Dental Cements Lecture Notes

Introduction

• Topic: Dental Cements
• Focus: Classifications, Zinc Phosphate, Zinc Polycarboxylate Cement

Dental Cements Overview

• Definition: Binders or adhesives in dentistry.
• Uses: Base, liner, filling material, adhesive.

Classification of Dental Cements

Based on Application or Uses

1. Type 1: Looting Agents

   • Indirect restorations (inlay, only, crown).
   • Fine vs. medium grain (cementation vs. bases/orthodontics).

2. Type 2: Restorative Applications

   • Filling cavities, treating caries.
   • Temporary vs. permanent materials.

3. Type 3: Liners and Bases

   • Liner: Thin layer for dentine.
   • Base: Thick layer for thermal insulation and absorption of occlusion forces.

Based on Ingredients or Composition

1. Water-Based Cements
2. Resin-Based Cements
3. Oil-Based Cements

Based on Setting Reaction

1. Acid-Base Reaction

   • Liquid (acid) + powder (base).
   • Examples: Zinc phosphate, zinc oxide eugenol, glass ionomer.

2. Polymerization Reaction

   • Chemically or light activated.
   • Examples: Resin cements.

3. Dual Cure and Tri-Cure Cements

   • Dual: Acid-base + polymerization.
   • Tri: Acid-base + two polymerization methods.
   • Examples: Resin-modified GIC, compomers.

ISO Standards Covering Cements

• ISO 9917-1: 2003: Water-based cements (powder-liquid systems).
• ISO 9172: 1998: Light-activated cements.
• ISO 4049: 2000: Polymer-based cements.

Historical Development

• 1873: Silicates (Fletcher), Zinc oxide (Tusel).
• 1879: Zinc phosphate (Dr. Pierce).
• 1930: Calcium hydroxide (Herman).
• 1968: Polycarboxylate cement (Dennis Smith).
• 1971: Glass ionomer cements (Wilson and Kent).

Ideal Properties of Dental Cements

• Low viscosity and film thickness: Improves seating and wetting.
• Long working time, rapid set: Allows sufficient handling time.
• Low solubility: Minimizes marginal leakage.
• High compressive and tensile strength: Mechanical durability.
• High proportional limit: Stiffness.
• Adhesion: Improves retention.
• Anti-cariogenic properties: Fluoride release.
• Biological compatibility: Mild pulpal response, non-acidic pH.

Zinc Phosphate Cement

Overview

• Oldest looting cement (introduced by Dr. Pierce in 1879).
• Forms: Powder-liquid system and pre-proportioned capsules.

Composition

• Powder: Zinc oxide, magnesium oxide, silica, other oxides.
• Liquid: Phosphoric acid, water, aluminum/zinc phosphates, aluminum/zinc ions.

Setting Reaction

• Acid-base reaction: Forms zinc aluminophosphate.
• Type: Exothermic reaction.

Classification

• Type 1: Fine grained for looting.
• Type 2: Medium grained for looting/filling.

Manipulation

• Glass slab cooling: Prolongs working time, reduces exothermic heat.
• Spatulation: Use stainless steel spatula.
• Ratios and Timing: 1.4g powder to 0.5ml liquid, 1-1.5 mins mixing.
• Setting Time: 2.5 to 8 mins.

Properties

• Mechanical: High compressive (104-119 MPa), moderate tensile (5.5 MPa), high stiffness.
• Solubility: Low (0.06%), potential marginal disintegration.
• Thermal Insulation: Good.
• Adhesion: Micro-mechanical.
• Biological: Highly acidic initially, moderate pulpal response.

Applications

• Looting: Indirect restorations (inlays, onlays, crowns).
• Base: Under amalgam restorations.
• Temporary Restorative: Short-term fillings.
• Orthodontics: Bands, brackets.

Advantages and Disadvantages

• Advantages: Long track record, good compressive strength.
• Disadvantages: No chemical adhesion, no anti-cariogenic property, acidic, poor aesthetics.

Zinc Polycarboxylate Cement

Overview

• Developed by: Dennis Smith (1968).
• Forms: Powder-liquid, water-settable, pre-capsulated.

Composition

• Powder: Zinc oxide, magnesium oxide, stannous fluoride.
• Liquid: Polyacrylic acid, copolymers, water.

Setting Reaction

• Acid-polyacrylate interaction: Forms zinc polyacrylate gel.
• Adhesion: Chemical via carboxylic groups.

Manipulation

• Glass slab: Cool to prolong working time.
• Powder-liquid ratio: 1.5 to 1.
• Mixing: 30-60 seconds, should be glossy.
• Timing: Working time 2.5 mins, setting time 7-9 mins.

Properties

• Mechanical: Moderate compressive strength, higher tensile strength than zinc phosphate.
• Solubility: Higher than zinc phosphate.
• Adhesion: Chemical bond to tooth structure.
• Biological: Mild pulpal response, higher pH after setting.
• Other: Limited fluoride release, good thermal insulation.

Applications

• Looting: Permanent restorations (inlays, onlays, crowns).
• Base: High strength.
• Orthodontics: Bands.

Advantages and Disadvantages

• Advantages: Less irritating to pulp, chemical adhesion.
• Disadvantages: Limited fluoride release, newer options available.