Delayed Tooth Eruption in Membrane Type-1 Matrix Metalloproteinase Deficient Mice

Membrane-type 1 matrix metalloproteinase (MT1-MMP) is expressed highly in mineralizing tissues including bones and teeth. Mice deficient in MT1-MMP ( &#109 / &#109 ) display severe defects in skeletal development including dwarfism, osteopenia, and craniofacial abnormalities. Death occurs in these mice by about 3 weeks of age. Since MT1-MMP is expressed by the ameloblasts of the enamel organ and by the odontoblasts of the dental papilla, we asked if the developing teeth were adversely affected in the knockout animals. Molars from MT1-MMP &#109 / &#109 mice and controls were examined by histological, X-ray, and SEM analysis at 4, 18-20, and 25 days of postnatal development. At 4 days of development the molars from the &#109 / &#109 mice appeared histologically normal. At 18-20 days of development, the first molars of the &#109 / &#109 mice had apparently normal tooth crowns with normal dentin and enamel; however, the roots were truncated and the teeth had not yet erupted. In contrast to the &#109 / &#109 mice, the first molars of the 18-20-day control animals had erupted. SEM analysis of a &#109 / &#109 first molar and incisor revealed a normal enamel prism pattern. However, X-ray analysis demonstrated that tooth eruption was delayed by approximately 5 days and that the tooth roots were abnormally short in the knockout animals. Since MT1-MMP-deficient mice have been demonstrated to display a generalized increase in bone resorption, these data suggest that inefficient growth of bone surrounding the tooth root complex causes a delay in tooth eruption.     

Establishment of Dental Epithelial Cell Line (HAT-7) and the Cell Differentiation Dependent on Notch Signaling Pathway

Rat incisors grow continuously throughout life. Producing a variety of dental epithelial cells is performed by stem cells located in the cervical loop of the incisor apex. To study the mechanisms for cell differentiation, we established a dental epithelial cell line (HAT-7) originating from a cervical loop epithelium of a rat incisor. Immunochemical studies showed that HAT-7 produced the cells expressing amelogenin, ameloblastin, or alkaline phosphatase (ALP). To illustrate a role of Notch signaling in the determinant of the cell fate, we examined expression patterns of Notch1 and Jagged1 in HAT-7 density dependently. At lower cell density, Notch1- or Jagged1-expressing cells were not seen. However, when they were fully confluent, cells began to express Notch1 or Jagged1 strongly. Some ALP-positive cells were almost consistent with Notch1-expressing cells but not Jagged1-expressing cells. These results suggested that the determinant of direction of differentiation was associated with Notch signaling pathway.     

Substance P Activates p38 Mitogen-Activated Protein Kinase to Promote IL-6 Induction in Human Dental Pulp Fibroblasts

Substance P (SP) induces the expression of proinflammatory cytokines, such as interleukin (IL)-6, which are implicated in pulp inflammation. To determine the signal pathway of SP-induced IL-6, we examined the activities of the mitogen-activated protein kinases (MAPKs) in human dental pulp cell (PF-10) cultures. SP induced the phosphorylation of p38 MAPK within 5 min; this activation persisted for up to 40 min and was independent of the activation of extracellular signal-related kinases (ERK-1 and ERK-2) that were induced after SP stimulation of PF-10 cells. As shown by electrophoretic mobility shift assay p38 MAPK was not involved in SP-induced activation of nuclear factor-kappa B (NF-κB). However, p38 MAPK mediated SP-induced IL-6 production, as shown by the use of specific inhibitors of this kinase. Our results suggest that the activation of p38 MAPK is important for NF-κB-independent regulator of neurogenic inflammation in dental pulp tissues.     

Review: Extracellular Matrix Regulates Tooth Morphogenesis

Mineralized tissues are unique in that they use proteins to attract and organize calcium and phosphate ions into a structured mineral phase, thus precise knowledge of the expression and extracellular distribution of matrix proteins is very important to understand their function. Tooth development is regulated by sequential and reciprocal interactions between neural crest-derived mesenchymal cells and the oral environment. However, the precise molecular mechanisms that mediate interactions between epithelium and mesenchymal cells are not clear, although basement membrane (BM) components have been shown to play important roles in these regulatory events. In addition, the extracellular matrix layer, whose main components are laminin, collagen IV, nidogen, and sulfated proteoglycan, and the BM layer are both considered to be involved with cell proliferation and differentiation. During tooth morphogenesis, extracellular matrices are dramatically changed. Further, the BM components, laminin and collagen IV support dental epithelium; however, in the late stage, they begin the processes of enamel matrix secretion and calcification, after which the BM structure between the dental epithelium and mesenchyme disappears. In addition, tooth abnormalities associated with several kinds of human diseases that cause mutations in the extracellular matrix, as well as the molecular mechanisms of the basement membrane and enamel matrix during tooth morphogenesis, are not clearly understood. In our review, we discuss the role of the extracellular matrix, with focus on the BM and enamel matrix during tooth morphogenesis.     

Effect of Apatite Crystals on the Activity of Amelogenin Degrading Enzymes In Vitro

The objective of the present study was to determine the effect of apatite crystals on the activity of amelogenin degrading enzymes in vitro. Current experimental data, together with previous reports support the view that among the different proteinases present in the enamel extracellular matrix, serine proteinase(s) are responsible for the massive degradation of amelogenins during the maturation stage. For our in-vitro experiments we used the recombinant amelogenin M179 as substrate and a “65%-satd. (NH₄)₂SO₄” fraction of enamel proteins as well as chymotrypsin as sources for serine-proteinase activity. We report preliminary experiments of amelogenin proteolysis in the presence of apatite crystals resulting in a different proteolysis pattern when compared to amelogenin proteolysis without apatite crystals. Quantitative analysis of the HPLC peaks corresponding to the proteolysis products indicates that the presence of apatite crystals in the proteolysis solution inhibits the ability of the serine-proteinases to degrade amelogenin. The present observations support the hypothesis that amelogenin degradation correlates with apatite crystal growth during enamel maturation.     

The Function and Structure of the Marsupial Enamel

The aims of this study are to clarify the structure of tubular enamel and the function of enamel tubules on the marsupial of opossum (Monodelphis domestica). Almost all enamel prisms, surrounded by interprismatic enamel, ran obliquely from the dentinoenamel junction (DEJ), and bent near the enamel surface. The enamel tubules are distributed in both enamel prisms and the interprismatic enamel near the DEJ. From the middle to the surface of the enamel, one enamel tubule ran within a single enamel prism. Most of enamel tubules continued from the DEJ to near the enamel surface. It is suggested that each enamel tubule developed in relation to one ameloblast. The fibers of odontoblastic process penetrated the DEJ from the dentinal tubules into the enamel tubules, and some branched across the enamel prisms. The odontoblastic process may be actively cross into the ameloblastic layer and may be involved in the formation of enamel tubules. After in vivo injection of tetracycline, tetracycline labeling showed that the odontoblastic tubules continued to enamel tubules. And strontium was detected in enamel tubules from the DEJ to the enamel surface, as was the dentinal tubules. In conclusion, there was active transport by the odontoblast and it's process through the enamel tubules.     

Stress distribution of different implant connections associated with multiple implant-supported prostheses

Abstract

In some clinical situations, the clinician may encounter previously installed implants that should be associated with other implants for a proper rehabilitation. The aim of this study was to evaluate the biomechanical behaviour of a multiple prosthesis joined by different implant connections using photoelasticity. Photoelastic models with a screwed fixed prosthesis supported by implants with different connection systems (Morse taper, external hexagon, internal hexagon, and Flexcone), and different combinations among them, were fabricated. Each assembly was placed in a circular polariscope, and axial and oblique (45°) loads of 100 N were applied on the occlusal surface of the crowns. The fringe patterns were photographed and the analysis was performed by counting the number of high-intensity fringes and also according to the stress distribution region where they appeared. Among implants of the same connection, the external connections obtained a greater number of high intensity fringes when compared to the internal connections. From the biomechanical point of view, the association between different types of connections obtained positive results.     

Effectiveness of online peer assisted learning as a teaching methodology for dental undergraduate students

IntroductionPeer-assisted learning (PAL) has been extensively used in professional courses. However, its effectiveness as an adjunct to teacher-assisted learning (TAL) has not been evaluated. The objective of this study was to evaluate the effectiveness of Online PAL as an independent teaching methodology and as an adjunct to TAL, for dental students.MethodsForty BDS year 3 students were divided into 2 groups of 20 each. Four year 5 students were chosen as tutors to teach 4 different topics using the Microsoft teams platform. The study was conducted in two parts. At first, two topics were taught to one group by the tutor (peer-led group) and the other group, by a teacher (teacher-led group). Next, the remaining two topics were taught to both groups by the teacher initially. This was followed by repeated teaching of the topics to peer-led group by tutors, while other group did self-study. Students’ perception and performance scores were compared using an independent sample t-test for all the topics.ResultsThe mean performance scores in the teacher-led group for topics 1 and 2 were 86.15 and 90.22, whereas scores in the peer-led group were 75.38 and 79.21 which was statistically significant (p < 0.05). The mean scores in the teacher-led group for topics 3 and 4 were 71.82 and 65.42, whereas in the peer-led group as an adjunct to TAL were 84.55 and 82.50. This was statistically significant (p < 0.01).DiscussionOnline PAL as an adjunct to teacher-assisted learning can be useful for teaching dental undergraduate students.