**1. Introduction**

202 Contemporary Approach to Dental Caries

[35] Stephen KW, Creanor SL, Russell JI, Burshell CK, Huntington E, Downie CFA. A 3-year

[36] WalshT, Worthington HV, Glenny AM, Appelbe P, Marinho VC, Shi X. Fluoride

[37] Winter GB, Holt RD, Williams F. Clinical trial of a low –fluoride toothpaste for young

adolescents. Cochrane Database Syst Rev.2010 Jan 20(1):CD007868.

1988;16:321-5.

children. Int Dent J 1989;39:227-235.

oral health response study of sodium monofluoro-phosphate dentifrice with and without zinc citrate: anticaries results. Community Dent Oral Epidemiol

toothpaste of different concentrations for preventing dental caries in children and

The advancement of technology through the application of molecular techniques for identification and analysis of complex bacterial communities have demonstrated the diversity of the oral microbiota and the presence of numerous strains not previously described. Dental plaque is formed by the initial adhesion of pioneer bacterial species to film acquired from enamel, followed by secondary co-aggregation of these bacteria to other microorganisms of different genera and species. This mature dental plaque has some characteristics of multicellular organisms, such as cooperation mechanisms to obtain nutrients, resistance to environmental and communication stresses in order to regulate their growth (Marsh and Martin, 2009).

The understanding of the dental plaque structure as a microbial biofilm sheds light on the clinical relevance of antimicrobials usage (Zanatta et al, 2007). Biofilms have a more tolerant phenotype to antimicrobial agents, stress and host defenses than planctonic cultures, making them difficult to control (Socransky and Haffajee, 2002). This means that the effectiveness of agents used to prevent dental caries, specifically those compounds targeted to combat cariogenic pathogens, should be evaluated in biofilms rather than in traditional liquid cultures (Tenover, 2006). According to Wade (2010), high concentrations of Chlorhexidine (CHX) nearly eliminate all cells, and this is not interesting for microbiota balance in the oral biofilm. Successful antimicrobial agents are able to maintain the oral biofilm at levels compatible with oral health but without disrupting the natural and beneficial properties of the resident oral microflora (Marsh, 2010).

In this chapter, the etiology of dental caries will be briefly introduced focusing on the role of biofilms for initiation and progression of this disease. It will be followed by a thorough review of literature taking into account recent and novel antimicrobial strategies for biofilm control. Recent advances in anti-plaque agents, including those chemoprophylactic, antimicrobial peptides (anti-quorum sensing approach) and probiotics/replacement therapy will be analyzed. Both the discovery of new and effective drugs to control pathogenic

Microbial Dynamics and Caries: The Role of Antimicrobials 205

Biofilm communities are complex and dynamic structures that accumulate through sequential and ordered colonization of multiple oral bacteria (Kolenbrander et al., 2002). The development of a biofilm like dental plaque can be divided arbitrarily into several distinct

*Adsorption of host and bacterial molecules to the tooth surface to form of a conditioning film* (acquired pellicle). Pellicle forms immediately following eruption or cleaning (Al-Hashimi and Levine, 1989) and directly influences the pattern of initial microbial colonization

*Passive transport of oral bacteria to the pellicle-coated tooth surface*. A non-specific reversible phase involving physic-chemical interactions among salivary bacteria and acquire enamel pellicle creates a weak area of net attraction facilitating reversible adhesion. Subsequently, strong, short-range interactions between specific molecules on the bacterial cell surface (adhesins) and complementary receptors in the pellicle can result in irreversible attachment (Lamont & Jenkinson, 2000) and can explain microbial tropisms towards surfaces. Many oral

*Co-aggregation (co-adhesion) of later colonizers to already attached early colonizers*. This coaggregation that also involves specific interbacterial adhesion-receptor interactions (often involving lectins) leads to increased biofilm diversity (Kolenbrander et al., 2000). Co-adhesion

*Multiplication of attached microorganisms to produce confluent growth*: Cell division leads to confluent growth and eventually, a three-dimensional spatially and functionally organized mixed-culture biofilm. Dental plaque functions as a true microbial community in which

*Active bacteria detachment from surfaces*: Bacteria can respond to environmental cues and

It has been suggested that oral biofilm formation consisted of two process involving separate mechanisms (Gibbons and van Houte, 1973). The first process was associated with adsorption of cells to the pellicle and required specific adhesions on the cell surface. The second step

Bacterial accretion through co-adhesion drives the temporal development of plaque biofilms that is characterized by bacterial successions and occurs over a time frame of weeks. The early biofilm consisted of pioneer organisms deposition followed by multiplication in morphologically distinct palisading columns of cocci (Rosan and Lamont, 2000). Pioneer species are predominantly streptococci (*S. sanguis*, *S. oralis* and *S. mitis*) (Marsh and Bradshaw, 1995). Although the oral streptococci initially predominate in plaque and can constitute up to 80% of early plaque, another significant colonizing species is *Actinomyces* 

Single cells of mainly Gram-positive coccoid cells can be seen by microscopy on pelliclecoated surfaces, together with a few rod-shaped organisms, after few hours (2-4h) of plaque formation (Marsh and Bradshaw, 1995). The attached cells then divide rapidly to form microcolonies in the first instance, which coalesce to form a confluent film of varying

may also facilitate the functional organization of dental plaque (Bradshaw et al., 1998).

properties are greater than the sum of the component species (Marsh, 2004).

involved a build-up of cells biding to each other in a process termed co-adhesion.

detach from surfaces, enabling cells to colonize elsewhere.

*naeslundii*, and some haemophili (Rosan and Lamont, 2000).

thickness (Nyvad and Fejerskov, 1989).

bacteria possess more than one type of adhesion on their cell surface.

phases:

(Marsh, 2004).

biofilms as well as new delivery systems for oral environment will be the future focus of this research field.
