To investigate the elemental and molecular composition, curing efficiency, setting shrinkage strain and hardness of vinyl-polysiloxane interocclusal recording materials.
The materials tested were Blu-Mousse Classic/BMC, Exabite II NDS/EXB, Futar Scan/FTS, O-Bite/OBT, Occlufast Rock/OFR, R-Si-Line Metalbite/RMB and Stone Bite/STB. Composition was examined by SEM/EDX and micro-ATR FTIR. Curing efficiency ( n : 7) was evaluated by micro-ATR FTIR on unset materials and following 3, 5, and 10 min after mixing. Setting shrinkage strain (% S , n : 7) was evaluated by the bonded-disk method as a function of time up to 10 min after mixing and Shore-D hardness measurements ( n : 7) were performed at setting time and after 72 h storage at room temperature. Statistical analysis was performed by one-way ANOVA and paired t -tests ( a : 0.05).
All materials were particle-filled vinyl-polysiloxane composites with different elemental composition. C, O and Si were found at highest concentration in all products, whereas Al, Na, Mg, Ti and Ca were additionally detected. Curing efficiency measurements ranked the products in three statistically homogeneous groups (OFR, EXB, OBT > FTS, RMB > BMC, STB) at all time intervals, except OFR which at 5 and 10 min was ranked in the second group. In all products, a statistically significant increase in % S max values was found in comparison with % S at setting time. Strain saturation was reached by all materials at different time intervals, except from BMC and OBT. Hardness differences were detected among materials for the same time interval and between time intervals per material.
Differences among materials were detected regarding the properties tested, which may imply variations in their clinical performance.
Interocclusal registrations used for mounting models on articulators are partly responsible for the occlusal quality and precision of the final prosthetic restorations. Accurate mountings can lead to restorations that require minimal occlusal modifications intraorally and consequent reduction of chairside clinical time . A wide range of materials has been used for interocclusal recordings; from wax to the most current elastomeric materials like vinyl-polysiloxanes. The latter are produced from impression materials by the addition of substances such as accelerators and fillers that eventually modify some of their properties significantly; the effect of this addition on the qualities of the parent materials still remaining unclear and unpredictable . The studies conducted on these materials so far, can be classified into two categories. In the first category, most studies focused on reproducing accurate records. The experimental set up consisted of occluding models of opposing arches mounted with interocclusal recording materials to be tested, and the testing method comprised of measurements between points, or differences detected at the condylar areas of the articulators . In the second category, studies on specific properties were performed, including rheology, volumetric and linear dimensional changes, compressive resistance and setting shrinkage . However, very few studies were based on standardized methods or methods complying with international specifications , since the latter apply better for elastomeric impression than interocclusal recording materials.
The objective of this study was to investigate the setting characteristics of a series of vinyl-polysiloxane interocclusal recording materials, including composition, microstructure, curing efficiency, setting shrinkage and hardness. Although considered as the most accurate and dimensionally stable group of interocclusal recording materials, there is limited information on the structure–property relationship of vinyl-polysiloxanes, especially during the early setting stages, that dominate their clinical performance. The null hypothesis was that no significant differences existed among the materials selected at the properties tested.
Materials and methods
The materials selected for the study, along with the working and setting times according to the manufacturers’ information, are listed in Table 1 .
|Product/batch||Code||Working time (s, 23 °C)||Setting time (s, 37 °C)||Manufacturer|
|Blu-Mousse Classic (BM-08119/08119)||BMC||120||120||Parkell Inc., Farmingdale, NY, USA|
|Exabite II NDS (0807071)||EXB||45||45||GC Int, Tokyo, Japan|
|Futar Scan (80061)||FTS||15||45||Kettenbach GmbH & Co., Eschenburg, D|
|O-Bite (604479)||OBT||30||90s||DMG, Hamburg, D|
|Occlufast Rock (53553)||OFR||30s||60||Zhermack Spa, Rovigo, I|
|R-Si-Line Metalbite (6802959)||RMB||20||40||R Dental GmbH, Hamburg, D|
|Stone Bite (811044.10 811031)||STB||30||50||Dreve Dentamid GmbH, Unna, D|
Elemental and molecular composition
Rectangular specimens were prepared from each material and sectioned after setting with a surgical steel blade. The sectioned surfaces, representing bulk structure, were sputter-coated with a thin layer of carbon (∼30 nm) in a sputter-coating unit (SCD 004 Sputter-Coater/OCD 30 unit, Bal-Tec, Vaduz, FL) and examined under a SEM (Quanta 200, FEI, Hilsboro, OR, USA) coupled to an energy-dispersive X-ray spectrometer (Sapphire CDU, EDAX Int, Mahwah, NJ, USA). The spectrometer was equipped with a liquid N 2 -cooled Si(Li) detector and a super-ultrathin Be window (SUTW+). Compositional backscattered electron images (BE) were obtained from each section, to identify phases by differences in mean atomic number, under high vacuum (10 −6 mbar), 15 kV accelerating voltage, 110 μA beam current and 160× nominal magnification. The same regions were analyzed by energy-dispersive X-ray spectrometry (EDX) under the same conditions, 150–100 s acquisition period with 30–34% detector dead time. Quantitative analysis was performed in a non-standard mode, after ZAF and C-coating corrections, using Genesis v 5.1 software (EDAX Int).
For the molecular composition, specimen surfaces were pressed, by means of a sapphire anvil, against the sampling surface of a diamond internal reflection element ( : 2 mm) of a micro-attenuated total reflectance accessory (micro-ATR, Golden Gate Mk II, Specac, Smyrna, GA, USA) attached to a Fourier-transform infrared spectrometer (Spectrum GX FTIR Spectrometer, Perkin-Elmer, Baconsfield, Bacon, UK). Spectra acquisition was performed under the following conditions: 4000–600 cm −1 wavenumber range, 4 cm −1 resolution, 20 scans co-addition (6 s per scan), single-reflection and 2 μm depth of analysis at 1000 cm −1 .
The micro-ATR set up described before was used to evaluate the curing efficiency of the materials as a function of time. Spectra were taken at 3, 5 and 10 min after mixing with the materials kept at 37 °C during the initial 3 and 5 min period, and then at room temperature (26 °C). Spectra of the unset materials were recorded as follows: The edge of a thin metallic spacer (0.05 mm) was placed vertically on the diamond surface, separating the sampling area of the refractive element into two equal parts. Each part was then covered with the corresponding unset material (base or catalyst) from each cartridge. The spectra taken under these conditions corresponded to a 1:1 component ratio, without mixing, and thus activating the fast polymerization reaction. All spectra were subjected to baseline and ATR corrections and the net peak absorbance intensities of the Si H groups (2158 cm −1 ) and Si CH 3 groups (1256 cm −1 ) were measured employing the tangent baseline technique. The peak of the Si H groups, which are consumed during polymerization, was selected as the analytical band, whereas the peak of the Si CH 3 groups that do not change during polymerization, was chosen as the reference band, to internally correct any photometric error due to changes in the refractive index during setting. The percentage amount of remaining Si H groups (%RHS) in the set materials relative to their unset controls was measured according to the equation:
% RHS = 100 × S HS × U MS S MS × U HS ,
where S and U are the net peak absorbance heights of set (S) and unset (U) materials of Si H (HS, 2158 cm −1 ) and Si CH 3 (MS, 1256 cm −1 ) group peaks, respectively. Seven specimens were tested per material and time interval.
Setting shrinkage strain
The shrinkage strain kinetics of the materials was evaluated by the bonded-disk method . Unset material disks ( ∼ 6 mm, h : 1 mm, n : 7) were placed on top of a microscopic glass-slide, at the center of a brass ring ( : 15 mm, h : 1 mm) and rapidly covered by a 100 μm-thick borosilicate glass cover-slip. Shrinkage strain was recorded as a function of time up to 10 min, following mixing at 37 °C and then storage at room temperature (26 °C), by an LVDT displacement transducer (GT 2000, RDP Electronics, Wolverhampton, UK, <100 μV sensitivity, ∼7 g weight), placed in vertical contact with the cover-slip at the center of the specimen and connected to a micro-computer transient recorder/data-logging system. The deflection of the cover-slip due to specimen shrinkage during polymerization was monitored as a function of time in mV units, after subtracting the initial from the final values, and then transformed to percentage displacement (% S ) by normalizing the values vs the displacement/voltage calibration coefficient of the setup. From the plotted data, the % S at the setting time and the % S max at 10 min were calculated.
Cylindrical samples of each material ( : 15 mm, h : 5 mm, n : 7) were constructed from a cylindrical plexiglass mold as follows: the mold was placed on a glass-slide, filled with material and a second glass-slide was pressed on top by a standard weight to remove the excess. Immediately after, the set up was transferred to an incubator at 37 °C and left to set for the setting time suggested by the manufacturer. The samples were then removed from the molds and Shore-D hardness measurements were made on top and bottom surfaces ( n : 2 × 2 per specimen) employing a Shore-D hardness tester (DX-DS, PCE Instruments, Durham, UK). Measurements were repeated after 72 h storage at room temperature (26 °C).
One-way ANOVA and Tukey tests were used to evaluate the mean differences among materials for curing efficiency, shrinkage strain and Shore-D hardness values per time interval. To evaluate differences in curing efficiency as a function of time for the same material, one-way ANOVA (one factor repetition) was used for curing efficiency, whereas paired t -tests were employed for shrinkage strain and Shore-D hardness measurements. In all measurements a 95% confidence level was used ( α : 0.05). Statistical analysis was performed by SigmaStat v 3.1 software (Jandel, St. Raphael, CA, USA).