Carla A. Evans

Relationship between rapid maxillary expansion and nasal cavity size and airway resistance: Short- and long-term effects

INTRODUCTION The availability of new, reliable, objective, and 3-dimensional techniques to assess the effects of rapid maxillary expansion on the morphology of the maxillary dental arch, nasal cavity dimensions, and nasal airway resistance led to the development of this research. METHODS Thirty-eight subjects participated in this study (mean age, 13 years). Data were collected before expansion, when the expander was stabilized, when the expander was removed, and 9 to 12 months after the expander was removed. Subjective assessment of improvement in nasal respiration was obtained when the expander was stabilized. Three-dimensional imaging and acoustic rhinometry were used to assess the virtual cast and the nasal cavity, respectively. RESULTS AND CONCLUSIONS The statistically significant short-term effects of RME were (1) mean increases in palatal area, volume, and intermolar distance; (2) a mean reduction of nasal airway resistance; and (3) mean increases in total nasal volume and nasal valve area. Our long-term findings were the following: (1) mean palatal area and intermolar distance were reduced, while palatal volume was stable, and (2) nasal airway resistance was stable, whereas mean nasal cavity volume and minimal cross-sectional area increased. Additionally, 61.3% of our subjects reported subjective improvement in nasal respiration. Weak correlations were found between all variables analyzed.

The Effect of Pulsed Ultrasound on Mandibular Distraction

AbstractThis study evaluated the effect of pulsed ultrasound on tissue repair and bone growth during mandibular osteodistraction. Twenty-one rabbits were divided into three groups of 7. The distraction started 72 h after surgically severing both sides of the mandible and proceeded at a rate of 1.5 mm/12 h for 5 days. Group 1 received pulsed ultrasound (nominally 200 μs pulse of 1.5 MHz at a 1.1 kHz pulse repetition frequency, 30 mW/cm2) for 20 min on both sides of the mandible every other day (alternating sides). Group 2 received the same pulsed ultrasound treatment on one side of the mandible every day for 20 min. Group 3 did not receive any ultrasound treatment. Bone formation at the distraction site was assessed by photodensitometry on head radiographs, a vibratory coherence test across the distraction site, a postmortem three-point bending mechanical stiffness test, and a postmortem histological examination. Statistical analyses performed using analysis of variance revealed that pulsed ultrasound enhanced bone formation at the distraction site with a high level of significance when assessed by the increase in new bone photodensity (p=0.001), vibratory coherence (p=0.001), mechanical stiffness (p=0.003), and qualitative histological studies, especially when the pulsed ultrasound treatment was directly applied daily.

Craniofacial applications of three-dimensional laser surface scanning.

Recent innovations in technology have generated a variety of techniques for medical imaging. One of these initially developed for industry is laser surface scanning. Laser surface scanning is a noninvasive method for acquiring three-dimensional (3D) images. In this article, the technology of 3D laser surface scanning is described, and a few applications are reported as it relates to craniofacial research and clinical practice. Advantages and disadvantages of this imaging modality are discussed. Three-dimensional laser surface scanning holds great promise as it relates to the documentation, analysis, and evaluation of treatment results in craniofacial anomalies.

Bond strength of visible light-cured glass ionomer orthodontic cement.

In this in vitro study, tensile strength tests were conducted with a visible light-cured glass ionomer cement (Fuji Ortho LC, GC America Inc.) bonded to extracted teeth under six different enamel surface conditions: (1) dry nonetched, (2) moist etched, (3) moist nonetched, (4) moist nonetched rebonded, (5) moistened with saliva substitute, and (6) moistened with human saliva. Two resin adhesives (Rely-A-Bond and Phase II, Reliance Orthodontic Products) were applied to dry and etched enamel and served as control agents. The glass ionomer cement approached the strength observed for resin adhesives and required the presence of moisture on the enamel surface for optimal performance.

Preferences for facial profiles between Mexican Americans and Caucasians.

The objective of this study was to determine differences between Mexican American and Caucasian judges in the acceptability of lip protrusion in computer animations of two male and two female persons of Mexican descent. Thirty Caucasians and 30 Mexican Americans of varying age, sex, education, and level of acculturation responded to facial profile computer animations that moved lips from an extreme protrusive to an extreme retrusive position. Judges were asked to complete two tasks: (1) to press the mouse button when the image was perceived to be most pleasing (MP) and (2) to determine the boundaries of a zone of acceptability (ZA) of lip protrusion by pressing the mouse button when the moving image became acceptable and releasing it when the image of the protrusion became unacceptable. In general, Mexican Americans preferred upper or lower lip positions to be less protrusive than did Caucasians. Larger mean ZAs for both upper and lower lip positions with male computer animation images and lower lip position for female computer animation images were found among Caucasians when compared with low-acculturated Mexican Americans. A significant mean difference in midpoint of acceptability (MA) for lip position between Caucasians and low-acculturated Mexican Americans was observed for both upper and lower lip position with female computer animation images.

Midfacial morphology in adult unoperated complete unilateral cleft lip and palate patients.

OBJECTIVE To examine lateral cephalometric radiographs of adult unoperated cleft lip and palate patients for the purpose of clarifying whether maxillary deficiencies observed in treated cleft patients result from intrinsic defects or surgical intervention early in life. MATERIALS AND METHODS This retrospective study examined lateral cephalograms of 30 adult patients with nonsyndromic complete unilateral cleft lip and palate (CUCLP). The lateral cephalograms were traced and evaluated for size and position of the cranial base, maxilla, maxillary dentition, mandible, and mandibular dentition as well as for vertical relationships. Comparisons with 30 adult noncleft individuals were made. RESULTS In unoperated adult cleft lip and palate patients, the cranial base angle was increased with the anterior cranial base reduced in length. The maxilla was found to be normal in size and somewhat prognathic in position. Both the maxillary and mandibular incisors were relatively upright. The mandible was smaller in size and posteriorly positioned. CONCLUSIONS The potential for normal growth of the maxilla exists in patients with CUCLP. It is likely that disturbances of maxillary growth in surgically operated cleft patients are related primarily to the surgical intervention.

ASSESSMENT OF 3-DIMENSIONAL COMPUTER-GENERATED CEPHALOMETRIC MEASUREMENTS

The purpose of this study was to assess the reliability of 3-dimensional computer-generated linear and angular measurements produced by different computer algorithms and various combinations of cephalogram projections compared with direct and CT measurements. A computer program was written to provide 4 computer algorithms and 4 combinations of cephalogram projections generating 22 linear and 10 angular 3-dimensional measurements from 20 landmarks. A new technique to produce biplanar cephalograms from a single x-ray source using a special facebow was developed, and its reliability was assessed. Sets of lateral, frontal, and basilar cephalograms of a human dried skull were taken both with 20 radiopaque landmark markers and without markers. Paired t tests based on marker position demonstrated reliability of the facebow; there were no statistically significant differences in repositioning the skull over time using the facebow at P <.05. In the ideal situation, with minimal head rotation and landmark identification error (with the facebow and radiopaque markers), the average error of linear measurements was 1. 5 mm and 3.5(o) for the angular measurements. Subsequent trials evaluated the errors in head position (within 5(o) of head rotation) and in landmark identification (by removing all markers); two-way ANOVA with Scheffé groupings concluded that the vector intercept with manual adjustment algorithm using the lateral-frontal biplanar projection provides not only greater accuracy but also clinical practicality for both linear (mean of 2.2 mm error) and angular (mean of 4.0(o) error) measurements compared with direct or CT measurements (P <.05). The effect of landmark identification error was found to be slightly greater than the head rotation error in the accuracy of 3-dimensional linear and angular measurements (mean, 2.85 mm error for linear and 4.4(o) error for angular measurements). Lastly, this study concluded that linear measurements in the transverse direction were found to have a slightly larger error than vertical measurements. Anteroposterior measurements have the least error.

Extracellular Matrix-mediated Tissue Remodeling Following Axial Movement of Teeth

Tooth eruption is a multifactorial process involving movement of existing tissues and formation of new tissues coordinated by a complex set of genetic events. We have used the model of the unopposed rodent molar to study morphological and genetic mechanisms involved in axial movement of teeth. Following extraction of opposing upper molars, lower molars supererupted by 0.13 mm. Labeled tissue sections revealed significant amounts of new bone and cementum apposition at the root apex of the unopposed side following supereruption for 12 days. Newly apposited cementum and alveolar bone layers were approximately 3-fold thicker in the experimental vs the control group, whereas periodontal ligament width was maintained. Tartrate-resistant acid phosphatase staining indicated bone resorption at the mesial alveolar walls of unopposed molars and provided in tandem with new bone formation at the distal alveolar walls an explanation for the distal drift of molars in this model. Microarray analysis and semiquantitative RT-PCR demonstrated a significant increase in collagen I, integrin β5, and SPARC gene expression as revealed by comparison between the unopposed molar group and the control group. Immunohistochemical verification revealed increased levels of integrin β5 and SPARC labeling in the periodontal ligament of the unopposed molar. Together our findings suggest that posteruptive axial movement of teeth was accomplished by significant formation of new root cementum and alveolar bone at the root apex in tandem with upregulation of collagen I, integrin β5, and SPARC gene expression.

Predictors of initial stability of orthodontic miniscrew implants

The purpose of this retrospective study was to elucidate potential confounding factors affecting initial stability of miniscrews inserted to enhance orthodontic anchorage. Four hundred and seven miniscrews inserted in 168 patients treated by 17 orthodontic residents were analysed in a consecutive chart review. The outcome variable was the stability of the miniscrew, measured as a dichotomous variable, 0 if the miniscrew loosened during a 1 week period after insertion to the time of orthodontic force application and a value of 1 otherwise. Potential confounding variables examined were gender, age, jaw, insertion site, tissue type, length and diameter of the miniscrew, and number of previous insertions. Generalized estimating equations (GEE) methods were used to estimate the influence of each factor on stability for the correlated binary outcomes of each patient. A weighted analysis for the GEE approach was also performed for the convergence calculation of the estimation procedure due to a value of 0 in one of the cells. Crude odds ratio (cOR) and adjusted odds ratio (aOR) and their 95 per cent confidence intervals (CI) were calculated for this purpose. The overall success rate after 1 week was 93.1 per cent (379/407). The screws inserted by more experienced clinicians (more than 20 miniscrews) were found to have approximately a 3.6-fold higher success rate of initial stability compared with those inserted by less experienced clinicians after adjusting for the insertion site (aOR = 3.63, P = 0.015). The results of the present study suggest that the initial stability depends on insertion site and clinician experience.

Effect of ultrasound on rabbit mandibular incisor formation and eruption after mandibular osteodistraction

Therapeutic ultrasound is known to enhance bone-fracture healing. The purpose of this article was to study the effect of therapeutic ultrasound on mandibular incisor development and eruption in 15 skeletally mature male New Zealand white rabbits undergoing mandibular osteodistraction. The surgical cuts were made anterior to the molars and consequently transected the mandibular incisors. The animals were divided into 3 groups of 5 rabbits each. Group I received ultrasound on both sides of the mandible every other day. Group II received ultrasound on the left side of the mandible every day. Group III did not receive ultrasound. Ultrasound was given for 20 minutes per application. Mandibular incisor eruption was measured directly on the rabbits and on lateral head radiographs. The animals were killed 4 weeks after surgery, and dissected mandibular specimens that contained the incisor segments were evaluated histologically. The lengths of the tooth segments increased in the ultrasound-treated animals, compared with the controls (group III). However, the rabbits in group II had greater increases in length of the mandibular incisor segments than those in group I. Histologic examination showed that the newly formed tissues at the distraction site and at the cut ends of the incisor segments consisted of osteodentin-like tissue and cementum. Thus, therapeutic ultrasound combined with distraction enhanced mandibular incisor growth and eruption.