Mohd Razi, MR; (2012) Effects of polyacrylic acid on brushite bone cement setting, mechanical properties, degradation and chlorhexidine release. Doctoral thesis , UCL (University College London).

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Abstract

In the field of Paediatric Dentistry, brushite cement has potential as an endodontic medicament and bone substitute material. Clinical applications however are limited due to their inherent properties, such as rapid setting time and poor mechanical properties. Antimicrobial e.g. chlorhexidine (CHX) could be incorporated into the cement for localised drug release. Aim and objectives: The aim of this study was to assess if partial replacement of citric acid (CA) by polyacrylic acid (PAA) can improve the properties of conventional brushite cements. The objectives were to assess the effects of varying PAA and CHX concentrations in brushite cements on their setting kinetics, final composition, microstructure of the cement, mechanical properties, degradation and CHX release profile. Materials and Methods: The cements consisted of equimolar β- tricalcium phosphate and monocalcium phosphate monohydrate (β-TCP/MCPM) and 6 or 11% (w/w) CHX. The liquid phase consisted of aqueous 800 mM CA and PAA solution at different ratios. Compositions with no CHX and/or PAA were used as control cements. Setting kinetics and final composition were determined using FTIR and Raman spectroscopy respectively. Brushite microstructure was examined using scanning electron microscopy. The cements were tested for microhardness and biaxial flexural strength (BFS). CHX release was quantified with UV spectroscopy and degradation by mass loss. Results: The setting times for compositions with PAA were delayed by up to 12 hours. FTIR indicated formation of dicalcium citrate and polyacrylate complexes could delay brushite formation. High CHX content inhibited the acid retarding effects and complex formation. Raman mapping demonstrated discrete regions of brushite and CHX in all set cements. Microscopically, PAA addition resulted in denser and less porous structure. The BFS ranged from 5.8 ± 1.3 MPa to 11.1 ± 1.2 MPa. CHX incorporation resulted in reduced BFS and modulus whilst PAA addition increased it. The average mass change was significantly different between compositions with and with no chlorhexidine; 12% and 0.2% respectively at the end of study period. The daily degradation rate ranged from 0.1 ± 0.03 wt% to 0.6 ± 0.15 wt%. PAA presence reduced CHX release from more than 90% to less than 20% over 4 weeks. Conclusion: PAA substantially slowed the setting reaction and chlorhexidine release characteristics, altered the final brushite crystal microstructure, increased mechanical properties but did not affect the degradation kinetics.

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