Complete Dentures in Prosthetic Dentistry II

Angle of mouth (commissance): Dentures should be designed to support the natural mouth angle, preventing angular cheilitis caused by continuous wetting from saliva.

Modiolus: The meeting point of facial muscles near the mouth angle, which can be displaced due to teeth loss, causing the appearance of sunken cheeks. Lower denture in the premolar region should have a thin margin to prevent the modiolus from lifting the denture.

Ala of the nose, ala tragus line: An imaginary line from the ala of the nose to the tragus of the ear is important for proper extension of upper dentures.

Intraoral landmarks: The oral cavity consists of a vestibule and oral cavity proper. After teeth extraction, the alveolar bone is resorbed, and the remaining part is called a residual ridge.

Maxillary anatomical landmarks: The alveolar ridge is the primary stress-bearing area in the upper jaw. The crest of the ridge is the highest point, and the maxillary tuberosity is a rounded prominence behind the distal end of the ridge, which should be included in the impression for good bearing surface.

Palatine vault: The palatine vault is formed by the hard palate anteriorly and the soft palate posteriorly. Its shape can be high and U-shaped, or flat and shallow, and it plays an important role in denture support and stability.

Incisive papilla: The incisive papilla is a pad of fibrous connective tissue overlying the nasopalatine canal and is used as a landmark for correct placement of artificial central incisors. Upper dentures should be relieved to avoid pressure on the incisive nerve, which may cause a burning sensation.

Torus palatinus: A raised, bony ridge running down the center of the hard palate, which needs to be relieved for proper denture fit if it's small. If it's too big, it may need to be removed surgically.

Rugae: Irregular shaped ridges in the anterior third of the hard palate that play a role in speech. They should not be disturbed during the impression process to ensure maximum comfort.

Fovea palatinae: Openings of the ducts of minor salivary glands, which are important landmarks for posterior border extension of the upper denture.

Mandibular anatomical landmarks: The alveolar ridge, which is important for proper extension and occlusal plane location of the mandibular denture. The retromolar pad should not be displaced during the impression process. The external oblique ridge and buccal shelf are areas of dense bone that should be covered by the lower denture to provide support and resist masticatory forces.

Impression process: Relief areas, such as the maxillary incisive papilla, median raphe, and torus palatinus, need to be relieved to eliminate excess pressure and ensure proper denture fit.

Border structures: Maxillary dentures have labial frenulum, labial vestibule, and buccal frenulum as border structures.

Stress-bearing areas: The primary stress-bearing areas, such as the crest of the ridge and the palatal flat areas, can resist the vertical forces of occlusion.

Relief areas: Genial tubercles, sharp bony prominences, and the mental foramen require relief areas in the denture to eliminate excessive pressure and promote proper fit.

Denture foundation area: The denture foundation area, which includes the surface of the oral vestibule, determines the amount of force applied to the denture. A larger surface area reduces the force applied, making it easier to support the denture.

According to the method of fabrication, there are stock trays and custom trays or special trays for making dental impressions.

Stock trays are ready-made and come in specific sizes, while custom trays are fabricated based on a particular patient's cast.

Stock trays are reusable after sterilization, while custom trays are unique to the patient and discarded.

Stock trays serve to carry impression material to the mouth and support it during polymerization. They are available in different materials and sizes.

Factors affecting selection of stock trays include the type of mouth, type of impression material, size of the arch, and the form of the arch.

Custom trays are made from a cast recovered from primary impression and used to make a final impression. They are more accurate and comfortable for the patient.

Custom trays can be made of metallic or non-metallic materials, such as cold cure acrylic resin, hot cure acrylic resin, or light cure acrylic resin.

The material choice for custom trays depends on various factors such as fabrication time, material properties, and hazardous effects.

Close-fit trays are directly adapted to the cast, while spacer and stop trays use a wax spacer to provide extra space for impression material with higher viscosity.

Criteria for special tray construction include not impinging on movable structures, extending borders beyond the vestibular sulcus, and ensuring sufficient rigidity and thickness.