Ryo Akatsuka

Characteristics of hydroxyapatite film formed on human enamel with the powder jet deposition technique

This study aimed to create hydroxyapatite (HAp) film by powder jet deposition with manipulating the blasting nozzle above human enamel and to examine the microstructural and mechanical properties of the HAp film and the bonding strength at the interface between the HAp film and the enamel substrate. HAp particles calcinated at 1200°C with an average size of 4.7 μm were used. The HAp particles were mixed with carrier gas (N₂) to form an aerosol flow and was accelerated and blasted from the nozzle onto the enamel substrate at room temperature and atmospheric pressure. To evaluate the microstructure, scanning electron microscope (SEM) images of the surface and cross section of the HAp films and a three-dimensional profile of the HAp films were observed. To evaluate the mechanical properties, the micro-Vickers hardness and the bonding strength of the HAp films to the enamel substrate were measured. The deposition area of the HAp film was over 3 × 4 mm. The average and maximum thickness were about 30 and 40 μm, respectively. No significant difference was observed between the hardness of the HAp film and the enamel (p > 0.05). The bonding strength of the HAp film was the same as the bonding strength between composite resin and enamel. Compared with previous reports, wider and thicker HAp film was created on the enamel substrate successfully. The HAp film, which has same hardness with enamel and same bonding strength to the enamel with composite resin, would be a candidate as dental restorative materials.

Effect of hydroxyapatite film formed by powder jet deposition on dentin permeability

A powder jet deposition (PJD) process can be used to create a thick hydroxyapatite (HA) film on the surface of a human tooth. This study aimed to investigate in vitro the ability of an HA film, applied using PJD, to diminish dentin permeability. Discs of human coronal dentin were cut perpendicular to the tooth axis and the smear layer was removed by EDTA treatment. The HA film was created by accelerating HA particles, calcinated at 1200°C, onto the dentin discs at room temperature and atmospheric pressure. The surfaces and cross-sections of the HA PJD-treated samples were observed using scanning electron microscopy. Their permeability was indirectly recorded with a split-chamber device utilizing a chemiluminescence technique. MS-coat, a commercial dentin-desensitizing agent, was also evaluated for its effect on reducing liquid flow through the dentin. The scanning electron microscopy images showed that the HA particles were successfully deposited onto the dentin and solidly into the dentin tubules. The permeability of dentin after application of the HA films was significantly lower than that following application of MS-coat. This study showed the potential clinical application of PJD techniques in desensitizing dentin hypersensitivity.

Evaluation of thermal stress in hydroxyapatite film fabricated by powder jet deposition.

This study aimed to create a thick hydroxyapatite (HA) film on the surface of a human tooth via a powder jet deposition (PJD) device for dental handpieces, and to examine the microstructural and mechanical properties of the HA film. In particular, the effects of thermal stress on this film were evaluated. The HA film was created by blasting 3.18-μm HA particles, calcinated at 1,200°C, onto the enamel substrate at room temperature and atmospheric pressure. An HA film with an area of 3 mm × 3 mm was prepared and polished. The following HA film parameters were evaluated from the three-dimensional surface profile: surface roughness, Vickers hardness, and bonding strength before and after artificial aging induced by 500 cycles of thermal cycling (5-55°C). The HA particles in the deposited film were densely packed, and the surface of the HA film was unchanged after thermal cycling. There were also no significant differences in the hardness and the bonding strength of the HA film before and after thermal cycling. The HA film created in this study demonstrated excellent microstructural and mechanical properties, even after the application of thermal stress.

Clinical Evaluation of Monolithic Zirconia Crowns: A Short-Term Pilot Report

PURPOSE This study aimed to prospectively evaluate the clinical performance of monolithic zirconia crowns made of yttria-stabilized tetragonal zirconia polycrystal. MATERIALS AND METHODS A total of 26 crowns placed on premolar or molar teeth in 18 patients were evaluated at the time of crown placement and at 2 weeks, 6 months, 1 year, and 2 years after placement. RESULTS Twenty-five crowns rated as satisfactory according to the California Dental Association quality evaluation system. Most of the abutment and antagonist teeth showed good periodontal condition. An enamel cracking occurred on one antagonist tooth 1 year after placement. CONCLUSION Monolithic zirconia crowns can be a clinically acceptable prosthetic option.

Development of Powder Jet Deposition Technique and New Treatment for Discolored Teeth

The powder jet deposition (PJD) process is for creation of a hydroxyapatite (HA) layer on human teeth. To develop the PJD device, the layer-forming properties have improved. Created HA layers with a new handpiece-type PJD device demonstrate excellent material properties in vitro. Titanium dioxide (TiO2) is known to cause whitening because of the selective reflection of the light. Therefore, we assessed the possibility of using the creation of TiO2-HA layers with the new PJD device as a new treatment for discolored teeth. In this study, the microstructural and mechanical properties of TiO2-HA layers were evaluated under the same conditions of the previous study. These properties were evaluated before and after 500 cycles of thermal cycling (5–55 °C). Furthermore, the CIE L*a*b* color system was used for color measurement and ⊿E* values for color differences were calculated. The maximum thickness of the TiO2-HA layers was about 60 μm. There were no significant differences in thickness, hardness, or bonding strength before and after thermal cycling. The layers showed an increased L* parameter and a decreased b* parameter, and the color difference ⊿E* was approximately 6.7 units. Creation of TiO2-HA layers by PJD might be a valuable new treatment for discolored teeth.

Hydroxyapatite Film for Dental Treatment by Powder Jet Deposition: A Review

This review summarized the powder jet deposition (PJD) method used to create a thick hydroxyapatite (HAp) film on a human tooth surface. The PJD method is a technology for creating ceramic films on ceramic substrates in which fine particles of ceramic were accelerated and the only deposition process that could be used in the room temperature and room pressure. The HAp film created in previous studies showed that excellent microstructure and mechanical properties. The possibility of making a new interface between the tooth and biomaterials using the PJD method was indicated.

Evaluation of Hydroxyapatite Film by Powder Jet Deposition after Artificial Aging

This study aimed to create a thick hydroxyapatite (HAp) film on the surface of a human tooth by using a newly developed powder jet deposition (PJD) device for dental handpieces, and sought to examine the microstructural and mechanical properties of the resulting HAp film. The film was evaluated on three-dimensional view, surface roughness, Vickers hardness, and bonding strength before and after artificial aging through thermal cycling (555°C) for 500 cycles (30 sec for each cycle, 20 sec of dwell time).The HAp particles in the deposited film were densely packed, and the HAp films three-dimensional microstructure and its rough surface were maintained after thermal cycling. There was no significant difference in either the HAp films Vickers hardness or the bonding strength between the film and the enamel substrate before and after thermal cycling. The HAp films created in this study demonstrated excellent microstructural and mechanical properties even after the application of thermal stress. We demonstrated the possibility of using a new type of powder jet deposition (PJD) method we developed to form a new type of interface between the tooth and biomaterials. Consequently, we propose the use of this method in new dental treatments.

Formation of hydroxyapatite film on tooth using powder-jet-deposition

Using a powder-jet-deposition process, a thick hydroxyapatite (HAp) film can be created on a human tooth surface. Two different types of HAp particles, calcinated at 1,200 and 1,300°C, were used. The HAp particle was mixed with nitrogen as the carrier gas to form an aerosol flow and then accelerated and blasted from the nozzle onto the enamel substrate at room temperature and atmospheric pressure. HAp particles in the deposited film were tightly packed. There was no gap between the HAp film and the enamel substrate. The bonding strength of the HAp film is almost the same as the composite resin on the enamel.