THE HUMAN MOUTH AS A BIOREACTOR

Today we are looking at something close and personal to us; our own mouth or our buccal cavity. But rather than looking at the mouth from the anatomical or physiological approach which interest the dental and the medical profession, we will be looking at the mouth from the point of view as a fermentor or bioreactor.

Many dental researchers in trying to understand the various microbiological and biochemical changes occurring in the mouth have always regarded the mouth as a continuous bioreactor or fermentor. In a way they are right in thinking so as the mouth does show many characteristics of a fermentor with the presence of high concentration of microorganisms and input of nutrients, food and oxygen in the fermentation broth of the saliva. The mouth does its function quite well by providing various micro habitats that support the growth of various types of microorganisms.

However, that is where the similarity ends. In treating the mouth as a bioreactor there is never the real intention in nature to cultivate high concentration of microorganisms as these microorganisms are responsible for various oral pathological problems. Secondly, even though in terms of functions the mouth is a bioreactor, but in its design and structure it differs from the construction of a normal fermentor. It is often the classical mistake of dental researchers in trying to understand the changes in the mouth, they would use normal fermentors to study the happenings of the mouth in vitro rather than in vivo. Although studying in vivo is far more difficult but more meaningful

We cannot say any conclusion based on lab scale fermentors can be really applicable to real understanding of the bioprocesses in the mouth if we cannot come with the accurate bioreactor model of the mouth.It is not good to oversimplify the bioreactor design and try to reach far reaching conclusions

We shall now look at the mouth as a bioreactor from the various points below:

THE VESSEL
-------------
From the point of view of the mouth as a fermentor or bioreactor, it is a vessel or container defined by the lips, cheeks, hard and soft palates, and glottis It is divided into two sections: the vestibule, the area between the cheeks and the teeth, and the oral cavity proper. It is not really well designed in terms of reactor geometry and therefore do not encouraged ideal mixings or circulations of the liquid in the mouth

THE STIRRER
---------------
The stirrer of the mouth bioreactor is the tongue. The efficiency of stirring carried by the tongue is not as efficient as the stirrer in fermentor, as in most times the tongue do not really move actively except when food or drink is introduced into the mouth or perhaps in 'french kissing'

FLUID CIRCULATION
---------------------
The endogenous source of fluid in the mouth bioreactor is provided by the salivary glands in the mouth which secretes the saliva periodically by the ducts into the mouth. There is not much saliva produced with the saliva amounting to about 1500 ml daily

The saliva liquid are generally viscous, making the environment rapidly anaerobic unless often oxygenated .

There are two main types of saliva circulation in the mouth:
1 General mixing circulation most times
2 Plug flow circulation periodically especially when swallowing saliva or food bolus


FEED
--------
The fermentor feed basically consist of food and drinks which we take in through the mouth regularly at intervals. Thus the mouth bioreactor is more a fed batch reactor. However when we are sleeping, there is no input of new feed until breakfast and the mouth will be in the batch mode when we are sleeping

AIR
------
Air is taken into the mouth during food and drink intake activities


SOURCE OF MICROORGANISMS
----------------------------------
The mouth as a bioreactor can be considered as a mixed culture septic bioreactor. The source of microorganisms could be introduced naturally and/or formed as natural oral flora of the human body. Sad to say, the mouth is a very dirty and disgusting place where all kinds of decompositions take place

ENVIRONMENTAL AND NUTRITIONAL PARAMETERS
---------------------------------------------------------
The mouth is an ideal environment which can support high concentration of microorganisms because it provide:
1 Water
2 Good temperature
3 Food or nutrients
4 Nice ph between 6.5 to 7.5
6 Lots of surfaces for microorganisms to hide and attach such as the surfaces of tongu and teeth
7 mixing for good mass transfer