Guided periodontal tissue regeneration in interproximal intrabony defects following treatment with a synthetic bioabsorbable barrier

This study evaluated guided periodontal tissue regeneration (GPTR) wound healing in interproximal intrabony periodontal defects following surgical treatment with a synthetic bioabsorbable barrier made from a copolymer of glycolide and lactide. Periodontal lesions were induced around the mandibular central incisor teeth of 10 adult male rhesus monkeys using orthodontic elastics. Once similar contralateral interproximal defects had been created, the elastics were removed and an oral hygiene program was initiated and maintained until completion of the study. Three weeks after commencing oral hygiene, flap surgery was performed in the mandibular incisor region and the root surfaces were thoroughly scaled and root planed to the apical portion of the defects. On the test sites, a bioabsorbable barrier was placed over the entire interproximal periodontal defect. Control sites did not receive a barrier. Five months after surgery, the animals were sacrificed and the teeth with their supporting periodontium were processed for light microscopic evaluation. Postoperative clinical healing progressed uneventfully and was similar in both control and test sites. Histologic observations from control specimens indicated reparative healing characterized by a long junctional epithelium with limited cementum and bone formation. Test specimens exhibited significantly more new connective tissue attachment, cementum deposition, and bone formation than the control sites (P < 0.001). The barriers had been completely resorbed with no apparent adverse effect on periodontal wound healing. It was concluded that this bioabsorbable barrier facilitated GPTR wound healing in interproximal intrabony periodontal defects.

Ultimate tensile strength of PDL of molars in rats after 1-hydroxyethylidene-1,1-bisphosphonate injections

OBJECTIVES AND METHODS

Administration during root formation of a bisphosphonate, 1-hydroxyethylidene-1,1-bisphosphonate (HEBP), at a dose corresponding to 10 mg P/kg body weight, has been found to interfere with the formation of acellular cementum in rats. The purpose of this study was to measure the force required to extract a tooth lacking normal acellular cementum, and to correlate this force and the ultimate periodontal strength with the morphology of the periodontal tissues at different time intervals after single or multiple injections of HEBP.

RESULTS

A single injection of HEBP given during root formation inhibited the formation of acellular cementum and resulted in a temporary reduction of the extraction force and the ultimate tensile strength. Ninety days after the injection of HEBP, both parameters were the same as in the controls. The increase in extraction force and ultimate tensile strength was associated with the onset of occlusal contact of the teeth. The organization of periodontal ligaments was improved after the teeth reached the occlusal level. After daily injections of HEBP for 3 days, there was a permanent reduction in root length and dento-alveolar ankylosis developed in the furcation area.

CONCLUSION

(1) A single or three injections of HEBP changed the formation of acellular cementum to that of an atypical hyperplastic cementum which increased the resorption risk at this site. (2) The ultimate tensile strength was markedly reduced in teeth lacking acellular cementum.

The modulatory role of cementum matrix on osteoblastic cells in vitro

The formation of new cementum is an important issue in clinical periodontology, as cementum is required to provide attachment for newly formed periodontal tissues to the root surface. In this study a model of cementogenesis in vitro was used in order to test the effects of root surface demineralization on the migration, attachment and formation of a cementum-like tissue by osteoblastic cells cultured on cementum and to test the specificity of cementum matrix in modulating those effects by comparison of root co-cultures with bone co-cultures. It was demonstrated that root surface demineralization did not significantly alter the orientation, number and attachment of cells to the root co-cultures. The results also demonstrated that cementum and bone matrix appear to behave differently in culture, as seen by their distinct action on the morphological profile of the attached cells and the extracellular matrix deposited by these cells. These results demonstrate that although cementum matrix appears to stimulate the production of cementum-like tissue, this action is not confined to cementum matrix alone, since a similar material was also deposited on dentine and bone surfaces. Thus, these results do not support a specific action of cementum matrix on the modulation of the cementoblast phenotype. The use of co-cultures of neonatal rat calvaria cells with root slices represents a promising model of cementogenesis in vitro; however, studies should be undertaken towards the identification of markers to distinguish between cementoblast and osteoblast phenotypes in order to further validate this model.

Expression of extracellular matrix proteins in human periodontal ligament cells during mineralization in vitro

Periodontal regeneration is a complex process that requires coordinated responses from several cell types within the periodontium. It is generally accepted that the periodontal ligament (PDL) has a heterogeneous cell population, where some of the cells may be capable of differentiating into either cementoblasts or osteoblasts. Thus, it has been hypothesized that PDL cells play a role in promoting periodontal regeneration. However, definitive evidence to support this concept is lacking. Previously, we reported that PDL cells induce biomineralization as determined by Von Kossa histochemistry and transmission electron microscopy. To further determine the osteoblast-like properties of PDL cells, human PDL cells were exposed to dexamethasone (DEX) in order to promote an osteoblast phenotype, and then cell activity monitored during mineral nodule formation in vitro. For mineralization studies, cells were cultured in DMEM containing 10% FBS and a) vehicle only; b) ascorbic acid (50 micrograms/ml) and beta-glycerophosphate (10 mM); or c) ascorbic acid, beta-glycerophosphate and DEX (100 nM) for 30 days. In addition, the effects of DEX on PDL cells in non-mineralizing media were determined. Cells were stained weekly to evaluate mineral-like nodules, using the Von Kossa method. Northern blot analyses for mRNA steady state levels for several bone-associated proteins, i.e., osteopontin (OPN), bone sialoprotein (BSP), alkaline phosphatase (ALP), osteocalcin (OCN), alpha 2(1)(type 1) collagen and osteonectin (ON), were performed. DNA levels were also determined during the 30-day mineralization period. Under phase contrast microscopy, PDL cells in non-mineralizing media treated with DEX exhibited a more spindle-shaped morphology when compared with similar cells not exposed to DEX. Mineralizing conditions were required to induce mineral nodule formation. However, in this situation, mineral induction was independent of DEX; and furthermore, DEX-treated cells did not exhibit a different morphological pattern when compared with non-DEX treated cells. Mineral-like nodules were first seen at day 15, in concert with an increase followed by a decrease in expression of type I collagen and ON mRNA in both DEX-treated and non-treated cultures. Using Northern blot analysis for detection of specific proteins, we found that PDL cells did not express OPN, BSP, OCN, or ALP under any of the conditions used in this study. DEX did not alter DNA content in the cultures during the mineralization period. These results confirm that human periodontal ligament cells can be induced to mineralize in vitro and indicate that dexamethasone does not significantly alter the extent and pattern of mineralization.

Periodontal regeneration by application of recombinant human bone morphogenetic protein-2 to horizontal circumferential defects created by experimental periodontitis in beagle dogs

The purpose of this study was to examine the regeneration of periodontal tissue after the application of recombinant human bone morphogenetic protein-2 (rhBMP-2) to horizontal circumferential defects created by experimental periodontitis. Twelve mandibular second premolars in 6 adult beagle dogs were subjected to experimental periodontal breakdown by placing silk ligatures around the teeth until the bone loss exceeded half of the root length. Flap surgery was then performed and the exposed cementum removed. The distance between the bone crest and cemento-enamel junction (CEJ) was about 5 mm. RhBMP-2 (40 micrograms/100 microliters) with a sponge-type carrier material made of gelatin and polylactic acid polyglycolic acid copolymer was placed in the furcation area (5 mm x 5 mm x 5 mm) and around the roots (10 mm x 5 mm x 2.5 mm x 2 pieces). In the control group, the same carrier material without rhBMP-2 was placed in the same manner. The flaps were replaced and sutured to cover these materials completely. Twelve weeks after surgery, the animals were sacrificed and serial sections were prepared in a bucco-lingual plane. Considerable new bone formation was observed in the rhBMP-2-treated sites. New cementum with Sharpey's fibers was observed on the instrumented root surface. On histometric analysis, the amount of new bone, new cementum, and connective tissue attachment was significantly greater in the rhBMP-2-treated group (paired t test; P < 0.01). These results indicate that suitable application of rhBMP-2 can produce considerable periodontal tissue regeneration, even in cases of horizontal circumferential defects.

Changes in the permselectivity of human teeth during caries attack

Previous studies have shown that enamel permselectivity can influence fluid composition within caries lesions during de- and remineralization. The permselectivity of human enamel, cementum, and dentin sections was examined, in a microwell model, by measurement of the membrane potential developed by KCl diffusion while the sections were immersed in solutions simulating resting (pH = 5.6) and cariogenic plaque fluid (pH = 4.8). In a second experiment, the effects of charged compounds (phytate and Zonyl-FSC) on the tooth permselectivity were examined. The average membrane potentials (+/- SD) in "resting plaque" solution were: sound enamel, 18.9 +/- 3.2 mV, n = 66; dentin, 0.9 +/- 9.2 mV, n = 59; and cementum, -0.8 +/- 8.2 mV, n = 42, with a positive sing indicating cation selectivity. The average membrane potentials became more negative in "cariogenic plaque" solution for all types of sections: sound enamel, 5.2 +/- 2.1 mV, n = 46; dentin, -8.1 +/- 7.4 mV, n = 45; and cementum, -14.3 +/- 8.0 mV, n = 34. In lesion enamel sections, the membrane potential was reduced from the non-lesion wells in both types of test solutions, while phytate treatment caused an increase of approximately 10 mV in potential (increased cation selectivity) in every enamel well in either "resting" or "cariogenic" solution. Treatment of enamel sections with Zonyl-FSC caused the membrane potential to become more negative in both test solutions, with many of the wells showing anion selectivity in the cariogenic "plaque-like" solution. However, the changes in enamel membrane potentials induced by Zonyl-FSC slowly increased toward the initial values after treatment, while the effects of the phytate pre-treatment persisted. Most dentin sections treated with phytate also showed an increase in potential after phytate treatment; however, Zonyl-FSC seemed to have little effect on the membrane potential of dentin. The results of this study suggest that modification of tooth permselectivity by surface-active agents may be a viable method of decreasing the rate of caries progression.

Tissue engineering, morphogenesis, and regeneration of the periodontal tissues by bone morphogenetic proteins

Tissue engineering is the emerging field of science developing techniques for fabrication of new tissues for replacement based on principles of cell and developmental biology and biomaterials. Morphogenesis is the cascade of pattern formation and the attainment of form of the various organs and the organism as a whole. The periodontium consist of the periodontal ligament, cementum, and alveolar bone. Bone has considerable potential for regeneration and therefore is a prototypic model for tissue engineering. The three main ingredients for tissue engineering are regulatory signals, responding stem cells, and extracellular matrix. Recent advances in molecular biology of the bone morphogenetic proteins (BMPs) have set the stage for tissue engineering of bone and related tissues, including the periodontium. Bone-derived BMPs, with a collagenous matrix as carrier, induced cementum and alveolar bone regeneration in surgically created furcation defects in the primate. It is noteworthy that there was morphogenesis of periodontal ligament and a faithful insertion of Sharpey's fibers into cementum. In the same furcation model, recombinant human osteogenic protein-1 (rhOP-1, also known as BMP-7), in conjunction with the collagenous carrier, induced extensive cementogenesis with insertion of Sharpey's fibers into the newly formed cementum. The observation that BMPs induce cementogenesis and periodontal ligament formation indicates that these proteins may have multiple functions in vivo not limited to cartilage and bone induction. The rapid advances in the molecular biology of BMPs and their receptors bode well for novel strategies to engineer the regeneration of the periodontal tissues.

Therapeutic delivery of calcitonin to inhibit external inflammatory root resorption. I. Diffusion kinetics of calcitonin through the dental root

Insertion of calcitonin into root canals of monkey teeth has been shown to inhibit external inflammatory root resorption and suppress inflammation. Regulation of this therapeutic event depends upon the rate of arrival (diffusion) of the hormone at sites of resorptive activity. In the present study, the diffusion characteristics of calcitonin through the dental root in an extracted human-tooth model are described, and the role of cementum in the diffusion process is also addressed. Root-canals were endodontically prepared to form a reservoir for [125I]-calcitonin, and macerated to remove organic material from dentinal tubules. In teeth with intact cementum, an initial period of delay (4-5 h) prior to the detection of calcitonin at the external tooth-root surface was followed by a rapid release of the calcitonin during the first 10.5 h (rate peaks at 6 h). Slower, sustained releases of calcitonin through intact cementum were measured for the following 9 days. Removal of cementum, to expose "smear-free" dentine, resulted in an earlier efflux of calcitonin (2 h) at external tooth surfaces and increased amounts of calcitonin release over 9 days. Biphasic delivery of calcitonin by such internal diffusion mechanisms suggests that loss of cementum will enhance therapeutic availability, while prolonged delivery to intact external dental-root surfaces following early intra-canal placement may also be useful for the therapeutic prevention of external inflammatory root resorption.

Effect of power settings on temperature change at the root surface when using a Holmium YAG laser in enlarging the root canal

The aim of this study was to determine the maximum amount of power, in watts, that a Holmium YAG laser could deliver via a 245-micron fiberoptic to the canal surface and still not raise the temperature (delta T) of the cementum by > 5 degrees C. Sixty single-rooted teeth were divided into three groups according to power selection (0.50, 0.75, and 1.00 W). The three main outcome variables were: change in apical temperature, change in coronal temperature, and maximum size of an endodontic file that could fit into the canal after lasing. The group means for apical delta T were: 1.00 W = 2.2 degrees C, 0.75 W = 2.68 degrees C, and 0.50 W = 1.58 degrees C. The group means for coronal delta T were: 1.00 W = 1.15 degrees C, 0.75 W = 0.99 degree C, and 0.50 W = 0.56 degree C. The group means for file size were: 1.00 W = 41.25, 0.75 W = 38.75, and 0.50 W = 40.75. The canal size was increased from a size 25 file up to approximately a size 40 file with all power groups. There were no significant differences between the groups for change in apical temperature (p = 0.32), coronal temperature (p = 0.17), or maximum file size (p = 0.86) when adjustments were made for tooth dimensions. In all groups studied, the delta T was < 5 degrees C. This represents a safe and predictable laser procedure.

Effects of polyglactin mesh combined with resorbable calcium carbonate or replamineform hydroxyapatite on periodontal repair in dogs

This study evaluates periodontal repair and biomaterial reaction following implantation of a polyglactin mesh with or without porous resorbable calcium carbonate (RCC) or porous replamineform hydroxyapatite (RHA) in conjunction with reconstructive surgery. Ligature- and surgically-induced interproximal periodontal defects of left and right mandibular premolar teeth in 7 dogs were used. Bilaterally, mesial defects of the 2nd, 3rd and 4th premolar teeth were treated with polyglactin mesh, polyglactin mesh and RHA, or polyglactin mesh and RCC, respectively. The polyglactin mesh, shaped according to the contour of the defect, was adapted to the experimental teeth; its coronal margin positioned immediately apical to the cemento-enamel junction. Gingival flap margins were adapted and sutured to cover the polyglactin mesh completely. Clinical healing was generally uneventful. The dogs were sacrificed to provide block sections for histologic evaluation at 1, 3, 6, 12, 26, 32 and 56 weeks following wound closure. Generally, cementum regeneration was observed beginning at week 6 in all groups. Bone regeneration was observed from week 3 in polyglactin mesh-treated groups, and from week 6 in polyglactin mesh+RCC or polyglactin mesh+RHA treated groups. Bone regeneration appeared enhanced in polyglactin mesh+RCC or polyglactin mesh+RHA treated defects at week 12 and 26, with little difference between the three experimental conditions at week 56. Polyglactin mesh degradation was observed at week 3 and appeared complete at week 12. The RHA did not appear to resorb, while the RCC was gradually replaced by bone from week 3. Within limitations of the study conditions, periodontal regeneration was observed following implantation of a polyglactin mesh with or without RCC or RHA in conjunction with reconstructive surgery. As a conclusion, there seems to be no significant difference in periodontal regeneration after 12 months of healing between the group treated with the membrane only, and the group treated with the membrane and the bone substitution material. Changes in connective fiber orientation over the 1st 12 weeks of healing may suggest that "fibrous encapsulation" observed in earlier studies may only represent a transient stage in periodontal regeneration.

Biologic responses of autogenous bone and beta-tricalcium phosphate ceramics transplanted into bone defects to orthodontic forces

This study was conducted to evaluate biologic responses of autogenous bone (particulate marrow and cancellous bone; PMCB) and beta-tricalcium phosphate ceramics (TCPC) to orthodontic stimuli. Nine dogs served as the experimental animals; three dogs underwent orthodontic tooth movement after grafting, three dogs received PMCB grafting without tooth movement, and three dogs received TCPC grafting without tooth movement. Immediately after extraction of the upper second and/or third incisors, the maxillary alveolar bone was resected bilaterally. Autogenous PMCB obtained from the iliac bone and TCPC were transplanted into each bone defect. Experimental tooth movement was initiated 2 to 4 weeks after the grafting and continued for 9 to 15 weeks. Sectional archwires with open-coll springs were used for distal movement of the upper first incisors into the extraction sites. Oxytetracycline and calcein were employed as bone markers. Sections of grafted areas including the teeth were prepared for light and fluorescence microscopy. The results revealed that both autogenous bone and TCPC presented similar adaptive changes to the original alveolar bone without any external stimuli. TCPC exhibited more prominent biodegradative responses to orthodontic force in association with new cementum formation. Root resorption was also less in the TCPC area than in the PMCB region. It is shown that TCPC is biodegradative in nature and adaptive for remodeling during orthodontic tooth movement. This finding indicates that TCPC may be a better biocompatible alternative to autogenous bone transplanted into bone defects subjected to orthodontic tooth movement.

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

BACKGROUND

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

RESULTS

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

CONCLUSIONS

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

Periodontal ligament cell population: the central role of fibroblasts in creating a unique tissue

BACKGROUND

Fibroblasts are the predominant cells of the periodontal ligament (PL) and have important roles in the development, function, and regeneration of the tooth support apparatus. Biological processes initiated during the formation of the PL contribute to the long-lasting homeostasic properties exhibited by PL fibroblast populations.

DEVELOPMENT

The formation of the PL is likely controlled by epithelial-mesenchymal and epithelial hard tissue interactions, but the actual mechanisms that contribute to the development of cellular lineages in the PL are unknown. Fibroblasts in the normally functioning PL migrate through the tissue along collagen fibres to cementum and bone and in an apico-coronal direction during tooth eruption. ADULT TISSUE: Cell kinetic experiments have shown that PL fibroblasts comprise a renewal cell system in steady-state and the progenitors can generate multiple types of more differentiated, specialized cells. Progenitor cell populations of the PL are enriched in locations adjacent to blood vessels and in contiguous endosteal spaces. In normally functioning periodontal tissues, there is a relatively modest turnover of cells in which apoptotic cell death balances proliferation. Large increases of cell formation and cell differentiation occur after application of orthodontic forces or wounding. As PL cells comprise multiple cellular phenotypes, it has been postulated that after wounding, the separate phenotypes repopulating the site will ultimately dictate the tissue form and type.

CONCLUSIONS

PL fibroblasts play an essential role in responses to mechanical force loading of the tooth by remodelling and repairing effete or damaged matrix components. In consideration of the important roles played by fibroblasts in PL homeostasis, they could be described as "the architect, builder, and caretaker" of the periodontal ligament.

Dual X-ray absorptiometry for alveolar bone: precision of peri-implant mineral measurements ex vivo

The precision of measurements of minor mineral changes in alveolar bone mineral content (ABMC) and alveolar bone mineral density (ABMD) on implant surfaces was determined in small regions (0.03 +/- 0.005 cm2) using dual X-ray absorptiometry (DXA). Dog hemimandibles with alveolar processes containing 17 implants were studied ex vivo. The precision was expressed as the coefficient of variation in percent (c.v. %). The ultra-high resolution protocol was applied to the mesial, distal and apical subregions of each implant. The line spacing was 0.0254 cm and the point resolution was 0.0127 cm. The mean c.v. (%) +/- s.d. for the ABMC in the mesial, distal and apical regions were 0.42 +/- 17, 0.47 +/- 0.21 and 0.48 +/- 0.18, respectively. For the ABMD these values were 0.42 +/- 0.16, 0.47 +/- 0.19 and 0.48 +/- 0.16. For each region approximately 68% of the 17 c.v. values were distributed within 1 s.d. from the mean c.v. These results indicate that measurements are highly reproducible (better than 0.48%) and that there are no differences in precision between several peri-implant regions. Changes as small as 0.85% in ABMC and ABMD in small areas adjacent to implant surfaces are measurable with a confidence level of 95%. Therefore the DXA technique will be expedient for our research evaluating the efficacy of the ceramic hydroxyapatite implant releasing agents affecting or inducing alveolar bone- and root cementum-like materials on its surface.

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

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

The potential role of growth and differentiation factors in periodontal regeneration

Polypeptide growth and differentiation factors (GDFs) are a class of biological mediators which have been shown to play a critical role in the stimulation and regulation of the wound healing process. Growth factors involved in repair and regeneration regulate several key cellular processes such as mitogenesis, chemotaxis, differentiation, and metabolism. The sequence of events necessary for periodontal regeneration relies on the above processes for osteogenesis, cementogenesis, and connective tissue formation. Numerous preclinical in vitro and in vivo studies have demonstrated that certain growth factors modulate putative components of periodontal wound healing resulting in substantial regeneration of the periodontium in animals. However, these therapies are currently considered to be in the experimental stage of development and no growth factor therapy to treat periodontitis in humans has received approval by the Food and Drug Administration (FDA). This informational paper reviews the various aspects of GDFs on cells and tissues involved in periodontal wound healing. This paper was prepared by the Committee on Research, Science and Therapy of The American Academy of Periodontology and is intended for members of the dental profession.

Orthodontically induced root resorption in rat molars after 1-hydroxyethylidene-1,1-bisphosphonate injection

A single injection of 1-hydroxyethylidene-1, 1-bisphosphonate inhibits the formation of acellular cementum in rat molars. Instead, an atypical hyperplastic cementum is formed. In this study the resistance of this cementum to resorption was tested by applying an orthodontic force. It was found that roots lacking acellular cementum were readily resorbed. The readiness with which the atypical hyperplastic cementum was resorbed without any increase in multinucleated osteoblasts may offer useful opportunities to study the different phases of hard-tissue resorption.

Induction of cementogenesis by recombinant human osteogenic protein-1 (hop-1/bmp-7) in the baboon (Papio ursinus)

Recombinant human osteogenic protein-1 (hOP-1), a member of the bone morphogenetic protein family, was examined for its efficacy in periodontal regeneration. Twelve furcation defects, surgically prepared in the first and second mandibular molars, were treated with bovine insoluble collagenous matrix in conjunction with 0.0 (control), 100 and 500 mu g of recombinant hOP-1 per g of matrix. After 60 days of healing, histological and histometric analyses on serial, undemineralized sections cut at 7 mu m showed substantial cementogenesis on the exposed dentine of furcations treated with both doses of hOP-1 (p < 0.01 vs control). Foci of nascent mineralization were seen within the newly deposited cementoid along the coronal areas of hOP-1-treated defects. Within the furcations, there were substantial amounts of residual collagenous carrier, interspersed with a mineralized matrix having histological features of cementum. This mineralized cementum-like material was predominantly deposited around the carrier, and blended into newly formed cementum along the root surfaces. In the apical area, the cementum-like material and the remaining alveolar bony housing were not connected; indeed the two components were separated by a fibrovascular tissue that had numerous features of the periodontal ligament space. Formation and insertion of Sharpey's fibres into newly formed root cementum were also observed. It is likely that the expression of specific cell phenotypes by hOP-1 is regulated, in part, by the extracellular matrix microenvironment, including dentine. Thus, exposed dentine, in the presence of exogenous hOP-1 at the doses tested, may preferentially modulate the expression of the cementogenic phenotype. These findings in a non-human primate show that hOP-1, at the doses tested, induced cementogenesis on surgically denuded root surfaces, indicating a specific function during repair and regeneration of periodontal tissues.

"Collagen adhesion" revisited

Histologic studies of periodontal reconstructive therapies have repeatedly shown a zone of nondescript connective tissue adaptation, or collagen adhesion, to the root surface between the apical extension of the junctional epithelium and the coronal extension of identifiable regenerated cementum. To clarify the nature of this zone, supra-alveolar periodontal defects were created bilaterally in the mandibular premolar region in three beagle dogs, and exposed roots were instrumented to remove the cementum. Flaps were then coronally advanced and sutured. Histologic analysis after 12 weeks of healing showed instrumented root dentin not associated with junctional epithelium, new cementum, root resorption, or ankylosis in 27 of 60 root surfaces. In 10 of these specimens subsequently examined by transmission electron microscopy, collagen fibrils were generally oriented parallel to and in close proximity to the root. A mechanism of collagen attachment was, in fact, functioning at sites of collagen adhesion; these areas may validly be included in the histologic attachment level reported in studies of periodontal reconstructive therapy.

Evaluation of guided tissue regeneration in the treatment of paired periodontal defects

The aim of the present study was to compare guided tissue regeneration with conventional surgery in matched periodontal defects within the same subject. Twenty pairs of sites in nine subjects were treated. Surgery was performed at both test and control sites on the same visit. Random allocation was not performed until all preparation and root instrumentation had been completed. Test defects were covered with e-PTFE membranes (Gore-Tex) and secured with sutures. Membranes were removed after 5-6 weeks with a second surgical procedure, whereas the control sites were not re-operated. At 12 months probing depth reductions were significantly greater at the Gore-Tex treated sites (P<0.05) but no difference in probing attachment level gains were found when compared with conventional flap surgery.

Spatial and temporal repair patterns of orthodontically induced surface resorption patches

Root resorption appears to be an inevitable sequel to orthodontic tooth movement, occurring either apically or along surfaces in and around the pressure zones. However, there is uncertainty as to the location of initial cementum repair in resorbed areas as well as the time of onset of repair. The aim of the present study was to map the spatial and temporal patterns of cementum repair in orthodontically induced areas of surface resorption following maxillary expansion. Two spatial patterns of repair of orthodontic surface resorption patches were observed with cementum deposition proceeding either from the periphery or starting somewhere in the center of the resorbing areas, although the deposition starting centrally was argued to be artifactual. Furthermore, onset of reparative cementum mineralization appeared to follow within 2 wk after release of the force, involving initially only acellular cementum formation. However, the pattern of formation changed gradually, favouring a slow deposition of cellular cementum at more advanced stages of healing.

Endodontic pathogens: propagation of infection through patent dentinal tubules in traumatized monkey teeth

Periapical pathology indicating endodontic infection, when present in marginal periodontitis-affected teeth, has recently been shown to be an aggravating factor in progression of marginal destruction. This has been associated with patency of dentinal tubules in the tooth cervix, an area normally devoid of cementum following periodontal therapy. These studies are, however hampered by that only circumstantial evidence such as presence of periapical destruction have been applied as criteria of endodontic infection. The purpose of the present investigation was to study to what extent a predefined selection of endodontic pathogens inoculated in the root canal can influence periodontal pathology and healing in areas of the root covered by or devoid of cementum, using root resorption as a histomorphometric marker. Exposed dentine surfaces, in the present study showed significantly larger areas of resorption in infected roots compared to non-infected roots, while cementum surfaces showed an almost identical distribution of tissue reactions regardless of root canal infection or not. It was concluded that endodontic pathogens or their products were not able to penetrate the cementum barrier. The significantly larger areas of resorption on exposed dentine surfaces in infected roots compared to non-infected roots indicated that endodontic pathogens or their products could spread through dentinal tubules to a root surface void of cementum. Extrapolated to the marginal situation this indicated that endodontic pathogens in the root canal might be able to aggravate marginal infection in areas of root devoid of cementum.