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Stickiness of dental resin composite materials to steel, dentin and bonded dentin
d e n t a l m a t e r i a l s 2 6 ( 2 0 1 0 ) 59–66
available at www.sciencedirect.com
journal homepage: www.intl.elsevierhealth.com/journals/dema
Stickiness of dental resin composite materials to steel, dentin and bonded dentin Kathrin Ertl a , Alexandra Graf b , David Watts c , Andreas Schedle a,∗ a b c
Central Research Unit, Bernhard Gottlieb University Clinic of Dentistry, Medical University of Vienna, Austria Section of Medical Statistics, Core Unit for Medical Statistics and Informatics, Medical University of Vienna, Austria School of Dentistry and Photon Science Institute, University of Manchester, Manchester, UK
a r t i c l e
i n f o
a b s t r a c t
Article history:
Objectives. Stickiness is a vital rheological parameter for the clinical handling behavior of
Received 14 July 2009
unset resin composite restoratives. The aim of this study was to investigate the stickiness
Accepted 22 August 2009
of three different resin composites at 23 ◦ C and 37 ◦ C tested on steel, dentin and dentin covered with different bonding agents. Methods. The stickiness instrument, used in this study consists of a vertical cylindrical stain-
Keywords:
less steel rod, with a flat circular end, and a platform with a cylindrical mold (diameter:
Stickiness
6.1 mm, depth: 2.2 mm). The test-material surface temperature and the speed of the rod can
Handling behavior
be modified. It moves slowly into the prepared mold which is filled with unset composite
Rheology
materials. The degree of stickiness is deducted from the height of the “elevation” the mate-
Resin composite
rial forms when the plunger is withdrawn from the mold until the steelhead detaches itself
Dentin
from the composite. In this study, stickiness was tested directly to the steel plunger and to
Bonding agents
dentin slices (uncovered or covered with two different bonding agents) fixed to the plunger
Clinical use
rod with a clamp. Results. The coefficients of variation (CVs) were generally less than 0.10, indicating that the stickiness instrument offers an adequately reproducible way of testing stickiness. The tested composite materials varied significantly in stickiness. For all investigated materials a decrease of peak heights with increasing speed was found (for all three materials: p < 0.0001). Generally the stickiness increased when increasing the temperature from 23 ◦ C to 37 ◦ C. Comparing the areas under the curve (Fig. 2), stickiness of resin composites was higher on dentin than on steel and least on bonded dentin. The order of stickiness of composites was not affected by testing the stickiness on the different materials. Significance. This method allows the characterization of composite resin materials stickiness to steel, as equivalent to dental steel instruments, and to bonded dentin as equivalent to the tooth cavity after preparation. An ideal material should have a sufficient difference between stickiness on steel and dentin so that it remains in the cavity and is not pulled back by the steel instrument. © 2009 Academy of Dental Materials. Published by Elsevier Ltd. All rights reserved.
∗ Corresponding author at: Bernhard Gottlieb University Clinic of Dentistry, Währingerstrasse 25a, Vienna A-1090, Austria. Tel.: +43 1 4277 67150; fax: +43 1 4277 67159. E-mail address: [email protected] (A. Schedle). 0109-5641/$ – see front matter © 2009 Academy of Dental Materials. Published by Elsevier Ltd. All rights reserved. doi:10.1016/j.dental.2009.08.006
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1.
d e n t a l m a t e r i a l s 2 6 ( 2 0 1 0 ) 59–66
Introduction
The use of resin composite materials for dental restorations has increased during the last decade primarily as an esthetic alternative to dental amalgam but also as a low cost alternative to gold and ceramic restorations. According to Ruddell et al. [1], the advantages of dental composites are relatively low costs, easy handling characteristics and high esthetics. The handling behavior of resin composite materials plays an important part in the clinical use. Resin composites have a lot of different handling characters that are often determined by the method of curing and by the size of their filler particles. Some handling characteristics are for instance pack-ability, flow, viscosity, thixotropy and shape stability. While plenty of refinements have been made in resin composite materials two handling characteristics of composites have not existed until recently: non-stickiness and fluid inject-ability [2]. The quality of being non-sticky is a fundamental part for the practitioner during the preparation. The resin composite material should not be sticking on the plunger while filling the cavity with the resin composite material; on the other hand the material should be sticky enough to stay in the prepared cavity. “The current flowable materials, while easily syringed into place, are difficult to manipulate because of their stickiness. Any attempt to move or smooth these materials is complicated by their sticking to instrument surface.” [2] Manufacturers try to minimize the stickiness by reducing the viscosity of the material [3]. Lee et al. [3] list three important conclusions: Firstly the connection between the viscosity and the stickiness; the more viscous a material is, the less sticky is it; secondly the exponential increase of viscosity with the increase of the percentage of the filler volume; thirdly the exponential decrease of the composite’s viscosity corresponding to a higher temperature. The last finding of Lee et al. defines one requirement for the handling of composite materials: the material should not tack while transferred from the packing containers to the prepared cavity into the mouth by not sticking to the instrument. Inserted in the cavity the material should have more sticky characters to tack onto the surrounding walls. The temperature change between the room and the mouth helps to achieve this requirement. Another problem in clinical dentistry with dental composites are porosities and voids in restorations. Opdam et al. [4] mention that the risk of voids and porosities increases when the material sticks to filling instruments because air will entrap. They have found porosities in 373 out of 480 restorations. Furthermore Tyas et al. [5] point out that a marginal opening appears when the material sticks to the condenser. Until now not much attention was given to the handling characteristic stickiness. Al Sharaa and Watts [6] focussed on stickiness in their study. They gained values for stickiness from the elevated profile of the resin composite material moved up from a stainless steel instrument (2 cm/s) and the projected areas of elevation which discriminated the stickiness between 12 commercial composite materials. In this present study, using an advanced instrument for testing stickiness, the speed of elevating the composite materials can be adjusted. Furthermore stickiness on steel, on
dentin and on bonded dentin, using different bonding agents has been observed. The major objective of this study was not only to investigate the stickiness of different resin composite materials but also the even more important question if stickiness changes under different conditions concerning: (1) speed of the instrument elevating the composite material; (2) temperature of the resin composites during placement; (3) surface material of the instrument’s contacting head. In line with these objectives the following null hypotheses were formulated: (1) the speed of the instrument elevating the composite materials does not influence stickiness; (2) composite materials tested at 23 ◦ C and 37 ◦ C show the same stickiness; (3) different materials (steel, dentin, dentin coated with bonding materials) covering the contacting head do not influence stickiness.
2.
Materials and methods
2.1.
Stickiness instrument and test procedure
In this study three different composite materials were selected out of 13 commercial resin composites, which have been tested on stickiness in a previous study by Watts [7]. Estelite, Filtek Supreme XT and Premise were chosen according to their widely spread stickiness characters, ranging from extremely low to extremely high stickiness (Table 1). An apparatus was designed specifically to measure the stickiness of resin composites. This apparatus is based on a rectangular support aluminium base (23.3 cm × 5 cm). On the front of the instrument, a magnifying viewing window is fixed. A circular temperature control stage, with a temperature range from 10 ◦ C to 50 ◦ C, is fixed on the rear of the base. The upright aluminium bar behind supports the linear drive assembly in turn. There are two adjustable arms, with two light emitting diode (LED) lights attached, projecting from the rear upright. The unit fixed on the rear part of the upright bar allows a flat-ended stainless steel rod to move a vertical-axial direction via a linear motor. The movement of the rod is supervised by the control unit. The rod tip’s surface fits into a prepared cylindrical cavity, of 6 mm in diameter and 3 mm in depth, constructed in a polytetrafluoroethylene (PTFE) disk placed in the temperature control stage. The resin composites were carefully packed into the PTFE mold such that minimal porosity and no external debris were incorporated. The probe moves axially down within a selected speed range 0.1–5.0 mm/s until its surface contacts the material. Dunking completely in the material the direction of the rod is changed which elevates the test material until the contact between the rod and the material is lost. Immediately after detaching the material from the instrument, a LED light cure unit (Stopford Rheology Ltd., Manchester) was used to cure the resin composites at 600 mW/cm2 for 40 s. This fixed the elevated composite material into position, allowing subsequent measurement of ‘peak height’ as an index of stickiness. Six different speeds for the upward movement of the rod, for each material, were chosen for the measurements. The distance x between the initial position of the rod and the mean peak height of the elevation was measured by letting down the rod from its upper position, until the peak
Kerr Italia S.r.l., Italia
Ethoxylated bis-phenol-Adimethacrylate, TEGDMA bis-GMA, UDMA, TEGDMA, and bis-EMA
3M-Espe, Dental Products, USA
Tokuyama Dental Corporation, Japan bis-GMA and Triethylene glycol dimethacrylate
71.2
57.7
84
72.5
0.2 m (silica–zirconia and composite filler, particle size range from 0.1 to 0.3 m) 0.4 m (prepolymerized filler 30–50 m, barium glass 0.4 m, silica filler 0.02 m) 0.6–1.4 m average cluster particle size, 5–20 nm primer particle size 71 82
Filtek Supreme XT
6HM (A3B)
Tri-modal composite restorative Universal restorative 443493 (A3,5) Premise
Submicron filled composite Estelite
ESA39428 (A3)
% fillers by weight Classification
61
height (mm) of the material’s elevation was reached and measured. For comparing the data the ‘areas under the curves of peak height vs. probe speed’ (mm2 /s) were calculated and analyzed. For measurements investigating stickiness of resin composites to surfaces other than stainless steel, a precision fixing clamp was attached to the rod, enabling disk surfaces of bovine dentin to be attached and lowered onto the resin composite paste surface, as detailed below.
2.2. Stickiness of resin composite pastes to various rod surfaces Estelite, Filtek Supreme XT and Premise were tested at 23 ◦ C and 37 ◦ C under various conditions (Table 2). The first test procedure was done on steel. The similarity of the steel rod to the working part of a dental instrument results in data that are close to clinical use. The stickiness of composite materials was further tested on dentin slices. The dentin slices were produced by the Bernhard Gottlieb University Clinic of Dentistry (Vienna, Austria). Bovine teeth were cut into small slices (width: 1 mm). The slices were ground until they had a circular shape with a diameter of 6 mm. Then the dentin slices were fixed to the steel rod with the help of an additional part (fixing clamp), which was produced by the Technical University of Vienna. The fixing clamp (diameter: 12 mm) has an impression with a diameter of 6 mm and a depth of 2 mm. On the other side of the fixing clamp is an elevation (diameter: 6 mm) which corresponds to the area of the flat-ended stainless steel rod of the stickiness instrument. On this elevation the small bovine dentin slices were attached with glass-ionomer luting cement (Ketac Cem Applicap, 3M Espe). Another test procedure was carried out on dentin slices, which were covered with two different bonding systems (a total etch system and a self etch system, Table 3). The test procedure for testing the stickiness on dentin slices was identical as described above.
2.3.
Batch and shade Material
Table 1 – Composite resin materials investigated in this study.
% filler by volume
Mean particle size
Monomer matrix
Manufacturer
d e n t a l m a t e r i a l s 2 6 ( 2 0 1 0 ) 59–66
Statistical methods
To investigate the repeatability of the peak height for speed = 1.905 mm/s, specimens were measured three times. Coefficients of variation (CVs) were calculated to measure the repeatability. To investigate the influence of speed and temperature on the peak height ANOVAs were calculated for the different materials (Estelite, Filtek Supreme XT, Premise). The stickiness of the different classes and materials was compared in terms of the area under the peak height-curve (as a function of speed). To investigate the influence of materials, classes and temperature on these ‘areas under the curve’, again an ANOVA was performed.
3.
Results
3.1.
Stickiness measurements
This study offered an adequately reproducible way of expressing stickiness, an important feature of dental composites handling characteristics. The coefficients of variation (CVs)
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d e n t a l m a t e r i a l s 2 6 ( 2 0 1 0 ) 59–66
Table 2 – The investigated materials in this study tested under different temperatures on the various surfaces.
Estlite Filtek Supreme XT Premise
Steel
Dentin
Bonding Optibond Solo Plus
Bonding Optinbond All in one
23 ◦ C and 37 ◦ C 23 ◦ C and 37 ◦ C 23 ◦ C and 37 ◦ C
23 ◦ C and 37 ◦ C 23 ◦ C 23 ◦ C and 37 ◦ C
23 ◦ C and 37 ◦ C 23 ◦ C and 37 ◦ C 23 ◦ C and 37 ◦ C
23 ◦ C and 37 ◦ C
Table 3 – Different bonding-systems used in this study. Material
Contribution/filler by weight
Procedure
Manufacturer
OptiBond Solo Plus
15% filled with 0.4 m barium glass
Kerr, Italia S.p.A.
OptiBond All in One
7%
Etch 15 s, dry lightly, apply adhesive for 15 s, air blow 3 s, light cure 20 s Scrub 20 s, apply second application, scrub 20 s, air blow 5 s, light cure 10 s
were generally less than 0.10. However, for some specimens larger CVs were found. The mean values of the peak heights for specimens repeated for three times, the corresponding standard deviations and CVs are listed in Table 4 separately for surfaces, materials and temperatures. This table is sorted by the CVs. The CV values for Estelite at 37 ◦ C on dentin and steel are zero because the endpoint of the stickiness instrument (12.32 mm) was reached in these measurements. For all investigated materials a decrease in peak heights with increasing speed was found (for all three materials: p < 0.0001; Null hypothesis 1 was rejected). Fig. 1 shows the peak heights for the different settings (temperature, rod surface) at different speeds separately for Estelite (A), Premise (B), Filtek Supreme XT (C) and for the different bondings of Filtek Supreme XT (D). For Estelite (p = 0.0468) and Premise (p = 0.0464) a significant difference of peak heights was found using different temperatures. No such difference was found for Filtek Supreme XT. Generally the stickiness increased when increasing the temperature from 23 ◦ C to 37 ◦ C (Null hypothesis 2 was rejected). However, for specimens tested with
Kerr, Italia S.p.A.
materials Estelite and Filtek Supreme XT using Optibond Solo Plus larger heights were found for 23 ◦ C. For specimens tested with Optibond All in One no such vice versa characteristic could be seen (D). The ‘areas under the curve’ (height vs. speed) used for ranking the materials are graphically depicted in Fig. 2. Fig. 2(A) shows these area-data for the stickiness on steel, Fig. 2(B) for the stickiness on dentin, Fig. 2(C) for dentin plates covered with Optibond Solo Plus and Fig. 2(D) for dentin plates covered with Optibond All in One. The overall ranking is given in Table 5, ranging from: 1.36 mm2 /s to 57.32 mm2 /s. On steel, dentin and ‘dentin covered with bonding agent’ (Optibond Solo Plus) always Estelite had the highest value for stickiness measured in terms of the ‘area under the curve’. The largest ‘area under the curve’ was found for Estelite on dentin at 37 ◦ C with a value of 57.44 mm2 . On steel, dentin and bonded dentin, generally Premise had the lowest values of stickiness. The lowest value of the area under the curve of 1.36 mm2 obtained with Premise was found on dentin covered with bonding agent (Optibond Solo Plus) at 23 ◦ C (Table 5).
Table 4 – The mean values (=mean) of the peak heights, the corresponding standard deviation (=std. dev.) and the coefficients of variation (=CV) of all replicated specimens. Surfaces Dentin Steel Dentin/Optibond All in One Steel Steel Dentin/Optibond Solo Plus Dentin/Optibond Solo Plus Steel Dentin Dentin/Optibond All in One Dentin/Optibond Solo Plus Dentin Steel Dentin Dentin Dentin/Optibond Solo Plus Steel Dentin/Optibond Solo Plus Dentin/Optibond Solo Plus
Material Estelite Estelite Filtek S. XT Premise Filtek S. XT Estelite Estelite Estelite Estelite Filtek S. XT Filtek S. XT Premise Filtek S. XT Premise Filtek S. XT Filtek S. XT Premise Premise Premise
Temperature
Mean
Std. dev.
37 37 37 37 23 23 37 23 23 23 23 23 37 37 23 37 23 23 37
12.319 12.319 1.747 0.775 1.168 1.676 1.266 3.073 9.246 1.008 1.029 0.940 1.643 1.384 5.918 0.940 0.402 0.347 0.237
0 0 0.026 0.013 0.0458 0.067 0.064 0.159 0.500 0.057 0.071 0.067 0.132 0.137 1.457 0.298 0.160 0.140 0.139
CV 0.000 0.000 0.015 0.016 0.039 0.040 0.051 0.052 0.054 0.057 0.069 0.072 0.080 0.099 0.246 0.317 0.397 0.403 0.588
d e n t a l m a t e r i a l s 2 6 ( 2 0 1 0 ) 59–66
63
Fig. 1 – Stickiness of (A) Estelite, (B) Premise, (C) Filtek Supreme XT on steel, dentin or bonded dentin (Optibond Solo Plus) and (D) Filtek Supreme XT on bonded dentin (Optibond Solo Plus vs. Optibond All in One); Filtek S. XT = Filtek Supreme XT; Bonded s/Bonded solo = dentin covered with Optibond Solo Plus; Bonded All in One = dentin covered with Optibond All in One.
On average over all surfaces and temperatures, a significant larger area under the curve was found for Estelite as compared to Filtek Supreme XT (p = 0.0198) and Premise (p = 0.0015). No significant difference in the areas under the curve was found between Filtek Supreme XT and Premise. Comparing the areas under the curve (Fig. 2), the stickiness of resin composites was higher on dentin than on steel and least on bonded dentin (Null hypothesis 3 was rejected). The order of stickiness of composites was not affected by testing the stickiness on the different materials. Estelite always stayed the stickiest material, followed by Filtek Supreme XT. Premise showed the least sticky character.
3.2.
Scanning electron micrograph (SEM) pictures
Fig. 3(A) and (B) shows a dentin surface with open dentin tubules. Fig. 4(A) and (B) depicts a dentin surface after etching and bonding with Optibond Solo Plus. No dentin tubules are visible due to coverage by the bonding agent.
4.
Discussion
In addition to physical and chemical properties, the handling characteristics of resin composites play an important role when selecting a material for clinical use. In previous studies clinicians evaluated the handling behavior of composite materials in clinical evaluations by simply manipulating them. One example is the group of 25 practitioners, operating in the United Kingdom called PREP (Product Research and Evaluation by Practitioners) Panel. The PREP group has conducted many research projects, mainly focussing on handling evaluations of materials and techniques [8,9,10]. They are often cooperating with manufacturers sponsoring them, to evaluate the handling of the material by using a questionnaire. However, Burke [8] questions that way of operating, because these evaluations are often carried out on hospitalbased patients and thus are not corresponding closely to dental practice. He mentions the fundamental importance in the development of new techniques for the evaluation of
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d e n t a l m a t e r i a l s 2 6 ( 2 0 1 0 ) 59–66
Fig. 2 – The ‘areas under the curve’ (mm2 /s) values used for ranking the materials; (A) stickiness on steel; (B) stickiness on dentin; (C) stickiness on bonded solo = dentin slices covered with Optibond Solo Plus; (D) stickiness on bonded all in one = dentin slices covered with Optibond All in One; NA = not investigated; Filtek S. XT = Filtek Supreme XT.
Table 5 – Overall ranking of the ‘areas under the curve of height vs. speed’ (mm2 /s)’ of all resin composite materials tested under different conditions and temperatures (◦ C) The area under the curve (=area). Surfaces Dentin/Optibond Solo Plus Dentin/Optibond Solo Plus Steel Dentin/Optibond Solo Plus Dentin/Optibond Solo Plus Dentin/Optibond Solo Plus Dentin/Optibond All in One Steel Dentin Steel Dentin/Optibond All in One Dentin Steel Dentin/Optibond Solo Plus Steel Dentin Dentin Steel Dentin
Material Premise Premise Premise Filtek S. XT Filtek S. XT Estelite Filtek S. XT Filtek S. XT Premise Premise Filtek S. XT Premise Filtek S. XT Estelite Estelite Filtek S. XT Estelite Estelite Estelite
Temperature 23 37 23 37 23 37 23 23 23 37 37 37 37 23 23 23 23 37 37
Area 1.36 1.44 2.06 2.80 3.76 4.63 4.91 4.96 5.05 5.12 7.03 7.32 7.43 9.53 23.39 28.02 38.79 52.26 57.44
handling properties of dental composites. For this reason, the stickiness instrument was developed as an objective way of measuring this important handling property of resin composite materials. It would be interesting in future studies to compare the results evaluated in practical situations and the results measured with the stickiness instrument. The values obtained by working with the stickiness instrument generally had a coefficient of variation smaller then 0.1, however for some settings higher coefficients of variations were found. This distinguishes the good reproducibility of the stickiness instrument. The three resin composites tested in this study showed different degrees of stickiness. The rank order of stickiness remained the same regardless whether materials were tested on steel, dentin or bonded dentin at 23 ◦ C or 37 ◦ C. For all materials, stickiness was highest on dentin followed by steel and bonded dentin at both temperatures. SEM pictures presented in this study show that on etched and bonded dentin all tubules are closed whereas on untreated dentin open tubules are visible. This increased surface due to the open dentin tubules compared to the bonding agent covered tubules might be a reason for the better attachment of composite to unbonded dentin.
d e n t a l m a t e r i a l s 2 6 ( 2 0 1 0 ) 59–66
Fig. 3 – (A) SEM micrograph of an uncovered dentin plate at a magnification of 800×. (B) SEM micrograph of an uncovered dentin plate at a magnification of 3200×.
Stickiness is probably influenced by viscosity and filler volume. According to Lee et al. [3], viscosity exponentially increased as the percentage of filler volume increased. Additionally, Bayne et al. [2] report on the differences of the materials properties as far as their element composition is concerned. Because of less filler loading, flowable composites have a low viscosity. The composition with special regard to filler loading of the tested composites is listed in Table 1. Filtek Supreme XT shows more stickiness than Premise corresponding to a lower filler content compared to Premise. These results are in line with the findings of Lee et al. Interestingly, Estelite shows highest stickiness although its filler loading in percent resembles that of Premise. In addition to submicron fillers (0.02–0.4 m) Premise has prepolymerized fillers 30–50 m, whereas in Estelite only submicron fillers (0.1–0.3 m) are found. The matrix of Estelite is based on the monomers BisGMA and TEGDMA. Bis-GMA has hydroxyl groups, which are responsible for the polarity of this composite material, thus favoring its sticky character. Although Estelite has a high filler content per volume, resembling that of Premise it is much more sticky than Premise. This is probably due to its higher TEGDMA content. Premise is the material with the least stickiness, which can be explained by the reduced quantity of highly polar substances in its composition. Filtek Supreme XT shows more stickiness than Premise, but much less than Estelite.
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Fig. 4 – (A) SEM micrograph of a dentin plate covered with a bonding agent (Optibond Solo Plus) at a magnification of 800×. (B) SEM micrograph of a dentin plate covered with a bonding agent (Optibond Solo Plus) at a magnification of 3200×.
In its composition, Bis-GMA is partly substituted by Bis-EMA, which does not contain hydroxyl groups. Therefore its polarity – and also its stickiness – is reduced in comparison to Estelite. A noticeable influence of temperature on stickiness was found for all materials. The increase of stickiness by increasing the temperature could be explained through the fact that the viscosity decreases under a higher temperature. With the exception of dentin plates covered with Optibond Solo Plus, all sample measurements followed this trend. Optibond Solo Plus covered dentin plates demonstrated decreases in stickiness under higher temperatures. Further measurements taken with dentin plates covered with another dentin bonding agent (Optibond All in One) again produced higher stickiness under higher temperatures. This finding could probably be explained by differences between dentin bonding agents (Table 3). However, further investigation has to be done to find a clear explanation for this phenomenon. Opdam et al. [11] compared two dental composites with different application techniques (packable vs. syringable) and different handling characteristics on their equality of a
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d e n t a l m a t e r i a l s 2 6 ( 2 0 1 0 ) 59–66
restoration by using two different forms (small restoration vs. large restoration). This study was performed by six practitioners, five dentists, and one dental student. The evaluation was taken by two independent examiners. The student obtained the best results for operating. The authors interpret these good results of the student, supposing a student more closely follows the protocol. In the study from Sano et al. [12] a group of undergraduate students and a group of dentists tested the operator variability of two dentin bonding systems. The results of this study indicate that the operator should be aware of the technique sensitivity of some adhesive systems. From a study by Bouillaguet et al. [13], investigating the effect of operator variability on the shear bond strength of adhesives to dentin and the effectiveness of education on bonding performance, all tested materials can give good results if a dentist has sufficient experience and receives sufficient education. The establishment of a register of the handling characteristics of resin composite materials is required as a guideline for practitioners. This register should include the detailed handling characteristics, such as the stickiness of composites and the suggested indications as a function thereof. E.g., flowable composites are best not use in situations involving high stress or associated with wear, but the properties of flowable composites are good for situations with difficult access or areas that require good penetration [14]. Bayne et al. [2] also suggest an “indication register”: “Ideally there should be a list of key property values for success of a restorative material for each specific clinical application. However, this list does not exist.” Further research with this stickiness instrument should be conducted to evaluate potential materials for dental working instruments, such as titanium or ceramic. These could be optimized for lowest stickiness characteristics.
5.
Conclusion
Overall, the main outcome of this study was, that (1) different resin composite materials differ significantly in stickiness, (2) stickiness decreases with increasing motion speed, (3) stickiness increases with increasing temperature (23 ◦ C vs. 37 ◦ C) and (4) resin composites stick better to dentin than to steel or bonded dentin. (5) Comparing stickiness on bonded dentin and on steel, Estelite was found to stick better on steel than on bonded dentin, whereas this difference was smaller for Filtek Supreme XT and Premise. Ideally, a composite material should stick to (bonded) dentin, but not to steel. This means, testing with the stickiness instrument, an ideal material should have a sufficient difference between these two test parameters. However, so
far it is not known, how large this difference should be. This could be evaluated by testing the materials clinically and comparing these clinical results with the values obtained with the stickiness instrument.
Acknowledgements We would like to express our special thanks to Prof. P. Bauer for statistical advise, Dr. I.E. Ruyter for helpful discussion concerning the physical and chemical properties of the composite resin materials, Prof. J. Wernisch for producing the scanning electron micrographs and for producing the fixing clamp for the stickiness instrument and S. Arrelano for producing the dentin slices.
references
[1] Ruddell DE, Maloney MM, Thompson JY. Effect of novel filler particles on the mechanical and wear properties of dental composites. Dent Mater 2002;18:72–80. [2] Bayne SC, Thompson JY, Swift JREJ, Stamatiades P, Wilkerson MA. Characterization of the first-generation flowable composites. J Am Dent Assoc 1998;129:567–77. [3] Lee JH, Um CM, Lee I. Rheological properties of resin composites according to variations in monomer and filler composition. Dent Mater 2006;22:515–26. [4] Opdam N, Roeters J, Peters T, Burgersdijk R, Kuijs R. Consistency of resin composites for posterior use. Dent Mater 1996;12:350–4. [5] Tyas M, Jones D, Rizkalla A. The evaluation of resin composite consistency. Dent Mater 1998;14:424–8. [6] Al-Sharaa KA, Watts DC. Stickiness prior to setting of some light cured resin-composites. Dent Mater 2003;19:182–7. [7] Watts DC. Rate-dependence of resin-composite stickiness during simulated clinical placement; in preparation. [8] Burke F. Evaluating restorative materials and procedures in dental practice. Adv Dent Res 2005;18:46–9. [9] Burke FJ, Crisp RJ, Balkenhol M, Bell TJ, Lamb JJ, McDermott K, et al. Two year evaluation of restorations of a packable composite in UK general dental practices. Br Dent J 2005;10:293–6. [10] Crisp RJ, Burke FJ. One-year clinical evaluation of compomer restorations placed in general practice. Quintessence Int 2000;31:181–6. [11] Opdam N, Roeters J, Joosten M, Veeke O. Porosities and voids in Class I restorations placed by six operators using a packable or syringable composite. Dent Mater 2002;18:58–63. [12] Sano H, Kanemura N, Burrow MF, Inai N, Yamada T, Tagami J. Effect of operator variability on dentin adhesion: students vs. dentists. Dent Mater 1998;17:51–8. [13] Bouillaguet S, Degrange M, Cattani M, Godin C, Meyer JM. Bonding to dentin achieved by general practitioners. Schweiz Monatsschr Zahnmed 2002;112:1006–11. [14] Leinfelder KF, Bayne SC, Swift Jr EJ. Packable composites: overview and technical considerations. J Esthet Dent 1999;11:234–49.
available at www.sciencedirect.com
journal homepage: www.intl.elsevierhealth.com/journals/dema
Stickiness of dental resin composite materials to steel, dentin and bonded dentin Kathrin Ertl a , Alexandra Graf b , David Watts c , Andreas Schedle a,∗ a b c
Central Research Unit, Bernhard Gottlieb University Clinic of Dentistry, Medical University of Vienna, Austria Section of Medical Statistics, Core Unit for Medical Statistics and Informatics, Medical University of Vienna, Austria School of Dentistry and Photon Science Institute, University of Manchester, Manchester, UK
a r t i c l e
i n f o
a b s t r a c t
Article history:
Objectives. Stickiness is a vital rheological parameter for the clinical handling behavior of
Received 14 July 2009
unset resin composite restoratives. The aim of this study was to investigate the stickiness
Accepted 22 August 2009
of three different resin composites at 23 ◦ C and 37 ◦ C tested on steel, dentin and dentin covered with different bonding agents. Methods. The stickiness instrument, used in this study consists of a vertical cylindrical stain-
Keywords:
less steel rod, with a flat circular end, and a platform with a cylindrical mold (diameter:
Stickiness
6.1 mm, depth: 2.2 mm). The test-material surface temperature and the speed of the rod can
Handling behavior
be modified. It moves slowly into the prepared mold which is filled with unset composite
Rheology
materials. The degree of stickiness is deducted from the height of the “elevation” the mate-
Resin composite
rial forms when the plunger is withdrawn from the mold until the steelhead detaches itself
Dentin
from the composite. In this study, stickiness was tested directly to the steel plunger and to
Bonding agents
dentin slices (uncovered or covered with two different bonding agents) fixed to the plunger
Clinical use
rod with a clamp. Results. The coefficients of variation (CVs) were generally less than 0.10, indicating that the stickiness instrument offers an adequately reproducible way of testing stickiness. The tested composite materials varied significantly in stickiness. For all investigated materials a decrease of peak heights with increasing speed was found (for all three materials: p < 0.0001). Generally the stickiness increased when increasing the temperature from 23 ◦ C to 37 ◦ C. Comparing the areas under the curve (Fig. 2), stickiness of resin composites was higher on dentin than on steel and least on bonded dentin. The order of stickiness of composites was not affected by testing the stickiness on the different materials. Significance. This method allows the characterization of composite resin materials stickiness to steel, as equivalent to dental steel instruments, and to bonded dentin as equivalent to the tooth cavity after preparation. An ideal material should have a sufficient difference between stickiness on steel and dentin so that it remains in the cavity and is not pulled back by the steel instrument. © 2009 Academy of Dental Materials. Published by Elsevier Ltd. All rights reserved.
∗ Corresponding author at: Bernhard Gottlieb University Clinic of Dentistry, Währingerstrasse 25a, Vienna A-1090, Austria. Tel.: +43 1 4277 67150; fax: +43 1 4277 67159. E-mail address: [email protected] (A. Schedle). 0109-5641/$ – see front matter © 2009 Academy of Dental Materials. Published by Elsevier Ltd. All rights reserved. doi:10.1016/j.dental.2009.08.006
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1.
d e n t a l m a t e r i a l s 2 6 ( 2 0 1 0 ) 59–66
Introduction
The use of resin composite materials for dental restorations has increased during the last decade primarily as an esthetic alternative to dental amalgam but also as a low cost alternative to gold and ceramic restorations. According to Ruddell et al. [1], the advantages of dental composites are relatively low costs, easy handling characteristics and high esthetics. The handling behavior of resin composite materials plays an important part in the clinical use. Resin composites have a lot of different handling characters that are often determined by the method of curing and by the size of their filler particles. Some handling characteristics are for instance pack-ability, flow, viscosity, thixotropy and shape stability. While plenty of refinements have been made in resin composite materials two handling characteristics of composites have not existed until recently: non-stickiness and fluid inject-ability [2]. The quality of being non-sticky is a fundamental part for the practitioner during the preparation. The resin composite material should not be sticking on the plunger while filling the cavity with the resin composite material; on the other hand the material should be sticky enough to stay in the prepared cavity. “The current flowable materials, while easily syringed into place, are difficult to manipulate because of their stickiness. Any attempt to move or smooth these materials is complicated by their sticking to instrument surface.” [2] Manufacturers try to minimize the stickiness by reducing the viscosity of the material [3]. Lee et al. [3] list three important conclusions: Firstly the connection between the viscosity and the stickiness; the more viscous a material is, the less sticky is it; secondly the exponential increase of viscosity with the increase of the percentage of the filler volume; thirdly the exponential decrease of the composite’s viscosity corresponding to a higher temperature. The last finding of Lee et al. defines one requirement for the handling of composite materials: the material should not tack while transferred from the packing containers to the prepared cavity into the mouth by not sticking to the instrument. Inserted in the cavity the material should have more sticky characters to tack onto the surrounding walls. The temperature change between the room and the mouth helps to achieve this requirement. Another problem in clinical dentistry with dental composites are porosities and voids in restorations. Opdam et al. [4] mention that the risk of voids and porosities increases when the material sticks to filling instruments because air will entrap. They have found porosities in 373 out of 480 restorations. Furthermore Tyas et al. [5] point out that a marginal opening appears when the material sticks to the condenser. Until now not much attention was given to the handling characteristic stickiness. Al Sharaa and Watts [6] focussed on stickiness in their study. They gained values for stickiness from the elevated profile of the resin composite material moved up from a stainless steel instrument (2 cm/s) and the projected areas of elevation which discriminated the stickiness between 12 commercial composite materials. In this present study, using an advanced instrument for testing stickiness, the speed of elevating the composite materials can be adjusted. Furthermore stickiness on steel, on
dentin and on bonded dentin, using different bonding agents has been observed. The major objective of this study was not only to investigate the stickiness of different resin composite materials but also the even more important question if stickiness changes under different conditions concerning: (1) speed of the instrument elevating the composite material; (2) temperature of the resin composites during placement; (3) surface material of the instrument’s contacting head. In line with these objectives the following null hypotheses were formulated: (1) the speed of the instrument elevating the composite materials does not influence stickiness; (2) composite materials tested at 23 ◦ C and 37 ◦ C show the same stickiness; (3) different materials (steel, dentin, dentin coated with bonding materials) covering the contacting head do not influence stickiness.
2.
Materials and methods
2.1.
Stickiness instrument and test procedure
In this study three different composite materials were selected out of 13 commercial resin composites, which have been tested on stickiness in a previous study by Watts [7]. Estelite, Filtek Supreme XT and Premise were chosen according to their widely spread stickiness characters, ranging from extremely low to extremely high stickiness (Table 1). An apparatus was designed specifically to measure the stickiness of resin composites. This apparatus is based on a rectangular support aluminium base (23.3 cm × 5 cm). On the front of the instrument, a magnifying viewing window is fixed. A circular temperature control stage, with a temperature range from 10 ◦ C to 50 ◦ C, is fixed on the rear of the base. The upright aluminium bar behind supports the linear drive assembly in turn. There are two adjustable arms, with two light emitting diode (LED) lights attached, projecting from the rear upright. The unit fixed on the rear part of the upright bar allows a flat-ended stainless steel rod to move a vertical-axial direction via a linear motor. The movement of the rod is supervised by the control unit. The rod tip’s surface fits into a prepared cylindrical cavity, of 6 mm in diameter and 3 mm in depth, constructed in a polytetrafluoroethylene (PTFE) disk placed in the temperature control stage. The resin composites were carefully packed into the PTFE mold such that minimal porosity and no external debris were incorporated. The probe moves axially down within a selected speed range 0.1–5.0 mm/s until its surface contacts the material. Dunking completely in the material the direction of the rod is changed which elevates the test material until the contact between the rod and the material is lost. Immediately after detaching the material from the instrument, a LED light cure unit (Stopford Rheology Ltd., Manchester) was used to cure the resin composites at 600 mW/cm2 for 40 s. This fixed the elevated composite material into position, allowing subsequent measurement of ‘peak height’ as an index of stickiness. Six different speeds for the upward movement of the rod, for each material, were chosen for the measurements. The distance x between the initial position of the rod and the mean peak height of the elevation was measured by letting down the rod from its upper position, until the peak
Kerr Italia S.r.l., Italia
Ethoxylated bis-phenol-Adimethacrylate, TEGDMA bis-GMA, UDMA, TEGDMA, and bis-EMA
3M-Espe, Dental Products, USA
Tokuyama Dental Corporation, Japan bis-GMA and Triethylene glycol dimethacrylate
71.2
57.7
84
72.5
0.2 m (silica–zirconia and composite filler, particle size range from 0.1 to 0.3 m) 0.4 m (prepolymerized filler 30–50 m, barium glass 0.4 m, silica filler 0.02 m) 0.6–1.4 m average cluster particle size, 5–20 nm primer particle size 71 82
Filtek Supreme XT
6HM (A3B)
Tri-modal composite restorative Universal restorative 443493 (A3,5) Premise
Submicron filled composite Estelite
ESA39428 (A3)
% fillers by weight Classification
61
height (mm) of the material’s elevation was reached and measured. For comparing the data the ‘areas under the curves of peak height vs. probe speed’ (mm2 /s) were calculated and analyzed. For measurements investigating stickiness of resin composites to surfaces other than stainless steel, a precision fixing clamp was attached to the rod, enabling disk surfaces of bovine dentin to be attached and lowered onto the resin composite paste surface, as detailed below.
2.2. Stickiness of resin composite pastes to various rod surfaces Estelite, Filtek Supreme XT and Premise were tested at 23 ◦ C and 37 ◦ C under various conditions (Table 2). The first test procedure was done on steel. The similarity of the steel rod to the working part of a dental instrument results in data that are close to clinical use. The stickiness of composite materials was further tested on dentin slices. The dentin slices were produced by the Bernhard Gottlieb University Clinic of Dentistry (Vienna, Austria). Bovine teeth were cut into small slices (width: 1 mm). The slices were ground until they had a circular shape with a diameter of 6 mm. Then the dentin slices were fixed to the steel rod with the help of an additional part (fixing clamp), which was produced by the Technical University of Vienna. The fixing clamp (diameter: 12 mm) has an impression with a diameter of 6 mm and a depth of 2 mm. On the other side of the fixing clamp is an elevation (diameter: 6 mm) which corresponds to the area of the flat-ended stainless steel rod of the stickiness instrument. On this elevation the small bovine dentin slices were attached with glass-ionomer luting cement (Ketac Cem Applicap, 3M Espe). Another test procedure was carried out on dentin slices, which were covered with two different bonding systems (a total etch system and a self etch system, Table 3). The test procedure for testing the stickiness on dentin slices was identical as described above.
2.3.
Batch and shade Material
Table 1 – Composite resin materials investigated in this study.
% filler by volume
Mean particle size
Monomer matrix
Manufacturer
d e n t a l m a t e r i a l s 2 6 ( 2 0 1 0 ) 59–66
Statistical methods
To investigate the repeatability of the peak height for speed = 1.905 mm/s, specimens were measured three times. Coefficients of variation (CVs) were calculated to measure the repeatability. To investigate the influence of speed and temperature on the peak height ANOVAs were calculated for the different materials (Estelite, Filtek Supreme XT, Premise). The stickiness of the different classes and materials was compared in terms of the area under the peak height-curve (as a function of speed). To investigate the influence of materials, classes and temperature on these ‘areas under the curve’, again an ANOVA was performed.
3.
Results
3.1.
Stickiness measurements
This study offered an adequately reproducible way of expressing stickiness, an important feature of dental composites handling characteristics. The coefficients of variation (CVs)
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d e n t a l m a t e r i a l s 2 6 ( 2 0 1 0 ) 59–66
Table 2 – The investigated materials in this study tested under different temperatures on the various surfaces.
Estlite Filtek Supreme XT Premise
Steel
Dentin
Bonding Optibond Solo Plus
Bonding Optinbond All in one
23 ◦ C and 37 ◦ C 23 ◦ C and 37 ◦ C 23 ◦ C and 37 ◦ C
23 ◦ C and 37 ◦ C 23 ◦ C 23 ◦ C and 37 ◦ C
23 ◦ C and 37 ◦ C 23 ◦ C and 37 ◦ C 23 ◦ C and 37 ◦ C
23 ◦ C and 37 ◦ C
Table 3 – Different bonding-systems used in this study. Material
Contribution/filler by weight
Procedure
Manufacturer
OptiBond Solo Plus
15% filled with 0.4 m barium glass
Kerr, Italia S.p.A.
OptiBond All in One
7%
Etch 15 s, dry lightly, apply adhesive for 15 s, air blow 3 s, light cure 20 s Scrub 20 s, apply second application, scrub 20 s, air blow 5 s, light cure 10 s
were generally less than 0.10. However, for some specimens larger CVs were found. The mean values of the peak heights for specimens repeated for three times, the corresponding standard deviations and CVs are listed in Table 4 separately for surfaces, materials and temperatures. This table is sorted by the CVs. The CV values for Estelite at 37 ◦ C on dentin and steel are zero because the endpoint of the stickiness instrument (12.32 mm) was reached in these measurements. For all investigated materials a decrease in peak heights with increasing speed was found (for all three materials: p < 0.0001; Null hypothesis 1 was rejected). Fig. 1 shows the peak heights for the different settings (temperature, rod surface) at different speeds separately for Estelite (A), Premise (B), Filtek Supreme XT (C) and for the different bondings of Filtek Supreme XT (D). For Estelite (p = 0.0468) and Premise (p = 0.0464) a significant difference of peak heights was found using different temperatures. No such difference was found for Filtek Supreme XT. Generally the stickiness increased when increasing the temperature from 23 ◦ C to 37 ◦ C (Null hypothesis 2 was rejected). However, for specimens tested with
Kerr, Italia S.p.A.
materials Estelite and Filtek Supreme XT using Optibond Solo Plus larger heights were found for 23 ◦ C. For specimens tested with Optibond All in One no such vice versa characteristic could be seen (D). The ‘areas under the curve’ (height vs. speed) used for ranking the materials are graphically depicted in Fig. 2. Fig. 2(A) shows these area-data for the stickiness on steel, Fig. 2(B) for the stickiness on dentin, Fig. 2(C) for dentin plates covered with Optibond Solo Plus and Fig. 2(D) for dentin plates covered with Optibond All in One. The overall ranking is given in Table 5, ranging from: 1.36 mm2 /s to 57.32 mm2 /s. On steel, dentin and ‘dentin covered with bonding agent’ (Optibond Solo Plus) always Estelite had the highest value for stickiness measured in terms of the ‘area under the curve’. The largest ‘area under the curve’ was found for Estelite on dentin at 37 ◦ C with a value of 57.44 mm2 . On steel, dentin and bonded dentin, generally Premise had the lowest values of stickiness. The lowest value of the area under the curve of 1.36 mm2 obtained with Premise was found on dentin covered with bonding agent (Optibond Solo Plus) at 23 ◦ C (Table 5).
Table 4 – The mean values (=mean) of the peak heights, the corresponding standard deviation (=std. dev.) and the coefficients of variation (=CV) of all replicated specimens. Surfaces Dentin Steel Dentin/Optibond All in One Steel Steel Dentin/Optibond Solo Plus Dentin/Optibond Solo Plus Steel Dentin Dentin/Optibond All in One Dentin/Optibond Solo Plus Dentin Steel Dentin Dentin Dentin/Optibond Solo Plus Steel Dentin/Optibond Solo Plus Dentin/Optibond Solo Plus
Material Estelite Estelite Filtek S. XT Premise Filtek S. XT Estelite Estelite Estelite Estelite Filtek S. XT Filtek S. XT Premise Filtek S. XT Premise Filtek S. XT Filtek S. XT Premise Premise Premise
Temperature
Mean
Std. dev.
37 37 37 37 23 23 37 23 23 23 23 23 37 37 23 37 23 23 37
12.319 12.319 1.747 0.775 1.168 1.676 1.266 3.073 9.246 1.008 1.029 0.940 1.643 1.384 5.918 0.940 0.402 0.347 0.237
0 0 0.026 0.013 0.0458 0.067 0.064 0.159 0.500 0.057 0.071 0.067 0.132 0.137 1.457 0.298 0.160 0.140 0.139
CV 0.000 0.000 0.015 0.016 0.039 0.040 0.051 0.052 0.054 0.057 0.069 0.072 0.080 0.099 0.246 0.317 0.397 0.403 0.588
d e n t a l m a t e r i a l s 2 6 ( 2 0 1 0 ) 59–66
63
Fig. 1 – Stickiness of (A) Estelite, (B) Premise, (C) Filtek Supreme XT on steel, dentin or bonded dentin (Optibond Solo Plus) and (D) Filtek Supreme XT on bonded dentin (Optibond Solo Plus vs. Optibond All in One); Filtek S. XT = Filtek Supreme XT; Bonded s/Bonded solo = dentin covered with Optibond Solo Plus; Bonded All in One = dentin covered with Optibond All in One.
On average over all surfaces and temperatures, a significant larger area under the curve was found for Estelite as compared to Filtek Supreme XT (p = 0.0198) and Premise (p = 0.0015). No significant difference in the areas under the curve was found between Filtek Supreme XT and Premise. Comparing the areas under the curve (Fig. 2), the stickiness of resin composites was higher on dentin than on steel and least on bonded dentin (Null hypothesis 3 was rejected). The order of stickiness of composites was not affected by testing the stickiness on the different materials. Estelite always stayed the stickiest material, followed by Filtek Supreme XT. Premise showed the least sticky character.
3.2.
Scanning electron micrograph (SEM) pictures
Fig. 3(A) and (B) shows a dentin surface with open dentin tubules. Fig. 4(A) and (B) depicts a dentin surface after etching and bonding with Optibond Solo Plus. No dentin tubules are visible due to coverage by the bonding agent.
4.
Discussion
In addition to physical and chemical properties, the handling characteristics of resin composites play an important role when selecting a material for clinical use. In previous studies clinicians evaluated the handling behavior of composite materials in clinical evaluations by simply manipulating them. One example is the group of 25 practitioners, operating in the United Kingdom called PREP (Product Research and Evaluation by Practitioners) Panel. The PREP group has conducted many research projects, mainly focussing on handling evaluations of materials and techniques [8,9,10]. They are often cooperating with manufacturers sponsoring them, to evaluate the handling of the material by using a questionnaire. However, Burke [8] questions that way of operating, because these evaluations are often carried out on hospitalbased patients and thus are not corresponding closely to dental practice. He mentions the fundamental importance in the development of new techniques for the evaluation of
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d e n t a l m a t e r i a l s 2 6 ( 2 0 1 0 ) 59–66
Fig. 2 – The ‘areas under the curve’ (mm2 /s) values used for ranking the materials; (A) stickiness on steel; (B) stickiness on dentin; (C) stickiness on bonded solo = dentin slices covered with Optibond Solo Plus; (D) stickiness on bonded all in one = dentin slices covered with Optibond All in One; NA = not investigated; Filtek S. XT = Filtek Supreme XT.
Table 5 – Overall ranking of the ‘areas under the curve of height vs. speed’ (mm2 /s)’ of all resin composite materials tested under different conditions and temperatures (◦ C) The area under the curve (=area). Surfaces Dentin/Optibond Solo Plus Dentin/Optibond Solo Plus Steel Dentin/Optibond Solo Plus Dentin/Optibond Solo Plus Dentin/Optibond Solo Plus Dentin/Optibond All in One Steel Dentin Steel Dentin/Optibond All in One Dentin Steel Dentin/Optibond Solo Plus Steel Dentin Dentin Steel Dentin
Material Premise Premise Premise Filtek S. XT Filtek S. XT Estelite Filtek S. XT Filtek S. XT Premise Premise Filtek S. XT Premise Filtek S. XT Estelite Estelite Filtek S. XT Estelite Estelite Estelite
Temperature 23 37 23 37 23 37 23 23 23 37 37 37 37 23 23 23 23 37 37
Area 1.36 1.44 2.06 2.80 3.76 4.63 4.91 4.96 5.05 5.12 7.03 7.32 7.43 9.53 23.39 28.02 38.79 52.26 57.44
handling properties of dental composites. For this reason, the stickiness instrument was developed as an objective way of measuring this important handling property of resin composite materials. It would be interesting in future studies to compare the results evaluated in practical situations and the results measured with the stickiness instrument. The values obtained by working with the stickiness instrument generally had a coefficient of variation smaller then 0.1, however for some settings higher coefficients of variations were found. This distinguishes the good reproducibility of the stickiness instrument. The three resin composites tested in this study showed different degrees of stickiness. The rank order of stickiness remained the same regardless whether materials were tested on steel, dentin or bonded dentin at 23 ◦ C or 37 ◦ C. For all materials, stickiness was highest on dentin followed by steel and bonded dentin at both temperatures. SEM pictures presented in this study show that on etched and bonded dentin all tubules are closed whereas on untreated dentin open tubules are visible. This increased surface due to the open dentin tubules compared to the bonding agent covered tubules might be a reason for the better attachment of composite to unbonded dentin.
d e n t a l m a t e r i a l s 2 6 ( 2 0 1 0 ) 59–66
Fig. 3 – (A) SEM micrograph of an uncovered dentin plate at a magnification of 800×. (B) SEM micrograph of an uncovered dentin plate at a magnification of 3200×.
Stickiness is probably influenced by viscosity and filler volume. According to Lee et al. [3], viscosity exponentially increased as the percentage of filler volume increased. Additionally, Bayne et al. [2] report on the differences of the materials properties as far as their element composition is concerned. Because of less filler loading, flowable composites have a low viscosity. The composition with special regard to filler loading of the tested composites is listed in Table 1. Filtek Supreme XT shows more stickiness than Premise corresponding to a lower filler content compared to Premise. These results are in line with the findings of Lee et al. Interestingly, Estelite shows highest stickiness although its filler loading in percent resembles that of Premise. In addition to submicron fillers (0.02–0.4 m) Premise has prepolymerized fillers 30–50 m, whereas in Estelite only submicron fillers (0.1–0.3 m) are found. The matrix of Estelite is based on the monomers BisGMA and TEGDMA. Bis-GMA has hydroxyl groups, which are responsible for the polarity of this composite material, thus favoring its sticky character. Although Estelite has a high filler content per volume, resembling that of Premise it is much more sticky than Premise. This is probably due to its higher TEGDMA content. Premise is the material with the least stickiness, which can be explained by the reduced quantity of highly polar substances in its composition. Filtek Supreme XT shows more stickiness than Premise, but much less than Estelite.
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Fig. 4 – (A) SEM micrograph of a dentin plate covered with a bonding agent (Optibond Solo Plus) at a magnification of 800×. (B) SEM micrograph of a dentin plate covered with a bonding agent (Optibond Solo Plus) at a magnification of 3200×.
In its composition, Bis-GMA is partly substituted by Bis-EMA, which does not contain hydroxyl groups. Therefore its polarity – and also its stickiness – is reduced in comparison to Estelite. A noticeable influence of temperature on stickiness was found for all materials. The increase of stickiness by increasing the temperature could be explained through the fact that the viscosity decreases under a higher temperature. With the exception of dentin plates covered with Optibond Solo Plus, all sample measurements followed this trend. Optibond Solo Plus covered dentin plates demonstrated decreases in stickiness under higher temperatures. Further measurements taken with dentin plates covered with another dentin bonding agent (Optibond All in One) again produced higher stickiness under higher temperatures. This finding could probably be explained by differences between dentin bonding agents (Table 3). However, further investigation has to be done to find a clear explanation for this phenomenon. Opdam et al. [11] compared two dental composites with different application techniques (packable vs. syringable) and different handling characteristics on their equality of a
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restoration by using two different forms (small restoration vs. large restoration). This study was performed by six practitioners, five dentists, and one dental student. The evaluation was taken by two independent examiners. The student obtained the best results for operating. The authors interpret these good results of the student, supposing a student more closely follows the protocol. In the study from Sano et al. [12] a group of undergraduate students and a group of dentists tested the operator variability of two dentin bonding systems. The results of this study indicate that the operator should be aware of the technique sensitivity of some adhesive systems. From a study by Bouillaguet et al. [13], investigating the effect of operator variability on the shear bond strength of adhesives to dentin and the effectiveness of education on bonding performance, all tested materials can give good results if a dentist has sufficient experience and receives sufficient education. The establishment of a register of the handling characteristics of resin composite materials is required as a guideline for practitioners. This register should include the detailed handling characteristics, such as the stickiness of composites and the suggested indications as a function thereof. E.g., flowable composites are best not use in situations involving high stress or associated with wear, but the properties of flowable composites are good for situations with difficult access or areas that require good penetration [14]. Bayne et al. [2] also suggest an “indication register”: “Ideally there should be a list of key property values for success of a restorative material for each specific clinical application. However, this list does not exist.” Further research with this stickiness instrument should be conducted to evaluate potential materials for dental working instruments, such as titanium or ceramic. These could be optimized for lowest stickiness characteristics.
5.
Conclusion
Overall, the main outcome of this study was, that (1) different resin composite materials differ significantly in stickiness, (2) stickiness decreases with increasing motion speed, (3) stickiness increases with increasing temperature (23 ◦ C vs. 37 ◦ C) and (4) resin composites stick better to dentin than to steel or bonded dentin. (5) Comparing stickiness on bonded dentin and on steel, Estelite was found to stick better on steel than on bonded dentin, whereas this difference was smaller for Filtek Supreme XT and Premise. Ideally, a composite material should stick to (bonded) dentin, but not to steel. This means, testing with the stickiness instrument, an ideal material should have a sufficient difference between these two test parameters. However, so
far it is not known, how large this difference should be. This could be evaluated by testing the materials clinically and comparing these clinical results with the values obtained with the stickiness instrument.
Acknowledgements We would like to express our special thanks to Prof. P. Bauer for statistical advise, Dr. I.E. Ruyter for helpful discussion concerning the physical and chemical properties of the composite resin materials, Prof. J. Wernisch for producing the scanning electron micrographs and for producing the fixing clamp for the stickiness instrument and S. Arrelano for producing the dentin slices.
references
[1] Ruddell DE, Maloney MM, Thompson JY. Effect of novel filler particles on the mechanical and wear properties of dental composites. Dent Mater 2002;18:72–80. [2] Bayne SC, Thompson JY, Swift JREJ, Stamatiades P, Wilkerson MA. Characterization of the first-generation flowable composites. J Am Dent Assoc 1998;129:567–77. [3] Lee JH, Um CM, Lee I. Rheological properties of resin composites according to variations in monomer and filler composition. Dent Mater 2006;22:515–26. [4] Opdam N, Roeters J, Peters T, Burgersdijk R, Kuijs R. Consistency of resin composites for posterior use. Dent Mater 1996;12:350–4. [5] Tyas M, Jones D, Rizkalla A. The evaluation of resin composite consistency. Dent Mater 1998;14:424–8. [6] Al-Sharaa KA, Watts DC. Stickiness prior to setting of some light cured resin-composites. Dent Mater 2003;19:182–7. [7] Watts DC. Rate-dependence of resin-composite stickiness during simulated clinical placement; in preparation. [8] Burke F. Evaluating restorative materials and procedures in dental practice. Adv Dent Res 2005;18:46–9. [9] Burke FJ, Crisp RJ, Balkenhol M, Bell TJ, Lamb JJ, McDermott K, et al. Two year evaluation of restorations of a packable composite in UK general dental practices. Br Dent J 2005;10:293–6. [10] Crisp RJ, Burke FJ. One-year clinical evaluation of compomer restorations placed in general practice. Quintessence Int 2000;31:181–6. [11] Opdam N, Roeters J, Joosten M, Veeke O. Porosities and voids in Class I restorations placed by six operators using a packable or syringable composite. Dent Mater 2002;18:58–63. [12] Sano H, Kanemura N, Burrow MF, Inai N, Yamada T, Tagami J. Effect of operator variability on dentin adhesion: students vs. dentists. Dent Mater 1998;17:51–8. [13] Bouillaguet S, Degrange M, Cattani M, Godin C, Meyer JM. Bonding to dentin achieved by general practitioners. Schweiz Monatsschr Zahnmed 2002;112:1006–11. [14] Leinfelder KF, Bayne SC, Swift Jr EJ. Packable composites: overview and technical considerations. J Esthet Dent 1999;11:234–49.