Year: 2018
Type: dissertation
Abstract: Dental caries is a common multifactorial disease where a frequently low pH in the dental\nbiofilm (dental plaque) plays an important role for caries occurrence and progress. The\nplaque-pH is lowered by acid formation from sugars by biofilm bacteria that also help to\nrestore the pH by alkali formation from urea and the amino acid arginine. Despite the\nimportance of pH for caries to occur, in vivo studies comparing the dental plaque-pH after\nacid and alkali formation are scarce. This may be due to the lack of methods that easily can be\napplied in the clinic. In this thesis, the dental plaque-pH after acid and alkali formation in vivo\nin relation to the individual caries status were examined. Two chair-side methods were also\ndeveloped; the ‘strip method’ to measure in situ the interproximal, supragingival plaque-pH\n(Study I) and a microtiter plate format of RUT (Rapid Urease Test) to grade bacterial urease\nactivity in vitro and ex vivo (Study III). Hopefully studies on pH and alkali formation in the\ndental plaque can contribute to finding measures for assessment of the individual caries risk.\nStudies on plaque-pH after sugar and urea challenges, pre- and post-adaptation periods to\nrespectively acid and alkali formation from 1-week daily rinses with sucrose and urea, were\nexamined in caries-free and caries-active individuals (Study II). Furthermore, the number of\nacid tolerant bacteria was examined as well as the ability of isolated acid tolerant bacteria to\nform acid from sugars and sugar alcohols in vitro (Study II, V). The pH response to a sugar\nchallenge after 6-week usage of fluoride toothpaste with arginine was also examined in\nrelation to caries (Study IV). Similar plaque-pH values and Stephan curves were obtained\nusing the ‘strip method’ and the well-known ‘microtouch method’ before and up to 60 min\nfollowing a sugar challenge (Study I). RUT showed a strong in vitro urease activity for the\nwell-known urease active Helicobacter pylori and for strains of Haemophilus parainfluenzae\nbut not for the more common plaque bacteria Actinomyces spp. and Streptococcus mitis\n(Study III). A higher urease activity in plaque at sites in the lower front compared to plaque at\nother sites was found as well (Study III, IV). Adaptation to acid formation resulted in lower\nplaque-pH after a sugar challenge and an increased number of acid tolerant bacteria in cariesfree\n(CF) individuals (Study II). Adaptation to alkali formation resulted in somewhat higher\npH values after a urea challenge in caries-active (CA) individuals (Study II). In concordance,\nacid formation was numerically increased in bacteria isolated from the CF group after acid\nadaptation and decreased in isolates from the CA group after alkali adaptation (Study V). In\nCA but not CF individuals, the usage of fluoride toothpaste with arginine resulted in increased\nplaque pH-values as well as increased saliva buffer capacity and pH (Study IV). It can be\nconcluded that the ‘strip method’ and ‘RUT’ are applicable as chair-side methods, for the\nassessment of plaque acidogenicity and urease activity, respectively. Adaptation to sugar\nincreased the acid formation and decreased the pH in the dental plaque in caries-free\nindividuals. Adaptation to urea and arginine decreased the acid formation and increased pH in\nthe dental biofilm in caries-active individuals.
Author: Haidar Hassan
Language: English
Subfield: Periodontics
Field: Dentistry
Domain: Health Sciences
Open Access status: green
OpenAlex ID: W2807615304