In Vitro Implant Impression Accuracy Using a New Photopolymerizing SDR Splinting Material Adolfo Di Fiore, DDS;*,† Roberto Meneghello, MSc, Eng, PhD;‡ Gianpaolo Savio, MSc, Eng, PhD;§ Stefano Sivolella, DDS;¶ Joannis Katsoulis, PD Dr. Med. Dent., MAS;**,†† Edoardo Stellini, DDS‡‡
ABSTRACT Purpose: The study aims to evaluate three-dimensionally (3D) the accuracy of implant impressions using a new resin splinting material, “Smart Dentin Replacement” (SDR). Materials and Methods: A titanium model of an edentulous mandible with six implant analogues was used as a master model and its dimensions measured with a coordinate measuring machine. Before the total 60 impressions were taken (open tray, screw-retained abutments, vinyl polysiloxane), they were divided in four groups: A (test): copings pick-up splinted with dental floss and fotopolymerizing SDR; B (test): see A, additionally sectioned and splinted again with SDR; C (control): copings pick-up splinted with dental floss and autopolymerizing Duralay® (Reliance Dental Mfg. Co., Alsip, IL, USA) acrylic resin; and D (control): see C, additionally sectioned and splinted again with Duralay. The impressions were measured directly with an optomechanical coordinate measuring machine and analyzed with a computer-aided design (CAD) geometric modeling software. The Wilcoxon matched-pair signed-rank test was used to compare groups. Results: While there was no difference (p = .430) between the mean 3D deviations of the test groups A (17.5 μm) and B (17.4 μm), they both showed statistically significant differences (p < .003) compared with both control groups (C 25.0 μm, D 19.1 μm). Conclusions: Conventional impression techniques for edentulous jaws with multiple implants are highly accurate using the new fotopolymerizing splinting material SDR. Sectioning and rejoining of the SDR splinting had no impact on the impression accuracy. KEY WORDS: accuracy, edentulous jaw, implant impression technique, impression copings, passive fit, splinting material
INTRODUCTION The accuracy is an important factor for the success and survival of an implant-retained prosthesis. The precise transfer of the three-dimensional (3D) intraoral implant relationship to the master cast is a critical step to achieve a passive fit.1–4 The insufficient accuracy during the impression-making technique and/or manual steps during prosthesis fabrication may lead to misfit of the prosthesis and subsequent to technical, mechanical, and biological complication such as occlusal discrepancies screw or abutment loosening, fracture of the prosthetic components, implant fractures, and loss of osseointegration.5–8 Differently from natural teeth, osseointegrated implants have no periodontal ligament to compensate any inaccuracy of implant-retained prosthesis.9 Inaccurate frameworks of implant-retained prosthesis can cause stress at the implant/bone interface, plaque accumulation, affecting soft and/or hard tissues
*Clinical assistant, Department of Prosthodontics, Dental School, University of Padova, Padova, Italy; †PhD student, Mechatronics and Product Innovation Engineering, Department of Management and Engineering, University of Padova, Padova, Italy; ‡assistant professor, Departments of Civil, Environmental and Architectural Engineering, University of Padova, Padova, Italy; §adjunct professor, Departments of Civil, Environmental and Architectural Engineering, University of Padova, Padova, Italy; ¶clinical assistant, Departments of Oral Surgery, Dental School, University of Padova, Padova, Italy; **scientific associate, Department of Reconstructive Dentistry and Gerodontology, School of Dental Medicine, University of Bern, Bern, Switzerland; ††adjunct associate professor, Department of Preventive and Restorative Sciences, University of Pennsylvania School of Dental Medicine, Philadelphia, PA, USA; ‡‡dean, Dental School, University of Padova, Padova, Italy Corresponding Author: Dr. Adolfo Di Fiore, Department of Prosthodontics, Dental School, University of Padova, via Venezia 90, Padova 35100, Italy; e-mail: [email protected] © 2015 Wiley Periodicals, Inc. DOI 10.1111/cid.12321
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around the implants.10,11 However, the accuracy of the master cast is dependent on the clinical and laboratory variable such as the type of impression material, direct and indirect impression technique, splinting or surface treatment of impression copings, dimensional changes in dental stone during setting, and implant master cast realization.12–19 To ensure maximum accuracy for an implant-supported fixed dental prosthesis (FDP), the intraoral splinting of transfer copings before recording of the definitive impression has been recommended to preserve their 3D intraoral relationship and minimize the effects of the factors that may cause distortion in the x, y, z-axes.17,20–22 Different methods for splinting implant transfer copings with acrylic resin,17 prefabricated acrylic resin,23 photopolymerizable acrylic resin,12 bite registration with the addition of silicone and bite registration with polyether24 have been tested. Suggested methods of splinting transfer copings include the use of a matrix of dental floss25 or orthodontic wire.26 The acrylic resin still remains the most common material to splinting transfer copings. However, when a large volume of acrylic resin is used to splint transfer copings intraorally, distortion may result from polymerization shrinkage. It has been reported that the total shrinkage of acrylic resin is between 6.5% and 7.9% in the first 24 hours.23,27 Another technique that has been suggested involves splinting the transfer copings with acrylic resin (first step) and performing an additional step of sectioning and rejoining the resin (second step) to reduce the effects of polymerization shrinkage.28 With this procedure, however, clinical chair-side time is increased. Based on the need to obtain maximally accurate FDPs, the purpose of this in vitro study was to evaluate three-dimensionally the accuracy of implant impressions using a new resin splinting material, “Smart Dentin Replacement” (SDR). The null hypothesis was that there would be no significant difference in the accuracy between the splinting and impression approaches.
as a clinically relevant simulation model (master cast). The model must possess the characteristics of stiffness, strength, and dimensional stability to allow the execution of all impression techniques without errors of distortion. The reference model resembled a mandibular implant-supported Toronto-Bridge situation. Initially, the basis of the master model was designed and on it have been realized the locations of insertion of the analogues. The upper part of the master model was designed with a cavity for the insertion of a self-curing resin to prevent any movement of the analogues. The analogues (Certain implant lab analog 4.1 mm (D) IILA20 Biomax 3i, Implant Innovations, Palm Beach Gardens, FL, USA), with a diameter of 4.1 mm and with an external hexagon, were secured with self-curing resin (Eco Cryl Cold, Protechno, Vilamalla Girona, Spain). The six analogues were positioned symmetrically to correspond to the mandibular first molar, first premolars, and lateral incisors bilaterally (Figure 1). The interimplants’ distance in the x-axis between the center of analogue 1 and the center of the analogue 6 was 47.5 mm, between the center of analogue 1 and the center of analogue 5 was 41.2 mm, between the center of analogue 1 and the center of analogue 4 was 31.2 mm, between the center of analogue 1 and the center of analogue 3 was 16.22 mm, and between the center of analogue 1 and the center of analogue 2 was 6.2 mm (Figure 2). The inter-implants’ distance in the y-axis between the center of analogue 1 and the center of the analogue 6 was 47.5 mm, between the center of analogue 2 and the center of analogue 5 was 35.0 mm, and between the center of analogue 3 and the center of
MATERIALS AND METHODS Fabrication of Master Model A virtual model of a mandibular edentulous with six implant analogues was designed by mean of a computeraided design (CAD) software (Dassault Systèmes SolidWorks Corporation, Waltham, MA, USA) and subsequently manufactured in titanium by a CNC machine tool (Dyamach Italia s.r.l., Mussolente VI, Italy) to serve
Figure 1 Master CAD model in 3D with six dental implant analogues.
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Figure 2 The inter-implants distance in the y-axis between the center of analogues.
analogue 4 was 15.0 mm. In the z-axis, the analogues in positions 1 and 6 were placed at a height equal to 0 mm. The analogues in positions 2 and 5 were placed 1.1 mm higher than those in positions 1 and 6, and those in positions 3 and 4 were placed 2.3 mm higher, always taking as reference those in positions 1 and 6. The analogues in positions 1 and 6 are inclined by 10 degrees distally and 10 degrees buccally. The analogues in positions 2, 3, 4, 5 are all parallel to each other. Measurement Procedure The master model was measured with a coordinate measuring machine (SmartScope Flash, CNC 300, Optical Gaging Products, Rochester, NY, USA), an optomechanical system that is capable of moving a measuring probe to determine the spatial coordinates of points on a workpiece surface. All measurements were performed at the Department of Civil, Environmental, and Architectural Engineering of the University of Padova.The coordinates of the probed points were transferred into a 3D CAD geometric modeling software program (Rhinoceros 5.0 Beta, Robert McNeel & Associates McNeel Europe,Barcelona,Spain) and analyzed with a taskspecific evaluation protocol, programmed in IronPython programming language, to estimate the position and orientation of each analogue. The measuring system is capable of a maximum permissible error (E,in micron) that is 10 times lower than both the performance of scanners commonly
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used in framework digital manufacturing and the expected position errors of the implant analogue surfaces: E1(z) = 2.5 + 5L/1,000 μm, E2(xy) = 1.8 + 5L/1,000 μm, E3(xyz) = 2.8 + 5L/1,000 μm (with L, in millimeters, equal to the measured distance, according to International Organization for Standardization norm 10360). Uncertainty in experimental measurements was lower the 5 μm and was mainly influenced by the implant analogue’s upper surface form error and by the system calibration method. Measurements consisted of the acquisition of a set of 30 points on the upper surface and the second set of more than 200 points on the external profile of each analogue. To evaluate both position and orientation, the first set of points was used to construct the upper plane of the analogues, while the second set of points was used to obtain fitting circles that were constrained to lie on those planes; thus, the spatial (x,y,z) coordinates of the center of the fitting circles estimate the positions of analogues. The fitting algorithms implemented for the 3D geometries reconstruction were validated in a previous study, and their contribution to the experimental measurement uncertainty is negligible.29,30 Impression Procedure Plastic directed-flow disposable trays (3M ESPE Directed Flow Impression Tray, 3M ESPE, St. Paul, MN, USA) were used to simplify and streamline the impression techniques. The performance of stock plastic trays and the directedflow impression trays was better than the performance of stock perforated metal trays.31 Six windows were created in the plastic stock to expose the coping screws. Vinyl polixiloxane (Acquasil putty/light body, Dentsply, Milford, DE, USA) was used according to the manufacturer’s instructions as impression material for each group; 24 copings pick-up (Certain, Biomax 3i, Implant Innovations), 6 for each group, were used for impression techniques. The fitting surface of all components was cleaned with isopropyl alcohol before each impression.29 The impression was made in a controlled-temperature environment (22°C 1 2°C) with a relative humidity of 45% 1 10%.The samples were divided into four groups based on impression technique. The exact number of the samples for each group was calculated with a pilot study. Four groups with a 15 impression cast were evaluated: Group A: The copings pick-up was splinted with an SDR® (Smart Dentin Replacement, Dentsply). The dental floss was used to create a matrix around the copings pick-up where SDR will be placed. The splint
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Figure 3 The copings pick-up splinted with SDR® (Group A).
was allowed to photopolymerize for 2 minutes. The putty impression material was mixed for 30 seconds by hands and loaded inside the plastic tray; at the same time, the light material was syringed around the copings pick-up, followed by immediate placement of the tray on the master model until it contacted the base of the master model. The impression material was allowed to set for 10 minutes from the start of the mixing. After the impression had polymerized, the transfers were unscrewed and the tray was separated from the master model. The abutment analogues were then fit to the impression coping using 10 Ncm of torque (Figure 3). Group B: The copings pick-up was splinted with an SDR. The dental floss was used to create a matrix around the copings pick-up where the SDR will be placed. The splinting was allowed to photopolymerize for 2 minutes and afterwhich will be sectioned with a cutting disk (diamond-coated disk 150 μm thick, Intensiv, Montagnola, Switzerland) to span the spaces between the adjacent copings pick-up. The splinting was rejoined with SDR in the spaces between the transfers. This additional step was performed to reduce the effects of polymerization shrinkage. The impression was made in a similar procedure as group A (Figure 4). Group C: The copings pick-up was splinted with a Duralay® acrylic resin (Reliance Dental Mfg. Co., Alsip, IL, USA). The dental floss was used to create a matrix around the copings pick-up where the Duralay will be placed by means of the“Brush Technique.”The splinting was allowed to auto-polymerize for 4 minutes. The impression was made in a similar procedure as group A (Figure 5). Group D: The copings pick-up was splinted with a Duralay acrylic resin. The dental floss was used to create a
Figure 4 The copings pick-up splinted with SDR®. The splinting material was sectioned and rejoined to reduce the effects of polymerization shrinkage (Group B).
matrix around the copings pick-up where the Duralay will be placed by means of the“Brush Technique.”The splinting was allowed to auto-polymerize for 4 minutes and afterwhich will be sectioned with a cutting disk (diamondcoated disk 150 μm thick, Intensiv) to span the spaces between the adjacent copings pick-up. The splinting was rejoined with Duralay in the spaces between the transfers. This additional step was performed to reduce the effects of polymerization shrinkage. The impression was made in a similar procedure as group A (Figure 6). The impression was measured in the same manner of the master model with the optomechanical coordinate measuring machine (SmartScope Flash, CNC 300, Optical Gauging Products) and analyzed by
Figure 5 The copings pick-up splinted with Duralay® acrylic resin (Group C).
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Figure 6 The copings pick-up splinted with Duralay® acrylic resin. The splinting material was sectioned and rejoined to reduce the effects of polymerization shrinkage (Group D).
means of the aforementioned 3D CAD geometric modeling software (Rhinoceros 5.0 Beta, Robert McNeel & Associates). To evaluate the positional accuracy of each impression, the estimated centers of the were aligned, using a least-square best fitting algorithm, to the corresponding analogues on the master model; the algorithm “optimizes” the position and orientation of the impression while considering the 3D distances between each transfer and the relative analogue. Three-dimensional distances between centers and their components along the x-, y-, and z- axes were calculated at each position for all impression. Statistical Analysis The material of splinting transfer copings was considered as the statistical unit. The primary variable was the distance (μm) of the center of the copings pick-up compared with the center of the respective analogue of the master model with coordinate measuring machine. A pilot study was conducted to generate data on the
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expected effect size and standard deviation to allow for power calculations. The number of sample provided for the calculation was three impression techniques for group A and for group C. The level of statistical significance was set as α = 0.05 and with a statistical power of 80%. The test group average (group A) was 17.04 μm (SD 8.13 μm) while the control group average (group C) was 24.81 μm (SD 9.95 μm). Null hypothesis for difference between averages was supposed to be 10 μm. Twelve impressions for group were then estimated after power calculation. The sample size was set to 15 per group because a 30% bias (three per group) was expected. The Wilcoxon matched-pairs signed-rank test (one-tailed) was used to compare groups. The level of statistical significance was set as α = 0.05 and with a statistical power of 80%. Statistical analysis was performed using statistical software SPSS 16.0 (SPSS Inc., Chicago, IL, USA). RESULTS The deviation in the center point position at each implant analogue level is described in Table 1. The mean values are reported along x-, y-, and z-axes, as well as on the resultant 3D levels. The mean 3D deviation values were used as the value in comparative statistics between groups. The mean 3D deviation value of the center point position for group A was 17.49 μm, for group B was 17.39 μm, for group C was 24.95 μm, and for group D was 19.12 μm (Table 1). Six numerical values were recorded for each impression that correspond to deviations of the six copings pick-up from the position of the six analogues, then for each impressions was performed the average of the six deviations to obtain a single numerical value. The value obtained will be used to perform the Wilcoxon matched-pairs signed-ranks test (one-tailed). A statistically significant difference was present between group A and group D (p value = .0017),
TABLE 1 Mean Deviations(μm) of the Central Point for Each Group of Impression Techniques in Three Axis and 3D Δx
Δy
Δz
3D
Group
Mean
SD
Mean
SD
Mean
SD
Mean
SD
A B C D
7.06 6.70 10.11 10.46
6.05 4.86 6.47 7.55
12.55 12.38 19.31 14.10
8.34 7.81 11.8 7.67
5.76 6.14 7.27 3.15
6.08 6.57 5.51 2.51
17.49 17.39 24.95 19.12
8.16 7.26 9.89 8.08
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TABLE 2 Comparative Statistical Analysis Between the Four Groups Group
A B C D
p Value
— .43 .003 .0017
.43 — .003 .002
.003 .003 — .002
.0017 .002 .002 —
between group A and group C (p value = .003), between group B and group C (p value = .003), between group B and group D (p value = .002), and between group C and group D (p value = .002). No statistically significant difference was present between group A and group B (p value = .43) (Table 2). DISCUSSION Accuracy is an important factor for the success and survival of an implant-retained prosthesis.32,33 The precise transfer of the 3D intraoral relationships of implants from the mouth to the master cast is a critical step to achieve a passive fit.1–4 In literature, several studies have indirectly estimated the accuracy of implant impression techniques by evaluating the fit of fabricated frameworks on the resultant casts with strain gauges and compared the fit of the frameworks on the master cast.12,20,34,35 Other studies have evaluated the accuracy of the implant impressions by measuring inter-implant distances of the working casts in relation to a reference control cast.2,24,36,37 Recently, optical scanning, photogrammetry, optical microscope, laser videography, and computerized coordinate measuring machine are some of the techniques that have been used in the assessment of inter-implant 3D deviations.30,38 In the four different impression techniques examined in the present study, distortion was always detected, and it is important to remember that this study only evaluated the steps in the process of prosthesis fabrication. Different studies have been conducted to investigate the variable affecting the accuracy of the different processes in implant prosthodontics, such as the different direct or indirect impression techniques,22 the use of different impression materials,24 the use of different trays,31 splinting or surface treatment of impression copings,12 the relative implant angulation,3 machining tolerances of the components provided by the manufacturer,39,40 and accuracy of the laboratory process.41,42 However, the error can be introduced in each of these
different clinical procedures, like excessive dimensional changes of the impression material or dimensional stability of different material of trays. In this study, the authors have tried to reduce the errors that may develop during the impression procedure. The vinyl polixiloxane was used as an impression material because it was more accurate with respect to polyether18 and/or irreversible hydrocolloid.31 Plastic directed-flow disposable trays were used because the performance of stock plastic trays and the directed-flow impression trays was better than the performance of stock perforated metal trays.31 Furthermore, in the master model the analogues in position 1 and 6 were inclined by 10 degrees distally and 10 degrees buccally. Instead the analogues in position 2,3,4,5 were all parallel to each other, because reproduce a realistic clinical situation and the results might have been different if the implants were placed all parallel. Different methods for splinting implant transfer copings with acrylic resin,17 prefabricated acrylic resin,23 photopolymerizable acrylic resin,12 bite registration addition silicone and bite registration polyether24 have been tested, but there are no studies in the literature that evaluate SDR as splinting material. SDR is a flowable composite mainly used in restorative dentistry. SDR is characterized by a remarkably low polymerization stress, in combination with a low polymerization shrinkage and a high depth of cure. Thanks to the stress decreasing resin technology, it is the first flowable composite that can be used as a bulk-fill base material in increments of up to 4mm in Class I and II cavities.43–45 In this study, significant differences in center point deviation were noted between group A and group D (p value = .0017), between group A and group C (p value = .003), between group B and group C (p value = .003), between group B and group D (p value = .002), and between group C and group D (p value = .002). No statistically significant difference was present between group A and group B (p value = .43). The deviation of the center point in the x-axis for group B was the least (6.7 μm) when compared with other groups, whereas group D showed the greatest deviation (10.46 μm) in the x-axis. The deviation of the center point in the y-axis for group B was the least (12.38 μm) when compared with other groups, whereas group D showed the greatest deviation (19.31 μm) in the y-axis. The deviation of the center point in the z-axis for group D was the least (3.15 μm) when compared with other groups, whereas group C showed the greatest deviation (7.27 μm) in the z-axis. As described in previous
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studies,24,30 the most significant deviation is observed in the horizontal plane (x-and y-axes) rather than in the vertical direction (z-axis), regardless of the technique or material. In the literature, more studies have reported increased accurate implant impressions with the splint techniques than with the unsplint techniques.12–24 Some authors suggested possible problems with the splint techniques, such as distortion of the splint materials,46 and another, as Kim and colleagues38 conclude, is that the unsplint techniques were more accurate during the impression-making procedure. It was interesting that more studies advocating the splint technique were found within recent literature. Five out of seven studies recommending the splint techniques were published after 2003,18 as opposed to two older studies which appeared before 1996. However, the use of new splinting materials like composite resin or light polymerizing acrylic resin resulted in better results.22 The present study showed that the accuracy of impression produced with SDR sectioned and reunited (group B) has the lowest deviation compared with groups where the Duralay acrylic resin (group C, group D) was used. No statistically significant difference was present between group A (with SDR not sectioned) and group B (with SDR sectioned and reunited) (p value = .43). The techniques of groups A and B resulted more accurate respect the techniques of groups C and D. An ideal impression technique would require minimal time, is comfortable for the patients, will give the best results, and inexpensive. Compared with other authors that use prefabricated acrylic resin,23 photopolymerizable acrylic resin,12 bite registration with the addition of silicone and bite registration with polyether24 and metal burs,47 the use of SDR as splinting material is an excellent solution. SDR is characterized by a remarkably low polymerization stress, in combination with a low polymerization shrinkage. Thanks to the low polymerization shrinkage, the step of sectioning and rejoining the splinting material to reduce the effects of polymerization shrinkage is not necessary to obtain maximum accuracy in the impression technique. With this procedure, however, the time and clinical cost are decremented, and instead the patient’s comfort is increased. Opposite, the use of the Duralay acrylic resin as splinting material is necessary, the step of sectioning and rejoining the splinting material to reduce the effects of polymerization shrinkage. In this procedure, with respect to the use of the SDR, time and clinical cost are increased, and the patient comfort is decreased. One of
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the limitations of this paper was the absence of a control procedure without splinting copings pick-up. However, in the literature many studies have already demonstrated that greater accuracy of implant impression was obtained with the split technique than with the unsplit technique,17,20,21,34,48 but more studies should be conducted to obtain additional conclusions about this topic. Nevertheless, the use of SDR was more accurate than Duralay, and with the SDR it was not necessary to section and rejoin the splinting material. CONCLUSION Within the limitations of this study, we can conclude that the conventional impressions using SDR as splinting material between the implants were highly accurate and statistically more precise than the ones splinted with Duralay. Sectioning and rejoining the SDR splinting material had no significant impact on the impression precision. CONFLICT OF INTEREST The authors have no commercial or financial dealings that may pose a conflict of interest or potential conflict of interest. REFERENCES 1. Barrett MG, de Rijk WG, Burgess JO. The accuracy of six impression techniques for osseointegrated implants. J Prosthodont 1993; 2:75–82. 2. Wee AG, Aquilino SA, Schneider RL. Strategies to achieve fit in implant prosthodontics: review of the literature. Int J Prosthodont 1999; 12:167–178. 3. Conrad HJ, Pesun IJ, DeLong R, Hodges JS. Accuracy of two impression techniques with angulated implants. J Prosthet Dent 2007; 97:349–356. 4. Lee H, Ercoli C, Funkenbusch PD, Feng C. Effect of subgingival depth of implant placement on the dimensional accuracy of the implant impression: an in vitro study. J Prosthet Dent 2008; 99:107–113. 5. Eckert SE, Merw SJ, Cal E, Ow RK. Analysis of incidence and associated factors with fractured implants: a retrospective study. Int J Oral Maxillofac Implants 2000; 15:662–667. 6. Duyck J, Naert I. Influence of prosthesis fit and the effect of luting system on the prosthetic connection preload: an in vitro study. Int J of Prosthodont 2002; 15:389–396. 7. Eliasson A, Wennerberg A, Johansson A, Ortorp A, Jemt T. The precision of fit of milled titanium implant frameworks (I-Bridge) in the edentulous jaw. Clin Implant Dent Relat Res 2010; 12:81–90.
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37.
38.
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41.
42.
implants. Part 1 – Influence of transfer copings surface abrasion. J Prosthodont 2008; 17:641–647. Assunção WG, Tabata LF, Cardoso A, Rocha EP, Gomes EA. Prosthetic transfer impression accuracy evaluation for osseointegrated implants. Implant Dent 2008; 17:248–256. Kim S, Nicholls JI, Han CH, Lee KW. Displacement of implant components from impressions to definitive casts. Int J Oral Maxillofac Implants 2006; 21:747–755. Ma T, Nicholls JI, Rubenstein JE. Tolerance measurements of various implant components. Int J Oral Maxillofac Implants 1997; 12:371–375. Cehreli MC, Akça K. Impression techniques and misfitinduced strains on implant-supported superstructures: an in vitro study. Int J Periodontics Restorative Dent 2006; 26:379–385. Ortorp A, Jemt T, Bäck T, Jälevik T. Comparisons of precision of fit between cast and CNC-milled titanium implant frameworks for the edentulous mandible. Int J Prosthodont 2003; 16:194–200. Schmitt SM, Chance DA. Fabrication of titanium implantretained restorations with nontraditional machining techniques. Int J Prosthodont 1995; 8:332–336.
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43. Ilie N, Hickel R. Investigations on a methacrylate-based flowable composite based on the SDR™ technology. Dent Mater 2011; 27:348–355. 44. Roggendorf MJ, Krämer N, Appelt A, Naumann M, Frankenberger R. Marginal quality of flowable 4-mm base vs conventionally layered resin composite. J Dent 2011; 39:643– 647. 45. Koltisko B, Dai Q, Jin X, Bertrand S. The polymerization stress of flowable composites. J Dent Res 2010; 89:321. 46. Spector MR, Donovan TE, Nicholls JI. An evaluation of impression techniques for osseointegrated implants. J Prosthet Dent 1990; 63:444–447. 47. Del Acqua MA, Chavez AM, Castanharo SM, Compagnoni MA, Mollo Fde A Jr. The effect of splint material rigidity in implant impression techniques. Int J Oral Maxillofac Implants 2010; 25:1153–1158. 48. Stimmelmayr M, Erdelt K, Güth JF, Happe A, Beuer F. Evaluation of impression accuracy for a four-implant mandibular model – a digital approach. Clin Oral Investig 2012; 16:1137–1142.
ABSTRACT Purpose: The study aims to evaluate three-dimensionally (3D) the accuracy of implant impressions using a new resin splinting material, “Smart Dentin Replacement” (SDR). Materials and Methods: A titanium model of an edentulous mandible with six implant analogues was used as a master model and its dimensions measured with a coordinate measuring machine. Before the total 60 impressions were taken (open tray, screw-retained abutments, vinyl polysiloxane), they were divided in four groups: A (test): copings pick-up splinted with dental floss and fotopolymerizing SDR; B (test): see A, additionally sectioned and splinted again with SDR; C (control): copings pick-up splinted with dental floss and autopolymerizing Duralay® (Reliance Dental Mfg. Co., Alsip, IL, USA) acrylic resin; and D (control): see C, additionally sectioned and splinted again with Duralay. The impressions were measured directly with an optomechanical coordinate measuring machine and analyzed with a computer-aided design (CAD) geometric modeling software. The Wilcoxon matched-pair signed-rank test was used to compare groups. Results: While there was no difference (p = .430) between the mean 3D deviations of the test groups A (17.5 μm) and B (17.4 μm), they both showed statistically significant differences (p < .003) compared with both control groups (C 25.0 μm, D 19.1 μm). Conclusions: Conventional impression techniques for edentulous jaws with multiple implants are highly accurate using the new fotopolymerizing splinting material SDR. Sectioning and rejoining of the SDR splinting had no impact on the impression accuracy. KEY WORDS: accuracy, edentulous jaw, implant impression technique, impression copings, passive fit, splinting material
INTRODUCTION The accuracy is an important factor for the success and survival of an implant-retained prosthesis. The precise transfer of the three-dimensional (3D) intraoral implant relationship to the master cast is a critical step to achieve a passive fit.1–4 The insufficient accuracy during the impression-making technique and/or manual steps during prosthesis fabrication may lead to misfit of the prosthesis and subsequent to technical, mechanical, and biological complication such as occlusal discrepancies screw or abutment loosening, fracture of the prosthetic components, implant fractures, and loss of osseointegration.5–8 Differently from natural teeth, osseointegrated implants have no periodontal ligament to compensate any inaccuracy of implant-retained prosthesis.9 Inaccurate frameworks of implant-retained prosthesis can cause stress at the implant/bone interface, plaque accumulation, affecting soft and/or hard tissues
*Clinical assistant, Department of Prosthodontics, Dental School, University of Padova, Padova, Italy; †PhD student, Mechatronics and Product Innovation Engineering, Department of Management and Engineering, University of Padova, Padova, Italy; ‡assistant professor, Departments of Civil, Environmental and Architectural Engineering, University of Padova, Padova, Italy; §adjunct professor, Departments of Civil, Environmental and Architectural Engineering, University of Padova, Padova, Italy; ¶clinical assistant, Departments of Oral Surgery, Dental School, University of Padova, Padova, Italy; **scientific associate, Department of Reconstructive Dentistry and Gerodontology, School of Dental Medicine, University of Bern, Bern, Switzerland; ††adjunct associate professor, Department of Preventive and Restorative Sciences, University of Pennsylvania School of Dental Medicine, Philadelphia, PA, USA; ‡‡dean, Dental School, University of Padova, Padova, Italy Corresponding Author: Dr. Adolfo Di Fiore, Department of Prosthodontics, Dental School, University of Padova, via Venezia 90, Padova 35100, Italy; e-mail: [email protected] © 2015 Wiley Periodicals, Inc. DOI 10.1111/cid.12321
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around the implants.10,11 However, the accuracy of the master cast is dependent on the clinical and laboratory variable such as the type of impression material, direct and indirect impression technique, splinting or surface treatment of impression copings, dimensional changes in dental stone during setting, and implant master cast realization.12–19 To ensure maximum accuracy for an implant-supported fixed dental prosthesis (FDP), the intraoral splinting of transfer copings before recording of the definitive impression has been recommended to preserve their 3D intraoral relationship and minimize the effects of the factors that may cause distortion in the x, y, z-axes.17,20–22 Different methods for splinting implant transfer copings with acrylic resin,17 prefabricated acrylic resin,23 photopolymerizable acrylic resin,12 bite registration with the addition of silicone and bite registration with polyether24 have been tested. Suggested methods of splinting transfer copings include the use of a matrix of dental floss25 or orthodontic wire.26 The acrylic resin still remains the most common material to splinting transfer copings. However, when a large volume of acrylic resin is used to splint transfer copings intraorally, distortion may result from polymerization shrinkage. It has been reported that the total shrinkage of acrylic resin is between 6.5% and 7.9% in the first 24 hours.23,27 Another technique that has been suggested involves splinting the transfer copings with acrylic resin (first step) and performing an additional step of sectioning and rejoining the resin (second step) to reduce the effects of polymerization shrinkage.28 With this procedure, however, clinical chair-side time is increased. Based on the need to obtain maximally accurate FDPs, the purpose of this in vitro study was to evaluate three-dimensionally the accuracy of implant impressions using a new resin splinting material, “Smart Dentin Replacement” (SDR). The null hypothesis was that there would be no significant difference in the accuracy between the splinting and impression approaches.
as a clinically relevant simulation model (master cast). The model must possess the characteristics of stiffness, strength, and dimensional stability to allow the execution of all impression techniques without errors of distortion. The reference model resembled a mandibular implant-supported Toronto-Bridge situation. Initially, the basis of the master model was designed and on it have been realized the locations of insertion of the analogues. The upper part of the master model was designed with a cavity for the insertion of a self-curing resin to prevent any movement of the analogues. The analogues (Certain implant lab analog 4.1 mm (D) IILA20 Biomax 3i, Implant Innovations, Palm Beach Gardens, FL, USA), with a diameter of 4.1 mm and with an external hexagon, were secured with self-curing resin (Eco Cryl Cold, Protechno, Vilamalla Girona, Spain). The six analogues were positioned symmetrically to correspond to the mandibular first molar, first premolars, and lateral incisors bilaterally (Figure 1). The interimplants’ distance in the x-axis between the center of analogue 1 and the center of the analogue 6 was 47.5 mm, between the center of analogue 1 and the center of analogue 5 was 41.2 mm, between the center of analogue 1 and the center of analogue 4 was 31.2 mm, between the center of analogue 1 and the center of analogue 3 was 16.22 mm, and between the center of analogue 1 and the center of analogue 2 was 6.2 mm (Figure 2). The inter-implants’ distance in the y-axis between the center of analogue 1 and the center of the analogue 6 was 47.5 mm, between the center of analogue 2 and the center of analogue 5 was 35.0 mm, and between the center of analogue 3 and the center of
MATERIALS AND METHODS Fabrication of Master Model A virtual model of a mandibular edentulous with six implant analogues was designed by mean of a computeraided design (CAD) software (Dassault Systèmes SolidWorks Corporation, Waltham, MA, USA) and subsequently manufactured in titanium by a CNC machine tool (Dyamach Italia s.r.l., Mussolente VI, Italy) to serve
Figure 1 Master CAD model in 3D with six dental implant analogues.
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Figure 2 The inter-implants distance in the y-axis between the center of analogues.
analogue 4 was 15.0 mm. In the z-axis, the analogues in positions 1 and 6 were placed at a height equal to 0 mm. The analogues in positions 2 and 5 were placed 1.1 mm higher than those in positions 1 and 6, and those in positions 3 and 4 were placed 2.3 mm higher, always taking as reference those in positions 1 and 6. The analogues in positions 1 and 6 are inclined by 10 degrees distally and 10 degrees buccally. The analogues in positions 2, 3, 4, 5 are all parallel to each other. Measurement Procedure The master model was measured with a coordinate measuring machine (SmartScope Flash, CNC 300, Optical Gaging Products, Rochester, NY, USA), an optomechanical system that is capable of moving a measuring probe to determine the spatial coordinates of points on a workpiece surface. All measurements were performed at the Department of Civil, Environmental, and Architectural Engineering of the University of Padova.The coordinates of the probed points were transferred into a 3D CAD geometric modeling software program (Rhinoceros 5.0 Beta, Robert McNeel & Associates McNeel Europe,Barcelona,Spain) and analyzed with a taskspecific evaluation protocol, programmed in IronPython programming language, to estimate the position and orientation of each analogue. The measuring system is capable of a maximum permissible error (E,in micron) that is 10 times lower than both the performance of scanners commonly
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used in framework digital manufacturing and the expected position errors of the implant analogue surfaces: E1(z) = 2.5 + 5L/1,000 μm, E2(xy) = 1.8 + 5L/1,000 μm, E3(xyz) = 2.8 + 5L/1,000 μm (with L, in millimeters, equal to the measured distance, according to International Organization for Standardization norm 10360). Uncertainty in experimental measurements was lower the 5 μm and was mainly influenced by the implant analogue’s upper surface form error and by the system calibration method. Measurements consisted of the acquisition of a set of 30 points on the upper surface and the second set of more than 200 points on the external profile of each analogue. To evaluate both position and orientation, the first set of points was used to construct the upper plane of the analogues, while the second set of points was used to obtain fitting circles that were constrained to lie on those planes; thus, the spatial (x,y,z) coordinates of the center of the fitting circles estimate the positions of analogues. The fitting algorithms implemented for the 3D geometries reconstruction were validated in a previous study, and their contribution to the experimental measurement uncertainty is negligible.29,30 Impression Procedure Plastic directed-flow disposable trays (3M ESPE Directed Flow Impression Tray, 3M ESPE, St. Paul, MN, USA) were used to simplify and streamline the impression techniques. The performance of stock plastic trays and the directedflow impression trays was better than the performance of stock perforated metal trays.31 Six windows were created in the plastic stock to expose the coping screws. Vinyl polixiloxane (Acquasil putty/light body, Dentsply, Milford, DE, USA) was used according to the manufacturer’s instructions as impression material for each group; 24 copings pick-up (Certain, Biomax 3i, Implant Innovations), 6 for each group, were used for impression techniques. The fitting surface of all components was cleaned with isopropyl alcohol before each impression.29 The impression was made in a controlled-temperature environment (22°C 1 2°C) with a relative humidity of 45% 1 10%.The samples were divided into four groups based on impression technique. The exact number of the samples for each group was calculated with a pilot study. Four groups with a 15 impression cast were evaluated: Group A: The copings pick-up was splinted with an SDR® (Smart Dentin Replacement, Dentsply). The dental floss was used to create a matrix around the copings pick-up where SDR will be placed. The splint
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Figure 3 The copings pick-up splinted with SDR® (Group A).
was allowed to photopolymerize for 2 minutes. The putty impression material was mixed for 30 seconds by hands and loaded inside the plastic tray; at the same time, the light material was syringed around the copings pick-up, followed by immediate placement of the tray on the master model until it contacted the base of the master model. The impression material was allowed to set for 10 minutes from the start of the mixing. After the impression had polymerized, the transfers were unscrewed and the tray was separated from the master model. The abutment analogues were then fit to the impression coping using 10 Ncm of torque (Figure 3). Group B: The copings pick-up was splinted with an SDR. The dental floss was used to create a matrix around the copings pick-up where the SDR will be placed. The splinting was allowed to photopolymerize for 2 minutes and afterwhich will be sectioned with a cutting disk (diamond-coated disk 150 μm thick, Intensiv, Montagnola, Switzerland) to span the spaces between the adjacent copings pick-up. The splinting was rejoined with SDR in the spaces between the transfers. This additional step was performed to reduce the effects of polymerization shrinkage. The impression was made in a similar procedure as group A (Figure 4). Group C: The copings pick-up was splinted with a Duralay® acrylic resin (Reliance Dental Mfg. Co., Alsip, IL, USA). The dental floss was used to create a matrix around the copings pick-up where the Duralay will be placed by means of the“Brush Technique.”The splinting was allowed to auto-polymerize for 4 minutes. The impression was made in a similar procedure as group A (Figure 5). Group D: The copings pick-up was splinted with a Duralay acrylic resin. The dental floss was used to create a
Figure 4 The copings pick-up splinted with SDR®. The splinting material was sectioned and rejoined to reduce the effects of polymerization shrinkage (Group B).
matrix around the copings pick-up where the Duralay will be placed by means of the“Brush Technique.”The splinting was allowed to auto-polymerize for 4 minutes and afterwhich will be sectioned with a cutting disk (diamondcoated disk 150 μm thick, Intensiv) to span the spaces between the adjacent copings pick-up. The splinting was rejoined with Duralay in the spaces between the transfers. This additional step was performed to reduce the effects of polymerization shrinkage. The impression was made in a similar procedure as group A (Figure 6). The impression was measured in the same manner of the master model with the optomechanical coordinate measuring machine (SmartScope Flash, CNC 300, Optical Gauging Products) and analyzed by
Figure 5 The copings pick-up splinted with Duralay® acrylic resin (Group C).
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Figure 6 The copings pick-up splinted with Duralay® acrylic resin. The splinting material was sectioned and rejoined to reduce the effects of polymerization shrinkage (Group D).
means of the aforementioned 3D CAD geometric modeling software (Rhinoceros 5.0 Beta, Robert McNeel & Associates). To evaluate the positional accuracy of each impression, the estimated centers of the were aligned, using a least-square best fitting algorithm, to the corresponding analogues on the master model; the algorithm “optimizes” the position and orientation of the impression while considering the 3D distances between each transfer and the relative analogue. Three-dimensional distances between centers and their components along the x-, y-, and z- axes were calculated at each position for all impression. Statistical Analysis The material of splinting transfer copings was considered as the statistical unit. The primary variable was the distance (μm) of the center of the copings pick-up compared with the center of the respective analogue of the master model with coordinate measuring machine. A pilot study was conducted to generate data on the
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expected effect size and standard deviation to allow for power calculations. The number of sample provided for the calculation was three impression techniques for group A and for group C. The level of statistical significance was set as α = 0.05 and with a statistical power of 80%. The test group average (group A) was 17.04 μm (SD 8.13 μm) while the control group average (group C) was 24.81 μm (SD 9.95 μm). Null hypothesis for difference between averages was supposed to be 10 μm. Twelve impressions for group were then estimated after power calculation. The sample size was set to 15 per group because a 30% bias (three per group) was expected. The Wilcoxon matched-pairs signed-rank test (one-tailed) was used to compare groups. The level of statistical significance was set as α = 0.05 and with a statistical power of 80%. Statistical analysis was performed using statistical software SPSS 16.0 (SPSS Inc., Chicago, IL, USA). RESULTS The deviation in the center point position at each implant analogue level is described in Table 1. The mean values are reported along x-, y-, and z-axes, as well as on the resultant 3D levels. The mean 3D deviation values were used as the value in comparative statistics between groups. The mean 3D deviation value of the center point position for group A was 17.49 μm, for group B was 17.39 μm, for group C was 24.95 μm, and for group D was 19.12 μm (Table 1). Six numerical values were recorded for each impression that correspond to deviations of the six copings pick-up from the position of the six analogues, then for each impressions was performed the average of the six deviations to obtain a single numerical value. The value obtained will be used to perform the Wilcoxon matched-pairs signed-ranks test (one-tailed). A statistically significant difference was present between group A and group D (p value = .0017),
TABLE 1 Mean Deviations(μm) of the Central Point for Each Group of Impression Techniques in Three Axis and 3D Δx
Δy
Δz
3D
Group
Mean
SD
Mean
SD
Mean
SD
Mean
SD
A B C D
7.06 6.70 10.11 10.46
6.05 4.86 6.47 7.55
12.55 12.38 19.31 14.10
8.34 7.81 11.8 7.67
5.76 6.14 7.27 3.15
6.08 6.57 5.51 2.51
17.49 17.39 24.95 19.12
8.16 7.26 9.89 8.08
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TABLE 2 Comparative Statistical Analysis Between the Four Groups Group
A B C D
p Value
— .43 .003 .0017
.43 — .003 .002
.003 .003 — .002
.0017 .002 .002 —
between group A and group C (p value = .003), between group B and group C (p value = .003), between group B and group D (p value = .002), and between group C and group D (p value = .002). No statistically significant difference was present between group A and group B (p value = .43) (Table 2). DISCUSSION Accuracy is an important factor for the success and survival of an implant-retained prosthesis.32,33 The precise transfer of the 3D intraoral relationships of implants from the mouth to the master cast is a critical step to achieve a passive fit.1–4 In literature, several studies have indirectly estimated the accuracy of implant impression techniques by evaluating the fit of fabricated frameworks on the resultant casts with strain gauges and compared the fit of the frameworks on the master cast.12,20,34,35 Other studies have evaluated the accuracy of the implant impressions by measuring inter-implant distances of the working casts in relation to a reference control cast.2,24,36,37 Recently, optical scanning, photogrammetry, optical microscope, laser videography, and computerized coordinate measuring machine are some of the techniques that have been used in the assessment of inter-implant 3D deviations.30,38 In the four different impression techniques examined in the present study, distortion was always detected, and it is important to remember that this study only evaluated the steps in the process of prosthesis fabrication. Different studies have been conducted to investigate the variable affecting the accuracy of the different processes in implant prosthodontics, such as the different direct or indirect impression techniques,22 the use of different impression materials,24 the use of different trays,31 splinting or surface treatment of impression copings,12 the relative implant angulation,3 machining tolerances of the components provided by the manufacturer,39,40 and accuracy of the laboratory process.41,42 However, the error can be introduced in each of these
different clinical procedures, like excessive dimensional changes of the impression material or dimensional stability of different material of trays. In this study, the authors have tried to reduce the errors that may develop during the impression procedure. The vinyl polixiloxane was used as an impression material because it was more accurate with respect to polyether18 and/or irreversible hydrocolloid.31 Plastic directed-flow disposable trays were used because the performance of stock plastic trays and the directed-flow impression trays was better than the performance of stock perforated metal trays.31 Furthermore, in the master model the analogues in position 1 and 6 were inclined by 10 degrees distally and 10 degrees buccally. Instead the analogues in position 2,3,4,5 were all parallel to each other, because reproduce a realistic clinical situation and the results might have been different if the implants were placed all parallel. Different methods for splinting implant transfer copings with acrylic resin,17 prefabricated acrylic resin,23 photopolymerizable acrylic resin,12 bite registration addition silicone and bite registration polyether24 have been tested, but there are no studies in the literature that evaluate SDR as splinting material. SDR is a flowable composite mainly used in restorative dentistry. SDR is characterized by a remarkably low polymerization stress, in combination with a low polymerization shrinkage and a high depth of cure. Thanks to the stress decreasing resin technology, it is the first flowable composite that can be used as a bulk-fill base material in increments of up to 4mm in Class I and II cavities.43–45 In this study, significant differences in center point deviation were noted between group A and group D (p value = .0017), between group A and group C (p value = .003), between group B and group C (p value = .003), between group B and group D (p value = .002), and between group C and group D (p value = .002). No statistically significant difference was present between group A and group B (p value = .43). The deviation of the center point in the x-axis for group B was the least (6.7 μm) when compared with other groups, whereas group D showed the greatest deviation (10.46 μm) in the x-axis. The deviation of the center point in the y-axis for group B was the least (12.38 μm) when compared with other groups, whereas group D showed the greatest deviation (19.31 μm) in the y-axis. The deviation of the center point in the z-axis for group D was the least (3.15 μm) when compared with other groups, whereas group C showed the greatest deviation (7.27 μm) in the z-axis. As described in previous
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studies,24,30 the most significant deviation is observed in the horizontal plane (x-and y-axes) rather than in the vertical direction (z-axis), regardless of the technique or material. In the literature, more studies have reported increased accurate implant impressions with the splint techniques than with the unsplint techniques.12–24 Some authors suggested possible problems with the splint techniques, such as distortion of the splint materials,46 and another, as Kim and colleagues38 conclude, is that the unsplint techniques were more accurate during the impression-making procedure. It was interesting that more studies advocating the splint technique were found within recent literature. Five out of seven studies recommending the splint techniques were published after 2003,18 as opposed to two older studies which appeared before 1996. However, the use of new splinting materials like composite resin or light polymerizing acrylic resin resulted in better results.22 The present study showed that the accuracy of impression produced with SDR sectioned and reunited (group B) has the lowest deviation compared with groups where the Duralay acrylic resin (group C, group D) was used. No statistically significant difference was present between group A (with SDR not sectioned) and group B (with SDR sectioned and reunited) (p value = .43). The techniques of groups A and B resulted more accurate respect the techniques of groups C and D. An ideal impression technique would require minimal time, is comfortable for the patients, will give the best results, and inexpensive. Compared with other authors that use prefabricated acrylic resin,23 photopolymerizable acrylic resin,12 bite registration with the addition of silicone and bite registration with polyether24 and metal burs,47 the use of SDR as splinting material is an excellent solution. SDR is characterized by a remarkably low polymerization stress, in combination with a low polymerization shrinkage. Thanks to the low polymerization shrinkage, the step of sectioning and rejoining the splinting material to reduce the effects of polymerization shrinkage is not necessary to obtain maximum accuracy in the impression technique. With this procedure, however, the time and clinical cost are decremented, and instead the patient’s comfort is increased. Opposite, the use of the Duralay acrylic resin as splinting material is necessary, the step of sectioning and rejoining the splinting material to reduce the effects of polymerization shrinkage. In this procedure, with respect to the use of the SDR, time and clinical cost are increased, and the patient comfort is decreased. One of
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the limitations of this paper was the absence of a control procedure without splinting copings pick-up. However, in the literature many studies have already demonstrated that greater accuracy of implant impression was obtained with the split technique than with the unsplit technique,17,20,21,34,48 but more studies should be conducted to obtain additional conclusions about this topic. Nevertheless, the use of SDR was more accurate than Duralay, and with the SDR it was not necessary to section and rejoin the splinting material. CONCLUSION Within the limitations of this study, we can conclude that the conventional impressions using SDR as splinting material between the implants were highly accurate and statistically more precise than the ones splinted with Duralay. Sectioning and rejoining the SDR splinting material had no significant impact on the impression precision. CONFLICT OF INTEREST The authors have no commercial or financial dealings that may pose a conflict of interest or potential conflict of interest. REFERENCES 1. Barrett MG, de Rijk WG, Burgess JO. The accuracy of six impression techniques for osseointegrated implants. J Prosthodont 1993; 2:75–82. 2. Wee AG, Aquilino SA, Schneider RL. Strategies to achieve fit in implant prosthodontics: review of the literature. Int J Prosthodont 1999; 12:167–178. 3. Conrad HJ, Pesun IJ, DeLong R, Hodges JS. Accuracy of two impression techniques with angulated implants. J Prosthet Dent 2007; 97:349–356. 4. Lee H, Ercoli C, Funkenbusch PD, Feng C. Effect of subgingival depth of implant placement on the dimensional accuracy of the implant impression: an in vitro study. J Prosthet Dent 2008; 99:107–113. 5. Eckert SE, Merw SJ, Cal E, Ow RK. Analysis of incidence and associated factors with fractured implants: a retrospective study. Int J Oral Maxillofac Implants 2000; 15:662–667. 6. Duyck J, Naert I. Influence of prosthesis fit and the effect of luting system on the prosthetic connection preload: an in vitro study. Int J of Prosthodont 2002; 15:389–396. 7. Eliasson A, Wennerberg A, Johansson A, Ortorp A, Jemt T. The precision of fit of milled titanium implant frameworks (I-Bridge) in the edentulous jaw. Clin Implant Dent Relat Res 2010; 12:81–90.
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