METHODS: 30 extracted maxillary premolars were prepared and randomly assigned to three groups equally according to the type of crown used. The first was the CEREC group: monolithic feldspathic crowns (CEREC Blocs). The second was the E.Max group: monolithic lithium disilicate crowns (IPS e.Max Press). The third group was the Cercon group: bilayered partially stabilized zirconia crowns (Cercon). All crowns were cemented using dual-cured resin cement (ParaCore). The specimens were then subjected to thermocycling (5-55°C/500 cycles) and loaded to failure at an angle of 45° to the occlusal surface of the crown. Failure data was statistically analyzed using one-way ANOVA and Tukey's HSD post hoc test at α= 0.05. Fractographic analysis was performed to determine the fracture modes of the failed specimens.
RESULTS: The mean fracture values for CEREC, E.Max and Cercon groups were 387± 60 N, 452 ± 86 N, and 540 ± 171 N, respectively. Significant differences were found between CEREC and Cercon groups (P< 0.05). Catastrophic fracture within the ceramic crown was the major failure mode of the CEREC group. For E.Max and Cercon groups, the major failure mode was exhibiting severe tooth fracture while the ceramic crown remained intact.
CLINICAL SIGNIFICANCE: CEREC, IPS e.Max Press and Cercon crowns are clinically applicable as they exceeded the normal masticatory forces. However, the CEREC crown is preferred as it maintains the integrity of the natural abutment.
METHODS: 75 human mandibular molars were randomly divided into five equal groups. Teeth were standardized, endodontically-treated and restored according the assigned group as follows: amalgam core only, prefabricated titanium post in the distal canal and amalgam core, composite core only; fiber post in the distal canal and composite core. One group of untreated sound teeth was used as a control. Non-precious metal crowns were fabricated and cemented on the prepared specimens with Rely X U200 resin cement. All specimens were subjected to a compressive load at crosshead speed 0.5 mm/minute, 25° to the long axis of the tooth. Failure loads and modes were recorded.
RESULTS: Mean failure loads among the groups were significantly different (P= 0.035). Post-hoc multiple pair-wise comparisons revealed the amalgam core and composite core groups produced significantly lower fracture resistance than the control group (P= 0.041 and P= 0.025, respectively) and no significant differences among the different intra-radicular techniques (P> 0.05). The composite core with fiber post and amalgam core with titanium posts showed the highest percentage of favorable failures (67%) and non-favorable failures (87%) respectively.
CLINICAL SIGNIFICANCE: The composite core with fiber post is the most appropriate intraradicular restoration in cases of severely compromised molars.
METHODS: 80 teeth were selected and divided into two groups which were stained with black coffee and red wine respectively. The stained specimens were subdivided into four subgroups to be bleached with Opalescence, LumiBrite, WhiteLight and strawberry extract. Color measurements were made using spectrophotometer at baseline level, after staining, after bleaching and 1 week after bleaching. The ΔE₀₀ was calculated post bleaching (ΔE₀₀1), after 1-week follow up (ΔE₀₀2) and color changes between 1-week follow up and baseline (ΔE₀₀3). Data were analyzed by paired t-test and ANOVA with a significant difference of P< 0.05.
RESULTS: Paired t-test showed significant differences in ΔE₀₀1 and ΔE₀₀2 for both stained specimens (P< 0.001). For black coffee stained specimens, Whitelight had significantly higher ΔE₀₀2 compared to the other bleaching agents (P< 0.05). For red wine stain, Whitelight also showed the significantly lowest ΔE₀₀1 (P< 0.001) and the highest ΔE₀₀2 (P< 0.001) compared to other groups. LumiBrite showed the significantly lowest ΔE₀₀3 for red wine stained specimens (P< 0.05). Whitelight had the poorest bleaching efficacy with deterioration effect after 1-week follow up. Opalescence, LumiBrite and strawberry extract had clinically perceptible and comparable bleaching efficacy. Strawberry extract appeared to be a potential natural bleaching agent with a desirable effect.
CLINICAL SIGNIFICANCE: Commercial tooth bleaching agents can cause several undesirable side effects such as damage to enamel, hypersensitivity and even affecting the pulp. Strawberry extract is a natural, effective bleaching agent that may have reduced side effects.