Three-dimensional finite-element analysis of maxillary protraction with and without rapid palatal expansion.
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The aims of this study were to determine the reaction of the craniofacial bones on the protraction force transferred to the maxillary body, and whether or not the midpalatal suture had opened during skeletal Class III treatment. A computerized tomograph was obtained from a dry skull with a normal occlusion to construct a three-dimensional finite-element model (3D.FEM) of the craniofacial bones and the maxillary teeth to simulate actual bone reactions. A protraction force of 500 g was applied at the first premolar region, directed 20 degrees inferior to the occlusal plane. The displacement and the stress distribution of the craniofacial bones and sutures were then calculated using the ANSYS 5.3 program dividing the analysis into two simulations, based on whether or not the midpalatal suture was opened. The results showed that there was less compressive stress and greater tensile stress in the circumaxillary suture areas when the midpalatal suture was opened. The amount of displacement and deformation when the midpalatal suture was opened also demonstrated a decrease in upward-forward rotation of the maxilla and zygomatic arch and greater amounts of displacement in the frontal, vertical, and lateral directions compared with no opening of the midpalatal suture. Analysis of these results showed that maxillary protraction produce similar changes to normal downward and forward growth of the maxilla and was achieved with accompanying opening of the midpalatal suture. (+info)
Rapid maxillary expansion in adults: cranial stress reduction depending on the extent of surgery.
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The objective of this study on surgically assisted rapid maxillary expansion (RME) was to examine the extent of stress reduction in the midface and the cranial base with various surgical procedures. Four finite element models of the skull were generated (one without and three with different surgical incisions), in which a virtual RME (5 mm gap width) was simulated. In all four simulations, von-Mises stresses were measured at 30 anatomical structures of the midface and cranial base (in MPa) and compared. The highest von-Mises stresses were measured with the model that did not involve any osteotomies. A reduction of the observed stresses was found after isolated weakening of the zygomaticoalveolar crest on both sides. The model with a complete lateral osteotomy from the piriform aperture to the pterygopalatal junction clearly showed lower stresses than the model with isolated weakening of the zygomaticoalveolar crest. The lowest stress values, however, were seen on the model with a complete osteotomy at the Le Fort I level. In order to prevent complications at the cranial base, surgical assistance is an important aspect of RME in adults. The extent of osteotomies can be varied. The older the patient and the less the bone elasticity, the more extensive should be the surgical weakening in order to minimize the stresses induced at the cranial base and the midface. In older patients, a complete lateral osteotomy from the piriform aperture to the pterygopalatal junction seems to reduce stresses at the cranial base more effectively than isolated weakening of the zygomaticoalveolar crest. (+info)
Evaluation of the effects of rapid maxillary expansion in growing children using computer tomography scanning: a pilot study.
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The principle of rapid maxillary expansion (RME) as a method to expand the transverse dimension of the palate and maxillary dental arch is by no means new, and previous studies have reported the effects of the method using a variety of radiographic methods. In the present study, the effect of a Hyrax splint appliance was studied in a group of nine growing children (six females, three males; mean age 8 years 1 month) undergoing orthodontic treatment. The changes were evaluated on pre- and post-treatment computer tomographic scans taken using a low-dosage protocol. The results demonstrated a clear appliance-induced effect in all patients, although the relative contribution of dental, alveolar, and skeletal changes varied from subject to subject. The average expansion, measured at the molar crowns, was 3.6 mm, whereas the actual sutural opening, the main aim of RME, was as low as 1.6 mm. The findings of this study raise doubts as to the efficiency of the Hyrax appliance and further comparative studies are recommended to evaluate other methods of maxillary expansion. (+info)
Mechanical force-induced midpalatal suture remodeling in mice.
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Mechanical stress is an important epigenetic factor for regulating skeletal remodeling, and application of force can lead to remodeling of both bone and cartilage. Chondrocytes, osteoblasts and osteoclasts all participate and interact with each other in this remodeling process. To study cellular responses to mechanical stimuli in a system that can be genetically manipulated, we used mouse midpalatal suture expansion in vivo. Six-week-old male C57BL/6 mice were subjected to palatal suture expansion by opening loops with an initial force of 0.56 N for the periods of 1, 3, 5, 7, 14 or 28 days. Periosteal cells in expanding sutures showed increased proliferation, with Ki67-positive cells representing 1.8+/-0.1% to 4.5+/-0.4% of total suture cells in control groups and 12.0+/-2.6% to 19.9+/-1.2% in experimental/expansion groups (p<0.05). Starting at day 1, cells expressing alkaline phosphatase and type I collagen were seen. New cartilage and bone formation was observed at the oral edges of the palatal bones at day 7; at the nasal edges only bone formation without cartilage appeared to occur. An increase in osteoclast numbers suggested increased bone remodeling, ranging from 60 to 160% throughout the experimental period. Decreased Saffranin O staining after day 3 suggested decreased proteoglycan content in the secondary cartilage. Micro-CT showed a significant increase in maxillary width at days 14 and 28 (from 2334+/-4 microm to 2485+/-3 microm at day 14 and from 2383+/-5 microm to 2574+/-7 microm at day 28, p<0.001). The suture width was increased at days 14 and 28, except in the oral third region at day 28 (from 48+/-5 microm to 36+/-4 microm, p<0.05). Bone volume/total volume was significantly reduced at days 14 and 28 (50.2+/-0.7% vs. 68.0+/-3.7% and 56.5+/-1.0% vs. 60.9+/-1.3%, respectively, p<0.05), indicative of increased bone marrow space. These findings demonstrate that expansion forces across the midpalatal suture promote bone resorption through activation of osteoclasts and bone and cartilage formation via increased proliferation and differentiation of periosteal cells. Mouse midpalatal suture expansion would be useful in further studies of the ability of mineralized tissues to respond to mechanical stimulation. (+info)
Comparison of nasal volume changes during rapid maxillary expansion using acoustic rhinometry and computed tomography.
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The purpose of this study was to compare nasal volume changes using acoustic rhinometry (AR) and computed tomography (CT). The subjects were 10 children (6 girls and 4 boys, with an age range of 12-14 years) who required rapid maxillary expansion (RME) on the basis of their individual malocclusion. All patients were found to have normal nasal cavities following anterior rhinoscopic examination. AR and CT were undertaken at the start of treatment (t(1)) and 6 months after expansion (t(2)). Volume changes due to expansion were evaluated using Wilcoxon's test, and the correlation between the two methods was assessed with correlation analyses. Both methods demonstrated that nasal volume significantly increased following the use of RME (P<0.05). Correlation analyses showed no difference in volume (P>0.05) using either of the two methods. (+info)
Ultrasound bone cutting for surgically assisted rapid maxillary expansion under local anesthesia. Preliminary results.
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Surgically assisted rapid maxillary expansion (SARME) is a well-established therapy for correction of maxillary transverse deficiency in adults, when consolidation of sutures has just been completed. It can be performed either under general or under local anesthesia and it can be accomplished with many surgical techniques. One of the most critical steps of SARME is the detachment of the pterygo-maxillary junction, due to the risks connected to such procedure. When required to obtain specific expansion patterns, the pterygo-maxillary separation has been suggested until now only for interventions under general anesthesia, due to the dangerousness and the rawness of this surgical step in awake patients. The authors introduce the use of an ultrasonic bone-cutting device to perform all osteotomic steps of SARME under local anesthesia on an outpatient basis, including pterygo-maxillary detachment. This ultrasonic device is unique in that the osteotomic action occurs only when the tool is employed on mineralized tissues, while it stops on soft tissues. It works in a linear pattern of vibration and it allows precise osteotomies without producing any heat damage to osteotomic surfaces and without any dangerous hammer-related stroke. Due to its precision and safety, this device named Piezosurgery, allows patients to undergo all the steps of SARME under local anesthesia, also without hospitalization. (+info)
Multitomographic evaluation of the dental effects of two different rapid palatal expansion appliances.
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Rapid palatal expansion (RPE) is widely used in the treatment of transverse maxillary deficiencies. Generally, there are two types of RPE appliances: banded and bonded expanders. The purpose of this prospective study was to compare the dental effects of banded and bonded appliances. The study consisted of 23 patients (13 females and 10 males) with a bilateral maxillary deficiency. Twelve patients (seven females and five males) with a mean age of 14.8 +/- 0.3 years were treated with banded RPE and 11 patients (six females and five males) with a mean age of 15.1 +/- 0.7 years with bonded RPE. Multitomographic radiographs were taken before (T0) and at the end (T1) of expansion while the patients were wearing an acrylic mandibular appliance in which ball bearings and bars were embedded. Statistical analyses of the measurements at T0 and T1 were undertaken with a paired t-test, and the difference between the groups assesed with a Student's t-test. In both groups, the angle between the radiographic image of the bar and the axial inclination of the upper first premolar and molar teeth was (5.34 and 2.73 degrees for the right premolars, 5.17 and 2.28 degrees for the left premolars, 11.83 and 3.73 degrees for the right molars, and 9.75 and 5.64 degrees for the left molars in the banded and bonded groups, respectively. The distance from the vestibular cortical plate to the palatal root of these teeth (1.17 and 1.23 mm for the right premolars, 2.46 and 1.09 mm for the left premolars, 2.75 and 0.64 mm for the right molars, 2.23 and 0.96 mm for the left molars in the banded and bonded groups, respectively) increased (both P < 0.01). These increases indicated buccal tipping of the teeth. Comparison of the two groups showed that tipping of the first molar and premolar teeth in the banded group was significantly more than in the bonded group (P < 0.01 and P < 0.001, respectively). (+info)
Success rate and efficiency of activator treatment.
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In a retrospective multicentre study, the success rate and efficiency of activator treatment were analysed. All patients from two University clinics (Giessen, Germany and Berne, Switzerland) that fulfilled the selection criteria (Class II division 1 malocclusion, activator treatment, no aplasia, no extraction of permanent teeth, no syndromes, no previous orthodontic treatment except transverse maxillary expansion, full available records) were included in the study. The subject material amounted to 222 patients with a mean age of 10.6 years. Patient records, lateral head films, and dental casts were evaluated. Treatment was classified as successful if the molar relationship improved by at least half to three-fourths cusp width depending on whether or not the leeway space was used during treatment. Group comparisons were carried out using Wilcoxon two-sample and Kruskal-Wallis tests. For discrete data, chi-square analysis was used and Fisher's exact test when the sample size was small. Stepwise logistic regression was also employed. The success rate was 64 per cent in Giessen and 66 per cent in Berne. The only factor that significantly (P < 0.001) influenced treatment success was the level of co-operation. In approximately 27 per cent of the patients at both centres, the post-treatment occlusion was an 'ideal' Class I. In an additional 38 per cent of the patients, marked improvements in occlusal relationships were found. In subjects with Class II division 1 malocclusions, in which orthodontic treatment is performed by means of activators, a marked improvement of the Class II dental arch relationships can be expected in approximately 65 per cent of subjects. Activator treatment is more efficient in the late than in the early mixed dentition. (+info)