Core build up and Amalgam bonding

12th October

Learning outcomes To know the definition of a core build

up. To understand the advantages and

disadvantages of amalgam as a restorative material

To understand the aims of amalgam bonding

To know the clinical stages to perform a bonded amalgam

Core Definition

'that part of a preparation for an indirect restoration consisting of restorative material'.

Types of Core Materials

Amalgam Composite Glass Ionomer Resin Reinforced Glass Ionomer Compomer

AMALGAM

Advantages

Not especially technique sensitive Strong in bulk section Sealed by corrosion products

Disadvantages

Best left to set for 24 hours before tooth preparation

Weak in thin section Mercury content may be of concern to some

patients and dentists Potential electrolytic action between core and

metal crown Not intrinsically adhesive

How is the amalgam retained as the core?

Retention Form

Resistance Form

How is the amalgam retained as the core?

Mechanical Retentive grooves and notches

Pin Placement Adhesion

Amalgam BondingA technique to bond amalgam to the cavity.

Aims Behind ‘Bonded Amalgams’ Conserve more tooth structure by

reducing the need to remove sound tooth tissue for mechanical retention.

Increased Amalgam retention. Reduce marginal leakage Reduce the need for dentine pins. Potentially reduce sensitivity Improve fracture resistance Improved amalgam margins

Materials for Amalgam Bonding

Resin Cements ( Panavia) Adhesive Bonding Agents

-initially designed for composites

-OptiBond solo-Amalgambond-Scotchbond multipurpose

OptiBond solo

How do they work?

Etching dentine opens up dentinal tubules enabling adhesive resin to flow into dentine and is retained micromechanically

Adhesive resin adheres to amalgam roughness micromechanically and by 4-META adhesive

Claimed Advantages of Amalgam Bonding Techniques

Decreased microleakage YES

Increased amalgam retention YES, if cavity lacks mechanical

retention Avoids risk of using pins

YES, 20% of pins perforate, 80oC rise

Claimed Advantages of Amalgam Bonding Techniques

Improved amalgam margins Depends on adhesive used. Panavia

weakens amalgam at margins Technique may reduce incidence of

ditching Tooth reinforcement

YES, if large cavity NO, if small cavity

Clinical Indications Not recommended for routine amalgam

cavities with sufficient mechanical retention and undercuts. No evidence of increased benefit to balance increased costs.

Useful for large multisurface amalgams to avoid use of pins

Useful for amalgam repairs Some easier to use than others

Bonding Agents Technique Place matrix band ( lightly vaselined) Etch 10% phosphoric acid Wash and dry Apply adhesive ( Kerr Optibond solo) Blow off excess solvent Light cure Pack amalgam

Limitations of Technique

Increased cost of restoration Technique sensitive? Not in use long enough to permit

adequate evaluation of clinical performance

Adhesion may breakdown over time

Amalgam Bonding

Summary Amalgam is an excellent core build-up

material for posterior teeth Excellent interim restoration for posterior

teeth Adhesives can be used to improve

retention in large amalgam restorations and cores

Adhesives and preparation features can often substitute for pin retention for cores

References R. W. Wassell, E. R. Smart G. St. George. Crowns

and other extra-coronal restorations: Cores for teeth with vital pulps. BDJ 2002 May,192(9): 499-509

Setcos J.C, Staninec M, Wilson N.H.FThe development of resin-bonding for amalgam restorations. BDJ 1999 Apr, Vol186 (7): 328-330

Staninec M, Setcos Bonded amalgam restorations: current research

and clinical procedure.Dent Update. 2003 Oct;30(8):430-4, 436