A finite element analysis of stress distribution with various directions of intermaxillary fixation using orthodontic mini-implants and elastics following mandibular advancement with a bilateral sagittal split ramus osteotomy.

OBJECTIVE: This finite element analysis (FEA) aimed to assess the stress distribution in the mandible and fixation system with various directions of the intermaxillary fixation (IMF) using mini-implants (MIs) and elastics following mandibular advancement with a bilateral sagittal split ramus osteotomy (BSSRO). MATERIALS AND METHODS: A total of nine mandibular advancement models were set according to the position of the MIs (1.6 mm in diameter, 8 mm in length) and direction of the IMF elastics (1/4 inch, 5 oz). Major and minor principal stresses in the cortical and cancellous bones, von Mises stresses in the fixation system (miniplate and monocortical screws), and bending angles of the miniplate were analysed. RESULTS: Compressive and tensile stress distributions in the mandible and von Mises stress distributions in the fixation system were greater in models with a Class III IMF elastic direction and a higher IMF elastic force than in models with a Class II IMF elastic direction and a lower IMF elastic force. The bending angle of the miniplate was negligible. CONCLUSIONS: Stress distributions in the bone and fixation system varied depending on the direction, amount of force, and position of IMF elastics and MIs. Conclusively, IMF elastics in the Class II direction with minimal load in the area close to the osteotomy site should be recommended.

Interdisciplinary treatment of mutilated dentition and transverse maxillary deficiency with microimplant-assisted rapid palatal expansion, microimplants, and dental implants.

OBJECTIVE: This case report demonstrates an interdisciplinary approach to treat a 26-year-old male patient with hyperdivergent Class II skeletal pattern, maxillary transverse deficiency, slight anterior open bite, and multiple hopeless teeth with root rests. CLINICAL CONSIDERATIONS: An interdisciplinary treatment was required for oral hygiene improvement, caries treatment, extraction of residual roots and hopeless teeth, maxillary expansion using microimplant-assisted rapid palatal expansion, improvement of skeletal and dental relationship using orthodontic microimplants, and prosthetic restorations with the aid of dental implants. CONCLUSION: Consequently, esthetic and functional occlusal rehabilitation was achieved. CLINICAL SIGNIFICANCE: Hyperdivergent Class II facial and skeletal patterns with multiple missing teeth can be effectively treated using orthodontic skeletal anchorage. In young adults, the transverse discrepancy can be resolved using MARPE, which is also useful for improving the sagittal and vertical relationships. In the case of multiple missing teeth, orthodontic treatment can provide the proper space to facilitate dental implants to achieve optimal esthetics and function.

A cone-beam computed tomography evaluation of posterior available space in both arches relative to various skeletal patterns.

INTRODUCTION: This study aimed to evaluate the posterior available space (PAS) in both dental arches of adult patients with varying skeletal patterns using cone-beam computed tomography. METHODS: A sample of 114 adult patients (56 males and 58 females) was divided into 3 groups according to ANB angle and facial height ratio. Using C-mode cone-beam computed tomography images from these patients, maxillary PAS (MxPAS) and mandibular PAS (MnPAS) were measured in the distobuccal and palatal roots of the maxillary second molars and the distal roots of the mandibular second molars, respectively. The planes perpendicular to the tooth axes of the second molars in the coronal views and parallel to the posterior occlusal planes in the sagittal views were set at 3 heights of furcation, middle, and apex of the roots. For each plane, the shortest posterior distances from the roots to the inner and outer cortices were measured parallel to the furcation line connecting the furcations of the molars in the axial views. Posterior cortical bone thickness, defined as the distance from the inner cortex to the outer cortex, was measured. RESULTS: PAS was significantly greater in males than in females and in the maxilla than in the mandible (P <0.01). All MxPAS gradually increased from the furcation to the apex with significance (P <0.05), but there was no difference in MnPAS. MxPAS was significantly greater (P <0.05) in subjects with Class II and III malocclusion than subjects with Class I malocclusion, whereas MnPAS showed no difference. MxPAS showed no significant differences in facial height ratio, whereas MnPAS was significantly greater (P <0.05) at furcation in normovergent subjects than in others. Posterior cortical bone thickness was greater (P <0.001) in the mandible than in the maxilla. CONCLUSIONS: PAS was different according to sex and skeletal patterns. It would be helpful to evaluate PAS when distalizing the molars in either arch.

Hemimandibular hyperplasia treatment with condylectomy and orthodontic camouflage treatment using miniplate.

A 13-year-old growing female patient presented with hemimandibular hyperplasia of the right side, Class III hypodivergent skeletal pattern, and severe facial asymmetry. Corrective surgery was deferred until her growth had been completed. When the patient was 16 years old, a low condylectomy was performed on the hyperplastic side of her mandible to prevent its progressive condylar hyperplasia, while simultaneous orthodontic camouflage treatment was performed with the intrusion of the maxillary right posterior teeth using temporary skeletal anchorage devices without additional orthognathic surgery. A low condylectomy caused anterior and lateral open bite after the downward and backward movement of the chin, which improved Class III appearance. The intrusion of the maxillary right posterior teeth followed by compensating extrusion of the mandibular posterior teeth contributed to improve the patient's facial asymmetry with correction of the transverse occlusal plane and lip canting. After 30 months of treatment, an acceptable esthetic outcome and functional occlusion were achieved. The treatment results were well maintained for 1-year retention.

Craniomaxillofacial Changes Using High-Pull J-Hook Headgear and Mini-Implant Anchorage in Adolescents: A Structural Superimposition Method.

OBJECTIVE: The aim of this study was to compare the craniomaxillofacial changes when using high-pull J-hook headgear (HPJH) and mini-implants (MIs) as maxillary anchorage in adolescents. STUDY DESIGN: 40 female adolescents with dentoalvolar protrusion were divided into 2 groups; the HPJH group (n=20) and the MI group (n=20). Lateral cephalograms taken before treatment (T0) and after anterior tooth retraction (T1) were superimposed on the stable structures and then craniomaxillofacial changes were evaluated. RESULTS: The cranial base angle, SNB, and facial angle decreased in the HPJH group but increased in the MI group. ANB decreased more in the MI group than in the HPJH group. Mandibular plane angle increased in the HPJH group but decreased in the MI group. Facial height index increased in the MI group while it showed no change in the HPJH group. Mandibular true rotation occurred clockwise in the HPJH group and counterclockwise in the MI group. Maxillary central incisors were intruded and retracted more in the MI group than in the HPJH group. Maxillary first molars were extruded in the HPJH group and were intruded in the MI group. Maxillary first molars were protracted more in the HPJH group than in the MI group. Mandibular central incisors were retracted more in the HPJH group than the MI group. Mandibular first molars were extruded more in the MI group than in the HPJH group. CONCLUSION: More favorable craniomaxillofacial changes occurred in the MI group than in the HPJH group.

Assessment of bone density changes following two-jaw surgery using multidetector computed tomography: A pilot study.

OBJECTIVE: The aim of this retrospective study was to evaluate the pre- and postsurgical bone densities at alveolar and extra-alveolar sites following twojaw orthognathic surgery. METHODS: The sample consisted of 10 patients (mean age, 23.2 years; range, 18.0-27.8 years; 8 males, 2 females) who underwent two-jaw orthognathic surgery. A three-dimensional imaging program (Invivo 5) was used with multidetector computed tomography images taken preand postoperatively (obtained 32.3 ± 6.0 days before surgery and 5.8 ± 2.6 days after surgery, respectively) for the measurement of bone densities at the following sites: (1) alveolar bone in the maxilla and mandible, (2) extra-alveolar sites, such as the top of the head, menton (Me), condyle, and the fourth cervical vertebrae (C4). RESULTS: When pre- and postsurgical bone densities were compared, an overall tendency of decrease in bone density was noted. Statistically significant reductions were observed in the densities of cancellous bone at several areas of the maxillary alveolar bone; cortical and cancellous bone in most areas of the mandibular alveolar bone; cortical bone in Me; and cancellous bone in C4. There was no statistically significant difference in bone density in relation to the depth of the alveolar bone. In a comparison of the bone densities between groups with and without genioplasty, there was almost no statistically significant difference. CONCLUSIONS: Accelerated tooth movement following orthognathic surgery may be confirmed with reduced bone density. In addition, this study could offer insights into bone metabolism changes following orthognathic surgery, providing direction for further investigations in this field.

Mandibular condyle bone density in adolescents with varying skeletal patterns evaluated using cone-beam computed tomography: A potential predictive tool.

INTRODUCTION: The aim of this study was to evaluate the bone density of mandibular condyles in adolescents with varying skeletal patterns using cone-beam computed tomography. The null hypothesis was that there is no difference in the bone density of mandibular condyles in adolescents across various facial height ratios, ANB angle classifications, sexes, and age categories. METHODS: We divided 120 adolescent patients, 56 boys and 64 girls, into 3 groups according to 3 criteria: (1) age (early, 10 to <14 years; middle, 14 to <17 years; late, 17 to <20 years); (2) facial height ratio or Jarabak quotient (hyperdivergent: facial height ratio, <62%; normovergent: facial height ratio, 62% to ≤65%; and hypodivergent: facial height ratio, >65%); and (3) ANB angle classification (Class I, 1° to ≤4°; Class II, (>4°); and Class III, <1°). The total, cortical, and cancellous bone densities were measured and compared on the axial slice with the largest mediolateral diameter of the mandibular condyle using C-mode cone-beam computed tomography. RESULTS: Cortical bone density increased as age increased and showed statistically significant differences between the early and middle (P = 0.041) and the early and late adolescent groups (P = 0.031). Condylar bone density increased as facial height ratio decreased, and cancellous bone density showed statistically significant differences between the hyperdivergent and hypodivergent groups (P = 0.038). The cortical, cancellous, and total bone densities increased as ANB angle increased and showed statistically significant differences between the Class II and Class III groups (P = 0.022, P = 0.006, and P = 0.003, respectively). CONCLUSIONS: The null hypothesis was rejected. Condylar bone density increased as facial height ratio decreased and ANB angle increased. These findings may be useful in predicting the vertical and horizontal skeletal growth patterns of growing adolescents.

Effects of acid etching and calcium chloride immersion on removal torque and bone-cutting ability of orthodontic mini-implants.

INTRODUCTION: The 2-fold purpose of this study was to evaluate the effects of acid etching and calcium chloride immersion on removal torque and the bone-cutting ability of orthodontic mini-implants (OMIs). METHODS: For the removal torque part of the study, 3 types of OMIs (titanium alloy) were evaluated in a rabbit model: OMIs with acid surface etching with and without calcium chloride immersion (ECG and EG, respectively) and a control group (CG), in which the OMIs had an untreated, machined surface. We inserted 126 OMIs (42 OMIs per type) into both tibias of 21 male rabbits (5 months of age) with body weights of 3.0 to 3.5 kg. Removal torque was evaluated after 1, 4, and 7 weeks. To determine the OMIs' bone-cutting ability, total insertion time to place an OMI 6 mm into artificial bone was measured (6 OMIs per group). RESULTS: Removal torque values for the EG (3.97 ± 0.52 Ncm) and ECG (4.21 ± 0.44 Ncm) were statistically and significantly higher than those of the CG (3.02 ± 0.53 Ncm) 1 week after implantation (P <0.05). The ECG (6.54 ± 0.50, 6.61 ± 0.66 Ncm) showed the highest removal torque value followed by the EG (5.68 ± 0.58, 5.89 ± 0.70 Ncm) and CG (3.43 ± 0.62, 3.38 ± 0.54 Ncm) at 4 and 7 weeks after implantation (P <0.05). Removal torque did not change over time with the CG, but with the ECG and EG, it was significantly higher in weeks 4 and 7 than in week 1 (P <0.05). Total insertion time was significantly greater for the EG than for the ECG and CG (P <0.05). CONCLUSIONS: Treating OMIs with a calcium chloride solution improved the initial bone reaction by preventing contamination of the implant surface, and increasing the surface roughness of OMIs by acid etching enhanced their stability without decreasing the bone-cutting ability compared with OMIs without surface treatment.

Evaluation of factors influencing the success rate of orthodontic microimplants using panoramic radiographs.

OBJECTIVE: The purpose of this study was to investigate factors influencing the success rate of orthodontic microimplants (OMIs) using panoramic radiographs (PRs). METHODS: We examined 160 OMIs inserted bilaterally in the maxillary buccal alveolar bone between the second premolars and first molars of 80 patients (51 women, 29 men; mean age, 18.0 ± 6.1 years) undergoing treatment for malocclusion. The angulation and position of OMIs, as well as other parameters, were measured on PRs. The correlation between each measurement and the OMI success rate was then evaluated. RESULTS: The overall success rate was 85.0% (136/160). Age was found to be a significant predictor of implant success (p < 0.05), while sex, side of placement, extraction, and position of the OMI tip were not significant predictors (p > 0.05). The highest success rate was observed for OMIs with tips positioned on the interradicular midline (IRML; central position). Univariate analyses revealed that the OMI success rate significantly increased with an increase in the OMI length and placement height of OMI (p = 0.001). However, in simultaneous analyses, only length remained significant (p = 0.027). Root proximity, distance between the OMI tip and IRML, interradicular distance, alveolar crest width, distance between the OMI head and IRML, and placement angle were not factors for success. Correlations between the placement angle and all other measurements except root proximity were statistically significant (p < 0.05). CONCLUSIONS: Our findings suggest that OMIs positioned more apically with a lesser angulation, as observed on PRs, exhibit high success rates.

Effectiveness of pulsed electromagnetic field for pain caused by placement of initial orthodontic wire in female orthodontic patients: A preliminary single-blind randomized clinical trial.

INTRODUCTION: The purpose of this 2-arm parallel trial was to assess the effects of pulsed electromagnetic field (PEMF) on the reduction of pain caused by initial orthodontic tooth movement. METHODS: Thirty-three female patients (mean age, 16.8 ± 3.8 years) who began orthodontic treatment using fixed appliances were examined. In the pilot study, male patients were less likely to use the PEMF device (epatchQ; Speed Dental, Seoul, Korea) and answer a survey consistently, so eligibility criteria were female patients who were periodontally and systemically healthy at the initiation of treatment and had no history of dental pain in the prior 2 weeks or who used no medications (anti-inflammatory or analgesic drugs) during the experiment period. Each patient had brackets bonded on the maxillary teeth, and a 0.014-in nickel-titanium archwire was tied with elastomeric rings. Their maxillary arches were randomly divided into left and right sides in a split-mouth design: a normal PEMF device (experimental group) was used on 1 side, and a PEMF device with an inversely inserted battery (placebo group) was used on the opposite side of the arch for 7 hours on 3 consecutive nights. A Google survey link was sent to the patients' mobile phones via text message, and they were instructed to record their current pain on the survey. The survey was sent a total of 6 times after insertion of the initial archwire at 0 (T0), 2 (T1), 6 (T2), 24 (T3), 48 (T4), and 72 (T5) hours. Patients recorded the degree of pain in resting and clenching states using a numeric rating scale (NRS) from 1 (no pain) to 10 (worst pain). PEMF devices were used after T2. Generalized linear mixed models, along with ancillary pairwise analyses, were used to model and evaluate the differences in pain reported over 72 hours. RESULTS: The NRS scores did not differ across the groups during the before-PEMF phase for resting (mean difference, -0.07; 95% confidence interval [CI], -0.73 to 0.59; P = 0.842) and clenching (mean difference, -0.28; 95% CI, -1.11 to 0.56, P = 0.513). During the after-PEMF phase, NRS scores in the experimental group were significantly lower than those in the placebo group during both resting (mean difference, -1.46; 95% CI, -2.06 to -0.85; P = <0.001) and clenching (mean difference, -1.88; 95% CI, -2.74 to -1.02, P = <0.001). The NRS scores did not differ across the groups during the before-PEMF phase for either state but were significantly lower in the experimental group than in the placebo group at T3, T4, and T5 (P <0.01). The average NRS score in the clenching state was significantly greater than in the resting state. CONCLUSIONS: PEMF was effective in reducing orthodontic pain caused by initial archwire placement. REGISTRATION: The trial was not registered. PROTOCOL: The protocol was not published before trial commencement.

Relationship between maturation indices and morphology of the midpalatal suture obtained using cone-beam computed tomography images.

OBJECTIVE: The purpose of this study was to determine whether predicting maturation of the midpalatal suture is possible by classifying its morphology on cone-beam computed tomography (CBCT) images and to investigate relationships with other developmental age indices. METHODS: The morphology of the midpalatal suture was assessed by using CBCT images of 99 patients. Axial plane images of the midpalatal suture were classified into five stages according to the classification scheme. To make the assessment more accurate, the morphology and fusion of the midpalatal suture were additionally investigated on coronal cross-sectional planar images and volume-rendered images. Bone age was evaluated using the hand and wrist method (HWM) and cervical vertebrae method (CVM); dental age (Hellman's index), sex, and chronological age were also assessed. To evaluate relationships among variables, Spearman's rho rank test was performed along with crosstabs using contingency coefficients. RESULTS: The HWM and CVM showed strong correlations with the maturation stage of the midpalatal suture, while other indices showed relatively weak correlations (p < 0.01). Through crosstabs, the HWM and CVM showed high association values with CBCT stage; the HWM demonstrated slightly higher values (p < 0.0001). Based on the HWM, the midpalatal suture was not fused until stage 6 in both sexes. CONCLUSIONS: Among developmental age indices, the HWM and CVM showed strong correlations and high associations, suggesting that they can be useful in assessing maturation of the midpalatal suture.

Comparison of the bonding strengths of second- and third-generation light-emitting diode light-curing units.

OBJECTIVE: With the introduction of third-generation light-emitting diodes (LEDs) in dental practice, it is necessary to compare their bracket-bonding effects, safety, and efficacy with those of the second-generation units. METHODS: In this study, 80 extracted human premolars were randomly divided into eight groups of 10 samples each. Metal or polycrystalline ceramic brackets were bonded on the teeth using second- or third-generation LED light-curing units (LCUs), according to the manufacturers' instructions. The shear bond strengths were measured using the universal testing machine, and the adhesive remnant index (ARI) was scored by assessing the residual resin on the surfaces of debonded teeth using a scanning electron microscope. In addition, curing times were also measured. RESULTS: The shear bond strengths in all experimental groups were higher than the acceptable clinical shear bond strengths, regardless of the curing unit used. In both LED LCU groups, all ceramic bracket groups showed significantly higher shear bond strengths than did the metal bracket groups except the plasma emulation group which showed no significant difference. When comparing units within the same bracket type, no differences in shear bond strength were observed between the second- and third-generation unit groups. Additionally, no significant differences were observed among the groups for the ARI. CONCLUSIONS: The bracket-bonding effects and ARIs of second- and third-generation LED LCUs showed few differences, and most were without statistical significance; however, the curing time was shorter for the second-generation unit.

Forced eruption of impacted maxillary central incisors with severely dilacerated roots.

Treatment of impacted dilacerated incisors is challenging for clinicians because of the prominent position of the teeth and the abnormality of their roots. We report on 2 patients who had horizontally upward impacted and severely dilacerated maxillary central incisors. The first patient's root perforated the labial plate without significant resorption, and the second patient's root was resorbed. Both patients were treated by a surgical-orthodontic approach, and the crowns of the impacted teeth were brought into the arches by closed forced eruption. Therefore, if impacted teeth have dilacerated roots, patients should be told of the possibility of root resorption.

Orthodontic Treatment of Maxillary Incisors with Severe Root Resorption Caused by Bilateral Canine Impaction in a Class II Division 1 Patient.

This case report shows the successful alignment of bilateral impacted maxillary canines. A 12-year-old male with the chief complaint of the protrusion of his maxillary anterior teeth happened to have bilateral maxillary canine impaction on the labial side of his maxillary incisors. Four maxillary incisors showed severe root resorption because of the impacted canines. The patient was diagnosed as skeletal Class II malocclusion with proclined maxillary incisors. The impacted canine was carefully retracted using sectional buccal arch wires to avoid further root resorption of the maxillary incisors. To distalize the maxillary dentition, two palatal miniscrews were used. After 25 months of treatment, the maxillary canines were well aligned without any additional root resorption of the maxillary incisors.

Bone density effects on the success rate of orthodontic microimplants evaluated with cone-beam computed tomography.

INTRODUCTION: The purpose of this study was to evaluate the effect of bone densities on the success rate of orthodontic microimplants with cone-beam computed tomography images. METHODS: We examined 127 orthodontic microimplants implanted into the maxillary buccal alveolar bone of 71 patients (53 female, 18 male; mean age, 19.2 years) with malocclusion. The cortical, cancellous, and total bone densities were measured with Simplant Pro 2011 software (version 13; Materialise, Leuven, Belgium), and the correlations between these measurements and the orthodontic microimplant success rates were evaluated with cone-beam computed tomography. RESULTS: The overall success rate was 85.0% (108 of 127). Sex, age, and side of placement were not significant factors for success in the results (P >0.05). The density of the cortical bone increased apically (3, 5, and 7 mm) from the alveolar crest, but in the cancellous bone it decreased. Whereas the orthodontic microimplant success rates significantly increased as cancellous bone density and total bone density increased (P <0.01), cortical bone density did not have a significant effect on the success rate (P >0.05). CONCLUSIONS: The success rate of orthodontic microimplants significantly increased with higher cancellous and total bone densities, whereas cortical bone density did not have a significant effect.

Accuracy of three-dimensional printing for manufacturing replica teeth.

OBJECTIVE: Three-dimensional (3D) printing is a recent technological development that may play a significant role in orthodontic diagnosis and treatment. It can be used to fabricate skull models or study models, as well as to make replica teeth in autotransplantation or tooth impaction cases. The aim of this study was to evaluate the accuracy of fabrication of replica teeth made by two types of 3D printing technologies. METHODS: Fifty extracted molar teeth were selected as samples. They were scanned to generate high-resolution 3D surface model stereolithography files. These files were converted into physical models using two types of 3D printing technologies: Fused deposition modeling (FDM) and PolyJet technology. All replica teeth were scanned and 3D images generated. Computer software compared the replica teeth to the original teeth with linear measurements, volumetric measurements, and mean deviation measurements with best-fit alignment. Paired t-tests were used to statistically analyze the measurements. RESULTS: Most measurements of teeth formed using FDM tended to be slightly smaller, while those of the PolyJet replicas tended to be slightly larger, than those of the extracted teeth. Mean deviation measurements with best-fit alignment of FDM and PolyJet group were 0.047 mm and 0.038 mm, respectively. Although there were statistically significant differences, they were regarded as clinically insignificant. CONCLUSIONS: This study confirms that FDM and PolyJet technologies are accurate enough to be usable in orthodontic diagnosis and treatment.

Effects of various toothpastes on remineralization of white spot lesions.

OBJECTIVE: The purpose of this in vitro study was to examine the effects of fluoridated, casein phosphopeptide.amorphous calcium phosphate complex (CPP-ACP)-containing, and functionalized ß-tricalcium phosphate (fTCP)-containing toothpastes on remineralization of white spot lesions (WSLs) by using Quantitative light-induced fluorescence (QLF-D) Biluminator™ 2. METHODS: Forty-eight premolars, extracted for orthodontic reasons from 12 patients, with artificially induced WSLs were randomly and equally assigned to four treatment groups: fluoride (1,000 ppm), CPP-ACP, fTCP (with sodium fluoride), and control (deionized water) groups. Specimens were treated twice daily for 2 weeks and stored in saliva solution (1:1 mixture of artificial and human stimulated saliva) otherwise. QLF-D Biluminator™ 2 was used to measure changes in fluorescence, indicating alterations in the mineral contents of the WSLs, immediately before and after the 2 weeks of treatment. RESULTS: Fluorescence greatly increased in the fTCP and CPP-ACP groups compared with the fluoride and control groups, which did not show significant differences. CONCLUSIONS: fTCP- and CPP-ACP-containing toothpastes seem to be more effective in reducing WSLs than 1,000-ppm fluoride-containing toothpastes.

Evaluation of the relationship between upper incisor exposure and cephalometric variables in Korean young adults.

OBJECTIVE: The purpose of this study was to classify Korean young adults into 3 groups on the basis of upper incisor exposure rates (UIERs) and to compare the skeletal, dental, and soft tissue variables. METHODS: Samples were obtained from 127 students at the College of Dentistry, Wonkwang University in South Korea. Facial photographs of frontal posed smiles and lateral cephalograms of the subjects were taken. The subjects were divided into 3 groups on the basis of UIERs and 20 measurements were compared among the 3 groups. The correlations between the variables were determined. RESULTS: Male and female subjects showed significant differences in the group distribution. Male subjects showed higher frequencies of low smiles, and female subjects showed higher frequencies of high smiles. The vertical height of the anterior alveolar process of the maxilla directly correlated with the UIER. However, the UIER showed no significant correlation with the vertical height of the anterior basal bone or the inclination of the upper incisor axis. In female subjects, the upper central incisor clinical crown length showed an inverse correlation with the UIER. However, this variable showed no significant correlation with the UIER in male subjects. CONCLUSIONS: The UIER was directly correlated with the levator muscle activity of the upper lip and inversely correlated with the upper lip thickness, yet there was no correlation between the UIER and upper lip length at rest.