Abstract
Objectives
To evaluate the stickiness of unset resin-composites, at different speeds and temperatures, in terms of maximum probe separation-force ( F max ) and work-of-separation ( W s ).
Materials and methods
Eight commercial light-cured resin-composites were selected. Each material was placed in a cylindrical mold ( φ = 7 mm × 5 mm depth) held at 25 °C or 37 °C. The maximum force ( F max , N) and work probe separation ( W s , N mm) were measured by using a texture analyzer to register force/displacement. A flat-ended stainless-steel probe ( φ = 6 mm) was mechanically lowered onto and into the surface of the unset sample. When a ‘trigger’ compressive force of 0.05 N was registered, data-acquisition commenced. Descent continued until a compressive force of 1 N was reached, which was held constant for 1 s. Then the probe was moved vertically upward at constant speed. This was varied over the range 2, 4, 6 and 8 mm/s. The tensile force produced on the probe by the sticky resin-composite was plotted against displacement and the maximum value was identified ( F max ). W s was obtained as the integrated area. Data was analyzed by multivariate ANOVA and multiple pair wise comparisons was done by using a Tukey post hoc test to establish homogenous subsets (at p = 0.05).
Results
F max and W s were taken as potential measures of stickiness. They ranged from 0.47 to 3.68 N and from 0.11 to 2.84 N mm, respectively. Multivariate ANOVA showed a strong interaction of withdrawal speed, temperature and materials on both F max and W s ( p < 0.001).
Conclusion
F max and W s are useful parameters for characterizing the handling-stickiness of resin-composite materials, additional to previously reported stickiness-strain or ‘peak-height’. The resin-composites investigated could be differentiated, mostly showing increases in F max and W s stickiness with increased temperature and probe-withdrawal speed.
1
Introduction
In restorative dentistry, resin-composite restorative materials are far more widely used than any other restorative material . Along with good esthetic and favorable mechanical properties, the viscoelastic nature of the material is also very important. The rheological property of unset resin-composites is directly related to its handling characteristics, such as ease of placement, restoring the occlusal morphology, adaptation against the tooth surface and stickiness to the instrument.
The rheological behavior of resin-composites can influence operator decision regarding selection of a particular material for an application. An ideal material should flow around and into every corner of the prepared cavity and stay there when the load is removed. In addition it should not stick to the instrument (i.e. should have low stickiness), but still should attach to the walls of the cavity for proper adaptation. In other words there should be a balance between the stickiness and adaptation to the cavity wall and stickiness to the instrument . In recent years many attempts have been made by manufacturers to reduce stickiness by altering filler content and reducing viscosity of the monomer matrix .
Currently used condensation procedures and stickiness ‘pull back’ of materials may result in macroscopic voids and microscopic porosities in the restoration . Presence of these voids and porosities can lead to discoloration, decrease in the wear resistance and ultimately may lead to restoration failure and subsequent replacement . Highly sticky materials need extensive manipulation for proper placement, which might lead to an increase in marginal porosities and contraction gaps .
In 2003 Al-Sharaa and Watts described a new method for evaluation of stickiness of some light-cure resin-composites . In their study, they used a flat-ended steel probe to assess the stickiness of eight resin-composites, measured as the height of the peak obtained by curing the material shortly after it separated from the probe. This present study is designed to complement the previously reported measurements of ‘peak-height’ stickiness-strain, by focusing on force parameters.
The aim of this study was to evaluate the stickiness of unset resin-composites, at different speeds and temperatures, in terms of maximum probe separation-force ( F max ) and work-of-separation ( W s ). The null hypothesis was that: increase in speed and temperature has no effect on stickiness of unset resin-composite.
2
Materials and methods
Eight commercial resin-composites were selected on the basis of their matrix resin composition and filler content ( Table 1 ).
| Materials | Code | Lot no. | Manufacturer | Resin system | Filler % vol |
|---|---|---|---|---|---|
| Clearfil Majesty Esthetic | CME | 00001A | Kuraray Medical, Germany | Bis-GMA | 66% |
| Clearfil Majesty posterior | CMP | 00006A | Kuraray Medical, Germany | Bis-GMA, TEGDMA | 82% |
| Filtek Silorane | FS | 7AR | 3M ESPE, St. Paul, USA | Siloranes | – |
| Filtek Z250 | Z250 | 6EH | 3M ESPE, St. Paul, USA | Bis-GMA, UDMA, Bis-EMA | 60% |
| Tetric EvoCeram | TEC | H29941 | Ivoclar Vivadent, USA | Dimethacrylates | 53–55% |
| XRV Herculite | XRV | 07-1032E/05-1263D | Kerr, USA | Bis-GMA TEGDMA | 59% |
| Quixfil | Qu | 0703002499 | Dentsply, Germany | UGDMA, TEGDMA | 66.4% |
| Grandio | Gr | 630877 | Voco, Cuxhaven Germany | Bis-GMA, TEGDMA | 87% |
For maximum separation force ( F max , N) and work of probe-separation ( W s , N mm) a texture analyzer ( Fig. 1 ) was used (TA.XT2i, Stable Micro Systems, Godalming, Surrey, UK). The analyzer comprised a stainless steel cylindrical probe ( φ = 6 mm) connected to a force transducer, which measured the force acting on the probe. Modifications were carried out to measure the above mentioned handling characteristics. A thermostatically controlled frame ( φ = 70 mm) with a cylindrical cavity ( φ = 7, depth = 5 mm) was constructed ( Fig. 2 ). This frame was fixed to the stainless steal stand. The temperature of the mold cavity was regulated using an adjustable power supply unit with a thermocouple in close proximity to the sample. Each specimen was placed in the mold cavity at 25 °C or 37 °C.
In the ‘bonding’ phase the flat-ended stainless-steel probe was mechanically lowered onto and into the surface of the unset sample. When a ‘trigger’ compressive force of 0.05 N was registered, data-acquisition commenced. The probe descended further, into the sample surface layer, until a compressive force of 1 N was recorded, which was held constant for 1 s.
During the ‘debonding’ phase, the probe was moved vertically upward at a predetermined constant velocity of 2, 4, 6 or 8 mm/s. As the specimen material adhered to the probe, it become elongated and exerted a tensile force on the transducer, the magnitude of the force and elongation depending on the viscoelastic properties of the material.
Data were entered into statistical software (SPSS ver. 16, SPSS Inc., Illinois, USA) and analyzed with multivariate ANOVA (speed, temperature and material as independent variables). Multiple pair-wise comparisons using a Tukeys post hoc test were conducted to establish homogenous subsets (at p = 0.05).
2
Materials and methods
Eight commercial resin-composites were selected on the basis of their matrix resin composition and filler content ( Table 1 ).
| Materials | Code | Lot no. | Manufacturer | Resin system | Filler % vol |
|---|---|---|---|---|---|
| Clearfil Majesty Esthetic | CME | 00001A | Kuraray Medical, Germany | Bis-GMA | 66% |
| Clearfil Majesty posterior | CMP | 00006A | Kuraray Medical, Germany | Bis-GMA, TEGDMA | 82% |
| Filtek Silorane | FS | 7AR | 3M ESPE, St. Paul, USA | Siloranes | – |
| Filtek Z250 | Z250 | 6EH | 3M ESPE, St. Paul, USA | Bis-GMA, UDMA, Bis-EMA | 60% |
| Tetric EvoCeram | TEC | H29941 | Ivoclar Vivadent, USA | Dimethacrylates | 53–55% |
| XRV Herculite | XRV | 07-1032E/05-1263D | Kerr, USA | Bis-GMA TEGDMA | 59% |
| Quixfil | Qu | 0703002499 | Dentsply, Germany | UGDMA, TEGDMA | 66.4% |
| Grandio | Gr | 630877 | Voco, Cuxhaven Germany | Bis-GMA, TEGDMA | 87% |
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