Ó 2015 Eur J Oral Sci
Eur J Oral Sci 2015; 1–5 DOI: 10.1111/eos.12181 Printed in Singapore. All rights reserved
European Journal of Oral Sciences
Discrepancies in marginal and internal fits for different metal and alumina infrastructures cemented on implant abutments
Fernanda Faot1, Dalton Suzuki2, Plinio M. Senna3, Wander J. da Silva4, Ivete A. de Mattias Sartori2 1
Department of Restorative Dentistry, School of Dentistry, Federal University of Pelotas, Pelotas, RS; 2Implantology Division, Latin American Institute of Dental Research and Education, Curitiba, PR; 3Health Sciences Centre, Unigranrio University, Duque de Caxias, RJ; 4Piracicaba Dental School, University of Campinas, Piracicaba, SP, Brazil
Faot F, Suzuki D, Senna PM, da Silva WJ, de Mattias Sartori IA. Discrepancies in marginal and internal fits for different metal and alumina infrastructures cemented on implant abutments. Eur J Oral Sci 2015; 00: 000–000. © 2015 Eur J Oral Sci Cemented crowns are increasingly being used on dental implants instead of on screw-retained prostheses because of the reliability of internal Morse taper implant– abutment connections. However, there is a lack of information on the fit of metal ceramic and premachined alumina infrastructures. Therefore, the aim of this study was to evaluate the marginal and internal fits of different metal and alumina infrastructures cemented on universal post abutments. A total of 45 abutments (6 mm in height and 3.3 mm in diameter) were divided into five groups on the basis of their infrastructure material: cobalt–chromium (CoCr), nickel–chromium (NiCr), nickel– chromium–molybdenum–titanium (NiCrMoTi), gold (Au), and premachined alumina. The alumina group showed marginal overextension, and the Au group showed the highest discrepancy in marginal fit among the metal alloys. The CoCr and alumina groups showed the lowest discrepancies in internal fit. In conclusion, the alumina cylinders exhibited the best internal fit, despite their horizontal overextension. Among the metal alloys, CoCr exhibited the best fit at critical regions, such as the cervical and occlusal areas.
The clinical success of single crowns supported by dental implants and retained by screws or cement has been well documented (1, 2). However, when a Morse taper implant–abutment connection is used, which allows the abutment to contact the implant through its own interface, cement is preferred to screws for retaining the crown (3). The increased implant– abutment contact area, together with the Morse taper effect, provides relatively high abutment stability that minimizes the occurrence of screw loosening and the need to maintain screw access through the crown for reversibility (4). Additionally, Morse taper connections, from a biological perspective, tend to keep the cementation line far from the peri-implant bone. The most common abutment for a cemented prosthesis is the universal post, for which only a few components are necessary to solve single edentulous spaces in the anterior and posterior regions (4). To simplify laboratory procedures, manufacturers of most implant systems advocate the use of prefabricated plastic cylinders when casting metal–ceramic infrastructures on the universal post abutment (5). However, although plastic
Prof. Fernanda Faot, Prosthodontics Division, School of Dentistry, Federal University of Pelotas, Rua Goncßalves Chaves, 457, Pelotas, RS, Brazil, 96015-560. E-mail: [email protected] Key words: dental implants; dental internal fit; dental marginal adaptation; metal ceramic alloys; prosthesis Accepted for publication February 2015
cylinders are able to compensate for alloy contraction (6) and improve cement flow (7, 8), inappropriate fitting may occur and compromise the clinical longevity of the cemented crowns through early loss of retention or peri-implantitis (9–11). Moreover, the use of plastic cylinders does not guarantee that the crown will fit because different alloys with different casting properties can be used (12). To solve these problems, alternative premachined alumina cylinders can be used on universal post abutments, offering good aesthetic properties. Nevertheless, the internal fit of these all-ceramic crowns, which is critical to their structural strength (13–16), has not been evaluated on implant abutments after firing. Given the lack of information on the marginal and internal fits of metal–ceramic infrastructures and premachined alumina cylinders on universal implant abutments, the aim of this study was to evaluate the discrepancy in the fit of different metal and alumina infrastructures cemented on implant abutments. The null hypothesis was that there would be no difference in fit between different metal alloys and alumina infrastructures.
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Material and methods
A
B
Experimental design Universal abutments for cemented crowns (3.3 mm in diameter and 6.0 mm in height) and their respective prefabricated plastic and alumina cylinders (Neodent, Curitiba, PR, Brazil) were selected for the study (Fig. 1). A total of 45 abutments were fixed on Morse taper implant replicas, and prefabricated plastic cylinders were engaged on the abutments. Specimens were randomly divided into five groups, on the basis of their infrastructure material (n = 9): cobalt–chromium (CoCr) (Jelbond Premier; Jelenko, San Diego, CA, USA), nickel–chromium (NiCr) (Fit Cast Titanium; Talmax, Curitiba, PR, Brazil), nickel–chromium–molybdenum–titanium (NiCrMoTi) (Tilite Premium; Talmax), gold (Au) (Stabilor G; DeguDent, S~ ao Paulo, SP, Brazil), and premachined alumina cylinders (Neodent). After casting the metal alloy or firing the alumina cylinders, the infrastructures were cemented on the abutments under constant load. The marginal horizontal fit and internal fit were evaluated. Infrastructure preparation To standardize the casting of the metal infrastructures, one implant replica with the universal abutment was fixed in a type IV gypsum support (Durone IV; Dentsply, Petr opolis, RJ, Brazil). The infrastructure was waxed on the plastic cylinder with flat surfaces. A mould was fabricated with laboratory silicone (Zetalabor; Zhermack, Badia Polesine, Rovigo, Italy) to standardize the thickness, uniformity, and reproducibility of the waxing cylinder patterns for all cast metal alloys. Metal alloys were cast in accordance with the manufacturers’ instructions and were cleaned with glass-bead blasting. Alumina cylinders were submitted to one heating cycle to simulate application of feldspathic ceramic. Cementation procedure All copings were cemented with glass ionomer cement (Meron; Voco Dental Products, Greensboro, NC, USA), in accordance with the manufacturers’ instructions. Cement was inserted into the infrastructure by using an explorer and was seated on the abutment by digital pressure for extravasation of the cement. After the initial setting of the cement, the assemblies were positioned on the table of a universal testing machine (Instron 3382; Instron,
A
B
C
Fig. 2. Surface pattern with mirrored surface of the embedded metal (A) and alumina (B) infrastructures.
Norwood, MA, USA). A compressive load of 50 N was vertically applied until polymerization of the cement was complete. Marginal horizontal fit Each assembly was fixed in a brass base with six sides, to standardize assessment of the symmetrical horizontal imbalances at six different positions. Two measurements (right and left) were made with a monocular microscope under 209 magnification (model 183S-032; Marcel Aubert, Bienne, Switzerland). The vertical axis (Y) of the lens was aligned with the long axis of the sleeve, and measurements were made on the horizontal axis (X). The arithmetic mean of 12 measurements was recorded for each assembly. Internal fit Assemblies were placed on a cylindrical device (30 mm in diameter and 15 mm in thickness) and embedded in Bakelite (Multifast Black; Struers, Copenhagen, Denmark) through hot-press mounting (LaboPress-1; Struers) at a pressure of 15 kN for 10 min. All assemblies were ground under constant refrigeration (Labopol 5; Struers), using silicon carbide sandpaper with progressive grit sizes (#220, #320, #500, #800, and #1000), until the central parts of the abutments were reached. Polishing was performed in a polishing machine (LaboPol-21; Struers) with 1-lm diamond paste (Struers) until the metal became a mirrored surface (Fig. 2). The specimens were washed with water and dried at room temperature. The thickness of the cementation line was analysed, under 2009 magnification, with an optical microscope (model BX-60; Olympus, Hamburg, Germany), followed by image capturing and processing (OMNIMET Software; Buehler, Lake Bluff, IL, USA). The thickness of the cementation line was measured at three predetermined positions on both sides of the abutment (Fig. 3). The landmarks for measurements were as follows: the cervical region (i.e. the distance between the central portion of the chamfer finish line and its internal portion in the coping; A and B in Fig. 3); the axial region (i.e. located in the middle portion of the axial walls, 3 mm above the chamfer; C and D in Fig. 3); and the occlusal region (i.e. located on the occlusal wall, positioned 0.5 mm from the hexagonal area of the abutment; E and F in Fig. 3). Statistical analysis
Fig. 1. Dimensions of the implant abutment (A) and its respective plastic (B) and alumina (C) prefabricated cylinders.
All analyses were performed in the SAS software package (version 9.0; SAS Institute, Cary, NC, USA) at a signifi-
Fit of cemented implant crowns
Fig. 3. Location points of the measurement of cementation thickness: cervical (A and B), axial (C and D), and occlusal (E and F).
cance level of 5%. Normality of the error distribution and the degree of non-constant variance were checked for each response variable using the SAS/LAB package. Data were analysed by one-way ANOVA. Tukey’s HSD post-hoc test (a = 0.05) was used to compare the marginal and internal fits between materials.
Results The results of marginal horizontal fit are presented in Fig. 4. Alumina copings showed the largest discrepancy in marginal horizontal fit (P < 0.05). The Au group showed the largest discrepancy among the metal alloy groups (P < 0.05). The results of internal fit are shown in Fig. 5. The CoCr, NiCrMoTi, and alumina groups showed the best internal fit at the cervical region (P < 0.05). At the occlusal region, the alumina cylinder showed a better internal fit than the other materials (P < 0.05). No significant differences in internal fit were observed among the materials at the axial region (P > 0.05).
Discussion Poor fit between crowns and abutments favours the occurrence of micromovements, which can lead to cement failure, prosthesis dislodgment, and abutment
Fig. 4. Discrepancy in marginal horizontal fit (lm) for the different infrastructure materials. Bars show mean SD. Different letters indicate a significant difference between the groups (P < 0.05). Au, gold; CoCr, cobalt–chromium; NiCr, nickel–chromium; NiCrMoTi, nickel–chromium–molybdenum–titanium.
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Fig. 5. Discrepancy in internal fit (lm) for cemented copings at the cervical, axial, and occlusal regions. Bars show mean SD. Different letters indicate a significant difference between the groups in each region (P < 0.05). Au, gold; CoCr, cobalt–chromium; NiCr, nickel–chromium; NiCrMoTi, nickel–chromium–molybdenum–titanium.
overload (10, 13). Standard abutments and premachined components are intended to facilitate the manufacture of cemented prostheses. The present study evaluated the marginal horizontal and internal fits of different infrastructures cemented on an implant abutment. To date, there is no consensus regarding which methodology best simulates the clinical conditions of poor prosthesis fit. Which cement is used in the methodology is an important consideration, as cement interposition may contribute to an increase in marginal discrepancy (7–9, 11, 13). Studies have described different measurement techniques, such as the sectional view, the direct view, and the replica view, after impression or clinical examination (14, 17). Additionally, the number and the location of the measurements can vary between studies (18). Here, we adopted two measurement techniques: the direct view was used to measure the marginal horizontal discrepancy; and the sectional view was used to evaluate the internal adaptation. The measurements obtained showed low means for all study groups and a uniform cement thickness along the infrastructure–abutment interfaces. These findings allow us to reject the hypothesis that the viscosity of the cement agent and the settlement forces were responsible for discrepancies in measurements. Au alloys are commonly used as a reference in comparative studies on casting deformation (19, 20). However, in the present study, the Au copings exhibited twice as much discrepancy as the other alloys. The lower resistance of Au, compared with alloys made from non-noble metals, may result in insufficient flow to the cervical area and difficulties in obtaining accurate measurements on thin and delicate margins (21, 22). Therefore, the abutment with the narrow chamfer finish line (Fig. 1), used in the present study, may favour higher discrepancy values for the Au alloy. Although distortions of alumina cylinders are related to the buccal and lingual areas owing to the heating cycles needed for the feldspathic ceramic layer (23), they exhibited the best internal fit in the present study.
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On the other hand, a marked overextension was clearly observed with the alumina cylinders compared with the metal infrastructures. Alumina cylinders have overextended edges because of their specific anatomical design that is intended to maintain their marginal structural integrity. However, the presence of an overhang or overextension in an implant-supported prosthesis does not seem to cause deleterious effects in peri-implant tissues to the same degree as in conventional prostheses. This difference can be explained by the histological differences between the soft-tissue barriers at the implant and teeth; namely, periodontal tissue provides an area of connective tissue attachment that responds much more strongly to the inflammatory process (24). Although the values found in the present study seem to suggest an extension error, they agree with those reported by SIADAT et al. (5), who conducted a comparative study of horizontal fit with metal copings. Higher values of overhang are frequently observed in cemented implant prostheses because of the thin finish line. This characteristic of most prosthetic abutments results from the necessity of compensating between the cervical diameter of the crown and the diameter of the implant or prosthetic component. The use of prefabricated components was insufficient to guarantee an accurate fit over the abutment. The difference in the discrepancies of internal fit between the CoCr and Au copings showed that, even when we controlled the technical casting steps and used prefabricated plastic cylinders, the casting process itself caused distortions during prosthesis fabrication (6, 12, 21). Thus, for each alloy, the castability properties, such as melting temperature, coefficient of thermal expansion, and density, and the use of different investment materials, are factors that can interfere directly with the accuracy of plastic cylinders (22, 25). It is difficult to compare the internal cervical discrepancy values found in this study with such values in other studies, as the literature is inconclusive regarding a standardized region or point from which to make the measurements. In our study, the locations of points A and B did not refer to the portion involved in sealing the coping or cylinder, but to the inner bevel in the cervical area. Only QUANTE et al. (26) reported landmarks at the same location. They described similar fit-discrepancy values to ours for this region, ranging from 74 to 99 lm, despite using a different measurement technique (silicone indicator paste). Accordingly, we suggest that the flow of cement film in this region was uniform for all materials studied, which would guarantee final settlement and appropriate retention (7, 8). The internal discrepancy values in the axial walls (range: 50 8 lm to 64 27 lm), found in this study, are acceptable for the stability of cemented prostheses (15, 26). The values observed for occlusal discrepancy are consistent with those of other studies (6, 12, 17, 21). The difference between the discrepancies in axial and occlusal fits can be related to the fact that the expansion was directed towards the occlusal region, because the casting ring limited axial expansion (6, 12, 21). Furthermore, thermal expansion can enable further
broadening of the occlusal surface during wax removal, thereby increasing the internal occlusal imbalance. The higher values of poor occlusal fit for the Au copings suggest that the narrow finish line of the universal post and its occlusal convergence angle (2.30°) may not favour the flow properties of Au alloys (19, 22). A thick cementation line on the occlusal surface can lead to the development of microfractures, which, consequently, can result in micromovements that finally dislodge the prosthesis (7–10). Few published studies are available regarding the applicability of CoCr alloys for implant prosthetic infrastructures (27). The performance of this alloy in the present study favours its use in implantology as an alternative alloy, especially in light of its lower cost than Au, biocompatibility, and corrosion resistance. This study examined the fit of different metal alloys and the alumina cylinder on only one type of universal post abutment. Other abutments, with different diameters, heights, occlusal convergence angles, and finish lines, are commercially available and may produce different results. In addition, using other cement agents or measurement techniques for the internal and marginal fits would lead to different discrepancies in fit for the cemented crowns. Within the limitations of this study, we can conclude that alumina copings exhibited horizontal overextension related to their structural strength and had the best internal fit at the occlusal surface of the implant abutment. Among the metal alloys, CoCr showed a better internal fit at critical regions, such as the cervical and occlusal areas. Acknowledgements – The authors thank NEODENT for supplying the prosthetic components. Conflicts of interest – The authors declare no conflicts of interest.
References 1. PREISKEL HW, TSOLKA P. Cement- and screw-retained implant-supported prostheses: up to 10 years of follow-up of a new design. Int J Oral Maxillofac Implants 2004; 19: 87–91. 2. WALTON TR. Changes in the outcome of metal-ceramic toothsupported single crowns and FDPs following the introduction of osseointegrated implant dentistry into a prosthodontic practice. Int J Prosthodont 2009; 22: 260–267. 3. CEHRELI MC, AKCA K, IPLIKCIOGLU H, SAHIN S. Dynamic fatigue resistance of implant-abutment junction in an internally notched morse-taper oral implant: influence of abutment design. Clin Oral Implants Res 2004; 15: 459–465. 4. WEIGL P. New prosthetic restorative features of Ankylos implant system. J Oral Implantol 2004; 30: 178–188. 5. SIADAT H, ALIKHASI M, MIRFAZAELIAN A, ZADE MM. Scanning electron microscope evaluation of vertical and horizontal discrepancy in cast copings for single-tooth implant-supported prostheses. Implant Dent 2008; 17: 299–308. 6. MILAN FM, CONSANI S, CORRER SOBRINHO L, SINHORETI MA, SOUSA-NETO MD, KNOWLES JC. Influence of casting methods on marginal and internal discrepancies of complete cast crowns. Braz Dent J 2004; 15: 127–132. 7. KERN M, SCHALLER HG, STRUB JR. Marginal fit of restorations before and after cementation in vivo. Int J Prosthodont 1993; 6: 585–591.
Fit of cemented implant crowns 8. PIEMJAI M. Effect of seating force, margin design, and cement on marginal seal and retention of complete metal crowns. Int J Prosthodont 2001; 14: 412–416. 9. WHITE SN, YU Z, TOM JF, SANGSURASAK S. In vivo marginal adaptation of cast crowns luted with different cements. J Prosthet Dent 1995; 74: 25–32. 10. OLIVERA AB, SAITO T. The effect of die spacer on retention and fitting of complete cast crowns. J Prosthodont 2006; 15: 243–249. 11. BOTTINO MA, VALANDRO LF, BUSO L, OZCAN M. The influence of cervical finish line, internal relief, and cement type on the cervical adaptation of metal crowns. Quintessence Int 2007; 38: e425–e432. 12. AL WAZZAN KA, AL-NAZZAWI AA. Marginal and internal adaptation of commercially pure titanium and titanium-aluminum-vanadium alloy cast restorations. J Contemp Dent Pract 2007; 8: 19–26. 13. TUNTIPRAWON M, WILSON PR. The effect of cement thickness on the fracture strength of all-ceramic crowns. Aust Dent J 1995; 40: 17–21. 14. KOKUBO Y, OHKUBO C, TSUMITA M, MIYASHITA A, VULT VON STEYERN P, FUKUSHIMA S. Clinical marginal and internal gaps of Procera AllCeram crowns. J Oral Rehabil 2005; 32: 526– 530. 15. AL-MAKRAMANI BM, RAZAK AA, ABU-HASSAN MI, SULAIMAN E, LOON LJ, YAHYA NA. Marginal integrity of turkom-cera compared to other all-ceramic materials: effect of finish line. Int J Prosthodont 2011; 24: 379–381. 16. SUBASI G, OZTURK N, INAN O, BOZOGULLARI N. Evaluation of marginal fit of two all-ceramic copings with two finish lines. Eur J Dent 2012; 6: 163–168. 17. LAURENT M, SCHEER P, DEJOU J, LABORDE G. Clinical evaluation of the marginal fit of cast crowns–validation of the silicone replica method. J Oral Rehabil 2008; 35: 116–122.
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18. GROTEN M, AXMANN D, PROBSTER L, WEBER H. Determination of the minimum number of marginal gap measurements required for practical in-vitro testing. J Prosthet Dent 2000; 83: 40–49. 19. SUTHERLAND JK, RITSCO RG, BUDD SR. Marginal adaptation of implant-supported metal-ceramic crowns fabricated with gold cylinders. J Prosthodont 1998; 7: 100–105. 20. OYAGUE RC, TURRION AS, TOLEDANO M, MONTICELLI F, OSORIO R. In vitro vertical misfit evaluation of cast frameworks for cement-retained implant-supported partial prostheses. J Dent 2009; 37: 52–58. 21. WOSTMANN B, BLOSSER T, GOUENTENOUDIS M, BALKENHOL M, FERGER P. Influence of margin design on the fit of high-precious alloy restorations in patients. J Dent 2005; 33: 611–618. 22. KELLY JR, ROSE TC. Nonprecious alloys for use in fixed prosthodontics: a literature review. J Prosthet Dent 1983; 49: 363–370. 23. BALKAYA MC, CINAR A, PAMUK S. Influence of firing cycles on the margin distortion of 3 all-ceramic crown systems. J Prosthet Dent 2005; 93: 346–355. 24. BERGLUNDH T, LINDHE J, ERICSSON I, MARINELLO CP, LILJENBERG B, THOMSEN P. The soft tissue barrier at implants and teeth. Clin Oral Implants Res 1991; 2: 81–90. 25. PAULINO SM, LEAL MB, PAGNANO VO, BEZZON OL. The castability of pure titanium compared with Ni-Cr and Ni-Cr-Be alloys. J Prosthet Dent 2007; 98: 445–454. 26. QUANTE K, LUDWIG K, KERN M. Marginal and internal fit of metal-ceramic crowns fabricated with a new laser melting technology. Dent Mater 2008; 24: 1311–1315. 27. DE TORRES EM, RODRIGUES RC, DE MATTOS MDAG, RIBEIRO RF. The effect of commercially pure titanium and alternative dental alloys on the marginal fit of one-piece cast implant frameworks. J Dent 2007; 35: 800–805.
Eur J Oral Sci 2015; 1–5 DOI: 10.1111/eos.12181 Printed in Singapore. All rights reserved
European Journal of Oral Sciences
Discrepancies in marginal and internal fits for different metal and alumina infrastructures cemented on implant abutments
Fernanda Faot1, Dalton Suzuki2, Plinio M. Senna3, Wander J. da Silva4, Ivete A. de Mattias Sartori2 1
Department of Restorative Dentistry, School of Dentistry, Federal University of Pelotas, Pelotas, RS; 2Implantology Division, Latin American Institute of Dental Research and Education, Curitiba, PR; 3Health Sciences Centre, Unigranrio University, Duque de Caxias, RJ; 4Piracicaba Dental School, University of Campinas, Piracicaba, SP, Brazil
Faot F, Suzuki D, Senna PM, da Silva WJ, de Mattias Sartori IA. Discrepancies in marginal and internal fits for different metal and alumina infrastructures cemented on implant abutments. Eur J Oral Sci 2015; 00: 000–000. © 2015 Eur J Oral Sci Cemented crowns are increasingly being used on dental implants instead of on screw-retained prostheses because of the reliability of internal Morse taper implant– abutment connections. However, there is a lack of information on the fit of metal ceramic and premachined alumina infrastructures. Therefore, the aim of this study was to evaluate the marginal and internal fits of different metal and alumina infrastructures cemented on universal post abutments. A total of 45 abutments (6 mm in height and 3.3 mm in diameter) were divided into five groups on the basis of their infrastructure material: cobalt–chromium (CoCr), nickel–chromium (NiCr), nickel– chromium–molybdenum–titanium (NiCrMoTi), gold (Au), and premachined alumina. The alumina group showed marginal overextension, and the Au group showed the highest discrepancy in marginal fit among the metal alloys. The CoCr and alumina groups showed the lowest discrepancies in internal fit. In conclusion, the alumina cylinders exhibited the best internal fit, despite their horizontal overextension. Among the metal alloys, CoCr exhibited the best fit at critical regions, such as the cervical and occlusal areas.
The clinical success of single crowns supported by dental implants and retained by screws or cement has been well documented (1, 2). However, when a Morse taper implant–abutment connection is used, which allows the abutment to contact the implant through its own interface, cement is preferred to screws for retaining the crown (3). The increased implant– abutment contact area, together with the Morse taper effect, provides relatively high abutment stability that minimizes the occurrence of screw loosening and the need to maintain screw access through the crown for reversibility (4). Additionally, Morse taper connections, from a biological perspective, tend to keep the cementation line far from the peri-implant bone. The most common abutment for a cemented prosthesis is the universal post, for which only a few components are necessary to solve single edentulous spaces in the anterior and posterior regions (4). To simplify laboratory procedures, manufacturers of most implant systems advocate the use of prefabricated plastic cylinders when casting metal–ceramic infrastructures on the universal post abutment (5). However, although plastic
Prof. Fernanda Faot, Prosthodontics Division, School of Dentistry, Federal University of Pelotas, Rua Goncßalves Chaves, 457, Pelotas, RS, Brazil, 96015-560. E-mail: [email protected] Key words: dental implants; dental internal fit; dental marginal adaptation; metal ceramic alloys; prosthesis Accepted for publication February 2015
cylinders are able to compensate for alloy contraction (6) and improve cement flow (7, 8), inappropriate fitting may occur and compromise the clinical longevity of the cemented crowns through early loss of retention or peri-implantitis (9–11). Moreover, the use of plastic cylinders does not guarantee that the crown will fit because different alloys with different casting properties can be used (12). To solve these problems, alternative premachined alumina cylinders can be used on universal post abutments, offering good aesthetic properties. Nevertheless, the internal fit of these all-ceramic crowns, which is critical to their structural strength (13–16), has not been evaluated on implant abutments after firing. Given the lack of information on the marginal and internal fits of metal–ceramic infrastructures and premachined alumina cylinders on universal implant abutments, the aim of this study was to evaluate the discrepancy in the fit of different metal and alumina infrastructures cemented on implant abutments. The null hypothesis was that there would be no difference in fit between different metal alloys and alumina infrastructures.
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Material and methods
A
B
Experimental design Universal abutments for cemented crowns (3.3 mm in diameter and 6.0 mm in height) and their respective prefabricated plastic and alumina cylinders (Neodent, Curitiba, PR, Brazil) were selected for the study (Fig. 1). A total of 45 abutments were fixed on Morse taper implant replicas, and prefabricated plastic cylinders were engaged on the abutments. Specimens were randomly divided into five groups, on the basis of their infrastructure material (n = 9): cobalt–chromium (CoCr) (Jelbond Premier; Jelenko, San Diego, CA, USA), nickel–chromium (NiCr) (Fit Cast Titanium; Talmax, Curitiba, PR, Brazil), nickel–chromium–molybdenum–titanium (NiCrMoTi) (Tilite Premium; Talmax), gold (Au) (Stabilor G; DeguDent, S~ ao Paulo, SP, Brazil), and premachined alumina cylinders (Neodent). After casting the metal alloy or firing the alumina cylinders, the infrastructures were cemented on the abutments under constant load. The marginal horizontal fit and internal fit were evaluated. Infrastructure preparation To standardize the casting of the metal infrastructures, one implant replica with the universal abutment was fixed in a type IV gypsum support (Durone IV; Dentsply, Petr opolis, RJ, Brazil). The infrastructure was waxed on the plastic cylinder with flat surfaces. A mould was fabricated with laboratory silicone (Zetalabor; Zhermack, Badia Polesine, Rovigo, Italy) to standardize the thickness, uniformity, and reproducibility of the waxing cylinder patterns for all cast metal alloys. Metal alloys were cast in accordance with the manufacturers’ instructions and were cleaned with glass-bead blasting. Alumina cylinders were submitted to one heating cycle to simulate application of feldspathic ceramic. Cementation procedure All copings were cemented with glass ionomer cement (Meron; Voco Dental Products, Greensboro, NC, USA), in accordance with the manufacturers’ instructions. Cement was inserted into the infrastructure by using an explorer and was seated on the abutment by digital pressure for extravasation of the cement. After the initial setting of the cement, the assemblies were positioned on the table of a universal testing machine (Instron 3382; Instron,
A
B
C
Fig. 2. Surface pattern with mirrored surface of the embedded metal (A) and alumina (B) infrastructures.
Norwood, MA, USA). A compressive load of 50 N was vertically applied until polymerization of the cement was complete. Marginal horizontal fit Each assembly was fixed in a brass base with six sides, to standardize assessment of the symmetrical horizontal imbalances at six different positions. Two measurements (right and left) were made with a monocular microscope under 209 magnification (model 183S-032; Marcel Aubert, Bienne, Switzerland). The vertical axis (Y) of the lens was aligned with the long axis of the sleeve, and measurements were made on the horizontal axis (X). The arithmetic mean of 12 measurements was recorded for each assembly. Internal fit Assemblies were placed on a cylindrical device (30 mm in diameter and 15 mm in thickness) and embedded in Bakelite (Multifast Black; Struers, Copenhagen, Denmark) through hot-press mounting (LaboPress-1; Struers) at a pressure of 15 kN for 10 min. All assemblies were ground under constant refrigeration (Labopol 5; Struers), using silicon carbide sandpaper with progressive grit sizes (#220, #320, #500, #800, and #1000), until the central parts of the abutments were reached. Polishing was performed in a polishing machine (LaboPol-21; Struers) with 1-lm diamond paste (Struers) until the metal became a mirrored surface (Fig. 2). The specimens were washed with water and dried at room temperature. The thickness of the cementation line was analysed, under 2009 magnification, with an optical microscope (model BX-60; Olympus, Hamburg, Germany), followed by image capturing and processing (OMNIMET Software; Buehler, Lake Bluff, IL, USA). The thickness of the cementation line was measured at three predetermined positions on both sides of the abutment (Fig. 3). The landmarks for measurements were as follows: the cervical region (i.e. the distance between the central portion of the chamfer finish line and its internal portion in the coping; A and B in Fig. 3); the axial region (i.e. located in the middle portion of the axial walls, 3 mm above the chamfer; C and D in Fig. 3); and the occlusal region (i.e. located on the occlusal wall, positioned 0.5 mm from the hexagonal area of the abutment; E and F in Fig. 3). Statistical analysis
Fig. 1. Dimensions of the implant abutment (A) and its respective plastic (B) and alumina (C) prefabricated cylinders.
All analyses were performed in the SAS software package (version 9.0; SAS Institute, Cary, NC, USA) at a signifi-
Fit of cemented implant crowns
Fig. 3. Location points of the measurement of cementation thickness: cervical (A and B), axial (C and D), and occlusal (E and F).
cance level of 5%. Normality of the error distribution and the degree of non-constant variance were checked for each response variable using the SAS/LAB package. Data were analysed by one-way ANOVA. Tukey’s HSD post-hoc test (a = 0.05) was used to compare the marginal and internal fits between materials.
Results The results of marginal horizontal fit are presented in Fig. 4. Alumina copings showed the largest discrepancy in marginal horizontal fit (P < 0.05). The Au group showed the largest discrepancy among the metal alloy groups (P < 0.05). The results of internal fit are shown in Fig. 5. The CoCr, NiCrMoTi, and alumina groups showed the best internal fit at the cervical region (P < 0.05). At the occlusal region, the alumina cylinder showed a better internal fit than the other materials (P < 0.05). No significant differences in internal fit were observed among the materials at the axial region (P > 0.05).
Discussion Poor fit between crowns and abutments favours the occurrence of micromovements, which can lead to cement failure, prosthesis dislodgment, and abutment
Fig. 4. Discrepancy in marginal horizontal fit (lm) for the different infrastructure materials. Bars show mean SD. Different letters indicate a significant difference between the groups (P < 0.05). Au, gold; CoCr, cobalt–chromium; NiCr, nickel–chromium; NiCrMoTi, nickel–chromium–molybdenum–titanium.
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Fig. 5. Discrepancy in internal fit (lm) for cemented copings at the cervical, axial, and occlusal regions. Bars show mean SD. Different letters indicate a significant difference between the groups in each region (P < 0.05). Au, gold; CoCr, cobalt–chromium; NiCr, nickel–chromium; NiCrMoTi, nickel–chromium–molybdenum–titanium.
overload (10, 13). Standard abutments and premachined components are intended to facilitate the manufacture of cemented prostheses. The present study evaluated the marginal horizontal and internal fits of different infrastructures cemented on an implant abutment. To date, there is no consensus regarding which methodology best simulates the clinical conditions of poor prosthesis fit. Which cement is used in the methodology is an important consideration, as cement interposition may contribute to an increase in marginal discrepancy (7–9, 11, 13). Studies have described different measurement techniques, such as the sectional view, the direct view, and the replica view, after impression or clinical examination (14, 17). Additionally, the number and the location of the measurements can vary between studies (18). Here, we adopted two measurement techniques: the direct view was used to measure the marginal horizontal discrepancy; and the sectional view was used to evaluate the internal adaptation. The measurements obtained showed low means for all study groups and a uniform cement thickness along the infrastructure–abutment interfaces. These findings allow us to reject the hypothesis that the viscosity of the cement agent and the settlement forces were responsible for discrepancies in measurements. Au alloys are commonly used as a reference in comparative studies on casting deformation (19, 20). However, in the present study, the Au copings exhibited twice as much discrepancy as the other alloys. The lower resistance of Au, compared with alloys made from non-noble metals, may result in insufficient flow to the cervical area and difficulties in obtaining accurate measurements on thin and delicate margins (21, 22). Therefore, the abutment with the narrow chamfer finish line (Fig. 1), used in the present study, may favour higher discrepancy values for the Au alloy. Although distortions of alumina cylinders are related to the buccal and lingual areas owing to the heating cycles needed for the feldspathic ceramic layer (23), they exhibited the best internal fit in the present study.
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Faot et al.
On the other hand, a marked overextension was clearly observed with the alumina cylinders compared with the metal infrastructures. Alumina cylinders have overextended edges because of their specific anatomical design that is intended to maintain their marginal structural integrity. However, the presence of an overhang or overextension in an implant-supported prosthesis does not seem to cause deleterious effects in peri-implant tissues to the same degree as in conventional prostheses. This difference can be explained by the histological differences between the soft-tissue barriers at the implant and teeth; namely, periodontal tissue provides an area of connective tissue attachment that responds much more strongly to the inflammatory process (24). Although the values found in the present study seem to suggest an extension error, they agree with those reported by SIADAT et al. (5), who conducted a comparative study of horizontal fit with metal copings. Higher values of overhang are frequently observed in cemented implant prostheses because of the thin finish line. This characteristic of most prosthetic abutments results from the necessity of compensating between the cervical diameter of the crown and the diameter of the implant or prosthetic component. The use of prefabricated components was insufficient to guarantee an accurate fit over the abutment. The difference in the discrepancies of internal fit between the CoCr and Au copings showed that, even when we controlled the technical casting steps and used prefabricated plastic cylinders, the casting process itself caused distortions during prosthesis fabrication (6, 12, 21). Thus, for each alloy, the castability properties, such as melting temperature, coefficient of thermal expansion, and density, and the use of different investment materials, are factors that can interfere directly with the accuracy of plastic cylinders (22, 25). It is difficult to compare the internal cervical discrepancy values found in this study with such values in other studies, as the literature is inconclusive regarding a standardized region or point from which to make the measurements. In our study, the locations of points A and B did not refer to the portion involved in sealing the coping or cylinder, but to the inner bevel in the cervical area. Only QUANTE et al. (26) reported landmarks at the same location. They described similar fit-discrepancy values to ours for this region, ranging from 74 to 99 lm, despite using a different measurement technique (silicone indicator paste). Accordingly, we suggest that the flow of cement film in this region was uniform for all materials studied, which would guarantee final settlement and appropriate retention (7, 8). The internal discrepancy values in the axial walls (range: 50 8 lm to 64 27 lm), found in this study, are acceptable for the stability of cemented prostheses (15, 26). The values observed for occlusal discrepancy are consistent with those of other studies (6, 12, 17, 21). The difference between the discrepancies in axial and occlusal fits can be related to the fact that the expansion was directed towards the occlusal region, because the casting ring limited axial expansion (6, 12, 21). Furthermore, thermal expansion can enable further
broadening of the occlusal surface during wax removal, thereby increasing the internal occlusal imbalance. The higher values of poor occlusal fit for the Au copings suggest that the narrow finish line of the universal post and its occlusal convergence angle (2.30°) may not favour the flow properties of Au alloys (19, 22). A thick cementation line on the occlusal surface can lead to the development of microfractures, which, consequently, can result in micromovements that finally dislodge the prosthesis (7–10). Few published studies are available regarding the applicability of CoCr alloys for implant prosthetic infrastructures (27). The performance of this alloy in the present study favours its use in implantology as an alternative alloy, especially in light of its lower cost than Au, biocompatibility, and corrosion resistance. This study examined the fit of different metal alloys and the alumina cylinder on only one type of universal post abutment. Other abutments, with different diameters, heights, occlusal convergence angles, and finish lines, are commercially available and may produce different results. In addition, using other cement agents or measurement techniques for the internal and marginal fits would lead to different discrepancies in fit for the cemented crowns. Within the limitations of this study, we can conclude that alumina copings exhibited horizontal overextension related to their structural strength and had the best internal fit at the occlusal surface of the implant abutment. Among the metal alloys, CoCr showed a better internal fit at critical regions, such as the cervical and occlusal areas. Acknowledgements – The authors thank NEODENT for supplying the prosthetic components. Conflicts of interest – The authors declare no conflicts of interest.
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