Impact strength of denture base and reline acrylic resins: An in vitro study

Effect of surface prereacted glass ionomer nanofillers on fluoride release, flexural strength, and surface characteristics of polymethylmethacrylate resin

OBJECTIVE

Dentures should have proper fluoride release and physical properties. We evaluated how surface prereacted glass ionomer (S-PRG) nanofillers influenced fluoride release, flexural strength, and surface characteristics of polymethylmethacrylate (PMMA) resin.

MATERIALS AND METHODS

PMMA resin disc (n = 14) and rectangular (n = 5) specimens containing 0, 20 wt% microparticles, and 20 wt% nanoparticles of S-PRG were prepared. Six-disc specimens were examined for surface roughness; eight-disc specimens were immersed in 5 ml of deionized water for 24 h before analyzing the fluoride levels on days 1-3, 12, and 15. They were recharged with 1000 ppm fluoride solution for 24 h and stored in deionized water for five cycles. Fluoride release was examined. The flexural strength of the rectangular specimens was determined using a three-point bending test. Data were analyzed by two-way repeated-measures ANOVA.

RESULTS

S-PRG nanofiller had the highest fluoride exchange rate and did not significantly change the surface roughness compared with the microparticle and control groups; however, the nanofillers agglomerated and reduced the flexural strength to below 65 MPa.

CONCLUSIONS

Incorporating 20 wt% nanofillers into resin enhanced the fluoride exchange property greater than microfillers at the same content, but diminished the mechanical properties of the resin.

CLINICAL SIGNIFICANCE

Incorporating 20 wt% S-PRG nanofillers in resin denture base can improve the fluoride releasing property without affecting the surface roughness.

Chest ultrasound in neonates: What neonatologists should know

For many years, ultrasound was thought to have no indications in pulmonary imaging because lungs are filled with air, creating no acoustic mismatch, as encountered by ultrasound wave beam. Lung ultrasound (LUS) was started in adult critical care settings to detect pleural effusion and acquired more indications over time. In the neonatal intensive care unit (NICU), the use of chest ultrasound has gained more attention during the last two decades. Being a radiation-free, bedside, rapid, and handy tool, LUS started to replace chest X-rays in NICU. Using LUS depends upon understanding the nature of normal lungs and the changes induced by different diseases. With the help of LUS, an experienced neonatologist can detect many of the respiratory problems so fast that interventional therapy can be introduced as early as possible. LUS can diagnose pleural effusion, pneumothorax, pneumonia, transient tachypnoea of the newborn, respiratory distress syndrome, pulmonary atelectasis, meconium aspiration syndrome, bronchopulmonary dysplasia, and some other disorders with very high accuracy. LUS will be helpful in initial diagnosis, follow-up, and predicting the need for further procedures such as mechanical ventilation, diuretic therapy, surfactant therapy, etc. There are some limitations to using LUS in some respiratory disorders such as bullae, interstitial emphysema, and other conditions. This review will highlight the importance of LUS, its uses, and limitations.

Influence of Different Reline Materials and Processing Methods on Flexural Strength of Denture Base Material

Background/Aim: Relining is defined as the procedure used to resurface the tissue side of a denture with new base material, thus producing an accurate adaptation is provided at the denture foundation area. During mastication, relined dentures have to withstand masticatory forces to prevent fracture. The aim of this study was to evaluate the flexural strength of acrylic resin denture base relined with different methods and materials.

Material and Methods: Fourteen experimental groups and one control group were determined to consider different reline materials and processing methods. Acrylic resin specimens were prepared with the dimensions of 65× 10× 1.5 mm and reline materials (1.5 mm thickness) were placed on acrylic resins. Reline material was not used in control group specimens. Flexural strength values of relined and control specimens were measured with three-point bending test at a speed of 5 mm/min. Data were analyzed with using one way Anova and Student t tests.

Results: The highest flexural strength values were shown in control group (86.51±1.08 MPa). There were significant differences among relined specimens (p< 0.05). For the relined specimens, the highest flexural strength values were found in the relined specimens with denture base material (77.90±1.93 MPa), and the lowest values were found in relined with autopolymerize acrylic material (59.81±1.50 MPa).

Conclusions: Relining of the heat cure denture base material significantly decreases the flexural strength for all processing methods and materials.

Effect of adding TiO2 nanoparticles on the SEM morphology and mechanical properties of conventional heat-cured acrylic resin

Background. The current study evaluated the compressive, flexural and impact strengths of heat-cured acrylic resins reinforced by TiO₂ nanoparticles (NPs).

Methods. TiO₂ NPs were provided and characterized using scanning electron microscopy (SEM) to determine their morphology and crystalline structure. For three mechanical tests, 12 acrylic resin groups (n=9), totaling 108 specimens, were prepared using a special mold for each test, with TiO₂ nanoparticle contents of 0, 0.5, 1 or 2 wt% in different groups. After curing, the compressive, flexural and impact strengths of the specimens were examined according to ISO 1567.

Results. In the SEM and XRD study of TiO2 NPs, anatase was identified as the major crystalline phase followed by rutile (average particle size: 20.4 nm). SEM images showed that the nanocomposite with 1 wt% NPs had a more homogenized blend. 1 wt% TiO₂ nanocomposite exhibited a higher, but non-significant, impact strength compared to the controls. ANOVA showed significant differences in the impact and flexural strengths between nanocomposites with various contents of TiO2 NPs.

Conclusion. The nanocomposite with 1 wt% TiO2 NPs exhibited fewer micro-pores and micro-cracks in the SEM crosssections. A non-significant increase was also observed in the impact strength with TiO₂ NPs at 1 wt%. Further increase in TiO₂ NPs decreased both the impact and flexural strengths. The compressive strength of the heat-cured acrylic resin was not affected by the incorporation of NPs.

A comparative study of the mechanical properties of clear and pink colored denture base acrylic resins

Context

Pink colored acrylic does not always satisfactorily replicate the natural gingival color, especially in individuals with pigmented mucosa. In such situation clear acrylic denture base material can be used. Hence, there is a need of a comparative study of the mechanical properties of the clear and pink colored denture base resins.

Aims

The aim of this study is to compare the mechanical properties, i.e., tensile, flexural, compressive, and impact strength (IS) of clear and pink colored denture base resins.

Settings and Design

This was comparative in vitro study.

Materials and Methods

A total of 80 specimens were divided into two groups of 40 specimens each of clear and pink colored acrylic resin. Specimens for testing flexural, tensile, compressive, and ISs of acrylic resin (10 in each group) were divided. A universal testing machine was used for measuring flexural, tensile, and compressive strength (CS) while the Izod/Charpy impact tester was used for IS.

Results

The mean tensile strength for clear resin (n = 10) was 30.90 ± 1.663 MPa and that for pink resin (n = 10) was 31.30 ± 8.166 MPa. The mean residual flexural strength for clear resin (n = 10) was 75.60 ± 17.212 MPa, whereas for pink resin (n = 10) was 76.10 ± 14.130 MPa. The mean CS for clear resin (n = 10) was 84.60 ± 2.503 MPa and for pink resin (n = 10) was 85.40 ± 16.222 MPa. The mean IS for clear resin (n = 10) was 11.50 ± 5.104 MPa. While for pink resin (n = 10) was 11.90 ± 1.370 MPa.

Conclusions

The results show that clear acrylic resin denture base material has mechanical properties similar to that of pink acrylic resin denture base material.

Efficacy of Denture Cleansers on Impact Strength of Heat polymerized Acrylic Resins

Purpose:

The study was aimed to compare and evaluate the changes in the impact strength of heat cure denture base resins when treated using denture cleansers.

Methodology:

Study was conducted with sample size of 40 and dimesion 65 mm length, 10 mm width, and 3 mm thickness as per the ISO 1567. Distilled water has been used as control group, in which 10 samples were immersed of 40 samples. Of remaining 30 samples, 10 were treated with Clinsodent, 10 were treated with VI-Clean, and 10 were treated with Clanden denture cleansers. The impact strength of these specimens from each group was tested with the help of Charpy-type pendulum impact strength tester. The energy absorbed to fracture the specimens was recorded, and impact strength was calculated and was analyzed using Kruskal–Wallis ANOVA and Mann–Whitney test.

Results:

Impact strength of samples was significantly reduced after immersion in denture cleansers Clinsodent, VI-Clean, and Clanden solutions when compared to control group.

Conclusion:

Clinsodent, VI-Clean, and Clanden denture cleansers decrease the impact strength of heat cure denture base resin after immersion. Hence, the study concludes that denture cleansers should be used with caution and advised to follow manufacturer's instructions.

Effects of thermal cycling on surface roughness, hardness and flexural strength of polymethylmethacrylate and polyamide denture base resins

BACKGROUND

The purpose of this study was to evaluate the effects of thermal cycling on the surface roughness, hardness and flexural strength of denture resins.

METHODS

Polyamide (PA; Deflex and Valplast) and polymethylmethacrylate (PMMA; QC-20 and Acron MC) denture materials were selected. A total of 180 specimens were fabricated and then divided into 3 groups. The first group (group 1) acted as a control and was not thermocycled. The second group (group 2) was subjected to thermocycling for 10,000 cycles in artificial saliva and 5,000 cycles in distilled water. The last group (group 3) was thermocycled for 20,000 cycles in artificial saliva and 10,000 cycles in distilled water. The surface roughness were measured with a profilometer. The hardness of the resins were measured with a Vickers Hardness Tester using a 100-gf load. The flexural strength test was performed using the universal test machine with a crosshead speed of 5 mm/min. Data were analyzed using statistical software. The results of the measurements in the 3 different tests were analyzed by Kruskal-Wallis test with Bonferroni correction. Multiple comparisons were made by Conover and Wilcoxon tests.

RESULTS AND CONCLUSIONS

There was a significant difference between the PMMA and PA groups in terms of surface roughness, hardness and transverse strength before and after thermal cycling (p&lt;0.001). Thermal cycling did not change the surface roughness, hardness and flexural strength values of either the PMMA or PA group (p&gt;0.001).