تحسين طلاء غرسات الاسنان المحضرة بتقنية الرش باللهب

Improving the Coating of Dental Implants Prepared by Flame Spraying Technique

Abstract
Despite the widespread application and clinical success of metallic materials in orthopaedic surgeries and implants, significant challenges remain regarding their long-term stability within biological environments. Key concerns include poor osseointegration, postoperative corrosion, and susceptibility to bacterial infections. Consequently, there is growing interest in improving the surface properties of metallic implants to enhance their integration with bone tissue and reduce infection risks.
In this study, biocompatible coatings were applied to titanium alloy (Ti6Al4V) and stainless steel (316L) substrates using the flame spray technique. The coatings consisted of calcium phosphate (CaP) either alone or as composites with silver (5%), magnesium (5%), and silver-magnesium (10%) additives. Prior to coating, the substrates were polished using 500-grit silicon carbide paper to optimize surface smoothness. The coated samples were intended to serve as surgical implants capable of promoting bone bonding and preventing bacterial colonization.The structural, morphological, and chemical properties of the coatings were characterized using X-ray diffraction (XRD), field-emission scanning electron microscopy (FESEM), energy-dispersive X-ray spectroscopy (EDX), Fourier-transform infrared spectroscopy (FTIR), adhesion testing (ASTM D3359), and wettability measurements (contact angle).
Antibacterial efficacy was evaluated against Streptococcus mutans using the zone of inhibition method, while biocompatibility and ion release behavior were assessed following a one-month immersion in simulated body fluid (SBF).
XRD and optical microscopy confirmed the presence of hydroxyapatite (HA) in all coatings, with additional diffraction peaks corresponding to silver and magnesium in the composite layers. FESEM analysis revealed porous coating morphologies with Nano-scale particle sizes for titanium and stainless steel. FTIR spectra verified the formation of HA by identifying characteristic functional groups and bond vibrations. EDX confirmed the elemental composition of the coatings and minimal impurity levels. Contact angle results showed enhanced hydrophilicity after CaP coating with complete wetting observed in samples containing silver and magnesium, indicating improved surface properties. Adhesion test results indicated excellent coating adhesion, with Ti6Al4V and composite-coated stainless steel samples achieving ASTM classification B4 (<5% removal), while CaP-coated stainless steel samples showed slightly lower adhesion (ASTM 3B, <15%).
Antibacterial test results showed that all coatings inhibited the growth of Streptococcus mutans, with the CaP–Ag–Mg coating on the titanium substrate exhibiting the highest antibacterial activity. This is attributed to the synergistic effect of silver and magnesium within the nanostructure, enhancing bacterial resistance and reducing the risk of infection. Post-immersion analysis in SBF showed the spontaneous formation of a new hydroxyapatite layer. FESEM images showed that all samples possessed uniform nanoscale partical sizes with variations depending on the type of formulation. The magnesium-silver formulation exhibited the smallest and most homogeneous grain sizes, contributing to improved surface porosity. Cross-section images also revealed variations in the thickness of the deposited layer, with the highest thickness recorded in the multi-element samples, especially after immersion, indicating high bioactivity and the formation of a continuous and uniform hydroxyapatite layer. Atomic absorption spectrometry revealed ion release levels of chromium and titanium well below toxic limits.
In conclusion, the developed coatings significantly improved the biocompatibility, antibacterial properties, and osseointegration potential of metallic implants, indicating their promise for enhanced performance in biomedical applications.