| Abstract | Istovremena svjetlosna polimerizacija caklinsko-dentinskog adhezijskog sustava i prvog sloja kompozitnog materijala, tj. co-curing metoda, jedna je od predloženih tehnika za smanjenje polimerizacijskog skupljanja i povećanje rubnog brtvljenja nadomjestaka. Svrha ovog in vitro istraživanja bila je ispitati utječu li različite metode polimerizacije caklinsko-dentinskih
adhezijskih sustava i kompozitnog materijala, različiti caklinsko-dentinski adhezijski sustavi, različite dubine presjeka zuba, vrsta zuba i starenje uzoraka na veznu čvrstoću dentina. Ispitana su tri komercijalno dostupna caklinsko-dentinska adhezijska sustava: G-Premio Bond, Clearfil SE Bond 2 i Adper Single Bond 2 koja su bila stvrdnjavana polimerizacijskom svjetlošću odvojeno ili istovremeno s kompozitnim uzorkom. Napravljeno je ukupno 480 dentinskih uzoraka koji su nasumično raspoređeni u 24 eksperimentalne skupine (2 načina polimerizacije x 3 caklinsko-dentinska adhezijska sustava x 4 vremenske točke mjerenja) po 20 uzoraka po skupini. Nakon uranjanja uzoraka u destiliranoj vodi i skladištenja u inkubatoru, smična vezna čvrstoća testirana je nakon mjesec dana, 3 mjeseca, 6 mjeseci i 1 godine. Nakon testiranja vezne čvrstoće, slomljeni uzorci su bili pregledani s lupama povećanja 3,6 x kako bi se karakterizirala vrsta frakture. Za statističku analizu koristila se analiza varijance i Weibullova analiza. Skupine kod kojih su caklinsko-dentinski adhezijski sustav, ne ovisno koji, i kompozitni materijal bili polimerizirani odvojeno pokazali su statistički značajno veće vrijednosti u odnosu na uzorke polimerizirane „co-curing“ metodom. Usporedba vezne čvrstoće između različitih caklinskodentinskih adhezijskih sustava koji su polimerizirani istom metodom pokazala je statistički značajnu razlika između svih skupina (p < 0,001), pri čemu je Clearfil SE Bond 2 pokazivao najveće vrijednosti. Starenjem uzoraka došlo je do pada u veznoj čvrstoći, pri čemu su prve promjene zabilježene nakon 6 mjeseci. Veću veznu čvrstoću pokazali su okluzalni tj. površinski dijelovi dentina u odnosu na radikularne dijelove. Nije opažena statistički značajna razlika između maksilarnih i mandibularnih trećih molara u veznoj čvstoći. Adhezijske frakture bile su opažene u najvećem postotku. Eksperimentalne skupine s najvišom prosječnom veznom čvrstoćom nakon 1 i 3 mjeseca starenja nisu pokazivale najveću pouzdanost materijala. |
| Abstract (english) | Adhesion serves as the basis for modern restorative dentistry. As an intermediary material, a dental adhesive system binds restorative materials to hard dental tissues and improves the retention, marginal sealing, and resistance of the tooth-restoration interface. Polymerization stress, however, is the biggest restriction in the field of resin composite and one of the primary causes of the clinical failure of today's adhesion systems. Polymerization shrinkage, which happens when monomers are transformed into polymers during the curing process of composite resins, causes a reduction in total volume. As a result, internal contraction stresses and stresses at the restoration's edges may emerge. If the bond strength is compromised by contraction pressures, pulp injury, postoperative sensitivity, marginal microleakage, marginal staining, and
secondary caries will result. Numerous variables, such as the configuration factor, cavity shape, application procedure and elastic modulus of the restorative material, all affect the creation of stress. To decrease polymerization shrinkage and improve the marginal sealing of restorations, several clinical treatments and approaches have been proposed. One of the suggested techniques is the co-curing process, which involves light curing both the resin adhesive and the initial layer
of the composite resin at the same time. The aim of this in vitro study was to evaluate the effects of different methods of polymerization of adhesion systems and composite resin, different adhesion systems, different depths of dentin sections, types of teeth and aging of samples on dentin shear bond strength.
Materials and Methods: A mid-coronal section of 222 intact third human molars with completed root formation was
made to create flat bonding substrates. Specimens were prepared using a low-speed saw, embedded in an acrylic resin and wet grounded to create a flat bonding area. Three bonding agents; G-Premio Bond (GC), Clearfil SE Bond 2 (Kuraray) and Adper Single Bond 2 (3M ESPE) were applied to the dentin. The application of each adhesion system was performed in two different ways. In half of the specimens, bonding agents were light cured immediately after their application (conventional application). The other half were not light cured until resin composite application (co-curing technique). Composite cylinders (diameter = 2.38 mm, height = 2 mm) were prepared using a bulk-fill composite SDR Plus Bulk Fill
Flowable (Dentsply Sirona). A total of 480 specimens were prepared (3 adhesives × 2 method of application × 4 aging times x 20 specimens per experimental group). Shear bond strength was evaluated after 1 month, 3 months, 6 months and 1 year of water storage in incubator at 37 °C by loading the specimens in bond strength testing machine UltraTester. Bond strength
was tested by loading specimens in a testing machine at a constant crosshead speed of 1 mm/min until fracture. Shear dentin bond strength was measured according to a ISO 29022: 2013 protocol. The fractured fragments were examined with a optical loupes to characterize the failure mode. Bond strength data (MPa) were analyzed using analysis of variance (ANOVA) and Weibull statistics (reliability analysis). In brittle materials (such as adhesion systems or dental composites) there are defects that affect the strength of the material. The source of these errors are inhomogeneities in the material, such as air bubbles, microcracks and pores. The stress at which the material cracks depends on the distribution of these errors, so the variability of the measured bond strength values cannot be attributed to experimental / measurement errors, but is at least partly due to the natural properties of the material. Conventional statistics (ANOVA) do not take this into account, but attribute it all to experimental error or measurement error.
Results: The highest mean bond strength was obtained for Clearfil SE Bond 2 conventional one month after storage (38.48 MPa), whilst the lowest bond strength was observed when co-curing was used after one year (particularly, Adper Single Bond 2 7.83 MPa). The results showed a statistically significant difference between conventional and co-curing methods in all materials (p < 0.001). Within each bonding system, bond strength values attained by co-curing were significantly lower than the corresponding values attained by conventional curing. Between all the different experimental groups in which the adhesion systems were applied and polymerized by the same method (conventional or “co-curing”), with the exception
of Adper Single Bond 2 and G-Premio Bond conventionally, a statistically significant difference was observed. Although G-Premio Bond showed a higher mean bond strength compared to Adper Single Bond 2, the difference was not demonstrated in the group comparison. Over time a decrease in mean bond strength values was observed in all experimental groups. After 6 months, there was a decrease in bond strength compared to 1 month and an additional decrease in bond strength occurs after 12 months. After one year bond strength was significantly lower compared to 1, 3 and 6 months. In the occlusal parts of the teeth, on average, a statistically significantly higher bonding strength was recorded compared to the radicular parts of the teeth. Between maxillary and mandibular teeth, no difference in bond strength was recorded. The frequency of adhesion fractures was 86 %, while cohesion fractures were not observed. In descriptive statistics, the experimental group Clearfil SE Bond 2 conventional had the highest mean value at all time points. The same applies to the characteristic strength in the reliability analysis. The lowest variability (the highest Weibull modulus) after one month of aging was recorded with G-Premio Bond conventional, after 3 months with Clearfil SE Bond 2 co-curing, and after 6 and 12 months with Clearfil SE Bond 2 conventional.
Conclusion: Under the limitations of this study, it can be concluded that bond strength is influenced by differences in polymerization of adhesive systems and composite resin, types of adhesive systems, depth of dentin section, and aging time. In the experimental model adopted for this study, specimens prepared with the conventional application technique produced higher shear bond strength according to conventional statistics and reliability analysis. The materials with the highest mean bond strength are not always materials with the highest reliability. |
