Impression making is a critical step in prosthodontics and orthodontics, as it captures the details of the oral cavity for the fabrication of dental prostheses. There are several techniques for making impressions, each with its own principles and applications. Here, we will discuss three primary impression-making techniques: Mucostatic, Mucocompressive, and Selective Pressure Impression Techniques.

1. Mucostatic or Passive Impression Technique

• Proposed by: Richardson and Henry Page
• Materials Used: Plaster of Paris and Alginate
• Key Features:
  • Relaxed Condition: Records the oral mucous membrane and jaws in a normal, relaxed condition.
  • Tray Design: Utilizes an oversized tray to accommodate the relaxed tissues.
  • Tissue Contact: Achieves intimate contact of the tissues with the denture base, which enhances stability.
  • Peripheral Seal: This technique has a poor peripheral seal, which can affect retention.
  • Outcome: The resulting denture will have good stability but poor retention due to the lack of a proper seal.

2. Mucocompressive Impression Technique

• Proposed by: Carole Jones
• Materials Used: Impression compound and Zinc Oxide Eugenol (ZoE)
• Key Features:
  • Functional Recording: Records the oral tissues in a functional and displaced form, capturing the active state of the tissues.
  • Retention: Provides good retention due to the compression of the tissues during the impression process.
  • Displacement Issues: Dentures made using this technique may tend to get displaced due to tissue rebound when the tissues return to their resting state after the impression is taken.

3. Selective Pressure Impression Technique

• Proposed by: Boucher
• Materials Used: Special tray with Zinc Oxide Eugenol (ZoE) wash impression
• Key Features:
  • Stress Distribution: Loads acting on the denture are transmitted to the stress-bearing areas of the oral tissues.
  • Tray Design: A special tray is designed such that the tissues contacted by the tray are recorded under pressure, while the tissues not contacted by the tray are recorded in a state of rest.
  • Balanced Recording: This technique allows for a more balanced impression, capturing both the functional and relaxed states of the oral tissues.

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.

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.

Maxillary Connector Specifications

• Beading:
  • 0.5 mm deep groove around borders to ensure tissue contact and prevent food entrapment.
• Finish Line Angle:
  • Less than 90° for smooth transition between metal and acrylic.
• Relief:
  • Provided around rugae and mid-palatal raphe to avoid impingement.

 Occlusion Concepts

 Jaw Relation Records

Reference Planes & Landmarks

 Articulators & Theories

Occlusion & Jaw Relations synopsis

• Facebow (accurate hinge axis): Fully adjustable rods.
• Facebow use: Multiple unit restorations.
• Posselt: Described border movements.
• Fisher angle: Intersection of protrusive & non-working condylar paths (~5°).
• Curve of Spee: Anterior to posterior curve.
• Von Spee curve: Natural dentition.
• Sharp tooth pain: A-delta fibers.
• Sound change with anterior teeth position: “F” sounds.
• Centric relation: Posterior to intercuspal by 0.5–1 mm.