DLX6 and MSX1 from saliva samples as potential predictors of mandibular size: A cross-sectional study

INTRODUCTION

Morphologic features of the mandible are influenced by the genes of each individual. Mandible size is important to orthodontists because the mandible is the mechanism by which the lower face influences facial esthetics and dental function. To date, no biological marker has been identified that indicates eventual mandible size. This study aimed to correlate the expression of DLX5, DLX6, EDN1, HAND2, PRRX1, and MSX1 to mandible size.

METHODS

Fifty-nine orthodontic patients aged >6 years who had available cephalometric radiographs were studied. Patients were classified on the basis of condylion-to-gnathion measurements. Messenger RNA was isolated from saliva and subjected to real-time quantitative polymerase chain reaction.

RESULTS

Threshold cycle values for subjects with small mandibles (>1 standard deviation [SD] from the mean) had the least expression of DLX6 and MSX1. Threshold cycle values for subjects with large mandibles (>1 SD) had less expression of DLX6 and MSX1 than subjects within 1 SD but more than those with small mandibles.

CONCLUSIONS

DLX6 and MSX1 are related to mandible development and size. This finding could be used to improve treatment planning for medical and dental professionals seeking to understand the impact of genetics on bone growth.

The Class II Carriere Motion appliance

OBJECTIVES

To determine three-dimensional treatment changes produced by the Class II Carriere Motion appliance (CMA) in Class II adolescent patients with Class I and Class II skeletal relationships.

MATERIALS AND METHODS

The sample included 59 adolescents (16 boys and 43 girls) with unilateral or bilateral Class II molar and bilateral Class II canine relationship. They were divided into group 1 with skeletal Class I (N = 27; ANB 2.90° ± 1.40°; 13.30 ± 1.53 years) and group 2 with skeletal Class II (N = 32; ANB 6.06° ± 1.64°; 13.26 ± 1.76 years). Cone beam computed tomography images were traced with Invivo software pretreatment (T1) and post-CMA usage (T2). The treatment changes in 36 measurements were calculated in each group, and the changes in 16 measurements were compared between them.

RESULTS

In group 1 and 2, maxillary first molars underwent significant distal movement (1.92 mm ± 0.80 mm and 1.67 mm ± 1.56 mm, respectively) with distal tipping and rotation, maxillary canines underwent significant distal movement (2.34 mm ± 1.07 mm and 2.24 mm ± 1.91 mm, respectively) with distal tipping and rotation, and mandibular molars underwent significant mesial movement (-1.37 mm ± 1.23 mm and -2.51 mm ± 1.51 mm, respectively) with mesial tipping. Between the groups, there were significant differences in mandibular molar mesial movement and the U1-SN changes (P < .05).

CONCLUSIONS

The CMA corrected Class II malocclusion through distal tipping and rotational movement of maxillary canines and molars and corrected mesial tipping of mandibular molars. Significantly more mandibular molar mesial movement and maxillary incisor flaring were observed in patients with skeletal Class II.

Long-term stability of maxillary and mandibular arch dimensions when using rapid palatal expansion and edgewise mechanotherapy in growing patients

Objective

The purpose of this study was to assess the long-term stability of rapid palatal expansion (RPE) followed by full fixed edgewise appliances.

Methods

This study included 67 patients treated using Haas-type RPE and non-extraction edgewise appliance therapy at a single orthodontic practice. Serial dental casts were obtained at three different time points: pretreatment (T₁), after expansion and fixed appliance therapy (T₂), and at long-term recall (T₃). The mean duration of the T₁-T₂ and T₂-T₃ periods was 4.8 ± 3.5 years and 11.0 ± 5.4 years, respectively. The dental casts were digitized, and the computed measurements were compared with untreated reference data.

Results

The majority of treatment-related increases in the maxillary and mandibular arch measurements were statistically significant (p < 0.05) and greater than expected for the untreated controls. Although many measurements decreased postretention (T₂-T₃), the net gains persisted for all of the measurements evaluated.

Conclusions

The use of RPE therapy followed by full fixed edgewise appliances is an effective method for increasing maxillary and mandibular arch width dimensions in growing patients.

Mandibular asymmetries and associated factors in orthodontic and orthognathic surgery patients

OBJECTIVES

To estimate the prevalence of mandibular asymmetries in orthodontic and orthognathic surgery patients and to investigate demographic and skeletal factors associated with this disharmony.

MATERIALS AND METHODS

Cone-beam computed tomography images of 1178 individuals aged 19 through 60 years with complete dentitions were analyzed. Outcomes were classified as relative mandibular symmetry, moderate asymmetry, and severe asymmetry. Factors recorded included sex, age, side of mandibular deviation, sagittal jaw relationship, vertical skeletal pattern, angle of the cranial base, and maxillary asymmetry. Ordinal logistic regression was used to estimate simple and adjusted odds ratios (OR) for the individuals with moderate and severe mandibular asymmetry, as well as 95% confidence intervals.

RESULTS

Prevalence values of 55.2%, 27.2%, and 17.6% were observed for relative mandibular symmetry, moderate asymmetry, and severe asymmetry, respectively. An independent association with the side of mandibular deviation and the presence of maxillary asymmetry was observed, both for subjects with moderate mandibular asymmetry (left side: OR = 1.50; 95% CI: 1.01-2.24 / maxillary asymmetry: OR = 2.07; 95% CI: 1.11-3.76) and for those with severe asymmetry (left side: OR = 2.09; 95% CI: 1.27-3.44 / maxillary asymmetry: OR = 4.93; 95% CI: 2.64-9.20).

CONCLUSIONS

Moderate and severe mandibular asymmetries were present in 44.8% of the sample, being associated with the side of mandibular deviation and with maxillary asymmetry.

Accuracy of clear aligners: A retrospective study of patients who needed refinement

INTRODUCTION

The purpose of this study was to determine the accuracy of specific tooth movements with Invisalign (Align Technology, Santa Clara, Calif).

METHODS

The study sample included 20 Class I adult patients treated with Invisalign; they completed their first series of aligners and had to have a "refinement" series. Initial and predicted models were obtained from the initial ClinCheck (Align Technology). The starting point of the refinement ClinCheck was used to create the achieved models. Predicted and achieved models were superimposed over the initial ones on posterior teeth using the 3-dimensional Image Analysis open-source software Slicer CMF. Three hundred ninety-eight teeth were measured for vertical, horizontal, and rotational movements, and transverse widths were measured. The amount of predicted tooth movement was compared with the achieved amount for each movement.

RESULTS

Horizontal movements of all incisors seemed to be accurate, with small (0.20-0.25 mm) or insignificant differences between predicted and achieved amounts. Vertical movements and particularly intrusions of maxillary central incisors were found to be less accurate, with a median difference of 1.5 mm (P <0.001). All achieved rotations were significantly smaller than those predicted, with the maxillary canines exhibiting the greatest difference of 3.05° (P <0.001).

CONCLUSIONS

The most inaccurate movements identified in this study were intrusion of the incisors and rotation of the canines.

Orthodontic treatment of a patient with maxillary lateral incisors with dens invaginatus: 6-year follow-up

INTRODUCTION

Dens invaginatus is an anomaly of dental development in which calcified tissues, such as enamel and dentin, are invaginated into the pulp cavity. This morphologic alteration is more frequent in maxillary permanent lateral incisors and makes them more susceptible to carious lesions and pulp alterations.

METHODS

This case report describes a patient with maxillary lateral incisors affected by dens invaginatus. The maxillary right lateral incisor had already undergone endodontic treatment, and the maxillary left one had a periapical lesion. Additionally, the patient had a Class II Division 1 malocclusion, with anterior open bite, posterior crossbite, and an impacted mandibular left second molar.

RESULTS

The orthodontic treatment involved extraction of the maxillary lateral incisors and 2 mandibular premolars, resulting in proper overjet and overbite with good arch coordination and occlusal stability.

CONCLUSIONS

Treatment results were stable, as evaluated in a 6-year posttreatment follow-up.

Craniofacial features affecting mandibular asymmetries in skeletal Class II patients

OBJECTIVES

The aim of this study was to evaluate the characteristics affecting different intensities of mandibular asymmetry in skeletal Class II adults using three-dimensional images. This study is clinically relevant since it allows professionals to evaluate the morphological components related to these deformities and more carefully obtain correct diagnosis and treatment plan for such patients.

METHODS

Cone-beam computed tomography data of 120 Class II patients (40 with relative symmetry, 40 with moderate asymmetry, and 40 with severe asymmetry) were imported to SimPlant Ortho Pro^® 2.0 software (Dental Materialise, Leuven, Belgium). Three reference planes were established and linear measurements were performed from specific landmarks to these planes, comparing the deviated side and the contralateral side in each group, as well as the differences between groups. The correlation between midline mandibular asymmetry and other variables was also evaluated. Statistical analyses considered a significance level of 5%.

RESULTS

Comparing the values obtained on the deviated side and on the contralateral side, there were significant differences for patients with moderate asymmetry and severe asymmetry. However, differences were seen more often in severe mandibular asymmetries. In those patients, there was a significant correlation of the gnathion deviation with lower dental midline deviation, difference in the lateral gonion positions, difference in the mandibular rami heights, and difference in the jugale vertical displacements.

CONCLUSIONS

For skeletal Class II patients with mandibular asymmetry, some craniofacial features are related to chin deviation and require proper evaluation, including the bilateral differences in the ramus height, mandibular body length, transverse and vertical positioning of the gonion and jugale points.

Long-term stability of rapid palatal expansion in the mixed dentition vs the permanent dentition

INTRODUCTION

Palatal expansion has been a popular and proven technique for transverse discrepancies used in orthodontics for decades. The short-term effectiveness of the technique is understood, yet questions remain regarding the long-term stability, with much debate surrounding the optimum treatment timing to initiate expansion for the most beneficial and stable results, especially with regard to mixed dentition treatment. The purpose of this study was to determine the long-term stability of palatal expansion performed in the mixed dentition vs the permanent dentition.

METHODS

Fifty-four subjects were grouped as follows: 24 in the mixed dentition and 30 in the permanent dentition at the start of treatment. All patients had been treated with the Haas type of palatal expansion appliance followed by nonextraction fixed edgewise mechanics. Digitized dental casts were evaluated at 3 times: before treatment (T1), after treatment (T2), and at the long-term retention (T3). Intermolar widths were computed by subtracting measurements between time points, and comparisons between the groups were made to determine expansion and stability differences.

RESULTS

Significant intermolar width increases were observed from T1 to T2 with significant relapses from T2 to T3, and an overall net gain remained at T3 in each group. No significant differences were found for relapse between the mixed and permanent dentitions.

CONCLUSIONS

There are no differences for the long-term intermolar width stability in patients treated with palatal expansion in the mixed dentition vs the permanent dentition.

Posttreatment evaluation of maxillary canine positions in 15-year-old subjects

INTRODUCTION

Esthetic improvement is a primary reason that people seek orthodontic treatment. The maxillary canine is considered by many to have great importance for both function and esthetics. Limited information is available about the position of the maxillary canine in relation to skeletal landmarks and whether the position can influence esthetic perceptions. The purposes of this study were to evaluate the normal maxillary canine position in relation to skeletal landmarks, to determine posttreatment 3-dimensional maxillary canine position with cone-beam computed tomography images, and to see whether maxillary canine position influences esthetic perceptions.

METHODS

The Bolton standard template was used as the control sample, and the maxillary canine position was determined by implementing a Cartesian coordinate system. The right and left maxillary canines of 96 treated patients (48 boys, 48 girls; 15 years old) were analyzed by digitization of the cone-beam computed tomography volumes. The subjects' posttreatment smile photographs were ranked and quantified by 9 orthodontic residents who completed a Q-sort. Correlations were determined between canine positions and esthetic outcomes.

RESULTS

The only difference between the right and left canine positions was the anteroposterior position of the root apex. Statistically significant sex differences were found for the superoinferior position of the right and left canine cusp tips, the mediolateral right and left canine root apices, and the mediolateral left canine cusp tips. No correlation was determined between the maxillary canine position and the esthetic perception.

CONCLUSIONS

The maxillary canine position in relation to skeletal landmarks was determined and does not appear to significantly impact the esthetic perception, according to this study.

Surgical treatment of adolescent internal condylar resorption (AICR) with articular disc repositioning and orthognathic surgery in the growing patient--a pilot study

Background

The aim of this study was to better understand how surgical repositioning and stabilization of anteriorly displaced articular discs using the Mitek mini-anchor technique affects condylar growth in growing patients with adolescent internal condylar resorption (AICR).

Methods

Twenty-two adolescent patients diagnosed with AICR and anterior temporomandibular disc displacement were compared to untreated control subjects without AICR matched for age, sex, and Angle classification. Pre-surgical (T1 and T2) and post-surgical (T3 and T4) mandibular tracings were superimposed on natural stable structures to evaluate the horizontal, vertical, and total changes in the position of condylion.

Results

The treated group showed an overall decrease in condylar height pre-surgically and statistically significant changes in condylar growth direction between the pre- and post-surgical observation periods. Pre-surgically, the treated group showed significantly more posterior condylar growth than the control group; they also showed inferior condylar growth, while the controls showed superior growth. Controls and patients in the treated group showed no significant differences in condylar growth post-surgically.

Conclusions

Adolescent patients diagnosed with AICR and anterior disc displacement treated with mandibular ramus and maxillary osteotomies, along with Mitek anchors to reposition internally deranged discs, showed post-surgical normalization of condylar growth.

A finite element analysis of the maxillary first molar PDL with maxillary protraction in a mixed dentition Class III malocclusion

OBJECTIVES

To analyze the stress distribution on the PDL of the maxillary first molar in a mixed dentition Class III malocclusion, using a Hyrax-type appliance and maxillary protraction.

SETTING AND SAMPLE POPULATION

A Class III malocclusion in the mixed dentition was reconstructed based on CBCT images.

MATERIAL AND METHODS

The 3D FEM comprised the maxilla, alveolar bone, right first permanent molar teeth, and PDL and consisted of 1 133 497 nodes and 573 726 elements. Maxillary protraction force was applied to a hook positioned close to the deciduous canines with 600 g and at 15°, 30°, and 45° downward angles to the maxillary occlusal plane.

RESULTS

Analysis was carried out from the top and buccal view of the sagittal plane. The magnitude of the stresses at 15°, 30°, and 45° of protraction angulation resulted in the highest stress magnitude being in the region between the distobuccal and palatal roots, as well as on the distal surface of the mesial root. The vector direction in this area showed traction and mesial movement. With 30° and 45° protraction angulations, the stress was located only between the distobuccal and palatal roots, and the vector direction was more extrusive at 15°.

CONCLUSIONS

The suggested orthodontic movement is in the mesial direction with a small amount of extrusion with 15° angulation and greater extrusion with 30° and 45°.

Extraction vs no treatment: Long-term facial profile changes

INTRODUCTION

Long-term soft tissue response to extraction orthodontic treatment has been a subject of interest for years. The purposes of this study were to investigate long-term soft tissue profile changes in an extraction sample and to compare them with profile changes in an untreated sample.

METHODS

A premolar extraction-treated sample (n = 47) and an untreated control sample (n = 57) were studied. Descriptive statistics were collected, and individual t tests were used for comparison and contrast of the treated and untreated samples.

RESULTS

We found that the untreated soft tissue profile changed in the downward and forward direction. The treated soft tissue profile change was similar, but with more of a forward component than in the untreated sample. Most noteworthy was the finding that the soft tissue profiles of both the untreated and the treated samples were similar at the end point.

CONCLUSIONS

The following conclusions were derived from the study. (1) There was no substantive difference in the soft tissue profiles of the samples, but there were some differences in the directional changes between them. (2) The changes for the untreated sample were the greatest for the lips and the chin, with the change occurring in the downward and forward direction. (3) The soft tissue profiles of the extraction sample also had the greatest measurable changes in the lips and the chin, but the changes had more of a forward component than they did in the untreated sample. (4) Extraction treatment does not adversely impact soft tissue profile changes over time.

Facial divergence and mandibular crowding in treated subjects

OBJECTIVE

To understand the relationships between facial divergence, vertical growth, and postretention mandibular crowding.

MATERIALS AND METHODS

Seventy-five white extraction patients were evaluated immediately posttreatment (15.4 years) and again 16.6 years later. Hyperdivergent subjects, subjects with open bite or severe deep bites were not evaluated. Changes in incisor irregularity and tooth-size arch-length discrepancies (TSALD) were evaluated and correlated with measures of divergence and skeletal growth.

RESULTS

Incisor irregularity increased 0.9 mm and TSALD increased 0.7 mm after treatment; 68% of the subjects had less than 3.5 mm incisor irregularity at postretention. Male patients showed significantly more growth than female patients did. Female patients, who were significantly more hyperdivergent than male patients, showed weak to moderately weak associations between posttreatment facial divergence and crowding. Female posttreatment changes in anterior face height, lower incisor eruption, and changes in arch depth were also related to crowding; male patients showed moderate relationships between posttreatment changes in arch width and crowding.

CONCLUSIONS

Greater vertical growth, incisor eruption, and especially facial divergence are related to greater posttreatment mandibular crowding.

Maxillary growth and maturation during infancy and early childhood

OBJECTIVE

To describe maxillary growth and maturation during infancy and early childhood.

MATERIALS AND METHODS

Serial cephalograms (N=210) of 30 subjects (15 females and 15 males) from the Bolton-Brush Growth Study were analyzed. Each subject had a series of six consecutive cephalograms taken between birth and 5 years of age, as well as one adult cephalogram. Twelve maxillary measurements (eight linear and four angular) and seven landmarks were used to characterize maxillary growth. Maturation of the linear measures was described as a percentage of adult status.

RESULTS

Maxillary and anterior cranial base size increased in both sexes between 0.4 and 5 years of age. The linear anteroposterior (AP) measures (S-SE, SE-N, ANS-PNS) increased almost as much as the vertical measures (S-PNS, SE-PNS, N-A, N-ANS) over the first 5 years. After 5 years of age there was significantly more vertical than AP growth. The size and shape changes that occurred were greatest between 0.4 and 1 years; yearly velocities decelerated regularly thereafter. Overall linear growth changes that occurred between 0.5 and 5 years of age (a span of 4.5 years) were generally greater than the changes in maxillary growth that occurred between 5 and 16 years (a span of 11 years). The linear measures showed a gradient of maturation, with the AP measures being more mature than the vertical measures. Male maxillae were less mature than female maxillae at every age.

CONCLUSIONS

The maxilla undergoes its greatest postnatal growth change during infancy and early childhood, when relative AP growth and maturation are emphasized.

Mandibular rotation during the transitional dentition

Objective:

To determine whether dentoalveolar changes or vertical condylar growth is more closely related to the true forward rotation of the mandible during the transition between the late primary and early mixed dentition stages of development.

Materials and Methods:

The sample included 50 subjects (25 males and 25 females) with Class I (N  =  25) and Class II (N  =  25) molar relationships. They were selected based on the availability of lateral cephalograms at two developmental stages: T1: last film with complete primary dentition (5.8 ± 0.4 years) and T2: first film with permanent incisors and permanent molars fully erupted (8.0 ± 0.2 years). Seventeen landmarks were identified and 22 measurements were calculated. The mandibles at T1 and T2 were superimposed using natural reference structures in order to measure true mandibular rotation.

Results:

The mandible underwent −2.4° ± 2.6° of true rotation, 1.9° ± 2.4° of remodeling, and −0.6° ± 1.8° of apparent rotation. There were no significant sex or Class differences in true rotation, remodeling, and apparent rotation. There was a moderate correlation (r  =  0.76) between true rotation and remodeling and a moderately low correlation (r  =  0.40) between true rotation and apparent rotation. There was a weak correlation between true rotation and SNA (r  =  0.28). True rotation was most closely associated with the increases in U1/S-N (r  =  −0.34), increases in U1/PP (r  =  −0.36), and decreases in Id-Me (r  =  0.36).

Conclusions:

Independent of sex and Class, the true mandibular rotation that occurred between the late primary and early mixed dentition was mostly masked by angular remodeling, resulting in limited amounts of apparent rotation. True rotation was significantly related to anterior dentoalveolar changes but not to the vertical growth changes that occurred.

High-resolution imaging of gigahertz polarization response arising from the interference of reflected surface acoustic waves

The surface polarization caused by traveling SAWs at 1.585 GHz has been imaged using a dynamic homodyne electrostatic force microscope technique. Instead of measuring topographic changes caused by the SAW, the reported technique measures polarization in the piezoelectric substrate arising from mechanical stress caused by the SAW. The polarization associated with this stress field modulates the scanning probe cantilever deflection amplitude, which is extracted using a lock-in-based technique. High-resolution imaging is presented with images of the interference arising from a metal reflector on a SAW device. A mathematical model combining SAW generation and force interactions between the probe and the substrate was used to verify the experimental data. In addition to overcoming the challenge associated with detecting and imaging polarization effects at gigahertz frequencies, this imaging technique will greatly assist the development of SAW-based devices that exploit the reflection and interference of SAWs in areas as diverse as microfluidic mixing, cell sorting, and quantum entanglement.

Stability changes of miniscrew implants over time

PURPOSE

To quantify in vivo changes in miniscrew implant (MSI) stability over time using resonance frequency analysis, and to determine if pilot holes and placement sites affect changes in MSI stability.

MATERIALS AND METHODS

Twenty-two self-tapping MSIs (1.6 mm wide and 9 mm long) were placed in the maxillae of 2 adult beagle dogs (20 months old). The Osstell Mentor was used to measure the implant stability quotient (ISQ) weekly for 8 weeks. A split-mouth design was used to evaluate the effects of 1.1-mm wide, 3-mm deep pilot holes.

RESULTS

The MSIs that failed showed significantly (P < .05) greater decreases in ISQ values during the first 3 weeks than the MSIs that remained stable. All of the MSIs that failed (41%) had been placed in nonkeratinized tissue. MSIs that remained stable throughout the study also showed significant decreases in ISQ values during the first 3 weeks, followed by increases during the fourth and fifth weeks. Changes in ISQ values of MSIs inserted into bone with and without pilot holes were comparable (P > .05).

CONCLUSION

Stability of unloaded MSIs decreased during the first 3 weeks and increased thereafter. Although the effects of pilot holes on stability could not be confirmed, placement of MSIs into nonkeratinized tissue negatively affected their stability and increased the likelihood of failures.

Posterior occlusion changes with a Hawley vs Perfector and Hawley retainer. A follow-up study

OBJECTIVE

To characterize postorthodontic settling of the posterior occlusion of patients wearing Hawley retainers vs patients who initially wore Perfector retainers and then switched to Hawley retainers.

MATERIALS AND METHODS

This follow-up study was based on 40 patients (25 Perfector and 15 Hawley), who were part of a larger sample of 50 patients randomly assigned to wear either Hawley or Perfector retainers. The Perfector patients were given Hawley retainers 2 months after retainer delivery. Occlusal bite registrations were scanned and traced to quantify posterior areas of contact and near contact (ACNC). A seven-item questionnaire was used to assess the patient's perception of occlusion. Measurements were obtained at the on the day of retainer delivery, 2 months post delivery, 6 months post delivery, and 8 months post delivery.

RESULTS

ACNC increased significantly (P < .05) during the first 6 months of retainer wear. The ACNC of the Hawley and Perfector/Hawley groups increased by 129% and 105%, respectively, over 8 months of retention. The greatest increases in ACNC occurred during the first 2 months. The ACNC further increased between 2 and 6 months in both groups. The Perfector/Hawley group also showed slight increases in ACNC between 6 and 8 months. Overall group differences were not statistically significant. The Perfector/Hawley group perceived greater improvements in occlusion than the Hawley group, but group differences after 8 months were small.

CONCLUSIONS

Substantial amounts of settling occurred at decelerating rates during the first 6 months after retainer delivery. No significant differences in ACNC were found between the Hawley and Perfector/Hawley groups after 8 months of retainer wear.

Comparison of the effects of Hawley and perfector/spring aligner retainers on postorthodontic occlusion

INTRODUCTION

The purpose of this study was to evaluate the short-term changes in posterior occlusion produced by perfector/spring aligner and Hawley retainers.

METHODS

In this prospective clinical study, we randomly assigned 50 patients who had completed full orthodontic treatment to a Hawley retainer group or a perfector/spring aligner retainer group. Objective and subjective measures were collected when the retainers were delivered (T1) and approximately 2 months later (T2). Blu Mousse (Parkell Bio-Materials, Farmingdale, NY) was used to quantify posterior areas of contact (<50 microm) and near contact (50-350 microm). The patient's perception of occlusion was assessed by using a 7-item questionnaire.

RESULTS

Areas of contact and near contact (ACNC) in the Hawley group increased significantly (P <0.05) from 6.71 mm(2) at T1 to 10.97 mm(2) at T2; ACNC in the perfector/spring aligner group increased from 8.44 mm(2) at T1 to 12.95 mm(2) at T2. There were no significant (P <0.05) differences in the increases of ACNC between the Hawley group (4.50 mm(2)) and the perfector/spring aligner group (3.26 mm(2)). Spearman correlations showed that ACNC at T1 were positively related with ACNC at T2 and negatively related with T2 to T1 ACNC changes. In comparison with the Hawley group, the patients wearing perfector/spring aligner retainers reported significantly greater improvements in how well their back teeth fit together, how well they could chew tough meats, and how much pain they felt when they bit down.

CONCLUSIONS

ACNC increased substantially and similarly in patients wearing Hawley and perfector/spring aligner retainers. Changes over time were perceived to a greater extent by patients wearing perfector/spring aligner retainers.

Third-Order Torque and Self-Ligating Orthodontic Bracket–Type Effects on Sliding Friction

Objective: To examine the influence of third-order torque on kinetic friction in sliding mechanics involving active and passive self-ligating brackets.

Materials and Methods: Wire-slot frictional forces were quantified and compared across five sets of brackets and tubes within a simulated posterior dental segment with −15°, −10°, −5°, 0°, +5°, +10°, and +15° of torque placed in the second-premolar bracket; a working archwire was pulled through the slots.

Results: Increasing the torque from 0° to ±15° produced significant increases in frictional resistance with all five sets of brackets and tubes. At 0° and ±5° of torque, generally less friction was created within the passive than within the active self-ligating bracket sets, and the conventional bracket sets with elastomeric ligation generated the most friction. At ±10° of torque, apparently with wire-slot clearance eliminated, all bracket-and-tube sets displayed similar resistances, with one exception at +10°. At ±15° of torque, one passive set and one active set produced significantly larger frictional resistances than the other three sets.

Conclusions: Third-order torque in posterior dental segments can generate frictional resistance during anterior retraction with the archwire sliding through self-ligating bracket slots. With small torque angles, friction is less with passive than with active self-ligating brackets, but bracket design is a factor. Frictional forces are substantial, regardless of ligation if the wire-slot torque exceeds the third-order clearance.

Class II Non-Extraction Patients Treated with the Forsus Fatigue Resistant Device Versus Intermaxillary Elastics

Objective: To evaluate the Forsus Fatigue Resistant Device (FRD) as a compliance-free alternative to Class II elastics.

Materials and Methods: A sample of 34 (14 female, 20 male) consecutively treated nonextraction FRD patients (12.6 years of age) were matched with a sample of 34 (14 female, 20 male) consecutively treated nonextraction Class II elastics patients (12.2 years of age) based on four pretreatment variables (ANB, L1-GoMe, SN-GoMe, and treatment duration). Pretreatment and posttreatment cephalometric radiographs were traced and analyzed using the pitchfork analysis and a vertical cephalometric analysis. t-Tests were used to evaluate group differences. Group differences were evaluated using t-tests.

Results: No statistically significant differences were found in the treatment changes between the groups. There was a general trend for mesial movement of the maxilla, mandible, and dentition during treatment for both groups. The mandibular skeletal advancement and dental movements were greater than those in the maxilla, which accounted for the Class II correction. Lower incisor proclination was evident in both groups. Vertically, the maxillary and mandibular molars erupted during treatment in both groups, while lower incisors proclined. With the exception of lower molar mesial movements and total molar correction, which were significantly (P &lt; .05) greater in the Forsus group, there were no statistically significant group differences in the treatment changes.

Conclusions: The Forsus FRD is an acceptable substitute for Class II elastics for noncompliant patients.

Posttreatment occlusal variability among angle Class I nonextraction patients

OBJECTIVE

To test the hypothesis that variability among posttreatment Angle Class I, nonextraction patients is not related to patient and treatment factors.

MATERIALS AND METHODS

One hundred thirty-eight subjects were randomly selected from the archives of the Department of Orthodontics, St Louis University. Patient factors evaluated included age, sex, mandibular plane angle, and ANB angle; treatment factors included active treatment time and supervising orthodontist. Objective Grading System (OGS) scores for six of the criteria (excluding interproximal contacts and root angulations) and the anterior Bolton ratio were measured on the posttreatment study casts.

RESULTS

The partial mean overall OGS score was 24.9 +/- 8.0. Occlusal contact was the most important component contributing to the overall score, followed by alignment. Variation in the OGS scores was explained by sex, pretreatment mandibular plane and ANB angles, the posttreatment anterior Bolton ratio, and treatment duration. The partial overall OGS scores increased by approximately one point for every 4 degrees increase in the mandibular plane angle and nearly one point for every 3 additional months of treatment. Approximately 16% and 15% of the variation in alignment and buccolingual inclination, respectively, was due to the treating orthodontist.

CONCLUSIONS

Posttreatment occlusal variability among Class I nonextraction patients can be partially explained by patient- and treatment-related factors.

Patients' satisfaction with physician assistant services

Research on patient satisfaction with physician assistants in rural primary care medical practices is lacking. This study attempted to: determine patients' satisfaction with family practice PAs in rural communities, assess patient perceptions of "comfort" with PAs in a range of hypothetical medical procedures, analyze patients' reactions to PAs as a function of patient characteristics, and document perceptions of changes in medical practices after PAs are employed. Findings support reports that patients are highly satisfied with PA services and extends those observations to rural primary care practices. Reaction to PAs is more favorable among women, more favorable in patients with more education, and more favorable among those with greater contact with PAs.

PA roles in a tertiary medical center

This study describes the common elements of PA roles within tertiary medical centers, and compares physicians' perceptions of PA utilization with those of the PAs they supervise. The sample included 23 PAs employed by a university-based tertiary care center and a university-affiliated VA medical center. Variables examined included employment settings, patients seen, hours worked, and other job descriptors. Descriptions of the tasks performed by the PAs were also acquired. The results suggest that PAs employed in tertiary care settings contribute substantially to the provision and continuity of patient care, particularly in the area of patient education.

Medical practice revenue and salaries of physician assistants

Significant salary differences between male and female PAs have been noted. Several variables--hours worked per week, weeks worked per year, number of patients seen per week, and average fee per patient--were examined to assess their contribution to the differences in salary for PAs practicing in family medicine, internal medicine, and pediatrics. Although female PAs were found to earn significantly less than their male colleagues, the discrepancy could largely be explained when salary was examined as a proportion of revenue generated for the practice. The survey findings are compared with research findings on male and female physicians' salaries.

Practice characteristics of male and female physician assistants

In a national survey of 3,294 non-military responding physician assistants, sociodemographic and practice characteristics of male and female physician assistants were compared. Differences by specialty, practice setting, size of community, and hours of work were generally similar in nature, but smaller in magnitude, than those reported for physicians, and may not be of practical significance.

Effect of inhibition of DNA synthesis on histone synthesis and deposition

We have reinvestigated the degree of coupling between DNA and histone synthesis in mammalian cells. In at least one cell line (HTC cells), the coupling is not nearly as tight as had previously been inferred from experiments with HeLa cells. The site of deposition of such histones which continue to be made in the presence of sufficient hydroxyurea to depress DNA synthesis almost totally has been studied. Deposition seems to be on material which absorbs at 260 nm. This material is not a part of the bulk chromatin and binds histone in a relatively tight manner. The possible role of such a material in histone synthesis and deposition is discussed.

Characterization of plasmids determining hemolysin and bacteriocin production in Streptococcus faecalis 5952

Two plasmids designated pOB1 and pOB2 were isolated from Streptococcus faecalis strain 5952 and found to have molecular weights of approximately 46 X 10(6) and 28 X 10(6), respectively. pOB1 was found to determine hemolytic activity and was transmissible, whereas pOB2 appeared to determine a bacteriocin that is specifically inhibitory to S. faecalis strains harboring the 26-megadalton plasmid pAM539.

Analysis of plasmid deoxyribonucleic acid in a cariogenic strain of Streptococcus faecalis: an approach to identifying genetic determinants on cryptic plasmids

Streptococcus faecalis strains ND539 and OG1 have been previously shown to be cariogenic in gnotobiotic animals. Deoxyribonucleic acid analyses have revealed the presence of a single 26-megadalton plasmid designated pAM539 in the former strain, whereas the latter strain was found to be plasmid-free. By gene transfer experiments, it was possible to construct isogenic pairs of strains that differed only with regard to the presence or absence of pAM539. Comparative studies of isogenic pairs showed that the presence of pAM539 conferred bacterial sensitivity to a bacteriocin produced by S. faecalis strain 5952.

Evidence for a composite state of an F'his, gnd element and a cryptic plasmid in a derivative of Salmonella typhimurium LT2

A method designed to select mutants constitutive for expression of the histidine operon has been applied to a Salmonella typhimurium LT2 strain containing an F'his,gnd element and a cryptic plasmid. One of the mutants isolated, strain AA0019, has not only increased levels of histidinol phosphate phosphatase (hisB), but also increased levels of gluconate-6-phosphate dehydrogenase (gnd). Ultracentrifugation studies of extrachromosomal deoxyribonucleic acid (DNA) isolated from strain AA0019 revealed the presence of a single species of covalently closed circular (CCC) DNA that sedimented more rapidly through neutral and alkaline sucrose gradients than any of its possible plasmid precursors. From neutral sucrose gradients, sedimentation coefficients of 130, 100, and 86S were derived, corresponding to the CCC DNA of the large plasmid in strain AA0019, the F'his,gnd element and the cryptic LT2 plasmid, respectively. An Escherichia coli plasmid-free strain that upon mating had received the large 130S plasmid also contained 86S and 100S CCC DNA components. A histidine-requiring derivative of strain AA0019 obtained after acridine orange treatment retained the cryptic plasmid DNA. Apparently, the large plasmid in strain AA0019 consists of the F'his,gnd element and the cryptic LT2 plasmid of the parental strain.