Periodontium
The periodontium includes specialized tissues which have two main functions including surrounding and supporting the teeth to maintain them within the mandibular and maxillary bones. The word periodontium is from the Greek terms peri-, which means "around" and -odont, which means "tooth". The literal translation of periodontium is "around the tooth". Periodontics is a specialty dental practice which focuses on the care and maintenance of these tissues. The specialty provides the support required to maintain proper function of the teeth. The periodontics practice consists of four main areas which include:
- Alveolar Bone Proper
- Cementum
- Gingiva
- Periodontal Ligament (PDL)
These components are differentiated based on their location, biochemical properties and architecture. Each of these various components change throughout the lifetime of the structure. As an example, when the teeth respond to various forces, bite pressure or slowly migrate over time, the bone structure resorbs on the side which is experiencing the pressure and bone is added on the side which has increased tension. In addition, the cementum adapts as wear is applied to the occlusal surfaces of the teeth by the apical deposition. The periodontal ligament (PDL) is in an area which experiences a high rate of turnover. This allows the tooth to be suspended in the alveolar bone in addition to responding to any forces which are present. While each area is essentially static, and each area represents its own unique function, the components also function in harmony together as one unit.
The tissues which are located in the periodontium form together to represent an active group of tissues. The alveolar bone is surrounded by the subepithelial connective tissue of the gingiva. The connective tissue of the gingiva is covered by the gingival epithelia. The cementum which covers the root of the tooth, is connected to the adjacent cortical surface of the alveolar bone through the alveolar crest, horizontal and oblique fibers of the periodontal ligament.
The Periodontium and External Forces
The primary function of the periodontium is to support teeth while they are being used. The periodontium relies on the stimulation received in order to preserve the structure. For this reason, a continual state of balance must exist between the periodontal structures and the application of the external forces.
In its response to external forces, the alveolar bone is under constant physiologic remodeling. This is particularly in response to the occlusal forces. Bone is either eliminated or resorbed from the areas where it is not necessary and it is added to areas where additional support is required. The socket wall is a reflection of the general responsiveness to these outside forces. Osteoblasts and newly formed osteoid line the areas which experience tension in addition to the lines of compression which are lined by osteoclasts. These continuous forces also influence the density, number, and overall alignment of trabeculae which is located within the bone. The bony trabeculae are aligned in the path of tensile and compressive stresses. They exist to provide adequate resistance to the occlusal forces with the minimum amount of bone structure. As these forces increase and grow, the bony trabeculae increase both in their number and density. Bone is also added to the respective external surfaces.
The PDL is reliant on stimulation from regular function in order to preserve the overall structure. Within the physiologic limits, the PDL can accommodate the increased function through increased width. Forces which exceed this adaptive capacity, result in injury or trauma from the occlusion. When the occlusal forces are reduced, the PDL can atrophy and become thin. This condition is called disuse atrophy.