BackgroundThe ecological plaque hypothesis explains caries development as the result of the enrichment of acid tolerant bacteria in dental biofilms in response to prolonged periods of low pH. Acid production by an acid tolerant microflora causes demineralisation of tooth enamel and thus, individuals with a greater proportion of acid tolerant bacteria would be expected to be more prone to caries development. Biofilm acid tolerance could therefore be a possible biomarker for caries prediction. However, little is known about the stability of biofilm acid tolerance over time in vivo or the distribution throughout the oral cavity. Therefore the aim of this study was to assess intra-individual differences in biofilm acid-tolerance between different tooth surfaces and inter-individual variation as well as stability of acid tolerance over time.ResultsThe majority of the adolescents showed low scores for biofilm acid tolerance. In 14 of 20 individuals no differences were seen between the three tooth sites examined. In the remaining six, acid-tolerance at the premolar site differed from one of the other sites. At 51 of 60 tooth sites, acid-tolerance at baseline was unchanged after 1 month. However, acid tolerance values changed over a 1-year period in 50% of the individuals.ConclusionsBiofilm acid tolerance showed short-term stability and low variation between different sites in the same individual suggesting that the acid tolerance could be a promising biological biomarker candidate for caries prediction. Further evaluation is however needed and prospective clinical trials are called for to evaluate the diagnostic accuracy.

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BackgroundA newly developed, anodized titanium oxide surface containing anatase has been reported to have antimicrobial properties that could reduce bacterial adherence to abutments.PurposeTo investigate if abutments with the anodized surface improve healing and soft tissue health in a randomized controlled study.Materials and MethodsTest abutments with a nanostructured anodized surface were compared with control machined titanium abutments. In total, 35 subjects each received a pair of test and control abutments. The primary endpoint was reduction of biofilm formation at test abutments at the 6‐week follow‐up. Secondary endpoints included several soft tissue assessments. qPCR for gene markers was used to indirectly evaluate healing and soft tissue health.ResultsNo significant differences in biofilm formation were observed between test and control abutments, but soft tissue bleeding upon abutment removal was significantly lower for test abutments compared with control abutments (P = 0.006) at 6 weeks. Keratinized mucosa height was significantly greater at test abutments compared with control abutments at the 6‐week, 6‐month, and 2‐year follow‐ups. Significant gene expression differences indicated differences in healing and tissue remodeling.ConclusionsAbutments with an anodized and nanostructured surface compared with a conventional, machined titanium surface had no significant effect on bacterial colonization and proteolytic activity but were associated with better soft tissue outcomes such as a lower bleeding index at abutment removal and consistently greater height of keratinized mucosa throughout the 2‐year follow‐up, suggesting improved surface‐dependent peri‐implant healing and soft tissue health.

Background In caries, low pH drives selection and enrichment of acidogenic and aciduric bacteria in oral biofilms, and development of acid tolerance in early colonizers is thought to play a key role in this shift. Since previous studies have focussed on planktonic cells, the effect of biofilm growth as well as the role of a salivary pellicle on this process is largely unknown. We explored acid tolerance and acid tolerance response (ATR) induction in biofilm cells of both clinical and laboratory strains of three oral streptococcal species (Streptococcus gordonii, Streptococcus oralis and Streptococcus mutans) as well as two oral species of Actinomyces (A. naeslundii and A. odontolyticus) and examined the role of salivary proteins in acid tolerance development. Methods Biofilms were formed on surfaces in Ibidi® mini flow cells with or without a coating of salivary proteins and acid tolerance assessed by exposing them to a challenge known to kill non-acid tolerant cells (pH 3.5 for 30 min) followed by staining with LIVE/DEAD BacLight and confocal scanning laser microscopy. The ability to induce an ATR was assessed by exposing the biofilms to an adaptation pH (pH 5.5) for 2 hours prior to the low pH challenge. Results Biofilm formation significantly increased acid tolerance in all the clinical streptococcal strains (P < 0.05) whereas the laboratory strains varied in their response. In biofilms, S. oralis was much more acid tolerant than S. gordonii or S. mutans. A. naeslundii showed a significant increase in acid tolerance in biofilms compared to planktonic cells (P < 0.001) which was not seen for A. odontolyticus. All strains except S. oralis induced an ATR after pre-exposure to pH 5.5 (P < 0.05). The presence of a salivary pellicle enhanced both acid tolerance development and ATR induction in S. gordonii biofilms (P < 0.05) but did not affect the other bacteria to the same extent. Conclusions These findings suggest that factors such as surface contact, the presence of a salivary pellicle and sensing of environmental pH can contribute to the development of high levels of acid tolerance amongst early colonizers in oral biofilms which may be important in the initiation of caries.