Objective: To test the null hypothesis that alteration in masticatory function due to liquid-diet feeding during growth does not affect jaw-opening reflex (JOR) maturation. Materials and Methods: Soon after weaning, 70 female Wistar rats were divided into two equal groups and fed either solid (control group) or liquid (experimental group) diets. At 5, 9, and 13 weeks, the rats were anesthetized and the JOR was recorded in the anterior belly of the digastric muscles as evoked by a low-intensity electrical stimulation of the left inferior alveolar nerve. Results: There were similar tendencies at each recording age. Peak-to-peak amplitude of the JOR was significantly smaller, and the latency was significantly longer in the experimental group, although the duration was not significantly different between the two groups. Conclusions: These data suggest that long-term masticatory functional change due to liquid-diet feeding during growth may impede the learning for JOR maturation, and thus may affect the masticatory performance in the adult. (Angle Orthod. 2009;79:299-305.)
Objective:To assess the immediate effects of temporary bite-raising using light-cured orthodontic band cement on the superficial masseter and anterior temporalis electromyography (EMG) activity in healthy adults.Materials and Methods:Surface EMG signals were recorded bilaterally from the superficial masseter and anterior temporalis muscles of 30 volunteers with a normal occlusion, before and after having temporary bite-raising. The bite-raising was done by adding light-cured orthodontic band cement (3x5x2 mm WxLxH) on the lingual cusps of both upper first molars. The measurements were recorded (i) at rest, (ii) while clenching in centric occluding position and (iii) while chewing on an artificial test food. The EMG activity at rest and during clenching, the maximum voltage, and the duration of the identified EMG signal burst while chewing the artificial test food before and after temporary bite-raising were statistically compared using the paired t-test or the Wilcoxon signed-rank test based on the normality of the variables. The significance level was set at 5%.Results:After temporary bite-raising, we found no significant change in integral EMG activity at rest position for the superficial masseter (mean difference (MD)=7.5 μVs) and for the anterior temporalis muscle (MD=36.8 μVs); however, the integral EMG activity during clenching was significantly reduced for the superficial masseter (MD=201.2 μVs) and for the anterior temporalis muscle (MD=151.8 μVs). During mastication, the maximum voltage of the identified burst was significantly reduced on the preferred chewing side of the superficial masseter and anterior temporalis muscles (MD=127.9 and 47.7 μV, respectively), while no significant change was found for the duration of the identified burst (MD=-34.1 and 3.4 ms, respectively) after temporary bite-raising.Conclusion:The results point to an altered neuromuscular behavior during clenching and chewing immediately after temporary bite-raising with light-cured orthodontic band cement. This information is relevant for orthodontists to inform their patients what will happen to their masticatory muscle activity when this bite-raising method is used.
Intermittent hypoxia (IH) has been associated with skeletal growth. However, the influence of IH on cartilage growth and metabolism is unknown. We compared the effects of IH on chondrocyte proliferation and maturation in the mandibular condyle fibrocartilage and tibial hyaline cartilage of 1-week-old male Sprague–Dawley rats. The rats were exposed to normoxic air (n = 9) or IH at 20 cycles/h (nadir, 4% O2; peak, 21% O2; 0% CO2) (n = 9) for 8 h each day. IH impeded body weight gain, but not tibial elongation. IH also increased cancellous bone mineral and volumetric bone mineral densities in the mandibular condylar head. The mandibular condylar became thinner, but the tibial cartilage did not. IH reduced maturative and increased hypertrophic chondrocytic layers of the middle and posterior mandibular cartilage. PCR showed that IH shifted proliferation and maturation in mandibular condyle fibrocartilage toward hypertrophic differentiation and ossification by downregulating TGF-β and SOX9, and upregulating collagen X. These effects were absent in the tibial growth plate hyaline cartilage. Our results showed that neonatal rats exposed to IH displayed underdeveloped mandibular ramus/condyles, while suppression of chondrogenesis marker expression was detected in the growth-restricted condylar cartilage.
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