Action Mechanism of Fibroblast Growth Factor-2 (FGF-2) in the Promotion of Periodontal Regeneration in Beagle Dogs

Fibroblast growth factor-2 (FGF-2) enhances the formation of new alveolar bone, cementum, and periodontal ligament (PDL) in periodontal defect models. However, the mechanism through which FGF-2 acts in periodontal regeneration in vivo has not been fully clarified yet. To reveal the action mechanism, the formation of regenerated tissue and gene expression at the early phase were analyzed in a beagle dog 3-wall periodontal defect model. FGF-2 (0.3%) or the vehicle (hydroxypropyl cellulose) only were topically applied to the defect in FGF-2 and control groups, respectively. Then, the amount of regenerated tissues and the number of proliferating cells at 3, 7, 14, and 28 days and the number of blood vessels at 7 days were quantitated histologically. Additionally, the expression of osteogenic genes in the regenerated tissue was evaluated by real-time PCR at 7 and 14 days. Compared with the control, cell proliferation around the existing bone and PDL, connective tissue formation on the root surface, and new bone formation in the defect at 7 days were significantly promoted by FGF-2. Additionally, the number of blood vessels at 7 days was increased by FGF-2 treatment. At 28 days, new cementum and PDL were extended by FGF-2. Moreover, FGF-2 increased the expression of bone morphogenetic protein 2 (BMP-2) and osteoblast differentiation markers (osterix, alkaline phosphatase, and osteocalcin) in the regenerated tissue. We revealed the facilitatory mechanisms of FGF-2 in periodontal regeneration in vivo. First, the proliferation of fibroblastic cells derived from bone marrow and PDL was accelerated and enhanced by FGF-2. Second, angiogenesis was enhanced by FGF-2 treatment. Finally, osteoblastic differentiation and bone formation, at least in part due to BMP-2 production, were rapidly induced by FGF-2. Therefore, these multifaceted effects of FGF-2 promote new tissue formation at the early regeneration phase, leading to enhanced formation of new bone, cementum, and PDL.

[Revascularization? Only as the last resort!]

Revascularization has been suggested for treatment of necrotic immature permanent teeth. The desirable outcome of the treatment is continuous growth of the root, maturation of the dentin walls underneath the cervical seal and apical closure. Despite of increasing numbers of case reports, a uniform treatment protocol has not been set. This procedure has many shortcomings of which tooth discoloration is the most prevalent and easy to observe. The severe discoloration is attributed to the use of Mincocycline in the antibiotic dressing, or to the use of MTA for the seal. The maturation of the root is not predictable and does not always occur. The outcome should be evaluated radiographically and clinically. Sensibility testing may not be possible due to the large MTA plug in the root canal. It is recommended only when alternative procedures such as apexificaiton, pulpotomy or pulp capping are impossible. The patient and his parents should be aware of the potential discoloration and must be committed to routine follow ups. Currently, this procedure should be limited to incisor or premolar teeth in which the crown is longer than the root, or the canal's width is larger than that of the dentinal wall.

Rare courses of the mandibular canal in the molar regions of the human mandible: a cadaveric study

The inferior alveolar artery, vein and nerve send some branches to the molar teeth via the mandibular canal to the mental foramen. The present study attempted to define the presence and course of the mandibular canal in the mandible with the alveolar process by macroscopic cadaveric dissection and computerized tomography (CT) in order to provide information that might prevent injuries to vessels and nerves at risk during root canal treatment. We identified the position of the mandibular canal within a 30% ratio of the distance from inferior border of mandible to the apices of the root for 39 out of 131 sides (mesial root of first molar, 20%; distal root of first molar, 22.6%; mesial root of second molar, 27.8% and distal root of second molar, 47%) on panoramic X-ray observation. In one cadaver (male, 64 years old), the root apex of the second molar was in close proximity to the upper bony mandibular canal. Macroscopic dissection and computerized tomography showed that the main trunks of the inferior alveolar artery, vein, and nerve were in tight contact with the apex of the second molar. These observations of the anatomic course of the mandibular canal will be important to consider during root canal treatment of mandibular teeth.

Distribution of the epithelial rests of Malassez and their relationship to blood vessels of the periodontal ligament during rat tooth development

BACKGROUND

There is some evidence that the epithelial cell rests of Malassez partition the root surface from the periodontal ligament blood vessels, and may protect the root from resorption.

OBJECTIVE

The aim of the present study was to determine the distributions of the epithelial rests of Malassez (ERM) and blood vessels in the periodontal ligament (PDL) of the developing rat first molar before, during and after emergence.

METHODS

Four Sprague-Dawley rats were sacrificed at two days, one week, two weeks, three weeks, four weeks and six weeks of age. After processing, the maxillae were embedded in paraffin, and sectioned longitudinally and transversely. The sections were stained with a double immuno-histochemical technique which utilised a keratin antibody AE1-AE3 (1:2,000) and an endothelial antibody Factor VIII (1:10,000) to enable simultaneous labelling of ERM and blood vessels. ERM and blood vessel counts were obtained from the mesio-buccal roots of three week, four week and six week-old rats, whilst qualitative observations were made for the earlier developmental stages.

RESULTS

ERM cells and cell clusters were found in the tooth third of the PDL width at the three, four and six week stages. Cells and cell clusters increased in number with age, especially in the upper third of the mesio-buccal root. The largest numbers of cells and clusters were found on the distal surfaces of the roots in all age groups. Cells and clusters in all root surfaces increased from three to four weeks, but decreased from four to six weeks. The greatest number of blood vessels was found in the bone-side third of the PDL. The distal surface had the highest proportion of blood vessels, and the palatal surface the least proportion. The number of blood vessels in all surface quadrants did not vary much from three to four weeks of age, but increased from four to six weeks of age, possibly as a reaction to tooth emergence and occlusal function. Physiological root resorption was only observed after tooth emergence, and appeared to be related to loss of continuity of the ERM network and the incursion of blood vessels.

CONCLUSIONS

Orthodontic root resorption can be regarded as an exaggerated response to loss of PDL homeostatic control, possibly mediated by the epithelial rests of Malassez.

Clinical management of the avulsed tooth: present strategies and future directions

The aim of this review article is to supplement the recently published International Association of Dental Traumatology (IADT) guidelines on treatment of the avulsed tooth. A thorough discussion on the reasoning behind each guideline is presented. In addition, the author's views on alternate treatment strategies and future directions, along with recent research on the subject of the avulsed tooth, are also presented.

Ultrastructural changes in postcapillary-sized venule morphology in aged mouse periodontal ligament

The aim of this study was to compare the postcapillary-sized venule (PCV) morphology of four young ALCA mice (35 days) and four colony-related aged mice (365 days) using the transmission electron microscope (TEM). Right and left mandibular first molar mesial roots with associated periodontal ligament (PDL) and bony socket, were used for TEM assessment. Five PCV profiles were selected at each 160 microm interval, from the alveolar crest to the tooth apex. PCV profile dimensions were measured on standardised micrographs magnified x2900. Age affects were tested using multiple regression analysis. The number of PCV profiles in the tooth third of the PDL was higher in aged mice (p < 0.01) and comprised predominantly apericytic vessels (p < 0.001). The number of PCV profiles increased significantly (p < 0.001) in aged mice in the PDL middle circumferential third halfway down the molar root. Age had no significant affect on PCV diameter. Aged PDL permeability studies are needed to investigate whether the changes in aged PCV profile number are associated with functional modification of the PDL microvasculature.

Pulsed Nd:YAG laser irradiation of the tooth pulp in the cat: I. Effect of spot lasing

BACKGROUND AND OBJECTIVE

The purpose of the present study was to evaluate physiologically pulpal nerve responses and to elucidate histopathologically the pulp tissue reactions to "spot irradiation" with a pulsed Nd:YAG laser.

STUDY DESIGN/MATERIALS AND METHODS

Antidromic compound action potentials and the pulpal blood flow (PBF) were recorded from the canine tooth of a sodium pentobarbitone-anesthetized cat. The laser irradiation-induced pulp tissue changes were histologically investigated.

RESULTS

The coronal antidromic compound action potentials disappeared in all the teeth tested during lasing, and the time needed to erase them was significantly shortened with increases in lasing power (P < 0.05). The radicular PBF increased when spot irradiation was performed, and the coronal PBF also temporarily increased with low-powered lasing. Histologic investigation revealed that spot irradiation with the laser produced severe damage in the pulp tissue in a dose-dependent manner.

CONCLUSION

The present study suggests that spot irradiation with a pulsed Nd:YAG laser risks producing nerve injury and irreversible tissue damage in the pulp with lasing for the purpose of desensitizing hypersensitive dentin.

Dental blood supply in the segmentally resected mandible

There are approximately 30,000 new cases of oral and pharyngeal carcinoma treated in the United States each year. A large number of these patients go on to receive segmental resection of the mandible, and have natural teeth remaining on the surgical side. To the best of our knowledge, there has not been a thorough discussion of the blood supply to these remaining teeth. Radiographic evidence of periapical pathology in these teeth is unusual, despite the compromised vascular supply. The purpose of this article is to report a case and review the literature on blood supply to teeth after segmental mandibulectomy. Microscopic examination was conducted on the pulpal tissue of a premolar retained on the side of, and anterior to, a segmental mandibular resection. Although abnormal, the pulp tissue showed evidence of a vascular supply 4 yr after mandibular surgery. A literature review was performed, and a discussion is given to explain the continued vascularity of the dentition through collateral and retrograde circulation. Despite the compromised dental circulation on the surgical side, unless radiographic evidence of periapical pathology occurs, endodontic therapy or extraction is not necessary. Due to the compromised nature of the circulation however, these teeth may be more susceptible to caries or restorative dental procedures that may lead to pulpal necrosis.

Neurokinin-1 receptor expression in the mature dental pulp of rats

Substance P induces inflammatory reactions in peripheral tissues including the dental pulp, but its regulatory effects in target tissues are dependent on receptor signalling. Here the expression of the substance-P receptor neurokinin-1 (NK1) in the mature molar pulp of the rat was examined in order to localize the main target areas for substance P. A polyclonal antibody directed against the C-terminal of the receptor was used, and immunohistochemistry was performed by the avidin-biotin peroxidase complex method. The results showed that the NK1 receptor was intensely expressed along vessel-like structures in the odontoblast and subodontoblast layer. A granulated and diffusely distributed NK1-receptor labelling was found along larger blood vessels in the root pulp and pulp proper. NK1 receptor-positive cells were frequently observed in the cell-rich zone beneath the odontoblast layer. The results indicate that, in the mature rat molar pulp, the main targets for substance P acting through the NK1 receptors are tissues related to blood vessels in the odontoblast and subodontoblast area. Furthermore, the expression of NK1 receptors on cells located in the subodontoblast area could indicate that substance P also affects cell functions in this area.

Effect of inferior alveolar nerve axotomy on periodontal and pulpal blood flow subsequent to experimental tooth movement in rats

The aims of this study were to evaluate the effect of inferior alveolar nerve (IAN) axotomy on periodontal (PDL) and pulpal blood flow incident to experimental tooth movement and to investigate whether nerve fiber regeneration coincides with blood flow changes. The first right mandibular molar was moved mesially for 3, 7, and 14 days after ipsilateral IAN axotomy in 29 rats. Four rats served as unoperated controls. At the end of each experimental period fluorescent microspheres (FM) were injected into the left ventricle and thereafter counted in serial sections in the PDL and pulp of the right and left first mandibular molars. The number of FM per tissue volume was taken as a measure of blood flow. Re-innervation of nerve fibers was mapped immunohistochemically 7, 14, and 21 days after IAN axotomy in 9 rats that had no orthodontic appliance. The statistical analysis showed no significant differences in the number of FM/mm3 PDL between the denervated and the contralateral side at 3 and 7 days. At 14 days the PDL on the denervated side showed a significant increase in the number of FM/mm3, coinciding with the initial periodontal nerve fiber re-innervation. In the pulp no significant differences were found between the denervated and the contralateral, innervated side in any experimental period. It can be concluded that IAN axotomy postpones an increase in periodontal blood flow until a sensory tissue re-innervation is established, thus indicating that neurogenic mechanisms play an important role in the development of the inflammatory reaction induced by experimental tooth movement.

Effect of experimental tooth movement on nerve fibres immunoreactive to calcitonin gene-related peptide, protein gene product 9.5, and blood vessel density and distribution in rats

The effect of experimental tooth movement on nerve fibers immunoreactive to calcitonin gene-related peptide (CGRP) and to protein gene product (PGP) 9.5 were studied, as well as the coincidence of these responses with changes in blood vessel density and distribution in the periodontal ligament (PDL) and pulp of young Wistar rats. The first right maxillary molar was moved mesially by an orthodontic appliance for 3, 7, 14 and 21 days. Sagittal and horizontal serial sections were incubated alternately with antibodies to CGRP, PGP 9.5 and laminin. Nerve and blood vessel density and distribution between the experimental and control sides were compared in the apical and cervical PDL, and in root and coronal pulp. The most pronounced changes occurred in the 7 day group. CGRP and PGP 9.5 immunoreactive nerves in the apical PDL showed increased density, being distributed towards the alveolar bone and frequently found in bone resorption lacunae. Numerous nerve fibres were often present adjacent to hyalinized tissue, but were never found near or within root resorption lacunae. Nerve sprouting was also present both in the root and coronal pulp. Increased nerve and blood vessel density generally coincided with each other. At day 14, periodontal nerves and blood vessels were still disorganized compared with the controls. Tissues near cellular cementum and root resorption lacunae were consistently devoid of nerve fibres. After 21 days, PDL nerve and blood vessel density and distribution were nearly at control level. However, nerve fibres were regularly found inside root resorption areas. In conclusion, experimental tooth movement induces dynamic changes in density and distribution of periodontal and pulpal nerve fibres, indicating their involvement in both early stages of periodontal remodelling and later in the regenerative processes of the PDL, generally occurring in concerted action with modulation of blood vessels.

Wound healing and revascularization: a histologic observation of experimental tooth root fracture

We used dogs as an animal model to generate tooth root fracture and to observe the wound-healing process of the fracture. Histologic examination of the specimens revealed that the early reaction of the wound healing was infiltration of inflammatory cells particularly at the coronal part of the fracture, whereas less inflammation but more abundant collagen fibers were seen at the apical part of the fracture (15 and 30 days). Inflammation lasted for more than 90 days and then subsided. At day 180, bone tissue healing was observed. Revascularization of the pulp tissues reached a high level at the same stage that bone healing took place. Our data suggest that in tooth root fracture, the regeneration of blood vessels is important in the wound-healing process and the revascularization is synchronized with the fracture wound healing. In this animal model the complete hard tissue healing could take as long as 6 months.

Irreversible pulpal damage of teeth adjacent to recently placed osseointegrated implants

Three cases of necrosis of previously vital teeth next to osseointegrated implant insertion sites are presented. In two cases, the teeth were in the anterior part of the lower jaw and exhibited the same pattern of evolution of pulpal damage (i.e. a relatively short time to become nonvital).

Nerve fibres and cells immunoreactive to neurochemical markers in developing rat molars and supporting tissues

The distribution of nerve fibres immunoreactive to calcitonin gene-related peptide (CGRP), substance P (SP) and neuropeptide Y (NPY) was compared to the general neurochemical markers for nerves and neuroendocrine cells protein gene product 9.5 (PGP 9.5) and neurone-specific enolase (NSE), by use of the avidin-biotin peroxidase complex method in developing dental structures in rats aged 13 to 27 days. A substantially greater part of the nerve fibres was immunoreactive to CGRP and SP than to NPY. In the bell stage, nerve fibres immunoreactive to PGP 9.5, CGRP and SP were found in the dental follicle but not in the dental papilla and stellate reticulum. In the advanced bell stage, after initiation of dentine and enamel formation, PGP 9.5, CGRP- and SP-immunoreactive fibres were found in the dental papilla, while the first NPY-immunoreactive fibres were observed in the papilla when root formation started. Concomitant with the beginning of root development, a subodontoblastic nerve plexus was gradually formed and PGP 9.5-, CGRP- and SP-immunoreactive fibres were found within the dentinal tubules. From the start of root formation, CGRP-, SP- and NPY-immunoreactive nerves were shown in the developing periodontal ligament, although a mature distribution pattern was not observed until root formation was nearly completed. Ameloblasts, odontoblasts and cell-like structures in the outer enamel epithelium and within the dental lamina were PGP 9.5-immunoreactive at the bell stage. As the tooth matured, the immunolabelling gradually decreased, but was still present in some odontoblasts after tooth eruption. NSE-immunoreactive, cell-like structures were found in the periphery of the dental follicle, and persisted close to alveolar bone in the periodontal ligament when the tooth reached occlusion. Hence, it may be concluded that sensory nerves containing SP and CGRP are present in the pulp in advance of sympathetic nerves immunoreactive to NPY.

Studies on peri-root tissue formation around new type artificial root made of dense hydroxyapatite

The aim of this study was to examine the wound healing process and tissue development around a new type of artificial root made of dense hydroxyapatite. The newly tailored artificial roots, which have characteristic corrugated configurations with smooth root surfaces, were implanted immediately after extraction of the premolars of adult dogs. After preliminary experiments, the following studies were carried out: for the observation of tissue formation around the artificial root, artificial root with surrounding tissue were extirpated after fixed periods (6-32 weeks) of implantation; to study tissue formation at the artificial root surface, undecalcified specimens with polished surfaces for microanalysis and decalcified specimens for light microscopic observation were prepared after 72 weeks of implantation. The following results were obtained: around the artificial roots in the jawbone, fibrous tissue formation with angled orientation, bone formation resembling alveolar bone proper, and calcified substance formation attaching to the root surface were observed.

Vascular architecture of cat pulp using corrosive resin cast under scanning electron, microscopy

Vascular casts of cat premolar pulps in various stages of growth were made by injection of low-viscosity resin into the pulpal blood vessels. Examination under a scanning electron microscope revealed that, in the young pulp, the main arterioles ascend in the center of the pulp and venules run along the side of the root canal space. The subodontoblastic vascular plexus of the pulp could be distinguished by its characteristic three layers: 1. the terminal capillary network located in the odontoblastic layer; 2. a second layer of the capillary network which is composed of pre- and postcapillaries running parallel to each other; and, finally, 3. the venular network which has a lattice type appearance. The pulp cavity is reduced in size with age (maturation stage), in which the characteristic three vascular layers are changed into a one-layer coarse terminal capillary network which converges directly with the main venules. At this stage the blood vessels, especially the main venules, are also fewer in number.