The Effect of Air Abrasion of Metal Implant Abutments on the Tensile Bond Strength of Three Luting Agents Used to Cement Implant Superstructures: An In Vitro Study Jasvinder Jugdev, BDS, MSc1/Ali Borzabadi-Farahani, DDS, MScD2/Edward Lynch, BDS, PhD3 Purpose: To assess the effect of airborne particle abrasion of metal implant abutments on tensile bond strength (TBS) of TempBond, Retrieve, and Premier implant cements. Materials and Methods: Specimens were designed to replicate a single metal implant crown cemented to both smooth and airborne particle– abraded Osteo-Ti implant abutments with zero degrees of taper. Twenty castings were fabricated and cemented to either a smooth surface abutment (SSA) or to an airborne particle–abraded abutment (AAA). TBS was measured with a 50-kg load and a crosshead speed of 0.5 cm/min in a universal testing machine. Each cement was tested 10 times on both abutment types. Results: The mean TBS values (standard deviations, 95% confidence intervals) of SSAs for TempBond, Retrieve, and Premier cements were 115.89 N (26.44, 96.98–134.81), 134.43 N (36.95, 108.25–160.60), and 132.51 N (55.10, 93.09–171.93), respectively. The corresponding values for AAAs were 129.69 N (30.39, 107.95–151.43), 298.67 N (80.36, 241.19–356.16), and 361.17 N (133.23, 265.86-456.48), respectively. There was no significant difference in TBS among the dental cements when used with an SSA. Air abrasion of abutments did not increase the TBS of TempBond but significantly increased crown retention with Retrieve and Premier. For SSAs, all failures were adhesive on the abutment surface; for AAAs, mostly cohesive cement failures occurred. Conclusion: The retention of copings cemented with Retrieve or Premier to zero-degree-taper abutments was significantly increased after airborne particle abrasion of the abutments. However, this was not significant when TempBond was used. Airborne particle abrasion of abutments and the use of Retrieve or Premier can be recommended for nonretrievable prostheses. Although TempBond functioned similarly to the two other cements in SSAs, it is advisable to limit its use to provisional prostheses; its long-term performance needs to be assessed clinically. Int J Oral Maxillofac Implants 2014;29:784–790. doi: 10.11607/jomi.3167 Key words: airborne particle abrasion, dental implants, luting cements, tensile bond strength
D
ental implant restorations can be cemented or screw retained. Screw-retained restorations are successful, especially when placed into edentulous jaws.1,2 However, they suffer from some disadvantages,
1Former
Postgraduate Student, University of Warwick, Coventry, United Kingdom; Private Practice, Witney, Oxfordshire, United Kingdom. 2Clinical Teaching Fellow, Orthodontics, Warwick Dentistry, Warwick Medical School, University of Warwick, Coventry; Locum Consultant Orthodontist, Maxillofacial Unit and Orthodontics, Northampton General Hospital, Northampton, United Kingdom; Visiting Professor, Department of Orthodontics, School of Dentistry, Shahid Beheshti University of Medical Sciences, Tehran, Iran. 3Director, Restorative Dentistry, Warwick Dentistry, Warwick Medical School, University of Warwick Coventry, United Kingdom. Correspondence to: Dr Jasvinder Jugdev, Thirty Three Dental, 33 Market Square, Witney, Oxfordshire, OX28 6AD, United Kingdom. Email:[email protected] ©2014 by Quintessence Publishing Co Inc.
such as screw loosening and screw fracture. 3 Consequently, cement-retained prostheses are often the restoration of choice for treating dental implant patients.4 Nevertheless, a dilemma is whether temporary (retrievable) or permanent (nonretrievable) cement should be used. Retrievability serves as a safety mechanism.5 Nevertheless, retrievable cements must be soft to allow the prosthesis to be removed without causing harm to the underlying implant superstructure and may fail prematurely, causing debonding of the prosthesis. The ideal properties for an implant luting material are strength; resistance to occlusal and masticatory forces, temperature fluctuations, and humidity; and the ability of the prosthesis to be removed as required for periodic maintenance. Luting agents for implant abutments are required to function in a different mode—ie, opposing two metallic surfaces—whereas crowning a tooth involves surfaces that normally consist of enamel, dentin, or a restorative material.6 The retentive strength of a luting cement is dependent on
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the nature of the luting material,7–9 the implant system used, the in vitro conditions,7,10–16 and the height, taper, and surface preparation of the abutment. It has been demonstrated that the taper, surface area, and surface texture of preparations will affect the retention of castings on natural teeth.17 Limited available information suggests that greater occlusocervical dimension and less occlusal convergence result in higher tensile resistance to coping dislodgement.18,19 With correct occlusal considerations,20 it is hoped that a cemented crown will remain in situ. However, implant crowns can debond prematurely, and an understanding of the cause of debonding will help clinicians to select the best luting agents. Previous studies have tested the retentive strength of various luting agents.5,16,21,22 However, there is limited information for some commercially available cements. Therefore, the objective of this study was to assess the retentive strength (tensile bond strength) of three commonly used dental luting agents when used to restore single dental implant crowns on smooth surface abutments (SSAs) or airborne particle–abraded implant abutments (AAAs). The null hypothesis for this study was posed in two parts: (1) There is no difference in the tensile bond strength (TBS) of the three different luting cements tested for implant restorations on both SSAs and AAAs; and (2) there is no difference in the failure profiles of the three different luting cements tested on both SSAs and AAAs.
MATERIALS AND METHODS Specimen Preparation
The laboratory design followed that of previous in vitro studies.16,21,23 Twenty implant analogs and abutments (Anchor Lock, Universal Analogues, and Threaded Post Zero Degrees, Osteo-Ti Limited) were connected using low-profile post screws (Osteo-Ti Limited) and torquetightened to 20 Ncm using the manufacturer’s torque wrench. Ten of the abutments were kept in their original form (SSAs), while the other 10 were airborne particle abraded with 50-µm aluminium oxide particles (AAAs). The occlusal access cavity of each abutment was sealed with cotton wool. The implant analogs were seated into autopolymerizing acrylic resin (Boswell Trim, Boswell Corporation); a darker shade of acrylic resin was used for those implant abutments that were subjected to airborne particle abrasion (Fig 1). This procedure was performed to create a block of approximate dimension 10 × 10 × 20 mm to enable secure (clamped) placement into the lower arm of the universal testing machine. The implant assembly was fixed perpendicular to the surface
Fig 1 Implant analogs with abutments seated into acrylic resin blocks. Left: AAA; right: SSA.
of the acrylic resin block using a dental surveyor (Ney Dental International). To manufacture the metal copings, a single implant analog, which was not subjected to airborne particle abrasion, was selected and covered with two thin layers of a nano-filled light-cured protective coating (Optiglaze, GC Corporation) to act as a die spacer. The manufacturer of this material claims that a single coating provides between 25 and 50 µm of spacing. Twenty copings were then fabricated using the wax dipping technique in melted inlay wax (blue inlay wax, Kerr Dental) and then had a 2- to 3-mm internal diameter circular attachment hand waxed onto the occlusal surface to allow for connection to the upper arm of the universal testing machine. The wax patterns were then sprued, invested in a phosphate-bonded investment material (GC VEST, GC Corporation), and cast in nickel-chrome ceramic bonding alloy (Unitech PhaseN Premium, Unitech; 64% nickel, 24% cobalt, 11% molybdenum, 1% silicon). Following casting in a centrifugal casting machine (Degussa Compact, Dentsply), the copings were deinvested, checked for structural integrity, and placed into an ultrasonic bath containing a proprietary soap solution for 10 minutes to remove debris. Any positive internal irregularities were removed with a dental laboratory handpiece. The internal surfaces of the castings were then abraded with 50-µm aluminium oxide particles. The castings were then subjected to steam cleaning for 5 seconds and allowed to air dry. They were then tried onto the implant abutments to ensure an accurate fit (Figs 2 and 3).
Cements Tested
TempBond (Kerr Dental), a zinc oxide–eugenol cement; Premier implant cement (Premier Dental Products Company), a noneugenol temporary resin cement (an acrylic/urethane cement); and Retrieve temporary cement (Osteo-Ti Limited) were used for this study. The composition of Retrieve temporary cement has not been disclosed by the manufacturer, but it appears to The International Journal of Oral & Maxillofacial Implants 785
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Jugdev et al
Fig 2 Copings seated onto abutments. Note the 2- to 3-mm loop on the occlusal surface to facilitate connection with the upper arm of the universal testing machine.
Fig 3 Internal surfaces of the castings.
to fracture the cement lute was then recorded in kilograms and subsequently converted to Newtons. Each of the three cements was tested 10 times on both SSAs and AAAs. The nature of the cement failure at decementation was also recorded as cohesive or adhesive. After testing, the copings and abutments were placed into a soap solution and cleaned in an ultrasonic bath for 15 minutes. The cleaned abutments and copings were then rinsed in distilled water, air-dried, and examined under a ×10 magnification lamp. Any cement that had remained in either the abutment or the copings was then carefully removed using hand excavators. After cleaning, the specimens were reused for the next cement to be tested; overall, 60 tests were performed.
Statistical Analyses Fig 4 Test assembly within the universal testing machine.
have the properties and handling characteristics of a polyurethane cement. All cements were mixed by the same examiner according to the manufacturers’ instructions. A thin layer was placed into the inner surface of the castings, which were cemented onto the abutments (ensuring that a small excess of cement would be extruded) under a standardized load force of 1 kg. After the initial setting process, the excess cement was removed using a no. 2 pattern Ward’s carver. The cements were then allowed to set for 30 minutes.
Assessment of TBS and Cement Failures
Tensile testing was undertaken with a universal testing machine (Zo20, Zwick/Roell) using a jig that was designed to ensure that the samples would be subjected to vertical forces only (Fig 4). Each specimen was pulled from the abutment using a 50-kg load cell at a crosshead speed of 0.5 cm/minute. The force required
SPSS software (version 17) was used for statistical analyses. The means, standard deviations (SDs), and 95% confidence intervals (CIs) of the mean and the mean differences were calculated for TBS values of all combinations of cements and abutment types used (smooth surface and air-abraded abutments). Subsequently, data were subjected to one-way analysis of variance (ANOVA) with Bonferroni post hoc tests to detect significant differences in TBS for the various combinations of cements and/or abutment types. Bar graphs were produced to illustrate the data graphically. The cement failure characteristics at decementation (cohesive or adhesive) were also evaluated using the chi-square test. Any P < .05 was considered as statistically significant.
RESULTS Comparison of TBS Values
The mean TBS values (SD, 95% CIs) of the SSAs for TempBond, Retrieve, and Premier cements were 115.89 N (26.44, 96.98 to 134.81), 134.43 N (36.95, 108.25 to 160.60), and 132.51 N (55.10, 93.09 to 171.93), respectively (Fig 5). The corresponding values for the AAAs
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Jugdev et al
Assessment of Cement Failures
Significant differences were seen in the cement failure profiles in the six tested groups (chi-square = 42.50, degrees of freedom = 5, P = .000). For the SSA group, all the cements failed adhesively at the implant abutment (Table 2). For the AAA group, 70% of the failures were cohesive in nature, ie, the cement failed within itself, leaving residue on both the abutment and the internal surface of the castings. The remaining 30% of the samples in the AAA group failed adhesively at the abutment surface. The airborne particle abrasion of implant abutments therefore significantly (P < .01) changed the cement failure profile in all cement groups (TempBond, chi-square = 20; Retrieve, chi-square = 10.769; Premier, chi-square = 10.769). Therefore, the null hypothesis of this part of the study was fully rejected.
DISCUSSION This study assessed the TBS of three cements using zero-degree, 6-mm-long dental implant abutments on both SSAs and AAAs. When SSAs were used, all cements tested provided similar TBS. However, when cemented to AAAs, both Retrieve and Premier provided much stronger retention. Zinc oxide–eugenol cements, such as TempBond, show high water solubility and require sufficient time for a complete setting reaction to maximize their retention.9,14 The present study demonstrated that abutment surface preparation had no effect on the TBS of TempBond, which demonstrated the lowest retentive value. Premier demonstrated
500 TBS (N) at decementation
were 129.69 N (30.39, 107.95 to 151.43), 298.67 N (80.36, 241.19 to 356.16), and 361.17 N (133.23, 265.86 to 456.48), respectively. ANOVA revealed significant differences in TBS among the various combinations of cements and/or abutment types (F = 22.429, P < .01); however, there was no significant difference among the tested cements when used with an SSA (P > .05) (Table 1). For the AAAs, statistically significant differences were demonstrated between TempBond and both Retrieve (P < .01) and Premier (P < .01). However, no statistically significant difference was found between Retrieve and Premier (P > .05). Overall, the Premier cement demonstrated the highest mean retentive strength. For the TempBond cement, airborne particle abrasion of abutments did not increase the TBS significantly (P > .05). The greatest TBS difference was observed between Premier in the AAA group and TempBond in the SSA group (95% CI of the mean difference = 147.82 to 342.74 N). Overall, the null hypothesis of this part of the study was partially rejected.
400 300 200 100 0 TempBond TempBond Retrieve + SSA + AAA + SSA
Retrieve + AAA
Premier + SSA
Premier + AAA
Cement and abutment type Fig 5 Mean TBS (○) and SD/95% CI at decementation.
the highest retentive value for both types of abutments. The retentiveness of Retrieve was similar to that of Premier. The copings cemented to SSAs debonded at significantly lower forces than those cemented to AAAs. Nonetheless, the TempBond residue was the easiest to remove from the implant abutments and internal surfaces of castings. The residual cement left by the Retrieve and Premier cements proved very difficult to remove. This is important clinically, as a cement that is difficult to remove may result in damage to the implant abutment and internal surface of the casting, resulting in greater chair time, possible damage to the implant components, or loss of osseointegration of the implant during cement removal.5 Further, in case of excess cement that is expelled subgingivally, periodontal surgery may be required to completely remove the excess cement.24 Comparison of the present findings with those of previous studies is challenging, as the cemented test samples were not permitted to set for 24 hours and were not subjected to thermocycling. The manufacturer of Premier states that the material will reach its full set within 4 to 5 minutes at 37°C, and TempBond should achieve its full set within 7 minutes. The manufacturer of Retrieve did not provide information about its setting time. In the clinical environment, a patient is discharged and loads the newly cemented implant crown soon after these setting times. Thus, the 30-minute setting period that was allowed in the present study should prove satisfactory. Whereas some studies have reported no significant effect of thermocycling on the retentive strength of cements,25,26 there are contradictory reports as well.23,27,28 Overall, it appears that thermocycling reduces retention of the cements,23,27,28 a matter that can be examined in future investigations. The International Journal of Oral & Maxillofacial Implants 787
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Table 1 Results of ANOVA (with Post Hoc Bonferroni Tests) Showing Differences in TBS Among the Various Combinations of Cements and Abutments Group 1 TempBond with SSA
TempBond with AAA
Retrieve with SSA
Retrieve with AAA Premier with SSA
Group 2
Mean difference
TempBond with AAA
–13.80
> .999
Retrieve with SSA
–18.53
> .999
Retrieve with AAA
–182.78
.000
Premier with SSA
–16.61
> .999
Premier with AAA
–245.28
.000
Retrieve with SSA
–4.74
> .999
P
95% CI –111.26 to 83.66 –115.99 to 78.92 –280.24 to –85.32 –114.07 to 80.84 –342.74 to –147.82 –102.20 to 92.72
Retrieve with AAA
–168.98
.000
Premier with SSA
–2.82
> .999
–266.44 to –71.52
Premier with AAA
–231.48
.000
–328.94 to –134.02 –261.70 to –66.78
–100.28 to 94.64
Retrieve with AAA
–164.24
.000
Premier with SSA
1.92
> .999
Premier with AAA
–226.75
.000
Premier with SSA
166.16
.000
Premier with AAA
–62.50
.810
–159.96 to 34.96
Premier with AAA
–228.66
.000
–326.12 to –131.20
Table 2 Cement Failure Profiles for Combinations of Cements and Abutments Cement failure (%) Cement/abutment type
Adhesive
Cohesive
TempBond with SSA
10 (100)
0
TempBond with AAA
0
10 (100)
10
Retrieve with SSA
10 (100)
0
10
Retrieve with AAA
3 (30)
7 (70)
10
Premier with SSA
10 (100)
0
10
Premier with AAA
3 (30)
Total
36 (60)
7 (70) 24 (40)
Total 10
10 60
The variability of the results on AAAs could be a result of the small sample size of the present study or construction and testing variations, such as discrepancies in the cement film thickness.6,10 A greater sample size and the use of new components for each round of testing may reduce the variability seen here. This study restricted dislodgment forces to pure tensile testing only. However, in the clinical situation, dental implant crowns are subjected to many other forces as well.6,15 Masticatory forces create a combination of tensile, compressive, and shear forces, and these integrated forces can induce high displacement forces on the implant crown, resulting in a fracture of the cement lute or dislodgement of the crown. However, it is almost impossible to reproduce these combined forces within a laboratory setting. Therefore, the testing method used in this study has become popular with researchers29
–95.54 to 99.38 –324.21 to –129.29 68.70 to 263.62
because it is easy to standardize and replicate between institutions, allowing comparison with previous studies. Similar to previous studies, a sample size of 10 SSAs and 10 AAAs was chosen.16,21,30 The copings and implant abutments were reused during recording of the data. Repeated cementation and cleaning may have influenced the retentive strength of the cements, with surface oxidation of the fitting surface of the alloy used for the copings. However, repeated cementation31 and surface oxidation32 did not significantly affect the TBS of dental luting cements in other studies, although it must be noted that the luting agent used in these previous studies was zinc phosphate and the substructures were prepared human teeth. It is therefore difficult to draw comparisons with the present study; future studies can address this issue by avoiding reuse of the copings. The location of the cement failure was recorded during this investigation, as it is an important factor when selecting luting agents when retrievability is required. Similar methods have been used to evaluate the bond failure between orthodontic brackets and adhesives.33,34 The tested cements all failed adhesively on SSAs with the lowest recorded dislodging forces, as no cement residue remained attached to the surface for all test samples. Cohesive failures formed the majority of decementations for the AAAs, as residual cement remained attached to both the implant abutments and internal surfaces of the castings. This was in conjunction with the recorded higher TBS values with AAAs. Nonetheless, in vivo trials are required to validate the present findings in a clinical setting.
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The AAAs demonstrated higher retentive values compared to the SSAs with all cements tested. However, the increase in tensile load required for the TempBond cement was not statistically significant. This may be a result of the small sample size, which could not detect the differences, or the larger surface area created by airborne particle abrasion, similar to the findings of Cano-Batalla et al.29 The Osteo-Ti implant company states that airborne particle abrasion of abutments results in a threefold increase in the retentiveness of their Retrieve cement versus an SSA. This study found a mean increase in TBS of around 2.22. Similar to several studies,6,12,26,35,36 only one type of implant abutment was used, and a different outcome may have been achieved if different implant abutments of varying degrees of taper, surface area, and texture had been used. Although Breeding et al37 demonstrated no significant difference in the retentive values of noble metal castings cemented to both titanium implant abutments and prepared human premolar teeth, most previous studies reported that these results differ from those obtained with natural teeth.10,21,38 Therefore, the present findings cannot be generalized. The decision about which cement to use should be based on how much retention is required versus the ease of retrievability. Retention of a crown is dependent on the cement used, the surface preparation of the implant abutment, and other variables such as the internal surface characteristics of the coping and the height and taper of the implant abutment.16 Permanent and temporary cements have been suggested for luting single-unit and multiple-unit implant-supported restorations, respectively.11,39 Provisional cements act as a “safety valve”6 and are the cement of choice when intervention may be required, ie, damage to the prosthesis, fracture or loosening of the abutment screw, and when the prosthesis must be modified after failure of adjacent implants.6,37 The TempBond cement provided a similar retentive strength to the other cements tested in this study on SSAs. However, considering the high water solubility of the TempBond cement,9,14 it is advisable to limit its use to provisional prostheses before the present findings have been validated in long-term clinical trials. The more retentive cements, such as resin or polyurethane, are more suitable when future retrievability is not necessary.6,16
CONCLUSION Within the limitations of this study, the retention of cast crown copings cemented with Retrieve or Premier to dental implant abutments with zero degrees of taper was significantly increased after airborne particle
abrasion of the abutments. However, this was not significant when TempBond was used. Airborne particle abrasion of implant abutments and the use of Retrieve or Premier can be recommended for use in nonretrievable prostheses. Although TempBond functioned similarly to the two other cements with smooth surface abutments, it is advisable to limit its use to provisional prostheses, as its long-term performance needs to be assessed with clinical trials.
ACKNOWLEDGMENTS The authors would like to thank Osteo-Ti for supplying the implant components. The authors reported no conflicts of interest related to this study.
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18. Bernal G, Okamura M, Munoz CA. The effects of abutment taper, length and cement type on resistance to dislodgement of cement-retained, implant-supported restorations. J Prosthodont 2003;12:111–115. 19. Bresciano M, Schierano G, Manzella C, Screti A, Bignardi C, Preti G. Retention of luting agents on implant abutments of different height and taper. Clin Oral Implants Res 2005;16:594–598. 20. Davies S, Gray R, Young M. Good occlusal practice in the provision of implant borne prostheses. Br Dent J 2002;192:79–88. 21. Squier RS, Agar JR, Duncan JP, Taylor TD. Retentiveness of dental cements used with metallic implant components. Int J Oral Maxillofac Implants 2001;16:793–798. 22. Kokubo Y, Kano T, Tsumita M, Sakurai S, Itayama A, Fukushima S. Retention of zirconia copings on zirconia implant abutments cemented with provisional luting agents. J Oral Rehabil 2010;37:48–53. 23. Lim HP, Yoo JM, Park SW, Yang HS. Fracture load of implant-supported zirconia all-ceramic crowns luted with various cements. Int J Prosthodont 2010;23:361–363. 24. Pauletto N, Lahiffe BJ, Walton JN. Complications associated with excess cement around crown on osseointegrated implants: A clinical report. Int J Oral Maxillofac Implants 1999;14:865–868. 25. GaRey DJ, Tjan AH, James RA, Caputo AA. Effects of thermocycling, load-cycling, and blood contamination on cemented implant abutments. J Prosthet Dent 1994;71:124–132. 26. Mehl C, Harder S, Schwarz D, Steiner M, Vollrath O, Kern M. In vitro influence of ultrasonic stress, removal force preload and thermocycling on retrievability of implant retained crowns. Clin Oral Implants Res 2012;23:930–937. 27. Bani Sakher A, Ludwig K, Kern M. Retention of pre-fabricated titanium posts cemented with three different cements [abstract 2468]. J Dent Res 2003;82:B-319. 28. Cattani-Lorente MA, Godin C, Meyer JM. Mechanical behavior of glass-ionomer cements affected by long-term storage in water. Dent Mater 1994;10:37–44.
29. Cano-Batalla J, Soliva-Garriga J, Campillo-Funollet M, Munoz-Viveros CA, Giner-Tarrida L. Influence of abutment height and surface roughness on in vitro retention of three luting agents. Int J Oral Maxillofac Implants 2012;27:36–41. 30. Kim Y, Yamashita J, Shotwell JL, Chong KH, Wang HL. The comparison of provisional luting agents and abutment surface roughness on the retention of provisional implant-supported crowns. J Prosthet Dent 2006;95:450–455. 31. Felton DA, Kanoy BE, White JT. Recementation of dental castings with zinc phosphate cement: Effect on cement bond strength. J Prosthet Dent 1987;58:579–583. 32. Felton DA, Kanoy BE, White JT, Bayne SC. Porcelain-fused-to-metal surface oxidation effects on cemented casting retention. J Prosthet Dent 1987;58:677–686. 33. Eslamian L, Borzabadi-Farahani A, Mousavi N, Ghasemi A. The effects of various surface treatments on the shear bond strengths of stainless steel brackets to artificially-aged composite restorations. Aust Orthod J 2011;27:28–32. 34. Eslamian L, Borzabadi-Farahani A, Mousavi N, Ghasemi A. A comparative study of shear bond strength between metal and ceramic brackets and artificially aged composite restorations using different surface treatments. Eur J Orthod 2012;34:610–617. 35. Nejatidanesh F, Savabi O, Ebrahimi M, Savabi G. Retentiveness of implant-supported metal copings using different luting agents. Dent Res J (Isfahan) 2012;9:13–18. 36. Kurt M, Külünk T, Ural C, Külünk Ş, Danişman Ş, Savaş S. The effect of different surface treatments on cement-retained implant-supported restorations. J Oral Implantol 2013;39:44–51. 37. Breeding LC, Dixon DL, Bogacki MT, Tietge JD. Use of luting agents with an implant system: Part I. J Prosthet Dent 1992;68:737–741. 38. Covey DA, Kent DK, St Germain HA Jr, Koka S. Effect of abutment size and luting cement type on the uniaxial retention force of implant supported crowns. J Prosthet Dent 2000;83:344–348. 39. Hill EE. Dental cements for definitive luting: A review and practical clinical considerations. Dent Clin North Am 2007;51:643–658.
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D
ental implant restorations can be cemented or screw retained. Screw-retained restorations are successful, especially when placed into edentulous jaws.1,2 However, they suffer from some disadvantages,
1Former
Postgraduate Student, University of Warwick, Coventry, United Kingdom; Private Practice, Witney, Oxfordshire, United Kingdom. 2Clinical Teaching Fellow, Orthodontics, Warwick Dentistry, Warwick Medical School, University of Warwick, Coventry; Locum Consultant Orthodontist, Maxillofacial Unit and Orthodontics, Northampton General Hospital, Northampton, United Kingdom; Visiting Professor, Department of Orthodontics, School of Dentistry, Shahid Beheshti University of Medical Sciences, Tehran, Iran. 3Director, Restorative Dentistry, Warwick Dentistry, Warwick Medical School, University of Warwick Coventry, United Kingdom. Correspondence to: Dr Jasvinder Jugdev, Thirty Three Dental, 33 Market Square, Witney, Oxfordshire, OX28 6AD, United Kingdom. Email:[email protected] ©2014 by Quintessence Publishing Co Inc.
such as screw loosening and screw fracture. 3 Consequently, cement-retained prostheses are often the restoration of choice for treating dental implant patients.4 Nevertheless, a dilemma is whether temporary (retrievable) or permanent (nonretrievable) cement should be used. Retrievability serves as a safety mechanism.5 Nevertheless, retrievable cements must be soft to allow the prosthesis to be removed without causing harm to the underlying implant superstructure and may fail prematurely, causing debonding of the prosthesis. The ideal properties for an implant luting material are strength; resistance to occlusal and masticatory forces, temperature fluctuations, and humidity; and the ability of the prosthesis to be removed as required for periodic maintenance. Luting agents for implant abutments are required to function in a different mode—ie, opposing two metallic surfaces—whereas crowning a tooth involves surfaces that normally consist of enamel, dentin, or a restorative material.6 The retentive strength of a luting cement is dependent on
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the nature of the luting material,7–9 the implant system used, the in vitro conditions,7,10–16 and the height, taper, and surface preparation of the abutment. It has been demonstrated that the taper, surface area, and surface texture of preparations will affect the retention of castings on natural teeth.17 Limited available information suggests that greater occlusocervical dimension and less occlusal convergence result in higher tensile resistance to coping dislodgement.18,19 With correct occlusal considerations,20 it is hoped that a cemented crown will remain in situ. However, implant crowns can debond prematurely, and an understanding of the cause of debonding will help clinicians to select the best luting agents. Previous studies have tested the retentive strength of various luting agents.5,16,21,22 However, there is limited information for some commercially available cements. Therefore, the objective of this study was to assess the retentive strength (tensile bond strength) of three commonly used dental luting agents when used to restore single dental implant crowns on smooth surface abutments (SSAs) or airborne particle–abraded implant abutments (AAAs). The null hypothesis for this study was posed in two parts: (1) There is no difference in the tensile bond strength (TBS) of the three different luting cements tested for implant restorations on both SSAs and AAAs; and (2) there is no difference in the failure profiles of the three different luting cements tested on both SSAs and AAAs.
MATERIALS AND METHODS Specimen Preparation
The laboratory design followed that of previous in vitro studies.16,21,23 Twenty implant analogs and abutments (Anchor Lock, Universal Analogues, and Threaded Post Zero Degrees, Osteo-Ti Limited) were connected using low-profile post screws (Osteo-Ti Limited) and torquetightened to 20 Ncm using the manufacturer’s torque wrench. Ten of the abutments were kept in their original form (SSAs), while the other 10 were airborne particle abraded with 50-µm aluminium oxide particles (AAAs). The occlusal access cavity of each abutment was sealed with cotton wool. The implant analogs were seated into autopolymerizing acrylic resin (Boswell Trim, Boswell Corporation); a darker shade of acrylic resin was used for those implant abutments that were subjected to airborne particle abrasion (Fig 1). This procedure was performed to create a block of approximate dimension 10 × 10 × 20 mm to enable secure (clamped) placement into the lower arm of the universal testing machine. The implant assembly was fixed perpendicular to the surface
Fig 1 Implant analogs with abutments seated into acrylic resin blocks. Left: AAA; right: SSA.
of the acrylic resin block using a dental surveyor (Ney Dental International). To manufacture the metal copings, a single implant analog, which was not subjected to airborne particle abrasion, was selected and covered with two thin layers of a nano-filled light-cured protective coating (Optiglaze, GC Corporation) to act as a die spacer. The manufacturer of this material claims that a single coating provides between 25 and 50 µm of spacing. Twenty copings were then fabricated using the wax dipping technique in melted inlay wax (blue inlay wax, Kerr Dental) and then had a 2- to 3-mm internal diameter circular attachment hand waxed onto the occlusal surface to allow for connection to the upper arm of the universal testing machine. The wax patterns were then sprued, invested in a phosphate-bonded investment material (GC VEST, GC Corporation), and cast in nickel-chrome ceramic bonding alloy (Unitech PhaseN Premium, Unitech; 64% nickel, 24% cobalt, 11% molybdenum, 1% silicon). Following casting in a centrifugal casting machine (Degussa Compact, Dentsply), the copings were deinvested, checked for structural integrity, and placed into an ultrasonic bath containing a proprietary soap solution for 10 minutes to remove debris. Any positive internal irregularities were removed with a dental laboratory handpiece. The internal surfaces of the castings were then abraded with 50-µm aluminium oxide particles. The castings were then subjected to steam cleaning for 5 seconds and allowed to air dry. They were then tried onto the implant abutments to ensure an accurate fit (Figs 2 and 3).
Cements Tested
TempBond (Kerr Dental), a zinc oxide–eugenol cement; Premier implant cement (Premier Dental Products Company), a noneugenol temporary resin cement (an acrylic/urethane cement); and Retrieve temporary cement (Osteo-Ti Limited) were used for this study. The composition of Retrieve temporary cement has not been disclosed by the manufacturer, but it appears to The International Journal of Oral & Maxillofacial Implants 785
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Jugdev et al
Fig 2 Copings seated onto abutments. Note the 2- to 3-mm loop on the occlusal surface to facilitate connection with the upper arm of the universal testing machine.
Fig 3 Internal surfaces of the castings.
to fracture the cement lute was then recorded in kilograms and subsequently converted to Newtons. Each of the three cements was tested 10 times on both SSAs and AAAs. The nature of the cement failure at decementation was also recorded as cohesive or adhesive. After testing, the copings and abutments were placed into a soap solution and cleaned in an ultrasonic bath for 15 minutes. The cleaned abutments and copings were then rinsed in distilled water, air-dried, and examined under a ×10 magnification lamp. Any cement that had remained in either the abutment or the copings was then carefully removed using hand excavators. After cleaning, the specimens were reused for the next cement to be tested; overall, 60 tests were performed.
Statistical Analyses Fig 4 Test assembly within the universal testing machine.
have the properties and handling characteristics of a polyurethane cement. All cements were mixed by the same examiner according to the manufacturers’ instructions. A thin layer was placed into the inner surface of the castings, which were cemented onto the abutments (ensuring that a small excess of cement would be extruded) under a standardized load force of 1 kg. After the initial setting process, the excess cement was removed using a no. 2 pattern Ward’s carver. The cements were then allowed to set for 30 minutes.
Assessment of TBS and Cement Failures
Tensile testing was undertaken with a universal testing machine (Zo20, Zwick/Roell) using a jig that was designed to ensure that the samples would be subjected to vertical forces only (Fig 4). Each specimen was pulled from the abutment using a 50-kg load cell at a crosshead speed of 0.5 cm/minute. The force required
SPSS software (version 17) was used for statistical analyses. The means, standard deviations (SDs), and 95% confidence intervals (CIs) of the mean and the mean differences were calculated for TBS values of all combinations of cements and abutment types used (smooth surface and air-abraded abutments). Subsequently, data were subjected to one-way analysis of variance (ANOVA) with Bonferroni post hoc tests to detect significant differences in TBS for the various combinations of cements and/or abutment types. Bar graphs were produced to illustrate the data graphically. The cement failure characteristics at decementation (cohesive or adhesive) were also evaluated using the chi-square test. Any P < .05 was considered as statistically significant.
RESULTS Comparison of TBS Values
The mean TBS values (SD, 95% CIs) of the SSAs for TempBond, Retrieve, and Premier cements were 115.89 N (26.44, 96.98 to 134.81), 134.43 N (36.95, 108.25 to 160.60), and 132.51 N (55.10, 93.09 to 171.93), respectively (Fig 5). The corresponding values for the AAAs
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Jugdev et al
Assessment of Cement Failures
Significant differences were seen in the cement failure profiles in the six tested groups (chi-square = 42.50, degrees of freedom = 5, P = .000). For the SSA group, all the cements failed adhesively at the implant abutment (Table 2). For the AAA group, 70% of the failures were cohesive in nature, ie, the cement failed within itself, leaving residue on both the abutment and the internal surface of the castings. The remaining 30% of the samples in the AAA group failed adhesively at the abutment surface. The airborne particle abrasion of implant abutments therefore significantly (P < .01) changed the cement failure profile in all cement groups (TempBond, chi-square = 20; Retrieve, chi-square = 10.769; Premier, chi-square = 10.769). Therefore, the null hypothesis of this part of the study was fully rejected.
DISCUSSION This study assessed the TBS of three cements using zero-degree, 6-mm-long dental implant abutments on both SSAs and AAAs. When SSAs were used, all cements tested provided similar TBS. However, when cemented to AAAs, both Retrieve and Premier provided much stronger retention. Zinc oxide–eugenol cements, such as TempBond, show high water solubility and require sufficient time for a complete setting reaction to maximize their retention.9,14 The present study demonstrated that abutment surface preparation had no effect on the TBS of TempBond, which demonstrated the lowest retentive value. Premier demonstrated
500 TBS (N) at decementation
were 129.69 N (30.39, 107.95 to 151.43), 298.67 N (80.36, 241.19 to 356.16), and 361.17 N (133.23, 265.86 to 456.48), respectively. ANOVA revealed significant differences in TBS among the various combinations of cements and/or abutment types (F = 22.429, P < .01); however, there was no significant difference among the tested cements when used with an SSA (P > .05) (Table 1). For the AAAs, statistically significant differences were demonstrated between TempBond and both Retrieve (P < .01) and Premier (P < .01). However, no statistically significant difference was found between Retrieve and Premier (P > .05). Overall, the Premier cement demonstrated the highest mean retentive strength. For the TempBond cement, airborne particle abrasion of abutments did not increase the TBS significantly (P > .05). The greatest TBS difference was observed between Premier in the AAA group and TempBond in the SSA group (95% CI of the mean difference = 147.82 to 342.74 N). Overall, the null hypothesis of this part of the study was partially rejected.
400 300 200 100 0 TempBond TempBond Retrieve + SSA + AAA + SSA
Retrieve + AAA
Premier + SSA
Premier + AAA
Cement and abutment type Fig 5 Mean TBS (○) and SD/95% CI at decementation.
the highest retentive value for both types of abutments. The retentiveness of Retrieve was similar to that of Premier. The copings cemented to SSAs debonded at significantly lower forces than those cemented to AAAs. Nonetheless, the TempBond residue was the easiest to remove from the implant abutments and internal surfaces of castings. The residual cement left by the Retrieve and Premier cements proved very difficult to remove. This is important clinically, as a cement that is difficult to remove may result in damage to the implant abutment and internal surface of the casting, resulting in greater chair time, possible damage to the implant components, or loss of osseointegration of the implant during cement removal.5 Further, in case of excess cement that is expelled subgingivally, periodontal surgery may be required to completely remove the excess cement.24 Comparison of the present findings with those of previous studies is challenging, as the cemented test samples were not permitted to set for 24 hours and were not subjected to thermocycling. The manufacturer of Premier states that the material will reach its full set within 4 to 5 minutes at 37°C, and TempBond should achieve its full set within 7 minutes. The manufacturer of Retrieve did not provide information about its setting time. In the clinical environment, a patient is discharged and loads the newly cemented implant crown soon after these setting times. Thus, the 30-minute setting period that was allowed in the present study should prove satisfactory. Whereas some studies have reported no significant effect of thermocycling on the retentive strength of cements,25,26 there are contradictory reports as well.23,27,28 Overall, it appears that thermocycling reduces retention of the cements,23,27,28 a matter that can be examined in future investigations. The International Journal of Oral & Maxillofacial Implants 787
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Table 1 Results of ANOVA (with Post Hoc Bonferroni Tests) Showing Differences in TBS Among the Various Combinations of Cements and Abutments Group 1 TempBond with SSA
TempBond with AAA
Retrieve with SSA
Retrieve with AAA Premier with SSA
Group 2
Mean difference
TempBond with AAA
–13.80
> .999
Retrieve with SSA
–18.53
> .999
Retrieve with AAA
–182.78
.000
Premier with SSA
–16.61
> .999
Premier with AAA
–245.28
.000
Retrieve with SSA
–4.74
> .999
P
95% CI –111.26 to 83.66 –115.99 to 78.92 –280.24 to –85.32 –114.07 to 80.84 –342.74 to –147.82 –102.20 to 92.72
Retrieve with AAA
–168.98
.000
Premier with SSA
–2.82
> .999
–266.44 to –71.52
Premier with AAA
–231.48
.000
–328.94 to –134.02 –261.70 to –66.78
–100.28 to 94.64
Retrieve with AAA
–164.24
.000
Premier with SSA
1.92
> .999
Premier with AAA
–226.75
.000
Premier with SSA
166.16
.000
Premier with AAA
–62.50
.810
–159.96 to 34.96
Premier with AAA
–228.66
.000
–326.12 to –131.20
Table 2 Cement Failure Profiles for Combinations of Cements and Abutments Cement failure (%) Cement/abutment type
Adhesive
Cohesive
TempBond with SSA
10 (100)
0
TempBond with AAA
0
10 (100)
10
Retrieve with SSA
10 (100)
0
10
Retrieve with AAA
3 (30)
7 (70)
10
Premier with SSA
10 (100)
0
10
Premier with AAA
3 (30)
Total
36 (60)
7 (70) 24 (40)
Total 10
10 60
The variability of the results on AAAs could be a result of the small sample size of the present study or construction and testing variations, such as discrepancies in the cement film thickness.6,10 A greater sample size and the use of new components for each round of testing may reduce the variability seen here. This study restricted dislodgment forces to pure tensile testing only. However, in the clinical situation, dental implant crowns are subjected to many other forces as well.6,15 Masticatory forces create a combination of tensile, compressive, and shear forces, and these integrated forces can induce high displacement forces on the implant crown, resulting in a fracture of the cement lute or dislodgement of the crown. However, it is almost impossible to reproduce these combined forces within a laboratory setting. Therefore, the testing method used in this study has become popular with researchers29
–95.54 to 99.38 –324.21 to –129.29 68.70 to 263.62
because it is easy to standardize and replicate between institutions, allowing comparison with previous studies. Similar to previous studies, a sample size of 10 SSAs and 10 AAAs was chosen.16,21,30 The copings and implant abutments were reused during recording of the data. Repeated cementation and cleaning may have influenced the retentive strength of the cements, with surface oxidation of the fitting surface of the alloy used for the copings. However, repeated cementation31 and surface oxidation32 did not significantly affect the TBS of dental luting cements in other studies, although it must be noted that the luting agent used in these previous studies was zinc phosphate and the substructures were prepared human teeth. It is therefore difficult to draw comparisons with the present study; future studies can address this issue by avoiding reuse of the copings. The location of the cement failure was recorded during this investigation, as it is an important factor when selecting luting agents when retrievability is required. Similar methods have been used to evaluate the bond failure between orthodontic brackets and adhesives.33,34 The tested cements all failed adhesively on SSAs with the lowest recorded dislodging forces, as no cement residue remained attached to the surface for all test samples. Cohesive failures formed the majority of decementations for the AAAs, as residual cement remained attached to both the implant abutments and internal surfaces of the castings. This was in conjunction with the recorded higher TBS values with AAAs. Nonetheless, in vivo trials are required to validate the present findings in a clinical setting.
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The AAAs demonstrated higher retentive values compared to the SSAs with all cements tested. However, the increase in tensile load required for the TempBond cement was not statistically significant. This may be a result of the small sample size, which could not detect the differences, or the larger surface area created by airborne particle abrasion, similar to the findings of Cano-Batalla et al.29 The Osteo-Ti implant company states that airborne particle abrasion of abutments results in a threefold increase in the retentiveness of their Retrieve cement versus an SSA. This study found a mean increase in TBS of around 2.22. Similar to several studies,6,12,26,35,36 only one type of implant abutment was used, and a different outcome may have been achieved if different implant abutments of varying degrees of taper, surface area, and texture had been used. Although Breeding et al37 demonstrated no significant difference in the retentive values of noble metal castings cemented to both titanium implant abutments and prepared human premolar teeth, most previous studies reported that these results differ from those obtained with natural teeth.10,21,38 Therefore, the present findings cannot be generalized. The decision about which cement to use should be based on how much retention is required versus the ease of retrievability. Retention of a crown is dependent on the cement used, the surface preparation of the implant abutment, and other variables such as the internal surface characteristics of the coping and the height and taper of the implant abutment.16 Permanent and temporary cements have been suggested for luting single-unit and multiple-unit implant-supported restorations, respectively.11,39 Provisional cements act as a “safety valve”6 and are the cement of choice when intervention may be required, ie, damage to the prosthesis, fracture or loosening of the abutment screw, and when the prosthesis must be modified after failure of adjacent implants.6,37 The TempBond cement provided a similar retentive strength to the other cements tested in this study on SSAs. However, considering the high water solubility of the TempBond cement,9,14 it is advisable to limit its use to provisional prostheses before the present findings have been validated in long-term clinical trials. The more retentive cements, such as resin or polyurethane, are more suitable when future retrievability is not necessary.6,16
CONCLUSION Within the limitations of this study, the retention of cast crown copings cemented with Retrieve or Premier to dental implant abutments with zero degrees of taper was significantly increased after airborne particle
abrasion of the abutments. However, this was not significant when TempBond was used. Airborne particle abrasion of implant abutments and the use of Retrieve or Premier can be recommended for use in nonretrievable prostheses. Although TempBond functioned similarly to the two other cements with smooth surface abutments, it is advisable to limit its use to provisional prostheses, as its long-term performance needs to be assessed with clinical trials.
ACKNOWLEDGMENTS The authors would like to thank Osteo-Ti for supplying the implant components. The authors reported no conflicts of interest related to this study.
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Jugdev et al
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