Drifting of teeth in the mandible studied in adult human autopsy material.

OBJECTIVES: Increase in lower anterior crowding is a general problem among adult Caucasians. The tooth movement responsible for this phenomenon, however, is not fully elucidated. Aim of this study was to describe signs of ongoing tooth movement reflected in the thickness of the bundle bone around mandibular teeth and the distribution of eroding surfaces of the alveolar wall in human autopsy material. MATERIAL AND METHODS: The distribution of bundle bone and eroding surfaces was assessed histomorphometrically on 106 mandibular teeth, and the surrounding bone obtained at autopsy from 35 deceased persons ranging from 19 to 55 years of age. By examining the mesio-distal and bucco-lingual aspects at the cervical and apical levels of the roots, a pattern of tooth movements could be established. RESULTS: The distribution of the bundle bone thickness and the vectors of eroding surfaces enabled the direction of tooth movement to be reconstructed. Mesial and lingual displacement was prevalent for the anterior teeth. CONCLUSION: The signs of ongoing displacement of lower teeth support the concept of crowding occurring in adult individuals and support the maintenance of retainers, even following cessation of growth.

The role of orthodontics in the regeneration of the degenerated dentition.

The demand for regeneration of a degenerated dentition has been increasing as a result of the development of societies, where the life expectancy is increasing and fighting age-related changes is in focus. Whereas removable dentures were acceptable and considered a norm earlier, patients do, to an increasing degree,demand fixed prosthetics; consequently, the development of implants has had an important impact. The balance in the chewing organ will change with time, due to age-related changes within the bone and the loss of teeth due to caries or periodontal disease, and malocclusions may develop or aggravate. The re-establishment of an aesthetical and functional satisfactory solution cannot be reached by replacing teeth by fixed prosthodontics and implants. The aim of this update was threefold: firstly, to demonstrate that age-related changes, often unnoticed by both the patient and the general dentist, can lead to degeneration of the dentition; secondly, to explain how an interdisciplinary approach can make regeneration of even severe degeneration possible; and finally, to show the importance of the general dentist in the maintenance of the obtained results. Treatments should not aim for short-term results but focus on maintainable results.

Unilateral and bilateral dental transpositions in the maxilla-dental and skeletal findings in 63 individuals.

AIM: This was to elucidate dental and skeletal findings in individuals with unilateral and bilateral maxillary dental transpositions. MATERIAL AND METHODS: The sample comprised of radiographic materials from 63 individuals with maxillary dental transpositions from the Departments of Odontology at the Universities of Copenhagen and Aarhus and by the Danish municipal orthodontic service. The cases were divided into three groups: unilateral transposition of the canine and first premolar (Type 1U), bilateral transposition of canine and first premolar (Type 1B), and unilateral transposition of canine and lateral incisor (Type 2). The dentitions were analysed regarding agenesis and dental morphological anomalies on panoramic radiographs, and craniofacial aspects were cephalometrically analysed on profile images The results were statistically evaluated. RESULTS: All groups demonstrated increased occurrences of agenesis (Type 1U and Type 1B: 31 agenesis in 15 patients; and Type 2 three agenesis in three patients). Taurodontic root morphology was most dominant in Type 1U. Peg-shaped lateral incisors showed an increased occurrence, though not in Type 1U. Skeletally, Type 1B and Type 1U demonstrated maxillary retrognathia (more pronounced in Type 1B). Type 2 showed a significant posterior inclination of the maxilla. CONCLUSION: Transpositions of maxillary canines involve dental and skeletal deviations. Dental deviations were predominantly taurodontic root morphology and agenesis. Regarding skeletal deviations, bilateral transpositions of the canines and the first premolars are associated with skeletal changes. Unilateral transpositions are possibly a localised deviation with minor or no skeletal involvements. The results indicate a possible difference in the aetiologies of unilateral and bilateral transpositions.

Multi-level synchrotron radiation-based microtomography of the dental alveolus and its consequences for orthodontics.

Multilevel synchrotron radiation-based microtomography has been performed on a human jaw segment obtained at autopsy by cutting increasingly smaller samples from the original segment. The focus of this study lay on the microstructure of the interface between root, periodontal ligament (PDL) and alveolar bone in order to find an answer to the question why alveolar bone remodels during orthodontic loading, when the associated stress and strain levels calculated with finite element analyses are well below the established threshold levels for bone remodeling. While the inner surface of the alveolus appears to be rather smooth on the lower resolution scans, detailed scans of the root-PDL-bone interface reveal that on a microscopical scale it is actually quite rough and uneven with bony spiculae protruding into the PDL space. Any external (orthodontic) loading applied to the root, when transferred through the PDL to the alveolar bone, will cause stress concentrations in these spiculae, rather than be distributed over a "smooth surface". As osteocyte lacunae are shown to be present in these spiculae, the local amplified stresses and strain can well be registered by the mechano-sensory network of osteocytes. In addition, a second stress amplification mechanism, due to the very presence of the lacunae themselves, is evidence that stresses and strains calculated with FE analyses, based on macroscopical scale models of teeth and their supporting structures, grossly underestimate the actual mechanical loading of alveolar bone at tissue level. It is therefore hypothesized that remodeling of alveolar bone is subject to the same biological regulatory process as remodeling in other bones.

The relationship between upper airways and craniofacial morphology studied in 3D. A CBCT study.

OBJECTIVES: To assess whether morphology and dimension of the upper airway differ between patients characterized by various craniofacial morphology. SETTING AND SAMPLE POPULATION: Ninety young adult patients from the Postgraduate Clinic, Section of Orthodontics, Department of Dentistry, Health, Aarhus University, Denmark, with no obvious signs of respiratory diseases and no previous adeno-tonsillectomy procedures. Thirty patients were characterized as Class I (-0.5 < ANB < 4.5), 30 as Class II (ANB > 4.5), and 30 as Class III (ANB < -0.5). MATERIAL AND METHODS: Cone-beam computed tomography (CBCT) scans obtained in a supine position for all patients. Cephalometric landmarks were identified in 3D. Sagittal and transversal dimensions, cross sections, and partial and total volumes of the upper airway were correlated with the cephalometric measurements in all three planes of space. The cross-sectional minimal area of the upper airway was assessed as well. RESULTS: No statistical significant relationships between dimension and morphology of upper airways and skeletal malocclusion were found. CONCLUSION: Differences in craniofacial morphology as identified by the sagittal jaw relationship were not correlated with variation in upper airway volumes. A clinical significant relation was detected between minimal area and total upper airway volume.

Alveolar bone preservation subsequent to miniscrew implant placement in a canine model.

OBJECTIVE: To assess the effects of transcortical screws on alveolar (bone) ridge preservation following extraction. DESIGN: Four adult beagle dogs had mandibular premolars extracted bilaterally. After 6 weeks, using a split-mouth design, two transcortical screws were inserted unilaterally below the alveolar crest on the experimental side in the region of the extraction. The dogs were killed after 12 weeks. The bone at the extraction sites was analyzed using µCT and 3D analysis. A cylindrical core was placed around the actual and a virtual screw placed in the identical location on the control side. The bone volume within the cylinders was quantified. An insertion of a dental implant was simulated bilaterally at the insertion site. The height of the clinical crown and the alveolar crest were determined on both sides. The bone turnover was assessed histomorphometrically on un-decalcified bucco-lingual sections stained with basic fuchsine and toluidine blue. RESULTS: Comparison of the two sides revealed a significant difference both with regard to the bone volume and morphology. The transcortical screw caused an increase in bone density and less ridge atrophy. When simulating a dental implant placement on both sides, the bone preservation on the experimental side led to a need for a shorter clinical crown compared to the control side. A higher activity level of the bone in the experimental side was demonstrated histologically. CONCLUSION: In this dog model the insertion of a mini-implant across the healing alveolar process results in increased density not only adjacent to the screws, but also in the region where a potential dental implant would be inserted. In humans, the insertion of transcortical screws may maintain bone when for various reasons insertion of a permanent dental implant has to be postponed.

Transversal maxillary dento-alveolar changes in patients treated with active and passive self-ligating brackets: a randomized clinical trial using CBCT-scans and digital models.

OBJECTIVE: To assess transversal tooth movements and buccal bone modeling of maxillary lateral segments achieved with active or passive self-ligating bracket systems in a randomized clinical trial. MATERIALS AND METHODS: Sixty-four patients, with Class I, II, and mild Class III malocclusions, were randomly assigned to treatment with passive (Damon 3 MX) or active (In-Ovation R) SLBs. Impressions and cone-beam CT-scans were taken before (T0) and after treatment (T1). Displacement of maxillary canines, premolars and molars, and buccal alveolar bone modeling were blindly assessed. RESULTS: Twenty-one patients in the Damon and 20 in the In-Ovation group completed treatment according to the prescribed protocol. Eight Damon and 10 In-Ovation patients were excluded as the treatment approach had to be changed because of deviation from the recommended initial plan, while three Damon and two In-Ovation patients did not complete the treatment. Transversal expansion of the upper arch was achieved by buccal tipping in all but one patient in each group. No statistical significant difference in inter-premolar bucco-lingual inclination was found between the two groups from T0 to T1. The bone area buccal to the 2nd premolar decreased on average of 20% in the Damon and 14% in the In-Ovation group. Only few patients exhibited widening of the alveolar process. CONCLUSION: The anticipated translation and buccal bone modeling using active or passive SLBs could not be confirmed. Because of the large interindividual variation, a patient-specific analysis seems to be mandatory as individual factors like pre-treatment teeth inclination and occlusion influenced the treatment outcome of the individual patients.

An analysis of different approaches to the assessment of upper airway morphology: a CBCT study.

BACKGROUND: Upper airway morphology and respiration have been assigned an important role in the development of the craniofacial complex. Several studies advocate lateral cephalograms to evaluate the upper airway. Although this method has been widely used, a two-dimensional projection of a three-dimensional anatomical structure is questionable. OBJECTIVE: To correlate linear measurements (sagittal and transversal), cross-sectional areas, and volumes of the upper airway determined on Cone Beam CT (CBCT) data sets. MATERIAL AND METHODS: CBCT-scans of 34 patients were used to perform a 3D evaluation of the upper airway. Linear sagittal measurements reproducing those usually performed on lateral cephalograms, linear transversal measurements, cross-sectional areas, partial and total volumes (TV) were computed. RESULTS: The analysis showed a weak correlation (r < 0.8) between most of the linear measurements. The correlations between sagittal, transversal, and cross-sectional area with partial volumes were weak, except for the lower part of the nasopharynx which was highly correlated (r > 0.9) with sagittal measurement and with area. The upper part of the velopharynx presented a good correlation (0.8 < r < 0.9) between area and volume. Good correlation between most transversal measurements and the corresponding areas was found. Minimal sagittal, minimal transversal, and minimal area were weakly correlated with TV. CONCLUSIONS: Upper airway cannot be accurately expressed by single linear measurements as performed on cephalograms. The TV alone does not depict the morphology of the airway. A CBCT-based 3D analysis gives a better picture of the anatomical characteristics of the upper airways and therefore can lead to an improvement of the diagnosis.

Strains in periodontal ligament and alveolar bone associated with orthodontic tooth movement analyzed by finite element.

INTRODUCTION: Orthodontic tooth movement (OTM) is achieved by applying an orthodontic force system to the brackets. The (re)modeling processes of the alveolar support structures are triggered by alterations in the stress/strain distribution in the periodontium. According to the classical OTM theories, symmetric zones of compression and tension are present in the periodontium, but these do not consider the complex mechanical properties of the PDL, the alveolar structures' morphology, and the magnitude of the force applied. MATERIALS AND METHODS: Human jaws segments obtained from autopsy were microCT-scanned and sample-specific finite element (FE) models were generated. The material behavior of the PDL was considered to be nonlinear and non-symmetric and the alveolar bone was modeled according to its actual morphology. A series of FE-analyzes investigated the influence of the moment-to-force ratio, force magnitude, and chewing forces on the stress/strain in the alveolar support structures and OTM. RESULTS: Stress/strain findings were dependent on alveolar bone's morphology. Because of the nonlinear behavior of the PDL, distinct areas of tension, and compression could not be detected. Secondary load transfer mechanisms were activated and the stress/strain distribution in the periodontium was concealed by occlusal forces. CONCLUSIONS: We could not confirm the classical ideas of distinct and symmetrical compressive and tensile areas in the periodontium in relation to different OTM scenarios. Light continuous orthodontics forces will be perceived as intermittent by the periodontium. Because roots and alveolar bone morphology are patient-specific, FE-analysis of orthodontic loading regime should not be based on general models.

Influence of steroid drugs on orthodontically induced root resorption.

OBJECTIVES: To investigate the effect of acute and chronic corticosteroid treatment on orthodontically induced root resorption. DESIGN: 'Split mouth' design performing orthodontic tooth movement in 64, 6-month-old male rats divided into three groups: acute (n = 22), chronic (n = 23) and control group (n = 19). Acute and chronic group received corticosteroid treatment (8 mg/kg/day) for 3 and 7 weeks, respectively, while no pharmacological treatment was performed in the control group. Performed at the Department of Orthodontics, School of Dentistry, University of Aarhus, Aarhus, Denmark. EXPERIMENTAL VARIABLE: The upper left first molar was moved mesially for 21 days in all three groups with 25 g of force. Undecalcified histological sections were cut at the coronal and apical level. OUTCOME MEASURE: The number of intersections hitting resorption lacunae (ES), defined as a scalloped surface with or without cementoclasts, over the total number of intersections hitting the root surface (RS) were recorded and expressed as percentage. RESULTS: The acute group showed significantly more root resorption at the mesio-coronal level compared with the control and the chronic group. CONCLUSION: This could be ascribed to the lack of balance between blastic activities (inhibited by the drug) and the clastic activities (enhanced or unchanged by drug administration) occurring in the initial phase of drug administration. As a consequence, a careful monitoring of patients undergoing acute corticosteroid treatment is suggested.

Influence of sensory deprivation and perturbation of trigeminal afferent fibers on corticomotor control of human tongue musculature.

Several recent studies with transcranial magnetic stimulation (TMS) have demonstrated changes in motor evoked potentials (MEPs) in human limb muscles following modulation of sensory afferent inputs, but little is known about the regulation of the human tongue motor control. To test the effect of local anesthesia (LA) of the lingual nerve and topical application of capsaicin stimulation on tongue MEPs. Fourteen volunteers participated (21-30 years) in two randomized sessions; before, during a nerve block of the lingual nerve or topical capsaicin application (30 microl 5%) on the tongue, and after anesthesia or pain had subsided. EMG electrodes were placed on the tongue and the first dorsal interosseous (FDI) muscle (control). EMG signals were amplified, filtered (20 Hz-1 kHz), and sampled at 4 kHz (Nicolet, USA). TMS were delivered with a figure-of-eight coil (Magstim 200, UK). Scalp sites at which EMG responses were evoked in the relaxed tongue or FDI at the lowest stimulus strength were determined, i.e., motor threshold (T). MEPs were assessed using stimulus-response curves in steps of 10% T. Eight stimuli were presented at each stimulus level. The proximal hypoglossal nerve was activated by TMS delivered over the parieto-occipital skull distal to the right ear. Eight stimuli were delivered at 50% of maximum stimulator output. ANOVAs were used to analyze latency and peak-to-peak amplitudes. Capsaicin evoked mild pain (2.8+/-0.5), and a strong burning sensation (6.2+/-0.4) on 0-10 visual analogue scales. MEP amplitudes in tongue and FDI were not influenced by capsaicin (P>0.44) but by stimulus strength (P<0.001). MEP latencies in tongue (8.9+/-0.2 ms) and FDI (22.4+/-0.4 ms) were not affected by capsaicin (P>0.19). Hypoglossal nerve stimulation evoked a short-latency (3.6+/-0.9 ms) response (mean amplitude 65+/-9 microV); but was unaffected by capsaicin (P>0.54). LA did not have any effect on FDI MEPs but was associated with a significant facilitation of tongue MEPs at T+50% and T+60% about 50 min after the nerve block in the recovery phase. Also in this condition, the direct motor responses evoked by hypoglossal nerve stimulation remained constant. No direct effect of a strong burning sensation could be shown on peripheral or central corticomotor pathways to the relaxed tongue musculature, however, LA of the lingual nerve (cranial nerve V) seems able to induce a delayed change in corticomotor control of tongue musculature (cranial nerve XII) possibly related to unmasking effects at the cortical level but not completely excluding excitability changes at the brain stem level.

A histomorphometric evaluation of factors influencing the healing of bony defects surrounding implants.

PURPOSE: The authors' aim was to perform a histomorphometric study of the healing of bone defects created adjacent to titanium and hydroxyapatite (HA) -coated implants and covered with either a resorbable or a nonresorbable membrane in combination with different filler materials and to evaluate to what degree coating, membrane, and/or filler influenced the healing of the defects. MATERIALS AND METHODS: Posterior teeth were extracted from the mandibles of 10 baboons, and 12 implants were placed in each animal in the edentulous areas. The implants were either titanium or HA-coated, the membranes were either Vicryl, Gore-Tex, or Resolut, and the filler was either demineralized freeze-dried bone (DFDB), autogenous bone, or Biocoral. The implants were observed for either 3, 6, 9, 12, or 18 months. The volume of newly generated tissue and the relative contribution of bone, marrow, and filler were evaluated, as was relative extension of resorption, formation, and quiescent surface. RESULTS: The results indicated that autogenous bone is still the gold standard, but both the DFDB and Biocoral compared favorably to it. Both filler materials were being gradually replaced by bone; this process was not yet finished at 18 months postsurgery. DISCUSSION: Since even the sterilization of DFDB cannot exclude the possibility of a disease transmission, it is important to find an appropriate substitute. Both filler and membranes contributed to the re-establishment of the original volume; better results were achieved with the Vicryl and Gore-Tex membranes than with the Resolut. Biocoral can be considered an effective material. CONCLUSION: A bony defect is not necessarily a contraindication for the placement of an implant. (More than 50 references.)

The finite element method: a tool to study orthodontic tooth movement.

Orthodontic tooth movement is achieved by (re)modeling processes of the alveolar bone, which are triggered by changes in the stress/strain distribution in the periodontium. In the past, the finite element (FE) method has been used to describe the stressed situation within the periodontal ligament (PDL) and surrounding alveolar bone. The present study sought to determine the impact of the modeling process on the outcome from FE analyses and to relate these findings to the current theories on orthodontic tooth movement. In a series of FE analyses simulating teeth subjected to orthodontic loading, the influence of geometry/morphology, material properties, and boundary conditions was evaluated. The accurate description of alveolar bone morphology and the assignment of non-linear mechanical properties for the PDF elements demonstrate that loading of the periodontium cannot be explained in simple terms of compression and tension along the loading direction. Tension in the alveolar bone was far more predominant than compression.

Contrast-enhanced MRI compared to histological findings in the temporomandibular joint of antigen-induced arthritis in young rabbits.

OBJECTIVE: To study the correlation between histological findings and Magnetic Resonance Imaging (MRI) findings in experimentally induced arthritis in the temporomandibular joint (TMJ) of growing rabbits and to study the effect of intraarticular corticosteroid injections. METHODS: Arthritis was induced by ovalbumin in the left TMJ of 44 pre-sensibilized rabbits. Nine animals died during this procedure. Eight of the remaining animals with induced arthritis were treated with intraarticular corticosteroid injections one week after induction of arthritis. Twelve rabbits served as controls. MRI enhanced with Gadolinium-DTPA was performed on all animals 1 to 2 weeks after induction of arthritis and again before sacrifice and the degree of enhancement was calculated. Histology of the condyle was performed and degree of villous hyperplasia, synovial thickness, infiltration of inflammatory cells and pannus was graded. RESULTS: TMJ arthritis was successfully induced in the rabbits and was verified by enhancement of the MRI and by histological changes one week after the induction. Joints treated with intraarticular corticosteroid injections revealed complete inhibition of the inflammation. CONCLUSION: Enhancement of MRI in antigen-induced arthritis in the TMJ associated well with inflammatory changes shown histologically. An intraarticular corticosteroid injection prevents the initial inflammatory response in experimentally induced TMJ arthritis.

Secretion of osteopontin from MG-63 cells under a physiological level of mechanical strain in vitro--a [35S] incorporation approach.

To gain insight into the early response of osteoblastic cells to a physiological level of mechanical strain in vitro, the secretion of osteopontin by MG-63 osteosarcoma cells was assessed by [35S] incorporation and autoradiography. First, osteopontin secreted from MG-63 cells was immunolocalized at 60-64 kDa (Mr) by polyacrylamide gel electrophoresis. A uniform physiological level of strain was generated by a vacuum added to the convex side of a half-ball shaped silicon rubber membrane on which the cells were cultured on the concave side. After labelling proteins with [35S]-methionine/cysteine (147 microCi/ml), the membranes were exposed to a strain of 0.5 per cent (5000 microepsilon), 3 cycles/minute (sine wave) with 10 minutes on and off. At 1, 2 and 4 hours after strain, the supernatants were collected and analysed by 10 per cent sodium dodecyl sulphate-polyacrylamide gel electrophoresis and autoradiography. The results showed that osteopontin was secreted by the strained cells at significantly higher amounts than the non-strained cells at all three time points (P < 0.05), with the first hour being the most prominent. A physiological level of mechanical strain increased the secretion of osteopontin from MG-63 cells in an early phase. This finding implies an accelerated process of bone remodelling, which suggests that the application of light and intermittent forces would result in the cellular reaction identified in relation to orthodontic tooth movement. The results indirectly indicate that the level of force presently used might be too high.

Tissue reaction to orthodontic tooth movement in acute and chronic corticosteroid treatment.

OBJECTIVES: To study tissue reaction to orthodontic loading during the course of short- and long-term corticosteroid administration. DESIGN: 'Split-mouth' design to perform orthodontic tooth movement in 64 six-month-old male rats divided into groups: no drug administration (n = 19), acute (n = 22) and chronic (n = 23) 8 mg/kg/day corticosteroid treatment. Performed in the Department of Orthodontics at Aarhus University. EXPERIMENTAL VARIABLE: The upper left first molar was moved for 21 days. Bone markers were administered at 7 and 2 days before sacrifice. Histological sections were cut at the coronal level. OUTCOME MEASURE: Tooth movement rate, alveolar socket area, the relative extension of alveolar wall with erosion, and the mineralizing surfaces were measured and compared in the three groups. RESULTS: Tooth movement rate increased in the chronic group. The mechanical load induced an enlargement of the alveolar wall that was less pronounced in both medicated groups. In the acute group the drug suppressed bone resorption and formation without mechanical stimulus. Force application resulted in significant increase in the relative extension of resorption and formation in both drug groups; it was particularly pronounced in the chronic group. CONCLUSION: Because acute corticosteroid ingestion reduces bone turnover, in these patients orthodontic treatment might best be postponed until a time the patient is free of the drug. Chronic steroid ingestion leads to an increased biological reaction to mechanical perturbation indicating that the orthodontic force level should be reduced and controlled more frequently in patients on chronic steroid treatment.

Tissue reaction to orthodontic tooth movement in different bone turnover conditions.

OBJECTIVES: To study the tissue reaction to orthodontic load in normal, high, and low bone turnover states. DESIGN: 'Split mouth' design performing orthodontic tooth movement in 52, 6-month-old male rats with: normal (n = 19), high (n = 16), and low bone turnover (n = 17), the latter two being obtained by induction of hyperthyroidism and hypothyroidism, respectively. Performed at the Department of Orthodontics at Aarhus University. EXPERIMENTAL VARIABLE: The upper left first molar was moved for 21 days. Bone markers were administered 7 and 2 days before killing. Histological sections were cut at the coronal and apical levels. OUTCOME MEASURE: Alveolar socket area, periodontal ligament width, the relative extension of alveolar wall with erosion surfaces, and the mineralizing surfaces were measured and compared in the three groups. RESULTS: Alveolar socket, periodontal ligament width, and erosion surface were larger on the treated than on the control side in the three groups. The normal and hypothyroid groups showed a wider periodontal ligament at the bucco-distal site at the coronal level, while the hyperthyroid group showed a widening which was not spatially oriented. The normal and hyperthyroid groups showed higher erosion at the corono-mesial site. The mineralizing surfaces were larger on the treated than on the control side in the normal and hypothyroid groups, but not in the hyperthyroid group. CONCLUSION: In the hyperthyroid group, the widening of the periodontal ligament was not spatially oriented and the increased erosion was not accompanied by increased formation, as observed in the normal and hypothyroid groups.

Two-vector mechanics.

The conventional orthodontic appliance is not without its limitations for certain types of tooth movements; in particular, if the appliance cannot access the area to elicit the type of force vector for a particular displacement. Examples of such movements are: space closure by translation, uprighting and intrusion of posterior teeth, intrusion with retraction and lingual root torque of anterior teeth. In this paper we describe a mathematical method to design an appliance system that overcomes these difficulties. This system includes two statically determined elements and allows for highly controlled force vector application point and direction. A clinical case of midline discrepancy is shown to demonstrate the clinical use and utility of this method.

Expansion: how much can the periodontium tolerate?

Arch length discrepancy can be resolved either by extraction or expansion. Normally, the choice of the clinician is founded on evidence-based treatment outcome reports. The adverse effect related to either approach is considered carefully before deciding. In the adult patient, the retraction of soft tissues consequent to extractions may be undesirable. Also, the deep bite may be difficult to correct if incisor proclination is to be avoided. Expansion has been reported to elicit gingival dehiscences. This is a report of a borderline case where the crowding is resolved acceptably through extreme expansion, but without any adverse periodontal effects.

Resorption of the temporomandibular condylar bone according to subtypes of juvenile chronic arthritis.

OBJECTIVE: To evaluate the relative impact of sex, type of onset, course of disease, age at onset, duration of disease and status of HLA-B27, antinuclear antibodies (ANA), and rheumatoid factor on the risk of developing a condylar erosion. METHODS: Condylar changes of the temporomandibular joint (TMJ) were diagnosed on orthopantomograms from 169 consecutive patients with juvenile chronic arthritis (JCA). A multiple regression analysis was applied to establish the relative weight of the independent variables affecting the severity of the condylar erosion. RESULTS: It was found that 62.1% of the patients exhibited condylar resorption. The highest prevalence was seen in children with a polyarticular onset or course of disease and early age at onset and severe resorption was also frequent in these groups. Patients with positive ANA also had a high prevalence but with a mild degree of resorption. In contrast, HLA-B27 positive patients had a lower risk of TMJ involvement and resorptive changes of the condyle. CONCLUSION: Polyarticular and early onset arthritis are associated with a high risk for TMJ involvement and a severe condylar bone loss can be expected. ANA positive patients have a high prevalence, and B27 positive patients have a low prevalence of TMJ arthritis but in both subgroups, the outcome of the bone resorptive process is mild.