Abstract
Penetration of oral bacteria through root fillings leads to their long term failure. Dimensionally stable alkaline cements have been developed. A saliva challenge model was used to compare resistance to bacterial penetration of these alkaline cements to conventional root fillings that combine gutta percha (GP) with epoxy resin sealers. A sample of 140 human roots with single straight canals prepared to standard length and canal size were obturated with mineral trioxide aggregate (MTA) (Nex MTA or MTAmix), with an alkaline calcium hydroxide hard setting cement (Supercal), or with GP and a resin cement (either AH-Plus or Zirmix). Negative control roots were sealed with wax, while positive controls were left open. The test assemblies were gamma sterilised, then the coronal root face was exposed daily to fresh stimulated human saliva diluted in broth. Bacterial penetration was determined by assessing growth in sterile brain-heart infusion (BHI) medium in contact with the root apex. Using Kaplan–Meier survival analysis, in order of performance from highest to lowest: Negative control, Supercal, Nex MTA, Zirmix, MTAmix, GP + AH-Plus, and the positive control. In addition, statistically significant differences were noted between Supercal and AH-Plus, and between the two MTA cements. It can be concluded that alkaline cements, particularly Supercal, can show considerable resistance to bacterial penetration from constant saliva challenge, and provide superior sealing ability in comparison to resin cements. While this property is due mostly to dimensional stability, the release of hydroxide ions could be a contributing factor to impaired bacterial survival, and this aspect should be explored further.
Highlights
In endodontics, a range of materials are used to fill the root canal of a tooth after chemo-mechanical preparation has been completed
The working hypothesis for the study was that alkaline cements provide better resistance against bacterial penetration than the combination of gutta percha (GP) with an epoxy resin cement
The time required for bacterial penetration was lower for epoxy resin cements than either the root filling to reach the apex varied widely, with SupercalTM giving the longest time of four weeks
Summary
A range of materials are used to fill the root canal of a tooth after chemo-mechanical preparation has been completed. A common approach to filling the root canal uses gutta percha (GP) cones [3] as a core material These cannot provide a hermetic seal due to the lack of adhesion to dentine [4]. Once coronal leakage has occurred, these voids create a pathway along which bacteria may penetrate through the root filling, for example through the sealer, along the walls of the root canal system, or at the interface between the GP core and resin cement [6,8]. The set cement is a dense rigid material, within which freely available excess calcium hydroxide is trapped which has not been incorporated chemically into the set reaction products Release of this excess calcium hydroxide can occur when water comes into contact with the surface of the set cement, but contact with water does not result in dissolution of the cement [12]. The working hypothesis for the study was that alkaline cements provide better resistance against bacterial penetration than the combination of GP with an epoxy resin cement
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