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36 ◊Page 34 RESTORATIVE Dental Tribune Middle East & Africa Edition | 3/2017 Figure 21: Preoperative OPG Figure 22: Diagnostic wax-up Figure 23: Full arch bridge with individual cemented porcelain-fused-to-metal crowns cemented onto pink porcelain framework cemented with Panavia over gold copings Figure 24: Left view Figure 25: Right view showing screw block Figure 26: Cemented in the mouth over the abut- ments with Temp Bond Figure 27: UCLA abutments in the mouth Figure 28: Gold copings picked up in the acrylic/gold framework with Panavia and oxyguard present prosthesis offers several advantages when compared to a screw retained, in that the super-structure may be more passively attached. A screw is a combination of inclined planes and wedges, and one of the most ef- fi cient machine designs. Misch de- scribed that a torque force of twenty Newtons per centimeter squared applied to a screw when screwing down a framework is suffi cient to move two railway cars apart! The same forces on a non-passive casting has a tendency to distort the super- structure and the bone and / or the implant. As a result, the fabrication of a passive fi nal restoration is highly unlikely when the screw retention is the method of fi xation. Passive Fit The cement retained restoration may offer a better chance of a pas- sive fi t in some areas of the implant abutment crown interface, but be- cause of the distortion previously described during impression tech- niques, casting and then porcelain application, very often spacers need to be incorporated under the frame- work to achieve adequate fi ts leaving large cement spaces in the posterior areas of the bridge. Alternatively, by means of a fi t checker, the internal aspects of the bridge can be adjust- ed to achieve adequate fi t with the same result of open cement mar- gins and loss of retention. In order to achieve retrievability of the res- toration, the cemented prosthesis is usually cemented with a soft ce- ment, but unfortunately one of the problems of the softer cement is that of cement washout. Parel (2000) has maintained that this can then lead to excess stress being placed on certain abutments and implants due to ce- ment washout under the crowns on top of other abutments. Again, this leads to potential problems with over stressing of implants. Aesthetics A further problem that has been observed with the large porcelain- fused-to-metal full arch bridge, is hat of less than ideal aesthetics. It is a daunting task for the technician to build pink porcelain to restore the lost soft tissues combined with the need to restore functioning pros- thetic teeth at the same time (Figures 1 & 2). A technician only has a limited number fi rings available to him to build up this fi nal fi xed restoration prior to the porcelain becoming too translucent and losing its natural colour. The fi nal result is that the aesthetics may not be as good as is possible with individual crowns in a full mouth reconstruction, because of these constrictions. Maintenance Porcelain is a very brittle material and has the potential to fracture un- der parafunctional and / or impact loading. Although acrylic has been recommended by Cibirca (1992) as the veneering material for a full arch bridge because of its dampen- ing effect, this has been questioned by Davis (1988), as porcelain has been shown to be more benefi cial under static loading. Changing from a screw-retained design of restora- tion with access holes in the centre of the occlusal and palatal surfaces, to a cement-retained restoration, will increase the strength of the fi nal porcelain-fused-to-metal bridge. However, there is still the potential for fracture or cracking during long term function. Should this occur then it may be impossible to retrieve this from the mouth and repair the porcelain in the laboratory due to the contamination of the porcelain by saliva. This contamination makes the porcelain more liable to explode whilst in the furnace. Very often, re- shaping of the bridge or composite repair have been the only options to maintain the bridge long-term in function, with again loss of form, function and aesthetics. The alterna- tive, which is both time-consuming and expensive, is stripping the por- celain and remaking it on the same framework. This paper now describes a brand new technique for improving the aesthetics, maintenance and, most importantly, fi r of the full arch porcelain-fused-to-metal implant retained restoration using a pick up copying technique over the custom made abutments. Case Study This male patient was referred to me from his general dental practitioner in Leeds for placement of implants and a fi xed bridge in his lower jaw. The patient has most of his upper dentition and the referring practi- tioner had previously reconstructed this as a porcelain-fused-to-metal restoration. The patient was anxious to have a similar style of restoration in the lower jaw to oppose his upper porcelain-fused-to-metal bridge. It was the intention that the fi nal resto- ration would have individual crowns cemented to a passive fi tting pink porcelain-fused-to-metal frame- work, cemented over eight custom made UCLA abutments. Implants Eight ‘Bränemark’ implants (Nobel- Biocare) were inserted into the lower jaw with a view to fabri- cating a fi xed porcelain- fused-to-metal bridge as the fi nal reconstruction (Figures 3 & 4). Three months after placement of the implants and prior to uncovering a closed mouth impression was taken to allow the fabrica- tion of a gothic arch trac- ing with centre pin regis- tration for determination of centric relation jaw relationship and vertical dimension. With these records a wax try-in was produced with teeth to assess the fi nal position of the replacements and soft tissue defect. This informa- tion was used to construct a screw retained acrylic provisional as de- scribed by Zinner (1994), designed to load the implants transitionally and also allow time for the patient to assess form, function, shape and aesthetics prior to the defi nitive res- toration. UCLA Abutments After six months of wearing the pro- visional bridge impressions were taken for construction of the lower fi nal fi xed restoration. This was done with traditional pick up impression copings (Figure 5) rather than trans- fer impression copings for greater accuracy (Carr, 1991) and for the fab- rication of a master model. It was ex- pected that this master model pro- cessed from the pick up impression would still be inaccurate because of the large span of the arch, and the inaccuracies in the impression tech- niques (Carr, 1991; Hsu, 1993) but this inaccuracy would be compen- sated for later on during the restora- tion. Eight custom made gold UCLA abutments milled to a 4() taper were Figure 29: Acrylic/gold bridge cemented in the mouth over the UCLA abutments with Temp Bond made (Figure 6) got placement onto the implants and the fi t was verifi ed in the mouth with the aid of an acryl- ic locating jig (Figure 7). On top of the abutments, copings were made in precious metal to be fi tted over the top of the gold custom-made abut- ments. These were transferred to the mouth and verifi ed for the fi tting of the margins (Figure 8). Technical Aspects Prior to the waxing and casting of the fi nal framework, a spacer technique was applied to the precious metal copings ranging from 0.2mm thick- ness distally in the anterior region to 0.6mm disto-bucally in the most posterior areas to accommodate casting inaccuracies and framework distortion due to multiple fi rings. The wax try-in verifi ed at the com- mencement of prosthetic treatment formed a matrix for the framework design. The original try-in was waxed to the master model and a silicone putty matrix formed to encompass the teeth and soft tissue replace- ment. Inlay wax is poured into the resulting space. This allowed the wax ÿPage 37 Join Hands-On Training 04 & 05 May 2017 www.cappmea.com/cadcam DUBAI Hands-On Training in Dubai The 5 principles of Occlusion for modern day Advanced Restorative Procedures Tutor: Prof. Paul Tipton, UK Date: 04 May 2017 | 09:00 - 18:00 Accreditation: 7 CE Credits | HAAD 7 CME Treatment Planning for Advanced Comprehensive Full Mouth Dentistry Tutor: Prof. Paul Tipton, UK Date: 04 May 2017 | 09:00 - 18:00 Accreditation: 7 CE Credits | HAAD 7.5 CME Venue: InterContinental Hotel Festival City, Dubai, UAE Course Abstract The morning session will consist of a seminar on occlusion and will cover the following topics: • The 5 principles of occlusion • RAP V centric relation • Mutually protected occlusion • The importance of anterior guidance • Non- working side interferences • Posterior stability Course Abstract The morning session will be a lecture on advanced treatment planning (with Prof. Paul Tipton) Stabilisation and will cover the following: • Maintenance • Occlusion • Surgery • Diagnosis • Treatment planning