Computer Aided Diagnosis and Design of Implant Abutments

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1 Article submitted for publication to Journal of Prosthodontics David A. Felton Computer Aided Diagnosis and Design of Implant Abutments Jef M. van der Zel, PhD, MSc, Professor Computerized Dentistry Academic Center for Dentistry Amsterdam Universiteit van Amsterdam and Vrije Universiteit Abstract Purpose: Minimal invasive implant therapy has recently gained a growing interest as a standard prosthodontic treatment, providing complete restoration of the occlusal function. A new treatment method (CADDIMA) is recently developed which combines both CT- and optical laser-scandata for planning and design of surgical guides, implant abutments and prosthetic devices. In this article the new procedure for minimal invasive implant prosthodontics is described, explained and evaluated for a single clinical case with regard to reproducibility of the drill hole angulation using geometric matching of cone beam Head-CT and optical imaging data. Methods: A NewTom 3G cone beam CT-scanner (QR s.r.l., Verona, Italy) and a modified lasertriangulation scanner D200c (3Shape A/S, Copenhagen Denmark) were used for imaging. An impression with 3 markers was placed in the patient during CT-scanning and on the gypsum model during optical scanning, so that the surface of mucosal tissue with remaining dentition and antagonists could be observed in a combined 3Dview with the bone structure in the region of interest by the operator using Cyrtina CAD software (Oratio B.V., Hoorn The Netherlands). Surgical guides (N=5) were designed and produced for both the pilot and the final drill. Results: The positioning of the implant in a virtual cross-sectional view with mucosa and antagonists resulted in an snap-fitting drillguide supported by mucosa and dentition and eliminates the traditional flap surgery by limiting the intrusion size to the diameter of the implant. The difference between the planned and placed implant abutment orientation was within 4.3 o (± 2.96 o (N=5)). Conclusion: The new approach gives the operator full control over the design of the implant prosthondontics for planning of proper occlusal relations and shows promise for further evaluation.. This study was financially supported by a grant TSIT2020 from SenterNovem, The Hague, The Netherlands INDEX WORDS: Dental CAD/CAM, stereolithographic guides, guided implantology. The results of this study were presented at the joint meeting of the Continental European Division (CED) and the Scandinavian Division (NOF) of the IADR on September 15 th 2005 at the RAI Congress Centre Amsterdam, The Netherlands, Abstract No

2 Introduction Implantation, the optimal aesthetic and functional restoration has been available for many years, but not as convenient and accessible as at this moment. In recent years, dental implant rehabilitation has faced demands from prosthetic and esthetic arenas that call for increasingly ideal outcomes, which require precise surgical planning and placement. Implant dentistry has evolved into one of the most predictable treatment alternatives in dental clinical science. Versteken et al. (1) recognized that a planning system for oral implant surgery based on a true three-dimensional approach allows the interactive placement and adjustment of axialsymmetric models representing implants in the jawbone structures visible on computerized tomographic volume data and outperforms the manual planning practice based on twodimensional dental computerized tomographic images printed or on film. Versteken et al (2) then developed a preoperative planning system for oral implant surgery which takes as input computed tomographies (CT's) of the jaws. A technique was developed for scanning and visualizing an eventual existing removable prosthesis together with the bone structures. The benefits of a 3-D approach are then evident where a prosthesis is involved in the planning. Massey etal (3) analyzed implant placement in the posterior maxilla and concluded that only 20% of implants placed by implantologists could be classified as ideal with regard to orientation. Sarment et al (4) describes a computer-aided design and manufacturing method that makes it possible to use data from computerized tomography to not only plan implant rehabilitation, but also to transfer this information to the surgery. The technique uses stereolithography, a laser-driven polymerization process that fabricates an anatomic model and surgical templates. This novel approach is illustrated with two advanced cases, demonstrating that the technique not only allows for the precise translation of the treatment plan directly to the surgical field, but also offers many significant benefits over traditional procedures. Tardieu et al (5) present a case of immediate loading of mandibular implants using a 5-step procedure. The first step consists of building a scannographic template, the second step consists of taking a computerized tomographic (CT) scan, and the third step consists of implant planning using SurgiCase software. The final 2 steps consist of implant placement using a drill guide created by stereolithography and placement of the prosthesis. Using a CT scan-based planning system, the surgeon is able to select the optimal locations for implant placement. By incorporating the prosthetic planning using a scannographic template, the treatment is optimized from a prosthetic point of view. Furthermore, the use of a stereolithographic drill guide allows a physical transfer of the implant planning to the patient's mouth. The scannographic template is designed so that it can be transformed into a temporary fixed prosthesis for immediate loading, and the definitive restoration is placed 3 months later. This article describes a newly developed implant procedure CADDIMA (Computer Diagnosis and Design of Implant Abutments) to be used to virtually place dental implants and construct a precise guide splint and temporary prosthesis for delivery at the time of implant placement.. The therapy was developed to improve surgical and restorative accuracy, allowing for predictable placement of implantprosthetics taking account of loading of implants through use of CT imaging, laseroptical imaging, stereolithographic guides and individualized prosthetic restoration design. The software allowes precise planning for implant placement after which the planned case is sent to a manufacturing facility for splint and prosthesis construction. The guide splint and final prosthesis are returned to the clinical site for implant placement. The objective of this work is also to evaluate the effectiveness of combining an optical imaging method and CT-scanning, so-called: geometric matching for implant planning, hole drilling, implant placement and custom prosthetic restoration design by an integrated software package.a clinical case study was used to demonstrate the possibilities of the new computer aided implant planning and placement therapy, explains the new procedure 2

3 and shows the diagnostic and design features of the Cyrtina CAD software package (Oratio B.V., Hoorn, The Netherlands). Materials and methods The treatment procedure consists of four phases: - Scanning phase: optically scan marker plate, checkbite and model and computerized tomographic scan with marker plate; - Planning phase: implant planning after geometric matching of the scans; - Surgical phase: drilling of the implant hole using a stereolithographic surgical guide; - Restorative phase: placement of the implant, abutment and prosthetic device. Instead of performing the procedure by different partners, the procedure can be also be handled by the same general practioner from scan diagnostics until the final reconstruction. Co-operation between the different partners can however be important to achieve an optimal clinical as well as esthetical result. Careful planning can avoid bone grafts in some cases. Optical scanning An impression is made of the implant jaw as well as a registration bite of the opposing jaw. A scannographic guide is produced over the gypsum cast and markers, in this study alumina balls of 4 mm diameters are adhesively fixed to the guide. Fig. 1. D200c laseroptical scanner A modified lasertriangulation scanner D200c (3Shape A/S, Copenhagen, Denmark) was used for high accuracy optical scanning (Figure 1) of the gypsum surface, the reference markers on the scanguide, the gysum cast of the implant jaw and an antagonist registration bite. The optical scan technique has been described previously (9). The accuracy of the modified laseroptical scanner is within 10 micrometers. Using optical scandata of the mucosa and remaining dentition in stead of CT scandata enables a more precise reconstruction of the supporting side of the drillguide resulting in a stable seating of the surgical guide during transmucosal drilling of the implant hole. 3

Fig. 2. Gypsum cast of mandible Fig. 3. Check bite of antagonists The gypsum cast was scanned with and without the registration bite in place (Figure 2).

Fig. 4. Scannographic guide on model. Fig. 5. Scannographic guide in patients mouth.

4). The scannographic guide is reproducibly fitted in the mouth in a position that was found when fitting the guide on the model (Figure 5). 3D CT scanning A NewTom 3G cone beam CT-scanner (QR s.r.l., Verona, Italy) was used for imaging of the bone (Figure 6).

4 Fig. 2. Gypsum cast of mandible Fig. 3. Check bite of antagonists The gypsum cast was scanned with and without the registration bite in place (Figure 2).The surface of mucosal tissue with remaining dentition and a registration bite with an impression of the antagonists are optically scanned. Black-white contrast is used for convenience (Figure 3). Fig. 4. Scannographic guide on model. Fig. 5. Scannographic guide in patients mouth. A scannographic guide with 3 markers was placed in the patient during CT-scanning and on the gypsum model during optical scanning to obtain a combined 3D-view of the Region of Interest (ROI) (Figure 4). The scannographic guide is reproducibly fitted in the mouth in a position that was found when fitting the guide on the model (Figure 5). 3D CT scanning A NewTom 3G cone beam CT-scanner (QR s.r.l., Verona, Italy) was used for imaging of the bone (Figure 6). Axial slices are generated in the 3D jaw bone structure (Figure 7). The basis for the clinical patient data is a computertomogram (CT), made at a CT scan center. The dentist supplies the CT scan center surgical and prosthetic plan data that can be important for the generation of the CT scan, e.g. slice thickness and format of the data. In this study a slice distance of 200 micrometers was used. The CT data were stored on a CD-ROM or send as attachment by in DICOM3 format. Further processing is done with a newly developed viewer and planning software package. The NewTom is one of a new generation of cone-beam CT scanners that allow us to obtain 3-D information, including cross-sectional views of proposed implant sites, at a relatively low radiation dose. Some orthodontists are using this type of imaging to replace the usual 4

panoramic and cephalometric views. It delivers threedimensional information about the horizontal and vertical build-up of the jaw bone.

The radiation effective dose for a full-head NewTom image is the equivalent of about four to six panoramic radiographs, depending on whether the salivary glands are counted separately or not.

A 3D-view of mandible showing region of interest and position of nervus alveolar inferior (Figure 8).

An overview of the sections of the mandible (l) and a 3D-view of of the nervus alveolar inferior.

5 panoramic and cephalometric views. It delivers threedimensional information about the horizontal and vertical build-up of the jaw bone. The CT data are distortion corrected (1:1) and allow assessment of bone density, delineation of critical structures. There is some published information on radiation doses from the NewTom (6). The radiation effective dose for a full-head NewTom image is the equivalent of about four to six panoramic radiographs, depending on whether the salivary glands are counted separately or not. To put this into perspective, the cone-beam CT requires times less radiation than a conventional CT scanner. Fig. 6. NewTom 3G Cone Beam CT-scanner. Fig. 7 Axial view sliced. A 3D-view of mandible showing region of interest and position of nervus alveolar inferior (Figure 8). Clearly visible is the thick mucosal tissue layer at the Region Of Interest (ROI) for implant placement. Fig. 8. An overview of the sections of the mandible (l) and a 3D-view of of the nervus alveolar inferior. Implant planning A virtual implant is chosen from a range of implant options varying in lengths, diameters and manufacturer options. The virtual implant is then placed in the optimal position according to the critical information defined by inter-maxillary relations, designated critical structures, and the 3D and cross-sectional views. In partial or completely edentulous cases, the software can ensure that the implants are placed parallel to each other according to the required prosthetic configuration, thereby guaranteeing optimal post-operative rehabilitation. 5

6 The patient is informed of the objectives and outcomes of the treatment following the planning stage. This educational process, using state of the art technology, results in greater comprehension by the patient, who is consequently less anxious and more cooperative. Because the operator will see the bone scan and the antagonist- and mucosal surface in one view, the implant can be placed in line with the direction of loading by chewing forces. This unique feature makes planning of a specified implant a reassuring activity, knowing that the prosthetic device on the implant that occludes with the antagonist will have a predictable occlusal loading. It also enables the design of a prosthetic device in occlusion, which can be placed as a temporary restoration first and after a healing period be replaced by a permanent restoration. Fig. 9. CADDIMA planning stage. In Figure 10 a virtual surgical guide is shown on the jaw with the planned implant in position (left). Also shown is the inside of the surgical guide obtained by optical scan of the gypsum model (right). D Fig. 10. Virtual surgical guide on model (D=drill depth). Drill guide inside optically scanned surface (right). Through a combination of high accuracy optical surface digitization of the implant jaw with a controlled design of the cervical and mucosal bounderies are designed to give maximum stability during drilling. 6

Fig. 11. Surgical guide on model with final 3,6mm drill. Fig. 12. Surgical guide seated in patient s mouth. Based on the drilling sequence of the Helix implant (Dyna Dental Engineering B.V.

Before starting the drills are checked whether they will pass easily through the hole until the level of the physical stop on the drill or the hand piece.

7 Fig. 11. Surgical guide on model with final 3,6mm drill. Fig. 12. Surgical guide seated in patient s mouth. Based on the drilling sequence of the Helix implant (Dyna Dental Engineering B.V. Bergen op Zoom, The Netherlads), two customized surgical guides were produced to accommodate a pilot and an end drill. Before starting the drills are checked whether they will pass easily through the hole until the level of the physical stop on the drill or the hand piece. The surgical guide produced by stereolithography fits perfectly on the work model (Figure 11). The surgical guide is positioned in the patient s mouth (Figure 12) in a unique and stable position with a snap-fit, in order to transfer the pre-operative treatment plan. No drilling cylinders were used, because the drills only cut at the tip of the drill. The drill depth D (Figure 10) as well as the implant placement control depth are pre-operatively incorporated in the design of the height stop of the surgical guide at the implant insertion hole. The hole is drilled until the drill touches the guide. In some situations the guide might be fixed to the jaw by using small osseosynthesis screws. As only one guide will be used for the complete implant placement, including drilling and the actual placement, the final positioning of the surgical guide is extremely important. The use of a trephine with the same diameter as the final drill is recommended, especially when appreciable amount of keratinized tissue is present at the implant site. Prosthetic design After the abutment has been fixed to the implant with a fixing screw (Figure 13) a temporary restoration in functional contact (7,8,9) with the antagonist is cemented with temporary cement (Figure 14). 7

Fig. 13. Abutment on implant. Fig. 14. Crown (temporary/final) in occlusion. After a healing period the temporary can be replaced by the permanent restoration.

For this purpose the appropriate implant and final drill with regard to diameter and length are introduced into the dataset.

An implant was screwed in the drilled hole and a straight circular zirconia abutment was screwed into the implant using a torque of 35 Ncm. (Figure 15).

8 Fig. 13. Abutment on implant. Fig. 14. Crown (temporary/final) in occlusion. After a healing period the temporary can be replaced by the permanent restoration. In-vitro model study Five surgical guides were produced for both the pilot and final drill with respectively 1.5 and 3.6 mm diameter were used. For this purpose the appropriate implant and final drill with regard to diameter and length are introduced into the dataset. Holes were drilled through the drill guide in a gypsum model using a pilot drill and a final drill consecutive. An implant was screwed in the drilled hole and a straight circular zirconia abutment was screwed into the implant using a torque of 35 Ncm. (Figure 15). Then a cylindrical zirconia coping was placed on the abutment with a temporary cement (Figure 16). Then the direction and position of a cylindrical zirconia abutment was optically scanned. Helix implants (Dyna Dental Engineering B.V., Bergen op Zoom, The Netherlands) were used. Fig. 15. Cyrtina abutment on implant on model. Fig. 16. Cyrtina coping on abutment on implant. The gypsum model was scanned with the abutment and coping on the model and repeated with the scannographic guide (fig. 4) on the model. This way the difference between the 8

9 planned and placed direction could be determined. The difference between the planned and placed implant abutment orientation was within 4.3 (S.D. 2.96) degrees (N =5). Discussion Van Steenberghe et al. (10) assessed the accuracy of surgical drilling guides for placement of implants based on three-dimensional computerized tomography (3D-CT) data for the maxillary-zygomatic complex by matching the preoperative CT images with postoperative ones in order to assess the deviation between the planned and installed implants. The angle between the planned and actually placed implants was < 3 degrees in four out of six cases. Di Giacomo et al (11) evaluated the match between the positions and axes of the planned and clinically placed implants with a stereolithographic surgical guide and found the match to be within 7.25 degrees +/ degrees. Sarment et al ( 12) compared the accuracy of a conventional surgical guide to that of a stereolithographic surgical guide. He used a cone beam CT scanner and epoxy edentulous mandibles, planning for 5 implants on each side of the jaw was performed using a commercially available software package. The average distance between the planned implant and the actual osteotomy was 1.5 mm at the entrance and 2.1 mm at the apex when the control guide was used. The same measurements were significantly reduced to 0.9 mm and 1.0 mm when the test guide was used. Within the limits of this study, the results obtained are in line with the studies discussed above and provide enough grounds for further clinical investigations. Conclusion In the new procedure, which is aimed at experienced implant practitioners and novice dentists alike, the clinician uses a snap-fit surgical guide to navigate the implant to an orientation within 5 o of the orientation according to the plan. This presurgical planning procedure with a virtual cross-sectional view together with a view of the antagonist jaw and the mucosal surface allows fabrication of a provisional fixed prosthesis before the implant surgery for immediate postoperative loading, because it gives the operator full control over the design of the implant prosthesis for planning of proper occlusal relations. This innovative protocol can enhance prosthodontic-driven placement of implants in a fully monitored flapless surgery. Acknowledgement I gratefully acknowledge the support from Mr. Siebe van der Zel, MSc and Mr.Simon Vlaar, BSc, Oratio B.V., Hoorn, The Netherlands for supplying the surgical guides and abutments and Dyna Dental Engineering B.V., Bergen op Zoom, The Netherlands for supplying the implants. 9

10 References 1. Verstreken K, Van Cleynenbreugel J, Marchal G, Naert I, Suetens P, van Steenberghe D. Computer-assisted planning of oral implant surgery: a three-dimensional approach. Int J Oral Maxillofac Implants Nov-Dec;11(6): Verstreken K, Van Cleynenbreugel J, Martens K, Marchal G, van Steenberghe D, Suetens P. An image-guided planning system for endosseous oral implants. IEEE Trans Med Imaging Oct;17(5): Massey BC, Alder ME. Analyzing Implant Placement in the Posterior Maxilla. J Dent Res 2002; Abstr Sarment DP, Sukovic P, Clinthorne N. Accuracy of implant placement with a stereolithographic surgical guide. Int J Oral Maxillofac Implants Jul- Aug;18(4): Tardieu PB, Vrielinck L, Escolano E. Computer-assisted implant placement. A case report: treatment of the mandible. Int J Oral Maxillofac Implants Jul- Aug;18(4): Ludlow JB, Davies-Ludlow LE, Brooks SL. Dosimetry of two extraoral direct digital imaging devices: NewTom cone beam CT and Orthophos Plus DS panoramic unit. Dentomaxillofac Radiol 2003;32: Van Steenberghe D, Malevez C, Van Cleynenbreugel J, Serhal CB, Dhoore E, Schutyser F, Suetens P, Jacobs R. Accuracy of drilling guides for transfer from threedimensional CT-based planning to placement of zygoma implants in human cadavers. Clin Oral Implants Res Feb;14(1): Olthoff LW, van der Zel JM, de Ruiter WJ, Vlaar ST, Bosman F: Computer modeling of occlusal surfaces of posterior teeth with the CICERO CADCAM system, J Prosth Dent, 2000;84, 2: Van der Zel JM, Vlaar S, De Ruiter WJ, Davidson CL: The CICERO system for CADCAM fabrication of full-ceramic crowns, J Prosth Dent 2001;85, 3: Van der Zel JM, Bites for the Computer, ISBN , Vossiuspers, University of Amsterdam, Amsterdam, Di Giacomo GA, Cury PR, de Araujo NS, Sendyk WR, Sendyk CL Clinical application of stereolithographic surgical guides for implant placement: preliminary results. J Periodontol Apr;76(4): Sarment DP, Al-Shammari K, Kazor CE. Stereolithographic surgical templates for placement of dental implants in complex cases. Int J Periodontics Restorative Dent Jun;23(3):

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