Bonding strength of the hydroxyapatite film on tooth using powder-jet-deposition

Objectives: Using a powder-jet-deposition (PJD) process, a thick hydroxyapatite (HAp) film can be created on a human tooth surface. The microstructure and mechanical characteristics of the HAp film are investigated. The microstructure of the deposited HAp film is dense and the hardness is almost same as a human enamel substrate. This paper reveals a bonding strength at the interface between the HAp film and the enamel substrate.

Methods: The HAp particles calcinated at 1200 °C are used. The HAp particle is mixed with carrier gas (N₂) to form an aerosol flow and is accelerated and blasted from the nozzle onto the enamel substrate at room temperature and atmospheric pressure. The distance between the nozzle and substrate is 1.0 mm. The acceleration pressure is 0.5 MPa. The HAp films of the area of 3 mm x 4 mm are prepared. The bonding strength between the HAp films and enamel substrate is evaluated through a micro-tensile test.

Results: The HAp particle in the deposited film is densely packed, and the maximum film thickness is over about 40 mm. Micro-Vickers hardness of the film and enamel substrate is measured using a 200 mN load, which is 530.6+/-52.9 and 548.0+/-37.2. There is no significant difference (p=0.42, Mann-Whitney U-test). Through a micro-tensile test, there is no sample destroyed at the interface between the enamel and the HAp film. The bonding strength between the HAp films and enamel substrate is 14.1+/-5.2 MPa and that of a composite resin is 16.6+/-2.0 MPa. There is no significant difference (p=0.52, Steel-Dwass's multiple comparison test).

Conclusion: The bonding strength of the HAp film is almost same as in the case of a composite resin which is normally used in a dental treatment. We are proposing a new dental treatment using the PJD technique.