Various types of restorations are used to reinstate the shape and function of teeth, including intracoronal restorations, extracoronal restorations, fixed partial dentures, removable dentures, and implant-supported restorations. ¹ Introduction of intraosseous dental implants has revolutionized the reconstruction of edentulous patients. ² , ³ Prosthetic reconstruction by dental implants is stable treatment for edentulous patients and is considered a standard treatment in dentistry due to advances in technologies related to osseointegration. ² , ³ , ⁴

Knowing the factors that stabilize the hard and soft tissue around the implants in the long time is clinically important. ⁵ The retention of implant-supported restorations, ⁷ retention's components of prosthesis supported by implant, ⁸ material, geometry, length, type of surface roughness of abutment and implant veneer, ⁹ , ¹⁰ , ¹¹ veneer cleaning method for re-cementing, ¹² physical, chemical and bioactive properties of the adhesive cement, are among the most important factors. ¹³

Fixed implant-supported dentures can be held in place by screw or cement. ¹⁴ Each type of gripping mechanism has advantages and disadvantages. Screw restorations are easily recoverable and have better repair capability and the ability to clean due to the ability to open these screw channels. ¹⁵ Additionally, there is a lower probability of preimplantitis due to the lack of cement stimulation around the implant tissues in this type of restoration. ¹⁶ The cemented implant prosthesis has the advantage of passive matching and occlusal integration. ¹⁴ , ¹⁷ , ¹⁸ Furthermore, implant restoration retrieval may be necessary in conditions such as cosmetic, mechanical, and biological problems in fixed implant prostheses. ¹⁹ , ²⁰

The choice of type of luting is an important factor in providing adequate retention of implant restorations maintained by cement. ²¹ Temporary cement are the most common luting materials used for these veneers. The cement should be strong enough to hold the prosthesis but, at the same time, should be weak enough to allow the dentists to remove the restoration comfortably and safely. ²² However, in some cases, such as insufficient abutment height, it may be necessary to select a luting agent with higher bond strength. ²³ Moreover, after carefully assessing the health of the tissue and bone around the implants in cases of decementation of the restorations, physicians may prefer to replace the temporary cement with a permanent one. ²²

A cemented implant restoration sometimes needs to be re-cemented. ²⁴ In these cases, permanent or temporary cement can be used to re-cement the repaired restorations. ²⁴ Resin-based luting agents have been suggested in many cases because they provide high levels of trapping with low microleakage. ²² Temporary cement left inside the prosthesis can act as a source of contamination and reduce the final cement retention. ²⁵ , ²⁶ Additionally, this residual cement can prevent the micron roughness of the inner surface of the restoration and smooth it, thus reducing the final cement retention. ²⁷ Furthermore, a temporary cement containing eugenol disrupts the resin cement bonding. This is due to the reduction of free radicals due to the action of eugenol and limits the polymerization of the resin. ²⁸ As a result, complete removal of temporary cement before permanent cementation of the restoration is proposed. Different methods have been proposed for cleaning the inside of the restoration before its re-cementing. Residual cement extraction solutions, ²⁹ hand tools such as curette, ³⁰ ultrasonic bath with alcohol, sandblasting with alumina particles, and etching and burning of the remaining cement ³¹ are used for this purpose. However, most of these methods tested on tooth-supported restorations. ³²

The effect of different cleaning methods on the removal of eugenol-containing and eugenol-free temporary cement residues from implant-based zirconia prostheses and their role in the final tensile bond force (TBF) of these zirconia has not yet been investigated. The purpose of this study was to investigate the effect of different methods of cleaning zirconia copings cemented by two types of temporary cement (eugenol and noneugenol) on the removing force of the copings.

Preparation of analogs and abutments

Fifty implant analogs (OPR, Zimmer, SwissPlus, Carlsbad, CA, USA) were vertically mounted in their own self-cure acrylic resin cylinder with size 10 mm × 20 mm. The alignment of analogs was confirmed by an expert surveyor. Abutment analog junction was placed 1 mm upper the resin cylinder. Fifty abutments (FMS, Zimmer, SwissPlus, θ 4.8, Carlsbad, CA, USA) with 7 mm height were screwed onto the analogs with a 30 Ncm torque force through a calibrated prosthetic torque wrench (Zimmer Dental, Carlsbad, CA, USA).

Copings preparation

Abutments were scanned separately. A computer-aided design/computer-aided manufacturing (CAD/CAM) device (Amann Girrbach, North America, Charlotte, USA) with a 30 μm space for the luting agent was used to fabricate 50 zirconia copings (Kerox, Sóskút, Hungary). Copings were designed with an occlusal loop. Loops were drilled in order to prepare adequate grip in universal testing machine tensile test. Stereomicroscope (×4 magnifications) was applied to assess the marginal fits of coping. Copings with unsuitable fit were excluded from the test. An ultrasonic bath containing ethanol 96% (5 min at 30°C) was used for cleaning all copings and abutments. After that, copings and abutments were washed by distilled water and dried. Teflon was used to fill the screw access of the abutments.

In vitro conditions

The 50 copings were divided into four experimental groups (N = 40) and a control group [N = 10, Table 1].{Table 1}

The manufactures guidelines were applied to cemented control copings using Panavia SA luting plus (Kuraray, Kurashiki, Japan). Forty copings of the test groups were resin cemented (Panavia SA luting plus, Kuraray, Kurashiki, Japan). The other four groups were cemented using the temporary cement with and without eugenol (TempBond and TempBond NE, Kerr, Hamm, Germany) (Temp and TempNE groups in first cementation process). For this purpose, the internal walls of copings were covered with cement using a brush and pushed down by pressure hand for 10 s. Guidelines of the American Dental Association specification (No. 96) were then applied to loaded samples by a 5 kg force for 10 min. Samples were soaked in distilled water (24 h at 37°). Prepared samples were tested by 5000 thermal cycles (5°C–55°C, 30 s dwell time) to pretend the oral condition. Copings were tested by a universal testing machine (Type LFML, Walter + Bai AG, Löhningen, Switzerland) to assess the TBF. ³³ Abutment's internal surface was cleaned using a dental excavator mechanically. Additionally, the internal surfaces were next cleaned by CleanPolish paste (Kerr, Hamm, Germany) and dental polishing paste (Kerr, Hamm, Germany) by prophy brushes for 1 min. Following the copings cleansing process, samples cementing with permanent resin cement and aging were done. Then in Newton units, the removing force of the copings was measured.

Preparation of Temp-S and TempNE-S groups

Sandblast with 50 μm aluminum oxide particles under 1.5 bar pressure at distance of 1 cm at 45° for 15 s, rinse with isopropyl alcohol 70% for 30 s, and then wash with water for 30 s and dry with air.

Preparation of Temp-SU and TempNE-SU groups

Sandblast with 50 μm particles of aluminum oxide under 1.5 bar pressure at distance of 1 cm at 45° for 15 s, rinse with isopropyl alcohol 70% for 30 s, then rinse with water for 30 s and place the copings in an ultrasonic bath (isopropyl alcohol 70% 30°C, 15 min), and then rinse with water for 30 s and air dry.

Data analysis

For statistical analysis, Levene test, two-way analysis of variance (ANOVA), and Tamhane post hoc tests were applied. A significance level of α = 0.05 was used in the measurements. SPSS statistical package (IBM SPSS Statistics, v24; IBM Corp, Armonk, NY, USA) was used in all tests.

Table 2shows the mean ± standard deviation of TBF (N) of the experimental groups. The highest and lowest TBF values were found for the TempNE-SU (554.7 ± 31.5 N) and TempNE (58 ± 7 N) groups.{Table 2}

The Levene test used to analyze the homogeneity of the collected data showed no significant differences between the type of temporary cement and the method of treatment variances (P = 0.37) Table 3. Hence, it was appropriate to use a two-way ANOVA test, which showed a significant difference (P < 001) between the two temporary cement that were used Table 3.{Table 3}

Tamhane post hoc test was used for pair-wise comparison of the study groups Table 4. There were no significant differences in TBF values between the groups where isopropyl alcohol was used in ultrasonic bath (Temp-SU and TempNE-SU). Similarly, there were no significant differences in TBF values between the groups where only sandblast was used (Temp-S and TempNE-SU). Two groups of isopropyl alcohol in ultrasonic bath combined with sandblast showed significantly higher TBF values than two groups which only sandblast was used. The control group (luted with resin cement) showed a statistically similar TBF value in comparison to groups of ultrasonic bath combined with sandblast treatment, and higher values than groups which only sandblast was used. According to the temporary cement of first cementation, the TempNE group showed significantly lower values than the Temp group. The detailed TBF values of all the studied groups are presented in Table 4.{Table 4}

The aim of this study was to investigate the effect of different methods of cleaning zirconia copings cemented by two types of temporary cement (eugenol and noneugenol) on the force of removing copings after re-cementing with permanent cement to titanium implant abutment. Findings showed that the mean value of TBF in eugenol temporary cement was 122 ± 21 N, which was statistically higher than the values of eugenol temporary cement (58 ± 7 N). In both eugenol and noneugenol temporary cement, the groups treated with sandblasting and isopropyl alcohol bath in ultrasonic had higher TBF values than the group treated with sandblasting alone. The values of TBF in temporary cement with eugenol and without eugenol in the same cleaning method were statistically similar.

TBF values in various studies for eugenol-free temporary cement were in the range of 23–85 N, ¹² , ³⁴ , ³⁵ for temporary cement with eugenol were in the range of 115–164 N, ³⁰ and for permanent resin cement were reported in the range of 314–820 N, ²⁴ , ³⁰ , ³⁶ which was consistent with the TBF values of the present study.

Scarce studies have been conducted on this regard. Keum and Shin ³⁷ reported that plastic curettes were not operative in improving the TBF of the permanently cemented prosthesis. Nevertheless, the use of rubber cups with pumice or sandblasting enhanced the TBS. In a survey of Song et al., ¹ increased TBF of zinc phosphate-coated copings was reported in the use of sandblasting.

Higher amounts of TBF in the sandblasted and alcohol bath in the ultrasonic group than in the control group may be due to the fact that the alcohol bath has the ability to remove the remaining eugenol completely and sandblasting may cause porosity in the inner surface of the copings and thus increase the amount of TBF. After that, the highest values of TBF belonged to the sandblast and ultrasonic groups when temporary TempBond cement with eugenol was used; these results were consistent with the results of the above studies. ³⁸ As a result of sandblasting with aluminum oxide particles, surfaces may become rough and irregular, increasing the possibility of cement sticking and increasing the final TBF. ³⁹

Although the findings of the present study and previous researches ¹ , ⁴⁰ were somewhat similar, there were some significant differences in methodology. All copings in the present study were designed and prepared by CAD/CAM technology to eliminate any possible bias or carelessness. A new change that had not been made in previous studies was the sandblasting process described and the use of an ultrasonic bath with isopropyl alcohol simultaneously.

There has been a controversial issue about the possibility of negative interactions between resin cement and eugenol-containing cement from the past to the present. Ribeiro et al. ⁴¹ investigated dentin residual eugenol on the final bond strength of total etched and self-etched resin cement after standard cleaning processes. They found that eugenol residue significantly reduced the bond strength of indirect restorations bonded with resin cement. Similar findings have been obtained by Carvalho et al. ⁴² However, the effect of reducing the bond strength by eugenol was seen only in self-etched cement. In keeping with this, the findings of the present study were different from previous researches because the group that was cleaned by combined sandblasting and ultrasonic method, with or without eugenol temporary cement were not significantly different from control group contained PANAVIA™ resin cement. These findings could support the hypothesis that the combined cleaning method can neutralize the effect of eugenol, and the method of cleaning the remaining cement is a more important factor than whether the temporary cement has eugenol or not. Additionally, the present study was performed on titanium implant abutments and not natural teeth and dentin.

The results of the present study showed that the use of isopropyl alcohol bath in combination with sandblast is the best way to remove cement residues with or without eugenol and significantly increased the final cement retention. This finding was consistent with the study of de Oliveira et al. ⁴³ who observed the effect of different cleaning protocols and materials on the bond strength of fiber post and root dentin. After testing a solution of saline, acetone, ethanol 70%, and isopropyl 70%, they found that in the group of alcohols, higher bond strength was obtained. Similar findings were obtained by Safari et al. ²⁴ They investigated the role of abutment diameter, cement type, and re-cementation process on the final bond strength of low-code metal copings supported by implants. The result of their study showed that resin cement has the highest values of TBF and also increasing the diameter of the abutment caused an increase in the TBF. However, re-cementation with resin cement did not significantly change the TBF after the use of temporary cement containing eugenol.

Our study has certain limitations, including not examining abutments with different shapes, lengths, diameters and not investigating other methods of cleaning copings, and not investigating semi-permanent implants with resin cement which are recommended in future studies.

Cleaning of cemented zirconia copings with or without eugenol temporary cement by sandblasting with ultrasonic containing isopropyl alcohol produced a similar TBF to the control group, but the sandblasting method alone reduced the final cement retention values. The method of cleaning the inner surface of the copings was a more important factor in the final TBF of the copings compared to the initial temporary cement type.

Author contributions

Behnz Ebadian: Supervised the research, designed the research, contributed analysis tools, and wrote the paper. Mohammad Jowkar: Data collection, performed the analysis, and drafted the article. Farshad Bajoghli: Wrote the paper and data interpretation. Amirhossein Fathi: Data collection and wrote the paper. Mahmoud Sabouhi: Supervised the writing and critical revision of the article.

Data availability statement

Data are available whenever needed.

Acknowledgment

This study was supported by Isfahan University of Medical Sciences (grant no: 3400526). We wish to thank the Research Deputy of Isfahan University of Medical Sciences, Iran.

Financial support and sponsorship

Nil.

Conflicts of interest

The authors of this manuscript declare that they have no conflicts of interest, real or perceived, financial or nonfinancial in this article.