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Bridge Design

Bridge Design . MJDF Tutorial. Bridges purpose. Fixed appliance that is used to replace a missing tooth or teeth When considering a bridge;

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Bridge Design

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  1. Bridge Design MJDF Tutorial

  2. Bridges purpose • Fixed appliance that is used to replace a missing tooth or teeth • When considering a bridge; • Why are do they need a bridge? Hypodontia, poor OH + caries, periodontal disease, trauma, fear of dreaded RCT (possible implication for conventional bridges), failing old bridge • Assessment and planning for a bridge is very important

  3. Types of bridges • Fixed-fixed • Cantilever • Fixed-Moveable • Conventional • Resin bonded (RBB) • Hybrid (rarely used) 

  4. Considerations - selecting • RBB vs Conventional • Fixed-fixed, cantilever, fixed-moveable. • Assessment : span length/how many teeth missing, position of teeth missing, periodontal surface area, endo status, mobility, coronal tooth tissue of adjacent teeth(quantity and quality), restorations present, OH and periodontal status, occlusion/occlusal demands, grinding/parafunctional habits, occlusal clearance, angulation, crown/root ratio • Patient factors – needle phobia, aesthetic considerations, motivation and OH,  • Financial considerations to patient (RRB cheaper than conventional)

  5. Resin Bonded Bridge • Adhesive wing is used to retain the bridge. Materials- NiCr or CoCr • Usually cantilever design, mixed opinions on fixed-fixed (“Fixed-fixed adhesive bridgework has a lower survival rate and there is evidence that they are twice as likely to fail compared to cantilever designs”), however increased surface area for bonding, if one wing fails repeatedly then can remove however difficulty in diagnosing a failed wing, secondary caries under failed wings. • Coverage of retainer – full palatal coverage to incisal edge (surface area for bonding) --- aesthetics concern with shine through – make patient aware, assess smile style (smiles with mouth open then not as obvious against dark background of oral cavity.) - Cover onto occlusal surfaces for posteriors – increased surface area, increased rigidity, increased retention and resistance

  6. RBB • Type of material bonding to : enamel > resin composite > glass ionomer cement (GIC) > dentine = amalgam. • Replace old restorations with new resin restorations for increased bond. • Prep vs no-prep: stabilisation with rest seat, occlusal clearance, may go into dentine = poorer bond, increased caries risk if bond failure as exposed dentine, no affect on tooth if continued failure when no prep. • Less of an issue if this fails in comparison to conventional. Can usually re-bond. (studies with high success rates when including rebonds)

  7. RBB • Retainer thickness should be 0.7mm minimum (anteriors) to have sufficient rigidity, thicker in posteriors due to increased occlusal demands, thicker also on longer spans. Reduces flex in bridge. (min 0.7mm needs specified to lab as found to be 0.5mm in study on failures) • In tilted or bulbous abutment teeth consider proximal surface prep to reduce bulbosity, this allows for increased connector height which results in less flex of bridge framework and also increased surface area - proximal surface prep can also decrease the size of embrasure spaces to prevent Black triangles occurring

  8. Retainer wing type • Metal wing better success rates than porcelain wings. Limited data on porcelain wings. “success of all-ceramic RBBs has been estimated at 72.5% at 3 years, compared to 82.8% for metal RBBs for the same period” ( not including rebond data). 5-year survival= 88% for metal wing. (Average life span= 7 years 10 months) • Occlusal clearance is important when planning porcelain wing as needs to be thicker to gain enough rigidity, may mean more destructive prep. Although no issue with darkening tooth. Still loss of translucency = matt appearance • Metal wing can be made thinner but has issue of shine through and darkening abutment tooth. • Cementation: sandblast with 50 micron alumina powder (ideally immediately before cementation- 40% reduction in bond strength if wait 24 hours). • Use a chemically-active cement (4-META, or more commonly MDP e.g. Panavia)

  9. RBB indications and contraindications • Indications: • Minimally restored/ unrestored abutment teeth • Patients not suitable for implants • Needle-phobic patients • Cantilever- good quality failure • Contraindications: • Heavily restored teeth • Poor abutment tooth – small surface area, periodontally involved. • Mal-aligned abutment teeth resulting in poor aesthetics or poor path of insertion • Poor OH/ high caries rate

  10. Conventional bridge • Bridge where the retainer is a crown/inlay (rare). • Similar principles apply when considering; thorough assessment and planning needed. • Connector thickness of minimum 2mm desired with conventional bridges, as great a thickness of retainer desired also. This reduces the stress through the luting cement by reducing flexibility of prosthesis. • Mainly fixed-fixed or cantilever design. • Survival = 94% at 5 years

  11. Conventional Bridge • More destructive, requires further tooth prep. Risk of pulp necrosis. • Preparation for a PBC/bridge retainer removes 62-73% of coronal tooth tissue. Figures for pulpal necrosis may be as high as 32% of bridge retainers!!! • Relies more on operator skill with regards to prep. • Better aesthetics with abutment tooth. • Failure can be catastrophic.

  12. Fixed-fixed bridges • Where there is an abutment at each end of span, all connectors in bridge are rigid. Meaning loads/forces are spread among abutments more. • Indicated where long span, increased loads on bridges and need for more retention and rigidity. (consider mobility of abutment teeth 3-1 = increased stress and flex on bridge) • Abutment teeth at each end of span should have similar retention and resistance forms, to spread forces along the bridge. • Path of insertion needs planned and considered before starting the preparations. Risk of pulpal exposure when paralleling preps. • Operator skill important in creating parallel preps.

  13. Cantilever Bridges • Good for anterior teeth or smaller gaps. • Not as successful when used posteriorly. • Mesial cantilever using distal abutment is more predictable (increased biomechanical levering forces on abutment if distal cantilever). • Easier for patients to clean.

  14. Fixed-moveable Conventional Bridge • Main indication is when there is notably differing axial inclinations whereby considerable tooth reduction would be required to have the preparations align which could result in pulpal exposure. Allows for differing paths of insertion of retainers, limiting tooth reduction and chance of pulpal exposure. Also useful if widely differing retainers with regard to resistance/retention form. • Fixed-moveable design; moveable connector should be in distal aspect of minor retainer. (Always the more anterior tooth, regardless of size) Female portion should be in distal of minor abutment and male portion should be in mesial of pontic.

  15. Pontic Design • Modified ridge lap most commonly used as best combination of aesthetics and cleanability. • Bullet/conical-shaped or hygienic design advised for posteriors as less aesthetic concerns. Make sure patient is aware of gap under pontic if choosing hygienic design.

  16. References • Dental update articles: • Gulati,J et al(2016). Resin-Bonded Bridges - the Problem or the Solution? Part 1; Assessment and Design. Dental Update. 43 (1), 506-521. • Gulati, J et al. (2016). Resin-Bonded Bridges - the Problem or the Solution? Part 2: Practical Techniques. Dental Update. 43 (1), 608-616. • Ibbetson, R. (2018). A Contemporary Approach to the Provision of Tooth-Supported Fixed Prostheses Par 1: Indications for Tooth Replacement and the Use of Fixed Bridges Retained by Crowns. Dental Update. 45 (1), 10-20. • Ibbetson, R. (2018). A Contemporary Approach to the Provision of Tooth-Supported Fixed Prostheses Part 2: Fixed Bridges Where the Abutment Teeth Require Minimal or No Preparation. Dental Update. 45 (1), 90-100. • Oxford Clinical Handbook of dentistry.

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