An assessment of mast cells and myofibroblasts in denture-induced fibrous hyperplasia.

OBJECTIVES: The pathogenesis of denture-induced fibrous hyperplasias has not been examined in detail to explain how tissue injury results in fibrous hyperplasia of the oral mucosa. PATIENTS AND METHODS: We examined the presence of mast cells and myofibroblasts in 33 denture-induced fibrous hyperplasias (DIFH) compared with 10 healthy gingival tissues. The parameters examined included mast cell numbers, tissue distribution, degranulation, and cell subtypes using immunohistochemistry. The presence of myofibroblasts and their likely origin was also examined by double immunofluorescense staining. Furthermore, we investigated the synthesis of osteopontin and TGF-ß, considered to be involved in the transformation of a fibroblast to a myofibroblast. RESULTS: The results demonstrated that the mast cell numbers are significantly increased in the DIFH compared with non-disease controls. The mast cell localization in lesions was higher in the superficial areas with inflammatory cell infiltration compared with the deep fibrotic area (P < 0.01). The number of tryptase-positive mast cells was significantly higher compared with chymase-positive ones. The TGF-ß- or osteopontin-positive cell infiltration into the lesion was found in high numbers. The presence of myofibroblasts was identified in 14 of 33 cases (42%), and some of these cells showed apoptosis when assessed by the TUNEL assay. On the survey of the origin of myofibroblasts, results showed αSMA and vimentin positivity indicating these transformed from fibroblasts. CONCLUSION: These results are the first to show that mast cells and myofibroblasts can be detected in DIFH, indicating important roles of these cells in the pathogenesis of this lesion.

High bone-implant contact achieved by photofunctionalization to reduce periimplant stress: a three-dimensional finite element analysis.

OBJECTIVE: A recent study demonstrated that UV treatment of titanium implants (photofunctionalization) enabled a higher level of osseointegration by establishing a 98.2% bone-implant contact (BIC) as opposed to a 53.0% BIC around untreated implants. This study examined whether, and how, the BIC increase affects the periimplant mechanical stress. MATERIALS AND METHODS: Three-dimensional finite element analysis was performed on implants of different degrees of BIC (53.0% and 98.2%) based on the report of photofunctionalization. The different lengths of implants (7, 10, and 13 mm) were also tested. RESULTS: Increasing the implant length from 7 to 13 mm diminished the periimplant stress level by only 15% under vertical load, whereas increasing BIC from 53.0% to 98.2% diminished it by 50%. Consequently, stress around 7-mm implants with 98.2% BIC was even lower than that around 13-mm implants with 53.0% BIC. High-stress areas, which were observed around implants in all lengths with 53.0% BIC, disappeared on implants with 98.2% BIC even on 7-mm implants. Similar results were obtained under oblique load. CONCLUSIONS: This study demonstrated that a BIC increase from 53.0% to 98.2%, which can be achieved by photofunctionalization, improves distribution and diffusion of periimplant stress more effectively than using longer implants, providing a potential novel strategy to counteract stress-induced periimplant marginal bone loss.

Antimicrobial activity of Gel-entrapped catechins toward oral microorganisms.

The oral cavity contains almost half of the commensal bacterial population present in the human body. An increase in the number of these microorganisms may result in systemic diseases such as infective endocarditis and aspiration pneumonia as well as oral infections. It is essential to control the total numbers of these microorganisms in order to suppress disease onset. Thus, we examined the antimicrobial activity of a newly developed gel-entrapped catechin (GEC) preparation against oral microorganisms. The minimum inhibitory concentration (MIC) of GEC was determined based on the relationship between a modified agar diffusion method and a broth microdilution method. GEC inhibited the growth of the Actinomyces, periodontopathic bacteria and Candida strains tested, but did not inhibit the growth of the oral streptococci that are important in the normal oral flora. Commercially available moisture gels containing antimicrobial components showed antimicrobial activity against all of the tested strains. After a series of washes and after a 24-h incubation, GEC retained the antimicrobial activity of the catechins. Catalase prevented GEC-induced growth inhibition of Actinomyces naeslundii and Streptococcus mutans suggesting that hydrogen peroxide may be involved in the antimicrobial activity of catechins. These results suggest that GEC may be useful for controlling oral microorganism populations and reducing the accumulation of dental plaque, thereby helping to prevent periodontal disease and oral candidiasis.

Retentive force and magnetic flux leakage of magnetic attachment in various keeper and magnetic assembly combinations.

STATEMENT OF PROBLEM: Magnetic attachments are commonly used for overdentures. However, it can be difficult to identify and provide the same type and size of magnetic assembly and keeper if a repair becomes necessary. Therefore, the size and type may not match. PURPOSE: This study evaluated the retentive force and magnetic flux strength and leakage of magnetic attachments in different combinations of keepers and magnetic assemblies. MATERIAL AND METHODS: For 6 magnet-keeper combinations using 4 sizes of magnets (GIGAUSS D400, D600, D800, and D1000) (n=5), retentive force was measured 5 times at a crosshead speed of 5 mm/min in a universal testing machine. Magnetic flux strength was measured using a Hall Effect Gaussmeter. Data were statistically analyzed using a 1-way ANOVA, and between-group differences were analyzed with Tukey's HSD post hoc test (α=.05). RESULTS: The mean retentive force of the same-size magnet-keeper combinations was 3.2 N for GIGAUSS D400 and 5.1 N for GIGAUSS D600, but was significantly reduced when using larger magnets (P<.05). Magnetic flux leakage was significantly lower for corresponding size combinations. CONCLUSIONS: Size differences influence the retentive force and magnetic flux strength of magnetic attachments. Retentive force decreased due to the closed field structure becoming incomplete and due to magnetic field leakage.

Ultraviolet treatment restores bioactivity of titanium mesh plate degraded by contact with medical gloves.

Titanium mesh plate (Ti mesh) used for bone augmentation inadvertently comes into contact with medical gloves during trimming and bending. We tested the hypotheses that glove contact degrades the biological capability of Ti mesh and that ultraviolet treatment (UV) can restore this capability. Three groups of Ti mesh specimens were prepared: as-received (AR), after glove contact (GC), and after glove contact followed by UV treatment. The AR and GC meshes were hydrophobic, but GC mesh was more hydrophobic. AR and GC meshes had significant amounts of surface carbon, and Si content was higher for GC mesh than for AR mesh. UV mesh was hydrophilic, and carbon and silicon content values were significantly lower in this group than in the AR and GC groups. The number, alkaline phosphatase activity, and mineralization ability of attached osteoblasts were significantly lower in the GC group than in the AR group and markedly higher in the UV group than in the AR group. In conclusion, glove contact caused chemical contamination of Ti mesh, which significantly reduced its bioactivity. UV treatment restored bioactivity in contaminated Ti mesh, which outperformed even the baseline Ti mesh.

Three-dimensional finite element analysis of the effects of implant diameter and photofunctionalization on peri-implant stress.

Previous finite element analyses of peri-implant stress assumed a bone-implant contact (BIC) ratio of 100%, even though the BIC ratio is known to be approximately 50% or less. However, the recent development of ultraviolet treatment of titanium immediately before use, known as photofunctionalization, significantly increased the BIC ratio, to 98.2%. We used a unique finite element analysis model that enabled us to examine the effects of different BIC ratios on peri-implant stress. A three-dimensional model was constructed under conditions of vertical or oblique loading, an implant diameter of 3.3, 3.75, or 5.0 mm, and a BIC ratio of 53.0% or 98.2%. Photofunctionalization and larger implant diameters were associated with reduced stress on surrounding tissues. Under vertical loading, photofunctionalization had a greater effect than increased implant diameter on stress reduction. Under oblique loading, increased implant diameter had a greater effect than photofunctionalization on stress reduction.

[Shock absorption of mouthguard materials--influence of temperature conditions and shore hardness on shock absorption].

PURPOSE: To consider changes in the physical properties of mouthguard materials with the change of temperature, shock-absorbing examination and Shore hardness measurement of existing MG materials and other elastic materials were carried out. METHODS: Both examinations were done under two temperature conditions: at room temperature (25 degrees C) and simulated intraoral temperature (37 degrees C). In addition, a comparative study of the relation between Shore hardness and shock absorption of the materials was made. A self-made drop impact machine was used for the shock-absorbing examination. The thickness of a sample was assumed to be 3 mm. The loading was applied by dropping 3 kinds of steel ball, phi 10 mm (4.0 g), phi 15 mm (13.7 g), and phi 20 mm (32.6 g) from a height of 60 cm. The shock absorption of all materials was compared by the maximum impact force. Shore hardness was measured based on the JIS standard. RESULTS: The shock absorption of each material showed a different tendency depending on the loading condition. Furthermore, the shock absorption of the same material showed different results depending on the temperature condition. Shore hardness measurements tended to show low values with the condition of 37 degrees C for all materials. CONCLUSION: From the relation between shock absorption and Shore hardness, it was confirmed that there is a correlation between hardness and the maximum impact force in the materials that showed shock absorption by elastic deformation. Some materials showed high shock absorption compared with existing MG materials.

Use of Rat Mature Adipocyte-Derived Dedifferentiated Fat Cells as a Cell Source for Periodontal Tissue Regeneration.

Lipid-free fibroblast-like cells, known as dedifferentiated fat (DFAT) cells, can be generated from mature adipocytes with a large single lipid droplet. DFAT cells can re-establish their active proliferation ability and can transdifferentiate into various cell types under appropriate culture conditions. The first objective of this study was to compare the multilineage differentiation potential of DFAT cells with that of adipose-derived stem cells (ASCs) on mesenchymal stem cells. We obtained DFAT cells and ASCs from inbred rats and found that rat DFAT cells possess higher osteogenic differentiation potential than rat ASCs. On the other hand, DFAT cells show similar adipogenic differentiation, and chondrogenic differentiation potential in comparison with ASCs. The second objective of this study was to assess the regenerative potential of DFAT cells combined with novel solid scaffolds composed of PLGA (Poly d, l-lactic-co-glycolic acid) on periodontal tissue, and to compare this with the regenerative potential of ASCs combined with PLGA scaffolds. Cultured DFAT cells and ASCs were seeded onto PLGA scaffolds (DFAT/PLGA and ASCs/PLGA) and transplanted into periodontal fenestration defects in rat mandible. Micro computed tomography analysis revealed a significantly higher amount of bone regeneration in the DFAT/PLGA group compared with that of ASCs/PLGA and PLGA-alone groups at 2, 3, and 5 weeks after transplantation. Similarly, histomorphometric analysis showed that DFAT/PLGA groups had significantly greater width of cementum, periodontal ligament and alveolar bone than ASCs/PLGA and PLGA-alone groups. In addition, transplanted fluorescent-labeled DFAT cells were observed in the periodontal ligament beside the newly formed bone and cementum. These findings suggest that DFAT cells have a greater potential for enhancing periodontal tissue regeneration than ASCs. Therefore, DFAT cells are a promising cell source for periodontium regeneration.

Osteogenic cell sheets reinforced with photofunctionalized micro-thin titanium.

Cell sheet technology has been used to deliver cells in single-sheet form with an intact extracellular matrix for soft tissue repair and regeneration. Here, we hypothesized that titanium-reinforced cell sheets could be constructed for bone tissue engineering and regeneration. Fifty-µm-thick titanium plates containing apertures were prepared and roughened by acid etching, some of which were photofunctionalized with 12 min of UV light treatment. Cell sheets were prepared by culturing rat calvarial periosteum-derived cells on temperature-responsive culture dishes and attached to titanium plates. Titanium-reinforced osteogenic cell sheet construction was conditional on various technical and material factors: cell sheets needed to be double-sided and sandwich the titanium plate, and the titanium plates needed to be micro thin and contain apertures to allow close apposition of the two cell sheets. Critically, titanium plates needed to be UV-photofunctionalized to ensure adherence and retention of cell sheets. Single-sided cell sheets or double-sided cell sheets on as-made titanium contracted and deformed within 4 days of incubation. Titanium-reinforced cell sheets on photofunctionalized titanium were structurally stable at least up to 14 days, developed the expected osteogenic phenotypes (ALP production and mineralization), and maintained structural integrity without functional degradation. Successful construction of titanium-reinforced osteogenic cell sheets was associated with increased cell attachment, retention, and expression of vinculin, an adhesion protein by photofunctionalization. This study identified the technical and material requirements for constructing titanium-reinforced osteogenic cell sheets. Future in vivo studies are warranted to test these titanium-reinforced cell sheets as stably transplantable, mechanically durable, and shape controllable osteogenic devices.

Periodontal tissue regeneration by transplantation of rat adipose-derived stromal cells in combination with PLGA-based solid scaffolds.

Regeneration of damaged periodontium is challenging due to its multi-tissue composition. Mesenchymalstem cell-based approaches using adipose-derived stromal cells (ASCs) may contribute to periodontal reconstruction, particularly when combined with the use of scaffolds to maintain a space for new tissue growth. The aim of this study was to assess the regenerative potential of ASCs derived from inbred or outbred rats in combination with novel solid scaffolds composed of PLGA (Poly D,L-lactic-co-glycolic acid) (PLGA-scaffolds). Cultured ASCs seeded onto PLGA scaffolds (ASCs/PLGA) or PLGA-scaffolds (PLGA) alone were transplanted into periodontal fenestration defects created in F344 or Sprague Dawley (SD) rats. Micro-CT analysis showed a significantly higher percentage of bone growth in the ASCs/PLGA groups compared with the PLGA-alone groups at five weeks after surgery. Similarly, histomorphometric analysis demonstrated thicker growth of periodontal ligament and cementum layers in the ASCs/PLGA-groups compared with the PLGA-alone groups. In addition, transplanted DiI-labeled ASCs were observed in the periodontal regenerative sites. The present investigation demonstrated the marked ability of ASCs in combination with PLGA scaffolds to repair periodontal defects.

The relationship between missing occlusal units and oral health-related quality of life in patients with shortened dental arches.

This study aimed to investigate the relationship between missing occlusal units and oral health-related quality of life (OHRQoL) in subjects with shortened dental arches (SDAs). Subjects with SDAs (N = 115) were recruited consecutively from 6 university-based prosthodontic clinics. OHRQoL was measured using the Japanese version of the Oral Health Impact Profile (OHIP-J). An increase of 1 missing occlusal unit was associated with an increase of 2.1 OHIP-J units (95% CI: 0.6-3.5, P = .02) in a linear regression analysis. Missing occlusal units are related to OHRQoL impairment in subjects with SDAs.