Basic principles of arch prosthetics

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D.M. Korol, M. D. Korol, D.D. Kindii, L.S Korobeinikov, O. D. Odzhubeiskaia, R.V. Kozak, T.P. Maliuchenko,

V.D. Kindii, A.D.Dorubets

BASIC PRINCIPLES OF ARCH PROSTHETICS

Manual

for students of Dental faculties of Higher Medical Educational Establishments

of IV accreditation level

Poltava–2017

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BBC 56.6я73,

UDC 616.314-089.28/29-03(075.8)

Published by decision of the Central Methodical Commission of Higher State Educational Establishment of Ukraine «Ukrainian Medical Stomatological Academy», protocol № 23-01-9/413, as of 03.11 2016.

The manual was compiled by the staff of Department of Propedeutics of Prosthetic Dentistry, Higher State Educational Establishment of Ukraine «Ukrainian Medical Stomatological Academy» and medical college of Higher Medical Educational Establishment of Ukraine «Ukrainian Medical Stomatological Academy»:

Korol Dmitrii Mikhailovich − Doctor of Medical Sciences, Professor, Head of Department;

Korol Mikhail Dmitrievich − Doctor of Medical Sciences, Professor;

Kindiy Dmitriy Danilovich − Candidate of Medical Sciences, associate Professor;

Korobeinikov Leonid Sergeevich − Candidate of Medical Sciences, associate Professor;

Odzhubeiskaia Olga Dmitrievna − Candidate of Medical Sciences, associate Professor Kozak Ruslan Vasilievich − Candidate of Medical Sciences, associate Professor Maliuchenko Tatiana Petrovna – dentist, teacher of medical college;

Kindiy Victor Danilovich – Candidate of Medical Sciences;

Dorubets Andrij Dmitrievich – Candidate of Medical Sciences.

Reviewers:

Makieiev Valentyn Fedorovych – Professor, Department of Prosthetic Dentistry, Danylo

Halytsky Lviv National Medical University.

Yanishen Ihor Volodymyrovych – Doctor of Medical Sciences, Associate Professor, Head of Department of Prosthetic Dentistry, Kharkiv National Medical University.

D.M. Korol, M. D. Korol D.D. Kindiy, L.S. Korobeinikov, O.D. Odzhubeiskaia, V.R. Kozak, T.P. Maliuchenko, V.D. Kindii, A.D.Dorubets Basic principles of arch prosthetics. − Poltava: PE Miron I. A., 2017. – 120 р.

The manual was compiled to help students of Dental faculties in mastering the subject “Orthopedic stomatology” − namely, the section “Arch prosthetics”.

The authors will be grateful for the constructive comments and suggestions in improving the presented material.

Recommended by the State Institution “Central Methodical Cabinet for higher medical education” as manual for English speaking graduate students of Dental faculties (Committee minutes dated 27 October 2016 № 3).

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PREFACE

The development of prosthetic dentistry provides improvement of different dental prostheses to increase the level of dental care efficiency.

The manual is aimed to provide comprehension of the present day views on the arch prostheses production considering theoretical and practical value of classical techniques.

The manual contains the programme material on prosthetic dentistry educational discipline and concerns the issues discussed in the section «Arch prosthetics». The current methods of arch prostheses fixation are widely covered in the manual as well as planning approaches and prosthesis design choice. Particular attention is paid to the basic technological stages of prostheses manufacturing. The text is illustrated with the color drawings improving the presented material comprehension, the list of questions is directed on self-control of acquired knowledge.

The authors will be sincerely grateful to colleagues for constructive remarks and useful suggestions in improving the presented material.

Authentic translation from Ukrainian Language.

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SECTION I.

PLANNING OF ARCH PROSTHESIS CONSTRUCTION

Part 1. Structural elements of arch prosthesis The basic structural elements of arch prosthesis are:

1. supporting elements;

2. connecting (fixing) elements;

3. leveling elements;

4. elements preventing displacement;

5. elements preventing spontaneous expulsion.

Supporting elements

Supporting elements provide conditions for periodontal gingival way of functional load transmission and improve fixation of arch construction.

Supporting elements include occlusal onlays, supporting artificial crowns, prosthetic bridges, root inlays, root pins and implants.

Connecting (fixing) elements

Connecting elements perform the fixing function of the removable arch prosthesis to the natural teeth. According to the method of connection with arch prosthesis basis, fixation elements can be:

1) rigid;

2) semimobile (elastic);

3) mobile (hinged).

According to the structure, fixation elements can be:

1) clasps;

2) anchor clamps;

3) dental bars;

4) telescopic (double) crowns;

5) magnetic pins.

Leveling elements

Leveling elements perform the function of connecting the certain parts of prosthesis into the single structure, provide redistribution of mechanical load and comfort conditions of prosthesis usage. These elements include saddles, lingual, palatal and vestibular arches.

Elements preventing prosthesis displacement

Elements which prevent prosthesis shifting perform the resistance function in horizontal plane in case of eventual arch prosthesis displacement in anterior- posterior or lateral directions.

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These elements include all fixation units of construction. Moreover, in case of periodontal tissues diseases the set of arch prosthesis can include splinting elements (claw like hooks, multi-staged continuous clasps, Elbrecht splint, etc.).

Crowns and prosthetic bridges can be considered as mediated elements preventing possible shifting of arch construction.

Elements preventing spontaneous prosthesis expulsion

Almost all fixation elements can be considered as preventing spontaneous expulsion of arch prosthesis. The main condition of their preventive action is pe- ripheral location which is maximally distant from the axis of prosthesis rotation.

Independent occlusal inlays and back action claspers can serve as example.

Fig. General view of arch prosthesis on the upper jaw in the oral cavity Questions for individual control

1. What types of the main structural elements of arch prosthesis do you know?

2. What structural elements of arch prosthesis refer to supporting?

3. What structural elements of the arch prosthesis belong to fixation?

4. What structural elements of the arch prosthesis belong to leveling?

5. What structural elements of the arch prosthesis belong to the shift preventing elements?

6. What structural elements of the arch prosthesis belong to the elements that prevent expulsion?

7. How are the fixation elements divided according to way of connection with the prosthesis basis?

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Fig. Arch prosthesis for the upper jaw with the multi-unit clasp as construction shifting protector

Fig. Arch prosthesis for the lower jaw with arch modified to multi-unit clasp

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Fig. Arch prosthesis for the upper jaw with independent occlusal inlays

Fig. The frame of arch prosthesis with elastic and rigid retainers on the cast

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Part 2. Methods of arch prosthesis fixation The methods of arch prosthesis fixation include:

1. adhesion;

2. sticking;

3. anatomical retention;

4. artificial fixation elements.

Adhesion

Adhesion is the bonding between two congruent surfaces reinforced by thin layer of liquid between them. In the arch prosthesis, adhesion of plastic saddle surface to the mucous membrane of the prosthetic bed acts due to the presence of oral fluid between them.

Sticking

Sticking is one of adhesion forms when molecular cohesion force between the liquid and prosthesis surface is more powerful, than the strength of the in- termolecular coupling in the liquid.

Anatomical retention

Anatomical retention is the complex of anatomical features in the jaw structure which provides fixation of the arch prosthesis and its stabilization during functioning. The elements of anatomic retention include:

1. alveolar parts of the jaws;

2. vault of the palate ; 3. maxillary tuberosities;

4. interdental spaces;

5. perigingival area of the teeth crowns with pronounced undercuts.

Artificial fixation elements

Artificial fixation elements are special physical and physico mechanical direct and indirect retainers. Direct retainers are placed proximately on the abutment teeth. Their function is to fix arch prosthesis and prevent its vertical displacement. Direct retainers are nominally divided into:

1. intracoronal;

2. extracoronal.

Attachments are the examples of intracoronary retainers and clasps − extracoronal retainers.

Clasps are the most common variant of arch prosthesis fixation.

Indirect retainers, located on the structure periphery in position, that they do not coincide in direction with the axis of prosthesis rotation, make impossible spontaneous throwing of arch construction. Such structures include occlusal inlays, extensions, continuous bar retainers.

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Questions for individual control

1. What are the methods of arch prosthesis fixation?

2. What is prosthesis adhesion?

3. What is prosthesis sticking?

4. What is anatomical retention?

5. What belongs to anatomic retention elements?

6. What is the function of fixation elements?

7. What two groups are fixation elements of arch prosthesis distributed into?

Fig. Arch prosthesis for the lower jaw with extracoronal attachment retainers on the fixed bridge porcelain fused to metal construction

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Part 3. Clasp fixing system of arch prosthesis Classification of clasps

1. According to manufacturing method:

a) bent;

b) cast.

2. According to shape of cross-section profile:

a) round;

b) semiround;

c) tape.

3. According to covering degree of tooth or group of teeth:

a) singe armed;

b) double armed;

c) mesiodistal;

d) double;

e) multi-unit.

4. According to function:

a) retaining;

b) supporting;

a) supportive-retaining.

5. According to method of basis connection:

a) rigid;

b) semimovable (elastic);

c) movable (hinged).

6. According to production material:

a) metal;

b) plastic.

7. According to clasp shoulder location:

a) dental;

b) alveolar;

c) dentoalveolar.

Requirements for the clasps of the arch prosthesis 1. Do not harm periodontal tissues of the abutment teeth.

2. Perform the function in different clinical conditions securely.

3. Minimal affect the arch prosthesis esthetics.

4. Do not prevent the normal teeth joining.

5. Do not change its properties in the oral cavity conditions.

6. Be able to additional activation.

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Fig. Arch prosthesis for the upper jaw with clasp fixation system next to working cast

Fig. Arch prosthesis on the upper jaw with plastic clasps

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1. How are the clasps divided according to manufacturing way?

2. How are the clasps divided according to form of shoulder section?

3. How are the clasps divided according to covering degree of abutment tooth surface?

4. How are the clasps divided according to function?

5. How are the clasps divided according to manufacturing material?

6. How are the clasps divided according to clasp shoulder location?

7. What requirements for the clasps of the arch prosthesis do you know?

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Part 4. The molar clasps of arch prosthesis

The first cast molar clasp was produced by Polk E. Akers in 1926. Over time, his construction was included to Ney system, which provides for five clasp types.

Ney system of molar clasps The first type

Akers clasp, consisting of two rigid pointed covering shoulders and one occlusal inlay.

The second type

Roach clasp, consisting of separate elongated occlusal inlay, body and two T- shaped (split) shoulders.

The third type

Clasp, combining Akers and Roach shoulders, therefore, is called compound.

The fourth type

Single-armed clasp with one or two occlusal inlays and extended shoulder, that covers the tooth from the distal side. Depending on location of occlusal inlay and body, clasp can have opposite or rear opposite effect.

The fifth type

Dental ring clasp with two occlusal inlays, that almost completely covers the retainer tooth on perimeter.

For more effective arch prosthesis fixation in case of replacement of unilateral finite (distally unbounded) defects, Bonville, Jackson and Raihelman supportive- retaining clasps are the most convenient designs.

For additional teeth splinting and construction stabilization the multi-unit clasp is used.

Fig. Five types of Ney system clasps

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Fig. Bonville mesio distal clasp

Fig. Jackson’s clasp

Fig. The supportive-retaining clasp on the retainer tooth of working cast

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Fig. Fixation of arch prosthesis on the upper and lower jaws by Roach clasps (the second type of Ney system)

1. How many types of clasps does Ney system provide?

2. Name and characterize the first type of clasps according to Ney system.

3. Name and characterize the second type of clasps according to Ney system.

4. Name and characterize the third type of clasps according to Ney system.

5. Name and characterize the fourth type of clasps according to Ney system.

6. Name and characterize the fifth type of clasps according to Ney system.

7. What supportive-retaining clasps are used in unilateral distal unlimited defects of dentition?

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Part 5. The anchor fixation system of arch prosthesis

Anchor fixation system is based on the usage of active retaining elements that work on principle of snap closure. The system also includes two fixation elements: patrixes and matrixes.

One of them (more often − patrix) is located on the retainer tooth and the other is the part of the arch construction.

The advantage of anchor fixation units is in their small size that enables to locate the fixation elements in the most uncomfortable parts of the basis.

The disadvantage of anchor fixation units is wearing of the elements due to the constant taking off and putting on the prosthesis. Periodical changing of matrix parts requires special attention.

Crossbars or passive holding elements are constructed on the principle of door latch. In the closed position it does not load retainer tooth. In this case the wearing out of the elements is minimal, which makes this fixation type more rational in relation to long-term effect and reliability.

The disadvantage of crossbar fixation system is in difficulties of laboratory manufacturing, since every step of this system formation requires absolute fabrication precision and fitting of all the elements.

Fig. Arch prosthesis with locking fixation system and activating key

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1. Characterize the anchor fixation type of arch prosthesis.

2. How many elements does the anchor fixation unit consist of?

3. What are the elements of anchor fixation unit?

4. What advantages of anchor fixation units do you know?

5. What disadvantages of anchor fixation units do you know?

6. What is the difference between the anchor fixation unit and crossbar?

7. What is the advantage of crossbars in arch prosthesis?

Fig. Locking connection of arch prosthesis with the fixed bridge prosthesis

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Part 6. Telescopic system of arch prosthesis fixation

In its simplest variant, the telescopic fixation system is the combination of two crowns (internal and external). In this case the internal crown in the form of cap perfectly fits the shape of prepared tooth, and external reproduces its anatomical shape.

Nowadays, there are two types of telescopic systems according to the manufacturing method:

1. stamped;

2. cast.

Stamped telescopic system is easy to manufacture, cast – prevails much in terms of accuracy.

According to covering degree of retainer teeth, telescopic systems can be:

1. closed;

2. opened;

3. partial with parallel walls.

The clinical possibility of preparation of hard tissues thick layer in retainer teeth (based on the thickness of two crowns) is the condition for telescopic system formation.

In comparison with other fixation systems, telescopes provide more rational redistribution of the functional load from arch structure on retainer teeth along their axis.

Fig. Arch prosthesis for the lower jaw with telescopic fixation system

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1. Give the general characteristics of telescopic fixation system.

2. What elements does the telescopic fixation system consist of?

3. What manufacturing methods of telescopic system fixation do you know?

4. How is telescopic fixation system classified according to the covering degree of retainer teeth?

5. What condition is important for planning and manufacturing of telescopic system fixation?

6. What can be considered as advantage of telescopic fixation system in arch prosthesis over the other methods?

7. What is the advantage of cast telescopic system over stamped?

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Part 7. Attachments

Attachments are mechanical devices for fixation, retention and stabilization of removable prostheses.

Attachment fixation system consists of two elements:

1. patrix;

2. matrix.

Attachments belong to direct fixation elements and provide transmission of functional load along the axes of retainer teeth to the periodontal tissues.

The functions of this system are the following:

1. resistance (resistance to prosthesis movement from the prosthetic bed);

2. retention (resistance to prosthesis movement from the prosthetic bed);

3. stabilization (resistance to prosthesis movement in horizontal plane);

4. fixation (resistance to prosthesis movement from retainer tooth);

5. redistribution of masticating pressure.

In comparison with clasp fixation system, attachments have the following advantages:

1. provide better fixation and stabilization;

2. provide better hygiene;

3. have better esthetic qualities;

4. have better mechanical reliability;

5. usage convenience due to small sizes;

6. convenience when combined with rigid splinting systems.

Indications for attachments usage

1. High aesthetic requirements of the patient to prosthetics.

2. Presence of secondary dentition deformities.

Fig. Arch prosthesis for the upper jaw with matrices for attachment fixation system

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3. Atypical position of the survey line of retainer teeth.

4. High clinical crown of retainer teeth.

5. Prosthetics of included dentition defects for providing removable dental bridges.

Questions for individual control 1. What is attachment?

2. How many elements does attachment consist of?

3. What are the functions of attachment?

4. What are the advantages of attachment fixation system over clasp?

5. What is the stabilization function of attachment fixation system?

6. What is the retention function of attachment fixation system?

7. What indications for attachment fixation system of arch prosthesis usage do you know?

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Fig. Bar retaining system on survey crowns with additional attachments in the oral cavity

Part 8. Bar retaining system Bar retaining system consists of two parts:

1. removable;

2. fixed.

Fixed part is the bar with circular, rectangular, elliptical or compound cross- section, connecting crowns or over radicular caps of the retainer teeth.

Removable part − “rider” is fixed in the arch prosthesis construction and ab- solutely fits the bar shape. The removable “rider” provides fixation and stabilization due to the tight fit on the bar.

According to the method of manufacturing the bar retaining construction can be of two types:

1. modeled individually;

2. modeled from standard industrial elements.

Indications for bar retaining of arch prosthesis are:

1. periodontal diseases combined with partial adentia;

2. single symmetrically located retainer teeth are remained on both sides;

3. large included defects of dentition in lateral area.

Special attention in the planning of bar retaining system should be paid for assessment of the clinical crowns height of retainer teeth and overall inter-alveolar space, as well as the degree of alveolar processes atrophy.

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1. What parts does the bar retaining system consist of?

2. What is the fixed part of bar retaining system?

3. What is the removable part of bar retaining system?

4. What shape of cross-section can the non-removable part of bar retaining system have?

5. What are the indications for the bar retaining system use in arch prosthesis?

6. What conditions are necessary for planning of bar retaining system in arch prosthesis?

7. What variants of bar retaining system manufacturing of arch prosthesis do you know?

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Part 9. Planning of arch prosthesis

The necessary condition of arch prosthesis planning is extensive clinical examination.

The stages of the clinical situation analysis 1. Determining the cause of tooth loss.

2. Evaluation of topography and extension of dentition defects.

3. Assessment of height, shape, and location of present natural teeth.

4. Determining of periodontal tissue condition of present natural teeth and assessment of their mobility degree.

5. Determining of dentition occlusive surfaces form.

6. Specification of occlusion type.

7. Analysis of teeth joining at different types of occlusion.

8. Evaluation of the inter-alveolar space and overall inter occlusive space.

Fig. Planning of arch prosthesis on the casts

Fig. Digital panoramic radiography

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9. Evaluation of form and degree of the alveolar processes atrophy.

10. Palpatory determination of the thickness and compressibility of mucous membrane, its pressure sensitivity.

11. Determine the general hygiene level of the oral cavity.

12. Identifying excessive gag reflex.

In addition to clinical examination, X-ray examination is compulsory, the most informative its type − orthopantomography (panoramic radiography).

Moreover, during the conversation with the patient it is necessary to clarify his/her attitude to the removable design usage to consider the wishes regard- ing prosthesis esthetics.

1. What is the prerequisite to start planning of arch prosthesis construction?

2. Is information on the extension and topography of dentition defects important while planning the design?

3. What signs does the doctor evaluate palpatory on the stage of clinical examination?

4. What questions does the doctor discuss with the patient at the stage of arch prosthesis planning?

5. What stages of the clinical situation analysis before planning of arch prosthesis do you know?

6. What method of roentgenologic examination is necessary for arch prosthesis planning?

7. What signs are taken into account while examining the natural teeth?

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Part 10. Classification of partially edentulous jaws

Despite the large number of dentition classifications on the basis of partial defects, the most common in daily practice still remains the classification of Kennedy, 1925. It divides the defects of dentition on the basis of their topography.

Class 1

Bilateral defects at the back of natural teeth (bilateral finite or distally unlimited defect).

Class 2

Unilateral defect at the back of natural teeth (unilateral or distally unlimited defect).

Class 3

Unilateral defect with natural teeth located in front and behind it (included or distally limited defect).

Class 4

Single but bilateral (crossed by the medial line) defect located in front of remained natural teeth (included defect in the anterior dentition area).

Fig. Class diagram of dentition defects by Kennedy

Fig. The frame of arch prosthesis for the upper jaw with 1 class dentition defects by Kennedy

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Fig. The frame of arch prosthesis for the upper jaw with 2 class and 2 subclass dentition defects by Kennedy

Fig. The frame of arch prosthesis for the upper jaw with 4 class dentition defects by Kennedy

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In the case of presence of several dentition defects together, smallest class is assigned, and the number of other defects will represent the subclass number.

1. Who is the author of the well-known classification of dentition defects?

2. What is the principle of dentition defects classification by Kennedy?

3. How many classes does the dentition defects classification by Kennedy comprise?

4. Are the subclasses assigned in the dentition defects classification by Kennedy?

5. What case represents 1 class of dentition defects in Kennedy classification?

Fig. The frame of arch prosthesis for the lower jaw with 1 class and 1 subclass by Kennedy

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Fig. Functional impression of the upper jaw

SECTION II.

CLINICAL AND LABORATORY STAGES OF ARCH PROSTHESIS MANUFACTURING

Part 11. Taking the functional impression

Not excluding the possibility of taking simple two-layer anatomical impressions, it is necessary to emphasize the factors, necessary for taking of functional impressions, namely:

1. functional impression enables to estimate precisely the correlation of arch prosthesis basis with the mucous membrane of the prosthetic bed;

2. functional impression facilitates the improvement of conditions for fixation and stabilization of prosthesis;

3. functional impression enables to redistribute more efficiently the load in different parts of the prosthetic bed;

4. functional impression enables to plan and create the optimal level of the mucous membrane compression, which can respond the level of masticatory pressure.

Adaptation of standard or manufacturing of individual impression spoon is the necessary condition for the functional impression taking. The form of the individual impression spoon is maximally fits the shape of the jaw and adapted to the individual location characteristics, severity and compressibility of the prosthetic bed soft tissues and the oral cavity.

Clinical indications for functional impressions taking are:

1. finite defects of dentition on the background of severe alveolar process atrophy;

2. transverse scar folds of the mucous membrane, having high attachment property;

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3. longitudinal folds of the prosthetic bed mucous membrane, requiring straightening when removing the impression;

4. large included dentition defects in combination with high clinical crowns of the retainer teeth;

5. any atypical form of the alveolar processes and dentition, which does not allow taking the high-quality anatomical impression.

1. What clinical conditions are necessary for functional impression taking?

2. What are the advantages of functional impression in arch prosthesis manufacturing?

3. What peculiarities of the clinical crowns of retainer teeth can be considered as the indication for functional impression taking?

4. What characteristics of the impression spoons for the functional impression taking do you know?

5. What peculiarities of dentition defects topography can be considered as indication for the functional impression taking?

6. Define the features of prosthetic bed mucosa – factors that indicate necessity of functional impression taking.

7. How does the functional impression affect the pressure, which acts on the tissues of prosthetic bed?

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Part 12. Technology of working cast manufacturing

For arch prosthesis manufacturing, it is advisable to produce two identical working casts of die stone.

The first model, the most accurate, is used in planning and modeling of the frame, teeth set-up and final fabrication of arch prosthesis.

The second model is used to make wax occlusion with templates and check the frame that is cast in metal.

Requirements for the models

1. The upper edge of the model cap is parallel to occlusal plane.

2. The side faces are set at right angles to the cap base of the cast.

3. The height of the cap is at least 2 −2,5 cm.

4. The width of the cast enables to locate it freely on the table of the parallelometer and in denture flask.

The cast should accurately imitate:

1. shape of the teeth;

2. gingival line;

3. relief line of the hard palate;

4. shape and relief of the alveolar process;

5. relief peculiarities of prosthetic bed mucosa along the borders of the future prosthesis.

1. How many working casts are advisable to produce for arch prosthesis manufacturing?

2. What working cast should be the most accurate?

3. What kinds of work are performed on the first working cast?

4. What kinds of work are carried out on the second working cast?

5. What are the requirements for the working cast?

6. What exactly should the working cast of the jaw display while arch prosthesis manufacturing?

7. What width should the cap of working cast have?

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Fig. A wax occlusion with the bite-block on the cast of the upper jaw

Part 13. Determining of the central correlation of the jaws According to complexity criterion of determining the central correlation, there are four groups of dentition defects.

The first group

The defects of dentition, which enable to compare the casts in the central occlusion position without wax occlusion with bite-block. These include:

1. intact dentition;

2. dentition with small symmetrical defects to the right and to the left (loss of one or two teeth);

3. dentition with the great number of small defects in different areas, but in case, that at least three pairs of opposing teeth, located on the principle of the triangle are preserved.

The second group

Defects, that preserve the fixed inter-alveolar height due to sufficient number of teeth-antagonists. Despite this, the location of these teeth does not allow to compare dentition in correct mesiodistal position without the wax occlusion with bite-block usage.

The third group

The third group includes the defects that do not have single pair of teeth- antagonists. This is so-called “unfixed” bite, which predetermines the obligatory usage of wax occlusion with bite-block.

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The fourth group

The fourth group is presented by edentulous jaws. Prosthetics with arch constructions can be performed in the presence of dentition defects of the first three groups.

1. How many groups of defects can be determined according to complexity degree of central occlusion specification?

2. What is used to define the central occlusion in case of the second, third and fourth groups of dentition defects?

3. What group of defects includes intact dentition?

4. What group includes the defects with the presence of teeth, but with

“unfixed” height of the bite?

5. What group do the dentition defects belong to, when there is no need to use the wax occlusion with the bite-block?

6. What group of dentition defects do the fully edentulous jaws belong to?

7. What are the criteria for dentition defects distribution in determining the central occlusion?

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Part 14. Parallelometry Parallelometer

Parallelometer is the device used to determine the relative parallelism of two or more surfaces of the teeth and other parts of dentition cast.

The main parts of the parallelometer are the following:

1. platform;

2. vertical stand;

3. horizontal bracket with possibility for tools fixation;

4. jointed table for cast attachment;

5. tools to define or create parallel surfaces, as well as to determine the depth of retention zone (lead, scalpel for wax, marker pins, etc.).

Parallelometry

Parallelometry is one of the most important stages of arch prosthesis planning, since it provides information on:

1. methods of prosthesis introduction;

2. position of the survey line;

3. depth of retention zone.

In combination with the topography assessment and extent of the dentition defects, condition, number and position of the retainer teeth, the presence of antagonists and the character of occlusive correlation, parallelometry enable to plan the optimal design from the point of view:

1. safety of fixation and stabilization of prosthesis;

2. esthetics of design;

3. maximal maintenance of natural teeth;

4. convenience of prosthesis usage.

Route of prosthesis introduction is the way from the initial touch of the supportive and retaining elements of the tooth surfaces to the final fitting of the occlusal inlays and the base prosthesis saddles at their places. The way of prosthesis removal is the reverse way – starting the separation of supportive and retaining elements from the surface of the retainer teeth and till completely design removal from the oral cavity.

Examination of the casts in the parallelometer enables to determine the way of prosthesis introduction:

1. vertical;

2. vertically right;

3. vertically left;

4. vertically posterior;

5. vertically anterior.

Three variants for determination of the prosthesis introduction way in the parallelometer can be used:

1. optional method;

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Fig. Parallelometer with the set of necessary tools

Fig. Work with the cast in the parallelometer

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2. method of cast inclination choice;

3. method of the bisectors determination.

Parallelometry is used to plan the construction and location of the supportive and retaining elements of arch prosthesis.

Fig. The inclination choice of the working cast in the parallelometer

Fig. The drawing of the survey line by the parallelometer lead

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Questions for individual control 1. What is parallelometer?

2. What is parallelometry?

3. What does the route of arch prosthesis introduction mean?

4. What does the route of arch prosthesis removal mean?

5. What are the main structural parts of the parallelometer?

6. What are the possible variants of model location in parallelometer?

7. What methods of parallelometry do you know?

Fig. The measurement of retention zone depth in the parallelometer

Fig. Drawing of retention part in supportive-retaining clasp according to survey line in parallelometer

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Part 15. The principles of clasp designing

The molar clasp construction is planned according to the parallelometry re- sults.

The survey line divides the tooth into two zones:

1. supportive (occlusal);

2. retaining (retentive).

All the elements of the clasp, located above the survey line, would be based upon the crown and transmit masticating pressure in the vertical direction.

The main supportive (occlusal) element of cast molar clasp is occlusal onlay.

The clasp elements, located below the survey line, will perform the retaining function and prevent prosthesis displacement in vertical direction. The main retention function is performed by the part of clasp shoulder (final1/3 shoulder part with thin pointed tip).

The body of the clasp is located in the zone of transition from supportive to retaining, which performs the stabilization function and prevents displacement of the arch prosthesis in horizontal plane.

The supportive-retaining clasps of the arch prosthesis should complete the following requirements:

1. clasp should occupy more than 180° of the retainer tooth circumference, passing from the axial sections, which differ, to those that converge;

2. occlusal inlay is modeled to prevent the movement of the clasp shoulders in direction of the tooth neck under the action of masticatory pressure;

3. reverse element, that will prevent the unacceptable orthodontic effect, should withstand each elastic retaining tip of the clasp.

4. removal pathway of elastic retention clasp tip should not be parallel to the common way of the prosthesis removing;

5. retentive force of the clasp should be minimal but sufficient to resist the average efforts of dislocation;

6. clasps on the retainer teeth, limiting the finite defect are planned, that not provide the direct lever effect;

7. reverse clasp elements should be located in definite finish crown area of the retainer tooth to prevent the risk of horizontal displacement.

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1. What laboratory stage provides the basis for further planning of the molar clasp construction?

2. What two zones does the survey line divide the crown of retainer tooth?

3. What function do the clasp elements located above the survey line perform?

4. What function do the clasp elements located below the survey line perform?

5. What part of the supportive-retaining clasp performs the stabilization function?

6. What part of the molar clasp performs the fixation or retention function?

7. What requirements for the molar clasps of the arch prosthesis do you know?

Fig. Drawing of the molar clasp in accordance with the survey line on the cast

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Part 16. The frame layout and the model duplication Planning for arch prosthesis construction includes the following stages:

1. specification of prosthesis introduction pathway;

2. drawing of survey lines on the retainer teeth;

3. choice of the supportive-retaining elements construction;

4. determination of the location zone of prosthesis arch;

5. choice of plastic basis fixation construction;

6. specification of the plastic basis limits;

7. make drawing of arch prosthesis frame on the model.

To get the accurate imitation of the working refractory cast, it is duplicated in the special flask using elastic silicone or hydrocolloid materials. Removing the working cast, the special refractory porcelain mass is filled to obtained elastic duplicating form.

Thus, the following phases of wax modeling and casting will be performed on the porcelain model, which makes impossible the deformation of the wax frame during its removal from the plaster model and unpredictable shrinkage of the molded frame and after alloy cooling.

For this reason the frame casting on the porcelain refractory model is com- monly used in daily practice and considered to be optimal.

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Fig. Full marking of arch prosthesis frame for the upper jaw on the cast Fig. The layout of the arch prosthesis construction on the cast

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Fig. The blocking of undercut in working cast for further duplication

Fig. The blocking of retention zone in the retainer tooth before duplication

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Fig. The placement of prepared working cast to the flask for duplication

Fig. Duplicating of working cast

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Fig. Complete filling of the flask by duplicating mass

Fig. Obtaining of duplicating form

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Fig. Filling of duplicating form by porcelain refractory mass

Fig. Drying of porcelain refractory cast

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1. How many stages of arch prosthesis planning do you know?

2. What casting method of the metal framework is the most common?

3. Why is casting method on the model more accurate in comparison with casting without model?

4. What is the purpose of working cast duplicating?

5. What materials are used to duplicate the working cast?

6. What is the first planning phase of arch prosthesis construction?

7. What is the final planning phase of arch prosthesis on the model?

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Part 17. Modeling of arch prosthesis frame on porcelain cast At the stage of frame wax modeling on the porcelain model according to the previous drawing it is marked:

1. supportive – retaining clasps;

2. arch for the upper or lower jaws;

3. branching;

4. retention meshes and loops for the plastic basis fixation;

5. occlusal inlays;

6. multi-unit clasps;

7. unguiform protuberances, etc.

After the final modeling the wax frame is compared with the previous picture on the plaster model and prepared for the sprues attachment.

Gating system can be considered the part of wax design.

The purpose of the gating system modeling is formation of channels for the fast and unimpeded ingress of liquid metal into the form that ultimately will ensure the accuracy of the arch prosthesis metal framework. When planning the sprues location, the following factors should be considered:

1. number of sprues;

2. sprues diameter and length;

3. direction of the sprues location;

4. accuracy of sprues fixation to the structural elements;

5. slickness of the sprues surface;

6. sprues availability for safe relieving after casting.

Factors influencing the choice of structural features of the gating system are:

1. length of the frame;

2. massiveness of the frame elements;

3. complexity of the frame elements;

4. location of gating cone;

5. metal for the frame manufacturing.

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Fig. Marked porcelain refractory model of the upper jaw, prepared to wax arch prosthesis modeling

Fig. Modeling of the arch of arch prosthesis frame on the upper jaw according to delineated limits

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Fig. Modeling of retention mesh for plastic basis fixation and the supportive- retaining clasp on the retainer tooth of the porcelain refractory model

Fig. Wax modeling of the arch transition to retention mesh for the plastic basis fixation on the porcelain refractory model

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Fig. The arch prosthesis frame of the upper jaw, made of wax

Fig. Wax modeling of arch prosthesis frame of the lower jaw

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Fig. Modeling of wax gating system on the refractory model

Fig. Modeling of the gating system for the wax frame of the arch prosthesis on the lower jaw

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Fig. Wax composition of arch prosthesis frame with the gating system and sprue cone

Fig. Preparation of wax composition on porcelain refractory model for making casting form

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1. What is the first wax modeling stage of arch prosthesis frame?

2. What stage of wax modeling is performed after modeling of supportive- retaining elements?

3. What factors should be considered before modeling the gating system?

4. What factor of sprues modeling is essential at the stage of final arch prosthesis processing?

5. What sprues parameters are considered when making the gating system?

6. What factors are considered when planning and modeling the gating system?

7. What is the purpose of gating system manufacturing before casting of the arch prosthesis frame?

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Part 18. Formation of the refractory model, preparation and metal pouring

Refractory porcelain model with the wax frame and gating system is attached by putty to the basis of special molding flask, with the walls of the metal cylinder. It is necessary to control the distance uniformity between the wax elements and the flask walls, as it will be important for the procedure of heat processes uniformity. Forming refractory mass that is poured to the molding flask and completely covers the model with the wax composition, requires the following criteria, namely:

1. have the same coefficient of thermal expansion with the refractory mass of the porcelain model;

2. should be resistant to cracking and damaging during firing and pouring metal;

3. withstand without deformation the temperature not lower than 1700°C during the firing.

4. should be gas permeable;

5. should be easily separated out of the metal surface of the frame and sprues.

Chemically there are several groups of forming refractory materials:

1. phosphate;

2. sulfate;

3. silicate.

The previous preheating of the mold is carried out in the special dental furnance with temperature control. This stage is aimed to:

1. full release of the form from the wax;

2. preliminary expansion of the porcelain model to compensate segregation during cooling;

3. perfect and fast pouring of liquid metal in the heated channels, which provides the high quality of even the smallest elements of the frame.

Metal casting can be done using:

1. oxyacetylene torch;

2. apparatus, that provides the effect of voltaic arc;

3. induction furnace, providing electrical current of high frequency.

Casting methods differ depending on the alloy and equipment.

Currently, three ways of metal casting are used in dental practice:

1. method of centrifugal force;

2. method of high pressure of hot steam;

3. method of vacuum generation.

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1. What device is used for immersing of the model with the wax composition to refractory mass?

2. What is the correlation of thermal expansion of the porcelain refractory model and refractory forming mass?

3. What temperature should refractory forming mass withstand without damaging and cracking?

4. Where is the preceding preheating of the mold carried out?

5. What is the purpose of the preceding mold preheating?

6. What kinds of refractory materials according to the chemical composition do you know?

7. What methods of metal pouring into refractory mould do you know?

Fig. Formation of the required shape for the refractory mold before metal pouring

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Part 19. Processing of arch prosthesis frame

Primary processing of the metal frame after sprues cutting is carried out by carborundum heads. The surface is cleaned up from possible overflow. The inner surface of the clasp shoulder is beyond the contact while the high-quality casting is provided, because any mechanical treatment can worsen the tight fitting of the clasp to the retainer tooth surface.

Final assessment of the metal frame quality of arch prosthesis is carried out in clinical setting, trying and fitting it in the oral cavity.

Evaluation criteria

1. The metal frame should not have overflows, pores, cracks, cavities and sharp angle.

2. The shape of the frame should coincide the previous drawing.

3. The frame should relatively easy fit the retainer teeth and tissues of the prosthetic bed in accordance with the chosen introduction way.

4. All the frame elements should have specified thickness and smooth passing modulations from one to another.

5. Arch should retreat from the mucous membrane of the prosthetic bed.

6. The clasps or other fixation elements must exactly fit the planned areas of the retainer teeth.

7. The framework elements, primarily occlusal inlays should not prevent the teeth joining.

The presence of sufficient space between the metal frame elements and the teeth of the opposite jaw is obligatory for further location of artificial teeth on the plastic basis.

The causes of incorrect frame reconstruction in the metal and its balancing can be:

1. inaccurate impression;

2. deformation or impression shrinkage before or during casting of the working cast;

3. damage of the working cast before the wax frame modeling;

4. shrinkage of the frame after casting;

5. deformation of the frame after mechanic processing.

After try-in the framework in the oral cavity, the final polishing is c a r r i e d out.

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Fig. The release of the metal frame from the forming mass

Fig. Cleaning of the cast frame from the fragments of forming masses

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Fig. Sandblasting of arch prosthesis frame

Fig. Tools for mechanical processing of arch prosthesis frame

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Fig. Polishing of arch prosthesis frame

Fig. Grinding of the arch prosthesis frame in the clasp area

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Fig. Polishing of arch prosthesis frame

Fig. Fitting of arch prosthesis frame on the model

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1. What can be considered as the first stage of metal frame processing of the arch prosthesis after casting and cleaning from the forming masses?

2. What surface of the supportive-retaining elements is beyond contact under condition of quality casting?

3. Where is the final quality control of the arch prosthesis frame manufacturing carried out?

4. What common quality criteria of the metal frame do you know?

5. Identify the clinical stage faults which can lead to balancing of the frame on retainer teeth.

6. What laboratory faults can cause the frame balancing on the retainer teeth?

Fig. The frame arch prosthesis of the lower jaw on the model

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Part 20. Setting of artificial teeth and basis modeling

Primarily working cast is compressed by preheated baseplate wax, which is cut along the outlined limits.

Warmed frame is put on the model. The position of occlusal inlays is the indicator of correct and complete fitting.

Artificial teeth matched by size, color and shape are set on the wax basis in close contact with the teeth-antagonists, imitating the individual form of dental arch.

At the final stage the definitive modeling of the arch prosthesis basis along its limits is carried out, specify the individual characteristics of artificial gums (dentogingival rolls and interdental papillae).

After checking the artificial teeth setting and modeled wax gums in the oral cavity, prosthesis is mounted and wax is changed for plastic.

Requirements for artificial teeth setting and wax basis modeling are the following:

1. artificial teeth should not be located deep, but rather can have the open necks to simulate the age-related gum recession;

2. special attention should be paid to modeling of the artificial interdental papillae, that improves the aesthetic view of the arch prosthesis;

3. edges of the plastic base should be rounded and comply with situation obtained when taking the functional impression.

Fig. Arch prosthesis with artificial teeth, fitted on wax basis

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Fig. Arch prosthesis for the upper jaw on the model

Fig. Arch prostheses of the upper and lower jaws

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1. What is the starting point of artificial teeth setting?

2. What parameters are important for artificial teeth selection?

3. What are the indicators for artificial teeth setting?

4. What stage of basis modeling can be considered as final after complete artificial teeth setting?

5. What are the requirements for the artificial teeth setting?

6. What are the requirements for the arch prosthesis basis?

7. What laboratory stage is the plastic basis of arch prosthesis manufactured in?

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Part 21. Setting of arch prosthesis

Completely manufactured arch prosthesis is evaluated in two stages: first on the working cast, then in the oral cavity. Manufactured arch prosthesis is evaluated according to the following criteria:

1. polishing quality of metal and plastic surfaces;

2. rounding of the plastic basis edges;

3. quality of the plastics polymerization;

4. way of prosthesis introduction and removal;

5. accuracy of the prosthesis fitting on the retainer teeth and prosthetic bed tissues.

Additionally, after prosthesis setting in the oral cavity the dentist evaluates:

1. absence of prosthesis balancing;

2. fixation surety;

3. position of arch and supportive-retaining elements relative to the mucous membrane and abutment teeth;

4. accuracy of the occlusive correlations of prosthesis with teeth-antagonists, both in central occlusion position and other articulation positions;

5. re-checking of the sizes and borders of the plastic basis;

6. integrity of the basis and mucous membrane.

Before the final prosthesis application, it is definitively polished and grinded in dental laboratory.

Fig. Arch prosthesis on the lower jaw with the clasp fixation system in the oral cavity

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1. What two phases is completely manufactured arch prosthesis testing conventionally divided into?

2. What should be considered primarily while checking the quality of completely manufactured arch prosthesis?

3. What parameters of the arch prosthesis basis are evaluated while checking?

4. What elements of arch prosthesis are evaluated according to fitting accuracy to the retainer teeth when setting design in the oral cavity?

5. What checking stage includes reliability assessment of the arch prosthesis fixation?

6. What laboratory work may precede the final delivery of arch prosthesis?

7. In what dentition positions are occlusal correlations of teeth-antagonists checked while testing the completed arch prosthesis?

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Part 22. Errors of orthopedic treatment, associated with manufacturing or using of arch prostheses

The doctor’s errors at the stage of arch prosthesis planning:

1. incorrect choice of retainer teeth;

2. wrong choice of prosthesis introduction method and location of the survey line;

3. incorrect choice of the supportive-retaining elements construction;

4. incorrect choice of the arch location;

5. incorrect choice of the plastic basis fixation place;

6. wrong choice of location and number of occlusal inlays.

Laboratory errors at the manufacturing stages of arch prosthesis:

1. incorrect location of the supportive-retaining elements and as consequence

− the inability of prosthesis setting or improper fixation on the abutment teeth;

2. inadequate blocking of working cast undercut and getting of the frame parts to retention areas, which leads to impossibility of accurate and complete prosthesis setting in the oral cavity;

3. technology abnormalities in preparation for casting and process of metal molding, which leads to uncontrolled metal shrinkage and deformation of the shape and size of metal frame elements;

4. technology disorders in changing wax for plastic and polymerization conditions, which leads to mismatching of the basis to the planned limits or injury of the prosthetic bed mucous membrane;

5. disregarding of rules in mechanical processing of arch prosthesis, which leads to excessive thinning or deformation of metal framework or mismatching of plastic base to the prosthetic bed relief.

1. What two groups can the errors of arch prosthesis manufacturing be relatively divided into?

2. What group includes the error at the stage of impression?

3. What laboratory errors of arch prosthesis manufacturing do you know?

4. What clinical errors of arch prosthesis manufacturing do you know?

5. What group includes the error at the stage of prosthesis choice?

6. What group includes the error at the stage of plastic polymerization?

7. What group includes the error at the stage of mechanical processing of arch prosthesis?

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SECTION III.

MATERIALS FOR THE ARCH PROSTHESIS MANUFACTURING

Currently the arch prosthetics is considered to be one of the most effective ways in prosthetic rehabilitation of partial adentia in various clinical situations.

One of the key factors for the qualitative breakthrough in manufacturing technology of arch prostheses is the widespread implementation of new modern and basic materials to clinical practice and prosthetic equipment.

Auxiliary materials

− materials for impressions;

− materials for cast duplication;

− forming materials;

− waxes;

− abrasive materials.

The main (structural) materials

− metal alloy;

− base polymers;

− artificial teeth;

− standard fixation elements.

Part 23. Impression materials

Requirements for impression materials used in arch prosthesis manufacturing are the following:

1. ultra-high precision of tissue prosthetic bed imitation;

2. minimum possible degree of linear and volumetric shrinkage;

3. possibility of taking the several identical in size models from one impression;

4. cosideration of pronouncement and compliance peculiarities of the prosthetic bed soft tissues. Impression materials that best meet the above men- tioned requirements include representatives of such groups:

1. alginate;

2. silicone;

3. polyester.

Positive properties of alginate impression materials:

1) easy to apply in the clinical setting without the use of additional devices and auxiliaries;

2) high elasticity, that allows to take impression easily in the presence of excessive undercuts and retention points (teeth inclination, pear-shaped alveolar process, presence of fixed bridge structures);

3) high fluidity of alginate materials, which allows to obtain high-precision impressions under minimal pressure (decompression impressions). This is es-

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pecially important in the presence of wide movable areas of the mucous membrane of prosthetic bed.

Negative properties of alginate impression materials are:

1) insufficient mechanical durability;

2) absence of adhesion to the spoon material;

3) rapid desiccation, as in 15-40 min these materials change the volume and shrink, which requires the fastest possible casting of plaster model.

Alginate impression material “Ipen” (Czech Republic) is prepared by knead- ing of green finely divided powder (10 g) with water at room temperature (20 ml) for 30-45 s. The curing time is 2,5 min.

Materials “Kromopan” and “Kromopan-2000” (Italy) with color phases in- dexation (violet, pink, white) are mixed with water by the ratio 9 g. of powder in 20 ml of liquid. According to instructions, the significant changes do not occur in material during 48 hours that is provided by the introduction of integrated alginate stabilizer to the mass.

Such materials as “Ortoprint” − with antiemetic supplement, “Hydro- resin” – with resin effect as well as “Dupalflex”, “Tricoloralgin”, “Palgaflex”,

“Alginoplast”, “Xanthalgin Select” (Germany) are widely used in dental mar- ket. Material “Propalgin” (France) has the long curing time (approximately 3 min. 45 s) which enables to use it for the functional impressions taking.

“JC Aroma Fine” is the alginate impression material (JC Corporation). Other materials: “Geltrate”, “Geltrate Plus”, “Kos Alginate” are also widely used. Ma- terial “Geltrate” is produced in three consistencies: normal, dense (used in high arched palate and orthodontics) and fast setting (for impression taking in gag reflex).

Silicone impression materials

The basis of these materials is linear polymer (dimethylsiloxane) with the active hydroxyl finite groups. Under the catalytic agent action (3-5% stan- num- titanorganic substance) linear polymer is crossed by condensation, cre- ating “cross-linked” polymer. To accelerate the curing process, initiators – the substances, which force the catalyst action may be used. The polymer curing process and elasticity degree can be regulated by the amount of linking agent, catalyst and filling compound.

There are two types of such materials: C-silicone and A-silicone, which differ in the principle of curing reaction: the first type is the polycondensation with organostannum catalysts adding; the second type is the polyaddition with the platinum catalysts adding. It is generally accepted, that the higher rate (minimal shrinkage, greater impression precision) has the second type of impression materials.

Some manufacturing companies produce silicone impression mass with the plasticizer adding, which retards the polymerization and disperses paste. The

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impression in this case becomes very plastic. Such mass can be used to correct the impression edges, if they have some defects. To obtain the silicone impression, the perforated moulding spoon is used.

The disadvantages of silicone materials are their chemical instability (the possibility of self-polymerization or chemical reaction with other materials) and significantly higher cost.

Materials “Sielast” series (69; 03; 05; 21) are composed of paste and liquid catalyst. In addition to the main component, the paste of material contains fillers, dyes, substances that correct the smell and taste. The plasticization (giving elastic properties) is regulated by the volume of paraffin oil.

The sets of silicone multipurpose pastes are widely known. They are

“Spidex”,”Coltex/Coltoflex”(Switzerland),”Dentaflex”(Czech Republic),”Khneton/

Sitran and” Cafo-Tevesil” (Germany).

On the Ukrainian market the following silicone impression materials are widely used: “Optosil P”, “Xantopren”, “DL-Knet”, “Panasil”, “Formacil P”, “Alfasil”,

“Gammasil”, “Deguflex” (Italy), etc.

Fig. The representative of the alginate group impression materials “Kromopan”

(Italy)

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Polyester mass is the promising group of high-precision impression mate- rials. These materials contain different polyesters, plasticizers, inert fillers. The characteristic properties of this group of materials are very low linear material shrinkage and high hydrophilicity.

Materials of new generation, the so-called “soft” polyesters, are comfortable for the patient, convenient to use, have controlled working hours and the optimal flow characteristic, provide the accurate imitation of the prosthetic bed.

Materials of this group do not provide the possibility of taking the two-layer impression, therefore, they are used primarily in prosthetics on implants. The representatives of polyesters group are: “Impregum™”, “Penta™ H”, “Garant™”,

“L Duosoft™”.

Work features with these materials involve ergonomics, ease of mixing and dosing due to the special equipment and additional auxiliaries.

Fig. The representative of C-silicone group of impression materials “Speedex”

(Switzerland)

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Fig. The representative of the polyether group of impression materials “Impregum”

(USA) Questions for individual control

1. What are the requirements for impression materials?

2. What manufacturing peculiarities of arch prosthesis should be considered when choosing impression material?

3. What group representatives of impression materials are optimal for the manufacturing of arch prosthesis?

4. What are the advantages and disadvantages of impression materials in alginate group?

5. What are the advantages and disadvantages of the impression materials in silicone group?

6. What are the advantages and disadvantages of impression materials in polyether group?

Basic principles of arch prosthetics

D.M. Korol, M. D. Korol, D.D. Kindii, L.S Korobeinikov, O. D. Odzhubeiskaia, R.V. Kozak, T.P. Maliuchenko,

V.D. Kindii, A.D.Dorubets