Biological problems of regenerative cementogenesis: synthesis and attachment of collagenous matrices on growing and established root surfaces

Hypercementosis in Late Pleistocene Homo sapiens fossils from Klasies River Main Site, South Africa

OBJECTIVE

To examine early Homo sapiens fossils from the Late Pleistocene site of Klasies River Main Site, South Africa for evidence of hypercementosis. The specimens represent seven adult individuals dated to between 119,000 and 58,000 years ago. These observations are contextualized in relation to the incidences of hypercementosis among recent human populations and fossil human samples and the potential etiologies of hypercementosis.

DESIGN

The fossils were investigated utilizing micro-CT and nano-CT scanning to visualize and measure cementum apposition on permanent incisor, premolar and molar roots. Cementum thickness was measured at mid-root level, and the volume of the cementum sleeve was calculated for the two fossil specimens that display marked hypercementosis.

RESULTS

Two of the fossils display no evidence of cementum hypertrophy. Three exhibit moderate cementum thickening, barely attaining the quantitative threshold for hypercementosis. Two evince marked hypercementosis. One of the Klasies specimens with marked hypercementosis is judged to be an older individual with periapical abscessing. The second specimen is a younger adult, and seemingly similar in age to other Klasies fossils that exhibit only minimal cementum apposition. However, this second specimen exhibits dento-alveolar ankylosis of the premolar and molars.

CONCLUSIONS

These two fossils from Klasies River Main Site provide the earliest manifestation of hypercementosis in Homo sapiens.

Insights into the aetiologies of hypercementosis: A systematic review and a scoring system

OBJECTIVES

This paper aims to better define hypercementosis, investigate its described potential aetiologies, and determine whether there are different patterns of cementum apposition and if they are a function of their supposed aetiology.

DESIGN

A literature review was undertaken using the Medline, DOSS, Scopus and Cochrane Library electronic databases. Two co-authors selected the published works independently, extracted the data in accordance with the PRISMA statement.

RESULTS

Among 546 articles, 75 articles were finally selected. Eight different supposed aetiologies were identified: (1) intensive masticatory effort, (2) systemic disease, (3) carious lesion and apical periodontitis, (4) impaction, (5) periodontal disease, (6) concrescence, (7) super-eruption, and (8) drugs. Some of these aetiologies can be combined in the same tooth. Hypercementosis manifestations are various in nature and extent with different patterns that may be aetiology-specific. To improve the description and associated consistency in the characterisation of hypercementosis, in this review but also in future studies, we propose a new qualitative scoring system to quickly characterise hypercementosis and determine its most relevant aetiology.

CONCLUSIONS

This systematic review demonstrates that hypercementosis is a complex and not yet well-defined condition. Some forms of apposition are specific to a given aetiology. The hypercementosis characterisation may contribute to document the oral condition and/or the individuals masticatory activity.

Amelogenin-Derived Peptide (ADP-5) Hydrogel for Periodontal Regeneration: An In Vitro Study on Periodontal Cells Cytocompatibility, Remineralization and Inflammatory Profile

A relevant alternative to enamel matrix derivatives from animal origin could be the use of synthetic amelogenin-derived peptides. This study aimed to assess the effect of a synthetic amelogenin-derived peptide (ADP-5), alone or included in an experimental gellan-xanthan hydrogel, on periodontal cell behavior (gingival fibroblasts, periodontal ligament cells, osteoblasts and cementoblasts). The effect of ADP-5 (50, 100, and 200 µg/mL) on cell metabolic activity was examined using Alamar blue assay, and cell morphology was assessed by confocal imaging. An experimental gellan-xanthan hydrogel was then designed as carrier for ADP-5 and compared to the commercial gel Emdogain^®. Alizarin Red was used to determine the periodontal ligament and cementoblasts cell mineralization. The inflammatory profile of these two cells was also quantified using ELISA (vascular endothelial growth factor A, tumor necrosis factor α, and interleukin 11) mediators. ADP-5 enhanced cell proliferation and remineralization; the 100 µg/mL concentration was more efficient than 50 and 200 µg/mL. The ADP-5 experimental hydrogel exhibited equivalent good biological behavior compared to Emdogain^® in terms of cell colonization, mineralization, and inflammatory profile. These findings revealed relevant insights regarding the ADP-5 biological behavior. From a clinical perspective, these outcomes could instigate the development of novel functionalized scaffold for periodontal regeneration.

Polymeric Nanotechnologies for the Treatment of Periodontitis: A Chronological Review

Periodontitis is a chronic infectious and inflammatory disease of periodontal tissues estimated to affect 70 - 80 % of all adults. At the same time, periodontium, the site of periodontal pathologies, is an extraordinarily complex plexus of soft and hard tissues, the regeneration of which using even the most advanced forms of tissue engineering continues to be a challenge. Nanotechnologies, meanwhile, have provided exquisite tools for producing biomaterials and pharmaceutical formulations capable of elevating the efficacies of standard pharmacotherapies and surgical approaches to whole new levels. A bibliographic analysis provided here demonstrates a continuously increasing research output of studies on the use of nanotechnologies in the management of periodontal disease, even when they are normalized to the total output of studies on periodontitis. The great majority of biomaterials used to tackle periodontitis, including those that pioneered this interesting field, have been polymeric. In this article, a chronological review of polymeric nanotechnologies for the treatment of periodontitis is provided, focusing on the major conceptual innovations since the late 1990s, when the first nanostructures for the treatment of periodontal diseases were fabricated. In the opening sections, the etiology and pathogenesis of periodontitis and the anatomical and histological characteristics of the periodontium are being described, along with the general clinical manifestations of the disease and the standard means of its therapy. The most prospective chemistries in the design of polymers for these applications are also elaborated. It is concluded that the amount of innovation in this field is on the rise, despite the fact that most studies are focused on the refinement of already established paradigms in tissue engineering rather than on the development of revolutionary new concepts.

Hydrogel Swelling-Mediated Strain Induces Cell Alignment at Dentin Interfaces

Cell and tissue alignment is a defining feature of periodontal tissues. Therefore, the development of scaffolds that can guide alignment of periodontal ligament cells (PDLCs) relative to tooth root (dentin) surfaces is highly relevant for periodontal tissue engineering. To control PDLC alignment adjacent to the dentin surface, poly(ethylene glycol) (PEG)-based hydrogels were explored as a highly tunable matrix for encapsulating cells and directing their activity. Specifically, a composite system consisting of dentin blocks, PEG hydrogels, and PDLCs was created to control PDLC alignment through hydrogel swelling. PDLCs in composites with minimal hydrogel swelling showed random alignment adjacent to dentin blocks. In direct contrast, the presence of hydrogel swelling resulted in PDLC alignment perpendicular to the dentin surface, with the degree and extension of alignment increasing as a function of swelling. Replicating this phenomenon with different molds, block materials, and cells, together with predictive modeling, indicated that PDLC alignment was primarily a biomechanical response to swelling-mediated strain. Altogether, this study describes a novel method for inducing cell alignment adjacent to stiff surfaces through applied strain and provides a model for the study and engineering of periodontal and other aligned tissues.

Incremental lines in human acellular tooth cementum - new insights by SEM analysis

BACKGROUND

Tooth cementum covers the surface of the root dentine and is produced and laid down in thin layers continuously throughout life. Functionally, different types of tooth cementum can be distinguished, which can be roughly divided into acellular (primary cementum) and cellular (secondary cementum) forms. One main type is acellular extrinsic fibre cementum (AEFC), which covers the cervical and middle third of the root. Light microscopic examinations of transverse sections of AEFC show lamellar patterns of alternating light and dark lines called growth or incremental lines. Following mammalian research, a seasonal rhythm of incremental line formation is also assumed in humans. Previous attempts at visualising incremental lines in the AEFC by scanning electron microscopy (SEM) were not particularly successful. The aim of the present study was to detect incremental lines in the AEFC and to analyse their underlying structure by SEM.

METHODS

For this purpose, non-embedded and resin-embedded transverse and longitudinal sections of three single-rooted teeth obtained from different patients were investigated. The thin sections were not pre-treated (e.g. by etching, grinding or coating).

RESULTS

Lamellar structures, which could be identified as incremental lines, were detectable in both transverse and longitudinal sections, with transverse orientation in the cross-section and longitudinal orientation in the longitudinal section. The lamellar pattern was created by broad fibre-rich layers alternating with narrow fibre-poor layers. The orientation of the collagen fibres changed from layer to layer from transverse to radial direction. The visibility of the layered structure discovered varied significantly.

CONCLUSIONS

The study demonstrate that it is possible, in principle, to detect incremental lines in AEFC and to identify their basic structure using SEM. Our results suggest that the density and orientation of the fibres play an essential role in the formation of incremental lines. Functional aspects seem to be of particular importance.

A Review of In Vivo and Clinical Studies Applying Scaffolds and Cell Sheet Technology for Periodontal Ligament Regeneration

Different approaches to develop engineered scaffolds for periodontal tissues regeneration have been proposed. In this review, innovations in stem cell technology and scaffolds engineering focused primarily on Periodontal Ligament (PDL) regeneration are discussed and analyzed based on results from pre-clinical in vivo studies and clinical trials. Most of those developments include the use of polymeric materials with different patterning and surface nanotopography and printing of complex and sophisticated multiphasic composite scaffolds with different compartments to accomodate for the different periodontal tissues' architecture. Despite the increased effort in producing these scaffolds and their undoubtable efficiency to guide and support tissue regeneration, appropriate source of cells is also needed to provide new tissue formation and various biological and mechanochemical cues from the Extraccellular Matrix (ECM) to provide biophysical stimuli for cell growth and differentiation. Cell sheet engineering is a novel promising technique that allows obtaining cells in a sheet format while preserving ECM components. The right combination of those factors has not been discovered yet and efforts are still needed to ameliorate regenerative outcomes towards the functional organisation of the developed tissues.

A novel hypothesis based on clinical, radiological, and histological data to explain the dentinogenesis imperfecta type II phenotype

Purpose/Aim: The aim of this study was to explore whether dentinogenesis imperfecta (DGI)-related aberrations are detectable in odontogenic tissues. Materials and Methods: Morphological and histological analyses were carried out on 3 teeth (two maxillary 1^st molars, one maxillary central incisor) extracted from a patient with DGI Type II. A maxillary 2^nd molar teeth extracted from a healthy patient was used as control. A micro-computed tomographic (μCT) data-acquisition system was used to scan and reconstruct samples. Pentachrome and picrosirius red histologic stains were used to analyze odontogenic tissues and their collagenous matrices. Results: Our findings corroborate DGI effects on molar and incisor root elongation, and the hypo-mineralized state of DGI dentin. In addition to these findings, we discovered changes to the DGI pulp cavity: Reactionary dentin formation, which we theorize is exacerbated by the early loss of enamel, nearly obliterated an acellular but still-vascularized DGI pulp cavity. We also discovered an accumulation of lamellated cellular cementum at the root apices, which we hypothesize compensates for the severe and rapid attrition of the DGI tooth. Conclusions: Based on imaging and histological data, we propose a novel hypothesis to explain the complex dental phenotypes observed in patients with DGI Type II.

Intravenous bisphosphonate therapy does not thicken cementum or change periodontal ligaments of cancer patients

OBJECTIVE

To test the hypothesis that intravenous (IV) bisphosphonate (BP) therapy thickens or alters the micromorphology of cementum and periodontal ligament (PDL) in cancer patients.

STUDY DESIGN

Thirty-two teeth extracted from 24 cancer patients and separated into test (patients who have undergone IV BP therapy, n = 16) and control (patients naive to BP therapy, n = 16) groups were studied. Cementum thickness was measured in 3 different areas of the dental root with polarized light microscopy. PDL was assessed by optical light microscopy and the immunohistochemical expression of periostin.

RESULTS

No significant difference was detected in cementum thickness (apical, P = .06; medium, P = .16; cervical, P = .18) between groups. The numbers of fibroblasts in PDL (P = .56), incremental lines of cementum (P = .51) and the immunohistochemical patterns of periostin expression in PDL (P = .68) did not differ between groups.

CONCLUSION

IV BP therapy does not thicken cementum or change the micromorphology of PDL.

Are Cementoblasts a Subpopulation of Osteoblasts or a Unique Phenotype?

Experimental studies have shown a great potential for periodontal regeneration. The limitations of periodontal regeneration largely depend on the regenerative potential at the root surface. Cellular intrinsic fiber cementum (CIFC), so-called bone-like tissue, may form instead of the desired acellular extrinsic fiber cementum (AEFC), and the interfacial tissue bonding may be weak. The periodontal ligament harbors progenitor cells that can differentiate into periodontal ligament fibroblasts, osteoblasts, and cementoblasts, but their precise location is unknown. It is also not known whether osteoblasts and cementoblasts arise from a common precursor cell line, or whether distinct precursor cell lines exist. Thus, there is limited knowledge about how cell diversity evolves in the space between the developing root and the alveolar bone. This review supports the hypothesis that AEFC is a unique tissue, while CIFC and bone share some similarities. Morphologically, functionally, and biochemically, however, CIFC is distinctly different from any bone type. There are several lines of evidence to propose that cementoblasts that produce both AEFC and CIFC are unique phenotypes that are unrelated to osteoblasts. Cementum attachment protein appears to be cementum-specific, and the expression of two proteoglycans, fibromodulin and lumican, appears to be stronger in CIFC than in bone. A theory is presented that may help explain how cell diversity evolves in the periodontal ligament. It proposes that Hertwig’s epithelial root sheath and cells derived from it play an essential role in the development and maintenance of the periodontium. The role of enamel matrix proteins in cementoblast and osteoblast differentiation and their potential use for tissue engineering are discussed.

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.

Structure of Peripheral Cementum of Normal Equine Cheek Teeth

The structure of peripheral cementum of mandibular and maxillary check teeth was studied In gross observation, light microscopy, and scanning and transmission election microscopy Teeth from four horses aged 4, 8, 17, and 30-years-old were examined. The cementum of the occlusal surface was thicker on the buccal aspect when compared with the lingual aspect of mandibular teeth. The cementum of the occlusal surface was thicker on tin-palatal aspect when compared with the buccal aspect of maxillary teeth. There was no peripheral cementum mi the interdental aspects of either mandibular or maxillary check teeth. In the adult tooth, cementum covered the crown and root surfaces. The peripheral com mum of the gingival region showed a dramatic increase in thickness compared with cementum covering the alveolar portion of the embedded tooth. At a microscopic level, three layers (primary, secondary, and tertiary) were identified within cementum. The increase in cementum in the gingival region was of tertiary cementum. All three layers contained vital cementocytes. There was a well-developed vascular system within the cementum. Nerve bundles were also present. Three cementoblast profiles were identified at the junction of the cementum with the periodontal ligament. The results reported in this paper show that cementum is a dynamic vital tissue. These findings should contribute in ii greater understanding of the etiology and pathogenesis of cemental caries and periodontal disease in the horse.

Evaluation of the nanostructure of cervical third cementum in health and chronic periodontitis: An in vitro study

Background:

During the progression of periodontal disease, the cementum undergoes alterations in its structure and composition. Understanding the nanostructure of cementum, in terms of its mechanical properties, will provide an insight into the milieu that periodontal ligament cells encounter in health and chronic periodontitis. This study aims to analyze the nanomechanical properties of the cervical third of the cementum (transverse section) in health and chronic periodontitis.

Materials and Methods:

Twenty teeth (10 healthy and 10 periodontally diseased) were collected and the nanomechanical properties of the transverse section of the cervical third cementum were evaluated with depth-sensing nanoindentation technique under dry conditions. A total of 100 nanoindentations were performed to analyze the modulus of elasticity and hardness of cervical third of the cementum.

Results:

The nanomechanical properties of the healthy cervical third cementum sections were significantly higher (P < 0.05) (hardness: 0.720 ± 0.305 GPa; modulus: 15.420 ± 3.902 GPa) than the diseased cementum section (hardness: 0.422 ± 0.157 GPa; modulus: 11.056 ± 3.434 GPa).

Conclusion:

The results of our study indicate that the hardness and modulus of elasticity of the cervical third cementum decreases significantly in chronic periodontitis.

Effect of Emdogain enamel matrix derivative and BMP-2 on the gene expression and mineralized nodule formation of alveolar bone proper-derived stem/progenitor cells

The objective of this study was to evaluate the effect of Emdogain (Enamel Matrix Derivative, EMD) and Bone Morphogenetic Protein-2 (BMP-2), either solely or in combination, on the gene expression and mineralized nodule formation of alveolar bone proper-derived stem/progenitor cells. Stem/progenitor cells were isolated from human alveolar bone proper, magnetically sorted using STRO-1 antibodies, characterized flowcytometrically for their surface markers' expression, and examined for colony formation and multilineage differentiation potential. Subsequently, cells were treated over three weeks with 100 μg/ml Emdogain (EMD-Group), or 100 ng/ml BMP-2 (BMP-Group), or a combination of 100 ng/ml BMP-2 and 100 μg/ml Emdogain (BMP/EMD-Group). Unstimulated stem/progenitor cells (MACS(+)-Group) and osteoblasts (OB-Group) served as controls. Osteogenic gene expression was analyzed using RTq-PCR after 1, 2 and 3 weeks (N = 3/group). Mineralized nodule formation was evaluated by Alizarin-Red staining. BMP and EMD up-regulated the osteogenic gene expression. The BMP Group showed significantly higher expression of Collagen-I, III, and V, Alkaline phosphatase and Osteonectin compared to MACS(+)- and OB-Group (p < 0.05; Two-way ANOVA/Bonferroni) with no mineralized nodule formation. Under in-vitro conditions, Emdogain and BMP-2 up-regulate the osteogenic gene expression of stem/progenitor cells. The combination of BMP-2 and Emdogain showed no additive effect and would not be recommended for a combined clinical stimulation.

Histological characteristics of newly formed cementum in surgically created one-wall intrabony defects in a canine model

PURPOSE

Periodontal regenerative therapies for defects created by severe periodontitis are mainly focused on bone regeneration. Although cementum regeneration needs to be better understood, it is believed to play an important role in periodontal regeneration. The first step toward a full understanding of cementum regeneration is to compare repaired cementum to pristine cementum. This study, which used histological techniques, was designed to focus on cementum regeneration and to compare pristine cementum to repaired cementum after surgical procedures with 8 and 24 week healing periods in a canine model.

METHODS

Buccal and lingual mucoperiosteal flaps of 10 beagle dogs were surgically reflected to create critical-sized defects. Intrabony one-wall defects, of which dimension is 4 mm width and 5 mm depth, were made at the distal aspect of mandibular second premolars and the mesial aspect of mandibular fourth premolars in the right and left jaw quadrants. Animals were sacrificed after 8 and 24 weeks post-surgery for histological specimen preparation and histometric analysis.

RESULTS

The repaired cementum was composed mostly of acellular cementum and cellular mixed fiber cementum and was thicker in the apical area than in the coronal area. The acellular cementum of the supracrestal area appeared to be amorphous. The newly formed cellular cementum was partially detached from the underlying circumpulpal dentin, which implied a weak attachment between new cementum and dentin, and this split was observed to a lesser extent in the 24 week group than in the 8 week group. The vertical height of the repaired cementum was greater in the 24 week group than in the 8 week group.

CONCLUSIONS

Within the limitations of this study, we can conclude that repaired cementum after root planing was mainly acellular cementum and cementum tissue that matured to a shape similar to pristine cementum as the healing progressed from 8 to 24 weeks.

Extracellular matrix expression and periodontal wound-healing dynamics following guided tissue regeneration therapy in canine furcation defects

AIM

Temporal and spatial expression pattern of extracellular matrix (ECM) components in furcation defects following guided tissue regeneration (GTR) compared with open-flap debridement (OFD).

MATERIAL AND METHODS

In 21 dogs, mandibular second and fourth pre-molars were treated with one non-resorbable and three different resorbable membranes. Third pre-molars were treated by OFD. After 2, 4, 8 weeks and 3, 6, and 12 months, tissues were analysed by immunohistochemistry for collagen I (Col-I) and III (Col-III), fibronectin (FN), bone sialoprotein (BSP), and osteopontin (OPN).

RESULTS

At 2 weeks, the defect was mainly occupied by FN+ granulation tissue (GT), which was sequentially replaced by new connective tissue expressing FN, Col-I, and increasingly Col-III. Following superficial resorptions by OPN+ osteoclasts and odontoclasts, cementum and bone formation ensued with strong expression of BSP and OPN along bone and tooth surfaces. Deposition of Col-I, FN, BSP and OPN+ cementoid and osteoid became evident after 4 weeks. Extrinsic fibres of cementum and bone stained intensely for Col-III. The newly formed periodontal ligament expressed FN, Col-I, and Col-III, but no BSP or OPN.

CONCLUSIONS

The spatial ECM expression was similar for OFD and the different GTR methods, although the timing and quantity of ECM expression were influenced by wound stabilization and inflammatory reactions.

Ovine periodontal ligament stem cells: isolation, characterization, and differentiation potential

Periodontal disease leads to destruction of the connective tissues responsible for restraining teeth within the jaw. To date, various conventional therapies for periodontal regeneration have shown limited and variable clinical outcomes. Recent studies have suggested that newly identified human periodontal ligament stem cells (PDLSCs) may offer an alternate and more reliable strategy for the treatment of periodontal disease using a cell-based tissue engineering approach. In the present study, we generated enriched preparations of PDLSCs derived from ovine periodontal ligament using immunomagnetic bead selection, based on expression of the mesenchymal stem cell-associated antigen CD106 (vascular cell adhesion molecule 1). These CD106+ ovine PDLSCs demonstrated the capacity to form adherent clonogenic clusters of fibroblast-like cells when plated at low densities in vitro. Ex vivo-expanded ovine PDLSCs exhibited a high proliferation rate in vitro and expressed a phenotype (CD44+, CD166+, CBFA-1+, collagen-I+, bone sialoprotein+) consistent with human-derived PDLSCs. Furthermore, cultured ovine PDLSCs expressed high transcript levels of the ligament/tendon-specific early transcription factor scleraxis. Importantly, ex vivo-expanded ovine PDLSCs demonstrated the capacity to regenerate both cementum-like mineral and periodontal ligament when transplanted into NOD/SCID mice. The results from the present study suggest that ovine PDLSCs may potentially be used as a novel cellular therapy to facilitate successful and more predictable regeneration of periodontal tissue using an ovine preclinical model of periodontal disease as a prelude to human clinical studies.

Mineralization process during acellular cementogenesis in rat molars: a histochemical and immunohistochemical study using fresh-frozen sections

This study was designed to detect tissue non-specific alkaline phosphatase (TNSALP) by Azo-dye staining, calcium by glyoxal bis (2-hydroxyanil) (GBHA) staining, bone sialoprotein (BSP) and osteopontin (OPN) by immunoperoxidase staining in developing rat molars, and also to discuss the mineralization process during acellular cementogenesis. To restrain a reduction in histochemical and immunohistochemical reactions, fresh-frozen undemineralized sections were prepared. Where the epithelial sheath was intact, TNSALP reaction was observed in the dental follicle, but not in the epithelial sheath. With the onset of dentin mineralization, the BSP- and OPN-immunoreactive, initial cementum layer appeared. At this point, cementoblasts had shown intense TNSALP reaction and GBHA reactive particles (=calcium-GBHA complex) appeared on the root surface. With further development, the reaction of TNSALP and GBHA became weak on the root surface. Previous studies have shown that the initial cementum is fibril-poor and that matrix vesicles and calciferous spherules appear on the root surface only during the initial cementogenesis. The findings mentioned above suggest that: during the initial cementogenesis, cementoblasts release matrix vesicles which result in calciferous spherules, corresponding to the GBHA reactive particles. The calciferous spherules trigger the mineralization of the initial cementum. After principal fiber attachment, mineralization advances along collagen fibrils without matrix vesicles.

Sequence of protein expression of bone sialoprotein and osteopontin at the developing interface between repair cementum and dentin in human deciduous teeth

Experimental periodontal regeneration studies have revealed the weak binding of repair cementum to the root surface, whereas attachment of cementum to dentin preconditioned by odontoclasts appears to be superior. The aim of this study has been, therefore, to analyze the structural and partial biochemical nature of the interface that develops between resorbed dentin and repair cementum by using human deciduous teeth as a model. Aldehyde-fixed and decalcified tooth samples were embedded in acrylic or epoxy resins and sectioned for light and transmission electron microscopy. Antibodies against bone sialoprotein (BSP) and osteopontin (OPN), two noncollagenous proteins accumulating at hard tissue interfaces in bone and teeth, were used for protein A-gold immunocytochemistry. Light microscopy revealed a gradually increasing staining intensity of the external dentin matrix starting after the withdrawal of the odontoclast. Labeling for both BSP and OPN was first detected among the exposed collagen fibrils and in the intratubular dentin matrix when odontoclasts had withdrawn but mesenchymal cells were present. Subsequently, collagen fibrils of the repair cementum were deposited concomitantly with the appearance of labeling for BSP and OPN over the intratubular, intertubular, and peritubular dentin matrix. Labeled mineralization foci indicated the advancing mineralization front, and the collagenous repair matrix became integrated in an electron-dense organic material that showed labeling for BSP and OPN. Thus, no distinct planar interfacial matrix layer lies between the resorbed dentin and the repair cementum. The results suggest that odontoclasts precondition the dentin matrix such that the repair cementum becomes firmly attached.

Effects of enamel matrix proteins on tissue formation along the roots of human teeth

OBJECTIVE

Enamel matrix-derived proteins (EMD) are thought to trigger the formation of acellular extrinsic fibre cementum (AEFC), while other reports indicate that EMD may have osteogenic potential. The aim of the present study was to characterize the tissues developing on the root surface following application of EMD.

METHODS

Twelve human periodontitis-affected teeth, scheduled for extraction, were treated with EMD. Two to 6 weeks later, the teeth were extracted, demineralized and processed for embedding in acrylic and epoxy resins. New tissue formation was analysed by light and transmission electron microscopy.

RESULTS

New tissue formation on the root was observed in the notch and on both scaled and unscaled root surfaces distant of the notch area in six defects. The newly formed tissues on the root were thick, collagenous, devoid of extrinsic fibres, and had an irregular surface contour. The presence of electron-dense, organic material in the collagenous matrix indicated at least partial mineralization. Embedded cells were numerous and the cells on the matrix surface were very large in size. Abundant rough endoplasmic reticulum and a prominent Golgi complex were evident. The presence of a split between the treated root surfaces and the newly formed tissue was a common observation, as was the presence of bacteria and host cells in the interfacial gap.

CONCLUSION

Following treatment with EMD, a bone-like tissue resembling cellular intrinsic fibre cementum may develop on the root surfaces, instead of AEFC. Furthermore, EMD may both induce de novo formation of a mineralized connective tissue on scaled root surfaces and stimulate matrix deposition on old native cementum. Interfacial bonding appeared to be weak after 6 weeks of healing.

Formation of human cementum following different modalities of regenerative therapy

The aim of the present study was to compare newly formed cementum following different types of regenerative therapy in humans. Eighteen patients, each displaying one advanced intrabony defect around teeth scheduled for extraction, were included in this study. The defects were treated with either guided tissue regeneration (GTR), enamel matrix protein derivative (EMD), EMD plus bioactive glass, bovine-derived xenograft (BDX), BDX plus GTR, or BDX plus EMD. After healing, the teeth were removed together with their surrounding soft and hard tissues. Cellular content, presence of artifactual splits between the new cementum and the old one or the dentin surface, and thickness of the new cementum were evaluated. Irrespective of treatment, the new cementum was of a reparative, cellular, extrinsic and intrinsic fiber type. There were no differences in cementum thickness among treatments. These findings indicate that in humans, (a) the new cementum formed after different types of regenerative therapy was, irrespective of the treatment, of a reparative, cellular, extrinsic and intrinsic fiber type, and (b) the regenerative modality does not seem to influence the type of newly formed cementum.

Healing of periodontal defects treated with enamel matrix proteins and root surface conditioning—an experimental study in dogs

Application of enamel matrix proteins has been introduced as an alternative method for periodontal regenerative therapy. It is claimed that this approach provides periodontal regeneration by a biological approach, i.e. creating a matrix on the root surfaces that promotes cementum, periodontal ligament (PDL) and alveolar bone regeneration, thus mimicking the events occurring during tooth development. Although there have been numerous in vitro and in vivo studies demonstrating periodontal regeneration, acellular cementum formation and clinical outcomes via enamel matrix proteins usage, their effects on the healing pattern of soft and hard periodontal tissues are not well-established and compared with root conditioning alone. In the present study, the effects of Emdogain (Biora, Malmö, Sweden), an enamel matrix derivative mainly composed of enamel matrix proteins (test), on periodontal wound healing were evaluated and compared with root surface conditioning (performed with 36% orthophosphoric acid) alone (control) histopathologically and histomorphometrically by means of the soft and hard tissue profile of periodontium. An experimental periodontitis model performed at premolar teeth of four dogs were used in the study and the healing pattern of periodontal tissues was evaluated at days 7, 14, 21, 28 (one dog at each day), respectively. At day 7, soft tissue attachment evaluated by means of connective tissue and/or epithelial attachment to the root surfaces revealed higher connective tissue attachment rate in the test group and the amount of new connective tissue proliferation in the test group was significantly greater than the control group (p<0.01). New bone formation by osteoconduction initiated at day 14 in the test and control group. At day 21, the orientation of supra-alveolar and PDL fibers established, and new cementum formation observed in both groups. At day 28, although regenerated cementum was cellular in all of the roots in the control samples, an acellular type of cementum (1.32+/-0.83 mm in length and 3.16+/-0.23 microm in width) was also noted in six roots of test samples with an inconsistent distribution on the root surfaces. The amount of new cementum was significantly higher in the test group than the control group samples (p<0.01). The width of the cellular cementum in the control group was more than the cellular cementum in the test group, but the difference was not statistically significant (p>0.05). A firm attachment of acellular cementum to the root dentin with functional organization of its collagen fibers was noted, and, the accumulation and organization of cellular cementum in the control group was more irregular than the cellular cementum formed in the test group. The amount of new bone was 2.41+/-0.75 mm in the test and 1.09+/-0.46 mm in the control group at day 28. The rate of bone maturation (the number of osteons) was found higher in the test group (10.75+/-0.85) than the control group (5.50+/-0.86). Under the limitations of the study, our results reveal that when compared with root surface conditioning, enamel matrix proteins have more capacity for stimulating periodontal regeneration via their positive effects on root surfaces, i.e. inhibition of gingival epithelium down growth and stimulation of connective tissue proliferation and attachment to the root surfaces during wound healing. An acellular type of cementum regeneration and new alveolar bone formation by an accelerated osteoconductive mechanism are also achieved with application of enamel matrix proteins.

Effect of enamel matrix derivative on human periodontal fibroblasts: proliferation, morphology and root surface colonization. An in vitro study

BACKGROUND

Several clinical trials have shown the effectiveness of Emdogain(R) (EMD) in promoting tissue regeneration, even though the underlining biological mechanism is still poorly known.

OBJECTIVES

The aim of the present study was to verify the effect of EMD on the proliferation of human periodontal ligament (PDL) fibroblasts and on their colonization and differentiation following contact with the root surface of extracted teeth in vitro.

METHODS AND RESULTS

Fibroblasts from PDL were seeded on Petri dishes and cell growth was evaluated by cell counting in the presence and absence of EMD, after 1, 3 and 8 d of culture. A significant effect of EMD upon cellular proliferation at d 3 and 8 was detected. When PDL cells were grown for 12 d with EMD on etched human root surface, a change in cell morphology was observed. Scanning electron microscopy revealed that cells grown on root EMD-treated surface present a body with a flattened surface closely adherent to the substrate and an outer smooth surface rounded in shape. From the flattened surface some thin and elongated cellular processes connecting with the substrate were also observable. PDL cells grown on EMD-treated surface showed lack of alkaline phosphatase activity, as some authors noticed in cementoblasts in vitro.

CONCLUSIONS

In conclusion, our data indicate that EMD enhances human PDL fibroblast proliferation. Furthermore, the cells in the presence of EMD show morphological changes that make them more similar to cementoblasts than to fibroblasts, suggesting a process of cellular differentiation that could play an important role in periodontal tissue repair.

Cementum and periodontal wound healing and regeneration

The extracellular matrix (ECM) of cementum resembles other mineralized tissues in composition; however, its physiology is unique, and it contains molecules that have not been detected in other tissues. Cementum components influence the activities of periodontal cells, and they manifest selectivity toward some periodontal cell types over others. In light of emerging evidence that the ECM determines how cells respond to environmental stimuli, we hypothesize that the local environment of the cementum matrix plays a pivotal role in maintaining the homeostasis of cementum under healthy conditions. The structural integrity and biochemical composition of the cementum matrix are severely compromised in periodontal disease, and the provisional matrix generated during periodontal healing is different from that of cementum. We propose that, for new cementum and attachment formation during periodontal regeneration, the local environment must be conducive for the recruitment and function of cementum-forming cells, and that the wound matrix is favorable for repair rather than regeneration. How cementum components may regulate and participate in cementum regeneration, possible new regenerative therapies using these principles, and models of cementoblastic cells are discussed.

Cementum: a phosphate-sensitive tissue

Ectopic calcification within joints has been reported in humans and rodents exhibiting mutations in genes that regulate the level of extracellular pyrophosphate, e.g., ank and PC-1; however, periodontal effects of these mutations have not previously been examined. These initial studies using ank and PC-1 mutant mice were done to see if such mineral deposition and resulting ankylosis were occurring in the periodontium as well. Surprisingly, results indicated the absence of ankylosis; however, a marked increase in cementum formation on the root surfaces of fully developed teeth of these mutant mice was noted. Examination of ank mutant mice at earlier ages of tooth root formation indicated that this striking observation is apparent from the onset of cementogenesis. These findings suggest that cells within the periodontal region are highly responsive to changes in phosphate metabolism. This information may prove valuable in attempts to design successful therapies for regenerating periodontal tissues.

The putative collagen binding peptide hastens periodontal ligament cell attachment to bone replacement graft materials

BACKGROUND

Bone replacement graft (BRG) materials are often used to treat periodontal defects, to promote cellular invasion, and to encourage bone regrowth. Periodontal ligament fibroblasts (PDLF) incorporate these materials and form the basis of the renewed connection between the existing and newly formed alveolar bone and the tooth surface. A peptide (P-15) that mimics the putative cell-binding domain of collagen has been reported to promote dermal fibroblast attachment and proliferation.

METHODS

PDLF were quantitatively examined for their ability to adhere to a variety of BRG materials fluorometrically. In addition, scanning electron microscopy was used to examine the changes in morphology exhibited by these cells as they attached and spread on several BRG materials. Finally, BRG materials containing the P-15 peptide were quantitatively examined for their ability to promote PDLF attachment and proliferation.

RESULTS

Freeze-dried allograft bone supports greater PDLF attachment than does several xenograft and alloplastic anorganic bone replacement materials. An anorganic BRG material containing the P-15 peptide promoted more rapid cell attachment and spreading than a similar anorganic BRG material lacking this peptide. Finally, none of the BRG materials examined promoted PDLF proliferation.

CONCLUSIONS

Our data indicate that the addition of the P-15 peptide increases the rapidity of PDLF attachment to xenogeneic bone replacement materials. This increase in the rate of attachment may have clinical significance in the context of the dynamic regulation of cell attachment during periodontal regeneration. However, this peptide does not promote an increase in stable cell attachment or proliferation in vitro.

Extracellular matrix molecules improve periodontal ligament cell adhesion to anorganic bone matrix

Bone replacement graft (BRG) materials are used in periodontal therapy to encourage new bone formation. Extracellular matrix proteins may improve periodontal ligament fibroblast (PDLF) attachment to these materials. We demonstrate that PDLFs adhere well to the extracellular matrix (ECM) proteins fibronectin, vitronectin, laminin, and collagen types I and IV. PDLFs express numerous ECM-receptor integrin subunit transcripts (alpha1, alpha2, alpha3, alpha4, alpha5, alpha11, beta1, beta5, and beta8) at high levels, while others (alpha6, alpha9, alphaV, beta3, beta6, and beta7) are expressed at reduced levels. Despite the fact that PDLFs adhere well to fibronectin and collagen type IV bound to plastic, and express integrins that recognize these ECM proteins, they do not attach well to anorganic bovine bone matrix (ABM) coated with these same proteins. However, the addition of vitronectin, laminin, or collagen type I to these same ABMs substantially increased PDL cell attachment. Thus, selective use of ECM proteins may be clinically useful in promoting cell attachment to ABM and bone regrowth.

A comparative study on the use of Bio-Oss and enamel matrix derivative (Emdogain) in the treatment of periodontal bone defects

The aim of the study was to evaluate the clinical and radiographic outcome following two different techniques of periodontal bone defects treatment. The study included 24 generally healthy subjects with advanced periodontitis. The patients were divided into two equal groups, according to the method applied. In the first group, a bovine-derived hydroxyapatite xenograft (Bio-Oss) combined with a resorbable collagen membrane (Bio-Gide) was used. The other group was treated with enamel matrix derivative (Emdogain). Clinical and radiographic examinations were performed prior to and 1 yr after surgery. The following parameters were evaluated: plaque index, gingival index, probing pocket depth, clinical attachment level, gingival recession, radiographic defect depth, and defect width. All clinical and radiographic parameters (except plaque index and gingival recession) were significantly reduced after treatment in both groups. No differences were revealed between the two groups of patients in examined parameters after treatment. The results demonstrated that the treatment of periodontal bone defects with both techniques leads to similar and significant improvements in clinical and radiographic parameters.

The initial attachment of cemental fibrils to the root dentin surface in acellular and cellular cementogenesis in rat molars

To elucidate the initial attachment mechanism of cemental fibrils to the root dentin surface in acellular and cellular cementogenesis, developing rat molars were observed by light microscopy and scanning electron microscopy combined with NaOH maceration. The NaOH maceration was used to observe details of the positional association of cemental and dentinal fibrils during cementogenesis. An initial hematoxylin stained, cementum layer began to form on the root dentin surface with the first dentin mineralization in both acellular and cellular cementogenesis. The initial attachment of cemental fibrils to the dentin surface also began at this point. At the initial attachment the intermingling of cemental and dentinal fibrils occurred only in places. With advanced cementogenesis the initial cementum layer became the fibril-poor cemento-dentinal junction. This suggests that cemental fibrils attach on the initial cementum layer, and not directly on dentinal fibrils, so that the layer results in the fibril-poor cemento-dentinal junction. The present study suggests that an intervening adhesive is necessary for the cemento-dentinal attachment at any stage of cementogenesis in rat molars.

Enamel matrix derivative in the treatment of human intrabony osseous defects

BACKGROUND

There is limited information available from clinical trials regarding the performance of enamel matrix derivative (EMD) in the treatment of periodontal intrabony defects. This randomized, double-blind, placebo-controlled, split-mouth study was designed to compare the clinical and radiographical effects of EMD treatment to that of placebo-controlled treatment for intrabony defects.

METHODS

Sixteen patients were included, each of whom had 1 or 2 pairs of intrabony defects located contralaterally in the same arch. Thirty-six intrabony defects were randomly assigned treatment with flap surgery plus EMD or flap surgery plus placebo. At baseline and at the 12-month follow-up evaluation visit, clinical and radiographic measurements were determined. Data were statistically analyzed using the Wilcoxon-signed rank test (alpha = 0.05).

RESULTS

At the 12-month visit, bleeding on probing for the EMD group was 0.11 +/- 0.32 compared to the placebo group, 0.61 +/- 0.50 (P <0.05). Probing depth reduction was greater in the EMD group (3.00 +/- 0.97 mm) compared to the placebo group (2.22 +/- 0.81 mm) (P <0.05). Mean values for clinical attachment gain in the EMD and the placebo groups were 1.72 +/- 1.07 mm and 0.83 +/- 0.86 mm, respectively (P <0.05). Vertical relative attachment gain was 38.5 +/- 22.6% in the EMD group and 21.4 +/- 25.2% in the placebo group (P<0.05). Radiographic bone density gain was greater in the EMD (20.2 +/- 16.6%) compared to the placebo group (-3.94 +/- 23.3%) (P<0.01).

CONCLUSIONS

Treatment with flap surgery and EMD, compared to flap surgery with placebo, produced a significantly more favorable clinical improvement in intrabony periodontal defects.

The fibrillar structure of cementum and dentin at the cemento-dentinal junction in rat molars

The cemento-dentinal junction was examined in demineralized rat molars with complete roots by scanning electron microscopy combined with NaOH maceration. It is established that the NaOH maceration removes interfibrillar substances and cells from connective tissues selectively without structural damage to collagen fibrils. The cementum was detached from the dentin by the maceration. The inner cementum surface facing the dentin and the outer dentin surface facing the cementum were observed. In acellular cementum, both the outer dentin surface and the inner cementum surface had a smooth appearance. There was little indication of fibrils intermingling between dentin and cementum. In contrast, both the inner cementum surface and outer dentin surface in cellular cementum had an uneven appearance due to the irregular arrangement of collagen fibrils. Point-like protrusions of fibril bundles were observed on both surfaces. Some (not all) of these point-like protrusions appeared to correspond to places of fibrillar intermingling between dentin and cementum.

The structure of the cemento-dentinal junction in rat molars

The cemento-dentinal junction was observed in the acellular and cellular cementum of rat molars by light and scanning electron microscopy. Scanning electron microscopy, combined with NaOH maceration, was used to observe the fibrous architecture directly in this region. Light microscopy revealed that the cemento-dentinal junction contains fewer collagen fibrils and more proteoglycans than the cementum and dentin. Scanning electron microscopy also showed that fibril intermingling is found only in some regions of the fibril-poor junction in macerated specimens. Prolonged maceration breaks down the cemento-dentinal junction in spite of the fibril intermingling. Only macerated specimens showed detachment here. It was established that NaOH maceration removes interfibrillar substances effectively, and does not damage the fibril structure or architecture. This suggests that the adhesion of proteoglycans is more important than fibril intermingling for preserving the cemento-dentinal attachment in the rat molar.

Apoptosis in the early developing periodontium of rat molars

Development of the periodontium involves a series of complex steps that result in the formation of root dentine, cementum, bone and fibres of the ligament. These precisely controlled and timed events require the participation of the enamel organ derived epithelial cells of Hertwig's (HRS) and ectomesenchymal cells of the dental follicle. These events involve rapid turnover of the tissues and cells, including disappearance of epithelial cells of HRS. Thus, it seemed likely to us that programmed cell death (apoptosis) may play a role in the development of the periodontium. Fragments of first molars, obtained from 14- and 29-day-old rats, were fixed in glutaraldehyde-formaldehyde and processed for light and electron microscopy. For the TUNEL method for detection of apoptosis, specimens were fixed in 4% formaldehyde and embedded in paraffin. Results confirmed that epithelial cells of HRS maintain a close relationship with the forming dentine root, and that they may become trapped in the dentino-cemental junction. Some of the epithelial cells exhibited ultrastructural features which are consistent with the interpretation that they were undergoing programmed cell death, i.e. apoptosis. Periodontal fibroblast-like cells showed typical images of apoptosis and engulfed apoptotic bodies. TUNEL positive structures were present in all corresponding regions. It seems therefore that apoptosis of epithelial cells of HRS and fibroblast-like cells of the periodontal ligament constitutes an integral part of the developmental process of the tissues of the periodontium.

The structure and function of the cemento-dentinal junction in human teeth

The structure and function of the cemento-dentinal junction were studied in human molars by light and electron microscopy. The cemento-dentinal junction was an approximately 1-3-micron-thick layer full of proteoglycans with mucopolysaccharides but containing fewer collagen fibrils than the root dentin and cementum. In places, cemental fibrils crossed the cemento-dentinal junction. These fibrils appeared to intermingle with dentinal fibrils. By enzymatic treatment of decalcified specimen with hyaluronidase and trypsin, the cemento-dentinal junction decreased or lost staining affinity to toluidine blue. Prolonged treatment caused the separation of cementum from the root dentin during routine histological processes. These data suggest that the adhesion of proteoglycans is more important than the intermingling of dentinal and cemental fibrils for the cemento-dentinal attachment.

Characterization of cementum derived growth factor as an insulin-like growth factor-I like molecule

Cementum is the thin calcified outer layer through which tooth-root surfaces are anchored to soft periodontal connective tissues. A variety of growth factors and adhesion molecules are sequestered in the extracellular matrix of cementum, and we have purified and characterized one of the growth factors. This growth factor, the cementum derived growth factor (CGF), was purified from bovine cementum by acetic acid extraction followed by heparin affinity chromatography and HPLC using cation exchange, molecular sieve, and reverse-phase columns. NaDodSO4-polyacrylamide gel electrophoresis of purified CGF preparation revealed the presence of two major protein bands migrating with Mr 18,000-22,000 and 14,000-16,000. The latter was associated with the major part of the mitogenic activity. The activity of CGF was inhibited by antibodies to insulin-like growth factor-I (IGF-I) and IGF-I receptor. Both CGF and IGF-I were mitogenic to human gingival fibroblasts and alveolar bone cells, but the bone cells responded better to CGF than to IGF-I. The IGF-I did not bind to heparin-sepharose, while CGF bound to it and was eluted with 0.6M NaCl from heparin-sepharose columns. Heparin-sepharose 0.2M NaCl fractions of cementum extracts contained IGF-I migrating with Mr 7,500, but its mobility was not affected by N-glycosidase treatment. Western analysis using anti-IGF-I antibodies showed that CGF preparations contained cross-reacting species migrating with Mr 18,000-22,000, 14,000-16,000 and 11,000-12,000, however after treatment with N-glycosidase the Mr 18,000-22,000 component was absent. Internal amino acid sequences of six tryptic peptides of CGF were determined by microsequencing. The sequence of one 15-amino acid long peptide was the same as the receptor binding domain of IGF-I, and another 9-amino acid peptide had 78 % homology to a sequence derived from an untranslated region of sheep IGF-I exon 1. Four other peptides had no apparent homology with IGF-I. From these results we conclude that the CGF is an IGF-I like molecule.

On the dynamics of periodontal tissue formation in degree III furcation defects. An experimental study in dogs

The aim of the experiment was to describe the formation of periodontal tissues in degree III furcation defects following GTR therapy. The study was performed in 8 foxhound dogs. The 2nd and 4th premolars in both sides of the mandible were extracted. Furcation defects were produced in the 3rd mandibular premolars. 3 weeks later, reconstructive surgery was performed. The dogs were scheduled for sacrifice 2, 4, 8, and 20 weeks after GTR therapy. Tissue blocks containing the experimental teeth were excised, demineralized in EDTA and embedded in paraffin. Serial sections were cut in the mesio-distal plane and parallel with the long axis of the roots. The microtome was set at 7 microns. The sections were stained in hematoxyline and eosin. From each biopsy, 3 sections representing the central part of the furcation, were selected for light microscopic examination. In the healed furcation sites, descriptive histological analysis of the newly-formed tissues was performed and the relative proportions of the hard and soft tissues were determined. It was demonstrated that at 2 weeks, the furcation defect contained granulation tissue and cell-rich connective tissue, while at 4 weeks the furcation was mainly occupied by connective tissue. At 8 weeks, woven bone occupied the central portion of the furcation, whereas connective tissue and cementum were observed in the lateral portions. The furcation area at 20 weeks was comprised of newly-formed cementum, periodontal ligament and bone. The onset of cementum formation had started as early as 2 weeks after GTR therapy. The cementum formation apparently occurred in 3 phases: organisation of collagen fibers adjacent and perpendicular to the root surface (phase 1), assembly of the collagen fibers and deposition of matrix (phase 2), and addition of cells and collagen fibers organised parallel to the root surface (phase 3). Bone formation took place through a process that included (1) organisation of a fibrous connective tissue, (2) differentiation of this tissue into woven bone and, (3) maturation of the woven bone into lamellar bone and bone marrow.

Effects of hydroxyapatite particles on periodontal ligament fibroblast-like cell behavior

Although hydroxyapatite (HA), a synthetic calcium phosphate, is used in restoring bone defects associated with periodontal diseases, its specific effect on the periodontal ligament fibroblast population during the regeneration process is unclear. To determine the cellular events occurring in the presence of HA, human periodontal ligament fibroblasts (HPLF) were isolated and maintained in culture. The specificity of the cells was evidenced by their morphology, deposition of extracellular matrix components, and alkaline phosphatase (ALP) activity (as a marker of osteoblastic differentiation of HPLF). Phase-contrast investigations revealed morphological alterations of cells in contact with HA particles. Transmission electron microscopy demonstrated the phagocytotic process of HPLF toward HA particles. Moreover, the presence of HA particles was significantly related to an increase in the protein synthesis activity and a decrease in the proliferation and ALP-specific activity of HPLF. These results provide new information on the phenotypic expression of HPLF, which is comparable to that of osteoblastic cells. A subpopulation of HPLF may be influenced by the presence of HA to undergo transient dedifferentiation prior to redifferentiating into osteoblasts. This process may be important as a means by which HA acts as an osteoconductive material. This experimental study improves our understanding of the cellular processes which occur during healing and regeneration of periodontal defects after implantation of biomaterials.

Expression of bone associated markers by tooth root lining cells, in situ and in vitro

Periodontal disease is marked by inflammation and subsequent loss and/or damage to tooth-supporting tissues including bone, cementum, and periodontal ligament. A key tissue in the initial process of periodontal development as well as regeneration following periodontal disease is cementum. Research efforts aimed toward understanding mechanisms involved in periodontal development and regeneration, and in particular the formation of root cementum, have been hampered by an inability to isolate and culture cells involved in cementum production (i.e., cementoblasts). Much has been learned regarding the processes and mechanisms involved in bone formation and function from experiments using bone cell cultures. Therefore, the purpose of this study was to develop a strategy whereby cementoblasts could be isolated, cultured, and characterized. As a first step, using in situ hybridization, we determined the timed and spatial expression of mineral-associated proteins during first molar root development in CD-1 mice. These proteins included dentin sialoprotein (DSP), osteopontin (OPN), bone sialoprotein (BSP), osteocalcin (OCN), and type I collagen. During root development in mice BSP, OPN, and OCN mRNAs were expressed selectively by cells lining the tooth root surface--cementoblasts--with high levels of expression at day 41. Importantly, at this time point BSP, OPN, and OCN mRNAs were not expressed throughout the periodontal ligament. These findings provided us with markers selective to root-lining cells, or cementoblasts, in situ, and established the time (day 41) for isolating cells for in vitro studies. To isolate cells from tissues adherent to the root surface, enzymatic digestion was used, similar to what are now considered classical techniques for isolation of osteoblasts. To determine whether cells in vitro contained root-lining cells and cementoblasts, cultured cells were analyzed for expression of mineral-associated proteins. Cells within this heterogeneous primary population expressed type I collagen, BSP, OPN, and OCN as determined by in situ hybridization. In contrast, cells within this population did not express dentin sialoprotein, an odontoblast-specific protein. These procedures have provided a means to obtain root-lining cells in vitro that can now be cloned and used for studies directed at determining the properties of root-lining cells, or cementoblasts, in vitro.

Age-related changes of the cementogenesis in the senescence-accelerated mouse (SAM)

Cementogenesis of the molars with aging was studied using senescence accelerated mouse (SAM) which included SAMP2/Iw and SAMP8@Iw as prone strains, and SAMR1/Iw as a resistant strain. Morphometric analysis was done for the cementum thickness at 2, 6, 12 and 16 months of age on 4 parts of the mice, i.e. at the mesial (M), the distal (D), the apical (A) and the furcational (F) cementum of the maxillary first molar. SAMR1/Iw was also studied at 20 months of age. Mean cementum thickness was statistically analyzed for age and strain differences. Mean thicknesses of the M and the D cementum in SAMP2/Iw and in SAMP8@Iw were usually higher than those in SAMR1/Iw. Furthermore, there were significant differences between SAMP2/Iw and SAMR1/Iw, and between SAMP8/Iw and SAMR1/Iw, both at 12 and 16 months of age. There was no difference in mean thickness in the F cementum in either strain and at any age. In the A cementum, SAMP2/Iw displayed significantly thicker cementum than SAMR1/Iw at 6, 12 and 16 months of age. The degree of molar eruption was thought to be more accelerated in SAMP2/Iw than in SAMR1/Iw. However, the thickness of the A cementum was not different for SAMP8@Iw and SAMR1/Iw in any age group. In this study, 2 conclusions were drawn as follows: first, that SAMP2/Iw and SAMP8@Iw exhibited more accelerated cementogenesis than SAMR1/Iw in the M and the D cementum. Secondly, several factors such as intrinsic factors, occlusal forces and degree of attrition affected the cementogenesis of the M and the D, the F and the A cementum, respectively.

Cementogenesis reviewed: a comparison between human premolars and rodent molars

BACKGROUND

Cementum continues to be the least-known mineralized tissue. Although recent advances in the field of molecular biology have contributed to an understanding of the involvement of molecular factors in cementum formation during development and regeneration, cementogenesis on a cell biological basis is still poorly understood. Virtually nothing is known about cementoblast origin, differentiation, and the cell dynamics during normal development, repair, and regeneration. This review describes the recent findings of cementogenesis on roots of human premolars and opposes them to those of teeth from other mammals, particularly the rodent molar.

METHODS

Using light and electron microscopy, light microscopic radioautography, and various measurements, a comprehensive insight into the development and repair of cementum during and after root formation and tooth eruption has been achieved for human premolars.

RESULTS

Cementum is a highly responsive mineralized tissue. This biological activity is necessary for root integrity and for bringing and maintaining the tooth in its proper position. With regard to cementum formation and periodontal fiber attachment, considerable species-particularities exist that are mainly based on differences in growth rates and tooth sizes. Since root development and initial cementogenesis last on the average 5-7 years in human premolars, cementum formation in these teeth is characterized by along-lasting phase of prefunctional development, with occurs independent of principal periodontal fiber attachment to the root and which may take 5 years or more. The first molar of the rat, however, is in functional occlusion 3 1/2 weeks after the onset of root formation. Since initial cementum formation and periodontal fiber attachment to the root occur almost at the same time in this tooth, the distinction between cells associated with one or the other process is very difficult to achieve, and cementogenesis cannot be described independent of periodontal fiber attachment to the root. Therefore, the determination of cementoblast origin in the rodent molar may be intricate.

CONCLUSIONS

Taking into account these species differences, the current description on the origin and differentiation of cementoblasts is inconsistent and the description of cementogenesis is still incomplete. This review calls into question the currently held concept of cementogenesis and offers a possible alternative.