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

Concepts Proposed to Attain Balanced Occlusion

Balanced occlusion is a critical aspect of complete denture design, ensuring stability and function during mastication and speech. Various concepts have been proposed over the years to achieve balanced occlusion, each contributing unique insights into the arrangement of artificial teeth. Below are the key concepts:

I. Concepts for Achieving Balanced Occlusion

1. Gysi's Concept (1914)

• Overview: Gysi suggested that arranging 33° anatomic teeth could enhance the stability of dentures.
• Key Features:
  • The use of anatomic teeth allows for better adaptation to various movements of the articulator.
  • This arrangement aims to provide stability during functional movements.

2. French's Concept (1954)

• Overview: French proposed lowering the lower occlusal plane to increase the stability of dentures while achieving balanced occlusion.
• Key Features:
  • Suggested inclinations for upper teeth:
    • Upper first premolars: 5° inclination
    • Upper second premolars: 10° inclination
    • Upper molars: 15° inclination
  • This arrangement aims to enhance the occlusal relationship and stability of the denture.

3. Sear's Concept

• Overview: Sears proposed balanced occlusion for non-anatomical teeth.
• Key Features:
  • Utilized posterior balancing ramps or an occlusal plane that curves anteroposteriorly and laterally.
  • This design helps maintain occlusal balance during functional movements.

4. Pleasure's Concept

• Overview: Pleasure introduced the concept of the "Pleasure Curve" or the posterior reverse lateral curve.
• Key Features:
  • This curve aids in achieving balanced occlusion by allowing for better distribution of occlusal forces.
  • It enhances the functional relationship between the upper and lower dentures.

5. Frush's Concept

• Overview: Frush advised arranging teeth in a one-dimensional contact relationship.
• Key Features:
  • This arrangement should be reshaped during the try-in phase to obtain balanced occlusion.
  • Emphasizes the importance of adjusting the occlusal surfaces for optimal contact.

6. Hanau's Quint

• Overview: Rudolph L. Hanau proposed nine factors that govern the articulation of artificial teeth, known as the laws of balanced articulation.
• Nine Factors:
  • Horizontal condylar inclination
  • Protrusive incisal guidance
  • Relative cusp height
  • Compensating curve
  • Plane of orientation
  • Buccolingual inclination of tooth axis
  • Sagittal condylar pathway
  • Sagittal incisal guidance
  • Tooth alignment
• Condensation: Hanau later condensed these nine factors into five key principles for practical application.

7. Trapozzano's Concept of Occlusion

• Overview: Trapozzano reviewed and simplified Hanau's quint and proposed his triad of occlusion.
• Key Features:
  • Focuses on the essential elements of occlusion to streamline the process of achieving balanced occlusion.

II. Monoplane or Non-Balanced Occlusion

Monoplane occlusion is characterized by an arrangement of teeth that serves a specific purpose. It includes the following concepts:

• Spherical Theory: Proposes that the occlusal surfaces should be arranged in a spherical configuration to facilitate movement.
• Organic Occlusion: Focuses on the natural relationships and movements of the jaw.
• Occlusal Balancing Ramps for Protrusive Balance: Utilizes ramps to maintain balance during protrusive movements.
• Transographics: A method of analyzing occlusal relationships and movements.

Sears' Occlusal Pivot Theory

• Overview: Sears also proposed the occlusal pivot theory for monoplane or balanced occlusion, emphasizing the importance of a pivot point for functional movements.

III. Lingualized Occlusion

• Overview: Proposed by Gysi, lingualized occlusion involves positioning the maxillary posterior teeth to occlude with the mandibular posterior teeth, enhancing stability and function.
• Key Features:
  • The maxillary teeth are positioned more centrally, while the mandibular teeth are positioned buccally.
  • This arrangement allows for better functional balance and esthetics.

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.

Complete Denture Occlusion

Complete denture occlusion is a critical aspect of prosthodontics, as it affects the function, stability, and comfort of the dentures. There are three primary types of occlusion used in complete dentures: Balanced Occlusion, Monoplane Occlusion, and Lingualized Occlusion. Each type has its own characteristics and applications.

Types of Complete Denture Occlusion

1. Balanced Occlusion

• Definition: Balanced occlusion is characterized by simultaneous contact of all opposing teeth in centric occlusion, providing stability and even distribution of occlusal forces.
• Key Features:
  • Three-Point Contact: While a three-point contact (one anterior and two posterior) is a starting point, it is not sufficient for true balanced occlusion. Instead, there should be simultaneous contact of all teeth.
  • Minimal Occlusal Balance: For minimal occlusal balance, there should be at least three points of contact on the occlusal plane. The more points of contact, the better the balance.
  • Absence in Natural Dentition: Balanced occlusion is not typically found in natural dentition; it is a concept specifically applied to complete dentures to enhance stability during function.
• Importance: This type of occlusion is particularly important for patients with complete dentures, as it helps to minimize tipping and movement of the dentures during chewing and speaking.

2. Monoplane Occlusion

• Definition: Monoplane occlusion involves a flat occlusal plane where the occlusal surfaces of the teeth are arranged in a single plane.
• Key Features:
  • Flat Occlusal Plane: The occlusal surfaces are designed to be flat, which simplifies the occlusion and reduces the complexity of the denture design.
  • Limited Interference: This type of occlusion minimizes interferences during lateral and protrusive movements, making it easier for patients to adapt to their dentures.
• Applications: Monoplane occlusion is often used in cases where the residual ridge is severely resorbed or in patients with limited jaw movements.

3. Lingualized Occlusion

• Definition: Lingualized occlusion is characterized by the positioning of the maxillary posterior teeth in a way that they occlude with the mandibular posterior teeth, with the buccal cusps of the mandibular teeth being positioned more towards the buccal side.
• Key Features:
  • Maxillary Teeth Positioning: The maxillary posterior teeth are positioned more towards the center of the arch, while the mandibular posterior teeth are positioned buccally.
  • Functional Balance: This arrangement allows for better functional balance and stability during chewing, as the maxillary teeth provide support to the mandibular teeth.
• Advantages: Lingualized occlusion can enhance the esthetics and function of complete dentures, particularly in patients with a well-defined ridge.

Anatomy of Maxilary Edentulous Ridge

LIMITING STRUCTURES

A) Labial & buccal frenum

- Fibrous band covered by mucous membrane.

- A v-shaped notch (labial notch) should be provided very carefully which should be narrow but deep enough to avoid interference

- Buccal frenum has the attachment of following muscles; levator anguli 

- It needs greater clearance on buccal flange of the denture (shallower and wider) than the labial frenum.

B) Labial & buccal vestibule (sulcus)

- Labial sulcus is bounded on one side by the teeth, gingiva and residual alveolar ridge and on the outer side by lips.

- Buccal sulcus extends from buccal frenum anteriorly to the hamular notch posteriorly.

- The size of the vestibule is dependant upon:

i) Contraction of buccinator muscle.

ii) Position of the mandible.

iii) Amount of bone loss in maxilla.

C) Hamular notch

It is depression situated between the maxillary tuberosity and the hamulus of the medial pterygoid plate. It is a soft area of loose connective tissue.

- it houses the disto-lateral termination of the denture.

- Aids in achieving posterior palatal seal.

- Overextension causes soreness.

- Underextension poor retention

D) Posterior palatal seal area (post-dam)

It is a soft tissue area at or beyond the junction of the hard and soft palates on which pressure within physiological limits can be applied by a complete denture to aid in its retention.

Extensions:

1. Anteriorly – Anterior vibrating line

2. Posteriorly – Posterior vibrating line

3. Laterally – 3-4 mm anterolateral to hamular notch

SUPPORTING STRUCTURES

 A) Primary stress bearing area / Supporting area

1. Posterior part of the palate

2. Posterolateral part of the residual alveolar ridge

B) Secondary stress bearing area / Supporting area

1. The palatal rugae area
2. Maxillary tuberosity

 RELIEF AREAS

A) Incisive papilla

- Midline structure situated behind the central incisors.

- It is an exit point of nasopalatine nerves and vessels.

- It should be relieved if not, the denture will compress the nerve or vessels and lead to necrosis of the distributing areas and paresthesia of anterior palate.

B) Mid-palatine raphe

 - Extends from incisive papilla to distal end of hard palate.

- Median suture area covered by thin submucosa

- Relief is to be provided as it is supposed to be the most sensitive part of the palate to pressure

 C) Crest of the residual alveolar ridge

 D) Fovea palatinae

Few areas like the cuspid eminence , fovea palatinae and torus palatinus may be relieved according to condition required.

→ 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.