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Saliva composition from birth to adolescence: a systematic review of the literature.Abstract
Highlights
- This systematic review provides insights into age-related changes in children’s and adolescents saliva composition.
- Unstimulated salivary flow decreases with age; stimulated flow increases.
- Salivary pH remains stable across ages; buffering capacity increases with age.
- Salivary sodium, calcium and potassium levels are lower in younger children compared to older children.
Background
This systematic review examined the saliva composition of healthy children from birth to 18 years of age by assessing the salivary flow rate, pH, buffering capacity, and ion levels. This review followed the PRISMA guidelines. A systematic search was performed using PubMed, the Cochrane Library, and Scopus. Information regarding the salivary flow rate, pH, buffering capacity, and ion levels in whole saliva was systematically collected, and a qualitative synthesis was performed. The methodological quality of the studies was assessed using the JBI Critical Appraisal Tools.
Highlight
Of the 3,268 retrieved studies, 41 were eligible for inclusion. Unstimulated salivary flow showed an age-related decrease, whereas stimulated salivary flow increased with age. The pH of the saliva remained consistent across different ages, whereas the buffering capacity showed an age-related increase. Salivary sodium, calcium, and potassium levels were lower in the younger children than in the older children. An investigation of salivary ion levels revealed lower average fluoride concentrations in Asian populations than in European populations. Most studies had a low or moderate risk of bias.
Introduction
Saliva is a clear exocrine secretion produced by three pairs of major (parotid, sublingual, and submandibular) and hundreds minor glands [1]. It is crucial for maintaining the quality of life of individuals, due to its multifaceted functions such as lubrication and protection of the oral tissues, buffering action and antibacterial activity. Furthermore, saliva plays an important role in digestion, taste perception and remineralization of teeth [2].
Although saliva primarily consists of water, it also contains a wide variety of proteins and ions, such as calcium, magnesium, potassium, sodium, bicarbonate, and phosphate [1]. The complexity of its composition is affected by many factors. For example, each salivary gland type secretes saliva with different characteristics and composition [3]. Most minor salivary glands secrete mucous saliva, which is abundant in mucins and proteins, playing a crucial role in lubricating and protecting oral tissues. However, some exceptions exist, such as the von Ebner’s glands, which secrete serous saliva containing enzymes like lingual lipase that aid in the initial digestion of lipids. The parotid glands, on the other hand, produce serous saliva, characterized by a watery consistency and enriched with enzymes like amylase [1]. The sublingual and submandibular glands produce a mixed, seromucous saliva [1].
A further distinction is made between unstimulated saliva, produced in rest, and stimulated saliva produced in response to mechanical, chemical or trigeminal stimuli. These types of saliva exhibit differences in composition [2]. Stimulated saliva, primarily secreted by the parotid gland, contains fewer proteins compared to unstimulated saliva, which is mostly secreted from sublingual and submandibular glands [4]. Additionally, various factors, such as diet, medication use, age, development, pathological insults, and stressors contribute to a divergent composition of saliva [4].
Although the morphological development of the salivary glands is completed during the prenatal stage, they continue their growth during childhood and reach full maturity in adulthood [[5], [6], [7]]. There are few studies on age-dependent changes in salivary quantity (flow rate) and quality (e.g., composition, viscosity, lubrication) [[4], [5], [6]]. However, the composition of saliva across various age groups remains poorly understood, and no comprehensive systematic review has been conducted to consolidate findings from various studies on saliva composition in children and adolescents. Hence, the primary aim of this systematic literature review was to evaluate the saliva composition from birth to the age of 18 years of age by assessing the salivary flow rate, pH, buffering capacity, and ion levels in whole saliva and to understand the age-induced alterations in saliva.
Section snippetsDiscussion
The aim of this study was to evaluate the human saliva composition from birth to adolescence and to understand the age-related alterations in saliva. The descriptive analysis showed that as children grow older, the salivary flow rate of unstimulated saliva decreases, whereas the flow rate of stimulated saliva increases [12,13,16,21,23,26,32]. It is important to acknowledge that this overall finding is based on studies that either investigated these age categories or reported separate results…
Conclusion
In conclusion, the findings of this systematic literature review indicate that most salivary parameters examined in this study are influenced by age. In general, unstimulated salivary flow rate decreases with age, whereas stimulated flow rate increase. Salivary pH appears to remain stable across age groups, while buffering capacity tends to increase. Furthermore, the concentrations of sodium, calcium, and potassium in saliva rise as children grow older. However, due methodological…
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