Cephalometric outcomes of a new orthopaedic appliance for Class III malocclusion treatment.

OBJECTIVE: To evaluate dental and skeletal effects of a new orthopaedic appliance for the treatment of Class III malocclusion in growing patients. MATERIAL AND METHODS: This retrospective cephalometric study was performed on a sample of 18 patients with a skeletal Class III malocclusion (4 males; 14 females; mean age 8.8 ± 1.5 years) treated with the Pushing Splints 3 (PS3) protocol. The control group consisted of 18 subjects (5 males; 13 females; mean age 9.1 ± 1.8 years) selected from a database of subjects with untreated Class III malocclusion. The cephalometric analysis was performed at the beginning (T0) and the end of the orthopaedic therapy (T1). Significant differences between the treated and control groups were assessed with independent samples t-test (P < 0.05). RESULTS: In the PS3 group, the post-treatment cephalometric values showed a forward displacement of the maxilla, resulting in a statistically significant increase of the SNA angle. ANPg and Wits appraisal improved significantly compared with the control group. Lingual inclination of mandibular incisors and buccal inclination of the upper incisors were significantly increased in comparison with the control group. No significant differences were recorded for backward mandibular rotation. LIMITATIONS: This study presents a short-term evaluation of the treatment and the use of a historical control group. CONCLUSIONS: The PS3 was effective for the treatment of Class III malocclusion in growing patients, with favourable maxillary advancement and control of the vertical skeletal relationships.

A New Appliance for Class III Treatment in Growing Patients: Pushing Splints 3.

Several orthopedic procedures have been used in early treatment to reduce the need for orthognathic surgery in skeletal Class III. The most used treatment is Rapid Maxillary Expansion and Facemask. This procedure also determines a clockwise rotation of the mandible, increasing the vertical dimensions of the lower third of the face. Therefore, the control of vertical dimension appears to be a key objective in Class III hyperdivergent patients. This article shows two skeletal Class III patients treated with a new appliance (Pushing Splints 3), that is able to correct sagittal discrepancy with a good control of the vertical growth. In both cases, Class I relationship with a proper Overjet and Overbite was achieved with improvement of profile. The final cephalometric values demonstrated a stable sagittal relationship and a good control of the vertical growth. The specific biomechanic features of the PS3 appliance permit the improvement of the sagittal jaw relationship, delivering at the same time vertical vectors that are able to control the alveolar and skeletal components of the vertical growth. This could be useful in the treatment of Class III hyperdivergent patients.

Differences in craniofacial growth of Class II individuals from different decades: A retrospective study.

OBJECTIVES: To detect changes in mandibular growth between a historical group (HG) from the American Association of Orthodontics Foundation Craniofacial Growth Legacy Collection (AAOF Legacy) and a contemporary group (CG) of normodivergent or hypodivergent Class II untreated subjects. SETTING AND SAMPLE POPULATION: The sample included radiographs from the AAOF Legacy and from the University of Naples 'Federico II' collected during a previous RCT. MATERIALS & METHODS: The HG was composed of 26 individuals (around 1960) from the AAOF Legacy (15 from the Burlington Growth Study, nine from the Oregon Growth Study and two from the Michigan Growth Study) who were matched by sex, age and race with the 26 individuals of the CG (around 2010). Two lateral cephalograms obtained at T0 and T1 (12 months) were selected, and one examiner performed the cephalometric measurements according to Pancherz's method. The normal distribution of data was confirmed by the Shapiro-Wilk test, MANOVA analysis and t test for paired and unpaired data were performed. The level of significance was set according to Bonferroni's correction. RESULTS: At T0 and T1, the between-group comparisons revealed greater linear dimensions for Maxillary base, Maxillary incisor and Mandibular incisor in the CG than in the HG (P ≤ 0.002). No significant difference was found in the growth rate for linear skeletal measurement between the HG and the CG. CONCLUSIONS: In this study, the cephalometric analysis showed larger maxillary dimensions for the CG than the HG, while no differences were shown between the growth rate and direction of the two groups.

Reproducibility of the assessment of the Fränkel manoeuvre for the evaluation of sagittal skeletal discrepancies in Class II individuals.

OBJECTIVES: The Fränkel manoeuvre is a procedure by which the mandible of Class II individuals is postured forward in dental Class I relationship. The evaluation of the resulting facial profile provides information concerning the components determining the sagittal discrepancy. Data concerning the reproducibility of its assessment are not available. This study aimed to evaluate the intra-observer and inter-observer reproducibility of the assessment of the manoeuvre and to assess whether the amount of clinical experience affects its reproducibility. METHODS: Two lateral photographs, one in centric occlusion, and the other with the mandible postured forward (Fränkel manoeuvre) of 100 Angle Class II individuals aged between 9 and 13 years were evaluated by six orthodontists (T0). Each examiner was asked whether the facial profile worsen or not with the manoeuvre after being trained by an expert orthodontist. The test was repeated after 2 weeks interval (T1). Intra-observer and inter-observer agreement were evaluated by computing the Cohen's K. RESULTS: The agreement (K values) between observations (T0 versus T1) for each examiner ranged from 0.49 to 0.72. The overall agreement was 0.65 [95% confidence interval (CI) = 0.54-0.75]. The agreement in the group with less clinical experience was 0.61 (95% CI = 0.46-0.76), while it was 0.68 (95% CI = 0.53-0.83) in the more experienced group. The amount of clinical experience did not affect intra-observer agreement (P = 0.50). The overall agreement between the examiners and the trainer was 0.74 (95% CI = 0.65-0.83) and 0.73 (95% CI = 0.64-0.83) at T0 and T1 respectively. CONCLUSION: The assessment of the Fränkel manoeuvre is reproducible and it is not influenced by the amount of clinical experience.

Short-Term Sensorimotor Effects of Experimental Occlusal Interferences on the Wake-Time Masseter Muscle Activity of Females with Masticatory Muscle Pain.

AIMS: To investigate the effects of the application of an acute alteration of the occlusion (ie, interference) on the habitual masseter electromyographic (EMG) activity of females with temporomandibular disorders (TMD)-related muscular pain during wakefulness. METHODS: Seven female volunteers with masticatory myofascial pain participated in a crossover randomized clinical trial. Gold foils were glued on an occlusal contact area (active occlusal interference, AI) or on the vestibular surface of the same molar (dummy interference, DI) and left for 8 days. The masseter electromyogram was recorded during wakefulness in the natural environment by portable recorders under interference-free, dummy-interference, and active-interference conditions. The number, amplitude, and duration of EMG signal fractions with amplitudes above 10% of the maximum voluntary contraction (activity periods, APs) were computed in all experimental conditions. Muscle pain, headache, and perceived stress were each assessed with a visual analog scale (VAS), and an algometer was used to assess masseter and temporalis pressure pain thresholds. Data were analyzed by means of analysis of variance. RESULTS: The frequency and duration of the recorded APs did not differ significantly between the experimental conditions (P>.05), but a small and significant reduction of the EMG mean amplitude of the APs occurred with AI (P<.05). Neither the VAS scores for muscular pain, headache, and perceived stress nor the pressure pain thresholds changed significantly throughout the entire experiment (P>.05). CONCLUSION: An active occlusal interference in female volunteers with masticatory muscle pain had little influence on the masseter EMG activity pattern during wakefulness and did not affect the pressure tenderness of the masseter and temporalis.

Effects of orthopedic maxillary expansion on nasal cavity size in growing subjects: a low dose computer tomography clinical trial.

OBJECTIVE: The aim of this retrospective clinical trial was to evaluate the effects of rapid maxillary expansion on skeletal nasal cavity size in growing subjects by use of low dose computer tomography. METHODS: Eight Caucasian children (three male; five female) with a mean age of 9.7 years (SD±1.41) were the final sample of this research that underwent palatal expansion as a first phase of orthodontic treatment. The maxillary expander was banded to the upper first molars and was activated according a rapid maxillary expansion protocol. Low-dose computer tomography examinations of maxilla and of the low portion of nasal cavity were performed before inserting the maxillary expander (T0) and at the end of retention (T1), 7 months later. A low-dose computer tomography protocol was applied during the exams. Image processing was achieved in 3 steps: reslicing; dental and skeletal measurements; skeletal nasal volume computing. A set of reproducible skeletal and dental landmarks were located in the coronal passing through the first upper right molar furcation. Using the landmarks, a set of transverse linear measurements were identified to estimate maximum nasal width and nasal floor width. To compute the nasal volume the lower portion of the nasal cavity was set as region of interest. Nasal volume was calculated using a set of coronal slices. In each coronal slice, the cortical bone of the nasal cavity was identified and selected with a segmentation technique. Dependent t-tests were used to evaluate changes due to expansion. For all tests, a significance level of P<0.05 was used. RESULTS: Rapid maxillary expansion produced significant increases of linear transverse skeletal measurements, these increments were bigger in the lower portion of the nasal cavities: nasal floor width (+3.15 mm; SD ± 0.99), maximum nasal width (+2.47 mm; SD ± 0.99). Rapid maxillary expansion produced significant increment of the total nasal volume (+1.27 cm(3) ± SD 0.65). The anterior volume increase was 0.58 cm(3) while the posterior one was 0.69 cm(3). CONCLUSION: In growing subjects RME is able to significantly enlarge the dimension of nasal cavity. The increment is bigger in the lower part of the nose and equally distributed between the anterior e the posterior part of the nasal cavity.

Evaluation of surface roughness of orthodontic wires by means of atomic force microscopy.

OBJECTIVE: To compare the surface roughness of different orthodontic archwires. MATERIALS AND METHODS: Four nickel-titanium wires (Sentalloy(®), Sentalloy(®) High Aesthetic, Titanium Memory ThermaTi Lite(®), and Titanium Memory Esthetic(®)), three ß-titanium wires (TMA(®), Colored TMA(®), and Beta Titanium(®)), and one stainless-steel wire (Stainless Steel(®)) were considered for this study. Three samples for each wire were analyzed by atomic force microscopy (AFM). Three-dimensional images were processed using Gwiddion software, and the roughness average (Ra), the root mean square (Rms), and the maximum height (Mh) values of the scanned surface profile were recorded. Statistical analysis was performed by one-way analysis of variance (ANOVA) followed by Tukey's post hoc test (P < .05). RESULTS: The Ra, Rms, and Mh values were expressed as the mean ± standard deviation. Among as-received archwires, the Stainless Steel (Ra  =  36.6 ± 5.8; Rms  =  48 ± 7.7; Mh  =  328.1 ± 64) archwire was less rough than the others (ANOVA, P < .05). The Sentalloy High Aesthetic was the roughest (Ra  =  133.5 ± 10.8; Rms  =  165.8 ± 9.8; Mh  =  949.6 ± 192.1) of the archwires. CONCLUSIONS: The surface quality of the wires investigated differed significantly. Ion implantation effectively reduced the roughness of TMA. Moreover, Teflon(®)-coated Titanium Memory Esthetic was less rough than was ion-implanted Sentalloy High Aesthetic.

Pain perception following first orthodontic archwire placement--thermoelastic vs superelastic alloys: a randomized controlled trial.

OBJECTIVES: Orthodontic thermoelastic archwires produce lighter and more biologic forces than superelastic archwires and could therefore offer the possibility of reducing initial orthodontic pain. Nevertheless, evidence concerning this issue is scarce. The aim of this study was to compare pain perception following first archwire placement in patients with thermal heat-activated (HANT) and superelastic (SE) nickel-titanium archwires. METHOD AND MATERIALS: Thirty subjects (11 males, 19 females; range, 11 to 26 years of age) were recruited. Metal brackets were bonded in the maxillary or mandibular arch. Round 0.016-inch HANT or 0.016-inch SE archwires were randomly placed and tied with elastic ligatures. Each patient was invited to score tooth pain for 7 days at different time points (8:00, 12:00, 16:00, 20:00, and 24:00) using the visual analog scale (VAS). RESULTS: In both groups, pain was highest at day 2 and lowest at day 7. Patients with HANT archwires had significantly lower VAS scores (P < .005) at days 2, 3, and 4 than subjects with SE archwires. This was also the case after adjusting for analgesic consumption, sports practicing, overlapping pain of different origin, and the concomitance of stressful events. The frequency of analgesic consumption was higher in the SE than in HANT group at day 3 (P < .05). No differences in pain perception were found between time points, nor was any correlation found between dental crowding and pain. No difference in pain perception was found between the maxillary and mandibular dental arches. CONCLUSION: Initial orthodontic pain is reduced when using HANT orthodontic archwires.

Calorimetric and thermomechanical properties of titanium-based orthodontic wires: DSC-DMA relationship to predict the elastic modulus.

Orthodontic treatment is strongly dependent on the loads developed by metal wires, and the choice of an orthodontic archwire should be based on its mechanical performance. The desire of both orthodontists and engineers would be to predict the mechanical behavior of archwires. To this aim, Gum Metal (Toyota Central R&L Labs., Inc.), TMA (ORMCO), 35°C Copper NiTi (SDS ORMCO), Thermalloy Plus (Rocky Mountain), Nitinol SE (3M Unitek), and NiTi (SDS ORMCO) were tested according to dynamic mechanical analysis and differential scanning calorimetry. A model was also developed to predict the elastic modulus of superelastic wires. Results from experimental tests have highlighted that superelastic wires are very sensitive to temperature variations occurring in the oral environment, while the proposed model seems to be reliable to predict the Young's modulus allowing to correlate calorimetric and mechanical data. Furthermore, Gum Metal wire behaves as an elastic material with a very low Young's modulus, and it can be particularly useful for the initial stage of orthodontic treatments.

Effect of N-acetyl cysteine on orthodontic primers cytotoxicity.

OBJECTIVES: The aims of this study were to evaluate the cytotoxicity of four orthodontic primers, including two hydrophilic and two hydrophobic materials, and to investigate the role of the reactive oxygen species (ROS) in induced cell damage. Moreover, the effects of the anti-oxidant N-acetyl cysteine (NAC) on primers toxicity was analyzed. METHODS: Human gingival fibroblasts (HGF) were exposed to different concentrations of primers (0-0.25 mg/ml) in the presence or absence of NAC, and the cytotoxicity was assessed by the MTT assay, while cell death was quantified by flow cytometry after propidium iodide staining. The increase in the induced ROS levels was detected by flow cytometry measuring the fluorescence of the oxidation-sensitive dye 2',7'-dichlorofluorescein diacetate (DCFH-DA). RESULTS: All materials decreased cell viability in a dose-related manner after a 24 h exposure period. Cytotoxicity of orthodontic primers based on concentrations which caused a 50% decrease in cell viability (TC50) in HGF was ranked as follows (median values): Eagle Fluorsure (0.078 mg/ml)>Transbond XT (0.081 mg/ml)>Transbond MIP (0.128 mg/ml)>Ortho solo (0.130 mg/ml). Moreover, in HGF cells, all materials induced a dose-dependent increase in ROS levels compared to untreated cells. Incubation of HGF with NAC significantly reduced ROS production and decreased the cell damage and cytotoxicity caused by all materials tested (p<0.001). SIGNIFICANCE: Our results suggested that hydrophilic primers were less cytotoxic than hydrophobic materials. Moreover, we demonstrated a major role of ROS in the induction of cell death since the antioxidant N-acetyl cysteine was able to prevent cell damage induced by all materials tested.

Relationship between molar dentoalveolar and craniofacial heights in children.

OBJECTIVES: The relationship between posterior dentoalveolar heights and craniofacial vertical pattern has been matter of debate. Increased posterior dentoalveolar heights have been reported to be present in long face subjects, while in few studies the amount of molar dentoalveolar heights was negatively influenced by the divergence of the jaws. This, in turn, was interpreted as a dentoalveolar compensatory mechanism by which the teeth and the alveolar process adapt to jaw relationship in order to maintain a functional occlusion. Although this dentoalveolar compensatory mechanism has been reported to be present in adults and in subjects with permanent dentition, currently it is not known whether it might occur also in an early phase of growth, i.e. before growth spurts. In this study we tested the hypothesis that a dentoalveolar compensatory mechanism is absent in children with still unexpressed vertical growth potential. METHODS AND MATERIALS: Cephalometric measurements obtained from 79 children younger than 9 were entered as independent variables in a multiple regression model. Maxillary and mandibular molar dentoalveolar heights were entered as dependent variables. RESULTS: Approximately 54% of the total variability was explained by the variability in anterior lower facial height (ANS-Me) and mandibular palatal plane angle (PP-MP). Both maxillary and mandibular molar dentoalveolar heights were significantly influenced by the length of the anterior lower facial heights as measured by ANSMe, and by the mandibulopalatal plane angle (PP-MP). Increases of ANS-Me and PP-MP had opposite effects on the amount of molar dentoalveolar heights. CONCLUSION: The findings suggest that an inverse relationship between posterior dentoalveolar heights and jaw divergence is already present when the vertical growth is stil incomplete.

Web-based randomised controlled trials in orthodontics.

Randomised controlled trials (RCT) are considered the best source of scientific evidence--the gold standard--when evaluating the efficacy of orthodontic treatments. Frequently, RCT are planned as multicentre trials, with the intention of increasing statistical power and raising the precision of outcome estimates. The management of large-scale RCT, however, requires even more thorough organisation than conventional RCT. Indeed, the need for high accuracy and standardisation in data collection, research aids, secretarial skills, staff and patient training, and organisational meetings, make these studies time-consuming, expensive and, in general, relatively complex to carry out well. A website was developed to support a large scale-orthodontic RCT which aimed to evaluate the efficacy of a functional appliance(www.ortodonzia.unina.it). Websites such as this can increase the quality of data collection, simplify the randomisation process, speed up data collection, and improve trial monitoring. Web-based RCT have the potential to help globalise orthodontic research and also increase our rate of acquisition of evidence in orthodontics.

Is unilateral posterior crossbite associated with leg length inequality?

It has been suggested that malocclusions may influence whole body posture, including leg length, but the current scientific evidence to support this statement is poor. The aim of the present study was to investigate a possible association between leg length inequality (LLI) and unilateral posterior crossbite. A survey was carried out in young adolescents recruited from three schools. The sample included 1,159 subjects (633 males and 526 females) with a mean age of 12.3 years (range 10.1-16.1 years), who underwent an orthodontic and orthopaedic examination performed independently by orthodontists and orthopaedists. The data were analysed by means of logistic regression analysis. One hundred and twenty subjects (10.3 per cent) were diagnosed as having LLI. A unilateral posterior crossbite was found in 142 of the 1,159 subjects (12.2 per cent). Logistic multiple regression analysis, controlling for potential confounding variables, failed to reveal a significant association between LLI and unilateral posterior crossbite (odds ratio = 1.0, confidence limits = 0.6-1.9). A unilateral posterior crossbite does not appear to be associated with LLI, at least in young adolescents.

Postural stability and unilateral posterior crossbite: is there a relationship?

The aim of this study was to test the hypothesis that unilateral posterior crossbite influences postural stability of the whole body. Twenty-six subjects (14 males and 12 females) affected with unilateral posterior crossbite were selected and compared with 52 controls matched for age and gender. Postural stability was assessed using a stabilometric platform. The following stabilometric measurements were assessed: weight distribution on foot area and speed of body sway. Tests were performed under two occlusal conditions: teeth in intercuspal position (ICP) and while keeping two cotton rolls between teeth without clenching. The weight distribution on foot area and the speed of body sway were not significantly influenced from crossbite (with and without lateral mandibular slide), occlusal conditions (ICP, cotton rolls), and gender. Therefore, the treatment of this malocclusion in order to prevent or to treat postural disorders is not justified.

Interexaminer reliability and validity for diagnosis of temporomandibular disorders of visual leg measurements used in dental kinesiology.

AIMS: To determine the reliability and the validity of visual leg measurements used in dental kinesiology, which suggests that a masticatory dysfunction, such as occurs in temporomandibular disorders (TMD), can influence the length and the internal rotation of lower limbs. METHODS: The leg-length inequality test and the internal foot-rotation test were performed independently by 3 different examiners on 41 subjects who were also screened for TMD. Data were analyzed by means of kappa statistics and by calculation of sensitivity and specificity values. RESULTS: Chance-corrected reliability was generally poor for both the leg-length inequality test (0.33 < or = k < or = 0.39) and the internal foot-rotation test (0.15 < or = k < or = 0.27). Sensitivity and specificity values of the tests to differentiate TMD and healthy subjects were below acceptable thresholds; they ranged from 0.41 to 0.57. CONCLUSION: Visual evaluations of leg-length inequality and internal foot rotation were unreliable and are not valid for TMD diagnoses. The results of chiropractic visual leg measurement procedures in dentistry should be interpreted with caution, particularly when clinical decisions may lead to nonreversible dental treatment.

Habitual daily masseter activity of subjects with different vertical craniofacial morphology.

Little is known about the habitual daily masticatory activity of subjects with different vertical craniofacial morphology. The purpose of the present study was to compare the daily long-term muscle activity of short-face subjects with that of long-face subjects as assessed in their natural environment. Digital photographs of the facial profile were obtained from a sample of 300 subjects and the ratio between anterior total and anterior lower facial height was assessed (Vertical Facial Index: VFI). Fourteen long-face and 16 short-face subjects were selected from the opposite tails of the frequency distribution of VFI. Long-term masseter activity was monitored for 8 h d(-1) in the natural environment by means of portable one-channel electromyograph recorders over three working days. Assessments included calculation of the number of activity periods (APs) per h (N/h), their mean amplitude (Amean), and their mean duration (Dur). The maximal electromyogram activity did not differ significantly between the short-face and the long-face subjects. There was no significant difference between the two groups investigated in N/h, in Amean and Dur. The findings suggest that habitual activity of masseter muscle in the natural environment was not influenced by the vertical craniofacial morphology as assessed in the present study.

The Relationship between molar dentoalveolar and craniofacial heights.

Excessive vertical growth of the posterior dentoalveolar region has been implicated in the etiology of the so-called long-face syndrome. In this study, we tested the hypothesis that molar dentoalveolar heights are positively related to vertical craniofacial features. Cephalometric measurements obtained from 82 adult subjects were entered as independent variables in a multiple regression model. Maxillary and mandibular molar dentoalveolar heights were entered as dependent variables. Approximately 70% of the total variance was explained by anterior lower facial height (ANS-Me) and the mandibular palatal plane angle (PP-MP). Increases of ANS-Me and PP-MP had opposite effects on the amount of molar dentoalveolar heights. The lowest values of molar dentoalveolar heights were found in subjects with a small ANS-Me distance but with a wide PP-MP angle. The findings suggest that individuals with a marked divergence of the jaws may also have a reduced molar dentoalveolar vertical development.

The additional value of a home physical therapy regimen versus patient education only for the treatment of myofascial pain of the jaw muscles: short-term results of a randomized clinical trial.

AIMS: To compare the short-term efficacy of patient education only versus the combination of patient education and home exercises for the treatment of myofascial pain of the jaw muscles. MATERIALS AND METHODS: Seventy myogenous temporomandibular disorder patients were assigned to 2 treatment groups. One group received patient education supplemented by general information about self-care of the jaw musculature. The other group received both education and a home physical therapy program. Treatment contrast, calculated from the mean normalized relative changes in anamnestic and clinical scores, was used to determine treatment success. Clinical outcome measures included pressure pain threshold (PPT) of the masseter, anterior temporalis, and Achilles tendon; pain-free maximal jaw opening; and pain on chewing, spontaneous muscle pain, and headache as rated on visual analog scales. RESULTS: After 3 months the success rate was 57% for the group that received education only and 77% for the group that received both education and home physical therapy (P = .157). The patients were then redivided into 2 groups: successfully treated patients and unsuccessfully treated patients. In the unsuccessfully treated group, pain-free maximal jaw opening increased significantly more among those who had been in the education and physical therapy group than among those who had been in the education-only group (P = .019). The change in PPT was significantly greater in successfully treated patients than in unsuccessfully treated patients (.009 < P < .039), independent of the treatment modality, with higher PPTs among successful patients. There were no significant differences between the successfully and unsuccessfully treated groups or between treatment modalities for any other variable. CONCLUSION: Over a period of 3 months, the combination of education and a home physical therapy regimen, as used in this protocol, is slightly more clinically effective than education alone for the treatment of myofascial pain of the jaw muscles.

Masseter thickness, endurance and exercise-induced pain in subjects with different vertical craniofacial morphology.

The aim of the study was to compare neuromuscular features of the masseter muscle in subjects with different vertical craniofacial morphology. Fifteen short-faced (mandibular plane-Frankfurt plane angle < 15 degrees) and 15 normal- to long-faced (mandibular plane-Frankfurt plane angle > or = 23 degrees) male students participated. The thickness of the masseter was assessed by ultrasonography. Onset and endurance of exercise pain were recorded during sustained biting at a level of 15% of maximum voluntary contraction and 30 micro V electromyographic activity. Pain and fatigue was measured on visual analog scales before and after the biting, as well as before and after 10 min chewing. Statistical comparison showed that the masseter muscle was significantly thicker (+15%) in the short-faced than the normal- to long-faced subjects. The pain onset time and endurance time were also consistently shorter in short-faced subjects, whereas the intensity of pain and fatigue did not differ significantly between the two groups. Multiple stepwise regression showed positive influence from the mandibular plane inclination and the masseter thickness on the pain onset time and endurance time. The present findings support the concept that subjects with different craniofacial morphology show neuromuscular differences.