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Journal of Oral Science, Vol. 51, No. 2, 255-259, 2009 Original
Panavia F: the role of the primer
André L. Faria-e-Silva1), Rafael R. Moraes1), Fabrício A. Ogliari2), Evandro Piva2) 1)Department of Restorative Dentistry, Piracicaba Dental School, State University of Campinas, Piracicaba, 2)Department of Restorative Dentistry, School of Dentistry, Federal University of Pelotas, Pelotas, RS, Brazil (Received 26 August 2008 and accepted 17 March 2009) Abstract: This study evaluated the rate of
polymerization (Rp) and degree of conversion (DC) of
Panavia F when self- or dual-activated, and the influence
of either using or not using a primer containing co-
initiators (ED Primer) mixed with the material. The
Introduction
conversion reaction was monitored using real-time
Resin-based luting agents are commonly used in infrared spectroscopy with an attenuated total
dentistry. During the cementation of indirect restorations reflectance device. The cement was mixed, put onto the
and intra-radicular posts using resin cements, proper device and irradiated for 20 s (dual-cured). A self-
polymerization of the luting material is essential for clinical cured group was also prepared. Similarly, dual- and
success of the restorations (1,2). Low values for degree self-cured groups were evaluated after mixing ED
of conversion (DC) might reduce the retention of the Primer with the cement. The DC was monitored for 1
indirect material or the post (3) and contribute to restoration h and the Rp was calculated. For the dual-cured mode,
the most significant effect of ED Primer was to reduce
Dual-cured resin cements were introduced to combine . For the self-cured mode, the primer was
the favorable characteristics of self- and light-cured agents.
shown to be essential for polymerization of Panavia F:
The rationale was to develop a material with extended without ED Primer, the reaction started only after
working time capable of reaching high DC in either the approximately 500 s, with a final DC of 50%, whereas
presence or absence of light (4). During the cementation a continuous increase in conversion was observed for
of posts and thick indirect restorations, exposed marginal the group mixed with ED Primer, with a final DC of
areas can benefit largely from the photo-activation, as 7 4 % . T h e E D p r i m e r i s e s s e n t i a l fo r p ro p e r
they are readily accessible to the curing light; however, a polymerization of Panavia F; the cement becomes
significant reduction in its intensity might occur due to independent of the light when the primer is used. (J Oral
reflecting and scattering effects. Therefore, in some Sci 51, 255-259, 2009)
situations, the polymerization reaction may be mainlyactivated by a chemical mechanism (self-cure). However, Keywords: degree of conversion; light-activation; it has been shown that dual-polymerized resin cementsmight depend on being exposed to light to achieve better Correspondence to Dr. André L. Faria-e-Silva, Department of Restorative Dentistry, Piracicaba Dental School, State University One of the most widely-used commercial dual-cured of Campinas, Av. Limeira, 901 – 13414-903 – Piracicaba, SP, resin cements is Panavia F (Kuraray Co., Osaka, Japan).
This system consists of two pastes and a self-etching primer (ED Primer) containing co-initiators, and it is Fax: +55-19-21065218E-mail: [email protected] recommended that the primer should be applied to the substrate before cementation. Until the present time, the USA) equipped with an attenuated total reflectance device effect of ED Primer on the properties of Panavia F had not composed of a horizontal ZnSe crystal, with a 45° mirror been clarified. Studies evaluating the polymerization and angle (Pike Technologies; Madison, WI, USA). Equal mechanical properties of this cement usually do not use amounts (27 mg) of base and catalyst pastes were weighed the primer. For instance, Kumbuloglu et al. (6) observed on an analytical balance, mixed for 15 s and placed onto that Panavia F is extremely dependent on light exposure the crystal. The material was covered with a Mylar strip to obtain better mechanical properties, and Garcia et al.
to avoid polymerization inhibition by contact with oxygen.
(7) detected lower bond strength to dentin when the cement A disc (2 mm thick × 10 mm in diameter) of resin was not light-cured; however, these authors did not use ED composite (Filtek Z250; 3M ESPE, St. Paul, MN, USA), shade A2, was prepared to simulate an overlaying On the other hand, on using ED Primer, Piwowarczyk laboratory-processed composite restoration. The disc was et al. (8) found that Panavia F presented higher bond placed over the Mylar strip and light-activation was carried strength after thermal cycles and water storage when the out through the composite for 20 s, with the light guide material was self-activated. It seems reasonable to think tip of the curing unit (Optilux501; Demetron Kerr, Orange, that the previously mentioned results (7,8) are related to CA, USA – 600 mW/cm2) placed in contact with the disc.
the non-application of ED Primer before luting, and Additionally, a self-activated group was obtained by therefore it is important to evaluate its effect on the luting shielding the luting material from the curing light.
In order to evaluate the impact of ED primer on the The aim of this study was to evaluate the DC and the polymerization of Panavia F, one drop of each of the rate of polymerization (Rp) of Panavia F when self- or dual- primer liquids A and B was mixed for 10 s and gently air- activated, and the influence of either using or not using dried for 5 s for solvent evaporation. Thereafter, 0.1 µL the primer containing co-initiators mixed with the material.
(1.4 mg) of this solution was dispensed onto a glass slab The working hypothesis was that the polymerization using a micropipette (model NPX2; Nichipet EX, Santa process of the dual-cured material would not be dependent Clara, CA, USA) and mixed with the base and catalyst on light exposure provided that the primer containing co- pastes of the dual cement for 15 s. The volume of ED Primer was determined after pilot experiments: after mixing theprimer with the resin cement, the mixture had a similar Materials and Methods
aliphatic-to-aromatic C=C peak ratio as that of the cement The dual-cured resin cement Panavia F and the self- etching primer ED Primer were tested. The composition To measure the DC, the IR Solution software (Shimadzu) of the materials is shown in Table 1. The DC of the luting was used in the monitoring scan mode with Happ-Genzel agent was measured using a Fourier transform infrared apodization, for collecting spectra in the 1,665 to 1,580 spectrometer (Prestige21; Shimadzu, Columbia, MD, cm–1 range, with resolution of 4 cm–1. With this setup, one scan was acquired every 6 s during polymerization. All (5 s) was lower than that for the dual-cured mode without analyses were performed under controlled temperature (23 ± 2°C) and humidity (60 ± 5%) conditions. The DC polymerization reaction was observed, but a continuous was calculated using a baseline technique (9), considering increase in conversion was observed until a final DC of the intensity of aliphatic C=C stretching vibration (peak approximately 74% was reached (Fig. 1). This value was height) at 1,635 cm–1 and using the symmetric ring higher than that observed for the dual-cured group without stretching at 1,608 cm–1 as an internal standard, from both polymerized and unpolymerized samples.
For the self-cured mode, the use of ED Primer promoted DC for each scan was determined by subtracting the a continuous increase in conversion during the first 500 percentage of remaining aliphatic C=C from 100%.
s, when the cement reached a DC of around 60% (Figure Conversion vs. time data was plotted and Hill’s three- 1). In addition, this group had a DC of approximately parameter non-linear regressions were used for curve 75% after 1 h. As shown in Fig. 2, the R max fitting. As the coefficient of determination was greater than than the values obtained without ED Primer, and the peak 0.9 for all curves, the Rp (%.s–1) was calculated using the in the polymerization rate curve was displaced to the left data resulting from the non-linear regressions, and the (around 1100 s for self-cured mode without ED Primer vs.
100 s for self-cured mode with ED Primer).
Discussion
The DC vs. time curves are shown in Fig. 1. Logarithmic The results of the present study indicated that the use time scale was used for a better comparison of the tested of a primer containing co-initiators is essential for the conditions. For the dual-cured mode without using ED polymerization of resin luting agent when it is not exposed Primer, a rapid increase in DC was found in the first 20 s to polymerizing light. The manufacturer classifies Panavia of the reaction. After this period, the reaction speed F as a dual-cure resin cement, that is, the material should decreased, reaching a plateau at 100 s, when the DC was be polymerized by both chemical and light activation.
around 60%. Without light-activation (self-cured mode) The photoinitiator system of the luting agent is based on and primer, the polymerization reaction only started after camphoroquinone, which absorbs energy when it is exposed approximately 500 s, and a continuous increase in DC until to visible light in the 400 to 500 nm wavelength range, and 2500 s was found. However, conversion stabilized with a reacts with tertiary amine to form an excited state complex that breaks down into reactive free radicals (10). On the With regard to the impact of ED Primer on the Rp, a rapid other hand, self activation is obtained through the reaction increase in DC in the first 60 s was found for the dual-cured between benzoyl peroxide and tertiary amine, generating mode. However, as shown in Fig. 2, the R max free radicals that will break the aliphatic C=C and initiate Fig. 1 Progress of polymerization of Panavia F conversion Fig. 2 Variation of rate of reaction of Panavia F for the four tested conditions (slopes of curves of Fig. 1).
slowing down the polymerization process. Indeed, the The slower reaction and the reduced DC of self-cured polymerization reaction occurred faster when the cement Panavia F when not mixed with ED Primer might be the was light-activated without using the primer. Nevertheless, result of a low amount of tertiary amine (diethanol-p- might be beneficial in clinical practice, toluidine) in the catalyst paste (11). The rationale is that as reduced rates of polymerization are generally linked with the mixture of the primer and cement may increase the lower shrinkage stress development (14).
amount of amine, improving the polymerization reaction, However, the reduction in the polymerization rate might and increasing the final DC. In addition, the primer is also be associated with the formation of fewer polymer much less viscous than the catalyst paste of the cement, growth centers, which could favor the formation of loosely and therefore the mixture of the co-initiators within the cross-linked polymers, with poorer mechanical properties bulk of the material is probably better when the primer is (15). Nonetheless, it is difficult to predict whether alteration applied. Another potential explanation for the beneficial in the Rp could alter the polymer network formation.
impact of ED Primer is that it contains T-isopropylic Moreover, although no additional increase in DC after 1h benzenic sodium sulfinate as a co-initiator in primer liquid was observed for any group in the present study, longer B. This salt might react with the acid resin monomers post-curing periods and the development of mechanical present in primer A, and with the resin cement itself, to properties should be evaluated in further studies.
produce free-radicals that would enhance the polym- According to the present results, the use of a primer containing accelerators and co-initiators was advantageous Most manufacturers recommend that clinicians should for increasing the DC and Rp of the dual-cured resin wait at least 5 min before finishing and polishing a recently cement system tested here; the use of the primer would luted restoration, as they would generally be placed under potentially increase the conversion of double bonds in occlusal loads approximately 10 min after the luting regions with compromised access to light. However, this procedure. In the present study, after 5 min, the luting agent beneficial effect would not occur in procedures such as the had a DC higher than 60% in the dual-cured mode, resin-coating technique (16), where the adhesive system irrespective of whether or not ED Primer was used.
is covered with low-viscosity composite to produce a tight However, a 2-mm-thick resin composite was used to seal that would reduce pulp irritation and post-operative simulate indirect light-activation, and it should be sensitivity. Therefore, the use of resin cement after the self- considered that the light reaching the cement layer might etching protocol recommended by the manufacturer would vary as a function of different curing devices and different be preferable, due to improvement in DC.
thicknesses, shades or opacities of the intervening It is also important to emphasize that there is a limitation involving the Rp data for light-cured samples, since one On the other hand, without light-activation and without scan was acquired every 6 s, and the photo-polymerization the primer, no significant conversion was found after 5 or reaction is very fast. Moreover, the effect of any primer 10 min, and it is assumed that this material would not containing co-initiators may occur mainly at the interface withstand the occlusal loading or even the finishing between the resin cement and the primer layer, and thus procedures in clinical practice. Nonetheless, the DC only a few micrometres thickness of the cement may increased to 52 and 65% at 5 and 10 min, respectively when undergo increase in DC. The remaining material would the ED Primer was used. These results again indicate the poorly polymerize when not exposed to light. The mixture importance of ED Primer for proper polymerization of of the primer and luting materials would overcome this Panavia F; the luting material becomes independent of the problem, but care should be taken to use a low proportion light when the primer is used. In other words, the luting of ED Primer in order not to decrease the working time material achieves proper polymerization when the ED of the Panavia F drastically, and impair the luting procedure.
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