health is an inextricable component in the well-being of mankind as it affects
the quality of one’s life by causing substantial pain and discomfort by
hindering an individual’s ability to talk, chew, smile, and speak (WHO, 2012). Human
oral cavity is heavily occupied by various microorganisms, most of which are
commensals such as bacteria, fungi, archaea, viruses and protozoa (Wade, 2013). However, oral
diseases are caused by alterations in the equilibrium of the complex ecosystem
in the oral cavity (Metwalli et
al., 2013). Poor oral hygiene, high intake of
fermented carbohydrate particularly sucrose, use of tobacco, stress and occurrence of diseases are some of the factors that contribute
to the alteration of the oral flora which leads to development of oral
diseases.  Being the most common disease
that affects mankind, oral disease is reported to be the fourth most expensive
disease to be treated in most low income or developing countries (Sheiham
and Yee, 2002). In addition, according to the U.S
Department of Health, 1998, about 4 to 8% of the global expenses are to treat
oral diseases (Werner et
al., 2016). “The lactic acid bacterium Streptococcus mutans and the yeast Candida albicans belong to the most
commonly found microorganisms in the oral cavity” (Krumina et
al., 2015).

Streptococcus mutans
are the causative agent of dental caries that occurs from the localised
dissolution of the tooth structure by a demineralization process that takes
place progressively through bacterial fermentation of dietary carbohydrates
that yields acidic by-products. The World Health Organization (WHO) has reported
that about 60-90% of school children and nearly 100% of adults are affected by
dental caries (WHO, 2012). In Malaysia alone, about 90% of the adults,
regardless of race are affected by dental caries, with ten tooth damaged by the
disease on average (NOHSA, 2010; Esa et al.,
Streptococcus mutans  are both acidogenic (acid-producing) and
aciduric (acid-tolerating). They are capable of fermenting sucrose and other
sugars to acid, leading to formation of carious lesions as a result from the
dissolution of tooth’s crystalline structure (Kabra et al., 2012) and produce acid constantly within the acidic
environment (Lee, 2014). In addition, Streptococcus
mutans produce extracellular polysaccharides (EPS) that facilitates
adherence and accretion of cariogenic bacteria, enhancing plaque formation on
tooth surfaces (Lee, 2014). Dental plaque is a complex biofilm consisting of a
community of microorganisms that develops naturally on tooth surfaces. The
microorganisms constituting the dental plaque plays a part in the defence
system of the host by protecting the oral cavity through colonization
resistance by hindering exogenous microorganisms which are often more
pathogenic (Babpour et al.,2009).
However, plaque build-up needs to be controlled by practicing good oral hygiene
as biofilm in the form of plaque is the causative perpetrator in dental caries
(Costerton et al., 1999; Gurenlian,
2007) because “microorganisms
growing in a biofilm are highly resistant to antimicrobial agents” (Donlan and Costerton, 2002).

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Although Streptococcus mutans are proven to be
the causative agent of dental caries (Loesche, 1986), recent findings
have reported the presence of Candida
albicans in carious lesions (Barbieri et al., 2007;
Metwalli et al., 2013), suggesting a synergistic activity between both
the microorganisms in the progression of dental caries. Evidently, in a study
done by Beighton et al., 1995, about 58.5% of Candida albicans were isolated
in carious lesions (Nikawa et al., 2003).  Apart
from implicated in dental caries, Candida
albicans also causes the most common fungal infection of the oral cavity,
known as oral candidiasis(Burket et al., 2008). Candida
albicans are part of the normal human microbiota. However, similar to Streptococcus mutans, overgrowth of the
Candida species results in disease  (Akpan and Morgan, 2002). The presence of the microorganism in the oral
cavity is estimated to range from 15% to 75% without any symptoms, in other
words, it remains benign (Ghannoum and Abu-Elteen, 1991; Akpan and Morgan,
2002). The fungi shifts from a harmless commensal to a disease causing pathogen
due to factors such as poor oral hygiene, compromised immune system, heavy
smoking, dental prosthetics and prolonged therapy with antibiotics (Akpan and
Morgan, 2002).  Overgrowth of Candida albicans must be controlled by
maintaining optimal oral hygiene as otherwise, the condition may lead to
discomfort and pain (Akpan and Morgan, 2002). The infection is more severe in
immunocompromised patients as the infection can be systemic, affecting the
entire body by spreading through the bloodstream or upper gastrointestinal
tract (Akpan and Morgan, 2002). The mortality rate for such condition ranges
from 71 to 79% (Fraser et al., 1992; Akpan
and Morgan, 2002)


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