Articulators in Prosthodontics

An articulator is a mechanical device that simulates the temporomandibular joint (TMJ) and jaw movements, allowing for the attachment of maxillary and mandibular casts. This simulation is essential for diagnosing, planning, and fabricating dental prostheses, as it helps in understanding the relationship between the upper and lower jaws during functional movements.

Classification of Articulators

Class I: Simple Articulators

• Description: These are simple holding instruments that can accept a static registration of the dental casts.
• Characteristics:
  • Limited to hinge movements.
  • Do not allow for any dynamic or eccentric movements.
• Examples:
  • Slab Articulator: A basic device that holds casts in a fixed position.
  • Hinge Joint: Mimics the hinge action of the jaw.
  • Barndor: A simple articulator with limited functionality.
  • Gysi Semplex: A basic articulator for static registrations.

Class II: Semi-Adjustable Articulators

• Description: These instruments permit horizontal and vertical motion but do not orient the motion of the TMJ via face bow transfer.
• Subcategories:
  • IIA: Eccentric motion is permitted based on average or arbitrary values.
    • Examples: Mean Value Articulator, Simplex.
  • IIB: Limited eccentric motion is possible based on theories of arbitrary motion.
    • Examples: Monson's Articulator, Hall's Articulator.
  • IIC: Limited eccentric motion is possible based on engraved records obtained from the patient.
    • Example: House Articulator.

Class III: Fully Adjustable Articulators

• Description: These articulators permit horizontal and vertical positions and accept face bow transfer and protrusive registrations.
• Subcategories:
  • IIIA: Accept a static protrusive registration and use equivalents for other types of motion.
    • Examples: Hanau Mate, Dentatus, Arcon.
  • IIIB: Accept static lateral registration in addition to protrusive and face bow transfer.
    • Examples: Ney, Teledyne, Hanau Universit series, Trubyte, Kinescope.

Class IV: Fully Adjustable Articulators with Dynamic Registration

• Description: These articulators accept 3D dynamic registrations and utilize a face bow transfer.
• Subcategories:
  • IVA: The condylar path registered cannot be modified.
    • Examples: TMJ Articulator, Stereograph.
  • IVB: They allow customization of the condylar path.
    • Examples: Stuart Instrument, Gnathoscope, Pantograph, Pantronic.

Key Points

• Face Bow Transfer: Class I and Class II articulators do not accept face bow transfers, which are essential for accurately positioning the maxillary cast relative to the TMJ.
• Dynamic vs. Static Registrations: Class III and IV articulators allow for more complex movements and registrations, which are crucial for creating functional and esthetic dental prostheses.

Applegate's Classification is a system used to categorize edentulous (toothless) arches in preparation for denture construction. The classification is based on the amount and quality of the remaining alveolar ridge, the relationship of the ridge to the residual ridges, and the presence of undercuts. The system is primarily used in the context of complete denture prosthodontics to determine the best approach for achieving retention, stability, and support for the dentures.

Applegate's Classification for edentulous arches:

1. Class I: The alveolar ridge has a favorable arch form and sufficient height and width to provide adequate support for a complete denture without the need for extensive modifications. This is the ideal scenario for denture construction.

2. Class II: The alveolar ridge has a favorable arch form but lacks the necessary height or width to provide adequate support. This may require the use of denture modifications such as flanges to enhance retention and support.

3. Class III: The ridge lacks both height and width, and there may be undercuts or excessive resorption. In this case, additional procedures such as ridge augmentation or the use of implants might be necessary to improve the foundation for the denture.

4. Class IV: The ridge has an unfavorable arch form, often with significant resorption, and may require extensive surgical procedures or adjuncts like implants to achieve a functional and stable denture.

5. Class V: This is the most severe classification where the patient has no residual alveolar ridge, possibly due to severe resorption, trauma, or surgical removal. In such cases, the creation of a functional and stable denture may be highly challenging and might necessitate advanced surgical procedures and/or the use of alternative prosthetic options like over-dentures with implant support.

It's important to note that this classification is a guide, and individual patient cases may present with a combination of features from different classes or may require customized treatment plans based on unique anatomical and functional requirements.

Kennedy's Classification is a system used in dentistry to categorize the edentulous spaces (areas without teeth) in the mouth of a patient who is fully or partially edentulous. This classification system helps in planning the treatment, designing the dentures, and predicting the outcomes of denture therapy. It was developed by Dr. Edward Kennedy in 1925 and is widely used by dental professionals.

The classification is based on the relationship between the remaining teeth, the residual alveolar ridge, and the movable tissues of the oral cavity. It is particularly useful for patients who are wearing or will be wearing complete or partial dentures.

There are four main classes of Kennedy's Classification:

1. Class I: In this class, the patient has a bilateral edentulous area with no remaining teeth on either side of the arch. This means that the patient has a full denture on the upper and lower jaws with no natural tooth support.

2. Class II: The patient has a unilateral edentulous area with natural teeth remaining only on one side of the arch. This could be either the upper or lower jaw. The edentulous side has a complete denture that is supported by the teeth on the opposite side and the buccal (cheek) and lingual (tongue) tissues.

3. Class III: There is a unilateral edentulous area with natural teeth remaining on both sides of the arch, but the edentulous area does not include the anterior (front) teeth. This means the patient has a partial denture on one side of the arch, with the rest of the teeth acting as support for the denture.

4. Class IV: The patient has a unilateral edentulous area with natural teeth remaining only on the anterior region of the edentulous side. The posterior (back) section of the same side is missing, and there may or may not be teeth on the opposite side. This situation requires careful consideration for the design of the partial denture to ensure stability and retention.

Each class is further divided into subcategories (A, B, and C) to account for variations in the amount of remaining bone support and the presence or absence of undercuts, which are areas where the bone curves inward and can affect the stability of the denture.

- Class I (A, B, C): Variations in the amount of bone support and presence of undercuts in the fully edentulous arches.
- Class II (A, B, C): Variations in the amount of bone support and presence of undercuts in the edentulous area with natural teeth on the opposite side.
- Class III (A, B, C): Variations in the amount of bone support and presence of undercuts in the edentulous area with natural teeth on the same side, but not in the anterior region.
- Class IV (A, B, C): Variations in the amount of bone support and presence of undercuts in the edentulous area with natural teeth remaining only in the anterior region of the edentulous side.

Understanding a patient's Kennedy's Classification helps dentists and dental technicians to create well-fitting and functional dentures, which are crucial for the patient's comfort, speech, chewing ability, and overall oral health.

Arrangement of Teeth in Complete Dentures

The arrangement of teeth in complete dentures is a critical aspect of prosthodontics that affects both the function and aesthetics of the prosthesis. The following five principal factors must be considered when arranging teeth for complete dentures:

1. Position of the Arch

• Definition: The position of the arch refers to the spatial relationship of the maxillary and mandibular dental arches.
• Considerations:
  • The relationship between the arches should be established based on the patient's occlusal plane and the anatomical landmarks of the residual ridges.
  • Proper positioning ensures that the dentures fit well and function effectively during mastication and speech.
  • The arch position also influences the overall balance and stability of the denture.

2. Contour of the Arch

• Definition: The contour of the arch refers to the shape and curvature of the dental arch.
• Considerations:
  • The contour should mimic the natural curvature of the dental arch to provide a comfortable fit and proper occlusion.
  • The arch contour affects the positioning of the teeth, ensuring that they align properly with the opposing arch.
  • A well-contoured arch enhances the esthetics and function of the denture, allowing for effective chewing and speaking.

3. Orientation of the Plane

• Definition: The orientation of the plane refers to the angulation of the occlusal plane in relation to the horizontal and vertical planes.
• Considerations:
  • The occlusal plane should be oriented to facilitate proper occlusion and function, taking into account the patient's facial features and anatomical landmarks.
  • The orientation affects the alignment of the teeth and their relationship to the surrounding soft tissues.
  • Proper orientation helps in achieving balanced occlusion and minimizes the risk of denture displacement during function.

4. Inclination of Occlusion

• Definition: The inclination of occlusion refers to the angulation of the occlusal surfaces of the teeth in relation to the vertical axis.
• Considerations:
  • The inclination should be designed to allow for proper interdigitation of the teeth during occlusion.
  • It influences the distribution of occlusal forces and the overall stability of the denture.
  • The inclination of occlusion should be adjusted based on the patient's functional needs and the type of occlusion being utilized (e.g., balanced, monoplane, or lingualized).

5. Positioning for Esthetics

• Definition: Positioning for esthetics involves arranging the teeth in a way that enhances the patient's facial appearance and smile.
• Considerations:
  • The arrangement should consider the patient's age, gender, and facial features to create a natural and pleasing appearance.
  • The size, shape, and color of the teeth should be selected to match the patient's natural dentition and facial characteristics.
  • Proper positioning for esthetics not only improves the appearance of the dentures but also boosts the patient's confidence and satisfaction with their prosthesis.

Bevels are the angulation which is made by 2 surfaces of a prepared tooth which is other than 90 degrees. Bevels are given at various angles depending on the type of material used for restoration and the purpose the material serves.

Any abrupt incline between the 2 surfaces of a prepared tooth or between the cavity wall and the Cavo surface margins in the prepared cavity

Bevels are the variations which are created during tooth preparation or cavity preparation to help in increased retention and to prevent marginal leakage.
It is seen that in Bevels Occlusal cavosurface margin needs to be 40 degrees which seals and protects enamel margins from leakage and the Gingival Cavo surface margin should be 30 degrees to remove the unsupported enamel rods and produce a sliding fit or lap joint useful in burnishing gold.


Types or Classification of Bevels based on the Surface they are placed on:

Classification of Bevels based on the two factors – Based on the shape and tissue surface involved and Based on the surface they are placed on –

Based on the shape and tissue surface involved:

1. Partial or Ultra short bevel
2. Short Bevel
3. Long Bevel
4. Full Bevel
5. Counter Bevel
6. Reverse / Minnesota Bevel

Partial or Ultra Short Bevel:

Beveling which involves less than 2/3rd of the Enamel thickness. This is not used in Cast restorations except to trim unsupported enamel rods from the cavity borders.

Short Bevel:

Entire enamel wall is included in this type of Bevel without involving the Dentin. This bevel is used mostly with Class I alloys specially for type 1 and 2. It is used in Cast Gold restoration

Long Bevel:

Entire Enamel and 1/2 Dentin is included in the Bevel preparation. Long Bevel is most frequently used bevel for the first 3 classes of Cast metals. Internal boxed- up resistance and retention features of the preparation are preserved with Long Bevel.

Full Bevel:

Complete Enamel and Dentinal walls of the cavity wall or floor are included in this Bevel. It is well reproduced by all four classes of cast alloys, internal resistance and retention features are lost in full bevel. Its use is avoided except in cases where it is impossible to use any other form of bevel .

Counter Bevel:

It is used only when capping cusps to protect and support them, opposite to an axial cavity wall , on the facial or lingual surface of the tooth, which will have a gingival inclination facially or lingually.

There is another type of Bevel called the Minnesota Bevel or the Reverse Bevel, this bevel as the name suggest is opposite to what the normal bevel is and it is mainly used to improve retention in any cavity preparation

If we do not use functional Cusp Bevel –

1. It Can cause a thin area or perforation of the restoration borders
2. May result in over contouring and poor occlusion
3. Over inclination of the buccal surface will destroy excessive tooth structure reducing retention

Based on the surface they are placed on:

1. Gingival bevel
2. Hollow ground bevel
3. Occlusal bevel or Functional cusp bevel

Gingival bevel:

1. Removal of Unsupported Enamel Rods.
2. Bevel results in 30° angle at the gingival margin that is burnishable because of its angular design.
3. A lap sliding fit is produced at the gingival margin which help in improving the fit of casting in this region.
4. Inlay preparations include of two types of bevel Occlusal bevel Gingival bevel

Hollow Ground (concave) Bevel: Hollow ground bevel allows more space for bulk of cast metal, a design feature needed in special preparations to improve material’s castability retention and better resistance to stresses. These bevels are ideal for class IV and V cast materials. This is actually an exaggerated chamfer or a concave beveled shoulder which involves teeth greater than chamfer and less than a beveled shoulder. The buccal slopes of the lingual cusps and the lingual slope of the buccal cusps should be hollow ground to a depth of at least 1 mm.

Occlusal Bevel:

1. Bevels satisfy the requirements for ideal cavity walls.
2. They are the flexible extensions of a cavity preparation , allowing the inclusion of surface defects , supplementary grooves , or other areas on the tooth surface.
3. Bevels require minimum tooth involvement and do not sacrifice the resistance and retention for the restoration
4. Bevels create obtuse-angled marginal tooth structure, which is bulkiest and the strongest configuration of any marginal tooth anatomy, and produce an acute angled marginal cast alloy substance which allows smooth burnishing for alloy.

Functional cusp Bevel:

An integral part of occlusal reduction is the functional cusp bevel. A wide bevel placed on the functional cusp provides space for an adequate bulk of metal in an area of heavy occlusal contact.

→ Following rules should be considered to classify partially edentulous arches, based on Kennedy's classification.

Rule 1:

→ Classification should follow, rather than precede extraction, that might alter the original classification.

Rule 2:

→ If 3^rd molar is missing and not to be replaced, it is not considered in classification.

Rule 3:

→ If the 3^rd molar is present and is to be used as an abutment, it is considered in classification.

Rule 4:

→ If second molar is missing and is not to be replaced, it is not considered in classification.

Rule 5:

→ The most posterior edentulous area or areas always determine the classification.

Rule 6:

→ Edentulous areas other than those, which determine the classification are referred as modification spaces and are designated by their number.

Rule 7:

→ The extent of modification is not considered, only the number of additional edentulous areas are taken into consideration (i.e. no. of teeth missing in modification spaces are not considered, only no. of additional edentulous spaces are considered).

Rule 8:

→ There can be no modification areas in class IV.