Tooth Crown :: anatomy & histology
Department of Periodontics, USC School of Dentistry, Los Angles, California, USA.
Most cited papers:
Oral Biology, Dental School, The University of Newcastle upon Tyne, Newcastle upon Tyne, NE2 4BW, UK. email@example.com
Most of what we know about the timing of human enamel formation comes from radiographic studies on children of known age. Here, we present new longitudinal data derived from a histological analysis of tooth enamel. Two samples, one from southern Africa and one from northern Europe, contained all anterior and molar tooth types. Two further samples contained only one tooth type: canines from a medieval Danish sample and third molars from a modern North American sample. Data were collected on 326 molars and 352 anterior teeth. Each tooth was sectioned and prepared for polarized light microscopy. We used daily enamel cross striations to determine cuspal enamel formation time, recorded the periodicity of long-period striae in the lateral enamel, and used this value to calculate enamel formation times for each decile of crown length. We present data that reveal some of the processes whereby differences in enamel formation times arise between our samples. Mean cuspal enamel formation times were similar in southern African and northern European anterior teeth, but differed in certain molar cusps. All the southern African anterior teeth completed enamel formation earlier. The greatest difference in mean chronological age at enamel completion was 5.2 vs. 6.2 years of age in lower canines. However, enamel completion times in the molar teeth showed few differences between the samples, with mean times for the longest forming cusps all falling between 3.0 years and 3.45 years. Our data suggest fewer differences between samples and smaller ranges of variation than in many radiographic studies and present a more realistic picture of worldwide variation in enamel formation times.
Institute of Medical Physics, Dental School, University of Vienna, Austria.
Optical coherence tomography (OCT) has been developed during the last 10 years as a new noninvasive imaging tool and has been applied to diagnose different ocular and skin diseases. This technique has been modified for cross-sectional imaging of dental structures. In this first preliminary study the technique was applied to obtain tomographic images of extracted sound and decayed human teeth in order to evaluate its possible diagnostic potential for dental applications. Classical OCT images based on reflectivity measurements and phase retardation images using polarization-sensitive OCT were recorded. It was demonstrated that polarization-sensitive OCT can provide additional information which is probably related to the mineralization status and/or the scattering properties of the dental material. One of the attractive features of OCT is that it uses near-infrared light instead of ionizing radiation. Furthermore, high transversal and depth resolution on the order of 10 microm can be obtained. Present limitations, e.g. the limited penetration depth, and possible solutions are discussed.
Ultrasonic determination of gingival thickness. Subject variation and influence of tooth type and clinical features.
Department of Periodontology, German Armed Forces Central Hospital, Koblenz, Germany.
The objectives of the present study were (I) to determine the validity and reliability of measuring gingival thickness (GTH) with a recently developed, commercially available ultrasonic device;(II) to measure GTH in relation to tooth type and age of proband;(III) to correlate GTH with varying forms of premolars, canines and incisors. Ultrasonic measurements were performed in 200 periodontally healthy, male probands representing 3 different age groups (20-25, 40-45, 55-60 years). In the maxilla, mean GTH varied between 0.9 mm (canines, 1st molars) and 1.3 mm (2nd molars). In the mandible respective mean values ranged between 0.8 mm (canines) and 1.5 mm (2nd molars). No differences in means and standard deviations (0.36-0.39 mm) were observed in different age groups. In order to correlate GTH with other clinical parameters and form of tooth, in 42 probands of the youngest age group, presenting with no attrition or abrasion, no artificial crown restorations and (following prophylaxis) no overt gingivitis and no periodontal probing depth in excess of 3 mm, detailed clinical measurements and stone model cast analyses were performed. By stepwise multiple linear regression analysis, 24%(p < 0.0001) of the variation of GTH was explained by probing depth, recession, width of gingiva and tooth type. The ratio of the width of the crown to its length was not included into the model. When performing analysis of covariance with the subject as factor, the model was improved, now explaining 41% of the variation of GTH. In this model, the influence of periodontal probing depth was decreased, and recession was not included. It was concluded that there are individual differences in GTH (i.e., different biotypes). However, thickness mainly depends on tooth type and is correlated with width of gingiva. There appears to be no association with shape and form of the tooth. Validity and reliability of measuring GTH with the ultrasonic device was found to be excellent.
University of Illinois, Chicago, USA. firstname.lastname@example.org
Rapid maxillary expansion (RME) in the adult is thought to be an unreliable procedure with several adverse side effects and, consequently, surgically assisted RME is considered the preferred procedure. The purpose of this paper is to study the efficacy of nonsurgical RME, and to determine the incidence of complications such as relapse of the expansion, pain and tissue swelling, tipping of the molars, opening rotation of the mandible and gingival recession. Rapid maxillary expansion using a Haas expander was examined in 47 adults and 47 children. A control group of 52 adult orthodontic patients who did not require RME was also studied. Students' t-test, and the analysis of variance followed by the Scheffe test were used to determine if there were significant differences among time periods and among the 3 study groups. The mean transarch width increase was similar in adults and children who had RME; 4.6 +/- 2.8 compared to 5.7 +/- 2.4 mm for the molars and 5.5 +/- 2.4 compared to 5.7 +/- 2.5 mm for the second premolars. In the adults, transarch expansion and the correction of the posterior crossbites were stable following discontinuance of retainers (mean 5.9 years). If the expander was properly fabricated, and turned no more than once a day, the procedure was well-tolerated. Rapid maxillary expansion in adults flared the molars buccally only 3 degrees per side. The mandibular plane and lower facial height were unchanged. The adults achieved 18% of their transmolar expansion at the height of the palate and the remainder with buccal displacement of the alveolus. The children achieved 56% of their expansion by an increase at the height of the palate with the remainder due to displacement of the alveolus. There was some buccal attachment loss (0.6 +/- 0.5 mm) seen in the female subjects associated with RME, but the extent was clinically acceptable. This resulted in significantly longer clinical crowns, but rarely caused exposure of buccal root cementum. Complications were infrequently observed or of minimal consequence. The results indicate that nonsurgical RME in adults is a clinically successful and safe method for correcting transverse maxillary arch deficiency.
Mesiodistal crown dimensions and tooth size discrepancy of the permanent dentition of Dominican Americans.
Division of Orthodontics, Columbia University School of Dental and Oral Surgery, New York, NY 10032, USA. email@example.com
The purpose of the study was to establish normative data on the mesiodistal crown dimensions of Americans of Dominican background. The Bolton tooth size analysis was performed on a sample of 54 Dominican Americans. The mean, range and standard deviation were calculated for the size of the teeth, and a coefficient of variation was obtained for the tooth size ratio. A 2-sample t-test was used to test for the statistical difference between means. In general, the values obtained for the Dominican American sample closely resembled previous data available for the African American population. The tooth size ratios obtained were compared to the Bolton ratios. The overall ratio was found to be 91.3, equivalent to the Bolton overall ratio, whereas the anterior ratio was 78.1, larger than the 77.1 Bolton ratio. The frequency of tooth size discrepancy outside 2 standard deviations from the Bolton mean was also calculated. An overall tooth size discrepancy was found in 11% of our sample, and 28% of the sample presented an anterior tooth size discrepancy.
Department of Orthodontics and the Department of Oral Surgery and Oral Medicine, University of Oslo, Norway.
The published literature contains no comprehensive studies that compare the outcome of premolar autotransplantation to the maxillary anterior region with natural incisors in the same patients. This article describes the gingival and periodontal conditions around premolars transplanted to the maxillary incisor region, subsequent to restoration. Forty-five premolars autotransplanted to the maxillary incisor region in 40 adolescent patients were evaluated after a mean observation period of 4.0 years. Mean age at surgery was 11.0 years. Established clinical criteria were used to assess tooth mobility, plaque and gingival indexes, probing pocket depth, and percussion. Recession and hyperplasia of interproximal gingival papillae were assessed according to a recently proposed index. Standardized radiography was used to evaluate presence of pathosis, pulp obliteration, root length, and crown-root ratios. Clinical variables for transplants did not differ from those of the natural incisors, except for increased mobility and more plaque in a few transplanted premolars. The interproximal gingival papillae adjacent to all transplanted teeth were normal or slightly hyperplastic. Radiographically, all transplants showed varying degrees of pulp obliteration, but no signs of pathosis. Crown-root ratios were similar for natural and transplanted teeth as were distances from cementoenamel junction to marginal bone. The overall status of the transplanted premolars and surrounding tissues indicated that this treatment modality may be recommended when maxillary incisors are missing in adolescents. In addition, tooth transplantation represents an inherent potential for bone induction and reestablishment of a normal alveolar process.
Enamel thickness and the topography of the enamel-dentine junction in South African Plio-Pleistocene hominids with special reference to the Carabelli trait.
Evolutionary Anatomy Unit, Department of Anatomy & Developmental Biology, University College London, London, WC1E 6BT, U.K. firstname.lastname@example.org
This study explores the internal morphology of early hominid teeth using high-resolution computed tomography. Data on Carabelli feature size, enamel thickness, and the topography of the enamel-dentine junction are considered together in order to examine the relationship among these variables in the maxillary molars of gracile and robust australopithecines from South Africa. In particular, one aim is to investigate the degree to which Carabelli feature size influences enamel thickness in the plane of the mesial cusps. The results demonstrate that maxillary molars attributed to Australopithecus africanus from Sterkfontein, Taung and Makapansgat possess larger Carabelli features and thinner enamel along the lingual wall of the protocone than do specimens attributed to Paranthropus robustus from Swartkrans and Kromdraai. Distinct differences in the position of the Carabelli feature at the level of both the enamel-dentine junction and tooth crown surface between early hominid species may help explain the observed disparity in enamel thickness at that region of the tooth crown as well as offer clues to the functional role of Carabelli's cusp. As the size and position of the Carabelli feature affects the linear thickness of enamel at this one particular region of the tooth crown, future comparative studies focusing on taxa that possess moderate to strong development of the Carabelli complex should use the linear thickness of enamel taken close to the protoconal dentine horn or at the maximum projection of the Carabelli's cusp.
Department of Restorative and Pediatric Dentistry, Faculty of Dentistry, Jordan University of Science and Technology, Irbid, Jordan.
Mesiodistal crown diameters were measured from dental casts of the permanent teeth of 198 Jordanians (86 males and 112 females), aged 13.4-19.1 years. The differences in the crown diameters between the right- and left-hand sides of the dental arch were not significant, suggesting that either right- or left-side measurements could be taken to represent the tooth size of the study population. Males had significantly larger teeth than females, ranging from p < 0.05 for the incisors to p < 0.001 for the first molars. In both sexes, the maxillary lateral incisors showed the greatest variability [coefficient of variation (CV) 8.8%] and the first molar the least (CV 5.8%) in mesiodistal diameter. Canines displayed greater sexual dimorphism in crown size than any other tooth class. The cumulative tooth widths of males exceeded those of females by a sum of 3.1 mm in the maxilla and 3.6 mm in the mandible. These differences were statistically significant (p < 0.01). Comparisons of the mesiodistal crown diameters between population groups showed that Jordanians have tooth sizes close to those of Iraqis, but significantly larger than those of Yemenite-Jews, Caucasians and Chinese.
Influence of substrate, shape, and thickness on microtensile specimens' structural integrity and their measured bond strengths.
Department of Dental Materials, School of Dentistry, University of Siena, Viale Bracci, Siena, Italy. email@example.com
OBJECTIVES To verify whether substrate, shape, or thickness of microtensile specimens have a significant influence on their measured bond strength. METHODS Sixty-four extracted molars provided microtensile specimens, which were prepared on enamel and dentin, in different shapes and thicknesses. The teeth were randomly divided into 16 groups (n = 4). Groups 1-8 included hourglass-shaped specimens. In Groups 1-4 specimens were prepared from enamel and in a thickness at the bonding interface of 0.5 mm x 0.5 mm, 1 mm x 1 mm, 1.5 mm x 1.5 mm, and 2 mm x 2 mm, respectively. In these same thicknesses, hourglasses were trimmed in Groups 5-8, but the specimens were prepared from dentin. Groups 9-16 included specimens obtained following the non-trimming technique. Groups 9-12 provided enamel sticks in the four evaluated thicknesses. In these same thicknesses and shape but from dentin were cut the specimens of Groups 13-16. Two specimens from each group were viewed using a scanning electron microscope. On the other ones, microtensile bond strength was measured and the values were statistically analyzed. RESULTS Substrate, shape, and thickness of the specimens had a significant effect on their recorded bond strength (p < 0.05). Higher bond strength values were recorded by dentin versus enamel specimens and by sticks versus hourglasses. Also, bond strength decreased as specimen thickness increased. SEM analysis revealed that the trimmed specimens, especially if from enamel, often exhibited lines of fracture in the area of action of the bur. SIGNIFICANCE It seems advisable to avoid the trimming action particularly on enamel specimens. If the hourglass shape is preferred, the cross-sectional area should not exceed 1 mm x 1 mm.
Oral Biology, Indiana University School of Dentistry, Indianapolis 46202-5782, USA. firstname.lastname@example.org
OBJECTIVE The number of older patients requiring restorative treatment are likely to increase due to improvements in oral health and increased longevity. However, aging odontometric data are lacking. The aim of this study was to determine possible changes in pulp cell density, pulp area, and dentinal thickness with age. STUDY DESIGN Incisors (50), canines (39), premolars (51), and molars (7) extracted from 60 patients aged between 10 and 59 years, were analyzed histomorphometrically for cell density (odontoblasts, subodontoblasts, and pulp core fibroblasts) and dentinal thickness. RESULTS With increasing patient age, in both crown and root aspects of teeth, dentinal thickness increased (P <.001), while the density of odontoblasts (P <.001), subodontoblasts (P = 0.001), and pulp fibroblasts (crown, P <.011; root, P =.0015) decreased. The degree of age-related changes in teeth appeared to be asymmetrical, with decreases in the root being greater than in the crown. At all ages pulp cell densities, including odontoblasts, within the crown were greater than in the root (P <.001), even though the calculated rate of dentinal deposition was greatest in the root. CONCLUSION Decreases in pulp cell density may reduce pulp repair activity after restorative treatments, although increases in dentinal thickness may aid pulp protection. An understanding of these age-related changes will influence the provision of restorative and endodontic care and benefit older patients.