Dental caries prevalence in children during temporary protective care according to type of abuse.

BACKGROUND: This study investigated the correlation between the prevalence of dental caries and the presence and type of abuse. METHODS: Participants were 534 children admitted for care at two child guidance centers (CGCs) in Niigata, Japan. Data pertaining to abuse, including the reason for temporary protective care and the type of abuse, and the oral examination results of the children, were collected. These results were then compared with those of a national survey and analyzed in relation to the presence and type of abuse. RESULTS: The odds ratio for decayed teeth was 4.1, indicating a higher risk in children admitted to the CGCs. However, no significant association was found between the presence of decayed, filled, or caries-experienced teeth and the presence of abuse. A significant positive association was observed between dental caries and one type of abuse, indicating a greater prevalence of dental caries in cases of neglect. The findings of this study suggest that the type of abuse, rather than its presence, is associated with dental caries. CONCLUSIONS: Our findings suggest that proactive support should be provided to children in problematic nurturing environments, regardless of whether they have been subjected to abuse.

Pilot study on the relationship between oral function or subjective symptoms and appetite.

OBJECTIVE: This pilot study evaluated the relationships between appetite and oral function, and between appetite and the subjective symptoms of decreased oral function. METHODS: Seventy-one adult dental clinic patients (22 males, 66.0 ± 14.0 years) participated in this study. A Council on Nutrition Appetite Questionnaire score of ≤28 indicated anorexia, and the Mini Nutritional Assessment Short-form, body mass index and skeletal muscle mass index were used to define subject characteristics. Seven oral function tests and seven subjective symptoms related to oral function were evaluated. The relationship between subject characteristics, oral function tests, subjective symptoms and anorexia was analysed using the chi-square test and univariate and multivariate logistic regression. RESULT: There were significant differences between the normal appetite group and the anorexia group for the 10-item Eating Assessment Tool (EAT-10) survey and the question 'Food remains in the oral cavity after eating' (p < .05). Univariate logistic regression found significant differences in the items of masticatory function, the EAT-10 survey and the question 'Food remains in the oral cavity after eating'. Multivariate logistic regression revealed significant differences in masticatory function (AOR 4.35; 95% CI: 1.03-18.35; p = .045) and EAT-10 (AOR 6.27; 95% CI: 1.40-24.02; p = .016). CONCLUSION: This pilot study investigated the influence of factors related to oral function on appetite. Relationships were found among poor masticatory function, poor swallowing function and anorexia.

RNA analysis based on a small number of manually isolated fixed cells (RNA-snMIFxC) to profile stem cells from human deciduous tooth-derived dental pulp cells.

BACKGROUND: Expression of stemness factors, such as octamer-binding transcription factor 3/4 (OCT3/4), sex determining region Y-box 2 (SOX2), and alkaline phosphatase (ALP) in human deciduous tooth-derived dental pulp cells (HDDPCs) can be assessed through fixation and subsequent immuno- or cytochemical staining. Fluorescence-activated cell sorting (FACS), a powerful system to collect cells of interest, is limited by the instrument cost and difficulty in handling. Magnetic-activated cell sorting is inexpensive compared to FACS, but is confined to cells with surface expression of the target molecule. In this study, a simple and inexpensive method was developed for the molecular analysis of immuno- or cytochemically stained cells with intracellular expression of a target molecule, through isolation of a few cells under a dissecting microscope using a mouthpiece-controlled micropipette. RESULTS: Two or more colored cells (~ 10), after staining with a chromogen such a 3,3'-diaminobenzidine, were successfully segregated from unstained cells. Expression of glyceraldehyde 3-phosphate dehydrogenase, a housekeeping gene, was discernible in all samples, while the expression of stemness genes (such as OCT3/4, SOX2, and ALP) was confined to positively stained cells. CONCLUSION: These findings indicate the fidelity of these approaches in profiling cells exhibiting cytoplasmic or nuclear localization of stemness-specific gene products at a small-scale.

Prevalence of an incompetent lip seal during growth periods throughout Japan: a large-scale, survey-based, cross-sectional study.

BACKGROUND: Systemic and local factors may lead to disruption of craniofacial growth and development, causing an imbalance between the orofacial skeleton, muscle and soft tissue, dental occlusion, and the dental arch during growth periods. We aimed to reveal whether the prevalence of incompetent lip seal (ILS) varies with age and region, as well as to clarify the factors related to an ILS, in a national, large-scale epidemiological study. METHODS: We surveyed 3399 children, from 3 to 12 years of age, visiting 66 pediatric dental clinics throughout Japan. For this survey, we employed a questionnaire consisting of 44 questions regarding daily health conditions and lifestyle habits. We evaluated the differences in ILS prevalence by age and region (using a Cochran-Armitage test for trend and a Kruskal-Wallis test), and the relationship between ILS and factors investigated in the questionnaire (using Spearman's rank correlation coefficient). RESULTS: We observed that 30.7% of Japanese children exhibited an ILS and that the ILS rate increased with age (p < 0.001). There were no regional differences in the rate of ILS in Japanese children (p = 0.506). We revealed that 12 of 44 survey items exhibited a statistically significant correlation with ILS (p < 0.001), using Spearman's rank correlation coefficient. These items involved orofacial morphology, mouth breathing, and possibly, allergic rhinitis. CONCLUSION: The rate of ILS seems to increase with age in children, throughout Japan. Therefore, this disorder may not self-correct during the growth periods in these children. Guidelines are required for pediatric dentists to recognize ILS among children aged 3-12 years.

Increased Expression of Cell Surface SSEA-1 is Closely Associated with Naïve-Like Conversion from Human Deciduous Teeth Dental Pulp Cells-Derived iPS Cells.

Stage-specific embryonic antigen 1 (SSEA-1) is an antigenic epitope (also called CD15 antigen) defined as a Lewis X carbohydrate structure and known to be expressed in murine embryonal carcinoma cells, mouse embryonic stem cells (ESCs), and murine and human germ cells, but not human ESCs/induced pluripotent stem cells (iPSCs). It is produced by α1,3-fucosyltransferase IX gene (FUT9), and F9 ECCs having a disrupted FUT9 locus by gene targeting are reported to exhibit loss of SSEA-1 expression on their cell surface. Mouse ESCs are pluripotent cells and therefore known as "naïve stem cells (NSCs)." In contrast, human ESCs/iPSCs are thought to be epiblast stem cells (EpiSCs) that are slightly more differentiated than NSCs. Recently, it has been demonstrated that treatment of EpiSCs with several reprograming-related drugs can convert EpiSCs to cells similar to NSCs, which led us to speculate that SSEA-1 may have been expressed in these NSC-like EpiSCs. Immunocytochemical staining of these cells with anti-SSEA-1 revealed increased expression of this epitope. RT-PCR analysis also confirmed increased expression of FUT9 transcripts as well as other stemness-related transcripts such as REX-1 (ZFP42). These results suggest that SSEA-1 can be an excellent marker for human NSCs.

piggyBac Transposon-Based Immortalization of Human Deciduous Tooth Dental Pulp Cells with Multipotency and Non-Tumorigenic Potential.

We aimed to immortalize primarily isolated human deciduous tooth-derived dental pulp cells (HDDPCs) by transfection with piggyBac (PB)-based transposon vectors carrying E7 from human papilloma virus 16 or complementary DNA (cDNA) encoding human telomerase reverse transcriptase (hTERT). HDDPCs were co-transfected with pTrans (conferring PB transposase expression) + pT-pac (conferring puromycin acetyltransferase expression) + pT-tdTomato (conferring tdTomato cDNA expression) and pT-E7 (conferring E7 expression) or pTrans + pT-pac + pT-EGFP (conferring enhanced green fluorescent protein cDNA expression) + pT-hTERT (conferring hTERT expression). After six days, these cells were selected in medium containing 5 µg/mL puromycin for one day, and then cultured in normal medium allowing cell survival. All resultant colonies were harvested and propagated as a pool. Stemness and tumorigenic properties of the established cell lines ("MT_E7" for E7 and "MT_hTERT" for hTERT) with untransfected parental cells (MT) were examined. Both lines exhibited proliferation similar to that of MT, with alkaline phosphatase activity and stemness-specific factor expression. They displayed differentiation potential into multi-lineage cells with no tumorigenic property. Overall, we successfully obtained HDDPC-derived immortalized cell lines using a PB-based transfection system. The resultant and parental cells were indistinguishable. Thus, E7 and hTERT could immortalize HDDPCs without causing cancer-associated changes or altering phenotypic properties.

Quantitative evaluation of toothbrush and arm-joint motion during tooth brushing.

OBJECTIVES: It is very difficult for dental professionals to objectively assess tooth brushing skill of patients, because an obvious index to assess the brushing motion of patients has not been established. The purpose of this study was to quantitatively evaluate toothbrush and arm-joint motion during tooth brushing. MATERIALS AND METHODS: Tooth brushing motion, performed by dental hygienists for 15 s, was captured using a motion-capture system that continuously calculates the three-dimensional coordinates of object's motion relative to the floor. The dental hygienists performed the tooth brushing on the buccal and palatal sides of their right and left upper molars. The frequencies and power spectra of toothbrush motion and joint angles of the shoulder, elbow, and wrist were calculated and analyzed statistically. RESULTS: The frequency of toothbrush motion was higher on the left side (both buccal and palatal areas) than on the right side. There were no significant differences among joint angle frequencies within each brushing area. The inter- and intra-individual variations of the power spectrum of the elbow flexion angle when brushing were smaller than for any of the other angles. CONCLUSIONS: This study quantitatively confirmed that dental hygienists have individual distinctive rhythms during tooth brushing. All arm joints moved synchronously during brushing, and tooth brushing motion was controlled by coordinated movement of the joints. The elbow generated an individual's frequency through a stabilizing movement. CLINICAL RELEVANCE: The shoulder and wrist control the hand motion, and the elbow generates the cyclic rhythm during tooth brushing.

Analysis of tooth brushing cycles.

OBJECTIVE: The aim of this study was to demonstrate the effectiveness of an analysis of tooth brushing cycles using a system that measures tooth brushing motion and brushing force with an accelerometer and strain tension gage attached to a toothbrush. BACKGROUND: Mechanical plaque removal with a manual toothbrush remains the primary method of maintaining good oral hygiene for the majority of the population. Because toothbrush motion has not been fully understood, it should be clarified by analysis of tooth brushing cycles. METHODS: Twenty healthy female dental hygienists participated in this study. Their tooth brushing motions were measured and analyzed using an American Dental Association-approved manual toothbrush to which a three-dimensional (3-D) accelerometer and strain tension gage were attached. 3-D motion and brushing force on the labial surface of the mandibular right central incisor and the lingual surface of the mandibular left first molar were measured, analyzed, and compared. Multilevel linear model analysis was applied to estimate variables and compare motion and forces related to the two tooth surfaces. RESULTS: The analysis of tooth brushing cycles was feasible, and significant differences were detected for durations and 3-D ranges of toothbrush motion as well as brushing force between the two tooth surfaces. CONCLUSION: The analysis used in this study demonstrated an ability to detect characteristics of tooth brushing motion, showing tooth brushing motion to change depending on the brushed location. These results also suggest that more detailed instructions might be required according to patient's oral condition.

Features of lateral cephalograms associated with difficult laryngoscopy in Japanese children undergoing oral and maxillofacial surgery.

BACKGROUND: Difficult laryngoscopy and tracheal intubation are occasionally encountered in children with congenital anomalies or micrognathia. However, no study has elucidated anatomical etiology in relation to craniofacial development. METHODS: Two hundred ten patients aged 8 months-18 years were analyzed. We analyzed the lateral cephalograms of: (i) eight patients in whom laryngoscopy was anticipated as difficult before anesthesia and who were unable to be intubated by direct laryngoscopy and needed fiberoptic bronchoscopy (group A); (ii) 11 patients in whom laryngoscopy was anticipated as difficult before anesthesia but who were able to be intubated by direct laryngoscopy (group B); and (iii) 191 patients in whom laryngoscopy was anticipated as easy before anesthesia and was actually found to be easy (group C). Eight cephalometric parameters were measured and age-parameter relationships were plotted. Logistic regression analysis was performed to characterize group A children for each of the cephalometric variables. RESULTS: Apparently insufficient growth of the mandible was observed in the group A children. Furthermore, the group A children of aged <4 years had undeveloped maxilla, longer mandibular plane-hyoid distances (≥1.3 cm), and deeper depth of the oropharynx; those of aged ≥4 years showed increased inclination of the mandible (sella-nasion plane to mandibular plane angle of ≥46.5°). CONCLUSIONS: Difficult laryngoscopy and tracheal intubation are expected in children aged <4 years with lower-positioned hyoid bone caused by caudal larynx as well as undeveloped maxilla and mandible, and in those aged ≥4 years with increased inclination of the mandible as well as undeveloped mandible.

Preoperative autologous blood donation and acute normovolemic hemodilution affect intraoperative blood loss during sagittal split ramus osteotomy.

INTRODUCTION: This study aimed to determine the effects of acute normovolemic hemodilution (ANH) using low-molecular-weight hydroxyethyl starch (LMW-HES) on intraoperative blood loss in patients who had received preoperative autologous blood donation (PABD) and had undergone sagittal split ramus osteotomy (SSRO). METHODS: Patients who had undergone SSRO were analyzed. All 250 patients received PABD of 400-800 mL until 2 weeks before surgery. ANH was performed by withdrawing whole blood, which was replaced by the same volume of LMW-HES. ANH was performed in 197 cases for 200 mL replacement (ANH-200) and in 5 cases for 400 mL replacement (ANH-400); it was not performed in 48 cases (ANH-0). RESULTS: Blood loss in ANH-200 was greater than that in ANH-0, despite no differences in hemoglobin concentrations at pre- and post-PABD, prothrombin time, activated partial thromboplastin time, fibrinogen and platelet counts between the groups before surgery. Blood loss increased as the total withdrawn blood (sum of PABD and ANH) increased. CONCLUSION: Increased intraoperative blood loss was associated with total withdrawn blood before the operation as well as ANH.

Comparison of normal permanent and primary dentition sagittal tooth-crown inclinations of Japanese females.

The purpose of this study was to clarify the characteristics of permanent and primary tooth-crown inclinations. Landmark points from cephalograms and dental casts of two groups; 23 women (mean 20.3 +/- 3.3 years) and 11 girls (mean 5.2 +/- 0.1 years) were digitized, and the coordinates were integrated and transformed to a standardized plane. The 3-dimensional crown inclinations were projected on the sagittal plane, and the angles between the tooth vectors and the FH plane were calculated. An independent-group t-test was used to test for group differences of each tooth inclination, and correlation coefficients were generated for the inclination angles among the permanent and primary teeth. Most maxillary tooth-crown inclinations showed significant age-related differences, while only the second premolar and primary second molar differed significantly in the mandible. The maxillary molars were parallel to the corresponding mandibular molars and correlated with each other, but the primary molars were not. Significant correlations were found between inclinations of most permanent teeth, but not the primary teeth. Maxillary tooth-crown inclinations change during growth, but tooth-crown inclinations of the mandibular teeth do not.

Lip-closing strength in children is enhanced by lip and facial muscle training.

OBJECTIVES: Weakening of lip-closing strength (LCS) associated with an incompetent lip seal (ILS) may affect the oral balance between the lip and tongue pressures. The purpose of this study was to evaluate the effects of lip-closing training in children with lower LCS and/or abnormal habits across different age groups and to compare its effects on increasing LCS in children with malocclusion and/or oral habits. MATERIAL AND METHODS: Lip-closing training was performed by 154 Japanese children aged 3-12 years using a specialized training device at home for 3 months. Children with oral habits and/or exhibiting less than standard LCS were included. LCS was measured using a digital strain force gauge at a dental clinic at the beginning (T0) and after each month (after 3 months: T3). RESULTS: Children had higher LCS responses after lip-closing training. The first month of lip-closing training was more effective than the subsequent months. With lip-closing training, the LCS increased from an average of 6.2 N (T0) to 11.4 N (T3) in Group I, 7.9 N (T0) to 12.8 N (T3) in Group II, and 6.8 N to 11.4 N in Group III. Anterior cross bite, including reverse bite, open bite, and tongue thrusting, significantly reduced training effects. CONCLUSION: Our findings showed that lower LCS in children with ILS resulted in greater responses to lip-closing training in a short period, but oral dysfunction, such as abnormal habits, inhibited the positive effects of training. Our results suggest that less detrimental effects of malocclusion and abnormal oral habits lip-closing training enhances LCS in younger children.

The Role of Genetically Modified Human Feeder Cells in Maintaining the Integrity of Primary Cultured Human Deciduous Dental Pulp Cells.

Tissue-specific stem cells exist in tissues and organs, such as skin and bone marrow. However, their pluripotency is limited compared to embryonic stem cells. Culturing primary cells on plastic tissue culture dishes can result in the loss of multipotency, because of the inability of tissue-specific stem cells to survive in feeder-less dishes. Recent findings suggest that culturing primary cells in medium containing feeder cells, particularly genetically modified feeder cells expressing growth factors, may be beneficial for their survival and proliferation. Therefore, the aim of this study was to elucidate the role of genetically modified human feeder cells expressing growth factors in maintaining the integrity of primary cultured human deciduous dental pulp cells. Feeder cells expressing leukemia inhibitory factor, bone morphogenetic protein 4, and basic fibroblast growth factor were successfully engineered, as evidenced by PCR. Co-culturing with mitomycin-C-treated feeder cells enhanced the proliferation of newly isolated human deciduous dental pulp cells, promoted their differentiation into adipocytes and neurons, and maintained their stemness properties. Our findings suggest that genetically modified human feeder cells may be used to maintain the integrity of primary cultured human deciduous dental pulp cells.

Induced Tissue-Specific Stem Cells (iTSCs): Their Generation and Possible Use in Regenerative Medicine.

Induced tissue-specific stem cells (iTSCs) are partially reprogrammed cells which have an intermediate state, such as progenitors or stem cells. They originate from the de-differentiation of differentiated somatic cells into pluripotent stem cells, such as induced pluripotent stem cells (iPSCs) and embryonic stem cells (ESCs), or from the differentiation of undifferentiated cells. They show a limited capacity to differentiate and a morphology similar to that of somatic cell stem cells present in tissues, but distinct from that of iPSCs and ESCs. iTSCs can be generally obtained 7 to 10 days after reprogramming of somatic cells with Yamanaka's factors, and their fibroblast-like morphology remains unaltered. iTSCs can also be obtained directly from iPSCs cultured under conditions allowing cellular differentiation. In this case, to effectively induce iTSCs, additional treatment is required, as exemplified by the conversion of iPSCs into naïve iPSCs. iTSCs can proliferate continuously in vitro, but when transplanted into immunocompromised mice, they fail to generate solid tumors (teratomas), implying loss of tumorigenic potential. The low tendency of iTSCs to elicit tumors is beneficial, especially considering applications for regenerative medicine in humans. Several iTSC types have been identified, including iTS-L, iTS-P, and iTS-D, obtained by reprogramming hepatocytes, pancreatic cells, and deciduous tooth-derived dental pulp cells, respectively. This review provides a brief overview of iPSCs and discusses recent advances in the establishment of iTSCs and their possible applications in regenerative medicine.

Tissue-Nonspecific Alkaline Phosphatase, a Possible Mediator of Cell Maturation: Towards a New Paradigm.

Alkaline phosphatase (ALP) is a ubiquitous membrane-bound glycoprotein capable of providing inorganic phosphate by catalyzing the hydrolysis of organic phosphate esters, or removing inorganic pyrophosphate that inhibits calcification. In humans, four forms of ALP cDNA have been cloned, among which tissue-nonspecific ALP (TNSALP) (TNSALP) is widely distributed in the liver, bone, and kidney, making it an important marker in clinical and basic research. Interestingly, TNSALP is highly expressed in juvenile cells, such as pluripotent stem cells (i.e., embryonic stem cells and induced pluripotent stem cells (iPSCs)) and somatic stem cells (i.e., neuronal stem cells and bone marrow mesenchymal stem cells). Hypophosphatasia is a genetic disorder causing defects in bone and tooth development as well as neurogenesis. Mutations in the gene coding for TNSALP are thought to be responsible for the abnormalities, suggesting the essential role of TNSALP in these events. Moreover, a reverse-genetics-based study using mice revealed that TNSALP is important in bone and tooth development as well as neurogenesis. However, little is known about the role of TNSALP in the maintenance and differentiation of juvenile cells. Recently, it was reported that cells enriched with TNSALP are more easily reprogrammed into iPSCs than those with less TNSALP. Furthermore, in bone marrow stem cells, ALP could function as a "signal regulator" deciding the fate of these cells. In this review, we summarize the properties of ALP and the background of ALP gene analysis and its manipulation, with a special focus on the potential role of TNSALP in the generation (and possibly maintenance) of juvenile cells.

Mandibular open-close motion in children with anterior crossbite occlusion.

Anterior crossbite (ACB) malocclusions are frequent; however, its characteristic functional features have not been fully described. The purpose of this study was to determine the characteristics of habitual mandibular open-close motion in children with ACB of their primary dentition. Two groups of children were selected for study; 17 with ACB (eight boys and nine girls; four years one month to seven years one month) and 19 with normal occlusion (eight boys and 11 girls; four years six months to six years seven months). The motion was recorded using an optoelectronic analysis system with six degrees-of-freedom. Mandibular incisor and condylar motion were analyzed by measuring their three-dimensional ranges and trajectories. Also estimated incisor and condylar pathways of the two groups were compared. Patients with ACB opened wider with more anterior-posterior condylar translation and more mandibular rotation. Although between-subject (inter-individual) variance of all variables in children with ACB was larger, they had less within-subject variance at the condyles. These results indicate that open-close mandibular motion in children with ACB is completely different from that of children with normal occlusion. The different motions might be related to morphological differences between the two groups.

Jaw motion during gum-chewing in children with primary dentition.

This study was undertaken to characterize jaw motion during mastication in children with primary dentition and to compare jaw motion with that in adults. The means and the variances of the traditional parameters for the chewing cycle, i.e., duration, excursive ranges and 3-D distances of travel at the lower incisor, molars and condyles were analyzed and compared in 23 children and 25 female adults. The duration of opening in children was significantly shorter than that of adults. Significant differences between children and adults were observed in lateral and vertical excursion of the incisor, lateral excursion at the molars, and vertical excursion at the condyles. Many of these measurements had larger between-subject and between-cycle variances in children than adults, suggesting that chewing motion in children has not yet matured. The results of this study indicate that chewing motion in children is different from that of adults.

A reproducibility method to test lip-closing strength in preschool children.

This cross-sectional study tested the reproducibility of a simple button-pulling system for measuring lip-closing strength in normal preschool children and compared their strength to that of normal adults. The sample consisted of 348 preschool children and 123 adults. Lip-closing strength was measured by inserting a button, fastened to a piece of string, into the vestibule between the incisors and lips with minimal mouth opening. The string was attached to a digital tension gauge and was pulled parallel to the floor. Maximum tension, with three repetitions, was recorded at the instant that the button was pulled out of the mouth. Multilevel statistical models were used to evaluate any differences in contractive muscle strength between age groups and between the genders. The strength in children increased significantly from three years to five years (p<0.01). Gender-related differences were found in adults but not in preschool children. Inter-individual variation at each age was larger than intra-individual variation. Measurement of lip-closing strength by button pulling is highly reproducible in children and has potential clinical and research applications.

Influence of food adhesivity and quantity in lip closing pressure.

Lip closing is an important motor act in food acquisition. Appropriate food capture in anticipatory and early oral stages of feeding is essential for mastication and swallowing. The aim of this study was to investigate the effect of food type and quantity on lip closing pressure during food capture with a spoon, and to identify normal lip function during food acquisition in healthy young adults. Twenty young healthy males (age range: 22-30 years) participated in this study. They were asked to eat the test food freely with a spoon. Test foods were yogurt and cream cheese, which were given in quantities of 3, 5 and 10 g in weight; 3 ml water was included as a reference. A strain gauge transducer was embedded in the spoon in advance, and lip closing pressures during food capture were measured and recorded. The Vicon motion analysis system was used to collect three-dimensional kinematic data of spoon operation. Positive pressure with lip closing during capture of adhesive food, such as cream cheese, significantly increased (P < 0.001). Moreover, positive pressure significantly decreased when food quantity increased (P < 0.01), irrespective of food type. Negative pressure that preceded positive pressure appeared more frequently during cream cheese intake and increased when food quantity on the spoon increased (P < 0.001). These findings indicated that participants sucked or squeezed the spoon further during capture of adhesive food. Maximum mouth opening occurred predominantly during the spoon insertion period, while mouth closing occurred predominantly during the spoon withdrawal period. After mouth closing, all subsequent lip pressure events appeared in the withdrawal period. Our results may be useful for comprehending normal lip function during food acquisition in healthy young adults. They may also aid in the diagnosis and management of abnormal lip function in oral hypofunction and dysfunction, which can be examined in future studies.

A cross-sectional study of developing resting masseter activity in different angle classifications in adolescence.

The purpose of this study was to determine whether the development of masseter muscle activity at mandibular rest position is characteristic for different angle classifications. The sample consisted of 64 boys and 108 girls, aged ten to 18. Electromyographic (EMG) activity from the right and left masseter muscles was recorded using an EMG scanner. First or second order polynomials were used to separately model the age-related changes in resting muscle activity of each gender and Angle's classification. The EMG activity of Class I boys and girls were expressed in positive second order polynomials. The EMG activities of Class II and Class III subjects were expressed in first order polynomials, and the EMG levels in Class III subjects were lower than in Class II subjects. These results indicated that development of resting activity levels might distinguish and characterize the anteroposterior mandibular position relative to craniofacial region.