Carious Lesions: Zones and Restorative Materials

• Mertz-Fairhurst sealed caries using composite, amalgam, and unsealed amalgam discovering caries continuation rates of 0.6%, 1.3%, and 8.9% respectively.
• Intact sealants prevent the progression of carious lesions.
• Cariogenic bacteria counts significantly decrease under dental restorations and the remaining bacteria do not cause caries.

Zones of a carious lesion

• Outer caries-infected dentine has a high bacterial load.
• Inner caries-affected dentine is translucent.
• Sound inner dentine is the innermost layer.

Restorative Materials

• Remineralization products include fluoride and Recaldent (CPP-ACP).

• Composites are used, with flowable composites ideal for MI cavities and others better for larger lesions.

• Glass Ionomer Cement (GIC) is bioactive and suitable for longer-term prognosis.

• Tri-calcium silicates like biodentine (Septodont) and MTA are also used.

• Enamel should be etched for 20 seconds with phosphoric acid.

• Poor adhesion occurs when prisms are parallel to the cavity surface.

• Composites shrink approximately 3% by volume, potentially cracking enamel.

• Finishing cavities with a fine diamond bur reduces cracking risks at the margins.

• Wet bonding steps in dentistry:

  • Use a rubber dam.
  • Etch the tooth surface.
  • Wash off all etching gel.
  • Remove excess water with a cotton pledget, avoiding air spray.
  • Apply ample adhesive using a microbrush.
  • Ensure the solvent evaporates until a shiny, non-rippling surface is achieved.

• The hybrid layer consists of intertubular dentine infiltrated with resin.

• A good adhesive layer should be of reasonable thickness and penetrate well into the dentine.

• The oxygen inhibition layer sits above the adhesive layer, facilitating bonding with the overlying composite.

Degradation of Adhesive Materials

• Inactive MMP precursors are activated by proteinases, chemical agents, or mildly acidogenic conditions.
• Secretion of MMPs leads to the breakdown of the adhesive interface.
• Adding MMP inhibitors to primers can help prevent degradation, although effectiveness varies.
• GIC functions through an acid-base reaction between poly-acrylic acid and alumino-silicate glass, involving ionic exchange between glass particles and the matrix.
• GIC undergoes a maturation process, rapidly occurring over 24 hours and reaching maximal retention at 6 months.
• Biodentine sets through a hydration reaction releasing Ca2+, Si4+, OH- and (CO3)2- ions, beneficial for remineralization and pulp stimulation.

Pulpal Actions of Calcium Hydroxide

• Mineralization
• Antibacterial activity
• Neutralization of acidic inflammatory pH
• Denaturation of pro-inflammatory cytokines