Composites in Dentistry

Composite is a compound of two or more different constituents with properties that are superior to those of the individual constituent.

COMPOSITION:
a) Resin Matrix
The matrix consists of Bis-phenol Glycidylmethacrylate (Bis-GMA) and Triethylene Glycol Dimethacrylate (TEGDMA). TEGDMA is used as a viscosity controller.

b) Fillers - silica
Addition of fillers increases the strength, hardness, abrasion resistance and decreases the polymerization shrinkage and water sorption.

c) Coupling agent
Organosilane, zirconates or titanates. They bond the filler particles to the resin matrix.

d) Inhibitor - Hydroquinone
Prevents premature polymerization

e) Opacifiers and coloring agents
Titanium dioxide and aluminum oxide are the opacifiers.
The coupling agent between filler particle and the resin is VINYL SILANE.

TYPES:
CHEMICALLY ACTIVATED COMPOSITES:
# Supplied in two pastes

• Basic Paste - Contains the initiator benzoyl peroxide
• Accelerator Paste - Contains tertiary amine as activator (N-dimethyl-p-toluidine)

# It is manipulated by mixing the proper proportions on a mixing pad with an agate spatula as metal spatula discolors the material.

# Cavity should be slightly overfilled.
# Shrinkage occurs towards the centre of the material.
LIGHT ACTIVATED COMPOSITES
# Consists of a single paste
Initiator - Camphoroquinone
Activator - diethyl-amino-ethyl-methacrylate or diketone

- They interact when exposed to light at wavelength of 400-500 nm i.e. blue region of the visible light spectrum.

- Ultraviolet light curing is not indicated because of its limited depth of penetration through tooth structure. It also poses a potential health hazard.

- The source of light is a tungsten halogen bulb.

- The tip should be kept as close as possible to the restoration and should be cured in increments.

- Each increment should not be greater than 2 mm and the exposure time should be 40-60 seconds.

- Darker shades require longer exposure time.

- Light emitted may cause retinal damage and can be prevented by using protective eyeglasses.

- Shrinkage occurs towards the light source.

- Cavity preparation for composites is beveled except when margins are in cementum.

Glass Ionomer Cement (GIC) - Composition, Properties, Composition and Modifications

- Glass Ionomer Cement is also known as Polyalkenoate cement / Man-made dentin / Dentin Substitute / Aluminosilicate Polyacrylic cement (ASPA)
COMPOSITION :

Powder / Liquid	Contents
Powder / Ion Leachable Glass	Silica           -          35 - 50 % Alumina      -           20 - 30 % NaF             -           3 - 6 % AlF3            -           1.5 - 2.5 % Aluminium Phosphate  -    4 - 12 % Traces of Barium, Strontium for radioopacity
Liquid	Polyacrylic acid        -        45 % Itaconic acid + Maleic Acid + Tricarballylic acid    - 5 % (Decreases Viscosity) Tartaric acid (Increases working time) Water   - 50 %

CLASSIFICATION:

Type I GIC - Luting cement

Type II GIC - Restorative Cement

Type III GIC - Liner

Type IV GIC - Fissure Sealant

Type V GIC - Orthodontic Cement

Type VI GIC - Core Build Up Cement

Type VIII and Type IX - Posterior packable GIC for atraumatic restorations

Among the first three types, the highest cumulative release of fluoride after 30 days is from glass ionomer liner.

- GIC was introduced as a potential replacement for silicate cement. It has been evolved as a hybrid from the silicate and polycarboxylate cement.

Light Polymerization:

The powder contains initiators for light curing and liquid component is modified with hydroxyethyl methacrylate (HEMA).

The polymerization starts when exposed to light and subsequently followed by acid base reactions. This is called dual cure GIC.

PROPERTIES:

GIC has low fracture toughness and wear resistance.

It is very sensitive to moisture, especially during initial setting reaction. During this period, absorption of water leads to weak cement and over drying will lead to cracks in the cement. Therefore, the surface of cement should be protected by coating with varnish or cocoa butter during setting. 

It bonds chemically to the tooth structure.

- The bond of enamel is always higher than that of dentin.

- It is relatively biocompatible, the pulpal reaction is greater than ZOE but less than Zinc Phosphate Cement.

- Due to continuous fluoride release, it has some anticariogenic property.

 

- Powder: Liquid ratio is 3:1 by weight. Mixing should be done by agate or plastic spatula.

- 10 % polyacrylic acid should be used for conditioning the cavity surface before insertion of the cement.

- Final finishing is done 24 hours after the insertion.

MODIFICATIONS OF GIC:

a) Miracle Mix or Silver Cement

Silver-Tin alloy powder is added to GIC Powder. None of the properties were improved and it gave a gray or blackish color to the cement. It is also called as silver alloy mix.

b) Glass Cermet or Cermet

Glass and metal ( Silver-tin-titanium) powders were sintered at high temperature and made to react with liquid. It improved the fracture toughness and wear resistance and at the same time maintained the esthetics.

c) Resin modified GIC

BisGMA, TEGDMA, are added to powder and HEMA to the liquid. With exposure of light polymerization is initiated along the methacrylate groups. After that the liquid reacts with the glass particles through acid base reaction. It improved the wear resistance and decreased the sensitivity to

water attack. 

d) Compomer (Polyacid modified composite resins)

It is a combination of composite and GIC. Glass particles are partially silanated (for bonding with the matrix) and are added as fillers in the composite resin. There is no water in the reaction. The properties were inferior to composites but superior to resin modified GIC.

e) Bilayered or Sandwich restoration

In this technique, GIC is used as a liner under composite restorations. It increases the retention form as GIC bonds both the tooth and composite and the fluoride content reduces secondary caries.

f) Tunneling restorations

Joining the occlusal lesion with the proximal lesion by means of a prepared tunnel under the involved marginal ridge. The marginal ridge remains intact. GIC is used as the restorative material in this technique.

g) Atraumatic restoration (ART)

Involves removal of affected tooth structure with hand instruments, followed up by restoring with GIC material (GC Fuji VIII).

h) High viscosity GIC

Used for atraumatic restorative treatment. They contain small particle sizes and a high P/L ratio, yielding greater compressive strength and excellent packability. Also used for core buildups, primary tooth fillings and intermediate restoration.

i) Calcium aluminate GIC

It is a hybrid product of calcium aluminate and  GIC. The GIC components are responsible for early properties (i.e. setting time, viscosity, and strength). The calcium aluminate contributes to basic pH, biocompatibility and reduction in microleakage. Also called as hydraulic cement.

Diagnosis of Hairy Leukoplakia

Hairy Leukoplakia is the second most common HIV-associated oral mucosal lesions after Candidiasis. It is non malignant and is not pathognomic for HIV since other immunodeficiencies such as cancer chemotherapy are also associated with hairy leukoplakia. The common site for this condition is on the lateral borders of tongue in form of vertical white folds.

Diagnosis of Hairy Leukoplakia	Features
Provisional Diagnosis	Characteristic gross appearance with or without non responsiveness to antifungal therapy
Presumptive Diagnosis	Light microscopy of histologic sections revealing hyperkeratosis, koilocytosis, acanthosis, and absence of inflammatory cell infiltrate OR Light microscopy of cytologic operations demonstrating nuclear beading and chromatin margination
Definitive Diagnosis	Insitu Hybridisation of histologic or cytologic specimen revealing positive staining for EBV DNA OR Electron microscopy of histologic or cytologic specimen showing herpes-like particles OR Epstein-Barr Virus was demonstrated with polymerase chain reaction technique.

Multiple Endocrine Neoplasia (MEN) Syndrome - Types

Multiple Endocrine Neoplasia (MEN) Syndrome
MEN - I	Hyperplasia of  pituitary gland with acromegaly Hyperplasia of parathyroid and adrenal cortex Hyperplasia of pancreatic islets with increased production of gastrin, insulin, and glucagon with peptic ulcers and gastric hypersecretion
MEN - II (Sipple's Syndrome)	Hyperplasia of parathyroid gland No tumors of pancreas. No peptic ulcer. Patients may have pheochromocytomas of the adrenal medulla and medullary carcinoma of the thyroid gland
MEN - III	Pheochromocytomas and Medullary carcinoma of the thyroid gland Oral neuromas that are common on lips, tongue and buccal mucosa. The lips are described as Bumpy lips.

Multiple Endocrine Neoplasia or MEN Syndrome are classified  into following types :

A. MEN - I

• Hyperplasia of  pituitary gland with acromegaly
• Hyperplasia of parathyroid and adrenal cortex
• Hyperplasia of pancreatic islets with increased production of gastrin, insulin, and glucagon with peptic ulcers and gastric hypersecretion

B. MEN - II

• Hyperplasia of parathyroid gland
• No tumors of pancreas. No peptic ulcer.
• Patients may have pheochromocytomas of the adrenal medulla and medullary carcinoma of the thyroid gland

C. MEN - III

• Pheochromocytomas and Medullary carcinoma of the thyroid gland
• Oral neuromas that are common on lips, tongue and buccal mucosa.
• The lips are described as Bumpy lips.