Steps in bridge construction

Lect.8 Crown and Bridge Dr. Ameer Hamdi AL-Ameedee
abutment: that part of a structure that directly receives thrust or pressure and it s a portion of a tooth, or that portion of a dental implant that supports and/or retains a prosthesis.
Ante s Law: [ By Irvin H. Ante, Toronto, Ontario Canada, dentist] an eponym in fixed partial prosthodontics for the observation that the combined pericemental area of all abutment teeth supporting a fixed partial denture should be equal to or greater in pericemental area than the tooth or teeth to be replaced; as formulated for removable partial prosthodontics, the combined pericemental area of the abutment teeth plus the mucosa area of the denture base should be equal to or greater than the pericemental area of the missing teeth.
artificial crown: a metal, plastic, or ceramic restoration that covers three or more axial surfaces and the occlusal surface or incisal edge of a tooth.
buccolingual relationship: any position of reference relative to the tongue and cheeks.
cantilever: a projecting beam or member supported on one end.
cantilever fixed partial denture: a fixed partial denture in which the pontic is cantilevered, (i.e., retained and supported only on one end by one or more abutments).
clinical crown: the portion of a tooth that extends from the occlusal table or incisal edge to the free gingival margin.
complete crown: a restoration that covers all the coronal tooth surfaces (mesial, distal, facial, lingual, and occlusal).
connector: n in fixed prosthodontics, the portion of a fixed partial denture that unites the retainer(s) and pontics.
crown: the highest part, as the topmost part of the skull, head or tooth; the summit; that portion
of a tooth occlusal to the dentinoenamel junction or an artificial replacement that restores missing tooth structure by surrounding part or all of the remaining structure with a material such as cast metal, porcelain, or a combination of materials such as metal and porcelain. To place on the head, as to place a crown on a tooth, dental implant, or tooth substitute-usage: implies fabrication of a restoration for a tooth on a natural tooth or dental implant.
crown fracture: micro- or macroscopic cleavage in the coronal portion of a tooth.
crown-root ratio: the physical relationship between the portion of the tooth within alveolar bone compared with the portion not within the alveolar bone, as determined by radiograph.
extracoronal retainer: that part of a fixed partial denture uniting the abutment to the other elements of a fixed partial denture that surrounds all or part of the prepared crown.
fixed partial denture: a partial denture that is luted or otherwise securely retained to natural teeth, tooth roots, and/or dental implant abutments that furnish the primary support for the prosthesis-usage: with respect to a fixed partial denture retained on dental implants, adjectives may be used to describe the means of attachment, such as screw retained, cement retained also called fixed prosthesis.
fixed partial denture retainer: the part of a fixed partial denture that unites the abutment(s) to the remainder of the restoration.
residual bone: that component of maxillary or mandibular bone, once used to support the roots of the teeth, that remain after the teeth are lost.
residual ridge: the portion of the residual bone and its soft tissue covering that remains after the removal of teeth.
span length: the length of a beam between two supports.
Steps in bridge construction:
1-Diagnosis: first step must be diagnosis the abutment teeth and surrounding oral tissues.
a-periodontal examination: proper oral hygiene must be found to prevent plaque accumulation on tooth and crown margins, which lead to caries.
b-Dention examination:
i-Visual: The occlusion, tooth crowding, spacing and tooth rotation must examined and future treatment will analyzed.
ii-Radiographic : This will reveal the shape and condition of tooth root and surrounding structures.
3-Final impression.
4-Teamporary restoration (provitional restoration).
5-Construction of working model.
6-Waxing.
7-Investing.
8-Wax elimination.
9-Casting.
10-Finshing and polishing.
11-Tray-in and final cementation of bridge.
Ceramic: Ceramics are compounds that involve a combination of metallic and nonmetallic elements, creating strength and aesthetics.
Dental Ceramics: Because of the wide variety of porcelain products available in the market, it is virtually impossible to provide a single composition for them all. Traditionally, porcelains were manufactured from a mineral called feldspar. These porcelains are referred to as feldspathic porcelains. As porcelain technology improved other specialized porcelains were introduced, like
reinforced core porcelains, opaquer porcelains, glass ceramics, glazes, etc. Obviously their composition would certainly differ from the traditional feldspathic porcelains.
Basic Structure: Basically porcelain is a type of glass. Therefore its basic structure is similar to that of glass. The basic structure therefore consists:
A-dimensional network of silica (silica tetrahedra).
B-Pure glass melts at too high a temperature for dental use.
C-Adding certain chemicals lowers the melting temperature by disrupting the silica network. The glass obtains porcelain like qualities when the silica network is broken by alkalies like sodium and potassium. This also lowers the fusion temperature. These chemicals are therefore known as glass modifiers or fluxes. Other substances which act like glass modifiers are alumina (Al,03) and boric oxide (B,03)· Boric oxide forms its own separate network in between the silica network. Adding certain opacifiers reduces the transparency and completes the transformation to dental porcelain.
Micro structural classification: At the micro structural level, we can define ceramics by the nature of their composition of glass-to-crystalline ratio. There can be infinite variability of the microstructures of materials, but they can be broken down into four basic compositional categories, with a few subgroups:composition category:
1 – glass-based systems (mainly silica),composition category.
2 – glass-based systems (mainly silica) with fillers, usually crystalline (typically leucite or, more recently, lithium disilicate),composition category.
3 – crystalline- based systems with glass fillers (mainly alumina) andcomposition category.
4 – polycrystalline solids (alumina and zirconia).
Dental porcelain is generally regarded as biologically inert. However, other toxicities may exist from some of the accessory materials, and the fillings may increase wear on opposing teeth.
Classification and description of ceramic systems:
The ceramic restorations available today may be metal bonded or made completely of ceramic. Based on the substructure or core material used we have two basic groups. They are further divided based on the fabrication method:
A-Metal-ceramic (metal bonded or PFM) restorations:
1-Cast metal ceramic restorations:
-Cast noble metal alloys.
- Cast base metal alloys.
- Cast titanium (ultra low fusing porcelain).
2- Swaged metal ceramic restorations:
- Gold alloy foil coping (Renaissance, Captek).
- Bonded platinum foil coping.
B- All ceramic restorations:
1. Platinum foil matrix constructed porcelains
- Conventional porcelain jacket crown
-Porcelain jacket crown with aluminous core
- Ceramic jacket crown with leucite reinforced core (Optec HSP)
2-Castable glass ceramics (Dicor)
3- Injection moulded (leucite reinforced) glass ceramics (IPS Empress)
4-Glass infiltrated core porcelains
- Glass infiltrated aluminous core (Inceram)
Glass infiltrated spinell core (Inceram spinel\)
5-Ceramic restoration with CAD-CAM ceramic core
- Glass ceramic blocks
- Feldspathic porcelain blocks Ceramic
6-restoration with copy milled ceramic core. (Celay)
1-Alumina blocks (Celay inceram)
2- MgAI20, (Inceram spinell).
Surface Staining, Characterization and Effects: Natural teeth come in variety of hues and colors. Some of them are present at the time of eruption (intrinsic, e.g. white fluorosis stains), while others are acquired over a period of time from the environment (extrinsic, e.g. cervical stains). Staining and characterization helps make the restoration look natural and helps it to blend in with the adjacent teeth . The stain powders are mixed with a special liquid, applied and blended with a brush. With more and more emphasis on recreating the natural look, effects are created using special techniques. This includes defects, cracks or other anomalies within the enamel.
Glazing: Before final glazing, the restoration is tried in the mouth by the dentist. The occlusion is checked and adjusted by grinding. Final alterations can be made to the shape of the restoration by the dentist. The restoration is now ready for the final step which is the glazing. The restoration is smoothed with a stone prior to glazing. Glazing is the process by which the restoration is given a smooth glossy surface.
Objectives of glazing:
1- Glazing enhances esthetics
2- Enhances hygiene
3- Improves the strength. Glazed porcelain is much stronger that unglazed ceramic. The glaze inhibits crack propagation.
4-Reduces the wear of opposing teeth. Unglazed porcelain can accelerate wear of the opposing natural teeth.
Use and application:
1-Inlays and onlays
2- Esthetic laminates (veneers) over natural teeth
3- Single (all ceramic) crowns
4- Short span (all ceramic) bridges
5- As veneer fore cast metal crowns and bridges (metal ceramics)
6- Artificial denture teeth (for complete denture and partial denture use)
7- Ceramic orthodontic brackets.
Classification according to fairing temperatures:
1-High fusing 1300°(for denture teeth)
2-Medium fusing 1101 to 1300°(for denture teeth)
3- Low fusing 850 to 1100°(for crown and bridge use)
4-Ultra low fusing less than 850 (used with titanium)
Classification according to Type:
1-Feldspathic or conventional porcelain
2-Aluminous porcelain
3- Leucite reinforced
4-porcelain Glass infiltrated alumina
5- Glass infiltrated spinell
6- Glass ceramic
Classification according to Use
1-Porcelain for artifical denture teeth
2- Jacket crown, veneer and inlay porcelain
3-Metal ceramics
4- Anterior bridge porcelain.
Classification according to Processing Method
1-Sintered porcelain
2- Cast porcelain
3- Machined porcelain.