Friction versus frictionless mechanics during maxillary en-masse retraction in adult patients with Class I bimaxillary dentoalveolar protrusion: a randomized clinical trial.

BACKGROUND: Extraction space closure is a challenging phase during orthodontic treatment that affects not only the total treatment duration but also the whole treatment outcome. OBJECTIVE: To compare the efficiency of friction and frictionless mechanics during en-masse retraction of maxillary anterior teeth in adult patients with bimaxillary dentoalveolar protrusion. TRIAL DESIGN: Two-arm parallel group, single-center randomized clinical trial. MATERIALS AND METHODS: Thirty-two adult patients with bimaxillary protrusion were recruited and randomly allocated to two different retraction mechanics. A friction group, using NiTi coil springs and a frictionless group using closing T-loops for en-masse retraction. Randomization in a 1:1 ratio was generated by Microsoft Excel. The randomization numbers were secured in opaque sealed envelopes for allocation concealment. Retraction started in all patients following first premolars extraction using miniscrews as a source of indirect anchorage. Activation was done on a monthly basis until complete retraction of anterior segment. The rate of retraction, amount of anchorage loss, the dental, and soft tissue changes were analyzed on digital models and lateral cephalograms taken before retraction and after space closure. BLINDING: The outcome assessor was blinded through data concealment during assessment. RESULTS: Two patients were lost to follow up, so 30 patients completed the trial. The rate of anterior segment retraction was 0.88 ±â€…0.66 mm/month in the frictionless group compared to 0.72 ±â€…0.36 mm/month in the friction group which was statistically significant. Anchorage loss of 1.18 ±â€…0.72 mm in the friction group compared to 1.29 ±â€…0.55 mm in the frictionless group with no significant difference. Comparable dental and soft tissue changes following en-masse retraction were reported in both groups, with no statistically significant difference. HARM: one patient complained of soft tissue swelling following miniscrew insertion, but the swelling disappeared after one week of using mouth wash. LIMITATION: The study focused only on the maxillary arch. CONCLUSION: Both mechanics have successfully achieved the required treatment objectives in patients with bimaxillary dentoalveolar protrusion. Frictionless group showed a faster rate of retraction than the friction group, which was statistically but not clinically significant. TRIAL REGISTRATION: Clinicaltrials.gov with the identifier NCT03261024.

The electrical activity of the masticatory muscles in children with cleft lip and palate.

BACKGROUND: Information regarding masticatory muscle function in children with cleft lip and palate (CLP) is limited. As a consequence, research on masticatory muscle activity in cleft subjects is needed. AIM: To assess masticatory muscle activity in children surgically treated for CLP as well as identify the possible factors associated with this activity. DESIGN: The sample comprised 82 children with mixed dentition and Class I occlusions (25 children with unilateral CLP and 57 subjects with no cleft abnormalities). A DAB-Bluetooth Instrument (Zebris Medical GmbH, Germany) was used to take electromyographical (EMG) recordings of the temporal and masseter muscles both in the mandibular rest position and during maximum voluntary contraction (MVC). RESULTS: Patients with clefts showed a significant increase in temporal muscle activity at rest compared with the controls. The presence of clefts and unilateral posterior crossbites are factors strongly associated with increased temporal muscle EMG potentials during rest position. CONCLUSIONS: Children with clefts have altered temporal muscle function. The presence of posterior crossbites affects the temporal muscle activity in cleft subjects. Early diagnosis and orthodontic treatment of malocclusions are necessary to achieve functional improvement in these patients.

The relationship between lip-closing force and dental arch morphology in patient with Angle Class I malocclusion.

Dental arch morphology and tooth position are affected by lip-closing force (LCF). This study aimed to quantitatively evaluate the relationships between the horizontal or vertical balance of the LCF generated during maximum voluntary pursing-like movements and dental arch length (DAL) or width (DAW) or the lingual inclination of the upper or lower 1st molars (LIUM, LILM) in patients with Angle Class I malocclusion. Sixteen subjects with Angle Class I malocclusion (median age: 23·4 ± 5·9 years) who had never undergone orthodontic treatment were randomly selected. LCF was measured in eight directions during maximum voluntary pursing-like lip-closing movements. Dental arch models were scanned and analysed to obtain DAW, DAL, LIUM and LILM measurements. Mandibular deviation was measured on posteroanterior cephalograms. A significant negative correlation was detected between maxillary DAL and upper LCF. Maxillary DAL, DAW and the DAL/DAW ratio displayed significant negative correlations with total LCF and upper LCF. However, no significant correlations were detected between any mandibular dental arch morphological parameter and LCF. The difference in the LIUM between the deviation and non-deviation sides exhibited a significant positive correlation with the difference in upper LCF between the deviation and non-deviation sides and was significantly negatively correlated with the difference in lower LCF between the deviation and non-deviation sides. These results suggest that upper LCF is related to maxillary DAL, and the horizontal balance of the LCF of the upper and lower lips is related to the LIUM during pursing-like lip-closing movements in patients with Angle Class I malocclusion.

Establishing the Cephalometric Values for Tetragon Analysis in Patients with Class I Occlusion: A Cephalometric Study.

OBJECTIVES: Proper application of the cephalometric norms for tetragon analysis for better understanding, diagnosis, and management of dentofacial deformities in the ethnic population. MATERIALS AND METHODS: A total of 204 subjects, inclusive of males (102) and females (102), were selected randomly from the outpatient department of Saveetha Dental College and Hospitals, in the age group ranging from 18 to 25 years, fulfilling the inclusion criteria. Assessment of each lateral cephalogram was done using tetragon analysis to evaluate the cephalometric values for individuals with class I occlusion using the FACAD(®) 3.4.0.3 A software. RESULTS: Statistically significant differences were found for all parameters between the ethnic population and the Caucasian norms. Four out of 14 parameters were found to be significantly different between male and female in the ethnic population. CONCLUSION: This study indicates that the local ethnic population have more prognathic maxillary and mandibular jaws, converging tendency of the jaw bases (resulting in reduced lower anterior facial height and horizontal growth pattern) as indicated by the analysis done in the tetragon and the trigon, and increased proclination of the upper and lower incisors.

Comparison of craniofacial growth of untreated Class I and Class II girls from ages 9 to 18 years: a longitudinal study.

INTRODUCTION: The purposes of this study were to examine and compare the craniofacial growth in girls with Class I or Class II occlusion from the ages of 9 to 18. METHODS: Twenty-five Class I (ANB, 1°-4°) and 21 Class II (ANB, >4°) untreated Caucasian girls were selected from the Burlington Growth Centre in Toronto, Ontario, Canada. Cephalograms of each subject at ages 9, 14, and 18 years were traced, and 29 parameters were measured. The growth changes in each parameter from ages 9 to 14, 14 to 18, and 9 to 18 were calculated, and comparisons of each parameter were made between the 2 groups. RESULTS: From ages 9 to 14, the Class I and Class II groups had similar skeletal growth patterns (increases of SNA and SNB angles, decreases of ANB, MP-SN, and gonial angles). Dentally, the Class II group showed less maxillary incisal proclination and more overbite than did the Class I group. From ages 14 to 18, the 2 groups also showed similar growth patterns, with little sagittal but continued vertical growth, and the MP-SN angle continued to decrease. From ages 9 to 18 (combined periods of 9-14 and 14-18), the 2 groups showed similar skeletal growth, with the exception of a slightly higher ANS-ME/N-Me in the Class I group. Dental changes were similar in the 2 groups, except that overbite increased slightly more in the Class II group. CONCLUSIONS: Overall, the craniofacial growth patterns of Class I and Class II girls were similar. With growth, the face became more flattened with a decrease of the ANB angle, and the mandible demonstrated forward rotation with decreases of the MP-SN and gonial angles, and an increase of PFH:AFH.

The inadequacy of the Y-axis of growth (SNGn) for the vertical pattern assessment in patients with sagittal discrepancies.

AIM: The aim of this cephalometric study was to evaluate the influence of the sagittal skeletal pattern on the 'Y-axis of growth' measurement in patients with different malocclusions. MATERIALS AND METHODS: Lateral head films from 59 patients (mean age 16y 7m, ranging from 11 to 25 years) were selected after a subjective analysis of 1630 cases. Sample was grouped as follows: Group 1 - class I facial pattern; group 2 - class II facial pattern; and Group 3 - class III facial pattern. Two angular measurements, SNGoGn and SNGn, were taken in order to determine skeletal vertical facial pattern. A logistic regression with errors distributed according to a binomial distribution was used to test the influence of the sagittal relationship (Class I, II, III facial patterns) on vertical diagnostic measurement congruence (SNGoGn and SNGn). RESULTS: RESULTS show that the probability of congruence between the patterns SNGn and SNGoGn was relatively high (70%) for group 1, but for groups II (46%) and III (37%) this congruence was relatively low. CONCLUSION: The use of SNGn appears to be inappropriate to determine the vertical facial skeletal pattern of patients, due to Gn point shifting throughout sagittal discrepancies. Clinical Significance: Facial pattern determined by SNGn must be considered carefully, especially when severe sagittal discrepancies are present.

Evaluation of the closest speaking space in different dental and skeletal occlusions.

STATEMENT OF PROBLEM: The closest speaking space (CSS) together with the vertical overlap of anterior teeth during the production of the /s/ sound have not been previously investigated with respect to differences in dental and skeletal orthodontic classifications. PURPOSE: The purpose of this study was to investigate the CSS in dental and skeletal occlusions and to analyze the cause and effect relationship of the CSS and the amount of the vertical overlap of anterior teeth. MATERIAL AND METHODS: Poly vinylsiloxane interocclusal registration material was placed bilaterally onto the occlusal surfaces of premolar and molar teeth of 155 native Turkish speaking adolescent and young adult dentate participants, who were then asked to pronounce the word seyis. The thinnest point between the maxillary and mandibular teeth was recorded in millimeters as the CSS. The occlusion of each participant was classified according to the Angle dental and Steiner skeletal classifications. The differences in CSS values within each classification were statistically analyzed with the Kruskal-Wallis test, and the correlation between the CSS and the vertical overlap was statistically analyzed with the Spearman Rho Correlation tests (P<.05). RESULTS: The differences in the CSS were only significant between Angle Class II division 2 and Class III groups (P=.034), while the differences in the CSS between skeletal classes were not significant. The correlation between the amount of CSS and the amount of vertical overlap was not significant. CONCLUSIONS: The results showed that regardless of dental and skeletal occlusions, average CSS values could be used to determine the occlusal vertical dimension of prosthetic restorations.

Bite force and its association with stability following Class II/1 functional appliance treatment.

The aims of this study were to investigate the value of pre-treatment maximal molar bite force as a predictive variable in determining post-treatment changes and stability following functional appliance treatment in Class II malocclusion children. Twenty-eight Class II malocclusion children having undergone functional appliance treatment were followed for at least 1 year post-treatment. Maximal molar bite force measurements, lateral cephalograms, and study casts were taken before treatment, after treatment, and after post-treatment follow-up. Relationships between pre-treatment maximal molar bite force and dental or cephalometric changes post-treatment were examined. Patients were divided into stable and unstable groups, based on dental sagittal changes (overjet and molar relationship), and differences between the two groups of patients determined. Post-treatment changes varied widely. Thirteen children showed dentoalveolar sagittal relapse, namely a shift in molars towards a Class II relationship and an increase in overjet, while 15 did not. The unstable group demonstrated a lower pre-treatment maximal molar bite force, as well as a more obtuse gonial angle, than the stable group. The gonial angle was found to be negatively correlated to maximal molar bite force and may thus be a cephalometric indicator partly reflecting the functional condition of the masticatory muscles. Children with a lower pre-treatment maximal molar bite force were more prone to dentoalveolar sagittal relapse following functional appliance treatment.

Effects of maxillary molar intrusion with zygomatic anchorage on the stomatognathic system in anterior open bite patients.

The aim of this study was to evaluate the effects of intrusion of the maxillary posterior teeth with zygomatic anchorage on the dentofacial system, on electromyographic (EMG) activity of the masticatory muscles, and on vibration of the temporomandibular joint. The study sample consisted of 19 subjects (13 females, 6 males) with a mean age of 17.7 years. Lateral cephalometric and posteroanterior (PA) radiographs, EMG, and electrovibratographic (EVG) records were obtained before (T0) and after (T1) intrusion. Paired t- and Wilcoxon signed ranks tests were used for statistical evaluation. Maxillary molar intrusion of 3.37 ± 1.21 mm was obtained with a force of 400 g in an average period of 6.84 ± 1.64 months. At T1, all measurements showed that facial growth direction, ANB angle, convexity, and overjet were decreased (P < 0.05). SNB angle, facial depth, and overbite were significantly increased (P < 0.05). Upper lip-E plane distance was increased (P < 0.05). Evaluation of the PA radiographs showed that the right and left molar reference angles were unchanged. EMG and EVG analysis showed that the stomatognathic system at T0 was maintained at T1. Intrusion of the maxillary posterior teeth with zygomatic anchorage is an effective treatment alternative for anterior open bite correction.

Evaluation of malocclusion in MPDS.

INTRODUCTION: Myofascial pain dysfunction syndrome (MPDS) is a disorder which is characterized by facial pain and limited mandibular function because of the complex nature of this disease. Malocclusion was never evaluated in MPDS patients to know its role. Electromyographic silent period durations of masseter were used for objective assessment of MPDS patients. AIM: To evaluation of role of malocclusion in MPDS patients and also to study the EMG masseteric silent period pattern in MPDS patients in different malocclusions. MATERIALS AND METHODS: Two groups, groups I and II of 75 subjects each, were included in this study. Groups I and II constituted the normal subjects and MPDS patients respectively. All these subjects in both the groups were again subdivided based on Angle's class I, II and III malocclusion. Electromyographic (EMG) silent period of masseteric muscle on both sides was measured for all the subjects in both the groups to know whether it differs according to the type of malocclusion. RESULTS: The silent period was more in group II (MPDS patients). There was no signifcant difference in the silent periods in Angle's class I, II and III malocclusion in group I, whereas in group II, there was a signifcant difference in the silent period in Angle's class II compared to Angle's class I and III. There was no signifcant difference between males and females. CONCLUSION: MPDS patients are more in Angle's class I malocclusion. Silent period is more in Angle's class II malocclusion of MPDS group. CLINICAL SIGNIFCANCE: The EMG masseter silent period duration can be advantageously utilized as an adjunct to clinical examination for diagnosis of myofascial pain dysfunction syndrome. It is enough if one side masseter muscle is measured for silent period duration.

The origin and development of malocclusions. When, where and how dental malocclusions develop.

This article describes the forces of the muscles from the stomatonathic system and how they interact in many children to change the normal forces of growth. Because of this change in muscle forces there is a change from normal teeth and bone growth positions to abnormal positions. These normal and/or abnormal changes in muscle forces are the basis for development into class one, class two and class three occlusions. This is very valuable information for the orthodontic clinician because these muscle forces are the fundamental basis for all orthodontic treatment. By knowing this an orthodontic clinician will be more able to diagnose and treat a malocclusion. This is exceptionally important for the dentist who is just starting to learn diagnosis, treatment planning, functional and fixed orthodontic treatment.

Lip pressure at rest and during function in 2 groups of patients with different occlusions.

INTRODUCTION: The influence of the forces exerted by the perioral musculature on the position of the teeth has been the object of many scientific studies. Of the forces from the soft tissues, those from the tissues in the passive resting state are believed to be more important than forces exerted on the teeth during various functions such as speech and swallowing. The aims of this study were to measure upper lip pressure at rest and during swallowing in 2 groups of patients with different occlusions and to evaluate any differences among the groups. METHODS: Fifty subjects were divided into 2 groups according to occlusal and skeletal patterns: Class I and Class II. Both groups were divided into 2 subgroups according to age: young patients (9-17 years) and adult patients (18-35 years). A force-sensing resistor device (Datalog, Flexiforce low type, Biometrics Ltd, Gwent, United Kingdom) with a transducer thickness of less of 1 mm was used for the measurements. The sensor was positioned on the midline between the maxillary incisors with a thin layer of soft wax. Labial pressure measurements were made with the lips at rest and during swallowing saliva. RESULTS: The average resting lip pressure was 24.59 ± 2.55 g/cm(2); during swallowing, the mean pressure was 24.87 ± 2.45 g/cm(2). No significant difference was found between lip pressure at rest and at function or between the two groups with different occlusions and skeletal patterns. There was a significant correlation between lip pressure and age. CONCLUSIONS: In healthy patients, (1) upper lip pressure does not change at rest and during swallowing, (2) upper lip pressure was similar in the 2 groups (Class I, 24.33 g/cm(2); Class II, 24.61 g/cm(2)), and (3) lip pressure was higher in adults than in young subjects. Further studies are needed to measure the pressure of the lower lip and to evaluate whether there are differences in labial pressure between subjects with labial competence and incompetence.

Mixed longitudinal evaluation of masticatory performance in children 6 to 17 years of age.

INTRODUCTION: The purposes of this study were to determine (1) how masticatory performance changes with age, (2) whether masticatory performance differs between the sexes, and (3) whether patterns of masticatory performance differ among subjects with various types of malocclusion. METHODS: A total of 450 children and adolescents (244 boys, 206 girls) were assigned to 4 age cohorts (ages 6, 9, 12, and 15 years) and followed for 3 consecutive years. The subjects were selected based on having about equal numbers of boys and girls, and about equal numbers of subjects with normal occlusion and Class I and Class II malocclusions. Masticatory performance was assessed by using the artificial food CutterSil (Heraeus Kulze, South Bend, Ind). The peer assessment rating index was used to quantify the severity of the malocclusions. RESULTS: Median particle size (MPS) decreased significantly from 6 to 17 years of age. There were no statistically significant differences in MPS between the 3 occlusal groups, but there were significant sex differences, with girls having smaller MPS than boys. Multilevel analysis showed greater decreases in MPS between 6 and 9 years, and after 12 years of age, than between 9 and 12 years of age. There were no significant correlations between MPS and the weighted peer assessment rating index. MPS showed significant intercorrelations between measures of MPS obtained at years 1, 2, and 3, with correlations tending to be highest for the oldest age cohort. CONCLUSIONS: Masticatory performance improves with age, and the changes appear to be influenced by the loss of the deciduous teeth during the late mixed dentition phase of dental development. Although there are limited sex differences in masticatory performance among subjects 6 to 17 years of age, mild forms of Class I and Class II malocclusions have little or no effect on masticatory performance.

Tongue movements in patients with skeletal Class III malocclusions evaluated with real-time balanced turbo field echo cine magnetic resonance imaging.

INTRODUCTION: The aim of this study was to evaluate the position and movements of the tongue in patients with skeletal Class III malocclusion. METHODS: Sixty-six patients (31 male, 35 female) with Class III malocclusion were divided into 3 groups according to cephalometric analysis. The first group comprised 23 patients (13 male, 10 female) with mandibular prognathism, the second group comprised 21 patients (9 male, 12 female) with maxillary retrognathism, and the third group comprised 22 patients (9 male, 13 female) with both maxillary retrognathism and mandibular prognathism. Twenty-two skeletal Class I patients (10 male, 12 female) were also included as the control group. RESULTS: Dentofacial morphology affects the position and the movements of the tongue during deglutition. Contact of the anterior portion of the tongue with the rugae area of the hard palate decreased in the Class III malocclusion groups. The posterior portion of the dorsal tongue was positioned more inferiorly, and the root of the tongue was positioned more inferiorly and anteriorly in patients with Class III malocclusion than in the control group. The tip of the tongue was also in a more anterior position in the Class III groups. When the deglutition stages were evaluated, we observed that the manner of bolus transfer was different in patients with skeletal Class III malocclusion than in those with skeletal Class I malocclusion. CONCLUSIONS: Tongue posture is affected by dentofacial structures, and adaptive changes occur in the tip, dorsum, and root of the tongue. Deglutitive tongue movements in patients with skeletal Class III malocclusion are also different from those with skeletal Class I malocclusion.

Tongue movements in patients with skeletal Class II malocclusion evaluated with real-time balanced turbo field echo cine magnetic resonance imaging.

INTRODUCTION: The aim of this study was to evaluate the deglutitive tongue movements in patients with skeletal Class II malocclusion. METHODS: Fifty-nine patients (26 male, 33 female) with skeletal Class II relationship were divided into 3 groups according to cephalometric analysis. Group 1 (n = 19) had mandibular retrognathism, group 2 (n = 20) had maxillary prognathism, and group 3 (n = 20) had both mandibular retrognathism and maxillary prognathism. Twenty-two skeletal Class I patients (10 male, 12 female) were also included as the controls. RESULTS: In the mandibular retrusion group, the posterior portion of the dorsal tongue moved downward at stage 2 and upward at stage 3; the root of the dorsal tongue was in an inferior and anterior position at stage 2. In patients with both mandibular retrognathism and maxillary prognathism, the middle portion of the dorsal tongue was positioned superiorly at stage 3 relative to stage 1; the tongue tip was retruded at stage 3 relative to stages 1 and 2. In the control group, the middle portion of dorsal tongue was positioned superiorly at stage 3 relative to stages 1 and 2; the posterior portion of the tongue moved upward at stage 2 and downward at stage 3, and tongue-tip retrusion was observed at stage 2 relative to stage 1. Contact of the anterior portion of the tongue with the rugae area of the hard palate decreased in the Class II malocclusion groups relative to the control group. The middle portion of the dorsal tongue was positioned more superiorly in patients with Class II malocclusion during all stages of deglutition. The root of the tongue was more inferior and anterior, and the tongue tip was retruded in patients with Class II malocclusion compared with the control group. The posterior portion of the dorsal tongue was more inferiorly positioned in patients with mandibular retrusion than in the other Class II groups or the controls. In the third stage of deglutition, this portion of the tongue had a superior position in groups 2 and 3 relative to the control group. CONCLUSIONS: Dentofacial morphology affects the position and movements of the tongue during deglutition, and adaptive changes occur in the tip, dorsum, and root of the tongue. Deglutitive tongue movements in patients with a skeletal Class II relationship are different from those with a skeletal Class I relationship.

A mixed longitudinal anthropometric study of craniofacial growth of Colombian mestizos 6-17 years of age.

The purpose of this study was to evaluate the craniofacial growth of Colombian mestizos. Four age cohorts, including a total of 458 children and adolescents (262 males and 216 females), were included in this mixed-longitudinal study. The cohorts were first measured at ages 6, 9, 12, and 15 and every year thereafter for 3 years. Eight anthropometric measurements were taken, including three cranial (head perimeter, head width, and head length), two craniofacial (maxillary and mandibular length), and three facial (face height, bizygomatic width, and bigonial width). Multilevel analyses showed that all dimensions increased between 6 and 17 years of age. The cranium grew less than the craniofacial, which in turn grew less than the facial dimensions. In addition, vertical dimensions showed more growth than antero-posterior dimensions, which in turn grew more than transverse dimensions. None of the measurement showed statistically significant growth differences between subjects with normal occlusion and Class I or Class II malocclusions. Males were generally larger than females and showed greater growth rates. Except for facial width, whose yearly velocities decreased regularly with age, an adolescent growth spurt was evident for most of the male measurements. Yearly velocities for females followed a simpler decelerating pattern. The results provide reference data for Colombian mestizos, for whom normative data of other ethnic groups are not applicable. While occlusion had little or no effect, there were gender differences, as well as important growth differences between cranial and facial measurements.

[Differences in maxillary growth vector of skeletal class I with various vertical growth types before and after growth spurts].

OBJECTIVE: To identify the differences in maxillary growth vector with different vertical skeletal patterns of skeletal class I before and after growth spurts. METHODS: One hundred and ninety four cases with different vertical skeletal patterns of skeletal class I were selected and categorized into six groups according to their vertical skeletal patterns and cervical vertebral stages: cervical vertebral maturation stage (CVMS)1,2-horizontal pattern (n=30); CVMS1,2-average pattern (n=32); CVMS1, 2-vertical pattern (n=33); CVMS5, 6-horizontal pattern (n=34); CVMS5, 6-average pattern (n=29); and CVMS5, 6-vertical pattern (n=36). Lateral cephalograms were taken on all of the cases. The angle SN-C axis (theta) and angel PP-C axis (alpha) were measured. RESULTS: (1) The skeletal class I with a vertical growth pattern had larger angle SN-C axis than those with a horizontal or average growth pattern before growth spurts (P(average-vertical) < 0.05, P(horizontal-vertical) < 0.001). (2) The skeletal class I with a vertical growth pattern had the largest angle SN-C axis after growth spurts, followed by those with an average growth pattern. Those with a horizontal growth pattern had the smallest angle SN-C axis. The differences were statistically significant (P(horizontal-average) < 0.05, P(horizontal-vertical) < 0.001, P(average-vertical) < 0.001). (3) The skeletal class I with the same vertical growth pattern had slightly larger angle SN-C axis after growth spurts than before growth spurts, but without statistical significance. (4) The skeletal class I had relatively stable angle PP-C axis and no significant differences were found before and after growth spurts or among those with various vertical skeletal facial types. CONCLUSION: The magnitude of angle SN-C axis is closely associated with vertical growth patterns and is weakly influenced by maxillofacial growth and development.

[Study of perioral force exerted on the teeth in preadolescent children with anterior crossbite].

30 preadolescent children with anterior crossbite were selected for the present study. Among them 15 were male and 15 children were female. Their age ranged from 8 to 12 years. The mean age was 10. 8 years. Their perioral forces were measured in the areas as following: the labial and lingual sides of mandibular and maxillar central incisors, the first premolars and molars of both sides. After analysis of the results, some conclusions were drawn as the following, the distribution of the perioral force of bilateral arch was symmetric, and there were no significant differences between genders. The values of the perioral force in the premolar and molar area were the largest. When the children were in their nature head position, the perioral force values of labial side were larger than those on the lingual side. On the lingual side of mandibular incisors negative values were found. The perioral force correlated with malocclusion. The position of the teeth decides the value of the perioral force. It has been well concluded that the forces exerted on the teeth were not the only factor that influenced teeth position. There are also other factors influencing the teeth poison. This needs further study.

Relationship between the angle of the coronoid process of the mandible and the electromyographic activity of the temporal muscle in skeletal Class I and III individuals.

The aim of the present study was to verify the relationship between the angle of the coronoid process of the mandible in the latero-lateral direction and electromyographic activity of the anterior part of the temporal muscle in skeletal Class I and III individuals. Forty-five volunteers were assessed subdivided into two groups, according to angle ANB, in Class I and III. Two radiographic examinations were performed, one lateral cephalogram to measure angle ANB and one frontal cephalogram to measure the angle of the coronoid process. The electromyographic examination of the volunteers' temporal muscles was performed. Statistical analysis of the data showed that the relationship between the angle of the coronoid process and the skeletal class was negative for both classes analysed. The relationship between electromyographic activity of the temporal muscle and angle of the coronoid process was negative for Class I individuals. In the Class III group, smaller angles of the coronoid process were related to higher values of electromyographic activity of the temporal muscle. There was no statistically significant difference between the electromyographic activity of the temporal muscle in skeletal Class I and III individuals. Based on the results obtained, it was concluded that there was no influence of the skeletal classes analysed on the angle of the coronoid; the angle of the coronoid process may be influenced by the electromyographic activity of the temporal muscle in the Class III group; the electromyographic activity of the temporal muscle is not influenced by the skeletal class in Class III individuals.

Duration of the pubertal peak in skeletal Class I and Class III subjects.

OBJECTIVE: To estimate and compare the duration of the pubertal growth peak in Class I and Class III subjects. MATERIALS AND METHODS: The data examined consisted of pretreatment lateral cephalometric records of 218 skeletal Class I or Class III subjects (93 female and 125 male subjects) of white ancestry. The duration of the pubertal peak was calculated from the average chronological age intervals between stages CS3 and CS4 of the cervical vertebral maturation in Class I vs Class III groups (t-test). RESULTS: In skeletal Class I subjects, the pubertal peak had a mean duration of 11 months, whereas in Class III subjects it lasted 16 months. The average difference (5 months) was statistically significant (P < .001). CONCLUSIONS: The growth interval corresponding to the pubertal growth spurt (CS3-CS4) was longer in Class III subjects than in subjects with normal skeletal relationships; the larger increases in mandibular length during the pubertal peak reported in the literature for Class III subjects may be related to the longer duration of the pubertal peak.