Robert R. White

A comparison of 2.0% chlorhexidine gluconate and 5.25% sodium hypochlorite as antimicrobial endodontic irrigants

Sodium hypochlorite, as an endodontic irrigant, poses problems including toxicity, odor, and discoloration of operatory items. An equally effective, but safer irrigant is desirable. Therefore, we compared the antimicrobial activity of 2.0% chlorhexidine gluconate with that of 5.25% sodium hypochlorite in an in vitro root canal system. Freshly extracted human teeth with pulpal pathosis were instrumented using chlorhexidine, sodium hypochlorite, or saline as irrigants. Microbiological samples were taken from the teeth immediately after accessing the canal, after instrumentation and irrigation, and after standing in an anaerobic atmosphere for 24 h. Irrigation with chlorhexidine or sodium hypochlorite significantly reduced the numbers of postirrigant positive cultures and colony-forming units compared with saline-irrigated teeth. The number of postirrigant positive cultures and the number of colony-forming units in positive cultures obtained from chlorhexidine-treated teeth were lower than the numbers obtained from sodium hypochlorite-treated teeth, but the differences were not statistically significant.

The influence of the smeared layer upon dentinal tubule penetration by endodontic filling materials. Part II.

Root canals in instrumented extracted teeth were filled using the following materials: pHEMA, silicone, and laterally condensed gutta-percha with sealer. Fractured and ground specimens were prepared and the materials were examined, in situ, using scanning electron microscopy. Under the conditions of this study, pHEMA, silicone, and the sealers were consistently seen to enter the dentinal tubules when the smeared layer was removed prior to filling. When the smeared layer was present during filling, tubular penetration was unpredictable and infrequent.

Microleakage—Full crowns and the dental pulp

Recent studies have described microleakage under full crowns cemented with several different cements. This study tested three different types of crown margin preparations--a chamfer, a shoulder, and a shoulder plus a bevel to determine whether or not the margin preparation could affect microleakage. All crowns were cemented with zinc phosphate cement. The crowns were tested for leakage in thermocycled dye. All crowns demonstrated significant leakage following the path of the dentinal tubules into the pulp. This could possibly be one of the causes of pulpal inflammation and even pulpal death under full crowns.

Hypoxia-amplified Proliferation of Human Dental Pulp Cells

INTRODUCTION Postnatal human dental pulp is a potentially promising source of progenitor cells. Sustaining and amplifying progenitor cell populations would be beneficial for basic science research with application in pulpal regeneration. Hypoxia has been observed to promote the undifferentiated cell state in various stem cell populations. The purpose of this study was to examine human dental pulp cells (DPCs) proliferation in normoxia and hypoxia. METHODS Dental pulp cells were obtained from third molars of adult patients and cultured in alpha modification of Eagles medium culture medium with 10% fetal bovine serum. For cell proliferation, DPCs were divided into two groups: (1) DPCs incubated in normoxic conditions (20% oxygen tension) and (2) DPC incubated in hypoxic conditions (3% oxygen tension). Cell proliferation assays were performed every 2 to 3 days from day 3 to day 14 by trypsinization and quantification of cells with a hemacytometer. Fluorescence-activated cell sorting analysis was completed to investigate stem cell markers, CD133, and STRO-1. RESULTS DPCs proliferated significantly more in hypoxia than in normoxia (ie, two-fold throughout the experiment, p < 0.0001). The primitive stem cell marker, CD133, decreased in hypoxia, whereas the osteoprogenitor marker, STRO-1, increased by 8.5-fold. CONCLUSIONS This study suggested that hypoxia is an effective treatment to amplify numbers of progenitor cells from human dental pulp.

A comparison of three methods of cleaning and shaping the root canal in vitro

The purpose of this study was to compare the relativeeffectiveness of three methods of endodontic instrumentation in vitro: hand instrumentation with K and H files, the Burns unifile, and ultrasonic instrumentation. Silicone models were used to evaluate the physical appearance of the prepared canals. Scanning electron microscopy was used to evaluate the thoroughness of debridement with each preparation technique. o 1. None of the three techniques delivered a cleancanal. There was no statistical difference in the three methods. 2. The K file and Hedstrom prepared a smoother,tapered canal more consistently than did the unifile or ultrasonics. The unifile was slightly better than ultrasonics in apical preparation and taper.

Eosinophil-derived transforming growth factors (TGF-α and TGF-β1) in human periradicular lesions

Inflammatory mediators of periradicular lesions are poorly understood. Transforming growth factors-α and -β 1 (TGF-α and TGF-β 1 ) have been linked with the cellular processes for both soft and hard tissue wound healing. The purpose of this study is to demonstrate the cellular sources of TGF-α and TGF-β 1 mRNA and protein in periapical lesions by in situ hybridization and immunohistochemistry. Nine periapical granulomas and nine periapical cysts were examined. TGF-α mRNA and protein were not detectable in the granulomas examined. However, eosinophils surrounding the periapical cysts demonstrated both TGF-α mRNA and protein. The vast majority of eosinophils present in the periapical granulomas and cysts also demonstrated TGF-β 1 mRNA and protein. Other cells producing TGF-β 1 were lymphocytes, fibroblasts, and monocytes. The presence of wound repair cytokines, such as TGF-α and TGF-β 1 , suggests a mechanism by which the host inflammatory response may participate in the repair and remodeling of periapical tissues.

Effect of Immediate and Delayed Post Preparation on Apical Dye Leakage Using Two Different Sealers

Eighty freshly extracted teeth were endodontically prepared and filled with gutta-percha and either a zinc oxide-eugenol-based sealer or AH26 to determine what effect these sealers, with widely differing properties, would have on apical microleakage after either immediate or delayed dowel space preparation. The teeth were randomly assigned to 1 of 4 groups, and the post space was made either immediately after filling or after being stored in 100% humidity for 1 wk. They were then immersed in a 2% methylene blue solution under vacuum, washed, and split longitudinally. The extent of dye penetration was read by five independent observers and the results analyzed. The only significant difference was in the delayed preparation group with zinc oxide-eugenol sealer, which showed greater leakage than the other groups.

Development of a clindamycin-impregnated fiber as an intracanal medication in endodontic therapy

The effectiveness of traditional endodontic intracanal medications in reducing bacterial numbers and preventing acute flare-ups and pain continues to be questioned. In the present study, a new local delivery device was developed that releases a substantive dose of clindamycin into root canals. Clindamycin-impregnated ethylene vinyl acetate (EVA) fibers were produced, and the sensitivity of common endodontic microbes to the fibers were established. An in vitro model was developed to persistently infect 32 extracted human teeth with endodontic pathogens to test the efficacy of the clindamycin/EVA fibers in reducing the number of colony-forming units. The clindamycin/EVA fibers were shown to be effective in reducing growth of common endodontic microbes on blood agar plates, and in significantly reducing growth of Prevotella intermedia, Fusobacterium nucleatum, and Streptococcus intermedius in extracted human teeth, thus indicating merit in further exploring the potential of these fibers as intracanal medications.

Presence of systemic ampicillin in pulp-extirpated root canals.

Ampicillin, administered systemically after pulp extirpation, was detected in the intracanal fluid of instrumented root canals. Pulpectomies were performed on single-rooted dog teeth at 72 h, 24 h, 3 h, and immediately before intravenous injection of ampicillin. Maintenance doses of ampicillin were administered i.m. every 12 h thereafter. Intracanal fluids were collected on paper points at 3, 24, and 72 h after initial injection of ampicillin, and the presence of ampicillin was determined using a Clostridium perfringens bioassay. Ampicillin could be detected in the fluid of half of the pulp-extirpated root canals as early as 3 h after the initial injection. The number of teeth with recoverable ampicillin increased with the time after the initiation of ampicillin administration (79% at 1 day and 100% at 3 days). The length of time between pulp extirpation and the initial administration of systemic ampicillin had no apparent effect on the access of the systemic ampicillin into the pulp-extirpated root canals.

Evaluation of the whole genome DNA-DNA hybridization technique to identify bacteria in histological sections of periradicular lesions.

Whole genome DNA-DNA hybridization has been used to identify bacteria in periradicular lesions partly because there is no amplification of the bacteria, therefore, minor contaminants are not detected. There are, however, potential pitfalls with this technique, including inability to distinguish dead bacteria, cross-reactions of species within a genus, and inability to detect species present in low numbers because of loss of DNA during extraction and purification. Alternatively, inadequate extraction and purification of DNA could result in false positives. Therefore, controls are required to monitor DNA loss, DNA cross-reactions, and DNA of pure cultures mixed with bacteria-free tissue to monitor for false positives. We determined that the quality of DNA extracted from histological sections of periradicular lesions is excellent for DNA-DNA hybridization. Although lesions contain large numbers of bacteria, histological sections through lesions barely contain sufficient quantity of bacteria for such analysis. This was confirmed by histological observation of sparsely distributed bacteria within lesions. Furthermore, we found that the bacteria are not distributed evenly throughout periradicular lesions, in numbers or species.