The impacted lower third molar and its relationship to tooth size and arch form.
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Adolescent↗
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The effect of congenital cardiac disease on facial growth in a monozygotic twin pair, studied by stereophotogrammetry.
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Cephalometry↗
The effect of heritability on Bolton tooth-size discrepancy.
The purpose of this study was to determine the possible effect of genetic factors on Bolton tooth-size discrepancy. Subjects who applied for orthodontic treatment and their siblings (106 females and 78 males) were included in the study. The ages of the subjects ranged from 13 to 21 years. The siblings were grouped according to gender: male-male (24 pairs), female-female (38 pairs) and male-female (30 pairs). Mesio-distal tooth size was measured using a pair of dividers with fine tips, and Bolton anterior and overall ratios were calculated. The effect of heritability on Bolton ratios was studied by means of Harvey's mixed model least-squared and maximum likelihood computer program (LSMLMW) model type II. Statistical analysis showed that heritability was effective on Bolton tooth-size discrepancy in all groups except the male-female group. Siblings of the same gender showed high heritability for anterior and overall ratios, but no statistically significant difference was observed in the siblings of different gender.
Adolescent↗
Anterior tooth morphology and its effect on torque.
This study was undertaken to determine the variation in crown-root angle (CRA) of the upper incisors and canines as well as the variation in their labial contour. In addition, the influence of the variability of the labial contour and of different bracket heights on torque was evaluated. Proximal radiographs were taken of 160 extracted maxillary teeth (81 incisors and 79 canines). They were digitized and analysed with Jasc Paint Shop Pro 7TM and Mathcad 2001 Professional. The incisal edge, the centre of the cemento-enamel junction (CEJ), and the root apex were digitized to define the crown and root long axis. For all teeth the CRA was measured. At several heights of the labial surface a tangent was determined, enabling measurement of the inclination of the labial surface. The CRA had great variability, ranging from 167 to 195 degrees for the canines (mean value 183 degrees) and from 171 to 195 degrees for the incisors (average 184 degrees). The mean inclinations of the labial surfaces for the incisors varied greatly. Between 4 and 4.5 mm from the incisal edge the standard deviations (SD) were the smallest and between 2 and 4.5 mm from the incisal edge the labial surface angle differed by approximately 10 degrees. For the canines the mean inclinations of the buccal surface also varied. This angle differed by around 10 degrees between 2 and 4.5 mm from the incisal edge, but the SD were much larger than for the incisors. It can be concluded that placement of a bracket on a tooth at varying heights, still within a clinically acceptable range, results in important differences in the amount of root torque.
Cuspid↗
An approach to maintain orthodontic alignment of lower incisors without the use of retainers.
The purpose of this investigation was to examine the long-term stability of orthodontic alignment of lower incisors without the use of retainers. The study sample comprised 56 patients treated according to a protocol that included over-correction of rotated teeth at an early stage of treatment and systematic enamel reduction (stripping) of the approximal surfaces in the mandibular anterior region, both during treatment and follow-up. Care was also taken to maintain dental arch form and to avoid lateral expansion of the lower dental arch and proclination of the incisors. Dental study casts were obtained pre-treatment, at the end of treatment, and 3 years post-treatment. Alignment of the mandibular incisors was recorded using Little's irregularity index. The inter-canine distance and the sum of the mesio-distal widths of the mandibular incisors and canines were also measured. The total amount of enamel removed from the approximal surfaces of the lower anterior teeth ranged from 0.3 to 5.0 mm (mean 1.9 mm). The mean increase in irregularity index score of 0.6 from post-treatment to 3 years follow-up indicated good stability. In 45 per cent of the patients the change in score during this period was less than 0.5, indicating that the treatment approach presented may be considered an alternative strategy to placement of lower retainers to safeguard the stability of alignment of mandibular incisors.
Cephalometry↗
Space conditions and dental and occlusal features in patients with palatally impacted maxillary canines: an aetiological study.
The aetiology of palatal canine impaction is unclear. The aim of this research was to investigate the occlusal features that could contribute to the aetiology of palatal maxillary canine impaction. The material consisted of the pre-treatment dental casts of 34 patients (27 female and seven male) with unilateral palatal canine impaction (impaction group). The average age of this group was 17.7 years (+/- 4.6). These were matched according to age, gender and type of malocclusion with a comparison group of pre-treatment dental casts from unaffected orthodontic patients. From the dental casts the following parameters were obtained: (1) dentoalveolar arch relationship, (2) missing or anomalous teeth, (3) the mesiodistal width of each maxillary tooth, (4) the upper arch perimeter, (5) the maxillary inter-premolar and inter-molar widths. The arch length-tooth size discrepancy was only calculated for subjects with no missing teeth. Palatal canine impaction occurred most frequently in subjects with a Class II division 2 malocclusion. There was an association between palatal canine impaction and anomalous lateral incisors (P = 0.01). The transverse arch dimension was significantly wider in the impaction group than in the comparison group (P < 0.01). There was no statistically significant difference in the mesiodistal width of maxillary teeth or in the arch length-tooth size discrepancy between the palatal canine impaction group and their matched comparisons (P > 0.05). These results suggest that the presence of an 'excess palatal width' and anomalous lateral incisor may contribute to the aetiology of palatal canine impaction.
Adolescent↗
Hypodontia in orthodontically treated children.
The frequency of hypodontia in orthodontically treated children, both male and female, and the association between tooth type, the upper or lower arch, the affected side and Angle's classification were studied using interviews, oral, study cast and panoramic radiographic examinations of 212 patients with a mean age of 12 years 7 months. A hypodontia frequency of 11.3 per cent was found for the total sample. This was higher than the incidence of hypodontia reported in other studies of orthodontically treated children. The most frequently missing teeth were the maxillary lateral incisors, and maxillary and mandibular second premolars. The missing teeth were more often absent on the right (54.2 per cent) than on the left (45.8 per cent) side, in both males and females. One tooth was absent in 29.2 per cent of patients, two in 58.5 per cent, but seldom three or more. Orthodontic space closure was the treatment of choice in 87.5 per cent of the subjects.
Anodontia↗
Third molar influence on dental arch crowding.
The aim of the present study was to measure the dental arches in order to assess the potential influence of third molars on lower incisor crowding. Changes in dental arch dimensions were assessed in 47 patients (36 females, 11 males) three years following either removal of the third molars or deciding to leave them in situ. A dental pantomogram (DPT) was taken at the start of the study and plaster study models were obtained at both the beginning and end of the observation period. The study models were used to measure crowding, and to prepare photocopies for linear measurements of the dental arch (length and width). Using the DPT, the ratio of retromolar space to the width of the crown of the third molar was calculated using the method originally described by Olive and Basford and later modified by Ganss (Ganss ratio). The results showed that the measurements of crowding and arch length and width had changed in 12 lower and two upper dental arches. The relationship between these results and the Ganss ratio was statistically significant. Calculation of the Ganss ratio may therefore assist investigations into the development of dental arch crowding and also help determine the indications for third molar removal.
Adolescent↗
Determination of Bolton tooth-size ratios by digitization, and comparison with the traditional method.
The Bolton Index is one of the most useful calculations for precise orthodontic diagnosis as it shows if there is a correct ratio between dental proportions. However, at times, this calculation is not applied because it is a long and time-consuming procedure compared with digital methods. A new digital method for measuring tooth sizes and for calculating the Anterior (ABI) and the Overall (OBI) Bolton Index was tested on 100 sets of study dental casts of the permanent dentition in a Spanish sample and compared with the traditional method. The reproducibility of this digital method versus the traditional one was analysed to determine intra- and inter-examiner measurement errors by calculating the coefficients of variation. The results demonstrated that the digital method provided results comparable with those of the traditional technique, since the regression parameters for each index showed that the correlation coefficients of the two methods were very high and similar to each other: r = 0.976 and r = 0.979 for the ABI and OBI, respectively. The results also showed more discrepancies in the ABI than in the OBI using both methods in this sample.
Adolescent↗
Comparison of tooth size discrepancies among different malocclusion groups.
This retrospective investigation was designed to compare tooth size discrepancies among subjects with different skeletal malocclusions in an orthodontic population. The study employed the pre-treatment models of 200 patients (100 males, 100 females, aged from 14 to 20 years) selected from the records of the Orthodontic Department, Shiraz Dental School. The subjects were from four malocclusion groups, Class I, Class II division 1, Class II division 2, and Class III, with the corresponding skeletal characteristics. Each group comprised 50 healthy individuals (25 males, 25 females). The mesio-distal dimensions of teeth were measured using digital electronic callipers (accurate to 0.01 mm) and the Bolton indices were determined. The data were statistically analysed using analysis of variance and Duncan's multiple range test, with the level of significance set at P < 0.05. The results revealed that the mean anterior ratio (79.01) for the whole sample was statistically significantly different from Bolton's (77.2) but no significant difference was found for the overall ratio. The posterior and overall ratios of the Class III malocclusion group were statistically greater than the other malocclusion groups (P < 0.05). The mean anterior ratio of the Class III group was greater than that of the Class II group. However, there was no difference when compared with the Class I malocclusion group. For the two types of Class II malocclusion, no significant ratio differences were observed.
Adolescent↗
Initial changes of centres of rotation of the anterior segment in response to horizontal forces.
This study investigated the changes in the initial centres of rotation (Crot) of the upper six anterior teeth in response to a horizontal load. Six upper anterior teeth were extracted, splinted as a unit, and embedded in dental stone after the roots were uniformly coated with silicone. An aluminium fixture was bonded to the anterior segment and three linear variable differential transformers (LVDTs) were attached to measure the microdisplacement of the segment. A pulley and dead weight assembly were used to apply a 200 g occluso-gingivally varying horizontal force to the segment. The changes in the Crot for the anterior segment to the horizontal load were recorded. The results showed that the centre of resistance (Cres) of the upper anterior segment was located 14.5 mm apical and 9.5 mm distal from the incisal edge of the central incisors. A linear functional axis (a trace of the measured Crot) was recorded. The functional axis maintained an angle of 14.5 degrees to the vertical axis of the anterior segment passing through the Cres of the segment. The Crot constant, which determines the tipping sensitivity of the segment, was 23 mm(2). The results demonstrate that the upper anterior segment may be slightly intruded when a horizontal force is applied and is less prone to tipping than a single tooth.
Humans↗
Genetic basis of adaptive shape differences in the cichlid head.
East African cichlids exhibit an extraordinary level of morphological diversity. Key to their success has been a dramatic radiation in trophic biology, which has occurred rapidly and repeatedly in different lakes. In this report we take the first step in understanding the genetic basis of differences in cichlid oral jaw design. We estimate the effective number of genetic factors that control differences in the cichlid head through a comprehensive morphological assessment of two Lake Malawi cichlid species and their F(1) and F(2) hybrid progeny. We estimate that between one and 11 factors underlie shape difference of individual bony elements. We show that many of the skeletal differences in the head and oral jaw apparatus are inherited together, suggesting a degree of pleiotropy in the genetic architecture of this character complex. Moreover, we find that cosegregation of shape differences in different elements corresponds to developmental, rather than functional, units.
Adaptation, Physiological↗
Morphology of anterior teeth associated with displaced canines.
This clinical study compared tooth dimensions of maxillary central and lateral incisors on the same side as a palatally impacted maxillary canine with those of the contralateral side with a normally erupted canine, in a group of 33 consecutively referred patients. The dimensions recorded were the mesio-distal width, labio-palatal depth, obtained from models of the four upper anterior teeth and total tooth length obtained from an orthopantomographic radiograph. The results showed that there was no statistically significant evidence to support the view that palatally impacted maxillary canines are associated with diminutive maxillary lateral incisors.
Adolescent↗
A study of transposed canines in a sample of orthodontic patients.
Tooth transposition is a positional interchange of two adjacent teeth. The most commonly transposed tooth is the permanent canine with either the first premolar or lateral incisor. The records of 54 subjects with transposed canines, both maxillary and mandibular, were collected. Pretreatment study models of these subjects were matched with a similar number of models from unaffected individuals. Bucco-lingual and mesio-distal tooth widths, arch depth and arch width were measured on each model. Thirty-four subjects (63 per cent) were female. Thirty-seven (68.5 per cent) of the cases involved the maxillary arch and thirty-three (89.2 per cent) of these upper arch transpositions were of the canine and first premolar. In cases involving the lower arch the canine was invariably transposed with the lateral incisor. Peg-shaped lateral incisors, supernumerary and/or congenitally absent teeth occurred in 19 subjects. There were some small, but significant differences in the dimensions of some teeth, however there were no statistically significant differences in arch depths, arch widths and most tooth dimensions in subjects with and without transposed canines. These factors do not appear to be related to the development of canine transposition.
Anodontia↗
The influence of maxillary incisor inclination on arch length.
This ex vivo study was designed to investigate Andrews' hypothesis that there is a space implication when incisors are torqued correctly. A working model was constructed to allow acrylic typodont incisors of varying known values of inclination to be substituted into the model. The arch lengths of the various 'set-ups' were measured using a reflex microscope linked to a PC. In order to quantify the space requirement of clinical relevance for adequate incisor torque, the method was repeated by substituting replicas of patients' 'natural' incisors. For both acrylic and natural incisors it was found that, as the inclination of the teeth increased, there was an increase in all arch lengths, this being greater for the natural incisors. This larger increase for the natural incisors was related not only to their increased size, but was also dependent on the morphology of the incisor. Those incisors which were parallel-sided showed the greatest increase in arch length, whereas the incisors that were relatively triangular in shape showed the smallest increase. When the inclination of an 'average' set of 21/12 is increased by 5 degrees, an increase in the arch length of approximately 1 mm may be expected.
Acrylic Resins↗
Orthodontic treatment outcome: the relationship between anterior dental relations and anterior inter-arch tooth size discrepancy.
OBJECTIVE: This study investigated the pre- (T1) and post-treatment (T2) relationship between anterior (canine to canine inclusive) inter-arch tooth size ratio and various dental and skeletal variables. DESIGN: Retrospective longitudinal clinical study. SETTING: Swedish Health Board Clinic 2000. SUBJECTS: Random selection of T1 and T2 orthodontic records of 137 Swedish patients (56 male and 81 female). The sample included non-extraction (77), and four premolar extraction (60) cases across a range of dental and skeletal malrelationships. MAIN OUTCOME MEASURES: Dental cast and lateral cephalogram measurements were recorded. Exploratory modelling investigated whether a significant relationship existed between the anterior inter-arch tooth size ratio and these measurements. RESULTS: Data was normally distributed with no statistically significant differences between males and females (P = 0.88) and extraction and non-extraction (P = 0.52) treatment modalities with respect to the anterior ratio. T1 bivariate regression analysis failed to show a relationship (p < 0.05) between variables. T2 bivariate analysis showed a statistically significant relation between three variables and anterior tooth size ratio. Multiple regression analysis led to a final model where maxillary inter-canine width (P = 0.002) and upper arch crowding (0.001) were statistically significantly related to the anterior inter-arch ratio. The coefficient of determination was however uniformly low (R(2) < 0.2) for all variables. CONCLUSION: The anterior inter-arch tooth size ratio was not associated with any common pre- or post-treatment variables in the population studied, therefore measurement of an anterior tooth size ratio pre-treatment was not clinically beneficial for determining anterior dental relations post-treatment.
Adolescent↗
Effects of alleles at the albino locus on odontometric traits in coisogenic mice.
The widths of all six molars were examined in coisogenic house mice of strain 129/J to determine whether they were being influenced by chinchilla alleles at the albino locus. Although genotype differences did not reach formal significance in the analyses of variance for any molar (or body weight) in either sex, the molar means for chinchilla homozygotes were less than those for the albinos in 11 of the 12, and for heterozygotes in 12 of 12 combinations. The difference between the two homozygous genotypes within each molar and sex averaged 0.25 standard deviations. Static allometry coefficients were calculated for each genotype and sex from partial regressions of the logarithms of each of the molars on the logarithms of the cube root of body weight, adjustment being made for the effects of litter size and the day the litter was born. These coefficients all were low in magnitude (negative allometry), and multivariate analyses of covariance showed that they differed significantly among genotypes in males, but not in females.
Albinism↗
Two bite marks on assailant. Primary link to homicide conviction.
Two distinctly different bite marks occurred on the same individual, the perpetrator of a single homicide. The bite marks were produced by different teeth in the upper arch of the decedent on two separate areas of the perpetrator's body. While either injury demonstrated the points of identity with the decedent's dental arch, the pair considered together allowed conclusive identity of the perpetrator. The bite mark evidence led to a plea of guilty to second-degree murder by the accused.
Bites and Stings↗