2,2'-(P-tolylimino)diethanol: Synthetic Intermediate and Dental Resin Additive

2,2'-(P-tolylimino)diethanol is an important fine organic chemical intermediate that combines an aromatic amine structure with dihydroxy functional groups. Its molecular structure contains a tertiary amine nitrogen atom and two reactive hydroxyethyl groups at its core. These dual functional groups confer excellent nucleophilic reactivity and cross-linking modification capabilities. It exhibits strong reactivity and can participate in various organic synthesis reactions, including esterification, condensation, and polymerization. In industrial production and laboratory research, it is primarily used as a key synthetic intermediate for high-end dyes, active pharmaceutical ingredients (APIs), and agricultural chemicals.

Novel self-healing dental resin with microcapsules

The healing liquid should have a relatively low viscosity to flow and fill the cracks in the resin matrix. TEGDMA is flowable and has been used as a dental monomer with acceptable biocompatibility. Furthermore, TEGDMA can form a polymer via free-radical initiation by using a peroxide initiator and a tertiary amine accelerator. A usual dental tertiary amine accelerator, 2,2'-(p-tolylimino)diethanol (DHEPT), has good solubility and stability in TEGDMA. Therefore, the present study proposed to test 2,2'-(p-tolylimino)diethanol incorporation in TEGDMA to serve as the self-healing liquid inside microcapsules for the first time. In the present study which was our first study, we focused on the synthesis and characterization of the self-healing microspheres, incorporation into resin, physical and mechanical properties, and fibroblast cytotoxicity. Then in our second study, we further added calcium phosphate and antibacterial monomer to the self-healing resin, and tested oral biofilm response. Accordingly, the objectives of this study were to investigate triethylene glycol dimethacrylate-2,2'-(p-tolylimino)diethanol as a self-healing liquid in PUF microcapsules for dental applications and to examine the mechanical properties and self-healing efficacy. The following hypotheses were tested: (1) The new TEGDMA-DHEPT-in-PUF microcapsules could be incorporated into a dental resin without decreasing the mechanical properties of the resin; (2) The microcapsule-containing resin would have a high self-healing capability after fracture; (3) The microcapsule-containing resin would have a low cytotoxicity against human fibroblasts.[1]

Novel self-healing dental resin containing microcapsules with polymerizable TEGDMA-DHEPT healing liquid in PUF shells were prepared via in situ polymerization, and exhibited a substantial self-healing capability. Once crack and damage ruptured the microcapsules, the released triethylene glycol dimethacrylate-2,2'-(p-tolylimino)diethanol healing liquid could react with the BPO in the resin matrix and polymerize to bond the cracked planes together. The shell wall of the microcapsules had a proper thickness with a smooth surface roughened by nanoparticle deposits, which promoted micromechanical interlocking of microcapsules in the resin matrix. The flexural strength and elastic modulus of the resin were not adversely affected when the microcapsule mass fraction was ≤ 15%. The inclusion of microcapsules increased the virgin fracture toughness of resin. The self-healing efficiency showed that about 65% recovery of the virgin fracture toughness could be achieved when using 15% microcapsules. The self-healing resin containing microcapsules appeared to have good cellular cytotoxicity in vitro. Therefore, the novel self-healing dental resin containing microcapsules with polymerizable triethylene glycol dimethacrylate-2,2'-(p-tolylimino)diethanol liquid in PUF shells may be promising for crack-inhibiting and self-healing dental restorations to prolong the lifetime.

Conversion of curing experimental dental resin composites

The effect of photoinitiator and co-initiator chemistry on the setting reaction and degree of conversion of dental resin-based composites (RBCs) has rarely been determined explicitly. This work examines the effect of type and concentration of photoinitiator and co-initiator on the rate of change of light transmission throughout polymerisation and degree of conversion of model RBC formulations. Specimens containing CQ and PPD cured with the halogen LCU did not have a significant effect on DC or changes in light transmission, although a significant increase in DC was observed for CQ compared with PPD specimens cured with the LED LCU. DABE and CEMA were more effective co-initiators than 2,2'-(p-tolylimino)diethanol. There was no significant increase in the DC of DABE or CEMA containing specimens irradiated with the QTH or LED LCU for each exposure time. In contrast, 2,2'-(p-tolylimino)diethanol-containing specimens required 20 and 40 s exposure to achieve a maximum conversion using the QTH and LED LCU, respectively. 2,2'-(p-tolylimino)diethanol specimens also exhibited a significantly decreased DC (p < 0.05) compared with DABE and CEMA irradiated with either LCU following 40 s irradiation. Although DC was not limited by co-initiator concentration, the absence of a co-initiator resulted in marked differences in light transmission and decreased DC throughout 40 s irradiation with each LCU type.[2]

References

[1]Wu J, Weir MD, Zhang Q, Zhou C, Melo MA, Xu HH. Novel self-healing dental resin with microcapsules of polymerizable triethylene glycol dimethacrylate and N,N-dihydroxyethyl-p-toluidine. Dent Mater. 2016 Feb;32(2):294-304. doi: 10.1016/j.dental.2015.11.014. Epub 2015 Dec 29. PMID: 26743969; PMCID: PMC5116152.

[2]Ogunyinka A, Palin WM, Shortall AC, Marquis PM. Photoinitiation chemistry affects light transmission and degree of conversion of curing experimental dental resin composites. Dent Mater. 2007 Jul;23(7):807-13. doi: 10.1016/j.dental.2006.06.016. Epub 2006 Aug 17. PMID: 16914191.