SSD: MEDS-16/A – Malattie Odontostomatologiche
Responsabili della ricerca: Maria Menini, Domenico Baldi
Finanziamento: Ivoclar Vivadent AG

Descrizione

Background
In recent decades, the use of non-invasive dental restorations, has become a very common and in- demand approach with the purpose to restore worn, misaligned, fractured, discolored, and malformed teeth.
In addition, the clinical indications for such restorations have been progressively increased with the development of innovative ceramic materials that have been introduced to the market.
The reduced thicknesses required by new biomimetic ceramic materials, together with effective adhesion to enamel and dentin, and new preparation methods using sonic and ultrasonic instruments have allowed a significant reduction in the invasiveness of preparation, leading to significant preservation of tooth structure, in accordance with established principles of minimally invasive dentistry.

Purpose of the research
The purpose of the present in vitro research is to evaluate whether minimal enamel preparation with ultrasonic instruments allows obtaining greater resistance to detachment than no enamel preparation of veneers made of two different materials: zirconia and lithium disilicate. Fracture resistance and marginal quality will be also evaluated.

Material and Methods
Human upper central incisors or lateral incisors will be randomly assigned to 4 groups with two different preparations: unprepared (NP), minimally invasive (MI) (exclusively enamel- bonded by invading the enamel thickness to a maximum of 0.3 mm) and rehabilitated with zirconia and lithium disilicate veneers.
All teeth should have intact enamel, and no composite restorations.
In the first group (NPZ), the extracted teeth will not undergo any enamel preparation and will be rehabilitated with zirconia veneers (IPS e.max ZirCAD Prime, Ivoclar).
In the second group (NPD) the extracted teeth will not undergo any enamel preparation and will be rehabilitated with lithium disilicate veneers (IPS e-max CAD, Ivoclar).
In the third group (MIZ) they will undergo enamel thickness preparation through dedicated ultrasonic inserts and silicone templates and will be rehabilitated with zirconia veneers. (IPS e.max ZirCAD Prime).
In the fourth group (MID) they will undergo enamel thickness preparation through dedicated ultrasonic inserts and silicone templates and will be rehabilitated with lithium disilicate veneers (IPS e-max CAD).
A silicone impression will be made on all teeth in both groups.
The veneers will be made of zirconia or lithium disilicate with a mean thickness of 0.5 mm.

After adhesive cementation with light polymerization and polishing, the specimens will undergo thermocycling to age the restorations similarly to the clinical situation.
Once thermocycled, they will be mechanically loaded on the incisal edge at a 45° angle at 50 N and at 100 N and up to failure.
At the end of each cycle, fissures and margin quality will be evaluated by SEM.
The veneers will be evaluated under the microscope looking for cracks, chips, and fractures.
Then the maximum force applied to have the veneer detached, fracture or chipping for each of the two groups will be evaluated.

Expected Results
The investigations carried out will allow evaluation of whether minimal enamel preparation with ultrasonic method allows better adhesion and resistance to chipping than complete no preparation. Furthermore, it will be evaluated if zirconia veneers could ensure better adhesion and resistance to chipping than lithium disilicate veneers.