Patent Application
20180250201
Disclosed herein is a two-component flowable composite that is intrinsically capable of adapting to tooth substrates. In addition, by incorporating a “Chemical Thickener” in two-component flowable compositions, of which would allow two orthogonal chemistries, nucleophile-initiated thiol/ene Michael addition and light-initiated radical polymerization to proceed sequentially. Thus it could to offer the advantage of further manipulation on such thickening paste with adequate working time prior to final curing by light.
SureFil SDRflow® set up as a standard for bulk-fill flowable as easy to use and excellent adaption due to its lower viscosity, lower curing stress and high depth of cure. However, it seems highly desirable if it can be further manipulated by the clinicians although the low viscosity make possible to achieve the best adaption, which is critical to minimize the failure of the bulk restoration. Therefore, in order to improve the SureFil SDRflow® while carry its signature feature of self-leveling, a possible phase change from lower viscosity to higher viscosity become a new twist. It is expected that this would be able to effectively balance between adaptation and manipulation.
A flowable composite should be able to undergo a rheological phase change from low viscosity to a firm paste upon a paste/paste mixing. Several approaches were proposed based on either chemistry and/or technology. If a chemistry could allow a selective cure for part of formulated material to building up its texture (viscosity) in given time, it should be possible to develop such a viscosity-increasable flowable that should delivery some feature we would like. For instance, a chemical approach can be based on a sequential curing mechanism, from which distinguished chain growth and network-formation are involved in. Consequently the initial paste offer lower viscosity for achieving good adaptation and then first curing mechanist is triggered for viscosity building-up but would not cause unnecessary cross-linking. Finally cross-linking is kicked in by light irradiation for strengthening the performance.
NMR Analysis: Nuclear magnetic resonance (NMR) spectra were recorded on a Varian 300 MHz spectrometer. Samples were prepared in CDCl3 at ca. 15% v/v. Chemical shifts are reported in parts per million (ppm) relative to TMS.
FTIR Analysis: Fourier transform infrared spectra (FTIR/ATR) were recorded on a Thermo Electron Nicolet 6700 Spectrometor.
Photo DSC: Differential Scanning calorimeter (Q2000, TA Instrument) with photocalorimetry accessory (PCA), from which UV/Visible light (250-650 nm) from a 200 W high pressure mercury source is transmitted to the sample chamber via an extended range, dual-quartz light guide with neutral density or band pass filters, was used to evaluate the photolysis and photopolymerization for the neat resin and/or any formulated resin system. Under both air and nitrogen, the test was performed. The light outputs and light spectrum can be tuned by using build-in filter, or additional UV filter or intensity-reducing filter.
Flexural strength and modulus are tested according to ISO 4049, 2×2×25 mm specimens were cured by three overlapped spot curing with Spectrum 800 with 13 mm light guide at 800 mw/cm2, 20″ for each spot on one side only. The cured specimens (6-10) were placed in DI water and stored at 37° C. for 24 hrs, then were sanded prior to the test at room temperature.
Compressive strength and modulus are tested according to ISO 9917, which is actually for water-based cements since ISO 4049 does not specify for compressive strength. ϕ4×6 mm glass slave as mold for specimen preparation (6). It was cured by Spectrum 800 at 800 mw/cm2 from both top and bottom, at 20″ each. The cured specimens (6-10) were placed in DI water and stored at 37° C. for 24 hrs, and then were sanded prior to the test at room temperature.
Shrinkage Stress was measured by using NIST/ADA's tensometer. Specimen with 2.25 mm in thickness (c-factor as 1.33) is cured for 60 seconds by DENTSPLY/Caulk's QHL light at 550 mw/cm2. The total stress at the 60th minute is taken to rank different materials.
Rheology property was measured by using TA's DHR Rheometor. ϕ40 mm 2° geometry is used for resin viscosity measurement and ϕ20 mm flat geometry was used for composite's evaluation. Oscillation test is set up at 175 Ps shear stress, 1 Hz shear frequency at 35° C.
Ross planetary mixer (120 F/20 in psi), SpeedMix (RT) and Resodyn (RT/20 In psi) are used in prepared filler blend and resin mixture and the flowable composite pastes.
digi syringe system with auto mixing tip was used to pack the individual base paste and catalyst paste, respectively.
There are different approaches based on either chemistry and/or technology in creating a viscosity-increasable flowable composite. If chemistry could allow a selective reaction for part of a formulated material to building up its texture (viscosity) in given time, it should be possible to develop such a viscosity-increasable flowable that should delivery some desirable features. For instance, a chemical approach can be based on a sequential curing mechanism, from which distinguished chain growth and network-formation are involved in. Consequently the initial paste offers lower viscosity for achieving good adaptation and then a first curing mechanism is triggered for viscosity building-up but would not cause unnecessary cross-linking. Finally cross-linking is initiated by light irradiation for strengthening the performance.
One example of conventional approach was based on a polyacid/polybase for such viscosity-increasing process, which was indeed able to promote viscosity increasing via non-radical reaction. It was found that the pair of acid/base in structure and composition would impact significantly on the viscosity profile and mechanical property. 10-MDP and Penta appear more effective to react with polyimidazole. Polyacrylic acid showed limited reactivity towards polyimidazole in absence of water. In addition, as expected, a significant increase in water absorption in all cured composites were found, which led to decrease in mechanical strength in wet specimen.
The potential benefits, however, are the improved moisture tolerant as such increased hydrophilicity. In addition, there was also challenge to achieve really good initial adaptation of the resulting as-mixed composite as required from the low viscosity and rapid viscosity increase to allow some kind manipulation plus offer adequate mechanical properties. It should be possible to achieve a balance between viscosity change and paste manipulation but it is also realized that it is remain very challenge for achieving superior mechanical strength as universal composite due to its intrinsic low filler loading without a significant change in filler. In order to achieve a rapid viscosity building-up, new polybase or polyacid resins or reactive filler might be necessary.
Another possible approach to realizing a dual-cure, viscosity-increasing process as described in the present disclosure would be a thiol/ene-based cure for initial chain extension for viscosity building-up while the paste remain as workable/manipulatable, then light irradiation to lead a fully cured material. It was expected that such two distinct chemistries would afford two-stage curing process so as to balance the adequate initial adaptation and subsequent manipulation from a single material. In addition, it was also expected that his approach would address the issues that were noticed in the conventional polyacid/polybase process, such as the increasing water absorption for inferior mechanical properties, relatively slow reaction and an initial higher viscosity. Chris Bowman's team at University of Colorado reported two-stage reactive polymer network forming systems, in which a base-catalyzed thiol-ene addition was set up for initial curing process and photo-initiated light curing to finalize the entire networking process, as shown in
From our comprehensive investigation on such thiol/ene systems, it was further discovered a remarkably stable pare that is composed of dimethacrylate and polytiol, more specifically EBPADMA and PETMP, which would allow to formulate a stable catalyst resin/paste with inclusion of DBU. Furthermore, a viscosity-increasing flowable should be readily resulted from a base paste that is composed of methacrylate resin and polyacrylate resins and photoinitiators for the 2nd step curing; and a catlystat paste that is composed of polytiol and methacrylate matrix and the catalysts of thiol/ene addition, DBU.
As an example, it was illustrated in
As shown in Table 1 when the resin compositions of polythiol resin (PETMP) and polyacrylate resin (TCDCDA or SR295) varied, the speed of viscosity increasing upon mixing the resin blend of PETMP in TPH resin and TCDCDA or SR295 in TPH Resin would change dramatically depending upon the the nature of the base catalyst (DBU, TEA and DABCO). Thus it did indicate that thiol-ene chemistry appears to proceed well and feasible to trigger the stage one network forming process for a viscosity-increasing composite without involving any radical polymerization. It was further found that only 0.3-0.4% of DBU is necessary to have a reasonable networking process for PETMP/TCDCDA system, from which DBU was discovered as the most effective catalyst for such thiol/ene reaction.
Further the flowability of such formulated composition would also vary depending upon the filler and filler content. As showed in Table 2, a variety of flowable compositions with 55-60% wt/wt of fillers was readily formulated by variable DBU contents and different acrylate resins (TDCDDA and SD 295) and different methacrylate resins (TPH resin, SDR resin and Isosorbide Resin). It was also concluded that higher concentration of DBU is more effective than DBU/TEA mixture; and SR295 is more effective than TCDCDA in term of promoting stage one network formation.
Furthermore, as showed in Table 4 and 5, excellent mechanical propertied, flexural strength of 136-152 MPa and flexural modulus of 6750-8200M, could be achieved from such two-stage cure/viscosity-increasing systems. In addition, lower polymerization stress of 2.3-2.8 MP vs. 3.3 MPa were also resulted from such two-stage cure process. Further lower polymerization stress of 2.07 MPa was found upon 90 min delayed light curing process, which indirectly confirmed the stage-one network formation process proceeded. In addition, it was also noted DBU could also act as accelerator for CQ/LTPO photopolymerization as evident by the effective curing under a single-band LED irradiation (IQ2 LED).
It was surprisingly found that both two urethane-based methacrylate resins (isosorbide-based resin and SDR resin) are not chemically compatible with PETMP, as evident by the gelation of IJ5-204 and IJ5-206, respectively. There is no any catalyst presented in these systems and they are all methacrylate resins. Thus it is speculated somehow the impurity in either isosorbide resin or SDR resin can significantly destabilize such thiol-ene system of polylthiol (PETMP) and methacrylates. However, the better stability demonstrated by other urethane-based resin (TPH resin) might suggest that there is no (or less) such “impurity” in TPH resin. Indeed a slow viscosity increasing in TPH resin/PETMP was eventually demonstrated they follow similar trend of instability after it was aged over night at RT though no gel was formed as showed by the viscosity of 17 Pa·s of IJ5-192 vs. 9 Pa·s for those freshly mixed resin blends, IJ5-184, IJ5-188 and IJ5-208. In addition, if freshly mixed isosorbide resin/PETMP or SDR resin/PETMP were immediately formulated into composites (IJ6-001 or IJ6-003 in Table 2), their stability got improved but they still tended to get stiff, which indicated a slower gelation process occurred within the pastes then resin blends.
Consequently, it was discovered that a remarkably stable pair of methacrylated resin and polythiol (PETMP) could be achieved from EBPADMA during the extensive resin screening study for improved resin stability: no any viscosity increase as measured after 42 days/RT aging (see
Other approach to stabilize polythiol/methacrylated resin system was also examined in TPH resin and SDR resin, respectively, see
As shown in
Further as showed in
As discussed previously, it was discovered an effective viscosity—increasing for paste/paste flowable could be achieved upon mixing, as evident by the distinct modulus crossover for EBPADMA/PETMP and a variety of methacrylate resins paired SR295 in presence of DBU. However, no such crossover was found when same mathacryate resin paired with TCDCDA with same amount of DBU. It was speculated that further increase of DBU might boost the thiol/ene reaction for pronounced viscosity-increase. Thus in this month additional DBU, from 0.56% to 1.12% was used in same resin formulation with TCDCDA. Lower mechanical strength was resulted from all composites, which suggests potential negative impact of excess DBU on the free radical polymerization process: showed by both EBPADMA/PETMP and Methacrylate resins (TPH, SDR, EBPADMA and Isosorbide Resin)/TCTCDA if DBU is loaded in 1.12%. Indeed, no modulus crossover occurred for all these formulations.
As showed in Table 5, flowable composites based on EBPADMA/PETMP-EBPADMA/SR295 (IJ6-117/IJ6-118) were formulated by using Resodyn. The mechanical property of such resulting paste/paste composite got improved in comparison to those made via SpeedMix (IJ6-115/IJ6-116, see Table 5). Although the compounding process showed slight impact on the viscosity of the individual flowable, no effect was found on the gel-time during the course of viscosity-increasing process. Accordingly, higher polymerization stress was also resulted due to the reduced porosity in these pastes made via Resodyn. Again, the thiol/ene reaction remains fast, which led to fail in catching up the gel-time at 35° C.
Additional flowable formulations based on EBPADMA/PETMP-TPH Resin/SR295 and EBPADMA/PETMP-EBPADMA/SR295 in presence on reduced DBU (0.86%, wt/wt) and different photoinitiator systems (CQ/EDAB/LTPO vs CQ/LTPO) were formulated as showed Ross mixer and Resodyn (Table 5), respectively. Further improved mechanical properties of such paste/paste composite were evidently resulted for pastes made via Ross Mixer. No significant difference between those pastes containing different photoinitiator systems were found, which confirmed the effectiveness for the CQ/LTPO system in absence of EDAB. It was also found TPH Resin-based system tended to building up the viscosity quickly though there was relative longer gel time. As expected even higher polymerization stress of 3.65 MPa (IJ6-154/IJ6-156 in Table 5) and 3.84 MPa (IJ6-160/IJ6-162 in Table 5) were resulted, which featured in IJ6-154 and IJ6-160 any they derived from same resin, IJ6-149, composing of TPH Resin/SR295 and CQ/EDAB/DBU.
It was surprisingly found that the individual catalyst pastes made from RossMixer got gelled by after aging at RT for a couple of weeks though the polythiol base paste made from RossMixer remains stable. However, it was also found that same catalyst pastes made from Resodyn also remain stable, which should be attributed to the thermal degradation of the acrylate resin (SR295). Thus such findings should also suggest that Resodyn process is a better option for compounding those heat-sensitive compositions.
Thus it is concluded that
| Number | Date | Country | |
|---|---|---|---|
| 62466431 | Mar 2017 | US |
