Lui Jl

Effect of one-step polishing system on the color stability of nanocomposites

OBJECTIVES This study was to compare the effect of three different one-step polishing systems on the color stability of three different types of nanocomposites after immersion in coffee for one day and seven days and determine which nanocomposite material has the best color stability following polishing with each of the one-step polishing system. METHODS The nanocomposites tested were Tetric EvoCeram, Grandio and Herculite Précis. A total of 120 discs (40/nanocomposite, 8mm×2mm) were fabricated. Ten specimens for each nanocomposite cured under Mylar strips served as the control. The other specimens were polished with OptraPol, OneGloss and Occlubrush immersed in coffee (Nescafé) up to seven days. Color measurements were made with a spectrophotometer at baseline and after one and seven days. Two way repeated measure ANOVA, two way ANOVA and Bonferroni tests were used for statistical analyses (P<0.05). RESULTS The immersion time was a significant factor in the discoloration of the nanocomposites. The effect of three one-step polishing systems on the color stability was also significant. The color change values of the materials cured against Mylar strips were the greatest. The lowest mean color change values were from the Occlubrush polished groups. The effect of the three different types of nanocomposite on the color change was significant. The highest color change values were with Tetric EvoCeram groups. The lowest color change values were with Herculite Précis groups. CONCLUSION The color change of nanocomposite resins is affected by the type of composite, polishing procedure and the period of immersion in the staining agent.

Hypersensitivity to a temporary crown and bridge material

Abstract The problem of hypersensitivity to dental materials is outlined, and a patient who exhibited an allergic response to a temporary bridge material is reported.

The Effect of Glass Fiber‐Reinforced Epoxy Resin Dowel Diameter on the Fracture Resistance of Endodontically Treated Teeth

PURPOSE To determine the effect of glass fiber-reinforced epoxy resin (FRC) dowels of different diameters on the failure load of endodontically treated teeth with different remaining dentine and reinforcing resin composite (RRC) thicknesses and the mode of failure in each group. MATERIALS AND METHODS Fifty extracted intact human maxillary central incisors were decoronated 2 mm incisal to the buccal cementoenamel junction and endodontically treated. The teeth were randomly assigned to one of five groups (n = 10): group B, dowel space prepared with size 0 dowel drill/size 0 FRC dowel/no RRC; group W, size 1 dowel space/size 1 FRC dowel/no RRC; group R, size 3 dowel space/size 3 FRC dowel/no RRC; group WR, size 3 dowel space/size 1 FRC dowel/RRC; group BR, size 3 dowel space/size 0 FRC dowel/RRC. Ferrules of 2 and 0.5 mm were prepared at the facio-lingual and proximal margin respectively. All specimens were restored with a Ni-Cr crown, thermocycled and loaded at 135° from the long axis in a universal testing machine at a 0.5 mm/min crosshead speed until fracture. Data were analyzed using ANOVA followed by post hoc comparisons (Bonferroni) with α = 0.05. RESULTS Mean failure loads (N) for groups B, W, R, WR, and BR were as follows: 1406 (SD = 376), 1259 (379), 1085 (528), 959 (200), and 816 (298). Significant differences were found between groups B and BR. Group B had the highest favorable failure mode. CONCLUSION Within the limitations of this study, the use of a smaller FRC dowel and RRC is recommended rather than enlargement of dowel spaces to accurately fit larger FRC dowels, as the enlargement of dowel space may increase the risk of unfavorable failure.

Bilateral 180° rotation of maxillary second premolars: A case report

Abstract A case of bilateral tooth rotation through 180 involving the maxillary second premolars in a 30-year-old male patient is presented.

Effect of aging on coronal microleakage in access cavities through metal ceramic crowns restored with resin composites.

PURPOSE The purpose of this in vitro study was to determine if packable resin composite with/without flowable resin composite has the ability to prevent coronal leakage in restored endodontic access openings following aging. MATERIALS AND METHODS Eighty simulated standardized access cavities of metal-ceramic crowns were fabricated and fixed on Vitrebond cavities filled with an epoxy resin. The specimens were randomly divided into two main groups: (1) Group A-Access cavities filled with only packable composite (Filtek P60); (2) Group B-Access cavities filled with Filtek P60 and a flowable composite (Filtek Z350) as liner. Each main group was further subdivided randomly into four subgroups according to water storage and thermocycling periods. All specimens were immersed in blue ink solution for 24 hours and then sectioned into quadrants. The extension of blue ink along the metal-ceramic crown/composite resin interface was measured linearly using image analyzer and then analyzed by three-way ANOVA and independent t-test with a Mann-Whitney test. The level of significance was set at p < 0.05. RESULTS All tested subgroups demonstrated different levels of microleakage. There was no significant difference related to restorative technique; however, there was a significant difference related to water storage and thermocycling. CONCLUSIONS All tested techniques and materials in this study showed microleakage. Packable composite while a flowable liner showed a marginally better result than packable composite alone. Excessive thermocycling resulted in significant differences among the test groups.

Push-out Bond Strength of Luting Agents to Fibre-Reinforced Post: an in vitro Study

The objective of this study was to investigate the effect of various luting agents on bond strength of fibre-reinforced posts to root canal dentine. 40 extracted single rooted sound premolar teeth were root filled, decoronated and randomly divided into four groups. Fibre posts, Aestheti-Plus (TM) (Bisco,Inc. Schaumburg, IL, USA) were cemented using four luting agents: Group A (control): Elite 1000 Zinc phosphate (GC Corp, Japan), Group B: Calibra (TM) Esthetic Resin Cement (Dentsply Caulk, USA), Group C: RelyX ARC Adhesive Resin (3M ESPE), Group D: RelyX Unicem Aplicap (3M ESPE). Each roots were sliced into 2 discs representing the coronal and middle portions of the root canal giving rise to 20 specimens per group. Bond strength was determined using push-out tests and data were analyzed using SPSS version 14.0. The mean bond strength of Group A to Aestheti-Plus (TM) post was 7.71 MPa (+/- 2.51) and Group B was 5.69 MPa (+/- 3.23). Group C exhibited the lowest mean bond strength, 4.29 MPa (+/- 3.53) while the highest bond strength was obtained from Group D, 7.98 MPa (+/- 2.61). One way ANOVA showed significant interaction between all groups (p=.001). Post-hoc Bonferroni test revealed that bond strength of Group C was significantly lower compared to Group A (p=.008) and D (p=.004). In conclusion, the mean bond strength of Aestheti-Plus (TM) post to root canal dentine was highest when cemented with RelyX Unicem followed by Elite 100, Calibra and RelyX ARC. However, the bond strengths of Calibra and RelyX Unicem were not significantly different from Elite 100 (R).