Variation in natural head position and establishing corrected head position.

Corrected head position (CHP) has been simulated by using the Frankfurt horizontal (FH) for over 100 years but FH varies between individuals. Because CHP is biologically relevant for orthodontic diagnosis and treatment planning, orthognathic surgical planning, and art, this study examined relationships between head position and selected cephalometric planes. Natural head position cephalograms of Aboriginal Australians and two contemporary samples from private orthodontic practices were analysed. Each sample comprised 40 individuals (20 males and 20 females). The Aboriginal Australian sample comprised longitudinal data (T1 early adolescent, T2 late adolescent, and T3 adult), enabling examination of natural head position (NHP) reproducibility over a period of approximately 8 years. Results of reproducibility differences revealed an absolute mean=2.9°, range=-7.9° to 8.2°, and standard deviation=3.6°. Stable basicranial line (SBL), neutral horizontal axis (NHA), FH, palatal plane (P plane), and Krogman-Walker plane (KW plane) demonstrated near parallelism and their mean angulations from the true horizontal (HOR) ranged between -4.6° and 2.4°. While NHP is not consistently reproducible at the individual level, the combined use of multiple planes such as SBL, P plane, and KW plane enables a more consistent CHP to be achieved.

Intrauterine hormone effects on tooth dimensions.

The human dentition is a complex adaptive system that is influenced by genetic, epigenetic, and environmental factors. Within this system, is sexual dimorphism related to the growth promotion of the Y chromosome, or to hormonal influences, or both? This study is the first to investigate both primary and permanent tooth sizes in females from opposite-sex dizygotic (DZOS) twin pairs compared with females from dizygotic same-sex (DZSS) and monozygotic (MZ) twin pairs to indicate the influence of intrauterine male hormone, including the initial testosterone surge, on dental development. Serial dental models of the primary, mixed, and permanent dentitions of 134 females from DZOS, DZSS, and MZ twins were examined. Mesiodistal, buccolingual, crown height, and intercuspal dimensions of all primary teeth and selected permanent teeth were determined by image analysis. Univariate and multivariate analyses showed statistically significantly larger crown size in DZOS females in both dentitions, with the crown height dimensions displaying the greatest increase in size. These findings strongly support the Twin Testosterone Transfer (TTT) hypothesis. We propose that the growth-promoting effects of the Y chromosome and intrauterine male hormone levels influence different tooth dimensions and contribute differentially to the sexual dimorphism of human teeth.

Ultrasonography, lateral cephalometry and 3D imaging of the human masseter muscle.

PURPOSE: To develop prediction equations to assist the clinician to derive cephalometric norms from the non-invasive investigations of ultrasonography (US) and 3D imaging. SETTING AND SAMPLE POPULATION: Adult volunteers from University of Adelaide participated in the study. METHODS: Eleven volunteers (eight women, three men; age range 22-30 years) were recruited for US and standard lateral radiographs measurements along with 3D facial imaging using a structured light technique. The three examinations were performed to assess the vertical and transverse dimensions of the face along with superficial masseter muscle dimensions. In total, 31 variables were statistically analysed for relationship among the three imaging modalities. RESULTS: Pearson's correlation coefficients showed highly significant correlations between lateral cephalometric (Co-Go to R3-R4) and US (volume--thickness) variables (r = 0.92, p < 0.0001; r = 0.95, p < 0.0001, respectively). Strong correlations were also observed with Co-Go and masseter muscle area derived from US r = 0.81 (p = 0.01). Similarly, strong correlations were seen between gonion-menton (Go-me) and facial width from 3D imaging (r = 0.83, p = 0.003). A high statistical significance (p > 0.0001) for curvilinear measurements compared with linear counterparts was revealed with the paired t-test. Factor analyses provided meaningful interrelationships for predictive equations generated for lateral cephalometric variables from 3D image coordinates. CONCLUSIONS: This preliminary investigation suggests that useful clinical information for treatment planning and follow-up can be gathered without repeated exposure to ionizing radiation. For more robust predictive equations, a larger sample would be required to validate such a model.

Ultrasound measurements of the masseter muscle as predictors of cephalometric indices in orthodontics: a pilot study.

This study investigated the potential of ultrasound measurements of the masseter muscle to accurately predict indices normally derived from cephalograms. Masseter muscle measurements on 11 adults (22 to 30 y) were made using lateral cephalometrics and extended field-of-view ultrasound. The ultrasound technique was validated in a simulation pilot study using 12 dry skulls and raw chicken breasts. Twenty cephalometric variables were analyzed against four ultrasound measurements of the masseter muscle. Highly significant correlations (r = 0.81-0.85, p = 0.001-0.002) between ultrasound measurements of the masseter muscle and cephalometric measurements representing the length of the superficial masseter muscle, the length and shape of the mandible and vertical facial proportions were demonstrated. Predictive equations from regression analyses were constructed to deduce ramus length and shape from the ultrasound measurements. The results provide pilot data suggesting that ultrasound is a potential clinical tool for sequential evaluation of masseter muscle length in orthodontics and facial muscle growth studies.

Trabecular anisotropy and collagen fibre orientation in the mandibular condyle following experimental functional appliance treatment using sheep.

In order to study the modifying effects of functional appliances on the mechanical environment of the temporomandibular joint (TMJ), we characterised the structure of the mandibular condyle subsequent to an experimental functional appliance intervention. Eight, four-month-old, castrated male Merino sheep, were randomly allocated to experimental and control groups (n = 4 in each group). Forward mandibular displacement was induced with an intraoral appliance. The study period was 15 weeks, during which time fluorochromes were administered to all of the animals. Midsagittal sections of the TMJ were selected for analysis and trabecular anisotropy was estimated using bone histomorphometry. Only the experimental group demonstrated that the trabecular bone in the central condylar region was less anisotropic when compared to the subchondral region. Also, the variation in trabecular anisotropy of the central condylar region was found to be smaller in the experimental group. The collagen fibre orientation was analysed under polarised light as the proportion of the dark or bright fibres observed in regions which existed before, and regions which formed during the experiment, as determined by the fluorochrome labels. In the experimental group, more bright collagen fibres were found in the most superior region of the mandibular condyle when compared with the controls. These results suggested that the experimental functional appliances changed the orientation and pattern of the mechanical forces acting on the mandibular condyle, and possibly increased the magnitude of the lateral functional forces applied to the most superior part of the condyle during such treatments.

Upregulation of immunoreactivity of endothelin-1 and alpha-SMA in PDL microvasculature following acute tooth loading: an immunohistochemical study in the marmoset.

OBJECTIVES: To test the hypothesis that a continuous mechanical tooth load would elevate immunoreactivity of endothelin-1 (ET-1) and alpha-smooth muscle actin (alpha-SMA) in the periodontal ligament (PDL) microvasculature. DESIGN: A randomized control study employing 1.5 h of loading to first molars. SETTING AND SAMPLE POPULATION: Orthodontic Research Laboratory, Dental School, Adelaide University. Four young adult, male marmoset monkeys were consecutively anaesthetized and treated. EXPERIMENTAL VARIABLE: An external telescoping frame applied a jaw closing load (120-200 g) transmitted occlusally, via a rubber pad, to randomly assigned mandibular left or right first molars. Contralateral molars were used as controls. OUTCOME MEASURE: Undemineralized, midsagittal, mandibular molar slices, approximately 150 microm thick were immunolabelled with ET-1 and alpha-SMA antibodies and examined in a confocal laser scanning microscope (CLSM) for vascular endothelium and smooth muscle immunolabelling. RESULTS: Three categories of post-capillary-sized venule endothelial cell immunolabelling occurred: endothelium labelled solely with ET-1; endothelium labelled solely with alpha-SMA; endothelium labelled with both ET-1 and alpha-SMA. In endothelial cells, the alpha-SMA showed a moderate cytoplasmic distribution with dense peripheral concentration. Loading increased arteriole alpha-SMA actin labelling. CONCLUSION: Scattered expression of ET-1 is the default state in primate PDL endothelial cells. Increased antigenicity of endothelial cells to both ET-1 and alpha-SMA, and of arteriolar smooth muscle to alpha-SMA, is a response to shear and compression loads.

Ultrastructural changes in postcapillary-sized venule morphology in aged mouse periodontal ligament.

The aim of this study was to compare the postcapillary-sized venule (PCV) morphology of four young ALCA mice (35 days) and four colony-related aged mice (365 days) using the transmission electron microscope (TEM). Right and left mandibular first molar mesial roots with associated periodontal ligament (PDL) and bony socket, were used for TEM assessment. Five PCV profiles were selected at each 160 microm interval, from the alveolar crest to the tooth apex. PCV profile dimensions were measured on standardised micrographs magnified x2900. Age affects were tested using multiple regression analysis. The number of PCV profiles in the tooth third of the PDL was higher in aged mice (p < 0.01) and comprised predominantly apericytic vessels (p < 0.001). The number of PCV profiles increased significantly (p < 0.001) in aged mice in the PDL middle circumferential third halfway down the molar root. Age had no significant affect on PCV diameter. Aged PDL permeability studies are needed to investigate whether the changes in aged PCV profile number are associated with functional modification of the PDL microvasculature.

Electropalatographic and cephalometric assessment of tongue function in open bite and non-open bite subjects.

Anterior open bite (AOB) and tongue thrust swallowing are frequently associated, but the relationship between the two remains unclear. Electropalatography (EPG), which is used in speech pathology to measure dynamic tongue function for diagnostic, therapeutic, and research purposes, is a suitable technique for the investigation of this relationship. The present clinical study examined the dentofacial pattern and tongue function in AOB and non-open bite children. EPG recordings of speech and swallowing, and lateral head radiographs were obtained from eight 10-year-old boys with tongue thrust swallowing behaviour and AOB, and from eight age-matched non-open bite controls. Analysis of data from the two groups indicated that although differences were small, the open bite children displayed trends for longer face morphology and greater upper incisor proclination, less consistent production of closures during speech, a more posterior pattern of EPG contact, and relatively sparse EPG contact during swallowing. The discovery of differing patterns of contact for the /d[symbol: see text]/ and /t[symbol: see text]/ phonemes indicates that these should be included when speech is used to test for the presence of fronted tongue behaviour.

A method for protrusive mandibular force measurement in children.

With this new method, protrusive mandibular force was studied in a homogeneous group of 69 children with similar occlusions. Maximum protrusive force ranged from 18.5 to 160 N (mean +/- SD = 81.3+/-31.6 N). Maximum protrusive force was significantly higher in males (90.7+/-30.2 N) than females (66.6+/-28.6 N) while fatigue time was not significantly different between the two groups (70.6+/-38.5 s for males and 65.1+/-33.6 s for females). Although protrusive force was stable in each session, it varied considerably between different experimental days within the same individual. No statistically significant correlation was found between maximum protrusive force and age, skeletal maturity, height, weight, overjet, maxillomandibular relation, facial height, facial widths or facial proportions.

Electropalatographic and cephalometric assessment of myofunctional therapy in open-bite subjects.

Myofunctional therapy (MFT) is often prescribed to correct tongue-thrust swallowing, with the expectation that anterior open bite (AOB) will reduce spontaneously if a more posterior tongue posture is learned. However, MFT has not been subjected to systematic evaluation. Electropalatography (EPG), which is used in speech pathology to measure dynamic tongue function for diagnostic, therapeutic and research purposes, is a suitable technique for the evaluation of MFT. This prospective clinical study assessed the effect of tongue re-education therapy on tongue function and dento-facial form in AOB patients. Electropalatography recordings of speech and swallowing, and lateral head cephalometric radiographs were obtained from eight 10-year-old boys with tongue-thrust swallowing behavior and AOB before and after a course of tongue re-education therapy. Although differences in cephalometric measurements before and after therapy were small, there was some evidence of a trend for upper and lower incisor eruption, with concomitant reduction of the AOB. Analysis of the EPG speech data was inconclusive, but the swallowing data showed trends for more consistent and more anterior patterns of EPG contact after therapy. Comparison of pre- and post-therapy EPG data with data from a parallel study using a group of age-matched controls indicated that some "normalisation" of swallowing behaviour had occurred. The results of this research imply that the therapy was partially successful in improving tongue function during swallowing and in reducing AOB. Further research on a larger sample over a longer observation period is required for more accurate assessment of soft and hard tissue changes.

Activator and Begg appliance management of a severe Angle Class II, division 1 malocclusion.

A male patient aged 12 years 11 months presented with the chief complaint of prominent, spaced upper teeth and was keen to overcome his dental problem.

Supernumerary teeth: a review of the literature and four case reports.

A review of the literature relating to supernumerary teeth is presented along with four case reports to illustrate some possible presentations, diagnostic features,and treatment options.

Microvascular luminal volume changes in aged mouse periodontal ligament.

Data for the microvascular bed in the aged periodontal ligament have not been established. This investigation tested the hypothesis that the luminal microvascular volume decreased in the aged ligament. Mice 35 days old and one year old were vascular-perfused and the mandibular first molar periodontal ligament processed for electron microscopy. Tissue quadrats from each circumferential third ligament region were recorded at 150-microns intervals from the alveolar crest to the apex for randomized sampling of blood vessel lumina. The data were analyzed with a generalized linear model at the p < 0.01 level for the interaction of the aging effect with differences across regions. Stereological parameters were established for vessel lumen volume, and for surface and length densities. Mean ligament width decreased from 119.9 +/- 16.94 (micron +/- SE) in young mice to 60.0 +/- 10.58 (micron +/- SE) in aged mice. The luminal volume of 8.63 +/- 1.37 (% +/- SE) in young ligament increased to 9.83 +/- 2.14 (% +/- SE) in aged ligament. Collecting venules and the combined group of arterio-venous anastomoses with terminal arterioles showed a two-fold increase in luminal volume density (p < 0.01). In aged ligament, regional shifts affected the microvascular bed distribution, but these changes were not consistent across regions, or with depth. The average cross-sectional tissue area served per capillary decreased from 2117 microns 2 to 1451 microns 2 for young and old. Average ligament thickness served per capillary dropped from 52.5 microns to 27.5 microns. These reductions in average diffusion distances indicated a change in the quality of the diffusion barrier with age.

Hypodontia of the permanent dentition. Case reports.

Hypodontia has been observed as one of the most common human dental developmental anomalies. It may be defined as agenesis of one or more teeth. The prevalence in the permanent lower central and lateral incisor region is low, ranging from 0.23 percent to 0.08 percent, respectively. This is compared with an overall incidence of hypodontia of 3.49 percent. However, significant racial variation occurs. Treatment options generally available are: no treatment, closure of spaces orthodontically, or prosthetic replacement. Aetiology, associated anomalies, and factors involved in treatment choice are discussed. A report of four cases of hypodontia of the permanent lower anterior teeth and their orthodontic management is presented.

RME-induced root resorption and repair: a computerised 3-D reconstruction.

This study was designed to evaluate the 3-D relation of epithelial rests of Malassez (ERM) to orthodontically induced resorption lacunae in human tooth roots. First premolars were extracted following rapid maxillary expansion, then they were prepared for transmission electron microscopy and sectioned. Serial 1 micron sections were used for the 3-D reconstructions and ultra thin sections were utilized to verify the identification of epithelial cells and blood vessel types. Each serial section was photographed and profiles of the resorption bays, epithelial cells and blood vessels were digitized and computer reconstructions performed with an IBM-based software programme. The reconstructions supported the view that epithelial cell and blood vessel relation to the resorption lacunae appeared to be related to the level of activity of the bay. Possible functional roles for epithelial cells in the resorptive process are discussed.

Evidence for endothelial junctions acting as a fluid flux pathway in tensioned periodontal ligament.

A continuous tension load of 1.0 N applied to the rat maxillary first molar for 30 min led to a significant increase (p < 0.05) in the mean number of junctions/microns of endothelial perimeter. The mean number of junctions/microns was compared with the mean number of tissue channels/microns 2 as previously reported by fitting linear and quadratic equations. An increase in the mean number of junctions/microns was associated with an increase in mean number of tissue channels/microns 2 (p < 0.01) in control and experimental periodontal ligament. Significant increases in the mean number of junctions/microns occurred in the middle-third zone for venous capillaries (p < 0.01) and in the tooth-third zone for postcapillary-sized venules (p < 0.001). It is concluded that the endothelial junctions of venous capillaries and postcapillary-sized venules provide significant pathways for fluid transport across the tensioned walls of the microvascular bed of the periodontal ligament.

An ultrastructural evaluation of the relationship between epithelial rests of Malassez and orthodontic root resorption and repair in man.

Contrary to previous reports, epithelial cell clusters with ultrastructural features similar to classically defined epithelial rests of Malassez were found, for the first time, in areas of repairing orthodontic root resorption. These observations were made on the buccal root surface of premolars extracted for orthodontic purposes from adolescent patients who had required rapid maxillary expansion. Ultrastructurally, the epithelial clusters ranged in size from 2-8 cells and were characterized by the presence of true desmosomes (macula adherens) and tonofilaments. Certain ultrastructural features of the epithelial cell clusters indicate that they may be involved in mediating repair cementogenesis subsequent to migration into the resorption bay.

A scanning electron microscope study of microcorrosion casts of the microvasculature of the marmoset palate, gingiva and periodontal ligament.

In the hard palate, sagittally oriented capillary loops, 8-10 microns in diameter and 70-250 microns high, extended perpendicularly from a subcapillary plexus to the connective tissue papillae. These loops formed a well-delineated vascular spine beneath the rugal crests. Capillary loop density was estimated to be 200-270/mm2 on the rugal crest, 75-160/mm2 on the rugal slopes and 70-140/mm2 in the trough. In the gingiva, the crevicular loop system was separated by a gap from the vestibular, palatal and col loop systems. Anastomoses occurred between these systems at a deeper level. The crevicular circular plexus varied from 1 to 4 vessels. Apical to the gingival margin the buccal vasculature was composed of occluso-apically orientated loops draining towards the vestibular sulcus. The capillary loops were 60-120 microns high near the gingival margin, compared with 40-60 microns near the mucogingival junction. The mucogingival margin was demarcated by a change in capillary orientation. The periodontal ligament contained mainly postcapillary-sized venules, 10-25 microns in diameter, orientated occluso-apically. Capillary loops, 50-100 microns long and directed at right angles to the root surface, occurred in the cervical third. These microvascular patterns of the marmoset are different from those of the mouse and rat.

Stereo-pair three-dimensional imaging of microvascular architecture in primate dental tissues.

The morphology of microvascular beds in dental tissues is poorly documented at the ultrastructural level. SEM stereo-pair imaging of microcorrosion casts reveals the markedly contrasting vascular architecture and capillary anastomoses within the nasopalatine foramen, soft palate and gingival regions of the marmoset. This primate was studied as an analogue for man to further our knowledge of periodontal anatomy and function.