Preparation -- principles and technique * * Impression material and technique

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  • Preparation -- principles and technique * * Impression material and technique
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  • Prosthodontics in dentistry Definition Prosthodontics is that discipline of dentistry pertaining the restoration of oral function, comfort, appearance (esthetics) and contiguous oral and maxillofacial tissue with artificial substitute.
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  • There are three main branches of prosthodontics
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  • 1- Fixed prosthodontics fixed prosthodontics pertains to the restoration or replacement of teeth with artificial substitutes that are supported on natural teeth, roots or implant and they are fixed ether by cement such as crown, post-crown, bridge, inlay and onlay. or by screw such as crown and bridge supported implant.
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  • Full metal single crownFull ceramic single crown Metal-ceramic bridgePost- crown
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  • 2-Removable prosthodontics Pertains to the replacement of missing teeth and contiguous oral structures with artificial substitutes (materials). That are readily removable such as metal-based acrylic partials,acrylic partial denture,complete denture and over - denture
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  • Metal-based acrylic partials Complete denture Acrylic partial denture Over-denture
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  • 3-Maxillofacial prosthodontics Pertains to the restoration (replacement) of developmental (conginital) or required defects of the stomatognathic system and associated facial structure with artificial substitutes (materials) such as abturators,nose ear eye denture.!
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  • Anatomical Crown Portion of a natural tooth covered by enamel and that extends from its cementoenamel junction (CEJ) to the occlusal surface or incisal edge
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  • Clinical Crown Its prepared potion of natural tooth,that extends from the occlusal surface or incisal edge to the bottom of gingival sulcus (free gingiva) known as abutment
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  • Artificial Crown Its a restoration of major surfaces or the entire coronal part of natural tooth,that restore (reestablish) anatomy,function and esthetics. Its made from metal, ceramics, acryl and gold.
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  • Fixed Restoration (prosthesis) Fixed restorations divided to two types of restoration. Fixed restoration Extra-coronalEntra-coronal
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  • Its restore (cover),external potion of a prepared tooth to tissue- compatible contour and obtain retention an resistance to displacement. Extra-coronal restoration
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  • Types of extra-coronal restorations 1- full veneer crown Its cover all surfaces od clinical crown, its maybe made from various materials (metal ceramic metal-ceramic, metal-acryl combination )
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  • Full metal crown Full (all) ceramic crown Metal-ceramic crown Gold crown
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  • 2- partial veneer crown its cover ( restore) only a portion of clinical crown such as (three quarter one half crown). One half crown
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  • 3- bridge (fixed partial denture(FPD) Bridge replace one or more missing teeth (named as a pontic) and supported on adjacent remaining teeth (named as abutment) bridge cover all surfaces of abutment to which the bridge is cemented Missing teeth ( pontic ) Adjacent remaining teeth (abutment)
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  • Missing teeth ( pontic ) Adjacent remaining teeth (abutment) Fixed bridge
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  • 4- resin-bonded bridge (Meryland bridge) replace one missing tooth in posterior area which cover and bonded to occluso-lingual surfaces, and replace maximum two teeth in anterior area which cover and bonded to lingual surface. The restoration bonds to the prepared surfaces by resin luting cement (etching enamel technique)
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  • Posterior resin bonded bridgeAnterior resin bonded bridge
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  • 5- laminates (facing) Cover only the facial surface of the tooth for esthetic purpose, they are fabricated from porcelain(ceramics) and bonded (micro-retention) to enamel by resin luting cement (etching enamel technique)
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  • Intra-coronal restoration Its restore the caries damaged areas of tooth crown by MO, MOD, OM surfaces preparations. Its obtain their retention and resistance to dispalcement its restoration within the coronal portion of teeth
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  • Types of intra-coronal restorations 1- inlay Its an intra-coronal restoration which used to restore the proximo-occlusal badly decaied surfaces (MO, MOD, OD caries ). Its made from ceramics or gold And cemented by resin luting cement or by glassionnemer cement
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  • 2- Onlay Its intra-coronal restoration, which is used to restore a more exstensively damaged posterior tooth and restore the most occlusal surface.
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  • Indications for fixed restoration 1- Missing of teeth ( kennedy`s classification) Class1, class2 - replace missing teeth with implant supported restoration Class3, class4 - replace missing teeth with fixed bridge or with implant supported restoration 2- tooth with large unsupported filling (weak walls) 3-discoloration of teeth (Tetracycline florsis) 4- endodontically treated teeth 5- post-crown restoration
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  • Factors affecting the success or failure of fixed restoration There are many factors related to the teeth and to the adjacet oral structures,that have direct influence on the success or failure of fixed restorations
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  • 1- Crown length Teeth must have adequate occlusocervical crown to achieve sufficient retention. Teeth with short clinical crown often dosen`t provide satisfactory retention,maybe additional length achieved through periodontal surgery or by orthodontic tratment.
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  • 2-Crown form Some teeth have a very tapered crown form (like mesiodense),which interferes with preparation parallelism. Its need to full coverage retainers to improve their retention and esthetic qualities.
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  • 3- Root length and form Abutment teeth must retain stability of prosthesis during function, abutment resist the occlusal force that will be transmitted to roots then to bone (as anchorage stability require anchorage). Roots with invert-taper form better than curved or malformed roots, also multirooted teeth provide greater stability (anchorage) than single-rooted teeth.
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  • Teeth with long roots act as a good abutment Teeth with invert-taper form of root are better abutment than curved or malformed roots
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  • 4- Crown-root Ratio A comparison of the tooth length projection out of the alveolar bone and the length embedded in the bone has been traditionally used as guideline In determining the suitability of a tooth as abutment (higher ratio less tooth will be able to resist additional occlusal forces). {Crown root Ratio can be determined by X-Ray panoramic or pre-apical }
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  • 1:1,5 ratio has generally been considered to be satisfactory, whereas a 1:1 is considered minimal. (requires condition of other factors such as number of teeth being replaced, tooth mobility and overall periodontal health)
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  • 5- Ante`s Low Abutment support may be evaluated by employing a rule referred to as (Ante`s low) says that the combined periodontal ligament area of the abutment teeth should be equal or exceed that teeth to be replaced Applying this rule is safe and useful guideline,when making fixed prosthesis (bridge) with long span ( replace two or more missing teeth )
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  • Ant`s low is useful for determining the prognosis of FPD Number denotes the root area precentage
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  • 6- Span Length The distance between two abutment teeth affects the feasibility of placing a fixed prosthesis. Replacement of one or two approximating tooth is routinely accomplished with a fixed prosthesis. however the loss of three adjacent teeth requires carefull evaluation of other factors such as crown-root ratio, root length, occlusion, periodontal health and mobility of tooth or post-crown
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  • Fixed prosthesis,replacing missing four adjacent teeth are sometimes fabricated but only in anterior area of mouth in which reduced forces encountered. Note : excessive long span is a common contraindication for FPD
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  • A bridge of shorten length will flex less compared to longer bar with same dimension Increase in length of the bar to twise its orginal value increase its flexibility by eightaa(8) times
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  • 7- Occlusion The occlusal forces on the prosthesis are related to: - the degree of muscular activity - the patient`s habits such as bruxism - the number of teeth being replaced - the leverage on the bridge - the adequacy of bone support
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  • Excessive occlusal forces can cause loosening of the restorations or fracture of ceramic and acrylic component in restorestion if present, and can also cause tooth mobility There are three types of force can be directed against a prosthesis during function ( tipping force twist {rotational} force path of insertion force).
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  • 1-Tipping force ca


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