to increased torquing forces. the thinner the pontic, the more deflection occurs. if the thickness of the pontic is reduced by 50% this causes an 8 times increase in deflection. choosing pontics with increased occlusogingival dimension and using high yield strength alloys to construct the prosthesis will help reduce deflection. indications for use replacement of a single tooth or a small spanning space. good oral health status and motivation of patient to maintain oral health. periodontal status of remaining dentition at a stable and satisfactory level. abutment teeth of good quality with minimal restorations and enough surface area and enamel present for adhesion. splinting of periodontally compromised teeth to improve occlusal stability, comfort and decrease mobility. (periodontally compromised teeth is also a contraindication). as a way of fixed retention after orthodontic treatment or extraction. patient unsuitable for implants. this may be due to inadequate bone levels, expense or patient not wanting to receive implants. contraindications size of saddle area too long. patients with parafunction e.g. bruxism. tooth mobility increases risk of de-bonding. malaligned teeth resulting in poor aesthetics and common path of insertion. abutment tooth quality inadequate for example may have a reduced surface area, reduced enamel or be heavily restored. increased risk of caries due to increased difficulty in maintaining oral hygiene around the bridgework. increased risk of loss of vitality. allergy to base metal alloys e.g. nickel poor patient motivation. active dental disease (caries, periodontal disease) and poor oral hygiene. types of artificial plastic teeth types of artificial plastic teeth (known in the industry as pontics) wash-through pontic (also known as hygienic pontic or sanitary pontic) dome pontic (also known as bullet or torpedo shaped) ridge lap pontic (also known as full saddle pontic) modified ridge-lap pontic ovate pontic a pontic aims to restore aesthetics, give occlusal stability and improve function. the hygienic pontic does not contact the underlying alveolar ridge, making it the most straightforward to keep clean. due to the poor aesthetics of this design it is most commonly employed to replace mandibular molars. the bullet pontic is the second most favourable in terms of being able to maintain good oral hygiene, with the pontic only contacting one point of the alveolar ridge. ridge lap and modified ridge lap pontics have superior aesthetics to the designs discussed previously, with the labial/buccal surface aiming to restore the appearance of a natural tooth from the incisal edge to the gingival margin. to minimise coverage of the soft tissues the lingual/palatal portion of the pontic is reduced to improve accessibility for maintaining good oral hygiene. for the modified ridge lap design the pontic only contacts the buccal aspect of the alveolar ridge. the ovate pontic comes into contact with the underlying soft tissue and hides the defects of the edentulous ridge with applying light pressure. it is commonly used in provisional bridges following extraction of teeth to improve the emergence profile and helps in shaping the gingiva around the future fixed prosthesis. types of bridges according to durability bridges can either be provisional (temporary / interim) or permanent. the provisional bridge is a transitional restoration that protects the teeth that are weakened by the preparation, and stabilises the dental tissues until the fabrication of the final restoration, moreover, it can pave the way to the aesthetics of the future permanent restoration and its appearance, which can help the patient accept the final profile. provisional restorations are designed to be used for a few weeks to months, they can be fabricated directly (by chair side), or indirectly ( in the dental laboratory). it is usually tried in a few times to check if it fits properly and if its margins are well adapting on the teeth surface and gingiva, it may need relining or a few adjustments. provisional bridges can either be made of acrylic resins or metal. the resins are the most commonly used, they are either made of cellulose acetate, polycarbonate or poly-methyl methacrylate. other chemically activated resins include poly-r methacrylates: these are methacrylates with ethyl or isobutyl substances added to increase the strength of material. also, commonly used resins include the bisgma based dimethacrylate, and the visible light urethane di-methylacrylate. dimethacrylate-based materials were found to be better than monomethacrylates for temporary restorations in terms of flexural strength and hardness. types of bridges according to material metal based, noble based metals such as gold, or base metal alloys such as nickel chromium. non-metal based. they can be either resin veneered, fibre-reinforced composite, porcelain fused to metal, or ceramics which are either silica, alumina, or zirconia. acrylic resin and porcelain fused to metal (pfm) unaesthetic display of metal in a porcelain fused to metal restoration acrylic resin was the first veneering material used to help restore the aesthetics of crown and bridges, the aim was to maintain a similar colour to natural teeth by attaching it on the labial surface of metal crown / bridges, however, resin veneered dental prosthetics lacked stability and abrasion resistance. porcelain fused to metal (pfm) was then introduced; the porcelain is composed of two layers (one opaque to cover the metal substructure and another translucent to provide an enamel illusion). still several researchers consider pfm the gold standard as it has been reported to have 95% success over a 10-year period, a reason why newer types of all-ceramic restorations are usually compared to pfm crowns / bridges to assess its success and durability. however, pfm restorations may show a grey colour at the cervical margins of the tooth showing the metal substructure. ips emax ips emax ceramics offer high aesthetic properties, that's why its use has been increasingly popular, however, there's insufficient evidence to determine the longevity of emax in bridges; some reports found fair short-term survival, but unfavorable medium-term survival. failures of restorations were most reported in the posterior teeth region. ips emax is available as press ingots or as ips emax cad-cam system. emax use in crowns or bridges is not recommended for patients who suffer from bruxism. zirconia zirconia is used in anterior, and posterior fixed bridges, also on implants. zirconia is fabricated using the dental cad-cam technology. it has high mechanical strength and it can withstand high occlusal forces compared to all ceramic materials. in addition it can resist crack propagation in the core material, however, cracks often occur in the veneering material leading to its fracture whether in the tooth supported or implant-supported bridges. reports found that the 3×3 mm designed connectors in zirconia bridges increased the strength to resist fracture by 20%. although the use of ceramic based fixed prosthesis have been popular as it achieves a lifelike, highly esthetic appearance, a cochrane review found insufficient evidence to support or refute the effectiveness of ceramic materials for fixed prosthodontic treatment over metal-ceramic. clinical stages of bridgework assessment: clinical assessment of the patient's suitability for bridgework. detailed history (including medical history), appropriate assessment of the suitability of the patient's oral environment (including occlusion, caries risk, periodontal risk, radiographic examination, sensibility testing), assessment of patient aims & motivation, abutment tooth selection and bridge design. primary impressions: primary impressions can be taken with alginate to make study casts. a facebow record should also be taken to enable the occlusion to be studied prior to provision of the prosthesis diagnostic wax up: this enables the patient to visualise how the definitive prosthesis will look. the wax up can also be used to construct a putty matrix which can be used subsequently to make a temporary restoration. restoration replacement: restorations in abutment teeth with questionable prognosis or old composite resin restorations for adhesive bridgework should be replaced. tooth preparation: this should be completed with reference to radiographs and study casts obtained during treatment planning. for conventional bridges, tooth preparation should aim to conserve tooth tissue, ensure a parallel path of insertion, achieve clearance in the occlusion and ensure well defined preparation margins. the taper of each preparation on the abutment teeth must be the same. this is known as parallelism among the abutments and allows the bridge to fit onto the abutment teeth. adhesive bridges require minimal preparation. master impressions: an accurate impression should be made of the prepared teeth, along with an impression of the opposing arch. the master casts are used to provide accurate information about the occlusion to the laboratory and construct the prosthesis. occlusal registration: an occlusal registration is needed when providing extensive bridgework to allow the opposing casts to be related accurately. this may not be necessary if only a small number of teeth are to be restored. temporary restoration: temporary restorations should be fabricated if possible to protect and maintain the prepared teeth until placement of the final restoration. try in: confirm the clinical acceptability before cementing definitively. assess the prosthesis on the master casts and identify the cause of any problems if present. a period of temporary cementation to assess clinical acceptability prior to definitive placement is sometimes used. final placement: once satisfied the prosthesis is clinically acceptable, cement and bond the bridgework definitively. review: assess the bridgework and manage any post-operative issues. restoration fabrication full dental bridge being machined using worknc dental cad/cam software. as with single-unit crowns, bridges may be fabricated using the lost-wax technique if the restoration is to be either a multiple-unit fgc or pfm. another fabrication technique is to use cad/cam software to machine the bridge. as mentioned above, there are special considerations when preparing for a multiple-unit restoration in that the relationship between the two or more abutments must be maintained in the restoration. that is, there must be proper parallelism for the bridge to seat properly on the margins. sometimes, the bridge does not seat, but the dentist is unsure whether it is because the spatial relationship between the abutments is incorrect, or whether the abutments do not actually fit the preparations. the only way to determine this is to section the bridge and try in each abutment by itself. if they each fit individually, the spatial relationship was incorrect, and the abutment that was sectioned from the pontic must now be reattached to the pontic according to the newly confirmed spatial relationship. this is accomplished with a solder index. the proximal surfaces of the sectioned units (that is, the adjacent surfaces of the metal at the cut) are roughened and the relationship is preserved with a material that will hold on to both sides, such as pattern resin™ from the company gc america. with the two bridge abutments individually seated on their prepared abutment teeth, the resin is applied to the location of the sectioning to reestablish a proper spatial relationship between the two pieces. this can then be sent to the lab where the two pieces will be soldered and returned for another try-in or final cementation. advantages of bridges dental bridges offer several advantages. they can usually be completed in only two dental appointments, restore the tooth back to full chewing function, require no periodic removal for cleaning, have a long life-expectancy and are aesthetically pleasing. bridge failures common reasons for bridge failures poor oral hygiene: as with any fixed prosthesis including bridges, maintaining good oral hygiene to prevent plaque formation around the bridge is key. this will ensure prolonged performance. a study examined the gingival health around the fixed bridges after a 14-day - 6 month post insertion found the surfaces were more plaque retentive, causing gingival inflammation regardless the material of fabrication of the bridge, unlike single crowns which didn't show the same effect. mechanical failures: these failures can occur due to loss of retention of the bridge due to improper cementation, construction or preparation. fracture of the metal coating or pontic can also lead to mechanical failures. fracture in connectors of bridges at the gingival side is a common finding in most all-ceram bridges. biological failures: these can occur due to caries in the tooth (one of the commonest causes of crown and bridge failures) or due to pulpal injury. problems with abutment teeth such as tooth fracture, secondary caries or periodontal disease can cause discomfort and put pressure on surrounding soft tissues to also cause a biological failure of the bridge. aesthetic failures: these can occur at the time of cementation and include; colour mismatch, roughness of margins or improper tooth contour. aesthetics failures can also occur over a period