Surface characterization and bonding properties of milled polyetheretherketone dental posts.

PEEK has been used in many dental applications except intra-radicular post. The aim of this study is to test polyetheretherketone (PEEK) as a dental post material through tensile bond strength (TBS) and surface roughness (SR), and to compare it with glass-fiber and cast-metal posts. Thus, 60 human maxillary central incisors with a single root were endodontically treated and divided into three groups (n = 20) according to the type of post (Group P: PEEK, Group F: Glass-fiber, Group M: Cast-metal). Appropriate surface treatment was employed for each group and SR was determined by a three-dimensional non-contact profilometer before cementation. All posts were luted to the canal dentin using self-etch resin cement (Panavia F2.0). Pull-out test was performed on a universal testing machine at a speed of 0.5 mm/min crosshead speed until failure, and TBS were calculated. One-way ANOVA, Tukey's HSD, and Pearson chi-squared tests were performed for statistical analyses (α = 0.05). According to the results, group F demonstrated the highest SR (2.93 ± 0.18 µm) and lowest TBS values (10.05 ± 0.53 MPa), while group P exhibited lowest SR (1.37 ± 0.11 µm) and highest TBS values (14.33 ± 0.58 MPa) (p < 0.001). No significant differences in failure modes were identified among groups, mostly adhesive (p = 0.243). As conclusion, PEEK may be a reliable and contemporary option for dental post systems when used with appropriate surface treatment and luting agent. This high-performance polymer may be a novel candidate as a contemporary dental post system due to its superior mechanical, chemical, thermal, and esthetical properties with low risk of fracture.

Surface roughness and wear behavior of occlusal splint materials made of contemporary and high-performance polymers.

With the development of a digital technology of computer-assisted manufacturing (CAD/CAM) and new age materials, the use of new types of occlusal splint is to consider. The aim of the present study was to evaluate the surface roughness (Ra) and wear behavior of different CAD/CAM materials against enamel antagonist through a simulated chewing test. A total of 75 specimens made from ethylene vinyl acetate (EVA), polymethyl methacrylate (PMMA), polycarbonate (PC), polyetheretherketone (PEEK), and polyethyleneterephthalate (PETG) as a control were polished to evaluate the Ra before loading by optical profilometry and further analyzed by scanning electron microscopy (SEM). Specimens of each group were subjected to thermomechanical fatigue loading in a chewing simulator (60000 cycles at 49 N with 5-55 °C thermocycling). The wear volume loss and change in Ra of each specimen after the simulated chewing were analyzed. One-way ANOVA, paired samples t test, and Pearson correlation analysis were performed for statistical analyzes. The result showed that the volume loss and Ra varied among the materials tested. EVA exhibited the greatest amount of Ra and volume loss (p < 0.001), while PEEK had the lowest values for both (p < 0.001). In terms of volume loss, there was no significant difference between PC and PMMA (p > 0.05). SEM investigations revealed different wear behaviors, especially in EVA. As PEEK showed significantly more favorable results, PEEK splints should be considered as a new therapeutic option for occlusal splint.

Can polylactic acid be a CAD/CAM material for provisional crown restorations in terms of fit and fracture strength?

This study aimed to evaluate polylactic acid (PLA) as a provisional crown material. Lower right first molar phantom tooth was used for the fabrication of 60 crowns. Samples were divided into three groups (n=20) according to the material: Group PL (PLA), Group PM (polymethyl methacrylate), and Group PE (polyetheretherketone). Each group was investigated for internal and marginal fit, fracture strength, and fracture mode. Data were analyzed using ANOVA, chi-squared test, and Tukey's tests (p≤0.05). The average marginal gap value of each group was: PE 56.00±4.67 µm, PM 61.15±4.44 µm, and PL 60.40±2.85 µm (p<0.001). The average internal gap value for each group was: PE 128.90±8.39 µm, PM 132.40±7.51 µm, and PL 130.75±9.76 µm (p=0.442). The average fracture strength of each group was: PE 840.90±13.23 N, PM 733.30±9.00 N, and PL 664.50±10.79 N (p<0.001). Results demonstrated that PLA may be a good option as a provisional crown material.

Thermal, structural and morphological characterization of dental polymers for clinical applications.

PURPOSE: Polymers are used in dentistry on a daily basis due to their mechanical, functional and aesthetic properties. However, such biomaterials are subject to deterioration in the oral environment. Thus, this study aimed to evaluate the structural properties of five commonly used dental polymers to determine their best clinical indications. METHODS: Four hundred-fifty samples of five dental polymers (polyethylenterephthalat - glycol modified (PG), polymethyl methacrylate (PA), ethylene vinyl acetate(E), polycarbonate (PC), polyetheretherketone (PK) were prepared to investigate their thermal, structural and chemical characteristics using energy dispersive spectroscopy (EDS), Fourier transform infrared analysis(FTIR), scanning electron microscopy (SEM), differential scanning calorimetry(DSC), thermogravimetric analysis(TGA), X-ray diffraction(XRD), and Shore D hardness test. Data were analyzed using one-way ANOVA, Tukey's HSD, and Levene's tests (α=0.05). RESULTS: PK (87.2) and PA (82.4) displayed the highest hardness values and smooth surfaces, as observed with SEM (p<0.001). Silica was detected in PK, PA, and E by EDS and XRD. The highest glass transition temperature was recorded for PC (145.00±2.00°C) and PK (143.00±1.87°C), while the lowest value was measured for E (50.00±2.12°C)(p<0.001).The highest mass loss was detected for PG (91.40±1.40%) by TGA. CONCLUSIONS: PA and PK polymers can be used for stress-containing treatments due to their mechanical properties. These two materials are also advantageous in terms of plaque accumulation as these polymers reveal smoother surfaces than other groups. Insufficient physical and thermal properties require the use of E with caution and only in limited clinical indications.

Effects of molecular weight and crystallizability of polylactide on the cellulose nanocrystal dispersion quality in their nanocomposites.

This study investigated how cellulose nanocrystals (CNC) dispersion quality and its percolation network formation could be influenced when using polylactide (PLA) with various molecular weights and crystallizability. In this context, systematic rheological experiments were conducted on PLA/CNC nanocomposites prepared through solution casting method using dimethylformamide (DMF) as the solvent. It was found that lower CNC percolation concentrations could be obtained when a PLA matrix possesses lower molecular weight as the shorter chains and CNCs interpenetration could be facilitated during their dissolution in the solvent. On the other hand, the CNC percolation concentration was further lowered when the PLA with higher crystallizability was used. During the solvent evaporation step that occurred at 85 °C, the isothermal heterogeneous crystallization of PLA around the dispersed CNCs could prevent the driving force of the CNCs towards their re-agglomeration. Therefore, the finest CNC dispersion was appeared in the highly crystallizable low molecular weight PLA through which the rheological properties were dramatically improved and the thermal stability was significantly extended to higher temperatures. The crystallization behavior of the prepared nanocomposites was also analyzed using differential scanning calorimeter and X-ray diffractometer. The thermal degradation behavior of the PLA/CNC nanocomposites were examined through thermogravimetric and rheological analysis.

Micro-UFO (Untethered Floating Object): A Highly Accurate Microrobot Manipulation Technique.

A new microrobot manipulation technique with high precision (nano level) positional accuracy to move in a liquid environment with diamagnetic levitation is presented. Untethered manipulation of microrobots by means of externally applied magnetic forces has been emerging as a promising field of research, particularly due to its potential for medical and biological applications. The purpose of the presented method is to eliminate friction force between the surface of the substrate and microrobot. In an effort to achieve high accuracy motion, required magnetic force for the levitation of the microrobot was determined by finite element method (FEM) simulations in COMSOL (version 5.3, COMSOL Inc., Stockholm, Sweden) and verified by experimental results. According to position of the lifter magnet, the levitation height of the microrobot in the liquid was found analytically, and compared with the experimental results head-to-head. The stable working range of the microrobot is between 30 µm to 330 µm, and it was confirmed in both simulations and experimental results. It can follow the given trajectory with high accuracy (<1 µm error avg.) at varied speeds and levitation heights. Due to the nano-level positioning accuracy, desired locomotion can be achieved in pre-specified trajectories (sinusoidal or circular). During its locomotion, phase difference between lifter magnet and carrier magnet has been observed, and relation with drag force effect has been discussed. Without using strong electromagnets or bulky permanent magnets, our manipulation approach can move the microrobot in three dimensions in a liquid environment.