Study Notes on Glass Iron Ore Cement (GIC) Lecture by Rebecca Wong

Speaker: Rebecca Wong
Topic: Glass Iron Ore Cement (GIC)
Importance of correct terminology: - Hyphen usage between terms: "glass iron ore" versus "iron ore cement". - Clarification on the scientific term: glass polyalkenoic cement. - Common use of the term: glass ionomer cement (GIC).

Overview of segmented topics: - Keywords and essential knowledge related to GIC. - Components and setting reaction of GIC. - Physical properties and clinical uses of GIC. - Commercial products available. - Current research directions on GIC.

Classification of dental materials: - GIC is one of two tooth-colored groups of direct restorative materials. - Direct restorative materials: placed directly into prepared cavity. - Indirect restorative materials: fabricated in a laboratory (crowns, bridges).
Bonding mechanism: - GIC forms a true chemical bond to tooth structure. - Contrast with resin composite, which primarily relies on micromechanical bonding.

Chemical nature: - An acid-base reaction characterized by ionic exchange between restoration and surrounding environment.
Biocompatibility of GIC: - GIC is biocompatible but has lower wear resistance compared to other materials.
Application procedure differences: - GIC requires a simple conditioning step prior to placement versus the etched primer bonding procedure for resin composites.
Successful GIC retention rates: - Influenced by clinical conditions such as non-carious cervical lesions. - Sclerotic dentin presence reduces bond strength due to its highly mineralized nature.
Protection after setting: - GIC needs to be protected from desiccation with a varnish (e.g., prytorem jelly, Vaseline). - Commercially available surface coats are also an option.

Implementation in developing countries: - Manual excavation of affected dentin without rotary instruments. - Placement of GIC following hand instruments’ use.

Hand mixed: - Powder and liquid mixed together in a specific ratio at the time of use.
Encapsulated: - Capsules with separated liquid and powder; membrane is broken prior to mixing in an amalgamator.
Application into cavity using a dispensing gun.

Basic glass powder - Types: Strontium or calcium, aluminofluorosilicate. - Unleachable with acid-base reaction.
Phosphate - Crucial for the setting reaction, typically aluminum phosphate.
Sodium salts - Integrated into the setting reaction.
Water - Vital in forming the polyacid used in the setting reaction.
Chelating agent - Typically tartaric acid or citric acid (5-10%). - Protects aluminum ions which are pivotal in the maturation stage, providing strength.
Radio opaque elements - Barium or zinc oxide for visibility in radiographs.

Initial reaction: - Mixing produces weak polyelectrolyte from acid reactions, leading to salt formation and cross-linking.
Sequential reactions: - Glass surface reacts with acid; ions released hydrate to form a gel matrix, initiating ionic crosslinking.
Chemical bonding: - Ionic bonding occurs between GIC and tooth structure during initial setting with carboxyl ions interacting with calcium.
Bond exchange: - Formation of an ionic exchange layer when the GIC is applied to tooth surfaces, involving carboxyl groups with calcium from hydroxyapatite.

Composition and set structure details: - Similar bonding and setting processes as described previously.
Issues with desiccation leading to madness and debonding of material.

Developed to enhance mechanical properties: - Incorporates light-cured particles for improved compressive and flexural strength. - Allows polishing on the same day of placement with reduced moisture sensitivity.
Composition of RMGIC: - Fluoroaluminosilicate glass, polyalkenoic acid, polymerizable resin (e.g., HEMA). - Setting mechanism combines acid-base reaction and addition polymerization.

Types: - Type 1: Luting cements used for crowns and bridges (low powder-to-liquid ratio). - Type 2: Aesthetic cements for anterior areas (conventional and RMGIC variants); reinforced cements for posterior restorations. - Type 3: Linings and fissure sealants, typically high powder-to-liquid ratios, often radiopaque.

Strength and adhesion: - GIC compressive strength: approximately $152 ext{ to } 220 ext{ MPa}$ . - Adhesion to enamel: approximately $3 ext{ to } 10 ext{ MPa}$ ; dentin: approx. $1 ext{ to } 4 ext{ MPa}$ . - Comparison with resin composites: adhesive strength of $27 ext{ to } 30 ext{ MPa}$ .
Benefits of GIC: - Less technique-sensitive than resin composites; tolerates moisture better; faster chairside time. - Positive aspects: fluoride release during pH reductions, bioactivity aiding tooth protection.

Restorative uses (direct restorations, liners, bases).
Luting agents and fissure sealants in orthodontic procedures.
Usage examples like Pitrabond, a resin-modified GIC used as a lining, and Vitrebond, with no conditioning needed.

Installation of GIC from capsules and tips, ensuring the angle is adjustable for convenience during procedures.
Importance of moisture control during application and manipulation of GIC materials.

Enhancements to GIC strength through various additions: - Metal additions (e.g. silver-tin alloy), fiber reinforcements (carbon, glass), and engineered nanoparticles. - Development efforts towards an improved glass carbomer that claims enhanced remineralization.
Challenges and ongoing investigations related to retention rates and overall performance.