Effect of Various Laser Surface Treatments on Repair Shear Bond Strength of Aged Silorane-Based Composite

The effect of different surface treatments and adhesive systems on shear bond strength in universal nanohybrid composite resin repair

BACKGROUND

The aim of this study is to evaluate the effect of different surface treatments and adhesives on shear bond strength (SBS) in the repair of composite resin restorations.

METHODS

In this study, 60 discs (2 mm x 10 mm) were prepared using a universal nanohybrid composite resin (GrandioSo, Voco, Germany). The discs were aged by exposure to 5000 thermal cycles between 5 and 55 °C for 30 s with an immersion procedure. Then samples were divided into 3 groups (n:20) according to the surface treatments (Group 1: no surface treatment, Group 2: roughening by bur, Group 3: roughening by Er, Cr: YSGG laser). Subsequently, the specimens were classified into two groups (n:10) according to the adhesive systems; a two-step self-etch adhesive (Clearfil SE bond (SE)), or a universal adhesive (Scotchbond Universal Plus (SB)). After surface treatments and adhesive applications, the same universal nanohybrid composite resin with a height of 2 mm and a diameter of 3 mm was placed in the center of the samples. The samples were then submitted to the SBS test using universal testing equipment (Autograph AGS-X; Shimadzu, Kyoto, Japan) with a crosshead speed of 1 mm/min. The failure modes were examined using a stereomicroscope. The surface topography of the roughened and fractured surfaces resin composite (n = 1) was assessed using scanning electron microscopy (SEM). Analyses were performed using IBM SPSS 25 programme (p < 0.05).

RESULTS

The highest bond strength was observed in the laser + SE group (22.69 ± 4.49), while the lowest was recorded in the control + SE group (14.12 ± 3.00). In the SE adhesive group, no significant difference was found between the laser + SE and bur + SE groups (p > 0.05). Similarly, in the SB adhesive group, there were no significant differences among the surface roughening procedures (p = 0.078). Additionally, no significant differences were observed between the adhesives according to various surface roughening procedures. The failure mode was predominantly cohesive in old composites.

CONCLUSION

The bond strength can be improved by surface treatments such as diamond burs, Er, Cr: YSGG laser application for better bonding strategies in the repair of nanohybrid resin composite restorations. There was no statistically significant difference in bond strength between the adhesives tested in this study.

The effect of different energy levels of the Er: YAG laser on the repair bond strength of a nanohybrid composite resin

This study evaluates the durability of repair microshear bond strength (µSBS) of nanohybrid composite resins which surfaces are treated with different laser parameters and bur. A total of 240 nanohybrid composite resin disk shaped specimens were prepared. Then, specimens were divided into eight test groups as regards to surface treatment types (Erbium (Er:YAG) laser with seven different parameters and bur). Half of the specimens in each group were subjected to 5000 thermal cycling (TC) and the other half to 20,000 TC. Universal testing machine was used for µSBS test. The data were analyzed with a two-way analysis of variance and Tukey test. Among the specimens treated with ER:YAG laser+5000 TC, we detected the highest mean µSBS test values in the subgroups L200 and L250. Among the specimens treated with ER:YAG laser+20,000 TC, the highest mean µSBS test values were seen in the L200 subgroup. The µSBS values after the 20,000 TC were significantly lower than those after 5000 TC for all different treatment types. Thermal cycling and laser energy levels have effects on repair µSBS. Considering the bond strength and durability it seems more effective to use Er:YAG laser at 200 mJ. To repair an aged nanohybrid composite resin, Er:YAG laser surface treatments may provide some benefits by acquiring a reliable bond strength with durability. This study may give information on which parameters are more suitable to use Er:YAG laser for the repair of nanohybrid composite resins.

Evaluation of the Combination of CO2 Laser and Bifunctional Bonding Agents for Composite Resin Repairs After 1 Year of Aging

Objective: to evaluate the bond strength of repairs to composite resin restorations treated with CO₂ laser and bifunctional monomers after 1 year of aging. Background: Adequate bond strength between a composite restoration and resin repair agent can be achieved through mechanical and/or chemical treatment. However, the longevity of such repairs is unknown. Methods: Resin blocks (volume: 125 mm³) were created. Failure surfaces were either not treated or were treated before the repair with a universal adhesive, a silane bonding agent and/or CO₂ laser. The blocks were distributed into six groups (n = 6 per group): resin+resin group (RRG), universal adhesive+resin group (ARG), silane+universal adhesive group (SAG), laser+silane+universal adhesive group (LSAG), laser+universal adhesive group (LAG), and laser+silane group (LSG). After treatment, repairs were made with another resin composite. "Sticks" (1.0 mm² in area and 1.0 cm in length) were cut from the specimens in each group and immersed in distilled water at 37°C. Microtensile bond strength was evaluated after 1 year of aging. Bond strength values were compared using the Kruskal-Wallis test and Dunn's test. Results: Bond strength was significantly higher in the LSAG compared with the RRG, adhesive system, LSG, whereas statistically similar results were found for the SAG, LSAG, and LAG. Bond strength was lowest in the RRG. The LSAG and LAG presented predominantly cohesive fractures. Conclusions: The bond strength of composite resin repairs was satisfactory over time. Treatment with CO₂ laser contributed to the maintenance of bond strength during the 1-year storage period and bifunctional monomers present in the universal adhesive on the irradiated repair surface were of fundamental importance to the maintenance of bond strength values, as demonstrated by microtensile bond test and fracture pattern analysis.

Removal of Composite Restoration from the Root Surface in the Cervical Region Using Er: YAG Laser and Drill-In Vitro Study

Background: Recently, the defects of the tooth surface in the cervical region are often restored using composite filling materials. It should meet the needs of the patients regarding esthetics and material stability. The aim of the study was to analyze the tooth root surface at the cervical region after the removal of the composite filling material by means of the Erbium-doped Yttrium Aluminium Garnet (Er: YAG) laser or drill using the scanning electron microscopy (SEM) and fluorescence microscopy. Materials and Methods: For the purposes of this study, 14 premolar teeth (n = 14) were removed due to orthodontic reasons. The rectangular shape cavities with 3 mm in width and 1.5 mm in height were prepared with a 0.8 mm bur on high-speed contra-angle in the tooth surface just below cemento-enamel junction (CEJ) and filled with the composite material. The composite material was removed with the Er: YAG laser at a power of 3.4 W, energy 170 mJ, frequency 20 Hz, pulse duration 300 μs, tip diameter 0.8 mm, air/fluid cooling 3 mL/s, and time of irradiation: 6 sec, at a distance from teeth of 2 mm (G1 group, n = 7) or a high-speed contra-angle bur (G2 group, n = 7). After the removal of composite material, the surfaces of teeth were examined using the scanning electron microscopy (SEM) and fluorescence microscopy. Results: The Er: YAG irradiation allowed to remove completely the composite material from the tooth cavity. The study confirmed, that the ends of collagen fibers were only partially denatured after the Er: YAG laser application. Conclusion: It has been proved that using the Er: YAG laser is an effective and safe method of composite removal for the dentin surface.