The role of collagen cross-linkers in the stability of the adhesive interface

The subject of the thesis is the stability of the adhesive interface created at the level of the dental substrate. The connection between polymerized adhesives and the remaining mineralized dentin occurs through the collagen fibrils extending from the underlying mineralized matrix towards the hybrid layer. The collagen fibrils contain bound, non-collagenous proteins such as growth factors and matrix proteases. These proteases play an important role during dentin maturation, but they become trapped and inactive after the collagen matrix mineralized. However, during adhesive procedures, the enzymes of the collagen matrix are exposed and activated, irrespective of the E&R or SE procedure employed, resulting in the progressive degradation of the collagen fibril anchoring the restorative material to tooth structure. This leads to solubilization of collagen and loss of retention of the adhesive restoration. Recent studies supported the use of protein cross-linking agents during bonding procedures to prevent dentin collagen degradation caused by endogenous enzymes to improve bond durability. Acrolein (ACR),1-ethyl-3- (3-dimethylaminopropyl) carbodiimide (EDC) and dicyclohexylcarbodiimide (DDC) are compounds claimed to be potent cross-linkers. The present series of studies aimed at investigating the effect of various collagen crosslinkers on dentin protease activity and their effect on bond-strength to the dentinal substrate. Thus, selected collagen cross-linkers were tested to determine their effect on MPa values on coronal and radicular dentin, the marginal infiltration at the resin dentin interfaces, the presence of endogenous enzymatic activity after treatment and the localization of the gelatinase activity on dentin. Additionally, the effect of the crosslinkers and the effect of treatment period (duration) on the degradation of collagen matrices were examined. The results obtained suggest that collagen crosslinkers can inactivate e the collagen degradation through the inactivation of dentin proteases. However, in vivo studies are essential to better understand the feasibility of the tested molecules as dentin conditioning

Nanoindentation and Raman spectroscopy measurements on dual-cure luting cement for dental conservative restoration

The employment of innovative all-ceramic materi-als and adhesive cement, as well as the development of new bonding procedures, allow clinicians to use minimally invasive approaches in conservative restorations. In particular, dual-cure cement allows for obtaining higher aesthetic and functional results. However, the reduced light transmission through ceramic materials could prevent the proper curing and affect the adhesion of these materials to the tooth surface. In this context, the development of an accurate measurement methodology to assess the extent of polymerization of dental resin-based luting cement and to correlate the conversion degree with the mechanical properties is of particular importance from the clinical and scientific point of view. A measurement approach that exploits Raman Spectroscopy and nano-hardness measurements is hereby proposed. In particular, in this study, two different light-curing protocols are employed on a dual-cure luting cement, usually used for the full-crown restoration of single-rooted teeth. The effect of different times and tack-curing steps on the polymerization shrinkage of resin-based luting cement is investigated. The pre-liminary results allow concluding that both curing protocols lead to a good polymerization, without significant differences in the degree of conversion along the cement-tooth interfacial surface, as proved by the almost constant ratio of the Raman vibration characteristic peaks. However, the nanoindentation modulus was lower in the case of the tack-cured protocol

Wear Behaviour of Polymer-Infiltrated Network Ceramics, Lithium Disilicate and Cubic Zirconia against Enamel in a Bruxism-Simulated Scenario

The present study aimed to evaluate the wear rate of polymer-infiltrated network composites and ceramics against enamel in a bruxism-simulated scenario. Ninety-six (n = 96) molars were divided into six groups (n = 16) according to their occlusal material: group 1—a polymer-infiltrated network ceramic (PINC); group 2—a second polymer-infiltrated network ceramic (PINC2); group 3—nanohybrid resin-based composite (CO); group 4—cubic zirconia (ZR); group 5—lithium disilicate (LS); and group 6—sound enamel (EN). A laser scanner was used to digitalize all of the occlusal surfaces before and after a fatigue test, which was conducted with a chewing simulator set at 80 N and semicircular movement in order to simulate bruxist movement and loads. Statistical analysis of volume loss was performed with a one-way ANOVA and post hoc Bonferroni test. ZR had significantly inferior wear to PINC (p ≤ 0.01) and CO (p = 0.04). LS wore the antagonist enamel significantly more than PINC, CO, PINC2 and EN (p ≤ 0.01). On the other hand, ZR wore the antagonist enamel significantly more than CO (p ≤ 0.01) and PINC2 (p = 0.05). In conclusion, PINCs better preserved antagonist enamel at the expense of a higher wear of their own. LS causes significantly higher enamel wear compared with PINCs. ZR caused significantly higher enamel wear compared with CO and PINC2, but it was wear-resistant

Influence of polymerization time on properties of dual-curing cements in combination with high translucency monolithic zirconia

Purpose: The aim of this in vitro study was to assess conversion degree (DC), micro-hardness (MH) and bond strength of two dual-curing resin cements employed under translucent monolithic zirconia irradiated with different time protocols. Methods: 84 square shaped samples of 1 mm thickness were prepared from high translucency zirconia blocks and divided into two groups (n = 24) according to the cement employed: (1) Rely-X Ultimate; (2) Panavia SA. Each group was further divided into 3 subgroups (n = 8) according to the irradiation time: (a) no light; (b) 20 s; (c) 120 s. Light curing was performed 60 s after the sample was placed on the diamond support of a FT-IR spectrophotometer with a high power multiLED lamp. Final DC% were calculated after 10 min. After 24 h, Vickers Test on the cement layer was performed. The same protocol was used to lute composite cylinders in order to evaluate microshear bond-strength test. ANOVA and Bonferroni tests were performed to find differences between MH and bond-strength to zirconia, while for DC% the Scheirer\u2013Ray\u2013Hare two-way test was used. Results: The two cements reached higher DC% in subgroup (b) and (c). As concern MH, statistics showed an increase in curing time was able to improve MH significantly. Bond-strength was not affected by irradiation time only for Panavia SA. Conclusions: The first null hypothesis has to be rejected since DC% and MH of the dual-cements tested were influenced by the curing time. The second null hypothesis is partially rejected since the bond strength was influenced by the curing time only for Rely-X Ultimate

The effect of carbodiimide on push-out bond strength of fiber posts and endogenous enzymatic activity

BackgroundTo investigate the effect of 0.3 M 1-ethyl-3(3-dimethylaminopropyl) carbodiimide (EDC) aqueous solution pretreatment on push-out bond strength (PBS) and matrix-metalloproteinases (MMPs) activity within radicular dentin when different post cementation strategies were employed.MethodsOne hundred and twenty monoradicular human teeth were endodontically treated and randomly divided into six groups, depending on the cementation strategy and root dentin pretreatment (n = 20): EAR: cementation with an etch-and-rinse adhesive (LuxaBond Total Etch, DMG) and resin cement (LuxaCore Z Dual, DMG); EAR/EDC: 1 min EDC pretreatment after etching + EAR; SE: cementation with a self-etch primer (Multilink Primer, Ivoclar Vivadent) and corresponding cement (Multilink Automix, Ivoclar Vivadent); SE/EDC: self-etch primer + EDC pretreatment + SE; SA: cementation with a universal self-adhesive cement (RelyX Universal, 3 M); SA/EDC: EDC pretreatment + SA. Slices were submitted to PBS test and interfacial nanoleakage evaluation 24 h after cementation or after thermocycling (40.000 cycles, 5-55 & DEG;C). To investigate the effect of EDC on MMPs activity, 4 additional first maxillary premolars per group were processed for in situ zymography analysis. Multivariate ANOVA and post hoc Tukey tests were used to analyze PBS values. The data from in situ zymography were analyzed with Kruskal-Wallis test and Dunn's pairwise multiple comparison procedures (& alpha; = 0.05).ResultsThe variables "EDC pretreatment", "root region" and "thermocycling" significantly influenced PBS (p < 0.05), while the variable "cementation strategy" had no influence (p > 0.05). Thermocycling significantly reduced PBS in SE and SA groups (p < 0.05). EDC was effective in preserving PBS after artificial aging. EDC pretreatment significantly reduced enzymatic activity at baseline in EAR and SE groups, and in SA group after thermocycling (p < 0.05).ConclusionsThe use of EDC prevents the reduction of bond-strength values after artificial aging and silences endogenous enzymatic activity within radicular dentin when different cementation strategies were employed