Steven D. Marshall

Cervical vertebrae maturation method: poor reproducibility.

INTRODUCTION The cervical vertebrae maturation (CVM) method has been advocated as a predictor of peak mandibular growth. This method relies on the clinicians ability to determine the stage of maturation of the vertebrae. Careful examination of reports of this technique shows methodologic flaws that can lead to inflated levels of reproducibility. The purpose of this study was to evaluate the reproducibility of CVM stage determination by using a more stringent methodology. METHODS Ten practicing orthodontists, trained in the CVM method, evaluated 30 individual and 30 pairs of cephalometric radiographs in 2 sessions to determine the CVM stage. Interobserver and intraobserver reliability was determined by using the Kendall coefficient of concordance and the weighted kappa statistic. RESULTS All degrees of interobserver and intraobserver agreement were moderate (Kendalls W, 0.4-0.8). Interobserver agreement levels for CVM staging of the 10 orthodontists at both times were below 50%. Agreement improved marginally with the use of 2 longitudinal radiographs. Intraobserver agreement was only slightly better; on average, clinicians agreed with their own staging only 62% of the time. CONCLUSIONS Based on these results, we cannot recommend the CVM method as a strict clinical guideline for the timing of orthodontic treatment.

Development of the curve of Spee

INTRODUCTION Ferdinand Graf von Spee is credited with characterizing human occlusal curvature viewed in the sagittal plane. This naturally occurring phenomenon has clinical importance in orthodontics and restorative dentistry, yet we have little understanding of when, how, or why it develops. The purpose of this study was to expand our understanding by examining the development of the curve of Spee longitudinally in a sample of untreated subjects with normal occlusion from the deciduous dentition to adulthood. METHODS Records of 16 male and 17 female subjects from the Iowa Facial Growth Study were selected and examined. The depth of the curve of Spee was measured on their study models at 7 time points from ages 4 (deciduous dentition) to 26 (adult dentition) years. The Wilcoxon signed rank test was used to compare changes in the curve of Spee depth between time points. For each subject, the relative eruption of the mandibular teeth was measured from corresponding cephalometric radiographs, and its contribution to the developing curve of Spee was ascertained. RESULTS In the deciduous dentition, the curve of Spee is minimal. At mean ages of 4.05 and 5.27 years, the average curve of Spee depths are 0.24 and 0.25 mm, respectively. With change to the transitional dentition, corresponding to the eruption of the mandibular permanent first molars and central incisors (mean age, 6.91 years), the curve of Spee depth increases significantly (P < 0.0001) to a mean maximum depth of 1.32 mm. The curve of Spee then remains essentially unchanged until eruption of the second molars (mean age, 12.38 years), when the depth increases (P < 0.0001) to a mean maximum depth of 2.17 mm. In the adolescent dentition (mean age, 16.21 years), the depth decreases slightly (P = 0.0009) to a mean maximum depth of 1.98 mm, and, in the adult dentition (mean age 26.98 years), the curve remains unchanged (P = 0.66), with a mean maximum depth of 2.02 mm. No significant differences in curve of Spee development were found between either the right and left sides of the mandibular arch or the sexes. Radiographic measurements of tooth eruption confirm that the greatest increases in the curve of Spee occur as the mandibular permanent incisors, first molars, or second molars erupt above the pre-existing occlusal plane. CONCLUSIONS On average, the curve of Spee initially develops as a result of mandibular permanent first molar and incisor eruption. The curve of Spee maintains this depth until the mandibular permanent second molars erupt above the occlusal plane, when it again deepens. During the adolescent dentition stage, the curve depth decreases slightly and then remains relatively stable into early adulthood.

Sutural growth restriction and modern human facial evolution: an experimental study in a pig model.

Facial size reduction and facial retraction are key features that distinguish modern humans from archaic Homo. In order to more fully understand the emergence of modern human craniofacial form, it is necessary to understand the underlying evolutionary basis for these defining characteristics. Although it is well established that the cranial base exerts considerable influence on the evolutionary and ontogenetic development of facial form, less emphasis has been placed on developmental factors intrinsic to the facial skeleton proper. The present analysis was designed to assess anteroposterior facial reduction in a pig model and to examine the potential role that this dynamic has played in the evolution of modern human facial form. Ten female sibship cohorts, each consisting of three individuals, were allocated to one of three groups. In the experimental group (n = 10), microplates were affixed bilaterally across the zygomaticomaxillary and frontonasomaxillary sutures at 2 months of age. The sham group (n = 10) received only screw implantation and the controls (n = 10) underwent no surgery. Following 4 months of post‐surgical growth, we assessed variation in facial form using linear measurements and principal components analysis of Procrustes scaled landmarks. There were no differences between the control and sham groups; however, the experimental group exhibited a highly significant reduction in facial projection and overall size. These changes were associated with significant differences in the infraorbital region of the experimental group including the presence of an infraorbital depression and an inferiorly and coronally oriented infraorbital plane in contrast to a flat, superiorly and sagittally infraorbital plane in the control and sham groups. These altered configurations are markedly similar to important additional facial features that differentiate modern humans from archaic Homo, and suggest that facial length restriction via rigid plate fixation is a potentially useful model to assess the developmental factors that underlie changing patterns in craniofacial form associated with the emergence of modern humans.

Nasal septal and premaxillary developmental integration: implications for facial reduction in Homo.

The influence of the chondrocranium in craniofacial development and its role in the reduction of facial size and projection in the genus Homo is incompletely understood. As one component of the chondrocranium, the nasal septum has been argued to play a significant role in human midfacial growth, particularly with respect to its interaction with the premaxilla during prenatal and early postnatal development. Thus, understanding the precise role of nasal septal growth on the facial skeleton is potentially informative with respect to the evolutionary change in craniofacial form. In this study, we assessed the integrative effects of the nasal septum and premaxilla by experimentally reducing facial length in Sus scrofa via circummaxillary suture fixation. Following from the nasal septal‐traction model, we tested the following hypotheses: (1) facial growth restriction produces no change in nasal septum length; and (2) restriction of facial length produces compensatory premaxillary growth due to continued nasal septal growth. With respect to hypothesis 1, we found no significant differences in septum length (using the vomer as a proxy) in our experimental (n = 10), control (n = 9) and surgical sham (n = 9) trial groups. With respect to hypothesis 2, the experimental group exhibited a significant increase in premaxilla length. Our hypotheses were further supported by multivariate geometric morphometric analysis and support an integrative relationship between the nasal septum and premaxilla. Thus, continued assessment of the growth and integration of the nasal septum and premaxilla is potentially informative regarding the complex developmental mechanisms that underlie facial reduction in genus Homo evolution. Anat Rec, 2010.

Nasal Septal Deviation and Facial Skeletal Asymmetries

During ontogeny, the nasal septum exerts a morphogenetic influence on the surrounding facial skeleton. While the influence of the septum is well established in long snouted animal models, its role in human facial growth is less clear. If the septum is a facial growth center in humans, we would predict that deviated septal growth would be associated with facial skeletal asymmetries. Using computed tomographic (CT) scans of n = 55 adult subjects, the purpose of this study was to test whether there is a correlation between septal deviation and facial asymmetries using three‐dimensional (3D) geometric morphometric techniques. We calculated deviation as a percentage of septal volume relative to the volume of a modeled non‐deviated septum. We then recorded skeletal landmarks representing the nasal, palatal, and lateral facial regions. Landmark data were superimposed using Procrustes analysis. First, we examined the correlation between nasal septal deviation and the overall magnitude of asymmetry. Next, we assessed whether there was a relationship between nasal septal deviation and more localized aspects of asymmetry using multivariate regression analysis. Our results indicate that while there was no correlation between septal deviation and the overall magnitude of asymmetry, septal deviation was associated with asymmetry primarily in the nasal floor and the palatal region. Septal deviation was unassociated with asymmetries in the lateral facial skeleton. Though we did not test the causal relationship between nasal septal deviation and facial asymmetry, our results suggest that the nasal septum may have an influence on patterns of adult facial form. Anat Rec, 299:295–306, 2016.

Effect of maxillary anteroposterior position on profile esthetics in headgear-treated patients

INTRODUCTION Headgears have been used to treat Class II malocclusions for over a century. The purpose of this retrospective study was to investigate the profile esthetic changes resulting from headgear use in growing Class II patients with protrusive, normal, and retrusive maxillae. METHODS Profile silhouettes were created from pretreatment and posttreatment lateral cephalometric tracings of growing Class II patients treated with headgear followed by conventional fixed appliances. Ten patients had an initially protrusive maxilla (FH:NA, >92°), 10 had an initially normally positioned maxilla (FH:NA, 88°-92°), and 10 had an initially retrusive maxilla (FH:NA, <88°). A panel of 20 laypersons judged the profile esthetics of the randomly sorted silhouettes. Descriptive statistics, correlation analysis, and anlaysis of variance (ANOVA) with post-hoc Tukey-Kramer tests were used to ascertain differences between groups and the effects of treatment. RESULTS A significant moderate correlation was found between initial ANB magnitude and the improvement in profile esthetic score with treatment (r = 0.49, P <0.01). No significant correlations were found between the initial anteroposterior position of the maxilla (FH:NA) and the initial, final, or change in profile esthetic scores. There were average improvements with headgear treatment in profile esthetics for all groups. CONCLUSIONS In Class II growing patients with protrusive, normally positioned, or retrusive maxillae, headgear treatment used with fixed orthodontic appliances is effective in improving facial profile esthetics: the greater the initial ANB angle, the greater the profile esthetic improvement with treatment.

Ask us. Long-term stability of maxillary expansion.

AThere is only second-level evidence that maxillary expansion obtained with fixed expansion appliances is stable in the long term. There is only weak indirect evidence of long-term expansion stability with the use of removable maxillary expansion appliances. Maxillary expansion, with fixed or removable expansion appliances, is a common orthodontic treatment. It is primarily used for the correction of posterior crossbites as a result of reduced maxillary width. Maxillary expansion is particularly important in eliminating mandibular functional shift, a finding commonly associated with deficient maxillary arch width in early dentition development that can have undesirable consequences on facial symmetry, and possibly temporomandibular joint function, if left untreated. Other applications suggested in the orthodontic literature include increasing arch perimeter in the absence of posterior crossbite to facilitate nonextraction edgewise treatment, and improving Class II interarch relationships by a spontaneous mandibular growth or positioning response to maxillary expansion. The increase in the transverse dimension of the maxillary arch by using expansion appliances is indisputable. The short-term treatment effects are both dental and skeletal, resulting in significant gains in maxillary intermolar width and maxillary perimeter arch width postexpansion. The longterm change in the maxillary transverse dimension posttreatment (ie, the amount of expansion remaining with time) is less well established, particularly in relation to expected transverse changes with growth in untreated persons with normal occlusion. Systematic reviews and meta-analyses are evidencedbased tools that use systematic literature searches, quality assessments and data extraction measures to summarize the literature for a particular treatment effect. They reduce bias in data interpretation. The Council on Scientific Affairs (COSA) used an evidence-based approach to the question of long-term stability of the maxillary transverse dimension changes associated with fixed or removable expansion appliances. A search of the literature for meta-analyses and systematic reviews via PubMed and Google Scholar, with the key words palate expansion, maxillary expansion, rapid maxillary expansion, and slow maxillary expansion, was conducted. Eight articles that surveyed the literature between 1979 and January 2005 were found.

Spatial determinants of the mandibular curve of Spee in modern and archaic Homo.

OBJECTIVES The curve of Spee (COS) is a mesio-distally curved alignment of the canine through distal molar cusp tips in certain mammals including modern humans and some fossil hominins. In humans, the alignment varies from concave to flat, and previous studies have suggested that this difference reflects craniofacial morphology, including the degree of alveolar prognathism. However, the relationship between prognathism and concavity of the COS has not been tested in craniofacially variant populations. We tested the hypothesis that greater alveolar prognathism covaries with a flatter COS in African-American and European-American populations. We further examined this relationship in fossil Homo including Homo neanderthalensis and early anatomically modern Homo sapiens, which are expected to extend the amount of variation in the COS from the extant sample. METHODS AND MATERIALS These hypotheses were tested using three-dimensional geometric morphometrics. Landmarks were recorded from the skulls of 166 African-Americans, 123 European-Americans, and 10 fossil hominin mandible casts. Landmarks were subjected to generalized Procrustes analysis, principal components analysis, and two-block partial least squares analysis. RESULTS We documented covariation between the COS and alveolar prognathism such that relatively prognathic individuals have a flatter COS. Mandibular data from the fossil hominin taxa generally confirm and extend this correlation across a greater range of facial size and morphology in Homo. DISCUSSION Our results suggest that the magnitude of the COS is related to a suite of features associated with alveolar prognathism in modern humans and across anthropoids. We also discuss the implications for spatial interactions between the dental arches.

Long-term skeletal effects of high-pull headgear followed by fixed appliances for the treatment of Class II malocclusions

OBJECTIVES The long-term skeletal effects of Class II treatment in growing individuals using high-pull facebow headgear and fixed edgewise appliances have not been reported. The purpose of this study was to evaluate the long-term skeletal effects of treatment using high-pull headgear followed by fixed orthodontic appliances compared to an untreated control group. MATERIALS AND METHODS Changes in anteroposterior and vertical cephalometric measurements of 42 Class II subjects (n = 21, mean age = 10.7 years) before treatment, after headgear correction to Class I molar relationship, after treatment with fixed appliances, and after long-term retention (mean 4.1 years), were compared to similar changes in a matched control group (n = 21, mean age = 10.9 years) by multivariable linear regression models. RESULTS Compared to control, the study group displayed significant long-term horizontal restriction of A-point (SNA = -1.925°, P < .0001; FH-NA = -3.042°, P < .0001; linear measurement A-point to Vertical Reference = -3.859 mm, P < .0001) and reduction of the ANB angle (-1.767°, P < .0001), with no effect on mandibular horizontal growth or maxillary and mandibular vertical skeletal changes. A-point horizontal restriction and forward mandibular horizontal growth accompanied the study group correction to Class I molar, and these changes were stable long term. CONCLUSIONS One phase treatment for Class II malocclusion with high-pull headgear followed by fixed orthodontic appliances resulted in correction to Class I molar through restriction of horizontal maxillary growth with continued horizontal mandibular growth and vertical skeletal changes unaffected. The anteroposterior molar correction and skeletal effects of this treatment were stable long term.

Sixteen-week analysis of unaltered elastomeric chain relating in-vitro force degradation with in-vivo extraction space tooth movement

Introduction: The purposes of this study were to evaluate whether unaltered elastomeric chain can continue to move teeth for 16 weeks and to relate it to the amount of force remaining for the same batch of elastomeric chains. Methods: The in‐vivo portion of the study had a sample of 30 paired extraction space sites from 22 subjects who were measured for closure of the space every 28 days. The altered side elastomeric chain served as the control and was replaced at 28‐day intervals whereas the experimental side remained unaltered. In the in‐vitro portion of the study, 100 each of 2‐unit and 3‐unit segments of the same batch of elastomeric chains were placed in a water bath, and the force was measured for 20 of each segment length at the 28‐day measurement points. Results: Statistically significant amounts of space closure occurred at both the altered and unaltered sites at all measurement time points. The mean space closure at the altered sites was minimally greater than that observed at the paired unaltered sites. The mean differences of space closure between the altered and unaltered sites ranged from a minimum of –0.05 mm at 4 weeks to a maximum of –0.14 mm at 8 weeks. The elastomeric chain force degraded rapidly by 4 weeks but continued a gradual diminution of force to 86 g at 16 weeks. Conclusions: Unaltered elastomeric chain continued to move teeth into extraction spaces for 16 weeks in this sample from both statistically and clinically significant standpoints. There were minimal and statistically insignificant differences in the mean space closure measurements between the paired altered and unaltered sites. The elastomeric chain force at 16 weeks was less than 100 g, yet at the same time point, teeth continued to move clinically. HighlightsElastomeric chains can continue to move teeth for a minimum of 16 weeks.Elastomeric chain measured in vitro demonstrated diminishing force to a mean of 86 g at 16 weeks.Use of a practice‐based network of clinicians is a promising approach for clinical research.