Some probiotics have been shown to have preventive effects on infectious diseases and allergies. Because their long-term enhancement of the immune responses of children, they have been recommended for infants in some countries. The most promising ones seem to be the combination of Bifidobacterium lactis BB-12 and Lactobacillus rhamnosus GG. Probiotic microbes are mainly ingested orally and the gastrointestinal tract is thus the primary target organ for them. However, the mouth is the first part of the gastrointestinal tract. Most probiotics are in theory cariogenic, thus their effects on oral health should be known. Several probiotics decrease levels of salivary mutans streptococci (MS), but in other respects very little is known about their effects on the oral microbiota. Also effects of probiotics on dental plaque should be studied. This study aims to find out the effects of the combination of BB-12 and LGG, delivered with a lozenge (4 weeks, twice a day) with a mixture of them on the amount of plaque and gingival health

The Food and Agriculture Organization (FAO) of the United Nations and the World Health Organization (WHO) have defined probiotics as "live micro-organisms, which when administered in adequate amounts, confer a health benefit to the host" (WHO 2002). They should preferably be of human origin, be able to temporarily colonize the gastrointestinal tract and survive in it. They must also be non-pathogenic and non-toxic.

Probiotics are used in the prevention and treatment of infectious diseases and allergies (Hatakka and Saxelin, 2008; Salminen et al., 2010). In some countries probiotics are recommended for infants and adults because of their long-term enhancement of the immune responses. Combinations of probiotics, like Bifidobacterium lactis BB-12 (BB-12) and Lactobacillus rhamnosus GG (LGG), appear to be most effective in this respect (Isolauri et al., 2000; Rautava et al., 2009; Smith et al., 2012). Probiotics are mainly ingested orally, and the gastrointestinal tract is thus the primary target organ for probiotic micro-organisms. However, when ingested in the form of for example tablets, chewing gums, cheese and milk, the oral cavity is exposed to the probiotics. With the world-wide increase in the use of probiotics their effects of on oral health have become a hot topic.

Many types of probiotic bacteria have been explored but the most widely studied species are those that belong to the genera Lactobacillus and Bifidobacterium. Yogurt and fermented milk products are considered the simplest source of probiotic administration for humans. The proven effects of probiotics in general health has led to more research in the oral health field including dental caries, periodontal disease and halitosis. Some clinical studies have demonstrated a decrease in the cariogenic mutans streptococci counts and in dental plaque (Näse et al. 2001, Ahola et al. 2002, Nikawa et al. 2004, Caglar et al. 2007, Twetman & Keller 2012). Probiotics have also shown improvements in the periodontal status in patients with periodontal disease (Riccia et al. 2007, Shimauchi et al. 2008, Teughels et al. 2013, Yanine et al. 2013). Recently, Toiviainen et al. (2015) found that the combination of Lactobacillus rhamnosus GG (LGG) and Bifidobacterium strain Bifidobacterium lactis (BB-12) improved the periodontal health in healthy adults by reducing the plaque amount and subsequently the gingival inflammation without affecting the oral microbiota.

More evidence is necessary to confirm the efficacy of the combination of LGG and BB-12 in the oral health.

Inclusion Criteria:

• Healthy Adolescent - ASA I & II
• No Antibiotics use
• No intake of commercially available probiotics products during the intervention

Exclusion Criteria:

• Adolescents have ASA III or IV
• Antibiotics use
• refuse to stop taking commercially available probiotics products during intervention

Sample size determination was based on the data by Toiviainen et al. (2015). A sample size of 104 subjects (92 + 10% to provide cover in case of subject drop out) was predicted to provide 80% power with an α of 0.05.

4 weeks

limitations of this study include:

1. short period: only 4 weeks to reach maximum compliance
2. number of participants: just above the minimum sample size due to refusal of many parents to give consent for their children participation.