Three-unit bridge

This three unit bridge broke in 2011 after seven weeks in vivo (Figure 12). When the patient was seen by the dentist, both connectors were broken, but the pontic section was still in place from mechanical interlocking. The connector shown on the right (Fig. 12c) fractured first, and continued occlusal loading and usage caused the second connector (Fig. 12a) to break from bending. Only the middle unit, the pontic was available for examination, but fortunately it had... 

Figure 12. Case B6. Middle molar unit of a three-unit bridge. The wing photos (a) and (c) show the fractured connectors on each side, (d) and (e) are close-ups of both broken connectors after gold coating. The right connector broke first and has a flatter and straighter fracture plane.

The strength or load-bearing capability of a three-unit bridge, for example, is of particular interest for clinical applications. Kappert (1998) has conducted in vitro investigations of this topic. In these investigations, anatomical three-unit bridges (two abutments and one pontic) and a connector cross section of 4 mm X 4 mm were fabricated and placed on metal dies, without bonding them. 

Dental crowns and bridges are fabricated according to the viscous flow process described in Section 4.4.2.3.B, in which the biomaterial IPS EMPRESS is introduced. The basic ifabrication principles, therefore, remain unchanged. As a result, dental technicians can fabricate precision restorations quickly and easily. The quality of the IPS EMPRESS 2 material, however, provides several benefits as far as processing is concerned. The special features of the material are illustrated in the following example of the fabrication of a three-unit bridge. 

Figure 4-42 Finite element calculation of a loaded three-unit bridge, a) Scheme of a three-unit bridge consisting of 30,000 tetra-hedra elements (PATRAN/P3). b) When the bridge is subjected to loading of 600 N, the maximum tensile stress in the connector area is approximately 110 MPa.

The microstructure and composition of materials in the class Figure 4-45 Microstmcture of a three-unit bridge of... 

Figure 4-47 Postoperative view of IPS EMPRESS 2 restoration (three-unit bridge), a) Clinical situation (courtesy Sorensen), b) Three-unit bridge on a mirror (courtesy Edelhofl)-c) and d) Dental bridges of IPS EMPRESS 2 (c) in comparison to a bridge of a metal framework (d) (courtesy Edelhoff).

As the number of units in a restoration increases, the strength of the alloy must also increase. The two end members of the three-unit bridges are called abutments. They are supporting the middle... 

FIGURE 14.11 (See color insert following page 212.) Goldtech Bio2000 three unit bridge. (From The Argen Corporation. With permission.)... 

Goldtech Bio2000 three unit bridge. (From The Argen Corporation. With... 

The cyclo-P3 unit can also behave as a three electron bridging ligand (45) to give a variety of homo and heterometallic triple-decker sandwich complexes which are treated in a recent review (100). 

Before discussing the structural features of tetraorganomagnesiates in the solid state it should be noted that structures in which the presence of separated anionic and cationic moieties can be distinguished are rare. In most cases such units are linked via electron-deficient bonds, i.e. two-electron three-center bridge-bonded carbon atoms between magnesium and the counter cation. 

Reactions carried out with M2(DBA)3 (M — Pd, Pt DBA = dibenzylidene-acetone) and 3,5-di-t-butyl-l,2-benzquinone gave as major products the M(DBSQ)2 complexes [229]. In the case of palladium, an additional product Pd2[Pd(DBSQ)2]2 was detected, whose molecular structure consists of two planar cw-Pd(DBSQ)2 units bridged by two Pd atoms. The Pd atoms are sandwiched between semiquinone rings of adjacent Pd(DBSQ)2 units with three Pd — C lengths and an allyl structure 961 for the semiquinone rings ... 

Applying these thoughts to Fig. 3.4, leads to an extension of the state diagram as demonstrated in Fig. 3.5. Now, we have to include virtual charge-transfer states localized on each single modular unit. For a three-module bridge, for instance, the perturbation expression for an electron-transfer reaction extends to... 

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