Incisors function
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Functions of Incisors: A Comprehensive Overview
Introduction to Incisors Function
Incisors are the front teeth located in both the upper and lower jaws, primarily designed for cutting and shearing food into manageable pieces. These teeth play a crucial role in the initial phase of food ingestion and are also involved in various non-food-related tasks.
Structural and Mechanical Properties of Incisors
Enamel Cap and Tooth Deformation
The enamel cap of incisors is a critical element in controlling their mechanical behavior under load. Studies on the mandibular central incisors of the primate Macaca mulatta have shown that the enamel cap's morphology significantly influences tooth deformation. When compressed, these incisors exhibit considerable deformation in the lingual direction, which is orthogonal to the applied load. This deformation is more pronounced when the teeth are in the mandible, reflecting the additional freedom of movement provided by supporting structures. The enamel cap's stiffness overlying the more pliable dentin directs this deformation behavior, highlighting its importance in the tooth's mechanical response.
Biting Efficiency and Incisal Orientation
The efficiency of incisors in biting is influenced by their structural orientation and the friction at the tooth-food interface. Broad-edged 'spatulate' incisors, characteristic of catarrhines and platyrrhines, are used for peeling fruits, removing bark, and stripping leaves. In humans, the apex angle of the incisor and the coefficient of friction are critical factors determining biting efficiency. The optimal efficiency is achieved when the angle between the apex bisector and the direction of applied force is zero, although friction complicates this, especially for lower incisors. This model applies to both humans and frugivorous primates, providing a foundation for understanding the mechanics of incision.
Regenerative Capacity and Development
Stem Cell Regulation in Rodent Incisors
Rodent incisors continuously grow throughout life due to the presence of epithelial and mesenchymal stem cells. The epithelial stem cells, which are progenitors of ameloblasts, reside in the cervical loops at the base of the incisors. FGFR2b signaling is crucial for the development and maintenance of these stem cell niches. Downregulation of FGFR2b signaling during embryonic stages leads to abnormal development, while postnatal attenuation results in impaired incisor growth and enamel formation. However, the regenerative capacity is retained, as the incisors can resume growth and reform enamel upon release of the signaling blockade.
Role of FGF10 in Stem Cell Compartment Formation
FGF10 is essential for the formation and maintenance of the stem cell compartment in developing mouse incisors. In FGF10-null mice, the cervical loop fails to form, leading to limited growth of the dental epithelium. This indicates that FGF10 acts as a survival factor for the stem cell population, ensuring continuous renewal and proper development of the incisor.
Clinical and Aesthetic Importance
Permanent Maxillary and Mandibular Incisors
Permanent incisors, which erupt between 6 and 8 years of age, are vital for shearing and cutting food. They are highly visible during eating, smiling, and talking, thus holding significant aesthetic value. The unique characteristics, arch position, and development of each incisor contribute to their function and importance in dental health.
Intrusion of Incisors in Periodontal Disease
In patients with severe periodontal disease, elongated and spaced incisors are common issues. Various methods for intruding these incisors have been evaluated, showing that low forces and healthy gingiva status are crucial for successful intrusion. This treatment can reduce clinical crown length and improve the marginal bone level, although root resorption may occur.
Conclusion
Incisors are essential for the initial phase of food ingestion, playing a significant role in cutting and shearing food. Their structural properties, regenerative capacity, and clinical importance highlight their multifaceted functions. Understanding the mechanical behavior, developmental biology, and clinical management of incisors can provide valuable insights into their role in both health and disease.
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