Biomimetic Calcium Phosphate Coating for Orthodontic Applications
Authors:   , Li Menghong 
Published: August 2024

Anchorage management is a key factor for successful orthodontic treatments, as it is essential to maximize desired tooth movements and mitigate unwanted forces. Skeletal anchorage, mainly miniscrew implants (MSIs) fixed to the bone, is widely used in daily orthodontic practice to achieve effective orthodontic tooth movement. Nevertheless, the clinical use of MSIs is associated with relatively low success rate, due to lack of osseointegration between implant surface and surrounding bone tissue. Therefore, this thesis aims to improve the osseointegration of MSIs by surface modification.
In chapter 2, we comprehensively reviewed clinically applied surface modifications of MSIs, that is sandblasting, large-grit, acid etching (SLA), anodic oxidation (OA) and ultraviolet photofunctionalization (UVP). These techniques have positively influence in vitro and in vivo. However, the biological improvement in clinical studies is not so significant. Considering the limitation of current studies, finding an alternative to modify MSIs for bone tissue regeneration is proposed.
In chapter 3, the biomimetic calcium phosphate (BioCaP) coating was successfully applied on medical grade smooth stainless steel (SSL) surface, with the immersing period in a biomimetic modified Tyrode (BMT) solution for 48 hours, followed by the same period in a supersaturated calcium phosphate solution (CPS). This optimum coating condition was selected because of the improved roughness and wettability of SSL surface after coating. Moreover, the cell seeding efficiency, cell spreading area and cell proliferation of human osteoblast-like cell MG63 were increased on the BioCaP coated SSL surface in vitro.
To further explore the drug-carrier capability, and increase the osteogenic capability of the BioCaP coating, in chapter 4, BMP2 was incorporated into the BioCaP coating on smooth SSL surface, and compared with uncoated porous Ti, smooth SSL, and smooth SSL with the BioCaP coating. It showed that the BMP2 incorporated BioCaP coating was hydrophilic, with curly crystal-like morphology. In vitro studies showed that the cell seeding efficiency, cell proliferation, and osteogenic differentiation on this surface were significantly higher than that of SSL surface.
In chapter 5, we aimed to evaluate the osteoconductivity of the BioCaP coating in vivo. The time-course osteointegration process of Ti mini-pin implants furnished with the BioCaP coating in a model of metaphyseal tibial was investigated, and bovine serum albumin (BSA) was involved as a model protein. A significant increase in BIC% occurred as early as at week 1 in the crystalline BioCaP coating group, compared with that at week 2 in no coating group and amorphous seeding layer group. These findings demonstrate that the BioCaP coating enhances the osteoconductivity of Ti mini-pin implants in vivo. Therefore, such surface modification has the potential in increasing the success rate of MSIs in orthodontic clinics.
In chapter 6, anticancer drug-incorporated BioCaP coating on calcium phosphate particles have been proposed. Modified curcumin (mcur) was selected in this study because it can promote osteogenesis and selectively kill osteosarcoma cells.This mcur@BioCaP suppressed osteosarcoma cell and fibroblasts, and promoted osteogenesis. This mcur@BioCaP with osteogenic differentiation capability and enhanced anti-osteosarcoma effects can be a promising strategy for osteosarcoma post-surgical treatment.
Based on the research described in this thesis, it can be concluded that the currently available surface modifications on miniscrew implants do not provide significant clinical improvement. Our research findings demonstrate that the BioCaP coating can be successfully applied on metallic surfaces and improves their biocompatibility and osteoconductivity. Moreover, the incorporation of BMP2 into this coating can be a promising proposal to facilitate early osseointegration. Taken together, the BioCaP coating can be a promising technique to increase the success rate of miniscrew implants in orthodontic applications.