External apical root resorption and vectors of orthodontic tooth movement.

INTRODUCTION: External apical root resorption is nearly ubiquitous in people treated orthodontically. This study predicted the extent of external apical root resorption by the vector of the incisor movement. METHODS: Cone-beam computed tomography scans of 93 white American adolescents (45 boys, 48 girls) with a Class I malocclusion who received comprehensive orthodontics were analyzed. Half were treated with 4 first-premolar extractions, and the others were treated without extractions. An x, y, z coordinate system was registered on the maxillae, superimposing on foramina, to quantify vectors of maxillary incisor movements. Multiple linear regression identified significant predictors of resorption for each incisor. RESULTS: Strongly predictive models (R2 = 77%-86%) were obtained. All directions of incisor movement tested (anteroposterior, mediolateral, craniocaudal, torquing) increased the risk of resorption in a dose-response fashion. Intrusion was most damaging. The patient's sex, age, and duration of treatment were not predictive. CONCLUSIONS: Root resorption is a very frequent consequence of tooth movement, especially intrusion and torquing, though no direction is harmless, and most corrections occur in combination. Incisor apical resorption was significantly greater in the extraction sample (ca 0.5 mm).

A Retrospective Mixed Longitudinal Study of Tooth Formation in Children With Clefts.

OBJECTIVE: To test for systematic age changes in cleft children based on dental age. DESIGN: Retrospective case-control longitudinal study. SETTING: One orthodontic solo practice. PATIENTS: Nonsyndromic, complete cleft lip and palateCLP cases, either unilateral or bilateral (102 children; 370 radiographs), between 4 and 16 years of age. INTERVENTIONS: Children were treated with a team approach, but only orthodontic radiographs were studied. MAIN OUTCOME MEASURE: The principal outcome measure was dental age of the cleft cases compared to a sex-specific sample of phenotypically normal children (1107 children), from the same geographical region. Multiple panoramic radiographs taken during the course of orthodontic treatment were examined to track patterns of dental age as children matured. Analysis used linear mixed models primarily testing for sex, cleft type (unilateral, bilateral), and hypodontia differences. Initial expectation was that cleft children would exhibit delayed dental ages from postnatal stressors and would become more deviant with maturity. RESULTS: In childhood (4-6 years), both sexes were significantly delayed (P < .001), but dental age normalized around 8 to 10 years. Boys experienced faster maturation thereafter than girls (P < .001). Only trivial differences occurred between unilateral CLP and bilateral CLP samples.Hypodontia further depressed maturation rates (P < .001). Dental age improved in a decidedly curvilinear fashion (P < .001), with greater change at earlier ages. CONCLUSIONS: This report agrees with other contemporary studies, showing childhood catch-up. Older studies observed that clefting caused significant delays that worsened with growth. This potential "seachange" suggests better recovery and quicker normalization of children with clefts, perhaps due to improved management.

Evidence favoring a secular reduction in mandibular leeway space.

OBJECTIVE: Researchers have documented secular trends in tooth size among recent generations. This study was a test for a change in mandibular leeway space. MATERIALS AND METHODS: Dental casts from participants in the Denver Growth Study (23 boys, 22 girls; born in the 1930s) were compared with casts from a contemporary series of orthodontic patients (23 boys, 22 girls; born in the 1990s). All were phenotypically normal, healthy American whites. RESULTS: Analysis of variance (accounting for sex) showed that the cumulative mandibular primary canine plus first and second primary molar size (c + m1 + m2) was slightly larger in the recent cohort (23.53 mm earlier vs 23.83 mm recent cohort; mean difference: 0.30 mm; P = .009), principally due to larger second primary molars (m2) in the recent cohort. In turn, the sum of the permanent canine and two premolars (C + P1 + P2) was significantly larger in the recent cohort (21.08 mm earlier vs 21.80 mm recent cohort; mean difference: 0.72 mm; P = .002). Larger teeth in the contemporary series produced a mean leeway space per quadrant of 2.03 mm versus 2.45 mm in the earlier cohort-a clinically and statistically significant reduction (P = .030). Some tooth types (primary second molar and permanent canine) were significantly larger in boys than in girls, but the sex difference in leeway space was not statistically significant. CONCLUSION: Results suggest that mandibular leeway space is decreasing in 21st century American whites and may present a challenge to orthodontists in managing tooth size-arch length discrepancies.

Comparison of Amount of Primary Tooth Reduction Required for Anterior and Posterior Zirconia and Stainless Steel Crowns.

PURPOSE: To determine if aggressiveness of primary tooth preparation varied among different brands of zirconia and stainless steel (SSC) crowns. METHODS: One hundred primary typodont teeth were divided into five groups (10 posterior and 10 anterior) and assigned to: Cheng Crowns (CC); EZ Pedo (EZP); Kinder Krowns (KKZ); NuSmile (NSZ); and SSC. Teeth were prepared, and assigned crowns were fitted. Teeth were weighed prior to and after preparation. Weight changes served as a surrogate measure of tooth reduction. RESULTS: Analysis of variance showed a significant difference in tooth reduction among brand/type for both the anterior and posterior. Tukey's honest significant difference test (HSD), when applied to anterior data, revealed that SSCs required significantly less tooth removal compared to the composite of the four zirconia brands, which showed no significant difference among them. Tukey's HSD test, applied to posterior data, revealed that CC required significantly greater removal of crown structure, while EZP, KKZ, and NSZ were statistically equivalent, and SSCs required significantly less removal. CONCLUSIONS: Zirconia crowns required more tooth reduction than stainless steel crowns for primary anterior and posterior teeth. Tooth reduction for anterior zirconia crowns was equivalent among brands. For posterior teeth, reduction for three brands (EZ Pedo, Kinder Krowns, NuSmile) did not differ, while Cheng Crowns required more reduction.

Compliance by state-subsidized and self-pay orthodontic patients.

INTRODUCTION: Medicaid is a needs-based program in the United States that subsidizes medical and dental care for minors. The purpose of this study was to test for compliance differences between self-pay and Medicaid-supported patients. METHODS: Medicaid patient records (n = 88) were perused retrospectively for characteristics that distract from an orthodontist's workflow (missed appointments, broken brackets, treatment duration, and so on) and compared with a sample (n = 145) of self-pay patients from the same teaching clinic. Differences in treatment difficulty were adjusted by subject selection and statistically (analysis of covariance). RESULTS: Medicaid patients were younger (mean age, 14.1 vs 14.9 years) and significantly more likely to be dismissed from treatment (19% vs 4%), generally for noncompliance. Broken brackets and missed appointments were more common in the Medicaid sample. There was no difference in the number of appointments in those completing treatment, but treatment duration was significantly longer for the Medicaid patients who completed treatment (29 vs 25 months). Commute distance and estimated driving time were significantly shorter for the Medicaid-assisted group. CONCLUSIONS: Greater difficulty in managing Medicaid patients may partly explain why they are underserved. Prospective studies are needed to clarify the causes of the differences.

Relapse revisited--again.

INTRODUCTION: Long-term changes in the dentitions of orthodontic patients have been studied. However, most studies in the literature report findings after only a few years posttreatment. In this study, we examined records an average of 24 years after active treatment. The purpose was to answer 2 questions: (1) does irregularity increase with time after treatment, and (2) how much relapse can be expected if a conservatively treated sample is recalled 2.5 decades after active treatment? METHODS: The sample consisted of dental casts of 52 women who were treated in the mid-1970s to the early 1980s with 0.022 × 0.028-in standard edgewise appliances. Each was given a maxillary Hawley retainer and either a mandibular Hawley or a banded canine-to-canine retainer at debanding. Retention lasted 24 to 32 months. The same practitioner treated all the patients. The sample is one of convenience; specifically, inclusion depended only on each patient's willingness to return for a recall examination. Records were collected at 3 examinations for each patient: start of treatment, end of the active phase of treatment, and long-term retention recall. The long-term maxillary and mandibular casts were measured and occluded in maximum intercuspation. Variables were measured, including incisor overjet and overbite, buccal segment relationship of the first molars and canines, and incisor irregularity in each arch. Variables were measured on the casts with digital readout sliding calipers precise to 0.001 mm. RESULTS: Mandibular incisor irregularity at recall was less than 3.5 mm in 77% of the patients examined. Correction of the maxillary incisor irregularity remained relatively stable over the time interval studied. Buccal segment Class II correction remained stable at the recall examination. CONCLUSIONS: Orthodontic treatment can yield reasonably good long-term stability in both occlusal correction and tooth alignment.

Using LOINC to link 10 terminology standards to one unified standard in a specialized domain.

Despite the existence of multiple standards for the coding of biomedical data and the known benefits of doing so, there remain a myriad of biomedical information domain spaces that are essentially un-coded and unstandardized. Perhaps a worse situation is when the same or similar information in a given domain is coded to a variety of different standards. Such is the case with cephalometrics - standardized measurements of angles and distances between specified landmarks on X-ray film used for orthodontic treatment planning and a variety of research applications. We describe how we unified the existing cephalometric definitions from 10 existing cephalometric standards to one unifying terminology set using an existing standard (LOINC). Using our example of an open and web-based orthodontic case file system, we describe how this work benefited our project and discuss how adopting or expanding established standards can benefit other similar projects in specialized domains.

Sex differences in the uptake of orthodontic services among adolescents in the United States.

INTRODUCTION: The purpose of this study was to test whether girls are treated orthodontically for milder occlusal issues than are boys, thus accounting for the greater uptake of orthodontic services among girls compared with boys. METHODS: The dental aesthetic index (DAI) was used to score the severity of esthetic occlusal issues in 357 white adolescents. Half of the subjects were from private practices; the others were from a university specialty clinic. RESULTS: Average DAI scores were statistically significantly lower (milder) in girls than boys in both venues; this confirms the assumption that the actual uptake of services is greater in girls because of heightened concern for their esthetic occlusal issues. Average DAI scores predictably were higher in the teaching setting because of selection for more complex cases, but the sex difference was still evident statistically. There was no association between DAI score and age at the start of treatment among these adolescents. Spacing and incisor irregularity showed the greatest sex differences among the DAI variables, possibly because girls are more attuned to these esthetic issues. CONCLUSIONS: These results complement studies that have recorded adolescents' perceptions of orthodontic need. The actual uptake of orthodontic treatment is greater in girls because they (and their parents) seek treatment for milder occlusal issues.

Inter-observer agreement on subjects' race and race-informative characteristics.

Health and socioeconomic disparities tend to be experienced along racial and ethnic lines, but investigators are not sure how individuals are assigned to groups, or how consistent this process is. To address these issues, 1,919 orthodontic patient records were examined by at least two observers who estimated each individual's race and the characteristics that influenced each estimate. Agreement regarding race is high for African and European Americans, but not as high for Asian, Hispanic, and Native Americans. The indicator observers most often agreed upon as important in estimating group membership is name, especially for Asian and Hispanic Americans. The observers, who were almost all European American, most often agreed that skin color is an important indicator of race only when they also agreed the subject was European American. This suggests that in a diverse community, light skin color is associated with a particular group, while a range of darker shades can be associated with members of any other group. This research supports comparable studies showing that race estimations in medical records are likely reliable for African and European Americans, but are less so for other groups. Further, these results show that skin color is not consistently the primary indicator of an individual's race, but that other characteristics such as facial features add significant information.

Sex differences in esthetic treatment needs in American black and white adolescent orthodontic patients.

OBJECTIVE: To test whether the severity of malocclusions in adolescents who actually entered orthodontic treatment is different between the sexes, as this might explain the preponderance of girls in orthodontic practices. MATERIALS AND METHODS: Severity was gauged with the 10-grade esthetic component of the Index of Orthodontic Treatment Need (IOTN) scored on the pretreatment intraoral photographs (n = 562) in a university-based specialty program. The samples of American White (n = 401) and American Black (n = 161) adolescents were free of craniofacial defects. Nonparametric statistics were used for analysis. RESULTS: There is a significant sex difference in the IOTN in White teenagers due to milder, more esthetic cases among the girls. No sex difference occurs in the sample of Blacks, with both sexes having IOTN scores on a par with White males. The severity of malocclusion is independent of the age at start of treatment (within range of 12 to 19 years). CONCLUSIONS: Greater subjective self-perceptions of occlusal issues seem to account for the preponderance of White girls in the patient pool, though why the sex difference is not evident in American Blacks is complex. We speculate that sex differences are larger in private practices, since there are fewer selection criteria for entering treatment.

Bilateral asymmetry of tooth formation is elevated in children with simple hypodontia.

OBJECTIVE: Tooth formation normally progresses symmetrically between sides; the goal in this study was to test the clinical impression that left-right asymmetry in tooth formation is elevated in children with simple hypodontia. MATERIALS AND METHODS: Data from panoramic X-rays of American white children (5-14 years of age) with simple hypodontia (n=158) were compared to a comparable group from the same practises with all teeth present (n=206). Children with hypodontia were otherwise phenotypically normal, with no cleft or recognized syndrome. Crown-root formation of each tooth (ignoring third molars) was scored using an 11-grade scheme. Analysis relied on chi-square goodness-of-fit tests and odds ratios. RESULTS: Hypodontia typically occurs unilaterally; it is more common in girls than boys; and it most frequently affects second premolars (omitting third molars). No evidence of a side preference was found as regards absence of the tooth or tooth formation. Tooth formation was decidedly more frequently asymmetric in those with hypodontia, though again the distribution by side was random in the sample. Summed over all tooth types, asymmetric formation occurred in 18.6% of cases with hypodontia compared to 11.9% in controls, and this is significant by chi-square (P=0.03), with an odds ratio of 1.43 (CL: 1.02, 2.04). All tooth types exhibit elevated developmental asymmetry in the hypodontic sample despite only one or a few teeth being agenic. CONCLUSIONS: Increased asymmetry suggests a breakdown in the rigour of developmental timing in cases with simple hypodontia. In concert with increased frequencies of other growth issues in such cases, such as side differences in size and morphology, hypodontia is best viewed as a symptom of an anatomically broad relaxation of developmental canalization between homologous structures, not an isolated dental feature.

Influence of tooth crown size on malocclusion.

INTRODUCTION: Malocclusion is an increasingly common, multifactorial problem. The most prevalent malocclusion results from excess tooth size compared with the size of the supporting bone; this creates a tooth-size arch-size discrepancy. Although the causes of malocclusion are obscure in most instances, a contributing factor appears to be tooth size. The goal of this study was to test whether the dimensions of the crowns of the permanent teeth differ in young men with naturally good occlusions compared with those who required orthodontic treatment. METHODS: Tooth crown dimensions (mesiodistal and buccolingual) were measured in 2 samples of American white men. One group (n = 42) had naturally good occlusion; the other group (n = 90) required orthodontic treatment to correct tooth-size arch-size discrepancy. RESULTS: The means of 23 of the 24 tooth crown dimensions-involving the 14 tooth types (central incisor through first molar) in both arches-were significantly larger in subjects with malocclusions than in those with good occlusions. Multivariable analysis showed that mesiodistal size of the maxillary lateral incisor was the most significant difference between the 2 samples, but this might reflect the composition of the sample (maxillary lateral incisor size is notoriously variable in white men). CONCLUSIONS: Tooth size is not necessarily the foremost cause of malocclusion in a patient, but it should be evaluated.

Defining new dental phenotypes using 3-D image analysis to enhance discrimination and insights into biological processes.

AIMS: In studying aetiological interactions of genetic, epigenetic and environmental factors in normal and abnormal developments of the dentition, methods of measurement have often been limited to maximum mesio-distal and bucco-lingual crown diameters, obtained with hand-held calipers. While this approach has led to many important findings, there are potentially many other informative measurements that can be made to describe dental crown morphology. Advances in digital imaging and computer technology now offer the opportunity to define and measure new dental phenotypes in 3-D that have the potential to provide better anatomical discrimination and clearer insights into the underlying biological processes in dental development. Over recent years, image analysis in 2-D has proved to be a valuable addition to hand-measurement methods but a reliable and rapid 3-D method would increase greatly the morphological information obtainable from natural teeth and dental models. Additional measurements such as crown heights, surface contours, actual surface perimeters and areas, and tooth volumes would maximise our ability to discriminate between samples and to explore more deeply genetic and environmental contributions to observed variation. The research objectives were to investigate the limitations of existing methodologies and to develop and validate new methods for obtaining true 3-D measurements, including curvatures and volumes, in order to enhance discrimination to allow increased differentiation in studies of dental morphology and development. The validity of a new methodology for the 3-D measurement of teeth is compared against an established 2-D system. The intra- and inter-observer reliability of some additional measurements, made possible with a 3-D approach, are also tested. METHODS AND RESULTS: From each of 20 study models, the permanent upper right lateral and upper left central incisors were separated and imaged independently by two operators using 2-D image analysis and a 3-D image analysis system. The mesio-distal (MD), labio-lingual (LL) and inciso-gingival (IG) dimensions were recorded using our 2-D system and the same projected variables were also recorded using a newly developed 3-D system for comparison. Values of Pearson's correlation coefficient between measurements obtained using the two techniques were significant at the 0.01 probability level for variables mesio-distal and incisal-gingival with labio-lingual significant at the 0.05 level for the upper left side only, confirming their comparability. For both 2-D and 3-D systems the intra- and inter-operator reliability was substantial or excellent for variables mesio-distal, labio-lingual, incisal-gingival actual and projected and actual surface area. The reliability was good for inter-operator reliability measurement of the labio-lingual dimension using 3-D. CONCLUSIONS: We have developed a new 3-D laser scanning system that enables additional dental phenotypes to be defined. It has been validated against an established 2-D system and shown to provide measurements with excellent reliability, both within and between operators. This new approach provides exciting possibilities for exploring normal and abnormal variations in dental morphology and development applicable to research on genetic and environmental factors.

Morphogenetic fields within the human dentition: a new, clinically relevant synthesis of an old concept.

This paper reviews the concept of morphogenetic fields within the dentition that was first proposed by Butler (Butler PM. Studies of the mammalian dentition. Differentiation of the post-canine dentition. Proc Zool Soc Lond B 1939;109:1-36), then adapted for the human dentition by Dahlberg (Dahlberg AA. The changing dentition of man. J Am Dent Assoc 1945;32:676-90; Dahlberg AA. The dentition of the American Indian. In: Laughlin WS, editor. The Physical Anthropology of the American Indian. New York: Viking Fund Inc.; 1951. p. 138-76). The clone theory of dental development, proposed by Osborn (Osborn JW. Morphogenetic gradients: fields versus clones. In: Butler PM, Joysey KA, editors Development, function and evolution of teeth. London: Academic Press, 1978. p. 171-201), is then considered before these two important concepts are interpreted in the light of recent findings from molecular, cellular, genetic and theoretical and anthropological investigation. Sharpe (Sharpe PT. Homeobox genes and orofacial development. Connect Tissue Res 1995;32:17-25) put forward the concept of an odontogenic homeobox code to explain how different tooth classes are initiated in different parts of the oral cavity in response to molecular cues and the expression of specific groups of homeobox genes. Recently, Mitsiadis and Smith (Mitsiadis TA, Smith MM. How do genes make teeth to order through development? J Exp Zool (Mol Dev Evol) 2006; 306B:177-82.) proposed that the field, clone and homeobox code models could all be incorporated into a single model to explain dental patterning. We agree that these three models should be viewed as complementary rather than contradictory and propose that this unifying view can be extended into the clinical setting using findings on dental patterning in individuals with missing and extra teeth. The proposals are compatible with the unifying aetiological model developed by Brook (Brook AH. A unifying aetiological explanation for anomalies of tooth number and size. Archs Oral Biol 1984;29:373-78) based on human epidemiological and clinical findings. Indeed, this new synthesis can provide a sound foundation for clinical diagnosis, counselling and management of patients with various anomalies of dental development as well as suggesting hypotheses for future studies.

Accounting for measurement error: a critical but often overlooked process.

AIMS: Due to instrument imprecision and human inconsistencies, measurements are not free of error. Technical error of measurement (TEM) is the variability encountered between dimensions when the same specimens are measured at multiple sessions. A goal of a data collection regimen is to minimise TEM. The few studies that actually quantify TEM, regardless of discipline, report that it is substantial and can affect results and inferences. This paper reviews some statistical approaches for identifying and controlling TEM. Statistically, TEM is part of the residual ('unexplained') variance in a statistical test, so accounting for TEM, which requires repeated measurements, enhances the chances of finding a statistically significant difference if one exists. METHODS: The aim of this paper was to review and discuss common statistical designs relating to types of error and statistical approaches to error accountability. This paper addresses issues of landmark location, validity, technical and systematic error, analysis of variance, scaled measures and correlation coefficients in order to guide the reader towards correct identification of true experimental differences. CONCLUSIONS: Researchers commonly infer characteristics about populations from comparatively restricted study samples. Most inferences are statistical and, aside from concerns about adequate accounting for known sources of variation with the research design, an important source of variability is measurement error. Variability in locating landmarks that define variables is obvious in odontometrics, cephalometrics and anthropometry, but the same concerns about measurement accuracy and precision extend to all disciplines. With increasing accessibility to computer-assisted methods of data collection, the ease of incorporating repeated measures into statistical designs has improved. Accounting for this technical source of variation increases the chance of finding biologically true differences when they exist.

Hypodontia: an epidemiologic study of American black and white people.

INTRODUCTION: There are numerous epidemiologic studies of hypodontia, but most focus on white populations that, because of small teeth and slow development, might not represent the status of other peoples. The purpose of this study was to contrast the distributions of hypodontia in an adolescent sample of American blacks (n=600) with a comparable sample of whites (n=1100). METHODS: Panoramic radiographs of 1700 unrelated adolescents between 12 and 18 years were scrutinized for hypodontia. Those with syndromes and major genes contributing to congenital absence were omitted. RESULTS: The prevalence of people with missing teeth is significantly lower in blacks (11%) than in whites (27%), as is the number of missing teeth per person. When all tooth types were combined for a summary value, the frequency of missing teeth in whites (1.5% of the expected 32 teeth per person) was significantly higher than in blacks (0.6%), with an odds ratio of 2.52 (95% confidence limits [CL]: 2.07, 3.08). Differences between black and white people are disproportionately large where hypodontia is most common, notably in 2 tooth types: (1) the difference is statistically significant for third molars, with the odds ratio 3.18 higher in whites (CL: 2.43, 4.17) for all quadrants combined, and (2) for second premolars (combining all quadrants), whites are 1.75 times more likely to exhibit congenital absence (CL: 1.06, 2.90). In contrast, significant sex differences were found only for the third molars (absence more common in females), and the sex differences were greater in whites than in blacks. CONCLUSIONS: Extrapolations from the literature, based largely of studies of white subjects, do not readily apply to American blacks or, potentially, to other racial groups.

An epidemiological study of hyperdontia in American blacks and whites.

OBJECTIVE: To test the null hypothesis that American blacks do not have a higher frequency of extra permanent teeth than whites. MATERIALS AND METHODS: Panoramic radiographs of adolescent orthodontic patients, either American whites (n = 1100) or American blacks (n = 600), were reviewed systematically. RESULTS: The frequencies of supernumerary incisors, premolars, and molars were each significantly more common in blacks. While incisors are the most common extra teeth in whites (and extra molars are least common), just the opposite ranking occurs in blacks. Overall, the odds ratio was 8.8 (95% confidence limits = 3.9, 20.0), confirming that American blacks are significantly more likely (almost 9 times more likely) to possess extra permanent teeth than American whites. CONCLUSIONS: The hypothesis is rejected. Both the frequencies and the patterns of extra permanent teeth are significantly different in blacks and whites, suggesting different frequencies of the relevant (but unidentified) factors governing the developmental mechanisms that result in hyperdontia.

Racial diferences in tooth crown size gradients within morphogenetic fields / Diferencias raciales en el gradiente del tamaño de la corona dental dentro de los campos morfogenéticos

Los dientes se arreglan en campos morfogenéticos, los cuales son ubicaciones anatómicas en los maxilares que regulan tipos de dientes, específicamente incisivos, caninos, premolares y molares en primates. Cada campo está compuesto por dos o tres dientes (salvo el canino aislado), y hay una gradiente de tamaño característica correspondiente a la direccionalidad dentro de cada campo, generalmente con el diente mesial siendo más grande y más estable que el diente distal, variable. El presente estudio se enfoca en las diferencias raciales en la inclinación de las gradientes mesiodistales del tamaño coronal. Grupos con gradientes “inclinadas” demuestran una reducción apreciable del tamaño desde el diente estable al variable, mientras que otros grupos, con gradientes “planas”, tienen dimensiones coronales más similares a través del campo. Esta encuesta de estudios publicados en todo el mundo (107 grupos) evalúa variación entre grupos (en vez de entre individuos) de las gradientes calculadas para los incisivos, premolares y molares en cada arcada. Los caucásicos suelen tener las gradientes más inclinadas; los indígenas de Australia las más planas. Las correlaciones entre las diferentes gradientes de los distintos tipos de diente son significativos estadísticamente, pero menores, lo cual sugiere que factores microevolucionarios han influido sobre las gradientes de los distintos grupos de maneras diferentes. De los siete grupos geográficos evaluados, los Amerindios son los más distintivos. Especulamos brevemente sobre la naturaleza del señalamiento molecular en el desarrollo que determina estas gradientes.

Teeth are arranged in morphogenetic fields, which are anatomical locations in the jaws that regulate tooth types, namely incisors, canines, premolars, and molars in primates. Each field is composed of two or three teeth (except for the isolated canine), and there is a characteristic size gradient corresponding to directionality within each field, generally with the mesial tooth being larger and more stable than the distal, variable tooth. Focus of the present study is on racial differences in the steepness of these mesial-distal crown size gradients. Groups with “steep” gradients have appreciable size reduction from the stable to the variable tooth, while other groups, with “shallow” gradients, have more similar crown dimensions across a field. This worldwide survey of published studies (107 groups) assessed intergroup (rather than inter-individual) variation in size gradients calculated for the incisors, premolars, and molars in each arcade. Caucasians tend to have the steepest gradients; aboriginal Australians tend to have the most shallow gradients. Correlations among the gradients of different tooth types are significant statistically, but modest, suggesting that microevolutionary factors have influenced the gradients of different groups differently. Of the seven geographic groupings evaluated, Amerindians are the most distinctive. We briefly speculate on the nature of the developmental molecular signaling that determines these gradients.

Proportional analysis of longitudinal craniofacial growth using modified mesh diagrams.

OBJECTIVE: To study the craniofacial changes of adolescents followed longitudinally with their heads oriented in natural head position. MATERIALS AND METHODS: Longitudinal cephalograms of adolescents (n=28) with normal occlusion, selected from among 900 candidates, were taken at 13 and again at 18 years of age. Modified elaborate mesh diagrams were developed defined by 90 anatomic landmarks and an additional 172 interpolated points for each cephalogram using a preset computer program. Detailed proportional and disproportional craniofacial changes were showed by both statistical and graphical methods. RESULTS: In females, most craniofacial regions exhibited growth that was proportionate to the mesh core rectangle reference on extracranial true vertical. In males, there was an upward, disproportional enhanced shift of the anterior cranial base and a downward enhanced shift of the mandibular symphysis and inferior border of the corpus. CONCLUSIONS: This elaborate mesh analysis, based on mesh core rectangle and referenced on estimated natural head position, provides a novel graphical as well as quantitative method of assessing craniofacial growth. From 13 to 18 years of age, two sexes with normal occlusion displayed different growth patterns referenced on estimated natural head position. In females, most craniofacial regions exhibited growth proportional to the mesh core rectangle. In males, there was an upward, enhanced shift of the anterior cranial base and a downward enhanced shift of the mandibular symphysis and inferior border of the corpus.

Bilateral asymmetry in the tooth relationships of orthodontic patients.

OBJECTIVE: To quantify the nature and extent of bilateral dentoalveolar asymmetries in routine adolescent orthodontic patients. MATERIALS AND METHODS: Eight left-right pairs of occlusal dimensions were measured from dental casts (n=211 subjects) with proportionate samples of class I, II, and III malocclusions. RESULTS: Directional asymmetry is a subtle, but pervasive feature of the dental arches, with systematically larger dimensions on the left side. Prior studies attribute this sidedness to compensations for hemispheric laterality. Patient's sex did not influence the magnitude of asymmetry, but patients with class II malocclusion exhibited significantly greater asymmetries, particularly in the anterior segment. Inspection suggests that this is attributable to the lack of coupling and guidance of the teeth between the jaws. There is a significant association between the severity of class II buccal-segment relationship and the extent of left-right asymmetries. CONCLUSION: Clinically, these lateralities need to be anticipated, particularly in class II malocclusions, and incorporated into the treatment plan.