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Biomedical subjects

R Hickel

Publications and source records attributed to R Hickel.

At least 37 records · Page 2Linked to original sources
PubMed2001

Cytotoxicity of dental composite components and mercury compounds in lung cells.

OBJECTIVE: The effect of dental composite components triethyleneglycoldimethacrylate (TEGDMA) and hydroxyethylmethacrylate (HEMA), as well as mercuric chloride (HgCl2) and methylmercury chloride (MeHgCl) was investigated on the release of lactatedehydrogenase (LDH) from alveolar epithelial lung cell lines in vitro. METHODS: The confluent cell layers from the A549 (human, malignant) and the L2 cells (rat) were incubated with various concentrations of HEMA, TEGDMA, MeHgCl and HgCl2 at 37 degrees C in 2% (v/v) CO2 atmosphere for 8h. In further experiments the L2 cells were incubated with the same compounds for 6-48 h. LDH release was measured and the values were expressed as percentage of the LDH content. The values were plotted on a concentration log-scale and the substance concentration at the maximum slope was assessed as effective concentration (EC50). RESULTS: A significant (p<0.05) increase in the LDH release was found in the L2 cells after 8-h incubation with HEMA (4 mmol/l), TEGDMA (2 mmol/l), MeHgCl (0.01 mmol/l) and HgCl2 (0.015 mmol/l), and in A549 cells with HEMA (14 mmol/l), TEGDMA (15 mmol/l), MeHgCl (0.15 mmol/l) and HgCl2 (0.05 mmol/l), compared to controls. The EC50 values from compounds in the L2 cells are shown in the following table (mean; sem in parentheses; n=3-6; #n=1): [see text]. SIGNIFICANCE: The toxic effect of HgCl2 and MeHgCl from the L2 cells was about 100-700-fold higher than of the dental composite components. A significant (p<0.05) time dependent increase of toxicity was observed with TEGDMA, HEMA and MeHgCl.

Animals↗
PubMed2001

Polymerization contraction stress in light-cured packable composite resins.

OBJECTIVE: Determination of the polymerization contraction stress of packable composites (ALERT, Surefil, Solitaire, Solitaire 2) and a packable ORMOCER material (Definite) in comparison with a conventional hybrid composite (Tetric Ceram). METHODS: Contraction force generated by the test materials (10 replications each) was measured by polymerizing the composites filled in a plastic tray between two aluminum attachments mounted in a Stress-Strain-Analyzer testing machine (specimen size: 4x4x2 mm, C-factor=0.33). Contraction force was recorded for 300s under a standard exposure condition (40s, 800mW/cm(2)). Maximum contraction stress (MPa), force rate (N/s), relative force rate (%/s) of each material were statistically analyzed by ANOVA (alpha=0.05) and post-hoc Tukey's test. RESULTS: Maximum contraction stresses of the packable materials were 4.60 +/- 0.32MPa (ALERT), 4.16 +/- 0.18MPa (Definite), 3.36 +/- 0.08MPa (Solitaire 2), 3.33 +/- 0.23MPa (Solitaire) and 3.13 +/- 0.18MPa (Surefil), which were significantly higher than that of Tetric Ceram (2.51 +/- 0.14MPa). Tetric Ceram exhibited the significantly lowest force rate. Force/time curves were S-shaped. Solitaire especially showed a longer pre-gelation phase before contraction force was recorded. SIGNIFICANCE: High contraction stress and rapid contraction force development can lead to failure of bond to tooth structure. This study suggested that, packable composite resins are less capable of reducing the contraction stress during the early setting stage, thus not superior in maintaining the bond with cavity walls to conventional hybrid composite Tetric Ceram.

Analysis of Variance↗
PubMed2001

Cytotoxicity of dental composite components and mercury compounds in pulmonary cells.

The cytotoxic potentials of the dental composite components triethyleneglycoldimethacrylate (TEGDMA) and 2-hydroxy-ethylmethacrylate (HEMA) as well as mercuric chloride (HgCl2) and methyl mercury chloride (MeHgCl) were investigated. Proliferating A549 and L2 cell monolayers were cultured in the absence or presence of composite components or mercurials. Twenty-four hours later the tetrazolium salt XTT (sodium 3'-[1-phenyl-aminocarbonyl)-3,4-tetrazolium]bis(4-methoxy-6-nitro)benzenesulphonic acid) was added. Formazan formation was quantified using a microtiter plate reader. EC50 values were obtained as half-maximum-effect concentrations from fitted curves. EC50 values were in A549 cells (mean values +/- standard deviation; n = 12; micromol/l); HEMA 8854+/-1882; TEGDMA 1821+/-529; HgCl2 41+/-7 and MeHgCl 27+/-3. EC50 values in L2 cells were: HEMA 191+/-28; TEGDMA 112+/-16; HgCl2 25+/-6 and MeHgCl 8+/-6. All tested substances induced a dose-dependent loss of viability in A549 and L2 cells after 24 h. The EC50 values of both mercurials were significantly (p < 0.05) lower compared to the values of both composite components. TEGDMA was about 5-fold (A549 cells) and about 2-fold (L2 cells) more toxic compared to HEMA. It is to be assumed that the risk of lung cell damage by dental composite components is even more unlikely.

Acrylic Resins↗
PubMed2001

Marginal quality and microleakage of adhesive class V restorations.

OBJECTIVES: The aim of this in vitro study was to determine the marginal quality and microleakage of composite resin class V restorations. METHODS: Standardized mixed class V cavities (diameter: 4mm, depth: 2mm) with half of the finish lines limited within dentin were cut in 90 freshly extracted human molars and randomly assigned to nine groups (n=10). After etching enamel and dentin, the cavities were restored with nine different restorative systems (Syntac Sprint/Tetric Ceram=SS, Syntac Single-Component/Tetric Ceram=SC, Onestep/Aeliteflo=OS, Aquaprep+Onestep/Aeliteflo=OA, Prime & Bond 2.1/TPH=PB, Optibond Solo/Prodigy=OP, Singlebond/Z100=SB, Tenure Quik/Marathon=TQ, Solobond M/Arabesk=SM) using a wet-bonding procedure. After finishing and polishing, the teeth were stored for 24h in distilled water at 37 degrees C before they were subjected to thermocycling (5/55 degrees C, 1000x). Epoxy replicas were made for margin analysis in the SEM. Specimens were stained in methylene blue, sectioned, and evaluated for microleakage. Dye penetration was scored on a 0-3 ordinal scale. RESULTS: Statistical analysis (Kruskal-Wallis H-test, Mann-Whitney U-test) revealed significant differences (P<0.05) among the groups at dentin and enamel margins for the microleakage scores as well as for the results of the quantitative SEM margin analysis. SC revealed a significantly higher percentage of perfect margins in the SEM than OS and SM in enamel and dentin, respectively. OA exhibited significantly more leakage in enamel than all other groups. CONCLUSIONS: None of the tested restorative systems achieved a perfect seal in dentin and enamel of mixed class V cavities. Marginal quality and sealing ability of adhesive systems to dentin, using a wet-bonding procedure, is still inferior compared with enamel margins.

Barium Compounds↗
PubMed2001

The effect of working tip angulation on root substance removal using Er:YAG laser radiation: an in vitro study.

OBJECTIVES: The present investigation attempted to determine the amount of cementum and/or dentin removal with Er:YAG laser radiation, dependent on the angulation of a specially-developed application tip. MATERIAL AND METHODS: Subject of the study were 150 extracted incisors, canines, premolars, and molars. Source of laser radiation was an Er:YAG laser device emitting pulsed infrared radiation at a wavelength of 2.94 microm with a pulse duration of 250 micros and a pulse repetition rate of 10 pps. The samples of the 3 study groups were irradiated with 380 laser pulses at radiation energies of 60 mJ (group A), 100 mJ (group B), or 180 mJ (group C). In each group, 10 samples were treated at working tip angulations of 15 degrees , 30 degrees , 45 degrees , 60 degrees , and 90 degrees. The substance removal was determined 3-dimensionally using a newly developed laser scanning system (100,000 surface points per sample, accuracy 5 microm) and a special image-analysing software (Match 3D). Statistical analysis was completed with ANOVA followed by multiple comparisons using the Scheffé-test and with linear regression analysis according to Pearson-Bravais (p < 0.05). RESULTS: Strong dependence of substance removal, both determined as maximum depth of the defects (0.5% quantil) as well as defect volume, on the angulation of the working tip was shown. At 60 mJ, the depth of the defects was 41.39 (+/- 32.55) microm at an angulation of 15 degrees and that at 90 degrees was 181.39 (+/- 74.42) microm (R2= 0.921). For the radiation energy at 100 mJ, the depth of the defects ranged from 51.96 (+/- 26.86) microm at 15 degrees to 306.64 (+/- 62.44) microm at 90 degrees (R2 = 0.983). Choosing radiation energies at 180 mJ, the depth of the defects ranged from 64.73 (+/- 27.73) microm at 15 degrees to 639.89 (+/- 47.28) microm at 90 degrees , on average (R2 = 0.853). CONCLUSIONS: The results of the present study provide clear evidence that besides the physical radiation parameters, also the parameters of clinical handling, in particular the angulation of the application tip, has a strong influence on the amount of root substance removal using Er:YAG laser radiation.

Aluminum Silicates↗
PubMed2001

Distribution and excretion of TEGDMA in guinea pigs and mice.

The monomer triethyleneglycoldimethacrylate (TEGDMA) is used as a diluent in many resin-based dental materials. It was previously shown in vitro that TEGDMA was released into the adjacent biophase from such materials during the first days after placement. In this study, the uptake, distribution, and excretion of 14C-TEGDMA applied via gastric, intradermal, and intravenous administration at dose levels well above those encountered in dental care were examined in vivo in guinea pigs and mice as a test of the hypothesis that TEGDMA reaches cytotoxic levels in mammalian tissues. 14C-TEGDMA was taken up rapidly from the stomach and small intestine after gastric administration in both species and was widely distributed in the body following administration by each route. Most 14C was excreted within one day as 14CO2. The peak equivalent TEGDMA levels in all mouse and guinea pig tissues examined were at least 1000-fold less than known toxic levels. The study therefore did not support the hypothesis.

Animals↗
PubMed2001

The suitability of packable resin-based composites for posterior restorations.

BACKGROUND: Packable composites, promoted for the restoration of stress-bearing posterior teeth, have captured clinicians' interest. METHODS: The authors tested three packable composites (Alert, Jeneric/Pentron; Solitaire, Heraeus Kulzer, Wehrheim, Germany; SureFil, Dentsply De Trey, Konstanz, Germany); a new packable organically modified ceramic, or ormocer (Definite, Degussa AG, Hanau, Germany); a hybrid composite (Tetric Ceram, Ivoclar Vivadent, Schaan, Liechtenstein) and an ion-releasing composite (Ariston pHc, Ivoclar Vivadent, Schaan, Liechtenstein). They determined modulus of elasticity according to EN 24049:1993 of the European Committee for Standardization. They measured Vickers hardness using a 200-gram load for 40 seconds. To determine the materials' depth of cure, they used both a scraping method (International Standards Organization standard CD 4049:1997) and a hardness profiling method. RESULTS: The authors calculated means and standard deviations from 10 replications of each test and used one-way analysis of variance and post hoc Tukey tests (alpha = .05). The materials had significant differences (P < .001) in all characteristics. Solitaire had the significantly lowest elastic modulus and microhardness; Alert had the highest values for these characteristics. Ariston pHc exhibited the significantly lowest depth of cure. There was a significant correlation between the two methods of measuring depth of cure (r2 = 0.9945; P = .021). CONCLUSIONS: The material group of packable composites is rather inhomogeneous in terms of mechanical and physical data. Our data suggest that bulk curing of packable composites in deep cavities still is not recommendable. CLINICAL IMPLICATIONS: The clinician needs to select packable composites carefully, as it seems that not all of these materials quality for stress-loaded posterior restorations.

Analysis of Variance↗
PubMed2001

Longevity of restorations in posterior teeth and reasons for failure.

PURPOSE: This article compiles a survey on the longevity of restorations in stress-bearing posterior cavities and assesses possible reasons for failure. MATERIALS AND METHODS: The dental literature predominantly of the last decade was reviewed for longitudinal, controlled clinical studies and retrospective cross-sectional studies of posterior restorations. Only studies investigating the clinical performance of restorations in permanent teeth were included. Longevity and annual failure rates of amalgam, direct composite restorations, glass ionomers and derivative products, composite and ceramic inlays, and cast gold restorations were determined for Class I and II cavities. RESULTS: Annual failure rates in posterior stress-bearing restorations are: 0% to 7% for amalgam restorations, 0% to 9% for direct composites, 1.4% to 14.4% for glass ionomers and derivatives, 0% to 11.8% for composite inlays, 0% to 7.5% for ceramic restorations, 0% to 4.4% for CAD/CAM ceramic restorations, and 0% to 5.9% for cast gold inlays and onlays. CONCLUSION: Longevity of dental restorations is dependent upon many different factors that are related to materials, the patient, and the dentist. The principal reasons for failure were secondary caries, fracture, marginal deficiencies, wear, and postoperative sensitivity. A distinction must be made between factors causing early failures and those that are responsible for restoration loss after several years of service.

Bicuspid↗
PubMed2001

Three-year clinical evaluation of composite and ceramic inlays.

PURPOSE: To evaluate the 3-yr clinical performance of composite and ceramic inlays in posterior teeth. MATERIALS AND METHODS: 47 composite inlays (Tetric, Blend-a-Lux, Pertac) and 24 ceramic inlays (Empress) were placed by seven student operators under supervision of an experienced dentist. Clinical assessment of 58 inlays (81.7%) was performed after 3 yrs using amodified USPHS criteria and statistically analyzed with Mann-Whitney U test and Fisher's exact test. RESULTS: A total of 100% of the ceramic inlays and 89% of the composite inlays were assessed to be clinically excellent or acceptable. Three composite inlays failed during the first yr and one had to be replaced during the second evaluation period. All composite inlay failures were recorded on molars, revealing a significantly higher failure rate compared with premolars (Fisher's test, P = 0.041). Ceramic inlays revealed a significantly better "anatomic form of the surface" (P = 0.027) and "integrity of the restoration" (P = 0.035). Inlays in small cavities performed better for "marginal integrity" (P = 0.033) and "discoloration at the margin" (P = 0.038).

Adult↗
PubMed2001

Clinical performance of a resin-modified glass-ionomer and a compomer in restoring non-carious cervical lesions. 5-year results.

PURPOSE: To evaluate the 5-yr clinical performance of a resin-modified glass-ionomer cement and a polyacid-modified resin composite in restoring non-carious cervical lesions. MATERIALS AND METHODS: Non-carious cervical lesions in 46 incisors, canines, and premolars were restored either with Fuji II LC (n=18) or with Dyract (n=28) in 16 healthy patients. The lesions were restored without cavity preparation strictly according to the manufacturer's instructions. The restorations were clinically evaluated single blind after 5 yrs using modified USPHS criteria. RESULTS: The percentage of Alfa ratings were as follows (Dyract/Fuji II LC): color match 81.3%/28.6%, surface texture 93.8%/21.4%, anatomic form 75.0%/28.6%, marginal integrity (enamel) 62.5%/42.9%, marginal integrity (dentin) 68.8%/28.6%, marginal discoloration (enamel) 56.3%/42.9%, marginal discoloration (dentin) 68.8%/21.5%. Five-yr data revealed a significant difference between the clinical ratings of Dyract and Fuji II LC for all criteria except marginal integrity and marginal discoloration in enamel. A total of five Dyract restorations and four Fuji II LC restorations failed within the study period. CLINICAL SIGNIFICANCE: A considerably high and almost similar overall failure rate was found for both restorative materials in restoring non-carious cervical lesions. However, retained Dyract restorations presented superior clinical performance compared to Fuji II LC restorations.

Acrylic Resins↗
PubMed2001

Wear evaluation of MZ100 compared to ceramic CAD/CAM materials.

The material and antagonist wear of two CAD/CAM ceramic materials, the laboratory-processed IPS Empress ceramic, and the composite mill block material MZ100 were tested in an artificial wear simulator with human enamel as the antagonistic material. The material samples underwent 50,000 test cycles (1 cycle per second, 50 N) in distilled water. The wear of the material samples and of the opposing enamel was documented after 30,000 and 50,000 cycles with replicas, digitized, and evaluated with a 3D evaluation system. The loss of volume and height caused by wear was calculated. No significant difference between the ceramic materials could be found either in the amount of material or in the amount of antagonist wear. The material wear of MZ100 differed significantly from Vita Mark II only in terms of volume loss. Regarding height loss, MZ100 exhibited a significantly higher wear than all ceramic materials. The wear of the enamel antagonists does not differ significantly between the ceramic materials. With MZ100, however, a significantly smaller amount of enamel wear was found when compared with Empress and Vita Mark II. Despite the highest material wear, MZ100 had the lowest material wear rate, the lowest enamel wear rate, and the lowest total wear rate. The laboratory-processed IPS Empress material had a clearly higher material wear rate than the CAD/CAM materials.

Aluminum Silicates↗
PubMed2000

Steady-state transfer and depletion kinetics of mercury from amalgam fillings.

In 29 volunteers with a low amalgam load, the number of amalgam-covered tooth surfaces and the occlusal area of the fillings were determined. Before and at select times after removal of all amalgams, concentrations of total mercury were measured by cold-vapor atomic absorption in plasma and erythrocytes as well as in urine together with the excretion rate. Absorbed daily doses were estimated from intraoral Hg emission by two separate methods. The transfer of Hg from the fillings via the oral cavity and blood to urinary excretion was evaluated according to the most representative combination of parameters. This consisted of occlusal area (1), absorbed dose (2), Hg concentration in plasma (3) and urinary excretion (4). Pairwise correlation coefficients were 0.49 for parameters 1 vs. 2, and 0.75 each for parameters 2 vs. 3 and 3 vs. 4. Within 9 days after removal of the fillings, a transient increase in Hg levels was observed in plasma only; in the group without a rubber dam, concentrations increased significantly above pre-removal values at days 1 and 3, whereas they decreased significantly below pre-removal values at day 30 in the rubber-dam group and at day 100 in both groups. Excretion rates decreased significantly at day 100 in the protected group. Peak plasma-Hg was 0.6 ng/ml on average at day 1 and decreased with halftimes of 3 and 43 days in subjects protected by a rubber dam. The results indicated that concentrations of total mercury in plasma responded rapidly to changes in the amalgam status and reflected the actual absorption most reliably. Notably, plasma-Hg levels were sensitive enough to detect a transient attenuation of the additional exposure after using a rubber dam during the removal of only a few fillings. However, being small in magnitude and lasting 100 days at best, the rubber-dam effect had minor toxicological relevance.

Adult↗
PubMed2000

Mechanical properties of new composite restorative materials.

OBJECTIVE: Determination of flexural strength, flexural modulus, fracture toughness, Vickers hardness, and wear resistance of condensable composites (Solitaire, Surefil, Alert) and an ormocer (Definite) in comparison with a hybrid composite (Tetric Ceram) and an ion-releasing composite (Ariston pHc). METHODS: Flexural strength, flexural modulus, and fracture toughness were determined in 3-point bending. Single-edge notched-bend specimens were used to evaluate fracture toughness. Microhardness was measured with a Vickers indenter. Wear was determined in a pin-on-block-design with a Degusit antagonist at 50 N load and quantified by a replica technique after 6000, 10000, 30000, and 50000 load cycles using a 3D-laser scanner. All results were statistically analyzed with ANOVA and post hoc Tukey HSD tests. RESULTS: Alert exhibited the highest flexural modulus, K(IC), and hardness, but lowest wear resistance. Solitaire presented the highest wear resistance, but significantly lower flexural strength, flexural modulus, K(IC), and hardness than all other materials. No significant correlation could be detected between hardness and wear of the tested composites with Pearson's correlation coefficient. SIGNIFICANCE: The condensable composites differed significantly in their mechanical properties. This study suggested that, besides the filler content level and filler size, other factors like matrix-filler interactions highly influence the fracture and wear behavior of the materials.

Composite Resins↗
PubMed2000

A 2-year clinical study of composite and ceramic inlays.

Objective long-term clinical data are necessary to evaluate the performance of dental restorations. This prospective clinical trial evaluated composite and ceramic inlays for clinical acceptability as restorative materials in posterior teeth and provided 2-year results. The study involved 7 student operators placing 47 composite inlays (Tetric, blend-a-lux, Pertac) and 24 ceramic inlays (Empress) under the supervision of an experienced dentist. Clinical assessment of 56 inlays (78.9%) was performed after 2 years with modified USPHS criteria and statistically analyzed using the Mann-Whitney U test and Fisher's exact test. All the ceramic inlays and 90% of the composite inlays were considered clinically excellent or acceptable. During the first year 3 composite inlays failed and during the second evaluation period 1 had to be replaced. Ceramic inlays produced significantly better "anatomic form of the surface" (P = 0.038) and "integrity of the restoration" values (P = 0.043). Inlays in small cavities exhibited superior "marginal integrity" (P = 0.026) and "marginal discoloration" values (P = 0.034). Fisher's test revealed a significantly higher failure rate in molars than in bicuspids (P = 0.034). Posterior tooth-colored inlays exhibited a success rate of 100% for ceramic inlays and 90% for composite inlays even if placed by relatively inexperienced but supervised student operators.

Adult↗
PubMed2000

Mechanical properties and wear behavior of light-cured packable composite resins.

OBJECTIVES: Determination of flexural strength, flexural modulus, fracture toughness and wear resistance of three packable composites (Solitaire, Surefil, ALERT) and a packable ormocer (Definite) in comparison with an advanced hybrid composite (Tetric Ceram) and an ion-releasing composite (Ariston pHc). METHODS: Flexural strength, flexural modulus and fracture toughness of each material were determined in three-point bending (each test n = 10). Single-edge notched-bend specimens were used to evaluate the fracture toughness (K1C). Wear of the materials (n = 8) was determined in a pin-on-block-design with a spherical Degusit antagonist at 50 N vertical load and quantified by a replica technique using a 3D-laser scanner. Replicas were made after 6000, 10,000, 30,000 and 50,000 load cycles. The mean wear rate (MWR (micron 3 cycle-1)) was obtained by a linear regression analysis in the steady-state of the time-wear-curve. All results were statistically analyzed with ANOVA and post hoc Tukey HSD tests (p < 0.05). RESULTS: ALERT exhibited the highest flexural modulus (12.5 +/- 2.1 GPa) and K1C (2.3 +/- 0.2 MN m-3/2), but the lowest wear resistance (8275 micron 3 cycle-1). Solitaire presented the highest wear resistance (1591 micron 3 cycle-1), but significantly lower flexural strength (81.6 +/- 10.0 MPa), flexural modulus (4.4 +/- 0.3 GPa), and K1C (1.4 +/- 0.2 MN m-3/2) than all other materials. Surefil revealed a significantly higher flexural modulus (9.3 +/- 0.9 GPa) and wear resistance (3028 micron 3 cycle-1) than Tetric Ceram (6.8 +/- 0.5 GPa; 5417 micron 3 cycle-1) and Ariston pHc (7.3 +/- 0.8 GPa; 7194 micron 3 cycle-1). SIGNIFICANCE: The tested packable composite resins differed significantly in their mechanical properties. This study suggested that fracture and wear behavior of the composite resins are highly influenced by the filler system. Overall, Surefil demonstrated good fracture mechanics parameters and a low wear rate.

Analysis of Variance↗
PubMed2000

Lack of antimicrobial effect on periodontopathic bacteria by ultrasonic and sonic scalers in vitro.

BACKGROUND: The purpose of this study was to assess the antimicrobial effects of a sonic and ultrasonic scaler generally used for subgingival scaling on gram-negative and gram-positive periodontopathic bacteria. METHOD: Actinobacillus actinomycetemcomitans, Porphyromonas gingivalis, Campylobacter rectus, or Peptostreptococcus micros were suspended in Schaedler's broth medium and treated by a sonic or a magnetostrictive ultrasonic scaler for 30 s and 150 s in vitro. Bacterial suspensions treated by an ultrasonic cell disruptor served as a positive control and untreated bacterial suspensions served as a negative control. Following sonication, samples were serially diluted, streaked on blood agar plates and incubated for 2-5 days at 37 degrees C. RESULTS: Treatment by the sonic or ultrasonic scaler for up to 150 s did not reduce the viability of any of the tested periodontal pathogens. Compared to untreated controls, the viability of A. actinomycetemcomitans and P. gingivalis was significantly (p<0.05) reduced only following ultrasonication with the cell disruptor after 30 s (0.72 and 0.54 log CFU/ml, respectively) and of A. actinomycetemcomitans, P. gingivalis, C. rectus, and P. micros after 150 s (1.98, 1.34, 1.95 and 1.98 log CFU/ml, respectively). CONCLUSION: The data of the study may indicate that the assessed sonic and ultrasonic scaler used for subgingival debridement do not result in killing of the tested periodontal pathogens.

Colony Count, Microbial↗