Influence of patient age and sex on orthodontic treatment: evaluations of Begg lightwire, standard edgewise, and straightwire techniques.

The nature of the planned orthodontic correction--primarily skeletal or dental--ought to be influenced by the age and the sex of the patient. Jaw growth should contribute more in younger adolescents and faster-growing boys, and the correction should be primarily dental in patients with little growth potential. Influences of age and sex were studied in 154 Class II Division 1 young people between 10 and 18 years of age at the start of treatment. Variations among 3 orthodontic techniques, Begg lightwire, standard edgewise, and straightwire, were also examined. The Johnston method of cephalometric analysis was used to partition changes into their skeletal and dental components. Analysis of covariance was used to identify changes because of patient age, patient sex, and treatment technique. Technique differences were localized to 2 areas: (1) less root torquing in the Begg group that left the maxillary incisors more upright than in the other groups and (2) more mesial molar crown tipping in the straightwire group because of using preangulated brackets. The patient's age had the greatest influences on (1) translation and mesial crown tipping of the molars (both changes were larger in younger patients) and (2) mandibular growth, which was greatest in younger patients and declined linearly with age. Forward movement of the maxillary molars was greatest in young patients, but this was exceeded at all ages by mesial translation of the lower molars, thus providing a net improvement in molar relationship. Linear growth was greater in males for all facial dimensions, but the sex difference of consequence was the large forward growth of the mandible that contributed significantly to the sagittal correction in boys but not in girls. One would not expect the effects of age and sex to be large because there is so much individual variation in the malocclusions and tempos of growth. Still, the present study shows that these factors produce readily measurable and systematic influences on the nature of the skeletodental correction.

Cephalometric comparison of maxillary second molar extraction and nonextraction treatments in patients with Class II malocclusions.

This retrospective cephalometric study compared the nature of the skeletodental correction of maxillary second-molar extraction and nonextraction treatments in correcting Class II malocclusions. The sample comprised 50 Class II, deep-bite, low-angle adolescents; half were treated with maxillary second-molar extraction and half were treated without extraction. Pretreatment and posttreatment lateral cephalograms were analyzed. Analysis relied primarily on the method of Lysle Johnston that evaluates sagittal changes in the teeth and supporting bones relative to the functional occlusal plane. All 18 cephalometric variables examined were statistically equivalent between the 2 groups at the start of treatment. In contrast, several skeletodental treatment changes differed significantly. The maxillary second-molar extraction group exhibited distal movement of the maxillary first molar (1.2 mm vs 0.0 mm), and there was greater flaring of the mandibular incisors in the nonextraction group (9.1 degrees vs 3.5 degrees ). The upper incisor root was torqued lingually in both groups, but there was more anterior crown movement in the nonextraction group (2.0 mm vs 0.0 mm). Also, the extraction group finished active treatment 7 months sooner on average. Sagittal molar correction in the maxillary second-molar group was a result of distalizing in the maxillary arch, whereas anchorage was expended in the mandibular arch to correct the malocclusion in the nonextraction group. In properly selected Class II malocclusions, maxillary second-molar extraction is a viable alternative treatment choice.

Secular trend in tooth size in urban Chinese assessed from two-generation family data.

Environmental improvements can lead to greater size of skeletodental structures as the population comes closer to expressing its genetic growth potential. Such secular trends have been documented in many human settings, especially for increased stature and faster tempos of growth. The present study is based on 185 same-sex parent-offspring pairs of data for maximum buccolingual crown diameters of the permanent teeth from a cohort in Beijing, China, where parents experienced much of their development during and after World War II with the deprivations of the changing regime. Their offspring enjoyed the relative stability of the established Communist system, where nutrition and stability were much improved. There were significant increases in buccolingual diameters of the premolars and molars in the offspring. Increase for premolars and molars was about 1%, but larger in females than males (1.6% vs. 0.5%). Opposite changes occurred in the incisors and canines (i.e., larger parental dimensions), but we contend that these are an age-related artifact brought on by greater passive eruption of older individuals' teeth that exposes a broader portion of the crown at the gingival margin. The secular trend in crown size coincides with other research in contemporary China, disclosing increases in body size and faster tempos of growth as health and nutrition continue to improve.

Tissue contributions to sex and race: differences in tooth crown size of deciduous molars.

This study describes size of constituent deciduous tooth crown components (enamel, dentine, and pulp) to address the manner in which males characteristically have larger teeth than females, and the observation that teeth of American blacks are larger than those of American whites. Measurements were collected (n = 333 individuals) from bitewing radiographs using computer-aided image analysis. Tissue thicknesses (enamel, dentine, pulp) were measured at the crown's mesial and distal heights of contour. Deciduous mesiodistal molar crown length is composed of about 1/7 enamel, 1/3 dentine, and 1/2 pulp. Details differ by tooth type, but males typically have significantly larger dentine and pulp dimensions than females; there is no sexual dimorphism in marginal enamel thickness. Males scale isometrically with females for all variables tested here. Blacks significantly exceed whites in size of all tissues, but tissue types scale isometrically with blacks and whites with one exception: enamel thickness is disproportionately thick in blacks. While the absolute difference is small (5.56 mm of enamel in blacks summed over all four deciduous molar tooth types vs. 5.04 mm in whites), the statistical difference is considerable (P < 0.001). Aside from enamel, crown size in blacks is increased proportionately vis-à-vis whites. Principal components analysis confirmed these univariate relationships and emphasizes the statistical independence of crown component thicknesses, which is in keeping with the sequential growth and separate embryonic origins of the tissues contributing to a tooth crown. Results direct attention to the rates of enamel and dentine deposition (of which little is known), since the literature suggests that blacks (with larger crowns and thicker enamel) spend less time in tooth formation than whites.

Apical root resorption in patients treated with comprehensive orthodontics.

External apical root resorption (EARR) is a common--but seldom extreme--consequence of orthodontic treatment. Incisors are most at risk, perhaps because of their single roots and because they typically are moved farther than other teeth. We followed a cohort of patients (n = 153) treated with comprehensive orthodontics. EARR was scored on the upper incisors with a qualitative five-grade ordinal scale. There was no EARR at the start of treatment, but most (> 80%) exhibited slight-to-moderate EARR by the end of treatment (i.e., a loss of 1-2 mm). Cases treated with premolar extractions experienced more EARR because their incisors were retracted farther; however, the sum of the effects of patients' sex and age, and severity of the malocclusion, and the kind of mechanics used accounts for little of the overall variation in EARR. Instead, it appears that genetically-based inter-individual variation in susceptibility to EARR is the most influential factor. Research should be directed at understanding the biochemical nature of susceptibility so prospective patients can be screened to identify those at particular risk.

The reassertion of latent growth patterns following orthodontic treatment.

This study reports on evaluation of the occlusion in 16 young adults who had been treated orthodontically an average of 10 years previously. Cases were from among dental students who, we assume, have high dental "IQs" and greater than average concern for stability of their orthodontic correction. Relapse of the orthodontic correction was substantial; both dental and skeletal dimensions relapsed--returned toward pretreatment conditions--to statistically and clinically obvious extents. Relapse is greater here than some other studies because of our longer recall period. Results focus attention on the importance of prolonged posttreatment retention and greater awareness on the patient's part of the role of posttreatment facial growth on relapse from adolescence into adulthood.

Effects of patient age and sex on treatment: correction of Class II malocclusion with the Begg technique.

When children are treated orthodontically during a phase of active growth-notably adolescence-there is the opportunity to harness growth to achieve some of the correction, especially in the sagittal plane in which differential jaw growth can harmonize dental relationships. All correction must be from tooth movement when there is no growth. Three questions were addressed in the present study: (1) how much orthodontic correction is achieved by bone growth? (2) do the proportions of tooth and bone movement depend on patient age? and (3) do the jaws of boys and girls grow at discernibly different rates during treatment? A sample of 139 children aged 9 to 17 years at the start of treatment with Class II division 1 malocclusions was studied cephalometrically using Johnston analysis. Maxillary and mandibular growth were highest in the youngest children, with rates decreasing to effectively zero in the oldest adolescents. Means adjusted for age were significantly higher for boys than for girls for upper and lower jaw growth. Age had little influence on the amount of tooth movement except for a marked decline with age in the mesial movement of the maxillary first molar, which was greatest in the youngest patients of both sexes. The amount of orthodontic correction was independent of age, but in the youngest quartile of the sample, most of the correction (87%) was due to differential jaw growth in the youngest quartile of the sample, and the rest (13%) resulted from tooth movement, whereas in the oldest quartile, most of the correction was due to tooth movement (64% tooth movement and 36% bone growth). Overall, the influence of age and sex had significant influences on multiple skeletodental variables, suggesting that research designs need to account for these demographic sources of variability. Although all cases were treated to a Class I occlusion, the nature of the correction was affected measurably by the patient's age and sex.

Growth of the anterior dental arch in black American children: a longitudinal study from 3 to 18 years of age.

Dental arch size and form change systematically because of tooth emergence and because teeth migrate into shorter and broader arch forms in the deciduous dentition and again in the permanent dentition. The present longitudinal analysis describes changes in arch form in a cohort of 52 black American children (Nashville, Tenn) between the ages of 3 and 18 years. The anterior (incisor-canine) arch dimensions were analyzed. Incisor-to-canine depth remained static in both arches between 3 and 5 years but shortened significantly between 12 and 18 years. Intercanine width broadened significantly in both arches, first during the deciduous dentition, then again as the primary teeth were supplanted by the permanent incisors and canines. But there was no change in intercanine width once the permanent canines were in functional occlusion (approximately 11-18 years). These changes alter anterior arch form (the ratio depth/width). This index decreased significantly during the deciduous phase as the arches broadened; the index increased from 6 to 10 years as teeth were replaced, then again decreased during the duration of the study (approximately 10-18 years). Dimensions of these black American children all exceed comparable values for white American children, although the anterior shapes are indistinguishable. The present data focus attention on the dynamics of arch form in which considerable, protracted change occurs by physiologic migration, not just during the short phase of tooth replacement.

Maxillary arch size and shape in American blacks and whites.

American blacks have larger teeth than whites, but they less frequently exhibit crowding--apparently because of larger arch dimensions. This study quantified differences in arch size and shape in these 2 constituents of the US population. Eighteen dental and bony landmarks were digitized from the maxilla of each of 332 subjects with permanent, intact dentitions, proportionately divided between blacks and whites, men and women. Linear, angular, and area measurements were computer-generated. Arch widths averaged 10% greater in blacks than whites, and mesiodistal arch depths had a greater difference, at 12%. Blacks, with a more square palate and significantly larger palatal index, were distinguished from whites primarily by greater intercanine and interpremolar widths. Arch perimeter was greater in blacks by 8%, and cross-sectional area of the arch was 19% greater in blacks than whites, so blacks and whites differ substantially for these parameters not only in size, but in shape as well. These differences are relevant in prosthodontics and orthodontics since individualization of treatment leads to more effective treatment by working within the patient's natural arch form instead of making patients fit a single standard.

Directions of orthodontic tooth movements associated with external apical root resorption of the maxillary central incisor.

External apical root resorption is a multifactorial problem encountered in all disciplines of dentistry, but it is most commonly seen in cases treated orthodontically. Specific tooth movements that are most likely to exacerbate external apical root resorption are poorly understood. Purpose of the present investigation was twofold: (1) to quantify apical and incisal movements of the maxillary central incisor in the sagittal and vertical planes from cephalograms and (2) to use stepwise multivariate linear regression analyses to see which tooth movements and skeletodental relationships are most predictive of external apical root resorption. The sample consisted of 110 adolescents with similar pretreatment malocclusions (Class I crowded or bimaxillary protrusive) and treatment planned similarly (extraction of four first premolars) by experienced private practitioners. Each of three practitioners used a different orthodontic appliance; the sample was divided proportionately into cases treated with Tweed standard edgewise technique, Begg lightwire technique, and Roth-prescription straightwire technique. Lateral cephalograms were analyzed at the start, middle, and end of treatment. There was no statistical difference in average external apical root resorption between sexes or among techniques. Measures of tooth movement were highly predictive, explaining up to 90% of the variation in root resorption. Apical and incisal vertical movements and increase in incisor proclination were the strong predictors of external apical root resorption for each regression model. Incisor intrusion with increase in lingual root torque together were the strongest predictors of external apical root resorption. In contrast, distal bodily retraction, extrusion, or lingual crown tipping had no discernible effect.

Postorthodontic dental changes: a longitudinal study.

The conventional adolescent orthodontic patient is treated during a phase of active growth, but growth of the skeletodental complex continues after treatment and into adulthood at a much slower pace. Selection of orthodontic diagnostic and treatment regimens that produce stable and esthetic dental relationships is a continual endeavor for the orthodontic specialist. Patients should be recalled for long periods of time and the results evaluated. The present longitudinal study was completed on 36 individuals, all of whom had received comprehensive orthodontic treatment. Dental changes were assessed from cephalograms for the in-treatment period (ca. 12 to 15 years of age), posttreatment to first recall (0 = 22 years of age), and first to second recall period (0 = 30 years of age). There was considerable change in the absolute locations of the teeth, but, in reality, these changes are almost wholly attributable to growth of the bony reference structures, not dental changes per se. Growth proceeded at a very slow pace after the first recall (ca. 22 to 30 years of age ). Dental relationships, eg., FMIA, IMPA, 6L angulation, exhibited no systematic change after treatment.

A radiographic assessment of enamel thickness in human maxillary incisors.

Crown sizes of human teeth are sexually dimorphic, with male larger than female. This holds for most human groups, though the extent of dimorphism varies among populations. It is not known whether size dimorphism is due to differences in enamel thickness, dentine differences, or some combination of the two. This study examined the pattern of variation in enamel thickness on the mesial and distal margins of the four maxillary permanent incisors. Standardized periapical radiographs of the incisors of 115 adolescent American whites were measured. Enamel was significantly thicker on the distal than the mesial margins of both the lateral and central incisors, with a mean difference of 0.1 mm. There was no sexual dimorphism in the maximum mesial or distal enamel thicknesses. In contrast, the widths of the dentine of the crowns were significantly greater in males, by an average of 6.5%. Sexual dimorphism in mesiodistal diameters of the incisors seems, then, to be due to the dentine component, which is the size attained at the end of the bell stage of tooth formation. Sex-specific correlations between enamel thickness and crown width of the dentine were low (and lower for males), indicating considerable independence between regulatory mechanisms of dentine and enamel development.

Genetic influence on dental arch form in orthodontic patients.

Human arch form varies considerably. This study analyzed the size and shape of the maxillary and mandibular dental arches of 320 adolescents from 155 sibships. A broad battery of measurements (k = 48) was computer-generated from Cartesian coordinates of cusp tips and line angles of the permanent teeth, and heritability estimates were generated from intraclass correlations, controlling for sex and age where indicated. Arch size has a modest genetic component, on the order of 50%, although this estimate may contain shared environmental influences. Tooth rotations have low h2 estimates, most of them indistinguishable from zero. Arch shape, assessed as length-width ratios, also has a modest transmissible component, suggesting that arch length and width growth factors are largely independent. Highest heritability estimates, as a group, were for transverse arch widths, which averaged about 60%. Several measures of left-right asymmetry also were analyzed (k = 31), and, while the arches are systematically asymmetric (generally with left > right), there is only weak evidence of a transmissible component for directional asymmetry and essentially none for fluctuating asymmetry. In all, arch size and shape are seen to be more subject to environmental influences than to heredity. These findings direct attention toward the need to better understand what extrinsic factors modulate arch size and shape during development.

Identification of race and sex from palate dimensions.

Measurements of the width and depth of the palate were used to predict the race (American black or white) or sex or both of an individual. The sample consisted of 332 living subjects with permanent dentitions, and measurements were made between cusp tips, so palate size includes bony and dental components. Blacks, with a more square palate, were distinguished from whites primarily by greater interpremolar widths and P1-to-M2 depths. Simultaneous prediction of race and sex had a correct classification of 48%, which is about twice that expected from chance. Pooling the two sex increases correct classification of race to 83%. Formulas also are provided for each variable separately to accommodate fragmentary remains. Resilience of palatal structures to traumatic and natural forces makes this method practical in several forensic situations.

Sibling similarities in the tempo of human tooth mineralization.

The extent of tooth mineralization is a useful estimate of a child's physiological age it reflects the rate at which the child is developing towards maturity. As it is not known to what degree dental age is regulated by the genotype, this investigation estimated familial resemblance in the tempo of tooth mineralization. Panoramic radiographs of the children in 185 sibships were scored for stages of tooth formation, and dental age was calculated from sex-specific standards. Intraclass correlations of mineralization tempo were computed for maxillary and mandibular canines, premolars, second molars, and third molars. Correlations of mineralization tempo were significantly different than zero for all 10 teeth and ranged from 0.17 (SE = 0.06) for the mandibular second molar to 0.43 (SE = 0.05) for the mandibular second premolar. Intraclass correlations increased significantly when multiple teeth were used to more comprehensively define each child's dental age. Using an unweighted average of all 10 tooth types yielded a correlation of 0.41 (SE = 0.05). It appears, then, that a considerable proportion of the total variability in tooth-mineralization rate can be attributed to transmissible effects operating in the population under investigation.

Relapse revisited.

Rather little is known about the changes in orthodontic treatment results exceeding a decade after treatment. The purpose of this study was to quantify changes in tooth relationships in a series of cases (n = 36) at 6 years and again at 15 years after treatment. The rate of change decreased with time, supporting the contention that most "relapse" occurs soon after treatment; continued change generally cannot be distinguished from normal aging processes that occur, regardless of whether a person had been treated orthodontically. There were minor, but statistically significant, associations between increased incisor irregularity ("relapse") and parasagittal growth of the jaws. Greater irregularity occurred when mandibular growth exceeded that of the maxilla, decreasing overjet and crowding the lower incisors within the containing arch of the maxilla. Overall, relapse tended to be less in these cases treated by a single experienced specialist that in university-based samples treated by multiple, orthodontic residents.

A longitudinal study of arch size and form in untreated adults.

Adulthood-the lengthy phase following attainment of biologic maturity-often is perceived as a period of "no change" or one of slow deterioration. Recent skeletodental studies discount this stereotype. Changes in arch size and shape were studied here in a longitudinal series of 60 adults with intact dentitions. Full-mouth study models were taken at about 20 years of age and again at about 55 years. Some variables-particularly those between arches (incisor overbite and overjet, molar relationship) and mandibular intercanine width-remained age-invariant. In contrast, all other measures of arch width and length changed significantly (P < 0.01): Arch widths increased over time, especially in the distal segments, whereas arch lengths decreased. These changes significantly altered arch shape toward shorter-broader arches. The data suggest that changes during adulthood occur most rapidly during the second and third decades of life, but do not stop thereafter. Possible mechanisms driving these changes in tooth position are discussed.

A heritable component for external apical root resorption in patients treated orthodontically.

External apical root resorption (EARR) is a common and occasionally critical problem in orthodontic patients. Mechanical forces compress the periodontium, leading to localized resorption of cementum that exposes dentin to destruction by clastic activity. Factors controlling occurrence and extent of EARR are poorly understood, but there may be a familial (genetic) factor in susceptibility. A sample of full siblings (103 pairs) was studied, all of whom were treated with the same technique by one orthodontist. Crown and root lengths were measured on cephalograms and panoral films before and after treatment. Six roots were scored on each patient, and decrease in root length was the dependent variable. Generalized linear models were used to quantify within and among sibship variances while controlling for sex, age, and severity of malocclusion (FMA, ANB, AOBO, overjet, NAP) as covariates. Results showed significantly greater among-than within-sibship variances, meaning there is a substantive genetic factor in susceptibility to EARR. Heritability estimates were fairly high, averaging 70% for three roots, although low for the mandibular incisor, probably because of little variation. No evidence was found for a sex or age difference in susceptibility. Quantification of a transmissible component suggests it would be useful to search for the biochemical factors controlling the familial differences in susceptibility.