Symmetry and fluctuation of cell movements in neural crest-derived facial mesenchyme.

In the face, symmetry is established when bilateral streams of neural crest cells leave the neural tube at the same time, follow identical migration routes and then give rise to the facial prominences. However, developmental instability exists, particularly surrounding the steps of lip fusion. The causes of instability are unknown but inability to cope with developmental fluctuations are a likely cause of congenital malformations, such as non-syndromic orofacial clefts. Here, we tracked cell movements over time in the frontonasal mass, which forms the facial midline and participates in lip fusion, using live-cell imaging of chick embryos. Our mathematical examination of cell velocity vectors uncovered temporal fluctuations in several parameters, including order/disorder, symmetry/asymmetry and divergence/convergence. We found that treatment with a Rho GTPase inhibitor completely disrupted the temporal fluctuations in all measures and blocked morphogenesis. Thus, we discovered that genetic control of symmetry extends to mesenchymal cell movements and that these movements are of the type that could be perturbed in asymmetrical malformations, such as non-syndromic cleft lip. This article has an associated 'The people behind the papers' interview.

Bilateral oral focal mucinosis on the palate of a 2-year-old child: a case report.

BACKGROUND: Oral focal mucinosis (OFM) is an uncommon benign oral lesion. The aetiology of the lesion is unknown. Histologically, it appears as a well-circumscribed myxomatous mass surrounded by denser, collagenous connective tissue. Most cases of OFM were found in adults. It is very unusual for young children to have OFM. CASE REPORT: A case of OFM in a 2-year-old child is reported. The patient was presented with non-painful bilateral enlargements on the palate. The overlying mucosa was smooth and not ulcerated and appeared in the same colour as the adjacent tissue. The histology of the lesion showed myxomatous mass indicative of OFM. Treatment consisted of surgically removing the lesions under general anaesthetic. CONCLUSION: Paediatric dentists should consider OFM in their differential diagnosis of soft tissue oral lesions in children.

The effect of bleaching time on dentin fracture toughness in vitro.

STATEMENT OF PROBLEM: A recent study reported a decrease in dentin fracture toughness after the application of peroxide bleaching products to dentin in vitro. PURPOSE: The objective of the present study was to investigate this in vitro decrease in fracture toughness further by evaluating the effect of different peroxide application times on dentin fracture toughness. MATERIALS AND METHODS: Compact test fracture toughness specimens were prepared from coronal human. These were divided into five groups (N = 12) and subjected to either bleach (10% carbamide peroxide) and/or placebo gel for a total of 336 consecutive hours (0 and 336, 84 and 252, 168 and 168, 252 and 84, 336 and 0 hours of bleach and placebo application time, respectively). The gel materials were changed every 6 hours. Fracture toughness testing was done 24 hours after the end of bleaching using tensile loading at 10 mm/min. Results were analyzed by analysis of variance and linear regression (p < 0.05). RESULTS: Dentin fracture toughness after 252 and 336 hours was significantly reduced compared to the 0- and 84-hour bleach times. An association between fracture toughness and bleach time (r(2) = 0.82) with an inverse linear regression line (K(1C) = -0.0032 [hour] + 3.386) was found. CONCLUSIONS: A significant correlation was found between bleach time and dentin fracture toughness. Dentin fracture toughness was reduced over time during the 336-hour course of in vitro bleaching. CLINICAL SIGNIFICANCE: The results suggest that it would be prudent to minimize the length of time for clinical bleaching procedures when dentin is directly exposed to bleach.