In vitro comparisons of casting retention on implant abutments among commercially available and experimental castor oil-containing dental luting agents

In vitro comparisons of casting retention on implant abutments among commercially available and experimental castor oil-containing dental luting agents Lígia A. P. Pinelli, DDS, MSc, PhD,a Laiza M. G. Fais, DDS, MSc, PhD,b Weber A. Ricci, DDS, MSc, PhD,c and José M. S. N. Reis, DDS, MSc, PhDd Araraquara Dental School, São Paulo State University (UNESP), Araraquara, São Paulo, Brazil Statement of problem. Although cement-retained implant prostheses are widely used, the quantification of optimal retention remains controversial, and new dental luting agents should be evaluated. Purpose. The purpose of this study was to compare, in vitro, the casting retention on implant abutments after cementation with 3 commercially available luting agents and an experimental luting agent (castor oil polyurethane, COP) with variable weight percentages (wt%) of calcium carbonate (CaCO3). Material and methods. Seventy-two palladium-silver cast copings were fabricated and divided into 6 groups: Temp Bond interim cement (TB); zinc phosphate cement (ZP); Rely X ARC resin cement (RX); pure COP (COP); COP + 10% wt% CaCO3 filler (COP 10); and COP + 50% wt% CaCO3 filler (COP 50). After cementation, the specimens were stored in distilled water at 37°C for 24 hours and subjected to removal force tests in a universal testing machine (5 kN; 0.5 mm/min). Statistical analyses were performed with the Kruskal-Wallis and Student-Newman-Keuls tests (α=.05). Results. The median values of casting retention (N) were as follows: TB=57.20 ±10.4; ZP=343.56 ±50.3; RX=40.07 ±9.7; COP=258.98 ±41.4; COP 10=466.57 ±79.3; and COP 50=209.63 ±31.4. The Kruskal-Wallis test showed significant differences among the groups (P<.01). TB and RX had the lowest mean retention values; COP, COP 10, and COP 50 were equal to ZP, and COP 10 had the highest retention. Conclusions. The casting retention on implant-abutments provided by COP was similar to that of copings cemented with zinc phosphate and may be influenced by the addition of calcium carbonate. (J Prosthet Dent 2013;109:319-324)

Clinical Implications

A castor oil polyurethane luting agent may be useful for cementing implant crowns because its retentive capacity can be easily modified with variable amounts of calcium carbonate. Implant-supported fixed prostheses may be cemented or screwretained on the implant abutments.1 The choice between these retention mechanisms has focused mainly on aspects such as retrievability,2 passivity, occlusion, and esthetics.3-5 Retrievability may no longer be an essential

requirement because of substantial increases in the success, predictability, and survival rates of dental implants.6 Therefore, cementation may be preferable, particularly in single-unit restorations or short-span prostheses.5 Additional advantages have been suggested for cement-retained over

screw-retained prostheses,7,8 including more equitable stress distribution,8 improved axial loading of implants,1 greater ease of superstructure adjustments,9,10 the elimination of the risk of screws loosening,7,11 and better esthetics due to the absence of screw access holes.1,12

This study was provided financial support by FAPESP (Fundação para o Amparo à Pesquisa do Estado de São Paulo, Brazil). Associate Professor, Department of Dental Materials and Prosthodontics. Postdoctoral student, Department of Dental Materials and Prosthodontics. c Associate Professor, Department of Social Dentistry. d Associate Professor, Department of Dental Materials and Prosthodontics. a

b

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Volume 109 Issue 5 The choice between using interim or definitive dental luting agents for cementation has been evaluated. According to Squier et al,7 there is little evidence and substantial controversy regarding the selection of these materials. One of the basic properties of any dental luting agent is its retentive strength, which is influenced not only by the material itself 13,14 but also by other variables that affect crown or casting retention, for example, the axial wall inclination angle, the surface area15 and height of the abutment,16,17 surface roughness,7,17-19 and the cementation techniques used. The use of definitive dental luting agents could compromise the reversibility of the prosthesis because of their high adhesion capacity. Additionally, the argument that metal abutments do not require reinforcement has led to interim luting agents being generally chosen.5 However, clinical failures associated with the high solubility20 and low strength of interim luting agents14,16 have prompted the development of new materials. More recently, a new polyurethane-based material has been developed at the São Carlos Chemistry Institute (São Paulo, Brazil).21 This castor oil polyurethane (COP) is extracted from Ricinus communis22-25 and has been successfully used in medicine26 for bone prostheses27 because of its biocompatibility, antimicrobial properties, and ease of handling.26,28 Its retention characteristics as a den-

tal luting agent are unknown. The purpose of this in vitro study was to analyze the casting retention on implant abutments after cementation by using 3 formulations of COP with variable amounts of calcium carbonate and an inorganic filler that imparts radiopacity and antibacterial/fungicidal actions; both are important in facilitating the removal of excess cement and avoiding periodontal tissue damage.29 The null hypothesis was that no significant difference among the groups would be found in terms of casting retention on implant abutments.

MATERIAL AND METHODS Seventy-two external connection implant analogs (Connection Implant Systems Ltd, Arujá, Brazil) measuring 3.75 mm in diameter and 4.0 mm in length and 72 prefabricated screw-retained titanium abutments measuring 5 mm in length (Connection Implant Systems Ltd, Arujá, Brazil) were used. Each abutment was attached to the implant analog with 35 Ncm torque,7,16,30 and the occlusal access of each abutment was filled with an interim sealant (Fermit; Ivoclar Vivadent, São Paulo, Brazil).15,31 Seventytwo cast copings were fabricated. A die spacer (True Spacer; Talladium Intl Implantology, Curitiba, Brazil) was applied over each implant abutment to standardize the space for the dental luting agents. To fabricate the wax pattern, a cast metal

1 Wax pattern with loop on occlusal surface.

The Journal of Prosthetic Dentistry

ring adjusted to the abutment diameter was positioned over the analog/ abutment assembly, and molten wax (Dentaurum: J.P. Winkelstroeter KG, Pforzheim, Germany) was poured into the cast metal ring. A glass slab with a mass of 1 kg was placed on top of the metal ring for 5 minutes until the wax cooled. The wax pattern was removed and carved. For the removal test, loops were created over the occlusal surface15,32-34 of the wax pattern (Fig. 1) with sprue wax (Ø2 mm; Clássico Ltd, São Paulo, Brazil). The patterns were sprued, invested in a phosphate-bonded investment (Heat Shock; Polidental, São Paulo, Brazil), and cast in palladium-silver alloy (Pors-on 4; Degussa Dental Ltda, São Paulo, Brazil).16,31 Copings were devested and cleaned with hydrofluoric acid in an ultrasonic bath for 10 minutes. The copings were inspected with a stereoscopic magnifying glass (×10) (Citoval; Carl Zeiss Intl, Jena, Germany). Debris and positive internal irregularities were removed with a round tungsten carbide bur (#1014; KG Sorensen, Cotia, Brazil).15 All analog/ abutment/coping assemblies were examined under a stereoscopic magnifying lens to ensure complete seating of the coping. Six dental luting agents were evaluated. Their manufacturers and compositions are listed in Table I. All materials were proportioned and mixed according to the manufacturers’ instructions. For TB, equal amounts (by weight) of zinc oxide eugenol base and catalyst pastes were mixed on a paper pad. ZP was mixed for 90 seconds with a spatula, following the incremental technique.35 The ratio of 1.4 g/0.4 mL recommended by the manufacturer was converted to 1.4 g of powder/1.54 g of liquid to ensure the standardization of the mixture. In the RX group, the cement was provided in a paste-paste clicker dispenser and was dispensed (1:1), standardized by weight, and mixed for 10 seconds. The components of the COP dental luting agents (COP, COP 10, and

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Table I. Experimental groups and dental luting agents used Groups

Dental Luting Agent

Manufacturer

Composition

TB (n=12)

Temp Bond

Kerr,

Base paste: Zinc oxide, inert oils (plasticizer)

Orange, Calif

and hydrogenated resins Reactor paste: Eugenol; zinc acetate (accelerator) and fillers

ZP (n=12)

Zinc Phosphate

SS White,

Powder: Zinc oxide, magnesium oxide

Rio de Janeiro, Brazil

Liquid: Phosphoric acid, aluminum hydroxide,

3M Brazil,

Paste A: Bis-GMA, triethylene glycol,

Sumaré, Brazil

dimethacrylate, zirconia/silica filler,

zinc oxide, distilled water RX (n=12)

Rely X ARC

photoinitiators, amine, pigments Paste B: Bis-GMA, triethylene glycol dimethacrylate, benzoic peroxide and zirconia/silica filler COP (n=12)

Pure COP*

Poliquil,

Polyol: trifunctional polyester (castor oil) 370 mg KOH/g

São Paulo, Brazil

Prepolymer: MDI** COP 10 (n=12)

COP 10%

Poliquil

Polyol: trifunctional polyester (castor oil) 370 mg KOH/g Prepolymer: MDI** Powder (filler): CaCO3 10% w/w

COP 50 (n=12)

COP 50%

Poliquil

Polyol: trifunctional polyester (castor oil) 370 mg KOH/g Prepolymer: MDI** Powder (filler): CaCO3 50% w/w

* COP- Castor oil polyurethane ** Methylene diphenyl diisocyanate

COP 50) were supplied in individual amber flasks containing the prepolymer, polyol (liquid), and calcium carbonate (powder). These compounds were weighed on a digital scale (Sartorius-Werke AG, Göettingen, Germany) accurate to 0.0001 g. A ratio of 1:0.7 (prepolymer:polyol) was used. The amounts of calcium carbonate in weight percentage (COP 10=10%; COP 50=50%) were established in relation to the sum of the polyol and prepolymer weights. After proportioning, COP was mixed for 2 minutes on a polytetrafluoroethylene plate.21 All dental luting agents were applied to the intaglio surface of the copings with a disposable brush (Microbrush KG Brush Fino; KG So-

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rensen),16 with the minimum quantity necessary to obtain an even distribution.36 Each coping was placed over the implant abutment, and finger pressure was applied to the occlusal surface of the coping for 10 seconds. Then, according to ADA specification No. 96, copings were placed under a force of 49 N for 10 minutes.30,37 For RX, the excess luting agent was removed, and the marginal region was light polymerized for 40 seconds while the force was still on the coping. All analog/abutment/coping assemblies were stored in distilled water at 37°C for 24 hours before the removal force test. Removal force testing was conducted in a universal testing machine

(EMIC DL 2000; EMIC - Equipment and Systems Testing Ltd, São José dos Pinhais, Brazil) with a 5.0 kN load cell at a crosshead speed of 0.5 mm/min. To prevent the application of nonuniaxial tensions during testing, the analog/abutment/coping assembly was engaged to the base of the test machine with a hinged device (Fig. 2A). The load cell and an apparatus connected to a horizontal pin were attached to the upper cross bar of the testing machine. This horizontal pin passed through the occlusal loop of each specimen (Fig. 2B). After load application, the force (in newtons) at which tensile bond failure occurred was recorded. Sample size was determined in a

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Table II. Kruskal-Wallis mean ranks and Student-Newman-Keuls test comparison of experimental groups

500

Groups

Mean Ranks

Newtons

400 300 200 100

CO P CO P 1 CO 0 P 50

RX

ZP

TP

0

TB

16.83A

ZP

54.66BC

RX

8.17A

COP

44.42BC

COP 10

59.46C

COP 50

35.46B

Kruskal-Wallis: H=57.82; P<.01 Different uppercase letters indicate significant differences

Experimental Groups 2 Test assembly attached to tensile testing machine. A, Analog/abutment/ coping assembly engaged in hinged device. B, Horizontal pin passing through occlusal loop.

3 Removal force median values (in newtons) for different experimental groups.

pilot study. A power analysis was performed with the results of this pilot study determining that 12 specimens (n=12) provide a power equal to .996 when P<.05 is used. To compare the removal force values of the 6 experimental groups, the data were statistically analyzed with the Kruskal-Wallis test, followed by the Student-Newman-Keuls test (α=.05).

DISCUSSION

RESULTS The median retentive force (in newtons) of the experimental groups is shown in Figure 3. Statistical analysis revealed significant differences among the experimental groups (P<.01). According to the mean rank and P values obtained by the KruskalWallis and Student-Newman-Keuls tests (Table II), TB and RX had similar removal force values (P<.05), with the lowest retention. The results from COP 50 were statistically similar to ZP and COP and lower (P<.05) than COP 10. There was no significant difference among the removal force values of ZP, COP, and COP 10.

The null hypothesis of this study was rejected based on the significant differences among the removal forces of the experimental groups. The interim cement Temp Bond (57.75 N) and the resin cement Rely X ARC (42.63 N) showed the lowest removal force values. The results for Temp Bond corresponded to those reported by other authors when similar methodologies were used. Akça et al5 revealed retentive values ranging from 40.6 N to 81.6 N, depending on the abutment used. Pan et al31 reported means of 36.6 N, while Maeyama et al8 observed values of 56 N. Despite the advantages of this interim zinc oxide and eugenol-based cement, such as satisfactory adhesion, resistance to bacterial infiltration,36 and ease of removal,14 low retention values were expected. However, higher retention values were expected for Rely X ARC, a resin cement that is recommended for definitive cementation but was not observed. This dual-polymerizing material does not rely on any additional

The Journal of Prosthetic Dentistry

mechanisms for metal adhesion. It is likely that the smooth surfaces of the abutments, in addition to the lack of surface treatment such as airborneparticle abrasion or metal primers affected the retention of Rely X ARC in the present study. This effect would explain the low retention values observed for the resin cement, which were similar to the values of the interim cement. According to Maeyama et al,8 airborne-particle abrasion and/or proper priming of the abutment may increase coping retention. It was reported that metal primers act as adhesives because of the presence of active monomers that promote a chemical bond between the cement and the surface oxides on metals.33 Ernst et al32 attributed the lower retention of resin cements to the lack of an adhesive system, and they recommended the use of adhesives in combination with resin cements. Another factor that may be associated with the lower retention observed for the resin cement in the present study is the fact that metal copings and abut-

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May 2013 O OH OH 4 Molecular structure of ricinoleic acid. ments block the light; that is, the cement was polymerized only by means of chemical reaction. Furthermore, the analog/abutment/coping assemblies were immersed in distilled water soon (10 minutes) after cementation but may not have been held there long enough for the chemical polymerization to take place, thereby affecting the properties of the material.13 The experimental dental luting agents showed retention values that were statistically equal to those of zinc phosphate cement. The latter presented values similar to those reported by Lewinstein et al,34 Tan et al,15 and Pan et al31 but higher than 61 N and 154.8 N, which were observed by Akça et al,5 and higher than 158 N, which was found by Maeyama et al.8 These discrepancies may reflect methodological differences such as variation in the surface roughness of the abutments, axial wall modifications, and the presence of grooves.30,34 Zinc phosphate cement had a higher retention among the commercially available dental luting agents evaluated in this study, possibly due to the occurrence of micromechanical attachment between the superstructure and the abutment surface.18 Regarding the experimental castor oil polyurethane dental luting agents, although the formulations (pure COP, COP + 10% CaCO3, and COP + 50% CaCO3) did not show statistically significant differences from the zinc phosphate cement, COPs presented with different retentive strengths as a function of the addition and of the amounts of CaCO3 in their formulations. The addition of calcium carbonate is responsible for conferring

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radiopacity to COP. Moreover, this filler provides the release of calcium ions, facilitating ion exchange at the bone/resin matrix interface,26 which may be beneficial in subgingival abutment/restoration margins. The results shown in Table II suggest the presence of increased retention when 10% CaCO3 was added to COP. However, the retention decreased when 50% CaCO3 was added to COP. These findings may be explained by differences in consistency, fluidity, and flow during cementation. While pure COP presented excessive flow during cementation, COP 10 exhibited adequate flow and completely coated the internal surface of the coping. However, the addition of 50% CaCO3 made COP more viscous, resulting in a thicker cementation line, which may have induced mechanical failure. COP dental luting agents, like other polyurethanes, rely on a reaction between an isocyanate and hydroxyl group. However, COP has advantages due to the presence of highly reactive groups in the ricinoleic acid structure: a carbonyl group on the first carbon, a double bond (or unsaturation) on the ninth carbon, and a hydroxyl group on the twelfth carbon (Fig. 4).24 These groups favor polarization of the material and satisfactory interaction with metallic substrates.25 Therefore, the highly reactive polymeric structure of COP, which acts as a powerful adhesive on metal,23 may explain the high retention values observed for the experimental COP dental luting agents. Several studies have evaluated the retention of copings cemented with different luting agents. However, the amount of retentiveness required for cement-retained implant prostheses remains controversial. Maeyama et al8 ranked dental luting agents into 3 ascending levels of retention: zinc oxide (56 N), zinc phosphate (158 N) and glass ionomer (132 N), and glass ionomer reinforced with resin (477 N) and resin cement (478 N). These authors recommend intermediate retention materials for cement-retained implant prostheses. However, the choice

for each particular patient should be based on the need/desire for reversibility, the amount of required retention, the expected ease of removal,3 and the cost.7 Based on the results of this study, the COP dental luting agents are deemed strong enough to resist masticatory stresses and provide retention similar to that of zinc phosphate cement, a permanent cementation material. However, the limitations and additional properties of COP should be investigated in future studies. According to Ayad et al,12 assessing the behavior of materials under nonuniaxial forces to replicate dynamic forces from mastication and parafunctional habits is also important. Moreover, the specimens should also be artificially aged by mechanical and thermal cycling. Another possible advantage of COP is the absence of potential irritation or an inflammatory tissue response. Such adverse effects may restrict the use of some dental luting agents in subgingival restoration margins, especially when there is a risk of cement overflow.3,4,29 In this context, the use of COP derived from Ricinus communis may be effective because of its bactericidal properties, tissue compatibility, potential to stimulate healing, satisfactory mechanical properties, and low cost22; therefore, this too deserves further investigation.

CONCLUSION Within the limitations of this in vitro study, the following conclusions were drawn: 1. The retention of COP dental luting agents may be influenced by the amount of calcium carbonate added. 2. Among the experimental dental luting agents evaluated, pure COP and COP with the addition of 50% calcium carbonate had removal forces similar to those of zinc phosphate and higher than those of Rely X ARC and Temp Bond.

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Volume 109 Issue 5 REFERENCES 1. Hebel KS, Gajjar RC. Cement-retained versus screw-retained implant restorations: achieving optimal occlusion and esthetics in implant dentistry. J Prosthet Dent 1997;77:28-35. 2. Schweitzer DM, Berg RW, Mancia GO. A technique for retrieval of cement-retained implant-supported prostheses. J Prosthet Dent 2011;106:134-8. 3. Agar JR, Cameron SM, Hughbanks JC, Parker MH. Cement removal from restorations luted to titanium abutments with simulated subgingival margins. J Prosthet Dent 1997;78:43-7. 4. Pauletto N, Lahiffe BJ, Walton JN. Complications associated with excess cement around crowns on osseointegrated implants: a clinical report. Int J Oral Maxillofac Implants 1999;14:865-8. 5. Akca K, Iplikcioglu H, Cehreli MC. Comparison of uniaxial resistance forces of cements used with implant-supported crowns. Int J Oral Maxillofac Implants 2002;17:536-42. 6. Buser D, Mericske-Stern R, Bernard JP, Behneke A, Behneke N, Hirt HP, et al. Long-term evaluation of non-submerged ITI implants. Part 1: 8-year life table analysis of a prospective multi-center study with 2359 implants. Clin Oral Implants Res 1997;8:161-72. 7. Squier RS, Agar JR, Duncan JP, Taylor TD. Retentiveness of dental cements used with metallic implant components. Int J Oral Maxillofac Implants 2001;16:793-8. 8. Maeyama H, Sawase T, Jimbo R, Kamada K, Suketa N, Fukui J, et al. Retentive strength of metal copings on prefabricated abutments with five different cements. Clin Implant Dent Relat Res 2005;7:229-34. 9. Chee W, Felton DA, Johnson PF, Sullivan DY. Cemented versus screw-retained implant prostheses: which is better? Int J Oral Maxillofac Implants 1999;14:137-41. 10.Chee WW, Torbati A, Albouy JP. Retrievable cemented implant restorations. J Prosthodont 1998;7:120-5. 11.Behneke A, Behneke N, d’Hoedt B. The longitudinal clinical effectiveness of ITI solid-screw implants in partially edentulous patients: a 5-year follow-up report. Int J Oral Maxillofac Implants 2000;15:633-45. 12.Avivi-Arber L, Zarb GA. Clinical effectiveness of implant-supported single-tooth replacement: the Toronto Study. Int J Oral Maxillofac Implants 1996;11:311-21. 13.Mojon P, Hawbolt EB, MacEntee MI, Ma PH. Early bond strength of luting cements to a precious alloy. J Dent Res 1992;71:1633-9.

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28.Pinheiro CR, Guinesi AS, Pizzolitto AC, Bonetti-Filho I. In vitro antimicrobial activity of Acroseal, Polifil and Epiphany against Enterococcus faecalis. Braz Dent J 2009;20:107-11. 29.Wadhwani C, Hess T, Faber T, Piñeyro A, Chen CS. A descriptive study of the radiographic density of implant restorative cements. J Prosthet Dent 2010;103:295-302. 30.Mansour A, Ercoli C, Graser G, Tallents R, Moss M. Comparative evaluation of casting retention using the ITI solid abutment with six cements. Clin Oral Implants Res 2002;13:343-8. 31.Pan YH, Ramp LC, Lin CK, Liu PR. Comparison of 7 luting protocols and their effect on the retention and marginal leakage of a cement-retained dental implant restoration. Int J Oral Maxillofac Implants 2006;21:587-92. 32.Ernst CP, Wenzl N, Stender E, Willershausen B. Retentive strengths of cast gold crowns using glass ionomer, compomer, or resin cement. J Prosthet Dent 1998;79:472-6. 33.Kunt GE, Ceylan G, Yilmaz N. Effect of surface treatments on implant crown retention. J Dent Sci 2010;5:131-5. 34.Lewinstein I, Block L, Lehr Z, Ormianer Z, Matalon S. An in vitro assessment of circumferential grooves on the retention of cement-retained implant-supported crowns. J Prosthet Dent 2011;106:367-72. 35.Ayad MF, Johnston WM, Rosenstiel SF. Influence of tooth preparation taper and cement type on recementation strength of complete metal crowns. J Prosthet Dent 2009;102:354-61. 36.Baldissara P, Comin G, Martone F, Scotti R. Comparative study of the marginal microleakage of six cements in fixed provisional crowns. J Prosthet Dent 1998;80:417-22. 37.Mathews MF, Breeding LC, Dixon DL, Aquilino SA. The effect of connector design on cement retention in an implant and natural tooth-supported fixed partial denture. J Prosthet Dent 1991;65:822-7. Corresponding author: Dr Lígia Antunes Pereira Pinelli Rua Humaitá 1680 Centro, Araraquara, SP 14801-903 BRAZIL Fax: +55-16-3301-6406 E-mail: [email protected] Copyright © 2013 by the Editorial Council for The Journal of Prosthetic Dentistry.

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