A giant peripheral ossifying fibroma of the maxilla with extreme difficulty in clinical differentiation from malignancy: a case report and review of the literature.

BACKGROUND: Peripheral ossifying fibroma is a nonneoplastic inflammatory hyperplasia that originates in the periodontal ligament or periosteum in response to chronic mechanical irritation. Peripheral ossifying fibroma develops more commonly in young females as a solitary, slow-growing, exophytic nodular mass of the gingiva, no more than 2 cm in diameter. While various synonyms have been used to refer to peripheral ossifying fibroma, very similar names have also been applied to neoplastic diseases that are pathologically distinct from peripheral ossifying fibroma, causing considerable nomenclatural confusion. Herein, we report our experience with an unusual giant peripheral ossifying fibroma with a differential diagnostic challenge in distinguishing it from a malignancy. CASE PRESENTATION: A 68-year-old Japanese male was referred to our department with a suspected gingival malignancy presenting with an elastic hard, pedunculated, exophytic mass 60 mm in diameter in the right maxillary gingiva. In addition to computed tomography showing extensive bone destruction in the right maxillary alveolus, positron emission tomography with computed tomography revealed fluorodeoxyglucose hyperaccumulation in the gingival lesion. Although these clinical findings were highly suggestive of malignancy, repeated preoperative biopsies showed no evidence of malignancy. Since even intraoperative frozen histological examination revealed no malignancy, surgical resection was performed in the form of partial maxillectomy for benign disease, followed by thorough curettage of the surrounding granulation tissue and alveolar bone. Histologically, the excised mass consisted primarily of a fibrous component with sparse proliferation of atypical fibroblast-like cells, partly comprising ossification, leading to a final diagnosis of peripheral ossifying fibroma. No relapse was observed at the 10-month follow-up. CONCLUSIONS: The clinical presentation of giant peripheral ossifying fibromas can make the differential diagnosis from malignancy difficult. Proper diagnosis relies on recognition of the characteristic histopathology and identification of the underlying chronic mechanical stimuli, while successful treatment mandates complete excision of the lesion and optimization of oral hygiene. Complicated terminological issues associated with peripheral ossifying fibroma require appropriate interpretation and sufficient awareness of the disease names to avoid diagnostic confusion and provide optimal management.

Consideration of mouth opening when using positioning stents during radiotherapy for tongue cancer: a retrospective study.

Background: The aim was to clarify the range of mouth opening required to minimize the development of oral mucositis on the palate while using a positioning stent during radiotherapy in patients with tongue cancer. A positioning stent is used to reduce the severity of oral mucositis; however, requirements for fabricating the device have not been standardized. In particular, the range of mouth opening required while using a stent to prevent radiation-induced oral mucositis has not been determined. Materials and methods: We retrospectively analyzed medical records and computed tomography (CT) images of nine patients who had undergone radiotherapy for tongue cancer. Irradiation dose for the palate and range of mouth opening while using the positioning stent was calculated from CT images and the radiotherapy treatment planning program. Results: The irradiation dose presented as medians and interquartile range (IQR) for the palate was 1.6 (IQR: 1.1-2.2) Gy with the use of the positioning stent and 37.2 (IQR: 17.5-44.1) Gy without the use of the positioning stent. The range of mouth opening was 19-37 [mean ± standard deviation (SD): 26 ± 5.6] mm, and it correlated with the attenuation amount of irradiation dose to the palate (r = 0.673, p = 0.0467). Regression equation was y = 0.21x + 19. Conclusions: Our study may be useful for deriving the relationship between the attenuation amount of irradiation of the palate with the positioning stent and the amount of mouth opening required for this attenuation.

Morphological Investigation of Residual Ridge in Japanese Edentulous Elderly for Fabrication of Edentulous Stock Tray.

The objective of this study was to determine the size of the residual ridge in edentulous elderly Japanese persons for preparation of edentulous stock trays and clarify any correlations among the items measured. The participants comprised 74 patients requesting construction of a complete denture for the maxilla, mandible, or both. The length, width, and anterior and posterior height of the maxillary and mandibular residual ridge was measured on a prepared working model using a caliper. For each of the maxillary and mandibular edentulous residual ridges, correlations among measurement items were analyzed employing Pearson's correlation coefficient. In participants who were edentulous in both the maxilla and mandible, correlations between the maxillary and mandibular measurement items were analyzed employing Pearson's correlation coefficient. The results revealed that the mean maxillary length of the residual ridge was 55.21±4.07 mm, while mean mandibular length was 56.03±4.04 mm. The mean posterior width of the maxillary jaw was 48.79±4.14 mm, while that of the mandibular jaw was 57.33±3.24 mm. A strong correlation was found between the length and width of the residual ridge in both the maxilla and mandible, but no strong correlation was detected between the height in the anterior tooth region and any other item measured. These findings suggest that the size of any given item can be estimated by measuring either the length or width of the residual ridge when selecting a stock tray. We also propose that it is necessary to prepare stock trays with several different heights in the anterior tooth region, regardless of the length and width of the tray, or to adjust the length of the tray.

Accuracy and retention of denture base fabricated by heat curing and additive manufacturing.

PURPOSE: The aim of the present study was to compare the accuracy and retentive force of an experimental denture base fabricated using additive manufacturing and heat curing. METHODS: A maxillary edentulous jaw model made of silicon was used. The shape data for the working cast and wax pattern of the experimental denture base were obtained using a dental laboratory scanner. Fabrication of the experimental denture bases was performed using heat curing and additive manufacturing. The shape data for the experimental denture bases was captured using an optical scanner. The shapes of the two experimental denture bases were compared with the shape of the working cast. A digital force gauge was used to measure the traction force. Pulling was maintained until the experimental denture base separated from the elastic model. Retention was set as the maximum value for the traction force. In order to compare the retentive force of the two experimental denture bases. RESULTS: The experimental denture base fabricated using additive manufacturing was more accurate than the experimental denture base fabricated using heat curing. The experimental denture base fabricated using additive manufacturing demonstrated greater retentive force than the experimental denture base fabricated using heat curing. CONCLUSIONS: In this study, the experimental denture base fabricated using additive manufacturing was more accurate and obtained greater retentive force than the experimental denture base fabricated using heat curing.

Relationship between masticatory function and frailty in community-dwelling Japanese elderly.

BACKGROUND: Frailty likely results in impaired functioning, and frail individuals requiring long-term care have recently attracted the attention of researchers. In the oral health field, the number of elderly individuals who require intervention for retaining occlusion has been increasing, as has the number of remaining teeth and required prosthetic treatment. Additionally, the number of elderly with reduced masticatory function has also been increasing, and frailty is a suspected factor. AIMS: The aim of this study is to clarify the relationship between frailty and masticatory function decline. DESIGN: A cross-sectional study. METHODS: A total of 747 participants (total mean age 73.6 ± 5.8 years old) underwent a comprehensive examination at the Tokyo Metropolitan Institute of Gerontology. Three masticatory functions were evaluated: maximum occlusal force, mixing ability, and self-reported chewing ability. Frailty was determined using all 25 questions of the Basic checklist developed by the Japanese Ministry of Health, Labour and Welfare, following the method reported by Satake et al. RESULTS: Binomial logistic analysis clarified the relationship between frailty and evaluation of each of the three masticatory functions. Significant correlations of pre-frailty or frailty with maximum occlusal force, mixing ability, and subjective chewing ability were observed. CONCLUSION: All three masticatory functions (maximum occlusal force, mixing ability, and self-reported chewing ability) were associated with pre-frailty or frailty in community-dwelling Japanese elderly.

Maxillofacial prosthetic treatment factors affecting oral health-related quality of life after surgery for patients with oral cancer.

STATEMENT OF PROBLEM: After oral cancer surgery, tissue defects can cause deformity and limited mobility, complicating many essential functions. For patients with mandibular, tongue, and oral floor defects, evidence regarding the effects of maxillofacial prosthetics on their oral health-related quality of life (OHRQoL) is lacking. Therefore, maxillofacial prosthetic reconstruction has been implemented with no clear treatment goals. PURPOSE: The purpose of this clinical study was to identify factors affecting the improvement of OHRQoL by using maxillofacial prosthetic treatment after surgery to repair maxillary, mandibular, tongue, and oral floor defects. MATERIAL AND METHODS: All individuals who agreed to maxillofacial prosthetics after surgery for oral cancer were enrolled. Oral function and OHRQoL were evaluated before maxillofacial prosthesis placement and 1 month after final adjustments. The oral functions evaluated included masticatory function, swallowing function, and articulatory function. The Oral Health Impact Profile (OHIP-J54) was used to evaluate OHRQoL. Factors affecting changes in the OHIP-J54 score for participants' background and oral functions before and after treatment were analyzed through logistic regression analysis (stepwise method). RESULTS: Participants included 34 men and 16 women with an average age of 72.4 ±8.7 years. "Psychological discomfort" was correlated with the patient's sex and masticatory function. "Physical disability" was related to articulatory function. "Handicap" was related to the swallowing function. "Additional Japanese questions" were related to the patient's sex. CONCLUSIONS: Participants' sex and their oral functions, including masticatory, swallowing, and articulatory functions, were associated with improved OHRQoL because of maxillofacial prosthetics after surgery for oral cancer.

Anti-infective control in human bronchiolar epithelial cells by mucin phenotypic changes following uptake of N-acetyl-L-cysteine.

PURPOSE: Aspiration pneumonia is infection of the respiratory tract resulting from accumulation of sputum in the larynx. N-acetyl-L-cysteine (NAC) might regulate mucin (MUC) expression and activate inherent anti-infective system in bronchiolar epithelial cells after cellular uptake, and therefore, serve as the preventative agent for chronic lung disease including aspiration pneumonia. The purpose of this in vitro study was to evaluate the effect of uptake of NAC by human bronchiolar epithelial cells on bacterial infection and regulations of mucin expression in association with cellular redox status under co-culture with a representative pathogen for hospital- and community-acquired pneumonia, Streptococcus pneumoniae. MATERIALS AND METHODS: Human bronchiolar epithelial cells preincubated with or without 20 mM NAC for 3 h were co-cultured with or without bacteria for 8 h and evaluated with respect to cellular redox balance, expressions of various types of MUC, proinflammatory cytokines and mediators, and bacterial infection state by biochemical, genetic, and immunofluorescent assays. RESULTS: Markedly increased intracellular reactive oxygen species and oxidized glutathione levels plus increased release and expression of proinflammatory cytokines and mediators were observed in cells co-cultured with bacteria. These bacteria-induced cellular redox disturbance and proinflammatory events were prevented and alleviated by pretreatment with NAC. Cells co-cultured with bacteria did not increase expression of anti-infective membranous MUC4 but exhibited increases in gel-forming MUC5AC expression and bacterial infection. However, NAC-pretreated cells avoided bacterial infection along with enhancement of MUC4, but not MUC5AC, expression. CONCLUSION: Uptake of NAC by human bronchiolar epithelial cells prevented bacterial infection and upregulated membranous, but not gel-forming, MUC expression along with the increase in intracellular antioxidant level under co-culture conditions with S. pneumoniae.

Ultraviolet-C irradiation to titanium implants increases peri-implant bone formation without impeding mineralization in a rabbit femur model.

OBJECTIVES: Volume and bone quality of peri-implant supporting bone, in particular, at implant neck region, as well as bone-implant contact ratio, is important for long-term stability of implants. Ultraviolet-C (UVC) irradiation is known to enhance the osseointegration capability of titanium implants. However, the histological determination was performed only on a rat model, but not pre-clinical animal model such as a rabbit model. The purpose of this study was to determine the effects of UVC irradiation on titanium implants on the volume and mineral density of peri-implant supporting bone formation in a rabbit femur model. MATERIALS AND METHODS: Acid-etched pure titanium screw implants with or without 3 mW/cm2 UVC irradiation for 48 h were placed in rabbit femur diaphyses. Peri-implant bone tissue formation was analyzed at 3 and 8 weeks post-operatively by histology and micro-CT-based bone morphometry after calibration with hydroxyl apatite phantoms. RESULTS: UVC pre-irradiated implants accumulated a higher density of cells and thicker and longer bone tissue attachments that continued into the inner basic lamellae of the surface of existing cortical bone at 3 and 8 weeks than the implants without irradiation. Although the bone mineral density around both implants was equivalent to that of the existing cortical bone, bone volume was greater with UVC pre-irradiation in two-thirds or more of the apical region throughout the observation period. CONCLUSIONS: These results indicate that UVC treatment increased the volume of cortical-like bone tissue in the coronal region of titanium implants without deterioration of bone mineral density.

Specific ultraviolet-C irradiation energy for functionalization of titanium surface to increase osteoblastic cellular attachment.

PURPOSE: The objective of this in vitro study was to examine the influence of the total energy of ultraviolet-C preirradiation on the number and morphology of osteoblastic cells attached to turned or acid-etched titanium surfaces, and physicochemical properties of the surface. MATERIALS AND METHODS: Rat bone marrow-derived osteoblasts were incubated with turned or acid-etched titanium disks preirradiated with ultraviolet-C at 1 or 3 mW/cm(2), resulting in total energies of 10, 100, 250, 400, 500, 600, 750, or 1000 J/cm(2). Osteoblast attachment to the surface was evaluated using the WST-1 assay. Physicochemical changes of the titanium were evaluated by measuring water wettability and X-ray photoelectron spectroscopy analysis. RESULTS: Number of attached cells was greater on turned or acid-etched surface preirradiated with 500 or 750 J/cm(2) of 3 mW/cm(2) ultraviolet-C than on the nonirradiated surface, respectively. However, the further irradiation energy did not increase the numbers on both types of the surfaces. These phenomena were also seen on the surfaces preirradiated at different ultraviolet-C intensities. Ultraviolet-C irradiation induced superhydrophilicity on both types of surface even with the less irradiation energy. The amount of carbon on ultraviolet-C preirradiated titanium surfaces decreased gradually with an increase in the total irradiation energy. CONCLUSION: Specific ultraviolet-C energy used to irradiate turned or acid-etched surfaces increased the number of osteoblastic cells attached to each of the surface. This was canceled by overirradiation, despite maintenance of both the acquired superhydrophilicity and the accompanying reduction in carbon on each surface.

A 5-year activity report from the Oral Cancer Center, Tokyo Dental College.

The Tokyo Dental College Oral Cancer Center was established on April 1st, 2006 at our Ichikawa General Hospital for the purpose of providing multimodal treatment for oral cancer. This report summarizes the Center's activities over the last 5 years. The total number of oral cancer patients treated was 360 (April 2006 to March 2011), with 205 primary cases. We investigated the following treatment-related items: 1) site, 2) age, 3) sex, 4) pathological examination, 5) staging, 6) systemic disorder, 7) double cancer, 8) treatment, and 9) prognosis. Out of 205 patients, 60% were men and 40% were women. Men in their 60s and women in their 80s were seen the most. The most common site was the tongue, at 42%, followed by the mandibular gingiva, maxillary gingiva, oral floor, and buccal mucosa. Squamous cell carcinomas were seen most frequently, at 94% (15% were stage I, 33% stage II, 15% stage III, and 34% stage IV). The most common treatment method was surgical treatment, at 83%. The 5-year survival rate at all stages was 85.4%. At the Oral Cancer Center, oral surgeons take the initiative in establishing treatment in cooperation with other departments and branches. Since the establishment of the Ambulatory Center for Maxillary Prosthetics in October 2011, 26 patients have undergone treatment. Related departments and branches work in teams, enabling comprehensive treatment, from the preoperative state to postoperative functional recovery. We wish to use these strengths to improve oral cancer treatment in Japan and will continue to work toward providing the best possible care for our patients.

Nanometer-thin TiO2 enhances skeletal muscle cell phenotype and behavior.

BACKGROUND: The independent role of the surface chemistry of titanium in determining its biological properties is yet to be determined. Although titanium implants are often in contact with muscle tissue, the interaction of muscle cells with titanium is largely unknown. This study tested the hypotheses that the surface chemistry of clinically established microroughened titanium surfaces could be controllably varied by coating with a minimally thin layer of TiO(2) (ideally pico-to-nanometer in thickness) without altering the existing topographical and roughness features, and that the change in superficial chemistry of titanium is effective in improving the biological properties of titanium. METHODS AND RESULTS: Acid-etched microroughened titanium surfaces were coated with TiO(2) using slow-rate sputter deposition of molten TiO(2) nanoparticles. A TiO(2) coating of 300 pm to 6.3 nm increased the surface oxygen on the titanium substrates in a controllable manner, but did not alter the existing microscale architecture and roughness of the substrates. Cells derived from rat skeletal muscles showed increased attachment, spread, adhesion strength, proliferation, gene expression, and collagen production at the initial and early stage of culture on 6.3 nm thick TiO(2)-coated microroughened titanium surfaces compared with uncoated titanium surfaces. CONCLUSION: Using an exemplary slow-rate sputter deposition technique of molten TiO(2) nanoparticles, this study demonstrated that titanium substrates, even with microscale roughness, can be sufficiently chemically modified to enhance their biological properties without altering the existing microscale morphology. The controllable and exclusive chemical modification technique presented in this study may open a new avenue for surface modifications of titanium-based biomaterials for better cell and tissue affinity and reaction.

Bone integration capability of alkali- and heat-treated nanobimorphic Ti-15Mo-5Zr-3Al.

The role of nanofeatured titanium surfaces in a number of aspects of in vivo bone-implant integration, and, in particular, their potential advantages over microfeatured titanium surfaces, as well as their specific contribution to osteoconductivity, is largely unknown. This study reports the creation of a unique nanobimorphic titanium surface comprised of nanotrabecular and nanotuft-like structures and determines how the addition of this nanofeature to a microroughened surface affects bone-implant integration. Machined surfaces without microroughness, sandblasted microroughened surfaces, and micro-nano hybrid surfaces created by sandblasting and alkali and heat treatment of Ti-15Mo-5Zr-3Al alloy were subjected to biomechanical, interfacial and histological analyses in a rat model. The presence of microroughness enabled accelerated establishment of biomechanical implant fixation in the early stages of healing compared to the non-microroughened surfaces; however, it did not increase the implant fixation at the late stages of healing. The addition of nanobimorphic features to the microroughened surfaces further increased the implant fixation by as much as 60-100% over the healing time. Bone area within 50 µm of the implant surface, but not beyond this distance, was significantly increased by the presence of nanobimorphic features. Although the percentage of bone-implant contact was also significantly increased by the addition of nanobimorphic features, the greatest improvement was found in the soft tissue intervention between the bone and the implant, which was reduced from >30% to <5%. Mineralized tissue densely deposited with calcium-binding globular proteins was observed in an extensive area of nanobimorphic surfaces after biomechanical testing. This study clearly demonstrates the nanofeature-enhanced osteoconductivity of titanium by an alkali- and heat-treated nanobimorphic surface compared to that by microfeatured surfaces, which results not only in an acceleration but also an improvement of bone-implant integration. The identified biological parameters that successfully detect the advantages of nanofeatures over microfeatures will be useful in evaluating new implant surfaces in future studies.

Effects of pico-to-nanometer-thin TiO2 coating on the biological properties of microroughened titanium.

The independent, genuine role of surface chemistry in the biological properties of titanium is unknown. Although microtopography has been established as a standard surface feature in osseous titanium implants, unfavorable behavior and reactions of osteogenic cells are still observed on the surfaces. To further enhance the biological properties of microfeatured titanium surfaces, this study tested the hypotheses that (1) the surface chemistry of microroughened titanium surfaces can be controllably varied by coating with a very thin layer of TiO(2), without altering the existing topographical and roughness features; and (2) the change in the surface chemistry affects the biological properties of the titanium substrates. Using a slow-rate sputter deposition of molten TiO(2) nanoparticles, acid-etched microroughened titanium surfaces were coated with a TiO(2) layer of 300-pm to 6.3-nm thickness that increased the surface oxygen levels without altering the existing microtopography. The attachment, spreading behavior, and proliferation of osteoblasts, which are considered to be significantly impaired on microroughened surfaces compared with relatively smooth surfaces, were considerably increased on TiO(2)-coated microroughened surfaces. The rate of osteoblastic differentiation was represented by the increased levels of alkaline phosphatase activity and mineral deposition as well as by the upregulated expression of bone-related genes. These biological effects were exponentially correlated with the thickness of TiO(2) and surface oxygen percentage, implying that even a picometer-thin TiO(2) coating is effective in rapidly increasing the biological property of titanium followed by an additional mild increase or plateau induced by a nanometer-thick coating. These data suggest that a super-thin TiO(2) coating of pico-to-nanometer thickness enhances the biological properties of the proven microroughened titanium surfaces by controllably and exclusively modulating their surface chemistry while preserving the existing surface morphology. The improvements in proliferation and differentiation of osteoblasts attained by this chemical modification is of great significance, providing a new insight into how to develop new implant surfaces for better osseointegration, based on the established microtopographic surfaces.

Influence of anterior palatal coverage on perception and retention in complete dentures.

STATEMENT OF PROBLEM: Oral perception is adversely affected by palatal coverage in complete denture wearers. PURPOSE: The purpose of this study was to determine whether an opening in an anterior palatal base enhanced oral perception and the effect of the size of the opening on retention. MATERIAL AND METHODS: Ten healthy dentate individuals (5 men, 5 women; age range: 22-29 years) participated in the perception test. The time required to sense a nylon thread embedded in test food was measured. The test was performed with 3 types of experimental palatal form: no-opening; small-opening, where the opening was located in the anterior region of the palatal base; and large-opening, where the opening was located between the incisive papilla and the third palatal rugae. No palatal coverage was used as a control. Retention force was measured by pulling and loading tests. In the pulling test, pulling force was applied to 2 points on the experimental denture base, and in the loading test, loading force was applied to 6 points. Response times (sec) and retention forces (N) were analyzed using a 1-way ANOVA for repeated measurements followed by the Bonferroni test for multiple comparisons (α=.05). RESULTS: A significant difference was observed in response time in fiber perception between bases with or without a small opening (P =.017). In the pulling test, retention force with the small-opening type was 4% lower at the molar region, and 35% lower at the center of gravity than in the no-opening type. Retention force in the large-opening type was lower than in the small-opening type. In the loading test, retention force was 13 N or higher in all 3 types. CONCLUSIONS: The small-opening type of palatal coverage improved oral perception and demonstrated sufficient retention force.

Response of Merkel cells in the palatal rugae to the continuous mechanical stimulation by palatal plate.

The aim of the present study was to investigate the responses of Merkel cells that are numerous in the palatine rugae, due to the continuous mechanical stimulation exerted by the palatal plate. Forty golden hamsters were used in this experiment. The palatal plate was made of adhesive resin and it was set on the palate of the animal. To exert a continuous pressure, a 0.8 mm elevation on the internal surface of the palatal plate was created at the middle portion of the fourth palatine ruga. Thereafter, the number of Merkel cells in the mucosa was calculated by immunohistochemical observation. Morphological changes of Merkel cells were examined by electron microscopy. There was significant difference among the control and any of the treated groups on the number of CK20 positive Merkel cells (p < 0.05) and that numbers were decreased at the sites where continuous mechanical stimulation was exerted. Degeneration of the cytoplasm mitochondria and nerve endings, and a decrease in both the number of neurosecretory granules and cytoplasmic processes were observed. Furthermore, the presence of nuclear chromatin aggregation and fragmentation was recognized. The continuous mechanical stimulation by the palatal plate affected the responses of Merkel cells and nerve endings, thus inducing a decrease in the number of Merkel cells. A portion of these changes was also associated with the expression of apoptosis.

[Can diffusion tensor imaging predict the functional outcome of supra-tentorial stroke?].

We used diffusion tensor imaging (DTI) to assess wallerian degeneration of the pyramidal tract after the onset of supra-tentorial stroke, and correlation of the extent of Wallerian degeneration with the motor function at 3 months after stroke. Twenty eight patients with supra-tentorial acute stroke were examined, two weeks and one month after stroke by DTI. We measured fractional anisotropy(FA) of affected side/ unaffected side (FA ratio) in the cerebral peduncle. We used modified Rankin Scale (mRS) for assessment of motor function at 3 months after stroke. FA ratio was significantly reduced at 2 weeks after stroke (0.833 +/- 0.146) compared to on admission (0.979 +/- 0.0797). But no significant change of FA ratio was seen between two weeks and one month after stroke in 7 cases examined (0.758 +/- 0.183 vs. 0.754 +/- 0.183). In all patients in whom the FA ratio was under 0.8 at 2 weeks after stroke, motor function showed poor recovery (mRS 4 and 5) at 3 months after stroke. When FA ratio was over 0.8 at 2 weeks after stroke, motor function at 3 months after stroke showed good recovery (mRS 0 to 3) expect for three elderly patients. With the use of DTI, Wallerian degeneration could be detected in the corticospinal tracts at midbrain level during the early phase of supra-tentorial stroke. We conclude that DTI may be useful for early prediction of motor function prognosis in patients with supra-tentorial acute stroke.

Characterization of the peri-implant epithelium in hamster palatine mucosa: behavior of Merkel cells and nerve endings.

The purpose of this study was to investigate the relationship between Merkel cells and nerve elements during tissue regeneration after receiving dental implants. Golden hamsters were divided into 3 groups and titanium alloy implants were fixed in their left-side maxilla through the third palatine rug. Animals were sacrificed at 1, 2, 3, 4, 5, 6, and 7 days after the implantation and tissues were characterized at the immunohistochemical and morphological levels. CK 20 and PGP 9.5 antibodies which react with Merkel cells and nerve fibers were used. Immunohistochemically, no CK 20-positive Merkel cells were seen in the peri-implant epithelium throughout the 7 days. However, starting at day 4, PGP 9.5-positive nerve fibers appeared in the connective tissue, and by day 7, nerve fibers had invaded the more superficial layer of the peri-implant epithelium compared to the mucosa removal control group. At the electron microscopic level, the intercellular spaces of the regenerating epithelium in the mucosa removal control group were small. In contrast, intercellular spaces of the peri-implant epithelium tended to be wide and regenerating nerve fibers invaded those intercellular spaces. In both the mucosa removal control group and the implantation group, the basal lamina and connective tissues regenerated completely. However, clear Merkel cells containing neurosecretory granules were not observed. Taken together, our results indicate that Merkel cells in the hamster palatine mucosa do not regenerate in the peri-implant epithelium. However, regenerative nerve fibers seem to play essential roles as part of the defense and sensory systems around the peri-implant epithelium to compensate for the weakened defense mechanism.