Structure, chemical composition and mechanical properties of coronal cementum in human deciduous molars

OBJECTIVES

It was hypothesized that the coronal cementum containing collagen forms a weak junction with enamel unlike the well integrated DEJ and CDJ.

METHODS

The hypothesis was investigated in two parts: (1) evaluate the structure, chemical composition and mechanical properties of coronal cementum and its junction with enamel using scanning electron microscopy, micro-X-ray computed tomography, and atomic force microscopy. The chemical composition and mechanical properties were determined by evaluating the spatial variations of inorganic (PO(4)(3-)nu(1) mode at 960 cm(-1)) and organic (C-H deformation at 1452 cm(-1); C-H stretch at 2940 cm(-1)) contents using Raman microspectroscopy and elastic modulus and hardness values using nanoindentation. (2) Estimate the strength and evaluate the microstructure of coronal cementum interface with enamel using SEM and MicroXCT.

RESULTS AND CONCLUSIONS

Coronal cementum is heterogeneous because it is a combination of laminar acellular afibrillar cementum and acellular extrinsic fiber cementum with relatively higher organic content. It integrates micromechanically via a scallop-like weak interface with enamel unlike the biomechanically efficient DEJ and CDJ and is continuous with primary root cementum. A single tooth could exhibit all three types of cementum enamel junctions; an overlap, butt and a gap depending on the sectioning plane. The elastic modulus of coronal cementum (11.0+/-5.8 GPa) is significantly lower (p<0.05; Student's t-test with 95% confidence interval) than primary cementum (15.8+/-5.3 GPa).

Evaluation of human recession defects treated with coronally advanced flaps and either purified recombinant human platelet-derived growth factor-BB with beta tricalcium phosphate or connective tissue: a histologic and microcomputed tomographic examination

The current study examined the histologic and microcomputed tomographic (micro CT) outcomes of the treatment of gingival recession defects with either a subepithelial connective tissue graft (CTG) or 0.3 mg/mL recombinant human platelet-derived growth factor (rhPDGF-BB) on a beta tricalcium phosphate (beta-TCP) matrix. Gingival recession defects were surgically created in six premolar teeth with no more than 3 mm of keratinized marginal tissue, an osseous crest 2 to 3 mm apical to the newly created gingival margin, and recession depth of at least 3 mm. The defects were left untouched for 2 months; then, four defects were grafted with rhPDGF-BB + beta-TCP + a wound healing dressing, and two defects received CTGs. A coronally advanced flap covered each grafted site. Nine months later, sections were obtained for examination. All four sites treated with rhPDGF-BB + beta-TCP showed connective tissue fibers (Sharpey fibers) perpendicularly inserting into newly formed cementum and alveolar bone. In the two sites treated with CTGs, a long junctional epithelium was seen coronal to the osseous crest and connective tissue fibers ran parallel to the adjacent root surfaces, with no evidence of insertion into cementum or bone. There was no evidence of regeneration of cementum, inserting connective tissue fibers, or supporting alveolar bone. Regeneration of the periodontium in gingival recession defects is possible through growth factor-mediated therapy.

Histologic evaluation of an Nd:YAG laser-assisted new attachment procedure in humans

This report presents histologic results in humans following a laser-assisted new attachment procedure (LANAP) for the treatment of periodontal pockets. Six pairs of single-rooted teeth with moderate to advanced chronic periodontitis associated with subgingival calculus deposits were treated. A bur notch was placed within the pocket at the clinically and radiographically measured apical extent of calculus. All teeth were scaled and root planed with ultrasonic and hand scalers. One of each pair of teeth received treatment of the inner pocket wall with a free-running pulsed neodymium:yttrium-aluminum-garnet (Nd:YAG) laser to remove the pocket epithelium, and the test pockets were lased a second time to seal the pocket. After 3 months, all treated teeth were removed en bloc for histologic processing. LANAP-treated teeth exhibited greater probing depth reductions and clinical probing attachment level gains than the control teeth. All LANAP-treated specimens showed new cementum and new connective tissue attachment in and occasionally coronal to the notch, whereas five of the six control teeth had a long junctional epithelium with no evidence of new attachment or regeneration. There was no evidence of any adverse histologic changes around the LANAP specimens. These cases support the concept that LANAP can be associated with cementum-mediated new connective tissue attachment and apparent periodontal regeneration of diseased root surfaces in humans.

The tooth attachment mechanism defined by structure, chemical composition and mechanical properties of collagen fibers in the periodontium

In this study, a comparison between structure, chemical composition and mechanical properties of collagen fibers at three regions within a human periodontium, has enabled us to define a novel tooth attachment mechanism. The three regions include, (1) the enthesis region: insertion site of periodontal ligament (PDL) fibers (collagen fibers) into cementum at the root surface, (2) bulk cementum, and (3) the cementum-dentin junction (CDJ). Structurally, continuity in collagen fibers was observed from the enthesis, through bulk cementum and CDJ. At the CDJ the collagen fibers split into individual collagen fibrils and intermingled with the extracellular matrix of mantle dentin. Under wet conditions, the collagen fibers at the three regions exhibited significant swelling suggesting a composition rich in polyanionic molecules such as glycosaminoglycans. Additionally, site-specific indentation illustrated a comparable elastic modulus between collagen fibers at the enthesis (1-3 GPa) and the CDJ (2-4 GPa). However, the elastic modulus of collagen fibers within bulk cementum was higher (4-7 GPa) suggesting presence of extrafibrillar mineral. It is known that the tooth forms a fibrous joint with the alveolar bone, which is termed a gomphosis. Although narrower in width than the PDL space, the hygroscopic CDJ can also be termed as a gomphosis; a fibrous joint between cementum and root dentin capable of accommodating functional loads similar to that between cementum and alveolar bone. From an engineering perspective, it is proposed that a tooth contains two fibrous joints that accommodate the masticatory cyclic loads. These joints are defined by the attachment of dissimilar materials via graded stiffness interfaces, such as: (1) alveolar bone attached to cementum with the PDL; and (2) cementum to root dentin with the CDJ. Thus, through variations in concentrations of basic constituents, distinct regions with characteristic structures and graded properties allow for attachment and the load bearing characteristics of a tooth.

Human dental follicle cells acquire cementoblast features under stimulation by BMP-2/-7 and enamel matrix derivatives (EMD) in vitro

The dental follicle (DF) surrounding the developing tooth germ is an ectomesenchymal tissue composed of various cell populations derived from the cranial neural crest. Human dental follicle cells (HDFC) are believed to contain precursor cells for cementoblasts, periodontal ligament cells, and osteoblasts. Bone morphogenetic proteins (BMPs) produced by Hertwig's epithelial root sheath or present in enamel matrix derivatives (EMD) seem to be involved in the control of DF cell differentiation, but their precise function remains largely unknown. We report the immunolocalization of STRO-1 (a marker of multipotential mesenchymal progenitor cells) and BMP receptors (BMPR) in DF in vivo. In culture, HDFC co-express STRO-1/BMPR and exhibit multilineage properties. Incubation with rhBMP-2 and rhBMP-7 or EMD for 24 h increases the expression of BMP-2 and BMP-7 by HDFC. Long-term stimulation of these cells by rhBMP-2 and/or rhBMP-7 or EMD significantly increases alkaline phosphatase activity (AP) and mineralization. Expression of cementum attachment protein (CAP) and cementum protein-23 (CP-23), two putative cementoblast markers, has been detected in EMD-stimulated whole DF and in cultured HDFC stimulated with EMD or BMP-2 and BMP-7. RhNoggin, a BMP antagonist, abolishes AP activity, mineralization, and CAP/CP-23 expression in HDFC cultures and the expression of BMP-2 and BMP-7 induced by EMD. Phosphorylation of Smad-1 and MAPK is stimulated by EMD or rhBMP-2. However, rhNoggin blocks only Smad-1 phosphorylation under these conditions. Thus, EMD may activate HDFC toward the cementoblastic phenotype, an effect mainly (but not exclusively) involving both exogenous and endogenous BMP-dependent pathways.

Effect of two different approaches for root decontamination on new cementum formation following guided tissue regeneration: a histomorphometric study in dogs

BACKGROUND AND OBJECTIVE

The aim of the present study was to evaluate comparatively the effect of two different approaches for root decontamination on new cementum formation following guided tissue regeneration (GTR).

MATERIAL AND METHODS

Nine mongrel dogs were used to obtain bilateral chronic class III furcation defects by placing cotton ligatures around both third mandibular premolars. The teeth were randomly assigned to receive one of the following treatments: scaling and root planing, by means of hand and rotatory instruments, in order to remove soft and hard deposits as well as all root cementum (group A); or removal of only soft microbial deposits, by polishing the root surface with rubber cups and polishing paste, aiming for maximum root cementum preservation (group B). Both groups were treated with GTR, with the use of resorbable polyglycolic-lactic acid membranes (RESOLUT XT).

RESULTS

Four months later, data analysis showed that a superior length (mm) (3.59 +/- 1.67 and 6.20 +/- 2.26 for groups A and B, respectively; p = 0.004) and a thicker layer (microm) (18.89 +/- 9.47 and 52.29 +/- 22.48 for groups A and B, respectively; p = 0.001) of new cementum was achieved by keeping the root cementum in place during root decontamination (group B). Regardless of the treatment modality, the new cementum was predominantly of a reparative, cellular extrinsic and intrinsic fiber type.

CONCLUSION

Within the limits of the present study, it may be concluded that root cementum preservation may affect the new cementum formation following GTR in class III furcation defects, and the treatment modality did not influence the type of newly formed cementum.

Advances in defining regulators of cementum development and periodontal regeneration

Substantial advancements have been made in defining the cells and molecular signals that guide tooth crown morphogenesis and development. As a result, very encouraging progress has been made in regenerating crown tissues by using dental stem cells and recombining epithelial and mesenchymal tissues of specific developmental ages. To date, attempts to regenerate a complete tooth, including the critical periodontal tissues of the tooth root, have not been successful. This may be in part due to a lesser degree of understanding of the events leading to the initiation and development of root and periodontal tissues. Controversies still exist regarding the formation of periodontal tissues, including the origins and contributions of cells, the cues that direct root development, and the potential of these factors to direct regeneration of periodontal tissues when they are lost to disease. In recent years, great strides have been made in beginning to identify and characterize factors contributing to formation of the root and surrounding tissues, that is, cementum, periodontal ligament, and alveolar bone. This review focuses on the most exciting and important developments over the last 5 years toward defining the regulators of tooth root and periodontal tissue development, with special focus on cementogenesis and the potential for applying this knowledge toward developing regenerative therapies. Cells, genes, and proteins regulating root development are reviewed in a question-answer format in order to highlight areas of progress as well as areas of remaining uncertainty that warrant further study.

Extracellular matrix-mediated tissue remodeling following axial movement of teeth

Tooth eruption is a multifactorial process involving movement of existing tissues and formation of new tissues coordinated by a complex set of genetic events. We have used the model of the unopposed rodent molar to study morphological and genetic mechanisms involved in axial movement of teeth. Following extraction of opposing upper molars, lower molars supererupted by 0.13 mm. Labeled tissue sections revealed significant amounts of new bone and cementum apposition at the root apex of the unopposed side following supereruption for 12 days. Newly apposited cementum and alveolar bone layers were approximately 3-fold thicker in the experimental vs the control group, whereas periodontal ligament width was maintained. Tartrate-resistant acid phosphatase staining indicated bone resorption at the mesial alveolar walls of unopposed molars and provided in tandem with new bone formation at the distal alveolar walls an explanation for the distal drift of molars in this model. Microarray analysis and semiquantitative RT-PCR demonstrated a significant increase in collagen I, integrin beta5, and SPARC gene expression as revealed by comparison between the unopposed molar group and the control group. Immunohistochemical verification revealed increased levels of integrin beta5 and SPARC labeling in the periodontal ligament of the unopposed molar. Together our findings suggest that posteruptive axial movement of teeth was accomplished by significant formation of new root cementum and alveolar bone at the root apex in tandem with upregulation of collagen I, integrin beta5, and SPARC gene expression.

Amelogenin-mediated regulation of osteoclastogenesis, and periodontal cell proliferation and migration

We previously reported that amelogenin isoforms M180 and leucine-rich amelogenin peptide (LRAP) are expressed in the periodontal region, and that their absence is associated with increased cementum defects in amelogenin-knockout (KO) mice. The aim of the present study was to characterize the functions of these isoforms in osteoclastogenesis and in the proliferation and migration of cementoblast/periodontal ligament cells. The co-cultures of wild-type (WT) osteoclast progenitor and KO cementoblast/periodontal ligament cells displayed more tartrate-resistant acid phosphatase (TRAP)-positive cells than the co-cultures of WT cells. The addition of LRAP to both co-cultures significantly reduced RANKL expression and the TRAP-positive cells. Proliferation and migration rates of the KO cementoblast/periodontal ligament cells were lower than those of WT cells and increased with the addition of either LRAP or P172 (a porcine homolog of mouse M180). Thus, we demonstrate the regulation of osteoclastogenesis by LRAP, and the proliferation and migration of cementoblast/periodontal ligament cells by LRAP and P172.

Part one: The restoration of non-vital teeth: structural, biological, and micromechanical issues in maintaining tooth longevity

This manuscript will review research from 1967 to the present to find the best evidence for the reconstruction of non-vital teeth. The paper will review the contention that non-vital teeth are "more brittle" by analyzing the relevant physical properties of vital versus non-vital teeth; describe the structures of the tooth used to manage stress and strain; describe the formation of dentinal cracks and propagation of fracture planes through dentin; and analyze forces placed on human teeth and their effects on the tooth in Part One. In Part Two, the paper will describe the strength of various dowel and core designs relative to strength, retention, and durability and describe the results of testing various dentin bonding materials in strength and retention of dowels in non-vital teeth. The review will conclude with recommendations as to the materials and techniques in specific clinical situations best capable of single tooth reconstruction to ensure tooth longevity together with the scientific basis for their adoption.

An immunohistochemical study of the attachment mechanisms in different kinds of adhesive interfaces in teeth and alveolar bone of the rat

BACKGROUND AND OBJECTIVE

This study was designed to examine the histological and immunohistochemical nature of different kinds of adhesive interfaces in the rat molar region under identical experimental conditions and to discuss the structural and functional similarities between these adhesive interfaces.

MATERIAL AND METHODS

Four kinds of adhesive interfaces - an initial attachment layer for principal fibers on the developing alveolar bone surface, a reattachment layer for principal fibers on resorbed alveolar bone surface, cement lines on the alveolar bone surface unrelated to the principal fibers, and the cemento-dentinal junction - were examined in 25-d-old male Wistar rats. Routine histological staining, immunohistochemical staining for bone sialoprotein and osteopontin, and digestion tests with trypsin were conducted.

RESULTS

The adhesive interfaces showed very similar histological and immunohistochemical features: they were intensely hematoxylin-stainable, deficient in collagen fibrils, and rich in bone sialoprotein and osteopontin. After trypsin treatment the four adhesive interfaces had lost immunoreactivity to bone sialoprotein and osteopontin, and the two adjacent tissue parts held together finally separated at the adhesive interfaces.

CONCLUSION

The above findings suggest that (i) the different types of adhesive interfaces in the rat molar region have a common structure in that they are filled with highly accumulated bone sialoprotein and osteopontin and deficient in collagen fibrils; (ii) accumulated bone sialoprotein and osteopontin are closely associated with the adhesion at the interfaces; and (iii) the adhesive interfaces have a similar developmental process.

Root Cementum Modulates Periodontal Regeneration in Class III Furcation Defects Treated by the Guided Tissue Regeneration Technique: A Histometric Study in Dogs

BACKGROUND

Because the possibility of root cementum preservation as an alternative approach for the treatment of periodontal disease has been demonstrated, this study aimed to histometrically evaluate the effect of root cementum on periodontal regeneration.

METHODS

Bilateral Class III furcation defects were created in dogs, and each dog was randomly assigned to receive one of the following treatments: control (group A): scaling and root planing with the removal of root cementum; or test (group B): removal of soft microbial deposits by polishing the root surface with rubber cups and polishing paste, aiming at maximum cementum preservation. Guided tissue regeneration (GTR) was applied to both groups.

RESULTS

Four months after treatment, a superior length of new cementum (3.59 +/- 1.67 mm versus 6.20 +/- 2.26 mm; P = 0.008) and new bone (1.86 +/- 1.76 mm versus 4.62 +/- 3.01 mm; P = 0.002) and less soft tissue along the root surface (2.77 +/- 0.79 mm versus 1.10 +/- 1.48 mm; P = 0.020) was observed for group B. Additionally, group B presented a larger area of new bone (P = 0.004) and a smaller area of soft tissue (P = 0.008).

CONCLUSION

Within the limits of this study, root cementum may modulate the healing pattern obtained by guided tissue regeneration in Class III furcation defects.

A resin-modified glass ionomer cement barrier for treating degree II furcation defects: a pilot study in dogs

OBJECTIVE

The aim of this study was to evaluate in an animal model the healing of degree II furcation defects treated with: an experimental barrier of resin-modified glass-ionomer cement (GIC), a polylactic acid barrier (GUI), and flap surgery (CTR).

MATERIAL AND METHODS

In 3 beagles, 18 class II furcation defects were surgically produced in mandibular and maxillary premolars and exposed to plaque accumulation for 21 days. Following a full flap, notches were made at the base to the bone defect. GIC barriers were prepared immediately before use from a commercial product and fit to place with the same product. The GIC barriers were removed after 30 days and the dogs euthanized after 120 days. Histologic sections were analyzed in a computer-assisted microscope. Epithelium, new cementum with inserting fibers, and connective tissue lining the root surface in-between notches were measured and medians of percentage values calculated.

RESULTS

In the GIC, epithelium constituted 3.5% (median values) of the notch-to-notch root area; new cementum was 83.6% and connective tissue 12.9%. These values were 0%, 73.6%, and 26.4% for the GUI group and 35.6%, 43.2%, and 0% for the CTR group. Bone fill median values were 54.3% for GIC, 20.6% for GUI, and 24.6% for CTR.

CONCLUSION

GIC and GUI prevented epithelial migration and promoted the formation of new periodontal tissues in experimentally induced class II furcation defects in dogs.

[Effects of enamel matrix protein on the growth of human periodontal ligament cells on root cementum surfaces]

OBJECTIVE

To evaluate the effect of enamel matrix protein (EMP) on the attachment and proliferation of periodontal ligament cells (PDLC) on diseased cementum surfaces in vitro.

METHODS

Cementum chips were obtained from diseased roots exposed to periodontal pocket. Thirteen diseased root cementum chips were conditioned with EMP. Meanwhile, 13 diseased and 13 healthy cementum chips were treated with physiological saline as control. The growth and morphology of PDLC on the root surface were observed after 24 hours incubation by scanning electron microscope (SEM). PDLC attachment and proliferation were quantified using MTT assay at 16 or 72 hours.

RESULTS

The cells on EMP treated roots under SEM were growing robust like the cells on healthy roots. By contrast, the diseased cementum surface without conditioned with EMP was only partly covered with spindle-shaped cells, with filopodia appearing short and thin. MTT assay indicated that the number of adhered and proliferated cells on diseased cementum chips treated with EMP was significantly greater than that on diseased chips treated with saline (adhesion: 0.45 +/- 0.03 vs. 0.37 +/- 0.05, P < 0.05; proliferation: 0.71 +/- 0.02 vs. 0.55 +/- 0.08, P < 0.01), but less than that on healthy chips (adhesion: 0.45 +/- 0.03 vs. 0.67 +/- 0.08, P < 0.05; proliferation: 0.71 +/- 0.02 vs. 1.05 +/- 0.09, P < 0.05).

CONCLUSIONS

It was suggested that EMP could promote the growth of PDLC on the diseased root cementum surface.

Regulation of cementoblast gene expression by inorganic phosphate in vitro

Examination of mutant and knockout phenotypes with altered phosphate/pyrophosphate distribution has demonstrated that cementum, the mineralized tissue that sheathes the tooth root, is very sensitive to local levels of phosphate and pyrophosphate. The aim of this study was to examine the potential regulation of cementoblast cell behavior by inorganic phosphate (P(i)). Immortalized murine cementoblasts were treated with P(i) in vitro, and effects on gene expression (by quantitative real-time reverse-transcriptase polymerase chain reaction [RT-PCR]) and cell proliferation (by hemacytometer count) were observed. Dose-response (0.1-10 mM) and time-course (1-48 hours) assays were performed, as well as studies including the Na-P(i) uptake inhibitor phosphonoformic acid. Real-time RT-PCR indicated regulation by phosphate of several genes associated with differentiation/mineralization. A dose of 5 mM P(i) upregulated genes including the SIBLING family genes osteopontin (Opn, >300% of control) and dentin matrix protein-1 (Dmp-1, >3,000% of control). Another SIBLING family member, bone sialoprotein (Bsp), was downregulated, as were osteocalcin (Ocn) and type I collagen (Col1). Time-course experiments indicated that these genes responded within 6-24 hours. Time-course experiments also indicated rapid regulation (by 6 hours) of genes concerned with phosphate/pyrophosphate homeostasis, including the mouse progressive ankylosis gene (Ank), plasma cell membrane glycoprotein-1 (Pc-1), tissue nonspecific alkaline phosphatase (Tnap), and the Pit1 Na-P(i) cotransporter. Phosphate effects on cementoblasts were further shown to be uptake-dependent and proliferation-independent. These data suggest regulation by phosphate of multiple genes in cementoblasts in vitro. During formation, phosphate and pyrophosphate may be important regulators of cementoblast functions including maturation and regulation of matrix mineralization.

Influence of Orthodontic Dental Movement on the Healing Process of Teeth With Periapical Lesions

The purpose of this study was to histomorphologically evaluate (in dog's teeth) the influence of tooth movement in the healing of chronic periapical lesions. Thirty roots of incisors and premolars of two dogs (1-year-old) were used in this research. After pulpectomy, the root canals remained exposed to the oral environment for 6 months for achievement of periapical lesions. Twenty root canals were biomechanically prepared and received a calcium hydroxide dressing for 14 days before being filled with gutta-percha points and Sealapex sealer. After root canal treatment, some incisors were submitted to orthodontic movement, whereas the other roots remained without orthodontic movement. The orthodontic appliance was removed at 5 months and 15 days after treatment, the dogs were killed 15 days later and the specimens were prepared for histomorphological analysis. The results showed that the orthodontic movement delayed, but did not hinder, the periapical healing process.

Observations on healing following endodontic surgery in nonhuman primates (Macaca fascicularis): Effects of rhBMP-2

OBJECTIVES

The potential of recombinant human bone morphogenetic protein-2 (rhBMP-2) to enhance bone healing following endodontic surgery was tested. The pattern and timing of de novo bone formation and cementum regeneration, and the potential for root resorption and ankylosis to accompany bone formation were evaluated.

STUDY DESIGN

Pulpal infections were induced in maxillary and mandibular incisor teeth in young adult Cynomolgus monkeys. The teeth received conventional endodontic treatment immediately followed by surgical root resection. In a randomized split-mouth design, contralateral apical bone defects received rhBMP-2 in absorbable collagen sponge (ACS) carrier or served as sham-surgery controls to provide histological and radiographic evaluations following 1 (mandibular incisors) and 4.5 (maxillary incisors) month(s) postsurgery.

RESULTS

At 1 month postsurgery trabecular bone filled the apical bone defects. The newly formed bone appeared considerably more mature and had assumed characteristics of the contiguous resident bone at 4.5 months postsurgery. The resected root tips were almost completely covered by new cementum with a maturing functionally oriented periodontal ligament. Localized inflammatory infiltrates were associated with the filled root canals and extruded root-filling material. Root resorption and ankylosis were not observed. There were no apparent differences in healing patterns between sites implanted with rhBMP-2/ACS and those serving as sham-surgery controls.

CONCLUSIONS

Under conditions where the influence of infectious elements and irritation caused by root filling material are minimized, bone formation and cementum regeneration appears rapid following endodontic surgery. rhBMP-2/ACS did not offer an obvious benefit above and beyond that of the native osteogenic potential in this animal model.

Physical properties of human premolar cementum: hardness and elasticity

AIMS

To determine if the cementum on the maxillary right and left first premolars has identical physical properties.

METHODS

Ten normal maxillary first premolar teeth, extracted from five orthodontic patients with a mean age of 14.0 years, were used. The teeth had not been subjected to an orthodontic force. The hardness and elastic modulus of the cementum were measured on the buccal and lingual surfaces of the roots at three locations: cervical third, middle third and apical third.

RESULTS

There were no significant side-to-side differences in cementum hardness (Mean side-to-side difference: 0.0063 GPa; SD: 0.0279; p = 0.525) or elastic modulus (Mean side-to-side difference: -0.027 GPa; SD: 0.111; p = 0.814). The hardness and elastic modulus of the cementum decreased from cervical to apical regions on both root surfaces.

CONCLUSIONS

Similar physical properties of the cementum on the maxillary right and left first premolars suggest that intra-arch comparisons can be used to investigate root resorption caused by orthodontic forces.

Enamel matrix proteins associated with GTR and bioactive glass in the treatment of class III furcation in dogs

This study investigated, both histologically and histometrically, the efficacy of enamel matrix derived proteins (EMD) associated with bioactive glass (BG) and an absorbable membrane in the treatment of class III furcation defects in mongrel dogs. After surgical defect creation and chronification, the lesions were randomly divided into three groups according to the treatment employed: Test Group 1 - EMD + BG + membrane, Test Group 2 - EMD + membrane and Control Group - BG + membrane. After a 90-day healing period, the dogs were sacrificed. The descriptive analysis and the histometric data showed similar results for the experimental groups in all studied parameters (MANOVA, p > 0.05). The association of Emdogain® with bioglass and GTR, or with GTR only, showed similar results when compared with the ones obtained with bioglass associated with membrane in the treatment of class III furcation defects in dogs. The three modalities of treatment showed partial filling of the furcations, with bone and cementum regeneration limited to the apical portion of the defects.

Periodontal wound healing following GTR therapy of dehiscence-type defects in the monkey: short-, medium- and long-term healing

OBJECTIVE

To describe periodontal wound healing in dehiscence-type defects following guided tissue re-generation (GTR) therapy.

METHODS

Ten adult Macaca fascicularis monkeys were used. Buccal dehiscence-type defects were created at the maxillary second pre-molars and second molars. After 3 months, GTR surgery was performed. The animals were euthanized at 6 weeks, 6 months and 2 years after surgery. Block biopsies were harvested, and prepared for histological analysis.

RESULTS

A new attachment apparatus was structured already after 6 weeks of healing. A 10-20 microm thin layer of acellular extrinsic fibre cementum (AEFC) had formed along the instrumented root surface. At 6 months, the thickness of the supracrestal cementum was comparable with that at 6 weeks, while the thickness of the subcrestal cementum had increased to 40-60 microm. In this zone, the cementum consisted of an inner layer of AEFC attached to the circum-pulpal dentin and an outer layer of cellular mixed fibre cementum (CMFC). The numerical extrinsic fibre density was twice that at 6 weeks. At 2 years, the periodontal tissues resembled the pristine periodontium.

CONCLUSION

Periodontal healing following GTR therapy of recession-type defects will result in a restitutio ad integrum, i.e. healing by re-generation. A continuous maturation process occurs over at least 2 years.

Bioactive glass efficacy in the periodontal healing of intrabony defects in monkeys

The purpose of this study was the histomorphologic analysis of the efficacy of bioactive glass particles with a narrow size range (Biogran) in the periodontal healing of 2-wall intrabony defects in monkeys. The 2-wall defects were made in the mesial area of the left and right second premolars of four monkeys, filled with gutta-percha and, after 15 days, they were debrided and either naturally filled with coagulum (control) or implanted with bioactive glass (test). In the control sites, the junctional epithelium migrated up to the base of the defect. The presence of newly formed cementum was more significant in the test defects. Both control and test sites showed newly formed bone at the base of the defect. The test defects presented foci of newly formed bone around and within the glass particles localized in the middle third, distant from the defect walls. Histologic analysis showed that the 300- to 355-microm bioactive glass particles aided new periodontal insertion. In conclusion, the tested bioactive glass had better healing potential than debridement only. The graft material showed a promising inhibition of apical migration of the junctional epithelium and greater cementum deposition on the radicular surface of the intrabony defects. The replacement of bioactive glass particles by new bone occurred due not only to an osteoconductive property, but also to an osteostimulatory capacity. Future investigations should evaluate this potential comparatively or together with other grafting materials, regenerative techniques and biological modifiers, as well as assess the longitudinal stability of the new attachment.

Formation and resolution of ankylosis under application of recombinant human bone morphogenetic protein-2 (rhBMP-2) to class III furcation defects in cats

OBJECTIVES

Periodontal regeneration under application of bone morphogenetic protein (BMP) is compromised by ankylosis. Ankylosis disappearance following application of BMP has been observed in the case of a small defect, which might be beneficial change for periodontal regeneration. However, the histological observation of ankylosis disappearance has not been demonstrated in a large defect. The purpose of this present study was to confirm resolution of ankylosis during periodontal regeneration by recombinant human BMP-2 (rhBMP-2) applied to class III furcation defects.

MATERIAL AND METHODS

Class III furcation defects were created in the premolars of six adult cats. The rhBMP-2 material, prepared by applying rhBMP-2 to a combination of polylactic acid-polygricolic copolymer and gelatin sponge (PGS; 0.33 microg rhBMP-2/mm(3) PGS) or control material containing only PGS, was implanted into each defect. The cats were killed at 3, 6 or 12 weeks after surgery and serial sections were prepared for histological and histometrical observation.

RESULTS

Ankylosis was observed in some of the rhBMP-2/PGS group at 3 and 6 weeks, but not at 12 weeks. At 6 weeks, osteoclast-like cells were visible in the rhBMP-2/PGS group with ankylosis. Residual PGS was evident between the bone and root surface in the rhBMP-2/PGS group without ankylosis at 3 weeks.

CONCLUSIONS

Resolution of ankylosis by osteoclast-like cells possibly occurred under application of rhBMP-2. Residual PGS might play an important role in preventing ankylosis formation.