Lysosomal protease expression in mature enamel.

The enamel matrix proteins (amelogenin, enamelin and ameloblastin) are degraded by matrix metalloproteinase-20 and kallikrein-4 during enamel development and mature enamel is virtually protein free. The precise mechanism of removal and degradation of the enamel protein cleavage products from the matrix, however, remains poorly understood. It has been proposed that receptor-mediated endocytosis allows for the cleaved proteins to be removed from the matrix during enamel formation and then transported to the lysosome for further degradation. This study aims to identify lysosomal proteases that are present in maturation-stage enamel organ. RNA from first molars of 11-day-old mice was collected and expression was initially assessed by RT-PCR and then quantified by qPCR. The pattern of expression of selected proteases was assessed by immunohistochemical staining of demineralized mouse incisors. With the exception of cathepsin G, all lysosomal proteases assessed were expressed in maturation-stage enamel organ. Identified proteases included cathepsins B, D, F, H, K, L, O, S and Z. Tripeptidyl peptidases I and II as well as dipeptidyl peptidases I, II, III and IV were also found to be expressed. Immunohistochemical staining confirmed that the maturation-stage ameloblasts express cathepsins L and S and tripeptidyl peptidase II. Our results suggest that the ameloblasts are enriched by a large number of lysosomal proteases at maturation that are likely involved in the degradation of the organic matrix.

A 10-year prospective clinical and radiographic study of one-stage dental implants.

OBJECTIVE: The purpose of this prospective study was to evaluate one-stage dental implants clinically and radiographically after 10 years in function. MATERIAL AND METHODS: Twenty-five patients with a total of 68 implants [46 hollow screws (HS) and 22 hollow cylinders (HC)] who previously participated in 5-year prospective clinical study returned for a 10-year follow-up. For each patient, informed consent was obtained, medical and dental history was reviewed and soft and hard tissue conditions were evaluated using the modified plaque index, modified sulcus bleeding index, probing depth, suppuration, attachment level, distance from the implant crown margin to the coronal border of the peri-implant mucosa keratinized mucosa and periapical radiographs to calculate crestal bone-level changes. RESULTS: As expected, the mean crestal bone-level changes were the greatest in the first year following restoration placement, while only minimal changes were noticed in the subsequent years. HC implants showed a statistically significant higher mean crestal bone loss when compared with HS implants at year 10. Gender was also statistically significantly related to the mean crestal bone loss at years 1, 3, 5 and 10, with male subjects exhibiting more bone loss than female subjects. However, age and peri-implant soft tissue parameters showed low levels of correlation with the mean crestal bone-level changes, and proved to be weak predictors for the mean crestal bone loss at years 5 and 10. CONCLUSIONS: This study confirms that the mean crestal bone loss rates of the HS and HC implants are well within the clinically acceptable parameters. In addition, some of the clinical parameters could be used to assess and predict future crestal bone loss.

Placentation in garter snakes. II. Transmission EM of the chorioallantoic placenta of Thamnophis radix and T. sirtalis.

Transmission electron microscopy was used to examine the ultrastructure of the allantoplacenta of garter snakes during the last half of gestation. This placenta occupies the dorsal hemisphere of the egg and is formed through apposition of the chorioallantois to the inner lining of the uterus. The uterine epithelium consists of flattened cells with short, irregular microvilli and others that bear cilia. The lamina propria is vascularized and its capillaries lie at the base of the uterine epithelial cells. The chorionic epithelium consists of a bilayer of squamous cells that are particularly thin superficial to the allantoic capillaries. Neither the chorionic epithelium nor the uterine epithelium undergoes erosion during development. Although a thin remnant of the shell membrane intervenes between fetal and maternal tissue at mid-gestation, it undergoes fragmentation by the end of gestation. Thus, uterine and chorionic epithelial are directly apposed in some regions of the allantoplacenta, forming continuous cellular boundaries at the placental interface. During development, capillaries proliferate in both the uterine and chorioallantoic tissues. By late gestation, the interhemal diffusion distance has thinned in some areas to less than 2 microm through attenuation of the uterine and chorionic epithelia. Morphologically, the allantoplacenta is well adapted for its function in gas exchange. However, the presence of cytoplasmic vesicles, ribosomal ER, and mitochondria in the chorionic and uterine epithelial cells are consistent with the possibility of additional forms of placental exchange.

Placentation in garter snakes. III. Transmission EM of the omphalallantoic placenta of Thamnophis radix and T. sirtalis.

The omphalallantoic placenta is a complex organ that is unique to viviparous squamates. Using transmission EM and light microscopy, we examined this placenta in garter snakes in order to understand its structural organization and functional capabilities. The omphalallantoic placenta is formed from the uterine lining and the bilaminar omphalopleure, the latter of which is associated with the isolated yolk mass and allantois. A thin shell membrane separates the fetal and maternal tissues throughout gestation. The uterine epithelium contains cuboidal cells with large droplets or granules and appears to be secretory. Epithelium of the omphalopleure is specialized for absorption and contains cells with prominent microvilli and others with large cytoplasmic droplets or granules. The brush-border cells are rich in mitochondria and Golgi bodies and interdigitate extensively with adjacent cells, forming elaborate intercellular canaliculi. Their morphology is consistent with their proposed role in sodium-coupled water movement. During development, the isolated yolk mass becomes depleted as yolk droplets are digested by cells of the omphalopleure and allantois. However, the allantois does not fuse to or vascularize the inner face of the omphalopleure. Consequently, the distance between fetal and maternal circulatory systems remains large (about 250-300 microm), precluding efficient gas exchange and hemotrophic transfer. The morphology of the omphalallantoic placenta strongly suggests that it functions in nutrient transfer through uterine secretion and fetal absorption.