Restorative Materials In Dental Caries

Restorative Materials In Dental Caries

Discuss in detail anterior restorative materials and setting mechanism.
Answer:

Anterior restorative materials are:

• Composite resins
• Glass ionomer cement
• Silicate cement
• Porcelain
• Acrylic resins.

Thermal Properties:

• Thermal Expansion Coefficient: Thermal expansion can create additional strain on tooth resin bond, in due course of time this can cause material fatigue, bond failure, and also percolation of fluid in gaps. In ideal conditions, the thermal expansion coefficient of a restorative material should be close to the tooth structure.
• Thermal coefficient of tooth structure:
  • Enamel: 11.4 × 10^-6/0C
  • Dentin: 8.3 × 10^-6/0C

Thermal coefficients of various composite materials are:

• Conventional composite: 25 × 10^-6/0^C
• Microfiled composite: 55 to 68 × 10^-6/0^C
• Hybrid composite: 25 to 38 × 10^-6/0^C
• Small particle composite: 19 to 26 × 10^-6/0^C

Composites with high resin components such as microfiled resin show more thermal expansion coefficient.

Thermal Conductivity:

Thermal conductivity is the rate by which either heat or cold is transmitted through restoration. Ideally, restorative materials have low thermal conductivity for decreasing the transfer of excessive thermal stimuli to pulp.

The following are the thermal conductivity of composite materials:

• Microfiled composites: 12 to 15 × 10^-4Cal/Sec/cm².
• Hybrid composite: 25 to 30 × 10^-4Cal/Sec/cm².

Dimensional Stability:

Hygroscopic expansion which starts 15 min after polymerization reaches its equilibrium in 7 days. Microfilmed composites show more expansion as compared to hybrid varieties.

Retention of Thermal Conductivity: Composites adhere to tooth structure by micromechanical retention with the help of bonding agents.

Esthetics of Thermal Conductivity:

Composites are highly aesthetic materials and are supplied in various shades. In nano field and microfiled composites high resin content and the presence of microfibers lead to increased surface smoothness.

Composites with large filers have decreased surface smoothness which produces staining over a period of time.

Biocompatibility of Thermal Conductivity:

Properly polymerized composites are biocompatible till there is a proper thickness of dentin. In some cases where the pulp is exposed, pulp capping along with glass ionomer liner is done.

In proximity to gingival tissues correct technique is employed so that inflammatory responses should be prevented which are associated with overhangs and microleakage.

Solubility of Thermal Conductivity:

The solubility of resin-based composites is of concern as inorganic ions present as filers can leach into the surrounding environment causing the breakdown of restoration.

ADA specification requires that water sorption of all materials be less than or equal to 40 µm g/mm and solubility of all materials be less than or equal to 7.5 µm g/mm. Higher values of water sorption and solubility lead to reduced wear, abrasion resistance, and color instability.

The radiopacity of Thermal Conductivity:

To evaluate the integrity of composite resin radiographically the resin needs to be radiopaque. Radiopacity is provided by filers such as glass ceramics which consist of heavy metals, i.e. barium, strontium, and zirconium.

ADA specification no. 27 requires that composite resins have radiopacity equivalent to 1 mm of aluminum which is equal to dentin.

Setting Mechanism of Composite:

Settling of composite occurs through polymerization, so the method is known as polymerization.

• Chemically Activated Composite Resins: Self-cure resin occurs in a two-paste system, i.e. base paste and catalyst paste. The base paste consists of a benzoyl peroxide initiator and the catalyst paste consists of a tertiary amine activator. When two pastes are spatulated the amine reacts with benzoyl peroxide to form free radicals which starts polymerization.
• Light Activated Composite Resins: Light activation in visible light curing ranges between 460 and 470 nm wavelength. On activation, a photoinitiator, i.e. camphor quinone combines with an amine accelerator and releases free radicals which start the polymerization.
• Dual Cure Resins: A combination of chemical and light curing is used to overcome some of the drawbacks of light curing. Dual cure resins are supplied in two pastes. When they are mixed together a slow reaction is initiated. After the initial light cure, the remainder of the resin cures over a period of time by a chemical process.