Biomedical subjects

R Pilo

Publications and source records attributed to R Pilo.

At least 19 recordsLinked to original sources

PubMed2000

Furcation groove of buccal root of maxillary first premolars--a morphometric study.

Furcation grooves on the palatal aspect of the buccal roots of 35 maxillary first premolars, randomly selected, were assessed and found to exist in 97% of the sample. The buccal roots were sectioned into slices, 1 mm thick, and morphometric horizontal and vertical measurements were taken by a Toolmaker Microscope. The slice with the deepest invaginations served as the reference plane. The deepest invaginations were found to be at a mean distance of 1.18 mm from the bifurcation, with a mean depth of 0.4 mm. The canal had a kidney-shaped appearance in cross-section, and the mean distance from the invagination to the canal wall was 0.81 mm. It is thus hazardous to use rotary instruments for flaring these roots and any circular-shaped post space preparation at this level is contraindicated. The outcome of such procedures might be root thinning, perforation, or vertical root fracture, thus causing a poor prognosis.

Bicuspid↗

PubMed2000

Effect of various mixing ratios on antibacterial properties and hardness of endodontic sealers.

Most chemically cured two-component dental materials, including endodontic sealers, are marketed with mixing instructions but with no strict mixing ratios. The present study evaluated the antibacterial properties and hardness of three endodontic sealers: Roth's cement (RC), CRCS, and AH26, mixed to four controlled consistencies within the range of the manufacturer recommendations. Using Enterococcus faecalis as the test microorganism, antibacterial activity was evaluated by agar diffusion and direct contact test. Surface hardness of sealers with the same consistency was evaluated on week-old specimens by the Knoop Hardness Number tester. In the agar diffusion test, light consistency of RC showed larger zones of inhibition than heavier consistency, whereas no significant differences were found with AH26 or CRCS. In the direct contact test, RC and CRCS exhibited complete inhibition of bacterial growth at all consistencies, whereas AH26 with the heavier consistencies did not inhibit bacterial growth at 24 h samples. The hardness of AH26 and CRCS was significantly lower with lighter consistencies. It is concluded that endodontic sealers possess different antibacterial and physical properties according to their mixing consistencies.

Anti-Infective Agents, Local↗

PubMed2000

Residual dentin thickness in mandibular premolars prepared with gates glidden and ParaPost drills.

STATEMENT OF PROBLEM: The main factor that determines the prognosis of restored pulpless teeth is preservation of sound dentin. PURPOSE: This study evaluated the residual dentinal thickness (RDT) of mandibular premolars after preparation of post space with Gates Glidden and ParaPost drills. MATERIAL AND METHODS: Twelve extracted single canal mandibular premolars were embedded in clear polyester resin to the cementoenamel junction (CEJ) in a muffle device. Three horizontal sections were made 1, 3, and 5 mm apical to the CEJ. Mesiodistal (MD) and faciolingual (FL) axes were carefully marked and the RDT was measured for each slice. Each tooth slice was reassembled in the muffle device with orientation pins, then secured with stabilizing pins. This procedure was repeated after enlarging the root canal to K-40 file and preparing the coronal root canal space with Gates Glidden drills and ParaPost drills Nos. 3, 4, and 5. RESULTS: Residual dentinal thickness in a MD direction was 3.77 +/- 0.51 mm in the unprepared upper slice and 2.23 +/- 0.31 mm in the No. 5 ParaPost drill prepared lower slice, for a difference of 41%. The corresponding values for the FL direction were 4.35 +/- 0.51 mm and 4.08 +/- 0.46 mm, respectively (6%). CONCLUSION: The average dentinal thickness 5 mm below the CEJ in the mesial and distal directions after post space preparation approached the accepted minimal 1 mm. A conservative approach to post space preparation was advocated.

Analysis of Variance↗

PubMed1999

Comparison of microleakage for three one-bottle and three multiple-step dentin bonding agents.

PURPOSE: This in vitro study compared the ability of several recently introduced 1-bottle adhesives to their preceding multiple-step dentin bonding agents in reducing microleakage around Class V composite restorations. MATERIAL AND METHODS: Facial and lingual Class V cavities were prepared in 48 molar teeth, which were randomly divided into 6 equal groups. Three groups used the fourth-generation multiple-step systems, and 3 used the fifth-generation single-bottle adhesives. All cavities were restored by composite and subjected to thermocycling and intermittent occlusal loading. After immersion in 0.5% basic fuchsin, the teeth were cut faciolingually in 5 consecutive sections and evaluated for dye penetration using a binocular stereomicroscope. RESULTS: There was no statistically significant difference in the degree of microleakage comparing the adhesive's generation and manufacturer and the location of the cavity margins. A significant interaction was found between margin location and manufacturer, which implied that the sealing capacity at the enamel and cementum margins was material-specific. CONCLUSION: Scotchbond Multi-Purpose and Single Bond adhesives provided the best seal for enamel margins, and One-Step and Optibond FL adhesives were best for cementum margins.

Adhesives↗

PubMed1999

Effect of glaze thickness on the fracture toughness and hardness of alumina-reinforced porcelain.

STATEMENT OF PROBLEM: Although porcelain is the most esthetic restorative material available, it is subject to fracture during function. Glazing reduces the size of flaws in the surface of the porcelain and increases its resistance to crack propagation, but the optimum thickness of this glazed layer has not been determined. PURPOSE: This study compared the fracture toughness (Kc ) and Vickers hardness number (VHN) of an alumina-reinforced porcelain at different thicknesses of glaze. MATERIAL AND METHODS: Disks of feldspathic porcelain reinforced with 2% aluminum oxide were prepared and glazed for 0, 30, 60, 90, and 120 seconds. Fracture toughness and Vickers microhardness were determined with a microindentation technique. Thickness of the glazed layers was measured with a SEM. RESULTS: Mean Vickers hardness number and fracture toughness values both decreased significantly with glazing times from 0 to 60 seconds, and increased significantly with glazing times from 60 to 120 seconds (P <.001, ANOVA). SEM examination revealed an increase in glazed layer thickness with increased glazing time. CONCLUSIONS: Minimal and maximum thicknesses of glaze layers on alumina-reinforced porcelain resulted in a surface that was harder and more resistant to fracture than moderate glaze thicknesses.

Aluminum Oxide↗

PubMed1999

Analysis of strength properties of light-cured resin composites.

OBJECTIVES: To determine and correlate the compressive and tensile strengths of resin composites, to scale their failure probability and to analyze their failure mode under combined state of stresses. METHODS: Ten brands of composites were tested for compressive and diametral tensile strengths. A recently introduced device for testing of pure shear stresses was modified to adapt to smaller specimens. Uniformity of pure shear stress distribution in the significant section was verified by a photoelastic model. Loading specimens in pure shear up to failure determined their mode of fracture under combined state of stresses. RESULTS: Diametral tensile strength yielded values that were 20% of their respective compressive strength. Multiple comparison test indicated that strength properties of the tensile strength test were much more sensitive in predicting differences between resin composites when compared to a compressive strength test. Pertac (Espe) had the highest compressive strength, Graft LC (GC) and Z-100 (3M) had the highest diametral tensile strength. No correlation was found between tensile and compressive strengths. The Weibull modulus disclosed differences in the liability of the materials to fracture. When combined state of stresses were applied through the pure shear test, failure of each specimen occurred at the principal tensile planes. SIGNIFICANCE: Compressive strength cannot predict the ability of the resin composite to withstand tensile stresses. The importance of compressive strength is limited as failure of a brittle material occurs in tension.

Analysis of Variance↗

PubMed1999

A survey of output intensity and potential for depth of cure among light-curing units in clinical use.

OBJECTIVES: The light intensity of curing lights used in private dental offices was measured using commercial curing and heat radiometers and related to uniformity of cure depth of standardized composite specimens. METHODS: The intensity of 130 curing light from 107 dental offices was measured with curing and heat radiometers. Due to analogue readings, results were recorded in steps of 25 mW cm-2 and assigned a category number. A total of 50 lights were randomly selected to polymerize standardized 3 mm thick composite cylinders. The composite was irradiated for 50 s according to the manufacturer's instructions. The Knoop hardness value was measured at the top and bottom surfaces and the uniformity of cure depth was calculated from the ratio of these two values. RESULTS: Light intensity measured by the curing and heat radiometers was in the range of 25-825 and 0-325 mW cm-2, respectively. Functions of maximum likelihood estimation of the top and bottom surface hardness were 57 N/N + 1.3 and 80 N/N + 17.7, respectively (N = light intensity category number). The relationship between the logarithmic transformation of the hardness ratio and light intensity was linear (R2 = 0.84 p < 0.001). CONCLUSION: According to the manufacturer, a curing light is considered as unsuitable for use with a reading of < 200 mW cm-2 by the curing radiometer and > 50 mW cm-2 by the heat radiometer. Applying these criteria to the present study, 46% of the lights (without repetitions) required repair or replacement. The strong correlation found between the hardness ratio and light intensity verifies the usefulness of the curing radiometer in predicting the polymerization ability of the light activation units.

Composite Resins↗

PubMed1999

pH changes of glass-ionomer lining materials at various time intervals.

The purpose of this in vitro study was to evaluate pH changes of resin modified glass-ionomer (RMGI) and conventional glass-ionomer liners at short-term intervals after mixing to relate the timing of light activation on the acidity of RMGI lining materials. The RMGI liners tested were Vitrebond (3M), Variglass VLC (Dentsply), Fuji Lining LC (GC Dental Industrial Corp.) compared to a traditional glass-ionomer liner: Lining Cement (GC, control). Light activation of liners was carried out at different time intervals after mixing. The pH changes of each liner were evaluated immediately after mixing and thereafter every minute for 8 min using a surface pH meter. All liners tested exhibited a gradual increase in surface pH over time. The delay of light activation of RMGI lining materials after mixing did not significantly decrease the acidity of the liner during the first 9 min post-mixing.

Acids↗

PubMed1998

In vivo retrospective study of cement thickness under crowns.

PURPOSE: This study evaluated the cement thickness under crowns cemented with zinc phosphate cement that had been in clinical use for at least 10 years. MATERIAL AND METHODS: A total of 97 teeth were extracted because of periodontal disease as part of a new treatment plan. Teeth were sectioned and the cement thickness measured at predetermined points on the occlusal and axial walls with a measuring microscope at x150 magnification. RESULTS: Mean cement thicknesses on buccal and lingual walls were similar (116 microns and 109 microns, respectively), but much smaller than on occlusal walls (310 microns). Cement thicknesses at occlusal locations were significantly thicker in molars than in premolars. Poor correlations existed between cement thicknesses on buccal and lingual walls (0.26) and between these and the occlusal walls (0.35) implying that incomplete seating is strongly related to tilting or oblique seating. CONCLUSION: Under clinical conditions where more inherent difficulties exist, special measures must be taken to alleviate the consequences of cement fluid dynamics.

Analysis of Variance↗

PubMed1998

The influence of abutment angulation on strains and stresses along the implant/bone interface: comparison between two experimental techniques.

STATEMENT OF PROBLEM: Preangled abutments produce different stress distribution compared to straight abutments. PURPOSE: The objectives of this study were to (1) test the hypothesis that preangled abutments produce different stress distribution than straight abutments by using strain gauges attached to implants embedded in a medium simulating bone to determine strain distribution along the implant/bone interface; (2) test this hypothesis by photoelastic method; and (3) compare the two experimental techniques. MATERIALS AND METHODS: Five Integral Omniloc cylindrical implants 13 x 4 mm were polished to remove the hydroxyapatite coating, then six linear miniature strain gauges were attached, three on each side of the implant's surface. Two similar implants were embedded in a photoelastic material. Three abutments, straight, 15 degrees, and 25 degrees, were connected to each implant; strain versus applied compressive forces were recorded. Strain response to force parameter was defined as the slope of the strain-force curve. Isochromatic fringe patterns were also recorded. RESULTS: The strain gauge measurements showed higher, threefold and 4.4-fold, compressive strain concentration in the coronal zone of the implant when 15-degree and 25-degree angulated abutments were used, respectively, compared with the straight abutment; whereas the photoelastic method showed an increase of only 11% in fringe order. Tensile strains were also measured from the coronal contralateral position on the implant, where photoelastic models did not show a change in stress type. CONCLUSIONS: Data obtained from strain gauges bonded to implants embedded in a medium can represent a precise simulation of the clinical condition when analyzing stress distribution along the implant/ bone interface. Photoelasticity provides different information and therefore should be regarded as a complementary method.

Analysis of Variance↗

PubMed1998

Residual dentin thickness in mandibular premolars prepared with hand and rotatory instruments.

The residual dentin thickness in the coronal part of root canals of mandibular premolars after stepback preparation and flaring with Gates Glidden (GG) drills was assessed sequentially in a newly designed muffle device. Twelve extracted teeth were embedded in clear polyester resin, sectioned horizontally (1, 3, and 5 mm apically to the cementoenamel junction), and reassembled in the muffle device. The sequence of canal preparation was K-files to #40, then GG-2 and GG-4. After each procedure, the slices were separated and residual dentin thickness measured by a toolmaker microscope in four directions (buccal, lingual, distal, and mesial) and reassembled in the muffle device. Statistical analysis by three-way analysis of variance with repeated measures was undertaken. The difference in residual dentin thickness was highly significant with regard to instrument (control, K-40, GG-2, GG-4; p < 0.0001), slice (upper, middle, and lower; p < 0.0003), and direction (B, L, M, and D; p < 0.001). In each slice, the width of the mesial side was similar to the distal side, as was the buccal to the lingual sides. Reduction of residual dentin thickness in the mesiodistal direction, from the unprepared upper slice to the GG-4 prepared lower slice, was appreciably greater (35%) than in the buccolingual direction (5%).

Analysis of Variance↗

PubMed1998

A new muffle model system to study root canal morphology and instrumentation techniques.

A new muffle model system is presented using the principle of internal indexing. The system is composed of a metal stand, four pins, and a single Teflon mold that is used for the investment of all teeth. This system is very precise, reproducible, and versatile. The sectioned specimens can easily be stored assembled, as opposed to previous systems that rely on external indexing.

Dental Pulp Cavity↗

PubMed1997

Effect of irradiation time on tensile properties of stiffness and strength of composites.

PURPOSE: We compared the effect of irradiation time on the diametral tensile strength and stiffness of three visible light-cured composites. The sensitivity of the two mechanical properties to differentiate between the materials was also investigated. MATERIAL AND METHODS: Cylindrical specimens of three composites were cured for 20, 40, 80, and 120 seconds (n = 10) and loaded up to failure in a diametral tensile strength test. Stiffness and diametral tensile strength values were recorded. RESULTS: Irradiation time significantly influenced diametral tensile strength (p = 0.0017) and stiffness (p = 0.0002). With the same irradiation times the three tested materials demonstrated no significant difference when diametral tensile strength was studied (p = 0.31). However, stiffness values did show a significant difference (p = 0.0002). CONCLUSIONS: This study found that stiffness is more sensitive in disclosing differences in tensile properties between the materials than diametral tensile strength.

Bisphenol A-Glycidyl Methacrylate↗

PubMed1997

Effect of combinations of surface treatments and bonding agents on the bond strength of repaired composites.

STATEMENT OF PROBLEM: Enhancement of bond strength between new and old composite usually requires increasing the surface roughness to promote mechanical interlocking and coating of old composite with unfilled resin bonding agents to advance surface wetting and chemical bonding. PURPOSE: The purpose of this study was to evaluate the effect of combinations of surface treatments and bonding agents on the shear bond strength between new and old composite. MATERIAL AND METHODS: Six surface treatments, two bonding agents, and an untreated control comprised 18 different subgroups. RESULTS: The use of unfilled resin, alone or combined with silane, was the most effective procedure to enhance the shear bond strength of the repaired composite specimens, irrespective of the surface pretreatment processes. Silanation and unfilled resin slightly but not significantly improved the repair strength compared with unfilled resin alone. CONCLUSIONS: Different combinations of surface treatments and bonding agents affect shear bond strength differently. The highest shear bond strength values were achieved by grinding the surface with green Carborundum stone or sandblasting, whereas the lowest values were obtained with hydrofluoric acid as the surface treatment agent.

Analysis of Variance↗

PubMed1996

Surface roughness of tooth shoulder preparations created by rotary instrumentation, hand planing, and ultrasonic oscillation.

A dentinal shoulder with a smooth surface is necessary to ensure accurate adaptation of a porcelain crown. The surface roughness of dentinal shoulders prepared with different instruments was investigated in this in vitro study. Sixty shoulders, 1 mm wide, were prepared with coarse grit diamonds in extracted formalin-stored teeth. Of these 60 shoulders 20 were further refined with fine grit, and 20 more shoulders were refined with super-fine grit diamonds. The surface roughness (Ra) of the dentinal shoulders was recorded after each procedure. Thirty surfaces were further finished and refined with a hand chisel, and the other 30 surfaces were finished with a flat-ended diamond tip held in an ultrasonic generating device; the Ra was then recorded. These shoulder preparations were examined under a scanning electron microscope. The Ra of the dentinal shoulders prepared by the ends of the different grit diamonds was not significantly different (p > 0.05). Hand planing did not improve the Ra, and ultrasonic planing significantly increased the Ra (p < 0.05). Scanning electron micrographs revealed no apparent qualitative differences between surface roughness of the shoulders prepared by the diamonds or by the hand-planed surface. However, deeper scratches were evident at ultrasonically planed surfaces.

Crowns↗

PubMed1996

Long-term durability of adhesive systems bonded to fresh amalgam.

A strong durable resin bond to fresh amalgam is desired in composite-veneered amalgam restorations and in adhesive amalgam restorations. The purpose of this study was to evaluate the influence of long-term water storage on the durability of the shear bond strength of new adhesive systems bonded to fresh amalgam. Sixty cylindrical specimens composed of equal parts of amalgam and composite, with a layer of bonding material in between, were prepared for each adhesive system: All-Bond 2, Amalgambond Plus, High-Q. Bond, and Comspan. Specimens were divided into three subgroups and immersed in saline at 37 degrees C for either 48 hours, 3 months, or 6 months. After the immersion period, specimens were thermocycled and subjected to shear bond strength testing. Shear bond strength of Comspan and High-Q-Bond adhesives did not deteriorate significantly during the 6-month experiment and maintained a mostly mixed mode of failure. All-Bond 2 and Amalgambond Plus adhesives exhibited deterioration of the shear bond strength as a function of immersion time and shifted from dominantly mixed mode of failure to totally adhesive (All-Bond 2) or mostly adhesive failure (Amalgambond Plus). Incubation in saline for long periods should be a standard test in evaluating the bond of new adhesive systems to fresh amalgam, whereas short exposure time to water might be misleading.

Analysis of Variance↗

PubMed1996

Shear modulus--measurement methodology with application to light-cured resin composites.

OBJECTIVES: This study was conducted to test a novel methodology for shear modulus determination of light-cured resin composites. METHODS: Using a butterfly-shaped specimen, a special loading device was able to apply pure uniform shear stress on a significant region of the specimen. Validation of the method was proven by photoelastic experiments. Shear modulus was directly obtained through shear stress-strain curve where the strains were measured by a shear strain gauge rosette. The composite materials analyzed were one microfill (Silux Plus, 3M Dental Products) and four hybrids (Brilliant, Coltene; Herculite XRV, Kerr; Z-100, 3M Dental Products; Graft LC, GC). An analysis of variance was used to evaluate the G modulus (p<0.01). RESULTS: Modulus values varied between 2.54-8.01 GPa. The microfilled material presented the lowest value, and Graft LC presented the highest value. A statistically significant difference was found between all materials (p<0.01). SIGNIFICANCE: The described methodology can also be applied to other restorative materials, as well as to adhesion strength measurements.

Analysis of Variance↗

PubMed1994

The effect of irradiation time on the shear strength of composites.

OBJECTIVES: The purpose of this study was to determine the shear strength of composites at a specific depth by a double shear test and to relate it to irradiation time. METHODS: Aluminum molds filled with three different composites were irradiated for the manufacturer's recommended time, as well as for three longer and two shorter times. Fifteen cylindrical specimens were prepared for each combination of material and exposure time and subjected to a double shear test based on the principle of rivets connecting various structural members. The shear planes were symmetrically located 1.5 mm from both outer surfaces. RESULTS: Shear strength vs. irradiation time was directly but nonlinearly related. All test materials attained a maximum shear strength value which was not exceeded by a further increase of the exposure time. Maximum values obtained were 42.5 MPa for Heliomolar (Vivadent) and Durafill (Kulzer) and 66.9 MPa for P-50 (3M). Only the shear strengths using the shortest light activation time were significantly different for each product. SIGNIFICANCE: Shear strength of composites at a specific depth is a function of the combination of light energy and the attenuating power of the specific material. A double shear test might serve as an adjunct to microhardness in determining the extent of cure of composites at a specific depth. The advantage of this testing is the extra information to be gathered regarding the ability of composites to withstand internal stresses at a predetermined distance.

Acrylic Resins↗