Norihisa Akiba

A randomized controlled trial of the different impression methods for the complete denture fabrication: Patient reported outcomes

OBJECTIVES To compare the effect of conventional complete dentures (CD) fabricated using two different impression methods on patient-reported outcomes in a randomized controlled trial (RCT). METHODS A cross-over RCT was performed with edentulous patients, required maxillomandibular CDs. Mandibular CDs were fabricated using two different methods. The conventional method used a custom tray border moulded with impression compound and a silicone. The simplified used a stock tray and an alginate. Participants were randomly divided into two groups. The C-S group had the conventional method used first, followed by the simplified. The S-C group was in the reverse order. Adjustment was performed four times. A wash out period was set for 1 month. The primary outcome was general patient satisfaction, measured using visual analogue scales, and the secondary outcome was oral health-related quality of life, measured using the Japanese version of the Oral Health Impact Profile for edentulous (OHIP-EDENT-J) questionnaire scores. RESULTS Twenty-four participants completed the trial. With regard to general patient satisfaction, the conventional method was significantly more acceptable than the simplified. No significant differences were observed between the two methods in the OHIP-EDENT-J scores. CONCLUSIONS This study showed CDs fabricated with a conventional method were significantly more highly rated for general patient satisfaction than a simplified. CLINICAL SIGNIFICANCE CDs, fabricated with the conventional method that included a preliminary impression made using alginate in a stock tray and subsequently a final impression made using silicone in a border moulded custom tray resulted in higher general patient satisfaction. TRIAL REGISTRATION UMIN000009875.

Evaluation of the marginal fit at implant-abutment interface by optical coherence tomography.

Abstract. Vertical misfit of implant–abutment interface can affect the success of implant treatment; however, currently available modalities have limitations to detect these gaps. This study aimed to evaluate implant–abutment gaps in vitro using optical coherence tomography (OCT). Vertical misfit gaps sized 50, 100, 150, or 200 μm were created between external hexagonal implants and titanium abutments (Nobel Biocare, Göteborg, Sweden). A porcine gingival tissue slice, 0.5, 1.0, 1.5, or 2.0 mm in thickness, was placed on each implant–abutment interface. The gaps were evaluated by swept-source OCT at a center wavelength of 1330 nm (Panasonic Healthcare, Ehime, Japan) with beam angles of 90, 75 and 60 deg to the implant long-axis. The results suggested that while the measurements were precise, gap size and gingival thickness affected the sensitivity of detection. Gaps sized 100 μm and above could be detected with good accuracy under 0.5- or 1.0-mm-thick gingiva (GN). Around 70% of gaps sized 150 μm and above could be detected under 1.5-mm-thick GN. On the other hand, 80% of gaps under 2.0-mm-thick GN were not detected due to attenuation of near-infrared light through the soft tissue. OCT appeared as an effective tool for evaluating the misfit of implant–abutment under thin layers of soft tissue.

Influence of methyl mercaptan at early setting stages on the properties of self curing addition silicone resilient denture lining materials

PURPOSE The aim of the present study was to clarify the influence of early setting conditions on the properties of self curing addition silicone resilient denture lining materials. METHODS Four auto-mix types of commercial self curing addition silicone resilient denture lining materials were used. Agar plates containing various concentrations of methyl mercaptan (MMP) were prepared and cylindrical specimens (10mm in height and 10mm in diameter) of silicone liners were set on the agar plate. The Shore A hardness of the agar-contacted surface of the specimen was measured at 0, 1, 7 and 28 days after stored in 37 degrees C water. The viscoelastic properties (instantaneous elastic modulus, coefficient of viscosity and permanent deformation) of two silicone liners, which showed a great decrease in the Shore A hardness by agar contact, were determined by a creep meter. RESULTS The Shore A hardness, coefficient of viscosity, and instantaneous elastic modulus deceased when the specimen was set on the MMP containing agar plate, but the permanent deformation of these specimens increased. CONCLUSION The exposure to MMP at the early setting stage influenced the properties of self curing addition silicone resilient denture lining materials.

An objective estimation of the removability of three home reliners

The purpose of this study was to investigate methods for evaluating objectively the removability of three commercially available home reliners (Cushion Correct, Tafugurippu Pink A and Liodent Pink). After immersing each of the reliners in distilled water at 37ºC for 24 h, we compared their removability using the peel test with a finger, which was evaluated based on a visual analogue scale and the percentage of the residual area. An experimental rake-up test was also undertaken to quantify removability, evaluated based on the total amount of work required to remove it. The Tafugurippu Pink A product was easier to remove with a finger than the other two home reliner products, and required the least total amount of work to be removed in the experimental rake-up test. Furthermore, the rake-up test performed could possibly be used for objective evaluation of the removability of home reliner.

Effect of home reliner on occlusal relationships and oral mucosa

BACKGROUND For decades, many reports have expressed negative opinions about home reliner (HR), because it may result in residual ridge resorption. Recently, some clinical studies evaluated HR. However, the effect of HR on occlusal relationships and the oral mucosa remains unclear. Here, we dynamically analyzed the situation in which a patient applies HR to an upper complete denture. METHODS We numerically simulated the effect of HR on occlusal relationships and the oral mucosa. In the simulation, the thickness of HR was set to 2mm as a proper amount and 4mm as an excessive amount. The loading points were set at the center of the right and left occlusal surfaces of the denture. RESULTS Compared with the case without using HR, at proper amounts (2mm on the right and left sides), HR suppressed the depression of the ill-fitting denture, and stress on the oral mucosa was decreased. In the excessive HR model (4mm on the right and left sides), the vertical occlusal dimension was increased, and stress on the oral mucosa originally fitted with the denture base was increased. When the denture was modeled in an inclined position (2mm on the left side and 4mm on the right side), stress on the oral mucosa on the left buccal side was markedly increased. CONCLUSION It was found that when an improper amount of HR was applied, the occlusal vertical dimension increased and the oral mucosa was pressured more than that under non-HR conditions.

Influence of water immersion on the transmitted load of home reliners

This study aimed to clarify how composition and water immersion of home reliners affect the attenuation of the transmitted load. To conduct a transmitted load measurement, we used three different home reliners (Tafugurippu Pink A, Liodent Pink, and Cushion Correct), which were combined acrylic resin disks. They were immersed in distilled water and then placed on a silicone quasi-mucosa (φ20×1.5 mm), which was set on a pressure sensor (φ8×0.35 mm), followed by the application of static load. Subsequently, gel permeation chromatography (GPC) and gas chromatography (GC) were used to clarify the composition of each home reliner. The attenuation of the transmitted load began 3 h after immersion. Moreover, both GPC and GC revealed a difference in composition among the three products. Further, the difference in the vinyl acetate molecular weight distribution and ethyl alcohol content affected the attenuation of the transmitted load of home reliners after water absorption.

Hydrophilic nano-silica coating agents with platinum and diamond nanoparticles for denture base materials

Preventing microorganisms from adhering to the denture surface is important for ensuring the systemic health of elderly denture wearers. Silica coating agents provide high hydrophilicity but lack durability. This study investigated solutions to improve the durability of the coating layer, determine an appropriate solid content concentration of SiO2 in the silica coating agent, and evaluate the effect of adding platinum (Pt) and diamond nanoparticles (ND) to the agent. Five coating agents were prepared with different SiO2 concentrations with/without Pt and ND additives. The contact angle was measured, and the brush-wear test was performed. Scanning electron microscopy was used to investigate the silica coating layer. The appropriate concentration of SiO2 was found to be 0.5-0.75 wt%. The coating agents with additives showed significantly high hydrophilicity immediately after coating and after the brush-wear test. The coating agents with/without additives formed a durable coating layer even after the brush-wear test.

Effects of temperature-responsive hydrogel on viscosity of denture adhesives.

The cream type of denture adhesives after use cannot be easily removed from oral mucosa and have the potential risk to change the oral flora. The effects of the temperature-responsive hydrogel Pluronic F-127 (PF) on the complex viscosity of denture adhesives were evaluated. Carboxy methylcellulose (CMC) mass fractions (1, 2, 3 and 4%) were added to 20 and 25% PF hydrogels. Complex viscosity was measured over a temperature cycle (40→10→40°C) and fixed temperature points (23 and 37°C). Adhesive strength tests were performed with 2 resin plates at 23 and 37°C. One commercial cream-type denture adhesive, New Poligrip® (NP), was evaluated as a control. Complex viscosity values for PF20% groups at 23°C were lower than those for NP at 37°C. Adhesive strength of PF20% with CMC2%, was higher at 23°C when compared to NP at 37°C, which suggests that PF20%CMC2% is an effective adhesive and is easily removed after mouth rinsing.

Influence of monomer content on the viscoelasticity, water sorption and solubility of experimental fluorinated soft lining materials

The influence of monomer content on the viscoelasticity, water sorption and solubility of experimental fluorinated soft lining materials was investigated. Changes in the viscoelastic properties of the materials were also examined after thermal cycling. Four fluorinated soft lining materials containing different amounts of methoxy diethylene glycol methacrylate (MDGMA) and tridecafluorooctyl methacrylate (13FMA) were prepared. The viscoelastic displacement for specimens containing 13FMA was found to be less than that without 13FMA (p<0.05), and the values tended to decrease with increasing 13FMA content. Reduction of the MDGMA content and addition of 13FMA caused a decrease of water sorption and solubility (p<0.05). Thermal cycling was found to affect the viscoelastic deformation of the specimens without 13FMA and those specimens with relatively large amounts of 13FMA.