Shigeru Oda

Effects of the Er:YAG Laser Irradiation on Titanium Implant Materials and Contaminated Implant Abutment Surfaces

OBJECTIVE The purpose of this study was to examine the morphological changes and temperature increases of the titanium after Er:YAG laser irradiation, and also to investigate the effect of this laser on debridement of contaminated healing abutments. BACKGROUND DATA Mechanical instruments have been used for the cleaning of implant abutment surfaces, however, most of them are not appropriate for the application to titanium surface. Recently, the Er:YAG laser has been expected to have a promising ability for the debridement of implant surface. MATERIALS AND METHODS Experiments were composed of three parts. At first, ten titanium round plates were exposed to the Er:YAG laser irradiation at 30-200 mJ/pulse and the surface changes were observed by stereomicroscope and scanning electron microscope. Secondly, the surface temperature changes of 60 titanium plates during and after Er:YAG laser irradiation at 30 and 50 mJ/pulse were measured by thermographic equipment. At last, calculus on the surface of six contaminated healing abutments was removed by Er:YAG laser or ultrasonic scaler, and the treated surfaces were examined by stereomicroscope. RESULTS Under 50 mJ/pulse, distinct morphological changes were not observed and the elevation of surface temperature was minimal, especially in the use of water-cooling. The Er:YAG laser at 30 mJ/pulse and 30 Hz with water spray was capable of effectively removing plaque and calculus on the implant abutments without injuring their surfaces. CONCLUSION This study indicates that the Er:YAG laser can be a novel technical modality for the debridement of implant abutment surface.

Twist negatively regulates osteoblastic differentiation in human periodontal ligament cells

Periodontal ligament (PDL) is a thin fibrous connective tissue located between two mineralized tissues, alveolar bone and cementum, which maintains a constant width physiologically. The mechanisms by which PDL resists mineralization are not well understood. Twist is a basic helix loop helix protein that plays a central role in regulation of early osteogenesis. We investigated the localization of Twist in PDL and compared the expression of Twist and osteoblast‐related genes in PDL cells with those in osteoblast‐like cells in the presence or absence of recombinant human bone morphogenetic protein (BMP)‐2. Histochemical analysis showed that Twist was expressed along alveolar bone surface in PDL. PDL cells constitutively expressed Twist gene and the expression level was higher than that in osteoblast‐like cells. In osteoblast‐like cell culture, BMP‐2 enhanced osteoblast‐related gene expression, while Twist expression was slightly decreased. In contrast, BMP‐2 increased runt‐related transcription factor (Runx)‐2, but failed to enhance alkaline phosphatase (ALP) and osteocalcin (OCN) gene expression in PDL cells. Interestingly, unlike in osteoblast‐like cells, Twist expression was upregulated by BMP‐2 in PDL cells. We transiently knocked down Twist gene in PDL cells using a short interference RNA expression vector (siTwist) and found that ALP, osteopontin (OPN), bone sialoprotein (BSP) genes expression and basal level of ALP activity were slightly increased, whereas Runx2 and OCN genes were not affected. Collectively, these results suggest that Twist may act as a negative regulator of osteoblastic differentiation in PDL cells. J. Cell. Biochem. 100: 303–314, 2007.

The effect of chemical and/or mechanical conditioning on the Er:YAG laser-treated root cementum: analysis of surface morphology and periodontal ligament fibroblast attachment.

This study compared the surface morphology as well as the biocompatibility of dental root cementum treated with Er:YAG laser irradiation alone and with the laser irradiation followed by chemical and/or mechanical conditioning.

Periodontal Ligament Stem Cells Possess the Characteristics of Pericytes

BACKGROUND Periodontal ligament (PDL) contributes to maintaining homeostasis in periodontal tissues by supplying stem/progenitor cells. It has long been suggested that PDL stem cells/progenitors are located around blood vessels. Recently mesenchymal stem cells (MSCs) have been isolated and cultured from PDL in vitro, although the location of the stem cells in PDL is unclear. The purpose of this study is to test the characteristics of human PDL stem cells (PDLSCs) and examine their similarity to related vascular cell types, such as pericytes and endothelial cells. METHODS PDLSCs were obtained from healthy extracted teeth using the collagenase/dispase enzyme digestion method. MSC and pericyte characteristics of PDLSCs were examined by cell surface marker expression using flow cytometry. The expression of pericyte markers was tested using immunohistochemistry. Pericyte-like functions of PDLSCs were examined in co-culture of PDLSCs and umbilical vein endothelial cells on a gel matrix. RESULTS Cultured PDLSCs were positive for both MSC markers and pericyte markers, including cluster of differentiation 146 (CD146), neural/glial antigen 2 (NG2), and CD140b. When pericyte marker expression was explored in rat periodontal tissue sections, CD146- and NG2-positive signals were observed in the perivascular area of the PDL. Further, when the cells were cultured with human umbilical cord endothelial cells under conditions for forming capillary-like structures in vitro, PDLSCs localized adjacent to endothelial cells and contributed to the stability of the capillary-like structure. CONCLUSIONS PDLSCs possess pericyte-like characteristics and may localize as pericytes in the PDL. These data provide useful information for stem cell biology in periodontal research and stem cell-based periodontal therapy.

Effect of rhBMP-2 with PLGA/gelatin sponge type (PGS) carrier on alveolar ridge augmentation in dogs.

Recombinant human bone morphogenetic protein-2 has been shown to promote bone formation because of its osteoinductive property. The purpose of this study was to evaluate the efficacy of rhBMP-2 delivered on a poly (D, L-lactic-co-glycolic acid) copolymer/gelatin sponge (PGS) in vertical alveolar ridge augmentation on height-reduced edentulous mandible to verify the retention of rhBMP-2 withstanding the pressure of soft tissues. Coronal defects of the alveolar bone were created in six adult beagle dogs. After a healing period of 9 weeks, PGSs with or without rhBMP-2 (0 or 0.4 mg mL(-1)) were implanted on the defects(6 mm in height, 30 mm in length, 8 mm in width). Sixteen weeks after implantation, the bone mineral content (BMC) and the total bone area were measured by peripheral quantitative computed tomography. The BMC and the total bone area of the defect sites with rhBMP-2 group were significantly greater (133+/-33 mg mm(-1), 277+/-54 mm2, respectively) than those of the control group (80+/-19 mg mm(-1), 155+/-49 mm2, respectively) (P<0.01, P<0.0001, respectively; paired t-test). From the histological analyses, the height of newly formed bone in the experimental group was greater than that of the control group (4.3+/-0.9 mm, 0.22+/-0.28 mm, P<0.0001, n=6, paired t-test). These results indicate that PGS has characteristics of effective bone graft substitutes for implantation of rhBMP-2 on vertical alveolar ridge augmentation in huge defect of mandibles in dogs.

Histological evaluation of alveolar ridge augmentation using injectable calcium phosphate bone cement in dogs.

Alveolar ridge augmentation is an important procedure to restore tooth loss. Several types of graft materials have been used for augmenting the alveolar ridge. An injectable calcium phosphate cement (CPC) has been applied to periodontal bone defects and has shown favourable results. Thus, this CPC may work as an effective graft material for alveolar ridge augmentation. The aim of this study was to evaluate the effectiveness of the CPC for large-scaled (about 7 x 8 x 6 mm) ridge augmentation in dogs. Alveolar ridge defects were created bilaterally in the maxilla of six beagle dogs. The CPC was applied to one of the bilateral maxillary defects. The untreated defect on the contralateral side served as control. The animals were sacrificed at 6 months after surgery and decalcified histological specimens of the alveolar ridge were prepared histometrically and evaluated under a light microscope. Newly formed and reconstructed alveolar ridges covering the CPC were observed in all experimental sites. In the control sites, only slight newly bone formation was observed. Histomorphometrical analysis indicated that the CPC grafted group exhibited significantly (P = 0.0001) increased area and height in new bone formation compared with those of the control group. The results indicate that the CPC appears to be an effective material for alveolar ridge augmentation and may act as a space maintainer to conduct new bone formation.

Effect of a tunnel-structured β-tricalcium phosphate graft material on periodontal regeneration: a pilot study in a canine one-wall intrabony defect model

BACKGROUND AND OBJECTIVE Tissue regeneration is affected by the porosity, chemical properties and geometric structure of graft materials. Regeneration of severe periodontal defects, such as one-wall intrabony defects, is difficult because of reduced tissue support, and bone grafts are commonly used in such cases. In the present study, a tunnel-structured β-tricalcium phosphate (tunnel β-TCP) graft material designed to stimulate bone formation was fabricated. The objective of this pilot study was to evaluate the effect of this graft material on periodontal regeneration in one-wall intrabony defects in dogs. MATERIAL AND METHODS Six male beagle dogs were used in this study. First, the mandibular second and third incisors were extracted. Experimental surgery was performed 12 wk after tooth extraction. Bilateral 4 × 8 mm (width × depth) one-wall intrabony defects were created in the mesial side of the mandibular canines. At the experimental sites, the defects were filled with tunnel β-TCP, whereas the control defects were left empty. Twelve weeks after surgery, qualitative and quantitative histological analyses were performed. RESULTS There were no signs of clinical inflammation 12 wk after surgery. Coronal extension indicative of new bone formation was higher at the experimental sites than at the control sites, although the differences between both the sites in the newly formed cementum and connective tissue attachment were not significant. Newly formed periodontal ligament and cementum-like tissue were evident along the root surface at the experimental sites. The inner surface of the tunnels was partially resorbed and replaced with new bone. New blood vessels were observed inside the lumens of tunnel β-TCP. CONCLUSION Tunnel β-TCP serves as a scaffold for new bone formation in one-wall intrabony defects.

Ridge augmentation using recombinant human fibroblast growth factor-2 with biodegradable gelatin sponges incorporating β-tricalcium phosphate: a preclinical study in dogs

BACKGROUND AND OBJECTIVE Fibroblast growth factor-2 (FGF-2) regulates the proliferation and differentiation of osteogenic cells, resulting in the promotion of bone formation. Biodegradable gelatin sponges incorporating β-tricalcium phosphate (β-TCP) have been reported as a scaffold, which has the ability to control growth factor release, offering sufficient mechanical strength and efficient migration of mesenchymal cells. In this study, we evaluated the effects of the combined use of recombinant human FGF-2 (rhFGF-2) and gelatin/β-TCP sponge on ridge augmentation in dogs. MATERIAL AND METHODS Six male beagle dogs were used in this study. Twelve wk after tooth extraction, bilateral 10 × 5 mm (width × depth) saddle-type defects were created 3 mm apart from the mesial side of the maxillary canine. At the experimental sites, the defects were filled with gelatin/β-TCP sponge infiltrated with 0.3% rhFGF-2, whereas gelatin/β-TCP sponge infiltrated with saline was applied to the control sites. Eight wk after surgery, qualitative and quantitative analyses were performed. RESULTS There were no signs of clinical inflammation at 8 wk after surgery. Histometric measurements revealed that new bone height at the experimental sites (2.98 ± 0.65 mm) was significantly greater than that at the control sites (1.56 ± 0.66 mm; p = 0.004). The total tissue height was greater at the experimental sites (6.62 ± 0.66 mm) than that at the control sites (5.95 ± 0.74 mm), although there was no statistical significant difference (p = 0.051). Cast model measurements revealed that the residual defect height at the experimental sites (2.31 ± 0.50 mm) was significantly smaller than that at the control sites (3.51 ± 0.78 mm; p = 0.012). CONCLUSION The combined use of rhFGF-2 and gelatin/β-TCP sponge promotes ridge augmentation in canine saddle-type bone defects.

Comparative study of Er:YAG laser and rotating bur for bone ablation

Abstract The purpose of this study was to examine histologically the healing process of the bone defect created by Er:YAG laser irradiation in the long-term, in comparison with that created by conventional rotating bur. Two straight groove-like defects were prepared on the rat calvaria by Er:YAG laser or rotating bur. After operation, SEM analysis of the lased surface and histological observation of the healing process were performed. The results showed that the Er:YAG laser was capable of ablating bone tissue with the same effectiveness as the bur treatment, without causing severe thermal damage.The bone defect created by Er:YAG laser irradiation was repaired by new bone uneventfully within 2 months, almost equal to that of the bur treatment. These results suggest that the Er:YAG laser can be clinically applicable to periodontal bone surgery.

Ridge Preservation After Tooth Extraction With Buccal Bone Plate Deficiency Using Tunnel Structured β-Tricalcium Phosphate Blocks: A 2-Month Histologic Pilot Study in Beagle Dogs

BACKGROUND Reduction in alveolar ridge volume is a direct consequence of tooth extraction. Tunnel β-tricalcium phosphate (β-TCP) blocks were manufactured from randomly organized tunnel-shaped β-TCP ceramic. Efficacy of these blocks compared to extraction alone for alveolar ridge preservation after tooth extraction with buccal bone deficiency was evaluated. METHODS Maxillary first premolars of six beagle dogs were extracted after removing the buccal bone, and bone defects of 4 × 4 × 5 mm (mesio-distal width × bucco-palatal width × depth) were created. Fresh extraction sockets with buccal bone defects were filled with tunnel β-TCP blocks at test sites. Two months after the operation, histologic and histometric evaluations were performed. RESULTS Regarding histologic sections, coronal and middle horizontal widths of the alveolar ridge were significantly greater at test sites (3.2 ± 0.5 and 3.6 ± 0.4 mm, respectively) than at control sites (1.2 ± 0.3 and 2.0 ± 0.6 mm, respectively). The amount of woven bone was significantly greater at test sites (62.4% ± 7.9%) than at control sites (26.8% ± 5.3%), although that of connective tissue and bone marrow was significantly greater at control sites (38.1% ± 6.2% and 16.0% ± 6.9%, respectively) than at test sites (10.7% ± 5.7% and 4.1% ± 2.2%, respectively). Regarding basic multicellular units, no statistically significant difference was found between the test and control sites (0.5% ± 0.1% and 0.6% ± 0.1%, respectively). CONCLUSION Tunnel β-TCP blocks represent an effective bone-graft material for alveolar ridge preservation in fresh extraction sockets with buccal bone defects.