GYPSUM PRODUCTS

Presented by:

I. Prianka Dodiya,

II. Noori Dalvadi,

III. Meera Dobariya.

Guided by:

IV. Dr.Deval Shah,

V. Dr.Mansi Gohil,

VI. Dr.Apoorva Raval,

VII. Dr.Uzma Pathan.

What is gypsum ? Name the varieties of gypsum.

It is a natural mineral mined around the various parts of the world having a chemical formula, CaSO4·s2H2O(calcium sulphate dihydrate).

TYPES:·

Albaster:-pure white ,fine grained and translucent.

Satin spar :-fibrous needle like with silky lustre.

Selenite:-colourless, crystalline and transparent.

What are different uses of ‘plaster of Paris’? Impression of mouth and face(impression plaster)

For making moulds, study casts, diagnostic cast,prliminary cast, master cast, and dies over which dental prostheses and restorations are made.

To mount cast on articulator.

For bite registration

In dental investments.

Define cast,die and model. CAST:- It is positive ,dimensionally accurate replica of oral soft and

hard tissues of either the maxillary or mandibular jaw and used for the construction of dental appliances which fit on to the soft tissues of the oral cavity.

DIE:-It is a positive , dimensionally accurate replica of a prepared natural tooth and used for the construction of inlay , crown or bridges.

MODEL:-It is a positive, dimensionally accurate replica of oral soft and hard tissues used as a study model or for patient education .The progress of treatment can be shown to the patient with these models.

Classify the gypsum products according to ADA specification no.

According to ADA specification number 25:

TYPE I:Dental plaster,impression

TYPE II:Dental plaster,model

TYPE III:Dental stone, model

TYPE IV:Dental stone,die,high strength,low expansion

TYPE V:Dental stone,die,high strength,high expansion

What do you mean by calcination?

The process of heating gypsum for manufacturing plaster is known as calcination.

OR

Removing 3/4th of water of crystallization by burning of gypsum

Write the process for manufacturing of Dental plaster(β hemihydrate). ORWhat do you mean by “dry calcination” ? Give its reaction.

Gypsum is ground and heated in an open kettle on kiln at a temperature of to for manufacturing of beta type crystals or dental plaster. This process is known as “dry calcination”.

(beta hemihydrate)

C110C130

OHCaSOOHCaSOHeat

24130110

24 2

1.2.

Write the process for manufacturing of dental stone(α hemihydrate).

OHCaSOCaSO 24130120

4 2

1.

17 lbs/sq. inch pressure (alpha hemihydrate)

Write the process of manufacturing for alpha modified stone or improved stone.

Gypsum is calcined by boiling it in 30% calcium chloride solution . The chlorides are then washed away or autoclaved in presence of sodium succinate 0.5%.Than grinded to obtain alpha(α) modified stone.

Give the reaction for manufacturing of orthorhombic anhydrite.

anhydrite) anhydrite) e)hemihydrat dihydrate)

ic(orthohomb (hexagonal sulphate (calicum sulphate (Calcium2

1.2. 4

10002004

20013024

13011024 CaSOCaSOOHCaSOOHCaSO

Write the setting reaction of plaster.

HeatOHCaSOunreactedOHCaSOOHOHCaSO 224242224 2

1.)(2.23)(

Hemihydrate + water Dihydrate + unreacted hemihydrate + Heat

EXOTHERMIC REACTION

What are modifiers?

They are the chemicals added in order to alter some of the properties like expansion , setting time etc. or to enhance the other properties like working time , dimensional stability etc.

EX.:accelerator & retarder.

What are accelerator and retarder?

ACCELERATORS:-The substances which decreases the setting time of gypsum products by increasing the rate of reaction are called accelerator.

E.g., Tera alba, sodium sulphate, potassium sulphate and sodium chloride(low

concentration)

RETARDERS:-They are the substances which increases the setting time of gypsum products by decreasing the rate of reaction.

E.g., Borax, sodium chloride, sodium sulphate(high concentration) ,glue ,agar,

coagulated blood.

What is tera-alba?

It is finely powdered gypsum /white earth like substances used to control setting time of plaster of paris.It acts by providing additional nuclei of crystallization.

What are the theories of setting of gypsum product? Colloidal theory

Hydration theory

Dissolution precipitation theory

Define crystallization. Crystallization is the slow precipitation of crystals from a solution of a

substance. Crystallization can also refer to the solid-liquid separation and purification technique in which mass transfer occurs from the liquid solution to a pure solid crystalline phase

What are the stages(chemical) of crystallization?

Dissolution

Suspension

Saturation

Super saturation

Nuclear formation

Growth of nuclei

Crystallization

Spherulite formation

Name physical stages of gypsum product.

Fluid

Plastic

Firable

Carvable

What do you mean by spherulites?

“As the reaction proceeds gypsum is formed in the form of needle like clusters called spherulites”

What do you mean by water of crystallization?

The invisible water present in the gypsum is known as water of crystallization.

What is impression plaster? Give its uses.

Impression plaster is one of earliest rigid impression materials in dentistry.

USES:

For making impressions in complete denture and maxillofacial prosthesis.

For bite registration material.

What is soluble plaster? Give its mode of action.

When impression plaster contain potato starch to make the impression soluble

it is termed as ‘soluble plaster’.

MODE OF ACTION:

Impression Starch swells

Poured with in hot water and impression Cast get separated

the cast(after disintegrates

Hardening)

What is the chemical formula for dental plaster/β hemihydrate?

OHCaSO 24 2

1.

Write the composition of impression plaster?

Dental plaster

(Potassium sulphate)

Borax

Colouring and flavouring agent

42SOK

Write various uses of TYPE II gypsum product or model plaster and give its composition. MODEL PLASTER = LABORATERY PLASTER.

USES:

For making study cast and model.

To make moulds of curing dentures

For mounting cast on articulator

COMPOSITION:

Βeta hemihydrate + Modifiers

What do you mean by ‘hydrocal’?Give its uses.

It is the type III gypsum product called DENTAL STONE used for model preparation.

USES:

For preparing master casts and to make moulds.

Write the composition of dental stone(α hemihydrate).

Alpha hemihydrate + 2 to 3% coloring agent+ (accelerator) + borax (retarder)

42SOK

Write the various properties of dental stone,model?

COMPRESSIVE STRENGTH:- 3000 to 5000 psi

SETTING EXPANSION:- 0.06% to 0.12%

HARDNESS:- 82 KHN

What is the difference between the crystal structure of dental plaster and dental stone?

DENTAL PLASTER DENTAL STONE

Needle like crystals Rods and prism like crystals

Irregular in shape with capillary pores

Regular in shape

Loosely packed Closely packed

What is excess water?

The actual amount of water necessary to mix the calcium sulphate hemihydrate is greater than the amount required for the chemical reaction, this is called excess water.

What is a balanced stone?

A stone with a setting time established by the addition of proper quantities of both accelerator and retarder is called “balanced stone”.

Write the synonyms for TYPE IV gypsum products.

Class II stone

Die stone

Densite

Improved stone

Write the uses of die stone.

It is used when high strength and surface hardness is required

E.g., dies used for inlays , crown and bridge wax pattern.

Give the examples of TYPE V stone.

Hard rock

Jade rock

Resinrock XL5

Denflo HX

How type V is better than type IV stone?

It has higher compressive strength.

Setting expansion is increased from a maximum of 0.10 to 0.30% to compensate for the shrinkage of base metal alloys during solidification.

What do you mean by w/p ratio?

It is defined as water required for 100gm of powder.

What is the w/p ratio of the gypsum products?

Impression plaster : 0.50 to 0.75

Dental plaster : 0.45 to 0.50

Dental stone : 0.28 to 0.30

Die stone,Type 4 : 0.22 to 0.24

Die stone,Type 5 : 0.18 to 0.22

What is the of low and high water powder ratio on gypsum products?

LOW W/P RATIO(thick mix) HIGH W/P RATIO (thin mix)

Quick setting Slow setting

High expansion Low expansion

More strength Less strength

More surface hardness Poor surface hardness

Less porosity More porosity

Define mixing time and Give its value for gypsum products.

“It is the time from the addition of the powder to the water until mixing is complete.”

1 minute

Define working time and give its value for gypsum products,

“It is the time available to work with the mix for the intended purpose.’’

3 minutes.

What do you mean by setting time? Give its two types.

“ It is the time elapsing from the beginning of mixing until the material hardens.”

TYPES:-

1. Initial setting time

2.Final setting time

Define initial setting time.

“As the reaction proceeds,more hemihydrate crystals react to form dihydrate crystals.The viscosity of the mass is increased and it can no longer be poured.The material become rigid(but not hard).It can be carved but not moulded.This is known as initial setting time’’

What is final setting time?

“The time at which the material can be separated from the impression without distortion or fracture.’’

What are the methods to measure the setting time?

Loss of gloss method

Exothermic reaction

Penetration tests

What is induction period?

“Initial time during setting before release of exothermic heat”

What is loss of gloss method?

“The set plaster when loses it surface shine and smoothness it is considered as the end of working time and initial set has taken place this method is known as loss of gloss method.’’

What do you mean by exothermic reaction?

“The temperature rise of the mass which leads the setting of material.”

Which are the types of penetrometers?

Vicat needle.

Gillmore needle.

(Vicat needle) (Gillmore needle)

Give weight and diameter of vicat and gillmore needle.

Vicat needle : Weight - 300gm

:Diameter – 1mm

Gillmore needle :

I)Small : Weight - ¼ lb

:Diameter - 1/12’’(2.12mm)

II)Large : Weight - 1lb

: Diameter – 1/24’’(1.06mm)

Which are the factors affecting setting time?

Manufacturing process

Mixing and spatulation time(time and rate)

Water/powder ratio

Temperature

Modifiers

What is nuclei poisoning?

Presence of more than 20% of NaCl , colloids like coagulated blood etc. act as retarder to setting of plaster by wetting of the nuclei and their growth.

What is normal setting expansion?

It is a linear expansion during setting due to outward thrust of the growing crystals during setting which intermesh and intercept each other during growth.

What is hygroscopic expansion and how much it is?

It is increased expansion of setting plaster in presence of water .It can be double the amount of normal setting expansion.

USE:-

It is used to expand some gypsum bonded investments.

Write the factors controlling expansion.

Water powder ratio :- setting expansion

Modifiers :- setting expansion

:- 4% solution decreases the setting expansion from 0.5 to 0.06 %.

NaCl and borax :- setting expansion

42SOK

Write the factors affecting strength and give its two types.

Water powder ratio :- water , porosity , strength

Spatulation :- strength (within limit)

Addition of accelerators and retarders :- strength

TYPES:-

1.Dry strength

2.Wet strength

What is wet strength ? How much it is for model plaster, dental stone and die stone? It is strength when the set mass is still contains excess water and

specimen is wet to touch.

E.g.,

Model plaster – 12.5 Mpa

Dental stone - 31 Mpa

Die stone – 45 Mpa

What is dry strength? How much it is ?

It is strength when the set mass has no excess water and specimen is dry to touch. It is 2- 3 times more than wet strength.

What care should be taken with temperature to avoid shrinkage and reduction in strength of gypsum products?

Gypsum is stable only below about . Drying at higher temperature rapidly at or higher ,lose of water of crystallisation occurs which causes shrinkage and reduction in strength.

C40C100

What are divestment ?

It is mixture of die stone and anyone of the dental investments materials used to make die or master model.

What are model duplicating materials?

These are used to make study model during metal casting e.g., hydrocolloid impression materials.

What care should be taken during storage of powder?

As plaster is hygroscopic it should be kept in air tight containers. Otherwise when humidity is more than 70% plaster starts setting reaction and small crystals are produced. As hygroscopic expansion continues the entire hemihydrate mass is covered with more crystals of gypsum. Thus water penetrates the mass with difficulty, thereby delaying setting.

THE END