Rat Maxilla Research Articles

Effects of sympathectomy on experimentally induced pulpal inflammation and periapical lesions in rats

The role of sympathetic nerves in bone physiology is largely unknown. Recent studies have shown a correlation between sympathectomy and bone remodeling. The present experiments were aimed to study the effects of unilateral sympathectomy on bilateral experimentally induced pulpitis and periapical lesions in the rat maxilla and mandible. Adult male Sprague–Dawley rats were used. Experimental rats ( n=11) had the right superior cervical ganglion surgically removed (SCGx) and control rats ( n=5) had sham surgery. Pulpal inflammation and periapical bone lesions in the maxilla and mandible were created 14 days later in both experimental and control rats by exposing the dental pulp in the first and second molars and leaving them open to the oral microflora. The rats were perfused 20 days thereafter and the jaws processed for immunohistochemistry with neuropeptide Y (NPY) and ED1 as primary antibodies. Sympathectomy resulted in an almost complete loss of NPY-immunoreactive (IR) fibers in the right SCGx jaws. In the non-sympathectomized (non-SCGx) left side and in the control rats, sprouting of NPY-IR fiber was observed in the inflamed pulp tissue adjacent to reparative dentin formation and in the apical periodontal ligament of the partially necrotic first molars. Significantly more ED1-IR osteoclasts were found in the resorptive lacunae lining the periphery of the periapical lesions on the SCGx side compared with the non-SCGx side ( P<0.04) and the controls ( P<0.03). The size of the periapical lesions were larger on the SCGx side compared with the non-SCGx side ( P<0.03) in the mandible, but not in the maxilla. We conclude that inflammation causes sprouting of NPY-IR nerve fibers and that unilateral removal of the SCG increases both the area of the periapical lesions and the number of osteoclasts in the inflamed region.

Regeneration of nerve fibres in the peri-implant epithelium incident to implantation in the rat maxilla as demonstrated by immunocytochemistry for protein gene product 9.5 (PGP9.5) and calcitonin gene-related peptide (CGRP).

The response of nerve fibres in the peri-implant epithelium to titanium implantation was investigated with an experimental model using rat maxilla and immunohistochemical techniques. The latter employed antibodies to protein gene product 9.5 (PGP9.5), and to calcitonin gene-related peptide (CGRP). In control rats without an implantation, a dense innervation of PGP9.5- and CGRP-positive nerve fibres was recognized throughout the junctional epithelium, as has been previously reported. A titanium-implantation induced a remarkable inflammatory reaction, as well as the destruction of covering epithelial cells. By 3-5 days post-implantation, inflammatory reaction showed a tendency to disappear, and the peri-implant epithelium showed proliferation and down-growth along the implant. At this stage, no nerve fibres were found around the peri-implant epithelium. At 10 days, a few nerve fibres reached the basal cell layers of the peri-implant epithelium, and entered it 15 days after implantation when the peri-implant epithelial cells showed morphological features roughly resembling those of normal junctional epithelial cells. At the complete osseointegration stage (days 20-30), the PGP9.5- and CGRP-positive nerve fibres, thin and beaded in appearance, were found distributed in the peri-implant epithelium. After 20 days, the numerical density of the intraepithelial nerves in the peri-implant epithelium appeared the same as, or less than, that in the normal junctional epithelium. These findings indicate that the peri-implant epithelium shows the same innervation as that in normal junctional epithelium, and that the intraepithelial nerve fibres in the peri-implant epithelium might have diverse functions, which have been suggested in the literature.

EVOLUTION OF THE INTERNAL FIXATION OF LONG BONE FRACTURES

EVOLUTION OF THE INTERNAL FIXATION OF LONG BONE FRACTURES

Experimental study on wound healing of alveolar bone sockets in the rat maxilla after X-ray irradiation.

The purpose of this study was to examine the effects of radiation on the healing process of tooth extraction wounds. X-ray doses of 10 Gy were delivered once to the maxillofacial area of Wistar strain rats, and the maxillary first molar was extracted 7 days later. Animals were killed 3, 7, and 14 days after odontectomy, and thin sections of the maxilla were prepared. The specimens were stained with hematoxylin and eosin, azan, alkaline phosphatase and tartrate-resistant acid phosphatase (TRAP) stains for microscopic observation. The ratio of the area of the bone tissue to the area of the alveolar socket (BS/TS) and the numbers of TRAP-positive cells were evaluated. Seven days after odontectomy, BS/TS was significantly lower in the irradiated group than in the nonirradiated group. Alkaline phosphatase staining was observed along the rim of the bone 7 and 14 days after odontectomy in both groups, but it was milder in the irradiated group than in the nonirradiated group. TRAP-positive cells were present on the floor of the postextraction socket and the margins of the septal alveolar bone, and, 3 days after odontectomy, the number of TRAP-positive cells was significantly greater in the irradiation group than in the nonirradiation group.

Ultrastructural and immunoelectron microscopic studies of the peri-implant epithelium-implant (Ti-6Al-4V) interface of rat maxilla.

The role played by the internal basal lamina (IBL) and hemidesmosomes between an implant and the peri-implant epithelium (PIE) in the adherence of the epithelium to the implant is controversial. This study used rat maxilla implantation models to clarify the ultrastructure of the PIE-implant interface. Ti-6Al-4V implants were inserted either immediately or 2 weeks after the extraction of the upper left first molar of 6- or 4-week-old rats, respectively. The junctional epithelium (JE) of the upper right molars in the same animals was used as a control. Four weeks after implantation, the animals were sacrificed to prepare specimens for light and immunoelectron microscopy. Under light microscopy, the PIE appeared to attach to the implant surface. Ultrastructurally, IBL, consisting of the lamina densa and lamina lucida, and hemidesmosomes were formed only in the lower region, and rarely in the middle region, of the PIE-implant interface. In control teeth, the IBL and hemidesmosomes formed throughout the dento-JE interface. Laminin-1 was found in the IBL and also in the vesicles and vacuoles of the PIE and JE cells. Statistical analysis showed that there was also a significant difference in the amount of IBL between the PIE-implant and dento-JE interfaces. PIE attached to the implant via hemidesmosomes and IBL in the lower region of the PIE-implant interface. Although PIE cells may secrete laminin-1, which contributes to epidermal cell adhesion, the PIE which attaches to implants only in the lower region of the interface is considered to be the poorly adhered epithelium.

Tissue response to titanium implants in the rat maxilla: ultrastructural and histochemical observations of the bone-titanium interface.

The detailed mechanism of osseointegration, the most appropriate implant-bone interface, remains unclear in jaw tissues at the ultrastructural level in contrast to the many reports using long bones. The present study reports on tissue response to titanium-implantation on an animal model using rat maxilla. Animals were sacrificed at 1 to 28 days post-implantation and prepared tissue specimens, freed from implants by a cryofracture technique, were processed for transmission electron microscopy and histochemistry for tartrate resistant acid phosphatase activity (TRAPase). Different patterns in bone formation were recognized between lateral and base areas of implant cavities. In the lateral area with narrow gaps, bone deposition took place from the pre-existing bone towards the implant after active bone resorption by osteoclasts reactive to TRAPase. However, no distinct bone formation appeared in the lateral area where the implant had been installed close to the osteotomy margin. On the other hand, new bone formation was found at the base area without any apparent bone resorption. Interestingly, mononuclear cells reactive to TRAPase, presumably preosteoclasts, frequently occurred near preosteoblasts. Osseointegration around the implants was obtained in this model by 28 days post-implantation except for the lateral area with complete contact with implants, where the thin layer remained in contact with the implant surface. These findings indicate that ossification proceeds at different modes around the titanium implant in rat maxilla, depending on the nature of the recipient bones and the dimension of the gap between the implant and osteotomy margin.

Expression of collagen alpha1(I) mRNA variants during tooth and bone formation in the rat.

Collagen alpha1(I) mRNA is composed of two variants of 5 and 6 kb, differing in the length of the 3' untranslated region. In this work, the nucleotide sequences of the two rat mRNA variants were compared, and their expression pattern in cells forming bone, dentin, and cementum were analyzed. The sequences were determined from cDNA inserts of tooth and bone libraries plus directly from PCR fragments, obtained from bone. A total of 5721 bases of the rat collagen alpha1(I) sequence from cDNA of tooth and bone was determined. All sequences of the short variant were represented in the long variant. Only the alternatively poly-A additions gave rise to the variants in hard tissue. Two oligonucleotides were chosen as probes, one of which recognized, on Northern blots, the two bands of 5 and 6 kb, and the other the 6-kb variant only. The oligonucleotides were used in in situ hybridization experiments, for study of the distribution of the variants in different extracellular matrix-forming cells. Osteoblasts, odontoblasts, and cementum-associated cells were closely examined in sections from rat maxillae from 2 to 25 days of age. A similar or identical pattern of mRNA expression was observed with both oligonucleotides, indicating that the two mRNA variants were co-expressed in all cases.

Collagen mRNA expression during tissue development: the temporospacial order coordinates bone morphogenesis with collagen fiber formation.

Bone formation of the maxilla and premaxilla of rats was studied by in situ hybridization, using probes for fibrillar collagen mRNAs. Chondroblasts, osteoblasts, fibroblasts and peripheral bone cells differed in their expression patterns. Prospective nasal chondroblasts expressed collagen alpha1(II) and alpha1(XI) RNA from day 15 post coitum. Bone formation in the adjacent maxilla and premaxilla started around day 17: groups of osteoblasts, representing ossification centers, expressed collagen alpha1(I) RNA strongly, and alpha1(V), alpha2(V) and alpha1(XI) RNA weakly, but they were deficient in collagen alpha1(III) RNA. As the centers expanded, osteoblasts in the resulting bone domains expressed collagen alpha1(I) RNA in abundance, whereas collagen alpha1(III) RNA was absent. Bone domains were surrounded by fibroblasts containing collagens alpha1(I), alpha1(III) and alpha2(V) RNA. Widely separated fibroblasts underwent condensation into densely packed periosteum and sutural soft tissues. Cells at the periphery of fast-growing bone domains also displayed, apart from collagen alpha1(I) RNA, collagens alpha2(V) and alpha1(XI) RNA. Given the continuous recruitment of cells from the periosteum, peripheral bone cells represent differentiating osteoblasts synthetizing collagens alpha2(V) and alpha1 (XI) RNA transiently. Thus, gene expression during osteoblast differentiation reflects synthesis of fiber components during bone growth, since collagen V is located in the center of fibers consisting primarily of collagen I.

Influence of hydrocortisone and calciferous drugs on the structure of maxilla of wistar strain rats

Influence of hydrocortisone and calciferous drugs on the structure of maxilla of wistar strain rats

A Histological Study on Tissue Responses to Titanium Implantation in Rat Maxilla: The Process of Epithelial Regeneration and Bone Reaction

The present study aimed to establish a titanium implantation model using rat maxillae as well as demonstrate the chronological tissue responses to implantation. Pure titanium implants were inserted in the upper first molar extraction sites of Wistar rats 1 month after tooth extraction. The animals were sacrificed at 1 to 30 days postimplantation, and prepared tissue specimens were processed for light microscopy. The removal of implants from tissue blocks was done using 2 methods: mechanical removal or a cryofracture technique. In the early stages, peri-implant tissues showed severe damage to the oral epithelium and collagen bundles with significant inflammatory cell infiltration. The peri-implant epithelium grew apically along the implant by 10 days postimplantation, and regenerated to show a similar feature of junctional epithelium seen in normal rats at 15 days postimplantation, at which time no signs of inflammation were observed. The regenerated collagen bundles in the connective tissue were arranged circumferentially to the implants in the horizontal sections. New bone formation first appeared around the implants at 5 days postimplantation, covering the entire perimeter of implants by 30 days postimplantation. Scanning electron microscopic observations of the surface texture of the removed implants suggest the probability of an adhesive mechanism between the implants and the peri-implant epithelium and/or the alveolar bone. These findings indicate that this experimental model is useful for detailed analysis of peri-implant tissue because of its easy implantation procedure.

卵巣摘出ラットにおける上顎骨，下顎頭および大腿骨の構造変化に関する比較組織学的研究

Postmenopausal estrogen deficiency results in bone loss (osteoporosis) in humans and experimental animals. The acute and significant loss of trabecular bone in the ovariectomized (OVX) rat provides a useful experimental model of postmenopausal osteoporosis. Five months after ovariectomy of 3-month-old female rats, the mid and distal femurs, maxillae, and mandibular condyles were dissected and processed for light and backscattered electron microscopic examinations. Net trabecular bone values of femurs in OVX ats showed significant loss of trabecular (but not cortical) bones compared to those in sham-operated controls. Net bone volume in the maxillae of OVX rats was similar to that of controls. In mandibular condyles, OVX caused prominent bone loss similar to that in femurs. Throughout the observations, active osteoclastic bone resorption was rarely recognized, presumably due to the fact that the rats had been in the statistic post-OVX phase. These results suggested that, in this animal model of postmenopausal steoporosis, the bone loss is more prominent in trabecular bone areas formed by endochondral ossification such asmetaphyses of femurs and mandibular condyles than cortical bone areas formed by intramembranous ossification such as mid-diaphyses of femurs and maxillae.

Photofrin-mediated photodynamic therapy of rat palatal mucosa: Normal tissue effects and light dosimetry

Photodynamic therapy (PDT) is a treatment modality with potential application for premalignant lesions and squamous cell carcinoma of the oral mucosa. PDT in principle has dual selectivity. This may result from a ‘preferential’ retention of the photosensitizer in target tissue. In addition, the photodynamic activity will be limited to the irradiated area because PDT will not affect tissues in the absence of excitation light. The specificity of PDT is limited by the fact that normal tissues also retain the photosensitizer to some degree, which makes these tissues susceptible to PDT damage. To optimize PDT for oral malignancies, a study was undertaken on normal tissue to investigate the responses in rat palatal mucosa and surrounding anatomical structures. Eighty male Wistar rats were used in the study. Photofrin was administered i.v. at four doses (0, 2.5, 5 or 10 mg kg−1 body weight). Irradiation for PDT was performed 24 h later. An argon pumped dye laser system was used to produce light of two different treatment wavelengths (514.5 and 625 nm), and various energy density levels (0, 25, 50, 100 or 200 J cm−2). Early effects of PDT were studied at 2 days and late effects at 2 months after treatment. Twenty-four hours after i.v. administration of Photofrin, it was found that PDT affects normal tissues of the oral cavity both macroscopically and microscopically. Combinations of photosensitizer doses ≥5 mg kg−1 and light doses≥100 J cm−2 caused severe and permanent damage to the palatal mucosa and adjacent normal structures such as palatal bone and dentition. Light scattering and internal reflection usually raise the fluence rate in tissue above the irradiance of the incident beam. In an additional study using six male Wistar rats, the energy fluence rate at two treatment wavelengths (514.5 and 625 nm) was measured ex vivo in the palatal mucosa and adjacent anatomical structures. As expected, the energy fluence rates were wavelength, tissue and depth dependent. At the air-mucosa boundary, light of 625 nm was found to have a three-times higher fluence rate than the primary incident beam. Under similar conditions, the fluence rate of 514.5 nm was found to be less, but still twice as high as the primary incident beam. At deeper levels of the rat maxilla, fluence rates were still elevated compared with the incident beam. For 625 nm light, this phenomenon was observed up to the level of the nasal cavity. These increased fluence rates could largely explain the pattern of damage to normal mucosa and surrounding anatomical structures.

Ultrastructural and Immunocytochemical Characterization of the Bone-Single Crystal Sapphire Implant Interface in the Rat Maxilla

To evaluate the suitability of a new implant animal model, we examined the host response to single crystal sapphire implant into the rat maxilla socket and characterized the regenerating tissue-implant interface using a combination of morphological and immunocytochemical approaches. At 2, 4, and 8 weeks after implantation, animals were sacrificed and tissues processed for morphological or immunocytochemical studies. Results demonstrated that nonmineralized connective tissue was present between bone and the implant surface. However, in some situations at 8 weeks, direct bone contact was observed. Electron microscopy revealed that the interface between the implant and the regenerating tissues was characterized by the presence of either cells or an intervening extracellular matrix layer that had a variable appearance and thickness.The bone-implant interface was immunoreactive for osteopontin. The rat maxilla socket implant model, due to its ease of management and its similarities to other previous experimental animal models, seems to be useful for some specific implant experimental studies.

Effect of essential fatty acid deficiency on the fatty acid composition and arachidonic acid levels in rat maxillae and mandibles.

The fatty acid composition of total lipids and total phospholipids of maxillae and mandibles of rats fed an essential fatty acid-deficient (EFAD), marginally FAD (MEFAD), and a control diet was determined. Patterns typical of an EFA deficiency such as a decrease in the levels of linoleic acid and archidonic acid along with concomitant increase in the levels of palmitoleic acid, oleic acid, and 5,8,11-eicosatrienoic acid were observed in the EFAD groups. Concentrations of arachidonic acid were significantly lower in total lipids of mandibles and maxillae of rats in the EFAD, but not in the MEFAD rats, than those of the controls.

Effect of subperiosteally implanted polytetrafluoroethylene (PTFE) material on alveolar bone in the rat

The aim of this study was to examine the effect on osteocytes after subperiosteal implantation of polytetrafluoroethylene (PTFE) material in the rat maxilla. In four young conventional albino rats, mucoperiosteal flaps were elevated by sulcular incision, and segments (1 x 4 mm) of PTFE material were implanted between bone and flap tissue. After a healing period of 14 days, specimens containing implants and adjacent bone were processed for transmission electron microscopy. The specimens were stepwise reduced to obtain a total of 16 levels for thin sectioning. Osteocytes (n = 640) in alveolar bone underlying implanted material (region 1) and adjacent bone (region 2) were studied to determine the ratio of intact to degenerated cells. In alveolar bone covered by implanted material (region 1) and adjacent bone (region 2), 56% and 16% of the osteocytes, respectively, showed distinct signs of necrocytosis. This study has shown that subperiosteal placement of PTFE material results in partial necrosis of superficial alveolar bone.

Scintigraphy in the small animals using a human gamma camera--evaluation of bone scintigraphy in the rat mandible and maxilla

In order to obtain clear scintigrams of small animals, some improvements were brought on a pinhole collimator. Then, using a human gamma camera with this collimator improved, bone scintigraphy was attempted in the rat mandible and maxilla, experimentally to examine the desirable conditions of scintigraphy. The most desirable bone scan images were obtained under the conditions that the pinhole was 1.5 mm in diameter, the distance between the collimator and the object was 0 cm, and the exposure was 400.

The Effect of Decalcification on the Microspectrophotometric Determination of Dna

Conventional methods of decalcification using acids depolymerize nucleic acids. This is a serious handicap for microspectrophotometric studies on the DNA content of calcified tissues. in the investigation reported here we have evaluated different decalcifying agents for this purpose. Liver, spleen, and maxillae of adult Wistar rats were exposed to the action of nitric acid, picric acid, and EDTA.

Growth pattern of the rat maxilla from 16 days insemination age to 30 days after birth.

Growth pattern of the rat maxilla from 16 days insemination age to 30 days after birth.

Study of the healing process following operative interference with the continuity of the rat maxilla.

Study of the healing process following operative interference with the continuity of the rat maxilla.