A resin veneer bridge is a tooth-supported dental prosthesis that is firmly anchored to abutment teeth by means of crowns and whose aesthetically significant areas are coated with tooth-colored resin. A resin veneer bridge – like a ceramic veneer bridge – has a metal framework which is veneered with tooth-colored PMMA-based resin (polymethyl methacrylate) only on the esthetically important buccal or labial surfaces (surfaces facing the cheek or lip). A ceramic veneer bridge, on the other hand, can also be veneered on the occlusal surfaces bearing the masticatory load and the oral surfaces (surfaces facing the oral cavity). The metal framework itself is made of a gold-bearing alloy or non-precious metal alloys (NEM). So-called retentions (anchoring aids) must be placed in the area to be veneered to create a mechanical bond between the veneering material and the bridge framework. The resin material is inferior to a ceramic veneer in many respects. For example, it has neither their esthetics nor their excellent biocompatibility (body compatibility). Different elasticity behavior can lead to the facet (the veneer layer) becoming detached from the metal framework, and ultimately occlusal veneers have to be omitted due to their lower abrasion resistance. Due to the aforementioned limitations, the resin veneer bridge is generally only used as a long-term provisional restoration (to bridge longer periods of time until a definitive, higher-quality replacement).
Indications (areas of application)
- Gap closure – to replace missing teeth
- Preventing tooth migration – tipping into a gap, elongation of the antagonist (outgrowth of an opposing tooth from its bone compartment).
- Restoration of phonetics (phonation).
- Restoration of aesthetics
- Restoration of occlusion (chewing closure and chewing movements).
- Preservation of support zones – The interlocking of the maxillary and mandibular posterior teeth preserves the bite height.
- As a long-term provisional restoration
Contraindications
- Severely loosened abutment teeth
- Hypersensitivity / allergy to PMMA resins.
- Bruxism (teeth grinding or clenching) – risk of shearing off the resin veneer.
- Large, arched bridge spans – If, for example, all upper anterior teeth are missing when the formerly tooth-bearing jawbone is too arched, a fixed restoration with a bridge cannot be made for static reasons.
The procedure
I. Dentist
- Preparation of abutment teeth to receive the bridge anchors – If necessary, carious tooth structure must be removed and the tooth must be provided with a build-up filling before preparation (grinding the teeth).
- Choice of tooth color
- Preparation – Teeth are circularly ground and reduced in occlusal height (in the area of the occlusal surfaces) to make room for the material thickness of the subsequent bridge.
- Impressions of both jaws
- Bite taking – to transfer the dentition of the upper and lower jaw to the dental laboratory.
- Jaw relation determination – If support zones (occlusion/chewing of upper with lower molars) are resolved, the distance between the upper and lower jaw bases must be defined.
- Temporary restoration – fabrication of a simple plastic bridge made chairside (at the treatment site) as a transitional restoration to protect the prepared teeth and prevent tooth migration until the definitive (final) bridge is placed.
II. dental laboratory
- Production of plaster models based on the jaw impressions.
- Articulating – transferring the models into the so-called articulator (device for imitating the jaw joint movements) on the basis of the bite impression and jaw relation determination.
- Wax modeling – On the abutment teeth converted into plaster, the dental technician first models crowns made of wax, between which the subsequent wax pontic is inserted. So-called retentions (anchoring aids), e.g. in the form of small beads, are applied in the veneering area to create the mechanical bond between the metal framework and the veneering layer. As an alternative to wax modeling, the framework is designed on the computer using CAD/CAM technology.
- Metal casting – Casting channels made of wax are attached to the wax model. Then the modelation is embedded in a casting muffle. The wax is burned out in a furnace without leaving any residue. This creates cavities which are filled with molten metal via the casting channels in a vacuum centrifugal process. The process is known as lost wax casting. As an alternative to the casting process, the metal framework is sintered into a three-dimensional framework with the help of CAD/CAM technology in the so-called selective laser melting process by melting finest powder of special sintered metal layer by layer.
- Framework finishing – The cast metal framework is de-bedded after cooling, separated from the casting channels and finished to polish. The areas to be veneered are roughened in a micro-sandblaster with aluminum oxide (Al2O3) of grain size 50 to 250 µm to improve the mechanical bond to the veneering material. A framework sintered in CAD/CAM technology is also polished accordingly or pretreated in the veneering area.
- Bonding – In order to obtain a gap-free bond between metal and resin, the metal framework is chemically prepared in addition to the purely mechanical retentions in the veneering area. Various processes are available for this purpose, all of which are aimed at first generating a bonding oxide (depending on the process: alloy oxide or silicon oxide) on the metal surface, onto which a silane is then applied as a bonding agent. The bond created in this way is so resilient that in some processes the mechanical retentions can be dispensed with.
- A so-called opaquer (synonym: opaquer; covering varnish), which is applied to the created adhesive base, is to prevent the metal from shining through the veneering resin.
- Veneering – Over the opaquer, the tooth-colored acrylic is applied in layers in free modeling according to the individual tooth shape and color.
- Polymerization – Exposure to pressure and heat over a defined period of time gives the acrylic its final material properties. Air inclusions are reduced, the swelling behavior is improved and the risk of dye incorporation is reduced.
- Final polishing of metal and veneering, thereby avoiding too strong heat development.
III Dentist
- Removing the temporary restoration and cleaning the prepared teeth.
- Placement – The finished bridge is conventionally (with conventional cements, e.g. zinc phosphate or glass ionomer cement) permanently fixed to the abutment teeth.
- Removal of excess cement after its setting phase.
- Checking the occlusion (the chewing closure and chewing movements).
After the procedure
- Timely control date
- Regular recalls and optimization of oral hygiene techniques at home.
Possible complications
- Loosening of the cementum joint on an abutment tooth.
- Inadequate oral hygiene – resulting in the development of periodontal disease (periodontal disease) or caries (tooth decay) at the crown margin.
- Preparation-related pulpitis (dental pulp inflammation).
- Fracture (fracture)
- Chipping of the plastic veneer
- Aging and wear of the veneer due to thermal, chemical and mechanical stresses.
- Discoloration of the veneer due to dye deposition.
