Trends of dental arc variation in a young adult male population and their meaning in the concept of occlusion. (41/219)

To describe the variation of shape and size of dental arcs the method of principal components was applied. 27 measurements of every dental cast made from 50 young adult males with good occlusion were made, and the following parameters were calculated: 7 widths, 5 left chords, 5 right chords, 5 sagittal lengths (calculated as orthogonal to corresponding width) and 5 angles. Different sets of features were analyzed for both arcs together and for each arc separately. Three independent analyses by the method of principal components show a good description of the main trend of dental arc shape and size variation and a difference between the growth and variation of frontal and distal parts of the arcs. They also describe the variations of occlusion. The trends of dental arc variation ascertained help us to understand the nature of malocclusions and the causes of their preservation in evolution.  (+info)

Additional remains of Wadilemur elegans, a primitive stem galagid from the late Eocene of Egypt. (42/219)

The late Eocene prosimian Wadilemur elegans from the Jebel Qatrani Formation, northern Egypt, was originally interpreted as an anchomomyin adapiform primate based on limited information from the lower molars and distal premolars. Recently recovered fossils attributable to this species, including a proximal femur, the fourth upper premolar and first and second upper molars, and a mandible preserving the lower second premolar and lower canine and incisor alveoli, reveal a number of derived morphological similarities shared with crown strepsirrhines and, in particular, Miocene-to-Recent stem and crown galagids, to the exclusion of known adapiforms. Phylogenetic analysis of 359 morphological features scored across 95 living and extinct crown primate taxa supports a stem galagid placement for Wadilemur and older Saharagalago, and a close relationship between crown strepsirrhines and the Eocene African taxa "Anchomomys" milleri, Djebelemur, and Plesiopithecus (none of which appear to be closely related to European anchomomyins). This scheme of relationships supports the hypothesis that crown Strepsirrhini is of Afro-Arabian origin and that lemuriforms likely colonized Madagascar by crossing the Mozambique Channel. Wadilemur's known dental and postcranial morphology provides additional support for the hypothesis that galagids and lorisids had diverged by the close of the middle Eocene, and, by bolstering the approximately 37 million-year-old calibration point for crown lorisiform origins provided by Saharagalago, indirect support for the hypothesis of an ancient origin of crown Strepsirrhini and crown Primates.  (+info)

An in vitro comparison of root canal measurement in primary teeth. (43/219)

To compare the accuracy of root canal lengths in primary teeth determined by tactile sense, electronic apex locator, conventional radiography, and digital radiography in primary teeth. The study sample consisted of twenty 20 extracted, single-rooted primary teeth. A comparison was made between the working length measurements obtained by tactile sensation, electronic apex locator, conventional film, and digital radiography, using stereomicroscopic measurements to obtain real canal length. The mean readings obtained were 15.91+/-2.06 by tactile measurement, 15.94 94+/-1.42 by apex locator, 16.06+/-1.73 by conventional radiography, and 15.91+/-1.60 by digital radiography. No statistically significant differences were seen between the techniques.  (+info)

Determination of Bolton tooth-size ratios by digitization, and comparison with the traditional method. (44/219)

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.  (+info)

Tooth-size discrepancy and Bolton's ratios: a literature review. (45/219)

OBJECTIVES: To review the literature on Bolton's tooth-size discrepancies (TSD) with specific attention to the prevalence of TSD, and the possible influence of different classes of malocclusion, gender and racial group. Also examined were the validity of the standard deviations from Bolton's samples as an indicator of significant TSD, methods of measurement of TSD and their reproducibility. Based on the review, suggestions are made as to how future work could be improved. RESULTS AND CONCLUSIONS: Studies have reported from 20 to 30% of people with significant tooth-size anterior discrepancies and 5-14% for overall TSD. Bolton's original sample was appropriate for indicating what ratio is most likely to be associated with an excellent occlusion, but was not suited to indicating the size or prevalence of significant TSD. Most studies use samples that are not likely to be representative of orthodontic patients in the UK or, indeed, elsewhere. Although some statistically significant differences have been reported, gender and racial group seem unlikely to have a clinically significant influence on Bolton's tooth-size ratios. Class III malocclusions may have larger average ratios. Computerized methods of measurement are significantly more rapid. Most studies performed or reported their error analysis poorly, obscuring the clinical usefulness of the results. Studies are needed to properly explore the reproducibility of measurement of TSD and to appropriately determine what magnitude of TSD is of clinical significance.  (+info)

Comparison of tooth size discrepancies among different malocclusion groups. (46/219)

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.  (+info)

Loss of space and changes in the dental arch after premature loss of the lower primary molar: a longitudinal study. (47/219)

The purpose of the study was to evaluate the space changes, dental arch width, arch length and arch perimeter, after the unilateral extraction of lower first primary molar in the mixed dentition period. A longitudinal study was conducted among forty children in the age group of 6-9 years, who reported for extraction of lower first primary molar in the department of Pedodontics, Govt. Dental College, Trivandrum. Study models were made from alginate impression taken before extraction and after extraction at the periodical intervals of two months, four months, six months and eight months. The mesiodistal width of lower first primary molar of the non-extracted side was taken as the control. The results of the study showed statistically significant space loss in the extraction side ( P value < 0.01) and no significant space loss in the control side (P value > 0.05). The rate of loss was greatest in the first four months. The arch width, arch length and arch perimeter had no significant change from initial to eight months follow up. The present study challenges the use of a space maintenance under the circumstances of premature loss of mandibular primary molar for preventing space loss.  (+info)

Initial changes of centres of rotation of the anterior segment in response to horizontal forces. (48/219)

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.  (+info)