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Главная Methodical work 2 курс, 3 семестр Alginate impressions. Physical and chemical properties. Indications to applications, specimens. Methods of taking impressions with alginate mass. Complications 

Alginate impressions. Physical and chemical properties. Indications to applications, specimens. Methods of taking impressions with alginate mass. Complications

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ODESSASTATE MEDICAL UNIVERSITY

 

Department of orthopedic dentistry

 

 

 

 

 

 

 

 

Lecturer’s guidelines

for the practical class on the theme 5.2.18:

“Alginate impressions. Physical and chemical properties. Indications to applications, specimens. Methods of taking impressions with alginate mass. Complications”

 

(for the 5th year students of dental faculty)

 

 

 

 

 

It is approved

at the methodical meeting of the

department

        on “__”  ____200

        Minutes №

The head of the department

           Chulak L.D.

 

It is approved

at the methodical meeting of the

department

            on “__”  ____200

            Minutes №

The head of the department

               Chulak L.D.

 

It is approved

 at the methodical meeting of the

department

                  on “__”  ____200

                  Minutes №

The head of the department

              Chulak L.D.

 

 

It is approved

at the methodical meeting of the

department

             on “__”  ____200

             Minutes №

The head of the department

            Chulak L.D.

 

 

 

 

 

 

The theme of the class: “Alginate impressions. Physical and chemical properties. Indications to applications, specimens. Methods of taking impressions with alginate mass. Complications” – 2 hours

 

1. Importance of the theme. Beeswax was proposed as an impression material for the first time by Poorman at the beginning of the 17th century. Deficiency of wax as the impression material have made specialists find more perfect materials. Researchers and experts offered a lot of various impression materials (gutta-percha, wax compositions, etc.) which, however, did not meet dental requirements. In the 19th century Dveenel (1840) offered plaster fortaking impressions in the oral cavity, and in 1869 Stent developed thermoplastic impression mass. It is impossible to create one universal impression material which would be suitable for various cases of prosthesis, as it is impossible to combine various complexes of properties in one material.

For taking impression from the soft and firm objects having an undercut (inverse cone), it is necessary to use impression materials possessing various properties. It accounts for wide assortment of impression materials which are industrially manufactured.

            

2. Learning objectives

- To acquaint students with physical and chemical properties of alginate impression materials. - 1 level.

- Students should know indications and contra-indications to application of  alginate impression materials. - 2 level.

- To enable students to master the skills - 3 level:

a) Taking of impression by alginate impression materials.

- Formation of professional competence and skill of logical thinking in students.

- Formation of principles of medical ethics and deontology in students.

 

3. Interdisciplinary integration

The discipline

To know

To be able

Previous disciplines:

1. Anatomy.

 

 

 

2. Histology.

 

 

- A structure of the maxilla;

- A structure of the mandible;

- A structure of the temporomandibular joint

- Anatomy of the teeth

 

Structure of the mucous membrane of the oral cavity

 

 

To determine interrelation of the maxilla and mandible, palpate movement of the head of the mandible.

 

To determine clinically presence of the submucous layer in different sites of the mucous membrane of the oral cavity

The subsequent disciplines provided by this discipline:

1. Therapeutic dentistry.

 

 

 

 

 

 

2. Surgical dentistry.

                                               

                                               

 

 

To make therapeutic examination of the dental patient.

X-ray diagnosis of the maxillofacial area.

Classification of the caries cavities by Black.

.

Indications to extraction of the teeth.

Methods of anesthesia of the maxillofacial area

 

 

 

To make a plan of therapeutic sanation of the patient.

To assess condition of the maxillofacial area by a radiological picture.

 

 

To make a plan of surgical sanation of the patient

Intradisciplinary integration:

1. Microprosthesis

2. Fixed orthopedic constructions.

3. Removable orthopedic dentures

4. Medical errors in orthopedic dentistry. Possible complications in prosthesis. The medical responsibility.

 

The list of the medical documentation.

Algorithm of examination of the patient, making a diagnosis. A choice of the construction.

 

To fill in the medical documentation.

To make clinical examination of the patient, to make a diagnosis, to choose a construction

 

                                               

4. The contents of the theme.

Development and wide circulation of the alginate impression materials started at the beginning of the 40s of the 20th century. A lot of alginates in the modern dental market are evidence of their great clinical value.

Alginates are related to elastic impression materials. The raw material for them are seaweed Laminaria, Ascophyllum nodosum, Durvilla antarctica, Lessonia, etc. from which an alginic acid is obtained.

The powder of the alginate material contains well soluble in water sodium or potassium salts of the alginic acid (15 %), calcium sulphate (about 12 %), decelerator of cementation - sodium phosphate (2 %). Inorganic fillers (talc, zinc oxide) determine viscosity of the material and its stability after hardening and make the main bulk of the powder (up to 70 %). In addition the alginate powder contains a small amount of dye-stuffs, flavouring additives and aromatizers.

Unlike salts of the alginic acid with monovalent metals (sodium Na+), salts of alginic acids with bivalent metals (calcium Са2+) are poorly soluble in water because of crossing binds arising between polymeric molecules of alginic acids.

If water is added to the alginate powder sodium salts of the alginic acid and calcium sulphate are released into the solution. These salts dissociate into ions of sodium (Na +) and the alginic acid on the one hand, and ions of calcium (Са2 +) and sulphatic ions(SO42-)on the other hand.

After dissociation there is an opportunity of reaction of the alginic acid with the released ions of calcium. As a result, separate chains of alginic acids are crossly bound with ions of calcium that leads to formation of elastic gel and polymerization of the mass.

This reaction takes place very quickly, therefore presence of reaction decelerators is necessary for convenience of work.The decelerator, sodium phosphate (Na3PO4), is the first to bind the majority of calcium ions, forming poorly soluble calcium phosphate (Ca3(PO4)2). Thus reaction of alginate cementation is decelerated until the decelerator does not react completely. Manufacturers of the impression material can change time of hardening of the product by increasing or reducing the amount decelerator in the powder (1-2 % are usual). Quickly and normally hardening alginates are manufactured. Time of cementation can vary considerably depending on temperature of water for mixing. Cold water increases working hours, and warm water reduces them.

Propertiesof alginates.

Viscosity.Viscosity of the mixed alginate material depends to a great extent on amount of water added in mixing. Therefore it is necessary to adhere to proportions of water and powder which are offered by the manufacturer.

Accuracy of reproduction of details.Accuracy which the alginate impressions are capable of reproducing details of a relief, is determined by the size of granules of the powder and type of the formed macromolecules. The limit of accuracy of reproduction of fine objects makes nearly 50m (according to ISO 1563). This accuracy of reproduction of details is not so good as in silicon impression materials, therefore alginates should not be used for taking impressions for construction of working models on which there will be made inlays, cast and ceramic crowns, bridge dentures.

Stability of size.Water in polymerized alginate is free between macromolecules. Hence, depending on conditions in which the ready impression is kept, water can be or is easily absorbed by the material (in its excess), or the material can lose water and dry up. Accumulation or loss of water leads to change of the initial size of impressions, therefore plaster models should be received immediately after taking the impressions.

Elasticity.Thanks to presence of crossing - connected structure of macromolecules, polymerized alginate material has elasticity which allows to receive impressions of the areas with undercuts. However, the alginate impression material is easily destructed in rather low loadings for break. Therefore extensive undercuts such as wide interdental spaces and spaces under intermediate parts of bridge dentures should be isolated in the oral cavity of the patient before taking the impression with the alginate material.

Disinfection.The problem of disinfection of the alginate impression is that alginates can be in the aquatic environment only for a short time without significant absorption of water and changes in size. However, researches show that use of disinfection preparations does not worsen quality of impressions within several minutes.

Long storage of alginatematerials.The alginate powder can be stored in original packing till 3 years at a room temperature (23°С). The open packing after taking of the powder should be necessarily closed. The alginate powder should always be taken from the packing only by dry instruments.

Ideally, the alginate impression should be cast by plaster within 30 min after their taking. If impressions are transported into orthopedic dentallaboratory the impression should be in a plastic package together with a piece of wet fabric. This piece of fabric will not allow the impression to dry up. At the same time, the fabric should not touchalginate so that there was no local swelling of the material.

To prevent clinical - laboratory mistakes while working with alginate impression materials strict observance of technologies recommended by firm-manufacturer (Table1) is recommended.

Tab. 1 Possible mistakes while working with alginateimpression materials.

Mistake                        

 

Cause of the mistake

Solution

The alginate impression has come off the tray

Insufficient mechanical retention or chemical adhesion of the alginate material to the tray

Use the trays having punched walls or a thickening on edge of the tray. The trays having smooth edges should be pasted over with a strip of plaster or wax. Use adhesive for the trays.

 

Wrong storage of the alginate impression.  

Excess of the impression material along the distal edge of the tray should be cut off. If it cannot be made, without having damaged the important parts of the impression it is necessary to put the impression on the firm surface only by the impression material downwards.

The impression material "is punched" by the teeth to the bottom of the tray.

It is incorrectly mixed alginate material. The material is too fluid.

Follow rules of mixing the material, specified by the manufacturer.

 

Too big pressure in introduction of the tray

Pressure in introduction of the tray should be moderate.

 

The tray is too small or was introduced incorrectly.

Try on the tray before removal of the impression. There should be a space not less than 5 mm between edges of the tray and teeth.

Inexact or incomplete imprint of the occlusal  surfaces on the alginate impression and plaster model.

Insufficient pressure in introduction of the tray.

Pressure in introduction of the tray should be moderate.

 

 

Too liquid alginate material.  

Follow rules of mixing the alginate material, specified by the manufacturer.

Before introduction of the tray put a small amount of the alginate mass in the area of fissures of the chewing teeth, and also in the interdental spaces of the necessary area

Plaster excesses (bubbles) on the occlusal surfaces of plaster model.  

 

 

 

 

Breaking off of separately standing teeth in opening of the impression.

Air bubbles in the alginate impression.

Before introduction of the tray put a small amount of the alginate mass in the area of fissures of the chewing teeth, and also in the interdental spaces of the necessary area

The alginate impression remained on a model too long and has lost elasticity due to evaporation of water.

 Open the impression immediately after hardening of plaster (approximately in 30 min).

The teeth have the expressed equator or undercuts

Before opening of the impression it is necessary to shake the tray a little on either side.Pressure on the tray handle should be avoided. In presence of     Before opening слепкаit is necessary to shake a little the spoon from two parties{sides}. Pressure upon the handle слепочнойshould be avoided the spoon.

separately standing teeth, especially with big clinical crown, for prevention of theirbraking off in the impression it is necessary to place special pins.

 

The orthopedic constructions made by the alginate impressions correspond to a plaster model, but do not suit in the mouth.

There was a deformation of the alginate impression.

Wrong storageof the impression, its swelling in storage in water, or drying andshrinkage of the impression.   

Impressions shoud be cast in plaster during the first 30 min after their reception. In transportation the impression should be in a plastic package with wet fabric.

 

Alginate impression has come off from the tray (more often its indistal  parts) and it has not been noticed.

Excess of the impression material along the distal edgeof the tray should be cut off. It is necessary to put the impression on the firm surface only by the impression material downwards.

Excess elastic deformation:

1. The impression is removed from the mouth incorrectly.

2.The alginate layer is too small due to small size of the tray.

3.Too great pressure on the tray in hardening of the alginate material

 

1.In taking the impression out of the mouth the pressure on the tary should be symmentric.

2.Use the tray of necessary size.

3. After introduction of the tray into the mouth, leave the impression untill complete polymeralization of the alginate material, without applying additional pressure

 

 

However, despite advantages of alginate materials (high elasticity; good reproduction of a relief of the soft and hard tissues of the oral cavity; cheapness; easiness in work; possibility of sterilization), they also have drawbacks: absence of sticking to the trays; shrinkage as a result of water loss; less accuracy of the impression in comparison with silicon materials.

World leaders on manufacture of dental materials constantly update assortment of production, trying to reduce to a minimum the specified drawbacks of alginate impression materials.

Thus, at the present stage of development of orthopedic dentistry alginate impression materials occupy one of the leading positions among impression materials, owing to a combination of low price and high quality of the received impressions.

 

5. The plan and organizational structure of the class

Main stages of the class, their functions and contents

Educational aims

Training aids and controls

Materials of method.provision

Time (in min)

1.

The preparatory stage

-organization of the class;

- educational aims;

-control of initial level of knowledge

I

Questions, tests of different levels, situational tasks

Tables, slides, codograms

 

2

 

3

 

20

2.

The main stage

-determination of knowledge of the current material;

-management of patients;

-perfection of clinical and additional methods of a patient’s examination;

-taking impressions, casting of diagnostic models

II

 

 

 

III

Questions, tests of different levels, situational tasks

Thematic patients

 

 

Tables, slides, codograms

 

 

 

 

 

 

 

 

Orthopedic dental instruments

 

20

 

 

130

3.

The final stage

-control and correction of professional skill level;

- summing up of the class;

-task for the following class with reference to the literature

 

 

 

 

2

 

 

2

 

 

1

 

 

6. Materials of methodical provision of the class

6.1. Control materials of the preparatory stage of the class

  1. Requirements to impression materials.
  2.  Classification of impression materials.

    

6.2. Materials of methodical provision of the basic stage of the class:

A. Control questions.

  1. Physical and chemical properties of alginate impression mass.
  2. Indications and contraindications to application of alginate impression mass
  3. Specimens of alginate materials.

        

B. Control tests.

1. Apatient aged 49 has generalized parodontitis of moderate degree of severity. Fixed splint – dentures are made. What impressionmaterial is necessary to apply in this case?

- Plaster

- Protacryl-M

+Ipin

- Sielast-69

- Stens

 

2. A44 – year - old man is planned to construct whole piece splint for the mandible. Objectively: the dental formula:

17 16 15 14 13 12 11 | 21 22 23 24 25 26 27

.................... 43 42 41 | 31 32 33 34..............

Dental crowns of the mandible are high, the teeth are intact, mobility of I-II degree. What impression material is better for using?

- Repin

- Stens

- Plaster

+Stomalgin

- Sielast-69

 

3. A58- year-old patient has a fanlike divergence of the frontal teeth of the maxilla. What impression material is better for taking the impression.

+Stomalgin

- Plaster

- Stens

- Orthocor

- Repin

 

4. Apatient aged 49 has generalized parodontitis of moderate degree of severity. Fixed splint – dentures are made. What impressionmaterial is necessary to apply in this case?

- Plaster

-Protacryl-М

+Ipin

- Sielast-69

- Stens

 

5. As a result of a gunshot wound a 60 –year-old patient had an extensive defect of the nose. The patient has temporarily refused surgical treatment and he was offered construction of ectoprosthesis of the nose kept by means of a frame of glasses. What impression should be taken in the patient?

A.* Plaster, of the whole face

B.Thermoplastic mass, of the defect

C.Thermoplastic mass, of the whole face

D.Plaster, of the defect

E.Elastic mass, of the defect

 

          C. Control tasks.

1. The patient has referred to clinic of orthopedic dentistry with complaints on mobility of the teeth. It was decided to make Albrecht's removable splint. What immpression material is necessary to apply for taking the impression and why?

 

6.3. Control materials of the final stage of the class

1.  The technique of taking the impression with alginate impression material.

 

6.4. Materials of methodical provision of individual students’ work  with literature

Basic tasks

Instructions

Answer

Taking the impression with alginate impression material in one another.

 

 

 

 

 

 

 

 

 

                                                                                                                                  

7.Literature for lecturers.

8.Literature for students.

Main:

Additional:

10. Tasks for students’ research.

1.    The essay: “Modern alginate impression materials”

2.    “Algorithm of taking the anatomic impression with alginate material”.

3.   “Comparative analysis of volumetric shrinkage of alginate and silicon materials with time”

 

11. Atheme of the following class:

“Silicon impressions. Physical and chemical properties. Indications to application. Methods of taking combined impresiions. Final class”

 

 

 

 

 

 

 

 

The guidelines are composed

by the lecturer of the department                                                           Bas A.O.