Tetraoxaspiroalkanes for polymerization stress reduction of Silorane resins

Abstract

This study involved the synthesis and characterization of tetraoxaspiroalkane monomers and evaluated their potential to reduce polymerization stress when formulated in a Silorane resin system. The tetraoxaspiroalkane monomers had two main structural features (a) two different types of core ring structures (a 1,5,7,11-tetraoxaspirocyclic ring or a 2,4,8,10-tetraoxaspirocyclic ring) and (b) four different types of ring substituents (normal alkyl, allyloxyalkyl, trimethylsilylalkyl, or oxabicycloalkyl). The resin formulations contained (a) 20 mol % of a 1,5,7,11-or 2,4,8,10-tetraoxaspiroalkyl monomer; (b) a phenylmethylsilane containing two oxabicycloheptyl groups; (c) a cyclotetrasiloxane containing four oxabicycloheptyl groups; and (d) a photocationic initiator system. Three main aspects were studied (a) the photoreactivity of the formulations using PDSC, (b) photopolymerization stress, and (c) mechanical properties (flexural elastic modulus, ultimate strength, and work of fracture) which were measured using an electromagnetic mechanical testing machine. The main findings were (a) formulations containing 2,4,8,10-tetraoxaspiroalkane monomers had measured net enthalpies greater than those containing 1,5,7,11-tetraoxaspiroalkane monomers, and above those calculated for addition of an inert diluent; (b) all formulations containing tetraoxaspiroalkane monomers exhibited photopolymerization stress values that were 40-99% less than the nonaddition control; (c) the formulation containing a 1,5,7,11-tetraoxaspiroalkane monomer with an oxirane functionality had mechanical properties that were not significantly different from the nonaddition control.

Recent Advances and Developments in Composite Dental Restorative Materials

“…Whereas the polymerization of monomers with strained small ring structures is driven primarily by enthalpy change, the ring-opening polymerization of monomers with larger ring structures is also possible based on entropy effects. Several bicyclic monomers that engage in either radical or cationic double-ring-opening polymerization have been developed and examined for their potential to reduce polymerization shrinkage in dental materials (Miller et al ., 2005; Moon et al ., 2005; Chappelow et al ., 2008). A detailed mechanistic study of 2-methylene-7-phenyl-1,4,6,9-tetraoxaspiro[4.4]nonane, a bicyclic monomer known to provide ring-opened polymer, indicated significant issues, including susceptibility to moisture-induced side-reactions in cationic and radical-assisted cationic polymerizations (Ge et al ., 2006).…”

Dental Applications

“…Following the latter study, a great variety of compositions have been designed for ring-opening, expanding polymerizations, focused on eliminating or reducing the shrinkage as well as improving the physical and mechanical properties of composites. The focus has been primarily on SOC and SOC-type monomers with epoxy resins (72)(73)(74)(75)(76)(77)(78)(79)(80)(81)(82)(83)(84). This concept has been slow to achieve the desired productivity of marketable dental restoratives; however, a new commercially available resin restorative based on a silorane, ring-opening monomer (section "Shrinkage Concerns") has shown promising results.…”

“…A significant number of studies have also shown that the silorane based restorative has excellent physical and mechanical properties, low water sorption, good color retention and may be modified with reactive diluents-modifiers, such tetraoxaspiroalkanes. Clearly, composites made with silorane chemistry compare favorably to Z250 (3M ESPE), Tetric Ceram (Ivoclar Vivadent) and TPH (Dentsply Caulk) composites, that is, mechanical properties of silorane restoratives are comparable with or better than commonly used methacrylate-based formulations (140)(141)(142)(143)(144)(145)(146)(147)(148). In addition, the ambient light sensitivity of silorane systems is very low compared with methacrylate systems, which results in longer working time for the clinical dentist.…”

Synthesis of DOPO-based spiroorthocarbonate and its application in epoxy resin

“…If the ratio between them was appropriate, zero shrinkage, even a slight expansion in volume was possible. [2][3][4][5][6][7][8] Spiroorthocarbonates (SOCs) can be used as anti-shrinkage additives in the double ring-opening polymerization with a cationic initiator. [9] It aimed to offset chemically volume shrinkage and to overcome the adverse effects of volume shrinkage.…”