Alginate

The term irreversible indicates that, once the paste sets to a gel, the process cannot be reversed.

What is Irreversible Hydrocolloid (Alginate)

1. Ease in manipulation
2. Minimum equipment necessary
3. Flexibility of the set impression
4. Accuracy if properly handled
5. Low cost

Irreversible Hydrocolloid

What are the reasons for the wide use of alginates

1. Potassium alginate/sodium alginate (15-20%)
> To dissolve in water
2. Calcium Sulfate dihydrate (16%)
> React with dissolved alginate to form insoluble calcium alginate
> Reactor
3. Sodium phosphate/Trisodium phosphate (1- 2%)
> React with calcium sulfate (ions) to slow working time
> Provide proper gelation time
4. Diatomaceous earth/ Silicate powder (50-60%)
> Control consistency of the mix and flexibility of the impression
> Filler
> Controls strength, stiffness and texture
> Gives mixed material its body
5. Potassium titanium fluoride/Potassium sulfate/ Potassium zinc fluoride (3%)
> Accelerator – for the setting of the gypsum product
6. Zinc Oxide (7%)
> Filler
7. Colorant
8. Flavoring

Irreversible Hydrocolloid

Enumerate and describe the composition of Alginate

1. Type I/ Fast Setting
> Sets at 60 sec to 120 sec
2. Type II/Normal Setting/Regular Setting
> Sets at 2 min to 4.5 min

Irreversible Hydrocolloid

Enumerate and describe the Types of Alginates

1. Reprogel
2. Identic
3. Replica

Irreversible Hydrocolloid

give examples of a regular setting alginate material

Alginic acid
Seaweed

Irreversible Hydrocolloid

Substance is __________, which is extracted from __________

Potassium salt
Calcium sulfate dihydrate
water
Calcium alginic gel

Irreversible Hydrocolloid

____________ form of alginic acid (Potassium alginate) react with ______________ and _______ to form a __________________.

2NaPO4 + 3CaSo4 (Paste) → Ca2(PO4)2 + 3Na2SO4
KnAlg (potassium alginate) (paste) + n/2 CaSO4 → n/2K2SO4 + Can/2Alg (calcium alginate)

Irreversible Hydrocolloid

Write down the gelation process

1. Permanent Deformation

2. Flexibility

3. Strength

4. Dimensional Change

Irreversible Hydrocolloid

What are the properties of Alginate

3% permanent deformation when compressed 10% for 30 sec. Permanent deformation increases when:
- The amount of deformation during removal is increased
- Time that it is held under compression is increased
- Thinner mixes are used

Irreversible Hydrocolloid

Describe the Permanent Deformation property of Alginate

- Relative amount of water and powder used influence the flexibility of set alginate.
- decreased W/P = decreased flexibility
- increased W/P = increased flexibility

Irreversible Hydrocolloid

Describe the Flexibility property of Alginate

- Tear Strength – 2-4 lb/in
- Compressive Strength – 3500g/cm2
- Strength is increased if thick rather than thin mixes
- Tear and compressive strength at the time of removal of the impression increases if the time of removal is delayed.
> Gel strength doubled during the first 4 min. period
> Increase in amount of water will weaken the material
> Insufficient spatulation will result to insufficient mixing of material components
> Over mixing will break the Calcium alginate gel network, this would decrease the strength

Irreversible Hydrocolloid

Describe the Strength property of Alginate

- Loss of accuracy with increase in time of storage.
> Syneresis – evaporation of water if impression is stored exposed to air
> Imbibition – absorbs water and expands
> Impression can be stored in 100% relative humidity for about one hour

Irreversible Hydrocolloid

Describe the Dimensional Change property of Alginate

1. Normal-set alginate

2. Fast-set alginate

3. Working time

4. Setting time

Irreversible Hydrocolloid

Write down the Manipulation terminologies

Working time of 2 minutes and a setting time of up to 4½ minutes after mixing

Irreversible Hydrocolloid

Describe Normal-set alginate

Working time of 1¼ minutes and a setting time of 1 to 2 minutes

Irreversible Hydrocolloid

Describe Fast-set alginate

The time allowed for mixing the alginate, loading the tray, and positioning the tray in the patient's mouth

Irreversible Hydrocolloid

Describe Working time

The time required for the chemical action to be completed

Irreversible Hydrocolloid

Describe Setting time

> Must feel comfortable to the patient
> Should extend slightly beyond the facial surfaces of the teeth
> Should extend approximately 2 to 3 mm beyond the third molar, retromolar, or tuberosity area of the arch
> Depth to allow 2 to 3 mm of material between the tray and incisal or occlusal edges of the teeth

Irreversible Hydrocolloid

Describe the Tray-selection criteria

1. Material should be “fluffed” by shaking or turning the container upside down and right side up for about a minute.
2. Water is dispensed with a calibrated measuring cup.
3. The powder is added to the water contained in the rubber mixing bowl.
> Adult mandibular impression
- Two scoops of powder and two measures of water
> Adult maxillary impression
- Three scoops of powder and three measures of water
4. Once the powder has been wetted, the alginate should be mixed with a vigorous stropping action.
5. Mixing is continued for a minute and should result in a mix with a smooth, creamy consistency that does not drip off the spatula.
6. The mixed alginate is transferred to the tray. It is wise to have less alginate in the posterior than the anterior part of the tray.

Irreversible Hydrocolloid

Describe the manipulation of Alginate

Alginator

Irreversible Hydrocolloid

Mechanical mixer for alginate

1. The posterior portion of the tray is seated first and then the anterior portion.
2. The tray is held gently but firmly in position until the alginate sets.
3. It is advisable to allow the impression to remain in the mouth for 2 additional minutes.
4. In the removal of the impression, the seal between the impression and the peripheral tissues is broken by moving the cheeks or lips with the fingers.
5. The impression and tray are removed from the mouth with a single firm motion.

Irreversible Hydrocolloid

How do we make the Impression?

> The impression tray is centered over the central and lateral incisors.
> There is a complete "peripheral roll," which includes all of the vestibular areas.
> The tray is not "overseated," which would result in exposure of areas of the impression tray.
> The impression is free from tears or voids.
> There is sharp anatomic detail of all teeth and soft tissues.
> The retromolar area, lingual frenum, tongue space, and mylohyoid ridge are reproduced in the mandibular impression.
> The hard palate and tuberosities are recorded in the maxillary impression

Irreversible Hydrocolloid

How do we know if the Impression is Acceptable

Immerse the impression in 2% potassium sulfate solution in water
Absorbed potassium sulfate accelerates the setting of the gypsum product
Some alginate material has accelerators/ hardener for the gypsum product (fluoride)

Irreversible Hydrocolloid

Describe the compatibility of alginate with gypsum

> Some available disinfectants may result in a gypsum cast that have a lower surface hardness or diminished surface detail
> Current Protocol:
Impression -> thoroughly rinsed -> spray disinfectant -> wrapped in a disinfectant-soaked paper towel -> placed in a sealed plastic bag for 10 mins.

Irreversible Hydrocolloid

Describe the Disinfection of alginate

1. Iodophor
2. Sodium Hypochlorite
3. Glutaraldehyde

Irreversible Hydrocolloid

Give examples of alginate disinfectants

Storage temperature and moisture contamination
Materials stored for 1 month at 65*C are unsuitable for use
Should not stock for more than 1 year

Irreversible Hydrocolloid

Describe the Shelf Life of Alginates

Tearing
Distortion
Rough stone model
Irregular shaped voids
Grainy material
External Bubbles

Irreversible Hydrocolloid

What are the effects of Mishandling Alginate Impression Material?

- Inadequate bulk
- Moisture contamination
- Premature removal from the mouth
- Prolonged mixing

Irreversible Hydrocolloid

Describe the Tearing effect of Alginate

- Cast material not poured immediately into the impression
- Movement of tray during gelation
- Premature removal from the mouth
- Improper removal from the mouth
- Tray held in mouth too long

Irreversible Hydrocolloid

Describe the Distortion effect of Alginate

- Inadequate cleaning of impression
- Excess water left in impression
- Premature removal of cast
- Leaving cast within the impression too long
- Improper manipulation of gypsum material

Irreversible Hydrocolloid

Describe the Rough stone model effect of Alginate

- Moisture
- Debris in tissue

Irreversible Hydrocolloid

Describe the Irregularly shaped Voids effect of Alginate

- Improper mixing of the impression material
- Prolonged mixing
- Undue gelation

Irreversible Hydrocolloid

Describe the Grainy Material effect of Alginate

- Undue gelation
- Air incorporated during mixing

Irreversible Hydrocolloid

Describe the External Bubbles effect of Alginate

> Hybrids of alginate and silicone elastomers
> Alginates modified by the incorporation of silicone polymers
> Supplied as two pastes which are mixed together
> Setting characteristics fine-detail reproduction and tear resistance is similar to those of the conventional products.
> Show marginally better but have poor dimensional stability

Irreversible Hydrocolloid

Describe Modified Alginates

- Addition silicone impression material that are formulated to provide characteristics similar to alginate.
- Have improved dimensional stability, accuracy and elastic recovery
- Expensive
- Packed for automixing
e.g. Alginot (Kerr), Position Penta Quick (3M), Silgimix (Sultan Health Care), Status Blue (Zenith Dental Products)

Irreversible Hydrocolloid

Describe Alginate Substitutes and give examples