Abstract
Objectives: To examine the activity of jaw muscles at rest and during maximal voluntary clenching (MVC) in children with unilateral posterior crossbite (UPXB) and functional lateral shift in the early mixed dentition and to evaluate sex differences. Material and Methods: The sample included 30 children (15 males, 15 females) aged 6 to 10 years old, with UPXB and functional mandibular lateral shift (≥1.5 mm) in the early mixed dentition. sEMG activity coming from the muscle areas (anterior temporalis [AT], posterior temporalis [PT], masseter [MA] and suprahyoid [SH]) were obtained from both the crossbite (XB) and noncrossbite (NONXB) sides at mandibular rest position. sEMG acti-vity of the bilateral AT and MA muscles sides was obtained during MVC. Asymmetry and activity indexes were calculated for each muscle area at rest and during MVC; the MA/TA ratio during MVC was also determined. Results: At rest, no differences were found between sexes for any muscle areas or asymmetry and activity indexes. No differences were found between XB and NONXB sides. During MVC, however, significant sex differences were found in AT and MA activity, with higher sEMG values in males than in females, on both XB and NONXB sides. Asymmetry indexes, activity indexes and MA/AT ratios did not show significant differences between the sexes. Activity was symmetric both in males and in females. Conclusions: At rest, no sex differences were found, but during MVC males showed higher activity than did females in both XB and NONXB AT and MA muscle areas. Muscular activity was symmetrical at rest and during MVC in both sexes. Sexual dimorphism should be considered in the diagnosis and treatment of UPXB and lateral shift in the early mixed dentition. Key words:Unilateral crossbite, mandibular shift, jaw muscles, sEMG, early mixed dentition.
Highlights
Unilateral posterior crossbite (UPXB) is a frequent malocclusion in the early mixed dentition stage [1,2] that normally persists from childhood to adulthood if not treated, some authors have found instances of spontaneous correction after eliminating dummy- and finger-sucking [3]
Statistical analysis showed no significant differences among repeated sEMG or kinesiographic recordings. -Mandibular shift No significant differences were found in the amount of mandibular lateral shift, ranging from 1.95 to 3.24 mm in males and from 2.12 to 4.60 mm in females (Table 1). -Rest position Table 2 shows the mean values and 95% confidence intervals (CIs) of sEMG recorded in the eight examined muscle areas at rest
No differences were found between genders for any muscle areas, but during maximal voluntary clenching (MVC), significant sex differences were found in the activity of anterior temporalis (AT) and MA in both XB and NONXB sides, with higher sEMG values in males than in females
Summary
Unilateral posterior crossbite (UPXB) is a frequent malocclusion in the early mixed dentition stage [1,2] that normally persists from childhood to adulthood if not treated, some authors have found instances of spontaneous correction after eliminating dummy (pacifier)- and finger-sucking [3] In most cases it is accompanied by a functional mandibular lateral shift during closure toward the crossbite side [4] that has been associated with certain side effects such as asymmetrical mandibular growth [5,6], asymmetrical jaw muscle activity [7,8,9,10], changes in mandibular rest position and movements [11] and temporomandibular joint (TMJ) disorders [12]. The purposes of this study were to examine sEMG activity of jaw muscles at rest and during maximal voluntary clenching (MVC) in children with UPXB and functional mandibular lateral shift in the early mixed dentition and to evaluate sex differences
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