Bridges are used for replacing single or several missing teeth. Bridges are generally fixed but, in specific cases, also removable restorations (telescope bridges). Bridges are differentiated as single-span or long-span bridges according to the number of separate edentulous ridge segments they bridge. They can be supported on teeth, purely on implants (implant-supported bridges) or on teeth and implants (hybrid bridges)
Bridges are often retained on their anchors/abutments by (anchor-, abutment) crowns, but can also be retained using, e.g. inlays (inlay bridges, or adhesively bonded retention wings (adhesive bridge, acid-etched bridge, Maryland bridge) on one (single-winged bridge) or both (twin-winged bridge) adjacent teeth. Special systems use anchors adhesively bonded into holes drilled in the adjacent teeth.
All-zirconia bridgework and crowns
An essential component of a bridge is its pontic, which replaces at least one tooth. It is called a cantilever pontic if it is (in the case of a cantilever bridge) retained on one of the teeth adjacent to the space. Saddle bridges (fixed-fixed bridges) close tooth-bounded gaps between two anchors/abutments (teeth or implants) with one pontic retained on both abutments.
Zirconium dioxide free-end bridge on a stone model
The junction between the abutment crown and pontic is called a "connector". Its dimensions (apart from length of the span) are a decisive factor in ensuring the fracture resistance of a bridge.
Depending on the distance or amount of contact of the bridge pontic to the alveolar mucosa, bridges are referred to as self-cleansing bridges (with a "self-cleansing" pontic), sanitary bridges or tangential bridges. The periodontally unhygienic saddle bridge is no longer a relevant option. The ovate pontic is generally a convex egg-shaped pontic (with oval/ellipsoidal cross section) that appears to emerge from the alveolar ridge in the same way as a natural tooth, which is an advantage in terms of aesthetics.
A common path of insertion must be found for all abutments involved in order to fit a bridge. This is achieved by means of parallel preparation, separation of the bridge (sectioned bridge) by a slide attachment or telescope crowns as well as with implants using angled abutments, if necessary.
The bridge pontics and abutment crowns are collectively known as "units" of a bridge. This means that a full bridge (involving all teeth in one jaw) can be a maximum of 16 units.
4 unit VMK bridge
All the materials and procedures used with crowns can be used for fabricating and retaining bridges. Glass-fibre ribbons, with which pontics can be contoured and/or reinforced/retained, can also be used for temporary bridges.
For reasons of stability the number and total root surface of the bridge pontics must be at least as large as those of the teeth to be replaced. The flexibility of the bone segment of the mandible can lead to complications involving decementation of individual bridge abutment crowns.
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bovine enamel | Rinder-Schmelz |
Wax build-up technique Wax build-up technique The various anatomical structures (such as cusp tips and slopes as well as marginal ridges) are usually built up one after another by adding small portions of wax (often using differently coloured waxes for didactic purposes). The firm, special waxes first have to be melted at room temperature. This can be carried out by warming small portions on differently shaped working tips of hand instruments in an open flame (such as a gas burner) or using electrically heated instruments which provide for more accurate temperature control and avoid contamination (e.g. electric wax-knife, induction heaters, wax dipping units). The wax is applied drop-by-drop to ensure that the warmer molten wax added last fuses seamlessly with the firm, cooler material. After hardening, the wax pattern can be reduced by sculpting, milling guidance surfaces or drilling to add retainers. Modern procedures include flexible, occlusal preforms for adding contours to soft wax. In addition, wax preforms, such as for occlusal surfaces or bridge pontics, are available in various shapes and sizes. Recently, irreversible, light-curing materials have been introduced for use instead of reversible thermoplastic waxes. Wax preforms To ensure that the wax pattern can be released without being damaged, model surfaces, opposing dentition and preparations must be hardened/sealed with special lacquer (applied by spraying, brushing or dipping). These waxes are mostly relatively rigid/elastic after cooling. Attaching wax sprues to a removable framework supported on double crowns using a hand instrument When employing the lost wax technique, prefabricated wax sprues, bars and reservoirs are attached to the patterns. Once the pattern has been released and its sprues waxed onto the crucible former, it is invested in a casting ring with refractory investment material. The wax can then be burnt out residue-free and casting completed. Unlike standard wax build-up techniques, a diagnostic wax-up is not intended for fabricating an indirect restoration, but rather for simulating the appearance and/or external contouring for producing orientation templates. |