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Effectiveness of different adhesive primers on the bond strength between an indirect composite resin and a base metal alloy
Effectiveness of different adhesive primers on the bond strength between an indirect composite resin and a base metal alloy Aspasia Sarafianou, DDS, PhD,a Ioannis Seimenis, DDS, MSc,b and Triantafillos Papadopoulos, DDS, PhDc School of Dentistry, National and Kapodistrian University of Athens, Greece Statement of problem. There is a need for achieving reliable chemical bond strength between veneering composites resins and casting alloys through the use of simplified procedures. Purpose. The purpose of this study was to examine the shear bond strength of an indirect composite resin to a Ni-Cr alloy, using 4 primers and 2 airborne-particle-abrasion procedures. Material and methods. Fifty-six Ni-Cr (Heraenium NA) discs, 10 mm in diameter and 1.5 mm in height, were fabricated. Twenty-four discs were airborne-particle abraded with 50-μm Al2O3 particles, while another 24 were airborneparticle abraded with 250-μm Al2O3 particles. The following primers were applied on 6 discs of each airborne-particle-abrasion treatment group: Solidex Metal Photo Primer (MPP50, MPP250), Metal Primer II (MPII50, MPII250), SR Link (SRL50, SRL250), and Tender Bond (TB50, TB250). The Rocatec system was used on another 6 discs, airborne-particle abraded according to the manufacturer’s recommendations, which served as the control group (R). Two more discs were airborne-particle abraded with 50-μm and 250-μm Al2O3 particles, respectively, to determine the Al content on their surfaces, without any bonding procedure. The indirect composite resin used was Sinfony. Specimens were thermally cycled (5°C and 55°C, 30-second dwell time, 5000 cycles) and tested in shear mode in a universal testing machine. The failure mode was determined with an optical microscope, and selected specimens were subjected to energy dispersive spectroscopy (EDS). Mean bond strength values were analyzed using 2-way ANOVA followed by Tukey’s multiple comparison tests (α=.05) and compared to the control group using 1-way ANOVA followed by Tukey’s multiple comparison tests (α=.05). Results. The groups abraded with 50-μm particles exhibited significantly higher bond strength compared to the groups abraded with 250-μm particles. Group MPII50 exhibited the highest mean value (17.4 ±2 MPa). Groups MPP50, MPP250, and TB50, TB250 showed adhesive failures and significantly lower bond strength compared to group R. Groups MPII50, MPII250, and SRL50, SRL250 showed combination failures and no significant difference compared with group R. EDS revealed interfacial rather than adhesive failures. Conclusions. Airborne-particle abrasion with 50-μm Al2O3 particles may result in improved bond strength, independent of the primer used. The bond strength of Metal Primer II and SR Link specimens was comparable to that of specimens treated with Rocatec. (J Prosthet Dent 2008;99:377-387)
Clinical Implications
The development of a stable chemical bond between indirect veneering composite resins and metal frameworks can provide a reliable, esthetic, and cost-effective alternative to metal ceramic restorations. The results of this study indicate that clinically satisfactory metal-resin bond strength can be achieved by airborne-particle abrading Ni-Cr castings with 50-μm Al2O3 particles and using the proper adhesive primer. Presented at the International Association of Dental Research Pan-European Federation meeting, Dublin, Ireland, September 2006. Clinical Instructor, Department of Prosthodontics. Postgraduate student, Department of Prosthodontics. c Associate Professor, Department of Biomaterials. a
b
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Volume 99 Issue 5 The use of indirect light-polymerized composite resins has recently increased, due to the improvement in the properties of composite resin materials. New products exhibit enhanced mechanical properties, convenient handling, favorable esthetics, effective intraoral repair, and abrasion similar to natural tooth hard tissues.13 Initially, indirect composite resins were combined exclusively with mechanical retention.4,5 Resin veneer restorations based only on mechanical retention have demonstrated microleakage at the resin-metal interface, attributed to debonding as a result of repeated thermal and load cycling intraorally.6-8 In recent decades, a number of alloy surface modifications have been developed to achieve chemical adhesion.8-11 Despite these efforts, composite-to-metal bond strength remains inferior when compared to porcelain, resulting in intraoral failures. Systems used to enhance chemical bonding include silanes as coupling agents on a pyrollytically treated (Silicoater; Heraeus Kulzer GmbH, Wehrheim, Germany) or tribochemically treated (Rocatec; 3M ESPE, Seefeld, Germany) metal surface, acrylate monomers (Sebond; Schutz Dental GmbH, Rosbach, Germany), polyfluor methacrylates (SR Link; Ivoclar Vivadent, Schaan, Liechtenstein) as bonding agents, and tin plating (OVS; DeguDent GmbH, Hanau, Germany) of the alloy surface.12-16 In the Rocatec procedure, a highpurity aluminum oxide (Rocatec Pre; 3M ESPE) pretreats the metal framework to clean and activate the surface and standardize the surface roughness. A silicate layer is then created by airborne-particle abrasion with a special abrasive (Rocatec Plus; 3M ESPE), the particles of which are melted and retentively anchored on the surface. A silane layer (ESPE Sil; 3M ESPE) is then applied on the silicate-coated surface to produce a chemical bond with the veneering material.14 However, the previously mentioned methods are technique sensitive, time
consuming, and require the use of special devices. There is also conflicting data regarding the durability of the bond they provide, especially after extensive thermal cycling.17,18 Recently introduced adhesive primers simplify the resin adhesion procedure. After airborne-particle abrasion of the metal surface, they are easily and quickly applied with a brush. These primers contain carboxylic or phosphoric acid functional monomers, which react with oxides on the airborne-particleabraded alloy surface and the resin opaquer of the composite resin. Base metal alloys have shown increased bond strength to veneering resin, when surfaces are treated with metal primers containing carboxyl or phosphoric acid derivatives.19-22 Also, many investigators have tested the efficacy of various surface treatments on the improvement of the bond strength, in combination with different dental alloys and ceramics.23-26 In addition to micromechanical retention, airborneparticle abrasion has an important role in the development of chemical adhesion. Several investigators have reported that when abrading the metal surface with Al2O3 particles, oxides are released, generating a chemical bond with adhesive primers.27-30 The objective of this study was to examine the shear bond strength of a commercial indirect resin to a Ni-Cr alloy, using 4 different adhesive primers. The effect of airborne-particle abrasion with differently sized Al2O3 particles on the bond strength was also investigated. The null hypotheses were that the use of different adhesive primers would provide bond strength similar to the control group, and the use of differently sized airborne-particleabrasion particles would not have any effect on the bond strength.
MATERIAL AND METHODS Fifty-six wax discs, 10 mm in diameter and 1.5 mm in height, were fabricated. A U-shaped retentive wax loop was connected to the flat surface of the disc for retention of the casting
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in the embedding acrylic resin (Orthoplast; Vertex-Dental BV, Zeist, The Netherlands). The wax patterns were cast using a fixed prosthodontic Ni-Cr alloy (Heraenium NA; Heraeus Kulzer GmbH), according to the manufacturer’s instructions. Twenty-four castings were airborne-particle abraded using 50-μm Al2O3 particles (Treibacher Industrie AG, Althofen, Austria), while another 24 castings were airborne-particle abraded using 250-μm Al2O3 particles (Treibacher Industrie AG). Airborneparticle abrasion was performed for 5 seconds at 6 Atm air pressure, with a 45-degree angle at a 10-cm nozzlemetal surface distance. All specimens were cleaned in an ultrasonic bath for 5 minutes and dried using an oilfree air stream. The following primers were applied on 6 discs of every group treated with airborne-particle abrasion: Solidex Metal Photo Primer (MPP50, MPP250), Metal Primer II (MPII50, MPII250), SR Link (SRL50, SRL250), and Tender Bond (TB50, TB250) (Table I). All primers were applied with a brush in a uniform coating and allowed to air dry, according to the manufacturer’s instructions. The Rocatec system was used on another 6 discs (R) and served as the control. The discs were airborneparticle abraded according to the manufacturer’s directions, using a special airborne-particle-abrasion unit designed for the tribochemical silica-coating procedure (Rocatec Jr. Bonding System; 3M ESPE) (Table I). Airborne-particle abrasion was performed initially with 110-μm Al2O3 particles (Rocatec Pre; 3M ESPE) for 10 seconds to clean the surface. A second airborne-particle abrasion treatment was performed for 13 seconds using a special alumina powder (110 μm) with added silica particles (Rocatec Plus; 3M ESPE) to form a silica surface layer. Airborne-particle abrasion was performed at 2.8 Atm air pressure, at a distance of 10 cm. All specimens were cleaned in an ultrasonic bath for 5 minutes and dried using an oil-free air stream. On the
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Table I. Tested materials and groups Test Group Codes
Bonding Procedure
Manufacturer
MPP50 MPP250
Solidex Metal Photo Primer LOT No. 120495
Shofu, Kyoto, Japan
MPII50 MPII250
Metal Primer II LOT No. 0508082
GC Corp, Tokyo, Japan
SRL50 SRL250
SR Link LOT No. H15063
Ivoclar Vivadent, Schaan, Liechtenstein
TB50 TB250
Tender Bond LOT No. 2004006269
Micerium SpA, Avegno, Italy
Rocatec ESPE Sil LOT No. 227648
3M ESPE, Seefeld, Germany
R
MPP50, MPII50, SRL50, TB50 = Airborne-particle abraded with 50-µm Al2O3; MPP250, MPII250, SRL250, TB250 = Airborne-particle abraded with 250-µm Al2O3; R = Airborne-particle abraded with 110-µm Al2O3 (Rocatec Pre) and 110-µm silica-containing Al2O3 powder (Rocatec Plus)
specimens in group R, a silane coupling agent (ESPE Sil; 3M ESPE) was applied and allowed to air dry for 5 minutes. Two more castings were airborneparticle abraded, with 50-μm and 250-μm Al2O3 particles, respectively. Specimens were cleaned in an ultrasonic bath for 5 minutes and dried using an oil-free air stream. They were left free of any bonding procedure. For the specimens to be bonded, an adhesive tape with a central hole measuring 5 mm (Tesa AG, Hamburg, Germany) in diameter was positioned over the airborne-particle-abraded surface to determine the bonding area. An indirect microhybrid composite resin (Sinfony; 3M ESPE) was used for the veneering of the primed alloy surfaces. Two layers of resin opaquer (Sinfony Resin opaquer, LOT No. 154502; 3M ESPE) were applied on the metal surface. Each layer was polymerized for 10 seconds using a light-polymerizing device (Visio Alfa; 3M ESPE) and then under vacuum in a special unit (Visio Beta; 3M ESPE), according to the manufacturer’s instructions. A transparent plastic cylindrical tube with an internal diameter of 5 mm
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was positioned perpendicular to the treated alloy surface to add the veneering portion of the specimen. Two layers of dentin veneering resin (Sinfony Composite, LOT No. 224895; 3M ESPE), with a total thickness of 2 mm, were applied and polymerized following the same procedures. Thermal cycling was performed between 5°C and 55°C for 5000 cycles with a dwell time of 30 seconds in each bath, according to ISO 10477.31 All specimens were tested for shear bond strength in a universal testing machine (Tensometer 10; Monsanto, Akron, Ohio) at a crosshead speed of 0.5 mm/min. Failure load values were divided by the bonding area to determine the bond strength. Fractured surfaces were examined under an optical microscope (Eclipse ME 600; Nikon, Tokyo, Japan) at x20 magnification. The mode of fracture was arbitrarily classified as adhesive when the percentage of the veneering material remaining on the metal surface was less than 25%, cohesive when it was more than 75%, and combination when it ranged between 25 and 75%.32 The percentage distribution of the area covered by the resin was cal-
culated with a software program (SigmaScan Pro; SPSS Inc, Chicago, Ill). Selected specimens of all groups were examined using a scanning electron microscope (SEM) (Quanta 200; FEI Co, Hillsboro, Ore) equipped with a super ultrathin Beryllium window x-ray energy dispersive spectroscopy (EDS) (Sapphire; Edax Intl, Mahwah, NJ) with elemental area analysis (mapping) and elemental spot analysis, to determine the composition of characteristic sites of the fractured surfaces. Also, mapping was performed on the 2 airborne-particle-abraded nonprimed specimens to determine the aluminum (Al) content on their surfaces. Bond strength values were statistically analyzed using a 2-way ANOVA followed by Tukey’s multiple comparison tests at a significance level of α=.05, with the airborne-particleabrasion conditions (size of Al2O3 particles) and metal primers as factors. Mean bond strength values of each group were compared to the control group using the 1-way ANOVA followed by Tukey’s multiple comparison test (compared to reference) at a significance level of α=.05.
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Volume 99 Issue 5 RESULTS Mean shear bond strength values are presented in Table II. Two-way ANOVA (Table III) showed that there were significant differences among groups (P<.001). In addition, there was not a significant interaction between Al2O3 grain size and primers. Tukey’s multiple comparison tests showed that the group airborne-particle abraded using 50-μm Al2O3 particles exhibited significantly higher shear bond strength in comparison to the group abraded with 250-μm Al2O3 particles. Significant differ-
found between specimens treated with Metal Primer II and SR Link for either of the Al2O3 particle sizes used, when compared to Rocatec (Table IV). The mode of failure observed by optical microscopy (Fig. 1) (Table V) was adhesive for all Solidex Metal Photo Primer and Tender Bond groups. Specimens treated with Metal Primer II and SR Link, as well as Rocatec specimens, exhibited a combined, predominantly adhesive mode of failure. The observation of images obtained with SEM revealed that the surface relief of specimens
ences were found between all tested groups, except for MPP50 with TB50 and MPP250 with TB250, as indicated in Table II. The group showing the highest mean bond strength was the MPII50 (17.4 ±2 MPa). The 1-way ANOVA (F=18.529, df=8, and P<.001) showed that there were statistically significant differences among groups. Tukey’s multiple comparison tests revealed that specimens treated with Solidex Metal Photo Primer and Tender Bond exhibited significantly lower values compared to Rocatec, for both Al2O3 particle sizes used. No significant differences were
Table II. Mean shear bond strength values (in MPa) and SD of groups MPP50, MPP250, MPII50, MPII250, SRL50, SRL250, TB50, and TB250
Al2O3 Particle Size/Groups
MPP
MPII
SRL
TB
50 µm
9.4 (3.2)1,a
17.4 (2.2)1,c
13.0 (3)1,d
9.0 (3.1)1,a
250 µm
6.0 (1.0)2,a
15.2 (2.7)2,c
12.8 (2.8)2,d
3.9 (1.3)2,a
Same superscript number indicates no significant differences between airborne-particle-abrasion conditions for particular primer (P>.05). Same superscript lowercase letter indicates no significant difference between primers within airborneparticle-abrasion condition (P>.05).
Table III. Two-way ANOVA Source of Variation
df
SS
MS
F
P
Primer
3
754.65
251.55
38.94
<.001
Particle size
1
103.28
103.28
15.99
<.001
Primer x particle size
3
35.27
11.76
1.82
.159
Residual
40
258.39
6.46
Total
47
1151.59
24.50
Table IV. Mean shear bond strength values (in MPa) and SD of tested groups and control group Al2O3 Particle Size/Groups
MPP
MPII
SLR
TB
50 µm
9.4 (3.2)a
17.4 (2.2)b
13.5 (3)b
9.3 (3.1)a
250 µm
6 (1)a
15.2 (2.7)b
12.8 (2.8)b
3.9 (1.3)a
Rocatec surface treatment
15.9 (3.3)b
Same superscript lowercase letter indicates no significant difference between tested groups (P>.05).
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A
B
C
D
E
F
1 Representative images from optical microscope (x20). Gray surfaces represent metal and white surfaces represent resin fragments. A, SRL50 specimen (combined, predominantly adhesive mode of failure). B, SRL250 specimen (predominantly adhesive mode of failure). C, MPII50 specimen (predominantly adhesive mode of failure). D, MPII250 specimen (predominantly adhesive mode of failure). E, TB50 specimen (adhesive mode of failure). F, TB250 specimen (adhesive mode of failure).
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G
H
I 1 continued (2 of 2) G, MPP50 specimen (adhesive mode of failure). H, MPP250 specimen (adhesive mode of failure). I, R specimen (combined, predominantly adhesive mode of failure).
Table V. Mode of failure of groups tested Al2O3 Particle Size/Groups
MPP
MPII
SLR
TB
50 µm
adhesive
combination, PA
combination, PA
adhesive
250 µm
adhesive
combination, PA
combination, PA
adhesive
Rocatec surface treatment
combination, PA
PA: Predominantly adhesive
airborne-particle abraded with 50μm Al2O3 particles was more pronounced than that of the specimens airborne-particle abraded with 250μm Al2O3 particles. SEM mapping of a representative adhesively failing specimen (x250) showed 40.7 wt% for Ni, 14.8 wt% for Cr, and 5.5 wt% for Mo (Fig. 2, A). SEM mapping of
a representative combined, predominantly adhesively failing specimen (SRL250) showed concentrations of 24.02 wt% for Ni, 8.8 wt% for Cr, and 3.16 wt% for Mo (Fig. 2, B). Additionally, the wt% content of C and Ti was 24.8 wt% and 0.68 wt% for TB 250, and 46.51 wt% and 1.65 wt% for SRL250, respectively. Spot analysis of
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selected sites of a representative adhesively failing specimen (MPP250) verified that the white area contained high amounts of silicon with almost complete absence of alloy elements, while the dark area contained phosphorous and high amounts of alloy elements (Fig. 3) (Table VI). Mapping on the 2 airborne-particle-abraded,
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A
B
C 2 A, SEM image and mapping of representative adhesively failing specimen (x250). B, SEM image and mapping of representative combined, predominantly adhesively failing specimen (SRL250).
A
Table VI. Quantitative (wt%) elemental spot analysis B
3 SEM image of representative adhesively failing specimen. Arrow A: Spot analysis of dark area. Arrow B: Spot analysis of white area.
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in dark and white areas of representative adhesively failing specimen (MPP250) (Fig. 3)
Cr
Ni
Mo
Si
P
Dark area (arrow A)
11.27
29.30
4.25
0.85
0.16
White area (arrow B)
0.61
1.35
0.27
36.77
0.01
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Volume 99 Issue 5 nonprimed specimens revealed higher Al concentrations for the specimen abraded with 50-μm Al2O3 particles (11.24 wt%), when compared to that abraded with 250-μm particles (10.86 wt%). Mapping of fractured surfaces revealed great reduction of Al concentrations for all groups, ranging from 60% to 80%.
DISCUSSION According to the results of this study, no significant differences in mean shear bond strength were found between Metal Primer II and SR Link primer and the Rocatec procedure, while Solidex Metal Photo Primer and Tender Bond presented significantly lower mean bond strength values compared to Rocatec. Thus, the results support rejection of the first null hypothesis, which stated that the use of different adhesive primers would provide bond strength similar to that of the control group. According to the requirements of the revised ISO 10477, the minimum acceptable shear bond strength value is at least 5 MPa.31 However, Matsumura et al23 suggest that the resinto-metal shear bond strength necessary for the achievement of clinically satisfactory results should exceed 10 MPa. Although the bond strength values exhibited in the present study by MPP and TB fulfilled the ISO requirements, they still remained lower than the limits of clinical acceptability. The values corresponding to SRL and MPII exceeded 10 MPa, presenting no significant difference when compared to Rocatec, and were judged as clinically acceptable. Both primers contain phosphoric acid derivatives which can react with the metal oxides, creating the necessary metal-phosphate bonds to promote bonding. This might be a possible explanation for their high bond strength. Considering the different experimental conditions used by other investigators (type of alloy and veneering resin, number of thermal cycles, airborne-particle abrasion with dif-
ferent sizes of Al2O3 particles), the values reported in the present study are within the range observed in similar studies.21,32 A Ni-Cr alloy was used by Seimenis et al,32 who found shear bond strength values of 12.61 MPa, 14.9 MPa, and 16.55 MPa for MPP in combination with 3 veneering composite materials, namely Solidex (Shofu, Kyoto, Japan), Artglass (Heraeus Kulzer GmbH, Werheim, Germany), and Signum+ (Heraeus Kulzer GmbH, Hanau, Germany). The specimens were airborne-particle abraded with 250-μm Al2O3 particles and thermal cycled for 5000 cycles. Under the same conditions, the mean shear fracture strength of MPP primer with Sinfony in the present study was 6 MPa. This difference can be attributed to the use of additional mechanical retention (150-μm beads) used in the former study. A Ni-Cr alloy was also used by Almilhatti et al,21 who reported a mean shear bond strength of 11.94 MPa for Solidex with Solidex Metal Photo Primer. Specimens were stored in distilled water at 37°C for 7 days, and metal was airborne-particle abraded with 100-μm Al2O3 particles. This value is similar to the mean shear bond strength observed when Solidex Metal Photo Primer was combined with Sinfony in the present study (9.4 MPa). The following studies,13,17,24 in which Co-Cr alloy was used, yielded conflicting results. Kim et al17 reported mean shear fracture values of 10.3 MPa for Sinfony combined with the Rocatec procedure, when subjected to 5000 thermal cycles. The corresponding value recorded in the present study was 15.5 MPa. This increased bond strength could be attributed to the different alloy used. Yoshida et al13 reported mean shear strength values of 37.0 MPa and 27.7 MPa for MPII, when specimens were airborne-particle abraded with 50-μm Al2O3 particles and thermally cycled for 0 and 20,000 cycles, respectively. Yanagida et al24 reported a shear bond strength of 13.2 MPa after extended thermal cycling, when a Ti-6Al-7Nb alloy was
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primed with MPII and airborne-particle abraded with 50-μm Al2O3 particles. This result is similar to the results of the present study (17.4 MPa), in which MPII was used for priming a Ni-Cr alloy. The relatively higher bond strength observed in the present study could be attributed to the lower number of thermal cycles used (5000 instead of 20,000) and the type of alloy. Petridis et al25 reported mean shear values of 14.1 MPa when Targis Link (Ivoclar Vivadent) was used to prime a high-noble dental alloy in combination with Targis (Ivoclar Vivadent) veneering material after airborne-particle abrasion with 50-μm Al2O3 particles. Specimens were thermal cycled for 2500 cycles. This value is similar to those of the present study (9.3 to 17.4 MPa), when a Ni-Cr alloy was airborne-particle abraded with 50μm Al2O3 particles and primed with different primers to bond with Sinfony veneering material, after 5000 thermal cycles. Matsumura et al23 found mean shear fracture values of 20.6 MPa and 16.2 MPa between a gold alloy airborne-particle abraded with 50-μm Al2O3 particles, primed with Metal Primer II, and a veneering composite resin, when thermal cycled for 0 and 20,000 cycles, respectively. These results correspond to the mean shear fracture value of the present study (17.4 MPa), when a Ni-Cr alloy airborne-particle abraded with 50μm Al2O3 particles and primed with MPII was used with Sinfony veneering material and thermal cycled for 5000 cycles. In a study similar to the one by Matsumura et al,23 Yoshida et al,2 using a Ag-Pd alloy, recorded mean shear fracture values of 13.1 MPa and 4.6 MPa, which were lower than the corresponding value of the present study (17.4 MPa). This could be due to differences in the type of alloy and the number of thermal cycles used. It should be noted that the previously mentioned results are indicative for the materials used (Heraenium NA alloy, Sinfony composite resin) and the experimental limitations of the present study.
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May 2008 Regarding the particle size of the abrasion procedure, the 50-μm Al2O3 particles resulted in significantly higher shear bond strength compared to 250-μm particles for all the primers. Thus, the results support rejection of the second null hypothesis, which stated that the use of differently sized airborne-particle-abrasion particles would not have any effect on the bond strength. SEM images showed that treatment with 50-μm Al2O3 particles produced a more pronounced relief compared to that obtained with 250μm particles. This may lead to better interlocking of the resinous material in the superficial irregularities, resulting in enhanced micromechanical retention of the veneering material and higher shear bond strength during the application of the debonding forces. These results are in accordance with the findings of Petridis et al,25 who concluded that the Al2O3 particle size (50 μm and 250 μm) influences the resin-to-noble alloy shear bond strength. The authors suggested that airborne-particle abrasion with 50-μm Al2O3 particles resulted in improved microtopography and possibly better wettability and penetration of the primers into the microirregularities of the surface. Also, Mukai et al30 reported that the bond strength of a composite resin to a silver palladium alloy was influenced by the size of Al2O3 particles. Papadopoulos et al28 concluded that using 250-μm Al2O3 particles resulted in a significant increase in the roughness of commercially pure titanium (cpTi) surfaces. These investigators reported that, independent of the Al2O3 particle size, microroughness improved the mechanical interlocking between cpTi and porcelain. Kern and Thompson27 and Papadopoulos et al28 found that after airborne-particle abrasion, Al2O3 particles remain embedded in the alloy. According to the results of the present study, mapping of the airborne-particle-abraded, nonbonded specimens revealed increased quantities of oxygen and aluminium on the alloy surface abraded with 50-μm
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Al2O3 particles, compared to the alloy abraded with 250-μm particles. The amount of Al found on the airborneparticle-abraded surfaces was 10.86 wt% for surfaces airborne-particle abraded with 250-μm Al2O3 particles and 11.67 wt% for those airborneparticle abraded with 50-μm particles. This is in agreement with the findings of Petridis et al,29 who also observed similar increased amounts of these 2 elements on airborne-particle-abraded surfaces. The authors suggested that smaller particles might be able to better penetrate the alloy surface and be retained. This could be another possible explanation for the increased bond strength associated with airborne-particle abrasion with 50-μm Al2O3 particles. The precise role of the Al2O3 particles in the bonding mechanism is not clearly known. It has been suggested that the active monomers of the metal primers bond to the particles, thus, enhancing bond strength.27 According to Yoshida et al,13 airborne-particle abrasion can form a passive film of metal oxides, to which carboxylic acid and phosphoric acid derivatives contained in the primers present an affinity. Ozcan et al11 report that the Rocatec system uses the mechanical energy of silica-covered aluminium grains as these are blasted onto the metal surface. Regardless of the Al2O3 grain size used, there was a significant difference in bond strength among all the primers, with the exception of the primers MPP and TB (Table II). The mode of failure for the same primer for both airborne-particleabrasion treatments was similar. This signifies that priming probably depends primarily on the chemical affinity of each primer to the oxides of the metal surface. According to the results of the present study, a relationship was found between the mode of failure and magnitude of bond strength. More specifically, groups presenting clinically acceptable bond strength exhibited combined, predominantly adhesive failures. In these groups (SRL50, SRL250, MPII50, and MPII250), the
bond strength observed was actually the cohesive strength of the resin opaquer, which was lower than the adhesive bond strength. However, groups MPP50, MPP250, TB50, and TB250, which presented lower bond values, exhibited adhesive failures. In 2 studies by Almilhatti et al21 and Seimenis et al, 32 in which MPP was used to prime Ni-Cr alloy bonded to Solidex resin, the mode of failure observed was primarily adhesive. This is in agreement with the results of the present study, in which similar experimental conditions were used. In another 2 studies,26,17 where the Rocatec technique was used to treat the surface of a Co-Cr alloy, the mode of failure was primarily cohesive. This is also in agreement with the results of the present study, considering the differences in the conditions under which each experiment was performed. The previously mentioned results of optical microscopy were verified by mapping of selected specimens. More specifically, in a specimen presenting adhesive failure (TB250), mapping showed increased wt% for Ni, Cr, and Mo (Fig. 2, A), compared to a specimen presenting combined, predominantly adhesive failure (SRL250) (Fig. 2, B). Also, the wt% content of C and Ti was lower for TB250 compared to SRL250. The decreased amount of carbon and Ti and the increased amount of nickel, chromium, and molybdenum found on the TB250 specimen, in comparison to the corresponding amounts of the same elements in the SRL250 specimen, suggest the presence of higher amounts of primer and/or resin opaquer in the latter. The amounts of silicon and titanium may represent remnants of the resin opaquer, while phosphorus (P) remnants of the primer. This is qualitatively verified by spot analysis on selected, differently colored sites of an adhesively failing specimen (MPP250) in Figure 3. Spot analysis of a dark area (arrow A) showed high amounts of the basic alloy elements (Ni, Cr, Mo), corresponding to adhesive failure. The detected amounts of
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Volume 99 Issue 5 P in the same area indicate the presence of primer remnants. Spot analysis of a white area (arrow B) showed lower amounts of the basic alloy elements, compared to the dark area, and increased amounts of Si, indicating remnants of the composite resin opaquer (Fig. 3 and Table VI). The presence of P in the TB250 specimen in amounts lower than in the SRL250 specimen supports the view that part of the primer was retained on the metal surface. This suggests a mode of failure different than that observed with the optical microscope. It seems that adhesive failure occurred also, in part, within the layers of the metalprimer-resin opaquer, with areas of metal remaining partially covered by the primer. Failures of this nature occurring between the layers of the adhesive system have been referred to by Kern et al26 as “interface failures.” The nature of the mode of failure requires further clarification in future studies. Careful interpretation in the clinical application of the results is suggested, as the design of the present study did not consider factors existing in the oral environment, such as dynamic fatigue loading and pH changes. The efficacy of the tested systems in providing reliable bond strength should be affirmed by future research, incorporating long-term clinical studies.
CONCLUSIONS Considering the limitations of the present study, the following conclusions were drawn: 1. The bond strength between the Ni-Cr alloy and the composite resin evaluated was significantly higher after airborne-particle abrasion of the cast surface with 50-μm Al2O3 particles compared to 250-μm particles, independent of the primer used. 2. Significant differences were found between all the tested groups, except for groups MPP50 with TB50 and MPP50 with TB50. Group MPII50 exhibited the higher mean shear bond strength (17.4 ±2 MPa).
3. No significant differences in mean shear bond strength were found between primers Metal Primer II and SR Link and Rocatec, while primers Solidex Metal Photo Primer and Tender Bond presented significantly lower mean bond strength values compared to Rocatec. 4. The mode of failure was combined and predominantly adhesive for primers Metal Primer II and SR Link, and adhesive for primers Solidex Metal Photo Primer and Tender Bond.
REFERENCES 1. Berge M. Properties of prosthetic resinveneer materials processed in commercial laboratories. Dent Mater 1989;3:77-82. 2. Jones RM, Goodacre CJ, Moore BK, Dykema RW. A comparison of the physical properties of four prosthetic veneering materials. J Prosthet Dent 1989;61:38-44. 3. Staffanou RS, Hembree JH Jr, Rivers JA, Myers ML. Abrasion resistance of three types of esthetic veneering materials. J Prosthet Dent 1985;53:309-10. 4. Shue SL, Nicholls JI, Townsend JD. The effect of metal retentive designs on resin veneer retention. J Prosthet Dent 1987;58:297-305. 5. Barzilay I, Myers ML, Cooper LB, Graser GN. Mechanical and chemical retention of laboratory cured composite to metal surfaces. J Prosthet Dent 1988;59:131-7. 6. Staffanou RS, Hembree JH Jr, Rivers JA, Myers ML, Kilgore JL. Leakage study of three esthetic veneering materials. J Prosthet Dent 1985;54:204-6. 7. Jones RM, Moore BK, Goodacre CJ, Munoz-Viveros CA. Microleakage and shear bond strength of resin and porcelain veneers bonded to cast alloys. J Prosthet Dent 1991;65:221-8. 8. Matsumura H, Kawahara M, Tanaka T, Atsuta M. Surface preparations for metal frameworks of composite resin veneered prostheses made with an adhesive opaque resin. J Prosthet Dent 1991;66:10-5. 9. Tanaka T, Fujiyama E, Shimuzu H, Takaki A, Atsuta M. Surface treatment of nonprecious alloys for adhesion-fixed partial dentures. J Prosthet Dent 1986;55:456-62. 10.Laufer BZ, Nicholls JI, Townsend JD. SiOx-C coating: a composite-to-metal bonding mechanism. J Prosthet Dent 1988;60:3207. 11.Ozcan M, Pfeiffer P, Nergiz I. A brief history and current status of metal- and ceramic surface-conditioning concepts for resin bonding in dentistry. Quintessence Int 1998;29:713-24. 12.Hansson O, Moberg LE. Evaluation of three silicoating methods for resin-bonded prostheses. Scand J Dent Res 1993;101:243-51. 13.Yoshida K, Kamada K, Sawase T, Atsuta M. Effect of three adhesive primers for a noble metal on the shear bond strengths of three
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resin cements. J Oral Rehabil 2001;28:14-9. 14.Kourtis S. Bond strengths of resin-tometal bonding systems. J Prosthet Dent 1997;78:136-45. 15.van der Veen H, Krajenbrink T, Bronsdijk B, van de Poel F. Resin bonding of tin electroplated precious metal fixed partial dentures: one-year clinical results. Quintessence Int 1986;17:299-301. 16.Matsumura H, Taira Y, Atsuta M. Adhesive bonding of noble metal alloys with a triazine dithiol derivative primer and an adhesive resin. J Oral Rehabil 1999;26:87782. 17.Kim JY, Pfeiffer P, Niedermeier W. Effect of laboratory procedures and thermocycling on the shear bond strength of resinmetal bonding systems. J Prosthet Dent 2003;90:184-9. 18.Kern M, Thompson VP. Influence of prolonged thermal cycling and water storage on the tensile bond strength of composite to NiCr alloy. Dent Mater 1994;9:19-25. 19.Yoshida K, Taira Y, Matsumura H, Atsuta M. Effect of adhesive metal primers on bonding a prosthetic composite resin to metals. J Prosthet Dent 1993;69:357-62. 20.Matsumura H, Leinfelder KF. Effect of an adhesive primer on the integrity of occlusal veneer-metal interface and wear of composite resin veneered restorations. J Prosthet Dent 1993;70:296-9. 21.Almilhatti HJ, Giampaolo ET, Vergani GE, Machado AL, Pavarina AC. Shear bond strength of aesthetic materials bonded to Ni-Cr alloy. J Dent 2003;31:205-12. 22.Yoshida K, Taira Y, Sawase T, Atsuta M. Effects of adhesive primers on bond strength of self-curing resin to cobalt-chromium alloy. J Prosthet Dent 1997;77:617-20. 23.Matsumura H, Yanagida H, Tanoue N, Atsuta M, Shimoe S. Shear bond strength of resin composite material to gold alloy with varying metal surface preparations. J Prosthet Dent 2001; 86:315-9. 24.Yanagida H, Matsumura H, Atsuta M. Bonding of prosthetic composite material to Ti-6Al-7Nb alloy with eight metal conditioners and a surface modification technique. Am J Dent 2001;14:291-4. 25.Petridis H, Garefis P, Hirayama H, Kafantaris NM, Koidis PT. Bonding indirect resin composites to metal: Part 1. Comparison of shear bond strengths between different metal-resin bonding systems and a metal-ceramic system. Int J Prosthodont 2003;16:635-9. 26.Kern M, Thompson VP. Bonding to glass infiltrated alumina ceramic: adhesive methods and their durability. J Prosthet Dent 1995;73:240-9. 27.Kern M, Thompson VP. Sandblasting and silica-coating of dental alloys: volume loss, morphology and changes in the surface composition. Dent Mater 1993;9:155-61. 28.Papadopoulos T, Tsetsekou A, Eliades G. Effect of aluminum oxide sandblasting on cast commercially pure titanium surfaces. Eur J Prosthodont Rest Dent 1999;7:15-21. 29.Petridis H, Garefis P, Hirayama H, Kafantaris NM, Koidis PT. Bonding indirect resin composites to metal: part 2. Effect of alloy surface treatment on elemental composition of alloy and bond strength. Int
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May 2008 J Prosthodont 2004;17:77-82. 30.Mukai M, Fukui H, Hasegawa I. Relationship between sandblasting and composite resin-alloy bond strength by a silica coating. J Prosthet Dent 1995;74:151-5. 31.ISO 10477:2004. Dentistry-polymer-based crown and bridge materials. International Organization for Standardization. Geneva, Switzerland. Available at http://www.iso. org/iso/store.htm. 32.Seimenis I, Sarafianou A, Papadopoulou H, Papadopoulos T. Shear bond strength of three veneering resins to a Ni-Cr alloy using two bonding procedures. J Oral Rehabil 2006;33:600-8.
Corresponding author: Dr Triantafillos Papadopoulos Department of Biomaterials School of Dentistry University of Athens 2 Thivon St, 115 27 Athens GREECE Fax: 00302107461306 E-mail: [email protected] Copyright © 2008 by the Editorial Council for The Journal of Prosthetic Dentistry.
Noteworthy Abstracts of the Current Literature Implant-supported mandibular overdentures retained with a milled bar: a retrospective study Krennmair G, Krainhofner M, Piehslinger E. Int J Oral Maxillofac Implants 2007;22:987-94. Purpose: The aim of this retrospective study was to evaluate implant survival rate, peri-implant conditions, and prosthodontic maintenance for implant-supported mandibular overdentures rigidly retained with a milled bar. Materials and Methods: Patients with 4 interforaminal implants (cylindric or screw-type) supporting an overdenture on a milled bar treated between 1996 and 2004 were asked to participate in a retrospective study. The cumulative implant survival rate and peri-implant conditions (marginal bone loss, pocket depth, Plaque Index, Gingival Index, Bleeding Index, and calculus presence) were evaluated and compared between cylindric and screw-type implants. The incidence and type of prosthodontic maintenance and subjective patient satisfaction rating were also evaluated. Results: Fifty-eight of 67 patients (87.3%) and 232 implants (76 cylindric, 156 screw-type) were available for followup examination after a mean period of 59.2 ± 26.9 months. The cumulative implant survival rate was 99%, and no differences in peri-implant soft tissue conditions were noted between the different implant types used. The cylindric implants showed more pronounced marginal bone resorption than the screw-type implants (1.9 ± 0.6 mm vs 2.2 ± 0.6 mm; P=.02) but the difference was not clinically significant. A low incidence of prosthodontic maintenance evenly distributed throughout the overall follow-up period and a high subjective satisfaction rating by the patients were noted. Conclusion: Interforaminal screw-type and cylindric implants supporting a milled bar for rigid overdenture anchorage were associated with a high survival rate and excellent peri-implant conditions. The incidence of prosthodontic maintenance was low and evenly distributed throughout the follow-up period as a result of rigid denture stabilization by the milled bar. Rigid anchorage of a mandibular overdenture with a milled bar unites the prosthodontic advantages of removable and fixed prostheses. Reprinted with permission of Quintessence Publishing.
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Clinical Implications
The development of a stable chemical bond between indirect veneering composite resins and metal frameworks can provide a reliable, esthetic, and cost-effective alternative to metal ceramic restorations. The results of this study indicate that clinically satisfactory metal-resin bond strength can be achieved by airborne-particle abrading Ni-Cr castings with 50-μm Al2O3 particles and using the proper adhesive primer. Presented at the International Association of Dental Research Pan-European Federation meeting, Dublin, Ireland, September 2006. Clinical Instructor, Department of Prosthodontics. Postgraduate student, Department of Prosthodontics. c Associate Professor, Department of Biomaterials. a
b
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Volume 99 Issue 5 The use of indirect light-polymerized composite resins has recently increased, due to the improvement in the properties of composite resin materials. New products exhibit enhanced mechanical properties, convenient handling, favorable esthetics, effective intraoral repair, and abrasion similar to natural tooth hard tissues.13 Initially, indirect composite resins were combined exclusively with mechanical retention.4,5 Resin veneer restorations based only on mechanical retention have demonstrated microleakage at the resin-metal interface, attributed to debonding as a result of repeated thermal and load cycling intraorally.6-8 In recent decades, a number of alloy surface modifications have been developed to achieve chemical adhesion.8-11 Despite these efforts, composite-to-metal bond strength remains inferior when compared to porcelain, resulting in intraoral failures. Systems used to enhance chemical bonding include silanes as coupling agents on a pyrollytically treated (Silicoater; Heraeus Kulzer GmbH, Wehrheim, Germany) or tribochemically treated (Rocatec; 3M ESPE, Seefeld, Germany) metal surface, acrylate monomers (Sebond; Schutz Dental GmbH, Rosbach, Germany), polyfluor methacrylates (SR Link; Ivoclar Vivadent, Schaan, Liechtenstein) as bonding agents, and tin plating (OVS; DeguDent GmbH, Hanau, Germany) of the alloy surface.12-16 In the Rocatec procedure, a highpurity aluminum oxide (Rocatec Pre; 3M ESPE) pretreats the metal framework to clean and activate the surface and standardize the surface roughness. A silicate layer is then created by airborne-particle abrasion with a special abrasive (Rocatec Plus; 3M ESPE), the particles of which are melted and retentively anchored on the surface. A silane layer (ESPE Sil; 3M ESPE) is then applied on the silicate-coated surface to produce a chemical bond with the veneering material.14 However, the previously mentioned methods are technique sensitive, time
consuming, and require the use of special devices. There is also conflicting data regarding the durability of the bond they provide, especially after extensive thermal cycling.17,18 Recently introduced adhesive primers simplify the resin adhesion procedure. After airborne-particle abrasion of the metal surface, they are easily and quickly applied with a brush. These primers contain carboxylic or phosphoric acid functional monomers, which react with oxides on the airborne-particleabraded alloy surface and the resin opaquer of the composite resin. Base metal alloys have shown increased bond strength to veneering resin, when surfaces are treated with metal primers containing carboxyl or phosphoric acid derivatives.19-22 Also, many investigators have tested the efficacy of various surface treatments on the improvement of the bond strength, in combination with different dental alloys and ceramics.23-26 In addition to micromechanical retention, airborneparticle abrasion has an important role in the development of chemical adhesion. Several investigators have reported that when abrading the metal surface with Al2O3 particles, oxides are released, generating a chemical bond with adhesive primers.27-30 The objective of this study was to examine the shear bond strength of a commercial indirect resin to a Ni-Cr alloy, using 4 different adhesive primers. The effect of airborne-particle abrasion with differently sized Al2O3 particles on the bond strength was also investigated. The null hypotheses were that the use of different adhesive primers would provide bond strength similar to the control group, and the use of differently sized airborne-particleabrasion particles would not have any effect on the bond strength.
MATERIAL AND METHODS Fifty-six wax discs, 10 mm in diameter and 1.5 mm in height, were fabricated. A U-shaped retentive wax loop was connected to the flat surface of the disc for retention of the casting
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in the embedding acrylic resin (Orthoplast; Vertex-Dental BV, Zeist, The Netherlands). The wax patterns were cast using a fixed prosthodontic Ni-Cr alloy (Heraenium NA; Heraeus Kulzer GmbH), according to the manufacturer’s instructions. Twenty-four castings were airborne-particle abraded using 50-μm Al2O3 particles (Treibacher Industrie AG, Althofen, Austria), while another 24 castings were airborne-particle abraded using 250-μm Al2O3 particles (Treibacher Industrie AG). Airborneparticle abrasion was performed for 5 seconds at 6 Atm air pressure, with a 45-degree angle at a 10-cm nozzlemetal surface distance. All specimens were cleaned in an ultrasonic bath for 5 minutes and dried using an oilfree air stream. The following primers were applied on 6 discs of every group treated with airborne-particle abrasion: Solidex Metal Photo Primer (MPP50, MPP250), Metal Primer II (MPII50, MPII250), SR Link (SRL50, SRL250), and Tender Bond (TB50, TB250) (Table I). All primers were applied with a brush in a uniform coating and allowed to air dry, according to the manufacturer’s instructions. The Rocatec system was used on another 6 discs (R) and served as the control. The discs were airborneparticle abraded according to the manufacturer’s directions, using a special airborne-particle-abrasion unit designed for the tribochemical silica-coating procedure (Rocatec Jr. Bonding System; 3M ESPE) (Table I). Airborne-particle abrasion was performed initially with 110-μm Al2O3 particles (Rocatec Pre; 3M ESPE) for 10 seconds to clean the surface. A second airborne-particle abrasion treatment was performed for 13 seconds using a special alumina powder (110 μm) with added silica particles (Rocatec Plus; 3M ESPE) to form a silica surface layer. Airborne-particle abrasion was performed at 2.8 Atm air pressure, at a distance of 10 cm. All specimens were cleaned in an ultrasonic bath for 5 minutes and dried using an oil-free air stream. On the
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Table I. Tested materials and groups Test Group Codes
Bonding Procedure
Manufacturer
MPP50 MPP250
Solidex Metal Photo Primer LOT No. 120495
Shofu, Kyoto, Japan
MPII50 MPII250
Metal Primer II LOT No. 0508082
GC Corp, Tokyo, Japan
SRL50 SRL250
SR Link LOT No. H15063
Ivoclar Vivadent, Schaan, Liechtenstein
TB50 TB250
Tender Bond LOT No. 2004006269
Micerium SpA, Avegno, Italy
Rocatec ESPE Sil LOT No. 227648
3M ESPE, Seefeld, Germany
R
MPP50, MPII50, SRL50, TB50 = Airborne-particle abraded with 50-µm Al2O3; MPP250, MPII250, SRL250, TB250 = Airborne-particle abraded with 250-µm Al2O3; R = Airborne-particle abraded with 110-µm Al2O3 (Rocatec Pre) and 110-µm silica-containing Al2O3 powder (Rocatec Plus)
specimens in group R, a silane coupling agent (ESPE Sil; 3M ESPE) was applied and allowed to air dry for 5 minutes. Two more castings were airborneparticle abraded, with 50-μm and 250-μm Al2O3 particles, respectively. Specimens were cleaned in an ultrasonic bath for 5 minutes and dried using an oil-free air stream. They were left free of any bonding procedure. For the specimens to be bonded, an adhesive tape with a central hole measuring 5 mm (Tesa AG, Hamburg, Germany) in diameter was positioned over the airborne-particle-abraded surface to determine the bonding area. An indirect microhybrid composite resin (Sinfony; 3M ESPE) was used for the veneering of the primed alloy surfaces. Two layers of resin opaquer (Sinfony Resin opaquer, LOT No. 154502; 3M ESPE) were applied on the metal surface. Each layer was polymerized for 10 seconds using a light-polymerizing device (Visio Alfa; 3M ESPE) and then under vacuum in a special unit (Visio Beta; 3M ESPE), according to the manufacturer’s instructions. A transparent plastic cylindrical tube with an internal diameter of 5 mm
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was positioned perpendicular to the treated alloy surface to add the veneering portion of the specimen. Two layers of dentin veneering resin (Sinfony Composite, LOT No. 224895; 3M ESPE), with a total thickness of 2 mm, were applied and polymerized following the same procedures. Thermal cycling was performed between 5°C and 55°C for 5000 cycles with a dwell time of 30 seconds in each bath, according to ISO 10477.31 All specimens were tested for shear bond strength in a universal testing machine (Tensometer 10; Monsanto, Akron, Ohio) at a crosshead speed of 0.5 mm/min. Failure load values were divided by the bonding area to determine the bond strength. Fractured surfaces were examined under an optical microscope (Eclipse ME 600; Nikon, Tokyo, Japan) at x20 magnification. The mode of fracture was arbitrarily classified as adhesive when the percentage of the veneering material remaining on the metal surface was less than 25%, cohesive when it was more than 75%, and combination when it ranged between 25 and 75%.32 The percentage distribution of the area covered by the resin was cal-
culated with a software program (SigmaScan Pro; SPSS Inc, Chicago, Ill). Selected specimens of all groups were examined using a scanning electron microscope (SEM) (Quanta 200; FEI Co, Hillsboro, Ore) equipped with a super ultrathin Beryllium window x-ray energy dispersive spectroscopy (EDS) (Sapphire; Edax Intl, Mahwah, NJ) with elemental area analysis (mapping) and elemental spot analysis, to determine the composition of characteristic sites of the fractured surfaces. Also, mapping was performed on the 2 airborne-particle-abraded nonprimed specimens to determine the aluminum (Al) content on their surfaces. Bond strength values were statistically analyzed using a 2-way ANOVA followed by Tukey’s multiple comparison tests at a significance level of α=.05, with the airborne-particleabrasion conditions (size of Al2O3 particles) and metal primers as factors. Mean bond strength values of each group were compared to the control group using the 1-way ANOVA followed by Tukey’s multiple comparison test (compared to reference) at a significance level of α=.05.
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Volume 99 Issue 5 RESULTS Mean shear bond strength values are presented in Table II. Two-way ANOVA (Table III) showed that there were significant differences among groups (P<.001). In addition, there was not a significant interaction between Al2O3 grain size and primers. Tukey’s multiple comparison tests showed that the group airborne-particle abraded using 50-μm Al2O3 particles exhibited significantly higher shear bond strength in comparison to the group abraded with 250-μm Al2O3 particles. Significant differ-
found between specimens treated with Metal Primer II and SR Link for either of the Al2O3 particle sizes used, when compared to Rocatec (Table IV). The mode of failure observed by optical microscopy (Fig. 1) (Table V) was adhesive for all Solidex Metal Photo Primer and Tender Bond groups. Specimens treated with Metal Primer II and SR Link, as well as Rocatec specimens, exhibited a combined, predominantly adhesive mode of failure. The observation of images obtained with SEM revealed that the surface relief of specimens
ences were found between all tested groups, except for MPP50 with TB50 and MPP250 with TB250, as indicated in Table II. The group showing the highest mean bond strength was the MPII50 (17.4 ±2 MPa). The 1-way ANOVA (F=18.529, df=8, and P<.001) showed that there were statistically significant differences among groups. Tukey’s multiple comparison tests revealed that specimens treated with Solidex Metal Photo Primer and Tender Bond exhibited significantly lower values compared to Rocatec, for both Al2O3 particle sizes used. No significant differences were
Table II. Mean shear bond strength values (in MPa) and SD of groups MPP50, MPP250, MPII50, MPII250, SRL50, SRL250, TB50, and TB250
Al2O3 Particle Size/Groups
MPP
MPII
SRL
TB
50 µm
9.4 (3.2)1,a
17.4 (2.2)1,c
13.0 (3)1,d
9.0 (3.1)1,a
250 µm
6.0 (1.0)2,a
15.2 (2.7)2,c
12.8 (2.8)2,d
3.9 (1.3)2,a
Same superscript number indicates no significant differences between airborne-particle-abrasion conditions for particular primer (P>.05). Same superscript lowercase letter indicates no significant difference between primers within airborneparticle-abrasion condition (P>.05).
Table III. Two-way ANOVA Source of Variation
df
SS
MS
F
P
Primer
3
754.65
251.55
38.94
<.001
Particle size
1
103.28
103.28
15.99
<.001
Primer x particle size
3
35.27
11.76
1.82
.159
Residual
40
258.39
6.46
Total
47
1151.59
24.50
Table IV. Mean shear bond strength values (in MPa) and SD of tested groups and control group Al2O3 Particle Size/Groups
MPP
MPII
SLR
TB
50 µm
9.4 (3.2)a
17.4 (2.2)b
13.5 (3)b
9.3 (3.1)a
250 µm
6 (1)a
15.2 (2.7)b
12.8 (2.8)b
3.9 (1.3)a
Rocatec surface treatment
15.9 (3.3)b
Same superscript lowercase letter indicates no significant difference between tested groups (P>.05).
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A
B
C
D
E
F
1 Representative images from optical microscope (x20). Gray surfaces represent metal and white surfaces represent resin fragments. A, SRL50 specimen (combined, predominantly adhesive mode of failure). B, SRL250 specimen (predominantly adhesive mode of failure). C, MPII50 specimen (predominantly adhesive mode of failure). D, MPII250 specimen (predominantly adhesive mode of failure). E, TB50 specimen (adhesive mode of failure). F, TB250 specimen (adhesive mode of failure).
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G
H
I 1 continued (2 of 2) G, MPP50 specimen (adhesive mode of failure). H, MPP250 specimen (adhesive mode of failure). I, R specimen (combined, predominantly adhesive mode of failure).
Table V. Mode of failure of groups tested Al2O3 Particle Size/Groups
MPP
MPII
SLR
TB
50 µm
adhesive
combination, PA
combination, PA
adhesive
250 µm
adhesive
combination, PA
combination, PA
adhesive
Rocatec surface treatment
combination, PA
PA: Predominantly adhesive
airborne-particle abraded with 50μm Al2O3 particles was more pronounced than that of the specimens airborne-particle abraded with 250μm Al2O3 particles. SEM mapping of a representative adhesively failing specimen (x250) showed 40.7 wt% for Ni, 14.8 wt% for Cr, and 5.5 wt% for Mo (Fig. 2, A). SEM mapping of
a representative combined, predominantly adhesively failing specimen (SRL250) showed concentrations of 24.02 wt% for Ni, 8.8 wt% for Cr, and 3.16 wt% for Mo (Fig. 2, B). Additionally, the wt% content of C and Ti was 24.8 wt% and 0.68 wt% for TB 250, and 46.51 wt% and 1.65 wt% for SRL250, respectively. Spot analysis of
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selected sites of a representative adhesively failing specimen (MPP250) verified that the white area contained high amounts of silicon with almost complete absence of alloy elements, while the dark area contained phosphorous and high amounts of alloy elements (Fig. 3) (Table VI). Mapping on the 2 airborne-particle-abraded,
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A
B
C 2 A, SEM image and mapping of representative adhesively failing specimen (x250). B, SEM image and mapping of representative combined, predominantly adhesively failing specimen (SRL250).
A
Table VI. Quantitative (wt%) elemental spot analysis B
3 SEM image of representative adhesively failing specimen. Arrow A: Spot analysis of dark area. Arrow B: Spot analysis of white area.
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in dark and white areas of representative adhesively failing specimen (MPP250) (Fig. 3)
Cr
Ni
Mo
Si
P
Dark area (arrow A)
11.27
29.30
4.25
0.85
0.16
White area (arrow B)
0.61
1.35
0.27
36.77
0.01
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Volume 99 Issue 5 nonprimed specimens revealed higher Al concentrations for the specimen abraded with 50-μm Al2O3 particles (11.24 wt%), when compared to that abraded with 250-μm particles (10.86 wt%). Mapping of fractured surfaces revealed great reduction of Al concentrations for all groups, ranging from 60% to 80%.
DISCUSSION According to the results of this study, no significant differences in mean shear bond strength were found between Metal Primer II and SR Link primer and the Rocatec procedure, while Solidex Metal Photo Primer and Tender Bond presented significantly lower mean bond strength values compared to Rocatec. Thus, the results support rejection of the first null hypothesis, which stated that the use of different adhesive primers would provide bond strength similar to that of the control group. According to the requirements of the revised ISO 10477, the minimum acceptable shear bond strength value is at least 5 MPa.31 However, Matsumura et al23 suggest that the resinto-metal shear bond strength necessary for the achievement of clinically satisfactory results should exceed 10 MPa. Although the bond strength values exhibited in the present study by MPP and TB fulfilled the ISO requirements, they still remained lower than the limits of clinical acceptability. The values corresponding to SRL and MPII exceeded 10 MPa, presenting no significant difference when compared to Rocatec, and were judged as clinically acceptable. Both primers contain phosphoric acid derivatives which can react with the metal oxides, creating the necessary metal-phosphate bonds to promote bonding. This might be a possible explanation for their high bond strength. Considering the different experimental conditions used by other investigators (type of alloy and veneering resin, number of thermal cycles, airborne-particle abrasion with dif-
ferent sizes of Al2O3 particles), the values reported in the present study are within the range observed in similar studies.21,32 A Ni-Cr alloy was used by Seimenis et al,32 who found shear bond strength values of 12.61 MPa, 14.9 MPa, and 16.55 MPa for MPP in combination with 3 veneering composite materials, namely Solidex (Shofu, Kyoto, Japan), Artglass (Heraeus Kulzer GmbH, Werheim, Germany), and Signum+ (Heraeus Kulzer GmbH, Hanau, Germany). The specimens were airborne-particle abraded with 250-μm Al2O3 particles and thermal cycled for 5000 cycles. Under the same conditions, the mean shear fracture strength of MPP primer with Sinfony in the present study was 6 MPa. This difference can be attributed to the use of additional mechanical retention (150-μm beads) used in the former study. A Ni-Cr alloy was also used by Almilhatti et al,21 who reported a mean shear bond strength of 11.94 MPa for Solidex with Solidex Metal Photo Primer. Specimens were stored in distilled water at 37°C for 7 days, and metal was airborne-particle abraded with 100-μm Al2O3 particles. This value is similar to the mean shear bond strength observed when Solidex Metal Photo Primer was combined with Sinfony in the present study (9.4 MPa). The following studies,13,17,24 in which Co-Cr alloy was used, yielded conflicting results. Kim et al17 reported mean shear fracture values of 10.3 MPa for Sinfony combined with the Rocatec procedure, when subjected to 5000 thermal cycles. The corresponding value recorded in the present study was 15.5 MPa. This increased bond strength could be attributed to the different alloy used. Yoshida et al13 reported mean shear strength values of 37.0 MPa and 27.7 MPa for MPII, when specimens were airborne-particle abraded with 50-μm Al2O3 particles and thermally cycled for 0 and 20,000 cycles, respectively. Yanagida et al24 reported a shear bond strength of 13.2 MPa after extended thermal cycling, when a Ti-6Al-7Nb alloy was
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primed with MPII and airborne-particle abraded with 50-μm Al2O3 particles. This result is similar to the results of the present study (17.4 MPa), in which MPII was used for priming a Ni-Cr alloy. The relatively higher bond strength observed in the present study could be attributed to the lower number of thermal cycles used (5000 instead of 20,000) and the type of alloy. Petridis et al25 reported mean shear values of 14.1 MPa when Targis Link (Ivoclar Vivadent) was used to prime a high-noble dental alloy in combination with Targis (Ivoclar Vivadent) veneering material after airborne-particle abrasion with 50-μm Al2O3 particles. Specimens were thermal cycled for 2500 cycles. This value is similar to those of the present study (9.3 to 17.4 MPa), when a Ni-Cr alloy was airborne-particle abraded with 50μm Al2O3 particles and primed with different primers to bond with Sinfony veneering material, after 5000 thermal cycles. Matsumura et al23 found mean shear fracture values of 20.6 MPa and 16.2 MPa between a gold alloy airborne-particle abraded with 50-μm Al2O3 particles, primed with Metal Primer II, and a veneering composite resin, when thermal cycled for 0 and 20,000 cycles, respectively. These results correspond to the mean shear fracture value of the present study (17.4 MPa), when a Ni-Cr alloy airborne-particle abraded with 50μm Al2O3 particles and primed with MPII was used with Sinfony veneering material and thermal cycled for 5000 cycles. In a study similar to the one by Matsumura et al,23 Yoshida et al,2 using a Ag-Pd alloy, recorded mean shear fracture values of 13.1 MPa and 4.6 MPa, which were lower than the corresponding value of the present study (17.4 MPa). This could be due to differences in the type of alloy and the number of thermal cycles used. It should be noted that the previously mentioned results are indicative for the materials used (Heraenium NA alloy, Sinfony composite resin) and the experimental limitations of the present study.
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May 2008 Regarding the particle size of the abrasion procedure, the 50-μm Al2O3 particles resulted in significantly higher shear bond strength compared to 250-μm particles for all the primers. Thus, the results support rejection of the second null hypothesis, which stated that the use of differently sized airborne-particle-abrasion particles would not have any effect on the bond strength. SEM images showed that treatment with 50-μm Al2O3 particles produced a more pronounced relief compared to that obtained with 250μm particles. This may lead to better interlocking of the resinous material in the superficial irregularities, resulting in enhanced micromechanical retention of the veneering material and higher shear bond strength during the application of the debonding forces. These results are in accordance with the findings of Petridis et al,25 who concluded that the Al2O3 particle size (50 μm and 250 μm) influences the resin-to-noble alloy shear bond strength. The authors suggested that airborne-particle abrasion with 50-μm Al2O3 particles resulted in improved microtopography and possibly better wettability and penetration of the primers into the microirregularities of the surface. Also, Mukai et al30 reported that the bond strength of a composite resin to a silver palladium alloy was influenced by the size of Al2O3 particles. Papadopoulos et al28 concluded that using 250-μm Al2O3 particles resulted in a significant increase in the roughness of commercially pure titanium (cpTi) surfaces. These investigators reported that, independent of the Al2O3 particle size, microroughness improved the mechanical interlocking between cpTi and porcelain. Kern and Thompson27 and Papadopoulos et al28 found that after airborne-particle abrasion, Al2O3 particles remain embedded in the alloy. According to the results of the present study, mapping of the airborne-particle-abraded, nonbonded specimens revealed increased quantities of oxygen and aluminium on the alloy surface abraded with 50-μm
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Al2O3 particles, compared to the alloy abraded with 250-μm particles. The amount of Al found on the airborneparticle-abraded surfaces was 10.86 wt% for surfaces airborne-particle abraded with 250-μm Al2O3 particles and 11.67 wt% for those airborneparticle abraded with 50-μm particles. This is in agreement with the findings of Petridis et al,29 who also observed similar increased amounts of these 2 elements on airborne-particle-abraded surfaces. The authors suggested that smaller particles might be able to better penetrate the alloy surface and be retained. This could be another possible explanation for the increased bond strength associated with airborne-particle abrasion with 50-μm Al2O3 particles. The precise role of the Al2O3 particles in the bonding mechanism is not clearly known. It has been suggested that the active monomers of the metal primers bond to the particles, thus, enhancing bond strength.27 According to Yoshida et al,13 airborne-particle abrasion can form a passive film of metal oxides, to which carboxylic acid and phosphoric acid derivatives contained in the primers present an affinity. Ozcan et al11 report that the Rocatec system uses the mechanical energy of silica-covered aluminium grains as these are blasted onto the metal surface. Regardless of the Al2O3 grain size used, there was a significant difference in bond strength among all the primers, with the exception of the primers MPP and TB (Table II). The mode of failure for the same primer for both airborne-particleabrasion treatments was similar. This signifies that priming probably depends primarily on the chemical affinity of each primer to the oxides of the metal surface. According to the results of the present study, a relationship was found between the mode of failure and magnitude of bond strength. More specifically, groups presenting clinically acceptable bond strength exhibited combined, predominantly adhesive failures. In these groups (SRL50, SRL250, MPII50, and MPII250), the
bond strength observed was actually the cohesive strength of the resin opaquer, which was lower than the adhesive bond strength. However, groups MPP50, MPP250, TB50, and TB250, which presented lower bond values, exhibited adhesive failures. In 2 studies by Almilhatti et al21 and Seimenis et al, 32 in which MPP was used to prime Ni-Cr alloy bonded to Solidex resin, the mode of failure observed was primarily adhesive. This is in agreement with the results of the present study, in which similar experimental conditions were used. In another 2 studies,26,17 where the Rocatec technique was used to treat the surface of a Co-Cr alloy, the mode of failure was primarily cohesive. This is also in agreement with the results of the present study, considering the differences in the conditions under which each experiment was performed. The previously mentioned results of optical microscopy were verified by mapping of selected specimens. More specifically, in a specimen presenting adhesive failure (TB250), mapping showed increased wt% for Ni, Cr, and Mo (Fig. 2, A), compared to a specimen presenting combined, predominantly adhesive failure (SRL250) (Fig. 2, B). Also, the wt% content of C and Ti was lower for TB250 compared to SRL250. The decreased amount of carbon and Ti and the increased amount of nickel, chromium, and molybdenum found on the TB250 specimen, in comparison to the corresponding amounts of the same elements in the SRL250 specimen, suggest the presence of higher amounts of primer and/or resin opaquer in the latter. The amounts of silicon and titanium may represent remnants of the resin opaquer, while phosphorus (P) remnants of the primer. This is qualitatively verified by spot analysis on selected, differently colored sites of an adhesively failing specimen (MPP250) in Figure 3. Spot analysis of a dark area (arrow A) showed high amounts of the basic alloy elements (Ni, Cr, Mo), corresponding to adhesive failure. The detected amounts of
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Volume 99 Issue 5 P in the same area indicate the presence of primer remnants. Spot analysis of a white area (arrow B) showed lower amounts of the basic alloy elements, compared to the dark area, and increased amounts of Si, indicating remnants of the composite resin opaquer (Fig. 3 and Table VI). The presence of P in the TB250 specimen in amounts lower than in the SRL250 specimen supports the view that part of the primer was retained on the metal surface. This suggests a mode of failure different than that observed with the optical microscope. It seems that adhesive failure occurred also, in part, within the layers of the metalprimer-resin opaquer, with areas of metal remaining partially covered by the primer. Failures of this nature occurring between the layers of the adhesive system have been referred to by Kern et al26 as “interface failures.” The nature of the mode of failure requires further clarification in future studies. Careful interpretation in the clinical application of the results is suggested, as the design of the present study did not consider factors existing in the oral environment, such as dynamic fatigue loading and pH changes. The efficacy of the tested systems in providing reliable bond strength should be affirmed by future research, incorporating long-term clinical studies.
CONCLUSIONS Considering the limitations of the present study, the following conclusions were drawn: 1. The bond strength between the Ni-Cr alloy and the composite resin evaluated was significantly higher after airborne-particle abrasion of the cast surface with 50-μm Al2O3 particles compared to 250-μm particles, independent of the primer used. 2. Significant differences were found between all the tested groups, except for groups MPP50 with TB50 and MPP50 with TB50. Group MPII50 exhibited the higher mean shear bond strength (17.4 ±2 MPa).
3. No significant differences in mean shear bond strength were found between primers Metal Primer II and SR Link and Rocatec, while primers Solidex Metal Photo Primer and Tender Bond presented significantly lower mean bond strength values compared to Rocatec. 4. The mode of failure was combined and predominantly adhesive for primers Metal Primer II and SR Link, and adhesive for primers Solidex Metal Photo Primer and Tender Bond.
REFERENCES 1. Berge M. Properties of prosthetic resinveneer materials processed in commercial laboratories. Dent Mater 1989;3:77-82. 2. Jones RM, Goodacre CJ, Moore BK, Dykema RW. A comparison of the physical properties of four prosthetic veneering materials. J Prosthet Dent 1989;61:38-44. 3. Staffanou RS, Hembree JH Jr, Rivers JA, Myers ML. Abrasion resistance of three types of esthetic veneering materials. J Prosthet Dent 1985;53:309-10. 4. Shue SL, Nicholls JI, Townsend JD. The effect of metal retentive designs on resin veneer retention. J Prosthet Dent 1987;58:297-305. 5. Barzilay I, Myers ML, Cooper LB, Graser GN. Mechanical and chemical retention of laboratory cured composite to metal surfaces. J Prosthet Dent 1988;59:131-7. 6. Staffanou RS, Hembree JH Jr, Rivers JA, Myers ML, Kilgore JL. Leakage study of three esthetic veneering materials. J Prosthet Dent 1985;54:204-6. 7. Jones RM, Moore BK, Goodacre CJ, Munoz-Viveros CA. Microleakage and shear bond strength of resin and porcelain veneers bonded to cast alloys. J Prosthet Dent 1991;65:221-8. 8. Matsumura H, Kawahara M, Tanaka T, Atsuta M. Surface preparations for metal frameworks of composite resin veneered prostheses made with an adhesive opaque resin. J Prosthet Dent 1991;66:10-5. 9. Tanaka T, Fujiyama E, Shimuzu H, Takaki A, Atsuta M. Surface treatment of nonprecious alloys for adhesion-fixed partial dentures. J Prosthet Dent 1986;55:456-62. 10.Laufer BZ, Nicholls JI, Townsend JD. SiOx-C coating: a composite-to-metal bonding mechanism. J Prosthet Dent 1988;60:3207. 11.Ozcan M, Pfeiffer P, Nergiz I. A brief history and current status of metal- and ceramic surface-conditioning concepts for resin bonding in dentistry. Quintessence Int 1998;29:713-24. 12.Hansson O, Moberg LE. Evaluation of three silicoating methods for resin-bonded prostheses. Scand J Dent Res 1993;101:243-51. 13.Yoshida K, Kamada K, Sawase T, Atsuta M. Effect of three adhesive primers for a noble metal on the shear bond strengths of three
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Corresponding author: Dr Triantafillos Papadopoulos Department of Biomaterials School of Dentistry University of Athens 2 Thivon St, 115 27 Athens GREECE Fax: 00302107461306 E-mail: [email protected] Copyright © 2008 by the Editorial Council for The Journal of Prosthetic Dentistry.
Noteworthy Abstracts of the Current Literature Implant-supported mandibular overdentures retained with a milled bar: a retrospective study Krennmair G, Krainhofner M, Piehslinger E. Int J Oral Maxillofac Implants 2007;22:987-94. Purpose: The aim of this retrospective study was to evaluate implant survival rate, peri-implant conditions, and prosthodontic maintenance for implant-supported mandibular overdentures rigidly retained with a milled bar. Materials and Methods: Patients with 4 interforaminal implants (cylindric or screw-type) supporting an overdenture on a milled bar treated between 1996 and 2004 were asked to participate in a retrospective study. The cumulative implant survival rate and peri-implant conditions (marginal bone loss, pocket depth, Plaque Index, Gingival Index, Bleeding Index, and calculus presence) were evaluated and compared between cylindric and screw-type implants. The incidence and type of prosthodontic maintenance and subjective patient satisfaction rating were also evaluated. Results: Fifty-eight of 67 patients (87.3%) and 232 implants (76 cylindric, 156 screw-type) were available for followup examination after a mean period of 59.2 ± 26.9 months. The cumulative implant survival rate was 99%, and no differences in peri-implant soft tissue conditions were noted between the different implant types used. The cylindric implants showed more pronounced marginal bone resorption than the screw-type implants (1.9 ± 0.6 mm vs 2.2 ± 0.6 mm; P=.02) but the difference was not clinically significant. A low incidence of prosthodontic maintenance evenly distributed throughout the overall follow-up period and a high subjective satisfaction rating by the patients were noted. Conclusion: Interforaminal screw-type and cylindric implants supporting a milled bar for rigid overdenture anchorage were associated with a high survival rate and excellent peri-implant conditions. The incidence of prosthodontic maintenance was low and evenly distributed throughout the follow-up period as a result of rigid denture stabilization by the milled bar. Rigid anchorage of a mandibular overdenture with a milled bar unites the prosthodontic advantages of removable and fixed prostheses. Reprinted with permission of Quintessence Publishing.
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