Indirect Restorations: Crowns, Bridges, and Posts - Dental Revision PDF

**[Indirect Restorations]** [Crowns] - Extra-coronal restoration, fabricated outside of the mouth, covering all or most surfaces of a tooth to restore its external form - Ferrule - A band of material which totally encircles the tooth - Extends 1-2mm onto sound to...

**[Indirect Restorations]** [Crowns] - Extra-coronal restoration, fabricated outside of the mouth, covering all or most surfaces of a tooth to restore its external form - Ferrule - A band of material which totally encircles the tooth - Extends 1-2mm onto sound tooth tissue to guard against longitudinal fracture - Function - Provides structural integrity - Restore form and function - Protect cusps - Prevents flexing - Aesthetic - Porcelain/ composite anterior crowns - Why not crown everything? - Destructive - Crown prep weakens tooth - Potential for pulp damage if tooth still vital - Often fall flat at some point, rarely permanent - Expensive - Considerations when tx planning - What will dentition be like in 10yrs time? - Widespread caries more cost effective to manage pt conservatively as they move from dentate to edentulous - Can I meet my pt expectations - Will the pt be able to tolerate tx and maintain restoration - Limited mouth opening may contraindicate crowns - Can I justify the damage to this tooth - Have the occlusal discrepancies been identified? - Pivots- need management plan before prepping tooth - Is the mouth periodontally stable? - Crown margins should be placed supragingivally - Where subgingival, be aware of biologic width - Biologic width= the space that the body naturally maintains between the base of the gingival sulcus and the alveolar bone (approx. 2mm avg.) - Is the tooth endodontically stable? - Pre-crown: signs of endo failure or poor condensing then retreat as this can improve the internal environment of the tooth, leading to better foundations - Does the tooth have a stable core? - Will the prep be retentive? - Adequate crown height - Is there enough space for the restoration? - Biologic width - If a restorative margin is placed too deep below tissue and invades the biologic width, there may be bone resorption or gingival inflammation - Where possible, place supragingivally - min distance of 2-3mm should be maintained between crown margin and alveolar crest - NB: crown margins places subginginvally for aesthetic reasons usually result in compromised aesthetics because of gingival inflammation Crowns and endodontics - Crown preparations place pulp at increased risk: - High speed of stripping HTs poses threat of overheating with disturbance of micro-circulation - High speed stripping opens up a multitude of dentinal tubules that communicate directly with pulp- deeper the cut into dentine, the more permeable it is and the more vulnerable the pulp becomes to irritants in the oral environment - Direct pulp exposure - Dangers of root treating crowned teeth: - Crown doesn't necessarily replicate the tooth beneath - Access can lead to loss of orientation and increased risk of perforation - Cutting through crown decreases strength - Cutting through crown disturbs cement lute, pre-disposing to debonding and microleakage - Rubber dam clamps can crack cervical porcelain, causing fracture - Minimising damage to healthy, vital pulps: - Use water irrigation when using a high speed drill - Cut dentine with open dentinal tubules should not be desiccated with the 3in1 - Desiccated means dried out/ lacking moisture - Ensure you provide a good, well-fitting temp crown Post Crowns - Posts should be equal length to anticipated crown height, with min 5mm GP left apically - Long posts are more retentive than short posts - Parallel-sided posts are more retentive than tapered posts, but produce more internal stresses in root canals; increased risk of fracture - Threaded posts are more retentive than smooth posts, but produce more internal stresses in root canals; increased risk of fracture - Fibre posts are more flexible than cast posts less likely to fracture; failure often due to secondary caries. These posts are bonded so all remnants of GP on walls should be removed; alcohol can do this; they require 2-3mm ferrule - If placing post in multi-rooted tooth, should be placed in straightest and bulkiest canal - Distal root for lower molars - Palatal root for upper molars - Ideally, post-channel preparation should be undertaken at the same appointment as RCT fill as the practitioner is familiar with the canal system - Creating the post channel with a rubber dam minimises microbial activity Further notes on crowns: - Premolars or molars with only minimal access cavities and no other coronal tissue loss can be restored with amalgam or composite - Posterior teeth that have lost one or both marginal ridges require cuspal coverage - If there is no plan to crown a weakened posterior tooth (e.g. RCT is on probation or for financial reasons), physical cuspal coverage must be provided by the core material - Cusps adjacent to lost marginal ridges should be reduced in height by 3mm - Teeth with little or no coronal tissue remaining may require surgical crown lengthening or forced eruption to provide a ferrule - Need to consider whether the tooth is restorable or whether best to extract the tooth and place a bridge/ denture/ implant - Ferrule refers to presence of at least 1.5-2mm of circumferential tooth structure above the crown margin- helps to improve the resistance and retention of a post-retained restoration - Guidance teeth are repeatedly loaded non-axially during excursions and as a result, heavily restored or crowned teeth may be at risk of fracture or de-cementation, esp if these forces are heavy - Important to identify which teeth provide guidance before tooth prep - If you feel a tooth is insufficiently robust to carry guidance, move guidance onto other teeth - It is easy to introduce new interferences when placing restorations; checking preparation for adequate clearance not only in ICP but also lateral excursions and protrusive excursion can help minimise the chances of this occurring - Where RCP involves a tooth you're about to prepare, it is often best to remove the deflective contact at an appointment before you start preparing the tooth Occlusion- Records for Planning Crowns - Thorough occlusal examination - Study models - Give unimpeded view of ICP as you're able to view lingually (obv not possible chairside)- also gives info about inter-occlusal space - Articulated study models mounted on semi-adjustable articulator - Main purpose of an articulator is to construct restorations that require little, if any, chair-side occlusal adjustment - Diagnostic wax-up Copying Tooth Guidance - This is often necessary to maintain proper occlusion and function, especially in cases of: - Anterior guidance want to keep as losing may lead to excessive posterior wear or parafunctional habits like bruxism - Canine guidance or group function - Full-mouth rehabilitation - When pt has stable, comfortable occlusion - Restoring pathologic wear cases - If guidance is necessary before preparing teeth, there are two ways of copying this: - Putty matrix - On cast of the unprepared tooth surfaces - Custom incisal guide table - Involves moving study casts of pt's unrestored dentition on a semi-adjustable articulator through a full range of lateral and protrusive excursions with a mound of unset acrylic on the guide table, so the tip of the articulator guide pin shapes the acrylic dough into (once set) a permanent record of tooth movements - Facebow Dimensions of Colours - Hue - Name of colour (e.g. red, blue) - Value - Measure of the lightness or darkness - High value= light shade - Low value= dark shade - Chroma - Saturation of a particular colour Tooth Prep for Crowns - Functional (F) cusps can be remembered using PUBL - Palatal upper, buccal lower - Full metal - Occlusal- - 1mm NF cusp - 1.5mm F cusp - Axial 0.5-1mm - Finish= chamfer - Porcelain - Occlusal- - 2mm NF cusp - 2.5mm F cusp - Axial 0.8-1mm - Finish= shoulder/ heavy chamfer - PFM - Occlusal- - Same as porcelain - Axial- - 1.2mm for porcelain - 0.5-1mm for metal - The general rule is to produce the least taper compatible with the elimination of undercut - The exception is resin-bonded porcelain crowns, which require a taper of 20 degrees to avoid generating high seating hydrostatic pressures during luting, resulting in crown fractures - If the taper is too low, as used for traditional crowns, the fit becomes too tight and prevents sealing - Luting= cementing or bonding a restoration - Luting agent= cement used to fill the microscopic space between the tooth and the restoration - For incisors, reduce the incisal edge by 2mm whichever material is used, then the lingual aspect should be reduced by 1mm for porcelain and 0.5-1mm for metal Strategies to Enhance Retention - Shorter, over-tapered restorations are at an increased risk of de-cementation - Retention grooves cut in the axial surface of a preparation reduce the radius of rotation, increasing retention - Nature of the cement lute: - Conventional cements are strong in compression but weak in tension, so prep should be designed to limit tensile stresses in the lute - This is achieved by ensuring prep is not over-cut or over-tapered - One study recommended 3mm as the minimum preparation height, and if necessary, surgical crown lengthening should be considered - Axial grooves increase retention by reducing radius of rotation- should be kept 0.5mm away from the finish line to reduce risk of micro-leakage and must be parallel with the POI - Resin cements overcome low tensile strength and poor adhesion of conventional cements; they have a higher tensile strength when used with dentine bonding agents, but they're technique sensitive Provisional Restorations - Function of provisional restorations: - Comfort and tooth vitality - Over exposed dentine to prevent sensitivity and PAP - Prevent unwanted tooth movements by maintaining intercuspal and proximal contacts - Function - Aesthetics - Diagnosis - To assess the effect of aesthetic and occlusal change - QuickTemp - (BisAcryl resin) is commonly used to create provisional restorations; occasionally it may be necessary to use a stronger cement where retention is limited (e.g. PolyF Plus) - Eugenol cements - Can significantly reduce the bond of resin cements to composite cores - If planning on using a resin cement and composite core, bond the provisional restoration with non-eugenol TempBond [Bridges] Definitions: - Bridge - Prosthetic appliance that is definitively attached to remaining teeth and replaces a missing tooth/ teeth - Abutment - Tooth with provides attachment and support for a bridge - Retainer - Component that is cemented to the abutments to provide retention for the prosthesis - Pontic - Artificial tooth that is suspended from the abutments - Connector - Component that joins the pontic to the retainer - Saddle - Area of edentulous ridge over which the pontic lies - Support - Ability of the abutment teeth to withstand occlusal load on the pontic Types of Bridge - Fixed-fixed - Pontic is anchored to the retainers with rigid connectors at either end of the edentulous span - Abutment teeth have to be crown prepped so requires significant tooth reduction - Both abutments provide retention and support - Both preps must have same POI  - Fixed-Moveable - Pontic is anchored to the major retainer at one end of the span via moveable joint to mirror retainer at other end - The major abutment provides retention and support whilst the minor abutment allows for flexibility - Indicated in cases of differing abutment tooth mobility, non-parallel abutments (differing POIs), periodontally compromised minor abutment, long-span bridges - contraindications= short span bridges (unnecessary complexity), poor OH and if both abutments are strong, well aligned and equally retentive - Direct-Cantilever - Pontic is anchored at one end of the span only - Single abutment tooth provides all the support - Pontic extends beyond the abutment, without a second retainer - Minimal tooth prep compared with a conventional fixed-fixed bridge - Used for low-load areas (eg replacing a lateral incisor or first premolar) - Indications: - Single missing tooth in low occlusal load area - Healthy strong abutment tooth - Good OH - Contraindications - High occlusal load areas - Weak/ perio abutments - Parafunctional habits - Spring-Cantilever - Retainer and pontic are remote from eachother and connected by a metal bar which runs along the palate/ lingual surface - Usually upper lateral incisors are replaced from the premolars/molars - Often poorly tolerated - Pontic appears to 'float' in the edentulous space - Minimally invasive compared to fixed-fixed - Indications: - Single anterior tooth replacement - Pt wants a fixed prosthesis but not suitable for implants - Good perio abutment - Desire to preserve adjacent teeth - Contraindications - Heavy occlusal forces - Parafunctional habits - Poor palatal/lingual hygiene - Long-span edentulous spaces - Resin Bonded - Cast metal wing carrying the pontic is bonded to the abutment tooth using an adhesive resin cement - Minimal tooth prep - No crown prep needed - Typically used for anterior teeth and sometimes premolars - Metal or ceramic wings bonded to the palatal/lingual surfaces of adjacent teeth - Uses adhesive bonding instead of mechanical retention - Indications - Single missing tooth - Young pt where implant not option yet - Good enamel structure - Pts wanting a conservative option - Contraindications - Heavy occlusal forces - Deep overbite - Short clinical crowns (less bonding surface) - Poor enamel quality - Heavily restored or decayed abutment teeth - Compound/ hybrid - Combination of more than one of the aboveused whe abutments have different mobility, angulation or periodontal state - Provides a balance of rigidity and flexibility, depending on abutment condition Selection of Abutment Teeth - Need to consider: - Caries and periodontal status - Pulp vitality - Existing restorations - Retention - Larger teeth offer more retention - Three factors are important when assessing **support** (ability of abutment teeth to withstand the occlusal load on the pontic): - A\) Crown : root ratio - Should ideally be 2:3 but 1:1 is acceptable - B\) Root configuration - Wider splayed roots provide more support - C\) Periodontal surface area - "Ante's Law" states the combined periodontal area of the abutment teeth must be at least as great as that of the teeth being replaced; however no scientific evidence to back this - Canines are v difficult to replace with bridges because the adjacent teeth are poor in terms of support and retention they have to offer - Canines usually also subject to massive stresses in lateral excursion (canine guidance) Types of Pontic - Bridge pontics that impinge on the gingival soft tissues result in plaque accumulation and gingival inflammation - Pontics should be carefully designed; they should be convex, have smooth surfaces and only light contact on the edentulous ridge to allow cleaning with superfloss - Modified ridge lap - Most popular design - Good aesthetics - Makes minimal contact with the ridge - Can be difficult to clean - Ovate - Good aesthetics - Pt must have excellent OH - Hygienic - Easy to clean - Does not contact the ridge so inaesthetic - Used for posterior bridge work - Conical - Makes point contact with the ridge so easy to clean - Inaesthetic - Used for posterior bridge work Resin Bonded Bridges - Advantages - Less expensive than conventional bridges, CoCr dentures and implants - Minimal prep needed - Often no LA needed as prep within enamel - If de-bond occurs, there is potential to re-bond - Disadvantages - Tendency to de-bond - Metal may shine through - Inaesthetic Stages to Providing a Bridge 1. Impressions and facebow record 2. Models mounted on semi-adjustable articulator 3. Diagnostic wax-up- can act as a template for temp bridge 4. Preparations of abutment teeth 5. Elastomer impression 6. Temporary bridge 7. Occlusal registration 8. Mount working casts in ICP 9. Metal work try-in (if RBB) 10. Trial cementation (1wk, reassess and adjust if necessary) 11. Permanent cementation 12. Review