Biomedical subjects

Chiayi Shen

Publications and source records attributed to Chiayi Shen.

17 recordsLinked to original sources

PubMed2006

Effect of core and veneer thicknesses on the color parameters of two all-ceramic systems.

STATEMENT OF PROBLEM: Specific contributions of the core and the veneer thickness on the appearance of layered disk specimens are not well characterized. PURPOSE: This study examined the effect of varying core and veneer thickness on the color parameters of layered disk specimens made of 2 ceramic systems. MATERIAL AND METHODS: Disk specimens 16 mm in diameter with core/veneer thickness (mm) of 0.8/0.2 (baseline), 0.8/0.7, 0.8/1.2, 1.0/0.5, 1.3/0.2, and 1.8/0.2 were made from a leucite-reinforced ceramic (IPS Empress; 2B shade), and thickness (mm) of 0.5/0.5 (baseline), 0.5/1.0, 0.5/1.5, 0.8/0.7, 1.0/0.5, and 1.5/0.5 were made from a glass-infiltrated spinell ceramic (In-Ceram Spinell; A2 shade). Color parameters L*, a*, and b* of CIELAB color space were measured against a neutral gray background with a tri-stimulus colorimeter, and deltaE between disk group and its respective baseline group was calculated. Analysis of variance was used to determine the effect of material and core and veneer thickness on the color parameters (alpha = .05). RESULTS: Increasing the total disk thickness resulted in decrease of L* (P < .001) and an increase of a* (P < .001), b* (P < .001), and deltaE (P = .0236). For leucite-reinforced ceramic, the core thickness, veneer thickness, and their interaction exhibited significant influence on the mean values of a* and b* (P < .0028) but not on the mean values of L*. For spinell ceramic, the core thickness and veneer thickness exhibited significant influence on the mean values of L* and b* (P < .0272) but not on a*; the interaction demonstrated significant influence on b* (P = .0003) but not on L* and a*. CONCLUSION: The color appearance of the layered ceramic disk specimens is strongly influenced not only by the core thickness and veneer thickness, but also by their interaction.

Aluminum Oxide↗

PubMed2006

Two-year clinical evaluation of repair versus replacement of composite restorations.

PURPOSE: To investigate the effectiveness of alternative treatments to the replacement of resin-based composite (RBC) restorations through a prospective longitudinal cohort clinical study. MATERIALS AND METHODS: Forty patients aged 27 to 77 years (mean=55) with 88 RBC restorations, with one or more features that deviated from ideal, participated in the study. They were assigned to five treatment groups: repair (N=25), sealing of defective margins (N=13), resurfacing (N=18), replacement (N=16), and the no-treatment group (N=16). The replacement and no-treatment groups served as comparison groups and received random assignment. Two clinicians examined the quality of the restorations (N=88) prior to the assigned treatment, and at subsequent recalls (1 and 2 years) using a modified Ryge criteria (Alfa, Bravo, and Charlie, meaning clinically excellent, clinically acceptable with one or more features that deviated from ideal, and clinically unacceptable, respectively) that observed (1) color, (2) marginal adaptation, (3) anatomic form, (4) surface roughness, (5) marginal staining, (6) bulk discoloration, (7) contact, (8) secondary caries, (9) postoperative sensitivity, and (10) luster. RESULTS: At 1- and 2-year recalls, 66 (75%) and 58 (66%) restorations were examined. Kruskal-Wallis Test showed significant differences for marginal adaptation and marginal staining for both 1- and 2-year recall exams (p < .05). The repair, sealant, and replacement groups presented significant improvement when compared with the no-treatment group for marginal adaptation. The repair and replacement groups showed superior results when compared with the no-treatment group for marginal staining. CONCLUSION: RBC restorations that present less-than-ideal marginal adaptation and stained margins are better off being repaired. CLINICAL SIGNIFICANCE: Repair of resin-based composite (RBC) restorations is a conservative option for treatment of RBC restorations with inadequate marginal adaptation and marginal staining.

Adult↗

PubMed2005

Four-year clinical evaluation of a self-etching primer and resin-based restorative material.

PURPOSE: To evaluate the performance of a universal resin-based restorative material (Beautifil) in combination with a self-etching primer (Fluorobond) for posterior restorations. METHODS: 61 restorations, 26 Class I and 35 Class II, were placed by two clinicians in 31 patients under rubber dam isolation. Two other calibrated clinicians evaluated the restorations using USPHS/Ryge criteria observing the following characteristics: color match, marginal adaptation, anatomy, roughness, marginal staining, interfacial staining, contact, secondary caries, and luster. Chi-Square and Fisher's Exact Test were used for statistical analysis (alpha=0.05). RESULTS: All the restorations were assessed at baseline and alpha scores predominated for all criteria. All restorations were examined at the 1-year recall examination. 58 restorations were examined at the 2-year recall (23 Class I and 35 Class II), 47 (16 Class I and 31 Class II) at the 3-year recall. The present 4-year report covers 39 restorations (12 Class I and 27 Class II). Marginal adaptation, staining, anatomy, and color matching constitute the majority of the recorded changes. Chi-Square and Fisher's Exact Test of the frequency of clinical rating of each characteristic showed that there were no statistically significant differences at each recall with respect to the baseline observations (P> 0.05), except for occlusal marginal stain. Statistical significance was detected for the occlusal marginal stain at 1-year (P= 0.06), 2-year (P= 0.01) and 4-year (P= 0.002) when compared to baseline data.

Adult↗

PubMed2004

Effect of post-silanization drying on the bond strength of composite to ceramic.

STATEMENT OF PROBLEM: The temperature reported for thermally treating silanated ceramics to improve composite-ceramic bonding is often too high for chairside applications. PURPOSE: This study investigated whether post-silanization drying with a stream of warm air could enhance the composite/ceramic tensile bond. MATERIAL AND METHODS: Thirty-two ceramic blocks (6 x 6 x 9 mm), 16 of each ceramic, were fabricated and divided into 8 subgroups using 4 roughening procedures and 2 silanization protocols per ceramic (Eris and IPS Empress). Roughening included polishing to 1200 grit as control (P), airborne-particle abrasion (A), hydrofluoric acid etching (E), or a combination of abrasion and etching (AE). Silanated surfaces were dried with room-temperature air (SR) or 45+/-5 degrees C warm air (SH). An adhesive (Heliobond) was applied and light-polymerized before adding composite (Tetric Ceram). Thirty-three specimens (0.9 x 0.9 x 18 mm) were cut from a pair of blocks and stored in 37 degrees C distilled-water for 3 weeks. Each specimen was loaded under tension until failure in a universal testing machine (n=33). Strength (MPa) was calculated by dividing the failure load by the cross-sectional area. Mode of failure was investigated with scanning electron microscopy (SEM). Statistical analyses were performed with ANOVA and the Tukey HSD test (alpha=.05). RESULTS: The mean tensile bond strength values (SD) in MPa for P, A, E, and AE procedures were, respectively, 11.4 (5.4), 11.9 (5.4), 9.9 (2.6), and 15.8 (4.3) for Eris/SR; 17.8 (6.2), 20.4 (7.1), 18.0 (6.7), and 18.8 (3.9) for Eris/SH; 9.3 (2.8), 14.0 (4.0) 17.1 (3.7), and 23.2 (6.8) for IPS-Empress/SR; and 14.8 (4.5) 22.6 (4.8), 22.7 (5.0), and 28.7 (4.4) for IPS Empress/SH. ANOVA indicated the influence of ceramic material, roughening, and postsilanization drying was significant (P<.0001). The Tukey HSD test showed mean strength values higher for IPS Empress than for Eris, SH greater than SR, and AE producing the highest mean strength values. SEM examination showed there were greater areas of cohesive failure with SH specimens. CONCLUSION: Silane drying by a stream of warm air was effective in enhancing tensile bond strength of composite to ceramic.

Acid Etching, Dental↗

PubMed2004

Work of adhesion of resin on treated lithia disilicate-based ceramic.

OBJECTIVE: This study is to test the hypothesis that chemical etching and silane coating of a ceramic surface will influence the work of adhesion (WA) of adhesive resin to dental ceramic. METHODS: A hot-pressed lithia disilicate-based ceramic was used as a model material to investigate the influence of probing media and surface treatments on WA using a dynamic contact angle analyzer. Eighty ceramic specimens were randomly divided into eight experimental groups and treated as follows: (1 and 3) as polished; (2 and 4) etched with 9.5% hydrofluoric acid (HF) for 1 min; (5) etched with 4% acidulated phosphate fluoride (APF) for 2 min; (6) silane coated; (7) etched with HF for 1 min and silane coated; (8) etched with APF for 2 min and silane coated. Advancing and receding contact angles (theta(a) and theta(r)) were measured using high purity water (gamma = 72.6 mN/m) for groups 1 and 2, and a liquid resin (gamma = 39.7) for groups 3-8 as probing liquids. RESULTS: The liquid resin medium yielded a lower WA than water. Silanization produced a significantly lower WA (p < 0.001) than non-silanated surfaces. Etching alone consistently yielded a greater WA for all surface treatments (p < 0.001). SIGNIFICANCE: The silanated ceramic surface exhibited a lower surface energy and did not enhance bonding to the liquid resin by work of adhesion.

Acid Etching, Dental↗

PubMed2004

The effect of mechanical undercuts on the strength of composite repair.

BACKGROUND: The authors conducted an in vitro study to test the hypothesis that undercuts prepared in old composite restorations could improve the strength between the restoration and a flowable composite as repair material. METHODS: The authors used three composites to fabricate cylinders as repair substrates. The etched-only group was ground, etched, dried and built up with a flowable composite. For the undercut group, the authors introduced arrays of fissures on the surfaces before preparing the specimens for subsequent buildup in the manner described for the etched-only group. They made nonrepaired cylinders for baseline measures of strength. They sliced all finished cylinders into slender bars with a diamond saw. Flexure strength values were determined by a three-point-bending test. RESULTS: Nonrepaired bars exhibited statistically significantly higher flexure strength values than did repaired bars, as determined by Wilcoxon rank sum test. Two-way general linear model showed that both material (P < .0001) and undercut (P = .0207) exhibited a statistically significant influence on the repaired flexure strength. Repair substrate with elastic modulus close to that of repair material exhibited a greater percentage of recovery of the respective cohesive strength. Compared with the etched-only group, the undercut group yielded a higher mean flexure strength with one composite but a lower mean flexure strength with the other two. Examination of the fractured surfaces showed that a significant number of undercuts were filled only partially. CONCLUSION: Flexure strengths of repaired specimens always were lower than the cohesive flexure strengths of the materials being repaired. Undercuts did not generally improve repair strength. CLINICAL IMPLICATIONS: Small undercuts on the surface of composite often are difficult to fill completely, resulting in areas of stress concentration that result in no improvement in the repair strength.

Analysis of Variance↗

PubMed2004

The effect of surface finishing and storage solutions on the color stability of resin-based composites.

BACKGROUND: The authors tested the hypothesis that surface-finishing treatments and the type of storage solutions significantly affected the staining of resin-based composites, or RBCs, and unfilled resins, or URs. METHODS: Fifty-four RBC and 54 UR disks were polymerized through a polyester film strip (Mylar, DuPont, Wilmington, Del.) and polished in one of three groups: 1-micrometer aluminum oxide, 15-microm diamond plate and no treatment (polyester film). All specimens were immersed in water for two days and then in coffee, cola or red wine for seven more days at 37 C. The authors recorded tristimulus color measurements before the immersions; after one and two days in water; and after one, two, three and seven days in the storage solutions. RESULTS: Most of the color changes occurred between day 2 in water and day 7 in the staining solution. Analysis of variance showed that the finishing treatment and storage solution significantly influenced the overall color change (deltaE), and interactions occurred between the finishing treatment and the storage solution (P < .0001) for both materials. RBC specimens generally exhibited greater color changes than did UR specimens. The polyester film finishing exhibited the greatest amount of color change, while the diamond finishing exhibited the least amount of color change. Immersion in wine caused the greatest color change for both materials; cola and coffee resulted in the smallest color change for RBC and UR specimens, respectively. CONCLUSIONS: Finishing treatments and storage solutions significantly affect the surface staining of RBC materials. Polyester film finishing and red wine produced the greatest color change after seven days for RBC specimens. CLINICAL IMPLICATIONS: Clinicians should remove the polyester film-finished surface and advise patients that drinking wine could intensify surface staining on RBC restorations.

Aluminum Oxide↗

PubMed2003

Effect of surface topography on the bond strength of a composite to three different types of ceramic.

STATEMENT OF PROBLEM: Mechanical retention based on the surface topography is critical for the success of chairside repair of chipped or fractured ceramic prostheses with a composite. PURPOSE: The purpose of this study was to investigate whether the tensile bond strength of a composite to 3 dental ceramics was affected by surface roughening procedures on the ceramics. MATERIAL AND METHODS: Three ceramics, Eris (ERV), Empress 1 (E1C), and an experimental ceramic (EXC), were used to fabricate 12 rectangular blocks (5 x 5 x 10 mm). After polishing with a series of SiC papers (120 through 1200 grit size), 4 surfaces were created on each ceramic as follows: 1) as-polished (P); 2) airborne-particle abraded with 50 microm Al(2)O(3) (A); 3) etching with 5% hydrofluoric acid gel (E); and 4) a combination of airborne particle abrasion and etching (A/E). An adhesive (Heliobond) was applied on the roughened ceramic surface and a composite (Tetric Ceram) was built-up incrementally. Twelve groups of different ceramic/surface treatment combinations were prepared. Twenty ceramic/composite specimens per group (0.9 x 0.9 x 20 mm) were obtained from each block with a slow speed diamond saw. Each specimen was subjected to a tensile force at a crosshead speed of 0.5 mm/min using a universal testing machine until failure. The mode of failure was determined by scanning electron microscopy. ANOVA and Duncan's multiple range test (alpha=.05) were used to analyze the bond strength values. RESULTS: Specimens of all as-polished groups and EXC(A) group separated during sectioning. The mean bond strength values (SDs) in MPa for the remaining groups were as follows: ERV(A): 2.6 (0.8); E1C(A): 2.8 (1.1); ERV(E): 3.1 (1.3); ERV(A/E): 9.3 (1.3); E1C(E): 10.5 (1.5); E1C(A/E):13.5 (3.3); EXC(E): 19.2 (4.7); and EXC(A/E): 23.1 (5.4). ANOVA showed statistically significant differences in the bond strength for both ceramics (P<.0001) and surface treatments (P<.0001). Duncan's analysis yielded following statistical subsets of the bond strength values: EXC > E1C > ERV by ceramic; A/E > E > A by surface treatment. The mode of failure was a combination of adhesive and cohesive failures. CONCLUSION: The tensile bond strength of a composite to ceramic was significantly different depending on the surface topography of ceramic. Among the surfaces investigated, combined surface roughness was the most effective surface topography in terms of the bond strength increase.

Acrylates↗

PubMed2003

Relationships between skin temperature and temporal summation of heat and cold pain.

Temporal summation of heat pain during repetitive stimulation is dependent on C nociceptor activation of central N-methyl-d-aspartate (NMDA) receptor mechanisms. Moderate temporal summation is produced by sequential triangular ramps of stimulation that control skin temperature between heat pulses but do not elicit distinct first and second pain sensations. Dramatic summation of second pain is produced by repeated contact of the skin with a preheated thermode, but skin temperature between taps is not controlled by this procedure. Therefore relationships between recordings of skin temperature and psychophysical ratings of heat pain were evaluated during series of repeated skin contacts. Surface and subcutaneous recordings of skin temperatures revealed efficient thermoregulatory compensation for heat stimulation at interstimulus intervals (ISIs) ranging from 2 to 8 s. Temporal summation of heat pain was strongly influenced by the ISIs and cannot be explained by small increases in skin temperature between taps or by heat storage throughout a stimulus series. Repetitive brief contact with a precooled thermode was utilized to evaluate whether temporal summation of cold pain occurs, and if so, whether it is influenced by skin temperature. Surface and subcutaneous recordings of skin temperature revealed a sluggish thermoregulatory compensation for repetitive cold stimulation. In contrast to heat stimulation, skin temperature did not recover between cold stimuli throughout ISIs of 3-8 s. Psychophysically, repetitive cold stimulation produced an aching pain sensation that progressed gradually and radiated beyond the site of stimulation. The magnitude of aching pain was well related to skin temperature and thus appeared to be established primarily by peripheral factors.

Adult↗

PubMed2002

The influence of plasticizer loss on the viscoelasticity of temporary soft liners.

PURPOSE: This study examined the changes in mechanical properties of temporary soft liners introduced by the differential loss of alcohol and plasticizer in different storage media. MATERIALS AND METHODS: Four brands of temporary soft liners were used to prepare 128 specimens on Lucite LS substrates. Each group of specimens was stored in a different medium (air, 10% ethanol, water, and artificial saliva), selected to affect the levels of plasticizer and alcohol over time. Data on weight changes, plasticizer leaching, and recovery rate were recorded at the following intervals: baseline, 2, 7, 14, 28, 56, and 176 days. The storage media were periodically renewed except during the drying stage between day 56 and 176. Two-way analysis of variance and Duncan multiple-range tests were performed. RESULTS: Plasticizer leaching occurs at higher levels in artificial saliva than in other storage media (P <.0001). The mean recovery rates exhibited a statistically significant increase (indicating reduced viscoelasticity) in more of the artificial saliva specimens than in all other test groups (P <.0001). Comparatively, the rates of recovery were lower in the 10% ethanol storage medium (except Lynal) with a statistically significant difference attained with the higher air-stored specimens in Tempo and Coe-Comfort (P <.0001). During the drying phase, weight changes in the 10% ethanol group were higher than those in the other storage media. CONCLUSIONS: The study supports the contention that alcohol may have been retained in the 10% ethanol group in a manner that extended the viscoelasticity of the material. The roles of alcohol and plasticizer content in the mechanical properties of temporary soft liners depend on the type of temporary soft liners and on the nature/duration of service desired. Storing dentures lined with tissue conditioners under dry conditions and those lined with true soft-liners in an ethanol humidor may be justified to extend serviceability by minimizing the loss of the component most relevant to viscoelasticity.

Air↗

PubMed2002

Wetting characteristic of ceramic to water and adhesive resin.

STATEMENT OF PROBLEM: Maximum wetting of ceramic by adhesive resin is required to achieve optimal adhesion of the resin to ceramic. It is unknown whether the adhesion of the resin to the ceramic is affected by the surface topography and wetting by water or the adhesive resin. PURPOSE: This study was designed to characterize the effect of surface topography on the wetting of ceramics by water and adhesive resin. MATERIALS AND METHODS: Three materials, a veneering ceramic, Eris (ERV), and 2 core ceramics, Empress 1 core ceramic (E1C) and an experimental core ceramic (EXC), were used. Four surface-roughening procedures were used. They included polishing through 1200-grit SiC paper (P), air abrasion with 50 microm Al(2)O(3) (A), etching with 5% hydrofluoric acid gel (E), and a combination of airborne particle abrasion and etching (A/E). Forty bar specimens (15 x 10 x 1.5 mm) were prepared from each material (N=120). Twelve groups of 10 specimens each were prepared for the 4 surface-roughening procedures. Advancing (theta(A)) and receding (theta(R)) contact angles were measured with a CAHN Dynamic Contact Analyzer, on the basis of the Wilhelmy plate technique, with water and adhesive resin. The work of adhesion (W(A)) by the probing media was calculated by use of advancing contact angle data. The data were analyzed by t testing, analysis of variance, and Duncan's tests (alpha=0.05) to determine the statistical significance of differences in the contact angles between ceramic and water or resin as a function of surface roughening. RESULTS: In general, the mean theta(A) values were higher than the mean theta(R) values except for groups of E or A/E specimens with water used as a probing medium. E and A/E treatments yielded the lowest contact angle values, followed by A and P treatments (P<.001). The E1C exhibited the highest mean contact angles, whereas EXC exhibited the lowest mean contact angle except for the theta(R) with resin. The corresponding values for ERV were between those of E1C and EXC except for theta(R) values with resin. The resin medium yielded higher mean contact angles than the water medium for the same surfaces. W(A) ranged from 62.9 to 145.2 mJ/m(2). CONCLUSIONS: Within the limitations of this study, etching or a combination of air abrasion and etching were comparably effective in increasing the surface area for bonding. The most wettable surface as measured by the resin medium was EXC, followed by ERV and E1C.

Acid Etching, Dental↗

PubMed2002

Assessing fluoride concentration uniformity and fluoride release from three varnishes.

BACKGROUND: The authors investigated the fluoride content uniformity of three commercial fluoride varnishes, as well as their fluoride-release behaviors. METHODS: The authors examined 20 doses from each of two tubes of Duraphat (Colgate-Palmolive Co., New York) and Duraflor (Pharmascience Inc., Montreal), and 20 doses of individually packaged 0.25-milliliter and 0.40-mL units of CavityShield (OMNII Oral Pharmaceuticals, West Palm Beach, Fla.). Part of the dose was dissolved in chloroform, followed by fluoride extraction with distilled water. The authors painted the remaining varnish from five predetermined doses from each group onto plastic substrates for examination of fluoride release. Fluoride concentrations in the solutions were measured with a fluoride-selective ion electrode. RESULTS: One-way analysis of variance showed statistically significant differences between varnish groups. The fluoride content was more uniform in Duraphat and CavityShield than it was in Duraflor. The fluoride release profiles in terms of percentage of total fluoride released over time were different among different groups of varnishes and were similar among samples from the same test group. The authors found that Duraflor released consistently more fluoride in artificial saliva than did the other two varnishes. CONCLUSIONS: Fluoride content can vary between doses dispensed from the same tube. Uniformity also varies between different varnishes and affects the retention of fluoride in the varnish. CLINICAL IMPLICATIONS: Clinicians should be aware that the nonuniform appearance of fluoride varnish as squeezed out of the tube could indicate separation of ingredients, resulting in variation of fluoride content.

Analysis of Variance↗

PubMed2002

Replacement of resin-based composite: evaluation of cavity design, cavity depth, and shade matching.

OBJECTIVE: The aim of this study was to evaluate the effect of different cavity designs, cavity depths, and shade matching on the dimensions of Class I resin-based composite preparations during replacement of the restoration. METHOD AND MATERIALS: Forty Class I cavity preparations were prepared in extracted premolars. The occlusal depths varied from 1.5 to 2.5 mm. In 20 teeth, the buccal and lingual walls were perpendicular to the pulpal floor; in another 20, they were divergent to the pulpal floor. Impressions were made of all preparations. The cavities were restored with resin-based composite. All subgroups were further divided into another two subgroups (n = 5), in which half of the teeth were restored with shade that matched the tooth and the other half were restored with a resin composite that was three shades different from the tooth. After 168 hours in distilled water, the restorations were removed. New impressions were made, and a total of 80 stone casts were fabricated. The perimeter and area of the restorations were recorded with a video-based imaging system. The dimensions of the postoperative cavity preparations were compared to the initial cavity sizes. RESULTS: The depth of the original cavity preparation had a statistically significant effect on the change in cavity dimension, as measured by area and perimeter. The 2.5-mm-deep cavities showed greater loss of tooth structure. No statistically significant difference was found for different cavity designs or shade matching. CONCLUSION: Replacement of Class I resin-based composite restorations results in loss of tooth structure. The deeper the original cavity preparation, the greater the loss of tooth structure at the occlusal cavosurface margin during replacement.

Analysis of Variance↗

PubMedDate not supplied

Repair strength of dental amalgams.

This study tested the hypothesis that newly triturated amalgam condensed vertically on old amalgam was essential for establishing a bond between the new and old amalgams. Twelve rectangular bars were prepared with Dispersalloy and Tytin to establish their baseline flexure strength values. An additional 12 specimens were made and separated into 24 equal halves. All fracture surfaces were abraded with a flat end fissure bur. Twelve surfaces were paired with the original amalgam, and the remaining 12 surfaces were repaired with a different amalgam. At first, freshly triturated amalgam was condensed vertically on the floor of the specimen mold (Group A). The majority of specimens repaired with Group A failed to establish bond at the repair interface. All repair surfaces were abraded again and prepared by a second method. A metal spacer was used to create a four-wall cavity to facilitate vertical condensation directly on the repair surface (Group B). The specimens were stored in ambient air for seven days prior to flexure testing. The strength of specimens repaired with Group B ranged from 26% to 54% of the baseline specimens. ANOVA showed that amalgams repaired with a different amalgam yielded higher strength values than those repaired with the original amalgam, and the baseline specimens exhibited significantly higher strength values than all the repaired specimens.

Air↗

PubMedDate not supplied

Effect of surface finishing and storage media on bi-axial flexure strength and microhardness of resin-based composite.

This in vitro study tested the following null hypotheses: (1) surface finishing treatments do not significantly affect the biaxial flexure strength and microhardness of resin-based composites (RBC) and (2) storage media do not significantly affect these physical properties. Discs (81 RBC and 81 UR; 3M/ESPE) were prepared using a circular polyethylene mold (2.4-mm thick x 16.7 mm in diameter) that was polymerized through a Mylar strip and divided into three surface finishing treatment groups: 1 microm aluminum oxide slurry; 15 microm diamond and a Mylar strip. Randomly selected controls for each finishing group were stored at room temperature in individual vials. Test specimens were immersed in water, stored at 37 degrees C for two days and transferred for an additional seven days to one of three aqueous storage media at 37 degrees C: coffee (pH 5.1), cola (pH 2.4) or red wine (pH 3.7). Post immersion (nine days total), the specimens were tested for biaxial flexure strength (BFS) and Vicker's microhardness (VHN). ANOVA and Tukey's HSD test were used for statistical analysis. ANOVA results indicated that surface finishing treatments had a significant effect on the biaxial flexure strength and microhardness of the RBC and the UR specimens. BFS results for RBC specimens were AL>DD>ML (p<0.0001) and VHN results were AL, DD>ML (p<0.0001). Storage in wine medium reduced the VHN of UR specimens significantly. Both alternative hypotheses were accepted. In addition, the Mylar finishing group, because of the resin-rich surface layer, yielded the lowest mean values of BFS and VHN.

Aluminum Oxide↗

PubMedDate not supplied

Repair or replacement of amalgam restorations: decisions at a USA and a UK dental school.

Whereas replacement of failed restorations is the major treatment for adults in dental practice, repair is an important alternative with the potential to save tooth structure and increase the longevity of restorations at a lower cost. This in vitro study recorded the choices of treatment for the same set of teeth with defective Class II amalgam restorations by students and faculty at two dental schools (University of Manchester, UK and University of Florida, USA). Treatment options (monitor, refurbish, repair and replace) and reason(s) for the choice of treatment for 24 marked amalgam restorations were selected. Overall, participants more frequently chose replacement of restorations; whereas, repair was the least favored option. The reasons cited the most to replace restorations were secondary caries including unsightly appearance, partially lost restoration and tooth fracture; for repair, the major reasons included loss of part of the restoration and marginal ditching; and for refurbishment, the major reasons included poor anatomic form and marginal ditching. There was a significant difference between the students and faculties at the two sites in their choice of treatment (p<0.0001; Chi-square test). The treatment decision to "monitor" the restorations was more frequent for the Manchester site than the Florida site. Conversely, the combined treatment decisions to "refurbish, repair and replace" were more frequently chosen in Florida than in Manchester.

Adult↗

PubMedDate not supplied

Marginal gap repair with flowable resin-based composites.

This study was designed to test the hypothesis that the flowable/dentin interface has the weakest bond and highest frequency of failure when a resin-based composite is repaired using a flowable composite. Comparing three specific groups--dentin, flowable composite, and hybrid composite-under the Kruskal-Wallis test showed that the mean bond strength values at the flowable/dentin interface and within the dentin were significantly lower than those at the hybrid/flowable interface and within the flowable resin. Dentin near the pulp chamber yielded consistently lower bond strength values than dentin located at the dentino-enamel junction. Bonding at the flowable resin/dentin interface showed the weakest bond and highest frequency of failure.

Analysis of Variance↗