This study aimed to define the healthy oral microbiome using advanced sequencing technology (454 pyrosequencing). The researchers sampled and sequenced microbiomes from various intraoral niches (dental surfaces, cheek, hard palate, tongue, and saliva) in three healthy individuals. They found over 3600 unique sequences, 500 different operational taxonomic units (OTUs), and 88-104 higher taxa within each individual's oral cavity. The predominant taxa belonged to Firmicutes, Proteobacteria, Actinobacteria, Bacteroidetes, and Fusobacteria. Each sample harbored an average of 266 "species-level" phylotypes, with cheek samples being the least diverse and dental samples from approximal surfaces showing the highest diversity. Principal component analysis discriminated samples from shedding surfaces (mucosa) from those from solid surfaces (teeth). There was a significant overlap in higher taxa, phylotypes, and unique sequences among the three microbiomes, with 84% of higher taxa, 75% of OTUs, and 65% of unique sequences present in at least two of the three microbiomes. The study concluded that a major proportion of bacterial sequences of unrelated healthy individuals are identical, supporting the concept of a core microbiome at health.This study aimed to define the healthy oral microbiome using advanced sequencing technology (454 pyrosequencing). The researchers sampled and sequenced microbiomes from various intraoral niches (dental surfaces, cheek, hard palate, tongue, and saliva) in three healthy individuals. They found over 3600 unique sequences, 500 different operational taxonomic units (OTUs), and 88-104 higher taxa within each individual's oral cavity. The predominant taxa belonged to Firmicutes, Proteobacteria, Actinobacteria, Bacteroidetes, and Fusobacteria. Each sample harbored an average of 266 "species-level" phylotypes, with cheek samples being the least diverse and dental samples from approximal surfaces showing the highest diversity. Principal component analysis discriminated samples from shedding surfaces (mucosa) from those from solid surfaces (teeth). There was a significant overlap in higher taxa, phylotypes, and unique sequences among the three microbiomes, with 84% of higher taxa, 75% of OTUs, and 65% of unique sequences present in at least two of the three microbiomes. The study concluded that a major proportion of bacterial sequences of unrelated healthy individuals are identical, supporting the concept of a core microbiome at health.