RESEARCH AND EDUCATION
Effect of a zirconia primer on the push-out bond strength of zirconia posts to root canal dentin Mahshid Torabi Ardakani, DDS,a Rashin Giti, DDS,b Masume Taghva, DDS,c and Samane Javanmardi, DDSd Excessive loss of coronal tooth ABSTRACT structure and insufﬁcient reStatement of problem. The retention of zirconia ceramic posts to root canal dentin with resinmaining root structure for the based luting cements is relatively poor. retention of restorative matePurpose. The purpose of this in vitro study was to evaluate the effect of a new zirconia primer, a rials necessitate the use of a mixture of organophosphate and carboxylic acid monomers, on the push-out bond strength of post and core in some endzirconia posts to root canal dentin. odontically treated teeth.1 Material and methods. The root canals of 40 extracted human maxillary central incisors were Selecting the optimum restoraendodontically treated and the post spaces were prepared. Zirconia posts were luted with 2 tion for endodontically treated different resin luting agents (Panavia F and Clearﬁl SA luting cements) with and without the zirconia anterior teeth is determined by primer (Z-Prime Plus; Bisco). Three segments, each 2 mm high, were cut perpendicular to the post the demands of esthetics and from each root. Bond strength was determined by pushing out the post with a universal testing strength.2-4 Cast gold posts have machine. Three-way ANOVA and the Tukey HSD test was used to assess the effects of the zirconia primer, the 2 different resin luting cements, and different thirds of the root canal (a=.05). a long-term clinical success rate.5,6 With translucent ceramic Results. The zirconia primer signiﬁcantly increased the push-out bond strength of zirconia posts to crowns, the effect of the abutroot canal dentin. Clearﬁl SA luting cement provided signiﬁcantly higher bond strength than did ment shade on the ﬁnal shade of Panavia F. For all experimental groups combined, bond strength decreased from the coronal to the apical section. the restoration is a concern. In a ceramic crown with less than 1.6 Conclusions. A zirconia primer based on organophosphate/carboxylic acid monomers mm thickness, the color of the increased the bond strength of zirconia posts to root canal dentin bonded with both resin luting cements. (J Prosthet Dent 2015;-:---) underlying core might affect the esthetics of the deﬁnitive restoration.7 Root discoloration and a blue-gray effect on the post retention is one of the most common reasons for the gingival tissues are another esthetic consequence of cast failure of post-retained restorations.18,19 Accordingly, 8,9 posts. clinicians need to be aware of the bond strengths of The wide range of esthetic post systems, including various posts and their retention in order to reduce the ﬁber-reinforced composite resin posts and zirconia risk of root fracture. The use of adhesive cements to ceramic posts, are available.10-12 The use of zirconia as a cement post materials in the root canal can reinforce the post and core material was ﬁrst introduced in 199313 tooth structure and improve the retention of the post and because of its excellent mechanical properties, including the crown.20,21 To improve the bonding of resin cements high chemical stability, modulus of elasticity, and to silica ceramics, hydroﬂuoric acid (5-9.5%) is used to strength, as well as its esthetic properties.14-17 The loss of produce a porous surface, followed by the application of a
Supported by the Vice-Chancellory of Research, Shiraz University of Medical Science (grant 6329). This article is based on the thesis by R.G. a Private practice, Shiraz, Iran. b Resident, Department of Prosthodontics, School of Dentistry, Shiraz University of Medical Sciences, Shiraz, Iran. c Resident, Department of Prosthodontics, School of Dentistry, Shiraz University of Medical Sciences, Shiraz, Iran. d Resident, Department of Endodontics, School of Dentistry, Shiraz University of Medical Sciences, Shiraz, Iran.
THE JOURNAL OF PROSTHETIC DENTISTRY
Clinical Implications This in vitro study suggests that the application of a zirconia primer based on organophosphate/ carboxylic acid (Z-Prime Plus) with resin luting cements can improve the bond strength of zirconia posts to root canal dentin.
silane coupling agent to form a siloxane network with the silica in the ceramic material.22 However, this reaction is not effective for zirconia ceramics because of the lack of a silica phase.23-25 Speciﬁc monomers have been developed to improve the zirconia bond to adhesive resins, including 10-methacryloxy decyl dihydrogen phosphate (MDP),26-29 4-methacryloxy ethyl trimellitic anhydride (4-META), and other monomers.30,31 A new approach to improving the zirconia-resin bond strength involves mixing organophosphate and carboxylic acid monomers to form a zirconia primer. The organofunctional part of organophosphate monomer can be copolymerized with the monomers of resin luting agents, and its phosphoric acid groups are thought to create a bond with the metal oxide in zirconia.32 The other monomer in this primer is a carboxylic acid, which also contributes to the development of the bond.33 Because no study had focused speciﬁcally on this issue, the current study was designed to evaluate the effect of this zirconia primer (Z-Prime Plus; Bisco Inc) on the push-out bond strength of zirconia posts to root canal dentin with 2 different adhesive resin cements. The ﬁrst test null hypothesis was that the Z-Prime Plus primer cannot enhance the bond strength of zirconia posts to root canal dentin. The second test null hypothesis was that the bond strength of zirconia posts to root canal dentin does not vary between the 2 resin luting cements. The third null hypothesis was that the bond strength of zirconia posts to root canal dentin does not vary regionally. MATERIAL AND METHODS Forty single-rooted human maxillary permanent central incisors were used, after receiving approval from the ethics committee of Shiraz School of Dentistry. These teeth had been recently extracted from patients who required periodontal treatment. The inclusion criteria were absence of root caries or cracks and a 13 mm root length. Each tooth was decoronated with a double-faced diamond disk (DeguDent GmbH) 2 mm coronal to the cement-enamel junction. All root canals were instrumented by an endodontist (S.J.). The root canals were irrigated with 3% NaOCl, cleansed, and shaped with nickel-titanium rotary instruments (size S1, S2, and F3, Protaper; Dentsply Maillefer). Then the root canals were
THE JOURNAL OF PROSTHETIC DENTISTRY
rinsed with distilled water, dried with paper points, and obturated with gutta percha (Guttapercha; Ariadent) by using AH Plus sealer (AH Plus; Dentsply Maillefer). After endodontic treatment, the teeth were stored in water at room temperature (23 ±1 C) for 24 hours. Post spaces were prepared with the speciﬁc drills for the 1.4 mm zirconia posts (Cosmopost; Ivoclar Vivadent AG) produced by the manufacturer. A minimum of 4 mm of root ﬁlling material remained in the apical part of the root canals. After post space preparation, the root canals were rinsed with 5 mL of distilled water to remove the debris and dried with paper points (Paper Points; Ariadent). Specimens were divided into 4 groups (n=10) according to the type of adhesive cement and whether zirconia primer was applied on the zirconia posts as follows, ZP, zirconia primer+Panavia F; ZC, zirconia primer+Clearﬁl SA luting cement; P, Panavia F; and C, Clearﬁl SA luting cement. Table 1 summarizes the materials used in this study. The root canal dentin was etched for 15 seconds with 37% phosphoric acid gel (Denﬁl Etchant; Vericom Co Ltd) and rinsed for 1 minute with water. Excess water was removed with paper points without desiccating the dentin. For the ZP and ZC groups, zirconia posts were treated with an experimental zirconia primer and left undisturbed for speciﬁc times (reaction time) according to the manufacture’s instruction. The Panavia F resin luting system was used to bond zirconia posts to root canal dentin in the ZP and P groups. For these groups, equal amounts of ED primer liquids A and B were mixed and applied inside the canal with a brush and allowed to stand for 60 seconds. Equal amounts of Panavia F paste A and B were then mixed and applied to the canal with a Lentulo spiral drill (Mani Inc, Japan). The zirconia posts were covered with resin cement and seated to full depth with ﬁnger pressure. Excess cement was removed, and the teeth were polymerized for 40 seconds with a light-polymerization unit (Radiplus LED; SDI) at 1200 mW/cm2 on the cervical surface of the root canal in the direction of the long axis and obliquely on the buccal and lingual surfaces. For the specimens in the ZC and C groups, zirconia posts were cemented with the self-adhesive Clearﬁl SA luting cement. This cement was mixed according to the manufacturer’s instructions and applied to the root canals with a spiral paste ﬁller (Lentulo; Z-Prime Plus; Bisco). The seated posts were polymerized with the technique used for Panavia F after post insertion. After 24 hours, each root was sectioned perpendicularly to its long axis with a precision saw (Isomet; Buehler Ltd) at low speed under cooling water to make 4 root segments 2 mm in thickness. The ﬁrst slice was not used because it contained coronal dentin. The remaining segments represented the coronal, middle, and apical thirds of the roots (Fig. 1).
Torabi Ardakani et al
Table 1. Materials used and their characteristics Name
Type of Material
Ivoclar Vivadent AG
Organophosphate monomer, carboxylic acid monomer, other monomers
Adhesive resin cement
HEMA, MDP, 78w% silanized silica and silanized colloidal silica
Kuraray Medical Inc
Clearﬁl SA luting cement
Self-adhesive resin cement
Bis-GMA, MDP, TEG-DMA silanized barium glass, silanized colloidal silica
Kuraray Noritake Dental Inc
Figure 1. Sectioning of post specimens for push-out test.
The thickness of each root segment was checked with a digital caliper (Mini Electronic Caliper; Insize Co Ltd). The specimens were submitted to a micro-push-out test on a universal testing machine (Z020; Zwick/Roell). A compressive load was applied at 1 mm/min in the apicocoronal direction until failure occurred (Fig. 2). The bond strength was calculated in MPa by dividing the load at failure (N) by the area (mm2) of the bonded interface. The surface area of the bonded surface was calculated using the equation A=2pr×h, where A is the area of the bonded interface, p=3.14, r is the radius of the post segment (mm), and h is the thickness of the root segment (mm).34 Three-way ANOVA was used to assess the effects of the zirconia primer, different resin luting cements, and different sections of the root canal in this context. The Tukey HSD test was used for pairwise comparisons of different root segments. Software (SPSS 15.0; IBM Corp) was used for statistical analysis (a=.05). RESULTS The mean push-out bond strength values (MPa) and standard deviations for each group are listed in Table 2. All specimens fractured predominantly at the interface between the post and resin luting cement. The mean push-out bond strength for groups using the zirconia primer was 14.57 ±7.25 MPa, signiﬁcantly higher than the mean value in the other groups (9.28 ±6.78 MPa) (P