Hypoxia triggers a HIF-mediated differentiation of peripheral blood mononuclear cells into osteoclasts.

BACKGROUND: The source and mechanisms leading to osteoclast (OC) generation during tooth movement are not clearly understood. We hypothesized that during tooth movement, OC differentiate from peripheral blood mononuclear cells (PBMNC) downstream of the global hypoxia-inducible transcription factor hypoxia-inducible factor (HIF)-1α. OBJECTIVE: The objective of this study was to demonstrate up-regulation of OC growth factors from osteoblasts (OB) and subsequent conversion of PBMNC into functional OC under hypoxic stress. MATERIAL AND METHODS: Human primary PBMNC were cocultured with/without OB and subjected to either hypoxia (2.5% O2) or normoxia (21% O2) over 14 days. Levels of HIF, vascular endothelial growth factor (VEGF) and receptor activator for nuclear factor kappa-ß ligand (RANKL) were measured. Conversion of PBMNC into OC was measured using resorption and TRAP assays. RESULTS: Functional OC were only observed in response to hypoxia during coculture of PBMNC and OB and only after up-regulation of HIF, VEGF and RANKL in the hypoxic conditions. YC-1, a HIF inhibitor, reduced OC formation in response to hypoxia. CONCLUSION: Hypoxia triggers the differentiation of PBMNC into functional OC in the presence of OB in a HIF-dependent manner as would occur during orthodontic loading of the periodontal ligament space.

Effect of behavior modification on patient compliance in orthodontics.

The purpose of this study was to evaluate the effects of a reward system for improving patient compliance in orthodontic treatment. The sample consisted of 144 orthodontic patients (63 male, 81 female, average age 12.8 years), 6 to 12 months into their treatment. The sample was divided into above-average and below-average compliers, based on the orthodontic patient cooperation scale (OPCS). Each group was further divided into three subgroups: (a) a control group, which received only standard instructions; (b) an award group, which received compliance instructions and a written evaluation of compliance; and (c) a reward group, which received compliance instructions, a report card, and eligibility to receive rewards for adherent behavior. Two measurements of patient compliance were used: (1) the OPCS, which divided the sample into high and low compliers and was used to compare compliance before and after the 6-month experimental period; and (2) a clinical evaluation of compliance that was based on oral hygiene, appointment punctuality, appliance wear, and appliance maintenance. Evaluations were completed at each monthly appointment. Average compliance scores of above-average compliers showed no significant improvement with rewards. The average scores of patients with below-average compliance did not improve significantly. Only oral hygiene scores in the low compliance reward group were better than in the low compliance control group. Academic performance in school was found to be correlated (p < 0.001) with compliance. Above-average compliers remained above average in their compliance. The award/reward system may help motivate below-average compliers to comply with prescribed instructions.

Stiffness-deflection behavior of selected orthodontic wires.

Treatment of horizontal and vertical tooth discrepancies requires wires of low stiffness to produce forces as the teeth are leveled and aligned. In this investigation, the stiffness characteristics of several solid and multistrand nickel-titanium and stainless steel orthodontic wires were determined at selected clinically relevant deflections. Twenty specimens of 24 different wires were tested in both three-point and three-bracket bending modes. The unloading force deflection plot of each wire was described by a polynomial regression from which wire stiffnesses were obtained by mathematical differentiation. Graphs of the functional relationship between stiffness and deflection are presented. The results of this investigation show that wire stiffness can be altered not only by changing the size, but also by varying the number of strands and the alloy composition. An equally important finding was the dependence of stiffness on deflection for most of the wires measured. Comparisons were also made between the stiffness values obtained in three-point bending and the three-bracket bending systems.

Frictional resistances in stainless steel bracket-wire combinations with effects of vertical deflections.

This research evaluated the effects of different bracket-wire combinations and second-order deflections on kinetic friction. Thirteen different brackets, six with 0.018 x 0.025 inch slots and seven with 0.022 x 0.028-inch slots were evaluated with six different sizes and shapes of stainless steel orthodontic wire, i.e., 0.016, 0.016 x 0.022, 0.017 x 0.025, 0.018, 0.018 x 0.025 and 0.019 x 0.026 inch for four second order deflections of 0.00, 0.25, 0.50, and 0.75 mm. The wires were ligated into the brackets with elastomeric modules. Bracket movement was implemented by means of an Instron universal testing instrument (RMO, Denver, Colo.), and frictional forces were measured by a tension load cell and recorded on an X-Y recorder (Hewlett-Packard, Anaheim, Calif.). Second-order deflection was created by a specially designed and machined testing apparatus that allowed two alternate pairs of the four total brackets to be offset in increments of 0.25 mm. The kinetic frictional force increased for every bracket-wire combination tested as the second-order deflection increased. Friction also increased with an increase in wire size, whereas rectangular wires produced greater friction than round wires. Bracket designs that limited the force of ligation on the wire generated less friction at low second-order deflections (0.00 and 0.25 mm).

The effects of exogenous prostaglandin E2 on root resorption in rats.

This study evaluated the amount and depth of root resorption associated with varying concentrations and frequencies of injectable, exogenous prostaglandin E2 (PGE2) in conjunction with orthodontic tooth movement in rats. The sample consisted of 155 maxillary right and left first molars from 88, 8-week old, male Sprague-Dawley rats. The animals were divided into three control groups and two experimental groups. The control animals were divided into one nonappliance and two appliance groups. The experimental animals were divided into 2- and 4-week experimental time periods that were further subdivided based on single and weekly injection intervals of PGE2 and four different injectable concentration levels, i.e., 0.1, 1.0, 5.0, and 10.0 micrograms. A fixed orthodontic appliance was ligated between the maxillary incisors and maxillary first molars with closed-coil nickel-titanium springs. The appliance had an initial activating force of 60 gm. Serial histologic sections of the mesial root of the maxillary first molar were made, and a quantitative histomorphometric analysis of root resorption on the mesial and distal surfaces was performed. This study demonstrated increased root surface resorption when using exogenous PGE2 injections to enhance orthodontic tooth movement over a 2-week period with increasing root resorption on the mesial surface as compared with the distal surface in PGE2 treated teeth. No differences in root resorption were found with either multiple injections or increasing concentration in the 4-week experimental group. Local injection of PGE2 appeared to have no effect on the number or depth of resorption lacunae in either the 2- or 4-week groups.

A longitudinal cephalometric study of the soft tissue profile of short- and long-face syndromes from 7 to 17 years.

The longitudinal growth and development of the soft tissue drape for boys and girls with long and short vertical patterns was examined from age 7 to 17 years. The sample was taken from the Denver Growth Study and consisted of 32 subjects who were selected on the basis of their percentage of lower anterior vertical face height. All subjects were of northern European ancestry, and none had undergone orthodontic treatment. The sexual dimorphism was evident as anticipated for several soft tissue measurements. The boys showed continued growth through age 16 years in contrast to the girls who attained the adult size of the soft tissue integument around 14 years. A significant difference between vertical facial patterns was reported for all soft tissue variables with the exception of the soft tissue thickness at A point and the upper lip height. The boys and girls with long vertical patterns exhibited a thicker and longer soft tissue drape for the most variables when compared with those with short facial patterns. These soft tissue differences are believed to be compensatory mechanisms in long-face subjects, which may attempt to mask the vertical dysplasia, thereby producing a more normal facial profile. Individual growth assessments revealed that the perioral soft tissues follow a pattern similar to that of the mean group patterns. The subjects with long vertical facial patterns experienced their pubertal growth spurt earlier than the short-face subjects. This may have clinical implications in the timing of orthodontic intervention and treatment.

Fracture strength of ceramic brackets during arch wire torsion.

This study evaluated the fracture strengths of eight new vintage ceramic brackets with application of torsional forces. Palatal root torque was applied at the distal side of right maxillary central incisor brackets with 0.022-inch slots by means of a 0.0215 x 0.027-inch rounded edge stainless steel arch wire. A specially designed apparatus that attached to an Instron machine was used to test the ceramic brackets. The amount of torque, degrees of torsion at failure, and fracture locations were measured. The monocrystalline bracket did not break when the torquing test was applied; the portion of the wire outside the slot of the bracket twisted on itself. The mean torquing forces at failure ranged from 5755.2 gm-mm to 9316.5 gm-mm and could be separated into three statistically different groups. The mean torsional rotation at fracture ranged from 32.7 degrees to 68.1 degrees for the polycrystalline brackets. The results suggested that all the brackets studied were sufficiently strong to withstand the commonly accepted magnitudes of arch wire torquing forces. The present investigation showed higher angulation values for all the brackets than those reported by Holt who used the same apparatus with older style brackets.

Tomographic assessment of temporomandibular joints in patients with malocclusion.

There is a paucity of information on the morphological assessment of the temporomandibular joint in relation to varying skeletal and dental relationships. The purpose of this study was to evaluate the morphologic relationship of the condyle and fossa in patients with different malocclusions and skeletal relationships. Pretreatment records of 232 orthodontic patients, 95 males and 137 females, of Caucasian descent and ranging in age from 9 years 4 months to 42 years 6 months, were examined. Records included dental casts, lateral cephalometric radiographs, hand-wrist radiographs, and corrected tomograms of right and left TM joints. Nonconcentricity and mild asymmetry of the condyle-fossa relationship were commonly observed. The left condyle was found to be more anteriorly positioned than the right, with the mean percentage of joint space being 6.93% on the left side and -1.24% on the right. Skeletal and dental Class III patients demonstrated significantly more anteriorly positioned condyles (P < 0.05). There were no significant differences in condylar position between Class I and Class II groups based on ANB or Angle's classification. Further, no significant difference in condylar position was observed between groups based on overbite or crossbite.

Ceramic bracket design: an analysis using the finite element method.

This investigation was designed to generate finite element models for selected ceramic brackets and graphically display the stress distribution in the brackets when subjected to arch wire torsion and tipping forces. Six commercially available ceramic brackets, one monocrystalline and five polycrystalline alumina, of twin bracket design for the permanent maxillary left central incisor were studied. Three-dimensional computer models of the brackets were constructed and loading forces, similar to those applied by a full-size (0.0215 x 0.028 inch) stainless steel arch wire in torsion and tipping necessary to fracture ceramic brackets, were applied to the models. Stress levels were recorded at relevant points common among the various brackets. High stress levels were observed at areas of abrupt change in geometry and shape. The design of the wire slot and wings for the Contour bracket (Class One Orthodontic Products, Lubbock, Texas) and of the outer edges of the wire slot for the Allure bracket (GAC, Central Islip, N.Y.) were found to be good in terms of even stress distribution. The brackets with an isthmus connecting the wings seemed to resist stresses better than the one bracket that did not have this feature. The design of the isthmus for the Transcend (Unitek/3M, Monrovia, Calif.) and Lumina (Ormco, Glendora, Calif.) brackets were found to be acceptable as well. The Starfire bracket ("A" Company, San Diego, Calif.) showed high stresses and irregular stress distribution, because it had sharp angles, no rounded corners, and no isthmus. The finite element method proved to be a useful tool in the stress analysis of ceramic orthodontic brackets subjected to various forces.(ABSTRACT TRUNCATED AT 250 WORDS)

The effects of exogenous prostaglandins on orthodontic tooth movement in rats.

The long-term effects of varying concentrations and frequencies of injectable, exogenous prostaglandin E2 (PGE2) on the rate of tooth movement and the amount of root resorption were evaluated. There were 132 male Sprague-Dawley rats 8 weeks old that initially weighed 225 to 250 gm. Five animals were in a pilot study, while seven were baseline controls and eight were appliance controls. The remaining 112 animals were divided into two experimental time periods of 2 and 4 weeks. Then, each experimental time period was divided into four subgroups of 14 animals based on concentration levels of PGE2 injections, i.e., 0.1, 1.0, 5.0 and 10.0 micrograms. Half of these animals in the dosage subgroup received a single injection at appliance placement and the other half received weekly injections. A fixed orthodontic appliance consisting of closed-coil nickel-titanium springs were ligated between the maxillary incisors and maxillary first molars. The initial activating force was 60 gm. The results showed that injections of exogenous PGE2 over an extended period of time in rats did enhance the amount of orthodontic tooth movement. However, there was no statistically significant difference in tooth movement between the single and multiple injection groups or among the four concentration levels of PGE2 used in either the 2- or 4-week time periods. The amount of root resorption as seen from scanning electron micrographs did increase with the use of prostaglandin injections, specifically with increased numbers of injections and with increased concentrations of PGE2.

Skeletal and dental changes associated with the treatment of deep bite malocclusion.

A retrospective study of 132 treated orthodontic cases presenting at least 70% overbite was conducted using dental casts and lateral cephalometric radiographs from before and after treatment. These were 61 Class I, 27 Class II, Division 1, and 44 Class II, Division 2 malocclusion patients. Six different treatment modalities for the correction of the deep bite were compared. On the basis of the analysis of cephalometric measurements, no statistically significant differences were observed between the various treatment mechanics in the correction of the deep bite. Only in the Class II, Division 2 sample, total anterior face height increased significantly (p < 0.01) with all treatment modalities. The data were then grouped according to Angle classification regardless of the type of mechanics used. Within each Angle class, the changes from before to after treatment were statistically significant for almost all of the cephalometric measurements. These significant changes were due to both anticipated growth and orthodontic treatment. The treatment of overbite primarily affected the proclination of incisors and the extrusion of molars. Within each Angle classification, the patients were also separated according to whether the permanent teeth had been extracted. The nonextraction group was compared with the extraction group for the changes in each cephalometric measurement. It was found that the extraction of teeth did have a significant effect on the changes observed with treatment in all the Angle classes but was more pronounced in the Class I sample. The proclination of incisors was less and the mesial movement of molars was more in patients who were treated with the extraction of premolar teeth than those who were treated with the nonextraction procedures.

Lateral cephalometric analysis of skeletal patterns in patients with and without internal derangement of the temporomandibular joint.

Twenty-three female volunteers with normal temporomandibular joints (TMJ) were compared with 24 female patients with documented TMJ internal derangements. Magnetic resonance imaging and lateral cephalometric radiographs were used to investigate the relationship between TMJ disk displacement and skeletal facial form. Results indicated that the patients with internal derangements have significantly smaller mandibles and maxillae. However, these sagittal measurements of jaw length were not associated with disproportionate changes in other cephalometric variables. In general, no district relationship was found between the morphologic features of the face and the internal derangements of the temporomandibular joint.

Relative kinetic frictional forces between sintered stainless steel brackets and orthodontic wires.

The level of kinetic frictional forces generated during in vitro translation at the bracket-wire interface were measured for two sintered stainless steel brackets as a function of two slot sizes, four wire alloys, and five to eight wire sizes. The two types of sintered stainless steel brackets were tested in both 0.018-inch and 0.022-inch slots. Wires of four different alloy types, stainless steel (SS), cobalt chromium (Co-Cr), nickel-titanium (Ni-Ti), and beta-titanium (beta-Ti), were tested. There were five wire sizes for the 0.018-inch slot and eight wire sizes for the 0.022-inch slot. The wires were ligated into the brackets with elastomeric ligatures. Bracket movement along the wire was implemented by means of a mechanical testing instrument, and time dependent frictional forces were measured by a load cell and plotted on an X-Y recorder. For most wire sizes, lower frictional forces were generated with the SS of Co-Cr wires than with the beta-Ti or Ni-Ti wires. Increase in wire size generally resulted in increased bracket-wire friction. There were no significant differences between manufacturer for the sintered stainless steel brackets. The levels of frictional force in 0.018-inch brackets ranged from a low of 46 gm with 0.016-inch Co-Cr wire to a high of 157 gm with 0.016 x 0.025-inch beta-Ti wire. In comparing the data from a previous study by Kapila et al. 1990 performed at OUHSC with the same apparatus, the friction of sintered stainless steel brackets was approximately 40% to 45% less than the friction of the conventional stainless steel brackets.

Elastic energy/stiffness ratios for selected orthodontic wires.

This investigation determined the ratio of the energy available for orthodontic tooth movement to the stiffness and flexibility of a given wire. Twenty-five specimens each of five brands of orthodontic wire were tested in tension in the as-received condition. Force versus elongation diagrams were obtained and then converted into stress-strain data. Mean values were determined for the yield strength and yield strain for each brand of wire. The modulus of elasticity (E), modulus of resilience (R), and elastic compliance (C) were then calculated. Two ratios were established by using the three mechanical properties: (1) the modulus of resilience/modulus of elasticity (R/E) ratio and (2) the modulus of resilience/elastic compliance (R/C) ratio. The results confirmed that the use of these two ratios in combination permitted one to differentiate among the various types of orthodontic wires, with respect to stored energy and its relationship to the stiffness or flexibility of the wire.

Assessment of symphysis morphology as a predictor of the direction of mandibular growth.

The purpose of this study was to determine whether symphysis morphology could be used as a predictor of the direction of mandibular growth and to assess growth changes of the symphysis. Cross-sectional data included lateral cephalometric radiographs of 115 adults (58 women, 57 men) with the longitudinal sample a subset of 62 subjects (30 females, 32 males) at four age groups. The direction of mandibular growth was evaluated with seven cephalometric measurements that included Y-axis, SN to mandibular plane, palatal plane to mandibular plane, gonial angle, sum of saddle, articulare and gonial angles, percentage lower facial height, and posterior/anterior face height. The mandibular symphyseal dimensions studied were height, depth, ratio (height/depth), and angle. Symphysis morphology was found to be associated with the direction of mandibular growth, especially in male subjects with symphysis ratio having the strongest relationship. A mandible with an anterior growth direction was associated with a small height, large depth, small ratio, and large angle of the symphysis. Conversely, a posterior growth direction was associated with a large height, small depth, large ratio, and small angle of the symphysis. Symphysis dimensions continued to change until adulthood with male subjects having a greater and later occurring change compared with female subjects.

Longitudinal changes in the adult facial profile.

Longitudinal growth changes in the adult craniofacial complex were studied for 24 white male and 23 white female subjects between the ages of 18 and 42 years who had Class I or end-to-end molar relationships and no excessive protrusions or retrusions. The male profile straightened with age, and both lips became more retrusive. The males increased in all nose dimensions and in soft tissue thickness at pogonion, but decreased in upper lip thickness at labrale superius with a slight decrease in lower lip thickness at labrale inferius. The female profile did not become straighter with age, and the lips did not become more retrusive as with males. The females also increased in nose dimensions but decreased in soft tissue thickness at pogonion, decreased in upper lip thickness at labrale superius, and slightly increased in lower lip thickness at labrale inferius. For males most changes in hard tissue measurements had been accomplished by age 25 years, whereas soft tissue changes in the nose, lips, and chin occurred as much after age 25 years as from age 18 to 25 years. For females, both hard and soft tissue measurements had more changes after age 25 years than before. Those males who had high relative sagittal mandibular growth also experienced larger sagittal maxillary growth, and those who showed greater skeletal growth also had more soft tissue growth at the nose. The females also had good correlation between sagittal growth in the mandible and the maxilla. Later maturing males had greater adult craniofacial skeletal growth in several dimensions.

A cephalometric evaluation of nonextraction cervical headgear treatment in Class II malocclusions.

The effects of orthodontic treatment with the use of the cervical pull facebow headgear in patients with Class II malocclusions were evaluated with special reference to the dentition, the maxillary complex, the mandible, and the facial profile. The records of 85 patients, with a mean age of 11.3 +/- 1.7 years, were selected from a sample of 125 patient records requested from the office of John S. Kloehn in Appleton, Wisconsin. Dr. Kloehn has used traditional cervical pull facebow therapy in his practice. Over 100 linear and angular cephalometric measurements were made from the pretreatment and posttreatment records. These measurements were used to evaluate growth and/or treatment changes. The treatment sample was divided by size of the pretreatment FMA, sex, and the age range in which treatment was started, i.e., prepubertal, circumpubertal, and postpubertal. Overall, the results showed that the changes were very close to what would occur as a result of normal growth in Class I individuals. The maxillary permanent first molars continued to progress forward, the maxilla continued to grow forward, and the cranial base showed very little change, if any. The mandibular plane angle did not increase appreciably with treatment, regardless of the size of the pretreatment mandibular plane angle. Very few significant differences were found between sexes, pretreatment age groups, or between groups based on pretreatment Frankfort mandibular plane angle.

A longitudinal cephalometric study of transverse and vertical craniofacial growth.

Longitudinal growth changes were studied from posteroanterior cephalometric radiographs of 25 male subjects from 4 to 25 years of age and 25 female subjects from 4 to 20 years of age who had Class I skeletal and dental patterns. Growth for males continued past age 18 years for all skeletal measurements, except for maxillary width. Growth for females was completed by 17 years for all skeletal measurements. At 6 years of age the transverse measurements had a greater percentage of the adult size completed than vertical measurements for both males and females. Gender differences at age 6 years were in the mean widths for the cranium, face, and maxilla. At age 12 years the differences were in cranial width, maxillary width, and maxillary and mandibular intermolar width (6-6). There were gender differences at age 18 years for all the variables, except for nasal width and mandibular intermolar width (6-6). Regression lines provided strong-to-moderate predictive equations to determine the size of most of the measurements at age 18 years, if the value at age 6 years is known.

Perceptions of a balanced facial profile.

This research deals with the assessment of the role of the nose, lips, and chin in achieving a balanced facial profile. A survey instrument of constructed androgynous facial silhouettes was evaluated by 545 professionals. The silhouettes had varied nose, lips, and chin relationships, as well as changes in facial angle and angle of convexity. The varied facial profiles were graded on the basis of most preferred to least preferred. The data was computed, and it was found that in males, a straighter profile was preferred in comparison with a slightly convex profile for the females. Among the various unfavorable combinations, the worst ones were either with an extremely recessive chin or those with excessively convex faces. More lip protrusion was found acceptable for both male and female faces when either a large nose or a large chin was present. It is suggested that orthodontic treatment goals should be attuned to the achievement of balanced and harmonious facial features rather than rigid adherence to standard average dental and skeletal parameters. Treatment of adolescent children should also take into account the changes in the thickness of the soft tissue integument at the nose, lips, and chin.

An evaluation of the nasolabial angle and the relative inclinations of the nose and upper lip.

The purpose of this study was to develop a consistent and reproducible method of constructing a nasolabial angle that would also permit an evaluation of the relative inclination of the lower border of the nose and the upper lip, as well as their relationship to each other. Comparison of repeated individual measurements of soft tissue profile landmarks on 15 subjects, as completed by four orthodontists, revealed that the proposed method of constructing the nasolabial angle was consistent and reproducible by the same orthodontist and among different orthodontists. Normative data for the three nasolabial parameters were produced from a sample of 104 young white adults determined by the authors to have well-balanced faces. Mean and standard deviation values from this pooled sample demonstrated a lower border of the nose to Frankfort horizontal plane angle at 18 degrees +/- 7 degrees, upper lip to Frankfort horizontal plane angle 98 degrees +/- 5 degrees, and nasolabial angle 114 degrees +/- 10 degrees. No statistically significant difference was demonstrated between the values for men and women in this study, but the women did have a slightly larger nasolabial angle. A linear comparison of the three nasolabial parameters with six skeletal measurements revealed no significant relationship between the soft tissue profile of the nasolabial region and the underlying skeletal relationships.