Novel UV-Imaging Technique for Visualization of Coating on Hydroxyapatite

Objectives: The objective of the study was to develop imaging method that would enable visualization of coating on hydroxyapatite(HAP).
Methods: Pre-selected dense HAP-discs(n=3-5) were used for each experiment. Half of each HAP-disc surface was covered with tape. HAP-discs were individually treated with 1%polymer solutions of selected polymers at 37^oC for 2min. Treated discs were dried overnight and imaged utilizing a macro imaging set-up equipped with tri-band UV light source to determine presence of polymer coating. Imaging was carried out by employing UV-A(365nm), UV-B(302nm), and UV-C(254nm) light source respectively. Polymer coated discs were subsequently subjected to etching with 1%citric acid at 37^oC to remove the coating. Discs were imaged after 5min citric acid etching and an additional 10min citric acid etching. Sample images were blind-coded and were ranked by four panelists for presence of coating prior to citric acid etching and retention of coating after citric acid etching. The entire process of treatment/imaging/ranking was repeated four times.
Results: Coated HAP-discs were found to result in a characteristic pattern of image distinct to the individual disc/polymer. This characteristic pattern was found to be more discernable under UV-C light source. Coatings resistant to acid etching retained this characteristic pattern even after extended citric acid etching. Removal of coating during acid etching caused re-emergence of pattern distinct to that of individual native HAP surface. Polymer coatings with superior binding to HAP retained characteristic coating pattern even after extended citric acid etching and were consistently ranked highest by all panelist in all four trials.
Conclusions: UV imaging technique has been developed to visualize presence of polymer coating on HAP surface. Polymer coatings with superior binding to HAP surface could be differentiated from those that bind poorly by the employment of this novel imaging method. Extension of this method to enamel surface is being investigated.