Light-Cured Self-Etch Adhesives Undergo Hydroxyapatite-Triggered Self-Cure

In Vitro and In Vivo Efficacy of New Composite for Direct Pulp Capping

Objectives

To investigate physicochemical properties, dentin bonding, cytotoxicity, and in vivo pulp response of experimental self-adhesive composites tailored to direct pulp capping.

Materials and Methods

Experimental composites were prepared with beta-tricalcium phosphate and hydroxyapatite nanoparticles adsorbed with simvastatin and glutathione added at 0% (control resin), 1 wt% (Res 1%), and 10 wt% (Res 10%). A commercial light-curable calcium hydroxide (Ca(OH)₂) (Ultra-Blend Plus) was used as control material. The physicochemical properties investigated were flexural strength and modulus, calcium release, and degree of conversion. Dentin bonding was assessed by the push-out test. Proliferation and cell counting assays were performed to evaluate in vitro cytotoxicity using fluorescence microscopy. In vivo pulp capping was performed on molars of Wistar rats, which were euthanized after 14 days and evaluated by histological analysis.

Results

No statistical difference was observed in flexural strength and cell viability (p > 0.05). Res 10% presented higher modulus than control resin and Ca(OH)₂. Also, Res 10% attained statistically higher degree of conversion when compared to other experimental composites. Ca(OH)₂ showed higher calcium release after 28 and 45 days of storage, with no statistical difference at 45 days to Res 10%. All experimental composites achieved significantly higher bond strength when compared to Ca(OH)₂. While no significant difference was observed in the cell proliferation rates, resins at lower concentrations showed higher cell viability. In vivo evaluation of pulp response demonstrated no pulp damage with experimental composites.

Conclusions

The experimental composite investigated in this study achieved adequate physicochemical properties with minor in vivo pulpal inflammation and proved to be a valuable alternative for direct pulp capping.

Bis[2-(Methacryloyloxy) Ethyl] Phosphate as a Primer for Enamel and Dentine

Dental resin composites are commonly used in the restorative management of teeth via adhesive bonding, which has evolved significantly over the past few decades. Although current self-etch bonding systems decrease the number of clinical steps, the acidic functional monomers employed exhibit a limited extent of demineralization of enamel in comparison to phosphoric acid etchants, and the resultant superficial ionic interactions are prone to hydrolysis. This study evaluates the etching of primers constituted with bis[2-(methacryloyloxy) ethyl] phosphate (BMEP) of dental hard tissue, interfacial characteristics, and inhibition of endogenous enzymes. We examine the incorporation of 2 concentrations of BMEP in the formulation of experimental primers used with a hydrophobic adhesive to constitute a 2-step self-etching bonding system and compare to a commercial 10–methacryloyloxydecyl dihydrogen phosphate (10-MDP)–containing system. The interaction of the primer with enamel and dentine was characterized using scanning electron, confocal laser scanning, and Raman microscopy while the polymerization reaction between the BMEP primers and hydroxyapatite was evaluated by Fourier-transform infrared spectroscopy. The inhibitory effect against matrix metalloproteinase (MMP) enzymes of these primers was studied and percentage of inhibition analyzed using 1-way analysis of variance and Tukey’s post hoc test (P < 0.05). Results of the scanning electron microscopy micrographs demonstrated potent etching of both enamel and dentine with the formation of longer resin tags with BMEP primers compared to the 10-MDP–based system. The BMEP polymerized on interaction with pure hydroxyapatite in the dark, while the 10-MDP primer exhibited the formation of salts. Furthermore, BMEP primers were able to inhibit MMP activity in a dose-dependent manner. BMEP could be used as a self-etching primer on enamel and dentine, and the high degree of polymerization in the presence of hydroxyapatite can contribute to an increased quality of the resin polymer network, prompting resistance to gelatinolytic and collagenolytic degradation.

Influence of beam homogenization on bond strength of adhesives to dentin

OBJECTIVE

This study evaluated the effect of beam homogeneity on the microtensile bond strength (μTBS) of two adhesive resins to dentin.

METHODS

One polywave light-emitting-diode (LED) LCU (Bluephase Style, Ivoclar Vivadent AG) was used with two different light guides: a regular tip (RT, 1010 mW/cm² emittance) and a homogenizer tip (HT, 946 mW/cm² emittance). The emission spectra and beam profiles were measured from both light guides. Extracted third molars were prepared for μTBS evaluation using two adhesive systems: Excite F (EXF) and Adhese Universal (ADU). Bond strength was calculated for each specimen (n = 10) at locations that correlated with the output of the two LED chips emitting blue (455 nm) and the one chip that emitted violet light (409 nm) after 24-hs and after one-year water-storage. The μTBS was analyzed using a four-way analysis of variance (factors: adhesive system, light guide, LED wavelength, and storage time) and post-hoc Tukey test (α = 0.05).

RESULTS

EXF always delivered a higher μTBS than ADU (p < 0.0001), with the μTBS of ADU being about 20% lower than EXF. The light guide (p = 0.0259) and storage time (p = 0.0009) significantly influenced the μTBS. The LED wavelengths had no influence on the μTBS (p > 0.05).

SIGNIFICANCE

Homogeneity of the emitted light beam was associated with higher 24-h μTBS to dentin, regardless of the adhesive tested. Also, differences in the composition of adhesives can affect their compatibility with restorative composites and their ability to maintain bonding over one year.

Knoop Hardness of Self-Etch Adhesives Applied on Superficial and Deep Dentin

Statement of the Problem

Low pH of self-etch adhesives might cause suboptimal polymerization.

Purpose

This study aimed to evaluate the effect of dentin depth (deep and superficial) on polymerization efficacy of two self-etch adhesives, with different pH by means of Knoop hardness test.

Materials and Method

In this in vitro study, sixty sound molars were used to prepare 30 superficial dentin and 30 deep dentin specimens. Dentin specimens of each depth were randomly distributed into two equal subgroups (N=15) and bonded by either Adper Prompt L-Pop (strong self-etch adhesive) or Adper Easy Bond (mild self-etch adhesive). Knoop hardness test was employed to evaluate degree of cross-linking of the adhesives. Data were analyzed with SPSS 16, using two-way ANOVA to compare mean hardness values of the study groups (p< 0.05).

Results

There was no interaction effect between dentin depth and the type of adhesive (p= 0.36). Regardless of dentin depth, hardness of Adper Easy Bond was significantly higher than that of Adper Prompt L-pop (p< 0.001). Moreover, both the adhesives showed higher hardness when bonded to superficial dentin compared to deep dentin (p< 0.001).

Conclusion

Degree of cross-linking of the self-etch adhesive with mild acidity was more than that of the strong self-etch adhesive after light-curing. Surface hardness of both adhesives was higher on superficial dentin compared to deep dentin.

Tertiary Amine and Tooth Mineral Hydroxyapatite Facilely Trigger Self-cure of 10-MDP Based Adhesives

The present work aims to investigate if a novel self-cure system, mediated by tertiary amine ethyl 4-(dimethylamino)-benzoate (4E) and tooth mineral hydroxyapatite (HAp), would trigger polymerization of model adhesives based on a popular self-etch monomer, 10- methacryloyloxydecyl dihydrogen phosphate (10-MDP). The effect of 4E and HAp contents on degree of conversion (DC), polymerization rate (Rp), and induction period (IP) was investigated. The occurrence of such self-cure phenomenon in adhesives that underwent prior inadequate light cure was also evaluated. Model self-etch adhesives were prepared by using a monomer mixture of 10-MDP with 2-hydroxyethyl methacrylate at1:1 wt. ratio. 4E (0.3-1.3 wt%), and HAp (0.5-2 wt%) were added to the mixture. Benzoylperoxide and N,N-dihydroxyethyl-p-toluidine were used as conventional chemical-cure system, and trimethylbenzoyl-diphenylphosphine oxide as light-curing photoinitiator. The polymerization processes and mechanical properties of model adhesives were evaluated by real time ATR/FT-IR and nanoindentation, respectively. The 4E- HAp system successfully triggered self-cure of 10-MDP based model adhesives. DC, Rp and IP were apparently affected by both 4E and HAp contents. DC of self-cure of the model adhesives was much higher than that of the conventional chemical-cure system. 4E-HAp initiated self-cure further boosted DC to ~100% regardless of prior light exposure, and significantly improved elastic modulus and hardness, thus provided a novel polymerization method to effectively salvage curing of the adhesives after inadequate light-cure.