Scanning electron microscope study of early bacterial penetration of human enamel in initial caries

Abstract

Za istraživanje bakterijskog prodora u caklinu tokom najranijih manifestacija karijesnog procesa korištena je intaktna bukalna caklina 8 impaktiranih trećih trajnih donjih molara. Nakon čišćenja od organskih naslaga, svaka bukalna ploha je izrezana na pet segmenata od kojih je jedan korišten kao kontrolni uzorak, a četiri su fiksirana u utore na parcijalnim protezama dobrovoljaca. Uzorci su boravili u ustima 7, 14, 21 i 28 dana izloženi djelovanju karijesogenih faktora. Nakon odstranjenja organskih naslaga, uzorci su prelomljeni na pola. Na frakturnom poprečnom presjeku promatrana je scanning elektronskim mikroskopom bakterijska penetracija u caklinu. Kod četiri uzorka iz grupe koja je bila oralno eksponirana 7 dana nađene su na dubini od 5 do 10µm pojedinačne baktrije kokoidnog ili bacilarnog oblika. Broj bakterija i dubina do koje su prodrle u caklinu su rasli s duljinom vremena koje su uzorci proveli u ustima. U uzorcima od 28 dana oralne eksponiranosti zapažene su i pojedinačne bakterije i u kolonijama i do dubine od 60 do 90µm. Te bakterije unutar cakline preko sistema pora komuniciraju sa slinom i plakom, što im omogućuje produkciju metabolita, uključivo i mliječne kiseline, što im omogućuje da se same probijaju kroz caklinu, a time i mijenjaju tok i brzinu širenja karijesnog procesa.Bacterial penetration of enamel during initial manifestations of the carious process was studied in intact buccal enamel of 8 impacted third permanent molars. After cleaning them from organic plaque, each buccal plane was cut into five segments, one of them serving as a control specimen and the other four being fixed into slots on partial prostheses of our volunteers. The specimens were left in oral cavity for 7, 14, 21 and 28 days, where they were exposed to the action of cariogenic factors. After removal of the organic plaque, the specimens were broken in two and the bacterial penetration into enamel was observed on the fractured cross-section using scanning electron microscope. In 4 specimens from the group orally exposed during a 7-day period, individual coccoid or bacilliform bacteria were found to have penetrated 5 -1 0 µm deep. The number of bacteria and the depth of their penetration into enamel increased with the duration of oral exposition. Among the specimens oraly exposed during 28 days, bacteria were observed to be present both individually and in colonies, penetrating to the depth of 6 0 -9 0 µm. These bacteria could quite easily communicate with saliva and plaque via the pore system, which allowed them to produce metabolites, including lactic acids. This, in turn, allowed them to penetrate through the enamel, thus altering both the course and rate of the carious process progression