In vitro study of the penetration of Streptococcus sanguis and Prevotella intermedia strains into human dentinal tubules

An easily achievable strategy to promote the penetration of methylene blue into dentinal tubules

BACKGROUND

One critical issue that impairs the therapeutic effects of antimicrobial photodynamic therapy (aPDT) in root canal disinfection is the insufficient penetration of photosensitizer into dentinal tubules. Therefore, this study aimed to compare the treatments in enhancing photosensitizers' penetrability for aPDT in root canal therapy.

METHODS

Thirty premolars with a single root canal were randomly divided into three groups (n = 10), using Methylene blue (MB) as a photosensitizer and treated with different approaches: sonic-assisted diffusing group, ultrasonic-assisted diffusing group and the control without treatment. All specimens were observed by stereomicroscope to measure the penetration depth of MB into dentinal tubules.

RESULTS

Both sonic and ultrasonic treatments substantially improved the penetrability of MB. The former achieved a deeper penetration depth than the latter did in the same region of root (P<0.05). Regarding the dye penetration depths at different root regions, the control group showed a declining trend from coronal to apical. In contrast, the penetration depths of sonic and ultrasonic-assisted diffusing groups from highest to lowest were middle > coronal > apical (P<0.05).

CONCLUSIONS

This study showed that both sonic and ultrasonic treatments remarkably promoted MB's penetration depth into dentinal tubules. Maximum penetration was achieved when treated with a sonic approach.

Confocal laser scanning microscopy evaluation of roots subjected to activation protocol in endodontic microsurgery

This study evaluated the penetration of the irrigant subject to activation after performing retro-preparation in endodontic microsurgery. Forty mandibular premolars were prepared and filled. Subsequently, 1 mm from the root apex was cut using a multi-blade bur and the retro-preparation was performed. In group 1, the retro-cavity was cleaned with 2 mL of saline and then with 2 mL of 5.25% NaOCl gel mixed with 0.1% Rhodamine B. In group 2, the retro-cavity was cleaned with 2 mL of saline, 17% EDTA gel was activated ultrasonically for 30 s and 5.25% NaOCl gel was mixed with 0.1% Rhodamine B and activated for 30 s. After 7 days, the roots were cut at 1mm from the apex and the slices were evaluated with confocal laser scanning microscopy. The samples of group 2 showed statistically better results. The activation protocol proposed resulted in enhanced irrigant penetration when compared to the traditional.

Calcium hydroxide-loaded PLGA biodegradable nanoparticles as an intracanal medicament

AIM

To develop a formulation in which calcium hydroxide (Ca(OH)₂) was successfully loaded into poly(lactic-co-glycolic acid) (PLGA) biodegradable nanoparticles (NPs) to be used in the field of endodontics as an intracanal medicament, including NP optimization and characterization, plus drug release profile of the NPs compared with free Ca(OH)₂. Additionally, the depth and area of penetration of the NPs inside the dentinal tubules of extracted teeth were compared with those of the free Ca(OH)₂.

METHODOLOGY

Ca(OH)₂ NPs were prepared using the solvent displacement method. NPs was optimized with a central composite design to obtain a final optimized formulation. The morphology of the NPs was examined under transmission electron microscopy (TEM), and characterization was carried out using X-ray diffraction (XRD), Fourier transform infrared (FTIR) and differential scanning calorimetry (DSC). The drug release profile of the Ca(OH)₂ NPs and free Ca(OH)₂ was evaluated up to 48 h. Finally, the depth and area of penetration inside the dentinal tubules of extracted teeth were examined for both the Ca(OH)₂ NPs and free Ca(OH)₂ using the Mann-Whitney U test to determine any significant differences.

RESULTS

Utilizing the optimized formulation, the Ca(OH)₂ NPs had an average size below 200 nm and polydispersity index lower than 0.2, along with a highly negative zeta potential and suitable entrapment efficiency percentage. The spherical morphology of the Ca(OH)₂ NPs was confirmed using TEM. The results of the XRD, FTIR and DSC revealed no interactions and confirmed that the drug was encapsulated inside the NPs. The drug release profile of the Ca(OH)₂ NPs exhibited a prolonged steady release that remained stable up to 48 h with higher concentrations than the free Ca(OH)₂. After examination by confocal laser scanning microscopy, Ca(OH)₂ NPs had a significantly greater depth and area of penetration inside dentinal tubules compared with the free drug.

CONCLUSIONS

Ca(OH)₂-loaded PLGA NPs were successfully optimized and characterized. The NPs exhibited a prolonged drug release profile and superior penetration inside dentinal tubules of extracted teeth when compared to Ca(OH)₂ .

Comparison of the Effect of Three Irrigation Techniques and Root Canal Preparation Size on Sodium Hypochlorite Penetration into Root Canal Dentinal Tubules

Objective

This study aims to compare the effects of conventional syringe irrigation (CSI), passive ultrasonic irrigation (PUI), and innovative sonic-powered irrigation (EDDY) on the penetration of sodium hypochlorite (NaOCl) solutions into root canal dentinal tubules at different levels of the root canal.

Materials and Methods

One hundred ninety-two extracted first mandibular premolars of 17- to 25-year-old patients were decoronated 13 mm from the root apices and separated into two groups according to apical preparation sizes (APS) 25 and 40. The root canals were dried with a paper point and stained in crystal violet for 72 hours. Each APS group was separated into three groups according to irrigation techniques, as follows: CSI, PUI, and EDDY. Roots were perpendicularly resected to the long axis at three levels (coronal, middle, and apical). Photomicrographs were taken of all three cross-sections of each tooth under a stereomicroscope. The depth of the bleached zone was measured with ImageJ software. The data were analyzed by Welch's analysis of variance and an independent t-test (p = 0.05).

Results

No penetration was found at the apical level in the CSI25, CSI40, and PUI25 groups. The EDDY25 and EDDY40 groups showed the most significant penetration at the middle and apical levels compared to the other groups (p < 0.05).

Conclusions

Within the limitations of this study, irrigation techniques and APS affect the penetration depth of NaOCl into the root canal dentinal tubules. In terms of irrigation techniques, the penetration was deepest when EDDY was used, followed by PUI and CSI. In terms of APS, NaOCl penetrated deeper into APS40 than APS25. The use of the EDDY irrigation technique in APS25 can improve the penetration of NaOCl into root canal dentinal tubules at the apical level.

Effect of EDTA and QMIX Ultrasonic Activation on the Reduction of Microorganisms and Endotoxins in Ex Vivo Human Root Canals

Abstract The present study aimed to compare the effectiveness of QMiX and 17% EDTA associated to passive ultrasonic irrigation (PUI) or manual agitation (MA) on the reduction of E. faecalis, E. coli and LPS from root canals. Forty single rooted human teeth were randomly divided into four groups (n=10), according to the final irrigation protocol: EDTA+MA, QMiX+MA, EDTA+PUI, QMiX+PUI. Sample collections were obtained from the root canal content immediately before preparation (baseline-S1), after instrumentation (S2), after final irrigation protocol (S3) and 7 days after instrumentation and final irrigation (S4). The antimicrobial effectivity and on endotoxin content were analyzed by culture procedure (CFU/mL) and LAL assay (EU/mL), respectively. The results were statistically analyzed by Kruskal-Wallis and Friedman test (α=5%). QMiX+MA and QMiX+PUI reduced 100% of E. coli and E. faecalis bacteria and also prevented E. faecalisregrowth at S4. EDTA significantly reduced E. coli, but it was not effective in reducing E. faecalis. All protocols reduced EU/mL when compared to S1, however at S4 there was a significant reduction of EU/mL only in the QMiX+MA and QMiX+PUI groups in relation to S3 and S2, respectively. Final irrigation with QMiX associated with MA or PUI had superior antibacterial efficacy compared to EDTA, eliminating 100% of E. coli and E. faecalis strains. In addition, QMiX+PUI reduced 97.61% of the initial content of LPS.

Is it really penetration? Locomotion of devitalized Enterococcus faecalis cells within dentinal tubules of bovine teeth

OBJECTIVE

The aim of the present study was to evaluate the penetration characteristics of devitalized and vital E. faecalis cells into root dentinal tubules.

DESIGN

Thirteen root canals were incubated with devitalized (4days, 7days, 14days, 28days) and vital (28days) E. faecalis strains (streptomycin-resistant strains) after root canal enlargement (size 80, taper 0.02) with 3 % NaOCl solution. The smear layer was intentionally removed with 20 % EDTA before inoculation. Samples were processed for analysis by scanning electron microscopy (SEM) and DAPI (4',6-diamidino-2-phenylindole) staining. DAPI was conducted for fluorescence microscopic visualization of the bacterial penetration into dentinal tubules. The penetration depth was calculated with the measurement tool of the Axio Vision program (Zeiss, Jena, Germany).

RESULTS

Devitalized E. faecalis strains were able to penetrate into dentinal tubules of the root canal. Apikal penetration depths of the devitalized cells were 100.67μm±26.54μm after 7days, 230.67μm±111.5μm after 14days and 266.5μm±92.63μm after 28days of incubation. The total number and penetration depth of E. faecalis cells was lower compared to a vital suspension of E. faecalis (1002.45μm) after 28days. It was noted that bacterial penetration was not common to all of the dentinal tubules in the vital E. faecalis control and especially in the devitalized control.

CONCLUSIONS

Increased exposure times of devitalized bacteria into root canals lead to an increased number of penetrated dentinal tubules as well as to a deeper penetration.

Bacterial invasion into radicular dentine-an in vitro study

OBJECTIVES

We wanted to investigate differences in invasiveness into radicular dentinal tubules by monocultured and co-cultured bacteria frequently found in infected root canals.

METHODS

Fifty-one human roots were incubated for 8 weeks with monocultured Streptococcus gordonii ATCC 10558, Streptococcus sanguinis ATCC 10556, and with five capnophiles/anaerobes as well as with capnophiles/anaerobes co-cultured with a streptococcal species. Thereafter, bacterial samples were cultured from the inner, middle, and outer third of the root dentine of longitudinally broken teeth (n = 5). In addition, scanning electron microscopy (SEM) images were obtained.

RESULTS

Single gram-positive species were able to penetrate into the middle and outer third of the root dentine. Fusobacterium nucleatum ATCC 25586 was not found in any of the dentine specimens. Prevotella intermedia ATCC 25611 and Porphyromonas gingivalis ATCC 33277 were found in the inner and middle third. The bacterial load of streptococci was higher in all thirds in co-cultures compared to single infections. In co-cultures with streptococci, Actinomyces oris ATCC 43146 was found in the outer third in 9/10 samples, whereas P. intermedia ATCC 25611 was not detectable inside dentine. Co-culture with S. sanguinis ATCC 10556 enabled F. nucleatum ATCC 25586 to invade dentine; SEM images showed that F. nucleatum ATCC 25586 had a swollen shape.

CONCLUSIONS

Invasiveness of bacteria into dentinal tubules is species-specific and may change depending on culturing as a single species or co-culturing with other bacteria.

CLINICAL RELEVANCE

Oral streptococci may promote or inhibit invasion of capnophiles/anaerobes into radicular dentine.

Microbial invasion of dentinal tubules: a literature review and a new perspective

Various features of endodontic microbiology have been investigated using various methods. The aim of the present study was to review the existing literature on endodontic microbiology in dentinal tubules, and to present the features of two cases with endodontic pathology. An electronic search was performed with a search string created ad hoc. Ex vivo and in vitro studies were included, recording the method of detection and characteristics of analyzed teeth. Twenty studies fulfilled the inclusion criteria. Seven of them were in vitro laboratory studies on teeth inoculated after extraction, while 13 were ex vivo studies on extracted, infected teeth. Endodontic bacteria were detected in dentinal tubules, both as single units and as biofilm aggregates. Two similar in vitro cases presented here corroborate the latter findings. A number of techniques have been utilized to observe bacteria in the dentinal tubule ecosystem. Dentinal tubules are favorable niches for microbial survival, either in the form of monomicrobial or polymicrobial communities.

The effect of age on bacterial penetration of radicular dentin

The aim of this study was to determine the effects of patient's age on the prevalence and depth of bacterial penetration inside dentinal tubules. Fifty-six single-rooted teeth were divided in two groups based on the patient's age: young (ages 18-25) and old (age >or=60). Teeth were instrumented and inoculated with a standardized bacterial load and incubated for 20 days. Histological analysis was performed to determine the degree of infection of the dentinal tubules by counting the number of invaded tubules and the depth of penetration of bacteria inside the tubules. A significantly higher number of tubules were invaded by bacteria in the young group compared with the old group (p = 0.014). Also, the depth of invasion by bacteria was significantly higher in the young than in the old group (p = 0.033). These results suggest that bacterial infection of dentinal tubules occur to a lesser extent in older patients.

Photodynamic treatment of endodontic polymicrobial infection in vitro

We investigated the photodynamic effects of methylene blue on multispecies root canal biofilms comprising Actinomyces israelii, Fusobacterium nucleatum subspecies nucleatum, Porphyromonas gingivalis, and Prevotella intermedia in experimentally infected root canals of extracted human teeth in vitro. The 4 test microorganisms were detected in root canals by using DNA probes. Scanning electron microscopy showed the presence of biofilms in root canals before therapy. Root canal systems were incubated with methylene blue (25 microg/mL) for 10 minutes followed by exposure to red light at 665 nm with an energy fluence of 30 J/cm(2). Light was delivered from a diode laser via a 250-microm diameter polymethyl methacrylate optical fiber that uniformly distributed light over 360 degrees. Photodynamic therapy (PDT) achieved up to 80% reduction of colony-forming unit counts. We concluded that PDT can be an effective adjunct to standard endodontic antimicrobial treatment when the PDT parameters are optimized.

Residual bacteria in root apices removed by a diagonal root-end resection: a histopathological evaluation

AIM

To assess bacteria in the apical portion of the root end after 45 degrees root-end resection in teeth with persistent periapical lesions.

METHODOLOGY

The study included 27 apical root segments from patients with persistent periapical lesions. Histological sections of the coronal part of the amputated root segment were stained with Brown and Brenn to detect the presence of bacteria in the main root canal and/or in irregular root spaces and dentinal tubules. The quality of each root canal filling was evaluated using preoperative radiographs of filling, length of root filling as assessed from the distance between its apical end and the radiographic apex, diameter of apical preparation, and presence of apical perforations or deviations from the root canal. Two endodontists, blinded to the bacteriological results, independently evaluated the radiographs.

RESULTS

Bacteria were present in 23 (85.2%) specimens: five in only the main canal (21.7%), 10 in only the dentinal tubules and irregular spaces (43.5%), and eight in both irregular spaces and dentinal tubules and in the main root canal (34.8%). No correlation was found between the technical quality of the root filling assessed radiographically and bacterial presence in the central canal or irregular areas.

CONCLUSIONS

Infected irregular areas were found in the root tips of teeth with persistent periapical lesions. This was found regardless of the radiographic quality of the root filling. Diagonal, 45 degrees root-end resection may expose such contaminated irregularities to the periapical tissue.

The use of calcium hydroxide, antibiotics and biocides as antimicrobial medicaments in endodontics

Bacteria have been implicated in the pathogenesis and progression of pulp and periapical diseases. The primary aim of endodontic treatment is to remove as many bacteria as possible from the root canal system and then to create an environment in which any remaining organisms cannot survive. This can only be achieved through the use of a combination of aseptic treatment techniques, chemomechanical preparation of the root canal, antimicrobial irrigating solutions and intracanal medicaments. The choice of which intracanal medicament to use is dependent on having an accurate diagnosis of the condition being treated, as well as a thorough knowledge of the type of organisms likely to be involved and their mechanisms of growth and survival. Since the disease is likely to have been caused by the presence of bacteria within the root canal, the use of an antimicrobial agent is essential. Many medicaments have been used in an attempt to achieve the above aims but no single preparation has been found to be completely predictable or effective. Commonly used medicaments include calcium hydroxide, antibiotics, non-phenolic biocides, phenolic biocides and iodine compounds. Each has advantages and disadvantages, and further research is required to determine which is best suited for root canal infections.

Hemin nutritional stress inhibits bacterial invasion of radicular dentine by two endodontic anaerobes

AIM

To determine if anaerobic bacteria routinely found in infected dentine and root canals require the presence of heme in the environment in order for them to invade dentinal tubules.

METHODOLOGY

Noncarious, unrestored human teeth with single root canals were prepared for invasion experiments and soaked in either TSB-M supplemented with hemin (5 microg mL(-1)) (n = 12 roots), TSB-M media (n = 12 roots) or TSB-M media followed by hemin soak (n = 12 roots) for 2 days, then inoculated with either Prevotella intermedia ATCC 25611 or Peptostreptococcus micros ATCC 33270 and incubated anaerobically for 14 days. Roots were prepared for light microscopy, stained with Brown and Brenn or antisera raised to the bacteria, and invasion within tubules assessed using a tubule invasion index (TI). Data were analysed using Student's t-test and Mann-Whitney U-test.

RESULTS

Prevotella intermedia (TI = 0.7 +/- 0.04) and P. micros (TI = 0.96 +/- 0.08) showed low invasion when grown in the presence of hemin with cells generally restricted to the superficial 20 microm of the tubules, whilst neither bacteria invaded tubules (TI = 0) when hemin was absent from the growth media (P < 0.01).

CONCLUSIONS

Hemin was required in the growth medium for P. intermedia and P. micros to invade dentinal tubules.

Comparison of the antimicrobial activity of six irrigants on primary endodontic pathogens

The purpose of this study was to compare the antimicrobial activities of 6% and 3% sodium hypochlorite (NaOCl), 2% and 0.12% chlorhexidine gluconate (CHX), and 0.01% and 0.005% doxycycline (Doxy) on four microorganisms associated with primary endodontic infections. The agar diffusion test was used to measure antimicrobial activities of these agents against Peptostreptococcus micros, Prevotella intermedia, Streptococcus sanguis, and Lactobacillus acidophilus. Minimum inhibitory concentration analysis was performed using the macrodilution method. For three of the four microorganisms, the general order of antimicrobial effectiveness was 0.01% Doxy >0.005% Doxy >6% NaOCl >3% NaOCl >2% CHX > 0.12% CHX. For L. acidophilus, the order of effectiveness was 6% NaOCl >3% NaOCl >2% CHX > 0.01% Doxy >0.005% Doxy >0.12% CHX. The 6% NaOCl showed significantly greater zones of inhibition than 3% NaOCl for all endopathogens tested.

The Role of Apical Instrumentation in Root Canal Treatment: A Review of the Literature

The issue of final apical preparation size remains controversial despite considerable clinical and in vitro research. The astute clinician must be aware of this research before choosing any instrumentation system because the informed clinician's decision must be guided by the best available evidenced-based information. This review article generated a Medline-based search strategy to disclose these studies and provides a critique and summary of the results.

The Photo-Activated Antibacterial Action of Toluidine Blue O in a Collagen Matrix and in Carious Dentine

The main aim of this study was to determine the susceptibility to photo-activated disinfection (PAD) of Streptococcus mutans when the organism was present in a collagen matrix--an environment similar to that which would exist within a carious tooth. In addition, the susceptibility to PAD of bacteria present in carious human teeth was also determined. Light was delivered to the collagen and teeth using a system comprising a 0.8-mm diameter isotropic tip emitting light at 633 +/- 2 nm. A single concentration of TBO (10 microg/ml) was used with both collagen and dentine. Two contact times, 30 and 180 s, were evaluated in intact collagen and additionally, for 180 s only, in collagen partially disrupted by shredding. The effect of energy doses from 1.8 to 14.4 J on the kills attained was assessed by determining the number of surviving viable bacteria. In carious dentine, two contact times, 30 and 60 s and one energy dose, 4.8 J, were used. Antibacterial effects were less than those obtained using planktonic suspensions with a maximum mean log reduction of 1.4 in shredded collagen and dentine. Increasing contact time increased the antibacterial effectiveness in both substrates although this was not always of statistical significance. Shredding the collagen resulted in significantly increased bacterial kills compared to those obtained in intact collagen for the 30-second contact time. The collagen matrix appeared to be a suitable model for carious dentine with advantages of availability and reproducibility. The results of this study have shown that PAD can achieve appreciable kills of oral bacteria, including S. mutans, when the organisms are embedded in a collagen gel or are present in carious teeth.

Invasion of dentinal tubules by oral bacteria

Bacterial invasion of dentinal tubules commonly occurs when dentin is exposed following a breach in the integrity of the overlying enamel or cementum. Bacterial products diffuse through the dentinal tubule toward the pulp and evoke inflammatory changes in the pulpo-dentin complex. These may eliminate the bacterial insult and block the route of infection. Unchecked, invasion results in pulpitis and pulp necrosis, infection of the root canal system, and periapical disease. While several hundred bacterial species are known to inhabit the oral cavity, a relatively small and select group of bacteria is involved in the invasion of dentinal tubules and subsequent infection of the root canal space. Gram-positive organisms dominate the tubule microflora in both carious and non-carious dentin. The relatively high numbers of obligate anaerobes present-such as Eubacterium spp., Propionibacterium spp., Bifidobacterium spp., Peptostreptococcus micros, and Veillonella spp.-suggest that the environment favors growth of these bacteria. Gram-negative obligate anaerobic rods, e.g., Porphyromonas spp., are less frequently recovered. Streptococci are among the most commonly identified bacteria that invade dentin. Recent evidence suggests that streptococci may recognize components present within dentinal tubules, such as collagen type I, which stimulate bacterial adhesion and intra-tubular growth. Specific interactions of other oral bacteria with invading streptococci may then facilitate the invasion of dentin by select bacterial groupings. An understanding the mechanisms involved in dentinal tubule invasion by bacteria should allow for the development of new control strategies, such as inhibitory compounds incorporated into oral health care products or dental materials, which would assist in the practice of endodontics.

Efficacy of NaOCl/H2O2 irrigation and GaAlAs laser in decontamination of root canals in vitro

BACKGROUND AND OBJECTIVES

To investigate the bactericidal effect of an 809 nm semiconductor laser alone, and in combination with NaOCl/H(2)O(2) irrigation in root canals in vitro.

STUDY DESIGN/MATERIALS AND METHODS

A total of 72 human single-rooted teeth extracted for periodontal reasons were included. The crowns were removed, the roots shortened to a length of 12 mm, and the canals enlarged up to an apical size of #50 file. The specimens were autoclaved and incubated with a suspension of Streptococcus sanguinis (ATCC 10556). Laser irradiation was performed on a PC-controlled XY translation stage. A 200 micron optic fiber was used. Twelve specimens were irradiated at a power output of 1.5, 3.0, and 4.5 W in the cw-mode. The total irradiation time was 60 seconds per canal. Twelve specimens were rinsed with NaOCl and H(2)O(2) only, 12 were rinsed and laser treated, and 12 served as untreated controls. After laser treatment, the specimens were sonicated and the bacterial growth was examined by counting colony forming units on blood agar plates. Temperature changes at the outer root surface during irradiation were registered by means of thermocouples. Treated and control specimens were investigated by means of scanning electron microscopy.

RESULTS

Mean bacterial reductions of 0.35 log steps at a power output of 1.5 W, 1.44 at 3.0 W, and 2.84 at 4.5 W were calculated. Bacterial reduction by the NaOCl/H(2)O(2) solution alone was 1.48 and comparable to that achieved by irradiation at 3.0 W. With a log kill 2.85, the combination of rinsing and laser irradiation at 3.0 W resulted in a further significant bacterial reduction as compared to rinsing alone (P = 0.004). Irradiation did not result in excessive heat generation at the root surface. Carbonization of the root canal wall was observed in single teeth at 3.0 and 4.5 W and no controlled sealing of the dentinal tubules could be achieved in the root canal.

CONCLUSIONS

The application of the diode laser might be an adjunct to conventional endodontic treatment when used in combination with a NaOCl/H(2)O(2) solution.

Bactericidal effect of the Er:YAG laser on dental implant surfaces: an in vitro study

BACKGROUND

The aim of the in vitro study was to examine the bactericidal effect of an Er:YAG laser on common dental implant surfaces.

METHODS

Seventy-two titanium platelets with 3 different surfaces--sandblasted and acid-etched (SA), titanium plasma-sprayed (TPS), and hydroxyapatite-coated (HA)--were incubated with a suspension of Streptococcus sanguinis (ATCC 10556). Irradiation at pulse energies of 60 and 120 mJ and a frequency of 10 pps was performed on a computer-controlled XY translation stage. After laser treatment the specimens were sonicated and the bacterial growth examined by counting colony forming units on blood agar plates. Temperature elevations during irradiation were investigated using K-type thermocouples. Laser treated implant surfaces were analyzed by means of electron microscopy.

RESULTS

Compared to non-irradiated specimens, mean bacterial reductions of 99.51% (SA), 98.39% (HA), and 99.6% (TPS) at a pulse energy of 60 mJ and 99.92% (SA), 99.85% (HA), and 99.94% (TPS) at 120 mJ were calculated. At these laser parameters, no excessive temperature elevations or morphological implant surface alterations were detected.

CONCLUSIONS

Even at low energy densities, the Er:YAG laser has a high bactericidal potential on common implant surfaces. Clinical studies are justified to evaluate the applicability and efficacy of the Er:YAG laser in the treatment of peri-implantitis.

Patterns of microbial colonization in primary root canal infections

OBJECTIVE

The purpose of this study was to investigate the patterns of microbial infection of root canals in untreated teeth associated with chronic periradicular lesions by use of scanning electron microscopy.

STUDY DESIGN

Fifteen extracted teeth with extensive carious lesions, radiolucent lesions of varying sizes, and attached periradicular lesions after extraction were selected for study. After fixation, lesions were removed and the teeth were split into 2 halves. The teeth were then dehydrated, sputter-coated with gold, and then examined for the patterns of microbial colonization of the root canal system by using a scanning electron microscope.

RESULTS

All examined root canals were infected, and bacterial cells were seen in practically all areas of the root canal system. The pattern of colonization was not uniform between specimens and even within the same specimen. Most of the root canal walls of all specimens were heavily colonized by a root canal microbiota consisting of cocci and/or rods, often forming mixed communities. Spirilla were occasionally observed as single cells or as small clusters between other bacterial forms. Bacteria were often observed penetrating the dentinal tubules. Although a shallow penetration was the most common finding, bacterial cells could be observed reaching approximately 300 microm in some specimens. Yeastlike cells were observed in 1 specimen together with bacteria.

CONCLUSIONS

The root canals of teeth associated with periradicular lesions were heavily infected by bacteria and occasionally by fungi. The pattern of colonization of the root canal microbiota often showed the characteristic of a climax community, which may require special considerations regarding its elimination and prevention of clinical problems. In addition, the observed propagation of the infection to the entire root canal system in teeth associated with periradicular lesions suggests that proper therapeutic measures may be necessary to eliminate the root canal infection completely.