Medical knowledge | Dentistry » Waki-Nakamura - Adhesive strength between fiber reinforced composites and veneering composites and fracture

Adhesive Strength Between Fiber-Reinforced Composites and Veneering Composites and Fracture Load of Combinations of These Materials Tomonori Waki, DDSa/Takashi Nakamura, DDS, PhDb/Kazumichi Wakabayashi, DDS, PhDc/ Yoshihiko Mutobe, DDSc/Hirofumi Yatani, DDS, PhDd Purpose: This study examined the influence of the adhesive strength between fiberreinforced composites (FRC) and veneering composites on the fracture load of combinations of these materials. Materials and Methods: Six materials were used An experimental material called BR-100, Vectris, and FibreKor were the types of FRC. Estenia, Targis, and Sculpture were used as veneering composites. With the Estenia/BR-100 combination, the surface of the FRC was subjected to three different conditions before veneering. Ten specimens of each combination were fabricated and divided into two groups: One group was stored in 37°C distilled water for 24 hours, and the other was thermocycled (4°C/60°C, 10,000 cycles). Adhesive strength between

FRCs and veneering composites was determined using the compressive shear strength test. In addition, fracture loads of laminate specimens were determined. Results: Good adhesive strength was obtained by leaving an unpolymerized layer on the surface of the FRC or by performing silane and bonding treatment. In the Estenia/BR-100 combination, when the adhesive strength was low, the fracture load of the laminate specimens was also low. However, the difference in fracture load was not as large as that seen in adhesive strength. The fracture load of each laminate specimen was significantly lower after thermocycling. Conclusion: The adhesive strength between the FRCs and veneering composite had an effect on the fracture load of the combination. Int J Prosthodont 2004;17:364–368 I n current restoration procedures, natural tooth colors are required; at the same time, the amount of tooth reduction needs to be minimized under the concept of minimal intervention.1,2 Composite fixed partial

dentures (FPD) aStudent, Division of Oromaxillofacial Regeneration, Course for Integrated Oral Sciences and Stomatology, Osaka University Graduate School of Dentistry, Japan. bAssociate Professor, Division of Oromaxillofacial Regeneration, Course for Integrated Oral Sciences and Stomatology, Osaka University Graduate School of Dentistry, Japan. cInstructor, Division of Oromaxillofacial Regeneration, Course for Integrated Oral Sciences and Stomatology, Osaka University Graduate School of Dentistry, Japan. dProfessor, Division of Oromaxillofacial Regeneration, Course for Integrated Oral Sciences and Stomatology, Osaka University Graduate School of Dentistry, Japan. Correspondence to: Dr Tomonori Waki, Division of Oromaxillofacial Regeneration, Course for Integrated Oral Sciences and Stomatology, Osaka University Graduate School of Dentistry, 1-8 Yamadaoka, Suita, Osaka 5650871, Japan. Fax: + 81-6-6879-2947 e-mail: wakitomo@dent.osaka-uacjp 364 The International Journal of

Prosthodontics using inlay retainers that require less tooth reduction have therefore come into clinical use.3–5 Although the fiber-reinforced composites (FRC) used for FPD frameworks are reported to have high strength,6,7 one report points out that the composite veneered on the FRC frame might fracture at their interface.8 It is thus anticipated that the strength of combinations of FRCs and veneering composites will decrease if the adhesive strength between both materials is low. It is reported that the adhesive strength between FRCs and veneering composites can be improved by using an intermediate resin layer that employs interpenetrating polymer network bonding,9,10 or by air abrading and silane coating the FRC layer.11 However, such methods are usually used for repairing restorations For fabrication of FRC restorations, the oxygen-inhibited layer12,13 created after FRC polymerization may be effective for improving adhesive strength. This study was performed to clarify the

influence of the adhesive strength between FRC and veneering composites on the flexural strength of combinations of these materials, using an experimental FRC material with varying adhesion conditions. Two commercial products were also evaluated Waki et al Table 1 Materials Used Product Estenia, Kuraray Targis, Ivoclar Vivadent Sculpture, Jeneric/Pentron BR-100, Kuraray Vectris, Ivoclar Vivadent FibreKor, Jeneric/Pentron Monomer composition Type of composite Filler/fiber content (wt%)* Fiber diameter (µm) UTMA bis-GMA, UDMA bis-GMA, PCDMA UTMA bis-GMA, UDMA bis-GMA, PCDMA Veneering Veneering Veneering Fiber reinforced Fiber reinforced Fiber reinforced 92 (filler)14 80 (filler)14 78 (filler)14 48 (fiber) 60 (fiber) 66 (fiber) 11 15 (Vectris Pontic) 10 *Fiber content measured after washing away filler and monomer using an organic solvent. UTMA = urethane tetramethacrylate; bis-GMA = bisphenol-A-glycidyldimethacrylate; UDMA = urethane dimethacrylate; PCDMA =

polycarboxylate dimethacrylate. Three materials were used as framework FRCs: an experimental material (BR-100), and two commercial products (Vectris and FibreKor). All are glass-fiber materials preimpregnated with resin Used as veneering composites14 were Estenia, Targis, and Sculpture, which were combined with the FRC of their respective suppliers (Table 1). A3 dentin was the color of the veneering composite. 10 mm ⫻ 10 mm Materials and Methods FRC Veneering composite Adhesive Strength Between FRCs and Veneering Composites Compressive shear strength tests were carried out to examine the adhesive strength between FRCs and veneering composites as in a previous report.9 Specimens were prepared by first polymerizing FRC to a size of 10 mm ⫻ 10 mm ⫻ 2 mm using an acrylic resin mold, then curing veneering composites over each of them into a 3-mm-diameter cylinder using a metallic mold (Fig 1). The BR-100 was cured with a light-curing unit (␣Light 2, Kuraray) for 3 minutes. For

Vectris, bundled glass fibers (Vectris Pontic, Ivoclar Vivadent) were light and heat cured with a vacuum/pressure unit (VS-1, Ivoclar Vivadent) for 10 minutes. Then, woven glass fibers (Vectris Frame, Ivoclar Vivadent) were layered and light and heat cured (VS-1) for 10 minutes. FibreKor was cured with a light-curing unit (Cure-Light Plus, Jeneric/Pentron) for 15 minutes In the Estenia/BR-100 combination, the BR-100 was cured, and then the surface of the material was subjected to three conditions before Estenia was veneered. In the “no treatment” group, the unpolymerized layer was left on the surface without any treatment; in the “sandblasting” group, only sandblasting was performed; and in the “silane treatment” group, sandblasting, silane, and bonding treatments were performed. Estenia was light cured (␣Light 2) for 5 minutes and then heat cured in a KL-100 unit (Kuraray) at 110°C for 15 minutes (Table 2). In the Targis/Vectris combination, the surface of Vectris was

sandblasted and subjected to silane treatment, and Targis was layered over it and then light and heat cured in a Targis Power unit (Ivoclar Vivadent) for 25 minutes. ø = 3 mm 2 mm Fig 1 Shear bond strength test; FRC = fiber-reinforced composite. In the Sculpture/FibreKor combination, the FibreKor surface was not subjected to any special treatmentunpolymerized layers were not removedand Sculpture was veneered over it. Sculpture was light cured (Cure-Light Plus) for 5 minutes and then heat cured in a Curing Unit (Jeneric/Pentron) for 15 minutes in an atmosphere of nitrogen gas (Table 2). Ten specimens of each combination were fabricated and divided into two groups of five each. Specimens in group 1 were stored in 37°C distilled water for 24 hours. Those in group 2 were stored in 37°C distilled water and then thermocycled (4°C/60°C, 10,000 cycles of 1 minute each). Thereafter, they were subjected to shear strength testing using a universal testing machine (Auto Graph AGI,

Shimadzu) at a cross-head speed of 1 mm per minute (Fig 1). Fracture Load of Laminate Specimens Using metallic molds, laminate specimens measuring 4 mm ⫻ 25 mm ⫻ 2 mm were fabricated to examine the fracture load of the combinations of FRCs and veneering Volume 17, Number 3, 2004 365 Strength and Fracture Load of FRCs and Veneering Composites Table 2 Surface Conditions for Fiber-Reinforced Composites (FRC) Group FRC surface condition Estenia/BR-100 No treatment Sandblasting Silane treatment Targis/Vectris Sculpture/FibreKor No treatment (unpolymerized surface) Sandblasted (50-µm Al2O3, 0.1 MPa, 10 s) Sandblasted (50-µm Al2O3, 0.1 MPa, 10 s), silane and bonding treatments (Add-on Primer*, Modeling Liquid) Sandblasted (50-µm Al2O3, 0.1 MPa, 10 s), silane treatment (Targis Wetting Agent†) No treatment (unpolymerized surface) *Kuraray. †Ivoclar Vivadent. Veneering composite FRC 2 mm Supporting distance 20 mm Fig 2 Fracture load test for laminate specimens; FRC =

fiberreinforced composite. composites (Fig 2). The size of the specimens simulated posterior FPD frameworks as in a previous report.6 FRCs were used in the amount specified for the fabrication of posterior FPD frameworks by their respective manufacturers. BR-100 containing 15,000 unidirectional glass fibers with a diameter of 11 µm was used. The mean thickness of FRC in laminate specimens was 1.1 mm for BR100, 11 mm for Vectris, and 09 mm for FibreKor Over these FRCs, Estenia, Targis, and Sculpture were veneered to make 2.0-mm-thick specimens The FRC surfaces were treated (Table 2) as for the compressive shear strength test. After fabrication, specimens were polished using No. 1,200 waterproof sandpaper. Ten specimens of each combination were prepared and divided into two groups of five each. Specimens in group 1 were stored in 37°C distilled water for 24 hours. Those in group 2 were stored in 37°C distilled water and then thermocycled (4°C/60°C, 10,000 cycles of 1 minute each).

Thereafter, they were subjected to fracture load testing using a universal testing machine at a cross-head speed of 1 mm/min with an interfulcrum distance of 20 mm (Fig 2). Statistical comparison of the specimens subjected to both experiments was performed using one-way analysis of variance (ANOVA) and Bonferroni’s multiple comparison test. Analysis of differences between the group im- 366 The International Journal of Prosthodontics mersed in water for 24 hours and the thermocycled group was performed using the Student’s t test (P ⬍ .05) In addition, specimens used for fracture load testing were cut at a point 2 mm from the loading point, and the cross-section was observed with scanning electron microscopy (SEM). Results Adhesive Strength Between FRCs and Veneering Composites The Estenia/BR-100 combination showed adhesive strength ranging from 4.3 to 172 MPa after immersion in water for 24 hours (Table 3). The adhesive strength in the sandblasting group was significantly

lower (P ⬍ .05), less than one third of those obtained in the other groups. In the no treatment and silane treatment groups, the Estenia/BR-100 combination demonstrated cohesive failure of the FRC at the fracture surface, including peeling of fibers. In the sandblasting group, specimens showed interfacial separation between Estenia and BR-100 The adhesive strength of the thermocycled specimens tended to be lower than that of those immersed in water for 24 hours, but there was no significant difference. Fracture Load of Laminate Specimens The Estenia/BR-100 combination showed a fracture load ranging from 358 to 474 N after 24-hour water immersion (Table 3). In the sandblasting group, in which the Estenia/BR-100 combination had low adhesive strength, fracture load was also significantly lower than those in the other groups (P ⬍ .05), but the difference was not as large as that seen in adhesive strength. After thermocycling, the fracture load of each specimen showed a tendency to

decrease. All but the Targis/Vectris combination demonstrated a significant difference in fracture load between 24-hour water immersion and thermocycling. Under SEM observation, the border between the FRC and veneering composite was unclear in the Estenia/BR100 specimen of the no treatment group (Fig 3). In contrast, the same specimens of the sandblasting and silane treatment groups had a clear border between the two materials (Figs 4 and 5). Discussion The Estenia/BR-100 combination seemed to have good adhesive strength (15.1 to 172 MPa) because of the presence of unpolymerized layers on the FRC surface in the no treatment group and because of the treatment with silane coupling and bonding agents in the silane treatment group. Shear strength between FRC and repair resin ranges from 92 to 287 MPa,9 and the results of these two groups were also within this range. The Waki et al Table 3 Behavior of Specimens After Water Storage and After Thermocycling Group Estenia/BR-100, no

treatment After 24-h storage After thermocycling Estenia/BR-100, sandblasting After 24-h storage After thermocycling Estenia/BR-100, silane treatment After 24-h storage After thermocycling Targis/Vectris After 24-h storage After thermocycling Sculpture/FibreKor After 24-h storage After thermocycling Adhesive strength (MPa) Mean SD A Failure mode B C Fracture load (N) Mean SD 17.2 15.6 5.8 2.6 0 0 5 4 0 1 463 386 33 22 4.3 4.8 3.0 2.1 5 5 0 0 0 0 358 267 88 31 15.1 15.1 3.0 2.0 0 0 5 5 0 0 474 344 20 44 3.8 3.0 1.9 1.3 4 5 1 0 0 0 387 359 33 16 11.0 10.1 2.5 3.7 0 0 5 4 0 1 337 265 26 43 SD = standard deviation; A = fiber-reinforced composite (FRC)–veneering composite interface separation; B = cohesive failure within FRC; C = cohesive failure within veneering composite; thermocycling = 10,000 times at 4 and 60°C. Fig 3 (right) Cross-sectional SEM view of Estenia (V [veneering composite])/BR-100 (F [fiber-reinforced composite]) no treatment

group. Diffused layer between Estenia and BR-100 (A) is observed. Fig 4 (below ) Cross-sectional SEM view of Estenia (V)/BR-100 (F) sandblasting group. Clear border between Estenia and BR100 is observed Fig 5 (below right) Cross-sectional SEM view of Estenia (V)/BR-100 (F) silane treatment group. Dislodged glass fibers are observed on the BR-100 surface, but sites are filled with Estenia and bonding agent. results obtained in the no treatment group seemed attributable to the effect of free-radical polymerization on the oxygen-inhibited layer12,13; those obtained in the silane treatment group seemed attributable to interpenetrating polymer network bonding by the bonding agent, in addition to the effect of the silane coupling agent15 on glass fiber and inorganic fillers. However, all specimens of the same combination fabricated in the sandblasting group displayed interfacial separation and had only about one third of the adhesive strength obtained under the other conditions. This

suggests that sufficient adhesive strength could not be achieved by Volume 17, Number 3, 2004 367 Strength and Fracture Load of FRCs and Veneering Composites mechanical interlocking force with sandblasting alone, as in a previous report.16 A majority of the Targis/Vectris specimens showed low adhesive strength that caused interfacial separation even though they were treated with silane coupling agents. It was supposed that the silane coupling agent had not been sufficiently activated. All specimens of the Sculpture/FibreKor combination had cohesive failure of the FRC, indicating that they had attained sufficient adhesive strengths. This was probably because of the oxygen-inhibited layer12,13 created on the FiberKor surface, as with the Estenia/BR-100 combination tested in the no treatment group. After thermocycling, there was no difference in adhesive strength among the three conditions. That is, the adhesion durability seemed good under the conditions used in this study. The

Estenia/BR-100 combination showed a significantly lower fracture load in the sandblasting group than in the other two groups. Since this combination also had low adhesive strength in the sandblasting group, the adhesive strength between the FRC and veneering composite may have had an effect on the fracture load of the combination. The adhesive strength in the silane treatment group was about one third of the values achieved in the other groups, whereas the fracture load decreased by only about 20%. Thus, it appeared that the adhesive strength did not have as much effect on the fracture load. As for comparison between the other combinations, adhesive strength was lower in Targis/Vectris than in Sculpture/FibreKor. The fracture load, as already reported,7,17,18 was higher in Targis/Vectris than in Sculpture/FibreKor, probably because of factors other than adhesive strength In an experiment7 previously performed on each material, Sculpture showed higher flexural strength than Targis, and

Vectris had higher strength than FibreKor. Judging from these results, the fracture load of the combinations seemed to be largely affected by the strength of the FRC. In the present study, Vectris was 11 mm thick and FibreKor was 0.9 mm; the fact that FibreKor was thinner than Vectris might have had some effect on the result. It has been reported that FRC decreases in strength when stored in water.19,20 The decrease in the strength of each combination observed after thermocycling could be attributed to the effect of water immersion. After thermocycling, the fracture load of each combination showed a tendency to drop, although there was no significant difference in adhesive strength. This result was interpreted to mean that the fracture load of the combinations was affected by adhesive strength, but more influenced by the nature of the materials in each combination. However, the report8 that Targis fractures more than Vectris in their combination suggests that Targis itself is fragile,

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