Sesamin as a co-initiator for unfilled dental restorations

Effect of the Photo-initiator System Contained in Universal Adhesives on Radicular Dentin Bonding

CLINICAL RELEVANCE

The photo-initiator system based on an advanced polymerization system may be an alternative that can be used to overcome the disadvantages of radicular dentin, especially for the apical third.

SUMMARY

Objectives: The purpose of this study was to evaluate the effects of universal adhesives with different photo-initiator systems applied in etch-and-rinse (ER) and self-etch (SE) modes on dentin interaction (push-out bond strength [PBS], nanoleakage [NL], and degree of conversion [DC] within the hybrid layer) in the different root thirds after fiber post cementation.Methods and Materials: Roots of endodontically prepared human premolars were randomly divided into six groups according to one of three adhesive systems (Scotchbond Universal [SBU], Ambar Universal [AMB], and Ambar Universal APS [AMB-APS]) and two adhesive strategies (ER and SE) for each system. Posts were cemented, and PBS was tested at 0.5 mm/min. The NL was evaluated by scanning electron microscopy. DC was measured using micro-Raman spectroscopy. The data were analyzed by three-way analysis of variance and Tukey tests (α=0.05).Results: AMB-APS showed similar performance in all root thirds (p>0.05) and higher values of DC, especially in the apical third (p<0.0001). AMB and SBU showed the lowest values in the apical third (p<0.0001).Conclusions: The APS photo-initiator system contained in universal adhesives is a feasible alternative for improving radicular bonding procedure.

Piperonyl methacrylate: Copolymerizable coinitiator for adhesive compositions

OBJECTIVES

This study describes the synthesis of piperonyl methacrylate (PipM) and evaluates its effect when used as coinitiator in the photoinitiated radical polymerization of experimental adhesive resins.

METHODS

PipM was synthetized through an esterification reaction and characterized by FTIR and ¹H NMR spectroscopy. Adhesive resins containing camphorquinone as photoinitiator and PipM or ethyl-4-dimethyl amine benzoate (EDAB) as coinitiators were formulated. Scotchbond Multipurpose (SBMP) adhesive was used as commercial reference. All materials were analyzed for polymerization kinetics, flexural strength, elastic modulus, water sorption/solubility, shear bond strength to bovine enamel and dentin, characterization of hybrid layer by scanning electron microscopy (SEM), microbiological direct contact test, and cytotoxicity.

RESULTS

The adhesive with PipM presented higher degree of conversion and lower sorption/solubility when compared with other groups. Shear bond strength to enamel and dentin were similar for PipM and EDAB materials. The percentage of cellular viability was close to 100% and similar in the experimental groups and the commercial reference.

CONCLUSIONS

PipM presented similar or superior performance to the tertiary amine used as control, representing a potential alternative coinitiator for photopolymerizable dental materials.

CLINICAL SIGNIFICANCE

PipM could be potentially useful in the formulations of adhesive systems with enhanced chemical properties, which could mean improvement in the longevity of composite resin restorations.

A novel photoinitiating system producing germyl radicals for the polymerization of representative methacrylate resins: Camphorquinone/R3GeH/iodonium salt

OBJECTIVES

The aim of our study is to find an amine free photoinitiating system (PIS) for the polymerization of representative dental methacrylate resins. A photoinitiating system (PIS) based on camphorquinone (CQ)/triphenylgermanium hydride/diphenyl iodonium hexafluorophosphate is proposed and compared to the conventional CQ/amine couple. The polymerization monitoring of thin (∼20μm) and thick (1.4mm) samples of a bisphenol A-glycidyl methacrylate (Bis-GMA)/triethyleneglycol dimethacrylate (TEGDMA) blend (70%/30% w/w) and of a urethane dimethacrylate (UDMA) upon exposure to a commercial blue LED centered at 477nm under air or in laminate is described. Finally, the impact of the photoinitiating system composition on the final polymer color is evaluated in detail.

METHODS

FTIR and DSC experiments are used to record the photopolymerization profiles. ESR spectrometry and steady state photolysis are used to detect the produced radicals. Color measurements are carried out to determine the key parameters in the bleaching of the different dental formulations.

RESULTS

The efficiency of the newly proposed PISs for the photopolymerization of BisGMA/TEGDMA and UDMA for thin (20μm) or for thick (1.4mm) samples upon exposure to a dental blue LED under air is excellent. It is noticeably higher than that of the CQ/amine reference couple. Excellent bleaching properties are also observed under irradiation in presence of the new PISs. A good correlation is found between the sample bleaching and the amount of Ph3GeH in the formulation. The excited state processes could be established. The overall chemical mechanisms for the initiation step were also clarified.

Reasons for the yellowness of photocured samples by the benzophenone/1,3-benzodioxole photoinitiating system

Reasons for the yellowness in samples photocured by benzophenone/1,3-benzodioxole.

Influence of chemical structures of benzodioxole-based coinitiators on the properties of the unfilled dental resin

To investigate the influence of chemical structures of benzodioxole-based coinitiator on the initiating reactivity and the mechanical properties of cured samples for the unfilled dental resin, a mixture of 2,2-bis[4-(2-hydroxy-3-methacryloxyprop-1-oxy)phenyl]propane (bis-GMA) and triethylene glycol dimethacrylate (TEGDMA) (70/30 wt.%) was photoinduced by combinations of camphorquinone (CQ) and benzodioxole derivatives. 2-(N,N-Dimethylamino)ethyl methacrylate (DMEM) was used as control. The kinetics was monitored by a real-time Fourier transformation infrared spectroscopy (FTIR) and the dynamic mechanical analysis was performed on a dynamic mechanical analyzer (DMA). The cytotoxicity property of the cured samples was evaluated by MTT assay in vitro using VERO as reference cell lines. The results indicated that the 4-position phenyl ring substituents of the benzodioxole-based coinitiator had great influence on the initiating reactivity. Incorporating substituents with pi electron acceptors in the 4-position of phenyl ring led to the decrease of the rate of polymerization (R(p)) of the CQ/benzodioxole derivatives. However, the electron-donating substituents were useful to increase the reactivity. When compared with CQ/amine initiating systems, the combination of CQ and benzodioxole compounds caused lower R(p) but the comparable final double bond conversion. All the cured films initiated by CQ/benzodioxole derivatives had almost the same glass transition temperature (T(g)) and storage modulus. Indirect cytotoxicity assessment indicated low cytotoxicity of benzodioxole derivatives. These results were very useful for the design of benzodioxole derivatives with satisfactory reactivity and biocompatibility, and are very important for clinical applications.