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18 CASE STUDY In case of metals, we take a similar ap- proach, roughening the surface with a green diamond, not before impressions are taking, but only before bonding. Met- al primer (GC) is then applied twice with- out applying another layer of bonding. Roughening the metal crowns should only remove a little material [2,5,10]. This removal is not considered in lab fabrica- tion, as it is only performed immediately before bonding. The bonding layer thick- ens somewhat, which certainly has a pos- itive effect as a mechanical stress breaker (Fig. 8) . In the posterior region, a functional bridge is forgotten by the patients and is often loaded with very high chewing forces in everyday life. The only possibil- ity of guaranteeing this over an extended period is to shape the distal clasp element as a frictionless ring clasp. If the ring is open at any point due to grinding, abra- sion or overloading, the bridge loosens and can no longer be permanently stabi- lized by multiple bonding and overlayer- ing. In such an instance, new fabrication should be considered, rather than the patient showing up in the practice every two or three weeks for recementing. Especially when crossing the occlusal sur- faces, space problems may arise along the ring clasps if occlusion is over a large area. Only the targeted removal of sub- stance, possibly also from the antagonist, is successful here. As an alternative, the ring can also be placed around two teeth in order to remain closed (Fig. 9) . Four “golden rules” have emerged as prerequisites for trouble-free use of tem- porary cast Maryland bridges: • For a posterior bridge, the distal clasp element must be designed as a closed ring • Visible parts of the clasp should if possible be broad and flat • Blast visible vestibular clasps from both sides and inspect • Natural tooth surfaces are not chemically pre-treated, as otherwise the bridge cannot be removed In the case of front tooth bridges, we sometimes also omit the vestibular clasp shell for esthetic reasons. But here it is especially important to consider the stat- ics of the pontics. As the effect of the load during chewing is strictly defined by physical rules, a model cast Maryland bridge without vestibular element must be extended more orally to balance the leverage forces arising (Figs. 10 and 11) . Also if the vestibular clasp shells are ex- cluded altogether, with such front tooth bridges, which are only orally bonded, the occlusion surface has to be crossed at the end to ensure greater lateral support. The solely chemical bonding strength of compomers is insufficient to fix the bridge for months (Figs. 12 and 13) . The advancement of zirconium oxide as a dental material with a broad design scope in terms of shade has also opened up the indication of using bonded tem- poraries for esthetically highly discerning patients with a “gummy smile”. Fig. 7: The pontic and the coated clasps have the same tooth inclination. Fig. 13: ... and the temporary restoration is orally bonded. Interdental clasps are applied to counter balance. Fig. 8: Metal crowns are roughened with diamond burs and conditioned with metal primer. Fig. 14: Zirconium oxide bridges are used in highly esthetically demanding temporary restorations. Fig. 9: In case of low interocclusal space availability, the ring clasps are doubled or distally closed. Fig. 15: In case of zirconium restorations, as with cast Mary- land bridges, the clasp elements are designed as shells.