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At least 1,153 records · Page 64Linked to original sources
PubMed2001

Sex- and age-related differences in primary and secondary dentin formation.

Clinical studies carried out on dentin thickness in adults, as well as experimental studies carried out on ovariectomized animals, indicate that odontoblast activity, like that of osteoblastic cells, differs in the two sexes. To examine the evidence for differences in odontoblast activity before puberty, we have measured dentin thickness and other crown dimensions from bitewing radiographs of the lower first molars in 240 children aged 4-16 years. The radiographs were obtained from pedodontic clinics throughout Israel. Only teeth without caries or fillings were used, and the study population had minimal attrition. The results showed that dentin thickness, measured on the roof of the pulp chamber, was significantly greater in boys than in girls at all ages, and that the differences increased during puberty. The differences remained highly significant even when standardized for crown size. They demonstrate that dimorphism in dentin thickness is present even in the earliest stages of odontogenesis and increase with puberty.

Adolescent↗
PubMed2003

Molar intercuspal dimensions: genetic input to phenotypic variation.

Molecular studies indicate that epigenetic events are important in determining how the internal enamel epithelium folds during odontogenesis. Since this process of folding leads to the subsequent arrangement of cusps on molar teeth, we hypothesized that intercuspal distances of human molar teeth would display greater phenotypic variation but lower heritabilities than overall crown diameters. Intercuspal distances and maximum crown diameters were recorded from digitized images of dental casts in 100 monozygotic and 74 dizygotic twin pairs. Intercuspal distances displayed less sexual dimorphism in mean values but greater relative variability and fluctuating asymmetry than overall crown measures. Correlations between intercuspal distances and overall crown measures were low. Models incorporating only environmental effects accounted for observed variation in several intercuspal measures. For those intercuspal variables displaying significant additive genetic variance, estimates of heritability ranged from 43 to 79%, whereas those for overall crown size were higher generally, ranging from 60 to 82%. Our finding of high phenotypic variation in intercuspal distances with only moderate genetic contribution is consistent with substantial epigenetic influence on the progressive folding of the internal enamel epithelium, following formation of the primary and secondary enamel knots.

Adolescent↗
PubMed2004

Mouse cellular cementum is highly dependent on growth hormone status.

Cementum is known to be growth-hormone (GH)-responsive, but to what extent is unclear. This study examines the effects of extremes of GH status on cementogenesis in three lines of genetically modified mice; GH excess (giant), GH antagonist excess (dwarf), and GH receptor-deleted (GHR-KO) (dwarf). Age-matched mandibular molar tissues were processed for light microscope histology. Digital images of sections of first molar teeth were captured for morphometric analysis of lingual root cementum. Cross-sectional area of the cellular cementum was a sensitive guide to GH status, being reduced nearly 10-fold in GHR-KO mice, three-fold in GH antagonist mice, and increased almost two-fold in giant mice (p < 0.001). Cellular cementum length was similarly influenced by GH status, but to a lesser extent. Acellular cementum was generally unaffected. This study reveals cellular cementum to be a highly responsive GH target tissue, which may have therapeutic applications in assisting regeneration of the periodontium.

Animals↗
PubMed2004

Genetic analysis of crown size in the first molars using SMXA recombinant inbred mouse strains.

Tooth crown size may be determined by both genetic and environmental factors. The aim of this study was to identify quantitative trait loci (QTLs) affecting dental crown size and determine whether there is genetic independence between upper and lower teeth, using SMXA recombinant inbred strains of mice. Mesiodistal and buccolingual crown diameters (MD and BL, respectively) of the upper and lower first molars (M(1) and M(1), respectively) were measured. For each trait, mean values of substrains showed a continuous spectrum of distribution. Genome-wide scan detected QTLs exceeding suggestive threshold levels for MD of M(1) (chromosomes 7, 13, and 17), BL of M(1) (chromosomes 8 and 13), MD of M(1) (chromosomes 7 and 13), and BL of M(1) (chromosomes 3 and 15). These findings suggest that tooth crown size is controlled by multiple genes, and that there is some independence of genetic control between M(1) and M(1).

Animals↗
PubMed2004

Asymmetry in the condylar long axis and first molar rotation.

Asymmetric growth occurs frequently in the mandibulofacial region, but little attention has been given to asymmetry in the temporomandibular joint. The purpose of this study was to clarify the feature of asymmetry in the condylar long axis and its relation to upper first molar rotation. Records of 148 pre-orthodontic patients were used. The angle of the condylar long axis and that of the molar rotation were both larger on the left side than on the right side. Positive correlations were found between the corresponding bilateral measurements of condylar long axes and also between those of molar rotations, whereas no correlation was found between the condylar long axis and molar rotation. These findings were found in most subgroups classified by dental age, skeletal pattern, bite force balance, or gender. These results suggest that consistent left-right differences in the condylar long axis and first molar rotation are common.

Adolescent↗
PubMed2004

Modulation of clinical expression of plaque-induced gingivitis: effect of incisor crown form.

Evidence indicates that incisor crown form correlates with clinical periodontal features. It was hypothesized that incisor crown form may explain subject differences in gingivitis expression. The present experimental gingivitis study aimed to assess the effect of incisor crown form on plaque accumulation and gingival inflammation, and on individual susceptibility to plaque-induced gingivitis. Eighty-five periodontally healthy subjects were evaluated. A negative correlation was found between incisor crown width/crown length ratio and bleeding score (p = 0.045). From the 85 subjects, two groups of subjects with either 'long-narrow' or 'short-wide' incisor form were identified. The 'long-narrow' group had a significantly higher bleeding score than the 'short-wide' group (p = 0.014). No significant differences were found in the incisor crown width/crown length ratio between previously identified 'high responder' and 'low responder' subjects (Trombelli et al., 2004a). In conclusion, incisor crown form appears to affect the bleeding response of inflamed gingival tissues, while it exerts no influence on explaining differences in individuals' susceptibility to plaque-induced gingivitis.

Adult↗
PubMed2006

Inhibition of apoptosis in early tooth development alters tooth shape and size.

Apoptosis plays important roles in various stages of organogenesis. In this study, we hypothesized that apoptosis would play an important role in tooth morphogenesis. We examined the role of apoptosis in early tooth development by using a caspase inhibitor, z-VAD-fmk, concomitant with in vitro organ culture and tooth germ transplantation into the kidney capsule. Inhibition of apoptosis at the early cap stage did not disrupt the cell proliferation level when compared with controls. However, the macroscopic morphology of mice molar teeth exhibited dramatic alterations after the inhibition of apoptosis. Crown height was reduced, and mesiodistal diameter was increased in a concentration-dependent manner with z-VAD-fmk treatment. Overall, apoptosis in the enamel knot would be necessary for the proper formation of molar teeth, including appropriate shape and size.

Amino Acid Chloromethyl Ketones↗
PubMed2006

Tooth-size discrepancy and Bolton's ratios: a literature review.

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.

Ethnicity↗
PubMed1988

Factors influencing the development of molar occlusion: a longitudinal study.

Longitudinal records, in the form of study casts, of 35 Class I cases were examined for factors associated with changes of sagittal molar relationship during childhood. These were studied at two phases: between the deciduous and mixed dentitions, and between the mixed and permanent dentitions. During the first of these periods, there was a small, but general move to a less post-normal occlusion, although some cases were found to show a slight reverse trend. In the second period, the permanent molar relationship became less post-normal, but this was reflected only weakly in that of the canines. Throughout development, asymmetry of occlusal relation became more marked with age, an unexplained bias towards less post-normal occlusion on the left side developing in the second phase. The amount of change in this period was related to variations of deciduous molar size, especially that of the upper second molar.

Adolescent↗
PubMed1989

Morphology of the maxillary lateral incisor in cases of unilateral impaction of the maxillary canine.

Two groups of subjects who demonstrated unilateral maxillary canine impaction were examined, a Caucasian group and an Oriental group. It was found that there are significant differences between the groups for sex of patients seeking treatment, site of impaction (buccal/palatal), and arch form. The Oriental group was significantly more crowded in the canine area than the Caucasian group. In almost all cases the dimensions of the lateral incisor on the side of impaction were smaller than the non-impacted side, although five subjects from the Caucasian female sub-group did not conform to this pattern, and for the Oriental male sub-group the mesiodistal crown width was larger on the impacted side.

Adolescent↗
PubMed1992

Aesthetic tooth modification for patients with cleft lip and palate.

Alongside orthodontic treatment, tooth shape modification may be indicated for teeth associated with clefts of the lip and alveolus, and in non-carious teeth, minimal tooth preparation techniques appear to be most appropriate. Two methods of tooth shape modification are described. In one, hybrid composite materials, bonded to tooth enamel using the acid-etch technique, may be considered to provide a permanent, low cost, aesthetically satisfactory result, often without tooth preparation and with minimal operating time. Alternatively, indirect veneers may be appropriate for treatment of more severely malformed teeth.

Anodontia↗
PubMed1993

The development of a new method of cephalometric and study cast mensuration with a computer controlled, video image capture system. Part II: Study cast mensuration.

A computerized system for mensuration of dental casts, developed at the Royal Berkshire Hospital in Reading was tested against a conventional manual method and a computer controlled reflex microscope. Systematic errors, calibration, and handling aspects are discussed. Results showed that the computerized system provided data which while statistically different, were clinically comparable with the same measurements carried out using conventional manual or digitizing techniques. The results indicated that future research is required with respect to object illumination for all indirect techniques.

Analysis of Variance↗
PubMed1993

The relationship of crowding to the eruptive position of the lower permanent incisors.

The aim of this study was to examine the positions of newly erupted lower permanent incisors and their relationship to crowding. Forty-one crowded and 37 uncrowded dental casts of children in the early mixed dentition were examined by means of digitization using a reflex microscope. Two aspects of alignment were considered: rotation and labio-lingual displacement. Rotations of the incisors were defined as deviations from 'ideal' predicted angles. Displacement of the incisors was measured as the distance between the most labial and most lingually placed incisors. The study showed an increase in rotations amongst the crowded sample. The result of the investigation of the relationship between crowding and displacement was inconclusive. There would appear to be significant differences between the positions of newly erupted crowded and uncrowded incisors. Crowding, however, was not the only factor causing irregularity.

Child↗
PubMed1994

The palatal canine and the adjacent lateral incisor: a study of a west of Scotland population.

The hypothesis that palatally-displaced canines are associated with smaller than average lateral incisors or with congenital absence of adjacent lateral incisors was tested on a West of Scotland population. A retrospective study of the records of orthodontic patients attending Glasgow Dental Hospital was carried out. One-hundred-and-eighty-two subjects with palatally displaced canines were identified. The tooth length of lateral and central incisors was measured on radiographs and the crown widths of lateral incisors were measured on study casts. One-hundred-and-six extracted maxillary lateral incisors were examined to allow more accurate measurement of crown width and root length than was possible from radiographs. An association was sought between the size of the lateral incisor or its absence, the position of the adjacent maxillary canine, and between crown size and root length of the lateral incisor. The conclusions supported the hypothesis that there is a weak association between palatally displaced maxillary canines and lateral incisors of smaller than average crown width. There was weak support for the association between palatal canines and absence of the adjacent lateral incisor. There was no correlation between lateral incisor crown width and root length.

Adolescent↗
PubMed1995

Developmental changes in alignment of the lower labial segment.

The purpose of this study was to examine changes in lower incisor alignment at various developmental stages, from the time of eruption to the established permanent dentition and to try to predict the degree of crowding in the permanent dentition from that observed at earlier developmental stages. Forty-eight subjects (20 male, 28 female) with intact mandibular arches were selected from the Belfast growth study records. The lower incisor space condition was measured at each of four developmental stages: (1) initial eruption of the lower permanent incisors; (2) initial eruption of the permanent canines; (3) initial eruption of the second molars; (4) 3 years after eruption of the second molars. Differences in lower incisor space condition between each developmental stage were investigated and correlation analyses between the space conditions at each stage were carried out. On average, crowding of the lower incisors decreased to a statistically significant degree (- 0.9 mm) between stages 1 and 2, and increased between stages 3 and 4 (0.4 mm). Significant correlation coefficients between space condition at each developmental stage were found, but were considered unreliable as predictors of lower incisor crowding in the mature dentition.

Child↗
PubMed1996

The assessment of crowding without the need to record arch perimeter. Part I: Arches with acceptable alignment.

A simplified, mathematically determined technique for calculating arch perimeter (the overlap method) is described and its validity in determining an accurate assessment of crowding is tested. Indices, expressed in millimetres of crowding or spacing, were computed for both the whole arch and the labial segment alone. Study casts of 36 individuals with clinically acceptable lower arches were used to validate the method. The degree of crowding or spacing calculated was compared with a "clinical' assessment of each arch, in which the irregularity was measured directly using a steel ruler. Various calculation schemes were tested. Depending on exactly how the overlap was determined, the results varied slightly. Although the arches showed acceptable alignment, it was preferable to include a strategy for normalizing the positions of any rotated teeth before the overlaps were calculated. Repositioning any bucco-lingually displaced teeth into the line of the arch, however, was not useful. For the complete arch good agreement with the clinical assessment was reached on 31 occasions and for the labial segment, all but one appraisals were within 0.5 mm of each other. In the remaining instances (five complete arches and one labial segment), the degree of crowding or spacing was between 0.5 and 1 mm of the clinical assessment. Considering that clinical measurement of minor degrees of crowding and spacing cannot be precise, these results were considered acceptable. The method was easy to use, relying only on the recording of mesio-distal tooth widths and was acceptably reproducible. The technique would therefore appear to provide a valid yet simple research tool with which to record the degree of crowding. Its ability to cope with irregular and crowded arches will be the subject of a subsequent review.

Algorithms↗
PubMed1996

Late lower arch crowding in relation to skeletal and dental morphology and growth changes.

Skeletal and dental morphology, and related growth changes during a 3-year period following second permanent molar eruption, were compared in a group of 21 subjects who had no increase in lower arch crowding, with another group of 21 subjects whose lower arch crowding had increased by 1.0 mm or more during the same period. The crowding group showed a significantly greater increase in M3 space, forward movement of the second permanent molar and increase in the inter-incisal angle than the non-crowding group. None of the other parameters examined differed significantly.

Adolescent↗