Lecture notes
Dental Surgery BDS Crowns
- Module
- Dentistry
- Institution
- Cardiff University (CF)
A complete set of notes on all crowns/bridges teaching from the Dental Surgery BDS course at Cardiff University. All 5 years are covered.
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Assessment of Tooth● Restorability
● Caries/disease/fracture present
● Pulp exposure/status/size
● Amount of remaining tooth tissue (determine material)
● Clinical crown height
● Periodontal/gingival condition
● Pt factors: oral hygiene, pt compliance, cost
● Occlusal relationship
● Access
● Cause of extensive tooth damage: anterior = trauma > caries > wear, posterior = caries
> wear > trauma
Tests
● TTP
● Mobility
● Vitality: if tooth non-vital → RCT. Post & core for increased retention
● Check restoration is sound as core & doesn’t need replacing
Radiographs
● IOPA: pulp dimensions, PA tissues, root filling, PD tissues, presence of post
● BW: IP caries, pulp proximity
● OPT: overall - less detailed, higher radiation dose
Study Models
● Purpose: to assess occlusal space for crown, pre-op occlusion, clinical crown height, to
assist in constructing temp restorations & special trays
Treatment Plan
● Pain, disease, stable core, vital tooth or RCT, procedure
Impressions for Crowns
● Aim: accurate imp of prepped tooth, neighbouring teeth & CPs, opposing arch
● Technique: retract gingiva, 1 stage P&W + rigid stock tray, MB silicone + special, work w
healthy tissues
● Problems: poor retraction, poor flow of material, distortion (pulls away from tray), unclear
margins, doesn’t capture adjacent teeth, air bubbles/drags, separation of the 2 materials
(using 2 different brands)
Principles of Crown Prep
● Tooth reduction: balance b/t pulp protection & sufficient space
● Non-undercut
● Retentive: 6-10 degree taper (prevent removal along POI. Long, less tapered crown
more retentive)
● Resistance: prevent displacement by lateral forces. Long crown more resistance.
Improve rotation resistance w grooves
● Occlusal reduction: depends on functional/supporting cusp & material
● Margin type
- thin metal strong, thin ceramic weak
- clearly defined margin important (knife-edge, chamfer, shoulder, bevelled shoulder)
, ● Smooth edges → decreases stress → decrease # ptl
● Structural durability: must withstand forces of occlusion & provide acceptable aesthetics
Supracrestal Tissue Attachment
● Area of tissue bt JE & alveolar crest bone - made up of supracrestal fibres
● Provides seal against infection/disease of alveolar bone
● Subging margin may impinge on PD tissue attachments → gingival IF, chronic
pain & plaque accumulation → CT breakdown, apical movement of biological
width → alveolar bone resorption & PD pocketing
● Attachment = 2mm in health
Crown Margin
● Should be within a fraction of a mm above gingival margin - can be altered if short
clinical crown height & further retention required / if gingival recession
● Should be readily cleansable → prevent caries
Metal Ceramic Crowns (MCC)
● Strong - weak: all metal - MCC - all ceramic - composite
● Metal substructure strengthens overlying porcelain
● Substructure uses specific bonding alloys / melting point alloy >> ceramic / by adding pd
+ pt to au / by using base metal alloys
● Mechanical bonding to ceramic: sandblast metal surface
● Chem bonding to ceramic: oxide layer formation on metal surface
● Compression fit: difference in CoE of TE
● Place supragingivally where possible (subging → IF/recession)
● Traditionally v hard → use metal surfaces as occlusal/centric stops → can alter
metal alloy hardness → decreases wear
Prep
● Occlusal reduction: MC 1.5-2mm (buccal), 1-1.5mm (palatal/lingual)
● Chamfer/shoulder margin: MC 1.2mm (buccal shoulder), 0.5mm (palatal/lingual chamfer)
Posterior Crown
● Fn: mastication, maintain existing tooth structure, maintain occlusion, aesthetics,
hypoplasia/hypocalcification, if RCT (must), caries/toothwear/trauma that is threatening
vitality of pulp
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