Odontology (2012) 100:249–253 DOI 10.1007/s10266-011-0050-1 SHORT COMMUNICATION Evaluation of fit of cement-retained implant-supported 3-unit structures fabricated with direct metal laser sintering and vacuum casting techniques Raquel Castillo Oyagüe • Andrés Sánchez-Turrión José Francisco López-Lozano • Javier Montero • Alberto Albaladejo • Marı́a Jesús Suárez-Garcı́a • Received: 8 August 2011 / Accepted: 23 October 2011 / Published online: 11 November 2011 Ó The Society of The Nippon Dental University 2011 Abstract This study evaluated the vertical discrepancy of implant-fixed 3-unit structures. Frameworks were constructed with laser-sintered Co–Cr, and vacuum-cast Co–Cr, Ni–Cr–Ti, and Pd–Au. Samples of each alloy group were randomly luted in standard fashion using resin-modified glass-ionomer, self-adhesive, and acrylic/urethanebased cements (n = 12 each). Discrepancies were SEM analyzed. Three-way ANOVA and Student–Newman– Keuls tests were run (P \ 0.05). Laser-sintered structures achieved the best fit per cement tested. Within each alloy group, resin-modified glass-ionomer and acrylic/urethanebased cements produced comparably lower discrepancies than the self-adhesive agent. The abutment position did not yield significant differences. All misfit values could be considered clinically acceptable. Keywords Cement-retained implant-supported prostheses
Direct metal laser sintering
Vacuum casting Introduction The accuracy of fit between superstructures and implant abutments has been regarded as a prerequisite for the R. C. Oyagüe (&)
A. Sánchez-Turrión
J. F. López-Lozano
M. J. Suárez-Garcı́a Department of Buccofacial Prostheses, Faculty of Odontology, Complutense University of Madrid (UCM), Pza. Ramón y Cajal, s/n, 28040 Madrid, Spain e-mail: raquel.castillo@odon.ucm.es J. Montero
A. Albaladejo Department of Surgery, Faculty of Medicine, University of Salamanca (USAL), Campus Miguel de Unamuno, C/Alfonso X el Sabio, s/n, 37007 Salamanca, Spain longevity of implant-prosthetic restorations [1]. Noble alloys have been shown to have certain advantages over base metal alloys in terms of marginal adaptation, workability after casting, biocompatibility, and metal–ceramic bond [2, 3]. However, base metal alloys, such as Co–Cr or Ni–Cr, are often selected for the fabrication of conventional and implant-supported fixed dental prostheses (FDPs) [4] due to their greater Young’s modulus and hardness [5] and lower associated costs [6]. Regrettably, base metal alloys are more difficult to cast than noble alloys and may, thus, affect the quality of the cast frameworks [3, 6, 7]. Direct metal laser sintering (DMLS) of Co–Cr is a promising new technology that may avoid the distortions inherent in casting methods [3]. By means of a high energy-focused laser beam (such as a carbon dioxide laser), pieces are built up from successive layers of fused metalalloy powder in accordance with a sliced 3D computeraided design (CAD) model [8]. To date, very few studies have been published on the use of DMLS in the field of dentistry [3, 6, 9, 10], and none of them deals with the reliability of DMLS in obtaining accurate implant-supported FDPs. Moreover, cements that have been recommended for implant restorations (e.g., glass-ionomer, resin cements, or acrylic/urethane-based temporary agents) have mainly been tested for retention [11], and their effect on marginal fit deserves further attention. The purpose of this investigation was, thus, to evaluate the vertical discrepancy of cement-retained implant-fixed metallic frameworks. The null hypothesis stated that alloy and fabrication technique, cement type, and abutment position (or FDP retainer) have no effect on the vertical fit of implant-supported structures. 123 250 Materials and methods Four series of mandibular 3-unit structures for implantsupported FDPs, each with an intermediate pontic (spanning the first premolar to the first molar), were prepared using different dental alloys suitable for ceramic veneering (wall-thickness: 0.8 mm; connector size: 3 mm 9 3 mm). Titanium prefabricated implant abutments (height = 6 mm) were utilized (ref. PCM7013, Implant Microdent System, Barcelona, Spain). Group 1 (LS) was obtained by means of direct metal laser sintering (DMLS) of a Co–Cr powdered alloy (batch no. 10d0209, ST2724G, Sint-Tech, Clermont-Ferrand, France). Structures were computer-designed (Cercon Art software, Dentsply International, York, PA, USA) once the abutments had been scanned (Cercon Eye optical laser, Dentsply). Frameworks were then made using a DMLS TM device (PM 100 Dental, Phenix Systems , Clermont-Ferrand, France) by sintering 20-lm increments of alloy powders from the occlusal surface to the margins at a temperature of 1,650°C in an argon atmosphere. Group 2 (CC) was vacuum cast using a Co-Cr alloy (batch no. 0711/20cn, Gemium-cn, American GMG Inc., Union City, California, USA); Group 3 (CN) was vacuum cast using a Ni–Cr–Ti alloy (batch no. 112907, Tilite, Talladium Inc., California, USA); and Group 4 (CP) was vacuum cast using a noble Pd–Au alloy (batch no. 4060797, Jensen GmbH, Metzingen, Germany). As for the cast samples (Groups 2–4), wax patterns were prepared over burnout casting copings and invested in phosphatebased plaster (IPS Press Vest Speed, Ivoclar-Vivadent AG, Schäan, Liechtenstein) in cylinders without a metal ring. An induction centrifugal casting machine (MIE-200 C/R, Ordenta, Arganda del Rey, Madrid, Spain) was utilized under vacuum pressure (580 mmHg). The casting temperatures were 1,450°C for CC; 1,330°C for CN; and 1,260°C for CP. In Group 4 (CP), the investing liquid was mixed with deionized water in order to control the noble metal expansion. Investment residues were removed by sandblasting. Frames were neither retouched nor polished so as to avoid external variations. Structures from each alloy group were randomly assigned to three experimental subgroups (n = 12 each) according to the luting agent. Thus, subgroup 1 (FP) used the resin-modified glass-ionomer cement Fuji Plus (batch no. 0903051CE, GC Co., Tokyo, Japan); subgroup 2 (RXU) used the self-adhesive resin cement RelyX Unicem 2 Automix (batch no. 339349, 3M ESPE, Seefeld, Germany); and subgroup 3 (PIC) used the acrylic/urethanebased temporary agent Premier Implant Cement (batch no. 4154CI, Premier Dental Products Co., Plymouth Meeting, PA, USA). Axial surfaces of the abutments were varnished with a thin layer of mixed cement. Structures were then 123 Odontology (2012) 100:249–253 cemented under constant seating pressure. A customized clamp fitting a dynamometric key (Defcon, Impladent, Holliswood, NY, USA) was used with a torque of 25 N cm kept for 4 min to counteract the thyrotrophic behavior of cements in a standard manner. Samples of Subgroup 2 (RXU) were initially photo-activated around the margins (BluePhase, Ivoclar-Vivadent AG, Schäan, Liechtenstein: 600 mm W/cm2) to ensure optimal polymerization. Vertical misfit was assessed by measuring the distance parallel to the abutment axis between the margins of the structure’s retainers and their respective abutments under a scanning electron microscope (SEM: JSM-6400, JEOL, Tokyo, Japan) from 1009 to 1,0009 magnifications. The abutments of the cemented samples were fitted in a special support in order to situate the vertical gap perpendicularly to the optic axis of the microscope, thus guaranteeing repeatable projection angles. This study evaluated the vertical opening as it implies the absence of contact between structure and abutment, which mainly affects the passive fit. Thirty vertical measurements were taken on each of the following axial planes: buccal and lingual surfaces of all retainers, mesial surfaces of premolars, and distal surfaces of molars (180 measurements per framework). A blind observer calculated the discrepancies using image-analysis software (INCA-4.04, Oxford Instruments, Abingdon, UK) at marginal points equally distributed on each micrograph so as to minimize operator bias. Misfit data were initially analyzed by two-way analysis of variance (ANOVA) with repeated measurements of the abutment factor. In light of the fact that no interaction involving framework alloy/fabrication technique or cement type resulted in a significant intra-group difference between paired abutments, three-way ANOVA was performed, using the abutment position as an additional independent variable. Statistical significance was set in advance at P \ 0.05. All statistical analyses were handled with SPSS/PC ? v.17.0 (SPSS Inc., Chicago, IL, USA). Results For each of the cements tested, LS samples exhibited the best marginal adaptation (P \ 0.001), followed by CP structures, whereas CC and CN frames achieved the greatest misfit with no differences between the two groups (Table 1; Fig. 1). Within each alloy group, FP and PIC cements provided comparably lower discrepancies than RXU (P \ 0.05). The vertical misfit of LS structures bonded with RXU was statistically similar to that of CP frameworks luted with FP or PIC. The abutment position did not affect the vertical fit (P = 0.845). Interaction between alloy/fabrication technique and cement type proved to be of significance (P = 0.027). Odontology (2012) 100:249–253 251 Table 1 Mean misfit values of laser-sintered and vacuum cast cement-retained implant-supported structures in relation to the luting cement and the abutment position Vertical discrepancy recorded in the experimental groups (lm) Framework alloy and fabrication technique Laser-sintered Co–Cr Cement type Abutment Mean misfit (SD) Fuji Plus P 26 (8)a1 79 (15)d1 80 (14)d1 48 (6)b1 29 (7) a1 81 (12) d1 86 (13) d1 53 (7)b1 P 47 (8) b2 102 (16) e2 107 (12) e2 66 (8)c2 M 51 (6)b2 110 (15)e2 104 (13)e2 67 (9)c2 33 (6) a1 82 (14) d1 84 (15) d1 50 (6)b1 35 (9) a1 87 (12) d1 85 (13) d1 54 (7)b1 M RelyX Unicem 2 Automix Premier Implant Cement P M Vacuum cast Co–Cr Vacuum cast Ni–Cr–Ti Vacuum cast Pd–Au Different letters in the rows and numbers in the columns indicate statistically significant differences (P \ 0.05) P premolar, M molar Fig. 1 Representative scanning electron microscope (SEM) microphotographs of the experimental groups containing exact vertical misfit values (2509 magnifications; 20 kV; bar 200 lm). a Lasersintered Co–Cr (LS) sample with characteristic undulated surface topography luted with resin-modified glass-ionomer cement (FP) exhibiting an optimal fit (8.39 lm of vertical opening) (premolar abutment). b Vacuum-cast Co–Cr (CC) structure luted with acrylic/ urethane-based temporary agent (PIC) showing a greater misfit of 68.8 lm with a certain degree of cement washout (premolar abutment). c Vacuum cast Ni–Cr–Ti (CN) sample bonded with selfadhesive resin cement (RXU). The resinous agent seals the gap of 130 lm. Protruding filler particles and scarce, scattered porosities are present (molar abutment). d Vacuum cast Pd–Au (CP) framework bonded with self-adhesive resin cement (RXU). A discrepancy of 52.4 lm is filled by the luting agent, which also demonstrates protruding particles and presents no sign of dissolution (molar abutment) 123 252 LS samples showed rippled surfaces and undulated margins (Fig. 1a). Cast structures revealed a rough pattern (Fig. 1b–d) that was in contrast with the smooth texture of machined abutments (Fig. 1). Concerning the cements tested, FP (Fig. 1a) filled the marginal gaps; PIC (Fig. 1b) partly dissolved from the structure/abutment interfaces; and RXU appeared nearly intact at the marginal area (Fig. 1c, d). Discussion The development of CAD/CAM-based systems for dental applications has accelerated in the recent years, but few scientific data concerning their uses in the production of implant-fixed prostheses have been collected. In this study, the null hypothesis was partly rejected, as differences in misfit were found to depend on the alloy/manufacturing technique and the cement type. LS frameworks were confirmed to have the best fit (Table 1; Fig. 1). This finding agrees with the results obtained from comparing the fit of laser-sintered and cast 3-unit conventional Co–Cr FDPs [10] and may be attributed to the reduced number of steps required for DMLS as the abutments are directly scanned [3, 6, 9, 10]. With this system, impressions are not required, post-processing procedures are simplified, and restorations are deemed to be free of the porosity inherent to casting procedures [6]. The main drawbacks of digital impressions and DMLS are the difficulty in reference to reproducing subgingival margins, the need for trained technicians, and the cost of CAD/CAM-based equipments. Nevertheless, a reduction in the unit production cost with respect to the lost waxing technique has also been described [3, 6]. In spite of their excellent mechanical properties [4, 5], the casting of Co–Cr and Ni–Cr-based alloys is more technique-sensitive than the casting of noble alloys due to the superior melting points and potential for oxidation of the base metals [3, 6, 7]. This may explain why, in our study, CC and CN structures exhibited comparably greater discrepancies than cast CP frames regardless of the type of cement used (Table 1; Fig. 1c, d), a finding that is consistent with the results of Oyagüe et al. [1]. The resin-modified glass-ionomer and the acrylic/urethane-based cements supplied comparably lower discrepancies than the self-adhesive resin agent regardless of the type of framework tested (Table 1). Bottino et al. [12] obtained comparable results for conventional metal crowns. Such findings may be related to the higher plastic deformation in compression, and the lower viscosity of the resin-modified glass-ionomer, and the acrylic/urethanebased materials with respect to the resin cement [13]. 123 Odontology (2012) 100:249–253 Consistent with the prior research results [14], no differences in misfit between mesial and distal abutments were identified (Table 1). This accuracy may be explained by the precision of the manufacturing and luting systems and the technician’s experience [14]. The acceptable misfit ranges for implant-fixed FDPs are usually referred to as screwed prostheses. However, screwand cement-retained implant structures differ in their design, construction, and biomechanics [1]. Jemt [15] empirically concluded that the discrepancy of cementretained implant-supported crowns should not exceed 150 lm. Nonetheless, tolerable misfit levels that may prevent biomechanical failures of implant restorations have not been exactly quantified [1], and further research is necessary. Within the limitations of this study, the following conclusions can be drawn: (1) DMLS of Co–Cr may be an alternative to the casting of noble and base metal alloys to obtain well-fitted implant-supported prostheses, (2) even though Co–Cr and Ni–Cr–Ti samples demonstrated the greatest discrepancies, all of the experimental groups were within the clinically acceptable misfit range, and (3) resinmodified glass-ionomer and acrylic/urethane-based cements supplied a comparably better fit than the selfadhesive resin agent regardless of the type of alloy and fabrication method utilized. Acknowledgments This investigation was supported by research projects: UCM 41/2009 and UCM 164/2010. The authors would like to thank the Prótesis SA Dental Laboratory (Madrid) for the technical advice received and for manufacturing the structures. We are also grateful to the Centre of Data Processing, Computing Service for Research Support, Complutense University of Madrid (U.C.M.) for the assistance with the statistical analysis. References 1. Oyagüe RC, Turrión AS, Toledano M, Monticelli F, Osorio R. In vitro vertical misfit evaluation of cast frameworks for cementretained implant-supported partial prostheses. J Dent. 2009;37:52–8. 2. Yoshida K, Atsuta M. Effects of adhesive primers for noble metals on shear bond strengths of resin cements. J Dent. 1997;25:53–8. 3. Akova T, Ucar Y, Tukay A, Balkaya MC, Brantley WA. Comparison of the bond strength of laser-sintered and cast base metal dental alloys to porcelain. Dent Mater. 2008;24:1400–4. 4. Roach M. Base metal alloys used for dental restorations and implants. Dent Clin North Am. 2007;51:603–27. 5. Morris HF. Properties of cobalt-chromium metal ceramic alloys after heat treatment. J Prosthet Dent. 1990;63:426–33. 6. Ucar Y, Akova T, Akyil MS, Brantley WA. Internal fit evaluation of crowns prepared using a new dental crown fabrication technique: laser-sintered Co–Cr crowns. J Prosthet Dent. 2009;102:253–9. 7. Anusavice KJ. Phillips’ science of dental materials. Philadelphia: W.B. Saunders; 2003. Odontology (2012) 100:249–253 8. Traini T, Mangano C, Sammons RL, Mangano F, Macchi A, Piatelli A. Direct laser metal sintering as a new approach to fabrication of an isoelastic functionally graded material for manufacture of porous titanium dental implants. Dent Mater. 2008;24:1525–33. 9. Quante K, Ludwig K, Kern M. Marginal and internal fit of metalceramic crowns fabricated with a new laser melting technology. Dent Mater. 2008;24:1311–5. 10. Örtorp A, Jönsson D, Mouhsen A, Vult von Steyern P. The fit of cobalt-chromium three-unit fixed dental prostheses fabricated with four different techniques: a comparative in vitro study. Dent Mater. 2011;27:356–63. 11. Michalakis KX, Hirayama H, Garefis PD. Cement-retained versus screw-retained implant restorations: a critical review. Int J Oral Maxillofac Implant. 2003;18:719–28. 253 12. 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;38:425–32. 13. Xie D, Brantley WA, Culbertson BM, Wang G. Mechanical properties and microstructures of glass-ionomer cements. Dent Mater. 2000;16:129–38. 14. Gonzalo E, Suárez MJ, Serrano B, Lozano JF. A comparison of the marginal vertical discrepancies of zirconium and metal ceramic posterior fixed dental prostheses before and after cementation. J Prosthet Dent. 2009;102:378–84. 15. Jemt T. Failures and complications in 391 consecutively inserted fixed prostheses supported by Brånemark implants in edentulous jaws: a study of treatment from the time of prosthesis placement to the first annual checkup. Int J Oral Maxillofac Implant. 1991;6:270–6. 123