Periodontal Ligament :: anatomy & histology
Tooth movements are guided by specific contact areas between the tooth root and the jaw bone: A dynamic 3D microCT study of the rat molar.
Department of Structural Biology, Weizmann Institute of Science, 76100 Rehovot, Israel.
Teeth sustain high loads over a lifetime and yet intact tooth failure is rare. The different structures of the tooth, jaw bone and the intervening soft periodontal ligament enable the tooth to endure repeated loading during mastication. Although mechanical and functional properties of the different components are thoroughly investigated, the manner in which the whole tooth functions under load is still enigmatic. A custom-made loading system inside a microCT scanner was used to directly visualize the root movements in relation to the jaw bone as the rat molar tooth was loaded. At low loads no contact was observed between the root surface and the bone, whereas at higher loads three specific contact areas between the root surface and the jaw bone were observed. These contact areas restrict tooth movement in the buccal-lingual direction, but enable the tooth to rock in a "seesaw" like manner in the distal-mesial direction. The contact areas appear to play a role in determining tooth motion and in turn define the manner in which the whole tooth moves when loaded. These observations are important for understanding basic structure-function relations of the tooth-PDL-bone system, and have direct implications for better understanding pathological and therapeutic processes in orthodontics, periodontics and jaw bone regeneration.
Most cited papers:
The present study was designed to examine whether new attachment forms on root surfaces previously exposed to plaque by preventing the oral epithelium and the gingival connective tissue from participating in the process of healing following treatment. 4 roots in each of 3 monkeys were used as test units while the roots of contralateral teeth served as controls. A surgical procedure was first used to expose the coronal half of the buccal root surfaces. Plaque was allowed to accumulate on the exposed surfaces for a period of 6 months. Subsequently, soft tissue flaps were raised and the root surfaces were carefully scaled and planed. The crowns of the test and control teeth were resected and the mucosal flaps were repositioned and sutured in such a way that the roots were properly covered. Immediately prior to suturing, membranes (Millipore filter or Gore-tex membrane) were placed over the denuded root surfaces of the test teeth in order to prevent granulation tissue from the soft tissue flaps from reaching the roots during healing. The monkeys were sacrificed 3 months later. The jaws were removed and histological sections of test and control roots including their periodontal tissues were produced. New cementum with inserting collagen fibers was observed on the previously exposed surfaces of both test and control roots. However, the test surfaces exhibited considerably more new attachment than the control surfaces, indicating that the placement of the membrane favoured repopulation of the wound area adjacent to the roots by cells originating from the periodontal ligament.
The aim of the present study was to evaluate whether a regenerative surgical procedure, based on guided tissue regeneration, could predictably result in the formation of a new attachment in human teeth. The material included 12 teeth in 10 patients with advanced periodontal disease. Following flap elevation, scaling, root planing and removal of granulation tissue, a teflon membrane was placed over the denuded root surface in such a way that the epithelium and the gingival connective tissue were prevented from reaching contact with the root during healing. The flap was replaced on the outer surface of the membrane and secured with interdental sutures. This design of wound preparation gives preference to the cells originating from the periodontal ligament (PDL-cells) to repopulate the wound area adjacent to the root. Histologic analysis of the result of treatment was made in 5 of the 12 teeth scheduled for extraction. In the remaining 7 teeth, the result was evaluated using clinical measurements. The result of healing disclosed that in all teeth treated, substantial amounts of new attachment had formed. This suggests that predictable restitution of the attachment apparatus can be accomplished by using a method of treatment which is based on the principle of guided tissue regeneration.
Previous studies indicated that connective tissue attachment to the root surface appeared to be dependent upon a chronologic healing sequence related to fibrin and collagen interactions. It was the purpose of the present study to try and substantiate this hypothesis by using histologic techniques designed to differentiate between fibrin and collagen during healing at the root surface interface. In four squirrel monkeys, 24 normal teeth were extracted and reimplanted after either (i) surgically denuding the coronal root surface of connective tissue fibers and cementum by root planing or,(ii) surgical denudation followed by topical application of citric acid (pH = 1; 3 minutes). Three specimens were available for histological analysis 1, 3, 7 and 21 days after reimplantation. Mallory's phosphotungstic acid hematoxylin staining technique was used to differentiate between fibrin and collagen. Epithelium migrated rapidly along the denuded, non-acid-treated, root surfaces, had reached the alveolar crest at 3 days, and was within the ligament space to the level of root denudation at 21 days. Epithelium did not migrate apically along denuded root surfaces treated with citric acid. At 1 and 3 days, inflammatory cells were enmeshed in a fibrin network which appeared to be attached to the root surface by arcade-like structures. At 7 and 21 days, the region had repopulated with connective tissue cells, and collagen fibers had replaced the fibrin. It was concluded that collagen fiber attachment to the root surface was preceded by fibrin linkage, and that the linkage process occurred as an initial event in the wound healing response.
Department of Periodontics, University of Michigan School of Dentistry, Ann Arbor 48109.
This study tested the effects of using a Gore-Tex periodontal material on new connective tissue attachment in beagle dogs with natural periodontitis. Seven female beagle dogs with advanced periodontitis were selected and given thorough root debridement. Under general anesthesia four weeks later, mucoperiosteal flaps were raised involving all mandibular premolars and first molars. Gore-Tex periodontal material was adapted to all premolars, and the flaps were sutured tightly, keeping the material covered. The first molars acted as controls, receiving only surgery. Some material was removed in one month, while other materials were removed eight to 10 weeks after surgery. All dogs were sacrificed at three months. After processing, descriptive histology and histometrics were carried out, evaluating new connective tissue attachment, bone response and epithelial downgrowth. Results were statistically analyzed, using paired t tests. They showed new connective tissue attachment with cementum deposition in areas where the material was used. Also, the epithelial downgrowth was reduced in these areas. In the controls, minimal connective tissue attachment was found, with the area healing by a long junctional epithelium. Statistical analysis showed significant differences (P less than 0.05) favoring experimental areas both in the increase of new connective tissue attachment and in the decrease of epithelial downgrowth. No differences were found between areas where the material was removed in one month or left longer in place. No difference in bone response was found. Gore-Tex material was effective in blocking gingival epithelial downgrowth and connective tissue proliferation, promoting new attachment according to the principle of "guided tissue regeneration."
Department of Oral Surgery, School of Dental Medicine, University of Berne, Switzerland.
The aim of this study was to examine wound healing events around titanium implants in the presence of retained root tips whose periodontium could serve as a source for cells which could participate in the healing process. Hollow cylinder implants with a titanium plasma-sprayed surface were placed in the mandible of monkeys where the apical portions of previously removed teeth were retained. After a healing period of 12 months, free of functional loading, the implants with surrounding tissues were removed and specimens analyzed in undecalcified sections. This report describes histologic findings of six such implants. Microscopic analysis revealed that in regions where implants were close to retained roots, a periodontal ligament had formed around large portions of the implant. Furthermore, there was a distinct layer of cementum on the implant surface and a periodontal ligament with collagen fibers perpendicularly oriented to the implant surface, implanted into the cementum on the implant surface as well as to the opposing bone. This initial observation suggests that it may be possible to achieve an anchorage of certain dental implants with a periodontium simulating that found surrounding the normal tooth. Furthermore, these findings provide the basis for further studies on regeneration of all components of the periodontal attachment apparatus including cementum, periodontal ligament, and bone.
The present investigation was undertaken to examine whether a new connective tissue attachment will form on previously periodontitis-involved roots when reduced but healthy periodontal ligament tissue persists following periodontal treatment and the epithelium is prevented from migrating into the wound. In each of 4 monkeys, periodontal tissue breakdown was induced around one maxillary and one mandibular second premolar or first molar by placing orthodontic elastics around the teeth. The elastics were kept in situ until about 50% of the supporting tissues had been lost. 3 months following removal of the elastics, the crowns of the teeth were resected. The pocket epithelium and subjacent granulation tissue were excised and the cementum of the periodontitis-involved part of the roots was removed using a diamond bur. The roots were covered with a mucosal flap. The animals were sacrificed after 3 months of healing. The jaws were removed and histological sections of the experimental roots including their surrounding periodontal tissues were produced. The microscopic analysis disclosed that in all roots, new cementum with inserting collagen fibers had formed in the apical portion of the previously exposed root surfaces. It was always in continuity with the original cementum layer apical to the instrumental part of the root and was thickest in its apical portion, becoming gradually thinner in the coronal direction. In the roots, which for the entire length of the study remained covered by the oral mucosa, the extension in the coronal direction of this newly formed fibrous attachment amounted to an average of 1.0 mm with a range from 0.1 mm to 2.6 mm. These findings were interpreted to mean that new attachment is formed by coronal migration of cells originating from the periodontal ligament.
Department of Periodontology, University of Gothenburg, Sweden.
Recent studies have demonstrated extensive amounts of new attachment formation following reconstructive surgery based on the biological principle of guided tissue regeneration (GTR). The aim of the present investigation was to evaluate the effect of using a polytetrafluorethylene (PTFE) membrane in GTR-treatment of recession-type defects and to examine the interrelationship between the PTFE membrane and surrounding periodontal tissues. Full-thickness flaps were raised around 24 maxillary premolar and molar teeth in 6 monkeys. The buccal alveolar bone was surgically removed to a level corresponding to the apical third of the roots. The exposed root surfaces were scaled and planed. In 12 teeth, PTFE membranes were adjusted to cover the exposed root surfaces from a level 1 to 2 mm apical to the CEJ, to a level 3 to 4 mm apical to the alveolar crest. The coronal border of the membranes was tightly adapted to the root surfaces by sling sutures. Twelve teeth served as control teeth without placement of membranes. The flaps were placed with the margin coronal to the CEJ and sutured. The animals were sacrificed after 3 months of healing and all experimental teeth were subjected to histological analysis. The membranes were found to be incorporated with the surrounding connective tissue, and the apical extension of the junctional epithelium terminated at the coronal border of the membranes. The amount of new attachment formation was on the average 74.3% of the defect height in the test teeth, which corresponded to 100% of the membrane covered root portion. Newly formed connective tissue attachment in the controls amounted to an average of 36.9% of the defect height.(ABSTRACT TRUNCATED AT 250 WORDS)
Dental School, Cardiff, Wales, U.K.
The accurate modelling of teeth under orthodontic load in the laboratory has many shortcomings in that it has not been possible to integrate methods, such as three-dimensional models, photo-elastic stress analysis, laser holographic interferometry, and animal studies, to give comprehensive and repeatable results. In this study, using a three-dimensional finite element model of a human maxillary canine tooth, the maximum principal stresses in the periodontal ligament produced by various orthodontic forces were determined. 1 Newton tipping forces produced stresses at the cervical margin of the periodontal ligament as high as 0.196 N/mm2 and apical stresses up to -0.034 N/mm2, while rotatory forces of two equal, but opposing forces of 0.5 Newton at the cervical margin of the crown produced cervical margin stresses ranging between -0.035 and 0.051 N/mm2, and apical stresses of between 0.0018 and 0.0027 N/mm2. These stresses are examined and discussed in relation to previous clinical, laboratory, and histological studies.
Department of Oral Biology, School of Dental Medicine, State University of New York at Buffalo, Buffalo, New York, USA.
Immunolocalization of Bone Morphogenetic Protein-2 and -3 and Osteogenic Protein-1 during murine tooth root morphogenesis and in other craniofacial structures.
Bone Research Laboratory, Medical Research Council/University of the Witwatersrand, Medical School, Johannesburg, South Africa.
The distribution of Bone Morphogenetic Protein-2, and -3 (BMP-2 and BMP-3) and Osteogenic Protein-1 (OP-1, also known as BMP-7) during root morphogenesis and in other craniofacial structures was examined in sections of 12- to 18-d-old mouse heads using polyclonal and monoclonal antibodies. BMP-3 and OP-1 were localized in alveolar bone, cementum, and periodontal ligament, whereas BMP-2 was only localized in the alveolar bone of periodontium. All three BMPs were localized in predentine, dentine, odontoblasts, osteoblasts, osteocytes, osteoid, cartilage, chondrocytes and spiral limbus. BMP-2 and OP-1 were also localized in spiral ligament and interdentate cells of the cochlea, whilst BMP-3 was restricted to the spiral ganglion. BMP-3 was also localized in ducts of submandibular and sublingual salivary glands, acini of the lacrimal gland, Purkinje cells in the cerebellum, nerve fibres of the cerebellum and brain, afferent cells of the dorsal root ganglia, inferior alveolar nerve, and peripheral processes of the vestibulocochlear nerve. OP-1 was also localized in hair and whisker follicles, sclera of the eye and in ameloblasts. The demonstration of BMP-3 in the nervous system suggests that this protein may be neurotrophic during development and maintenance of the nervous system. The composite expression of BMPs/OPs during periodontal tissue morphogenesis suggests that optimal therapeutic regeneration may entail the combined use of different BMPs/OPs.