title: Degree of vinyl conversion, polymerization shrinkage and stress development in experimental endodontic composite.
abstract: This study explores degree of vinyl conversion (DVC), polymerization shrinkage (PS) and shrinkage stress (PSS) of the experimental amorphous calcium phosphate (ACP) composites intended for use as an endodontic sealer. Light-cure (LC), chemical cure (CC) or dual-cure (DC; combined light and chemical cure) resins comprised urethane dimethacrylate (UDMA), 2-hydroxyethyl methacrylate (HEMA), methacryloyloxyethyl phthalate (MEP) and a high molecular mass oligomeric co-monomer, poly(ethyleneglycol)-extended UDMA (PEG-U) (designated UPHM resin). To fabricate composites, a mass fraction of 60 % UPHM resin was blended with a mass fraction of 40 % as-made (am-ACP) or ground ACP (g-ACP). DVC values of copolymer (unfilled UPHM resin) and composite specimens were determined by infrared spectroscopy. Glass-filled composites were used as controls. PS and PSS of composites were determined by dilatometry and tensometry, respectively. LC copolymers attained extraordinary high DVC values at 24 h post-cure (95.7 %), compared to CC (52 %) and DC (79.3 %) copolymer specimens. While the DVC values of LC and DC am-ACP composites were reduced between 5 and 10 %, DVC values of DC g-ACP composites increased almost 8 % compared to the corresponding copolymers. High DVC attained in LC composites was, expectedly, accompanied with high PS values (on average 7 vol%). However, PSS developed in LC and especially DC composites did not exceed PSS values seen in other UDMA-based composites. Based on this initial evaluation, it is concluded that, DC, g-ACP filled UPHM composite shows promise as an endodontic sealer. However, further physicochemical evaluations, including water sorption, mechanical stability and ion release as well as a leachability studies need to be performed before this experimental material is tested for cellular responses and, eventually recommended for clinical utility.
authors.affiliation: Paffenbarger Research Center, American Dental association Foundation, National Institute of Standards and Technology, Gaithersburg, MD 20899, USA.
authors.forename: J N R
authors.initials: JN
authors.lastname: O'Donnell
authors.forename: D
authors.initials: D
authors.lastname: Skrtic
references.citation: Biomaterials. 1993 Sep;14(11):871-5
references.pmid: 8218741
references.citation: Dent Mater. 1999 Mar;15(2):128-37
references.pmid: 10551104
references.citation: Am J Dent. 2000 Aug;13(4):176-80
references.pmid: 11763926
references.citation: J Biomater Appl. 2007 Apr;21(4):375-93
references.pmid: 16684798
references.citation: Dent Mater. 2009 Jul;25(7):884-91
references.pmid: 19215975
references.citation: J Compos Mater. 2010 Feb 1;44(3):355
references.pmid: 20169007
references.citation: J Mater Sci Mater Med. 2004 Oct;15(10):1097-103
references.pmid: 15516870
references.citation: J Bioact Compat Polym. 2006;21(3):169-184
references.pmid: 18688290
references.citation: Dent Mater. 2000 Jul;16(4):292-6
references.pmid: 10831785
references.citation: J Dent Res. 1996 Sep;75(9):1679-86
references.pmid: 8952621
references.citation: J Res Natl Inst Stand Technol. 2003 Jun 01;108(3):167-82
references.pmid: 27413603
references.citation: J Bioact Compat Polym. 2008;23(3):207-226
references.pmid: 18607513
references.citation: Polym Int. 2007;56(4):497-505
references.pmid: 18714369
references.citation: J Dent Res. 1979 Sep;58(9):1887-99
references.pmid: 290653
references.citation: Acta Biomater. 2006 Jan;2(1):85-94
references.pmid: 16701862