Effect of "Megafiller" insertion on the wear of composite resins

Eight year results with direct ceramic restorations (Cerana)

BACKGROUND

Single-visit system ceramic restorations are now in use to provide an alternative to resin-based materials. Inserts have been shown to improve characteristics of composite restorations.

OBJECTIVE

To investigate the longevity of Cerana (Nordiska Dental, Sweden) in a prospective clinical trial.

METHODS

Cerana restorations use matched drills with pre-etched and silanated leucite inserts cemented using a conventional restorative composite resin material. The results of 33 Cerana restorations up to eight years (25 Class I, eight class II) are presented. Restorations were reviewed and assessed by two examiners using modified USPHS criteria for anatomical form (AF) A-C, marginal adaptation (MA) A-D, surface roughness (SR) A-D, marginal discoloration (MD) A-C, colour match (CM) A-C and discomfort (DT) A-D as well as retention.

RESULTS

The percentage of A scores for AF, MA, SR, MD, CM and DT at baseline (n = 33) were: 100, 100, 79, 100, 21, 100; after two years (n = 27) 100, 85, 33, 100, 19, 100 and after four years (n = 24) 96, 75, 17, 96, 25, 100. At six years (n = 20) 95, 70, 10, 95, 15, 100 and finally at the eight year recall (n = 18) 94, 61, 0, 94, 6, 100. AF was maintained in all except for one fractured marginal ridge. MA of the insert was good but composite was lost where exposed. SR increased to a B score for all inserts. MD at B grade was observed in 6% between composite and tooth but none between insert and composite. CM was stable in all cases. DT nil in all. There were no scores less than B. All reviewed restorations were retained, clinically acceptable and in function except for two lost for reasons not directly related to the Cerana insert. One class II restoration had a fractured marginal ridge but otherwise remains satisfactory.

CONCLUSIONS

The results suggest that these restorations can be expected to perform well. Cerana is acceptable in terms of aesthetics, patient acceptance, occlusal wear and ease of use and is a good alternative for a single-visit, tooth coloured restoration in suitable cavity shapes.

Bonding of ceramic insert to a laboratory particle filler composite

The push-out bond strength of cylindrical ceramic inserts (CI) to particulate filler resin composite (VC) was evaluated in this study. Various surface treatments to improve the adhesion of CI to resin composite were tested. Additionally, the effect of fiber-reinforced composite (FRC) laminate encapsulation around CI was tested. Feldspathic porcelain CI with a diameter of 3.1 mm was bonded to VC. Adhesive resin was used for bonding. In group 1, no surface treatment of CI was done. In group 2, CI was encapsulated with a thin layer of woven glass FRC. In group 3, the surface of the CI was tribochemically silica coated and silanized. In group 4, the surface of the CI was grit-blasted with 50 microm aluminum oxide and etched with hydrofluoric acid. In group 5, the grit-blasted CI was encapsulated with a layer of FRC. The specimens (n = 6/group) were either dry stored or thermocycled in water (6000 x 5-55 degrees C). The push-out test was carried out with a universal material testing machine. The highest push-out strength was achieved in group 5 (20.4 MPa) and the lowest in group 2 (11.5 MPa). ANOVA revealed that both surface treatment and storage condition had a significant effect on push-out strength (p < 0.05). We conclude that the additional glass FRC encapsulation can be used to increase the bond strength of insert to composite.

Bruxing-type dental wear simulator for ranking of dental restorative materials

An instrumented dental wear test simulator was developed to simulate jaw movement in the chewing process between two molar teeth. It simulated the natural impact with sliding masticatory action, known as bruxing (defined as the gnashing, grinding, or clenching of teeth) type of wear, in order to simulate a worst-case dental wear scenario. In vitro wear testing of dental restorative materials was performed. Impact and sliding wear were simulated on the machine, with water as the lubricant, on three metal alloys (Tytin, Valiant Ph.D., Galloy) and three composite resins (Silux Plus, Z100, P50). The impact force for each machine cycle was brought closer to the maximum natural masticatory forces by the use of a shock absorbing layer. To replicate the natural masticatory action, the specimens had a surface profile with the shape of a conical depression. Ranking of the materials' performance on the wear test simulator was seen to be consistent with published clinical ranking. Metal alloys showed greater wear resistance than composite resins. Among the different metal alloys, those with lower hardness and compressive strengths exhibited greater wear. Composite resins with large filler particles wore worse than those with small filler particles. Results were compared with previous work on impact with sliding on a flat surface without a cushioning layer. It was concluded that the magnitude of the impact force and the angle of approach during impact with sliding wear are important parameters in the in vitro wear ranking of dental restorative materials.

Mechanical properties of resin composites with filler particles aligned by an electric field

OBJECTIVES

To explore possible enhancement of the mechanical properties of resin composites by aligning the filler particles.

METHODS

The resin for the composites consisted of urethane dimethacrylate (UDMA) and 1,6-hexanediol dimethacrylate (HDDMA) mixed in the ratio of 90 to 10; the filler was silica-zirconia in two particle sizes, 1.7 microns (P50), which was mixed with the resin in the volume fractions of 29 and 48 vol%, and 0.7 micron (Z100), which was mixed with the resin in the volume fractions of 37 and 57 vol%. Particle alignment was obtained by applying a 60 Hz AC electric field across the composite before the resin was photopolymerized. The stress-strain behavior and the elastic modulus of the hardened composite were measured along the alignment axis in compression.

RESULTS

The elastic moduli of the aligned composites increased by as much as 20%, and the maximum stress sustainable in compression before significant deformation occurred was elevated. An electric field strength of the order of 1 kV mm-1 was required to obtain sufficient alignment.

SIGNIFICANCE

Besides conferring a structure to resin composites that is more like that of the natural tooth, particle alignment increased some of the mechanical properties and may have improved durability.