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Abstract
Of all major salivary glands, the human submandibular gland secretes the largest amount of saliva. Along with the sublingual duct, the main duct (Wharton's duct) is known to open into the sublingual caruncula; however, reports regarding this common opening structure are scarce and details unclear. The structure of Wharton's duct opening is quite different from that of parotid duct (Stensen's duct) opening in its overall size and diameter despite what is commonly noted in text books. About 85% of sialolith occurrences in humans is in the submandibular gland and duct, which causes local pain during swallowing in most cases. The details of Wharton's duct's inner structure is relatively unknown, and further investigation is necessary to understand its special characteristics and clinical applications. In this study, we observed the inner structure of the ducts' common opening area by scanning electron microscopy and confirmed a large number of blood vessels present in the connective tissue layer just under the epithelium. In addition, we confirmed the presence of smooth muscle in the same area using smooth muscle actin antibody. These structural findings suggest that Wharton's duct itself is likely responsible for the regulation of salivary flow.
Key words
Submandibular duct, sublingual caruncula, human, SEM, scanning electron microscopy, α-SMA, immunohistochemistry.
Introduction
The submandibular gland is one of the major salivary glands located in the submental triangle area and produces saliva, 60% of which is mixed saliva with mucus being its main component. Submandibular duct runs superior to the oral floor along the medial margin of mandibule up to the mental region at which point it merges into sublingual caruncula, sharing a common opening area with the sublingual duct.
Many cases of typical diseases involving the human submandibular gland have been reported, particularly sialolithiasis, adenoid cyst and cystic carcinoma (Witt, 2005; Saito et al., 2008). Most cases of sialolithiasis occur in the submandibular gland (80-90%), and some common symptoms of the main duct sialolithiasis include swelling of the gland before, during and after meals and severe local pain when saliva flows through the duct (Warden and Adamson, 1995).
Infectious diseases are most common in the parotid gland, which is likely associated with the structure and position of the Stensen's duct opening (Lerena et al.. 2007; Harrison, 2009; Amano...