|Year : 2013 | Volume
| Issue : 3 | Page : 216-221
Resin bond to root dentin: Influence of adhesive systems and solvent drying time
Fernanda Campos1, Hugo R Sarmento2, Maria L L Alves3, Marina Amaral1, LF Valandro4, Marco A Bottino1, Rodrigo O A Souza3
1 Department of Dental Materials and Prosthodontics, São Paulo State University, Sao Paulo, Brazil
2 Department of Dental Materials, Federal University of Pelotas, Pelotas/RS, Brazil
3 Department of Dentistry, Federal University of Rio Grande do Norte, Natal/RN, Brazil
4 Department of Dental Restorative Dentistry, Federal University of Santa Maria, Santa Maria, Brazil
|Date of Web Publication||28-Mar-2014|
Rodrigo O A Souza
Department of Dentistry, Federal University of Rio Grande do Norte, Natal/RN, Rua Praia de Guajirú, 9215, Ponta Negra, Natal/RN. Cep: 59.092-220
Source of Support: None, Conflict of Interest: None
Background: Endodontically treated teeth with damaged coronal tooth structure need an additional retention to provide a durable restoration. We evaluate different adhesive systems and solvent drying time on the push-out bond strength of fiber posts luted to root dentin.
Materials and Methods: For this in vitro study, the canals of 90 bovine teeth (16 mm in length) were prepared, the roots were embedded (14 mm) in acrylic resin and allocated into nine groups (n = 10), according to the "adhesive system" (Multi-bottle etch-and-rinse self-curing adhesive system-MBSC/ Scotchbond Multi-Purpose; Simplified etch-and-rinse dual-curing adhesive-SLC/One-Step; Simplified etch-and-rinse light-curing adhesive-SDC/Excite DSC) and "solvent drying time" (control, 50 s and 110 s). The fiber posts were luted using resin cement and composite cores were made. Each set of root/post/core was submitted to mechanical cycling (10.000.000 cycles, 84 N, 4 Hz). Each root was cut into four disk-samples (1.8 mm in thickness) and submitted to push-out testing. The data (MPa) were analyzed using analysis of variance (ANOVA) (two-way) and Tukey's test (5%).
Results: The factor "adhesive system" (P = 0.0081) influenced the bond strength significantly (ANOVA). The MBSC groups (6.0 ± 2.2 MPa) promoted higher bond strength than SLC groups (3.7 ± 2.1 MPa) b and was similar to SDC groups (4.4 ± 3.4 MPa) a, b (Tukey).
Conclusion: The solvent drying time did not affect the bond strength of fiber postluted to root dentin, regardless the adhesive solution used.
Keywords: Bond strength, dental bonding, fiber composite posts, mechanical cycling, post and core technique, prosthodontics, root dentin, solvent evaporation
|How to cite this article:|
Campos F, Sarmento HR, Alves ML, Amaral M, Valandro L F, Bottino MA, Souza RO. Resin bond to root dentin: Influence of adhesive systems and solvent drying time. Arch Int Surg 2013;3:216-21
|How to cite this URL:|
Campos F, Sarmento HR, Alves ML, Amaral M, Valandro L F, Bottino MA, Souza RO. Resin bond to root dentin: Influence of adhesive systems and solvent drying time. Arch Int Surg [serial online] 2013 [cited 2020 Jan 24];3:216-21. Available from: http://www.archintsurg.org/text.asp?2013/3/3/216/129567
| Introduction|| |
Endodontically treated teeth with damaged coronal tooth structure after decay, other restorations, or fractures frequently need an additional retention to provide a durable restoration.  Fiber posts have been used as an alternative method of retention for direct and indirect restorations.  Many advantages could be cited when fiber posts are compared to metal posts, such as good esthetics,  a modulus of elasticity similar to dentin,  chemical compatibility with composite materials,  and good biocompatibility. 
In this context, several studies have reported a high clinical success rate for teeth restored with cemented fiber posts. , However, despite the continued development of adhesive materials that provide effective bonding between tooth and post,  the displacement of the post or cement assembly from the root canal seems to be the most common type of failure for this type of restoration. 
Since the root dentin and cement interface are the weakest point in this kind of system, the success of fiber posts cemented to root dentin depends on several factors including c-factor,  endodontic cement,  heterogeneity of dentin tissue,  uncertainty of hybridization of the dentin walls of the root canal,  the shape and width of the root canal,  the shape and composition of the fiber post,  the adhesive system utilized,  and the application technique of the bonding agent. 
Concerning the adhesion clinical procedures, studies showed that increased solvent drying time significantly improved the microtensile bond strength between the coronal dentin and a composite resin. , The solvent in the adhesive systems could be evaporated over a longer period between the application of the adhesive solution and the placement of the composite resin.  Therefore, a more stable and homogeneous adhesive layer could be formed.  Additional studies have shown that the polymerization reaction of the adhesive systems can be negatively influenced by the presence of water and solvent. , The type of solvent could also affect the degree of conversion of the adhesive systems. 
There have been no studies that have verified if increasing the solvent drying time of different adhesive systems can affect the resin bond to root dentin. Thus, the aim of this current study was to evaluate the influence of some adhesive systems and solvent drying times on the resin bond to root dentin. The hypotheses were that (1) the multibottle adhesive and (2) the increasing of solvent drying times will generate higher bond strength values.
| Materials and Methods|| |
The brand, manufacturers, and batch numbers of the materials used for this in vitro experiment are presented in [Table 1]. The roots of 90 single-rooted bovine teeth were sectioned (length = 16 mm) and prepared to 12 mm, at low-speed under water cooling. Each specimen was embedded in chemically cured acrylic resin (Classico, Brazil) in order that the long axis of the tooth and the preparation was perpendicular to axis X. 
|Table 1: The brand names, material types, main components, manufacturers, and batch numbers of the products used in the current study|
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The specimens were allocated into nine groups, considering the variables "adhesive system" (three levels) and "solvent drying time" (three levels) (n = 10): MBSC cont -multibottle etch and rinse self-curing adhesive (MBSC-Scotchbond Multipurpose Plus, 3M ESPE, USA/ solvent: water) + no solvent drying time (control), MBSC 50 -MBSC + solvent drying time of 50 s, MBSC 110 -MBSC + solvent drying time of 110 s, SLC cont -simplified etch and rinse light-curing adhesive (SLC-One Step, Bisco, USA/ solvent: acetone) + no solvent drying time (control), SLC 50 -SLC + solvent drying time of 50 s, SLC 110 -SLC + solvent drying time of 110 s, SDC cont -simplified etch and rinse dual-curing adhesive (SDC-Excite DSC, Ivoclar Vivadent, Liechtenstein/ solvent: ethanol) + no solvent drying time (control), SDC 50 -SDC + solvent drying time of 50 s, SDC 110 -SDC + solvent drying time of 110 s.
The adhesive systems were applied as followed:
- Groups MBSC cont : Etching with 37% phosphoric acid (15 s); washing with 10 mL of water; removal of excess water using N o . A total of 80 absorbent paper points; one coat of activator® solution was applied (10 s) and air-dried (5 s); one coat of primer® solution was applied (10 s) and air-dried (5 s); catalyze® solution was applied (5 s) and the excess removed (5 s), for a total of 40 s of application.
- Groups SLC cont and SDC cont : Etching with 37% phosphoric acid (15 s); washing with 10 mL of water; the excess water was removed using N o . A total of 80 absorbent paper points; two coats of adhesive solution were brushed (Microbrush, Dentsply) (10 s) and air-dried (5 s), followed by removing the excess with N o . A total of 80 absorbent paper points, for a total of 40 s of application; light curing was performed for 20 s (Dabi Atlante, Sγo Paulo, Brazil; light intensity = 600 mW/cm 2 ). For groups MBSC 50 /SLC 50 /SDC 50 and MBSC 110 /SLC 110 /SDC 110 , the adhesive were left undisturbed for an additional 50 and 110 s, respectively, before light curing.
The resin cement (AllCem, FGM, Brazil) was manipulated and inserted into the root canal using a Lentulo # 40 (Dentsply/Maillefer, Switzerland), the fiber post was placed into the root canal and light cured from the coronal aspect for 40 s (Dabi Atlante, Brazil; light intensity = 600 mW/cm 2 ).
Composite cores and mechanical cycling
The composite cores (Llis, FGM, Brazil) were built-up, using standard acetate molds, and light-cured for 40 s (Dabi Atlante, Brazil; light intensity = 600 mW/cm 2 ). These sets of root/post/core were submitted to mechanical cycling (Erios, Brazil) for 1,000,000 cycles (84 N, 4 Hz, 45° of inclination).
Sample production and push-out testing
Each specimen was fixed on a cutting machine (adapted cutting machine) and cutted (perpendicular along the root axis) into four slices (thickness = 1.8 mm ± 0.2 mm). The first cervical slice (approx. 1 mm) was discarded, due to the excess of cement that could influence the results.
Each sample was positioned on a metallic device with a central opening (Ψ = 3 mm/larger than the canal diameter), with the coronal portion of the sample placed downward. For push-out testing, a metallic cylinder (Ψ extremity = 0.85 mm) induced a load on the fiber post. The test was performed in a universal testing machine (EMIC, Brazil) at a speed of 1 mm/min.
The bond strength (σ) in MPa was obtained using the formula σ = F/A where, F = load for sample rupture (N) and A = bonded area (mm 2 ). For area calculation, the formula to calculate the lateral area of a geometric figure with a circular straight cone trunk with parallel bases was applied, being A = π * g * (R 1 + R 2 ), where, π = 3.14, g = trunk generatrix, R 1 = smaller base radius, and R 2 = larger base radius. To calculate the conic trunk generatrix g, the Pythagoras theorem was used-"the square of the hypotenuse = the sum of the squares of the two catheti" (g 2 =h 2 + [R 2 -R 1 ] 2 ) where h = section height. R 1 and R 2 were obtained by measuring the internal diameters of the smaller and larger base, respectively, corresponding to the internal diameter between the root canal walls. These diameters and h were measured with a digital caliper (Starrett® 727, Starrett, Brazil).
Since each group was composed of 10 specimens, 10 bond strength values of each group (n = 10) were used for statistical analyses [two-way analysis of variance (ANOVA) and post-hoc Tukey's test, α = 0.05].
Evaluation of the type of failure
All of the specimens tested were analyzed under an optical microscope (magnification of ×50) (Optical microscope MF series, Mitutoyo, Japan) to evaluate the type of fracture of the samples as follows:
- fracture of the post (cohesive);
- failure between resin cement and root dentin (adhesive failure); 3) fracture of the root dentin (cohesive); and 4) mixed fracture (cohesive fracture of the cement combined with adhesive failure). Some samples were selected for analysis in a scanning electron microscope (JEOL-JSM-5400, Jeol Ltd, Tokyo, Japan) (×35-×5,000 magnification).
| Results|| |
The results of the ANOVA two-way test revealed that the push-out bond strength results were significantly affected by the adhesive system used (P = 0.0081), but the factor "solvent drying time" had no effect on the push-out bond strength (P = 0.54) [Table 2]. Therefore, the hypotheses were partially accepted.
|Table 2: Results of 2-way analysis of variance and the interaction terms for push-out bond strength depending on adhesive system and solvent drying time (*P < 0.05)|
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When considering the "adhesive system" factor, MBSC groups (6.0 ± 2.2 MPa) presented higher bond strength values than did SLC groups (3.7 ± 2.1 MPa), but both were similar to SDC groups (4.4 ± 3.4) (Tukey's test). When considering the factor "solvent drying time", the control, 50 s and 110 s groups had no significant difference [Table 3] and [Figure 1].
|Table 3: Mean (± standard deviation) push-out bond strength values (MPa), according to the three different adhesive systems and the three solvent drying time|
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|Figure 1: Means and standard deviations of the bond strength data (MPa), considering the adhesive system and the application time|
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The analysis of the samples tested in push-out revealed that 84.5 % of the fractures occurred at the cement-dentin interface ("adhesive" failure, Type 2) and 15.5% were mixed (Type 4). The pattern of failure was very similar in all groups. [Figure 2] shows a representative micrograph of a Type 2 fracture.
| Discussion|| |
The present study revealed that the adhesive type influenced the bond strength values. When the factor "adhesive system" was analyzed, MBSC groups presented higher values than SLC groups, and similar results to SDC groups adhesive. These results agree with other studies, ,, which also revealed higher bond strength values for multibottle etch and rinse self-curing adhesives and simplified etch and rinse dual-curing adhesive groups than simplified etch and rinse light-curing adhesive groups.
Although the simplified etch and rinse adhesives are advantageous, from the clinical point of view, by reducing the number of steps in the procedure,  they are a mixture of hydrophilic and hydrophobic monomers in the midst of a greater amount of solvents, when compared to multibottle adhesives. This composition makes the amount of hydrophobic monomers in the last layer of adhesive much lower than with a three-step adhesive, in which the final solution is composed of large amounts of hydrophobic monomers. The largest amount of hydrophobic monomers in the last layer of resin can lead to the formation of a uniform layer of resin with a lower concentration of imprisoned water and solvent,  resulting in better bonding at the adhesive interface. , Then, considering that the root dentin to cement interface is the weakest part of this procedure,  the simplified adhesive systems should not be the best option for luting fiber posts to root dentin. ,
The solvent drying time was evaluated in this current study, and none statistical difference between the control groups and groups with drying time of 50 and 110 s was depicted. Some studies have assessed the influence of solvent evaporation on bond strength  and in the degree of conversion of the monomers of adhesive systems. ,, According to the study of Borges et al.,  the type of solvent present in the adhesive system solution could affect the degree of conversion considering different solvent volatilization modes.
In the present study, tested adhesive systems were composed by water (MBSC-groups), ethanol (SDC-groups), or acetone (SLC-groups) as a solvent. The water has a lower vapor pressure when compared to the other solvents (ethanol and acetone);  nevertheless, the MBSC-groups obtained the highest bond strength values. The mixture of water and 2-hydroxyethyl methacrylate (HEMA) may have hindered the evaporation of water because the presence of this monomer increases the vapor pressure of water, making it difficult to evaporate from the solution.  Even with this difficulties, the MBSC-groups most likely have the best results, perhaps due to the formation of an adhesive layer with less water, because the latter solution system contains hydrophobic monomers.  Additionally, the adhesive systems that contain water as a solvent have the capacity to expand the collapsed net of collagen fibrils. 
However, the mode of volatilization of the solvent cannot affect the degree of conversion of adhesives solutions with acetone,  what could have occurred for the SLC groups. Moreover, as this is just a light-cured adhesive, the light may not have been correctly transmitted across the root canal, which might affect the polymerization.  These results are not in agreement to the findings of an in vitro study,  in which an increase in the solvent drying time resulted in higher bond strength values for the same SLC adhesive. Moreover, this phenomenon seems to have not occurred for the others adhesives, not only by the type of solvent, but mainly due to the cure mode, because they already begin to polymerize before the light application (in the case of the SDC adhesive) or after the catalyst solution application (in the case of the MBSC adhesive).
In the present study, a mixed protocol of evaporation of solvents was adopted, since the evaporation of the solvent was activated with a mild and short blast of air and a longer waiting time before applying the resin cement. Adhesive systems containing ethanol as a solvent (SDC groups), get a higher degree of conversion of monomers after passive evaporation of over 30 s.  However, an association between ethanol drying time and the values of bond strength was not observed in the present study, probably because the adhesive system of the SDC-groups had a type of polymerization that could convert many more monomers, even in the presence of a solvent in the solution, a phenomenon that seems to not increase with time.
In the present study, the evaporation of the solvent may have been hampered due to a small area of the adhesive layer in contact with the environment, once the depth is greater than the opening in a root canal. Then, the more cervical region of the root could have more solvent evaporated, what not lead to increasing in the total bond strength values.
When cementing fiber posts to root dentin, many factors determine the effectivenessof the bonding. It is necessary to consider that the stability of bonding is directly influenced by the frictional factor, that is, the capacity of the posts to remain in position, held by the friction and surface roughness of the cement.  The frictional factor acts strongly, even when using metal posts with nonadhesive cementation.  Another important factor to be considered is polymerization shrinkage, as it is known when restoring root cavity, since the C-factor is very pronounced.  Therefore, it is suggested that other studies should be performed with another cementation strategies. Furthermore, clinical studies should be conducted to confirm the in vitro research findings.
| Conclusion|| |
This study showed that adhesion to root dentin was dependent on the type of adhesive used, with better performance to multibottle etch-and-rinse self-curing and simplified etch-and-rinse dual-curing adhesives. In addition, solvent drying time does not affect the bond strength of a fiber post to the root dentin.
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[Figure 1], [Figure 2]
[Table 1], [Table 2], [Table 3]