widths of maxillary anterior teeth LI/CI for the both populations in both men and women but not for C/LI. No ideal ratio was detected for the W/H ratios. Specific population characteristics must be taken into consideration, especially when applying the proportions to Kurdish individuals.

The Precise Measurement Technology for Manufacturing Error of Cycloidal Gear Used in RV Reducer

According to problems in manufacturing and measuring process of cycloidal gear used in RV reducer, the profile coordinates of cycloidal gear captured by three coordinates measuring instrument Surveying and mapping do not coincide with the designed tooth profile coordinates in theory, it is difficult to precisely capture the addendum and dedendum of each cycloidal gear teeth, furthermore, the captured addendum and dedendum do not coincide with the actual tooth items. For these problems, this paper introduced a method can accurately calculating the manufacturing error of cycloidal gear.Based on the captured coordinate points of cycloidal gear tooth profile, firstly, find out 39 approximate addendums by calculating and comparing the radial radius of all points, divide the whole scanning points into 39 profile points groups by the 39 approximate addendums, with each group include a whole single tooth profile. Then, in each profile points group, interpolate the spline and precisely calculate the addendums and dedendums by fitting and recalculating radial radius.Set up the coordinate system of surveying and mapping profile by the 39 addendums. calibrate the coordinate system of surveying and mapping profile with the new coordinate system through coordinate transformation, calculate the radial runout error at top and root of tooth profile, pitch error, adjacent pitch error and accumulated pitch error as well as other manufacturing errors of the cycloidial gear at last.Through experiment, this process solve the problem in measuring process of cycloidal gear that the captured point by three coordinates measuring instrument could not be directly used for calculating the errors items.

A New Method of Designing the Tooth Surfaces of Spiral Bevel Gears With Ruled Surface for Their Accurate Five-Axis Flank Milling

The advantages of the five-axis flank milling of (developable) ruled surfaces include that (1) the machined surfaces could be very accurate and smooth and (2) the machining efficiency is high. Currently, spiral bevel gears are machined on the machine tools specially used for gear manufacturing. The disadvantages are that the cost is high for small batch, prototype, or repair. If a small group of spiral bevel gears are needed, the current methods are not valid. Thus, it is expected to machine the gears on five-axis computer numerical control (CNC) milling centers. Unfortunately, when tooth surfaces are designed based on the conventional gear manufacturing methods, they cannot be accurately machined in five-axis flank milling. This work is to develop the new technique for the five-axis flank milling of spiral bevel gears. First, a new method of designing the tooth surface of spiral bevel gears with ruled surface is proposed. Second, the cutter locations and orientations are calculated for five-axis flank milling the tooth surfaces. Third, the actual tooth surfaces are accurately represented with the cutter envelope surface in five-axis flank milling. It is confirmed that the difference of the actual tooth surface and the designed tooth surface is within the tolerance. Then, a pinion is generated to mesh with the gear, and the tooth contact analysis (TCA) is conducted. The good result demonstrates that the proposed method is valid, thus it can be used in industry.

A cross-sectional survey on the patterns of primary teeth eruption in 2 581 children

Objective: To investigate the patterns of primary teeth eruption by a cross-sectional survey in 0-40 months old children in Chongqing and to provide normal timetables of tooth eruption that are practical in general physical growth assessment. Method: Data of 2 581 0-40 months old healthy children were collected from January 2014 to January 2016 at Children's Hospital of Chongqing Medical University. General information was recorded by primary child health care doctors, including age, gender, gestation age, birth weight, time and sequence of first primary tooth eruption, number of teeth and age of totally primary teeth emergence. Median and constituent ratio were used in describing the age of tooth eruption and eruption characteristics at different age. Moreover, independent-sample t test, variance analysis, Pearson product-moment correlation and Logistic regression were also involved in data analysis. Result: Totally 2 581 children were involved in this survey, including 506 infants of 0-6 months old, 600 infants of 7-12 months old, 730 toddlers of 13-24 months old and 745 children of 25-40 months old. There were 1 473 boys and 1 108 girls, 89 preterm babies and 2 492 full term babies, 1 829 children with tooth erupted and 626 children with all primary teeth erupted.The age of the first primary tooth eruption was between 2-15 months old ( median age: 8 months old, 95%CI: 2.7-12.7)and for the last primary tooth emergence was between 23-35 months of age (median age: 31 months, 95%CI: 24.7-36.7). The time of first tooth eruption was positively correlated with that of total teeth emergence (r=0.879, P<0.05). Dental charts (number of tooth for age) of different gender were drawn according to teeth eruption information. The first primary tooth eruption was the incisor of mandible in 95.3% (1 743/1 829)infants and was the incisor of maxilla in 4.6% (84/1 829)infants. During the period of tooth emerging actively (number of teeth ≤16), the number of primary teeth might be calculated by formula: number of teeth=chronological age in months-age of first eruption in months+ 1. There was no statistically significant difference between the number of actual teeth and calculated by the present formula(t=-2.957, P=0.05). Conclusion: The median age of first primary tooth eruption and total teeth emergence was 8 and 31 months of age respectively. The first primary tooth eruption is incisor of mandible in most infants.The formula (number of teeth=chronological age in months-age of first eruption in months+ 1 )can be used to estimate the number of primary teeth. Dental charts might provide normal and supplement datasets for evaluating child physical growth.

Computational design and engineering of polymeric orthodontic aligners.

Transparent and removable aligners represent an effective solution to correct various orthodontic malocclusions through minimally invasive procedures. An aligner-based treatment requires patients to sequentially wear dentition-mating shells obtained by thermoforming polymeric disks on reference dental models. An aligner is shaped introducing a geometrical mismatch with respect to the actual tooth positions to induce a loading system, which moves the target teeth toward the correct positions. The common practice is based on selecting the aligner features (material, thickness, and auxiliary elements) by only considering clinician's subjective assessments. In this article, a computational design and engineering methodology has been developed to reconstruct anatomical tissues, to model parametric aligner shapes, to simulate orthodontic movements, and to enhance the aligner design. The proposed approach integrates computer-aided technologies, from tomographic imaging to optical scanning, from parametric modeling to finite element analyses, within a 3-dimensional digital framework. The anatomical modeling provides anatomies, including teeth (roots and crowns), jaw bones, and periodontal ligaments, which are the references for the down streaming parametric aligner shaping. The biomechanical interactions between anatomical models and aligner geometries are virtually reproduced using a finite element analysis software. The methodology allows numerical simulations of patient-specific conditions and the comparative analyses of different aligner configurations. In this article, the digital framework has been used to study the influence of various auxiliary elements on the loading system delivered to a maxillary and a mandibular central incisor during an orthodontic tipping movement. Numerical simulations have shown a high dependency of the orthodontic tooth movement on the auxiliary element configuration, which should then be accurately selected to maximize the aligner's effectiveness.

Tooth profile modification based on lateral- torsional-rocking coupled nonlinear dynamic model of gear system

In this paper, the influence of tooth profile modification on the vibration of a single gear is studied. Considering geometric eccentricity, gyroscopic moment, teeth to the partial load torque and backlash, a 10 degree of freedom (DOF) lateral-torsional-rocking coupled nonlinear dynamic model of a single gear system is proposed. Considering actual motion state and tooth profile modification, stiffness of the meshing model was studied using an analytical method. Results show influence of the modification amount with different modification types and different modification length on dynamic load. For the case of different modification lengths and modification types, with increasing modification amount, profile of dynamic load coefficient follows a ‘V’ type pattern. An optimal modification amount can be determined, where dynamic load of gear can be minimized. At the same time, when modification amount exceeds a certain critical value, dynamic load for modified gear was higher than the dynamic load for gear without modification. The optimum modification can effectively slow mutation of meshing stiffness and reduce the dynamic load of gear; the meshing force amplitude of modification gear is decreased significantly in the high order frequency, while the impact load caused by the alternation of single and double teeth is slowed down, and contact rate is basically unchanged.

Morphology is not Destiny: Discrepancy between Form, Function and Dietary Adaptation in Bovid Cheek Teeth

Mammal teeth have evolved morphologies that allow for the efficient mechanical processing of different foods, therefore increasing dietary energy uptake for maintenance of high metabolic demands. However, individuals masticate foods with biomechanical properties at odds with the optimal function of a given tooth morphology. Here, we investigate tooth form and function using two quantitative 3D methods at different scales on the same individuals of nine bovid species. Dental topometry quantifies the gross morphology, and therefore, reflects evolutionary adaptive patterns. Surface texture analysis infers mechanical occlusal events, which reflect the actual tooth function, and is free from the influence of morphology. We found that tough foods can be satisfactorily exploited by grazing species with enamel ridge morphologies not more complex than those found in intermediate feeders and browsers. Thus, the evolution of enamel complexity is likely determined by a balance between adaptation and constraints. Wider enamel ridges seem to be a common functional trait in bovids to compensate for severe wear from abrasive foods and/or chipping from hard foods. Our results demonstrate that supposedly essential functional adaptations in tooth morphology may not be required to process food efficiently. This emphasizes the large plasticity between “optimal” morphology and the potential function of the tooth, and underscores the need to appreciate (apparently) maladaptive structures in mammalian evolution as nevertheless effective functioning units.

Meshing Stiffness Calculation and Analysis of the Cycloidal Pump’s Rotor

In order to calculate the meshing stiffness of the cycloidal pump’s rotor, a method of relationship that deduces two generating curtate epicycloid is proposed, the radius values of the inner rotor’s actual tooth profile curvature was calculated and analyzed; Based on the formula of Hertz, the cycloidal pump rotor’s meshing stiffness calculation formula is inferred, the changing curve of cycloidal pump rotor’s meshing stiffness is made, some important parameters on its meshing stiffness are studied, the maximum value of meshing stiffness is when the outer rotor mesh with inner rotor’s outer convex profile curve, and the minimum value is when the outer rotor mesh with the center of inner rotor’s inner concave.

Prediction of space available for unerupted permanent canine and premolars in a Bangladeshi population

Objective: To test the use of Moyers prediction method and Tanaka and Johnston’s equations for use in a Bangladeshi population and to construct new probability tables and prediction formulae based on the actual tooth sizes in a sample of the Bangladeshi population.Design of the study: Descriptive cross-sectional study.Materials and Methods: The sample was consisted of 50 Bangladeshi males and 50 females aged between 17 and 23 years. Subjects without any previous orthodontic treatment fully erupted permanent teeth and with no dental anomalies were recruited. Dental study models were taken and measurements of the mesio-distal widths of teeth were carried out using digital caliper. The measured values were compared with predicted values derived from Moyers method and Tanaka and Johnston equations. Independent t tests were used to examine differences between genders. Correlation coefficients and linear regression equations were used to compare the actual Bangladeshi tooth widths with predicted values.Results: For Bangladeshi males, Moyers method at 50% tends to overestimate the actual value of the canines and premolars by 0.3 mm with a standard deviation of 0.08 mm, whereas the Tanaka and Johnston method tends to overestimate the actual value of the canines and premolars by 1.4 mm with a standard deviation of 0.11 mm. For Bangladeshi females, Moyers method at 50% tends to overestimate the actual value of the canines and For Bangladeshi females, Moyers method at 50% tends to overestimate the actual value of the canines and to overestimate the actual value of the canines and premolars by 1.4 mm with a standard deviation of 0.13 mm.Conclusion: The newly developed regression equations are more accurate for prediction of width of unerupted permanent teeth in a Bangladeshi population. Further studies are required based on larger sample size, to confirm the applicability of the new regression equations proposed.Ban J Orthod &amp; Dentofac Orthop, October 2012; Vol-3, No.1

Parameter Design of Tooth Profile for Internal Cycloid Gear Pump with Multi-Teeth Difference

Based on the principle of gear engagement, the equation of rotor tooth profile has been reduced in this paper and has drawn the actual cycloid tooth profile by MATLAB software, the data obtained from MATLAB Workspace is processed by EXCEL, so the parameter drawing of the full gear tooth profile curve is very easy in AutoCAD software platform. This design method has high accuracy and convenient to processing in CNC machining center.