I case report _ CAD/CAM The treatment of toothless jaws A case for CAD/CAM

Author_Dr Sven Rinke, Germany

_Prosthetic devices can be fittedin various ways. _Subjective criteria (patient satisfaction and quality Digital technologies have made their mark in implan- of life); tology for quite a while, and they provide options for _Objective criteria (probability of survival); and quality solutions. Classical indications for implant- _Necessary maintenance effort during the lifetime of prosthetic treatments include dentures for the tooth- the denture. less jaw. For this type of dentures, clinical studies doc- ument a high survival rate of about 85 to 90 % (Attard _Criterions for the selection of the type et al. 2004a, Attard et al. 2004b) with observation of denture periods of up to 20 years. Fixed as well as removable implant-prosthetic According to the number of the inserted implants, dentures in the toothless jaw, as opposed to the con- various prosthetic concepts have established them- ventional full denture, have proven to significantly selves for the fitting of supraconstructions (Zitzmann increase the patients’ satisfaction and to improve the and Marinello 2002). Generally, there is either a fixed ability to chew (Raghoebar et al. 2003, van der Bilt denture mounted on six to eight implants and borne 2006). This means that already the insertion of two to by these only, or a removable denture with a reduced four implants can lead to a clear improvement of the number of implants. quality of life. Therefore, the removable implant-sup- ported and implant-retained coverdenture prosthe- The decision process for the selection of a suitable sis is nowadays considered an effective therapy. How- denture depends, on the one hand, on subjective cri- ever, there was also evidence that, in particular, the teria (patient’s expectations, financial conditions) choice of fitting elements (magnets, ball-heads, and, on the other hand, clinical aspects (anatomic cri- bridges, telescopes) in a removable denture has an in- teria, technical and clinical reliability of implants and fluence on patient satisfaction. A comparative cross- supraconstruction). Accordingly, the success of the over study has shown that, with respect to stability prosthetics depends on these factors (Fig.1): and retention power as well as the achievable patient satisfaction, magnets are inferior to the fitting with ball-heads (Burns et al. 1995a, Burns et al. 1995b). A Fig. 1_Subjective and objective comparison of ball-head elements and over-denture prosthetic success criterions. attachments used for the fitting of an implant-re- tained Coverdenture prosthesis did not show any dif- ferences in terms of patient satisfaction (MacEntee et al. 2005); however, there proved to be a significant difference in the rate of technical complications. Within an observation period of three years, prosthe- sis fitted with ball-heads required 6.7 repairs, whereas the group of bridge-fitted prosthesis re- quired 0.8 repairs per patient only. Hence, overden- Fig. 1 ture attachments as fitting elements for removable implants 16 I 1_2010 case report _ CAD/CAM I

Fig. 2 Fig. 3 Fig. 4 Fig. 5 supraconstructions guarantee high patient satisfac- processes), and secondly, defect causatively con- Fig. 2_Fracture of a bar attachment tion. Thanks to their low rate of technical complica- nected with the design of the supra-construction. construction manufactured by cast- tions, they require less maintenance effort than alter- ing, in the area of the extension. native fitting elements (MacEntee et al. 2005), which For the fitting of attachments in the toothless up- Fig. 3_Casting of the implants in the is an important criterion for the long-term success of per jaw, the literature describes two versions. The fit- pick-up technique with a high- the prosthesis. High maintenance requirements re- ting of attachments on four implants in the anterior strength casting material. quire more practice visits and take the time of both, segment, and the fitting of two attachments on three Fig. 4_Tooth arrangement produced the patient and the care provider. Further, if there are to four implants on the lateral segments of the tooth- on the work model. technical complications that have led to the failure of less upper jaw (mostly after a previous sinus floor aug- Fig. 5_Virtual construction of the bar supra construction elements, an intervention by a mentation). Also for the application of attachments in attachment construction with distal dental technician might be needed for the new con- the toothless upper jaw data from clinical studies have attachments. struction or the replacement of individual compo- been published (Krennmair et al. 2008). Both attach- nents. This is also connected with further costs in ment concepts featured almost identical survival rates order to maintain the function. after five years—98.4 % for the attachments in the an- terior segment, and 97.4 % for the attachment fitting When evaluating overdenture attachment con- on six to eight implants in the lateral segments of the structions as fitting means, consideration must be upper jaw. given to the various types and forms there are. On the one hand, there are individually shaped bar attach- In particular the fitting by bar attachments seems ments, and on the other hand, there is the classic to be a therapy means with guaranteed success for the round bar, which can be manufactured either by cast- fitting of purely implant-supported coverdenture ing or by combination of pre-fabricated elements. prosthetics in the upper and lower jaw. It excels with a low rate of technical complications and, with that, low The overdenture attachment sitting on four im- maintenance requirements. Hence, bar attachments plants is a classic fitting element for a purely implant- constitute clinically tested fitting elements for im- supported coverdenture prosthesis in a toothless plant-retained and implant-fitted removable supra- upper or lower jaw. A retrospective study with 51 pa- constructions in the toothless upper and lower jaw. tients compared individually shaped bar attachments Clinical data for the fitting of removable supra-con- and round bars for the fitting of coverdenture pros- structions in the toothless upper jaw are missing for theses (Krennmair et al.2008). 26 patients were magnets as well as for ball-head attachments. Also the equipped with round bars, while 25 patients received application of so-called locators for the fitting of re- a supraconstruction with an individual bar attach- movable implant supraconstructions cannot be con- ment, on four implants each. After a surveillance pe- sidered to be based on evidence, according to the cur- riod of five years, the survival rate of the implants was rent data provided, as no results of clinical studies have 100 %. Larger technical complications, which required been presented by now for this fitting element. a renewal of the mounting elements, occurred in the round bars only, in form of fractures in the extension Telescopes as fitting elements for removable areas. The fractures on the extensions of the overden- supraconstructions are popular particularly in the ture attachments, which were exposed to high me- German-speaking countries, as they are very hygienic chanical stress, were due either to porosities in the cast and easy to expand. However, these advantages are object, or to inhomogeneities in the area of the points opposed by the high technical requirements and costs of attachment. Further, it was determined that low- at manufacture. Clinical studies on the suitability of grade complications (activation of hanks) would come double crowns as fitting elements in implant pros- up three times as often in the round bars as in the bar thetics show that they are generally suitable, and they attachments. Basically, two causes of defects can be point out the advantage of combining the natural derived from that: Firstly, defects due to faults in the teeth with implants for the fitting of a removable con- manufacturing technique (casting and joining struction, as opposed to attachments. implants 1_2010 I17 I case report _ CAD/CAM

Fig. 6 Fig. 7 Fig. 8

Fig. 6_Compartis ISUS bar attach- _Optimising the manufacturing In-vitro examinations with this CAM technology ment made of pure titanium; the at- technology showed that the precision achievable in such con- tachment could be inserted without structions, with median gap widths between 20 and manual after-processing. Despite of the high and well documented survival 30 µm is better than the accuracy of fit achieved with Fig. 7_Completed implant-retained rates of attachment constructions, the question arises cast frames made of noble metals (Takahashi and prosthesis for the lower jaw. whether the strategies can be further optimised in or- Gunne 2003). Modern scanning and software tech- Fig. 8_Good fit with a CAD/CAM pro- der to avoid defects attributable to the technique. The nology allows expanding this manufacturing princi- duced attachment construction made traditional way of manufacturing attachment con- ple also to the area of the virtual construction. Hence, of pure titanium. structions is by casting. However, the larger the cast the already well-known process of CNC cutting is sup- object, the more problems use to arise in terms of plemented with the option of a purely virtual con- porosity and warpage which, on the one hand, in- struction. Meanwhile there are several manufacturers crease the risk of mechanical failure and, on the other offering this technology (e.g. Compartis ISUS of hand, impair the proper fit (Jemt et al.1999; Fig. 2). DeguDent).

Relatively early, the well-known casting problems _Case presentation have led to the establishment of alternative tech- niques. The application of pre-fabricated implant The manufacturing process is documented below components, which then were mated by means of sol- on the example of an attachment utilising the Com- dering or laser welding, was one way to improve the partis ISUS system. After exposure of the implants, the fit; however, in particular with large constructions, next appointment is devoted, as usual, to making a this procedure has the disadvantage of very time- casting with impression material which has a high fi- consuming manual post-processing. Furthermore, nal hardness and hence guarantees a secure fixing of there is the risk that the mechanical ability to cope the casting posts (e.g. Impregum, 3M ESPE, or Mono- with pressure may be reduced in the area of the join- pren transfer, Kettenbach Dental; Fig. 3). ing point. In the ideal case, the casting appointment will al- In addition to that, from the economical point of ready include the determination of the jaw relations view, it would make sense to use largely biocompati- and a casting for the model for the opposite jaw. Af- ble material of sufficient mechanical strength for the ter that, the work model is manufactured with the manufacture, such as pure titanium or a Co-Cr alloy. help of a removable gingiva mask in the area of the However, the processing of such alternative materials implants. When the first checkbite is taken, a first pro- does not provide a sufficiently exact fit with the cur- visional model can be mounted straight away. Based rent casting techniques. In-vitro examinations of cast on this working material a tooth arrangement is pre- implant suprastructures made of non-metallic mate- pared from plastic. It is useful if the information about rials showed gaps of 200 to 300 µm between the the colour and the shapes of the teeth is already avail- suprastructure and the implant arrangement (DeTor- able during this work step (Fig. 4). res et al. 2007). Compared to that, cast structures made of noble metals featured median gaps of 40 to The tooth arrangement can be tried on at the next 50 µm (Takahashi and Gunne 2003). The use of alter- appointment, and corrected if needed. So, the exact native materials therefore requires an alternative jaw relations can be determined, and sufficient infor- processing technology, and be it just to achieve the mation will be collected for the definitive tooth necessary precision. In the ideal case, the supracon- arrangement. At this appointment, also the precision struction is cut from a prefabricated solid material in of the casting should be checked with a transfer jig. For order to safely exclude inhomogeneities. With this this key, the posts on the work model can be blocked thought in mind, the manufacture of supraconstruc- with plastic and a metal reinforcement. The key must tions with cutting technological means utilising the then fit onto the implants in the mouth without caus- CNC process started already more than ten years ago. ing tension or shifting around. For the exact determi- implants 18 I 1_2010 case report _ CAD/CAM I

nation of the accuracy of the casting fit it makes sense structure was made of a cobalt-chromium alloy and to perform the so-called Scheffield test. For this test, bonded with the galvanoplastic structure. The supra- a screw is mounted and fastened on the post on one construction was completed using the already exist- side of the distal implant. When fastening the screw, ing tooth arrangement. Several in-vitroexaminations the transfer jig must not lift off the other implants. prove the excellent accuracy of fit in these CAD/CAM manufactured constructions. In a comparison of five Further, there must not be any gaps. If the screw different techniques for the manufacture of implant can be fastened without making the transfer jig move supraconstructions, the CAD/CAM structures showed the conclusion can be drawn that the impression has a median accuracy of fit of 25 µm, while cast struc- exactly copied the situation in the mouth. In case that tures had median gaps of 78 µm width (Torsello et al. the test has a negative result a transfer defect can be 2008; Fig. 7). assumed. In such a case, the transfer jig should be sep- arated, and all posts should be fastened with screws, However, the advantage of the CAD/CAM technol- so that a new impression casting can be taken. ogy is not only the highly precise manufacture of suprastructures made of pure titanium and Co-Cr al- Once an exact impression has been secured and the loys; there is also its applicability to a broad range of tooth arrangement has been adjusted, the CAD/CAM indications. Starting out from the scan data, the vir- manufacture of the supraconstruction can begin. tual construction allows for a wide range of variations First, the work model and the tooth arrangement are in terms of various forms of supraconstructions, from sent to a Compartis ISUS Planning Centre. There, the the simple round bar to retaining element attach- virtual construction of the attachment is made ac- ments or to a bridge frame for fixed constructions. cording to the specifications of the dentist(s) and den- With a CAD/CAM system, it is also possible to virtually tal technician(s). In the present case, a bar attachment incorporate active holding elements such as extra- construction made of titanium with distal attach- coronal retaining joints, bars and press buttons. ments (Preci-Vertix, CEKA Germany) has been chosen. The tooth arrangement determines the space avail- In summary, it can be said that the CAD/CAM tech- able for the supraconstruction and the alignment to- nology is also ideal for the processing of alternative wards the chewing area. This information then con- materials on titanium and NEM basis. It provides stitutes the foundation for computer-assisted design these advantages: of the supraconstruction, the CAD process. For this purpose, first, special scan posts are screwed into the _High mechanical resilience thanks to homogeneous implants, in order to determine the position of the im- pore-free materials; plants with a first scan. Then a second scan is done _Tension-free fit thanks to precise CNC manufactur- with the wax arrangement, in order to determine the ing technology; available space and the orientation of the supracon- _Suitability for a large width of indications thanks to struction. Then, the desired supraconstruction is de- individual computer-assisted design. signed with the help of special software. This consti- tutes the basis for the manufacture of the supracon- The integration of the virtual design supplements struction utilising the CNC process (Fig. 5). the trusted manufacturing technology based on cut- ting and hence opens up possibilities of new indica- Dental technicians and care providers will then re- tions for using alternative materials in implant ceive the construction suggestion of the Compartis prosthodontics._ ISUS Planning Centre by email with the request for re- lease or for advice of possibly required changes. As Editorial note: Bibliographical reference is immedi- soon as the release is obtained the manufacture of the ately available for download at www.zwp- attachment begins. The Compartis ISUS system en- online.info/fachgebiete/implantologie. sures, particularly by applying modern cutting ma- chines and special cutting strategies with all the ma- terials, a perfect quality of the surfaces which dis- pense with the need for manual after-processing also as far as the retaining elements are concerned (Fig. 6). _contact implants Then the dental laboratory can commence with the manufacture of the secondary construction. In Dr med dent Sven Rinke, MSc, MSc the present case, first, a secondary structure was Geleitstr.68 made by means of electroplating (Solaris, DeguDent), 63456 Hanau, Germany and the plastic matrix for the Preci-Vertix retaining el- E-mail: [email protected] ements was incorporated. After that, a cast tertiary implants 1_2010 I19