Temperature Changes in Primary and Permanent Teeth Dentine of Varying Thicknesses Following Irradiation by Two Light Curing Units.

AIM: This study was performed to determine the temperature rise under human dentin discs of different thicknesses from primary and permanent teeth during the photo-curing process using quartz tungsten halogen (QTH) or light-emitting diode (LED). MATERIALS AND METHODS: The current experimental study sample consisted of 160 dentin discs of different thicknesses (0.5, 1, 1.5, and 2 mm), of which 80 dentin discs were prepared from sound lower second primary molars, and the remaining 80 dentin discs were prepared from sound lower third permanent molars extracted surgically for various reasons. A "K" type of thermal tentacle was placed in the center of an acrylic resin base, followed by the placement of a dentin disc. Then, the thermal changes were measured during the photo-curing of the composite using a second LED or QTH light curing unit for 20 s. Statistical evaluation was performed using the IBM SPSS Statistics® Version 20.0 software system (SPSS Inc., Chicago, IL, USA). RESULTS: The current study found that the temperature rise in primary teeth (1.17-2.96°C) is significantly lower compared to the rise in permanent teeth (1.55-3.33°C), regardless of the dentin disc thickness or light curing unit used. The temperature rise decreases significantly when the thickness of dentin discs increases, regardless of the type of teeth or light curing unit used (P<0.05). Furthermore, QTH causes less temperature rise (1.17-2.65°C) compared to LED (1.61-3.33°C). CONCLUSIONS: The temperature rise during polymerization of the resin composite with the second-generation LED appeared to be below 5.5°C. Hence, it appears to be safe for use during the restoration of primary teeth. Primary teeth dentin might be more effective than permanent teeth dentin in protecting the dental pulp.

Characteristics of experimental resin-modified glass-ionomer cements, containing alternate monomers to HEMA.

OBJECTIVE: Resin-modified glass ionomer cements (RMGICs) present several advantages (e.g. fluoride release), but their reported cytotoxicity has been associated with hydroxyethyl methacrylate (HEMA) monomer release. Therefore, different monomers were tested for use in RMGICs in order to improve their biocompatibility and reduce monomer release. METHODS: Eight experimental liquid compositions were prepared replacing different percentages of HEMA (conventional monomer used in commercial RMGICs) with hydroxypropyl-methacrylate (HPM) and/or tetrahydrofurfuryl-methacrylate (THFM), which are known to have better biocompatibility. Moreover, two commercial materials (Fuji-Plus and RelyX) and two compositions, based on these (home), were included as controls. Monomer release of all materials (commercial, home and experimental) were tested using high-performance liquid chromatography (HPLC) methods after immersing discs in deionized-water (DW) or ethanol:DW. Cytotoxicity of the materials extracts was tested on normal human oral fibroblast line (NHOF-1) using 3-(4,5-Dimethylthiazol-2-yl)-2,5-Diphenyltetrazolium Bromide (MTT) assay. RESULTS: Three experimental materials containing THFM (F3, R3 and R4) showed less or similar monomer release compared to corresponding commercial products. Furthermore, two experimental materials (F3 and F4) showed similar effects on NHOF-1 cells compared to the negative control medium. SIGNIFICANCE: The lower monomer release and higher cell viability of some experimental THFM compositions are encouraging. THFM partially replacing HEMA is potentially a suitable alternative for producing biocompatible RMGICs.

Novel fluoride rechargeable dental composites containing MgAl and CaAl layered double hydroxide (LDH).

OBJECTIVE: This study aims to incorporate 2:1 MgAl and 2:1 CaAl layered double hydroxides (LDHs) in experimental dental-composites to render them fluoride rechargeable. The effect of LDH on fluoride absorption and release, and their physico-mechanical properties are investigated. METHODS: 2:1 CaAl and 2:1 MgAl LDH-composite discs prepared with 0, 10 and 30wt% LDH were charged with fluoride (48h) and transferred to deionized water (DW)/artificial saliva (AS). Fluoride release/re-release was measured every 24h (ion-selective electrodes) with DW/AS replaced daily, and samples re-charged (5min) with fluoride every 2 days. Five absorption-release cycles were conducted over 10 days. CaAl and MgAl LDH rod-shaped specimens (dry and hydrated; 0, 10 and 30wt%) were studied for flexural strength and modulus. CaAl and MgAl LDH-composite discs (0, 10, 30 and 45wt% LDH) were prepared to study water uptake (over 7 weeks), water desorption (3 weeks), diffusion coefficients, solubility and cation release (ICP-OES). RESULTS: CaAl LDH and MgAl LDH-composites significantly increased the amount of fluoride released in both media (P<0.05). In AS, the mean release after every recharge was greater for MgAl LDH-composites compared to CaAl LDH-composites (P<0.05). After every recharge, the fluoride release was greater than the previous release cycle (P<0.05) for all LDH-composites. Physico-mechanical properties of the LDH-composites demonstrated similar values to those reported in literature. The solubility and cation release showed a linear increase with LDH loading. SIGNIFICANCE: LDH-composites repeatedly absorbed/released fluoride and maintained desired physico-mechanical properties. A sustained low-level fluoride release with LDH-composites could lead to a potential breakthrough in preventing early stage carious-lesions.

Polymerization shrinkage kinetics and degree of conversion of commercial and experimental resin modified glass ionomer luting cements (RMGICs).

OBJECTIVES: Tetrahydrofurfuryl-methacrylate (THFM) and hydroxypropyl-methacrylate (HPM) were used to partially or fully replace HEMA in experimental RMGICs. The experimental materials were compared with home and commercial products in terms of degree of conversion, polymerization shrinkage and exotherm. METHODS: Two commercial RMGICs used were Fuji-Plus (FP, GC, Japan) and RelyX-Luting (RX, 3M-ESPE, USA). Two additional in-house liquids were prepared based on the commercial materials liquids. Eight experimental liquid compositions (F1, F2, F3 and F4 based on Fuji-Plus; R1, R2, R3 and R4 based on RelyX-Luting) were prepared replacing 100% HEMA with HPM in F1 and R1 or 70%/30% HPM/THFM in F2 and R2. 50% HEMA was replaced with THFM in F3 and R3 compared to 30% in F4 and R4. All liquids were mixed with the corresponding commercial powder. Degree of conversion was determined using Fourier-transform infrared spectroscopy (FT-IR). Polymerization shrinkage and exotherm were measured using the bonded-disk method. RESULTS: Compositions containing HPM (F1 and R1) showed lower degree of conversion compared to experimental compositions containing THFM, home and commercial materials (p<0.0001). FP-commercial showed significantly higher polymerization shrinkage and exotherm compared to all other materials in both groups (p<0.0001). FP-commercial showed higher degree of polymerization shrinkage and exotherm at 5min compared to all materials due to the incorporation of an additional cross-linker (glycerol-dimethacrylate). In general, compositions containing THFM, presented polymerization shrinkage and degree of conversion values similar to their corresponding commercial products. SIGNIFICANCE: THFM monomer showed promising results and could be potentially useful in the development of new RMGICs with improved properties.

Layered Double Hydroxide Fluoride Release in Dental Applications: A Systematic Review.

This systematic review appraises studies conducted with layered double hydroxides (LDHs) for fluoride release in dentistry. LDH has been used as antacids, water purification in removing excess fluoride in drinking water and drug delivery. It has great potential for controlled fluoride release in dentistry, e.g., varnishes, fissure sealants and muco-adhesive strips, etc. The Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) Statement was followed with two reviewers performing a literature search using four databases: PubMed, Web of Science, Science Direct and Ovid Medline with no date restrictions. Studies including any LDH for ion/drug release in dentistry were included, while assessing the application of LDH and the value of the methodology, e.g., ion release protocol and the LDH production process. Results: A total of 258 articles were identified and four met the inclusion criteria. Based on two in vitro studies and one clinical study, LDH was previously studied in dental materials, such as dental composites and buccal muco-adhesive strips for fluoride release, with the latter studied in a clinical environment. The fourth study analysed LDH powder alone (without being incorporated into dental materials). It demonstrated fluoride release and the uptake of volatile sulphur compounds (VSC), which may reduce halitosis (malodour). Conclusion: LDHs incorporated in dental materials have been previously evaluated for fluoride release and proven to be clinically safe. LDHs have the potential to sustain a controlled release of fluoride (or other cariostatic ions) in the oral environment to prevent caries. However, further analyses of LDH compositions, and clinical research investigating any other cariostatic effects, are required.

The properties of experimental resin-modified glass-ionomer luting cements (RMGICs) containing novel monomers.

OBJECTIVES: To investigate working and setting times, compressive fracture strength (CFS), compressive modulus (CM), three-point flexure strength (TFS) and tensile flexure modulus (TFM) of commercial, control and experimental RMGICs. METHODS: RelyX Luting (RX, 3M-ESPE) and Fuji Plus (FP, GC), two control home liquids and eight new liquid compositions (F1-F4 and R1-R4) comprising different percentages of the monomer HPM (hydroxypropyl-methacrylate) and/or THFM (tetrahydrofurfuryl-methacrylate) with the original monomer HEMA (2-hydroxyethyl-methacrylate) were used in this study. The polymerization was initiated chemically (using benzene sulfonic acid sodium-salt in FP powder and potassium persulfate/ascorbic acid in RX powder). Home and experimental liquids were mixed with the corresponding commercial powder. An oscillating rheometer was used to measure the working and setting times (n=6). 20 cylinders per material (6.0±0.1mm height, 4.0±0.1mm diameter) were fabricated for CFS and CM testing, 20bars per material (25.0±0.1mm length, 2.0±0.1mm width, 2.0±0.1mm thickness) were made for TFS and TFM testing. RESULTS: All RX compositions showed longer setting times (p≤0.0001) and lower CFS values compared to their FP counterparts (p≤0.0001). The TFS testing showed that commercial and home RMGICs behaved as brittle materials with linear load/deflection curve while experimental materials showed plastic ductile deformation before fracture. F3, F4 and F2 showed significantly higher CFS values compared to the corresponding home material (p≤0.0001). SIGNIFICANCE: All new experimental compositions demonstrated working and setting times that are clinically acceptable. The new experimental FP compositions containing THFM (especially F3 and F4) demonstrated improved mechanical properties compared to their corresponding home material.

Development of experimental resin modified glass ionomer cements (RMGICs) with reduced water uptake and dimensional change.

OBJECTIVE: To investigate water uptake, desorption, diffusion coefficient, solubility and dimensional changes of four experimental RMGICs in deionized water (DW) and artificial saliva (AS), and compare with two commercial RMGICs and control home liquids based on the two commercial materials used. METHODS: Two commercial RMGICs, RelyX Luting (RX, 3M ESPE) and Fuji Plus (FP, GC), two control home liquids and four new liquid compositions (F1, F2, R1, R2) comprising different percentages of the monomer THFM (tetrahydrofurfuryl-methacrylate) with the original monomer HEMA (2-hydroxyethyl-methacrylate) were used in this study. Home and experimental liquids were mixed with the corresponding commercial powder. Disk-shaped specimens (16mm diameter 1mm thickness) were immersed in DW/AS at 37°C (n=6) and weighed at regular time intervals. Percentage weight change with time was recorded. At 24 weeks, disks were desorbed in an oven at 37°C to minimum weight. RESULTS: All new compositions showed lower water uptake and dimensional (volume) changes than the commercial products in both DW and AS. On desorption, FP showed higher weight loss compared to materials in the same group in both solutions (p<0.0001), with the exception of F2 in DW (p=0.283). RX had higher weight loss compared to R1 and R2 in DW and AS (p<0.0001). Fickian diffusion was confirmed for all materials immersed in DW and AS. SIGNIFICANCE: The experimental compositions in this study have shown promising results when tested in both DW and AS with lower water uptakes and volume changes than commercial materials. This may lead to wider applications than current commercial materials.