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The bucco-lingual and mesio-distal convergence angles in vital and rootfilled teeth prepared for complete crowns were measured microscopically on 190 stone dies. In vital teeth the mean convergence angles varied between approximately 19 and 27 degrees. In rootfilled teeth the mean angles varied between 12 and 37.
It has been argued that the prolonged retention of cusps in the human dentition is a relatively recent aberration due to the negligible abrasiveness of modern diets and that to achieve maximum efficiency and freedom from disease human teeth should be worn down as they are in many herbivorous mammals. Here we critically review the evidence that has been put forward to support this idea and, after discussing the design of occlusal surfaces in relation to the wide variety of mammalian diets, we conclude that cusps are adaptations for breaking food with specific physical properties.
The resistance to wear of composite resins is an important feature of their suitability for use as posterior restorative materials. The in vivo clinical evaluation of new materials requires an accurate and reliable method of assessing tooth wear. The purpose of this study was too investigate the possibility of using a new stereometric measuring instrument for this purpose. Tooth wear was experimentally produced on a lead cast. The volume and average depth lost was measured using a reflex microscope. A gravimetric method of wear measurement was used as a control. When the results of both methods were compared it was found that the mean difference in depth of wear measured between the two methods was 10 microns. The reflex microscope appears to be ideally suited to making objective comparisons between the wear characteristics of composite resins.
Taurodontism and a reduced tooth length are reported to occur in patients with oligondontia. The aim of this study was to evaluate the occurrence of these factors in Dutch patients with oligodontia. Panoramic radiographs of 117 patients with oligodontia and 91 controls were collected. Taurodontism of the mandibular first molars was recorded and the length of cuspids, bicuspids and first molars of the mandible were measured. In patients with oligodontia 28.9% showed taurodontism of one or two mandibular first molars. The prevalence of taurodontism in normal Dutch subjects was 9.9%. No significant differences were found between the two sexes in both groups. Neither was there a significant difference in the unilateral and bilateral occurrence of taurodontism. The present findings supported the hypothesis that taurodontism may be the result of an ectodermal defect and a manifestation of developmental instability in patients with oligodontia. The length of mandibular cuspids and first molars in females were significantly reduced. In males only the lower right first molar was significantly reduced. The reduced length of the teeth may also be the result of a defect in ectodermal cells. Both taurodontism and a reduced length are of importance considering dental therapy.
Molar crown preparations, as described in the literature, have standard forms dictated by the demands of retention, resistance and the physical properties of materials. Standard designs may not be appropriate for all patients because of ethnic variations in tooth shape, pulp size and dentine thickness. Accurate data on these features could assist clinicians to minimize the risk of accidental pulpal injury. The aim of this study was to compare the first molar crown and pulp dimensions between Asian (Chinese, Korean, Malay) and other ethnic groups, using measurements from the bitewing radiographs of 121 subjects. Comparisons revealed the following significantly different features of Asian first molars: larger total pulp areas in uppers (P < 0.0005); shorter crowns (P < 0.0005); narrower upper teeth at the cervix (P < 0.0005); wider pulps at the cervix of lowers (P < 0.02); more bulbous crowns (P < 0.0005 for uppers; P < 0.01 for lowers), and finally significantly thinner dentine interproximally at the cervix (P=0.001 for uppers; P=0.011 for lowers). Preparations with wide shoulders could pose hazards to the pulps in Asian subjects. This study emphasizes the value of bitewing films in assessing crown and pulp size and shape before making crown preparations. The experienced practitioner may intuitively include tooth and pulp morphology in treatment planning, but this appears not to be taught or documented in textbooks.
The shape of a patient's face is commonly used as a reference to select the shape of the maxillary central incisors in edentulous patients. The validity of this relationship has not been proved. The objective of this clinical study was to determine whether a relationship exists between maxillary central incisors and face shapes. Casts were made of the maxillas of 50 men and 50 women. A standardized digital photographic procedure was used to record frontal views of each subject's face and of the maxillary central incisors of the dental casts. The shapes of the maxillary central incisors were compared with the face forms. Shape matches were evaluated according to their Hausdorff distance (HDD). The function h(A,B) is called the directed HDD from shape A to shape B (this function is not a true distance). It reflects the distance of the point of shape A that is farthest from any point of shape B and vice versa. The similarity of both shapes is given as a non-negative number. The value 0.0 indicates that the figures are identical (after scaling and shifting). Higher values indicate that shapes differ more substantially. Significant differences on the 5% level were calculated using the non-parametric Mann-Whitney U and Kruskal-Wallis tests. The face shape from the chin margin to the eyebrow line (superior edges of the eyebrows) produced a better match than the one from the chin to the hairline (P < 0.0001). On average, the maxillary central incisors displayed a variability (0.084 +/- 0.028) that was higher by a factor of 1.9 than the face shapes (chin margin to the eyebrow line, 0.045 +/- 0.015). In the interindividual comparison, the shapes of the maxillary central incisors of women displayed a significantly smaller HDD than the ones of the men (P < 0.0001).
There is limited knowledge concerning tooth and gingival display in the maxillary premolar area during smiling. The purpose of this study was to investigate maxillary premolar and associated gingival display during smiling, and to reveal possible differences related to gender and age. The study consisted of 90 males and 113 females (mean age 38 years, s.d. = 13.83) receiving regular dental care. Two pictures of each subject, one with lips in maximum smile, and the other a retracted frontal view, were made. Clinical crown length, tooth and gingival display were measured for the left maxillary premolars. Central incisors and canines were used as controls. anova with Bonferroni post hoc multiple comparisons tests was used to assess any statistically significant impact of gender and age on tooth and gingival display, and determine differences among gender and age groups (at 5% significance level). Premolars were partially visible in more than 80% of the smiles, and displayed more than 65% of their clinical crown length during smiling. The least display (P < 0.001) was recorded for first and the greatest for second premolars. Tooth display was greater in females, but statistically significant only in central incisors (P < 0.05). No significant differences were revealed between age subgroups. Gingival display was greater for premolars compared with both central incisors (P < 0.001) and canines (P < 0.05). Displayed gingiva was found in first and second premolars in 44 and 49% of subjects, respectively. More gingival display was recorded in females and in younger subjects.
Feeding specializations such as herbivory are an often cited example of convergent and adaptive evolution. However, some groups such as lizards appear constrained in the evolution of morphological specializations associated with specialized diets. Here we examine whether the inclusion of plant matter into the diet of omnivorous lacertid lizards has resulted in morphological specializations and whether these specializations reflect biomechanical compromises as expected if omnivores are constrained by functional trade-offs. We examined external head shape, skull shape, tooth structure, intestinal tract length and bite performance as previous studies have suggested correlations between the inclusion of plants into the diet and these traits. Our data show that omnivorous lacertid lizards possess modifications of these traits that allow them to successfully exploit plant material as a food source. Conversely, few indications of a compromise phenotype could be detected, suggesting that the evolution towards herbivory is only mildly constrained by functional trade-offs.
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Measurements of permanent tooth sizes in four XX-males showed their teeth to be smaller than those of male controls and similar in size to those of female controls. The teeth of the XX-males were smaller than those of their first-degree male relatives and of the same size as those of three of their mothers. The teeth of three fathers of XX-males were similar in size to control males and the teeth of three mothers of XX-males were similar in size to control females. The detailed knowledge that exists regarding the sequence and timing of tooth crown development allows the following implications to be made from our results. Growth retardation in XX-males is of primary genetic origin and is due to the absence of the gene(s) normally located on the Y-chromosome. Growth retardation, compared to normal males, is apparent and final three years after birth, conceivably begins after 2--3 months of foetal life and persists during childhood. It is unlikely that XX-males have had a Y-chromosome at any stage. If maleness is caused by a recessively inherited translocation or a mutational acquisition of the testis-determining gene(s), the genes influencing growth are not involved in either mechanism.
Permanent and deciduous tooth crown sizes in two males with deletions of the long arm of the Y chromosome and their first-degree relatives were examined. The first proband with a deletion in the proximal part of Yq11 showed definitely smaller teeth than his father or population control males. The second proband with a deletion in the distal part of Yq11 showed large or normal sized teeth compared to his brother or population control males. These data support the results of earlier studies indicating a promoting effect of the Y chromosome on tooth growth, and suggest that the location of the growth-promoting gene(s) is in Yq11. It is postulated that statural growth is affected by the same gene(s).
PURPOSE: This study focuses on the curvature and inclination of the lingual surfaces of the maxillary anterior teeth from the transition point on the cingulum to the incisal edge. MATERIALS AND METHODS: On 32 sets of mounted casts, 768 measurements were made of the curvature of the lingual surfaces utilizing radius gauges. The inclination of the lingual surface relative to the occlusal plane was recorded. The relationship of the incisal edge of the mandibular teeth to the transition point on the cingulum of the maxillary teeth was determined. Centric occlusion contact was noted on each tooth. RESULTS: Significant differences were found between the measured areas of any one tooth and between the types of teeth. The average radius ranged from 20.5 mm on the mesial ridge of the canine to 5.3 mm in the fossa of the central. The average inclination of the lingual surfaces was 46 degrees. In centric occlusion, 97% of the canines and 59% of the centrals and laterals were in contact with the opposing teeth. These contacts occurred 2.8 mm incisal to the transition point. The centrals contracted two opposing teeth (45%), and canines contacted one opposing tooth (53%). CONCLUSIONS: The function and curvature of the incisor teeth vary considerably from those of the canines. Overcontouring the lingual surfaces of the maxillary incisors to gain contact is not normal and may be detrimental.
PURPOSE: Selecting artificial teeth for edentulous patients is difficult when pre-extraction records are not available. Various guidelines have been suggested for determining the width of the maxillary anterior denture teeth. This study was undertaken to evaluate the use of the nasal width as a guide for the selection of proper width maxillary anterior denture teeth in four racial groups of the Brazilian population. MATERIALS AND METHODS: One hundred and sixty subjects (40 Whites, 40 Mulattos, 40 Blacks, and 40 Asians) were selected. Using a sliding caliper, the nasal width and the intercanine distance were measured. The Pearson product-moment correlation coefficient was used to determine the relationship between the above measurements. A prediction was made of the percentage of subjects of the White, Mulatto, Black, and Asian populations in which the selection error due to the clinical application of the method of the nasal width would be within 0 to 2 mm, within 2 to 4 mm, and greater than 4 mm. RESULTS: The four racial groups showed a weak correlation between the intercanine distance and the nasal width. In 39.7% of the White, 55.7% of the Mulatto, 81.9% of the Black, and 48.2% of the Asian populations, errors greater than 4 mm would be present with the use of the nasal width. CONCLUSIONS: The correlation found between the intercanine distance and the nasal width was not high enough to be used as a predictive factor. The relationship between natural tooth width and artificial tooth width as predicted by the nasal width showed that the nasal width method is not accurate for all the studied groups.
OBJECTIVES: The widespread use and broad acceptance of osseointegrated dental implants as a means of retaining and supporting mandibular overdentures provide potentially stable three-dimensional reference structures, which have been used to examine the morphological changes of the surface contours of the mandibular ridges distal to implants. Unlike traditional methods that tended to measure changes in ridge morphology and quantity radiographically, this prospective study investigated the changes in the sagittal surface contours of the posterior residual ridges over a 1-year period by an alternative, non-radiographic method using serial casts of residual ridges of a group of patients. MATERIAL AND METHODS: The residual ridges of the serial casts produced were examined using a profiling apparatus and computer software programs that allowed the orientation, digitised recording and measurement of the sagittal surface contours of the posterior residual ridges of mandibular casts in terms of area (cm(2)). RESULTS: Statistical analysis revealed that the detected reductive changes in the surface contour of the posterior residual ridges following the wearing of an implant-retained mandibular overdenture over a 1-year period were highly significant (P<0.001). CONCLUSION: It is concluded that the methodology presented in this study can be used reliably as an alternative to radiographical examination for detecting changes that occur in the distal residual alveolar ridges of the implant containing edentulous mandible when implant-retained overdentures are used. Thus, the method presented may be used to contribute to a reduced exposure to ionising radiation for patients wearing implant-retained overdentures.
The purpose of the study was to examine the relationship between spacing and dental health in 15-year-old adolescents. The whole sample consisted of 156 subjects. Out of them, 74 females and 73 males with 6 anterior teeth made up the study group for examination of the upper jaw. 75 females and 75 males had 6 anterior teeth in the lower jaw and made up the study group for examination of the lower jaw. The Plaque Index (PlI) and the Gingival Index (GI) were recorded. Probing depths (PD) were measured as explained by Glavind & Løe. Filled surfaces (FS) were taken from the individual case sheets and controlled clinically. The spacing of the individuals was assessed by counting the number of proximal surfaces without visible contact with the adjacent proximal surfaces, on model casts. The sum of proximal surfaces without contact made up the Space Index (SpI) of the individual jaw. Parametric and non-parametric statistical methods were used to analyze the data. In both sexes and both jaws proximal surfaces without interdental contact had a more favourable periodontal condition than surfaces with contact. In the upper jaw of both sexes, proximal surfaces without interdental contact had a reduced number of filled surfaces compared to surfaces with contact. The linear relationship between SpI and FS was significant, i.e., an increased number of surfaces without contact was accompanied by a reduced number of filled surfaces. In the lower jaw, the differences between the SpI groups and the linear relationship between SpI and FS did not reach significance. In both sexes and both jaws, proximal surfaces without fillings had a more favourable periodontal state compared to surfaces with fillings. Indications are that the summation effect of the presence of interdental contact and the presence of fillings contributed to the differences in periodontal condition between surfaces with and without interdental contact.
The objective of the present study was to describe the topography of the furcation area of the maxillary and mandibular first molars. By using a photogrammetric method, the furcation areas of extracted teeth were plotted to obtain 3-dimensional contour maps. By comparing the individual 10 drawings of the maxillary and mandibular first molars, respectively, some morphological characteristics of the furcation areas could be described. Accordingly, the study showed the complexity of the furcation areas with presence of a number of small ridges, peaks and pits forming a mixture of convexities and concavities.
The measurement process of attachment loss has been criticized in recent years. Problems with clinical interpretation, precision of the measurement, and statistical manipulation of the obtained data, are some of the problems associated with the present methodology. The purpose of the present study was to propose an alternative measurement process which addresses some of the existing problems by estimating the lost attachment surface area (LAS) and the remaining attachment surface area (RAS) from a combination of clinical measurements. The results show that a linear combination of several sources of clinical information can be used to predict RAS and LAS. A diagnostic model for LAS (R2 = 81.5%) predicts the square root of LAS with information obtained from bucco-lingual attachment level measurements, the radiographic lost attachment area, the gingivitis index and the radiographic tooth length. This model increases the precision of the estimate of LAS by a factor of 1.86 when compared to the estimate of LAS using only attachment level measurements. A diagnostic model for RAS (R2 = 75.5%) predicts the square root of RAS with the information obtained from the remaining radiographic attachment area, the gingivitis index and the mobility index. Both linear inference models are constructed with measurements of anatomical landmarks to avoid the discrepancy between anatomical and clinical measurements in the produced estimates. It is concluded that modeling of periodontal data provides a simple, inexpensive, and precise diagnostic tool for predicting the lost and the remaining periodontal attachment of single-rooted teeth. Measurement processes of this type could provide a convincing basis for the evaluation of clinical decisions and research questions.