EFFECT OF THE ORAL ENVIRONMENT ON LONGEVITY OF AMALGAM

introduction  The oral environment forms complex factors that complicate application of amalgam restorative material and affect clinical performance and longevity.

oral environment factors that effect longevity of amalgam  Difficult access  Dynamic functional forces  Microbial activities  Bio-degradation  Moisture  Thermal  PH

Difficult access  Difficult access may present a problem with amalgam because it has limited working time and causing patient’s discomfort and minor tissue damage.

Dynamic functional forces  Excessive Mastication forces it will cause isthmus fracture in amalgam.

Microbial activities  Microbial activity is always present in the oral cavity it can’t be eliminated but can be controlled. If the microbial not controlled it will be leakage around amalgam restorations and effect longevity.

Bio-degradation  It is the gradual breakdown of material by specific biological activities in the mouth.  Biodegradation of the restorative material in the oral cavity results in physical/chemical damaging effect such as (tarnish, corrosion)

tarnish  Tarnish is due to formation of thin layer on the metal surface by reaction with sulfide, chloride, oxide or other chemicals.  Tarnish caused by moisture contamination and bad oral hygiene

corrosion  A chemical or electrochemical process in which a solid (metal) is attacked by an environmental agent.  In this process partial or complete dissolution occurs.  Metals are generally more susceptible to corrosive attack due to electrochemical reactions.

CLASSIFICATION OF CORROSION Two general types of corrosion reactions:  In chemical corrosion there is direct combination of metallic and non metallic element to form a chemical compound by oxidation, helogenation or sulfurization reactions. e.g. discoloration of silver by sulfur.  Chemical corrosion is almost invariably accompanied by electrochemical corrosion.

ELECRTOCHEMICAL CORROSION  GALVANIC CORROSION: this occurs between tow dissimilar metallic restoration, old and new amalgam,polished and unpolished amalgam.

ELECRTOCHEMICAL CORROSION  Concentration cell corrosion: Resulting from accumulation of certain types of food on a sites of amalgam making it different in its electric potential from other sites of amalgam.

moisture  (Saliva, water, gingival tissue, exudates ) affect properties of amalgam during handling and setting and hardening and delayed expansion in zinc- containing amalgam

Thermal  Cyclic thermal changes between below 10°C and above 55°C present in the oral cavity.  This cyclic lead to creep in amalgam and hypersensitivity.

Different pH Values  After exposures of the specimens for 2 hr or 24 hr in sealed glass bottles  The results have shown pH-independent mercury dissolution in the range of pH 3 to 8  a much faster dissolution at pH 1

1 School of Materials Science and Engineering, Georgia Institute of Technology, Atlanta , USA. PMID: [PubMed - indexed for MEDLINE]

Hamid Abdullah Al-harbi 4198 Abdulaziz Ali Al-asbli 4040 Abdulaziz assem al Muiny 4269 THANK YOU FOR LISTENING