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22 RESTORATIVE Dental Tribune Middle East & Africa Edition | 4/2017 Advanced restorative techniques and the full mouth reconstruction – The use of gold copings in bridgework Part 10 In the last part of the series, Paul Tipton looks at the use of gold copings in bridgework By Prof. Paul Tipton, UK Introduction From the studies produced by Lind- he and Nyman, described earlier in the series, it would certainly seem possible to succeed with long span bridgework, provided many of their criteria for success are followed, such as occlusal design, margin place- ment, oral hygiene etc. The other im- portant aspect of this type of longer span bridgework is to control the stress on cement lutes, where failure can readily occur. This is achieved in the Lindhe and Nyman bridgework design by using the technique only for mobile abutment teeth. When the prognosis of longer span bridge- work is in doubt because of the loss of many units or non-mobility of abutments; gold copings can be used (Robertson, 1986). Copings (other- wise known as telescopic crowns) were originally used to overcome problems of parallelism in relation to the path of insertion of fixed res- torations (Amsterdam, 1974). Type of Coping The gold coping is a thin crown, 0.7mm thick, that is waxed directly onto the dies and usually cast in yel- low gold. They are made parallel to each other and can be sandblasted by the technician for extra reten- tion (Fig. 1 to 3) (Newburg, 1978). The margins are polished, however; as they will be exposed in the mouth. These copings are permanently ce- mented over the remaining abut- ment teeth with a traditional hard cement, such as zinc phosphate. The long span bridgework is then made in the conventional manner and ce- mented over the gold copings with a softer cement such as zinc oxide and eugenol such as ‘Temp-bond’ (Kerrs). Should excess stress be transferred to the cement lut then one or more of the soft cement lutes will prefer- entially fail. Because the copings have been made parallel to each other there is reason- ably good retention of the bridge, however, even without cement. When all the cement lutes fail and the cement washes out the patient will usually re-attend for further ce- mentation with more soft cement. It is unlikely that caries will occur under the bridgework because the tooth structure is protected by the gold coping. Bridgework margins are placed above or incisal to the gold coping margins so that periodontal problems can be avoided. This style of bridge design does however re- quire more aggressive tooth removal as an extra 0.6-1mm is required for the extra thickness of the gold cop- ing and cement lute. Alternatively, a non-precious coping can be fabricat- ed when required, bringing the thick- ness of the coping down to 0.3mm. Screw Retention One or more screws can also be in- corporated into the restoration so that when the cement lute fails the bridge-work does not fall out of the mouth but is retained by the screws. This gives the patient added confi- dence in his restoration (Fig. 4 to 6) and is especially useful in the upper jaw. Careful preparation techniques are required for this type of reten- tion as the screw could (in certain situations) pull the coping off the tooth, leading to an increased risk of caries. The screws are usually placed into the end abutments, which re- quire special tooth preparation. The end abutment is prepared so that it is tilting distally, allowing for a dis- tal path of insertion of the coping. Bridgework usually unseats from an anterior-posterior direction of force and therefore the fit of the cop- ing on the tooth will resist this type of dislodgement, thus maintaining a cement seal between the coping and the tooth. The technician will upright and parallel the abutment by waxing and casting his gold cop- ing parallel to all the others for seat- ing of the bridge and correct path of insertion. Uses One of the major advantages of this style of bridgework is the flexibility is brings to a restoration. In theory, the bridge can be removed by untap- ping (and unscrewing) so that prob- lems with abutment teeth and peri- odontal disease can be treated. In this manner, periodontal maintenance is more easily achieved, root fillings and cast posts and cores can be fab- ricated without drilling through the superstructure and teeth can be re- moved, roots resected and the bridge modified prior to re-cementation (Fig. 7 to 11). Further abutments may be added by soldering new retainers or attach- ments and anticipating future modi- fications (Kaldahl, 1985). Be aware, however, that this type of bridge can- not then be removed for porcelain addition without the increased risk of porcelain fracture whilst in the furnace due to saliva contamination. Multiple unit bridgework when ce- mented on mobile abutments often fails to seat adequately unless vent- ing is performed. An alternative is the use of copings where an incom- plete seal and seat is less detrimental (Faucher; 1983). This type of bridge is often used as an interim prosthesis whilst implants are placed around the tooth abutments to take the pa- tient from a tooth-supported bridge to an implant-supported bridge without the need for a removable prosthesis. Aesthetics Aesthetics can be compromised by this type of bridge because – as previ- ously mentioned- extra tooth prepa- ÿPage 24 Fig. 1: Three root-filled anterior and posterior teeth Fig. 2: Sandblasted gold copings cemented in place with zinc phosphate Fig. 3: Three-quarter gold crown as a minor retainer in mandible Fig. 4: Full arch bridgework Fig. 5: Screw block placed in the posterior gold coping Fig. 6: Bridgework screwed into the gold copings Fig. 7: Combined complex perio/endo case Fig. 8: Occlusal view showing remaining compro- mised abutments Fig. 9: Gold copings cemented in place with zinc phosphate Fig. 10: Occlusal view Fig. 12: Patient presents with multiple tooth loss Fig. 11: Full arch bridgework cemented onto copings with Temp-bond as long-term provisional prior to de- finitive implant treatment Fig. 13: Diagnostic waxing performed Fig. 14: Tooth preparation guide Fig. 15: Preparation of the three teeth for the coping bridge Fig. 16: Silver dies anterior view