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Dental Tribune Middle East & African Edition Jan.-Feb. 2015

38 DENTAL TRIBUNE Middle East & Africa Edition | January-February 2015clinical Impression of multiple implants using photogrammetry: Description of technique and case presentation By David Peñarrocha-Oltra, Rubén Agustín-Panadero, Le- ticia Bagán, Beatriz Giménez, María Peñarrocha A bstract Aim: To describe a tech- nique for registering the positions of multiple dental implants using a system based on photogrammetry. A case is presented in which a prosthetic treatment was performed using this technique. StudyDesign:ThreeEurotekni- ka®dentalimplantswereplaced to rehabilitate a 55-year-old male patient with right posterior maxillary edentulism. Three months later, the positions of the implants were registered using a photogrammetry-based stereo-camera (PICcamera®). After processing patient and implant data, special abutments (PICabutment®) were screwed onto each implant. The PICcam- era® was then used to capture images of the implant positions, automatically taking 150 images in less than 60 seconds. From this information a file was ob- tained describing the relative positions – angles and distances – of each implant in vector form. Information regarding the soft tissues was obtained from an alginate impression that was cast in plaster and scanned. A Cr-Co structure was obtained using CAD/CAM, and its passive fit was verified in the patient’s mouth using the Sheffield test and the screw resistance test. Results and Conclusions: Twelve months after load- ing, peri-implant tissues were healthy and no marginal bone loss was observed. The clinical application of this new system using photogram- metry to record the position of multiple dental implants facili- tated the rehabilitation of a pa- tient with posterior maxillary edentulism by means of a pros- thesis with optimal fit. The pros- thetic process was accurate, fast, simple to apply and comfortable for the patient. Key words: Dental implants, photogrammetry, dental impres- sion technique, CAD/CAM. Introduction Dental implants are one of the most widely used therapies for the rehabilitation of partially or completely edentulous patients. It is scientifically proven that achieving proper passive fit of the implant-­supported prosthe- sis improves the long-term prog- nosis of this therapy (1-5). The classic system for fabricat- ing implant-supported prosthe- ses involves taking impressions, and after placement of the im- plant analogues, subsequent casting in plasterto makeim- pression transfers. In order to achievean adequate passive fit of the prosthesis, the first step must be to obtain a correct regis- tration of the three-dimensional position of the implants (6). Conventional impression tech- niques use abutments that, screwed onto the implants’ prosthetic platforms and en- compassed by setting material, should register and transfer the spatial position of the implant. These methods involve time- consuming clinical work and the use of impression materials and techniques that often fail to achieve a perfectly accurate master cast. Moreover, these techniques are generally un- pleasant for the patient (7,8). The literature reflects the in- creasing application of digital techniques at different stages of dental implant therapy (9). At the stage when impressions are taken, intraoral scanners are being introduced into clinical practice.The technique avoids the need for registering implant positions with impression mate- rials and plaster modelsand so avoids the slight dimensional distortions that these materials can causeand ensuresprecision when it comes to reproducing intraoral dimensions (7,10-12). These instruments are a prom- ising alternative for obtaining direct intraoral impressions in a fast and comfortable way for the patient. However, they are not indicated for implant rehabili- tations requiring more than 3-4 pieces. Photogrammetry is a novel op- tion for reliable, direct intraoral registration of the positions of multiple implants. It is a tech- niquefor determining the geo- metrical properties of objects and their spatial arrangement from photographic images. Its most important feature is the precision with which it can measure objects without direct contact. Photogrammetry is useful in many sciences and fields. It has been applied mainly to topogra- phy, but there are many non-top- ographic applications, including different areas of medicine such as radiology (to improve accu- racy), surgery (neurosurgery, plastic surgery, sinus surgery) or rehabilitation (13,14). In dentistry, this technique has been used to study the shapes and positions of teeth, dental arches and maxillary and man- dibular bones. In orthodontics, it allows the three-dimensional analysis of the variations of the palate while performing rapid palatal expansion techniques and evaluating the achieved dental movement (15-18). Re- cently, its application in dental implant surgery planning has also been reported (19). In the field of implant dentistry, it has been used to check the ac- curacy of other impression tech- niques, by analyzing the differ- ences between models obtained using different techniques and materials (20). As long ago as 1999, Jemt and Bäck (21) pro- posed photogrammetry as an alternative to conventional im- pression taking but since then no development of this applica- tion has been reported. The most important quality of this technology - measurement accuracy - is the key to success in implant impressions. Therefore, its application may be a very useful technique that will improve dental implant therapy. The aim of this report is to de- scribe this technique applied to record the position of multiple dental implants using a system based on photogrammetry. A case is presented in which a prosthetic treatment was per- formed successfully using this technique. PICcamera® The PICcamera® (PICdental, Madrid, Spain) is a stereocam- era that records implant posi- tions in the mouth by means of photogrammetry. It comprises two CCD cameras specially de- signed and optimized for clinical use, which accurately determine the position of the implants by means of the identification of abutments screwed on implants with unique individual coding (PICabutment®, PICdental). The camera has an infrared flash that constantly illuminates the scanned object while elimi- nating the shadows that occur with ambient light. The PIC- camera® needs to capture 50 three-dimensional photographs for every two PICabutment®. To do this, it automatically takes ten extraoral pictures per sec- ond with an error of less than 10 microns. The registered angles and distances between implants are interrelated and treated as a unit. System software calculates av- erage angles and distances between implants from these photographs, obtaining an ac- curate relative position of each implant in vector format. This is the PICfile® (PIC Dental), which contains all the information on implant positions, geometries, connections, healing abutments and screws that are later re- quiredby CAD/CAM software. Clinical Procedure A 55-year old male with no rel- evant medical history came to the Oral Surgery Unit of the University of Valencia request- ing the rehabilitation of hised- entulous right maxillary poste- rior region with dental implants. After checking the presence of enough residual alveolar bone height by means of a panoramic radiograph, three Euroteknika® (Euroteknika Iberia, Barcelona, Spain) implants were placed of 4.1 mm in diameter (Fig. 1). Three months later, the position of the implants was registered using the PICcamera® (PICden- tal). Firstly, the patient’s demo- graphic and medical data were entered into the system. Then, the positions and the references of the implants (manufacturer, model, platform diameter, di- ameter and height of the heal- ing abutments), and the code of each PICabutment® were in- troduced. The PICabutments® were screwed onto each implant (Fig. 1), and the PICcamera® was placed 15-­30 cm away from the patient’s mouth with a maxi- mum angle of 45º with respect to the PICabutments®. Once the camera had detected that the position was correct, it automatically captured 50 three-dimensional photographs foreach two attachments. For this clinical case, 150 pictures were taken in less than 60 sec- onds to obtain the relative posi- tion of each implant (angle and distance) in vector format. This information was automatically compiled into a vector PICfile® (PIC-dental). The healing abutments were placed and an alginate im- pression was taken and cast in plaster. The plaster model was scanned with a 3D scanner in open STL format to obtain infor- mation regarding the patient’s soft tissues (Fig. 1). This infor- mation was then introduced in the CAD software together with the PICfile®. The PICfile® and the digitized plaster model were aligned with the Exocad® software (Exocad GmbH, Darmstadt, Germany) using three-point registration and subsequently improved alignment by Best-­fit® (Fig. 1). This process transferred the relative position between im- plants to the digital model which provided the shape of the soft tis- sues, thus leaving the interfaces of the future prosthesis in rela- tion to the patient’s gingiva (Fig. 1). A model of the antagonist arch was also scanned,entered in the CAD software to provide occlus- al references, and the prosthetic structure was designed using Exocad® (Exocad, GmbH) in STL format (Fig. 2). The design was sent to be machined in chrome-cobalt (Cr-Co) by a five-­ axis milling machine (Fig. 2). To build a working model, the digital model was processed providing the specific geome- tries of the implant connections (Fig. 2) and it was manufactured by means of stereolithography using a 3D printer (Objet 250® Eden, Israel). The model was processed in a manner that al- lowed the addition of false gum for further work in the labora- tory (Fig. 2). Once the internal structure of the implant-supported fixed par- tial denture had been fabricated, its passive fit was checked in the patient’s mouth. The Sheffield and one-screw tests were used: a distal screw was placed–with the screw at 14 in this case - and a periapical radiograph was ob- tained to check the correct pros- thetic settlement on the other two implant connections (Fig. 2). The screw resistance tech- nique was used as a subjective omplementary test of the pas- sive fit. Distal screws (at 14 and 17) were screwed with a torque of 10 Ncm and then a medial screw was introduced verifying that the tactile sensation was soft and presented no resistance to screwing. After these verifica- tions, the Cr-Co structure was sent to the laboratory to have the ceramic loaded. The prosthesis,once finished, was screwed onto the implants (Fig. 3), with 25 Ncm torque. Occlusal adjustments were performed and the correct set- tlement on the implant con- nections was verified with a radiograph (Fig. 3). A follow-up plan was established and twelve Fig. 1. A) View at three months after the placement of three implants in the first quadrant;; B) Attachments (PICabutment®) with unique individual coding screwed onto implants; C) Digitized plaster model; D) Alignment by means of Best-­fit®from the PICfile® vector file and digi- tized plaster model; E) Relative interface positions of the future prosthe- sis in relation to the gums. Fig. 2. A) Upper and lower plaster models and design of the prosthetic structure; B) Machined metal structure in Cr-Co; C) Digital working model; D) Sterolithography working model with false gums; E) Check- ing the metal structure in the mouth; F) Periapical radiograph during the Sheffield test. > Page 39 A B C D E A B C D E F

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