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Dental Tribune Middle East & African Edition Jan. 2015

Dental Tribune Middle East & Africa Edition | February 2015 39CLINICAL < Page 38 months after loading, the peri- implant tissues were healthy and no peri-implant marginal bone loss was observed (Fig. 3). Discussion The provision of ten- sion-free connections between implants and the prosthetic structures they support is a re- quirement for the medium- and long-term success of implant- supported rehabilitations. This situation can only be achieved by carrying out a prosthodontic treatment with good passive fit. Passive fit depends on all the clinical and laboratory proce- dures involved in fabricating the prosthesis being performed precisely and accurately, keep- ing the margins of error and inexactitude of each step in the process to a minimum (1,22). In vitro studies have shown that discrepancies in the super- structure will be the cause of stress on the implantsupported prosthesis and subsequent fail- ure. As long ago as 1986, Balshi described mechanical failures which he associated with labo- ratory work carried out using imprecise working models. Jemt et al. (8) and Rubenstein et al. (23) suggested that the fit be- tween prosthesis and abutment is a key parameter for avoiding overloading of the fixing screw which leads to prosthetic failure. For this reason, the taking of im- pressions is a fundamental step for obtaining structures with a good passive fit. There is some controversy in the literature as to which impression technique is the most reliable. Bearing in mind that with con- ventional techniques it is impos- sible to achieve a perfect passive fit, Lee et al. (6), in a literature review of the precision of im- pression techniques, found that 35% of the tests performed con- sidered the open tray technique to be the most precise, 15% the repositioning technique and 50% found no statistically sig- nificant differences between the two. As for the number of implants in relation to precision, with three or less implants there did not appear to any difference between techniques, while with four or more the open tray tech- nique was found to be recom- mendable (6). The greater accu- racy of the open tray technique is corroborated by Del´Acqua MA et al. (24), who studied aver- age discrepancy with each type of impression coping, this being 116.97 μm for repositioning cop- ings and 57.84 μm for open tray copings. The concept of photogramme- try consists of ‘metering what is written in light,’ in other words, obtaining reliable metric in- formation from photographs. The photogrammetry method extends the two-dimensional information provided by pho- tos into three dimensions;using various cameras, the shape of each of the photographic ob- jects and their location in space are reconstructed in relation to an external system of reference points. To make the necessary calculations for reconstruction, special cameras are required that are able to identify this sys- tem of reference points. Photogrammetry has been ap- plied in various areas of medi- cine (13,14) and dentistry (15- 19). In implant dentistry, it has been used in vitro research to test the reliability of other im- pression techniques (20). As ear- ly as 1999, Jemt and Bäck (21) described its use for registering the positions of dental implants intraorally. They compared this technique with conventional impression taking, concluding that photogrammetry offered a valid alternative. Since then the technical advances have been considerable but have not been accompanied by any develop- ment of the application of pho- togrammetry for the purposes of implant dentistry. The present article presents this new system for registering, simply and pre- cisely, the positions of multiple dental implants. Photogrammetry allows the registering of the exact three- dimensional locations of the im- plants, transferring all the infor- mation required to fabricate the prosthesis directly from the pa- tient’s mouth to a computer file. The technique avoids the in- convenience accompanying conventional impression tech- niques. There is no need for impression abutments, implant body analogues, trays and im- pression materials. The PIC- camera measures angles and distances between prosthetic attachments placed on the im- plants, allowing the patient to- tal freedom of movement and the presence of blood, saliva or any other organic or inorganic residue does not affect meas- urement precision. Avoiding so many procedures and materials reduces the possibility of error, saves time – both the number of visits to the clinic and their dura- tion – economic cost and patient discomfort in comparison with conventional impression taking procedures. Photographic and video scan- ners share some of the advan- tages of photogrammetry. Scan- ners generate 3D images on the basis of a cloud of points that are able to reproduce surfaces. To join the points they use an al- gorithm called Best-­fit®, which make as many points as possi- ble coincide. Although practical evidence is limited, theoreti- cally these successive unions of clouds of points could cause an accumulation of error. For this reason, reliability diminishes progressively according to the increasing number of implants analyzed (25). But in contrast with intraoral video and photo- graphic scanners, photogram- metry generates director vectors of the exact position of the im- plants in relation to one another. The information that makes it possible to calculate the posi- tions of the implants is obtained without superimposing pho- tos, which potentially provides greater precision and a better prosthetic fit. With the implant positioning de- termined by the PICcamera ®, and an alginate impression tak- en of the soft tissues, the labora- tory can fabricate the prosthetic structure using CAD/CAM, with- out the need for casting attach- ments or milling (26). In addi- tion, the technique described in the present article does not re- quire any impression materials or cast models, which inevitably undergo dimensional changes that will reduce the precision of the prosthesis (27). In this way, the combination of registering implant positions by photogram- metry and fabrication by CAD/ CAM can potentially reduce the risk of errors occurring during the production of the prosthetic structure. The clinical evaluation of pas- sive fit between implants and prosthetic structures is difficult and not very objective. Diverse methods for checking fit have been suggested, but none has been established as a stand- ard test. In the present case, the Sheffield test and the one-­screw resist- ance test were used to check fit. The Sheffield test has been shown to be an efficient clini- cal test of passive fit, especially in cases with multiple implants and extensive prosthetics. The screw resistance test has the dis- advantage of introducing sub- jectivity into the evaluation, but is considered a precise way of detecting discrepancies (28). Registering implant positions with the PICcamera improves patient comfort in comparison with conventional impression taking techniques. The tech- nique avoids the introduction of impression materials which must be kept in place in the mouth for an average setting time of 5-8 minutes and can pro- voke nausea and discomfort. Furthermore, the photogram- metry procedure can be inter- rupted if necessary and taken up again later on. The clinical application of this novel photogrammetry system for registering the positions of multiple implants allowed the rehabilitation of a patient with extreme maxillary free end edentulism with a prosthesis of optimal fit. The prosthetic fabri- cation process was precise, fast, simple for the dentist and com- fortable for the patient. References 1. Wee AG, Aquilino SA, Schnei- der RL. Strategies to achieve fit in implant prosthodontics: a re- view of the literature. Int J Pros- thodont. 1999;12:167-78. 2. Heckmann SM, Karl M, Wich- mann MG, Winter W, Graef F, Taylor TD. Cement fixation and screw retention: parameters of passive fit. An in vitro study of three-­unit implant-­supported fixed partial dentures. Clin Oral Implants Res. 2004;15:466-73. 3. Windhorn RJ, Gunnell TR. A simple open-tray implant im- pression technique. J Prosthet Dent. 2006;96:220-1. 4. Akça K, Cehreli MC. Accuracy of 2 impression techniques for ITI implants. The Int J Oral Max- illofac Implants. 2004;19:517-23. 5. Cehreli MC, Akça K. Impres- sion techniques and misfit-­ induced strains on implant- supported superstructures: an in vitro study. Int J Periodontics Re- storative Dent. 2006;26:379–85. 6. Lee H, So JS, Hochstedler JL, Ercoli C. The accuracy of implant impressions: a system- atic review. J Prosthet Dent. 2008;100:285-91. 7. Kachalia PR, Geissberger MJ. Dentistry a la carte: in-­office CAD/CAM technology. J Calif Dent Assoc. 2010;38:323-30. 8. Jemt T, Rubenstein JE, Carls- son L, Lang BR. Measuring fit at the implant prosthodon- tic interface. J Prosthet Dent. 1996;75:314-25. 9. Rubio Serrano M, Albalat Estela S, Pe-arrocha Diago M, Pe-arrocha Diago M. Software applied to oral implantology: update. Med Oral Patol Oral Cir Bucal. 2008;13:e661-5. 10. Freedman M, Quinn F, O’Sullivan M. Single unit CAD/CAM restorations: a lit- erature review. J Ir Dent Assoc. 2007;53:38-45. 11. Persson ASK, Andersson M, Odén A, Sandborgh-Englund G. Computer aided analysis of digitized dental stone replicas by dental CAD/CAM technology. Dent Mater. 2008;24:1123-30. 12. Park J-I, Yoon T-H. A three- dimensional image-superimpo- sition CAD/CAM technique to record the position and angu- lation of the implant abutment screw access channel. J Prosthet Dent. 2013;109:57-60. 13. Thali MJ, Braun M, Wirth J, Vock P, Dirnhofer R. 3D surface and body documentation in fo- rensic medicine: 3-D/CAD Pho- togrammetry merged with 3D radiological scanning. J Foren- sic Sci. 2003;48:1356-65. 14. Aroeira RMC, Leal JS, De Melo Pertence AE. New method of scoliosis assessment: prelimi- nary results using computer- ized photogrammetry. Spine. 2011;36:1584-91. Full list of references is available from the publisher. Fig. 3. A) Placement of the finished prosthesis; B) Radiographic check-up after 12 months. A B David Peñarrocha-Oltra Master of Oral Surgery and Im- plant Dentistry. Department of Dental Medicine, University of Valencia, Spain Rubén Agustín-Panadero Associate Lecturer in Prosthetic. Department of Dental Medicine, University of Valencia, Spain Leticia Bagán Collaborating Lecturer in Oral Medicine. Department of Dental Medicine, University of Valencia, Spain Beatriz Giménez Master of Prosthetics. PhD stu- dent. Department of Prosthetics, Complutense University of Ma- drid, Spain María Peñarrocha Full Lecturer in Oral Surgery. Department of Dental Medicine, University of Valencia, Spain About the Authors www.qualident-online.com

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