Peter Yaman

Shear bond strength of a resin cement to densely sintered high-purity alumina with various surface conditions

Procera Sandvik AB is now manufacturing a densely sintered high-purity alumina core for an all-ceramic crown designed for anterior and posterior restorations. Whereas the material holds promise on the basis of in vitro strength tests, the ability to alter the surface and use conventional bonded resin cements has not been reported previously in the literature. Samples of the core were treated by means of one of four methods routinely used for all ceramic restorations, and then a commercially available resin cement was bonded to the surface. A shear bond test of the adhesion showed that the highest shear bond strengths of 11.99 +/- 3.12 MPa were obtained with air abrasion at 80 psi and 50-microm alumina particles.

Adhesive Resin Induces Apoptosis and Cell-cycle Arrest of Pulp Cells:

The application of an adhesive resin near or directly over the pulp was shown to induce pulp inflammation and lack of dentin regeneration. We hypothesize that the absence of dentin bridging is due to adhesive-resin-induced apoptosis of cells responsible for pulp healing and dentin regeneration. Mouse odontoblast-like cells (MDPC-23), undifferentiated pulp cells (OD-21), or macrophages (RAW 264.7) were exposed to SingleBond polymerized for 0–40 seconds. Annexin V and propidium iodide assays demonstrated that SingleBond induced apoptosis of MDPC-23, OD-21, and macrophages. The proportion of apoptotic cells was dependent on the degree of adhesive resin polymerization. Adhesive-resin-induced death of pulp cells was associated with activation of the pro-apoptotic cysteine protease Caspase-3. Interestingly, most cells exposed to adhesive resin that did not undergo apoptosis showed cell-cycle arrest. We conclude that an adhesive resin induces apoptosis and cell-cycle arrest of cells involved in the regeneration of the dentin-pulp complex in vitro.

Influence of post material and length on endodontically treated incisors: An in vitro and finite element study

STATEMENT OF PROBLEM Cast posts require sufficient length for prosthesis retention and root strength. For prefabricated metal and fiber posts, the effects of different post lengths on the strength and internal stress of the surrounding root need evaluation. PURPOSE The purpose of this study was to examine, using both experimental and finite element (FE) approaches, the influence of post material and length on the mechanical response of endodontically treated teeth. MATERIAL AND METHODS Sixty extracted incisors were endodontically treated and then restored with 1 of 3 prefabricated posts: stainless steel (SS), carbon fiber (CF), and glass fiber (GF), with intraradicular lengths of either 5 or 10 mm (n=10). After composite resin core and crown restorations, these teeth were thermal cycled and then loaded to fracture in an oblique direction. Statistical analysis was performed for the effects of post material and length on failure loads using 2-way ANOVA (α=.05). In addition, corresponding FE models of an incisor restored with a post were developed to examine mechanical responses. The simulated tooth was loaded with a 100-N oblique force to analyze the stress in the root dentin. RESULTS The SS/5 mm and all fiber post groups presented no statistical differences, with mean (SD) fracture loads of 1247 to 1339 (53 to 121) N. The SS/10 mm group exhibited a lower fracture load, 973 (115) N, and a higher incidence of unfavorable root fracture (P<.05). The FE analysis showed high stress around the apical end of the long SS post, while stress was concentrated around the crown margins in the fiber post groups. CONCLUSIONS Both long and short fiber posts provided root fracture resistance comparable to that of SS posts. For metal posts, extending the post length does not effectively prevent root fracture in restored teeth.

Polymerization shrinkage and depth of cure of bulk fill flowable composite resins.

OBJECTIVE To evaluate polymerization shrinkage and depth of cure of two bulk fill flowable composites, one nanohybrid composite modified to a flowable consistency, and one standard flowable composite, comparing the scraping method to the Knoop hardness test. METHODS Two bulk fill flowable composites, SureFil SDR flow (SSF) (Dentsply) and Venus Bulk Fill (VBF) (Heraeus Kulzer), one standard flowable, Filtek Supreme Ultra Flowable (FSUF) (3M/ESPE) (control), and one regular bulk composite that can be made flowable, SonicFill (SF) (Kerr), were used in this study. For polymerization shrinkage (PS), ten 2-mm samples were made for each composite and cured for 20 seconds and shrinkage was measured with a Kaman linometer. For hardness, ten specimens of each composite were made in a 10 × 10-mm mold and cured for 20 seconds; the bottom surface was scraped according to ISO 4049 specification, and the remaining thickness was measured with a micrometer. Hardness samples were prepared at 2-, 3-, 4-, and 5-mm thick ×14-mm diameter, cured for 20 seconds, and polished. After 24 hours of dry storage, a Knoop indenter was applied at 100 g load for 11 seconds. Three readings were made on the top and bottom of each specimen and averaged for each surface to calculate a Knoop hardness value and a bottom/top hardness ratio. One-way analysis of variance and Tukey tests were used to determine significant differences between thicknesses and between test methods for each material. RESULTS PS values were 3.43 ± 0.51%, 3.57 ± 0.63%, 4.4 ± 0.79%, and 1.76 ± 0.53% for FSUF, SSF, VBF, and SF, respectively. VBF showed significantly greater shrinkage (4.4 ± 0.79%), followed by FSUF (3.43 ± 0.51%) and SSF (3.57 ± 0.63%), which were similar, and SF (1.76 ± 0.53%), which had significantly less shrinkage (p<0.05). Values for the scraping method for depth of cure were significantly greater for SSF and VBF (>5.0 mm), followed by SF (3.46 ± 0.16 mm) and FSU (2.98 ± 0.22 mm). Knoop top hardness values (KHN) were: VBF 21.55 ± 2.39, FSUF 44.62 ± 1.93, SSF 29.17 ± 0.76, and SF 72.56 ± 2.4 at 2 mm and were not significantly different at 3-, 4-, and 5-mm thick within each material. Ratios for bottom/top values (depth of cure) for 2, 3, 4, and 5 mm were: VBF 0.80 ± 0.1, 0.78 ± 0.03, 0.67 ± 0.10, and 0.59 ± 0.07, respectively; SSF 0.74 ± 0.08, 0.72 ± 0.08, 0.69 ± 0.18, and 0.62 ± 0.08, respectively; SF 0.82 ± 0.05, 0.68 ± 0.05, 0.47 ± 0.04, and 0.21 ± 0.02, respectively; and FSUF 0.56 ± 0.08 at 2 mm and 0.40 ± 0.08 at 3 mm. The bottom/top ratio was .80 or less at all depths and decreased below 0.70 at 4-mm depth for VBF and SSF, at 3 mm for SF and at 2 mm for FSUF.

The effect of post type and length on the fracture resistance of endodontically treated teeth

STATEMENT OF PROBLEM Few studies have been conducted to determine a correlation between the flexural modulus of metal and fiber-reinforced posts and the fracture resistance and failure mode of teeth restored with posts. Questions remain as to whether a longer post length or a post with a higher flexural modulus will significantly improve the fracture resistance of a tooth restored with a prefabricated post and core. PURPOSE The purpose of this study was to compare the fracture resistance and mode of failure of endodontically treated teeth restored with 3 different post systems, including 2 fiber-reinforced posts (Light-Post and Snowlight) and a stainless steel post (ParaPost XP). MATERIAL AND METHODS Seventy single-rooted premolars were sectioned at the cemento-enamel junction and then endodontically treated. Teeth were distributed into 7 groups. Three different prefabricated posts were cemented into a post space either 5 or 10 mm in depth, and composite resin (ParaPost ParaCore automix) cores were fabricated. A composite resin core group without a post served as a negative control. Specimens were loaded at 90 degrees to the longitudinal axis until ultimate failure occurred. An initial failure load and mode of failure were also recorded. Statistical analysis was performed for initial and ultimate failure loads of groups by using 2-way ANOVA (P=.05). RESULTS The groups with ParaPost XP posts demonstrated significantly higher initial and ultimate mean failure loads when compared with the fiber-reinforced post groups. The highest mean (SD) initial failure load was with the ParaPost XP group with a 10-mm post length (170.05 (60.08) N), and the lowest was with the Snowlight group with the 5-mm post length (62.85 (18.47) N). CONCLUSIONS The stiffness and the load to initial fracture of the teeth restored with ParaPost XP posts were higher compared with the fiber-reinforced post groups.

Effect of core materials on stress distribution of posts

Severely damaged endodontically treated teeth require the use of a post and core for the retention of the restoration. The choice of material for a post and core and their stress-producing characteristics must be considered by the clinician. Two-dimensional photoelastic analysis of birefringent models was used to investigate the influence of different core materials on the stress distribution of nonthreaded cylindrical posts. Cast posts and cores and prefabricated posts with amalgam and composite resin cores were compared with posts without cores at installation and under two loading conditions. The findings indicate a significant difference between posts with and without cores. It appears that the stiffer core materials can shift the load from the apex to the coronal region.

In vitro effect of topical fluoride on dental porcelain

Fifty-seven porcelain samples were randomly subjected to a variety of topical fluorides for time intervals of 4 to 64 minutes. Half of each porcelain surface was masked to prevent contact with the fluoride. Measurements of roughness were made for the fluoride-treated and the untreated porcelain surfaces to evaluate the effect of the different fluoride preparations over time. The resulting surfaces were also examined using an SEM. Conclusions from this study include the following. Statistically significant differences in roughness were found among surfaces exposed to 1.23% acidulated phosphate fluoride gel, 8% stannous fluoride, and the control surfaces. There were no significant differences in roughness between the test and control surfaces with 0.05%, 0.2%, and 2% sodium fluoride solutions or 0.4% stannous fluoride gel. The dentist should be aware of the potentially deleterious effects of prescribing or administering a topical fluoride for patients with porcelain/metal restorations.

Marginal Adaptation and Color Stability of Four Provisional Materials

PURPOSE A number of provisional restorative materials exist on the market. This study tested marginal fit and color stability of three provisional restorative materials and a control. MATERIALS AND METHODS Two auto-cure materials, Protemp Garant and Integrity, and one dual-cure material, Luxatemp Solar, were tested against SNAP, a polyethyl methacrylate control. A maxillary right central incisor ivorine tooth was prepared for a full coverage all-ceramic crown, with a 1.5-mm chamfer margin. Four points were engraved at a point 1 mm below the facial, lingual, mesial, and distal margins, and replicas (n = 40) were produced by the manufacturer. Provisional crowns (n = 10 x 4) were fabricated on the individual replicas using a polyethylene coping template. The crowns were trimmed under magnification using an acrylic bur. The distance from the crown margins to a point tangent to the engraved markings was measured under 10x magnification and recorded. For color stability, 10-mm diameter x 2-mm thick discs (n = 10 x 4) were fabricated and immersed cyclically in tea for 1 week in a Tucillo/Nielson apparatus. Color measurements were recorded for each specimen at baseline and after staining. DeltaE values were calculated to determine the extent of the color change. RESULTS The means of the four marginal discrepancy measurements for each specimen were analyzed using a 1-way ANOVA and Tukey post-hoc comparison. Luxatemp Solar had statistically significant marginal discrepancy (319 microm, p < 0.05) when compared to the other provisional materials. A significant color change (DeltaE = 4.33, p < 0.05) was found for Protemp Garant. CONCLUSION The dual-cure temporary material (Luxatemp Solar) exhibited significantly more discrepancy at the margin than the auto-cure bis-acryl materials or acrylic control. Protemp Garant exhibited a clinically noticeable change in shade after 1 week in staining solution, whereas the other materials did not exhibit a clinically noticeable change. CLINICAL IMPLICATIONS Provisional crowns fabricated from SNAP, Protemp Garant, and Integrity exhibited similarly low marginal discrepancy. SNAP, Luxatemp Solar, and Integrity did not demonstrate a clinically detectable change in shade after 1 week in a staining solution.

Effect of adding opaque porcelain on the final color of porcelain laminates.

STATEMENT OF PROBLEM Increasing the opacity of porcelain laminates is one of the techniques most commonly used to mask the color of darkly stained teeth. PURPOSE OF STUDY Two different brands of porcelain (Fortune and Optec) disks that contained various amounts of modifying porcelains to alter opacity were cemented with untinted resin cement to a dark colored substrate. MATERIAL AND METHODS The color of the substrate was measured before and after cementation and the change in color was calculated. RESULTS Fortune porcelain showed a progressive increase in the amount of change produced as the modifying porcelain was increased, whereas Optec porcelain showed a decrease in the amount of change as modifying porcelain was increased. CONCLUSION A progressive increase of yellow was exhibited in the samples as the amount of opacity is increased.

In Vivo Evaluation of DIAGNOdent for the Quantification of Occlusal Dental Caries

The accurate diagnosis of non-cavitated occlusal caries is generally considered problematic. Induced fluorescence quantified by the DIAGNOdent device (KaVo) gives a reading from 0-99, which may help in the caries diagnostic process. There is some controversy around the implication of increased severity of decay with increased DIAGNOdent readings. This in vivo study assessed the correlation of depth and volume of decay as it was removed by traditional rotary handpieces with DIAGNOdent readings and determined sensitivities/specificities of the device at different cut-off points. Included in the current study were 31 patients providing 60 permanent molar and premolar occlusal surfaces suspected of dentinal decay. DIAGNOdent readings were recorded, along with lesion depth (as measured by periodontal probe) and volume measurements (as calculated from measuring the mass of a polyvinyl siloxane impression of the cavity, divided by the materials calculated density). Clinical detection of decay at the DEJ was used as the gold-standard to calculate an appropriate cut-off. Pearson correlation coefficients indicated that DIAGNOdent readings were weakly correlated with lesion depth (r = 0.47) and lesion volume (also r = 0.47). An appropriate cut-off point for the sample in the current study was calculated between 35 and 40; a more specific cut-off point could not be determined due to the sample size distribution. It was concluded that the DIAGNOdent device should be used as an adjunct in the caries diagnosis and treatment planning process.