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Year : 2015  |  Volume : 5  |  Issue : 1  |  Page : 25-30

Removal force of cast copings to abutments with three luting agents

Department of Oral Implantology, School of Dentistry, Cayetano Heredia University, Lima, Peru

Date of Web Publication2-Apr-2015

Correspondence Address:
Frank R Mayta-Tovalino
Department of Oral Implantology, School of Dentistry, Cayetano Heredia University, Lima
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Source of Support: None, Conflict of Interest: None

DOI: 10.4103/0974-6781.154426

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Purpose: The purpose of this study was to evaluate the removal force of cast copings over abutments cemented with 3 dental cements.
Methods: The experiment used 36 abutments divided into six groups (n = 6) Cast copings with CeraOne cemented with zinc oxide-free eugenol; with glass ionomer; with zinc phosphate and solid 5-mm-high abutments cemented with the same cements wax loops (3 mm in diameter) were made and added to the occlusal surface to allow for tensile testing, and the copings were cast in cobalt-chromium alloy using the lost wax method. The copings were sandblasted with 50-μm aluminum oxide particles to prevent irregularities and cleaned with acetone. The copings were cemented with a 49-N load for 10 min. Subsequently, they were separated with a universal testing machine (Tensometer; Monsanto) at a rate of 5 mm/min until the detachment. The effects of cement and abutment type were evaluated using the means and standard deviations of the loads and were analyzed with ANOVA and the Tukey test (α =0.05).
Results: The abutments with a height of 5.5 mm had a statistically significant (P < 0.001) higher tensile strength with a mean of 84.60 N (±8.82) than that of the CeraOne abutments with an average of 36.09 N (±11.66) when cemented with zinc oxide.
Conclusions: We conclude that the type of cement and abutment can significantly influence the retention of implant-supported crowns. The results do not suggest that any one type of cement is better than another, but they rank cements in order of retention capacity. Zinc phosphate provided the greatest retention while the eugenol-free zinc oxide provided the least (P < 0.001).

Keywords: Dental implant, luting agent, tensile strength

How to cite this article:
Mayta-Tovalino FR, Ccahuana-Vasquez VZ, Rosas-Díaz JC. Removal force of cast copings to abutments with three luting agents. J Dent Implant 2015;5:25-30

How to cite this URL:
Mayta-Tovalino FR, Ccahuana-Vasquez VZ, Rosas-Díaz JC. Removal force of cast copings to abutments with three luting agents. J Dent Implant [serial online] 2015 [cited 2020 Jul 10];5:25-30. Available from:

   Introduction Top

Treatment with dental implants to replace missing teeth is well documented. The prosthetic restorations are connected to the implant abutment screws or are cemented. The use of cemented implant restorations has gained in popularity over retaining screws because of their improved esthetics, [1],[2] passive fit, [3] reduced cost, and ease of fabrication with a simple laboratory technique.

Reversibility is an essential factor in these restorations. In the case of screw loosening, fracture, or perimplantitis, removing single or multiple crowns can mean the loss of the implant abutments. The abutments can be prefabricated, or custom made in stainless alloy, titanium, or zirconia ceramic. According to Hebel and Gajjar, [4] the form of the abutment, the material of which the abutment is made, and the type of luting agent can affect the longevity of these restorations.

Although screwed crowns are easier to remove if necessary, [5] the use of interim cements can add to the reversibility of cemented prostheses, according to Henry et al. [6] Levine et al. [7] and Santosa et al. [8] few published data are currently available regarding their long-term success. In particular, the choice of a suitable cement for a specific clinical situation is still based more on the experience of the clinician than on scientific data. Ideally, the cement must be strong enough to hold the implant prosthesis in place indefinitely but sufficiently weak to allow the clinician to remove it if necessary. Unfortunately, no evidence is available as to which cement is indicated or about the likely behavior of each cement. [2] In addition, implant abutments come in a wide variety of shapes and heights in order to improve aesthetics, preserve the health of the soft tissues, and provide adequate retention for the prostheses, all of which are fundamental to successful treatment.

Recommendations as to whether to use interim or definitive cements for implant-supported prostheses vary. [9] Water-based cements produce a variety of results and often do not behave predictably. Some studies suggest the use of interim cement for multiple implant prostheses and definitive cement for unit prostheses. The use of interim cements is considered suitable for a restoration likely to be removed in the future. In some situations where reversibility is not required, a permanent dental resin-based cement could be used. [10] For that reason, the purpose of this study was to evaluate the removal force of cast copings over abutments cemented with three dental cements.

   Materials and methods Top

Specimen preparation

Thirty-six abutments were distributed into six groups (n = 6). Cast copings with CeraOne abutments cemented with eugenol-free zinc oxide; with glass ionomer; and with zinc phosphate and solid 5-mm-high abutments cemented with the same luting agents. All specimens were embedded in acrylic resin-based on previous studies. [11],[12],[13]

Abutment casting

CeraOne abutment analogs were used (NACONIH code fix Titanium Implant System SP, Brazil) and 5.5-mm-high solid abutments (CMAAC 5.5 code, Titanium Fix Implant System SP, Brazil) to which a loop was added to the occlusal surface of each coping with a wax sprue (no. 10) to allow for tensile testing (Breeding et al., 1992). The copings were cast in a metal ceramic Co-Cr alloy (Metalloy CC Germany). The castings were sprued with a 5-mm diameter wax wire (Wax wire for placement of sprues, Dentaurum, Germany) and invested in phosphate-bonded investment (Hi -Temp, Whip Mix Co. Louisville, KY, USA) with an unrestricted expansion technique in a 9-cm diameter flexible ring (Dentaurum - Germany) [Figure 1]. They were cast with the lost wax method.
Figure 1: The cast copings were sprued with 5-mm wax sprues

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Sandblasting of cast copings

The castings were separated from the sprue with a carborundum disk, sandblasted, and their external surface refined slightly to produce intimate contact with the fixtures of the universal testing machine. The intaglio of the copings was sandblasted with 50-μm aluminum oxide particles (Ivoclar Vivadent). Before cementation, the abutments and copings were cleaned of impurities with distilled water for 15 min in an ultrasonic bath. The intaglio was examined for irregularities with a stereomicroscope (Leica Microsystems LAS EZ version 2.0.0 Switzerland) at ×80 magnification.

One interim cement (eugenol-free zinc oxide) and two definitive cements (glass ionomer and zinc phosphate) were used [Table 1]. Each cement was used as directed by the manufacturer. All cast copings were cemented by a calibrated operator. The copings for all specimens were cemented with a standardized force of 49 N applied along the axis of the abutment pair within 10 min, according to American National Standards Institute/American Dental Association. Specification No. 96. [14] Finally, all specimens were stored for 24 h in distilled water at 37°C.
Table 1: Luting agents used in the study

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Removal force test

The specimens were separated with a universal testing machine (Tensometer; Monsanto UK) in the Materials Laboratory of Pontificia Universidad Catolica del Peru. All specimens were subjected to a uniaxial load rate of 5 mm/min to cause the separation of the copings on the replicas [Figure 2] and [Figure 3]. The force values were recorded and expressed in newtons (N).
Figure 2: All specimens were subjected to a uniaxial load rate of 5 mm/min to remove the copings from the abutments. Removal force was expressed in newtons.

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Figure 3: Titanium abutment after tensile test

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Statistical analysis

For the univariate analysis, we obtained the mean and standard deviation, which were recorded in a frequency table. In addition, the sample was subjected to the Shapiro-Wilk test and found to have a normal distribution. For the bivariate analysis, the Tukey test and ANOVA test were used, establishing a significance level of P < 0.05. Statistical analysis was performed with Stata V° 12 (Data analysis and Statistical software).

   Results Top

We found that the 5.5-mm-high solid cemented abutments cemented with zinc phosphate required a mean force of 400.49 N ± 9.80 N to detach the coping from the cemented casting. In addition, a maximum value of 499.50 N and a minimum value of 186.20 N were obtained. The specimens had normal distribution [Table 2]. A comparison of in vitro resistance with tensile strength found that the removal force was higher for the 5.5-mm-high solid abutment group and was statistically significant (P < 0.001). In addition, the CeraOne abutments cemented with glass ionomer showed a mean force of 48.51 N as compared with the 5.5-mm-high solid abutments cemented with glass ionomer at 56.02 N; the difference was not statistically significant (P = 0.279). The CeraOne abutments cemented with zinc phosphate required a mean force of 459.62 N as compared with the 5.5-mm-high solid abutments at 400.49 N to displace the coping cemented on the abutment; the difference was not statistically significant (P = 0.355) [Table 2].

In assessing the in vitro removal force of cast cylinders and CeraOne abutments cemented with eugenol-free zinc oxide, glass ionomer, and zinc phosphate, it was found that CeraOne abutments had an average of 36.09, 48.51 and 459.62 N, respectively. The difference in the force required to achieve detachment among these groups was statistically significant (P < 0.001). Moreover, in assessing the resistance to tensile strength of cast cylinders of 5-mm-high solid abutments cemented with eugenol-free zinc oxide, glass ionomer, and zinc phosphate, it was found that 5.5-mm-high solid abutments had a mean of 84.60, 56.02 and 400.49 N, respectively. The difference in the removal force among these groups was statistically significant (P < 0.001) [Table 1].
Table 2: Mean tensile retention strength values of the three luting agents

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   Discussion Top

The success of oral rehabilitation with dental implants depends not only on osseointegration, but also on maintaining the integrity of the connection of the prosthetic restoration to the implant. [15] Implant restorations can be screw-retained, cemented, or a combination of both. Numerous advantages and disadvantages have been described for each type of retention. [16],[17] Dental cements can be used for interim or definitive bonding. Currently, resin cements are used for definitive cementation but have the disadvantage of being more expensive; zinc phosphate cements are more affordable. Cements with weaker physical properties, such as eugenol-free zinc oxide, are generally used as interim luting agents. [18],[19],[20]

In contrast, the retention of cemented restorations can be influenced by different factors such as the size of the abutment (height and width), the texture, the convergence angle between the abutment walls, and the cement used. [21] For an implant-supported prostheses, the cement must provide sufficient retention to prevent loosening during normal operation but should also allow the restoration to be removed without damaging the abutment. [22] Thus, the selection of cement is of importance and should be made with the specific patient and/or site in mind. The geometry of the abutment can also influence the function of cementation. Although a threshold force for clinical success has not been established, most failures have been reported in cements with a lower tensile strength.

This study showed that the highest removal force was provided by the zinc phosphate cement, followed by glass ionomer and eugenol-free zinc oxide in the CeraOne abutment group (P < 0.001). In addition, the zinc phosphate exceeded the other cementing agents in the solid abutment group (P < 0.001). This finding is expected because of the affinity of zinc phosphate cement to metallic structures, providing good retention between the Co-Cr casting coping and the titanium abutment, regardless of the height and shape of the abutment. These results were similar to those described by Al Hamad et al. [13] Akça et al. [18] but different from those described by Ergün et al. [10] who found that the resin cement Panavia F2.0 showed even greater retention than zinc phosphate, zinc polycarboxylate, or zinc oxide eugenol (P < 0.05). Mansour et al. also disagreed with the results of this study. They reported that zinc phosphate showed lower values than the protec cem resin cement and even the zinc polycarboxylate Durelon, which with most testing exhibits a lower removal force than that of zinc phosphate. [18],[23],[24] Glass ionomer and zinc polycarboxylate have adhesive properties and can adhere to the tooth structure by calcium-ion chelation and chelating to the titanium ions in the metal surface.

The retention strength of resin cements is attributed to the adhesion system. [22] Some authors found that the resin and glass ionomer cements were more retentive, [15],[23],[25] but the results obtained by this study are consistent with other authors, who also found that zinc phosphate had the greatest removal force, [26],[27] which tests the hypothesis that was raised at the beginning of the investigation. However, Akça et al. [18] Mansour et al. [9] Sheets et al. [19] and Wolfart et al. [28] claim that zinc polycarboxylate was more retentive than the glass ionomer, zinc phosphate, and zinc oxide cement.

In contrast with the present investigation, Squier et al. [20] compared the retentive forces of different luting agents used to cement crowns to implant abutments. They found similar removal forces for the cementing agents as in this study.

Meanwhile, Keith et al. [29] mentioned that one of the limitations of zinc phosphate is that when it is used to cement crowns on implants, it generates a higher marginal discrepancy compared with glass ionomer (P < 0.001); this may be a factor in bacterial filtration and accumulation of food particles. Gilson [30] and Myers [31] reported that the interim cementing agents provide adequate retention for cemented prostheses with multiple splinted abutments; similar results were found by this study. However, Sheets et al. [19] and Bernal et al. [25] found that the retention values for interim cementing agents were very low. Many authors have concluded that zinc oxide is more suitable for cementing implant prostheses when the reversibility of the restoration is important.

When cementing agents are not comparable among themselves, the values of the adhesive strength will probably be different and the tensile strength will be influenced by several variables such as angulated abutment, type of luting agent, abutment height, and sandblasting. [33],[34],[35],[36],[37],[38],[39],[40] The present study showed that 5.5-mm-high solid abutments had greater tensile strength than the CeraOne abutments in the three groups (eugenol-free zinc oxide, glass ionomer, and zinc phosphate). Another point to consider is that most studies related to the retention of implant prostheses use abutments of different types, heights, and diameters. In addition, the surface roughness of the abutment and the use of thermocycling can cause variation in the cementation of crowns on implants. For example, a survey done in the United States showed that dental schools teach the use of resin cements, followed by zinc oxide, glass ionomer, zinc phosphate, and zinc polycarboxylate as the protocol for cementing prosthesis implants. [27] For this reason, cementing techniques and the other variables described earlier should be standardized.

A limitation of this study was the use of a pull-off test. In a clinical situation, it is likely that other forces can contribute to the loosening of the implant crown. Masticatory forces create a combination of tensile and compressive stresses on the prosthesis. However, the pull-off test was used since it has been adopted in other studies and allowed the comparison of our results with previous investigations. [8],[12],[13],[32] Thus, these studies and the current research have determined that zinc phosphate cement provides the greatest retention required regardless of the type of abutment used. Therefore, the present in vitro study provides a basis for expanding knowledge about the retention of cemented implant restorations.

   Conclusions Top

  • Within the limitations of this in vitro study, it can be concluded that the influence of the type of abutment in the performance of cementing agents depends on the particular type of cement. Zinc phosphate cement showed the greatest increase in retention, followed by glass ionomer, while eugenol-free zinc oxide showed the lowest tensile strength (P < 0.001)
  • When the tensile strength of the CeraOne abutment was compared with that of the 5.5-mm-high solid titanium abutment cemented with eugenol-free zinc oxide, the latter was found to need greater traction and the difference was statistically significant at P < 0.001
  • When definitive cementing is needed, zinc phosphate is appropriate. However, if the prosthesis may require removal, cementation with a eugenol-free zinc oxide is appropriate. The geometry and dimensions of the abutment will play a role in adequate retention.

   Acknowledgment Top

We wish to thank Titaniumfix for supplying implant parts used in this study.

   References Top

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  [Figure 1], [Figure 2], [Figure 3]

  [Table 1], [Table 2]


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