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pubmed: Lassila LV



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Preparation and characterization of high radio-opaque E-glass fiber-reinforced composite with iodine containing methacrylate monomer.
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Preparation and characterization of high radio-opaque E-glass fiber-reinforced composite with iodine containing methacrylate monomer.

Dent Mater. 2017 Feb;33(2):218-225

Authors: He J, Vallittu PK, Lassila LV

Abstract
OBJECTIVE: The purpose of this study was to prepare radio-opaque E-glass fiber-reinforced composite (EFRC) with synthesized iodine containing methacrylate monomer.
METHODS: The synthesized iodine containing methacrylate monomer 2-hydroxy-3- methacryloyloxypropyl(2,3,5- triiodobenzoate) (HMTIB) was mixed with Bis-GMA and MMA in different mass ratio to prepare resin impregnating solution (RIS), and RIS without HMTIB was used as control. CQ and DMAEMA were added as photoinitiation system. E-glass fiber was thoroughly wetted by resin impregnating solution to prepare radio-opaque EFRC. Degree of double bond conversion (DC) was investigated by FT-IR analysis. Fiber volume fraction was analyzed by combustion and gravimetric analyzes. The Flexural strength (FS) and modulus (FM) of EFRC were measured using a three-point bending set up. Water sorption (WS) and solubility (SL) were measured until the mass variation of EFRC in distilled water kept stable. Radiographs were taken to determine the radiopacity of EFRC.
RESULTS: The FT-IR and 1H NMR spectra of HMTIB revealed that it was the same as designed. ANOVA analysis revealed that increasing HMTIB concentration in RIS would decrease DC and increase fiber volume fraction. When compared with control EFRC, all of HMTIB containing EFRCs had higher or comparable FS and FM, no matter before or after water immersion. WS of EFRC decreased with increasing HMTIB concentration, while SL was nearly kept the same. Radiopacity of EFRC increased with increasing HMTIB concentration.
SIGNIFICANCE: The synthesized monomer HMTIB could be used to prepare EFRC with high radiopacity. Moreover, HMTIB containing EFRC would also have high mechanical properties and low WS.

PMID: 28007395 [PubMed - indexed for MEDLINE]




Surface roughness and the flexural and bend strength of zirconia after different surface treatments.
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Surface roughness and the flexural and bend strength of zirconia after different surface treatments.

J Prosthet Dent. 2016 Oct;116(4):577-583

Authors: Hjerppe J, Närhi TO, Vallittu PK, Lassila LV

Abstract
STATEMENT OF PROBLEM: Different surface treatments are commonly used during the fabrication of zirconia fixed dental prostheses. However, such treatments can affect the properties of the zirconia framework material.
PURPOSE: The purpose of this in vitro study was to determine the effect of different surface treatments on the surface roughness and flexural and bend strength of zirconia.
MATERIAL AND METHODS: Seventy-two zirconia disks (n=8) and 72 zirconia bars (n=8) were sintered and divided into 9 groups for different surface treatments: sintered control, airborne-particle abraded with 50-μm aluminum oxide, airborne-particle abraded with Rocatec soft (30 μm), airborne-particle abraded with Rocatec (105 μm), grinding dry with a micromotor, turbine grinding under water cooling, grinding with silicon carbide paper, diamond paste polishing, and steam cleaning. The biaxial flexural strength of the disks (diameter 19 mm, thickness 1.6 mm) and 3-point bend test of the bars (thickness 2 mm, height 2 mm, length 25 mm) were measured dry at room temperature. One-way ANOVA followed by the Tukey HSD test (α=.05) and Pearson correlation test were used for statistical analysis.
RESULTS: Airborne-particle abrasion and silicon carbide paper grinding increased the flexural and bend strength of zirconia specimens (P<.05). The 3-point bend test gave 20% to 30% higher strength values than the biaxial test, but a strong correlation was shown between the test types. Surface roughness had a statistically significant negative effect on the strength values in the 3-point bend test.
CONCLUSIONS: The surface treatments tested affected the strength and surface roughness of zirconia framework material.

PMID: 27157604 [PubMed - indexed for MEDLINE]




Mechanical properties, fracture resistance, and fatigue limits of short fiber reinforced dental composite resin.
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Mechanical properties, fracture resistance, and fatigue limits of short fiber reinforced dental composite resin.

J Prosthet Dent. 2016 Jan;115(1):95-102

Authors: Bijelic-Donova J, Garoushi S, Vallittu PK, Lassila LV

Abstract
STATEMENT OF PROBLEM: Cycling masticatory loads decrease the strength of particulate filler composites (PFCs) and initiate the failure process by fatigue. The life expectancy of a composite resin restoration under stress remains difficult to predict.
PURPOSE: The purpose of this study was to determine the fracture resistance and the compressive fatigue limits (CFL) of anterior crown restorations made of a short-fiber reinforced composite resin (SFC), to investigate selected mechanical properties of the material following standard test methods, and to observe their correlation with the CFL.
MATERIAL AND METHODS: Specimens (n=10) were fabricated either from SFC (everX Posterior, GC Corp) or PFC (G-ænial anterior, GC Corp). The properties investigated were flexural strength (FS), compression strength (CS), diametral-tensile strength (DTS), and single-edge-notched-bend fracture toughness (FT) following ISO standards. Fracture resistance was determined by static load (n=10) and the CFL at 10000 cycles was determined using a staircase approach (n=20), both on anterior composite resin crowns. The results were analyzed with 1-way ANOVA (α=.05) or 2-way ANOVA (α=.05) followed by a Tukey B post hoc test and the Pearson-correlation analysis.
RESULTS: The SFC crowns had higher fracture resistance (954 ±121 N) than the PFC crowns (415 ±75 N) (P<.001) and higher CFL (267 ±23 N) than the PFC crowns (135 ±64 N) (P<.001). SFC revealed also higher FT (2.6 ±0.6 MPa·m(1/2)) than the PFC (1.0 ±0.2 MPa·m(1/2)) (F=69.313, P<.001). A significant correlation was observed only between the FT and the CFL (r(2)=0.899; P<.001).
CONCLUSIONS: SFC crowns showed good performance under static and fatigue loading. FT was the only in vitro test method that filtered as a clinically relevant parameter.

PMID: 26460170 [PubMed - indexed for MEDLINE]