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.

Monolithic zirconia crowns can be a clinically acceptable prosthetic option.

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.

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.

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