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Objectives: The aim of this study was to evaluate the effects of using different diameters of parallel cast posts with, or without ferrule, on the overall fracture resistance of Cast Post and Core (CPC).Material and methods: Forty (40) endodontically treated human maxillary central incisors were divided into four groups (n=10): [F1] 1.0 mm diameter post with ferrule; [NF1] 1.0 mm diameter cast post without ferrule; [F1.5] 1.5 mm diameter cast post with ferrule; [NF1.5] 1.5 mm diameter post without ferrule. For all teeth, the post space (9.0 mm, in depth) was prepared using ParaPostTM drill. CPC using base metal alloy were fabricated and were cemented using resin modified glass ionomer (RMGI) cement along with the PFM crowns. A universal testing machine (Instron) was used to apply horizontal force perpendicular to the long axis of the tooth at the center of lingual surface, until catastrophic failure. Data was submitted to two-way ANOVA and Scheffé tests (P

Purpose: Conventional denture base polymethyl methacrylate (PMMA) is low in strength, soft, and brittle on impact. Improvements in the mechanical properties of denture base materials have been sought by adding different reinforcing phases to the PMMA matrix. The purpose of this work was to study the effects of mica reinforcement on the mechanical properties, flexural strength, and microhardness of PMMA denture base resin. Materials and Methods: Wet ground muscovite mica and Lucitone 199 original shade denture base resin were used. Two micas were tested: W200 and P66 with average particle sizes (d50) of 131 μm and 30 μm, respectively. The mica was silane treated in a solution of 3-methacryloxypropyl trimethoxysilane, ethanol, and water, and then dried. The specimens were fabricated using the denture base resin manufacturer's instructions with a powder : liquid ratio of 21 g/10 ml and a mixing time of 30 seconds. Five treatment groups were produced with differing amounts of mica added to the PMMA denture base resin: (A) control group with 0 vol% mica, (B) 10 vol% W200 mica, (C) 20 vol% W200 mica, (D) 10 vol% P66 mica, (E) 20 vol% P66 mica. The mica replaced equal volumes of the PMMA powder component to minimize changes in viscosity. The three-point bending flexural strength specimens were 70 × 11 × 3 mm3. Seven specimens were prepared for each treatment group. The hardness specimens were prepared from the ends of the three-point bend specimens after they were broken (N = 7). After deflasking, the specimens were polished with 600 grit silicon carbide paper to achieve smooth surfaces. A standard three-point bending jig with a span length of 50 mm was attached to an Instron universal testing machine. The specimens were placed on the jig, and loading was carried out using a 1 mm/min crosshead speed until failure. Microhardness was measured using a Clark microhardness tester with a Knoop indenter. The load was set to 200 g and the dwell time to 15 seconds. ANOVA and Tukey tests were used for statistical analyses (Alpha = 0.05). Results: The flexural strength of the control group was between 77% and 94% higher than all the mica-containing groups (p≤ 0.05). No significant differences were found within the four mica groups. Microhardnesses of the 20% mica groups (both fine and coarse) were 33% and 26% higher than the control (p≤ 0.05). The 10% mica groups had higher hardness than the control group, but the increase was not statistically significant (p > 0.05). Conclusion: Mica additions to denture PMMA reduced flexural strength; however, with the specimens containing highest mica concentrations (20%), microhardness significantly increased.

Improving the adaptation of resin composites during placement is necessary to increase durability and reduce microleakage. Flowable resin liners have been introduced to improve adaptation in composite restorations. In addition, a device that lowers the viscosity of regular dental composites has been introduced (Calset, AdDent Inc, Danbury, CT, USA). This device lowers the viscosity of composites by preheating them to 54.4 degrees C, which should lead to improved adaptation. This study compared microleakage in Class II composite restorations prepared using: 1) preheated resin composite, 2) unheated composite and 3) a flowable liner followed by unheated composite. Class II cavities were prepared on the mesial and distal surfaces of extracted third molars. Ten preparations were restored with resin composite (Esthet-X, Dentsply, York, PA, USA) for each of the following four techniques: Control (Esthet-X with Prime & Bond NT, Dentsply), Flowable (f) (as Control but used Esthet-X Flow liner), Preheated (p) (as Control but with preheating composite to 54.4 degrees C) and Delay (d) (as Preheated but followed by a 15-second delay before curing). The teeth were restored, finished, stored in distilled water for 24 hours, then thermocycled between water bath temperatures of 5 degrees C and 55 degrees C with a one-minute dwell time for 1000 cycles. Tooth apices were sealed with epoxy and varnish was applied to within 1 mm of the restoration margins. The teeth were placed in 0.5% basic fuschin dye for 24 hours, rinsed, then embedded in self-curing resin. The embedded teeth were sectioned mesiodistally with a slow-speed diamond saw, providing multiple sections per restoration. Microleakage was rated by two evaluators using a 0-4 ordinal scale at the occlusal and cervical margins of each restoration and light microscopy (40x). The data were analyzed with Kruskal-Wallis ANOVA and pairwise testing with the Sign test (alpha=0.05). No statistical differences were observed among materials at the occlusal margin. However, at the cervical margin, the preheated samples P showed statistically lower microleakage than the controls and all other treatments. The D samples showed higher microleakage than the P and F samples. Ranked sum scores for the cervical were D (4516), C (3974), F (2756) and P (1958). There was a statistically greater amount of leakage at the cervical margins compared to the occlusal p

In 1890, Breuer applied an electrical field concept to root canals in an attempt at sterilization. Recently, Balson and Dovgan have renewed interest in the use of electricity to aid in canal disinfection. The purpose of this investigation is to determine if the use of the apex locator or apex locator in conjunction with low speed handpiece causes a previously unreported electrophoretic effect.Forty low-fat, dried sirloin steak cubes separated into four groups of 10 and immersed in 5.25% sodium hypochlorite for two minutes while connected to 1) an apex locator with no batteries, 2) one with batteries, or an apex locator and low speed handpiece set at either 3) zero or 4) 800 rotations per minute. Samples were dried and percentage of weight loss was calculated. ANOVA and Tukey Multicomparison tests were performed for statistical significance of α ≤ 0.05.ANOVA test and Tukey Multicomparison tests showed that there was a significant difference (α ≤ 0.05) between the groups. They revealed statistically significant differences between 800 rotations per minute and all other groups. This study showed that there were no significant differences between an apex locator with no batteries, one used with batteries and one used in conjunction with the low speed handpiece at zero rotations per minute. However, it was shown that there was significantly more tissue dissolution with an apex locator with low speed handpiece at 800 rotations per minute compared to the first three groups.These results did not support the original hypothesis that the apex locator with or without the low speed handpiece has an electrophoretic effect. However, the results do support the use of sodium hypochlorite agitation for increased tissue dissolution.

Objective: To measure the slot dimensions of an entire series of metal orthodontic brackets. Materials and Methods: Ten bracket series approximating five complete sets of brackets each were imaged and measured. Descriptive statistics were generated. Results: Slot dimension varied significantly from series to series as well as within the series themselves. About one-third of the brackets would not accommodate a full-size wire, and 15% to 20% are 0.001 inches or larger than the nominal advertised size. Conclusion: The clinician is unlikely to have on hand complete sets (upper and lower 5-5) of ideal brackets and should both expect and be able to be accommodate tooth movement through wire bending in three planes of space to overcome any bracket deficiencies.

Statement of problem. One of the most important physical properties of artificial teeth used in the restoration of the edentulous patient is wear resistance, and the ability of these teeth to maintain a stable occlusal relationship over time. Purpose. This study compared the in vitro wear of four different resin denture teeth against human enamel. Material and methods. Five denture tooth samples opposing five enamel abraders were positioned in a mechanical wear testing device for two 5,000 cycle wear periods (total of 10,000 cycles) under a 13.4 N load. All tests were conducted in human saliva, and the wear was measured at the end of each test period. Results. The wear of the Classic and Kenson acrylic resin denture teeth was much greater than the DB Plus and MLI composite teeth after 10,000 cycles. The wear of the KENSON denture tooth was also greater than the Classic tooth. No wear differences were found between the two composite teeth. Conclusions. The wear of DB Plus and MLI resin denture teeth was approximately 50% less than the wear of Classic and Kenson teeth when opposed by human enamel. (J Prosthet Dent 1998;79:152-5.) CLINICAL IMPLICATIONS This study revealed that the composite denture teeth demonstrated significantly better wear resistance than the acrylic resin teeth. The magnitude of the wear of the different tooth types would be clinically significant in patients, depending on their dietary habits and parafunctional activities. This fact coupled with other considerations such as the cusp forms selected and the occlusal contact relationships possible with their clinical use may also influence the wear patterns experienced.

This study compared enamel wear against low-fusing porcelain (Procera All-Ceramic) with the wear against feldspathic porcelain (Ceramco) and gold alloy (Olympia). Human enamel abraders were polished to a 3 microns variance on silicon carbide paper. Five enamel abraders were abraded against five disks that were fabricated from (1) gold alloy polished to 1 micron variance, (2) autoglazed feldspathic porcelain, and (3) autoglazed low-fusing porcelain. The enamel sample was tested in human saliva in a wear machine with a constant load of 1 pound during 10,000 rotational cycles. The amount of wear was determined with a stereomicroscope at magnification x64. Significant differences in mean enamel wear were found when abraded against Olympia gold (9 microns), Procera All-Ceramic (60 microns), and Ceramco feldspathic porcelain (230 microns). Significant differences in restorative material wear were found between Olympia gold (0.32 microns) and the porcelain materials, Procera All-Ceramic (4.3 microns) and Ceramco feldspathic porcelain (3.7 microns).

The proper functioning of soft denture liners depends to a great extent on their mechanical properties. As with many polymers these materials are affected by aging. Twelve soft denture liners were processed by a laboratory according to the manufacturers' directions. Five specimens of each material were tested without aging. Five additional specimens of each material were subjected to 900 hours of accelerated aging in a Weather-Ometer instrument. These were tested with a dynamic viscoelastometer at three frequencies and two temperatures, and data for 37 degrees C and 1 Hz was obtained. Two of the ethyl methacrylate resins demonstrated the largest increases in storage (E') and loss moduli (E") after aging. These materials also showed the greatest overall E' and E". One denture liner material exhibited 673% and 488% increases in E' and E", and other materials showed smaller increases. The effects of aging on the damping factor (tan delta) were varied and five materials showed increased tan delta. Only two ethyl methacrylate resins developed lower tan delta. All the silicone and polyphosphazine rubbers showed small changes after aging and had the lowest tan delta values. Significance of differences between materials and treatments was tested with ANOVA, Scheffé intervals, and t-tests at a = 0.05. The ethyl methacrylate soft denture liners were affected the most by accelerated aging, and the silicones and polyphosphazine were least affected. The ethyl methacrylate resins also had the greatest values of E', E", and tan delta after aging.

This study evaluated the mechanical properties of laser-welded cast and wrought titanium base and compared them with those of a brazed type IV casting gold alloy. Ultimate tensile strength, 0.2% yield strength, and percent elongation were recorded for joined and unjoined bars of the previously mentioned materials. Sections of titanium bars were laser-welded, and gold alloy bars were brazed. Both joining methods significantly reduced the ductility of the material. The strength of the cast gold alloy was superior to that of titanium. However, the strength of the laser-welded titanium equaled that of the brazed gold alloy, which suggests that dental restorations made of cast and wrought titanium would satisfy ordinary clinical requirements.

This research evaluated the dynamic viscoelastic properties of 12 laboratory-processed soft denture liners. Specimens, 1.4 x 3 x 40 mm, were prepared according to the manufacturer's instructions. Five specimens of each material were tested under applied strain frequencies of 1, 5, or 10 Hz and temperatures of 23 degrees C and 37 degrees C. The values at 37 degrees C and 1 Hz were judged most important because they closely approximate the service environment; therefore material comparisons were made for these conditions. Samples were tested with a custom-made dynamic viscoelastometer. The statistical significance of the results was tested by ANOVA and Scheffe's intervals test. Large differences in the storage modulus (elastic stiffness) were found. One acrylic resin, Verno-Soft, showed significantly higher storage moduli than the other materials. The viscous behavior of the materials was reflected by the loss modulus; here large differences were also found. Verno-Soft again exhibited much higher values than all of the other materials. Three other acrylic resins (Super Soft, Soft-Pak, and Justi Soft) also showed significantly higher loss moduli than the other materials. Significant differences were found in the damping factor between many of the materials. Most of the acrylic and vinyl resins had higher damping factors than the silicone and polyphosphazine rubbers. The values of the storage moduli, loss moduli, and the damping factor were affected by temperature and by applied strain frequency with some materials.

Conventional denture base polymethyl methacrylate (PMMA) is low in strength, soft, and brittle on impact. Improvements in the mechanical properties of denture base materials have been sought by adding different reinforcing phases to the PMMA matrix. The purpose of this work was to study the effects of mica reinforcement on the mechanical properties, flexural strength, and microhardness of PMMA denture base resin.Wet ground muscovite mica and Lucitone 199 original shade denture base resin were used. Two micas were tested: W200 and P66 with average particle sizes (d50) of 131 μm and 30 μm, respectively. The mica was silane treated in a solution of 3-methacryloxypropyl trimethoxysilane, ethanol, and water, and then dried. The specimens were fabricated using the denture base resin manufacturer's instructions with a powder : liquid ratio of 21 g/10 ml and a mixing time of 30 seconds. Five treatment groups were produced with differing amounts of mica added to the PMMA denture base resin: (A) control group with 0 vol% mica, (B) 10 vol% W200 mica, (C) 20 vol% W200 mica, (D) 10 vol% P66 mica, (E) 20 vol% P66 mica. The mica replaced equal volumes of the PMMA powder component to minimize changes in viscosity. The three-point bending flexural strength specimens were 70 × 11 × 3 mm(3) . Seven specimens were prepared for each treatment group. The hardness specimens were prepared from the ends of the three-point bend specimens after they were broken (N = 7). After deflasking, the specimens were polished with 600 grit silicon carbide paper to achieve smooth surfaces. A standard three-point bending jig with a span length of 50 mm was attached to an Instron universal testing machine. The specimens were placed on the jig, and loading was carried out using a 1 mm/min crosshead speed until failure. Microhardness was measured using a Clark microhardness tester with a Knoop indenter. The load was set to 200 g and the dwell time to 15 seconds. ANOVA and Tukey tests were used for statistical analyses (Alpha = 0.05).The flexural strength of the control group was between 77% and 94% higher than all the mica-containing groups (p≤ 0.05). No significant differences were found within the four mica groups. Microhardnesses of the 20% mica groups (both fine and coarse) were 33% and 26% higher than the control (p≤ 0.05). The 10% mica groups had higher hardness than the control group, but the increase was not statistically significant (p0.05).Mica additions to denture PMMA reduced flexural strength; however, with the specimens containing highest mica concentrations (20%), microhardness significantly increased.

This study determined the effect of Ibuprofen on tooth sensitivity from in-office bleaching with 38% hydrogen peroxide. A double-blind, randomized-controlled clinical trial was performed on healthy non-smoker patients who retain all anterior teeth (N=31). Patients with anterior restorations, calculus or heavy stain, and those who were taking medications or desensitizer products were excluded. After signing the informed consent, the patients were randomly divided into a Placebo group (n=16) that received a placebo (tinted oil in clear capsule) (Health Dimensions Inc, Compound Pharmacy, Farmington Hills, MI, U.S.A.) or an Ibuprofen group (n=15) that received a 600 mg, PO single dose of Ibuprofen (Advil Liquid Gel, Wyeth, Madison, NJ, USA). The patients were watched while taking the capsules 30 minutes prior to treatment. A single operator applied the 38% hydrogen peroxide (Opalescence Xtra Boost, Ultradent Products Inc) for 20 minutes on 12 anterior teeth. The hydrogen peroxide solution was then rinsed, the teeth were gently dried and the cycle was repeated, for a total application time of 40 minutes. A Visual Analog Scale (VAS) was used to evaluate the level of sensitivity 30 minutes before treatment, immediately after treatment, then 1 hour and 24 hours post-bleaching. The patients graded their maximum sensitivity levels during each period on a scale from 0 to 100 (0=no sensitivity, 100=unbearable sensitivity). The VAS scores were statistically analyzed to compare the groups' scores at different times and to compare the scores within each group at various times (Wilcoxon rank sum tests). The mean score and standard deviation of the Ibuprofen group immediately after bleaching was 5.0 +/- 9.9, at 1 hour--31.5 +/- 32.1 and at 24 hours--25.8 +/- 30.8; the placebo group at the time of treatment was 26.6 +/- 31.0, at 1 hour--30.9 +/- 30.5 and at 24 hours--31.1 +/- 32.6. When comparing the two groups at different times, the Ibuprofen group showed statistically significantly lower sensitivity scores immediately post-bleaching than the placebo group (p = 0.0216) but not at 1 hour (p = 0.84) or 24 hours post-bleaching (p = 0.54). When comparing times within the Ibuprofen group, the mean VAS score immediately after bleaching was significantly lower than 1 hour post-bleaching (p = 0.0024) and 24-hours post-bleaching (p = 0.0110), but the mean VAS score at 1 hour post-bleaching and 24-hours post-bleaching were not significantly different (p = 0.64). For the placebo group, the intragroup time effect was not significant. Within the limitations of the current study, the authors concluded that the use of an analgesic may help to reduce tooth sensitivity during in-office bleaching. In the current study, Ibuprofen (600 mg, PO single dose) reduced tooth sensitivity during but not after the treatment period.

Fractured metal prostheses can be analyzed for possible causes of failure using scanning electron microscopy (SEM). In this study, fractography is used to determine the cause of the failure and whether repair is practical. Energy-dispersive x-ray spectroscopy (EDS) is used to determine composition of the fractured prosthesis so that a repair process can be recommended. The technique is presented for the repair of a titanium framework for an implant-supported overdenture based on the analysis data.

This study evaluated the effects of two finishing techniques and pumice polishing on the surface roughness of eight different provisional materials. Provisional materials included polymethylmethacrylate-based Alike, Snap, Trim and Jetand composite-based provisional materials Temphase, Protemp 3 Garant, Luxatemp and Integrity. Baseline surface roughness was measured by a profilometer, then the provisional materials were finished using extra fine acrylic burs or medium abrasive disks. The surface roughness of each sample was measured following finishing using a profilometer as previously stated. Each surface was then polished with pumice and the surface roughness was measured again. The data were analyzed using repeated measures of ANOVA and Bonferroni pairwise comparisons (alpha = 0.05). The results indicated that with composite provisional materials, the unfinished surfaces are smoother than with bur or abrasive-disk finished surfaces. Pumice application did not smooth the surface finish for all materials. The different types of provisional materials required different finishing techniques to produce the smoothest finishes.

Polishing composite restorations at recall prophylaxis may affect their surface roughness. This investigation evaluated the effect of prophy paste on the surface roughness of a microfilled (Filtek A110) and a microhybrid (Filtek Z250) resin composite before and after simulated toothbrushing. Twenty, two-sided samples of both materials were fabricated in acrylic molds against a Mylar strip (baseline). Three roughness readings were recorded for each surface using a Surfanalyzer 5400 to determine the mean roughness. The samples were finished and polished with the Sof-Lex disk system and the surface roughness (Ra) was re-measured. Samples were randomly assigned and five surfaces for each material were polished with Nupro coarse, medium, fine or Clinpro prophy paste and the surface roughness measured again. All surfaces were brushed 60,000 times at 1.5Hz using a 2N brush-head force (Manly V-8 cross-brushing machine) in a 50:50 (w/w) slurry of toothpaste and water. The surface roughness was measured followed by the application of prophy paste as previously described and this final roughness recorded. Data were analyzed using repeated measures two-factor ANOVA with TUKEY HSD pairwise comparison as appropriate (alpha = 0.05). No significant difference in surface roughness was determined between the microfilled and microhybrid materials at baseline or disk treatment, yet significant differences were observed following brushing and/or prophy paste application. In conclusion, although baseline and disk treated surfaces were not significantly different in microfilled versus microhybrid composites, subsequent prophy paste application and/or simulated toothbrushing caused significant differences.

The traditional gold and porcelain fused to metal crowns have been challenged by the esthetic all-ceramic crown materials. Only previous experience with poor mechanical properties, lack of standardized tooth preparation, and processing challenges have prevented universal acceptance of all-ceramic crowns. However, stronger and tougher ceramics and unique processing methods for ceramics have been developed in the past 20 years. In this study, three new ceramic crown core materials were tested to compare their biaxial flexural strength and indentation fracture toughness. Ten specimens of Empress, In-Ceram, and Procera AllCeram ceramics were prepared according to their manufacturers' recommendations. The results revealed significant differences in flexural strength for the three materials (p < or = 0.05). The average flexural strengths of AllCeram, In Ceram, and Empress ceramics were 687 MPa, 352 MPa, and 134 MPa respectively. There was no statistically significant difference between the fracture toughness of Procera (4.48 MPa x m1/2) and In-Ceram ceramics (4.49 MPa x m1/2); however, both ceramics had significantly higher fracture toughness (p < 0.005) than Empress ceramic (1.74 MPa x m1/2).

PURPOSE Polishing and glazing porcelain surfaces of restorations is thought to help reduce the wear on the opposing occlusion because of reduced roughness. MATERIALS AND METHODS To test this theory, samples of a variety of dental porcelains were prepared and subjected to various polishing and self-glazing treatments commonly used in dentistry and then viewed using scanning electron microscope (SEM). Fine cracks were discovered in the surface of the samples that had been polished and then self-glazed. These cracks were typically greater than 50 microns in length with submicron surface openings and crack depths less than 20 microns. To establish the treatments responsible for the formation of these cracks, a more controlled study was performed. Samples of Vita VMK 68 no. 559 incisal porcelain (Vita Zahnfabrik, Bad Sachingen, Germany) were prepared and subjected to six treatments (sample size = 3): treatment no. 1, as-fired condition; treatment no. 2, self-glazed (32 degrees C per minute to 960 degrees C, then cooled); treatments no. 3 and 4, wet ground followed by 1 micron diamond polish (no. 4 was then self-glazed); treatments no. 5 and 6, ground and polished using a Shofu porcelain adjustment kit (Shofu Inc, Kyoto, Japan) (no. 6 was then self-glazed). The samples were observed using SEM. RESULTS Treatments no. 1, 2, 3, and 5 showed no cracking; however, treatments no. 4 and 6 showed cracking in all specimens (approximate levels 5,100 microns/mm2 and 3,600 microns/mm2, respectively). CONCLUSIONS Polishing followed by self-glazing produces fine surface cracks. The rougher surface resulting from the surface cracks and subsequent porcelain chipping may cause wear of opposing occlusal surfaces.

While ceramic-to-metal bonding has been used in many applications, the actual chemical and physical factors leading to optimum bond strength are not well understood. In this work, several variables affecting the bonding between dental porcelain and a palladium alloy (85% Pd, 10% Cu, and 5% Ga) were investigated: 1) precoating the metal by sputtering various oxides before porcelaining; 2) peroxidation of the metal base before porcelaining; 3) porcelaining under reducing atmosphere; and 4) surface roughening at controlled levels before porcelaining. Using a modification of the push doughnut shear bond strength test to measure bond strength the following results were obtained. 1) Compared with standard "control" samples, the aluminum oxide precoated specimens showed a bond strength improvement of 46%, while the copper, manganese, and tin oxide precoatings exhibited smaller effects. 2) Preoxidation of the metal base led to pronounced bond strengthening (152%) by surface roughening as well as oxide formation. 3) Porcelaining under a reducing atmosphere severely reduced bond strength (88% lower than the controls) indicating the role of oxidation during the standard firing cycle. 4) Mechanical roughening of the surface by controlled amounts gave pronounced improvements with greater notch depth. Coarse roughening produced the highest bond strength improvements (486%).