A laboratory study of coronal microleakage using four temporary restorative materials.

AIM: The aim of this study was to compare the sealing abilities of Fermin and Canseal with the more popular temporary coronal filling materials, Cavit and Caviton. METHODOLOGY: Standardized access cavities were prepared in 160 intact human permanent molar teeth. They were divided into five groups consisting of 32 samples. The teeth were restored using one of the temporary filling materials, namely: Fermin, Canseal at two powder to liquid ratios, Caviton and Cavit. Thermal cycling and/or load cycling were applied on the samples. Assessment of microleakage utilized methylene blue dye penetration. Grading of the microleakage pattern was from 1 to 3, with 3 providing the best seal. Results were analyzed using two-way anova and by Fisher's PLSD post hoc test (P < 0.05). RESULT: Microleakage along Fermin, Caviton and Cavit samples did not go beyond Leakage Grade 2. Dye penetration into these materials was noted. This was not observed in the two groups of Canseal tested. However, the two groups of Canseal exhibited total leakage notably after being subjected to thermal cycling. There was a statistically significant difference in the microleakage scores obtained between the materials and conditions tested (P < 0.0001). CONCLUSION: Fermin was found to exhibit the best seal amongst the four materials tested followed by Caviton, and Cavit. Thermal cycling influenced the seal of certain types of temporary filling materials more than load cycling.

Penetration of propylene glycol into dentine.

AIM: This study aimed to evaluate penetration of propylene glycol into root dentine. METHODOLOGY: Safranin O in propylene glycol and in distilled water were introduced into root canals with and without artificial smear layer. Dye diffusion through dentinal tubules was determined spectrophotometrically. The time required for dye to exit through the apical foramen using propylene glycol and distilled water as vehicles was also determined. The extent and areas of dye penetration on the split surfaces of roots were assessed using Adobe Photoshop and NIH Image Software. RESULTS: Propylene glycol allowed dye to exit faster through the apical foramen. The area and depth of dye penetration with propylene glycol was significantly greater than with distilled water (P < 0.0001). Smear layer significantly delayed the penetration of dye. CONCLUSION: Propylene glycol delivered dye through the root canal system rapidly and more effectively indicating its potential use in delivering intracanal medicaments.

The influence of interpatient and intrapatient rectum variation on external beam treatment of prostate cancer.

PURPOSE: The rectal dose/volume relationship and inherent variations thereof are fundamental parameters to guide dose escalation in prostate cancer treatment. This study evaluates the effect of rectal dose/volume variation on the risk of rectal complication for different planning target volume (PTV) constructions. METHODS AND MATERIALS: Thirty prostate patients with multiple daily CT scans obtained during the treatment course were included in this retrospective study. The dose distribution was calculated based on the pretreatment CT image alone. Treatment plans were generated by applying the four-field-box beam arrangement to each of three different PTVs: PTVs with 0.5-cm and 1.0-cm uniform margins, and a patient-specific PTV constructed using treatment imaging feedback. For each of the 30 patients, the rectal wall as manifested on each of multiple CT images was delineated after image bony registration to the pretreatment CT image, and applied to the corresponding treatment plan to obtain the rectal wall dose-volume histogram (DVH). Interpatient and intrapatient rectal dose/volume variations were quantified accordingly. The corresponding uncertainty and sensitivity of the risk of rectal complication to the variations were evaluated for each of the three PTVs. Finally, the efficacy of using multiple CT images to reduce uncertainty in planning evaluation was examined. RESULTS: Sensitivity of the risk of rectal complication to rectal dose/volume variation strongly depends on the clinical target volume (CTV)-to-PTV margin or prescription dose, or both. Compared to the conventional two-dimensional (2D) prostate cancer treatment, the sensitivity for a conformal treatment can be 3 times higher or more. Due to the interpatient rectal dose/volume variation, the individual normal tissue complication probability (NTCP) was distributed from 10% to 37% when a common prescription dose was applied for all patients. The intrapatient rectal dose/volume variation introduces at least +/- 25% uncertainty in the NTCP calculation for at least 10% or 25% of the patients treated with the PTV of 1.0- or 0.5-cm margin, respectively. These uncertainties were larger for the smaller PTV, with the standard deviation up to 20%. By applying multiple CT image feedback, the NTCP uncertainty could be reduced by a factor of 2. CONCLUSIONS: Shape and position variation of rectum has less influence on treatment planning in the conventional 2D treatment of prostate cancer. However, this influence is quickly growing with high treatment dose or small CTV-to-PTV margins. To reduce the variation and uncertainties in the treatment planning evaluation associated with the inter- and intrapatient rectal dose/volume variation, the iso-NTCP model and treatment image feedback technique can be applied in dose escalation trials of prostate cancer treatment.

Improvement in dose escalation using the process of adaptive radiotherapy combined with three-dimensional conformal or intensity-modulated beams for prostate cancer.

PURPOSE: Advances in technology allow the creation of complex treatment plans with tightly conforming doses. However, variations in positioning of the organ/patient with respect to treatment beams necessitate the use of an appreciable margin, potentially limiting dose escalation in many patients. To (1) reduce this margin and (2) test the hypothesis that the achievable level of dose escalation is patient dependent, a patient-specific, confidence-limited planning target volume (cl-PTV) was constructed using an adaptive radiotherapy (ART) process for prostate cancer treatment developed in-house. The potential dose escalation achievable with this ART process is quantified for both conformal radiotherapy (CRT) delivery and intensity-modulated radiotherapy (IMRT) delivery. MATERIAL AND METHODS: Patients with organ confined prostate cancer were entered prospectively into an ART process developed in-house. This ART process has been designed to improve accuracy and precision of dose delivery, consequently enhancing dose escalation. In this process, a cl-PTV is constructed for each patient in the second week of treatment based upon on-line portal and CT images acquired during the first week of treatment. The treatment prescription dose, defined as the minimum dose to the cl-PTV, is selected based on predefined dose-volume constraints for rectum/bladder and derived from the pretreatment planning CT image. In addition, the treatment modality (CRT or IMRT) is determined based on the level of dose escalation achievable and the risk of inaccurate targeting. The potential for both dose escalation and the application of IMRT was evaluated by comparing the prescription doses delivered using the ART process, with the cl-PTV, to those in the traditional treatment process, with a conventional generic PTV. In addition, the distributions of potential geometric target underdosing and normal tissue overdosing were also calculated to evaluate the quality of the conventional treatment plans. RESULTS: One hundred and fifty patients have been treated with the ART process. When compared to the treatment dose delivered with the conventional treatment process (generic PTV), an average 5% (2.5--10%) more dose could be delivered using the ART process with CRT, and 7.5% (2.5--15%) more dose could be delivered with IMRT. Of the 150 patients, 70% were treated to a minimum cl-PTV dose > or = 77.4 Gy (81.3 Gy ICRU isocenter dose). Dosimetric analysis revealed that 81 Gy to the cl-PTV (or 86.7 Gy ICRU) could be prescribed to at least 50% of patients if IMRT was applied using the ART process. In contrast, IMRT did not yield an obvious dose escalation gain if patients were treated using the generic PTV. Our results also demonstrate that the cl-PTV is significantly smaller than the conventional generic PTV for most patients, with a mean volume reduction of 24% (range, 5--43%). CONCLUSION: These results support our hypothesis that the achievable level of dose escalation using ART is patient dependent. By using the ART process to develop a cl-PTV, one can (1) optimize the dose level, (2) increase the applicability of IMRT, and (3) improve the quality of dose delivery. The ART process provides the foundation to identify a suitable option (CRT or IMRT) for the delivery of a safe treatment and dose escalation. It is now our standard of practice for prostate cancer treatment.

Bacterial eradication from root dentine by ultrasonic irrigation with sodium hypochlorite.

The study aimed to evaluate intracanal irrigation procedures in eradicating bacteria from surface, shallow and deep layers of root dentine using extracted human teeth. Artificial bacterial smear layer was successfully produced by rubbing a mixture of dental plaque and artificially decalcified dentine or carious dentine on root canal walls. The reservoir holes were 3.5 mm in depth, 1 mm in diameter prepared 1.5 mm apart and parallel to the root canals on the decrowned planes, in which five separate bacterial species were placed (Actinomyces israelii, Fusobacterium nucleatum, Propionibacterium acnes, Streptococcus mutans and Streptococcus sanguis). Bacterial eradication after irrigation of the prepared canals was determined by bacterial recovery (i) from the root canal surfaces and shallow layers where bacteria were smeared artificially and (ii) from deeper layers of root canal dentine reservoir holes. Ultrasonic irrigation with 5.5% and 12% NaOCl eradicated bacteria from artificial smear layer (P < 0.0001), whilst 12% NaOCl irrigation with a syringe was insufficient. Ultrasonic irrigation with water or 15% EDTA-failed to eradicate bacteria from smeared surfaces. Ultrasonic irrigation with 12% NaOCl killed A. israelii, F. nucleatum, P. acnes, S. mutans, and S. sanguis placed in reservoir channels, although for F. nucleatum, a very small number of bacteria remained in five samples out of 12. Ultrasonic irrigation with less concentrated NaOCl failed to eliminate bacteria completely from reservoir channels in most samples. Ultrasonic irrigation with 12% NaOCl appeared to eliminate bacteria efficiently from surface, shallow and deep layers of root dentine.

Inhibitory effects of metronidazole on anaerobic metabolism of phenylalanine and leucine by Peptostreptococcus anaerobius.

The metabolism of phenylalanine and leucine by Peptostreptococcus anaerobius and the effects of metronidazole on this metabolism were studied. The cells metabolized both phenylalanine and leucine under strict anaerobic conditions and produced hydroxylated products (i.e. phenyllactate from phenylalanine and hydroxyisocaproate from leucine). Other products were phenylpropionate, cinnamate and phenylacetate from phenylalanine; isocaproate, alpha-ketoisocaproate and isovalerate from leucine. Metronidazole inhibited the production of all end-products, with the exception of phenyllactate and hydroxyisocaproate which were increased. Similarly, when the reaction was carried out aerobically, the cells also metabolized both phenylalanine and leucine and all end-products were inhibited again with the exception of phenyllactate and hydroxyisocaproate. Our results suggest that the inhibitory mode of metronidazole is similar to that of oxygen.

Sterilization of infected root-canal dentine by topical application of a mixture of ciprofloxacin, metronidazole and minocycline in situ.

The aim of this study was to observe the potential of a mixture of ciprofloxacin, metronidazole and minocycline to kill bacteria in the deep layers of root canal dentine in situ. After the crowns of extracted teeth had been removed, the drug combination (0.5 mg of each drug), or sterile saline, as the control, was placed in the root canals which had been previously irrigated ultrasonically with G4M EDTA. The penetration and bactericidal efficacy were estimated by various procedures as follows. (1) A cell suspension of E. coli was placed into small cavities prepared parallel to the root canals on the cut planes of nine single-rooted teeth. The teeth were then entirely covered with blue inlay wax. At time 0, and at 5h, 24h and 48h after the drug combination had been applied, cells of E. coli were recovered from the cavities by washing the cavities several times with sterile saline solution, and were cultured on the surfaces of heart-infusion (HI) agar plates. Total colony-forming units were tuen counted. Bacterial recoveries decreased with time, and no bacteria were recovered 48 h after application of the drug combination, while bacteria survived in all cases with the controls, (2) After the drug combination or sterile saline had been placed into and sealed in the root canal with blue inlay wax, the teeth were placed into HI agar plates where cells of E. coli had been inoculated. After culturing, a clear zone caused by the inhibition of bacterial growth was observed around the teeth, but not in the control experiment. (3) After sampling infected root dentine of 12 freshly extracted teeth as positive controls, the drug combination (0.5 mg each) was placed in the root canals. No bacteria were recovered from the infected dentine of the root canal wall 24 h after application of the drug combination, except in one case in which a few bacteria were recovered. On the basis of these results, penetration through dentine and antibacterial efficacy of the drug combination can be expected against bacteria infecting the dentine of the root canal wall in situ when the drugs were placed in root canals which had been irrigated ultrasonically.

In-vitro antibacterial susceptibility of bacteria taken from infected root dentine to a mixture of ciprofloxacin, metronidazole and minocycline.

The aim of this study was to clarify the antibacterial effect of a mixture of ciprofloxacin, metronidazole and minocycline, with and without the addition of rifampicin, on bacteria taken from infected dentine of root canal walls. The efficacy was also determined against bacteria of carious dentine and infected pulps which may the precursory bacteria of infected root dentine. This efficacy was estimated in vitro by measuring bacterial recovery on BHI-blood agar plates in the presence or absence of the drug combination. Bacteria ranging in number from 10(2) to 10(6) occurred in samples of infected root dentine (27 cases). However, none was recovered from the samples in the presence of the drug combination at concentrations of 25 micrograms ml-1 each. The respective drug alone (10, 25, 50 and 75 micrograms ml-1) substantially decreased the bacterial recovery, but could not kill all the bacteria. Bacteria taken from carious dentine (25 cases) and infected pulps (12 cases) were also sensitive to the drug combination. These results may indicate that the bactericidal efficacy of the drug combination is sufficiently potent to eradicate bacteria from the infected dentine of root canals.

Pulpal response to a new light-activated fluoride releasing liner.

The purpose of this study was to investigate the degree of pulp irritation of a newly developed light-activated fluoride-releasing adhesive resin liner using canine teeth compared to the amount caused by a negative control, zinc oxide eugenol cement (ZOE), and a positive control, silicate cement (silicate). In the cases of unexposed pulp, this experimental liner showed none, slight or moderate pulpal changes at 3 d postoperatively. At 30 and 90 d, no pulpal response to the experimental liner was detected in almost all cases. These findings were similar to the ZOE and better than the silicate. There was less evidence of pulpal irritation produced by the experimental liner. This material seems to be safe to the pulp under the conditions of this study.

Direct observation of in vivo wear of composite resins.

This study developed a simple method for in vivo evaluation of wear on composite resins and examined the role of filler particles in this process. Experimental light-cured composite resins with two different filler systems were prepared: (1) 81 wt% fine quartz filler (Conventional type) and (2) 73 wt% organic filler (Microfilled type). The resin monomer consisted of 50 wt% Bis-GMA and 50 wt% TEGMA. These materials were placed in cylindrical cavities 2 mm in diameter located in the OCA (occlusal contact area) or the CFA (contact free area) in Au-Pd crowns, temporarily set in a volunteer's mouth. The crowns were removed at monthly intervals for longitudinal SEM observation. Results showed that the newly developed method was useful for observing the in vivo wear-patterns of composite resins. The two experimental composite resins with different filler systems showed quite different wear-patterns.

Bacterial invasion of non-exposed dental pulp.

Anaerobic procedures were adopted to demonstrate the early bacterial invasion of non-exposed dental pulps, and to isolate and identify the bacteria. Of 19 freshly extracted teeth which originally exhibited deep dentinal lesions, clinical examination and electric pulp testing showed that nine of them had no pulpal exposure. Thus the pulps of these teeth were covered by clinically sound dentine beneath the carious lesion. Bacteria were found to have invaded the pulps of six of these nine teeth. The predominant bacteria were obligate anaerobes belonging to the genera Eubacterium, Propionibacterium and Actinomyces. Other obligate anaerobes were Lactobacillus, Peptostreptococcus, Veillonella and Streptococcus. The bacterial composition resembled that of the deep layers of dentinal lesions described previously, suggesting that the bacteria isolated in this study had passed through some individual dentinal tubules, to invade the dental pulp.

Culture conditions for efficient recovery of bacteria from infected dental root canals.

For better bacterial recovery from endodontic lesions, several bacterial culture conditions were studied. Samples taken from endodontic lesions of 26 freshly extracted teeth, and the bacterial growth was determined in 11 kinds of growth media under aerobic (in air with or without addition of 5% CO2) or anaerobic conditions (in an anaerobic glove box). Among the media tested, bacteria of endodontic lesions were most efficiently recovered in brain heart infusion medium containing 4% sheep blood (BHI-Blood) under anaerobic conditions. For routine dental practice, serum can be substituted for blood which makes the media opaque, resulting in clear media, and thus bacterial growth can be judged more easily.

Plaque pH recovery by mouth-rinses with water.

A transistor pH electrode (pH-ISFET electrode) was placed in each of four human mouths and bacteria were allowed to accumulate on it for 1, 2 or 3 days. Changes of plaque pH were measured in situ after application of sucrose solution (0.1, 1 or 3%) and, then, quick pH recovery by mouth-rinses with water was estimated. Although the acidic pH after application of 0.1% sucrose was easily and quickly recovered from by a few mouth-rinses with water, rather frequent mouth-rinses with water were required to recover from the acidic pH of 2- or 3-day-old plaque after the application of a 1 or 3% sucrose solution. For example, 15 (mean, n = 4) mouth-rinses with water were required for the 3 day-old plaque pH to recover after the application of 3% sucrose solution.

Characterization of bacterial deposits formed in vivo on hydrogen-ion-sensitive field-effect transistor electrodes and enamel surfaces.

In order to clarify the bacteriological similarities of bacterial deposits formed on transistor pH electrodes (pH-ISFET) and enamel surfaces in vivo, bacteria were allowed to accumulate on indwelling electrodes in four human mouths, and the predominant bacteria were then isolated and characterized. Both the total number of bacteria accumulated per unit area and the population of predominant bacteria were similar for the electrodes and enamel surfaces, indicating that pH changes in the bacterial deposits formed on the electrodes can be representative of those occurring in natural dental plaque formed on enamel surfaces. Obligate anaerobes were predominant (68%) among the 346 isolates, and almost all the isolates were acidogenic. This may be a good reason why rapid pH-drop to pH 4 level was observed in every subject when 1% glucose or sucrose was applied to the bacterial deposits.

Bactericidal efficacy of metronidazole against bacteria of human carious dentin in vivo.

The bactericidal efficacy of metronidazole (MN) against bacteria of carious dentin was estimated by measuring bacterial recovery with or without application of MN to dentinal lesions in vivo. More than 10(3) colony-forming units of bacteria per milligram of sample were recovered from the samples of carious dentin. However, none were recovered from the samples of dentinal lesions which had been covered by alpha-tricalcium phosphate (TCP) cement containing MN in situ for 1 day, 1 month, 1 year and/or 2 years in vivo. Placebo experiments in which carious dentin was covered by TCP cement without MN showed that TCP itself was not bactericidal. Bactericidal efficacy of MN in situ is clearly demonstrated, indicating that MN is a valuable material in caries treatment to disinfect carious dentin.

Bactericidal efficacy of metronidazole against bacteria of human carious dentin in vitro.

The bactericidal efficacy of metronidazole against bacteria in carious dentin was clarified by measuring (1) the difference between bacterial recovery from suspensions of carious dentin on metronidazole-containing BHI-Blood agar plates (10 micrograms/ml) and control plates and (2) the difference between bacterial recovery from carious lesions of freshly extracted teeth, covered by alpha-tricalcium phosphate (TCP) cement containing metronidazole (5%) for 1-3 days and that covered by TCP only. More than 10(3) bacteria per milligram sample were recovered from carious dentin. More than 99% of the bacteria were, however, not recovered when samples were inoculated on metronidazole-containing BHI-Blood agar plates or when the lesions were covered by TCP cement containing metronidazole, indicating that metronidazole effectively disinfected the carious dentin.

Effect of casting methods on accuracy of peridental restorations.

The present study has shown that the accuracy of peridental gold alloy castings depends 1) on the type of casting machine used, 2) on the diameter of the casting sprue, and 3) on the strength properties of the investment material. The dependence between the accuracy and the three factors mentioned is based on erosion of the investment mold by the inflow of the liquid casting alloy. The vacuum casting technique proved to be a more gentle casting method than centrifugal and vacuum/pressure techniques.

A modified phosphate-bonded casting investment.

An experimental phosphate-bonded casting investment with negligible setting expansion and a thermal expansion of 1.6%, sufficient to compensate for the solid thermal shrinkage of conventional dental gold alloys and high-precious alloys for the porcelain fused to metal technique, is described. When used in a ringless casting technique the investment makes it possible to produce cast restorations with a consistent slidefit. In combination with a die spacer technique the new investment make if possible routinely to produce cast restorations with a consistent and known degree of loosefit.