Biofilm And Plaque --Precursors to Dental Diseases

The Diseases of the gums can broadly be classified into

• Gingivitis
• Periodontitis

GINGIVITIS is defined as an inflammation of the GINGIVA only.When the inflammation progresses to the other parts of the PERIODONTIUM it is termed as PERIODONTITIS.

Before we go into the nitty gritty world of gingivitis let,s understand the beginning of gum disease.

Many of you will be wondering that this is not possible as I take care of my teeth to the nth degree, but my friends don't forget about the bad bacteria lurking in your mouth!!!

As soon as we brush our teeth squeaky clean we remove any growth or covering on our tooth surfaces.

But this does not remain so as our teeth are constantly under a wet environment. The first step in plaque biofilm development is the 
adsorption of host and bacterial molecules to the tooth surface.

 Within minutes of tooth eruption or a cleaning, PELLICLE 

formation begins, which can be defined as a thin coat of salivary 

proteins. The pellicle acts like an adhesive 

by sticking to the tooth surface and encouraging a conditioning film

 of bacteria to attach to the pellicle. This 

conditioning film directly influences the initial microbial 

colonization, and continues to adsorb bacteria to the

 tooth surface.This early composition of the biofilm is able to 

withstand many of the frequent mechanisms of the oral cavity that

 contribute to bacterial removal such as swallowing, nose blowing, 

chewing, and salivary 

fluid outflow. The early colonizers are also able to survive in the 

high oxygen concentrations present in the 

oral cavity, without having much protection from other bacteria .

 Thus, this thin, initial biofilm is almost always 

present on the tooth surface as it forms immediately after cleaning. 

Passive Transport of Oral Bacteria to the Tooth Surface

Following pellicle formation, there is passive transport of oral 

bacteria to the tooth surface, which involves a reversible adhesion

 process. By using weak, long-range physicochemical interactions

 between the pellicle coated tooth surface and the microbial cell

 surface, an area of weak attraction is formed that encourages the 

microbes to reverse their previous adhesion to the pellicle and come 

off the tooth surface (hence the term "reversible adhesion"). This 

reversible adhesion then leads to a much stronger, irreversible 

attachment, as short-range interactions between specific molecules

 on the bacterial cells and the complementary receptor proteins on

 the pellicle surface occur. Because many oral microbial species

 have multiple adhesion types on their cell surface, they can thus

 participate in a plethora of interactions with both other microbes 

and with the host surface molecules.

 

Co-Adhesion of later colonizers to already attached early colonizers

The co-adhesion of the later colonizers to the already

 present biofilm continues to involve many specific 

interactions between bacterial receptors and adhesions.

 These interactions build up the biofilm to create a more

 diverse environment, which includes the development of

 unusual morphological structures like corn-cobs and 

rosettes.

The many interactions between these diverse bacterial 

species begin to create a number of synergistic and 

antagonistic biochemical interactions. For example, bacterial 

residing in food chains may help to contribute metabolically 

with other bacteria if they are located physically close to one

 another. Similarly, when obligate anaerobes and aerobes 

are involved in co-adhesion, these interactions can ensure 

the anaerobic bacteria’s survival in the oxygen-rich oral 

cavity.

Multiplication of the Attached Microorganisms

Eventually, the bacterial cells continue to divide until a three-

dimensional mixed-culture biofilm forms that is spacially and 

functionally organized. Polymer production causes the

 development of the extracellular matrix, which consists of

 soluble and insoluble glucans, fructans, and

 heteropolymers. This matrix is one of the key structural

 aspects of the plaque biofilm, much like that of other

 biofilms. Biofilms such as this are very thick, consisting of

 100-300 cell layers. The bacterial stratification is arranged

 according to metabolism and aerotolerance, with the

 number of gram-negative cocci, rods and filaments

 increasing as more anaerobic bacteria appear. As the

 biofilm thickens and becomes more mature, these anaerobic 

bacteria can live deeper within the biofilm, to further protect 

them from the oxygen-rich environment within the oral 

cavity.This biofilm is now composed of a variety of bacteria 

and is now known as DENTAL PLAQUE.

Plaque formation

At 24 hours the maturing dental plaque contains a wide variety of bacteria and it is possible to detect easily identifiable inter-species associations such as the well documented "corn-cob-configurations", although a wide variety of other inter-species associations will be present.

Further colonisation and growth of established bacteria takes place as the plaque matures to form a stable, climax, community. This pattern of development leading to a climax community has been termed "bacterial succession". The resulting community consists of individual microbes and microcolonies acting in complex consortia which can convey a range of beneficial properties. These include feeding synergies, improved antibiotic resistance and a host of cooperative mechanisms which are the subject of much current research.

Plaque response to environmental change

Although mature plaque has a degree of stability conferred by inter-species cooperativity, physical and metabolic associations and its actual physical density it does respond to environmental change albeit slowly. The best recorded response is that due to changes in diet.

High protein diet

Plaque formed on the teeth of individuals with a low carbohydrate, high protein diet, contains fewer acidogenic-aciduric organisms. The pH gradient will be different and the overall pH of the plaque alkaline because of the ammonia produced as a by-product of amino acid breakdown. The higher pH of the plaque will itself inhibit acidogenesis and favour Gram negative organisms which will be present in greater numbers. The proteolytic nature of the plaque will result in the presence of particular peptides such as putrescene and cadaverine which have a characteristic offensive odour.

High carbohydrate diet

If this same individual, previously on a high protein, low carbohydrate diet switched to a low protein, high carbohydrate diet the formed plaque would slowly adjust its microbiological composition. The resting pH of the plaque would reduce to somewhere between pH 6.3 to 6.8 (figures are approximate) as a result of the production of organic acid by-products from the fermentation of carbohydrate. This lower, more acid, pH favours aciduric organisms such as streptococci and lactobacilli and the proportion of these would greatly increase. This would be coupled with a reduction in the numbers of Gram negative anaerobic rods which do not flourish under these conditions.

High sucrose

If the change in diet included an increase in sucrose consumption then the plaque matrix would contain large amounts of extracellular polysaccharides of both the fructan and glucan variety.

Frequent carbohydrate

If the diet included frequent intake of carbohydrate eg snacking on confectionary then the plaque would contain significantly increased numbers of highly aciduric organisms such as Streptococcus mutans and lactobacilli.

Time scale

These changes would occur over a time period of a few days even if the plaque had not been removed from the teeth when the diet changed. It follows that individuals on such extremes of diet produce such characteristic plaque even though they practice normal oral hygiene.