Introduction

The acquired salivary pellicle (ASP) is a fundamental element in the maintenance of oral health, first observed by Alexander Nasmyth in 1839. This organic film forms on the surface of teeth as a result of interactions between saliva and dental hard tissues.  

Formation of the Acquired Salivary Pellicle

The formation of the ASP is a dynamic process influenced by both the adsorption and desorption of salivary biopolymers. The pellicle forms in several stages:

Fig. 1 Formation of acquired salivary pellicle (Chawhuaveang D. D., et al. 2021).

Initial Stage: Within seconds to a few minutes of saliva contact, salivary proteins such as proline-rich proteins, statherin, and histatins begin to adhere to the tooth surface. These proteins have calcium-binding domains that interact with hydroxyapatite crystals present on the tooth surface. The pellicle initially reaches a thickness of approximately 10-20 nm.

Developing Stage: After the initial attachment, more salivary proteins aggregate with the precursor proteins within 30-45 minutes. During this stage, protein-protein interactions lead to the formation of globular structures, with the diameter of these protein globes increasing as the stage progresses.

Maturation Stage: High-molecular-weight mucins gradually adhere to the pellicle. The thickness of the pellicle continues to increase, reaching an equilibrium between adsorption and desorption within 90-120 minutes. Mature ASP typically reaches a thickness of about 100-1000 nm.

Several factors influence pellicle formation, including the type of protein molecules, which affects protein-protein interactions in the developing stage. A longer formation time generally results in a pellicle with enhanced protective properties due to increased thickness and improved dynamic conditions.

Composition and Structure of the Mature Acquired Salivary Pellicle

The ASP is composed of proteins, lipids, carbohydrates, and other macromolecules, each contributing to its structure and function.

Proteins and Glycoproteins: Major components include salivary proteins and glycoproteins. These proteins play roles in immune response, antimicrobial activity, and remineralization. Despite extensive research, the functions of some proteins remain unclear.

Lipids: The pellicle contains approximately 25% lipids, including glycolipids and phospholipids. These lipids originate mainly from major salivary glands and affect the pellicle's permeability, which is crucial for its resistance to acids. Lipids also influence the pellicle's ultrastructure and bacterial adhesion, with hydrophobic properties impeding the attachment of microorganisms.

Carbohydrates: Carbohydrates in the pellicle mainly come from the submandibular and parotid glands and are present as complex compounds like glycoproteins and glycolipids. While the specific functions of carbohydrates in the pellicle are not well understood, they may serve as nutrients for biofilms and contribute to the pellicle's protective barrier.

The ASP exhibits a heterogeneous ultrastructure with a globular and pore-like surface. The basal layer is electron-dense, adhering to the enamel with filamentous structures. The middle layer has a loosely granular appearance, while the surface layer is densely aggregated with proteins, forming a knotted globular surface.

Functions of the Acquired Salivary Pellicle

The ASP performs several critical functions in maintaining oral health:

Lubrication: The pellicle reduces friction between teeth and oral structures during mastication and speech. It provides lubrication for tooth-to-soft-tissue and tooth-to-tooth contact, minimizing friction and offering some protection against abrasion and attrition.

Maintenance of Mineral Homeostasis: The ASP plays a role in maintaining calcium levels on the tooth surface, ensuring a supersaturated state that helps prevent dissolution. Calcium-binding proteins in the pellicle regulate hydroxyapatite crystal deposition and dissolution, protecting against demineralization during acid challenges.

Determination of Initial Microbial Colonizers: The pellicle acts as a substrate for bacterial attachment, influencing the initial microbial colonization of the oral cavity. Specific receptors on the pellicle facilitate the adhesion of bacteria such as Streptococcus species and Actinomyces species. Additionally, the pellicle affects the production of glucans, which promotes biofilm formation.

Protection from Acid Attacks: The pellicle serves as a barrier against acid contact and neutralizes acidity from the oral environment. Its perm-selective nature restricts mineral ion movement, while calcium-binding proteins help prevent hydroxyapatite dissolution.

Implications for Oral Diseases

The ASP plays a significant role in the development and management of various oral diseases:

Dental Caries: The pellicle influences bacterial colonization, the diffusion of acidic byproducts, and the transport of mineral ions, affecting the development of dental caries. The pellicle's bactericidal effects, attributed to proteins like cystatins, play a role in caries prevention.

Dental Erosion: The pellicle helps protect against dental erosion caused by non-bacterial acids. It reduces surface mineral loss and enamel roughness, though its effectiveness may be limited under severe erosive conditions.

Periodontal Disease: The pellicle can impact the progression of periodontal disease by enhancing bacterial adhesion and accelerating plaque formation. The composition of the pellicle on the cervical surface, influenced by gingival crevicular fluid, affects bacterial colonization and inflammatory responses.

Conclusion

The acquired salivary pellicle is a complex and dynamic film that plays a critical role in oral health. Its formation, composition, and functions are integral to lubrication, mineral homeostasis, microbial colonization, and protection against acid attacks. Understanding its role in oral diseases and exploring modification strategies provides valuable insights into improving oral health outcomes.