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.

The clinical implications of an edentulous stomatognathic system are considered under the following factors:

(1) modi?cations in areas of support .
(2) functional and parafunctional considerations.
(3) changes in morphologic face height, and temporomandibular joint (TMJ).
(4) cosmetic changes and adaptive responses

Support mechanism for complete dentures

Mucosal support and masticatory loads

- The area of mucosa available to receive the load from complete dentures is limited when compared with the corresponding areas of support available for natural dentitions.

- The mean denture bearing area to be 22.96 cm2 in the edentulous maxillae and approximately 12.25 cm2 in an edentulous mandible

- In fact, any disturbance of the normal metabolic processes may lower the upper limit of mucosal tolerance and initiate in?ammation

Residual ridge

The residual ridge consists of denture-bearing mucosa, the submucosa and periosteum, and the underlying residual alveolar bone.

The alveolar bone supporting natural teeth receives tensile loads through a large area of periodontal ligament, whereas the edentulous residual ridge receives vertical, diagonal, and horizontal loads applied by a denture with a surface area much smaller than the total area of the periodontal ligaments of all the natural teeth that had been present.

There are two physical factors involved in denture retention that are under the control of the dentist

- The maximal extension of the denture base
- maximal intimate contact of the denture base and its basal seat

 - The buccinator, the orbicularis oris, and the intrinsic and extrinsic muscles of the tongue are the key muscles that the dentist harnesses to achieve this objective by means of impression techniques.
 - The design of the labial buccal and lingual polished surface of the denture and the form of the dental arch are considered in balancing the forces generated by the tongue and perioral musculature.

Function: mastication and other mandibular movements

Mastication consists of a rhythmic separation and apposition of the jaws and involves biophysical and biochemical processes, including the use of the lips, teeth, cheeks, tongue, palate, and all the oral structures to prepare food for swallowing.

- The maximal bite force in denture wearers is ?ve to six times less than that in dentulous individuals.

- The pronounced differences between persons with natural teeth and patients with complete dentures are conspicuous in this functional context:

(1) the mucosal mechanism of support as opposed to support by the periodontium ;

(2) the movements of the dentures during mastication;

(3) the progressive changes in maxillomandibular relations and the eventual migration of dentures

(4) the different physical stimuli to the sensor motor systems.

Parafunctional considerations

- Parafunctional habits involving repeated or sustained occlusion of the teeth can be harmful to the teeth or other components of the masticatory system.

- Teeth clenching is common and is a frequent cause of the complaint of soreness of the denture-bearing mucosa.

- In the denture wearer, parafunctional habits can cause additional loading on the denture-bearing tissues

Force generated during mastication and parafunction

Functional (Mastication)

Direction -> Mainly vertical

Duration and magnitude -> Intermittent and light diurnal only

Parafunction

Direction -> Frequently horizontalas well as vertical

Duration and magnitude -> Prolonged, possibly excessive Both diurnal and nocturnal

Changes in morphology (face height), occlusion, and the TMJs

The reduction of the residual ridges under complete dentures and the accompanying reduction in vertical dimension of occlusion tend to cause a reduction in the total face height and a resultant mandibular prognathism.

In complete denture wearers, the mean reduction in height of the mandibular residual alveolar ridge measured in the anterior region may be approximately four times greater than the mean reduction occurring in the maxillary residual alveolar process

Occlusion

- In complete denture prosthodontics, the position of planned maximum intercuspation of teeth is established to coincide with the patient’s centric relation.

-The coincidence of centric relation and centric occlusion is consequently referred to as centric relation occlusion (CRG).

- Centric relation at the established vertical dimension has potential for change. This change is brought about by alterations indenture-supporting tissues and facial height, as well as by morphological changes in the TMJs.

TMJ changes

impaired dental ef?ciency resulting from partial tooth loss and absence of or incorrect prosthodontic treatment can in?uence the outcome of temporomandibular disorders.

Aesthetic, behavioral, and adaptive response

Aesthetic changes associated with the edentulous state.

- Deepening of nasolabial groove

- Loss of labiodentals angle

- Narrowing of lips

- Increase in columellae philtral angle

-  Prognathic appearance

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.

→ 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.

LIMITING STRUCTURES

A) Labial, lingual & buccal frenum

- It is fibrous band extending from the labial aspect of the residual alveolar ridge to the lip containing a band of the fibrous connective tissue the that helps in attachment of the orbicularis oris muscle.
- It is quite sensitive hence the denture should have an appropriate labial notch.
- The fibers of buccinator are attached to the buccal frenum.
- Should be relieved to prevent displacement of the denture during function.
- The lingual frenum relief should be provided in the anterior portion of the lingual flange. 
- This anterior portion of the lingual flange called sub-lingual crescent area.
- The lingual notch of the denture should be well adapted otherwise it will affect the denture stability.
 
B) Labial & buccal vestibule
 
-     The labial sulcus runs from the labial frenum to the buccal frenum on each side.
-     Mentalis muscle is quite active in this region.
-     The buccal sulcus extends posteriorly from the buccal frenum to outside back corner of the retromolar region.
-     Area maximization can be safely done here as because the fibers of the buccinator runs parallel to the border and hence displacing action due to buccinator during its contraction is slight.

-     The impression is the widest in this region.
 
C) Alveololingual sulcus

-     Between lingual frenum to retromylohyoid curtain.
-     Overextension causes soreness and instability.

It can be divided into three parts:
i) Anterior part :
-     From lingual frenum to mylohyoid ridge
-     The shallowest portion(least height) of the lingual flange
ii) Middle region :
-     From the premylohyoid fossa to the the distal end of the mylohyoid region
iii) Posterior portion :
-     From the end of the mylohyoid ridge end to the retromylohyoid curtain
-     Provides for a valuable undercut area so important retention
-     Overextension causes soreness and instability
-     Proper recording gives typical S –form of the lingual flange
 
D) Retromolar pad
-     Pear-shaped triangular soft pad of tissue at the distal end of the lower ridge is referred to as the retromolar pad.
-     It is an important structure, which forms the posterior seal of the mandibular denture.
-     The denture base should extend up to 2/3rd of the retromolar pad triangle.

E) Pterygomandibular raphe
 
 SUPPORTING STRUCTURES

A) Primary stress bearing area / Supporting area
 
1.    Buccal shelf area
-     Extends from buccal frenum to retromolar pad.
-     Between external oblique ridge and crest of alveolar ridge.

Its boundaries are:
1.    Medially the crest of the ridge
2.    Laterally the external oblique ridge
3.    Distally the retromolar pad
4.    Mesially the buccal frenum
The width of this area increases as the alveolar resorption continues.
 
B) Secondary stress bearing area / Supporting area
 
1.    Residual alveolar ridge
-     Buccal and lingual slopes are secondary stress bearing areas.
 
RELIEF AREAS
A) Mylohyoid ridge
 
-     Attachment for the mylohyoid muscle.
-     Running along the lingual surface of the mandible.
-     Anteriorly: the ridge lies close to the inferior border of the mandible.
-     Posteriorly it lies close to the residual ridge.
-     Covered by the thin mucosa which may be traumatized by denture base hence it should be relieved.
-     The extension of the lingual flange is to be beyond the palpable position of the mylohyoid ridge but not in the undercut.
 
B) Mental foramen
-     Lies on the external surface of the mandible in between the 1st and the 2nd premolar region.
-     It should be relieved specially in case it lies close to the residual alveolar ridge due to ridge resorption to prevent parasthesia.
 
C) Genial tubercle
-     Area of muscle attachment (Genioglossus and Geniohyoid).
-     Lies away from the crest of the ridge.
-     Prominent in resorbed ridges therefore adequate relief to be provided.
 
D) Torus mandibularis
-     Abnormal bony prominence.
-     Bilaterally on the lingual side near the premolar area.
-     Covered by thin mucosa so it should be relieved

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.