Pellicles

The addition of therapeutic or cosmetic agents to dentifrices has paralleled advances in knowledge about factors affecting the human dentition. Agents added to dentifrices can act directly on the host tooth stmcture or on specific oral accumulations, for example, the principal action of fluoride is on the tooth enamel. The primary action of an abrasive, however, is on an accumulated stained pellicle. Oral accumulations of interest to preventive dentistry are dental pellicles, dental plaque, dental calculus (tartar), microbial populations responsible for oral malodor, and oral debris (food residues, leukocytes, etc). Plaque is most important because of its potential to do harm. 

Abrasive. Dentifrices have the unique ability to remove extrinsic tooth stains, which are caused by agents such as berries, tea, smoking, antibiotics, and certain bacteria as they attach to the dental pellicle. These stains can be removed only by abrasive cleaning a toothbmsh alone is not adequately effective. It has been shown that only 4% of a test population were able to maintain thein teeth in an acceptably stain-free state without an abrasive and that 18% of the population were "heavy" stainers (2). However, colored materials found in dental plaque are removable without abrasives. 

Haut,/. skin hide membrane film pellicle crust bloom. — durchaichtlge —, cornea. — harte —, sclerotic coat. 

Hautchen, n, thin skin, film, pellicle, membrane. 

It has been known for many years that microbial contaminants may effect the spoilage of pharmaceutical products through chemical, ply sical or aesthetic changes in the nature of the product, thereby rendering it unfit for use (see Chapter 18). Active drug constituents may be metabolized to less potent or chemically inactive forms. Physical changes commonly seen are the breakdown of emulsions, visible surface growth on solids and the formahon of slimes, pellicles or sediments in hquids, sometimes... 

The bond strength to enamel (2-6 to 9-9 MPa) is greater than that to dentine (1-5 to 4-5 MPa) (Wilson McLean, 1988). Bond strength develops rapidly and is complete within 15 minutes according to van Zeghbroeck (1989). The cement must penetrate the acquired pellicle (a thin mucous deposit adherent to all surfaces of the tooth) and also bond to debris of calciferous tooth and the smear layer present after drilling. Whatever the exact mode of bonding to tooth stmcture, the adhesion is permanent. The principles and mechanism of adhesion have already been discussed in Section 5.2. 

Unlike the skin, the mucosae of the oral cavity are constantly maintained moist by the continual secretion of saliva from the three major salivary glands (submandibular, parotid, and sublingual) and the minor salivary glands located in or beneath the mucosae. The thickness of the salivary film (pellicle) has been calculated to be between 70 /rm and 100 /./m [23] however, both the composition and amount of saliva produced can vary between individuals, with time of day, disease states, and drug therapy [33], all of which must be taken into account when considering the oral cavity as a site for drug delivery. 

The function of the mucosal pellicle is to serve as a barrier between the oral epithelial surface and the external environment, and so it may also act as a barrier to drug delivery. However, there are limited studies assessing the role of the mucus layer in buccal permeability. In one study, treatment of the oral mucosa with anticholinergic agents resulted in an increased permeability of certain compounds, and it was suggested that the reduced salivary flow may have been responsible for the reduced barrier properties of the tissue [113]. In... 

Nordbo H, Sorensen R and Sonju T (1977) Furfurals in chlorhexidine-discolored pellicle. Scand J Dent Res 85, 606-609. 

The gradual increase in the formamlde fraction to solution increased the elapsed time before schlieren patterns appeared. For the solution composition formamlde/acetone (40/60), slow convection flow appeared suddenly after 650 seconds, but the formation of the pellicle at the nascent membrane Interface could be clearly seen 15 seconds after submersion in the water bath. Such pellicles could not be discerned for solutions cast from THF or pure acetone. 

In B.C. they are usually separated distributionally, but intermediate forms occur in intermediate localities. In Japan they may be temporally separated.The allocation of Gymnodinium breve to Ptychodiscus depends on the presence of a pellicle. Although not seen with TEM it can be seen with light microscopy. Geographic distribution is closely linked to taxonomy for, although some toxin producers appear to be endemic in a restricted sense, closely similar forms occur elsewhere (e.g.p, brevis) or the same species may be known by different names in different regions ( Gyrodinium aureolum ). 

Isolation and sequencing of the cellulose synthase gene(s) has not been accomplished yet however, DNA from Acetobacter xylinum containing this gene(s) was cloned into broad host-range plasmid vectors (82). These vectors were mobilized into Pel- mutants to test for complementation. To date, this approach has not produced a pellicle-forming transconjugant from a Pel- mutant of Acetobacter (82). The direct correlation between cellulose production and presence of plasmid DNA in Acetobacter has been reported... 

The model in Figure 9 predicts that each microfibril would rotate in the process of cellulose ribbon formation. If the A. xylinum cell were held stationary, then the ribbon would be left-hand twisted (2-5) however, if the ribbon were held stationary, then the cell would rotate (32). The latter case explains why ribbons appear untwisted in the pellicle of ribbons shown in Figure 1. Moreover, it has been demonstrated that an A. xylinum cell ceased rotation when Calcofluor (> 0.1 mM) was added to the solution... 

Chlorhexidtne is a symmetrical cationic molecule that is most stable as a salt the highly water-soluble digluconate is the most commonly used preparation. Because of its cationic properties, it binds strongly to hydroxyapatite (the mineral component of tooth enamel), the organic pellicle on the tooth surface, salivary proteins, and bacteria. Much of the chlorhexidine binding in the mouth occurs on the mucous membranes, such as the alveolar and gingival mucosa, from which sites it is slowly released in active form. 

Remineralisation occurs when partly dissolved crystals are induced to grow by precipitation of the mineral-forming ions Ca + and POl". This is a natural process that occurs as a result of the concentration of these ions in saliva [23] and it serves to oppose the demineralising effects of caries. The processes involved are complex [24] and involve dynamic activity at the interface between the tooth, the saliva, the pellicle and the plaque. Fluoride plays a role in enhancing these processes, and though this is not the only contribution that fluoride makes to protect the tooth from caries, it is nonetheless an important one. 

It is now known that teeth undergo a continuous process of demineralisation and remineralisation (see Table 2), which is driven by changes in the plaque composition [29]. In the presence of fermentable carbohydrates plaque microorganisms generate characteristic organic acids, that is, lactic and acetic [17], and these diffuse through the pellicle to the tooth surface and cause demineralisation [30]. Ions are then liberated from the mineral phase into this low pH liquid [31], and they diffuse outwards and re-precipitate at the surface layer of the demineralised lesion [32,33]. If this process is sufficiently rapid, there is a net loss of tooth mineral and irreversible cavity formation. 

Soft Gelatin Capsules Dissolution (or disintegration, if justified), microbial bioburden, pH, leakage, and pellicle formation. 

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