Development of self-adhesive, low shrinkage, re-mineralising and high strength dental composites

• Main Author: Ben Nuba, H. A.
• Published: University College London (University of London) 2016
• Subjects: 617.6
• Online Access: https://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.746108

Resin based restorative composite materials are widely used for restoring both anterior and posterior teeth. Their major drawbacks, however, include complex bonding procedures, polymerisation shrinkage and potential for bond failure ultimately resulting in bacterial microleakage, recurrent caries and pulpal inflammation. This project’s aim was to characterise self-adhesive, antibacterial releasing, remineralising and high strength dental composites. The new composites contain UDMA as a bulk dimethacrylate monomer and PPGDMA as a high molecular weight diluent monomer instead of conventional Bis-GMA and TEGDMA respectively. NTGGMA adhesive co-initiator was added instead of DMPT. Adhesion promoting monomers 4-META or HEMA (5 wt %) were also included to enhance bonding to dentine (ivory). The monomers were combined with silane treated glass filler. This glass was mixed with total calcium phosphate levels (MCPM and TCP of equal mass) of 0, 10, 20 or 40 wt %. Furthermore, CHX and glass fibre were each included at 5 wt %. The powder liquid ratio was 3:1 by weight. Commercial dental composites Z250, Ecusphere and Gradia and experimental formulations with 4-META or HEMA and solely 100 wt % glass particles were used as controls. The degree of conversion after 20 s light cure was determined by FTIR. Cure data was used with the composite compositions to calculate the polymerisation shrinkage. The depth of cure was measured using ISO 4049. Subsequently, the mass and volume change and CHX release upon water immersion were determined over 5 and 4 months respectively. The mechanical properties biaxial flexural strength and modulus were determined dry and after 24 h, 7 days and 28 days immersion in water. The adhesion properties were assessed using a push out and shear test. Dry and hydrated ivory dentine with and without phosphoric acid etching for 20 s were investigated. The experiential formulations had ~ 77 % conversion as compared to ~ 50 – 60 % for commercial composites. The polymerisation shrinkage was ~ 3.4 – 3.7 % and the depth of cure decreased linearly with CaP increase after cured for 20 and 40 s. The mass and volume change and CHX release increased linearly with CaP increase and formulations with HEMA had higher water sorption and CHX releases compared to 4-META formulations. Control experimental composites achieved a flexural strength of ~170 MPa with no CHX or CaP. This decreased with CHX addition or increased CaP. Provided the CaP level was less than 20 %, however, strength was greater or comparable to Gradia and above 70 MPa even after immersion in water for 28 days. 5 The commercial composite exhibited the lowest push out and shear bond strengths to dentine. Replacement of HEMA with 4-META, increasing CaP, acid-etching or hydration of dentine and addition of Ibond adhesive, all significantly increased bond strengths between the composite and dentine. The new material, with adhesive monomer 4-META and reactive calcium phosphate, shows potential as a high conversion, antibacterial releasing, high strength and self-adhering composite, which should reduce restoration failure resulting from shrinkage and secondary caries. The use of ivory made it possible to determine the differences in bonding capability of multiple commercial and experimental formulations under wide ranging conditions.