Effects of mica and glass on surface hardness of acrylic tooth material

Shaping ability of novel nickel-titanium systems in printed primary molars

BACKGROUND

Manual or mechanized instruments can be used for root canal preparation. Manual instrumentation using K-files is widely used in primary teeth, but there are many limitations. Mechanized root canal preparation can lead to easy access to all canals, decrease instrumentation time, and result in more funnel-shaped root canals, resulting in a more predictable uniform paste fill.

AIM

This study aimed to evaluate the shaping ability and instrumentation time of VDW.ROTATE™ and EdgeTaper Platinum™ during the preparation of resin-printed primary molars. Hand K-files were used as a reference for comparison.

DESIGN

Sixty-six resin-based maxillary second primary molars, obtained from extracted tooth cone-beam computed tomography (CBCT) image and printed on a three-dimensional printer, were divided into three groups: VDW.ROTATE™, EdgeTaper Platinum™, and K-files. The specimens were scanned using CBCT imaging before and after root canal preparation. Images were registered using a dedicated software, and changes (Δ) in the canal area, volume, and untouched canal surface were calculated. Instrumentation time was evaluated. Data were statistically analyzed using the SPSS program.

RESULTS

There was no significant difference among the tested file systems for Δ canal volume and area (p > .05). VDW.ROTATE™, however, showed significantly lower untouched canal surface area than other systems in all roots (p < .001). The VDW.ROTATE™ was found to be significantly faster (6.47 ± 0.39 min) than EdgeTaper Platinum™ (7.71 ± 0.73 min) and K-files (8.22 ± 0.72 min), (p < .05).

CONCLUSIONS

The shaping ability and the instrumentation time were directly influenced by the root canal instrumentation system used during the preparation of resin-printed primary molars, with VDW.ROTATE™ being the faster system and associated with the lower amount of untouched canal surface area.

Effect of Antibacterial Silver-Releasing Filler on the Physicochemical Properties of Poly(Methyl Methacrylate) Denture Base Material

Colonization of polymeric dental prosthetic materials by yeast-like fungi and the association of these microorganisms with complications occurring during prosthetic treatment are important clinical problems. In previously presented research, submicron inorganic particles of silver sodium hydrogen zirconium phosphate (S-P) were introduced into poly(methyl methacrylate) (PMMA) denture base material which allowed for obtaining the antimicrobial effect during a 90 day experiment. The aim of the present study was to investigate the flexural strength, impact strength, hardness, wear resistance, sorption, and solubility during three months of storage in distilled water. With increasing S-P concentration after 2 days of conditioning in distilled water, reduced values of flexural strength (107-72 MPa), impact strength (18.4-5.5 MPa) as well as enhanced solubility (0.95-1.49 µg/mm3) were registered, but they were at acceptable levels, and the sorption was stable. Favorable changes included increased hardness (198-238 MPa), flexural modulus (2.9-3.3 GPa), and decreased volume loss during wear test (2.9-0.2 mm3). The percentage changes of the analyzed properties during the 90 days of storage in distilled water were similar for all materials.

Comparison of apical centring ability between incisal-shifted access and traditional lingual access for maxillary anterior teeth

The aim of this study was to compare the apical centring ability of incisal-shifted access (ISA) with that of traditional lingual access (TLA). Fifteen three-dimensional printed resin models were prepared from the computed tomography data for a human maxillary central incisor and divided into ISA (n = 7), TLA (n = 7) and control (n = 1) groups. After access preparation, these models were shaped to the working length using K-files up to #40, followed by step-back procedures. An apical portion of the model was removed at 0.5 mm coronal to the working length. Microscopic images of each cutting surface were taken to measure the preparation area and the distance of transportation. TLA created a larger preparation area than ISA (P < 0.05). The distance of transportation (mean ± standard deviation) was 0.4 ± 0.1 mm for ISA and 0.7 ± 0.1 mm for TLA (P < 0.05). Access cavity preparation has a significant effect on apical centring ability. ISA is beneficial to maintaining apical configuration.

High-impact strength acrylic denture base material processed by autoclave

PURPOSE

To investigate the effect of two different cycles of autoclave processing on the transverse strength, impact strength, surface hardness and the porosity of high-impact strength acrylic denture base material.

METHODS

High Impact Acryl was the heat-cured acrylic denture base material included in the study. A total of 120 specimens were prepared, the specimens were grouped into: control groups in which high-impact strength acrylic resins processed by conventional water-bath processing technique (74°C for 1.5 h then boil for 30 min) and experimental groups in which high-impact strength acrylic resins processed by autoclave at 121°C, 210 kPa .The experimental groups were divided into (fast) groups for 15 min, and (slow) groups for 30 min. To study the effect of the autoclave processing (Tuttnauer 2540EA), four tests were conducted transverse strength (Instron universal testing machine), impact strength (Charpy tester), surface hardness (shore D), and porosity test. The results were analyzed to ANOVA and LSD test.

RESULTS

In ANOVA test, there were highly significant differences between the results of the processing techniques in transverse, impact, hardness, and porosity test. The LSD test showed a significant difference between control and fast groups in transverse and hardness tests and a non-significant difference in impact test and a highly significant difference in porosity test; while, there were a highly significant differences between control and slow groups in all examined tests; finally, there were a non-significant difference between fast and slow groups in transverse and porosity tests and a highly significant difference in impact and hardness tests.

CONCLUSIONS

In the autoclave processing technique, the slow (long) curing cycle improved the tested physical and mechanical properties as compared with the fast (short) curing cycle. The autoclave processing technique improved the tested physical and mechanical properties of High Impact Acryl.

Effect of mica reinforcement on the flexural strength and microhardness of polymethyl methacrylate denture resin

PURPOSE

Conventional denture base polymethyl methacrylate (PMMA) is low in strength, soft, and brittle on impact. Improvements in the mechanical properties of denture base materials have been sought by adding different reinforcing phases to the PMMA matrix. The purpose of this work was to study the effects of mica reinforcement on the mechanical properties, flexural strength, and microhardness of PMMA denture base resin.

MATERIALS AND METHODS

Wet ground muscovite mica and Lucitone 199 original shade denture base resin were used. Two micas were tested: W200 and P66 with average particle sizes (d50) of 131 μm and 30 μm, respectively. The mica was silane treated in a solution of 3-methacryloxypropyl trimethoxysilane, ethanol, and water, and then dried. The specimens were fabricated using the denture base resin manufacturer's instructions with a powder : liquid ratio of 21 g/10 ml and a mixing time of 30 seconds. Five treatment groups were produced with differing amounts of mica added to the PMMA denture base resin: (A) control group with 0 vol% mica, (B) 10 vol% W200 mica, (C) 20 vol% W200 mica, (D) 10 vol% P66 mica, (E) 20 vol% P66 mica. The mica replaced equal volumes of the PMMA powder component to minimize changes in viscosity. The three-point bending flexural strength specimens were 70 × 11 × 3 mm(3) . Seven specimens were prepared for each treatment group. The hardness specimens were prepared from the ends of the three-point bend specimens after they were broken (N = 7). After deflasking, the specimens were polished with 600 grit silicon carbide paper to achieve smooth surfaces. A standard three-point bending jig with a span length of 50 mm was attached to an Instron universal testing machine. The specimens were placed on the jig, and loading was carried out using a 1 mm/min crosshead speed until failure. Microhardness was measured using a Clark microhardness tester with a Knoop indenter. The load was set to 200 g and the dwell time to 15 seconds. ANOVA and Tukey tests were used for statistical analyses (Alpha = 0.05).

RESULTS

The flexural strength of the control group was between 77% and 94% higher than all the mica-containing groups (p≤ 0.05). No significant differences were found within the four mica groups. Microhardnesses of the 20% mica groups (both fine and coarse) were 33% and 26% higher than the control (p≤ 0.05). The 10% mica groups had higher hardness than the control group, but the increase was not statistically significant (p > 0.05).

CONCLUSION

Mica additions to denture PMMA reduced flexural strength; however, with the specimens containing highest mica concentrations (20%), microhardness significantly increased.