How to Select Dental Articulators for Fabrication of Complete Denture

1. If occlusal contacts are to be perfected in centric occlusion only, a simple sturdy hinge type articulator without provision for lateral or protrusive movements can be selected.
2. This type of instrument as been called one dimensional because only one interocclusal record is necessary for its adjustment and use.
3. If denture teeth are to have a cross arch and cross tooth balanced occlusion, the minimum requirement is a semi adjustable articulator.
4. This may be an instrument with individually adjustable condylar guidance’s in both horizontal and vertical plane. Example: hanau university series, whip mix articulator, dentatus articulator.
5. If more control of occlusion is desired a completely adjustable three dimensional articulator is used.
6. It requires a centric relation record , some means for controlling the height and inclinations of cusps.
7. The means for their adjustment may be interocclusal records or three dimensional graphic tracing made by kinematic face bow.

Uses of Dental Articulators:

1. To hold opposing casts in a predetermined fixed relationship.
2. To open and close
3. To produce border intraborder diagnostic sliding motions
4. To diagnose dental occlusal conditions in both natural and artificial dentition’s
5. To plan dental procedures that involve positions ,contours and relationships of both natural and artificial teeth as they relate to each other.
6. To aid fabrication of dental restoration and the lost dental parts.
7. To correct and modify completed dental restorations.
8. Helpful in teaching and studying of occlusion and mandibular movements.

Ideal Requirements of Dental Articulators:

1. It should hold casts in correct horizontal and vertical relationships.
2. It should provide a positive anterior vertical stop (incisal pin).
3. It should accept a face bow transfer record.
4. It should open and close in a hinge movement.
5. It should allow protrusive and lateral motion.
6. The moving parts should move freely and be accurately machined.
7. The non-moving parts should be a rigid construction.

Additional Requirements of Dental Articulators:

1. Adjustable horizontal and lateral condylar guide elements.
2. The condylar elements as a part of lower frame and condylar guides as a part of upper frame.
3. A mechanism to accept a third reference point from a face bow transfer record.
4. A terminal hinge motion locking device.
5. Removable mounting plates that can be repositioned accurately.
6. An adjustable incisal guide table.
7. Adjustable intercondylar width of condylar elements, when graphic tracing to be used to set and / or select condylar guidance.

Advantages of Dental Articulators:

1. Properly mounted casts allow the operator to visualize the patients occlusion especially from lingual view.
2. Patient co-operation is not a factor when using an articulator once the appropriate interocclusal records are obtained from patient.
3. The refinement of complete denture occlusion in mouth is extremely difficult because of shifting denture bases and resiliency of supporting tissues .This difficulty is eliminated when articulators are used.
4. Reduced chair time ,patients appointment time.
5. The patients saliva , tongue and cheeks are not factors when using an articulator.

Limitations of Dental Articulators:

1. An articulator may be made of metal or plastic. Metal articulators show errors in tooling (manufacture) or errors resulting from metal fatigue.
2. The articulator may not exactly simulate intraborder and functional movements of mandible
3. Errors in jaw relation procedures are reproduced as errors in denture occlusion. Articulators do not have any provision to indicate or correct these errors.

It is called Reversible Impression material because of its property of reversing their physical state, which in reusing the impression material for multiple number of impressions.

Agar Hydrocolloid was the first successful elastic impression material to be used in dentistry.

History of Agar Impression material:

It is was first discovered by Alphous Poller of Vienna in 1925 when he was trying to develop a material that could be sterilized and applied without pressure to the exposed surface of the dura matter for perfectly recording the convulsion and the bony margins of the skull.

Which was termed as ‘Negacol’ which was termed as “Dentacol” when introduced into dentistry.

Origin Of Agar Impression material:

• An Organic Hydrophillic Colloid (Polysaccharide) extracted from certain types of Seaweed
• It is a Sulphuric ester of a linear polymer of Galactose

Available as:

• Gel in collapsible tube (Used with a Tray)
• Multiple Cylinders in a glass jar (Syringe material)
• In bulk containers (for duplication)

Composition:

• Agar: 13-17%
• Borates: 0.2-0.5%
• Potassium Sulphate: 1-2%
• Wax: 05-1%
• Thixotrophic Materials: 0.3-0.5%
• Alkylbenzoates: 0.1%
• Coloring and Flavoring agents: Traces
• Water: Balance (Around 84%)

Functions of Each ingredient:

• Agar: Basic Constituent 13-17% used for tray material and 6-8%is used for Syringe material
• Borates: Improves Strength of the gel, (Also retards the setting of plaster or stone cast when poured into the finished impression – a disadvantage)
• Potassium Sulphate: It counters the retarding effect of borates, thereby ensures proper setting of the cast or die.
• Wax: It acts a Filler. Fillers affect the strength, viscosity and rigidity of the gel. Other Examples of fillers – Zinc Oxide, Diatomaceous Earth, Silica, Clay, Rubber etc..
• Thixotrpoic materials: It acts as plasticizer. Examples are: Glycerine and Thymol. Thymol acts as bactericide also.
• Alkylbenzoates: It acts as a Preservative
• Water: It acts as a Dispersion medium
• Coloring and Flavoring agents: Used for patient comfort and acceptance.

Materials Required for Manipulation of Agar :

• Agar Hydrocolloid Conditioner
• HydrocolloidMaterial
• Water cooled rim lock trays
• Hydrocolloid Syringe Material
• Duplicating Mould
• Rubber Hose

Materials used for Agar Impression

How does Agar Hydrocolloid Conditioner work:

It has 3 sections:

• Boiling Section (or) Liquefaction section
• Storage Section
• Tempering Section

Agar Hydrocolloid Conditioner

Boiling Section (or) Liquefaction section:

• Agar is placed in Boiling water at 100 degrees Centigrade for 10 Mins
• The Solution should be Homogenous and free of Lumps
• Everytime the material is reliquefied, three minutes should be added for the heating. This is because it is more difficult to break down the agar brush heap structures  after a previous use.

Storage section:

• 65-68 Degrees Centigrade is ideal temperature for Storage of Agar in Sol condition.
• It can be stored in the sol condition till required for impression taking.

Tempering Section:

• 46 degrees Centigrade for about 2 minutes with the material loaded in the tray.
• This is done to reduce the temperature so that it can be tolerated be the sensitive oral tissue
• It also makes the material viscous suitable for impression taking

 How to Use Water Cooled Rim Lock Impression Tray:

• Rim Lock Impression Trays have a feature of Water Circulation through the Tray.
• The Rim Lock is a Beeding on the inside edge of the tray which helps to retain the material (as Agar does not adhere to the tray)
• It has an Inlet and Outlet for connecting the water tubes
• The Tray should allow a space of 3mm occlusally and laterally and extend distally to cover all teeth

Water Cooled Rim Lock Impression Tray - Agar

How to take an Agar Impression:

Steps to Take the Impression:

1. Remove the Tray containing the Agar from the Tempering Section of the Hydrocolloid Conditioner.
2. The Outer surface of the Agar sol is scraped off
3. The water hoses are connected and the tray is positioned in the mouth by the dentist
4. Water is circulated at 18 to 21 degrees Centigrade through the tray until gelation occurs.
5. Rapid Cooling: (e.g ice cold water) is not recommended as it can induce distortion
6. To guide the tray into position, 3 stops of compound are prepared on non-involved teeth
7. A Post dam is constructed with compound to prevent distal flow of the impression material
8. In a deep palate case, compound is placed on the palatal aspect of the tray in order to provide a uniform thickness of the Hydrocolloid
9. The mandibular tray is prepared by placing compound on the distal aspect to limit the impression material
10. Black Tray compound is used as it is not affected in the tempering bath

Steps to Remove the Impression:

1. Wait for the Agar to turn into a Gel
2. Break the Peripheral seal around the Impression
3. Remove the Impression rapidly from the mouth with a Single stroke or snap (This is done to avoid distortion of the impression)
4. The Impression is Rinsed thoroughly with water ans the excess water is removed by shaking the impression

How to Store Agar Impression:

1. The Cast should be poured immediately
2. Storage of Agar Impression material should be avoided at any cost, as there is no storage medium available
3. Storage in Air results in 100% relative humidity which results in Shrinkage as a result of continued formation of the agar network agglomeration
4. If Storage is unavoidable, it should be limited to one hour in 100% relative humidity

How to Pour and Separate the Cast:

1. Use Gypsum products for pouring the Cast
2. Mix the Gypsum product and Pour it into the impression
3. When the Gypsum products have set, the agar impression must be removed promptly since the impression will Dehydrate and become Stiff and difficult to remove
4. Be careful while removing the Cast as the weaker portions may fracture
5. Prolonged contact will result in a rougher surface on the model, so  make sure the cast is removed immediately after the setting time of the gypsum product is finished

Uses Of Agar:

1. Used as a Cast Duplicating material (during fabrication of the cast metal removable partial denture)
2. For Full mouth impressions without deep undercuts
3. Used for Crown and and Bridge impressions before Elastomers were Discovered
4. Used as Tissue Conditioners

Materials Used To Disinfect Agar Hydrocolloid Impression:

1. Iodophor
2. Bleach
3. Glutaraldehyde

Advantages Of Agar Hydrocolloid Impression Material:

1. Helps in preparing Dies Accurately
2. It has Good Elastic Properties and Reproduces most undercut areas correctly
3. It has Good Recovery from Distortion
4. It is not Hydrophobic, hence gives good model surface
5. It is Palatable ans well tolerated by the patient
6. It is cheap when compared to synthetic elastic materials
7. The Main Advantage is: Agar can be Reused when used as a Duplicating Material

Note: Reuse is not recommended when used as an impression material

Disadvantages Of Agar Hydrocolloid Impression Material

1. Does not Flow as good as the newly developed materials
2. It cannot be Electroplated
3. Due to the heat it may be painful to the patient during Insertion or Gelation
4. Tears relatively easily
5. Greater Gingival retraction is required for providing adequate thickness of the material
6. Only one model can be poured
7. Expensive Equipment is required
8. A Plaster Hardener should be used to get a soft surface on Gypsum Cast
9. Contamination is very prevalent with this material due to Reuse and the lack of Sterilization technique

In Diagnosis and treatment planning of Fixed Partial denture fabrication the most important part is the classification of the edentulous ridges of the patient which helps us in determining the type of FPD we are going to use in the patient.

Class I: It is a ridge with loss of faciolingual width, with normal apicocoraonal height. It constitutes 32.4% of the edentulous ridges.

Class II: It is the ridge with loss of ridge height with normal ridge width.

Class III: It is the ridge with loss of both height and width.

Class IV: It indicates Normal Ridges.

Definition: The identification of the nature of an illness or other problem by examination of the symptoms.

Diagnosis is the evaluation of the existing condition, more specifically. It can also be described as

• The act or process of deciding the nature of a diseased condition by examination.
• A careful investigation of the facts to determine the nature of the Disease
• The determination of the nature, location and causes of the Disease.

Diagnosis for the prosthodontic care requires the use of general diagnostic skills and accumulation of knowledge from other aspects of dentistry and its supporting sciences.

Diagnosis in complete denture is a continuing process and is not accomplished in a short time. The dentist should be the first to recognize the problem and be ready to change the treatment plan to meet the new findings. These findings will be influenced mainly by:

• Gait
• Age
• Sex
• Complexion and Personality
• Cosmetic Index
• Patient’s mental attitude.
• Patient’s systemic status.
• Past dental history.
• Local oral conditions

Age:

The Decade which the patient belongs to is important to predicts the outcome of the Treatment. For example a patient in the Sixth decade of his life will have poor prognosis compared to a patient in the Fourth decade of life.

Sex:

This determines the main purpose of the dentures or for what they might be used, Males usually prefer comfort and function as compared to Females who prefer aesthetics over everything.

Complexion and Personality:

The Complexion of the patient determines the shade of the Teeth to be used and the personality of the patient determines the size and shape of the teeth.

Mental attitude (psychological factor)

The success of dental prosthesis is related to many factors, including functional, biological, technical, esthetic and psychological factors. Psychological factors include the preparedness of the patients and their mental attitudes towards dentures, their relationship with the dentist and their ability to learn how to use the dentures. Prosthodontists must fully understand their patients because such understanding predisposes the patient to accept the kind of the treatment they need.

De Van said “meet the mind of the patient before meeting the mouth of the patient”.

In the discussion with the patient, the dentist must seek an understanding of the patient’s health, particularly their attitude toward receiving new dentures.

House classified the patients into 4 categories:

1. Philosophical patients.
2. Exacting patients.
3. Indifferent patients.
4. Hysterical patients.

Philosophical patients

• These patients are rational, sensible, and calm and composed in a different situations.
• Their motivation is generalized as they desire dentures for the maintenance of health and appearance and feel that having teeth replaced is a normal acceptable process.
• These patients usually overcome conflicts and organize their time and habits; they eliminate frustrations and learn to adjust rapidly.
• The best mental attitude for denture acceptance is the philosophical type.

Exacting patients

• Exacting Patients have all the qualities of the Philosophical patients.
• But these patients have a bad quality of expecting each and every step of the procedure to be explained in detail
• And this requires extra hours spent prior to the treatment in patient education until an understanding is reached.

Indifferent patients

• These patients are apathic, uninterested and lack motivation.
• The do not care to their self image; they manage to survive without dentures and pay no attention to the instructions.
• They do not cooperate and mostly blame the dentists for their poor dental health.
• In most of them, questionable or unfavorable prognosis may be expected.
• For such patients, educational program in dental conditions and treatments is recommended before denture construction.

Hysterical patients

• These patients are excitable, apprehensive, emotionally unstable and hypertensive.
• They are neglectful of their oral health and unwilling to try to adapt to wear dentures.
• Additional professional help is required prior to and during treatment.
• Although these patients may try to wear the denture, they fail to use it as they expect it to look and function like the nature teeth.
• But these are the patients who if satisfied will be the best patients who will popularize your abilities to a lot of people

Social information

• Social Information is the establishment of patients identity.
• Personal information as the name, address, telephone number, work and hours of work might help the dentist in the primary estimation of the dental health and prognosis of the Denture.
• Social setting can help to understand the patient’s expectation and the dental status developed.
• Social information may clarify some habits, specifically those might contribute of their present conditions and those might help ensure success or failure for the treatment.

Systemic-medical status

• No prosthodontic procedure should be planned until the systemic status of the patient is evaluated.
• Many of the systemic diseases have local manifestations with no systemic symptoms and others have both local and systemic reactions.
• Some systemic diseases have a direct relation to the denture success even though, no local manifestations are apparent.

Debilitating diseases

These patients requires extra instructions in the oral hygiene and tissue rest, also frequent recall appointments should be arranged because the supporting bone may be affected to keep the denture bases adapted and the occlusion corrected. Debilitating diseases include, diabetes, tuberculosis, blood diseases… etc.

Cardiovascular diseases

Patients with cardiovascular diseases may require consultation with cardiologist as some denture procedures may be contraindicated.

Joint diseases

• Joint involvement, particularly osteoarthritis, presents different problems.
• If the disease involves the TMJ, alteration in the treatment plan may be essential.
• In extreme conditions, special impression tray and technique are often necessary because of the limited access from reduced ability to open the jaws.
• Furthermore, jaw relation records are difficult and occlusion correction must be made often because of the subsequent changes in the joints.