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Introduction: Our objective was to investigate the effect of low-frequency mechanical vibration (LFMV) on the rate of tooth movement, bone volume fraction, tissue density, and the integrity of the periodontal ligament. Our null hypothesis was that there would be no difference in the amount of tooth movement between different values of LFMV., Methods: Sixty-four male CD1 mice, 12 weeks old, were used for orthodontic tooth movement. The mice were randomly divided into 2 groups: control groups (baseline; no spring + 5 Hz; no spring + 10 Hz; and no spring + 20 Hz) and experimental groups (spring + no vibration; spring + 5 Hz; spring + 10 Hz; and spring + 20 Hz). In the experimental groups, the first molars were moved mesially for 2 weeks using nickel-titanium coil springs delivering 10 g of force. In the control and experimental groups, LFMV was applied at 5, 10, or 20 Hz. Microfocus x-ray computed tomography analysis was used for tooth movement measurements, bone volume fraction, and tissue density. Additionally, immunostaining for sclerostin, tartrate-resistant acid phosphatase (TRAP) staining, and picrosirius red staining were used on the histologic sections. Simple descriptive statistics were used to summarize the data. Kruskal-Wallis tests were used to compare the outcomes across treatment groups., Results: LFMV did not increase the rate of orthodontic tooth movement. Microfocus x-ray computed tomography analysis showed increases in bone volume fractions and tissue densities with applications of LFMV. Sclerostin expression was decreased with 10 and 20 Hz vibrations in both the control and experimental groups. Additionally, the picrosirius staining showed that LFMV helped in maintaining the thickness and integrity of collagen fibers in the periodontal ligament., Conclusions: There was no significant increase in tooth movement by applying LFMV when compared with the control groups (spring + no vibration)., (Copyright © 2015 American Association of Orthodontists. Published by Elsevier Inc. All rights reserved.)

Introduction: The aim of this pilot study was to investigate the effect of long-term bisphosphonate drug use (bone burden) on orthodontic tooth movement in a rat model., Methods: Sprague Dawley rats were used for orthodontic protraction of the maxillary first molars with nickel-titanium coil springs and temporary anchorage devices as anchorage. Four groups of 5 rats each were included in the study; the first 2 groups were dosed with alendronate or a vehicle during concurrent orthodontic tooth movement. The third and fourth groups were pretreated for 3 months with alendronate or vehicle injections, and bisphosphonate drug treatment was discontinued before orthodontic tooth movement. Tooth movement measurements were obtained at 0, 4, and 8 weeks using high-resolution in-vivo microcomputed tomography, and the tissues were analyzed with histology and dynamic labeling of bone turnover., Results: Appreciable tooth movement was achieved during the 8-week duration of this study with nickel-titanium coil springs and temporary anchorage devices. Both bisphosphonate treatment groups exhibited reduced tooth movement compared with the vehicle-dosed controls with a tendency toward more severe reduction in the bisphosphonate predosed group. Concurrent dosing of the bisphosphonate drug resulted in 56% and 65% reductions in tooth protraction at the 4-week and 8-week times, respectively. The impact of bisphosphonate bone burden in retarding tooth movement was even greater, with 77% and 86% reductions in tooth movement at 4 and 8 weeks, respectively., Conclusions: In this study, we used a robust rat model of orthodontic tooth movement with temporary anchorage devices. It has provided evidence that the bone burden of previous bisphosphonate use will significantly inhibit orthodontic tooth movement., (Copyright © 2013 American Association of Orthodontists. Published by Mosby, Inc. All rights reserved.)

Introduction: Miniscrews placed in bone have been used as orthodontic anchorage in extraction space closure with sliding mechanics. The movement patterns of the teeth depend on the force directions. To move the teeth in a desired pattern, the appropriate direction of force must be selected. The purpose of this article is to clarify the relationship between force directions and movement patterns., Methods: By using the finite element method, orthodontic movements were simulated based on the remodeling law of the alveolar bone. The power arm length and the miniscrew position were varied to change the force directions., Results: When the power arm was lengthened, rotation of the entire maxillary dentition decreased. The posterior teeth were effective for preventing rotation of the anterior teeth through an archwire. In cases of a high position of a miniscrew, bodily tooth movement was almost achieved. The vertical component of the force produced intrusion or extrusion of the entire dentition., Conclusions: Within the limits of the method, the mechanical simulations demonstrated the effect of force direction on movement patterns., (Copyright © 2012 American Association of Orthodontists. Published by Mosby, Inc. All rights reserved.)

Introduction: Our objectives were to investigate the eruptive patterns of the mandibular teeth and assess their associations with mandibular growth displacements., Methods: Cephalograms for a mixed-longitudinal sample of 124 French-Canadian girls were evaluated between 10 and 15 years of age. Vertical mandibular displacement and mandibular eruption were evaluated by using cranial and mandibular superimpositions, respectively. Multilevel modeling procedures were used to estimate each subject's growth change over time. Stepwise multiple regressions were used to determine the amount and relative magnitudes of variations in mandibular eruption explained by mandibular growth displacement, controlling for vertical maxillary tooth movements., Results: Cubic polynomial models explained between 91% and 98% of the variations in eruption and vertical growth displacement. All curves showed acceleration of eruption until approximately 12 years of age, after which eruption decelerated. The eruption of the mandibular teeth demonstrated greater relative variability than did vertical mandibular growth displacements. Independent of the overall movements of the maxillary molars, inferior mandibular growth displacement explained approximately 54% of the variation in mandibular molar eruption between 10.5 and 14.5 years of age., Conclusions: Inferior mandibular growth displacement and dental eruption followed similar patterns of change during adolescence. Based on their associations and the differences in variability identified, mandibular eruption appears to compensate for or adapt to growth displacements., (Copyright © 2011 American Association of Orthodontists. Published by Mosby, Inc. All rights reserved.)

Introduction: The purpose of this study was to explore the contributions of occlusion, maximum bite force, and chewing cycle kinematics to masticatory performance., Methods: A prospective cross-sectional study was performed on 30 subjects with Class I occlusion. Masticatory performance was measured with the test food Cuttersil (Heraeus Kulzer, South Bend, Ind) and the fractional-sieve technique. Blu-Mousse (Parkell Biomaterials, Farmingdale, NY) bite registrations were used to measure occlusal contact areas. The American Board of Orthodontics occlusal discrepancies were measured on the subjects' dental models. Maximum bite forces were recorded with a custom transducer, and 3-dimensional chewing cycle kinematics were tracked with an opto-electric computer system and Optotrak software (Northern Digital, Waterloo, Ontario, Canada)., Results: Masticatory performance was most closely correlated with occlusal contact area, indicating larger contact areas in subjects with better performance. Occlusal contact area and occlusal discrepancies were also related to bite force and chewing cycle kinematics. Maximum bite force was positively related with masticatory performance., Conclusions: Although masticatory performance is related, both directly and indirectly, to a number of morphologic and functional factors, it is most closely related to occlusal factors., (Copyright © 2011 American Association of Orthodontists. Published by Mosby, Inc. All rights reserved.)

Introduction: The aim of this study was to compare dental development in a group of children with mild-to-moderate hypodontia with a matched group., Methods: A study group of 70 children (43 girls, 27 boys) with hypodontia, aged 5.3 to 12.5 years, was matched for race, age, and sex with 140 healthy, normal control subjects. The children's dental ages were calculated by using a modified dental-age estimation method. Differences between dental and chronologic ages were analyzed by t tests, and the correlations between differences in dental and chronologic ages and the numbers of missing teeth were analyzed with the Spearman correlation test., Results: Dental development in children with mild-to-moderate hypodontia was significantly delayed compared with the control group (P <0.05); however, the mean difference did not exceed 0.3 years in either sex. No correlation was observed between the differences in dental and chronologic age and the severity of hypodontia., Conclusions: Children with mild-to-moderate hypodontia had delayed dental development of a few months; this was statistically significant. Because of individual variations, each patient should be carefully examined., (Copyright © 2011 American Association of Orthodontists. Published by Mosby, Inc. All rights reserved.)

Introduction: Although it has been suggested that orthodontic treatment might lead to changes in the dental pulp, no clinical study has attempted to investigate the incidence of pulp necrosis after orthodontic therapy. The purpose of this clinical trial was to determine whether pulp testing response is altered after rapid palatal expansion (RPE)., Methods: Twenty-five adolescent patients (9 boys, 16 girls; ages, 10-16 years) participated in the study. A hyrax appliance was cemented on the first permanent molars and first premolars (when fully erupted). The appliance was activated twice daily (0.5 mm) for 2 weeks. An electric pulp tester (EPT) was used to test at the buccal cusp tips of the molars and premolars. Teeth that did not respond to the EPT were subsequently tested thermally with Endo Ice (Hygienic Corporation, Akron, Ohio)., Results: All maxillary molars and erupted premolars of the 25 patients responded positively to pulp tests before cementation of the hyrax appliance. Of the 49 molars tested, 46 responded positively to the EPT, and 3 responded positively to the cold testing (CT). Of the 42 first premolars tested, 40 responded positively to the EPT and 2 to the CT. Of the 38 second premolars tested, 35 responded positively to the EPT and 3 to the CT. Two weeks after the initial activation of the hyrax appliance, 93 teeth in 17 subjects were tested. Of the 93 teeth, 73 teeth responded positively to the EPT and 20 to the CT. Three to 6 weeks after hyrax activation was discontinued, 59 teeth were tested; 48 tested positively to the EPT and 10 to the CT. One tooth (maxillary left first molar) did not respond to either EPT or CT. Finally, 3 to 9 months into retention, all molars and premolars of 23 subjects tested positive to pulp tests, 92 teeth to the EPT and 25 to the CT. The maxillary left first molar that had not responded to the tests at the 3-to-6 week check responded positively to the CT at the final check., Conclusions: After RPE therapy in children and adolescents, the pulp of the posterior permanent teeth examined in this study was vital.

Introduction: The transpalatal arch (TPA), which splints together 2 maxillary molars, has been believed to preserve anchorage. The purpose of this study was to clarify this effect from a mechanical point of view., Methods: The finite element method was used to simulate the movement of anchor teeth subjected to mesial forces with and without a TPA., Results: In the initial movement produced by elastic deformation of the periodontal ligament, stress magnitude in the periodontal ligament was not changed by the TPA. In the orthodontic movement produced by bone remodeling, the mesial force tipped the anchor teeth irrespective of the TPA. The tipping angles of anchor teeth with and without the TPA were almost the same. The anchor teeth without the TPA were rotated in the occlusal plane and moved transversely., Conclusions: The TPA had no effect on the initial movement. In the orthodontic movement, the TPA had almost no effect, preserving anchorage for mesial movement. However, the TPA prevented rotational and transverse movements of the anchor teeth. These results are valid when the assumptions used in this calculation are satisfied.

Lip paresthesia during mandibular molar orthodontic distalization is rare. When it occurs, it is often related to excessive dimensions of the mandibular second molar roots. In this clinical report, we describe a patient who developed lip paresthesia during orthodontic treatment. The paresthesia was relieved by immediate interruption of the forces applied to the mandibular second molars and pharmacologic therapy. Before fixed orthodontic treatment proceeds in patients with large tooth roots, it is important to diagnose the relationship between the roots and the mandibular canal to prevent nerve numbness and damage.

Introduction: Uprighting a tipped molar by using an uprighting spring is a fundamental orthodontic treatment technique. However, mechanical analyses have not been carried out for molar uprighting, and the mechanism of tooth movement has not been clarified. The purposes of this article were to clarify these mechanisms and to demonstrate the usefulness of mechanical simulations by which the effects of many factors on tooth movement can be estimated quantitatively., Methods: A 3-dimensional finite element method was used to simulate the uprighting of a second molar with a molar uprighting spring. The effects of a retainer and spring-arm bending on the tooth movements were shown quantitatively., Results: The retainer was useful to reduce the movement of anchor teeth. The same effect could be achieved by bending the spring arm in the lingual direction, but the molar was greatly rotated in the occlusal plane and was tipped in the buccal direction., Conclusions: The usefulness of a mechanical simulation method to predict orthodontic tooth movement in clinical situations was demonstrated.

Introduction: The purpose of this study was to analyze photoelastically the stress distribution around teeth in the simulated distal movement of mandibular molars with the skeletal anchorage system., Methods: Two types of the photoelastic mandibular dentition models were used, 1 before and 1 after distal movement of the second molar. The experiment was performed with 3 forms of traction--first-molar single traction, second-molar single traction, and simultaneous first- and second-molar traction. The direction of traction was set parallel to the occlusal plane and at an angle of 30 degrees downward to the occlusal plane., Results: In the first-molar single traction model, extremely high stress was generated around the first molar with traction parallel to the occlusal plane. With the traction 30 degrees downward to the occlusal plane, all models showed the stress around the molars extended distally and downward., Conclusions: Simultaneous traction of the first and second molars might be preferable to the sequential traction of each molar to prevent the unfavorable distal tipping of the first molar. Regardless of whether simultaneous or sequential traction is used, the downward traction to the occlusal plane seems to induce intrusion of the molars as well as their distal movement.

Introduction: The aim of this study was to evaluate the possible relationship between the exfoliation of the deciduous second molars (Es) and the onset of the pubertal growth spurt assessed with the cervical vertebral maturation method., Methods: The ability to identify the onset of the pubertal growth spurt (cervical stage 3, CS3) was evaluated in a sample of 123 patients with exfoliation of the Es (exfoliation group) with respect to a control group of 250 subjects in the late mixed dentition selected with random criteria. Tests of diagnostic performance were applied., Results: The comparison of the prevalence rates of CS3 in the exfoliation group vs the control group was not statistically significant. The positive likelihood ratio was smaller than 1, thus indicating lack of diagnostic power of the exfoliation of the deciduous second molars with regard to CS3., Conclusions: No significant relationship was found between the moment of exfoliation of the Es and the onset of the pubertal growth spurt.

Conventional wisdom suggests that orthodontists must apply added force to overcome friction during canine retraction (sliding mechanics), the result of which can be increased anchorage loading and anchorage loss. However, for a frictional force to be exerted mesially by the archwire against a canine during retraction, the archwire must be compressed between the canine and the anchor molar, and an equal but opposite force must be applied distally against the molar by the archwire. In other words, the frictional force that reduces the force of retraction on the canine must also reduce the protraction force on the molar. Emphasis on employing reduced-friction (eg, self-ligating) brackets during sliding mechanics to prevent added posterior anchorage loading is unwarranted and based more on bracket salesmanship than on orthodontic biomechanics.

Introduction: The aim of this study was to evaluate whether early loss of the permanent first molars has an effect on the developmental stages and eruptive conditions of the third molars., Methods: Panoramic radiographs and dental casts of 165 adolescent patients (103 boys, 62 girls) with unilateral early loss of a permanent first molar were used to assess the developmental stages of the third molars. The formation stages of third molars on the extraction sides were evaluated, and the formative conditions of the contralateral teeth were used as controls. The Mann-Whitney U test was used to assess sex differences in formation stages of the third molars. The Kruskal-Wallis analysis of variance (ANOVA) was used to determine whether there were significant differences in the developmental stages of the third molars between the various extraction quadrants. In addition, the Wilcoxon signed rank test and the paired t test were used to compare the differences in the developmental stages and eruptive conditions of the third molars between the extraction and control sides., Results: The Mann-Whitney U test showed no significant sex differences for the formation stage of the third molars. Therefore, the data from both sexes were pooled. No statistically significant differences were found in the developmental stages of the third molars between the various extraction quadrants in the same jaw and between those in the mandible and maxilla. However, statistically significant differences were found in developmental stages (P <.001) and eruptive conditions (P <.05) of the third molars between the extraction and control sides. The development of the third molars on the extraction side was significantly accelerated compared with the contralateral teeth., Conclusions: Early loss of the permanent first molars might have an accelerating effect on the development of the third molar on the extraction side compared with the contralateral teeth. Therefore, emergence of the third molars on the extraction side might be hastened, and these teeth might erupt earlier than the contralateral teeth.

Introduction: The purpose of this study was to compare and measure the amount of anchorage loss with titanium microimplants and conventional molar anchorage during canine retraction., Methods: Subjects for this study comprised 10 orthodontic patients (7 women, 3 men) with a mean age of 19.6 years (range, 18 to 25 years), who had therapeutic extraction of all first premolars. After leveling and aligning, titanium microimplants 1.3 mm in diameter and 9 mm in length were placed between the roots of the second premolars and the first molars. Implants were placed in the maxillary and mandibular arches on 1 side in 8 patients and in the maxilla only in 2 patients. A brass wire guide and an intraoral periapical radiograph were used to determine the implant positions. After 15 days, the implants and the molars were loaded with closed-coil springs for canine retraction. Lateral cephalograms were taken before and after retraction, and the tracings were superimposed to assess anchorage loss. The amount of molar anchorage loss was measured from pterygoid vertical in the maxilla and sella-nasion perpendicular in the mandible., Results: Mean anchorage losses were 1.60 mm in the maxilla and 1.70 mm in the mandible on the molar anchorage side; no anchorage loss occurred on the implant side., Conclusions: Titanium microimplants can function as simple and efficient anchors for canine retraction when maximum anchorage is desired.

Background: Bone remodeling laws have been used to simulate the movement of a single tooth, but the calculations for simulating the movement of several teeth simultaneously are time-consuming. The purpose of this article is to discuss a method that allows the simulation of more complex tooth movements., Methods: A 3-dimensional finite element method was used to simulate the orthodontic tooth movement (retraction) of a maxillary canine by sliding mechanics and any associated movement of the anchor teeth. Absorption and apposition of the alveolar bone were produced in proportion to the stress of the periodontal ligament., Results: In a reference case, the canine was retracted by a 2N force with 0.016-in square wire. The frictional coefficient between wire and bracket was 0.2. The movement of both the canine and the anchor teeth could be calculated with the elastic deformation of wire. The canine tipped during the initial unsteady state and then moved bodily during the steady state. It became upright when the orthodontic force was removed. The anchor teeth moved in the steady state and tipped in the mesial direction. The decrease in applied force by friction was about 70%. The tipping of the canine decreased when the wire size was increased or when the applied force was decreased., Conclusions: Simple assumptions were used in this calculation to simulate orthodontic tooth movements. The calculated results were reasonable in mechanical considerations. This method might enable one to estimate various tooth movements clinically. However, precise comparisons between calculated and clinical results, and the improvement of the calculation model, are left for a future study.

Purpose: The aim of this study was to assess dental anchorage qualities when the pendulum appliance is used for distal molar movement., Material: Thirty adolescents in various dentition stages received a modified pendulum appliance with a distal screw and a specially preactivated pendulum spring for bilateral molar distalization in the maxilla. The subjects were subcategorized into 3 groups of 10 according to the dental anchorage used: deciduous molars, premolars and deciduous molars, or only premolars. Dentoalveolar effects and side effects in the anchorage unit and in the molar area were determined by cephalometric analysis., Results: Statistical analysis of the measurements showed significant differences between groups in the extent of molar distalization and the resulting incisor protrusion. Distal tipping of the 6-year molars was significantly less severe (2.3 degrees +/- 1.58 degrees to the palatal plane and 2.55 degrees +/- 1.52 degrees to the anterior cranial base) in patients with premolar anchorage than in those with deciduous molar anchorage (6.15 degrees +/- 3.42 degrees and 6.35 degrees +/- 3.46 degrees ). Incisor protrusion was significantly more pronounced in patients with deciduous molar anchorage (2.75 +/- 1.4 mm) than in the other 2 groups (1.65 +/- 0.82 mm, mixed deciduous molar and premolar anchorage, and 1.75 +/- 0.75 mm, premolar anchorage). Additionally, incisor protrusion was translatory compared with controlled tipping in subjects with deciduous molar anchorage or premolar and deciduous molar anchorage., Conclusions: Deciduous molars and premolars can be used for anchorage for molar distalization with a pendulum appliance; however, anchorage with premolars only results in the least pronounced dentoalveolar side effects. The anchorage quality of deciduous molar and mixed deciduous molar/premolar anchorage is limited.

Management of retained deciduous second molars in the absence of permanent successors can be challenging. The purpose of this retrospective radiographic study was to examine long-term changes in retained deciduous mandibular second molars in adult patients. Specifically, we sought to answer the question, "If an adult has a retained deciduous mandibular second molar and a missing successor, is retaining the deciduous molar a viable treatment option?" From more than 6000 adult patients at the University of Iowa College of Dentistry, 20 were identified who initially had at least 1 retained deciduous mandibular second molar without a permanent successor and who had radiographs spanning 5 or more years after the initial visit. The mean (standard deviation) age at the initial examination was 36.1 (12.9) years, the mean age at the final examination was 48.5 (12.6) years, and the mean examination time span was 12.4 (7.7) years. Of the 28 retained deciduous molars initially identified, 24 (86%) continue to function. The remaining 4 were lost at a mean age of 51.0 (13.9) years and a mean time span after initial examination of 14.3 (10.0) years; this approximates the lifespan of some prosthetic appliances. These 4 mandibular deciduous molars were lost because of caries or periodontal breakdown. Furthermore, we found that the average shortening of all deciduous root lengths was negligible (0.16 mm), and only 6 teeth underwent a change in restoration status. Based on this study in adults and earlier studies in adolescents, we conclude that retaining healthy deciduous mandibular second molars is a viable treatment alternative.

Because adults dislike the visibility of orthodontic appliances, the use of the lingual orthodontic technique has increased over time. But few studies compare tooth movement of the lingual technique with that of the labial technique. In this study, human mandibular left teeth were aligned, and a 3-dimensional finite element model was made (consisting of 19382 nodes and 12150 elements). To compare the effect of compensating curves on canine retraction between the lingual and the labial orthodontic techniques, the compensating curve was increased on the.016-in stainless steel labial or lingual archwire, and a 150-g force was applied distally on the canine. The relative direction and the amount of tooth displacement of the finite element model were compared on a schematic displacement graph (magnified 10,000 times), and the compressive stress distributed on the root surface was observed. The pattern of tooth movement (with or without a compensating curve) was different between the labial and the lingual techniques. As the amount of compensating curve increased (0, 2, and 4 mm) in the archwire, the rotation and the distal tipping of the canine was reduced. The antitip and antirotation action of compensating curve on the canine retraction was greater in the labial archwire than in the lingual archwire.

The morphology of the skeleton is known to reflect functional demand. A change in the intramaxillary position of molars can be expected to influence the transfer of occlusal forces to the facial skeleton. A finite element analysis allows us to simulate the displacement of a molar in relation to the well-defined morphology of the maxilla. Three 3-dimensional unilateral models of a maxilla from a skull with skeletal Class I and neutral molar relationships were produced based on CT-scan data. The maxillary first molar was localized so that the contour of the mesial root continued into the infrazygomatic crest. When the molar was loaded with occlusal forces, the stresses were transferred predominantly through the infrazygomatic crest. This changed when mesial and distal displacements of the molars were simulated. In the model with mesial molar displacement, a larger part of the bite forces were transferred through the anterior part of the maxilla, resulting in the buccal bone being loaded in compression. In the model with distal molar displacement, the posterior part of the maxilla was deformed through compression; this resulted in higher compensatory tensile stresses in the anterior part of the maxilla and at the zygomatic arch. This distribution of the occlusal forces might contribute to the posterior rotation often described as the orthopedic effect of extraoral traction.

The mandibular anterior repositioning appliance (MARA) is a tooth-borne functional appliance for use in patients with Class II malocclusions; it positions the mandible forward into a Class I occlusion. The aim of this study was to investigate the MARA's dental and skeletal effects on anterior, posterior, and vertical changes in 30 Class II patients. The treatment group consisted of 12 boys with an average age of 11.2 years and 18 girls with an average age of 11.3 years. A pretreatment cephalometric radiograph was taken 2 weeks before treatment, and a posttreatment cephalometric radiograph was taken 6 weeks after removal of the MARA, with an average treatment time of 10.7 months. The mean and standard deviation were calculated for each cephalometric variable, and Student t tests were performed to determine the statistical significance of the changes. The results of the study showed that the MARA produced measurable treatment effects on the skeletal and dental elements of the craniofacial complex. These effects included a considerable distalization of the maxillary molar, a measurable forward movement of the mandibular molar and incisor, a significant increase in mandibular length, and an increase in posterior face height. The effects of the MARA treatment were then compared with those of the Herbst and Fränkel appliances. The treatment results of the MARA were very similar to those produced by the Herbst appliance but with less headgear effect on the maxilla and less mandibular incisor proclination than observed in the Herbst treatment group.

Clinical trials comparing activator and headgear treatment have shown comparable effectiveness in the total result achieved, but the mechanism of correction is still uncertain. Most studies have used conventional cephalometric methods to evaluate treatment effects, and this might be a factor for the inconclusive results. The aim of this retrospective investigation was to compare the effects of activator and cervical headgear treatment with a superimpositional cephalometric method that could discern between vertical and horizontal effects as well as skeletal, dental, and rotational treatment results. The sample consisted of 2 groups of Class II Division 1 patients, treated without extraction by the same clinician (22 patients were treated with a modified activator-type functional appliance, and 30 patients were treated with a combination of cervical headgear and fixed edgewise appliances). Lateral cephalometric radiographs taken at the beginning of treatment and after Class II molar correction were evaluated conventionally and with a superimpositional method. Regarding the conventional cephalometric measurements, the only difference in the anteroposterior dimension between the 2 treatment modalities was the significantly reduced SNA angle in the headgear group. Both appliances appeared to produce minimal changes in FMA and GoGn-SN angles, and there were no statistically significant differences between the treatment groups. Regional superimpositions showed differences in the movement of molars: the maxillary molar was found to move more posteriorly and inferiorly in the headgear group. Conversely, the mandibular molar was found to move toward the occlusal plane more in the activator group. Assessment of mandibular skeletal changes showed that the mandible moved anteriorly by approximately 1 mm more in the activator than in the headgear group. The overall effect of the 2 appliances was found to be clinically comparable. However, the individual components of change showed differences characteristic of each appliance.

This preliminary study evaluated relationships between masticatory performance and areas of interocclusal distance contact (<50 microm) and near contact (50-350 microm) of the buccal segments during maximum intercuspation. The sample included subjects with normal occlusion (n = 18) and Class I (n = 14), Class II (n = 13), and Class III (n = 6) malocclusions. Chewing performance was evaluated on the basis of the breakdown of CutterSil (Heraeus Kulze, South Bend, Ind); chewing ability was assessed by the number of chews necessary to swallow jerky and almonds. Impressions of the buccal segments, taken with Blu Mousse (Parkell Bio-Materials, Farmingdale, NY) impression material, were scanned and enlarged, and each subject's first molars and premolars were manually traced bilaterally to estimate the platform area. The areas of contact and near contact (ACNC) that measured between 0 and 350 microm thick were estimated optically on the basis of the amount of light transmitted through the impression. The results showed no significant differences in platform area between the right and left sides or between the malocclusion groups. ACNC were negatively related to median particle size and broadness of particle distribution. There were no correlations between ACNC and the number of chews necessary to swallow jerky or almonds. Subjects with normal occlusion had significantly larger ACNC than those with Class I, Class II, and Class III malocclusions, in descending order. Subjects with Class III malocclusions had the smallest areas of near contact (<350 microm). We concluded that ACNC are similar on the right and left sides; that subjects with larger ACNC are better able to break down foods; and that subjects with malocclusions have smaller ACNC than those with normal occlusions.

This study investigated maxillary and mandibular growth differences and their effect on the changes in molar relationships from early transitional dentition to adult permanent dentition. Various landmarks were identified and measurements made on the longitudinal cephalometric radiographs of 40 people. The subjects were classified into 3 groups based on the amount of sagittal skeletal growth difference between the jaws. In group A, the mandible grew more than did the maxilla; in Group B, growth was about the same; and in group C, the maxilla grew more than did the mandible. The results revealed that skeletal growth differences between the jaws significantly influenced the changes in molar relationship during the transitional dentition, not only by translating basal bones but also by altering the amount of physiologic mesial shift in the dentition. However, the skeletal growth difference during the permanent dentition did not influence the changes in molar relationship. The sagittal growth difference between the jaws was largely absorbed by a dentoalveolar compensation. Tooth movement showed different characteristic features depending on the amount of the skeletal growth difference: (1) If the mandible grew more than did the maxilla, the growth difference was mostly absorbed by mesial displacement of the maxillary first molars and counterclockwise rotation of the occlusal plane. Anterior occlusion was adjusted by mesial displacement and labial inclination of the maxillary incisors and lingual inclination of the mandibular incisors. (2) If the maxilla grew more than did the mandible, the growth difference was mainly absorbed by mesial displacement of the mandibular molars. Then the maxillary molars showed minimal mesial displacement. The occlusal plane also showed minimal rotational change. Anterior occlusion was adjusted by lingual tipping of the maxillary incisors and mesial displacement and labial tipping of the mandibular incisors.

Superimposition of serial cephalograms provides a limited description of tooth movement that could be complemented by data obtained from serial dental casts. The aim of this study was to develop a mathematical method for superimposing 3-dimensional data obtained from selected landmarks on longitudinally collected dental casts to describe maxillary first molar movement during headgear treatment. The material consisted of dental casts taken bimonthly from 36 children whose Class II Division 1 malocclusion was treated with straight-pull headgear during a 24-month period. Control data were collected from initial and final models of 38 subjects with a similar malocclusion who were not treated during a 24-month observation period. Spatial data from each subject's initial model were oriented similarly in an anatomically derived coordinate system, and a best-fit superimposition of palatal rugae landmarks from subsequent models allowed the measurement of molar movement. On average, headgear treatment resulted in distal movement of the molars, and the fitted net difference between treated and control subjects was 3.00 mm (SE, 0.37 mm; P < .001). Also, the headgear caused significantly more molar extrusion (0.56 mm; SE, 0.20 mm; P < .006) and buccal expansion (0.58 mm; SE, 0.17 mm; P < .001) on average than in the control group. Poor reliability of the method for measuring molar rotations indicated that they could not be determined accurately. Longitudinal description of molar movement for each subject revealed great individual variability in the amount and pattern of tooth movement. Several reasons could account for the wide range of individual variation and warrant exploration.

This prospective study was designed to establish how the positions of the molars and the condyles are related to incisor position in the mandibular rest position and how their positions are altered by changing head posture. Measurements of the mandibular rest position were taken on 24 men (age range, 23 to 35) with normal Class I occlusion, skeletal patterns, and temporomandibular joint function. The movements of 5 landmarks (lower incisor, and condyles and molars bilaterally) were tracked from maximum intercuspation into 4 independent rest positions (upright supported, upright unsupported, supine supported, and supine unsupported) using an optoelectric (Optotrak; Northern Digital, Waterloo, Ontario, Canada) computer system. The positions were based on minimal electromyographic and verbal instructions to swallow, lick the lips, and say "Mississippi." The results showed significant (P <.01) movements of the incisors, the molars, and the condyles into each of the 4 rest positions. Movements of the molars and the condyles into the supported upright posture and the unsupported upright posture differed slightly but significantly because of greater movement into the supported posture. Patterns of mandibular movement were entirely different between the upright and the supine rest positions; the mandible rotated anteriorly in the supine position and posteriorly in the upright position. We concluded that movement into the mandibular rest position from the intercuspal position is not a simple opening rotation of the mandible, and that the pattern of movement is influenced by head support and body postures.

Maxillary basal bone, dentoalveolar, and dental changes in Class II Division 1 patients treated to normal occlusion by using cervical headgear and edgewise appliances were retrospectively evaluated. A sample of 45 treated patients was compared with a group of 30 untreated patients. Subjects were drawn from the Department of Orthodontics, Araraquara School of Dentistry, Brazil, and ranged in age from 7.5 to 13.5 years. The groups were matched based on age, gender, and malocclusion. Roughly 87% of the treated group had a mesocephalic or brachicephalic pattern, and 13% had a dolicocephalic pattern. Cervical headgear was used until a Class I dental relationship was achieved. Our results demonstrated that the malocclusions were probably corrected by maintaining the maxillary first molars in position during maxillary growth. Maxillary basal bone changes (excluding dentoalveolar changes) did not differ significantly between the treated and the untreated groups. Molar extrusion after the use of cervical headgear was not supported by our data, and this must be considered in the treatment plan of patients who present similar facial types.

Eruption patterns and root growth were visualized with the use of a new technique, radiographic color-coding, for comparison of the development of autotransplanted premolars with contralateral control teeth. Rates of eruption and root growth were studied. The eruption pattern and rate was assessed relative to the first molar. Maximum rates were found to occur between 30 and 60 days after transplantation. There were no significant differences between transplants and their contralaterals. Two distinct categories of eruption patterns were demonstrated. One group showed a tendency toward an initial rate of transplant eruption that was somewhat faster than that of the contralaterals. The other group showed initially retarded eruption. Possible explanations were discussed. Because no significant differences between the transplants and the contralaterals were observed, it was concluded that autotransplantation is a sound treatment option for substitution of missing teeth, at least from a tooth development point of view.

This study was designed to explore the differences between friction and frictionless mechanics for maxillary canine retraction with the use of a new typodont simulation system, the Calorific machine system. The unit was designed to observe the whole process of tooth movement and is composed of 3 parts: a temperature regulating system, electrothermodynamic teeth, and an artificial alveolar bone component. The efficiency of maxillary canine retraction was compared with the sliding mechanics (along a.016 x.022-in stainless steel labial arch and nickel-titanium closed coil spring) and a canine retraction spring. The patterns of tooth movement obtained with both of these mechanics were measured 5 times each. Friction mechanics were superior to frictionless mechanics in terms of rotational control and dimensional maintenance of the arch (P <.0001); frictionless mechanics were shown to be more effective at reducing tipping and extrusion (P <.0001). However, the observed differences between the 2 methods were relatively small in terms of their clinical significance, and no differences were found in anchorage control (P =.2078). In conclusion, this study indicated that friction and frictionless mechanics perform similarly.

Interleukin-1beta (IL-1beta), interleukin-6 (IL-6), and tumor necrosis factor-alpha (TNF-alpha) are proinflammatory cytokines that are thought to play a role in bone remodeling, bone resorption, and new bone deposition. In the present work, in situ hybridization was performed to measure the messenger RNA expression of IL-1beta, IL-6, and TNF-alpha at 3, 7, and 10 days after the application of orthodontic force on the maxillary first molars of 12 rats. The contralateral side and 3 untreated rats served as controls. Measurements of the messenger RNA expression were selected as the means to investigate the role of orthodontic force in de novo synthesis of proinflammatory cytokines. After the application of force, the induction of IL-1beta and IL-6 was observed to reach a maximum on day 3 and to decline thereafter. No messenger RNA induction of either cytokine was measured in the control teeth. The messenger RNA expression of TNF-alpha was not detected at any time point of this study in the experimental or contralateral sides or in the control animals. Our data support the hypothesis that these proinflammatory cytokines may play important roles in bone resorption after the application of orthodontic force.

This prospective cephalometric study was undertaken to assess the mode and magnitude of Class II correction with nonextraction Begg mechanotherapy in growing children. The sample comprised subjects with similar malocclusion and age range (9-12 years) who were specifically selected for nonextraction Begg mechanotherapy. Cephalograms were analyzed to assess the skeletal, dental, and soft tissue changes that occurred after correction of the molar relationship, the overjet, and the overbite during the 9-month treatment period. The results revealed a significant improvement in the anteroposterior jaw relationship, suggested by the significant reduction in the ANB angle (1.62 degrees ) and in Wits AO-BO (1.42 mm). The mandibular length increase of 0.56 mm suggests that the Class II elastics used in nonextraction Begg mechanotherapy had a minimal stimulatory effect on mandibular growth. There was a significant increase in the anterior and posterior facial heights and the ramal height. Almost all of the dental changes were significant. The most striking feature were a significant retraction and extrusion of the maxillary incisors and proclination and intrusion of the lower incisors accompanied by extrusion of the mandibular molars. The maxillary incisors extruded by 1.64 mm under the influence of the undesirable downward component of the Class II elastic forces. The major contribution to overjet and molar correction was predominantly dentoalveolar.

The purpose of this study was to evaluate vertical facial changes in adult orthodontic patients and to evaluate the stability of these changes. Thirty-three patients (8 males and 25 females) were examined. The patients had been treated with full fixed edgewise appliance mechanics and exhibited at least 1.0 degrees of clockwise rotation of the mandible during treatment. Mandibular rotation was determined by the angular change in the Y-axis to the Frankfort plane. Twelve angular and 14 linear skeletal and dental measurements and 3 skeletal ratios were derived from pretreatment (T1), posttreatment (T2), and postretention (T3) cephalometric radiographs. Paired t tests were used to compare vertical changes that occurred as a result of orthodontic treatment and their stability or relapse tendency during the retention and postretention periods. Twenty-five percent (P <.001) of the opening rotation of the mandible recovered during the posttreatment period, resulting in a significant overall rotation that was maintained. Both treatment and posttreatment changes in the Y-axis angle showed a high correlation with the horizontal position of pogonion (r = -0.797 and -0.889, respectively). Only overjet showed a low correlation between treatment changes and posttreatment changes in the Y-axis angle. Stepwise regression analysis of pretreatment variables and treatment changes failed to predict the behavior of the Y-axis angle change.

The purpose of this investigation was to determine and quantify vertical changes in the position of the mandibular molars while maintaining arch perimeter with a fixed lingual arch. Twenty-three patients with a mean age of 10.4 +/- 0.6 years were selected to receive fixed lingual arch treatment as the only appliance in the mandibular arch. Average treatment time was 18.3 +/-+/- 0.6 months. Longitudinal records for 12 and 24 months of 24 individuals matched by ethnic origin, age, gender, and mandibular plane inclination were used as controls. Pretreatment and posttreatment cephalograms were used to determine positional changes. Statistically significant differences between the fixed lingual arch and control groups were found. The results of this investigation indicated that the mandibular fixed lingual arch is a useful tool to control the vertical development of the mandibular molars.

This retrospective cephalometric study compares the treatment effects produced in 40 patients treated with the Twin-block appliance to those seen in a matched sample of 40 children treated with the FR-2 appliance of Fränkel and to changes undergone in 40 untreated Class II controls from The University of Michigan Elementary and Secondary School Growth Study. The average starting ages for the Twin-block, Fränkel, and control groups were 10 years 5 months, 10 years 2 months, and 9 years 11 months, respectively. The T(2) to T(1) observation period was adjusted to an average of 16 months for all groups. Significant decreases in overbite and overjet were observed at the end of treatment in the Twin-block and Fränkel groups. Compared with the untreated subjects, statistically significant increases in mandibular length were observed in both treated groups. The Twin-block patients achieved an additional 3.0 mm of mandibular length, whereas the Fränkel group increased 1.9 mm more than did the controls. No significant restriction of midfacial growth was observed in either functional appliance group relative to controls. A significant increase in lower anterior facial height was evident in both treatment groups. Vertical increase in the Twin-block patients was significantly greater than in the FR-2 group. In general, more extensive dentoalveolar adaptation was observed with the tooth-borne Twin-block appliance than with the more tissue-borne FR-2 of Fränkel. The Twin-block and FR-2 samples both showed significant retroclination and extrusion (eruption) of the maxillary incisors. The Twin-block patients also exhibited distal movement of the upper molars; however, there was no extrusion. Slight lower incisor proclination was noted in both treatment groups, and lower molar extrusion was found to be significantly greater in the Twin-block group compared with the other 2 samples. No horizontal differences were detected in the lower molars among groups. The present study suggests, therefore, that Class II correction with the Twin-block appliance is achieved through normal growth in addition to mandibular skeletal and dentoalveolar changes. Class II correction with the FR-2 is more skeletal in nature, with less dentoalveolar changes noted.

The aim of this study was to simulate the stress response in the periodontium of the maxillary first molar to different moment to force ratios, and to determine the moment to force ratio for translational movement of the tooth by means of the finite element method. The three-dimensional finite element model of the maxillary first molar consisted of 3097 nodes and 2521 isoparametric eight-node solid elements. The model was designed to dissect the periodontal ligament, root, and alveolar bone separately. The results demonstrate the sensitivity of the periodontium to load changes. The stress pattern in the periodontal ligament for a distalizing force without counterbalancing moments showed high concentration at the cervical level of the distobuccal root due to tipping and rotation of the tooth. After various counterrotation as well as countertipping moments were applied, an even distribution of low compression on the distal side of the periodontal ligament was obtained at a countertipping moment to force ratio of 9:1 and a counterrotation moment to force ratio of 5:1. This lower and uniform stress in the periodontal ligament implies that a translational tooth movement may be achieved. Furthermore, high stress concentration was observed on the root surface at the furcation level in contrast with anterior teeth reported to display high concentration at the apex. This result may suggest that the root morphology of the maxillary first molar makes it less susceptible to apical root resorption relative to anterior teeth during tooth movement. The stress patterns in the periodontal ligament corresponded with the load types; those on the root appeared to be highly affected by bending and the high stiffness of the root.

The finite element method of analysis (FEM) was used to analyze theoretically the effects of a transpalatal arch (TPA) on periodontal stresses of molars that were subjected to typical retraction forces. The purposes of this investigation were (1) to construct an appropriate finite element model, (2) to subject the model to orthodontic forces and determine resultant stress patterns and displacements with and without the presence of a TPA, and (3) to note any differences in stress patterns and displacements between models with and without a TPA. Because anchorage is stress-dependent, a TPA must be able to modify periodontal stresses as a prerequisite for increasing orthodontic anchorage. A finite element model, consisting of two maxillary first molars, their associated periodontal ligaments and alveolar bone segments, and a TPA, was constructed. The model was subjected to simulated orthodontic forces (2 N per molar) with and without the presence of the TPA. Resultant stress patterns at the root surface, periodontal ligament, and alveolar bone, as well as displacements with and without a TPA, were calculated. Analysis of the results revealed minute differences of less than 1% of the stress range in stress values with respect to the presence of a TPA. Modification of bone properties to allow for increased displacement levels confirmed the ability of the TPA to control molar rotations; however, no effect on tipping was noted. Results suggested that the presence of a TPA has no effect on molar tipping, decreases molar rotations, and affects periodontal stress magnitudes by less than 1%. The final results suggest an inability of the TPA to modify orthodontic anchorage through modification of periodontal stresses.

The purpose of this study was to measure the forces produced by a lip bumper on the mandibular permanent first molars. The forces in a sample of 38 patients were measured bilaterally with specially designed gauges at rest but with their lips lightly touching, speaking the words church, phone, and pop, and swallowing water. Forces were compared between two types of lip bumpers, i.e., wire or shield, and between various anteroposterior and vertical positions of the lip bumper. The resting forces produced by the wire lip bumper 2 mm anterior to the incisors and vertically positioned at the middle of the incisor crown were 5.93 +/- 4.84 gm for the left side and 4.66 +/- 4.8 gm for the right. The forces were found to be significantly higher when the wire lip bumper was placed 4 mm anterior to the incisors and at a more gingival position, measuring 16.68 +/- 8.7 gm for the left side and 13.88 +/- 8.28 gm for the right. The shield lip bumper had higher forces both at the center of the incisor as well as when it was positioned gingivally. A large individual variation was observed. There were no statistically significant differences in force levels between male and female subjects. Speaking the words church, pop, and phone, produced forces between 11 and 23 gm, using a wire lip bumper. Swallowing produced the highest forces, between 32 and 36 gm. Lip thickness and height did not appear to affect the force levels.

The rationale of electrothermal bonding is based on the premise that when an electric current is passed across the beaks of tweezers holding a stainless steel orthodontic bracket, heat will be generated by virtue of the electrical resistance of the steel bracket. This study was carried out to evaluate the temperatures generated on the tooth surface at the bracket/tooth interface and within the pulp chamber during electrothermal bonding. Temperatures were recorded with 5 and 7.5 A current levels applied as a 1 second pulse with time intervals between pulses of 1, 2, 3, and 4 seconds. The data showed that after three pulses with a 5 A current, the temperature on the tooth surface ranged between 43.3 degrees C (4 second intervals) to 53.6 degrees C (1 second intervals). By using a 7.5 A current, the temperature ranged from 77.5 degrees C (4 second intervals) to 85.9 degrees C (1 second intervals). The pulp chamber temperatures were evaluated in vitro for a mandibular incisor, the maxillary central and lateral incisors, a canine, a premolar, and a molar. The pulp chamber temperature of a mandibular incisor responded most, whereas that of premolars and molars responded least to temperature changes on the labial surface. The increase in mandibular incisor pulp chamber temperature after three pulses was 2.1 degrees C for 5 A and 2.8 degrees C for 7.5 A current while for a premolar the increase ranged from 0.9 degree C to 1.6 degrees C. On the basis of current evidence the increase in pulp chamber temperatures during electrothermal bonding may be considered to be clinically safe.

The role of the interdigitation of posterior teeth in maxillomandibular growth and development was studied longitudinally in Macaca fascicularis monkeys. Fourteen monkeys were divided into a control group (n = 7) and an experimental group (n = 7). At the start of the study, the mean age of the animals was 29 weeks. At that stage the interdigitation in the experimental group was eliminated by grinding the cusps of the molars and canines. The animals were followed until 143 weeks of age and studied with the aid of tantalum implants and lateral radiographs. The findings indicated that elimination of the interdigitation resulted in a deviating anteroposterior relationship between the jaws and a significant inhibition of the vertical growth of the maxilla in the second half of the experimental period, while total face height was not noticeably affected. As a result, a more prognathic mandible and a more mesial occlusion developed. It can be concluded that the interdigitation plays a role in the regulation of vertical and anteroposterior facial growth and constitutes an important factor in the jaw relation in Macaca fascicularis monkeys.

A retrospective study of dental and maxillary skeletal changes occurring during a period of orthodontic treatment was made from pretreatment and posttreatment dental casts. Sixty maxillary expansion cases were examined. Thirty cases had maxillary expansion accomplished with a fixed rapid palatal expander and 30 were expanded with a quadhelix appliance. All cases were finished with full fixed edgewise appliances. Multiple linear regression analyses were completed for both groups with upper molar width change as the criterion and age, tipping of the upper molars, palatal width change and maxillary tipping as the predictors. All predictors were included in the analysis for the quadhelix group with a significant R2 value of 0.55. For the rapid expansion group, a significant R2 value of 0.33 was achieved with the inclusion of palatal width change and age only. The other variables did not meet the level of significance for entry into the model. Although both groups demonstrated similar amounts of maxillary dental expansion, the rapid expansion group demonstrated greater average skeletal expansion. In addition, there was a significant relationship between skeletal and dental expansion for the rapid expansion group, but not the quadhelix group. Palatal depth increased more on average in the rapid expansion group suggesting that there was greater dental eruption in that group. Expansion across the mandibular molars was greater on average in the quadhelix group. There was no difference in the degree of upper molar rotation or final upper and lower arch forms between the two groups.

Upper molar eruption and its clinical significance to vertical control were measured in a retrospective cephalometric study of 40 patients (20 with and 20 without transpalatal arches) treated in a private practice. Pretreatment and posttreatment cephalometric values were compared to determine how well the patients were matched. No statistically significant differences were noted between control and test groups for the following variables: maxillary and mandibular molar vertical eruption per year, maxillary complex vertical growth per year, effective horizontal condylar growth per year, ratio of effective horizontal pogonion movement to effective vertical pogonion movement, ratio of effective vertical condylar growth to the summation of maxillary, and mandibular vertical molar eruption plus maxillary complex vertical growth, beginning age, and ending age. The control group exhibited statistically greater forward positioning of pogonion and greater effective vertical condylar growth than did the treatment group.

Two groups of adolescent orthodontic patients, one from the Midwest and one from the Midsouth, were compared to test the clinical impression that the permanent teeth of southern children form and erupt at significantly later ages. Indeed, a marked difference is documented, with the Midsouth series achieving mineralization stages at least 1 1/2 years later on average. This suggests that regional differences are appreciably greater than previously suspected. Clinical consequences revolve on the use of conventional (generally Northeast-based) norms for tooth formation and eruption and predictive models of facial growth. In contrast, the analysis of rates of hand-wrist development (bone age) of these same subjects disclosed no difference; this further confirms the essential independence of development of the dental and osseous tissue systems.

Laser speckle interferometry, recently developed for noninvasive measurement of small displacements (microns), was used to study the movement of maxillary molars submitted to extraoral traction. Using an antenna-headgear at different horizontal levels, loadings of 700 gm were applied perpendicular to the long axes of these teeth. Bodily movement was observed when the traction line passed slightly occlusal to the trifurcation of the roots. Therefore, the center of resistance of the upper molar was experimentally localized at this level. Laser speckle interferometry proved to be a promising technique for dental research.

The effects of different combinations of segmented intrusion arch wires and anchorage units on the relative vertical positions of anterior and posterior teeth in the lower arch were demonstrated in four nongrowing baboons. Forces of between 90 and 100 g were delivered by the intrusion arch wires to the four lower incisor teeth in each animal over a period of 5 months. The dental and skeletal changes occurring during that period were assessed from lateral cephalometric radiographs. Lower incisor intrusion, determined by the vertical movement of an internal reference point, was demonstrated in each of the animals. However, the actual effects of the mechanics on the relative anterior and posterior vertical tooth positions, and consequently on the height of the lower face, were found to depend largely on the magnitude of the reactive moments acting on the anchorage units. It was suggested that in general, for a given intrusive force, the further forward the center of resistance is positioned in the anchorage unit, the smaller the reactive moment will be and the more incisor intrusion one might reasonably expect to achieve during arch leveling.