Pit-and-Fissure Dental Sealants

Applications/Use

Occlusal surfaces of newly erupted posterior teeth
Labial surfaces of anterior teeth with fissures
Occlusal surfaces of teeth in older patients with reduced saliva flow (because low saliva increases the susceptibility to caries)

Types

Polymerization method

Self-curing (amine accelerated)
Light curing (light accelerated)

Filler content

Unfilled-most systems are unfilled because filler tends to interfere with wear away from self-cleaning occlusal areas(sealants are designed to wear away, except where there is no self-cleaning action a common misconception is that sealants should be wear resistant)

Components

Monomer-BIS-GMA with TEGDM diluent to facilitate flow into pits and fissures prior to cure
Initiator-benzoyl peroxide (in self-cured) and diketone (in light cured)
Accelerator-amine (In light cured)
Opaque filler-I % titanium dioxide. or other colorant to make the material detectable on tooth surfaces
Reinforcing filler-generally not added because wear resistance is not required within pits and fissures

Reaction-free radical reaction 

Manipulation

Preparation

Clean pits and fissures of organic debris. Do not apply fluoride before etching because it will tend to make enamel more acid resistant. Etch occlusal surfaces, pits, and fissures for 30 seconds (gel) or 60 seconds (liquid) with 37% phosphoric acid . Wash occlusal surfaces for 20 seconds. Dry etched area for 20 seconds with clean air spray. Apply sealant and polymerize

Mixing or dispensing

Self-cured-mix equal amounts of liquids in Dappen dish for 5 seconds with brush applicator. Light cured-dispense from syringe tips 
Placement

-pits, fissures, and occlusal surfaces  --> Allow 60 seconds for self-cured materials to set. 

Finishing

Remove unpolymerized and excess material .Examine hardness of sealant. Make occlusal adjustments where necessary in sealant; some sealant materials are self-adjusting

Properties

Physical

Wetting-low-viscosity sealants wet acid etched tooth structure the best

Mechanical

Wear resistance should not be too great because sealant should be able to wear off of  self-cleaning areas of tooth
Be careful to protect sealants during polishing procedures with air abrading units to prevent sealant loss

Clinical efficacy

Effectiveness is 100% if retained in pits and fissures .Requires routine clinical evaluation for resealing of areas of sealant loss attributable to poor retention .
Sealants resist effects of topical fluorides
 

PHYSICAL PROPERTIES OF MATERIALS

Definite and precise terms are used to describe the physical properties of dental materials.

a. Hardness. Hardness is the measure of the resistance of a metal to indentation or scratching. It is an indication of the strength and wearability of an alloy or metal.

b. Ductility. Ductility is the measure of the capacity of a metal to be stretched or drawn by a pulling or tensile force without fracturing. This property permits a metal to be drawn into a thin wire.

c. Malleability. Malleability is the measure of the capacity of a metal to be extended in all directions by a compressive force, such as rolling or hammering. This property permits a metal to be shaped into a thin sheet or plate.

d. Flexibility and Elasticity. These terms differ in their technical definition but they are very closely related. Flexibility is the characteristic of a metal, which allows it to deform temporarily. The elasticity of a metal is used when it returns to its original shape when the load or force is removed.

e. Fatigue. Fatigue is the property of a metal to tire and to fracture after repeated stressing at loads below its proportional limit.

f. Structure (Crystalline or Grain Structure). Metals are crystalline and many of their physical properties depend largely upon the size and arrangement of their minute crystals called grains.

(1) Grain size. The size of the grains in a solidified metal depends upon the number of nuclei of crystallization present and the rate of crystal growth. In the practical sense, the faster a molten is cooled to solidification, the greater will be the number of nuclei and the smaller will be the grain size. Generally speaking, small grains arranged in an orderly fashion give the most desirable properties.

(2) Grain shape. The shape of the grains is also formed at the time of crystallization. If the metal is poured or forced into a mold before cooling, the grains will be in a flattened state. Metal formed by this method is known as cast metal. If the metal is shaped by rolling, bending, or twisting, the grains are elongated and the metal becomes a wrought wire.

g. Crushing Strength. Crushing strength is the amount of resistance of a material to fracture under compression.

h. Thermal Conductivity. Thermal conductivity is defined as the ability of a material to transmit heat or cold. A low thermal conductivity is desired in restorative materials used on the tooth whereas a high thermal conductivity is desirable where the material covers soft tissue.

Manipulation

Selection

o    Microfilled composites or hybrids for anterior class III, IV, V
o    Hybrids or midifills for posterior class I, II, III, V

Conditioning of enamel and / or dentin

Do not apply fluorides before etching.-->Acid-etch --> Rinse for 20 seconds with water --> Air-dry etched area for 20 seconds but do not desiccate or dehydrate --> Apply bonding agent and polymerize

Mixing (if required)--> mix two pastes for 20 to 30 seconds

o    Self-cured composite-working time is 60 to 120 seconds after mixing
o    Light-cured composite-working time is unlimited (used for most anterior and some posterior composite restorations)
o    Dual-cured composite-working time is > 10 minutes
o    Two-stage cured composite-working time is >5 minutes

Placement

use plastic instrument or syringe --> Light curing --> Cure incrementally in <2 mm thick layers. Use matrix strip where possible to produce smooth surface and contour composite .Postcure to improve hardness
 

Applications

a. Dentulous impressions for casts for prosthodontics

b. Dentulous impressions for pedodontic appliances

c. Dentulous impressions for study models for orthodontics

d. Edentulous impressions for casts for denture construction

Wax elimination (burnout):

Wax elimination or burnout consists of heating the investment in a thermostatically controlled furnace until all traces of the wax are vaporized in order to obtain an empty mold ready to receive the molten alloy during procedure.

• The ring is placed in the furnace with the sprue hole facing down to allow for the escape of the molten wax out freely by the effect of gravity .
• The temperature reached by the investment determines thethermal expansion. The burnout temperature is slowly increased in order to eliminate the wax and water without cracking the investment.
•For gypsum bonded investment, the mold is heated to650 -6870 c )to cast precious and semiprecious
precious alloys.
• Whereas for phosphate-bonded investment, the mold is heated up to 8340 c to cast nonprecious alloys at high fusing temperature.
The ring should be maintained long enough at the maximum temperature (“heat soak”) to minimize a sudden drop in temperature upon removal from the oven. Such a drop could result in an incomplete casting because of excessively rapid solidification of thealloy as it enters the mold.
• When transferring the casting ring to casting, a quick visual check of the sprue in shaded light is helpful to see whether it is properly heated. It should be a cherry-red color .

WAX BURNOUT AND HEATING THE RING

After the investment has set hard, the crucible former and the metal sprue former is removed carefully, and any loose particles at the opening of the sprue hole are removed with small brush.
The purpose of the wax burnout is to make room for the liquid metal. The ring is placed in the oven at 250C with the sprue end down, thus allowing the melted wax to flow, out for 30min or even up to 60min may be a good procedure to ensure complete elimination of the wax and the carbon.

Heating the ring: The object is to create a mold of such dimension, condition and temperature so that it is best suited to receive the metal.

Hygroscopic Low-Heat Technique. 

After the wax elimination the temperature of the same furnace can be set to a higher temperature for heating or else, the ring can be transferred to another furnace, which has already set to the higher temperature. In any case accurate temperature control is essential and therefore these furnaces have pyrometer and thermocouple arrangement. The ring is placed in the furnace with the sprue hole down and heated to 500C and kept at this temperature for 1 hour. In this low heat technique the thermal expansion obtained is less but together with the previously obtained hygroscopic expansion the total expansion amounts to 2.2 percent, which is slightly higher than what is required for gold alloys.

So this technique obtains its compensation expansion from three sources:
(1)   The 37º C water bath expands the wax pattern
(2)   The warm water entering the investment mold from the top adds some hygroscopic expansion
(3)   The thermal expansion at 500' C provides the needed thermal expansion.

High-Heat Thermal Expansion Technique. 

After the wax elimination, the ring should be placed in the furnace which is at room temperature and then the temperature is gradually raised, until it comes to 700C in 1 hour. Then the ring is heat soaked at this temperature for ½ hour. This slow rise in temperature is necessary to prevent 
This approach depends almost entirely on high-heat burnout to obtain the required expansion, while at the same time eliminating the wax pattern.  Additional expansion results from the slight heating of gypsum investments on setting, thus expanding the wax pattern, and the water entering the investment from the wet liner, which adds a small amount of hygroscopic expansion to the normal setting expansion.

Tooth Polishing and Cleansing Agents

1. Cleansing-removal of exogenous stains, pellicle, materia alba, and other oral debris without causing undue abrasion to tooth structure
2. Polishing-smoothening surfaces of amalgam, composite, glass ionomers, porcelain, and other restorative materials

Factors influencing cleaning and polishing

-    Hardness of abrasive particles versus substrate
-    Particle size of abrasive particles
-    Pressure applied during procedure
-  Temperature of abrasive materials

Structure

 Composition

-contain abrasives, such as kaolinite, silicon dioxide, calcined magnesium silicate, diatomaceous silicon dioxide, pumice. Sodium-potassium
-aluminum silicate, or zirconium silicate; some pastes also may contain sodium fluoride or stannous fluoride, but they have never been shown to produce positive effects
 

Reactions-abrasion for cleansing and polishing

Properties -  Mechanical
 
- Products with pumice and quartz produce more efficient cleansing but also generate greater abrasion of enamel and dentin
-Coarse pumice is the most abrasive
-The abrasion rate of dentin is 5 to 6 times faster than the abrasion rate of enamel, regardless of the product
-Polymeric restorative materials, such as denture bases, denture teeth, composites, PMMA veneers, and composite veneers, can be easily scratched during polishing
-Do not polish cast porcelain restorations (e.g., Dicor) that are  externally characterized or the color will be lost