Clinical Standards for Alveolar Ridge Abutments and Anatomy
Requirements for Alveolar Ridge Abutments
Abutment teeth: In a fixed prosthesis, forces normally absorbed by the missing tooth will be transmitted to the abutment teeth through pontics, connectors, and retainers.
Ideally, an abutment should be a living tooth. Endodontically treated teeth are more susceptible to fractures. These teeth are obliged to support the forces directed to the missing tooth in addition to the forces they target themselves.
Supporting tissues must be healthy and free of inflammation, with no mobility. The evaluated structures should take into account three factors: the crown-root ratio, the configuration of the root, and the supporting bone.
Essential Criteria for Abutment Teeth
Crown-Root Ratio Standards
The crown-root ratio is the measurement from the alveolar bone crest of the length of the occlusal tooth compared to the length of the root covered by bone.
- Ideal ratio: 2:3 for a tooth serving as a bridge abutment.
- Minimum acceptable: 1:1 for a piece to serve as a pillar.
Root Configuration and Prognosis
Teeth with short, blunt, or conical roots offer very poor support. Conversely, long roots formed irregularly with multiple divergent roots are those that offer a better prognosis.
Bone Support and Ante's Law
The bone support of the abutment tooth must have a periodontal area equal to or greater than the periodontal area of the tooth it is going to replace (Ante's Law).
Anatomy of the Jaw and Oral Mucosa
Types of Mucous Membranes
There are three types of oral mucosa: the palate, the gingival, and the buccal coating. The buccal coating is continuous with the mucosa of the cheek at the bottom of the buccal groove.
Palatal Mucosa Characteristics
The anterior palatal mucosa is resistant, thick, and firmly adherent to the bone. It includes the rugae and the incisive papilla covering the anterior palatine foramen. The posterior palate is thinner and becomes thicker towards the back.
Gingival Mucosa
The gingival mucosa is pink, inserted, and keratinized. The oral mucosa over a smooth thin coating is often reddish and more mobile.
Support Areas and Residual Alveolar Ridge
The support area is that part of the jaws which supports the prosthesis and is destined to receive the masticatory forces. It is categorized into:
- Primary support
- Secondary support
- Relief areas
The residual alveolar ridge typically presents in shapes such as U, V, or C.
Mucosal Lining of the Support Area
- Fibrous mucosa
- Adipose mucosa
- Glandular mucosa
Peripheral Sealing Zones
The peripheral sealing consists of:
- Zone 1: Marginal zone
- Zone 2: Subsequent closure or post-damming