Degree of Conversion and Oxygen-Inhibited Layer Effect of Three Dental Adhesives

Effect of two oxygen-inhibiting agents on the surface microhardness of giomer restorative materials

Giomers are bioactive hybrid restorative materials consisting of composite resin and glass ionomer filler pre-reacted on the surface, which maintain acceptable clinical qualities over time. One of the main factors that explains this is the surface hardness that is achieved by inhibiting the oxygen layer.

Aim

To compare the effect of blue and conventional Mylar strips used as oxygen inhibiting agents on the surface microhardness of giomer restorative materials.

Materials and Method

A total 96 giomer specimens were prepared in disc-shaped molds 2 mm tall x 5 mm in diameter (ISO 4049: 2019-05). The specimens were grouped according to type of giomer: Beautifil II (BII) or Beautifil II LS (BIILS), and according to the type of Mylar strip: conventional, blue, or control group without strip. They were subsequently subjected to the Knoop (KHN) microhardness test. The database was analyzed with Stata SE v18 statistical software, and two-way ANOVA was performed.

Results

Interaction was found between the type of giomer and Mylar strip (p=0.039). Significant differences were found between surface microhardness values according to the type of giomer (0.001) and the type of Mylar strip (0.001). Beautifil II LS presented significant differences between conventional Mylar strip vs. without Mylar strip (43.58 ± 1.65 vs. 40.44 ± 2.12) and between blue Mylar strip and without Mylar strip (44.69 ± 1.75 vs. 40.44 ± 2.12). In the Bonferroni Post hoc test, a significant difference was found between Conventional Mylar Strip and without Mylar Strip (p=0.001) and Blue Mylar Strip and without Mylar Strip (p=0.001).

Conclusion

The use of blue and conventional Mylar strips inhibits the oxygen layer on the Beautifil II and Beautifil II LS giomers, endowing them with high values of surface microhardness.

The impact of inorganic fillers, organic content, and polymerization mode on the degree of conversion of monomers in resin-matrix cements for restorative dentistry: a scoping review

PURPOSE

The main aim of the present study was to carry out a scoping review on the differences in degree of conversion of monomers regarding several types resin cements, indirect restorative materials, and light-curing procedures used in dentistry.

METHOD

A bibliographic review was performed on PubMed using the following search items: "degree of conversion" OR "filler" AND "resin cement" OR "inorganic cement" AND "organic" OR "radiopacity" OR "refractive" OR "transmittance" OR "type" AND "resin composite." The search involved articles published in English language within the last thirteen years. A research question has been formulated following the PICO approach as follow: "How different is the degree of conversion of monomers comparing several types of resin-matrix cements?".

RESULTS

Within the 15 selected studies, 8 studies reported a high degree of conversion (DC) of the organic matrix ranging from 70 up to 90% while 7 studies showed lower DC values. Dual-cured resin-matrix cements revealed the highest mean values of DC, flexural strength, and hardness when compared with light- and self-polymerized ones. DC mean values of resin-matrix cements light-cured through a ceramic veneer with 0.4 mm thickness were higher (~ 83%) than those recorded for resin-matrix cements light-cured through a thicker ceramic layer of 1.5 mm (~ 77%).

CONCLUSIONS

The highest percentage of degree of conversion of monomers was reported for dual-cured resin-matrix cements and therefore both chemical and light-induced pathways promoted an enhanced polymerization of the material. Similar degree of conversion of the same resin-matrix cement were recorded when the prosthetic structure showed a low thickness. On thick prosthetic structures, translucent materials are required to allow the light transmission achieving the resin-matrix cement.

CLINICAL RELEVANCE

The chemical composition of resin-matrix cements and the light-curing mode can affect the polymerization of the organic matrix. Thus, physical properties of the materials can vary leading to early clinical failures at restorative interfaces. Thus, the analysis of the polymerization pathways of resin-matrix cements is significantly beneficial for the clinical performance of the restorative interfaces.

Effect of Different Post-Curing Methods on the Degree of Conversion of 3D-Printed Resin for Models in Dentistry

The aim was to investigate the effects of different post-curing units on the chemical properties (degree of conversion) of 3D-printed resins for producing models in dentistry. The goal is to determine whether less-expensive post-curing units can be a viable alternative to the manufacturer's recommended units. Forty-five samples were fabricated with an LCD printer (Phrozen Sonic Mini, Phrozen 3D, Hsinchu City, Taiwan) using MSLA Dental Modeling Resin (Apply Lab Work, Torrance, CA, USA). These samples were divided randomly into four different groups for post-curing using four distinct curing units: Phrozen Cure V2 (Phrozen 3D, Hsinchu City, Taiwan), a commercial acrylic nail UV LED curing unit (SUNUV, Shenzhen, China), a homemade curing unit created from a readily available UV LED light produced (Shenzhen, China), and the Triad® 2000™ tungsten halogen light source (Dentsply Sirona, York, PA, USA). The degree of conversion was measured with FTIR spectroscopy using a Nicolet 6700 FTIR Spectrometer (Thermo Fisher Scientific, Waltham, MA, USA). Phrozen Cure V2 had the highest overall mean degree of conversion (69.6% with a 45 min curing time). The Triad® 2000 VLC Curing Unit had the lowest mean degree of conversion value at the 15 min interval (66.2%) and the lowest mean degree of conversion at the 45 min interval with the homemade curing unit (68.2%). The type of light-curing unit did not yield statistically significant differences in the degree of conversion values. There was a statistically significant difference in the degree of conversion values between the 15 min and 45 min curing intervals. When comparing individual light-curing units, there was a statistically significant difference in the degree of conversion for the post-curing units between the 15 min and 45 min curing time (p = 0.029).

Effect of Coloring Beverages on Color Stability of Single Shade Restorative Material: An In Vitro Study

BACKGROUND: Color mismatch between tooth structure and restoration is a common reason for restoration replacement. This is due, in part, to the diverse chemical structure of both substrates, which display a different staining potential resulting in a significant color mismatch. AIM: The aim of the study was to evaluates the color change of single shade resin composite and compare it to fibrous-filled resin composite (FRc) after storage in coloring beverages. METHODS: Trapezoidal Class V cavities were prepared on the buccal and lingual surfaces of 30 premolars. Cavities on the buccal surface were restored with Omnichroma (ON) and palatal surface with FRc. Specimens were stored on water, tea, and coffee solutions for 24 h and 72 h. The color change was measured after each immersion time and statistically analyzed using three-way analysis of variance (ANOVA) (α = 0.05). RESULTS: Three-way ANOVA showed that different materials had a significant effect on both ΔL and Δa (p < 0.001). For both materials, ON in coffee showed the highest Δb values when compared to FRc for the same period. No difference between ON and FRc when stored in tea for 24 h and 72 h. CONCLUSION: Structural color property of ON can enhance the color perception of restoration to compensate for any color change after consuming coloring food and beverages.

Rheological and Mechanical Properties of Resin-Based Materials Applied in Dental Restorations

Resin-based materials have been prevalent for dental restorations over the past few decades and have been widely used for a variety of direct and indirect procedures. Typically, resin-based dental materials are required to be flowable or moldable before setting and can provide adequate mechanical strength after setting. The setting method may include, but is not limited to, light-curing, self-curing or heating. In this review, based on different indications of resin-based dental materials (e.g., dental filling composite, dental bonding agent, resin luting cement), their rheological and mechanical properties were reviewed. Viscous and flexible properties were focused on for materials before setting, while elastic properties and mechanical strength were focused on for materials after setting. At the same time, the factors that may affect their rheological and mechanical properties were discussed. It is anticipated that the insightful information and prospections of this study will be useful to the future development and fabrication of resin-based dental restorative materials.

Closed Repair Technique: Innovative Surface Design for Polymethylmethacrylate Denture Base Repair

PURPOSE

This study aimed to evaluate the repair strength of a newly introduced repair technique involving zero-gap repair width.

MATERIALS AND METHODS

A total of 36 rectangular prism specimens with dimensions of 64 × 10 × 3.3 mm were prepared from heat-polymerized acrylic resin. Nine specimens were kept intact. The other specimens were sectioned into halves and modified to create repair gaps of 2.5-mm beveled (2.5B) as control, 0-mm beveled (ZB), and 0-mm inverse bi-beveled (ZIBB). The ZIBB group was prepared with a V-shaped internal groove on both halves (repair tunnel), while the intaglio and cameo surfaces were kept intact except for two small holes at the cameo surface for repair resin injection. The 2.5B and ZB groups were repaired conventionally while the ZIBB group was repaired by injecting repair resin into the tunnel through one of the holes until excess material oozed from the other hole. Repaired specimens were thermally cycled at 5 and 55°C for 10,000 cycles with 1 min dwell time. A 3-point bending test was conducted using a universal testing machine for flexural strength and elastic modulus measurement. Kruskal-Wallis/Mann-Whitney tests and ANOVA/post hoc Tukey tests were applied for data analysis (α = 0.05).

RESULTS

The flexural strength of repaired specimens was substantially lower than that of intact specimens, and significant differences were present between repaired groups (p ˂ 0.05). ZB and ZIBB had higher flexural strength (p ˂ 0.001) and elastic modulus (p ˂ 0.05) than 2.5B. Among the ZB and ZIBB groups, ZB showed the highest flexural strength, and ZIBB had the highest elastic modulus.

CONCLUSION

The closed repair technique improved the flexural strength and elastic modulus of repaired acrylic denture base.

Photoinitiators in Dentistry: Challenges and Advances

Photopolymerization is used in a wide range of clinical applications in dentistry and the demand for dental materials that can restore form, function and esthetics is increasing rapidly. Simultaneous with this demand is the growing need for photoinitiators that provide effective and efficient in situ polymerization of dental materials using visible light irradiation. This chapter reviews the fundamentals of Type I and II photoinitiators. The advantages and disadvantages of these photoinitiators will be considered with a particular focus on parameters that affect the polymerization process in the oral cavity. The chapter examines recent developments in photoinitiators and opportunities for future research in the design and development of photoinitiators for dental applications. Future research directions that employ computational models in conjunction with iterative synthesis and experimental methods will also be explored in this chapter.