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PubMed1989

[Effect of various implant materials on cementogenesis].

Various implant materials have been used to stimulate the regeneration of supporting bone lost from periodontal disease. In addition, the histologic features of bone regeneration associated with their implantation have been evaluated. Very little, however, seems to be known about the effect of implant materials on cementum formation. The aim of this study was to determine whether implant materials stimulate the cementogenesis on adjacent planed root surfaces. Twelve monkeys with healthy gingivae were used in this experiment. Following mucoperiosteal flap elevation, "windows" were chiseled in the bone to the proximal root dentin surfaces and adjacent root surfaces were planed. Each of the three implant materials [tricalcium phosphate (TCP), decalcified bone matrix (DBM) and hydroxyapatite (HA)] were then placed in the cuspid and incisor root "windows" before the flap was sutured back into the previous position. Windows with no implantation served as a control. Animals were sacrificed 2, 4 and 8 weeks postoperatively. Biopsy specimens including the tooth and surrounding bone were examined by light and electron microscopy. At 2 weeks, all implant particles were surrounded by fibrous tissue. On the other hand, fibrous tissues filled the control defect. On the planed root surfaces after the implantation of TCP and DBM, furthermore, cementoid tissue appeared. At 4 weeks, a considerable amount of new cementum was deposited on the root surfaces except in the implantation of HA. It was especially pronounced after implantation of TCP and DBM which promoted bone regeneration after resorption. These results suggest that resorbable implant materials such as TCP and DBM not only facilitate the formation of new bone, but also of new cementum.

Animals↗
PubMed2006

Pleiotropism of bone morphogenetic proteins: from bone induction to cementogenesis and periodontal ligament regeneration.

Bone morphogenetic and osteogenic proteins (BMPs/OPs), pleiotropic members of the transforming growth factor-beta (TGF-beta) supergene family, induce de novo endochondral bone formation and act as soluble signals of tissue morphogenesis, sculpting the architecture of multicellular mineralized structures, including the periodontal tissues. The presence of multiple forms of BMPs/OPs has a therapeutic significance and the choice of a suitable protein will be a formidable challenge to the practising periodontologist. Amino acid sequence variations in the carboxy terminal domain, the molecular basis of the structure/activity profile of each isoform, confer specialized and pleiotropic activities to each morphogenetic protein. Naturally derived BMPs/OPs regenerate cementum and alveolar bone in mandibular furcation defects of the primate Papio ursinus. Tissue morphogenesis induced by hOP-1 and hBMP-2 is qualitatively different when the morphogens are applied singly, indicating that the structure/activity profile amongst BMPs/OPs is controlling pleiotropic tissue induction and morphogenesis. Furcation defects of Papio ursinus with root surfaces exposed long-term to periodontal pathogens and filled with granulation tissue after inoculation of a pathogenetic human strain of Porphyromonas gingivalis twice a month for 12 months were implanted with hOP-1 osteogenic devices. Six months after surgery there was regeneration of alveolar bone and induction of cementogenesis, with Sharpey's fibres uniting the regenerated bone to the newly formed cementum. Although within the natural milieu of the bone matrix a plurality of morphogens may be required to initiate the cascade of pattern formation and the attainment of tissue form and function, recombinant y-irradiated hOP-1 delivered by a xenogeneic collagenous matrix induces complete periodontal tissue regeneration on periodontally affected root surfaces, showing an additional specific function of hOP-1 for tissue morphogenesis in clinical contexts. The pleiotropy of the signalling molecules of the TGF-beta superfamily is additionally highlighted by the redundancy of molecular signals initiating endochondral bone induction by the TGF-beta isoforms per se, powerful inducers of endochondral bone, but in the primate only. A novel approach in periodontal tissue regeneration is to induce heterotopic bone to be transplanted as morcellised autogenous grafts into established periodontal defects. The induction of bone develops a mosaic structure in which the osteogenic proteins of the TGF-beta superfamily singly, synergistically and synchronously initiate and maintain tissue induction and morphogenesis, with specific roles at different time points of the morphogenetic cascade.

Animals↗
PubMed1996

Cellular cementogenesis in rat molars: the role of cementoblasts in the deposition of intrinsic matrix fibers of cementum proper.

The formation of intrinsic fibers was examined in the advanced stage of rat cellular cementogenesis by light and electron microscopy. Using scanning electron microscopy, cementoblasts showed wing-like processes, partly encircling principal fibers. At the cementum-facing side of the cells these processes showed segmentation into finger-like processes, arranged in parallel with the cementum surface. Transmission electron microscopy showed many cytoplasmic fragments around intrinsic fibers at the cementum surface. These fragments contained microtubules and collagenous secretory granules that were arranged in parallel with the cementum surface and the intrinsic fibers. The wing-like processes contained microtubules and secretory granules that were arranged perpendicularly to the cementum surface and in parallel with the principal fibers. These observations suggest that: (1) the cytoplasmic fragments are cross-sectioned finger-like processes; (2) cementoblasts secrete intrinsic fibers from the finger-like processes and additional principal fibers from the wing-like processes; (3) cementoblasts constantly shorten their wing-like processes by forming finger-like processes. This development starts at the side facing the cementum and proceeds towards the periodontal ligament. With the segmentation, the cementoblasts change the arrangement of secretory granules to secrete intrinsic fibers around preformed principal fibers.

Animals↗
PubMed1997

Formation of an alternate lamellar pattern in the advanced cellular cementogenesis in human teeth.

The formation of an alternate lamellar pattern in the advanced stage of cellular cementogenesis in human molars was examined by light and electron microscopy. In longitudinal ultrathin sections, longitudinally oriented intrinsic fibril bundles appeared in close and parallel association with slender processes of cementoblasts on the cementum. Where transversely oriented intrinsic fibril bundles appeared, cementoblasts formed indentations to enclose the fibril bundles. Cytoplasmic fragments were also enclosed in the indentations. Scanning electron microscopy indicated that cementoblasts have developed two types of processes on their cementum-facing side - ridge- and finger-like. The cementoblasts formed groove-like compartments by ridge-like processes in cooperation with other cementoblasts. The compartments formed groups, and in each group the compartments were arranged in the same direction. The finger-like processes were arranged in parallel with the ridge-like processes in the compartments. These observations suggest that: (1) slender processes and cytoplasmic fragments are longitudinally and transversely cut finger-like processes, respectively; (2) the cellular indentations are transversely cut groove-like compartments; (3) the cementoblasts regulate the intrinsic fiber arrangement by the two types of processes; (4) the cementoblasts move the two types of processes synchronously and periodically to cause an alternate change in the intrinsic fiber arrangement. This dynamic sequence results in the alternate lamellar pattern of cellular cementum.

Collagen↗
PubMed2001

Bone morphogenetic protein-2 stimulates cell recruitment and cementogenesis during early wound healing.

BACKGROUND: The unique action of bone morphogenetic proteins (BMPs) on mineralised tissue formation indicates that BMPs are good candidates for use in stimulating periodontal regeneration. Relatively little is known about the mechanisms of actions of BMPs during periodontal regeneration, although recent evidence from our laboratory suggests that the effects of BMPs may be profoundly influenced by various factors including root surface conditioning, delivery systems and masticatory forces. AIM: The aim of this study was to investigate the effect of rhBMP-2 on cell recruitment during periodontal regeneration using a pulse-chase technique where cells are labelled with a thymidine analogue (BrdU) (pulse) and the migration of their progeny is followed (chase) during early wound healing. The relationship between the rhBMP-2 influence on cell recruitment from the periodontal ligament (PDL) and its ability to stimulate cementogenesis was also evaluated. METHOD: The buccal aspect of the distal root of the first molar was denuded of its PDL, cementum and superficial dentine through a bony window created in the mandible of 64 Wistar rats under general anaesthesia. Test animals were treated with 10 microL of 500 microg/ml rhBMP-2 in a collagen membrane sponge (n=32) and control defects received 10 microl of saline in a collagen sponge (n=32). All animals received an intraperitoneal single pulse injection of 40 mg/kg BrdU label 2 days postoperatively. Groups of test and control animals (n=8) were killed 2 hours later on day 2 and at 4, 7 and 10 days postoperatively. Mandibles were processed for histological examination. RESULTS: The results show that rhBMP-2 had a profound effect on proliferation and migration of cells in the adjacent and deeper aspects of the PDL at 7 and 10 days post periodontal wounding (p<0.05). Significantly greater new cementum formation occurred in the test group at 10 days (p=0.03). CONCLUSION: This study shows that following periodontal wounding rhBMP-2 stimulates cell recruitment by increasing proliferation and migration of cells from the adjacent unwounded PDL into the wounded area, thus promoting periodontal regeneration by increasing new cementum formation.

Alveolar Bone Loss↗
PubMed1990

Expression of attachment proteins during cementogenesis.

There is general agreement that during development the extracellular environment plays a critical role in controlling cell differentiation. Data generated from numerous studies support the possibility that cell attachment proteins and their corresponding cell receptors are possible candidates for this role. In particular, our studies are directed at identifying attachment proteins in mature cementum and establishing the function of these proteins during root formation. Fractionation of guanidine HCL/EDTA extracts of cementum revealed the presence of a bone-associated attachment, BSP, as well as fractions containing as of yet undetermined attachment proteins. Immunofluorescent examination of 1st molar tissues during root formation, obtained from 7 day-old mice neonates, for bone-associated attachment proteins indicated that osteopontin is expressed in the area of Hertwig's epithelial root sheath, but not in the region of the dental papillae. However, dental papillae cells, considered to have the capacity to form cementum, attached to osteopontin coated dishes, in vitro. Thus, unique attachment proteins, as well as those previously identified, were found in mature cementum and during root development. Future studies focused on identifying attachment proteins of mature cementum and determining the spatial and temporal localization of these proteins, pre- and post-cementogenesis, will provide important information necessary for establishing the function of these proteins during root development.

Animals↗
PubMed1994

Immunolocalization of osteopontin, osteocalcin, and dentin sialoprotein during dental root formation and early cementogenesis in the rat.

Using immunohistochemical methods we studied the tissue localization of the extracellular matrix proteins osteopontin (OPN), osteocalcin (OC), and dentin sialoprotein (DSP) during the formation of acellular and cellular cementum in newly born rats. In the layer of acellular cementum of developing incisor and molar teeth we found a very strong staining for OPN but not for DSP or OC. Many cells immediately adjacent to acellular cementum and PDL cells were also positive for OPN but not for DSP or for OC. In contrast, cellular cementum in molar teeth stained strongly for OPN and OC but not for DSP. Consistent with these observations, the cells engaged in the formation of cellular cementum (cementoblasts and cementocytes) reacted strongly for OPN and OC but not for DSP. In advanced stages of dentinogenesis, both crown and root odontoblasts and dentin stained for OPN, OC, and DSP. Cells and matrices of surrounding alveolar bone stained for OPN and OC but not for DSP. We conclude that cementoblasts and cementocytes of cellular cementum produce OPN and OC but not DSP and thus express an osteoblast-like, not an odontoblast-like, phenotype. The cells responsible for the production of acellular cementum are likely cells of the PDL in close contact with the dental root surface. These fibroblast-like cells express OPN but not OC or DSP and accordingly express only a partial osteoblastic phenotype.

Animals↗
PubMed1998

The regulation of fiber arrangement in advanced cellular cementogenesis of human teeth.

This study observed cellular cementum in fully formed human premolars by light and electron microscopy to elucidate how cementoblasts regulate the fiber arrangement in cementum. Cementoblasts had wing-like processes encircling the principal fibers, where Sharpey's fibers were dense. On the cementum-facing side, wing-like processes were segmented into finger-like processes in parallel with the cementum surface. Observations suggested that with the segmentation intrinsic fibers appeared around principal fibers in close association with finger-like processes. Where Sharpey's fibers were few or absent, where intrinsic fibers were the main fibrous element of the cementum, cementoblasts had only few or no wing-like processes, but had finger-like processes not associated with the wing-like processes on the cementum-facing side. On the basis of the origin of the finger-like processes the main results suggest that there are two kinds of cementoblasts: one has finger-like processes associated with wing-like processes and secretes intrinsic fibers from the finger-like processes to incorporate the principal fibers for tooth support. The second type has finger-like processes not associated with wing-like processes, this type secretes intrinsic fibers from the finger-like processes to adjust the cementum thickness.

Adult↗
PubMed2000

Epithelial Dlx-2 homeogene expression and cementogenesis.

The Dlx-2 (distal-less gene) homeoprotein transcription factor controls early tooth development but has not been studied during the late stages of biomineralization. Transgenic mice containing a Dlx-2/LacZ reporter construct were used to map the Dlx-2 expression pattern in cementoblasts, the dental cells most closely related to bone cells and therefore suggested to be uniquely positioned osteoblasts. During initial root formation, marked expression of Dlx-2 was evident in molar and incisor root epithelium, whereas dental papilla and follicle were negative. Dlx-2 was expressed in this epithelium from the apical loop to the area of its disruption. During acellular cementum formation in both incisors and molars, Dlx-2 expression was observed in the majority of differentiated cementoblasts from the apical region to the erupting zones. During cellular cementum formation, the presence of which characterizes growth-limited molars, Dlx-2 expression was restricted to the innermost cementoblasts and entrapped cementocytes. These data further support the hypothesis of a complex origin and fate of cementum-forming cells, as previously suggested by the expression patterns of a set of mesenchymal and epithelial markers, notably ameloblastin as shown here. Dlx-2 expression might constitute a landmark of cementoblast subpopulations of epithelial origin. (J Histochem Cytochem 48:277-283, 2000)

Aging↗
PubMed2004

Leucine-rich amelogenin peptide: a candidate signaling molecule during cementogenesis.

BACKGROUND: Cementum is a critical mineralized tissue; however, control of its formation remains undefined. One hypothesis is that enamel matrix proteins/peptides secreted by ameloblasts and/or epithelial rest cells contribute to the control of cementum formation via epithelial-mesenchymal interactions. Here, we focused on determining whether or not leucine-rich amelogenin peptide (LRAP), translated from an alternatively spliced amelogenin RNA, altered cementoblast behavior. METHODS: Immortalized murine cementoblasts (OCCM-30) were exposed to LRAP and evaluated for: 1) proliferative activity; 2) gene expression using Northern blot for Cbfal (core binding factor alpha-1); OCN (osteocalcin), OPN (osteopontin), and real-time reverse transcription-polymerase chain reaction (RT-PCR) for OPG (osteoprotegerin); and RANKL (receptor activator of NF-kappaB ligand); 3) signaling pathway using inhibitors of PKA (THFA), PKC (GF109203X), and MAPK (UO126); and 4) mineralization evaluated by von Kossa and Alizarin-red. RESULTS: LRAP had no effect on cell proliferation up to 6 days, with a decrease in cell growth observed at the highest dose by 9 days versus untreated cells. LRAP down regulated OCN and up regulated OPN in a dose- and time-response fashion, and inhibited the capacity of mineral nodule formation. Transcripts for OPG were increased in LRAP-treated cells compared to control, but RANKL mRNA levels were not affected. Core binding factor alpha (Cbfa) mRNA, expressed constitutively, was not affected by LRAP. Signaling pathway assays suggested involvement of the MAPK pathway, since the addition of the MAPK inhibitor suppressed OPN expression in LRAP-treated cells. CONCLUSION: Leucine-rich amelogenin peptide appears to have a direct effect on cementoblast activity that may prove significant during development as well as in regeneration of periodontal tissues.

Animals↗