Anatomical structures related to the removable metallic partial prosthesis
1-Introduction:
In PPAC all supporting tissues must be considered, because such a prosthesis fits on natural teeth and rests on the osteo-mucosal tissues of the crests and palate.
The action of the pressures is different in intensity depending on whether the contacts are direct or indirect through a first tissue which plays the role of shock absorber.
2-Anatomical elements related to the removable partial prosthesis with metal frame
A – Tissues directly influenced by the removable partial prosthesis with metal frame:
Enamel The quality of the enamel must always be assessed during the clinical examination of the partially edentulous, particularly on teeth with hooks; thus, a highly mineralized enamel resists any harmful action of the hook, the latter can cause scratches and cracks, which over time can result in bacterial attacks causing caries, and can go as far as the destruction of the crown.
Relations with the prosthesis
– Means of retention and stabilization
– Artificial teeth
The oral mucosa It lines the entire oral cavity (buccal plane, vestibule, alveolar ridges, palatine vault, inner surface of the cheeks and lips, etc.) and is in direct contact with the intrados, extrados and edges of the prosthesis.
Peripheral structures In the maxilla
- With the edges of the prosthesis
The insertion of the muscle or ligament fibers constitutes the extreme limit of the contours of the prosthesis. From the medial and anterior part to the posterior part we have:
– The frenulum of the upper lip, which is inserted on the fibromucosa and extends more or less in a fan shape in the internal face of the upper lip;
– The insertions of the myrtiform and canines ;
– The insertions of the buccinator muscle ;
– The pterygomaxillary groove located between the tuberosity and the pyramidal process of the palatine, on the one hand, and the hook of the internal wing of the pterygoid process on the other hand
– The soft palate , whose location at the posterior limit of the prosthesis gives it a role of extreme importance in the retention of the upper prosthesis.
- With the extrados of the prosthesis)
– the lip: in the anterior vestibular region, the prosthesis is in relation with the muscles of the upper lip. The convexity of the orbicularis in function is low, it allows a harmonious restoration of the contours of the upper lip without any risk of interference
– The cheeks : in the middle region of the jugal vestibule, the useful passive space between the edentulous arch and the internal face of the cheek is sufficient, and in cases of significant resorption, the horizontal direction of the muscle fibers of the buccinator allows the thickening of the edges of the base and the assembly of the premolars and molars outside the crest.
– The tongue : the extrados of the palatal region of the prosthesis is in relation to the tongue; it serves as a support point for the tip of the latter or its dorsal face during phonation and swallowing;
– The paratuberous region : in this region, the crossed arrangement of the masseter and buccinator muscle fibers, and the centripetal resorption of the alveolar rim, create a real pocket, or ampullary zone, described by Eisenring, the edge of the prosthesis at this level must occupy the entirety of this space.
In the mandible
In the anterior vestibular region
The edges of the lower denture are related to the mental muscles, the orbicularis oris and the incisive muscle of the lower lip.
The orientation of the different planes which constitute the polished surface must be such that at every point the peripheral organs tend to rest on them and thus contribute to the stability of the prosthetic restoration.
In the premolar region: opposite the first premolars, a muscular thickening is apparent. It corresponds to the intersection of all the muscles of
expression. This point is called modiolus because of its position at the center of the muscle fibers of the orbicularis, buccinator, zygomatic, canine and triangular. This imposes a hollowing out of the polished surface at its level and often even a more lingual position of the first premolar.
B – Tissues only indirectly influenced by the removable partial prosthesis with metal frame:
Dentine and pulp The dentine-pulp complex is indirectly influenced by the prosthesis
Bone tissue
Bone resorption after avulsion is a natural and inevitable phenomenon and occurs according to a well-defined pattern. Resorption is greater in width than in height and more marked in the vestibulo-lingual than mesio-distal direction.
Cancellous bone resorbs more than cortical bone. Although bone remodeling is greatest in the first month following an avulsion, bone loss continues throughout life.
3. The periodontium The gingiva We distinguish: – the free gingiva which is the marginal part surrounding the tooth and forming the gingivo-dental groove or sulcus, with a maximum depth of 2 mm under normal conditions, – the attached gingiva adhering to the underlying tissues and extending from the free gingiva to the mucogingival line. A minimum height of 2 mm is necessary to maintain periodontal health. It constitutes the support surface of the prosthesis. – The interdental papilla housed in the embrasure formed by contiguous teeth and protected by the contact point.
Cementum
This is the layer of calcified tissue that covers the root surface of the teeth, it extends from the neck of the tooth to the apex
The removable prosthesis will have little influence on this tissue, and the influence of the prosthesis is as for the enamel of mechanical order (arm of the hook).
The desmodont
It is a dense connective tissue which surrounds the dental roots, and connects the tooth to its alveolus thanks to the desmodontal fibers; in fact, the alveolar bone receives through the desmodont, all the useful or harmful forces transmitted to the level of the tooth; these forces will have an influence on the behavior of the periodontal ligament, which will immediately cause modifications in the structure of the alveolar bone.
Alveolar bone
Bony element providing the link between the dental organ and the maxillary basal bone, ensuring its continuity. It is divided into:
– the external cortex, which extends the cortex of the basal bone,
– the internal cortex (lamina dura or cribriform lamina), pierced with orifices ensuring the passage of blood vessels, it constitutes the internal wall of the alveolus. – The spongy bone, made up of lacunar
spaces separated by bony trabeculae . The alveolar bone is constantly being remodeled to ensure the consistency of its anatomical relationships with the teeth. Any irritation (inflammation, occlusal trauma) can lead to irreversible destruction.
Anatomical structures related to the removable metallic partial prosthesis
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