Comparison of light-transmittance in dental tissues and dental composite restorations using incremental layering build-up with varying enamel resin layer thickness

OBJECTIVES: To evaluate and compare light-transmittance in dental tissues and dental composite restorations using the incremental double-layer technique with varying layer thickness. MATERIALS AND METHODS: B1-colored natural teeth slabs were compared to dental restoration build-ups with A2D and B1E-colored nanofilled, supra-nanofilled, microfilled, and microhybrid composites. The enamel layer varied from 0.3, 0.5, or 1.2 mm thick, and the dentin layer was varied to provide a standardized 3.7 mm overall sample thickness (n = 10). All increments were light-cured to 16 J/cm2 with a multi-wave LED (Valo, Ultradent). Using a spectrophotometer, the samples were irradiated by an RGB laser beam. A voltmeter recorded the light output signal to calculate the light-transmittance through the specimens. The data were analyzed using 1-way analysis of variance followed by the post hoc Tukey's test (p = 0.05). RESULTS: Mean light-transmittance observed at thicker final layers of enamel were significantly lower than those observed at thinner final layers. Within 1.2 mm final enamel resin layer (FERL) thickness, all composites were similar to the dental tissues, with exception of the nanofilled composite. However, within 0.5 mm FERL thickness, only the supra-nanofilled composite showed no difference from the dental tissues. Within 0.3 mm FERL thickness, none of the composites were similar to the dental tissues. CONCLUSIONS: The supra-nanofilled composite had the most similar light-transmittance pattern when compared to the natural teeth. However, for other composites, thicker FERL have a greater chance to match the light-transmittance of natural dental tissues.

Fracture resistance of nanofilled composite resin restoration for the treatment of incisally fractured incisors:An in vitro study / 实用口腔医学杂志

Objective:To study the fracture resistance of nanofilled composite resin restoration for the treatment of incisally fractured in-cisors. Methods:30 extracted permanent maxillary central incisors were randomly divided into A, B and C groups (n=10). In group A and B, the teeth were cut obliquely from the mesial incisal angle. Labial reduction of 0. 5 mm for veneer and dovetails in the lingual surfaces were prepared. In group A, additional 2mm of the incisal edge were cut horizontally. The teeth were restored with nanofilled com-posite resin. The samples in group C were unprepared as the controls. The specimens were stored in artificial saliva and underwent 2 000 cycles of thermal cycling test. Fracture resistance of the teeth was measured by a test machine and the fracture mode was observed. Re-sults:The mean fracture load(N) of group A, B and C was 466.93 ±171.68, 444.5 ±173.00 and 474.77 ±97.55 respectively(P>0. 05). All fractures in the 2 test groups but 1 in the control group were in a favorable way. Conclusion:Incisally fractured incisors restored with nanofilled composite resins can achieve the fracture resistance similar to that of intact natural tooth. Failure modes of the restored teeth are in favorable way. Additional cut of 2 mm of the incisal edge dose not affect the fracture resistance of the restored teeth.

"Comparative Evaluation of Microleakage of Composite Restorative Materials".

To evaluate and compare the marginal leakage in class V cavities restored with three different tooth colored restorative materials using dye penetration system. Materials and methods: Thirty extracted premolars were randomly selected for this study. Standardized classV cavities were prepared and then divided into three equal groups. Group I was restored with nano filled composite, Group II was restored with hybrid composite and group III with polyacid modified composite. They were then subjected to thermo cycling, immersed in 2% methylene blue dye, sectioned and examined under stereomicroscope. Dye penetration for each section was recorded and data was analyzed. Results: Lowest micrileakage was recorded in group I and highest leakage recorded in Group III.Conclusion: Nanofilled composite resins provide a better sealing than hybrid and polyacid modified composites.

Influence of flowable materials on microleakage of nanofilled and hybrid Class II composite restorations with LED and QTH LCUs.

Background: Class II composite restorations are more frequently being placed with margins apical to the cementoenamel junction (CEJ) and margins within the dentin are prone to microleakage. Aims: This in vitro study was used to evaluate the influence of flowable composite and flowable compomer as gingival liner on microleakage in Class II composite restorations and compare a light-emitting diode (LED) unit with a quartz tungsten halogen (QTH) unit for light-activating composite resins. Materials and Methods: Mesioocclusal and distoocclusal Class II cavity preparations were made in 72 sound extracted premolars. The buccolingual width was 2.5 mm and the gingival margins of all the cavities were placed 1.0 mm apical to the CEJ. The boxes were prepared 1.5 mm deep axially, making 144 slot cavities. Teeth were randomly divided into the following two groups (n = 72): (I) Universal Filtek Supreme XT; Universal Filtek Supreme XT + Flwable Filtek XT and Universal Filtek Supreme XT + Dyract Flow and (II) Filtek Z250; Filtek Z250 + Flwable Filtek XT and Filtek Z250 + Dyract Flow. Flowable materials were injected into the gingival floor of the cavity to a thickness of 1.0 mm. Each increment was cured for 20 s. One-half of the subgroups in each group were cured with QTH and the other half with LED light curing units (LCUs). After 1 week of incubation at 37°C, the specimens were thermocycled (5-55°C, x1500), immersed in 0.5% basic fuchsine dye for 24 h and sectioned and microleakage was evaluated at the gingival margin by two examiners using a 0-3 score scale. The data were analyzed using the Kruskal-Wallis and Mann-Whitney U tests. Results: The groups utilizing flowable liners had significantly less microleakage (P < 0.05). No significant difference was identified between Universal Filtek Supreme XT and Filtek Z250 composites with and without flowable materials. There was no significant between utilizing flowable composite or flowable compomer and between each similar subgroup when polymerized with either the LED or the QTH LCUs. Conclusions: A layer of flowable materials at the gingival floor of Class II composite restorations may be recommended to improve the marginal seal of a restoration.

Comparison of the residual stress of the nanofilled composites / 대한치과보존학회지

"Residual stress" can be developed during polymerization of the dental composite and it can be remained after this process was completed. The total amount of the force which applied to the composite restoration can be calculated by the sum of external and internal force. For the complete understanding of the restoration failure behavior, these two factors should be considered. In this experiment, I compared the residual stress of the recently developed nanofilled dental composite by ring slitting methods. The composites used in this study can be categorized in two groups, one is microhybrid type-Z250, as control group, and nanofilled type-Grandio, Filtek Supreme, Ceram-X, as experimental ones. Composite ring was made and marked two reference points on the surface. Then measure the change of the distance between these two points before and after ring slitting. From the distance change, average circumferential residual stress (sigmatheta) was calculated. In 10 minutes and 1 hour measurement groups, Filtek Supreme showed higher residual stress than Z250 and Ceram-X. In 24 hour group, Filtek showed higher stress than the other groups. Following the result of this experiment, nanofilled composite showed similar or higher residual stress than Z250, and when comparing the Z250 and Filtek Supreme, which have quite similar matrix components, Filtek Supreme groups showed higher residual stress.