Titanium dioxide nanoparticles in food and personal care products

Titanium dioxide is a common additive in many food, personal care, and other consumer products used by people, which after use can enter the sewage system and, subsequently, enter the environment as treated effluent discharged to surface waters or biosolids applied to agricultural land, incinerated wastes, or landfill solids. This study quantifies the amount of titanium in common food products, derives estimates of human exposure to dietary (nano-) TiO(2), and discusses the impact of the nanoscale fraction of TiO(2) entering the environment. The foods with the highest content of TiO(2) included candies, sweets, and chewing gums. Among personal care products, toothpastes and select sunscreens contained 1% to >10% titanium by weight. While some other crèmes contained titanium, despite being colored white, most shampoos, deodorants, and shaving creams contained the lowest levels of titanium (<0.01 μg/mg). For several high-consumption pharmaceuticals, the titanium content ranged from below the instrument detection limit (0.0001 μg Ti/mg) to a high of 0.014 μg Ti/mg. Electron microscopy and stability testing of food-grade TiO(2) (E171) suggests that approximately 36% of the particles are less than 100 nm in at least one dimension and that it readily disperses in water as fairly stable colloids. However, filtration of water solubilized consumer products and personal care products indicated that less than 5% of the titanium was able to pass through 0.45 or 0.7 μm pores. Two white paints contained 110 μg Ti/mg while three sealants (i.e., prime coat paint) contained less titanium (25 to 40 μg Ti/mg). This research showed that, while many white-colored products contained titanium, it was not a prerequisite. Although several of these product classes contained low amounts of titanium, their widespread use and disposal down the drain and eventually to wastewater treatment plants (WWTPs) deserves attention. A Monte Carlo human exposure analysis to TiO(2) through foods identified children as having the highest exposures because TiO(2) content of sweets is higher than other food products and that a typical exposure for a US adult may be on the order of 1 mg Ti per kilogram body weight per day. Thus, because of the millions of tons of titanium-based white pigment used annually, testing should focus on food-grade TiO(2) (E171) rather than that adopted in many environmental health and safety tests (i.e., P25), which is used in much lower amounts in products less likely to enter the environment (e.g., catalyst supports, photocatalytic coatings).

Influence of residual bacteria on periapical tissue healing after chemomechanical treatment and root filling of experimentally infected monkey teeth

The purpose of this study was twofold: first, to determine the influence on the healing of the periapical tissues when selected bacterial strains and combinations thereof remain after root canal treatment; and, second, the relationship to healing of the quality of the root filling. In eight monkeys, 175 root canals, previously infected with combinations of four or five bacterial strains and with radiographically verified apical periodontitis, were endodontically treated, bacteriologically controlled, and permanently obturated. After 2-2.5 yr, the periapical regions were radiographically and histologically examined. Of these teeth, 48 root canals were also examined for bacteria remaining after removal of the root fillings. When bacteria remained after the endodontic treatment, 79% of the root canals showed non-healed periapical lesions, compared with 28% where no bacteria were found. Combinations of residual bacterial species were more frequently related to non-healed lesions than were single strains. When no bacteria remained, healing occurred independently of the quality of the root filling. In contrast, when bacteria remained, there was a greater correlation with non-healing in poor-quality root fillings than in technically well-performed fillings. In root canals where bacteria were found after removal of the root filling, 97% had not healed, compared with 18% for those root canals with no bacteria detected. The present study demonstrates the importance of obtaining a bacteria-free root canal system before permanent root filling in order to achieve optimal healing conditions for the periapical tissues.

Apical periodontitis development and bacterial response to endodontic treatment. Experimental root canal infections in monkeys with selected bacterial strains

In six monkeys, 160 root canals were inoculated with a combination of four bacterial strains belonging to species Streptococcus milleri, Peptostreptococcus anaerobius, Prevotella oralis, and Fusobacterium nucleatum. In two other monkeys, 24 root canals were inoculated with a five-strain combination consisting of these strains and a strain of Enterococcus faecalis. All strains were previously isolated from an infected monkey root canal. After 8-12 months, survival of the strains was recorded bacteriologically, and the reaction in the periapical region was radiographed. From 180 of 184 root canals, one or more of the bacterial strains were reisolated. The two facultative strains were more frequently reisolated than the anaerobic strains. Apical periodontitis was registered in the periapical region of more than 96% of root canals with reisolated bacteria but in none of those without reisolated bacteria. Endodontic treatment was carried out in two sessions with an interval of 14 d without interappointment dressings, and the effect was evaluated bacteriologically before and after each treatment. The chemo-mechanical treatment reduced significantly the number of strains and bacterial cells. The facultative bacteria were more resistant to the treatment than the anaerobic bacteria. The five-strain combination had a higher survival rate than the four-strain combination.

Circulating antibodies after experimental chronic infection in the root canal of teeth in monkeys

Root canals of 49 teeth with necrotic pulp tissue in five monkeys were infected with Streptococcus faecalis ss liquefaciens, Actinomyces bovis, Fusobacterium nucleatum, Peptostreptococcus anaerobius, and Bacteroides oralis in various combinations. After 6 months the root canals and the periapical tissues were subjected to radiographic, bacteriologic, and histologic examinations. Signs of periapical inflammation were radiographically registered in 41 teeth, most frequently in teeth inoculated with a mixed flora. In 11 out of 16 teeth infected separately with Strep. faecalis ss liquefaciens, apical periodontitis was observed. Sera from the monkeys prior to and after the experimental inoculation were analyzed by means of gel diffusion, hemagglutination (HA), and complement binding test for antibodies against different antigen preparations of the homologous bacterial strains used for the inoculation. Detectable antibodies were seen with antigens of B. oralis in all five monkeys. Agglutinating antibodies were demonstrated with lipopolysaccharide-antigen of B. oralis in titers between 1:40 and 1:320. A marked reduction of the antibody level against lipopolysaccharide (LPS) antigen after mercaptoethanol treatment indicated that a main part of the antibodies registered was of IgM-class. The study shows that certain antigens of bacterial origin from infected root canals, while affecting the periapical tissues, also stimulate the production of circulating antibodies.

Apical periodontitis induced by selected bacterial strains in root canals of immunized and nonimmunized monkeys

Experimental infections in root canals with Streptococcus faecalis ss. liquefaciens (Strep-MC4). Actinomyces bovis (Act-MC6) and Bacteroides oralis (Bact-MC3) were studied in four immunized and five nonimmunized monkeys. The immunization was performed using antigens of the homologous strains. The antibody level was checked by gel diffusion. In 56 root canals of the immunized animals and 60 root canals of the nonimmunized animals, viable cells of the three bacterial strains were enclosed in equal amounts of various combinations. After 6 months, samples from the root canals were subjected to qualitative and quantitative bacteriologic analyses and the apical area was radiographically and histologically examined. The analyses revealed no significant difference between the two groups of monkeys, although the viable cell recovery was slightly higher in most of the root canals of nonimmunized monkeys. The cell proportion of the strains within the different bacterial combinations was equal in root canals of the two groups of animals. The radiographic and histologic examinations revealed no significant difference between the two groups of animals regarding the number of teeth with periapical lesions. The radiographic examination, however, showed a more distinct limitation of the process in the immunized than in the nonimmunized monkeys. Histologically the lesions were more encapsulated and had a sparser cell infiltration in immunized than in nonimmunized monkeys. In the latter, inflammatory cells had often infiltrated the bone. Mixed infections gave a more severe periapical reaction than single strain infections in both animal groups.

Influence of combinations of oral bacteria on periapical tissues of monkeys

The present study deals with the ability of 11 bacterial strains, in various combinations, to induce periapical reactions. The indigenous oral bacteria were originally isolated from an experimental apical periodontitis in monkey. Eight of the strains were complete collection isolated from one root canal. These strains were inoculated together, in equal proportions, into 12 root canals. In addition, 63 canals were inoculated with other combination or separate strains. At the end of the experimental period it was found that in the mixed infections the Bacteroides oralis strain predominated in most root canals. In contrast, this Bacteroides strain was not reisolated in any of nine root canals when inoculated in a pure culture. Enterococci, however, survived as pure cultures in all canals. The mixed infections showed the greatest capacity of inducing apical periodontitis, as revealed by radiography, and most pronounced was the "eight-strain collection". The facultatively anaerobic streptococci induced only weak periapical reactions.

Predominant indigenous oral bacteria isolated from infected root canals after varied times of closure

The pulps of 24 root canals, eight in each of the three monkeys, were mechanically devitalized and exposed to the mouth flora for about 1 week and thereafter sealed. Microbiologic sampling and analysis was performed in 16 teeth (two of the monkeys) after 7 d of closure (initial samples). The teeth of the three monkeys represented observation times of 90, 180 and 1060 d. At the end of each observation period final samples were taken. Final sampling included samples from the main root canal, the dentin, and the apical region at the same sampling session. All microbiologic analyses were carried out quantitatively. Final root canal samples from the apical region showed a predominance of obligately anaerobic non-sporulating bacteria, in fact 85-98% of the bacterial cells were anaerobic. The most frequently found species were Bacteroides and Gram-positive anaerobic rods. A lower proportion of facultatively anaerobic bacteria was found. This was most pronounced for coliform rods in comparison with strains of B. melaninogenicus.

Influence on periapical tissues of indigenous oral bacteria and necrotic pulp tissue in monkeys

In nine monkeys (Macaca fascicularis) the pulps of 78 teeth were aseptically necrotized. Twenty-six of the pulp chambers were kept bacteria-free by sealing, while 52 were infected by the indigenous oral flora. The results were recorded clinically, radiographically and microbiologically at the beginning of the experiment and after 6-7 months. The final examination also included histologic recordings. The initially noninfected root canals were all sterile at the final samplings, indicating that the risk of contamination (including hematogenous) of root canals of this animal is very slight. It was shown that noninfected necrotic pulp tissue did not induce inflammatory reactions in the apical tissues. By contrast, teeth with infected pulp tissue showed inflammatory reactions clinically (12/52 teeth) and radiographically (47/52 teeth). Facultatively anaerobic streptococci, coliform rods and obligately anaerobic bacterial strains were most frequently found. In the final samples the number of obligately anaerobic strains increased. Some microorganisms which were isolated in the initial samples were not detected in the final samples. All infected teeth histologically examined showed strong inflammatory reactions in the periapical region.