Technical Report: Precisely Fitting Bars on Implants in Five Steps—A CAD/CAM Concept for the Edentulous Mandible Florian Beuer, Dr med dent, PhD,1 Josef Schweiger, CDT,1 Martin Huber, BSc,2 ¨ Engels, Dr med dent,1 & Michael Stimmelmayr, Dr med dent, PhD1,3 Jorg 1
Department of Prosthodontics, University of Munich, Munich, Germany CADStar, Bischofshofen, Austria 3 Private Practice, Oral Surgery, Cham, Germany 2
The article is associated with the American College of Prosthodontists’ journal-based continuing education program. It is accompanied by an online continuing education activity worth 1 credit. Please visit www.wileyhealthlearning.com/jopr to complete the activity and earn credit.
Keywords CAD/CAM; edentulous mandible; bar; implant prosthodontics. Correspondence Dr. Florian Beuer, Department of Prosthodontics, Ludwig Maximilians University, Goethestr. 70, 80336 Munich, Germany. E-mail: [email protected]
Abstract Various treatment concepts have been presented for the edentulous mandible. Manufacturing tension-free and precisely fitting bars on dental implants was previously a great challenge in prosthetic dentistry and required great effort. Modern computer aided design/computer aided manufacturing technology in combination with some clinical modifications of the established workflow enables the clinician to achieve precise results in a very efficient way. The innovative five-step concept is presented in a clinical case.
Conflict of Interest statement: Martin Huber is an employee of CADStar. Accepted July 31, 2013 doi: 10.1111/jopr.12121
The edentulous mandible represents a challenge for the dentist and dental technician. Implant-prosthetic rehabilitations offer a wide range of treatment concepts dependent on clinical, technical, and economic factors. When removable prostheses are used, implant-retained, mucosa-supported overdentures (IMOs) can be distinguished from implant-supported removable dental prostheses (IRDPs). The most cost-effective implant-retained solution with mucosa support is the use of two implants in the canine area supplied with two magnets, locator (or two ball) attachments.1,2 Four or more implants support a prosthesis securely without resilient movement.3 Long (milled) bar systems have been reported to support IRDPs, preventing rotational movements; however, these bar retainers have higher manufacturing expenses.4 In the past, such bars were either welded or soldered from prefabricated parts or soldered or cast in one piece.5 These fabrication techniques were associated with technical problems such as misfit, fractures, and biological complications. Branemark postulated passive fit for implant-supported prostheses.6,7 The absence of tension was thereby achieved only with considerable effort and always posed a great challenge for the dental technician.8 The bar frequently had to be sectioned to laser or solder it once more. Due to problems with conventional technology in producing
bars, other attachments have gained popularity. Promising results of double crowns used as attachments for implant-retained overdentures have been reported.9,10 The use of computer aided design/computer aided manufacturing (CAD/CAM) technology improved precision and reproducibility in the dental laboratory.11 Bar systems for retaining IRDPs can also be manufactured to a precise fit. To achieve maximum precision, special attention has to be paid to the important steps in the dental office, the dental laboratory, and the CAD/CAM production centers. This technical report shows five crucial steps in the working sequence: 1. Transfer of the oral situation into a master cast by special impression technique 2. Precise bite registration 3. The scan body (scan post) and 3D matching 4. Digitizing procedure 5. Five-axis high-speed cutting (HSC) machining To minimize the total error for a nearly passive fit of the bar, the individual errors during these five steps must be kept as small as possible. The probability that subsequent errors will compensate for previous ones is very low and grows, especially if the number of subsequent processing steps increases.
C 2014 by the American College of Prosthodontists Journal of Prosthodontics 23 (2014) 333–336
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Figure 1 Splinted pickup impression copings in the implants for the impression with open tray.
Figure 2 Screw-retained wax-up.
Five steps for a precisely fitting bar Transfer of the oral situation to the master cast by a two-step impression technique
A healthy 73-year-old female patient with four two-piece osseointegrated dental implants in the mandible was referred for prosthetic treatment at the authors’ institution. To achieve high precision, the authors used a two-step impression concept. First impression with a closed impression tray: Transfer impression posts with plastic caps were screwed in the implants, and an impression was made using an individualized standard impression tray (Master Impression Tray; Water Pik, Ft. Collins, CO). Therefore, the distal areas of the impression tray were customized with putty vinylpolysiloxane (Optosil; Heraeus Kulzer, Hanau, Germany) to guide the polyether (Impregum Penta Soft, 3M ESPE, Seefeld, Germany) during material setting. Following the removal of the impression from the mouth after a 5-minute setting time, the transfer impression caps were unscrewed from the implants, lab analogs were screwed to the transfer impression caps, and they were repositioned into the plastic caps fixed in the impression. The implants were rinsed with 0.2% chlorhexidine solution, and healing caps were screwed to the implants. A first model was fabricated in the dental laboratory. After a setting time of 72 hours, pickup impression posts were screwed on the lab analogs and splinted with acrylic resin (Pattern Resin; GC Europe, Leuven, Belgium) with an edge length of 4 mm × 4 mm. The bars were sectioned in the center between the impression posts with a cutting wheel (0.5 mm thick). Second impression: The impression posts with the resin bars were screwed in the respective implant in the patient’s mouth. The separations were examined for passive fit and reconnected with resin (Pattern Resin) in two sequences: first the distal bars, following polymerization of the resin; second the bar between the implants in the anterior (Fig 1). After polymerization of the resin (5 minutes), the impression was made using an individual open-bite custom tray (Lightplast; Dreve, Dortmund, Germany). The trans-occlusal screws were loosened after setting of the impression material, and the impression was removed from the mouth. Lab analogs were screwed to the impression posts fixed in the impression. Again, implants were rinsed as described above, and healing caps were screwed to the implants. 334
Figure 3 New scan bodies with an improved basis for subsequent mathematical matching algorithms of the Z-axis.
All impressions were made with regular-body polyether (Impregum; 3M ESPE) and remained in the mouth for 5 minutes counted from the start of mixing.12 Four hours after the impression was made,12 the casts were fabricated (Rocky Mountain Sahara; Klasse IV Dental GmbH, Augsburg, Germany). Bite record
A significant advantage in making bite records for manufacturing implant-retained prostheses is the opportunity to rigidly screw-retain the record to one or more implants. If the implants are strongly divergent, a few implants with the same insertion direction are used for screw-retaining the bite record. Used impression posts for transfer technique can be shortened and mounted in the resin bases of the bite record. This approach guarantees a solid seat of bite pattern and wax try-in (Fig 2), thus providing the basis for the precise dimensioning of the CAD-/CAM-fabricated implant bar. Scan body and 3D matching
Scan body design as well as the material used for the scan body shows a significant influence on the data quality obtained by the scanning process.13 A special scan body with patented geometry as well as patented surface coating was used for this patient (Figs 3 and 4).
C 2014 by the American College of Prosthodontists Journal of Prosthodontics 23 (2014) 333–336
Beuer et al
CAD/CAM Concept
Figure 5 CAD construction of the bar reconstruction. Figure 4 Digital image of the scan body.
Scan bodies must meet the following requirements:
r r r r r
Stability of the material. Diffuse surface structure. Rounded edges. Rotation lock for single tooth restoration. High diversity of the zero vectors.
High diversity of the zero vectors to support the best-fit algorithms was not taken into consideration with most scan bodies.13 To date, conical scan abutments are usually used. These are in the shape of a stub with an approximately 85◦ tapered angle. The fact that the geometry of the scan bodies is without structure in the vertical direction makes precise localization of the vertical position of the scan bodies in the Z direction difficult. Therefore, the special geometry of the new scan body offered an improved basis for subsequent mathematical matching algorithms. The geometry of the scan body was developed considering the iterative-closest-point algorithm theory and thus guarantees a significantly more precise matching result. The scan bodies are structured in the Z direction (Figs 3 and 4), so during the matching process, no deviation in vertical direction (z-axis) without increasing the inaccuracy of the best-fit algorithm is possible. To their best knowledge, the authors are the first to emphasize the importance of geometry of the scan body if a best-fit algorithm is used for identifying the implant position. Measurements showed a systematic error of the best-fit algorithm of 16 µm and a rotational accuracy of 0.13◦ of these new scan bodies during matching (unpublished information). Scanning device
The accuracy of 3D capturing is an important step in the working sequence representing the interface between the analog and digital approaches. White light projector scanners offer larger scanning fields than laser scanners do. Larger scanning fields require fewer scans to capture a clinical situation following fewer matching errors, therefore offering higher precision. However, this scan process with the white light projector method takes more time and is more expensive. After the wax-up and the master cast are scanned, the CAD construction of the bar reconstruction can be done on the computer (Fig 5).
Figure 6 Buccal view of the CAM-fabricated bar reconstruction (situation on master model).
Figure 7 Buccal view of the CAM-fabricated bar reconstruction (intraoral situation).
Five-axis HSC machining
Another important factor to achieve precise restorations is the milling unit. The milling paths are calculated by the CAM software and sent to a five-axis milling machine. As there is a deviation of the insertion axis of the bar and the implants, five milling axes are required. The usual deviation of the bar’s insertion axis from the axis of the implants requires the use of five-axis milling machines. Machines with high stiffness are required for milling highstrength materials; however, the stiffness of a machine is not only the result of great mass but also the correct distribution. The ideal situation is a heavy, highly stiff design of all rigid masses and optimization of mass and stiffness of the moving components. If stiffness is lacking, the machine might be bent and lose precision. Vibrations can dramatically reduce the life and cutting the performance of the tools.
C 2014 by the American College of Prosthodontists Journal of Prosthodontics 23 (2014) 333–336
335
CAD/CAM Concept
Beuer et al
as dental technicians and especially production centers have to work well as a team and carry out the respective steps in the workflow with perfection; however, following the presented concept might be a suitable way to achieve precisely fitting, implant-supported bars with reasonable effort (Figs 6 to 8).
References
Figure 8 Panoramic radiograph showing the precise fitting of the bar on the implants.
High speed cutting (HSC) machining offers the essential advantage that during the milling process, the resulting heat is dissipated with the milling chips so that neither the work piece nor the mill will overheat. Highly precise tool holders (e.g., the TRIBOS system) enable clamping tools with the highest true-running accuracy. The following values can be stated as a benchmark for five-axis HSC machining equipment:
r r r r
±2 µm tolerance in the CAM software. The accuracy is achieved by multicore algorithms and limited by the performance of today’s computer technology (personal communication Martin Huber BSc, CadStar). ±1 µm positioning accuracy of the axis. ±6 µm overall machine precision. ±3 µm tool tolerance.
The stated values result in an overall precision of ± 12 µm for computerized numerical control (CNC) processing. The accuracy was verified and tested according to the Association of German Engineers VDI guideline 3441 “Statistical Testing of the Operational and Positional Accuracy of Machine Tools” (unpublished data).
Conclusion The production of precisely fitting bar structures with passive seating on implants through CAD/CAM methods can be precise and reliable only if all described steps of the work flow are precisely adhered to. Compromises in only one step can lead to a failure of the overall result. The probability of a serial addition of errors in the individual steps is higher than the probability of accidental, reciprocal canceling of errors. Dentists as well
336
1. Strong SM: Attachment-retained overdentures: the most cost-effective implant solution for the edentulous arch. Gen Dent 2009;57:112-117 2. Tan AS, Walmsley AD: Mandibular implant-retained overdenture with magnets: a case report. Dent Update 2004;31:104108 3. Krennmair G, Krainhofner M, Waldenberger O, et al: Dental implants as strategic supplementary abutments for implant-tooth-supported telescopic crown-retained maxillary dentures: a retrospective follow-up study for up to 9 years. Int J Prosthodont 2007;20:617-622 4. Krennmair G, Suto D, Seemann R, et al: Removable four implant-supported mandibular overdentures rigidly retained with telescopic crowns or milled bars: a 3-year prospective study. Clin Oral Implants Res 2012;23:481-488 5. Karl M, Graef F, Wichmann M, et al: Passivity of fit of CAD/CAM and copy-milled frameworks, veneered frameworks, and anatomically contoured, zirconia ceramic, implant-supported fixed prostheses. J Prosthet Dent 2012;107:232-238 6. Branemark PI: Rehabilitation and osseointegration in clinical reality. Int J Oral Maxillofac Implants 2003;18:770-771 7. Branemark PI: On looking back with Per-Ingvar Branemark. Interview. Int J Prosthodont 2004;17:395-396 8. Janousch R: Spannungsfreie suprakonstruktionen mit hilfe des passivierungstrays (Article in German). Dental Dialogue 2001;2:488-504 9. Weigl P: Implant prosthodontics: what next? Quintessence Int 2003;34:653-669 10. Weigl P, Lauer HC: Advanced biomaterials used for a new telescopic retainer for removable dentures. J Biomed Mater Res 2000;53:320-336 11. Beuer F, Schweiger J, Edelhoff D: Digital dentistry: an overview of recent developments for CAD/CAM generated restorations. Br Dent J 2008;204:505-511 12. Luthardt RG, Walter M, Quaas S, et al: Comparison of the three-dimensional correctness of impression techniques: a randomized controlled clinical trial. Quintessence Int 2010;41:845-853 13. Stimmelmayr M, Guth JF, Erdelt K, et al: Digital evaluation of the reproducibility of implant scanbody fit-an in vitro study. Clin Oral Investig 2012;16:851-856
C 2014 by the American College of Prosthodontists Journal of Prosthodontics 23 (2014) 333–336
Department of Prosthodontics, University of Munich, Munich, Germany CADStar, Bischofshofen, Austria 3 Private Practice, Oral Surgery, Cham, Germany 2
The article is associated with the American College of Prosthodontists’ journal-based continuing education program. It is accompanied by an online continuing education activity worth 1 credit. Please visit www.wileyhealthlearning.com/jopr to complete the activity and earn credit.
Keywords CAD/CAM; edentulous mandible; bar; implant prosthodontics. Correspondence Dr. Florian Beuer, Department of Prosthodontics, Ludwig Maximilians University, Goethestr. 70, 80336 Munich, Germany. E-mail: [email protected]
Abstract Various treatment concepts have been presented for the edentulous mandible. Manufacturing tension-free and precisely fitting bars on dental implants was previously a great challenge in prosthetic dentistry and required great effort. Modern computer aided design/computer aided manufacturing technology in combination with some clinical modifications of the established workflow enables the clinician to achieve precise results in a very efficient way. The innovative five-step concept is presented in a clinical case.
Conflict of Interest statement: Martin Huber is an employee of CADStar. Accepted July 31, 2013 doi: 10.1111/jopr.12121
The edentulous mandible represents a challenge for the dentist and dental technician. Implant-prosthetic rehabilitations offer a wide range of treatment concepts dependent on clinical, technical, and economic factors. When removable prostheses are used, implant-retained, mucosa-supported overdentures (IMOs) can be distinguished from implant-supported removable dental prostheses (IRDPs). The most cost-effective implant-retained solution with mucosa support is the use of two implants in the canine area supplied with two magnets, locator (or two ball) attachments.1,2 Four or more implants support a prosthesis securely without resilient movement.3 Long (milled) bar systems have been reported to support IRDPs, preventing rotational movements; however, these bar retainers have higher manufacturing expenses.4 In the past, such bars were either welded or soldered from prefabricated parts or soldered or cast in one piece.5 These fabrication techniques were associated with technical problems such as misfit, fractures, and biological complications. Branemark postulated passive fit for implant-supported prostheses.6,7 The absence of tension was thereby achieved only with considerable effort and always posed a great challenge for the dental technician.8 The bar frequently had to be sectioned to laser or solder it once more. Due to problems with conventional technology in producing
bars, other attachments have gained popularity. Promising results of double crowns used as attachments for implant-retained overdentures have been reported.9,10 The use of computer aided design/computer aided manufacturing (CAD/CAM) technology improved precision and reproducibility in the dental laboratory.11 Bar systems for retaining IRDPs can also be manufactured to a precise fit. To achieve maximum precision, special attention has to be paid to the important steps in the dental office, the dental laboratory, and the CAD/CAM production centers. This technical report shows five crucial steps in the working sequence: 1. Transfer of the oral situation into a master cast by special impression technique 2. Precise bite registration 3. The scan body (scan post) and 3D matching 4. Digitizing procedure 5. Five-axis high-speed cutting (HSC) machining To minimize the total error for a nearly passive fit of the bar, the individual errors during these five steps must be kept as small as possible. The probability that subsequent errors will compensate for previous ones is very low and grows, especially if the number of subsequent processing steps increases.
C 2014 by the American College of Prosthodontists Journal of Prosthodontics 23 (2014) 333–336
333
CAD/CAM Concept
Beuer et al
Figure 1 Splinted pickup impression copings in the implants for the impression with open tray.
Figure 2 Screw-retained wax-up.
Five steps for a precisely fitting bar Transfer of the oral situation to the master cast by a two-step impression technique
A healthy 73-year-old female patient with four two-piece osseointegrated dental implants in the mandible was referred for prosthetic treatment at the authors’ institution. To achieve high precision, the authors used a two-step impression concept. First impression with a closed impression tray: Transfer impression posts with plastic caps were screwed in the implants, and an impression was made using an individualized standard impression tray (Master Impression Tray; Water Pik, Ft. Collins, CO). Therefore, the distal areas of the impression tray were customized with putty vinylpolysiloxane (Optosil; Heraeus Kulzer, Hanau, Germany) to guide the polyether (Impregum Penta Soft, 3M ESPE, Seefeld, Germany) during material setting. Following the removal of the impression from the mouth after a 5-minute setting time, the transfer impression caps were unscrewed from the implants, lab analogs were screwed to the transfer impression caps, and they were repositioned into the plastic caps fixed in the impression. The implants were rinsed with 0.2% chlorhexidine solution, and healing caps were screwed to the implants. A first model was fabricated in the dental laboratory. After a setting time of 72 hours, pickup impression posts were screwed on the lab analogs and splinted with acrylic resin (Pattern Resin; GC Europe, Leuven, Belgium) with an edge length of 4 mm × 4 mm. The bars were sectioned in the center between the impression posts with a cutting wheel (0.5 mm thick). Second impression: The impression posts with the resin bars were screwed in the respective implant in the patient’s mouth. The separations were examined for passive fit and reconnected with resin (Pattern Resin) in two sequences: first the distal bars, following polymerization of the resin; second the bar between the implants in the anterior (Fig 1). After polymerization of the resin (5 minutes), the impression was made using an individual open-bite custom tray (Lightplast; Dreve, Dortmund, Germany). The trans-occlusal screws were loosened after setting of the impression material, and the impression was removed from the mouth. Lab analogs were screwed to the impression posts fixed in the impression. Again, implants were rinsed as described above, and healing caps were screwed to the implants. 334
Figure 3 New scan bodies with an improved basis for subsequent mathematical matching algorithms of the Z-axis.
All impressions were made with regular-body polyether (Impregum; 3M ESPE) and remained in the mouth for 5 minutes counted from the start of mixing.12 Four hours after the impression was made,12 the casts were fabricated (Rocky Mountain Sahara; Klasse IV Dental GmbH, Augsburg, Germany). Bite record
A significant advantage in making bite records for manufacturing implant-retained prostheses is the opportunity to rigidly screw-retain the record to one or more implants. If the implants are strongly divergent, a few implants with the same insertion direction are used for screw-retaining the bite record. Used impression posts for transfer technique can be shortened and mounted in the resin bases of the bite record. This approach guarantees a solid seat of bite pattern and wax try-in (Fig 2), thus providing the basis for the precise dimensioning of the CAD-/CAM-fabricated implant bar. Scan body and 3D matching
Scan body design as well as the material used for the scan body shows a significant influence on the data quality obtained by the scanning process.13 A special scan body with patented geometry as well as patented surface coating was used for this patient (Figs 3 and 4).
C 2014 by the American College of Prosthodontists Journal of Prosthodontics 23 (2014) 333–336
Beuer et al
CAD/CAM Concept
Figure 5 CAD construction of the bar reconstruction. Figure 4 Digital image of the scan body.
Scan bodies must meet the following requirements:
r r r r r
Stability of the material. Diffuse surface structure. Rounded edges. Rotation lock for single tooth restoration. High diversity of the zero vectors.
High diversity of the zero vectors to support the best-fit algorithms was not taken into consideration with most scan bodies.13 To date, conical scan abutments are usually used. These are in the shape of a stub with an approximately 85◦ tapered angle. The fact that the geometry of the scan bodies is without structure in the vertical direction makes precise localization of the vertical position of the scan bodies in the Z direction difficult. Therefore, the special geometry of the new scan body offered an improved basis for subsequent mathematical matching algorithms. The geometry of the scan body was developed considering the iterative-closest-point algorithm theory and thus guarantees a significantly more precise matching result. The scan bodies are structured in the Z direction (Figs 3 and 4), so during the matching process, no deviation in vertical direction (z-axis) without increasing the inaccuracy of the best-fit algorithm is possible. To their best knowledge, the authors are the first to emphasize the importance of geometry of the scan body if a best-fit algorithm is used for identifying the implant position. Measurements showed a systematic error of the best-fit algorithm of 16 µm and a rotational accuracy of 0.13◦ of these new scan bodies during matching (unpublished information). Scanning device
The accuracy of 3D capturing is an important step in the working sequence representing the interface between the analog and digital approaches. White light projector scanners offer larger scanning fields than laser scanners do. Larger scanning fields require fewer scans to capture a clinical situation following fewer matching errors, therefore offering higher precision. However, this scan process with the white light projector method takes more time and is more expensive. After the wax-up and the master cast are scanned, the CAD construction of the bar reconstruction can be done on the computer (Fig 5).
Figure 6 Buccal view of the CAM-fabricated bar reconstruction (situation on master model).
Figure 7 Buccal view of the CAM-fabricated bar reconstruction (intraoral situation).
Five-axis HSC machining
Another important factor to achieve precise restorations is the milling unit. The milling paths are calculated by the CAM software and sent to a five-axis milling machine. As there is a deviation of the insertion axis of the bar and the implants, five milling axes are required. The usual deviation of the bar’s insertion axis from the axis of the implants requires the use of five-axis milling machines. Machines with high stiffness are required for milling highstrength materials; however, the stiffness of a machine is not only the result of great mass but also the correct distribution. The ideal situation is a heavy, highly stiff design of all rigid masses and optimization of mass and stiffness of the moving components. If stiffness is lacking, the machine might be bent and lose precision. Vibrations can dramatically reduce the life and cutting the performance of the tools.
C 2014 by the American College of Prosthodontists Journal of Prosthodontics 23 (2014) 333–336
335
CAD/CAM Concept
Beuer et al
as dental technicians and especially production centers have to work well as a team and carry out the respective steps in the workflow with perfection; however, following the presented concept might be a suitable way to achieve precisely fitting, implant-supported bars with reasonable effort (Figs 6 to 8).
References
Figure 8 Panoramic radiograph showing the precise fitting of the bar on the implants.
High speed cutting (HSC) machining offers the essential advantage that during the milling process, the resulting heat is dissipated with the milling chips so that neither the work piece nor the mill will overheat. Highly precise tool holders (e.g., the TRIBOS system) enable clamping tools with the highest true-running accuracy. The following values can be stated as a benchmark for five-axis HSC machining equipment:
r r r r
±2 µm tolerance in the CAM software. The accuracy is achieved by multicore algorithms and limited by the performance of today’s computer technology (personal communication Martin Huber BSc, CadStar). ±1 µm positioning accuracy of the axis. ±6 µm overall machine precision. ±3 µm tool tolerance.
The stated values result in an overall precision of ± 12 µm for computerized numerical control (CNC) processing. The accuracy was verified and tested according to the Association of German Engineers VDI guideline 3441 “Statistical Testing of the Operational and Positional Accuracy of Machine Tools” (unpublished data).
Conclusion The production of precisely fitting bar structures with passive seating on implants through CAD/CAM methods can be precise and reliable only if all described steps of the work flow are precisely adhered to. Compromises in only one step can lead to a failure of the overall result. The probability of a serial addition of errors in the individual steps is higher than the probability of accidental, reciprocal canceling of errors. Dentists as well
336
1. Strong SM: Attachment-retained overdentures: the most cost-effective implant solution for the edentulous arch. Gen Dent 2009;57:112-117 2. Tan AS, Walmsley AD: Mandibular implant-retained overdenture with magnets: a case report. Dent Update 2004;31:104108 3. Krennmair G, Krainhofner M, Waldenberger O, et al: Dental implants as strategic supplementary abutments for implant-tooth-supported telescopic crown-retained maxillary dentures: a retrospective follow-up study for up to 9 years. Int J Prosthodont 2007;20:617-622 4. Krennmair G, Suto D, Seemann R, et al: Removable four implant-supported mandibular overdentures rigidly retained with telescopic crowns or milled bars: a 3-year prospective study. Clin Oral Implants Res 2012;23:481-488 5. Karl M, Graef F, Wichmann M, et al: Passivity of fit of CAD/CAM and copy-milled frameworks, veneered frameworks, and anatomically contoured, zirconia ceramic, implant-supported fixed prostheses. J Prosthet Dent 2012;107:232-238 6. Branemark PI: Rehabilitation and osseointegration in clinical reality. Int J Oral Maxillofac Implants 2003;18:770-771 7. Branemark PI: On looking back with Per-Ingvar Branemark. Interview. Int J Prosthodont 2004;17:395-396 8. Janousch R: Spannungsfreie suprakonstruktionen mit hilfe des passivierungstrays (Article in German). Dental Dialogue 2001;2:488-504 9. Weigl P: Implant prosthodontics: what next? Quintessence Int 2003;34:653-669 10. Weigl P, Lauer HC: Advanced biomaterials used for a new telescopic retainer for removable dentures. J Biomed Mater Res 2000;53:320-336 11. Beuer F, Schweiger J, Edelhoff D: Digital dentistry: an overview of recent developments for CAD/CAM generated restorations. Br Dent J 2008;204:505-511 12. Luthardt RG, Walter M, Quaas S, et al: Comparison of the three-dimensional correctness of impression techniques: a randomized controlled clinical trial. Quintessence Int 2010;41:845-853 13. Stimmelmayr M, Guth JF, Erdelt K, et al: Digital evaluation of the reproducibility of implant scanbody fit-an in vitro study. Clin Oral Investig 2012;16:851-856
C 2014 by the American College of Prosthodontists Journal of Prosthodontics 23 (2014) 333–336
