Estimation procedures and optimal designs for estimation of the individual parameters and of the global parameters are discussed under various conditions of prior knowledge. The extension to nonlinear parametrization of the response function ís based on the asymptotical validity of the results for the linear parametrization. For the case where the error variance and the dispersion matrix are unknown, an iterative estimation procedure is suggested. An example based on dental plaque pH profiles demonstrates the improvement that is achieved (a) through using the optimal design or a design that ís close to the optimal, and (b) through taking into account prior information. (author's abstract) / Series: Forschungsberichte / Institut für Statistik

Xylitol, classified as a natural sugar substitute, has for about 35 years been known as an agent that may act against caries. The mechanism of action; how it inhibits mutans streptococci (MS) and the clinical dose-response relationship are not however fully investigated. The general aim of the investigations was to evaluate the effect of xylitol on oral ecology in children and adolescents. A series of experimental and controlled clinical trials were performed in which samples of saliva and plaque was collected and analysed with respect to xylitol content, pH, microbial composition and lactic acid production. In paper I, significantly reduced proportions of xylitol-sensitive MS in saliva were demonstrated after 18 weeks of regular use of two dose regimens of xylitol-containing tablets (1.7g and 3.4g xylitol/day) but the acidogenicity in dental plaque was not affected. In paper II, the effect on interdental plaque-pH of two different single dose intakes (2.0g and 6.0g) of xylitol was evaluated. The higher xylitol dose counteracted the pH-drop significantly (p<0.05) when the chewing was followed by a sucrose rinse while the lower dose did not differ from the control. In paper III, the xylitol concentrations in saliva after use of different common xylitol-containing products (0.1g-1.3g) were investigated. Statistically significant elevations of salivary xylitol levels were demonstrated for all products during the first 8-16 min when compared with baseline (p<0.05) but the individual variation was considerable. In samples of supragingival dental plaque, a high dose rinse (6.0g) increased the xylitol concentrations for a longer period (>30 min) than a low dose rinse (2.0g). In paper IV, it was demonstrated that 6.0g of xylitol in chewing gums, every day in 4 weeks, gave significantly less visible plaque and a significantly reduced sucrose-induced lactic acid formation (p<0.05) in saliva. Furthermore, the proportion of MS decreased significantly (p<0.05) compared to baseline. In paper V, the salivary uptake of [14C]-xylitol was compared with a specific assay determining xylitol-sensitive MS and a fair positive correlation (p<0.05) between the two assays was found. In a controlled trial, the proportions of MS and the salivary xylitol uptake decreased significantly (p<0.05) in the xylitol gum test group after 4 weeks compared to baseline which was in contrast to the control gum group. No serious adverse effects were reported in any of the investigations. The main conclusions from this thesis were: a) various xylitol-containing products increased the xylitol levels in saliva and plaque, b) 6.0g of xylitol could counteract the interdental pH-drop after sugar consumption and reduce lactic acid formation in saliva c) a daily dose of 6.0g xylitol reduced the amount of visible plaque and altered the salivary microbial composition, d) a transient shift of MS strains in saliva was demonstrated during periods of regular intake of xylitol products but no long-term impact was found after its termination. The relatively high amount of xylitol needed for a beneficial effect on the oral ecology calls for a further development of effective and safe routes for administration.

The prevalence of dental caries has decreased dramatically in most developed countries since the sixties and the number of remaining teeth in adults has increased during the last decades. Elderly as a group will during aging become an increasing risk group for caries. Especially older individuals with hyposalivation are at increased risk for coronal and root caries and need increased oral care. A large part of the time spent by the dental team is occupied by prevention and treatment of secondary caries, which is the main reason of replacement or repair of restorations. Traditionally, prevention of caries is directed against the different risk factors of the individual such as oral hygiene, intake of fermentable carbohydrates, cariogenic microflora and oral dryness. In some restorative materials the release of fluoride can be used to decrease the risk of secondary caries alone or in combination with other preventive methods. New alternative preventive methods are necessary to complete traditional methods in order to decrease the caries risk in elderly and/or to prevent secondary caries. Addition of methods with buffering properties have been suggested and developed to supplement the biological buffering capacity of saliva. The neutralizing effects of a hydroxyl ion-releasing resin composite and a prophylactic gel containing buffering properties on dental plaque acidogenicity was evaluated by the microtouch method. In this method, a skin reference electrode was validated in comparison with a glass capillary reference electrode and used in the subsequent studies. Change of plaque acidogenicity on proximal surfaces of aged restorations of the hydroxyl ion-releasing resin composite was compared intra-individually a conventional hybrid resin composite and a non-filled enamel proximal surface. Relative frequencies of cariogenic microorganisms in plaque on these surfaces were studied. The effect of a single application of the prophylactic gel with buffering substances was evaluated on plaque acidogenicity in healthy individuals with low and normal salivary secretion rate. It was compared intra-individually with the same gel without buffering substances. The effect of multiple applications of the prophylactic gel on plaque acidogenicity was studied in institutionalized elderly individuals with subjectively reported oral dryness and compared intra-individually with the same gel without buffering substances. Major results and conclusions from the studies are: • The use of the skin reference electrode, in combination with the microtouch electrode, showed high validity in comparison with the conventional glass capillary reference electrode • The hydroxyl ion-releasing composite resin countered plaque acidogenicity fall at two time points of the aged restorations and maintained it at levels where lesser demineralization occurs. No influence of the ion-release on the amount of cariogenic plaque microorganisms on the resin composite surface was observed • A single application of the prophylactic gel with buffering substances showed a neutralizing effect of plaque pH in healthy individuals with normal salivary secretion rate. No effect was observed in low secretion rate individuals. • Multiple applications of the prophylactic gel did not neutralize dental plaque acidogenicity in elderly individuals with subjective oral dryness

SyfteSyftet med denna laborativa pilotstudie in vitro var att undersöka hur den mikrobiella sammansättningen och pH i den orala biofilmen påverkades vid upprepad exponering för Stevia (steviosid och rebaudiosid A), sackaros eller en kombination av reb A och sackaros. Ett ytterligare syfte var att studera om isolat av orala bakterier kunde metabolisera reb A i buljongkultur. Material och metodBiofilmer från tre personer blev exponerade för 0,025 % steviosid, 0,025 % reb A eller 10 % Todd Hewitt (TH) under 15 minuter tre gånger dagligen i fyra dagar. Artbestämning gjordes i början och slutet av försöken. Biofilmerna exponerades för 0,025 % reb A och 10 % sackaros eller en kombination av dessa varefter pH-värdet mättes. Vidare studerades 23 bakteriestammar avseende förmåga att metabolisera 0,025% respektive 0,5% reb A. ResultatStreptokocker dominerade i samtliga biofilmer vid försökets slut oavsett om de exponerats för steviosid, reb A eller enbart TH. En pH-sänkning kunde ses hos biofilmerna som enbart blivit exponerade för sackaros eller för en kombination av sackaros och reb A. Däremot kunde endast en marginell pH-sänkning observeras efter exponering för enbart reb A. Ingen av de enskilda bakteriestammar som studerades kunde metabolisera reb A.SlutsatsIngen större skillnad i biofilmens bakteriesammansättning kunde ses efter upprepad exponering för steviosid eller reb A i förhållande till TH.Upprepade exponeringar av reb A i kombination med sackaros gav en liknande pH-sänkning som enbart sackaros, dock sågs ingen pH-sänkning efter exponering för enbart reb A. Enskilda bakteriestammar kunde inte metabolisera reb A. / AimsIn this in vitro laboratory pilot study, the effect on the microbial composition and pH of the oral biofilms after repeated exposure to Stevia (stevioside and rebaudioside A), saccarose or a combination, was investigated. Another aim was to study whether isolate of oral bacteria were able to metabolise reb A in broth bacteria culture.Material and MethodBiofilms from three adult individuals were repeatedly exposed to 0,025% stevioside, 0,025% reb A or 10% Todd Hewitt (TH). Samples were taken at the beginning and at the end of the experiment for cultivation and bacterial identification.Biofilms were exposed to 0,025% reb A and 10% saccharose, either separately or combined, followed by a pH-measurement. Furthermore, 23 bacterial species were studied in regards to ability to metabolize reb A. ResultsAll biofilms were dominated by Streptococcus regardless of whether they were exposed to stevioside, reb A, or TH. A pH-decrease was seen in biofilms exposed to saccharose or a combination of saccharose and reb A. However, only minor changes were noted after exposure to reb A.None of the species studied were able to metabolize reb A.ConclusionNo major differences in the bacterial composition of the biofilms were seen after repeated exposure to stevioside or reb A compared to TH.No pH-decrease after repeated exposure to reb A was noted. Exposure to reb A combined with saccharose resulted in a pH-decrease similar to exposure to saccharose. The bacterial species tested in this study were not able to metabolise reb A.