Penetrating corossion

Penetrating corrosionSeen in gamma-2 phase (Sn-Hg).This phase produces crystals which are long and blade like penetrating throughout the matrix.A penetrating matrix is formed because of intercrystalline contacts between the blades.This phase is prone to corossion in clinical restorations.Begins from the outside of the restoration along the crystals

Connecting to new crystals at intercrystalline contacts

This produces penetration corossion.

Generates a porous and spongy amalgam with minimal mechanical resistance.

This can be decreased by the use of more copper in the initial composition.

Mercuroscopic expansionFirst proposed by Jorgensen as an explanation for prevalence of marginal fracture associated with occlusal amalgam.

Electrochemical corrosion causes extrusion of restoration at the margins

During this phase mercury from Sn-Hg reacts with the Ag-Sn particles and produces further expansion

Mercuroscopic expansionMahlers scaleEstablished from No.1 11.Image of clinical restoration of interest is compared with a series of 5 photographs.

No. 2,4,6,8 and 10 Represent increasingly worse marginal breakdown.

Rest all deal with severity of marginal ditching:No. 1- Below the main scale imagesNo. 3,5,7 and 9 IntermediateNo. 10 Greater FailuresBulk fractures

Sensitivity or pain

Corrosion5Secondary caries

Marginal fractures

6Signs of failuresFracture LinesMarginal DitchingProximal OverhangsPoor anatomic contoursMarginal Ridge incompatibilityImproper Proximal ContactsRecurrent CariesPoor occlusal ContactsAmalgam Blues

7Reasons For FailuresImproper Case SelectionImproper Cavity PreparationFaulty Selection & manipulation of amalgam Errors in Matricing Procedures Post Operative Factors

8RECENT DEVELOPMENTs OF Dental AMALGAMLow mercury amalgamIndium in amalgam9Low mercury amalgam

In this approach the alloy particles are carefully selected so that they can pack together well.It is then possible to reduce mercury content to 15%-25%.Clinical properties are yet unknown.

Structure and strength of low-mercury dental amalgams prepared with liquid Hg47.4% In alloy

Two low-mercury amalgams: (1) low-copper lathe-cut and (2) high-copper (Tytin) were prepared by amalgamation with liquid Hg47.4% In alloyThe matrix phase of the low-mercury amalgam was found to be depleted of mercury, indicating that less mercury (compared with standard amalgam) combines with silver, thus producing a strong amalgam matrix. On the other hand, an increase was observed in the consumption of the initial (Ag3Sn)-phase, leading to an increase of the tin released. As a result, the potential of [HgSn]-phase formation in low-mercury amalgams increases which contributes to a deterioration in the strength of the investigated amalgam. The conclusion drawn was that low-mercury amalgam may be prepared with liquid Hg47.4%In alloy but, in order to eliminate 2-phase formation, novel and possibly tin-free amalgamable alloys should be developedJournal of Materials Science: Materials in Medicine 19980610,Volume 9,Issue 6,pp 347-354Indium in amalgam

Effect of indium on the clinical success of amalgam restorations There were no differences clinically or statistically regarding texture and luster and the margins of the restorations containingindiumincurred slightly less fracture than the non-indium-containing restorations.Uk pubmed centralClinical evaluation of high-copper dental amalgams with and without indium The margins of the indium-containing amalgam restorations incurred slightly less marginal breakdown, an effect that could be attributed to the addition of admixed indium and to the increase in silver-copper eutectic spheres which is found in these alloys. These amalgams also demonstrated a slightly darker appearance, and were slightly rougher than the non-indium-containing amalgam.Am J Dent.1992 Feb;5(1):39-41.Effect of Admixed Indium on Mercury Vapor Release from Dental Amalgam

Admixed indium significantly decreased the amount of mercury vapor released from dental amalgams. Dental amalgams with greater than or equal to 8% admixed indium released the least amount of mercury vapor.

Jada, October, 2012