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NEET MDS Synopsis - Lecture Notes

📖 Dental Materials

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COMPOSITE RESINS -Pit-and-Fissure Dental Sealants

Dental Materials

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
 

Tooth Polishing and Cleansing Agents

Dental Materials

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
 

Cement liners

Dental Materials

Cement liners

Applications (if remaining dentin thickness is <0.5 mm)

o    Used for thermal insulation where cavity preparation is close to the pulp
o    Used for delivering medicaments to the pulp

•    Calcium hydroxide stimulates reparative dentin or
•    Eugenol relieves pain by desensitizing nerves
•    Used to deliver F ion to enamel and dentin

Components

o    Paste of calcium hydroxide reactant powder, ethyl toluene sulfonamide dispersant, zinc oxide filler, and zinc stearate radiopacifier
o    Paste of glycol salicylate reactant liquid, titanium dioxide filler powder, and calcium tungstenate radiopacifier

Reaction

Chemical reaction of calcium ions with salicylate to form methylsalicylate salts Moisture absorbed to allow calcium hydroxide to dissociate into ions to react with salicylate Mixture sets from outside surface to inside as water diffuses

Manipulation

Dentin should not be dehydrated or material will not setMix drop of each paste together for 5 secondsApply material to dentin and allow I to 2 minutes to set

Properties

o    Physical-good thermal and electrical insulator
o    Chemical-poor resistance to water solubility and may dissolve
o    Mechanical-low compressive strength (100 to 500 psi)
o    Biologic-releases calcium hydroxide constituents, which diffuse toward the pulp and stimulate
o    reparative dentin formation

Spruing Technique

Dental Materials

I . Procedure for single casting :

A 2.5 mm sprue former is recommended
for molar crowns 2.0 mm for premolars & partial coverage crowns .

II . Procedure for multiple casting :

Each unit is joined to a runner bar .

A single sprue feeds the runner bar

4 . SPRUE FORMER DIRECTION
Sprue Should be directed away from the delicate parts of the pattern
It should not be at right angles to a flat surface .(leads to turbulance  porosity .)
Ideal angulation is 45 degrees .

5 . SPRUE FORMER LENGTH

Depends on the length of casting ring .. Length of the Sprue former should be such that it keeps the wax pattern about 6 to 8 mm away from the casting ring. Sprue former should be no longer than 2 cm. The pattern should be placed as close to the centre of the ring as possible.

Significance

Short Sprue Length:

The gases cannot be adequately vented to permit the molten alloy to fill the ring completelyleading to Back Pressure Porosity.

Long Sprue Length:

Fracture of investment, as mold will not withstand the impact force of the entering molten alloy.

Top of wax should be adjusted for :

6 mm for gypsum bonded investments .

3 -4 mm for phosphate bonded investments .
TYPES OF SPRUES

I . - Wax . II . Solid

- Plastic . Hollow
- Metal .