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2020
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CRASH COURSE IN FIXED PROSTHODONTICS WWW.DENTISCOPE.ORG DONE BY : SIMA HABRAWI EDIT BY : HAIF ALQAHTANI DENTISCOPE 2020 Crash Course in Fixed Prosthodontics Table of Contents Occlusion examina...
CRASH COURSE IN FIXED PROSTHODONTICS WWW.DENTISCOPE.ORG DONE BY : SIMA HABRAWI EDIT BY : HAIF ALQAHTANI DENTISCOPE 2020 Crash Course in Fixed Prosthodontics Table of Contents Occlusion examination........................................................................................................... 4 Assessing tooth restorability.................................................................................................. 5 Process of assessing tooth restorability...........................................................................................5 Ferrule effect.................................................................................................................................5 Diagnosis & treatment planning for single tooth restoration.................................................. 7 Bridge classification........................................................................................................................8 Treatment planning for missing teeth.................................................................................... 9 Biomechanical principles of tooth preparation..................................................................... 12 Finish lines................................................................................................................................... 14 All metallic restorations....................................................................................................... 16 Dental Ceramics.................................................................................................................. 17 Glass ceramics.............................................................................................................................. 19 Oxide ceramics............................................................................................................................. 20 All ceramic restorations....................................................................................................... 22 All ceramic anterior crown preparation......................................................................................... 23 Surface treatment of the ceramic.................................................................................................. 24 Surface treatment of the tooth..................................................................................................... 24 Metal Ceramic restorations.................................................................................................. 26 Framework design [ metal part ] of metal ceramic restorations..................................................... 27 Anterior PFM crowns........................................................................................................... 29 Procedure and guidelines............................................................................................................. 29 Posterior PFM crowns.......................................................................................................... 31 Procedure and guidelines............................................................................................................. 31 Porcelain veneers................................................................................................................ 33 Composite veneers....................................................................................................................... 33 Veneers....................................................................................................................................... 33 Veneers preparation.................................................................................................................... 33 Impressions......................................................................................................................................................... 35 Temporizing......................................................................................................................................................... 35 Bonding / cementation........................................................................................................................................ 36 Done By : Sima Habrawi Dentiscope 2020 Edit By : Haif AlQahtani Page 1 of 77 Crash Course in Fixed Prosthodontics Esthetic considerations and shade selection......................................................................... 37 Smile line..................................................................................................................................... 37 Length of maxillary incisors.......................................................................................................... 37 Length of lower incisors................................................................................................................ 37 Monotonous smile....................................................................................................................... 38 Metamerism................................................................................................................................ 38 Luster.......................................................................................................................................... 38 HUE............................................................................................................................................. 38 VALUE.......................................................................................................................................... 38 CHROMA...................................................................................................................................... 38 Shade guides................................................................................................................................ 39 Management of endodontically treated teeth...................................................................... 40 Post systems................................................................................................................................ 40 Custom made – cast metal post + core............................................................................................................... 42 Cementation of posts.......................................................................................................................................... 43 Fiber reinforced posts......................................................................................................................................... 43 Fluid control + soft tissue management................................................................................ 44 Single cord technique................................................................................................................... 44 Double cord technique................................................................................................................. 44 Hemostatic agents........................................................................................................................ 45 Impression in fixed prosthodontics....................................................................................... 46 Trays............................................................................................................................................ 46 Impression materials.................................................................................................................... 46 Impression techniques......................................................................................................... 49 1- Putty wash techniquee.......................................................................................................... 49 2- Dual phase technique............................................................................................................ 50 3- Monophase.......................................................................................................................... 50 4- Dual arch.............................................................................................................................. 50 Impression mistakes..................................................................................................................... 50 Minimal preparation bridges............................................................................................... 52 Bonded pontic and Fiber-reinforced resin bridge................................................................... 52 RPD flipper denture.............................................................................................................. 52 Done By : Sima Habrawi Dentiscope 2020 Edit By : Haif AlQahtani Page 2 of 77 Crash Course in Fixed Prosthodontics Inlay / onlay bridge............................................................................................................... 52 Cantilever bridge.................................................................................................................. 52 Resin bonded bridge............................................................................................................. 52 Preparation of RBB....................................................................................................................... 54 Working casts + interocclusal records of conventional bridges.............................................. 55 Working cast materials................................................................................................................. 55 Die systems.................................................................................................................................. 55 Pindex system.............................................................................................................................. 56 Interocclusal record materials....................................................................................................... 57 Provisional restorations....................................................................................................... 58 Temporization techniques............................................................................................................ 58 Cementation................................................................................................................................ 60 Try in & delivery of crowns................................................................................................... 61 Adjustment.................................................................................................................................. 64 Dental Cements................................................................................................................... 65 Biomechanical considerations + special problems in bridges................................................. 67 Problems with long span bridges.................................................................................................. 67 Pier abutment.............................................................................................................................. 68 Tilted molar abutments................................................................................................................ 69 Missing canine............................................................................................................................. 70 Pontics and edentulous ridges.............................................................................................. 72 Siebert ridge classification............................................................................................................ 72 Pontic designs.............................................................................................................................. 73 Ridge lap.............................................................................................................................................................. 73 Modified ridge lap............................................................................................................................................... 73 Ovate................................................................................................................................................................... 73 Conical................................................................................................................................................................. 74 Bullet / heart shaped........................................................................................................................................... 74 Sanitary/ hygienic................................................................................................................................................ 74 Modified hygienic................................................................................................................................................ 74 References........................................................................................................................... 76 Disclaimer......................................................................................................................... 77 Done By : Sima Habrawi Dentiscope 2020 Edit By : Haif AlQahtani Page 3 of 77 Crash Course in Fixed Prosthodontics Occlusion examination Occlusal problems can lead to : 1- Tooth wear [Attrition, abfraction] 2- Fracture of tooth or a restoration 3- Restoration de bonding 4- Bone resorption + gingival recession + tooth mobility 5- PDL sensitivity and pain Ideal bite : A. In static occlusion - ICP / MI : you ask the pt to tap down on the articulating paper There should be equal contacts on all cusp tips and fossa – heavier contacts posteriorly - pre mature contacts will be heavily stained with less stain on adjacent points Premature contacts are caused by high cusps – deflective contacts are caused by large cusps they will cause the tooth or mandible to deflect in ICP [ more harmful] To examine location of contact points → use articulating paper [ 40 um] To examine how heavy the contact is → use shimstock B. In dynamic occlusion – lateral excursion: You ask the pt to slide their jaw to the right and to the left side Lateral guidance Working side interferences Non working side interference seen on the markings on the markings on the buccal cusps in outer [ palatal] inner [ buccal ] the upper and inclines of the inclines of the lower arch upper palatal upper palatal cusps cusps Ideally there should not be any interference on working or non- working side [ non working side interference is needed in complete denture pts] C. In protrusion: ideally you should have Even contacts on all anterior teeth and no posterior interference. Occlusal analysis should be done before any restoration. – if the pt has an interference [do not adjust it because the pt is already accustomed to it] Do not create an interference yourself ! Place the articulating paper [ red facing the arch being examined ] then ask the pt to move their jaw to the right or the left then use the blue side to record ICP. Any pure red mark [ not over lapped by blue ] is an excursive mark [ can be guidance or interference] Done By : Sima Habrawi Dentiscope 2020 Edit By : Haif AlQahtani Page 4 of 77 Crash Course in Fixed Prosthodontics Assessing tooth restorability Process of assessing tooth restorability 1- Remove all caries and previous restorations 2- Asses remaining tooth structure [ ferrule vertically and horizontally ] 3- Asses crown root ratio 4- Endodontic considerations [ ease of RCT and post placement, check if there are curved canals, calcified canals, root resorption , root fracture / perforation , PA lesions etc ] 5- Periodontal considerations : A. Tooth factors [ pocket depth , CAL , bone loss, mobility , if there are endo perio lesions etc ] B. Patient factors [ if the pt has any systemic disease or risk factors like smoking ] Ferrule effect vertical measurement - from the gingival margin to the top of the remaining wall [ should be measured from buccal , lingual, mesial and distal using a probe with a rubber stopper] Vertical ferrule Class 1 ferrule Height of remaining tooth ≥ 2 mm at 4 locations [ ideal ] Class 2 ferrule Height of remaining tooth 0.5–2 mm [ acceptable if you do post + core ] Class 3 ferrule Height of remaining tooth < 0.5 mm [ un acceptable even with a post and core] horizontal measurement – thickness of the remaining walls at the level of the future crown margin [ should be measured from buccal , lingual, mesial and distal using gauge calipers or if space does not permit → use a probe with a rubber stopper] Horizontal ferrule Wall width should be at least: the minimum thickness of preparation +1mm Aesthetic Margin (AM) – metal-ceramic or all-ceramic Non-Aesthetic Margin (nAM) – metal only Class 1 Width of remaining wall ≥ 2.2 mm (AM) or ≥ 1.5mm (nAM) ferrule Class 2 Width of remaining wall ≥ 1.5mm (AM) or ≥ 1mm (nAM) ferrule Class 3 Width of remaining wall < 1.5mm (AM) or < 1mm (nAM) ferrule chamfer margin width = 0.5 mm shoulder margin width = 1.2 mm Done By : Sima Habrawi Dentiscope 2020 Edit By : Haif AlQahtani Page 5 of 77 Crash Course in Fixed Prosthodontics Extensively damaged tooth can gain retention and resistance by : 1- Ortho extrusion 2- Crown lengthening 3- RCT + post and core NOTE: if you are restoring the tooth with composite resin or using resin cement [ Ferric sulfate and Aluminum chloride astringents used with retraction cords - affect the bond strength of composite to dentin.] – if astringents contact the prep just rinse with water spray Q: when do you decide to crown a tooth ? If you don’t have enough ferrule and 1- You can’t place a large direct restoration with an good you place your margins sub contour, contact point and occlusal contacts. gingivally: 2- When most or all axial surfaces of a tooth are weakened 1- you can violate the biological or are restored OR you need to correct axial contours. width → bone resorption + 3- As an abutment for a bridge. gingival irritation 4- To minimize the risk of tooth fracture. 2- you won’t be able to get smooth 5- To include design features of a metal based RPD. and clear finish lines 3- it is difficult to record subgingival finish lines in an impression ** if the tooth has a previous restoration → check the margins and if there are any caries. If the margins are intact and free of caries you can keep the restoration and prepare the tooth around it. Done By : Sima Habrawi Dentiscope 2020 Edit By : Haif AlQahtani Page 6 of 77 Crash Course in Fixed Prosthodontics Diagnosis & treatment planning for single tooth restoration 1- Medical history + CC 2- Clinical examination : A. Extra oral – notice smile line [ this will let you know where to place your margins and what materials to use] B. Intra oral - Tooth restorability - Vitality and sensibility tests - Perio chart 3- Radio graphs : - OPG [ screening for all teeth + gives indication of bone height , any remaining roots , cysts etc ] - Bitewings + PA [ check for any PA pathology ] 4- Take primary impressions and pour diagnostic casts for : - Occlusal assessment - Diagnostic wax up - Making temporary restorations Tx options: 1- Nothing 2- RPD 3- Implants 4- FPD Q: why do we need to replace missing teeth? 1- Restore function and esthetics 2- Provide occlusal stability Bridge components - not all pts need their missing teeth replaced. Many pts can function with a shortened dental arch [ from premolar to premolar] - Pier abutment = a tooth surrounded by edentulous space from both sides Done By : Sima Habrawi Dentiscope 2020 Edit By : Haif AlQahtani Page 7 of 77 Crash Course in Fixed Prosthodontics BRIDGE CLASSIFICATION BASED ON PREPARATION CONVENTIONAL You remove tooth structure / restoration and replace it with a retainer MINIMAL PREP Resin bonded bridge or Maryland bridge [ wings on the palatal surface of teeth] Indicated when you have intact abutments that you want to preserve Or if the pt is young and you want a temp solution until the pt is old enough to get implants HYBRID Conventional + minimal prep retainers BASED ON DESIGN FIXED – FIXED Can be conventional or minimal prep Has a rigid connector at both ends of the pontic. The abutment teeth are rigidly connected together. FIXED – MOVABLE Can be conventional or minimal prep Stress breaker A rigid connector [usually at the distal end of the pontic] and a movable connector that allows some vertical movement of the mesial abutment tooth CANTILEVER Can be conventional or minimal prep Provides support for the pontic at one end only. May be attached to one or more retainers at one end SPRING Only conventional CANTILEVER Restricted to the replacement of upper incisor teeth. Preserves the intact anterior teeth when the posterior teeth needed crowning. Preserve diastemas Done By : Sima Habrawi Dentiscope 2020 Edit By : Haif AlQahtani Page 8 of 77 Crash Course in Fixed Prosthodontics Treatment planning for missing teeth How you will replace a missing tooth should be decided BEFORE extraction. A single missing tooth tx options [ most to least conservative ] : implant → RBB→ cantilever → 3 unit bridge Dynamic equilibrium = when the arch is intact and the teeth are in their correct positions due to the pressure from the lips, cheeks, tongue etc. When a tooth is extracted the balance will be lost, [ Ex: the most commonly extracted tooth is the first molar , when it is extracted the 2nd molar will tip mesially and the 2nd premolar will tip distally and the opposing will super erupt to achieve a new level of balance and equilibrium ] Q: what are the consequences of losing balanced occlusion? 1- The tilted teeth will cause occlusal interferences 2- Tilted teeth will change the interocclusal space available and affect how your occlusal reduction will be and also what materials to place + change bridge design 3- You might need to do elective RCT on the opposing super erupted tooth Q: what can you do if the opposing tooth is super erupted? A. Keep the occlusal plane as it is and reduce the thickness of the pontic B. Adjust the upper occlusal plane by enameloplasty + you might need to do elective RCT RPD indications FPD indications 1- cross arch stabilization is needed 1- two or fewer missing posterior teeth 2- bilateral missing spaces with more than 2 teeth 2- four or fewer missing incisors missing or multiple edentulous spaces 3- Short cantilevers 3- long edentulous span [free end saddle] 4- Good abutments with favorable loading 4- when you need ridge support or there has been 5- No gross soft tissue loss severe ST loss 6- Favorable occlusion (inter-arch space) 5- anterior space more than 4 incisors 6- space includes a canine + 2 other teeth 7- advanced age and systemic problems Done By : Sima Habrawi Dentiscope 2020 Edit By : Haif AlQahtani Page 9 of 77 Crash Course in Fixed Prosthodontics Avoid RPD in: pts with large tongue. Muscular dis-coordination. Xerostomia [ there ill be no lubrication + frictional trauma ] Avoid FPD in : Pts with active caries or perio disease Dry mouth / xerostomia [ at higher risk for marginal caries ] Q: why can’t you place a bridge if the canine + 2 other teeth are missing? Because the canine is involved in guidance and these teeth will be subjected to a lot of load Resin bonded Bridges Usually used to replace a single missing incisor or premolar [ sometimes a single molar can be replaced only if patient’s muscles are not too well developed/ low occlusal forces] Usually is a transitional / temporary restoration The pontic is retained by 1 or 2 palatal wings on teeth mesial and distal to the space The pontic should not have any load If the teeth are mobile you can have an ortho wire connecting the wings together Contraindications : deep bite / parafunctional habits short clinical crowns if abutments are not well aligned Implants- Indications : 1- Inadequate number of abutment teeth [ you can place 2 implants and a bridge or one implant and make a bridge with a natural tooth] 2- Inadequate strength to support a conventional FPD 3- A long span ban be replaced by multiple implants 4- Single missing tooth with sound adjacent teeth 5- If the pt has too many failed previous RPD → go for implants and fixed prostho NOTES: Implants have different micromechanical movements compared to natural teeth → unequally distributed load will lead to implant failure [ this can be avoided by connecting placed implants with a bridge so they have the same movement] Combining an implant and a natural tooth is not recommended because the tooth and the implant will respond differently to the occlusal loading and have different movements → the cement underneath will be crushed → recurrent caries Forces need to be as vertical as possible to the implant Done By : Sima Habrawi Dentiscope 2020 Edit By : Haif AlQahtani Page 10 of 77 Crash Course in Fixed Prosthodontics Q: how do you asses abutments for a bridge? 1- Take radiographs to check for any perio problems – bone loss – PA radiolucency and Crown root ratio. [ optimum C:R ratio is 2:3 and minimum acceptable is 1:1] 2- Asses pulp health if vital and asses quality of RCT if it was previously treated 3- Asses periodontal support [ pocket depth , inflammation and mobility ] 4- Remove all previous restorations an determine restorability When there is bone loss the center of rotation shifts more apically → tooth is easily harmed by lateral forces Q: when can you accept a low C:R ratio? 1- No opposing 2- Opposing periodontally weakened teeth or artificial teeth Cases where roots become more retentive Roots that are broader BL Widely separated roots Abnormal curvature in the apical 3rd Well aligned tooth Done By : Sima Habrawi Dentiscope 2020 Edit By : Haif AlQahtani Page 11 of 77 Crash Course in Fixed Prosthodontics Biomechanical principles of tooth preparation Biomechanical principles of tooth preparation: 1- Conservation of tooth structure [ be as conservative as possible ] Excessive removal of tooth structure can lead to : 1- Over tapered short tooth with poor retention and resistance 2- Pulp hypersensitivity → inflammation → necrosis [ it is contraindicated to do a crown for a pt below 18 because the pulp chamber is big and you can easily cause pulpal irritation] 2- Retention and resistance : affected by A. Taper : The walls of the prep should converge occlusally - When you hold the bur parallel to the long axis of the tooth this will cause a 3° taper [ you need a total of 6° taper ] Importance of taperness: 1- Allows full seating of the restoration during cementation 2- Compensates for inaccuracies during fabrication 3- Allows you to visualize the prep walls and margins – without taperness you might have an undercut and not detect it ** retention and resistance decrease as taperness increases Q: how do you check taperness? Look at the prep with one eye from a distance of 30 cm , you should see all margins and no undercuts [ as if there is a ring around the tooth] B. Freedom of displacement : maximum retention and resistance is achieved when you have only one path of withdrawal C. Length : the longer the prep the better it’s retention and resistance If you have a short tooth , the wider the prep the more retentive it is. D. Path of insertion : considered in 2 dimensions [ mesio distally and bucco lingually] must be determined before the preparation usually it is along the long axis of the tooth in bridges all abutments should have the same path of insertion Q: what to do if the tooth to be restored is tilted but adjacent teeth are well aligned? You design the prep to be parallel with the adjacent teeth but trim the tooth from one side more than the other Q: what to do if the tooth to be restored is well aligned but adjacent teeth are well tilted? Severe tilting might need ortho adjustment but mild tilting → trim a little bit from the teeth In anterior PFM crowns if you go along the long axis of the tooth you have more metal showing → so the incisal 3rd should be with the long axis of the tooth to reduce metal showing. E. Internal features : grooves, boxes , pins Done By : Sima Habrawi Dentiscope 2020 Edit By : Haif AlQahtani Page 12 of 77 Crash Course in Fixed Prosthodontics 3- Structural durability: the restoration should have enough bulk to withstand forces – this is provided by: A. Occlusal reduction : depends on the type of material used + pt’s occlusion [ if the tooth isnot touching the opposing you can be more conservative in your reduction ] Material Functional cusp Non functional cusp Full metal 1.5 mm 1 mm PFM 1.5 – 2mm 1-1.5 mm Full ceramic 2 mm 2 mm B. Functional cusp bevel : 45° wide bevel on the functional cusp to provide material bulk and withstand forces Q: what are the consequences if you don’t bevel the functional cusp? A. If the technician waxes the crown to the optimum thickness → over contoured cusp + high occlusion B. If the technician waxes the crown to the normal contour → thin metal under the ceramic If you attempt to gain clearance by increasing the inclination and not by bevelling → you will remove tooth structure + result in poor retention and resistance + might expose the pulp C. Axial reduction : provide rigidity and durability 4- Marginal integrity: Finish line → on the tooth margin → on the prosthesis Margin of the prosthesis will affect: 1- Esthetics 2- Periodontal health 3- Marginal seal 4- Tooth substance conservation 5- Impression taking We usually try to avoid subgingival margins but if the tooth already has a restoration that extends subgingivally : 1- If there is a pocket → place the finish line of the crown apical to the restoration margin and If the finish line becomes close to the bone → do crown lengthening 2- If crown lengthening is not indicated → place the finish line coronal to the restoration but make sure the finish line is perfect [ if the restoration is amalgam → less risk of secondary caries ] Finish lines: A. Knife edge: zero ledge → Conservative to the tooth but plaque retentive B. Chamfer: curved ledge → Reasonably conservative non-plaque retentive C. Shoulder: flat ledge → Most destructive – non-plaque retentive Done By : Sima Habrawi Dentiscope 2020 Edit By : Haif AlQahtani Page 13 of 77 Crash Course in Fixed Prosthodontics Finish lines FINISH LINES USES / NOTES CHAMFER used in : All metallic restorations + Lingual portion of PFM Distinct and easily identified Reasonably conservative and non plaque retentive Done by : round end tapered diamond bur or torpedo bur [ use only half of the bur tip ] Depth = 0.3 – 0.5 mm HEAVY Used in : all ceramic restorations CHAMFER Rounded internal angle + 90 degree cavo surface angle Done by : round end tapered diamond bur or torpedo bur [ use only half of the bur tip ] Depth = 1mm SHOULDER Used in : facial portion of PFM + can be used for all ceramic restorations [ but internal angle has to be rounded] BUTT JOINT The angle between the shoulder and axial wall can be 90 °, less, or more = 120° Shoulder can be beveled to minimize marginal leakage Done by : flat end tapered diamond bur ** most destructive type of finish line → Sharp 90° internal line angle → Concentrates stress on tooth → Coronal fracture Depth = 1.2 mm SLOPED used in : facial portion of PFM SHOULDER 120° sloped shoulder margin - No unsupported enamel BEVELED Used in: Facial finish line of PFM crowns when gingival SHOULDER esthetics not critical - Proximal box of inlays, onlays- Occlusal shoulder of onlays and mandibular ¾ crowns The bevel will : removes unsupported enamel allows the cast metal margin to be burnished against the prepared tooth structure → minimizes marginal discrepancy KNIFE EDGE Used in : Mandibular posterior teeth with very convex axial surfaces – Lingually tilted lower molars. Permits acute margin of metal Thin margin difficult to wax and cast + Susceptible to distortion Common mistakes in finish lines : 1- discontinuity 2- roughness – you can smoothen the margins using enamel hatchet 3- undercuts – due to improper taperness 4- insufficient proximal clearance → can damage the finish line during die preparation in the lab 5- marginal lip → if you insert more than half of the bur [ for chamfer you use a 1 mm diameter bur and insert it only half way] Done By : Sima Habrawi Dentiscope 2020 Edit By : Haif AlQahtani Page 14 of 77 Crash Course in Fixed Prosthodontics ** Margins ideally should be supragingival [ 0.5 mm away from gingiva] Done By : Sima Habrawi Dentiscope 2020 Edit By : Haif AlQahtani Page 15 of 77 Crash Course in Fixed Prosthodontics All metallic restorations ** the pt should have completed the stabilization phase [ perio and caries control ] – occlusal analysis is done and a study cast is poured → Make putty index - Depth guiding grooves then occlusal reduction Functional cusp [ upper palatal and lower buccal cusps] = 1.5 mm Non functional cusp = 1 mm Bevel the functional cusp at 45° If you don’t place a bevel : 1- thin casting 2- poor morphology of the restoration 3- occlusal interferences. - Buccal reduction (2 planes: incisal and gingival) chamfer margin = 0.3 -0.7 mm Gingival 3rd → parallel to long axis of the tooth - Lingual reduction ( one plane ) chamfer margin = 0.3 -0.7 mm - Proximal reduction: break the contact with a needle bur first then continue the margin with round end tapered bur. - Finishing - Placing seating grooves - 0.5 away from the finish line Placed in the axial surface with the greatest bulk to prevent any rotational tendencies during cementation + increase resistance and retention and help guide the casting to place. Done By : Sima Habrawi Dentiscope 2020 Edit By : Haif AlQahtani Page 16 of 77 Crash Course in Fixed Prosthodontics Dental Ceramics Ceramic uses in dentistry: 1- To veneer metal [ PM] or zirconia core. 2- To be applied on the tooth directly with no substructure 3- Ceramic gingiva 4- Denture teeth 5- Implants - Porcelain is a specific type of ceramics that contain: Feldspar + kaolin + quartz Fabrication of ceramics: 2 main ways wither you mix powder + liquid or use a block/ ingot of ceramic Powder + liquid Blocks / ingots Sintering Heat pressing Slip casting Machining/ milling 1- Sintering : powder and liquid are mixed and then applied on the cast using a brush then fired at high temp. 2- Slip casting: The master cast is duplicated in refractory material that can withstand high temp. The refractory is layered with the ceramic, but when it subject to high temperature it shrinks more than the ceramic, which helps separating the ceramic restoration from it. [ the ceramic slips off the cast] 3- Heat pressing: lost wax technique – then the ceramic is softened and poured into the mould that forms 4- Milling: a block of ceramic is cut by a machine Ceramics based on melting (fusing temperature): High melting → used when they make the actual ceramic block that will later be cut Average melting → use in all ceramic restorations Low melting → used in PFM Ultra low melting → for esthetic retouches All ceramic restorations can either be: A. Ceramic core [ zirconia ] B. One block all the same material Ceramics : Glassy Matrix + particles [ crystalline or glass particles that melt at high temperatures] The more the glassy phase the more translucent the ceramic is. The more the crystalline phase the stronger the ceramic and more resistant to crack propagation Ceramics used for all - Predominately poly crystalline → zirconia ceramic restorations have - Partially filled glass → lithium disilicate higher amount of - Predominantly glass → feldspar crystalline. Done By : Sima Habrawi Dentiscope 2020 Edit By : Haif AlQahtani Page 17 of 77 Crash Course in Fixed Prosthodontics Most to least esthetic: Feldspar → lithium disilicate → zirconia Strongest to weakest : zirconia → lithium disilicate → feldspar The more crystalline particles the more opaque the material gets Translucent ceramics Opaque ceramics [ predominantly glass and partially filled glass] [ polycrystalline oxide ceramics- can be veneered by glass ceramics ] 1. Feldspathic 1. Alumina based 2. Leucite reinforced [ ex: IPS empress] 2. Zirconia based 3. Lithium disilicate [ ex: IPS e.max] Since ceramic is brittle it can be strengthened by: 1- Glass infiltration – increasing the volume of crystals inside the glassy matrix 2- Dispersion strengthening : adding zirconia, lithium or aluminum to change the physical or optical properties 3- Transformation toughening [ for zirconia] Glassy ceramics are mostly used in cases where the shade of the tooth is okay and you need to change the shape or contour, opaque ceramics are used when you need to change the shade or mask discolorations like tetracycline. Done By : Sima Habrawi Dentiscope 2020 Edit By : Haif AlQahtani Page 18 of 77 Crash Course in Fixed Prosthodontics Glass ceramics 1- Feldspathic ceramic: Most conservative and most translucent ceramic but weakest Needs a thickness of at least 0.2 -0.3 mm for each shade change Used in cases where more than 50% of the enamel remains [ enamel Is needed for optimum bonding ] Not used in pts with abnormal occlusion / bruxism Most successful ceramic used in inlays and onlays ** Can be sintered or milled 2- Leucite ceramics [ ex: IPS empress]: Minimum working thickness = 0.8 mm potassium oxide [less than 50%] - is added to the glass matrix Stronger material because it is made from industrial dense blocks + leucite has the ability to alter the coefficient of thermal expansion → inhibits crack propagation Heat pressed or milled Strength increases 3- Lithium disilicate [ ex: IPS empress II , IPS e.max] Lithium oxide [ more than 50%] – is added to the glass matrix Strong + very translucent [ even though is contains more particles it is still translucent because lithium has low refractive index] Can be used for posterior crowns and 3 unit bridges not extending beyond the 2 nd PM [ it can’t withstand high occlusal loads or parafunctional habits] Heat pressed or milled IMP: when you first mill lithium disilicate it is purple in color [ because it is lithium metasilicate ] → try it inside pt’s mouth [ check fit and occlusion and adjust if needed ] → fire it again [ this should be done inside your clinic not an outside lab] to get the white restoration [ lithium disilicate]. after getting lithium disilicate you can add stains IMP: in PFM bridges the connector thickness should be minimum 3 mm [ height and width] – in lithium disilicate bridges the connector is thicker → pt can’t clean in between + the thick connector irritates the gingiva. 4- Zirconia – reinforced lithium disilicate : Lithium silicate glass + 10% zirconia crystals Highest strength of all glass ceramics Indicated when less than 50% of enamel remains - Q: how can you increase the strength of glassy ceramics? By using adhesive bonding with resin cements - All glassy ceramics are bonded to the tooth not cemented – only glassy ceramics can be etched - Ceramics used to layer metal or ceramic cores = feldspar or leucite reinforced - Ceramic used to cover alumina oxide cores = lithium disilicate - The main drawback of lithium disilicate bridges = the need for a thick connector - Glass ceramics are mainly used to layer metals or zirconia cores - Oxide ceramics are mainly used by them selves or to make the ceramic cores Done By : Sima Habrawi Dentiscope 2020 Edit By : Haif AlQahtani Page 19 of 77 Crash Course in Fixed Prosthodontics Oxide ceramics: [ cannot be etched ] 1- Alumina based ceramics: [ glass infiltrated with aluminum oxide particles – still has some glass matrix] In ceram alumina, In ceram spinell , In ceram zirconia → high content of crystalline → very opaque [used only as core material that will later be layered with feldspar] – but they are no longer available Procera: densely filled with aluminum oxide [ 99.9 % oxide particle and has no glass matrix or silica] – highest strength of alumina based material but it’s strength is lower than zirconia ** although Procera is considered a subcategory of alumina based ceramics , it is closer to zirconia in it’s properties. 2- Zirconia based ceramics: Highest strength = 100 % polycrystalline [ no glass- therefore cannot be etched ] Very damaging to the opposing tooth Polymorphic material [ exists at different forms in diff temperatures] Zirconia has 2 forms : A. Tetragonal form : at high temp – this form is very resistant to crack propagation B. Monoclinic form : at room temp or when it cools down - at this form zirconia increases in volume → cracks To stabilize zirconia in the tetragonal form – they heat zirconia until it reaches tetragonal form and then add Yittrium to form → ( 3Y-TZP) – [ stabilizing zirconia with yittirum will allows the transformation from tetragonal to monoclinic form to happen under external stress→ increase volume → closing of the crack. Repairing chipped ceramic: Zirconia can be A. bi- layered [ zirconia core and then layered with glass 1- Etch with hydrofluoric acid ceramic] – most common complication is chipping of 2- Silane coupling agent the porcelain veneer and least common is fracture 3- Bonding agent B. monolithic [ one block – the entire restoration will be 4- Flowable composite zirconia] 5- Then fill with the porcelain Latest advancements of zirconia: repair kit A. Zirconia became available in multilayers B. Highly translucent zirconia If after try in of zirconia you had to adjust occlusion you need to send it back to the lab for re glazing + provide the pt with a night guard. 3- Hybrid ceramics: ceramic + composite polymer Adding composite : it can be etched have very similar properties to enamel and dentine easy to polish + you can light cure stains in the clinic no need for 2nd firing – can be used directly after milling Ceramic component provides strength Strongest to weakest: zirconia → procera → In ceram [ alumina, spinell, zirconia] → lithium disilicate → leucite reinforced → feldspar Done By : Sima Habrawi Dentiscope 2020 Edit By : Haif AlQahtani Page 20 of 77 Crash Course in Fixed Prosthodontics Done By : Sima Habrawi Dentiscope 2020 Edit By : Haif AlQahtani Page 21 of 77 Crash Course in Fixed Prosthodontics All ceramic restorations Advantages of all ceramic Disadvantages of all ceramic Highly esthetic & translucent 1- reduced strength because: Permits characterization and shade modification Ceramic is brittle because there is no underlying metal There is no underlying metal supporting structure Fracture of all ceramic restorations is lessened by using resin adhesive bonding + making sure you have enough thickness of ceramic [ correct preparation + CSM should be 90°] ** sloping margins [not 90 °]→ not enough thickness of the material + if the pt has unfavorable occlusion → half moon fracture in labio gingival area 2- Porcelain is very aggressive and can cause wear of the opposing tooth [ specially if it is not glazed or you don’t give the pt a night guard] 3- When used in bridges they need thicker connectors which jeopardizes the periodontium and makes the bridge inaccessible for cleaning by the pt Indications Contraindications High esthetic areas When a more conservative restoration can be used Enough tooth structure remaining Unfavorable occlusal load [ An edge-to-edge [ in short clinical crowns go for PFM] occlusion / Deep bite / parafunctional habits] Favorable occlusal load Teeth with short clinical crowns Porcelain layering: Opaque To mask the color of the opaque core and initiate color [ 0.2 mm] Dentine Makes the bulk of the restoration + provides color [ 1.5 mm] Incisal Provides translucency enamel The thickness of the preparation is also determined by how much you need to change the shade of the tooth [ for every shade change you need to remove 0.2 -0.3 mm more] To be more conservative, in RCT teeth you can do internal bleaching first to brighten the discoloration before you prep for a crown. ** the pt should have completed the stabilization phase [ perio and caries control ] – occlusal analysis is done and a study cast is poured Done By : Sima Habrawi Dentiscope 2020 Edit By : Haif AlQahtani Page 22 of 77 Crash Course in Fixed Prosthodontics 1- Make putty index [ it can be cut bucco lingually or mesio distally to help you see the reduction from different aspects ] 2- Prepare the tooth All ceramic anterior crown preparation - Depth guiding grooves then incisal reduction (inclined lingually / palately) = 2mm [ preferably made before buccal reduction] - Depth guiding grooves then buccal reduction (2 planes: incisal and gingival) 1.2mm [ gingivally] → 1.5mm [ incisally ] with shoulder margin Gingival 3rd → parallel to long axis of the tooth - Lingual reduction (2 areas: gingival (cingulum) and lingual) 1.2 m [ gingivally ] → 1.5mm [ lingually ] with shoulder margin Gingival 3rd → parallel to long axis of the tooth Use a rugby bur to provide the concave lingual surface – make sure you don’t reduce the height of the cingulum [ this will compromise retention] You can use both shoulder and chamfer[ no butt joint better esthetic] margins with all ceramic restorations but minimum width of the margin should be 1 mm - Proximal reduction - Finishing IMP: Centric contacts should be confined to the middle third of the lingual surface; where porcelain is supported by tooth structure. + Anterior guidance should be smooth and shared with the adjacent teeth Q: why is it important to have very smooth crown preps [ regardless of the material being used]? Any sharp areas will be replicated in the impression then the coping or cast metal and will act as stress concentration areas that will cause crack propagation and fracture Minimum clinical crown height after crown prep should be [ 3mm anteriors and 4 mm posteriors] The occlusal or incisal reduction for all ceramic types is the same – but some ceramics can have different axial reduction Done By : Sima Habrawi Dentiscope 2020 Edit By : Haif AlQahtani Page 23 of 77 Crash Course in Fixed Prosthodontics Q: how can you modify the shade of the restoration without affecting the prep? By adding stains or by changing the shade of the underlying resin cement Posterior all ceramic crowns have less survival rate compared to anterior all ceramic PFM anterior or posterior crowns have similar survival rates Surface treatment of ceramics before delivery: Surface treatment is needed so the ceramic surface will accept the resin cement. Notes: You can only etch glassy matrix [ silica] Silane coupling agent can only bind to silica in porcelain [ if the ceramic is polycrystalline and has no glassy matrix ( silica ) → tribochemical coating ] Surface treatment of the ceramic A. Etching [ only glassy ceramics]: 1- Etch with hydrofluoric acid to create micro pores and mechanical interlocking 2- Condition the surface by applying silane coupling agent to lower the surface tension and increase wettability of the ceramic [ the primer is a bi functional monomer that binds to the Bis – GMA of the resin cement and the silica portion of porcelain] Feldspathic / leucite reinforced porcelain is etched with 5-10 % HF acid for 60 seconds Lithium disilicate porcelain is etched with 5-10 % HF acid for 20 seconds B. Sand blasting : using aluminum oxides particles under high pressure to create surface roughness on the ceramic fitting surface C. Tribochemical silica coating [ for zirconia and alumina oxide ceramics]: 1- Air blasting Alumina particles coated with silica under high pressure onto the ceramic fitting surface [ zirconia / alumina oxide are mainly polycrystalline with no glassy matrix ( no silica ) to bind with the silane coupling agent ] 2- Condition the surface with saline coupling agent [10 – MDP ( silane + phosphate monomer)] The only cement that works really well with zirconia is Panavia -21 [ self adhesive phosphate modified resin cement] IMP: if the ceramic is already pre- etched by the lab → after trying it inside the pt’s mouth just clean it with phosphoric acid to remove salivary proteins Surface treatment of the tooth Etch the tooth with 37 % phosphoric acid + bonding agent then apply resin cement Resin cements Light cured For thin ceramics [ ex: variolink veneer, Rely X veneer ] Dual cured For thick opaque ceramics [ ex: Rely X ARC ] Self adhesive resin cement For PFM and posts [ ex: Rely X unicerm , panavia ] Done By : Sima Habrawi Dentiscope 2020 Edit By : Haif AlQahtani Page 24 of 77 Crash Course in Fixed Prosthodontics Summary of tooth preparation Type of Occlusal – functional Occlusal – non Margins material cusp functional cusp All metallic 1.5 mm 1 mm Chamfer all over PFM 2 mm 1.5 mm Chamfer lingually Shoulder buccally All ceramic 2 mm 2 mm Chamfer or shoulder all over ** if you expect complications after cementation it is better to go for PFM [ because zirconia is very difficult to retrieve later and it cannot be trimmed] ** if you are bonding very thin ceramics anteriorly like veneers , just air spray the bonding agent and don’t cure it before cementing [ if you cure it you might have flexes of the bonding agent] Done By : Sima Habrawi Dentiscope 2020 Edit By : Haif AlQahtani Page 25 of 77 Crash Course in Fixed Prosthodontics Metal Ceramic restorations Metal Ceramic Can be: Base metal [ ex: cobalt chromium/ nickel chromium ] Porcelain is a specific type Less than 25 % noble metal content of ceramics that contain: ** importance of Chromium : it forms chromium oxide layer, which Feldspar + kaolin + quartz prevents corrosion of the underlying Nickel and Cobalt + bonds with the overlaying ceramic Noble [ ex: palladium silver ] 25% or more noble metal content High noble [ ex: gold palladium] 60% or more noble metal content including at least 40% gold ** gold and palladium have high resistance to corrosion The metal of choice should : 1- Be biocompatible 2- Have corrosion resistance 3- Have low coefficient of thermal expansion 4- Have a melting point higher than ceramic Porcelain layers: 2- Opaque porcelain: [ 0.2 mm] Conceals the metal Initiates the shade Provides the bond between ceramic and metal 3- Body : Bulk of the restoration - Provides most of the color 4- Enamel : provides translucency of the edges Q: how is the porcelain bonded to the metal? 1- Mechanical entrapment by air abrasion of the metal 2- Metal has a higher coefficient of thermal expansion than porcelain → porcelains draws [attracted to] the metal when it cools down after firing 3- Oxide layer that forms on the metal Q: what causes the complete separation of the porcelain from the underlying metal? Excessive oxide layer formation or contamination of the metal surface during firing Done By : Sima Habrawi Dentiscope 2020 Edit By : Haif AlQahtani Page 26 of 77 Crash Course in Fixed Prosthodontics Framework design [ metal part ] of metal ceramic restorations Porcelain metal junction: At the porcelain-metal interface, the ceramic material should be at least 0.5 mm thick. The framework should have a distinct margin so that the porcelain is not overextended. No abrupt contour change between the metal and porcelain. Axial aspect: Thickness of the metal layer: ideally 0.5mm (minimum 0.3mm) Thickness of porcelain layer: ideally 1mm (minimum 0.7mm) The metal layer should be convex (in the axial wall), but with no undercut [ undercuts can cause crazing of the porcelain] obtuse angle it is more supportive but can lead to a grey shade at the margin. Occlusal aspect: Upper anteriors: ICP should be on metal whenever possible because ceramic is very abrasive and is more susceptible to fracture - The metal-porcelain edge should be 1mm away of ICP. If the patient’s ICP contact is close to the incisal edge (a “shallow” overbite) the porcelain should be extended more towards the gingival margin to prevent fracture Upper posteriors: Full porcelain occlusal cover (with lingual metal collar) - provides good aesthetics but risk of porcelain fracture and wear of opposing tooth To be more conservative the porcelain can extend over the buccal cusp tip (1.5mm away from the ICP) - The metal ledge under the porcelain must be rounded to prevent ceramic fracture. Done By : Sima Habrawi Dentiscope 2020 Edit By : Haif AlQahtani Page 27 of 77 Crash Course in Fixed Prosthodontics Lower posteriors: Full porcelain occlusal cover (with lingual metal collar) - provides good aesthetics for 1st premolar but for the 2nd premolar and for molar a more conservative approach [ metal covering the functional cusp] Optionally, the mesial half of the occlusal surface can be veneered while the distal half is kept in metal and receives the occlusal contact. Marginal extent of the porcelain veneer: when possible, a 3mm lingual metal collar should be provided to minimize tooth prep (upper & lower) and If aesthetics allow, a 1-2mm buccal metal collar to further minimize tooth prep If the aesthetic needs are high (e.g. the crown margin shows on smile) → the margin can be made by porcelain only. Mesial and distal extent the porcelain veneer: Mesial surface: The porcelain-metal joint should be placed palatal or lingual to the contact point Distal surface: The porcelain-metal joint could be placed buccal to the contact point if the aesthetics allow it. Advantages of PFM Disadvantages - Combines the strength of metal and the - Removes significant amount of tooth structure esthetic appearance of the ceramic [more than all metal but less than all ceramic] - More conservative than all ceramic - If you place the facial margin sub gingivally for restorations [ lingually] aesthetics → irritation to the periodontium - Good resistance and retention since axial - Nickel in the metal can cause allergy walls are included in the prep - Esthetics is less compared to all ceramic - Easier prep compared to partial coverage restorations [ PFM looks very dull] crowns - Ceramic can fracture **supra gingival facial margin is indicated in lower anteriors and when the smile line is low and will cover the margin. Indications of PFM Contraindications of PFM - PFM is better than all ceramic for long - High esthetic demand → use all ceramic span bridges - Pt is allergic to nickel → use nickel free alloys ** For short span bridges PFM and all ceramic - A more conservative restoration can be done [ have similar success bleaching, resin bonded bridge ] - PFM if better if it is planned to retain a - No sufficient tooth structure remaining and the metal frame work of an RPD tooth needs a post and core - Young pt [ if they really need a posterior crown consider all metal – less risk of damaging the pulp] Done By : Sima Habrawi Dentiscope 2020 Edit By : Haif AlQahtani Page 28 of 77 Crash Course in Fixed Prosthodontics Anterior PFM crowns Procedure and guidelines ** the pt should have completed the stabilization phase [ perio and caries control ] – occlusal analysis is done and a study cast is poured 1- Make putty index [ it can be cut bucco lingually or mesio distally to help you see the reduction from different aspects ] 2- Prepare the tooth : - Depth guiding grooves then incisal reduction (inclined lingually/ palately ) = 2mm [ preferably made before buccal reduction] - Depth guiding grooves then buccal reduction (2 planes: incisal and gingival) 1.2mm [ gingivally] → 1.5mm [ incisally ] with shoulder margin Gingival 3rd → parallel to long axis of the tooth - Lingual reduction (2 areas: gingival (cingulum) and lingual) 0.5mm [ gingivally ] → 1.5mm [ lingually ] with chamfer margin Gingival 3rd → parallel to long axis of the tooth Use a rugby bur to provide the concave lingual surface – make sure you don’t reduce the height of the cingulum [ this will compromise retention] *always check the reduction with the putty index [ better stay 0.5 mm less than the reduction needed -because Proximal you reduction will reducetapered walls with more when shoulder you join different aspects of the prep] → chamfer transition [ the transition should be The prep has to be in 2 planes and follow the anatomy located lingual / palatal to the contact point] If the prep is made in 1 plane only, one of these will happen: 1- porcelain will be thin and un-aesthetic [B] 2- technician will make it thick enough but this will make the crown bulky [c] 3- the one plane will be too tilted palately providing sufficient thickness for the porcelain, but compromising the pulp/tooth. [D] Done By : Sima Habrawi Dentiscope 2020 Edit By : Haif AlQahtani Page 29 of 77 Crash Course in Fixed Prosthodontics PFM 5 year survival All ceramic 5 year survival PFM crowns slightly higher survival than all Posterior all-ceramic crowns have different ceramic crowns survival rates depending on the material used PFM bridges significantly higher survival than all- The frequencies of fractures (framework and ceramic bridges veneering material) are more for all-ceramic bridges Anterior all-ceramic crowns have a comparable survival rate to metal-ceramic crowns loss of retention, caries and loss of pulp vitality are similar between metal-ceramic and all-ceramic bridges. [ zirconia crowns have significantly higher secondary caries rates] Done By : Sima Habrawi Dentiscope 2020 Edit By : Haif AlQahtani Page 30 of 77 Crash Course in Fixed Prosthodontics Posterior PFM crowns Glazed porcelain is very abrasive → if the pt has parafunctional habits → give night guard or make occlusal surface metal Procedure and guidelines ** the pt should have completed the stabilization phase [ perio and caries control ] – occlusal analysis is done and a study cast is poured → Make putty index Preparation: - Depth guiding grooves then occlusal reduction Functional cusp [ upper palatal and lower buccal cusps] = 2mm Non functional cusp = 1.5 mm Bevel the functional cusp at 45° - Depth guiding grooves then buccal reduction (2 planes: occlusal and gingival) 1.2mm [ gingivally] → 1.5mm [ occlusally ] with shoulder margin Gingival 3rd → parallel to long axis of the tooth - Lingual reduction ( one plane) 0.5mm [ gingivally ] → 1 mm [ occlusally ] with chamfer margin - Proximal reduction A. Wing prep : wings are placed 1 mm palatal / lingual to the contact point – results in a vertical wall that aids in retention – perfect if you need to place a post B. Wingless prep: shoulder → chamfer transition [ the transition should be located lingual / palatal to the contact point] - Finishing – make sure all angles and walls are smooth Inadequate reduction to provide sufficient thickness of ceramic material may result in: 1. Poorly contoured restoration - cosmetic effect and the health of the surrounding gingiva. 2. Poor shade match and translucency of the restoration. Check : - Clearances should be verified in the static occlusion as well as in all excursive movements. - Axial walls should exhibit 6° convergence. - No undercuts + Smooth, continuous finish line following gingival contours. Done By : Sima Habrawi Dentiscope 2020 Edit By : Haif AlQahtani Page 31 of 77 Crash Course in Fixed Prosthodontics Done By : Sima Habrawi Dentiscope 2020 Edit By : Haif AlQahtani Page 32 of 77 Crash Course in Fixed Prosthodontics Porcelain veneers A. Direct veneers [ composite] B. Indirect veneers [ composite, acrylic resin, porcelain , gold] ** if the pt has erosion palately – gold can be used to cover the palatal surface and reduce sensitivity or gold can be used on the lower anteriors if the pt doesn’t mind esthetics Composite veneers Advantages Disadvantages Simple , quick Mono chromatic appearance [ same color all over] No need for lab Requires high skills + time consuming Cannot mask deep discolorations [ otherwise it will be overcontoured] Veneers Indications Contraindications 1- Mild discolorations 1- Heavy discolorations / fluorosis [will resist 2- Mild spacing or mal alignment etching] 3- Small diastema closures or tooth wear 2- Poor OH and high caries risk 4- Hypocalcifications 3- Mouth breathers 5- Correct lingually inclined teeth ** 4- Bruxism / edge to edge occlusion / crossbite 5- Labially inclined teeth ** mouth breathers will have constant wetting and drying of the labial surface → stresses on the veneers and more susceptible to caries Some cases of diastemas can be closed using partial veneers [ very technique sensitive, difficult to place and you might break them while placement because they are very thin] Veneers preparation You must remain in enamel but provide enough thickness of porcelain [ 0.5 mm] No undercuts or sharp line angles Enough interproximal clearance to place a mylar strip between adjacent teeth during bonding Any visibly accessible area should be covered with porcelain LA is given AFTER shade selection [ because it might affect the shade] Facial reduction: [ not uniform reduction to avoid exposing dentine] - A 3 wheeled diamond bur is used to create depth grooves facially [ cervically = 0.3 mm and incisal half = 0.5 – 0.7 mm ] – the wheels on the bur don’t have the same diameter [ the wheel used cervically is narrower [ 0.6 mm diameter ] than the wheel used incisally [ 1 mm diameter ] - If you don’t have a 3 wheel diamond bur you can use a round bur of 1 mm diameter and sink it half way only to create a 0.5 mm groove] Done By : Sima Habrawi Dentiscope 2020 Edit By : Haif AlQahtani Page 33 of 77 Crash Course in Fixed Prosthodontics - after making the depth guiding grooves → connect the grooves together using round end tapered diamond bur [ make sure you have 2 plane reduction ] - you always need a finish line because the technician needs to know where the restoration ends : Finish line is either knife edge or chamfer. you might not always do facial reduction but you always need a finish line proximal reduction: - extension of the facial reduction [ you should not break the contact ] breaking the contact : A. harder for the pt to clean the margins B. might cause tooth movement while you construct the veneer → you need to temporize C. can create undercuts if the path of insertion is labial cases where you need to break the contact: A. peg shaped laterals [ the technician needs to build up the shape of laterals ] B. crowding C. diastema D. minor class 3 restorations [ you need to end on sound tooth structure ] incisal reduction: [ not needed in all cases ] A. window veneer prep : veneer is taken close to but does not include the incisal edge ADV: Retain natural enamel on the incisal edge – used when occlusion doesn’t allow you to extend your prep palatally DISADV: incisal edge is weakened by the prep – difficult to hide the cement incisally B. Feather: veneer is taken up to the incisal edge but the edge is not reduced ADV: anterior guidance remains on natural tooth structure DISADV: veneer is prone to fracture at the incisal edge Path of insertion for feather or window: just stick the veneer labially C. Incisal overlap: The incisal edge is reduced and veneer extends palatally [ finish line cervically and finish line palatally] STRONGEST DESIGN Indicated when you need to increase the length of the teeth – the junction of porcelain and natural teeth should be 1 mm away from centric contact ADV: provides a positive seat for cementing DISADV: more aggressive + you need to modify the path of insertion of the veneer Lingual reduction : 0.5 mm chamfer finish line located ¼ down the lingual surface – 1 mm away from centric contact – the position of the lingual finish line will depend on the thickness of the tooth + patient’s occlusion [Extending lingually will increase the surface area for bonding → enhance retention ] Done By : Sima Habrawi Dentiscope 2020 Edit By : Haif AlQahtani Page 34 of 77 Crash Course in Fixed Prosthodontics Path of insertion = hinged path [ you place the veneer under the incisal edge then rotate it towards the facial surface – this is done to prevent over reduction of the gingival 3rd] – if the path of insertion was inciso gingivally → the gingival 3rd needs to be reduced more Impressions 1- Retraction cord placed 2- Take impression with PVS or polyether In PVS place light body around the teeth and then take the impression with heavy body Usually -no need to temporize after veneers – temporize only if: 1- Teeth are sensitive due to exposed dentine 2- You did incisal reduction [ specially in the lower veneers ] 3- You are replacing only one out of many veneers 4- Multiple preparations 5- If you broke the contact Temporizing Spot etching with [ free hand carving , vaccum tray or silicone index] Just place a spot of etchant other wise you wont be able to remove the restoration and you have to trim it changing the previous prep. Veneers for lower incisors: Should have incisal overlap To overcome the risk of over eruption – composite stops are placed on the palatal surface of opposing teeth Crowns have higher incidence of caries Veneers have higher esthetic potential because they preserve the optical properties of teeth During try in of veneers if the shade is okay you can go ahead then clear resin cement. if you need to adjust the shade → try chemical cured resin cement until the color is acceptable then remove the veneers and clean then with acetone The final color of the veneer is 90% from the porcelain color / tooth color and only 10% cement color Done By : Sima Habrawi Dentiscope 2020 Edit By : Haif AlQahtani Page 35 of 77 Crash Course in Fixed Prosthodontics Bonding / cementation 1- Rubber dam + Mylar strips between teeth [ to prevent veneers from sticking together ] + Teflon tape on adjacent teeth [ to protect them from etchant] 2- Clean the preps with pumice / polishing paste and rubber cup 3- Etch the tooth with 37% phosphoric acid and apply bonding agent [air thin and don’t cure] ** if there is any bleeding during cementation → stop and postpone to a different day 4- Etch the veneer fitting surface with hydrofluoric acid + wash 5- apply saline coupling agent and air thin then apply bonding agent and air thin 6- Apply resin cement onto the veneer and place it on the prep [ veneer is held with a sticky micrbrush] 7- Tack cure for 3 seconds → remove excess cement then light cure for 60 seconds Dual cured composites and mainly used with : A. Restorations outside the smile line B. Restorations more than 0.7 mm thick C. Opaque veneers 8- Finishing with diamond burs and polishing strips and discs then diamond paste + rubber cup Done By : Sima Habrawi Dentiscope 2020 Edit By : Haif AlQahtani Page 36 of 77 Crash Course in Fixed Prosthodontics Esthetic considerations and shade selection Q: what can you do to match between pt’s expectation and reality? 1- Diagnostic wax up : wax up the changes to be done or the Mock ups: after doing wax up on the restoration on the cast and show it to the patient [ you can cast – the cast is duplicated into also change It to a mock up that is tried inside the pt’s mouth stone and a vaccum tray is made. you for a while, or a provisional restoration that the pt can wear inject temporary crown material in for a while ] the vaccum tray and stick it inside the 2- Composite resin: you apply a small piece of composite to see pt’s mouth [ this way you can test for if the pt likes it or not. speech, phonetics and occlusion but 3- Water soluble ink: only used if you are going to remove from not esthetics ] the tooth structure [ if you are going to do enameloplasty to adjust the occlusal plane – the ink will only show the areas https://www.youtube.com/watch?v= that you will remove ] UkfsElWv_uM 4- Using computer softwares: those programs don’t give realistic results and the pt might have high expectations 5- Show the pt photographs of your previous cases Smile line : composed of the incisal edges of the maxillary anteriors , it Is parallel to the inner curvature of the lower lip and inter pupillary line and perpendicular to the facial midline. [ women show twice more of their maxillary incisors when their upper lip is at rest] When choosing the midline of the patient, you choose the closest structure towards the midline [ the nose or the philtrum ] Length of maxillary incisors : established by anterior guidance and phonetics [ saying letter F , the upper incisal edges should contact the wet line of the lower lip] Length of lower incisors : the incisal edges of the lower incisors should be 1 mm behind and 1 mm below the incisal edge of the maxillary incisors when the pt says the letter S. Long maxillary incisors will lock the anterior guidance → Pt can’t slide forward + TMJ problems + affects phonetics [ F sound] Long mandibular incisors → letter S will be affected + the teeth can hit the palate SMILE LINES: High smile line [ gummy smile] : pt exposes all of the anterior teeth + soft tissues Caused by short upper lip or very active lips or very pronounced skeletal make up Average smile line: pt exposes only 75-100 % of their teeth without exposing soft tissues Low smile line: pt exposes less than 75% of anterior teeth Done By : Sima Habrawi Dentiscope 2020 Edit By : Haif AlQahtani Page 37 of 77 Crash Course in Fixed Prosthodontics NOTE: old patients have low lip lines because with age muscle tone decreases → the upper lip becomes longer → low lip line. at the same time they start exposing their lower anteriors because the decrease in muscle tone will cause the lower lip to drag down exposing the teeth. Monotonous smile: the centrals, lateral and canines all look the same. The incisal portions of the long axes of the crowns are more mesial than the gingival segments+ the incisal / occlusal segments of teeth are always lingually inclined. [ teeth are mesially and lingually inclined] As you go posteriorly – the interproximal contacts of teeth become more gingival and the incisal embrasures increase [ the contact between centrals is in incisal 3rd , contact between central and lateral is junction between incisal and middle 3rd] Recued incisal embrasures are associated with older age and attrition – increased incisal embrasure are associated with a more youthful smile. Golden proportion: height to width ratio of 0.618 – each anterior tooth is 40% narrower than the tooth mesial to it. Metamerism: the object will look differently under different light sources How smooth the restoration is will determine the amount of light reflected Proper tooth reduction will allow the technician to layer ceramics properly → better esthetics but you might compromise remaining tooth structure If you don’t give the technician enough space to layer ceramics → the restoration will be over contoured to make it more esthetically pleasing Luster = the level of glaze of porcelain – over polishing porcelain will make the molecules fuse and it will increase it’s opacity! HUE = the color itself [ dentine provides most of the color in teeth but the color is modified by the translucency of enamel.] VALUE = how light or dark the color is. [ high value = light , low value = dark ] – 2 completely different colors can have the exact same value CHROMA= intensity or saturation of color [ high chroma = high saturation, low chroma = low saturation] Dentine affects the hue & chroma , enamel affects the value. Done By : Sima Habrawi Dentiscope 2020 Edit By : Haif AlQahtani Page 38 of 77 Crash Course in Fixed Prosthodontics Shade guides A. Vita classic : based on hues [ 4 letter and 4 colors ] As numbers rise => Chroma increases A1 -A4 (reddish-brownish) and Value decreases. B1 - B4 (reddish-yellowish) C1 - C4 (greyish shades) Chroma: (1= low, 4= high) Value: (1= D2 - D4 (reddish-grey) High, 4= low) B. Vita pan 3D master [ the only one approved by the ADA – produces least error] : based on value – can be converted to vita classic but not the opposite Value = 5 levels [ 1,2,3,4,5] Hue = M,L,R Drawbacks of shade guides: 1- They don’t cover the entire range of tooth colors 2- They lack the metal substructure if you are using them for PFM 3- The tabs are made from different type of porcelain than restorations 4- The tabs are thick while the porcelain placed in restorations is only 1.5 mm thick Q: how to minimize errors while choosing the shade of the restoration? 1- Choose the shade at the beginning of the appointment [ to avoid eye fatigue] + done under mid day light and under different light sources to prevent metamerism 2- Before shade selection the teeth should be cleaned from any stains and kept wet **Make sure you and your technician use the same type of shade guide 3- Patient should be upright , at your eye level and surroundings should be neutral 4- You choose the value first by squinting your eyes [ low amount of light is needed to activate the rods at the periphery of your retina which is responsible to differentiate values] If the shade of the tooth is between two tabs → choose the one with higher value and lower chroma [ can latter be adjusted by adding stains] 5- Choose hue by opening your eyes wide [ high amount of light is needed to activate the cones in the center of your retina which is responsible to determine hue] 6- Look at the middle of the tab when choosing dentine color, view it from both mesial and distal sides [ one eye will be dominant and will perceive the color ] – DON’T LOOK FOR MORE THAN 5 SECONDS [ YOU’LL LOSE SENSITIVITY TO YELLOW] Ideal light source is balanced day light with average color temp of 6,500 K and it should be around 30 cm away from the pt When checking shades it is recommended that the pt wears a grey bib [ because it has no complementary color – blue bibs will increase sensitivity to yellow / orange colors The centrals, laterals and premolars have similar color. The canine is a shade darker Mandibular incisors are a shade lighter than maxillary incisors Done By : Sima Habrawi Dentiscope 2020 Edit By : Haif AlQahtani Page 39 of 77 Crash Course in Fixed Prosthodontics Management of endodontically treated teeth Remaining tooth structure is more important for preventing fracture of the tooth and retention of the restoration than the post design. A post will not strengthen and reinforce the tooth – post preparation will further weaken the tooth Teeth with posts have more apical periodontitis - Teeth with less than 3mm remaining root filling have significantly more radiolucencies when significant tooth structure is lost and the remaining structure cannot retain the restoration→ a post + core is needed [ you still need a 2 mm ferrule] Tx options if you don’t have enough ferrule: 1- Crown lengthening 2- Orthodontic extrusion Q: what affects your choice of posts ? 1- Type of tooth 2- Amount of remaining tooth structure 3- Shape of the canal [ regular, wide and oval etc.] Post systems 1- Active posts (tapered/parallel): retention provided by the use of threads. Indicated in short, curved canals. [ ex: self threading or pre tapered ] 2- Passive posts: retention provided by the luting cement. Cast post and core Preformed passive posts (tapered/ parallel, smooth/serrated) Fiber posts (slight flexibility) NOTES: - threaded or serrated posts are more retentive than smooth surf posts - parallel sided posts are more retentive than tapered posts [ but they can cause root fracture apically] - Tapered posts act as wedges leading to root fracture - Parallel sided posts do not cause this wedging - cement retained posts → distribute masticatory forces evenly to the tooth [cement acting as a buffer between post and the tooth] Q: why is it better to have a post + core alone then a crown and not have it as one piece? 1- get better marginal adaptation 2- you can replace the crown separately without replacing the post 3- allows you to have different path of insertion for each of the crown and the post Done By : Sima Habrawi Dentiscope 2020 Edit By : Haif AlQahtani Page 40 of 77 Crash Course in Fixed Prosthodontics Factors affecting post retention: 1- Post length Retention increases with post length [ post should be as long as possible without jeopardizing the apical seal or strength of the remaining root structure] Posts shouldn’t be shorter than the remaining coronal height – if the root is short and the crown is long → you can leave an apical seal of a minimum 3mm Posts are not placed in curved roots 2- Post diameter Shouldn’t be greater than 1/3 of the diameter of the root At least 1mm wall thickness is needed circumferentially. Increased post diameter does NOT significantly improve post retention. Optimal post diameter measurements : Custom made post + core can be cast metal or CAD/ CAM milled You need to keep 4-5 mm of GP apically. Done By : Sima Habrawi Dentiscope 2020 Edit By : Haif AlQahtani Page 41 of 77 Crash Course in Fixed Prosthodontics Custom made – cast metal post + core Indications: Excessively flared canals or non circular - Very little preparation is needed for custom- made posts. In round canals : anti-rotational device or notch placed in coronal part of preparation. DISADV: 1- Less retentive than parallel sided post. 2- Wedging effect produced within root. 3- More time consuming + needs a lab 4- needs to be slightly undersized in comparison with the canal to achieve optimal internal seating. In post and core prep – the reduction for the crown prep is ALWAYS DONE FIRST - and the remaining coronal tissue is prepared perpendicular to the path pf placement of the post. GP can be removed by : warmed plugger or rotary instruments [ Gates Glidden ] or chemical Cast metal post + core fabrication Direct method Indirect method made in patient’s mouth using auto polymerized or light-polymerized Made in the lab resin. Used for single canal and good clinical access Procedure: Procedure : 1- Fit a prefabricated plastic post to the canal. [Must extend to 1- Cut ortho wire to length and the full depth of the prepared canal] shape it as “J” 2- Lightly lubricate the canal (dry the canal by air directed across 2- Coat wire with tray adhesive, the root surface not into the canal). lubricate the canals. 3- Use “brush-bead” technique to add resin to the occlusal half of 3- Use Lentulo spiral to fill the canals the dowel and seat. with elastomeric impression 4- Don’t allow the resin to fully set, loosen & reseat several times material (clock wise) while it’s rubbery. 4- seat the wire →use a syringe to fill 5- Trim the plastic post until it is 2mm occlusal to the finish line in more impression material then buildup the core. around the prepared teeth → 6- Finishing insert the tray. resin is not added to the apical portion of the prefabricated plastic 5- The removed impressed will have post as it corresponds in size to the twist drill used. an impression of the prepared https://www.youtube.com/watch?v=QFB50gSRGIs canal The marginal fit of a cast post is not as crucial as that of extra-coronal restoration because it will be covered by the final crown. Temporization for cast metal post: Use a wire of suitable diameter or an interim post - Core is then fabricated with autopolymerized resin by direct technique. Done By : Sima Habrawi Dentiscope 2020 Edit By : Haif AlQahtani Page 42 of 77 Crash Course in Fixed Prosthodontics Cementation of posts Luting agent has little effect on post retention or fracture resistance of dentin. Fiber post Cast post No pre treatment needed No pre treatment needed Check the fit and take radiograph Check the fit [ if the fit is tight you can remove Clean with alcohol shiney spots with a bur] Cement with rely X [ self adhesive resin cement] Cement wi
