Degree of conversion of polymer-matrix composite assessed by FTIR analysis

Edge chipping resistance of veneering composite resins

OBJECTIVES

To investigate the edge chipping resistance (ECR) of six veneering composite resins after different treatment protocols.

MATERIALS AND METHODS

Rectangular bar specimens were manufactured from Ceramage Incisal (CER; Shofu), dialog Vario Occlusal (DIA; Schütz Dental), Gradia Plus Heavy Body Enamel (GRA; GC Europe), in:joy incisal (INJ; Dentsply Sirona Deutschland), SR Nexco Paste Incisal (SRN; Ivoclar Vivadent), and Signum composite enamel (SIG; Kulzer). ECR was determined after five treatment protocols: (1) no treatment, (2) after storage in distilled water at 37 °C for 7 days, (3) storage in distilled water with an additional 10 000 thermal cycles (5 °C/55 °C), and hydrothermal treatment at 134 °C at a water vapor pressure of 0.2 MPa for a duration of (4) 3.5 min or (5) 23.5 min. Force was applied with the universal testing machine ZHU 0.2 (Zwick Roell) mounted with a Vickers diamond indenter until the chip fractured off the specimen and ECR values were computed by dividing the applied maximum force by the distance to the center of the applied force. Fracture analysis was performed employing light microscope imaging. Univariate and one-way ANOVA, Scheffé and Tukey-B post hoc, and partial eta squared (ƞ_p²) were computed (p < 0.05).

RESULTS

DIA presented consistently high ECR values, while CER showed low results. For some groups, seven days' storage in water and hydrothermal treatment for 3.5 min led to higher ECR results than observed in the initial state, while an additional 10 000 thermal cycles and hydrothermal treatment for 23.5 min resulted in lower ECR values.

CONCLUSIONS

The examined veneering composite resins differed in regard to their mechanical properties, with DIA possessing the highest resistance to chipping. While post-processing can initially increase a material's edge chipping resistance, intensified treatment protocols reduced the mechanical properties of veneering composite resins.

Impact of polymerization and storage on the degree of conversion and mechanical properties of veneering resin composites

To investigate the degree of conversion (DC), Martens hardness (HM), elastic indentation modulus (E_IT), and flexural strength (FS) of veneering resin composites (SR Nexco Paste (NP), Ceramage Incisal (CI), Gradia Plus (GP); n=60/group) cured with different polymerization devices (bre.Lux Power Unit, Labolight DUO, Otoflash G171, LC-3DPrint Box, PCU LED; n=12/subgroup) after storage. Otoflash G171 and Labolight DUO showed increased DC/HM/E_IT. CI presented the lowest DC and highest HM/E_IT. NP showed the highest DC and lowest HM/E_IT. Within Otoflash G171, Laboligth DUO and PCU LED, highest FS was observed for CI. Storage did not affect DC/HM/E_IT for specimens cured with Otoflash G171 or Labolight DUO. With storage not showing an influence on the tested parameters for polymerization devices that otherwise presented superior results, increased storage time cannot be recommended. For the tested resin composites, this study observed a high/low degree of conversion to coincide with respectively low/high amounts of fillers/mechanical properties.

Fourier-transform infrared spectroscopy/attenuated total reflectance analysis for the degree of conversion and shear bond strength of Transbond XT adhesive system

Objective

The objectives of this study were to evaluate the degree of conversion (DC) for Transbond XT curing light of intensity 1,600 mW/cm² by using variable curing durations and to determine the effect of the tested curing durations adopted in the current experiment on shear bond strength of Transbond XT resin cement.

Materials and methods

A total of 85 orthodontic ceramic brackets (Victory series; 3M Unitek) were utilized in the current experiment. The bonding system used in the current study was Transbond XT Primer followed by Transbond PLUS Color Change Adhesive (3M Unitek) that cured for 3, 6, and 9 seconds. The method was done by polymerization of the adhesive under a ceramic bracket for 40 ceramic brackets. The other 45 brackets were divided into three groups (n=15) according to the curing time duration (3, 6, and 9 seconds). The bonded specimens in each group were debonded using a shear load applied at the bracket bases by the blades of an Instron universal testing machine (ElectroPlus E1000; Instron) and directed in an occlusogingival direction with a crosshead speed of 0.5 mm/min utilizing 50 kg load cell.

Results

One-way ANOVA revealed that 6 and 9 seconds curing by the Ortholux light cure scored significantly higher values when compared to the 3 seconds curing.

Conclusion

Curing the Transbond XT for 6 and 9 seconds recorded a significant improvement of bond strength and DC.

The effect of thermocycling on the degree of conversion and mechanical properties of a microhybrid dental resin composite

Objective

The purpose of this study was to investigate the degree of conversion (DC) and mechanical properties of a microhybrid Filtek Z250 (3M ESPE) resin composite after aging.

Method

The specimens were fabricated using circular molds to investigate Vickers microhardness (Vickers hardness number [VHN]) and DC, and were prepared according to ISO 4049 for flexural strength testing. The initial DC (%) of discs was recorded using attenuated total reflectance-Fourier transforming infrared spectroscopy. The initial VHN of the specimens was measured using a microhardness tester under a load of 300 g for 15 seconds and the flexural strength test was carried out with a universal testing machine (crosshead speed, 0.5 mm/min). The specimens were then subjected to thermocycling in 5°C and 55°C water baths. Properties were assessed after 1,000–10,000 cycles of thermocycling. The surfaces were evaluated using scanning electron microscopy (SEM). Data were analyzed using 1-way analysis of variance followed by the Tukey honest significant difference post hoc test.

Results

Statistical analysis showed that DC tended to increase up to 4,000 cycles, with no significant changes. VHN and flexural strength values significantly decreased upon thermal cycling when compared to baseline (p < 0.05). However, there was no significant difference between initial and post-thermocycling VHN results at 1,000 cycles. SEM images after aging showed deteriorative changes in the resin composite surfaces.

Conclusions

The Z250 microhybrid resin composite showed reduced surface microhardness and flexural strength and increased DC after thermocycling.

Comparative Evaluation of the Depth of Cure and Degree of Conversion of Two Bulk Fill Flowable Composites

INTRODUCTION

Since the development of resin based composites, several improvements have been made to improve their physical and chemical properties. In an attempt to fasten and simplify the restoration process, a new class of resin based composite materials, called the bulk fill resin based composites have been introduced, which has been claimed to achieve a depth of cure of 4 mm without affecting the properties of the material.

AIM

To comparatively evaluate the depth of cure of two different bulk fill flowable composite resins by ISO 4049 method and to evaluate the degree of conversion of the same composite resins with Fourier Transform Infrared (FTIR) spectroscopy method.

MATERIALS AND METHODS

Composite resin specimens (n=10) per group were prepared with bulk fill flowable composites, Surefil SDR flow (Dentsply Caulk, Milford, DE, USA) designated as Group A and Filtek bulk fill (3M ESPE, St.Paul, MN, USA) designated as Group B. Depth of cure was determined according to "ISO 4049; Depth of Cure" method, and FTIR spectroscopy method was used to estimate the degree of conversion of both the bulk fill flowable composites. The degree of conversion of monomer to polymer was estimated individually in coronal half (Group A1 and B1) and pulpal half (Group A2 and Group B2) by dividing each specimens into two halves. The data were analysed using Student's unpaired t-test at 5% level of significance.

RESULTS

The mean depth of cure of Group A was 3.89 mm (±0.103) and for Group B was 3.54 mm (±0.129). The degree of conversion percentage for Group A1=78.51 (±47.8), Group A2= 31.9 (±22.4), Group B1=39.8 (±5.2), Group B2=37.4 (±6.4). Statistical analysis revealed significant difference in the depth of cure between the two bulk fill flowable composites with Group A higher than Group B. The degree of conversion of the coronal half of Group A1 was significantly higher when compared to Group B1.

CONCLUSION

Surefil SDR bulk fill resin has better depth of cure and degree of conversion compared to Filtek bulk fill composites.

Own brand label restorative materials-A false bargain?

OBJECTIVES

This study aims at evaluating and comparing mechanical, chemical, and cytotoxicological parameters of a commercial brand name composite material against two 'own brand label' (OBL) composites.

METHODS

Parameters included depth of cure, flexural strength, degree of conversion, polymerization shrinkage, filler particle morphology and elemental analyzes, Vickers hardness, surface roughness parameters after abrasion, monomer elution, and cytotoxicity.

RESULTS

The conventional composite outperformed the OBLS in terms of depth of cure (p<0.001), degree of cure at the first and last time intervals (p<0.001), hardness (p<0.001), and post-abrasion roughness (p<0.05). The polymerization volumetric shrinkage ranged from 2.86% to 4.13%, with the highest shrinkage seen among the OBLs. Both Monomer elution from the OBLs was statistically significantly higher (p<0.001). Statistically significantly higher cytotoxicity combined with altered morphology and loss of confluence was detected in the cells exposed to extracts from the OBLs.

CONCLUSIONS

The OBLs were in general outdone by the conventional composite.

CLINICAL SIGNIFICANCE

OBLs restorative materials have become pervasive in the dental market. Manufacturers often promise equal or better characteristics than existing brand-name composites, but at a lower price. Dentists are highly recommended to reconsider utilization of OBLs lacking sound scientific scrutiny, and our findings underscore this recommendation.

The effect of 4,4'-bis(N,N-diethylamino) benzophenone on the degree of conversion in liquid photopolymer for dental 3D printing

PURPOSE

The purpose of this preliminary study was to investigate the effects of adding 4,4'-bis(N,N-diethylamino) benzophenone (DEABP) as a co-initiator to a binary photoinitiating system (camphorquinone-amine) to analyze on the degree of conversion (DC) of a light-cured resin for dental 3D printing.

MATERIALS AND METHODS

Cylindrical specimens (N=60, n=30 per group, ø5 mm × 1 mm) were fabricated using bisphenol A glycerolate dimethacrylate (BisGMA) both with and without DEABP. The freshly mixed resins were exposed to light in a custom-made closed chamber with nine light-emitting diode lamps (wavelength: 405 nm; power: 840 mW/cm²) for polymerization at each incidence of light-irradiation at 10, 30, 60, 180, and 300 seconds, while five specimens at a time were evaluated at each given irradiation point. Fourier-transform infrared (FTIR) spectroscopy was used to measure the DC values of the resins. Two-way analysis of variance and the Duncan post hoc test were used to analyze statistically significant differences between the groups and given times (α=.05).

RESULTS

In the DEABP-containing resin, the DC values were significantly higher at all points in time (P<.001), and also the initial polymerization velocity was faster than in the DEABP-free resin.

CONCLUSION

The addition of DEABP significantly enhanced the DC values and, thus, could potentially become an efficient photoinitiator when combined with a camphorquinone-amine system and may be utilized as a more advanced photopolymerization system for dental 3D printing.

Dentin bond strength and degree of conversion evaluation of experimental self-etch adhesive systems

BACKGROUND

The aim of this study was to investigate the effect of different concentrations of 10-methacryloyloxydecyl dihydrogen phosphate (10-MDP) monomer in one-step self-etch experimental adhesives on dentinal microshear bond strength (µSBS), their degree of conversion and bonded micro structure.

MATERIAL AND METHODS

Composite resin cylinders (Clearfil AP-X) were bonded on human sound molar dentinal surfaces by using five experimental one-step self-etching adhesives (1-SEAs) containing 0% (E0), 5% (E5), 10% (E10), 15% (E15), 20% (E20) (by weight) 10-MDP monomer and Clearfil S3 Bond (CS3) as a control. After 24 hours, microshear bond strength was tested. The degree of conversion was also measured using Fourier transform infrared spectroscopy. Interfacial ultrastructure was observed under a scanning electron microscope in all the groups.

RESULTS

A higher microshear bond strength was observed with adhesives containing 10% and 15% 10-MDP in comparison to study groups (P<.05). Clearfil S3 Bond and 10% MDP had a significantly greater degree of conversion than other groups (P<.05).

CONCLUSIONS

The amount of functional monomer in 1-SEAs influences both the bonding performance and degree of conversion; 10% 10-MDP showed the best combination of bond strength and degree of conversion. Key words:Self-etch adhesives, 10-MDP, bond strength, degree of conversion.