## 2 Materials and Methods  
### Universal Adhesive Systems  
Two universal adhesive systems were selected for the experimentation:  
All-Bond Universal (Bisco Inc., Schaumburg, IL, USA, batch: 2200001890): single-bottle formulation optimized both for use in total-etch adhesive procedures and for use in self-etch mode (very similar adhesion values in both procedures). It contains MDP monomer, which significantly improves the durability of the seal and adhesion to indirect restorations (zirconia, alumina and metals); it is formulated with a low degree of acidity (pH > 3) with complete compatibility with self and light-curing and dual-curing composites/cementswithout the need for an additional activator; the solvent evaporates easily leaving a small residue of water. After polymerization it becomes highly hydrophobic for a long-time seal (reduced water absorption) without the need to add an additional layer of resin. Its low viscosity is meant to allow better penetration in etched surfaces, creating both chemical and mechanical adhesive bonds with the polymerization [5; 20].  
Universal Bond (Tokuyama Dental, Tokyo, Japan, batch: 103E21): is a two-component (Bottle A + Bottle B) self-curing adhesive system for direct and indirect restorations, usable with selective etching, total etching and self-etching techniques. The adhesive monomer is the 3D-SR (phosphoric acid monomer), which enhances the strength of adhesion to zirconium oxide or metals and gives strong adhesion not only to the dental surface but also to various materials including ceramics, CAD/CAM blocks or metal, in combination with various functional monomers, such as a new silane-based coupling agent or adhesive monomer to precious metals. In addition, a polymerization activator (BoSE technology) is present, obtaining high adhesion strength without the need for photo curing. It improves the bond strength of the polymerizable resinous material (adhesive resin cement, acrylic resin and composite resin) to indirect restorative materials, such as glass ceramic (porcelain), oxide-ceramic (zirconium oxide and alumina), metals (precious and non-precious) and resinous materials, including inorganic filler. It also contains multiple adhesive monomers, in addition to the new 3D-SR monomer, the 6-methacryloyloxy hexyl 2-thiouracil- 5-carboxylate (MTU-6) and the \(\gamma\)-methacryloxymethyl trimethoxy silane (\(\gamma\)-MPTTES), which are monomers for dental and prosthetic surfaces adhesion; there are also other monomers (HEMA, Bis-GMA and TEGDMA) to form adhesive layers. Acetone, isopropyl alcohol and water are used as solvents and a borate and peroxide-based catalyst as polymerization activators. In order to have a high storage stability, these functional components are kept separated into two bottles, and the adhesion strength is not inferior to traditional light-cured adhesives, thanks to the use of an extremely active polymerization catalyst [5; 9].  
To evaluate the effectiveness of adhesion on sound and DI-II-affected teeth, four samples, two sound upper third molars and two sound upper third molars affected by DI-II, extracted for periodontal reasons, were collected. All the samples received an X-ray in meso-distal and vestibular-buccal projections to ensure the absence of carious lesions or other issues.  
The samples were cleaned and stored in 0.1% chloramine-T at a temperature of 4 \({}^{\circ}\)C for 4 weeks and, subsequently, were stored in saline at 4 \({}^{\circ}\)C for another week prior to experimentation.