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ORIGINAL RESEARCH Table of Contents   
Year : 2009  |  Volume : 20  |  Issue : 3  |  Page : 332-336
Comparison of resin push-out strength to root dentin of bovine- and human-teeth

1 São José dos Campos Dental School, São Paulo State University, Brazil
2 Division of Prosthodontics, Department of Restorative Dentistry, Federal University of Santa Maria, Brazil
3 Department of Dental Materials and Prosthodontics, São Paulo State University at São José dos Campos, Brazil

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Date of Submission10-Apr-2008
Date of Decision16-Sep-2008
Date of Acceptance30-Oct-2008
Date of Web Publication30-Oct-2009


Aim : To compare the push-out strength of bovine- and human-root dentin and, thus, evaluate the suitability of bovine-root dentin to substitute human-root dentin for bond strength testing.
Materials and Methods : Ten single-rooted human-teeth and ten bovine incisors were prepared using a #3 bur of a fiber post system (12 mm long). The posts were duplicated with resin cement (Duolink). The root canals were treated with All Bond 2 adhesive system and the resin posts were cemented using Duolink. The specimens were cut perpendicular to their long axis, yielding disc-specimens with 1.5 mm thickness, which were submitted to a push-out test (1 mm/min). Ten bond strength values per group (n = 10) were used for statistical analysis (Student t test, a =.05).
Results : Statistically significant differences were found for the bond strength values between bovine- (4.1 ± 1.3 MPa) and human-root dentin (8.6 ± 5.7 MPa) (P =.0001).
Conclusion : The push-out strengths of bovine- and human-root dentin were statistically different.

Keywords: Bovine tooth, human-tooth, push-out test, root dentin

How to cite this article:
Galhano G, de Melo RM, Valandro LF, Bottino MA. Comparison of resin push-out strength to root dentin of bovine- and human-teeth. Indian J Dent Res 2009;20:332-6

How to cite this URL:
Galhano G, de Melo RM, Valandro LF, Bottino MA. Comparison of resin push-out strength to root dentin of bovine- and human-teeth. Indian J Dent Res [serial online] 2009 [cited 2019 Sep 19];20:332-6. Available from:
The adhesion between cement and dentin has been the subject of studies, [1],[2],[3],[4] which evaluate the bond strength of root dentin to different adhesive systems, as well as, analyze the formation of a hybrid layer by means of scanning electron microscopy. [5]

Evaluation of this bond strength invariably requires utilization of the tooth structure as a substrate. Extracted human-teeth are, however, becoming increasingly difficult to obtain due to the recent progress in conservative dental treatment and of their scatter from patient to patient. [6] Bovine teeth are often employed as substitutes of human- teeth in adhesion tests in the crown dentin, because of the ease of standardization and the difficulty to achieve enough intact human-teeth in vitro studies. [7],[8] Bovine teeth have been used in microtensile bond strength, [9] shear, [1],[10] pull-out of root post, [11] fracture resistance, [12] and microleakage tests. [13]

There is a little research for evaluating the suitability of bovine-root dentin for bond strength tests. Causton [14] stated that bovine-root dentin produces very different results in bond strength tests and should be avoided for bond strength tests without providing supporting data for this assertion. Otherwise, no difference was observed between human, bovine, and porcine teeth using the crown segment in microtensile testing. [9] Schilke et al., [15] evaluated the number and diameter of the dentinal tubules in the roots of bovine teeth and stated that the bovine-root dentin would not be suitable as a substitute for human dentin in bond strength tests. Nevertheless, the conditions for adhesion and the origin of bovine-teeth are easier to standardize for bond strength testing when compared to human-teeth. Various bovine teeth can be obtained from fewer animals, minimizing the differences of age, occlusal conditions and diet. From one animal, four inferior incisors (same age) can be used and, hence, the standard deviation of data may be decreased. Thus, bovine coronal dentin [9],[13] and root dentin [12] are often employed as a substitute for human dentin when conducting bond strength testing of restorative materials. Despite current studies that state that bovine coronal dentin can be substituted by human coronal dentin, [9] the bovine-root dentin should be studied in order to determine if it is an adequate substitute of the human-root dentin in bond strength test.

Thus, the primary goal of this study was to assess the behavior of an adhesive system in human and bovine-root dentin, verifying the possibility of utilizing bovine-root as a substrate for bond strength testing.

   Materials and Methods Top

Ten intact single-rooted human-teeth, extracted for orthodontic or periodontal reasons, were employed in the present study. The experiment also used ten single-rooted bovine-teeth. The bovine- and human-teeth were frozen for, at most, two months and were cleaned with periodontal curettes.

Preparation of the teeth-calibration of the root canals

The root size of each specimen was standardized at 16- mm length from the apex. After standardization, the root pulp was removed and the root canal was prepared with NiTi instruments. Root canal filling was not performed. Afterwards, root canal preparation was performed with Largo burs and with #3 burs from a double tapered quartz fiber-reinforced composite post system (FRC) (D.T. Light-Post® , Bisco Inc, Schaumburg, US), for cementation (working length of 12 mm from the cervical).

An acrylic resin base was prepared at the root portion of each tooth to allow the tooth to attach to the cutting machine. To assure that the sectioning was almost perpendicular to the long axis of the prepared root canal, precaution was taken to make this base perpendicular to the long axis of the preparation. A surveyor was employed for that purpose, on which the #3 bur of the FRC system was attached. The prepared teeth were positioned on the bur and an acrylic resin filling was made, up to 3 mm from the apex [Figure 1].

Duplication- and cementation-posts

A FRC #3 was molded in silicone (Aquasil, Dentsply- DeTrey, Konstanz, Switzerland; Batch # 0107001500) to create a mold to be filled with dual-cured resin cement (Duolink Composite Luting cement, Bisco Inc., Schaumburg, US; Batch # 0300014374). Twenty posts of resin cement were fabricated, which were substituted by the FRC in order to prevent failures between the FRC and resin cement, which would impair the evaluation of the adhesive systems bonding to human and bovine-root dentin.

For cementation, all teeth were treated with a dual-cured adhesive system (All Bond® 2 Universal Adhesive System, Bisco Inc, Schaumburg, USA; Batch # 0400003556), and the resin posts were cemented with Duolink, following the manufacturer's instructions.

Push-out strength test

Preparation of specimens: The specimens were fixated to a metallic base in the cutting machine (LabCut 1010, Extec Corp., Enfield, CT, US), and sectioned perpendicularly to the long axis of the root with a diamond disc under cooling. A 0.5 mm cut was initially performed and discarded, since there might have been cement overflow. Thereafter, six sections, measuring approximately 1.5 mm, were prepared.

Testing: Each specimen was positioned on a metallic device measuring 1 cm in height and 2 cm in diameter, with a central opening larger than the diameter of the root canal. The most coronal portion was always positioned downwards (apical-coronal load). For the push-out testing, a metallic cylinder (end diameter 0.85 mm) was applied on the space corresponding to FRC. Testing was performed in a universal testing machine (Emic DL-1000, Emic, Brazil), at a crosshead speed of 1 mm/min.

The bond strength measurements were calculated according to the formula:

R = F/A, where

F = load for rupture of the specimen (N)

A = interfacial area (mm 2 )

Calculation of the interfacial area (A) of the specimens: the formula employed was that of the lateral area of the frustum of a right circular cone with parallel bases [Figure 2]. A = π*g* (R 1 + R 2 ), where, A = interfacial area, π = 3.14, g = slant height of the cone or generatrix of the frustum, R 1 = radius of the smaller base, and R 2 = radius of the larger base. For calculation of the generatrix of the cone frustum g [Figure 2]b, the Pythagoras' theorem was employed: g 2 = h 2 + [R 2 − R 1 ] 2 , where g = generatrix of the frustum, R 1 = radius of the smaller base, R 2 = radius of the larger base and h = section's height.

The mean bond strength values of the disc-specimens of each specimen (tooth) were obtained and these values (n = 10) were analyzed by Student's t test, using a level of significance of 5%.

Morphological analysis in scanning electron microscopy

One human-tooth and one bovine-tooth were cut longitudinal to their long axis, exposing the root dentin. This exposed surface was conditioned with 32% phosphoric acid for 15-30 sec and washed with air-water spray. These specimens were prepared for SEM evaluation (JEOL- JSM- 5400, Jeol Ltd, Tokyo, Japan), in order to analyze the dentinal morphology of the human and bovine- root substrates: density of tubules and the differences among the cervical, middle, and apical thirds.

   Results Top

The results showed that the bond strength of the human- teeth (8.6 ± 5.7 MPa) presented a statistically significant difference (t = 2.424; df = 18; P = 0.026 < 0.05) when compared to the bond strength of the bovine-teeth (4.1 ± 1.3 MPa). The bond strength means and SD are displayed in [Figure 3].

While analyzing the SEM micrographs of different root thirds of the human and bovine-teeth [Figure 4], it was noted that the human-root dentin appears to present higher dentinal tubule density when compared to bovine- root dentin. The diameter of the tubules of the human-root dentin appeared to be larger than tubule diameter of the bovine-root dentin. When the cervical, middle, and apical thirds were compared, it was possible to observe that the cervical thirds of both the human and bovine-root dentin appear to present higher tubule density than the middle and apical regions.

   Discussion Top

The results obtained in this study showed that the push- out bond strength of human-root dentin is statistically higher than that of bovine-root dentin. This might have occurred because different root regions of the specimens were submitted to the push-out test, considering the standardization of the length of the specimens in 16 mm. All three regions of the human-root dentin (cervical, middle, and apical) were used for testing while only the middle- and apical-root portions of the bovine-teeth were used. Thus, the human-teeth may have had higher push-out bond strengths because some studies have found that the cervical third exhibits higher bond strength values than the middle and apical regions. [10,12] Thus, the values in the cervical third of the human-root dentin may have contributed to the increased push-out bond strength, while the bovine-teeth did not have that advantage. Ferrari et al., [16] found greater resin tag density in the cervical third of the root than in the middle and apical thirds in human- teeth. Ferrari et al., [5] also observed better formation of resin/dentin inter- diffusion zones (RDIZ) in the cervical root third (higher density of dentinal tubules), than in the apical and middle thirds (lower density of dentinal tubules) in human- teeth. Therefore, this utilization of different root regions of both substrates may be partly responsible for the difference in the push-out bond strength values.

The morphological analysis of root dentin of both substrates carried out in the current study [Figure 4] reinforces this hypothesis. It was noted that the human-root dentin seems to have a higher density of dentinal tubules than the bovine- root dentin. The tubule diameter of the human-root dentin appears to be larger than the tubule diameter of the bovine-root dentin. The cervical third of both the substrates seems to have a higher density of dentinal tubules than the middle and apical regions.

Considering the studies of density analysis of tubules and bond strength tests in different root canal regions, there seems to be a correlation between the higher density of dentinal tubules and increasing of bond strengths of adhesive systems to dentin. [2],[10],[12],[16] Therefore, this correlation may also be responsible for the difference in the push-out bond strength values between the human and bovine-teeth.

The results obtained in this study agreed with the results obtained by Schilke et al., [8] who found significant differences between bovine-root dentin and human dentin, using a shear bond strength test.

Another important factor to consider is that the standard deviation of the data for the bovine-teeth was approximately 30% (4.1 ± 1.3 MPa), while the standard deviation of the data for the human-teeth was more than 65% (8.6 ± 5.7 MPa). Nakamishi et al. [7] and Schilke et al., [8] found a lower standard deviation for data obtained from bovine- teeth than from human-teeth. This probably occurred due to the selection process of the bovine- and human-teeth for testing. Bovine tooth origin is easier to standardize and to control for bond strength testing when compared to the human-tooth origin. Various bovine- teeth can be obtained from few animals, minimizing the differences of age, occlusal conditions and diet. From one animal, 4-6 lower incisors (same age) can be used and allocated to the 4-6 different groups (one per group), which would be composed by "similar" substrates for adhesion In the current study, the bovine group was composed of 10 teeth from 3 animals, while the origin of the human- teeth is undefined. Nakamichi et al., [7] had already noted an increasing difficulty of obtaining human- teeth for adhesion testing.

However, there is controversy regarding the use of bovine- teeth as a substitute for human-teeth in adhesion tests. While some studies reported similarities to human-teeth, [3],[7],[9] other studies found discrepancies and stated several criticisms to the use of bovine-teeth as a substitute substrate. [4],[8],[17] It can be suggested that bovine-teeth could perhaps be used initially to evaluate the adhesive materials or technique before clinical implementation. The tests using bovine-teeth could be the first parameter in the evaluation process.

As a substitute for human-teeth, bovine-teeth are used in many investigations. [8] Different statements were found in the literature about the applicability of bovine coronal dentin, which is commonly used in adhesion tests. [4],[7],[18],[19] However, SEM observations indicate large differences in morphology of fracture surfaces of crown and root dentin. [2] Consequently, the bonding to root dentin should be considered different from bonding to crown dentin for both human and bovine-teeth.

It has been suggested that dentinal tubules exert only a minor influence on the mechanical properties of dentin. Alternatively, there are some studies on human [8] and bovine [20] dentin proving that the tubular structure does influence the bond strength. This can explain the difference observed between the human and bovine-root dentin, since tubule orientation, number, size and degree of intra tubular mineralization vary between human and bovine-teeth. [15]

Within the limitations of the current experiment, it can be concluded that, although a difference of push-out bond strength values of an adhesive system to bovine- and human- root canal dentin was determined, it cannot be stated that the root canal of bovine-teeth is not a good substitute for human-teeth in bond strength tests. Obviously, if the bovine-root dentin is used as a substitute, the regional differences in relation to the human-root dentin should be taken into consideration, for bovine-tooth roots are typically 16 mm long. It is also important to consider that the bonding mechanism of adhesive systems to bovine- and human-root dentin is apparently similar, [9] although these substrates show some morphological differences.

Further comparative studies between human and bovine- root dentin are warranted. These studies should address the differences between human and bovine-root dentine regard of the formation of RDIZ, the density and features of root dentinal tubules and the differences in adhesion tests (push- out, microtensile, pull-out tests). These studies would help in determining the suitability of using bovine-root dentin as a substitute for human-root dentin in bond strength tests involving resin materials.

   Conclusion Top

Within the limitations of the current experiment, it can be concluded that bovine-root dentin is different from human- root dentin when evaluated using the push-out test. Further studies should be conducted to confirm that bovine- root dentin can be used as a substitute for human- root dentin in push-out tests involving resin materials.

   References Top

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Correspondence Address:
Luiz Felipe Valandro
Division of Prosthodontics, Department of Restorative Dentistry, Federal University of Santa Maria
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Source of Support: None, Conflict of Interest: None

DOI: 10.4103/0970-9290.57378

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