In vitro wear of packable dental composites.

The in vitro abrasion and attrition wear of several packable composites were evaluated on the Oregon Health Sciences University oral wear simulator and compared to two popular commercial composites. In general, the wear of the packable composites was equivalent to that of the nonpackable microfill and minifill composites. The wear of the enamel cusps opposing the composites in the wear machine was also found to be similar to that of enamel opposing the nonpackable composites.

Contraction stress related to degree of conversion and reaction kinetics.

Polymerization shrinkage of composites bonded to cavity preparations generates stress on the tooth/restoration interface. The purpose of this study was to verify the influence of degree of conversion and speed of polymerization reaction on contraction stress. We prepared experimental composites with different curing rates by varying the concentration of inhibitor (butylated hydroxytoluene).

Dynamic mechanical analysis of storage modulus development in light-activated polymer matrix composites.

Objectives: The goal of this study was to evaluate the potential for using dynamic mechanical analysis of tubular geometry in a three-point flexure fixture for monitoring the storage modulus development of a light-activated polymer matrix composite.

Methods: Composite samples were inserted into PTFE tubes and tested in a three-point bend fixture in a dynamic mechanical analyzer (DMA) at 200 Hz with 20 microm amplitude. Samples were light activated for 60s (385 mW/cm(2) at the composite surface) and storage modulus (E') was measured continuously for the seven light-activated composites studied (one microfill, four hybrids and two unfilled resins).

Effect of filler fraction and filler surface treatment on wear of microfilled composites.

Objectives: The aim of this study was to determine the effect of filler content and surface treatment on the wear of microfilled composites.

Methods: Four microfilled composites with different filler contents (A=20, B=25, C=30, and D=35 vol.%) were made with a light-cured resin (Bis-GMA/UDMA/TEGDMA).

Effect of light power density on development of elastic modulus of a model light-activated composite during polymerization.

Purpose: Elastic modulus development during polymerization of a composite is a measure of the polymerization maturity and the restoration's ability to transfer stress to enamel and dentin. The characteristics of elastic modulus development in real time during cure are largely unknown. The purpose of this study was to evaluate the effect of light power density and total energy density on the early development of elastic modulus for a light-activated composite.

The in vitro cytotoxicity of eluates from dentin bonding resins and their effect on tyrosine phosphorylation of L929 cells.

Objectives: The aim of this study was to examine the relationship between the monomers eluted from dentin-bonding systems and their cytotoxicities, and to investigate the biochemical effect of the monomers on tyrosine phosphorylation, especially relating to the cell growth activity, of L929 cells in vitro.

Methods: The primers, uncured or cured adhesives (3M and Kuraray) were tested to determine the cytotoxicity of confluent L929 cells cultured by Eagle's MEM medium supplemented with 10% FCS. The area of cells affected by the eluted monomers were evaluated with an image analyzer and the concentrations of monomers eluted into the medium were measured with high performance liquid chromatography (HPLC) after 24h incubation.

Properties of packable dental composites.

The introduction of many new packable composites suggests that these products are rapidly gaining popularity. The purpose of this study was to evaluate the in vitro properties of a variety of packable composites and to determine if significant enhancements in physical and mechanical properties have been achieved for these materials compared with two popular nonpackable posterior composites. For the five packable and two regular composites tested (ALERT, Pyramid-Dentin, Pyramid-Enamel, Solitaire, SureFil, Heliomolar, and Z100), the values for fracture toughness, flexure strength, flexure modulus, hardness, and volumetric polymerization shrinkage were determined.

Mercury evaporation from amalgams with varied mercury contents.

This study examined the relationship between mercury content and mercury evaporation from amalgams during setting. Two different types of commercial high-copper amalgams (single composition and admixed types) were used. Cylindrical specimens of each amalgam were prepared with five different mercury contents according to ADA Specification No.

Assessing the effect of composite formulation on polymerization stress.

Background: In this study, the authors measured the magnitude of the polymerization stress of a variety of dental composite materials and explored the effect of a novel monomer, a methacrylated derivative of styrene-allyl alcohol, or MSAA, in reducing polymerization stress.

Methods: Eleven commercially available composites and a series of experimental composites were evaluated in a mechanical testing machine to measure the maximum stress generated during placement in a confined setting.

Results: A significant relationship between higher filler volume and increased polymerization stress was found among the commercial materials.

The effects of adhesive thickness on polymerization contraction stress of composite.

A layer of an unfilled adhesive resin placed between the tooth and composite restoration has been shown to absorb some of the stress generated in the composite during polymerization and to reduce interfacial leakage. The objectives of this study were to measure the change in polymerization contraction stress of bonded composite as the thickness of the resin adhesive was systematically varied, and to correlate the effects of the adhesive thickness and reduced stress on marginal leakage in class V cavities. The maximum contraction force of composite (Herculite XRV) was measured in a tensilometer as the thickness of the adhesive bonding agent (Scotchbond MP) was varied from 20 to 300 microm.

Cavity preparation factors and microleakage of Class II composite restorations filled at intraoral temperatures.

Purpose: To determine if alteration of any of the following factors could reduce microleakage following placement of Class II resin-based composites (RBC) at intraoral temperature: cavity preparation (vertical wall bevels), finishing technique (delayed vs. immediate), or postoperative re-bonding (marginal sealing). An additional purpose was to determine if a decalcification/clearing protocol was a valid technique for assessing three-dimensional microleakage.

In vitro evaluation of the marginal degradation of dental composites under simulated occlusal loading.

Objectives: Our objective was to use an in vitro oral wear simulator to compare the susceptibility to marginal breakdown of different classes of dental composites.

Methods: Two microfill composites (Silux Plus, 3M and Heliomolar, Vivadent), two minifills (Z100, 3M and Herculite, Kerr) and two midifills (Fulfil, Caulk and Clearfil, Kuraray) were placed in two increments (40 s cure) into class I cavities (5 x 3.5 x 2 mm3 deep) cut into the facial enamel surfaces of bovine incisors treated with an adhesive (Scotchbond MP, 3M).

Vaporization of Hg from Hg-in amalgams during setting and after abrasion.

Objective: The aim of this study was to determine if Hg vaporization during setting and after abrasion of amalgams could be reduced by adding indium to Hg prior to trituration.

Methods And Materials: Hg-In alloys (0,5,10,15 wt% In) were triturated with commercial amalgam alloys (Tytin, Kerr; Artalloy, Degussa; Sybraloy, Kerr) and condensed into cylinders (4 x 8 mm). In one experiment, Hg release during setting was measured in air (37 degrees C) with a Jerome 431 Hg analyzer (n = 4).

Evaluation of cure, properties and wear resistance of Artglass dental composite.

Purposes: (1) To evaluate the degree of conversion (DC) and the physical properties of a new dental composite, Artglass (Kulzer), designed primarily as a replacement material for porcelain in PFMs; and (2) to compare the efficacy of two different curing units for two dissimilar composites (Artglass and Charisma, Kulzer).

Materials And Methods: Specimens (n = 10) were prepared by curing either in a continuous light exposure unit (Triad II, Dentsply) or in a high intensity strobe unit (Uni XS, Kulzer) for 180 s. Specimens were aged 24 hrs in water at 37 degrees C and tested for fracture toughness (FT-MPa m1/2; x-head = 0.

Reduction of composite contraction stress through non-bonded microfiller particles.

Objectives: To determine the reduction in composite polymerization stress through the addition of non-bonded microfiller particles.

Methods: Microfillers that were unsilanated, silanated, and treated with a nonfunctional silane were added to dental resin and to a small-particle composite. The contraction stress generated by these materials was measured by polymerizing them between glass plates mounted in a mechanical testing machine.

Stress transfer from polymerization shrinkage of a chemical-cured composite bonded to a pre-cast composite substrate.

Objectives: (1) To develop and test a strain gauge-based method for evaluating the strain transferred through a bonded interface to a deformable substrate; and (2) to develop and test a finite element (FE) model for evaluating the stress development in a chemical-cured composite during polymerization.

Methods: A generic light-cured resin composite was used to fabricate a rectangular plate with an internal slot filled with a chemical-cured composite. Strain gauges on the surface of the composite in the channel and on the plate adjacent to the channel-plate interface were used to record strain continuously up to 500 s after mixing the composite paste.

Fluoride penetration into the hybrid layer from a dentin adhesive.

Purpose: To evaluate the in vitro microleakage of a new fluoride-containing dentin adhesive and to provide evidence for fluoride release from the adhesive and penetration into the dentin.

Materials And Methods: Class V preparations with margins in enamel and dentin were made in the buccal and lingual surfaces of six extracted human third molars. Six preparations were restored with Scotchbond Multipurpose (SBMP)/Z100 composite and six with a new fluoride containing dentin adhesive (FB)/Litefil composite.

In vitro aging of dental composites in water--effect of degree of conversion, filler volume, and filler/matrix coupling.

The purpose of this study was to evaluate the long-term effect of aging in water on the physical properties of experimental composites having systematically controlled differences in degree of conversion (DC), filler volume fraction (Vf), and percentage of silane-treated fillers. Composites were made with a 50% Bis-GMA:50% TEGDMA light-cured resin and a 1-2 microm (average size) strontium glass filler (+ 5 wt% SiO2 microfiller). For composites A-E, the DC was varied from 56-66% by changing the curing time; for D and F-I, the Vf was varied from 28-62 vol%; and for D and J-M, the percent of fillers with a silane coupling agent (gamma-MPS) was varied from 20-100%.

Laboratory evaluation of adhesively crimped surgical ball hooks.

The aim of this study was to examine the effect of the addition of sandblasting and/or dental adhesive on the stability of the crimpable hook when positioned and crimped onto surgical arch wires. Ninety crimpable ball hooks were divided into six test groups: crimp only; apply Panavia 21 and crimp; apply C & B Metabond and crimp; sandblast and crimp; sandblast, apply Panavia 21, and crimp; and sandblast, apply C & B Metabond, and crimp. Each hook was treated according to the criteria of the relevant test group and then crimped to the arch wire.

Effect of Pd and In on mercury evaporation from amalgams.

The amount of Hg vapor released from "synthesized" gamma 1 with 1% (wt) Pd was reported to be less than 30% of that from gamma 1 with no Pd. This study tested the hypothesis that Hg evaporation from Pd-containing amalgams decreases with Pd concentration and that In also reduces Hg vapor. Specimens (4 mm dia, 8 mm long) were prepared by triturating Ag-Sn(25%)-Cu(12%) alloy powder containing 0.

Wear and marginal breakdown of composites with various degrees of cure.

Loss of anatomical form due to wear has been cited as one factor limiting the clinical use of posterior composites. The physical properties and possibly the wear resistance of composite are influenced by the extent to which it is cured. The aim of this study was to vary degree of conversion (DC) in composites to test the hypothesis that resistance to wear and marginal breakdown could be improved by enhanced curing.

In vitro wear of composite with varied cure, filler level, and filler treatment.

For the clinical wear of composite filing materials to be reduced, compositional factors such as degree of cure, filler level, and silanation level should be optimized. An oral-wear-stimulating machine was used to explore the effects of these factors on abrasion and attrition wear as well as on opposing enamel wear. The composites were made from Sr glass (1-2 micron avg) and a 50/50 Bis-GMA/TEGDMA resin.

Microleakage of four Class II resin composite insertion techniques at intraoral temperature.

Twenty recently extracted human molars had standardized Class II slot cavities prepared on the mesial and distal surfaces with the gingival floor located on dentin. The teeth were embedded in a stone template, warmed to 37 degrees C, and restored immediately using one of two incremental placement techniques with visible light-cured composite (VLC), or one of two directed shrinkage placement techniques using an autocure/VLC composite combination. Teeth were stored at 37 degrees C for 2 weeks, thermocycled, stained, sectioned in the middle of the preparation, and evaluated for dye penetration.

Factors effecting dental composite wear in vitro.

The wear of posterior dental composite restorations takes place through a complex combination of wear mechanisms. To isolate and measure the contribution of the different tribological phenomena in a controlled manner, an oral wear simulator was employed. Results previously reported demonstrated the simulator's ability to form strong correlations with clinical results for both abrasion and attrition wear.

Surface characterization of amalgam made with Hg-In liquid alloy.

When amalgam was triturated with Hg-In liquid alloys instead of pure mercury, the resultant amalgams released a significantly smaller amount of mercury vapor during setting. To understand the mechanisms responsible for the drastic decrease in mercury evaporation from the In-containing amalgam, we used Auger Electron Spectroscopy to examine surface oxide films on amalgams made with Hg-10 wt% In or pure mercury. The surface of the In-containing amalgam was rapidly covered with both indium and tin oxide films.