Shogo Ozawa

Photoelastic stress analysis of implant-tooth connected prostheses with segmented and nonsegmented abutments.

STATEMENT OF PROBLEM There is some question about whether implant abutment selection affects the transfer of load between connected implants and natural teeth. PURPOSE The purpose of this study was to compare stress transfer patterns with either 1 or 2 posterior implants connected to a single anteriorly located simulated natural tooth with either 1 or 2 segmented and nonsegmented implant abutments under relevant functional loads by use of the photoelastic stress analysis technique. MATERIAL AND METHODS A model of a human left mandible, edentulous posterior to the first premolar, with two 3.75-mm x 13-mm screw-type implants embedded within the edentulous area, was fabricated from photoelastic materials. The implants were in the first and second molar positions. Two fixed partial denture prosthetic restorations were fabricated with either segmented conical abutments or nonsegmented UCLA abutments. Vertical occlusal loads were applied at fixed locations on the restorations. The photoelastic stress fringes that developed in the supporting mandible were monitored visually and recorded photographically. The stress intensity (number of fringes), stress concentrations (closeness of fringes), and their locations were subjectively compared. RESULTS Loading on the restoration over the simulated tooth generated apical stresses of similar intensity (fringe order) at the tooth and the first molar implant for both abutment types. Low-level stress was transferred to the second molar implant. Loading directed on the implant-supported region of the restoration demonstrated low transfer of stress to the simulated tooth. Nonvertical stress transfer with slightly higher intensity was observed for the nonsegmented abutment. CONCLUSION Within the limitations of this simulation study, stress distribution and intensity for the 2 implant conditions was similar for segmented and nonsegmented abutment designs. Magnitude of stresses observed for both abutment designs was similar for the single implant condition. Vertical loading produced more nonaxial stresses away from the force applied for the 1 implant condition with the nonsegmented abutment. Direct loading results were similar for both abutment designs. Specific recommendations for selection of implant abutment and application should be based on clinical criteria.

High-throughput gene expression analysis in bone healing around titanium implants by DNA microarray

OBJECTIVE Bone generation occurs around titanium implants; however, its underlying mechanisms are relatively unknown. We attempt to identify gene transcripts specifically upregulated in in vivo bone healing with titanium implants using DNA microarray. MATERIAL AND METHODS Titanium implants were placed into rat femurs, and total RNA was extracted from the implant-associated tissue at weeks 1, 2 and 4 of healing. As a control, RNA was extracted from the tissue undergoing osteotomy healing. The RNA samples were hybridized onto oligo DNA microarray. RESULTS Most of the 20,000 genes tested were expressed similarly in both the implant- and osteotomy-healing groups. Eighty-six genes were upregulated (>2-fold) in the implant-healing group compared with the osteotomy-healing group in at least one time point of healing. Twelve genes were upregulated in the implant healing at week 2 and earlier, while 31 genes were upregulated at week 2 and later. Only one gene was upregulated specifically at week 1, while three genes were consistently upregulated from weeks 1 to 4. The upregulated genes included collagenous and non-collagenous extracellular matrix (ECM)-related genes, proteoglycans and bone resorption-related genes. Pathway analysis revealed the involvement of ECM and receptor interaction in implant healing. CONCLUSIONS This study provides evidence that a set of gene transcripts is upregulated in the implant healing over the osteotomy healing, which seems to represent the coordinated biological events of long-lasting osteogenesis and bone remodeling required for osseointegration. Further studies are needed to identify the significance and biological roles of the transcripts in osseointegration. Proven reliability and usefulness of microarray technology should encourage future approaches to develop a high-throughput molecular assessment for osseointegration capacity of new implant surfaces.

Mechanical Stretch Increases the Proliferation While Inhibiting the Osteogenic Differentiation in Dental Pulp Stem Cells

Dental pulp stem cells (DPSCs), which can differentiate into several types of cells, are subjected to mechanical stress by jaw movement and occlusal forces. In this study, we evaluated how the uniaxial mechanical stretch influences proliferation and differentiation of DPSCs. DPSCs were isolated and cultured from male Sprague-Dawley rats. Cultured DPSCs were identified by surface markers and the differentiation capabilities as adipocytes or osteoblasts. To examine the response to mechanical stress, uniaxial stretch was exposed to cultured DPSCs. We evaluated the impact of stretch on the intracellular signaling, proliferation, osteogenic differentiation, and gene expressions of DPSCs. Stretch increased the phosphorylation of Akt, ERK1/2, and p38 MAP kinase as well as the proliferation of DPSCs. The stretch-induced proliferation of DPSCs was abolished by the inhibition of the ERK pathway. On the other hand, stretch significantly decreased the osteogenic differentiation of DPSCs, but did not affect the adipogenic differentiation. We also confirmed mRNA expressions of osteocalcin and osteopontin were significantly suppressed by stretch. In conclusion, uniaxial stretch increased the proliferation of DPSCs, while suppressing osteogenic differentiation. These results suggest a crucial role of mechanical stretch in the preservation of DPSCs in dentin. Furthermore, mechanical stretch may be a useful tool for increasing the quantity of DPSCs in vitro for regenerative medicine.

Transplantation of dental pulp stem cells suppressed inflammation in sciatic nerves by promoting macrophage polarization towards anti-inflammation phenotypes and ameliorated diabetic polyneuropathy.

Dental pulp stem cells (DPSCs) are thought to be an attractive candidate for cell therapy. We recently reported that the transplantation of DPSCs increased nerve conduction velocity and nerve blood flow in diabetic rats. In the present study, we investigated the immunomodulatory effects of DPSC transplantation on diabetic peripheral nerves.

Transplantation of cultured dental pulp stem cells into the skeletal muscles ameliorated diabetic polyneuropathy: therapeutic plausibility of freshly isolated and cryopreserved dental pulp stem cells

IntroductionDental pulp stem cells (DPSCs) are mesenchymal stem cells located in dental pulp and are thought to be a potential source for cell therapy since DPSCs can be easily obtained from teeth extracted for orthodontic reasons. Obtained DPSCs can be cryopreserved until necessary and thawed and expanded when needed. The aim of this study is to evaluate the therapeutic potential of DPSC transplantation for diabetic polyneuropathy.MethodsDPSCs isolated from the dental pulp of extracted incisors of Sprague–Dawley rats were partly frozen in a −80 °C freezer for 6 months. Cultured DPSCs were transplanted into the unilateral hindlimb skeletal muscles 8 weeks after streptozotocine injection and the effects of DPSC transplantation were evaluated 4 weeks after the transplantation.ResultsTransplantation of DPSCs significantly improved the impaired sciatic nerve blood flow, sciatic motor/sensory nerve conduction velocity, capillary number to muscle fiber ratio and intra-epidermal nerve fiber density in the transplanted side of diabetic rats. Cryopreservation of DPSCs did not impair their proliferative or differential ability. The transplantation of cryopreserved DPSCs ameliorated sciatic nerve blood flow and sciatic nerve conduction velocity as well as freshly isolated DPSCs.ConclusionsWe demonstrated the effectiveness of DPSC transplantation for diabetic polyneuropathy even when using cryopreserved DPSCs, suggesting that the transplantation of DPSCs could be a promising tool for the treatment of diabetic neuropathy.

Fabrication of an orbital prosthesis using a noncontact three-dimensional digitizer and rapid-prototyping system.

Conventionally, fabricating a facial prosthesis requires complicated steps and sophisticated skills. Particularly, the facial impression can be uncomfortable for the patient and can cause compression because of the weight of the material. The new approach presented in this report could simplify the fabrication of facial prostheses using a noncontact three-dimensional digitizer and binder multinozzle inkjet printer, without computed tomography or making a conventional impression. Treatment time was reduced, and the patient expressed satisfaction after 6 months follow-up.

Finite element study on the effect of abutment length and material on implant bone interface against dynamic loading.

PURPOSE Finite element study on the effect of abutment length and material on implant bone interface against dynamic loading. MATERIALS AND METHODS Two dimensional finite element models of cylinderical implant, abutments and bone made by titanium or polyoxymethylene were simulated with the aid of Marc/Mentat software. Each model represented bone, implant and titanium or polyoxymethylene abutment. Model 1: Implant with 3 mm titanium abutment, Model 2: Implant with 2 mm polyoxymethylene resilient material abutment, Model 3: Implant with 3 mm polyoxymethylene resilient material abutment and Model 4: Implant with 4 mm polyoxymethylene resilient material abutment. A vertical load of 11 N was applied with a frequency of 2 cycles/sec. The stress distribution pattern and displacement at the junction of cortical bone and implant was recorded. RESULTS When Model 2, 3 and 4 are compared with Model 1, they showed narrowing of stress distribution pattern in the cortical bone as the height of the polyoxymethylene resilient material abutment increases. Model 2, 3 and 4 showed slightly less but similar displacement when compared to Model 1. CONCLUSION Within the limitation of this study, we conclude that introduction of different height resilient material abutment with different heights i.e. 2 mm, 3 mm and 4 mm polyoxymethylene, does not bring about significant change in stress distribution pattern and displacement as compared to 3 mm Ti abutment. Clinically, with the application of resilient material abutment there is no significant change in stress distribution around implant-bone interface.

Innovative Approach for Interim Facial Prosthesis Using Digital Technology

Despite the important role of facial prosthetic treatment in the rehabilitation of head and neck cancer patients, delay in its implementation can be unavoidable, preventing patients from receiving a prompt facial prosthesis and resuming a normal social life. Here, we introduce an innovative method for the fabrication of an interim facial prosthesis. Using a 3D modeling system, we simplified the fabrication method and used a titanium reconstruction plate for facial prosthesis retention. The patient received the facial prosthesis immediately after surgery and resumed a normal social life earlier than is typically observed with conventional facial prosthetic treatment.

Development of three-dimensional facial expression models using morphing methods for fabricating facial prostheses

PURPOSE It is essential to fabricate a best-fit three-dimensional (3D) facial prosthesis model capable of facial expressions. In order for the facial prosthesis to remain in position, especially around marginal areas subject to movement, a new method of making 3D facial expression models using time-series data allowing changes in facial expression by morphing technique was developed. METHODS Seven normal subjects and seven patients with nasal defects or nasal deformities participated in this study. Three distinct facial expressions (i.e., a neutral expression, smiled, and open mouthed) were digitally acquired with a facial scanner. Prepared template models were transformed to homologous models, which can represent the form as shape data with the same number of point cloud data of the same topology referring to the scanning data. Finally, 3D facial expression models were completed by generating a morphing image based on two sets of homologous models, and the accuracy of the homologous models of all subjects was evaluated. RESULTS 3D facial expression models of both normal subjects and patients with nasal defects were successfully generated. No significant differences in shape between the scanned models and homologous models were shown. CONCLUSIONS The high accuracy of this 3D facial expression model in both normal subjects and patients suggests its use for fabricating facial prostheses.

Fabrication of Removable Partial Denture Designed in Consideration of Esthetics

症例の概要：40 歳，女性．下顎右側臼歯部のインプラントと天然歯と連結した固定式補綴装置が予後不良であり，インプラント除去後の補綴治療を希望して来科した．下顎両側遊離端欠損に対し，部分床義歯による補綴治療を行い，最終義歯として，磁性アタッチメントと把持機能を重視した設計の金属床義歯を製作した．考察：リジッドサポートの概念と審美的に有利な支台装置を選択した義歯により，患者の満足が得られた．術後2 年を経過したところで，支台歯の一つに歯根破折が生じ，抜歯後増歯修理を行ったが，義歯の安定は損なわれず経過は良好であった．結論：両側下顎臼歯部欠損症例に対し，審美性に配慮した金属床義歯を適用して，良好な結果を得た．