The aim of this RCT was to evaluate the clinical performance of two lithium disilicate pressed systems using a novel Functional Index for Teeth (FIT), which is made up of seven clinical variables showing, among other things, the possible correlation with the level of appreciation perceived by the patients.
The null hypothesis tested in this clinical study was that there was no statistically significant difference in the clinical performance of the two lithium disilicate systems. A sample of 60 patients in need of a single partial crown on posterior teeth (upper and lower premolars and molars), accessing the Department of Prosthodontics and Dental Materials of the University of Siena, Italy, in the time period between September 2015 and January 2016 were included in the study. Selected patients, periodontally healthy or successfully treated in need for one posterior restoration, had a media age of 37 (±7.5) years (between 18 and 70) (14F, 16M). Exclusion criteria were: no proper age (< 18 years), pregnancy, disabilities, prosthodontic restoration of the tooth, spontaneous sensitivity, pulpitic, non-vital or endodontically treated teeth, (profound, chronic) periodontitis, deep defects (close to pulp, < 1mm distance) or pulp capping, heavy occlusal contacts or history of bruxism, systemic disease or severe medical complications, allergic history concerning methacrylates, rampant caries, xerostomia, lack of compliance, language barriers, plaque index higher than 20.
Patients written consent to the trial was obtained after having provided a complete explanation of the aim of the study. The study protocol was approved by the Ethical Committee of University of Siena (clinicaltrial.gov # NCT 01835821). All procedures performed in this study involving human participants were in accordance with the ethical standards of the Institutional and National Research Committee and with the 1964 Helsinki declaration and its later amendments or comparable ethical standards. This study adheres to CONSORT guidelines.
Randomization and selection of the patients
After recruitment, oral hygiene instructions were given to the patients and prophylaxis was performed to establish optimal plaque control and gingival health.
The clinical assessment of periodontal parameters such as probing pocket depths (PPD)(22), bleeding on probing (BoP)(23), and full-mouth plaque index (PI)(22) was performed.
All restorative procedures were carried out under local anesthesia (Articaine with 1:100.000 epinephrine) by the same experienced operator. Intraoral radiographs were also taken before starting the treatment. In order to standardize the radiographic examination, X-ray individual tray was made for each sample tooth of each patient, in order to be sure to have the radiogram in the same position at each recall.
Randomization, allocation concealment and masking of examiners
Each participating patient was randomly assigned to one of the two experimental groups (n = 30), that were defined based on the material to be used for the restorative treatment:
Group 1: e.max press (Ivoclar-Vivadent, Schaan, Lichtenstein)
Group 2: LiSi press (GC Co., Tokyo, Japan)
Treatment assignment was noted in the registration and treatment assignment form that was kept by the study. Allocation concealment was performed by using opaque sealed, sequentially numbered envelopes. The statistician made the allocation sequence by means of a computer-generated random list and instructed a different subject to assign a sealed envelope containing the type of lithium disilicate material to be used. The opaque envelope has been opened before material selection and communicated to the operator. At the 3-year recall blinding of the examiner has been applied.
For standardization purposes, all clinical procedures were performed by the same trained operator. Following anesthesia, rubber dam was placed, all carious lesions were excavated, and any restorative material was removed. Preparation was performed using conventional diamond burs in a high-speed hand piece, with no bevel on margins. The preparation design was dictated by the extent of decay, pre-existing restorations and the preparation guidelines defined by the manufacturer of the restorative materials. The Residual Dentin Thickness (RDT) was evaluated on a periapical radiograph, and teeth with RDT thinner than 0.5 mm were excluded. Cavities’ preparation provided at least 0.5–1 mm space at the margin and 1.0–1.5 mm of clearance occlusally. Margins were mainly into enamel and only interproximal boxes had cervical margin below the cementum-enamel junction. At least one cusp was covered. Teeth were kept vital.
Hybridization of dentin with adhesive material (Adhese Bond Ivoclar-Vivadent, Schaan, Liechtenstein, in Group 1 and G-Premio Bond, (GC Co., Tokyo, Japan) in Group 2) and a thin layer of flowable has been applied on top (Tetric Flow (Ivoclar-Vivadent) and Genial Flow, (GC Co). After the final preparation, an impression of the prepared tooth was taken with an elastomeric material (Exa’lence, GC Co.), and poured in stone (FujiRock, GC Co.). The restoration was then waxed and pressed in lithium disilicate, strictly following the manufacturer’s instructions. A temporary restoration of the prepared tooth was provided and after one week the lithium disilicate restoration was luted following manufacturer’s instructions. The intaglio surface of the restoration was etched with 10% hydrofluoric acid for 1 minute, silanized with Monobond Plus (Ivoclar-Vivadent, Schaan, Lietchtenstein) in Group 1 and G-Multi Primer (GC Co.) in Group 2, and then luted using MultiLink Sprint (Ivoclar-Vivadent) in Group 1 and LinkForce (GC Co.) in Group 2. During cementation proper tooth isolation was provided by rubber dam.
All patients were enrolled in a dental hygiene program in which recalls were planned every 6 months. A clinical exam and standardized intraoral radiographs were performed immediately after the seating of the crowns (baseline), as well as after 1, 2, and 3 years of clinical service (follow-up).
A novel Functional Index for Teeth (FIT) was applied (Table 1). The FIT evaluation was performed at last recall (3-year follow-up) by an experienced operator (Figs 1–2).
The Mann-Whitney ‘U’ test was applied to verify the statistical significance of the difference between the two groups in the scores recorded for each assessed variable. The level of significance was set at p<0,05. The statistical analysis was handled by the PASW Statistics 18 software (IBM, Armonk, NY, USA).