A preliminary characterization of human cementum collagen

The action of microbial collagenases in dentinal matrix degradation in root caries and potential strategies for its management: a comprehensive state-of-the-art review

Conventional views associate microbial biofilm with demineralization in root caries (RC) onset, while research on their collagenases role in the breakdown of collagen matrix has been sporadically developed, primarily in vitro. Recent discoveries, however, reveal proteolytic bacteria enrichment, specially Porphyromonas and other periodontitis-associated bacteria in subgingivally extended lesions, suggesting a potential role in RC by the catabolism of dentin organic matrix. Moreover, genes encoding proteases and bacterial collagenases, including the U32 family collagenases, were found to be overexpressed in both coronal and root dentinal caries. Despite these advancements, to prove microbial collagenolytic proteases' definitive role in RC remains a significant challenge. A more thorough investigation is warranted to explore the potential of anti-collagenolytic agents in modulating biofilm metabolic processes or inhibiting/reducing the size of RC lesions. Prospective treatments targeting collagenases and promoting biomodification through collagen fibril cross-linking show promise for RC prevention and management. However, these studies are currently in the in vitro phase, necessitating additional research to translate findings into clinical applications. This is a comprehensive state-of-the-art review aimed to explore contributing factors to the formation of RC lesions, particularly focusing on collagen degradation in root tissues by microbial collagenases.

Research progress of biomimetic materials in oral medicine

Biomimetic materials are able to mimic the structure and functional properties of native tissues especially natural oral tissues. They have attracted growing attention for their potential to achieve configurable and functional reconstruction in oral medicine. Though tremendous progress has been made regarding biomimetic materials, significant challenges still remain in terms of controversy on the mechanism of tooth tissue regeneration, lack of options for manufacturing such materials and insufficiency of in vivo experimental tests in related fields. In this review, the biomimetic materials used in oral medicine are summarized systematically, including tooth defect, tooth loss, periodontal diseases and maxillofacial bone defect. Various theoretical foundations of biomimetic materials research are reviewed, introducing the current and pertinent results. The benefits and limitations of these materials are summed up at the same time. Finally, challenges and potential of this field are discussed. This review provides the framework and support for further research in addition to giving a generally novel and fundamental basis for the utilization of biomimetic materials in the future.

Dentinomimetics and cementomimetics of Moringa oleifera leaves extract

To evaluate the biomimetic remineralization capabilities of Moringa oleifera leaves (MOL) extract on coronal dentin and acellular cementum, two different concentrations (50 and 200 mg/ml) of MOL extract loaded in plain varnish (M1 and M2 groups respectively) were compared to fluoride varnish (FL group) and native surface (C group). Eighty sound premolar teeth were collected. Forty teeth (10 teeth in each group) were used for coronal dentin testing while the other forty (10 teeth in each group) were used for acellular cementum testing. Teeth in M1, M2, and FL groups were etched for 30 s and then received the specific varnish treatment. All samples were immersed in artificial saliva for 14 days and then collected, dried, and examined by scanning electron microscopy and energy dispersive X-ray spectroscopy (EDX). Histologically, FL group showed mineral deposition as discrete vesicular granules of various sizes on the surface of both coronal dentin and acellular cementum. Mineral deposition only occurred on some DTs openings while opened tubules remained. The surface of the acellular cementum revealed regular grooves, micro-fissures, and cracks. In the M1 and M2 groups, mineral deposition appeared as a homogenous continuous layer on coronal dentin and acellular cementum. Only a few DTs and cementum fissures were not filled completely. In L.S. sections of the coronal one-third, the DTs appeared almost sealed with varying lengths of mineral deposition. EDX results statistical analysis showed that the M2 group had the highest phosphate ions (P-) and calcium ions (Ca+2) at%. MOL has an extraordinary effect on the remineralization of coronal dentin and acellular cementum. It would have a promising ability to control dentinal hypersensitivity and formation of biomimetic cementum tissue.

Histology of human cementum: Its structure, function, and development

Cementum was first demonstrated by microscopy, about 180 years ago. Since then the biology of cementum has been investigated by the most advanced techniques and equipment at that time in various fields of dental sciences. A great deal of data on cementum histology have been accumulated. These data have been obtained from not only human, but also non-human animals, in particular, rodents such as the mouse and rat. Although many dental histologists have reviewed histology of human cementum, some descriptions are questionable, probably due to incorrect comparison of human and rodent cementum. This review was designed to introduce current histology of human cementum, i.e. its structure, function, and development and to re-examine the most questionable and controversial conclusions made in previous reports.

Molecular cloning, expression and immunolocalization of a novel human cementum-derived protein (CP-23)

Cementum is a unique mineralized connective tissue that covers the root surfaces of the teeth. The cementum is critical for appropriate maturation of the periodontium, both during development as well as that associated with regeneration of periodontal tissues, IU; however, one major impediment to understand the molecular mechanisms that regulate periodontal regeneration is the lack of cementum markers. Here we report on the identification and characterization of one such differentially human expressed gene, termed "cementum protein-23" (CP-23) that appears to be periodontal ligament and cementum-specific. We screened human cementum tumor-derived cDNA libraries by transient expression in COS-7 cells and "panning" with a rabbit polyclonal antibody against a cementoblastoma conditioned media-derived protein (CP). One isolated cDNA, CP-23, was expressed in E. coli and polyclonal antibodies against the recombinant human CP-23 were produced. Expression of CP-23 protein by cells of the periodontium was examined by Northern blot and in situ hybridization. Expression of CP-23 transcripts in human cementoblastoma-derived cells, periodontal ligament cells, human gingival fibroblasts and alveolar bone-derived cells was determined by RT-PCR. Our results show that we have isolated a 1374-bp human cDNA containing an open reading frame that encodes a polypeptide with 247 amino acid residues, with a predicted molecular mass of 25.9 kDa that represents CP species. The recombinant human CP-23 protein cross-reacted with antibodies against CP and type X collagen. Immunoscreening of human periodontal tissues revealed that CP-23 gene product is localized to the cementoid matrix of cementum and cementoblasts throughout the entire surface of the root, cell subpopulations of the periodontal ligament as well as cells located paravascularly to the blood vessels into the periodontal ligament. Furthermore, 98% of putative cementoblasts and 15% of periodontal ligament cells cultured in vitro expressed CP-23 gene product. Cementoblastoma cells and periodontal ligament cells contained a 5.0 kb CP-23 mRNA. In situ hybridization showed strong expression of CP-23 mRNA on cementoblast, cell subpopulations of the periodontal ligament and cells located around blood vessels into the periodontal ligament. Our results demonstrate that CP-23 represents a novel, tissue-specific-gene product being expressed by periodontal ligament subpopulations and cementoblasts. These findings offer the possibility to determine the cellular and molecular events that regulate the cementogenesis process during root development. Furthermore, it might provide new venues for the design of translational studies aimed at achieving predictable new cementogenesis and regeneration of the periodontal tissues.

X-ray microanalysis of human cementum

An energy dispersive x-ray microanalysis study was performed throughout the total length of cementum on five impacted human teeth. Mineral content of calcium, phosphorous, and magnesium were determined with an electron probe from the cemento-enamel junction to the root apex on the external surface of the cementum. The concentration profiles for calcium, phosphorous, and magnesium were compared by using Ca/P and Mg/Ca atomic percent ratio. Our findings demonstrated that the Ca/P ratio at the cemento-enamel junction showed the highest values (1.8-2.2). However, the area corresponding to the acellular extrinsic fiber cementum (AEFC) usually located on the coronal one-third of the root surface showed a Ca/P media value of 1.65. Nevertheless, on the area representing the fulcrum of the root there is an abrupt change in the Ca/P ratio, which decreases to 1.3. Our results revealed that Mg(2+) distribution throughout the length of human cementum reached its maximum Mg/Ca ratio value of 1.3-1.4 at.% around the fulcrum of the root and an average value of 0.03%. A remarkable finding was that the Mg/Ca ratio pattern distribution showed that in the region where the Ca/P ratio showed a decreasing tendency, the Mg/Ca ratio reached its maximum value, showing a negative correlation. In conclusion, this study has established that clear compositional differences exist between AEFC and cellular mixed stratified cementum varieties and adds new knowledge about Mg(2+) distribution and suggests its provocative role regulating human cementum metabolism.

Immunolocalization of a human cementoblastoma-conditioned medium-derived protein

Little is known about the molecular mechanisms that regulate the cementogenesis process, because specific cementum markers are not yet available. To investigate whether a cementoblastoma-conditioned medium-derived protein (CP) could be useful as a cementum biological marker, we studied its expression and distribution in human periodontal tissues, human periodontal ligament, alveolar bone, and cementoblastoma-derived cells. In human periodontal tissues, immunoreactivity to anti-CP was observed throughout the cementoid phase of acellular and cellular cementum, cementoblasts, cementocytes, cells located in the endosteal spaces of human alveolar bone, and in cells in the periodontal ligament located near the blood vessels. Immunopurified CP promoted cell attachment on human periodontal ligament, alveolar bone-derived cells, and gingival fibroblasts. A monoclonal antibody against bovine cementum attachment protein (CAP) cross-reacted with CP. These findings indicate that CP identifies potential cementoblast progenitor cells, is immunologically related to CAP species, and serves as a biological marker for cementum.

Extracellular matrix in tooth cementum and mantle dentin: localization of osteopontin and other noncollagenous proteins, plasma proteins, and glycoconjugates by electron microscopy

BACKGROUND

Noncollagenous proteins (NCPs) are considered to have multiple functions related to the formation, turnover, and repair of the collagen-based mineralized tissues. Collectively, they comprise a class of generally acidic, mineral-binding proteins showing extensive posttranslational modifications, including glycosylation, phosphorylation, and sulfation. METHODS. We have used colloidal-gold immunocytochemistry and lectin-gold cytochemistry, together with transmission electron microscopy, to examine the organic matrix composition of tooth cementum and the subjacent mantle dentin in rodent molar teeth. Molars were processed for immunocytochemistry using antibodies against osteopontin (OPN), osteocalcin (OC), bone sialoprotein (BSP), bone acidic glycoprotein-75 (BAG-75), albumin (ALB), and alpha 2HS-glycoprotein (alpha 2HS-GP), or for glycoconjugate cytochemistry using lectin-gold complexes.

RESULTS

Ultrastructurally, at the advancing root edge in developing molars, OPN and BSP initially were associated with small calcification foci in the mantle dentin. With progressing mineralization, OC and alpha 2HS-GP appeared diffusely distributed throughout the calcified mantle dentin, and diminished as a gradient toward the circumpulpal dentin. Immediately following disruption of Hertwig's epithelial root sheath, cementum deposition commenced at the root surface occasionally with the appearance of a cement line rich in OPN. Cementum matrix proper contained abundant OPN, BSP, OC, and alpha 2HS-GP, but no or little BAG-75 or ALB. Protein immunolabeling, as well as lectin labeling for beta-D-galactose and N-acetyl-neuraminic acid and/or N-glycolyl-neuraminic acid, both being prominent sugars of certain NCPs, was primarily concentrated between, and at the surface of, collagen fibrils in acellular extrinsic fiber cementum. OPN, BSP, OC, and alpha 2HS-GP were also prominent components of cellular cementum and of Sharpey's fibers. In cellular cementum, laminae limitantes sometimes present delimiting cementocyte lacunae and cell process-containing canaliculi were also rich in OPN. Along the root surface, occasional cementoblasts exhibited intracellular labeling for OPN over the Golgi apparatus and secretory granules.

CONCLUSIONS

We have identified OPN, BSP, OC, and alpha 2HS-GP as being prominent organic constituents of both mantle dentin and acellular and cellular cementum, and, have elucidated the details of their distribution at the ultrastructural level. The temporal appearance and spatial distribution of these organic moieties in the teeth root are similar to those seen during bone formation and are consistent with proposals that certain NCPs may be involved in regulating calcification and/or participating in cell-matrix and matrix-matrix/mineral adhesion events.

Cementum specific components which influence periodontal connective tissue cells

We have isolated two polypeptides from cementum one of which promotes the growth and the other the attachment of periodontal cells. One polypeptide, the cementum derived growth factor (CGF), was extracted from healthy human and bovine teeth by 1 M CH3COOH and purified by heparin-affinity chromatography and HPLC. The CGF is a 23 kDa polypeptide which is mitogenic to fibroblasts and smooth muscle cells. It is active alone, but its activity is highly potentiated by plasma-derived serum or EGF. It induces classical mitogenic signaling events, which include Ca++ mobilization, inositol phosphate hydrolysis, activation of phosphokinase C (PKC) and transcription of cellular protooncogenes c-fos and jun-B. The magnitude and pattern of activation of signaling events and their susceptibility to PKC inhibitors and pertussis toxin indicated that the CGF may be a distinct molecular species. The CAP is a 55 kDa polypeptide which promotes the attachment and spreading of fibroblasts, smooth muscle cells, bone cells and endothelial cells, but not epithelial cells. Antibodies to CAP immunostain cementum, but not other tissues. Root surfaces bind CAP. The CGF and CAP do not appear to be present in adjacent periodontal structures. Our data show that the CAP and CGF selectively interact with periodontal cell populations and affect their biological activities, and thus may influence the formation and regeneration of periodontal connective tissues.

Attempts to label matrix synthesis of human root cementum in vitro

The present study describes the dynamic process of both acellular extrinsic (AEFC) and acellular/cellular intrinsic fiber cementum (AIFC/CIFC) matrix production on growing human teeth. Selected erupting maxillary and mandibular premolars with roots grown to about 70%-95% of their final length were placed in organ culture immediately following extraction. Twelve teeth for short-time labeling were pulse-incubated for 15 min in medium containing 3H-proline and chased for various times in order to follow the migration and secretion of the tracer. Eight teeth for long-time incubation were labeled continuously for 5 h before being chased for 1-8 days in order to label cementum matrix accumulation. After decalcification in ethylene diaminetetraacetic acid (EDTA), their roots were subdivided into about 20 slices each. Epon-embedded sections were prepared for light- and electron-microscopic as well as autoradiographic examination. During CIFC-formation, cementoblasts revealed high intracytoplasmic silver grain concentrations within the first hour after 3H-proline administration. The release of the tracer occurred between 60 to 120 min after administration. After 2 h, cementoblasts and the cementum matrix appeared to be labeled about equally. After 5 h, most of the labeled proteins appeared to be localized in the cementoid. Silver grains increased in number over the cementum matrix from 5-24 h. Very high intracellular grain concentrations within very large cementoblasts corresponded to regions of rapid cementum formation. Tracer-halos around entrapped cells lend support to a multipolar mode of matrix production during CIFC-initiation. The fate of the tracer during the development of early AEFC-matrix was less clear. However, fibroblasts revealed dense intracytoplasmic grain accumulations within the first hour after 3H-proline administration. Thereafter, the tracer localization was vague. This indistinct grain localization reflected the particular mode of AEFC-matrix production characterized by addition of new fibril segments to pre-existing fibers of a collagenous fringe.

Isolation and partial characterization of a growth factor from human cementum

Cementum is the mineralized interface through which collagen fibers of periodontal connective tissues are anchored onto the tooth surface. We have isolated and partially characterized a mitogenic factor from human cementum which has properties different from other growth factors. Cementum was harvested from healthy human teeth, extracted in 1.0 M CH3COOH and mitogenic activities were fractionated by heparin-affinity chromatography. Proteins eluted by 0.4-0.6 M NaCl, which contained most of the cementum mitogenic activity, were precipitated by trichloroacetic acid and resolved by HPLC through ion-exchange and reverse-phase columns. NaDodSO4-polyacrylamide gel electrophoresis revealed that the purified preparation contained a M(r) 23,000 protein and this protein was associated with mitogenic activity. The purified cementum-derived growth factor (CGF) was active alone, but at suboptimal concentrations its activity was potentiated by small quantities of plasma-derived serum and epidermal growth factor (EGF). The activity was resistant to heat, but it was destroyed by trypsin digestion. Reduction and alkylation destroyed the mitogenic activity, however electrophoretic mobility was not affected. Binding of EGF to fibroblast membranes was not affected by the CGF and assays to detect platelet-derived growth factor were negative. These characteristics indicated that CGF is a distinct molecular species. Our data show that cementum contains several mitogenic factors and that CGF is the major cementum mitogen.

Isolation of human tumor cells that produce cementum proteins in culture

We have cultured cells from explants of a human cementum tumor. The cells obtained were multipolar, they formed network-like structures and they were alkaline-phosphatase positive. Immunostaining and Western blots using specific antibodies revealed that these cells produced bone sialoprotein and collagen types I and V, and they also mineralized in vitro. Conditioned medium was mitogenic to fibroblasts and mitogens present were separated by heparin-affinity chromatography. Based on affinity to heparin and antibody-inhibition studies, the heparin fractions were shown to contain cementum-derived growth factor, platelet-derived growth factor and fibroblast growth factors. The cementum tumor cells, but not gingival fibroblasts, were stained positively by an antibody to cementum-derived attachment protein. The attachment protein was separated by immunoaffinity chromatography, and Western blots revealed that the preparation contained 56-kDa and 43-kDa proteins as major bands. Cells pulse-labeled with radioactive amino acids contained a 43-kDa protein as the major component; however, this protein was absent after a cold chase in the presence of cycloheximide, but 56-kDa, 39-kDa and 26-kDa species became prominent. These data indicated that the 56-kDa cementum attachment protein is derived from a 43-kDa precursor. Our data show that the cells cultured from the cementum tumor represent cementum cells capable of synthesizing and secreting cementum proteins in culture.

Cell attachment activity of cementum proteins and mechanism of endotoxin inhibition

Cementum occupies a unique anatomical location where soft connective tissues of the periodontium are attached to root surfaces. Cell attachment properties of proteins present in cementum were studied. Human and bovine cementum were extracted with 0.5 mol/L CH3COOH followed by 4 mol/L guanidine, and proteins were separated by ion-exchange chromatography and SDS-polyacrylamide gel electrophoresis. Cells were labeled with radioactive amino acids and added to tissue-culture plastic plates incubated with cementum proteins, and attachment was measured. Results showed that cementum proteins promoted the attachment of smooth muscle cells, endothelial cells, and fibroblasts, but not epithelial cells. Fibroblasts attached more efficiently than other cell types, and they manifested spreading with re-organization of actin filaments. No attachment occurred to plates incubated with endotoxin from A. actinomycetemcomitans. Fewer fibroblasts attached to plates treated with cementum proteins in the presence of endotoxin, but cells pre-treated with endotoxin attached normally. Attachment was not inhibited when plates were incubated first with attachment proteins and then with endotoxin; however, it was decreased when endotoxin or bovine serum albumin preceded cementum proteins. Cementum proteins with Mr 68,000, 61,000, 55,000, and 36,000 (p68, p61, p55, and p36, respectively) manifested attachment activity, while protein(s) with Mr 23,000-24,000 did not. Western blots revealed that guanidine extracts contained three bands cross-reacting with anti-bovine sialoprotein-II antibody, but the p61, p55, and p36 were negative. We conclude that cementum contains bovine sialoprotein-II and at least four other fibroblast attachment proteins, and that they do not support epithelial cell attachment.(ABSTRACT TRUNCATED AT 250 WORDS)

Proteoglycans of bovine cementum: isolation and characterization

The proteoglycans associated with the mineralized matrix of bovine cementum have been studied biochemically and their distribution within this tissue localized immunohistochemically. Both hyaluronate and proteoglycans were fractionated by DEAE-Sephacel ion-exchange chromatography. The proteoglycans eluted in three separate peaks of which two contained alkali labile protein associated with glycosaminoglycans, and one appeared as free glycosaminoglycan chains. Analysis of the glycosaminoglycans identified chondroitin sulfate as the predominant species, although minor quantities of dermatan sulfate and heparan sulfate were also identified. Agarose-acrylamide gel electrophoresis and Sepharose CL-6B molecular sieve chromatography of the proteoglycans indicated them to be smaller in size with respect to periodontal ligament and gingival proteoglycans, but similar to bone and dentine proteoglycans. Amino acid analyses indicated subtle differences between cementum and bone proteoglycans. Using a monoclonal antibody (9-A-2) which recognizes the unsaturated disaccharide of chondroitinase ACII-digested glycosaminoglycans, chondroitin sulfate was identified in the pericellular environment within the lacunae housing the cementoblasts as well as in the extracellular matrix of cementum.

Isolation of a fibroblast attachment protein from cementum

Cementum forms the interface through which soft connective tissue of the periodontium is attached to the root surface. The interactions between cementum and connective tissue are not completely understood and whether cementum influences periodontal connective tissue formation and regeneration is not clear. We have examined the effect of cementum components on the attachment of gingival fibroblasts. Cementum was harvested from healthy human and bovine teeth and extracted sequentially in 0.5 M CH3COOH, 4 M guanidine and bacterial collagenase. Fibroblast attachment was measured using 51Cr-labelled human gingival fibroblasts on tissue culture plates previously incubated with cementum components. Results showed that all three extracts mediated fibroblast attachment and attachment was dependent on concentration and incubation time. The attachment activity was not destroyed by digestion with bacterial collagenase or by antibodies to fibronectin and laminin. However, it was inhibited by a peptide containing the amino acid sequence RGD. By gel filtration or HPLC using a DEAE-cellulose column several proteins with attachment activity were fractionated. SDS-polyacrylamide gel electrophoresis revealed that HPLC fraction eluted by 0.2-0.3 M NaCl contained a protein with molecular weight 55 kDa as a major component. This protein was isolated and shown to promote fibroblast attachment, and optimal attachment occurred at a concentration of 2 micrograms/ml. We conclude that cementum contains substances capable of mediating fibroblast attachment and that these substances play an important role in periodontal connective tissue formation and regeneration by facilitating fibroblast attachment to root surfaces.

Mitogenic activity of cementum components to gingival fibroblasts

Cementum forms the interface between root dentin and periodontal ligament through which periodontal connective tissue is attached to root surfaces. We have examined how cementum components influence the biological activities of gingival fibroblasts. Cementum was harvested from freshly extracted human teeth and extracted sequentially with 0.5 mol/L acetic acid, 4 mol/L guanidine-0.5 mol/L EDTA, and bacterial collagenase. The extracts were concentrated and analyzed for mitogenic activity to human gingival fibroblasts. DNA synthesis was assayed by measurement of [3H]thymidine incorporation by quiescent fibroblasts activated to divide, and cell growth was determined by the counting of cells over a 10-day period. Results showed that extracts of cementum stimulated quiescent gingival fibroblasts to synthesize DNA and grow. The stimulation was dose-dependent, and most of the stimulatory activity was extracted by acid. Addition of small quantities of serum potentiated the mitogenic activity to levels greater than those of control cultures containing 10% fetal calf serum. The mitogenic activity was heat-stable, but it was destroyed by trypsin. Neither platelet-derived growth factor (PDGF) nor epidermal growth factor (EGF) was detectable in the cementum extract, and extracts of human dentin and skin contained very little mitogenic activity. We conclude that cementum contains substances capable of regulating the growth of gingival fibroblasts, and that these substances may play an important role in gingival connective tissue formation and regeneration.

Collagenase in the human periodontal ligament

Collagenase activity was demonstrated by direct incubation to be present in human periodontal ligament. This activity was found in only one of two populations of ligament, i.e., those ligaments taken from teeth in which their attachment site was at least 2.5 mm apical to the cementoenamel junction. The collagenase was demonstrated to be of host origin because it degraded collagen into 3/4 and 1/4 alpha chain fragments characteristic of mammalian collagenases. The enzyme was shown to be inhibited in the presence of EDTA and to have a pH optimum of 7.5.