Bonding Strength of Lithium Disilicate Adhesive Crowns with Different Occluso-Cervical Preparation Heights and Cement Types

The aim of this study was to evaluate if adhesion technology with CAD/CAM can compensate for the reduction of occluso cervical preparation heights using different types of dental cement. The de-bonding failure types were then assessed. Here, 72 caries-free extracted human premolar teeth were prepared to have a remaining occlusal height of two, three, and four mm. IPS e.max lithium disilicate CAD/CAM crowns were cemented with adhesive resin cement Panavia SA, self-adhesive resin cement, RelyX Unicem Aplicap, and zinc phosphate cement. The cementation techniques were based on the manufacturer’s instructions. After thermocycling, all samples were tested for tensile bond strength via an Instron machine. One-way analysis of variance (ANOVA) with post hoc testing (P < 0.05) was performed. The means TBS for the two, three, and four-mm OCHP groups were 2.72±0.69, 3.06±0.82, and 3.25±0.79.0 MPa; ARC, SARC, and ZPC were 3.41±0.51, 3.45±0.41, 2.08±0.35 MPa, respectively with significant differences in both. The mixed cement had failures in the resin cement groups. Failure was predominantly cohesive in the zinc phosphate group. Resin cement had the highest SBS values versus ZPC values when both bonded to lithium disilicate crowns with different occlusal heights. The failure of the adhesive to the crown and/or to the tooth were the highest for the four types of resin cement. Around 25% were cohesive failures with resin cement, but this was predominately adhesive in crowns in zinc phosphate regardless of the preparation heights.

Aesthetic and functional rehabilitation in a patient with anterior skeletal open bite using lithium dissilicate glass-reinforced ceramic: a case report

The aim of this clinical report is to present the replacement of unsatisfactory metal-ceramic crowns of elements 12, 11, 21 and 22, by lithium disilicate glass-reinforced ceramic crowns in a patient with skeletal anterior open bite. A patient sought care at the Dental Hospital at the School of Dentistry of UFU, complaining of odor between the metal-ceramic crowns of the antero-superior teeth. After clinical and radiographic examination, invasion of the biological space was noticed, surgery was indicated in order to restore the biological space. After healing, the pre-existing cast metal posts were masked using an opaque composite resin and the teeth were reprepared for full all-ceramic crowns. Impressions were taken in two steps, using PVS associated to retraction cords. The ceramic copings were obtained in lithium disilicate ceramic, and the veneering was performed by stratification. After testing the ceramics crowns in relation to, fit, function and aesthetic results, cementation was completed using modified absolute isolation, followed by prophylaxis of preparations with pumice and saline, surface treatment of the ceramic restorations and luting using self-adhesive resin cement. Finally, an occlusal splint was produced to control the effects of bruxism and orofacial pain symptoms. The anterior open skeletal bite was a challenging factor for the rehabilitation of this patient; however, one must consider the entire process that the patient would undergo if choosing for orthognathic surgery, and the patient should be aware of the case limitations. In addition, the use of lithium disilicate glass-reinforced ceramics proved the versatility of this material for anterior aesthetic restorations.

Does Resin Cement Type and Cement Preheating Influence the Marginal and Internal Fit of Lithium Disilicate Single Crowns?

This paper assesses the effect of cement type and cement preheating on the marginal and internal fit of lithium disilicate single crown. Methods: 40 maxillary premolars were selected, restored with lithium disilicate single crowns. Teeth were randomly assigned into four groups (n = 10) based on cement type (Panavia SA or LinkForce) and preheating temperature (25 °C or 54 °C). After fabrication of the restoration, cements were incubated at 25 °C or 54 °C for 24 h, and each crown was cemented to its corresponding tooth. After 24 h, all specimens were thermally aged to (10,000 thermal cycles between 5 °C and 55 °C), then load cycled for 240,000 cycles. Each specimen was then sectioned in bucco-palatal direction and inspected under a stereomicroscope at x45 magnification for marginal and internal fit evaluation. The data were statistically analyzed (significance at p ≤ 0.05 level). Results: At the mid-buccal finish line, mid-buccal wall, palatal cusp, mid-palatal wall, mid-palatal finish line, and palatal margin measuring points, there was a significant difference (p ≤ 0.05) between the lithium disilicate group cemented with Panavia SA at 25 °C and the group cemented with LinkForce at 25 °C, while there was no significant difference (p > 0.05) at the other points. At all measuring points, except at the palatal cusp tip (p = 0.948) and palatal margin (p = 0.103), there was a statistically significant difference (p ≤ 0.05) between the lithium disilicate group cemented with Panavia SA at 54 °C and the group cemented with LinkForce at 54 °C. Regardless of cement preheating, statistically significant differences were found in the buccal cusp tip, central groove, palatal cusp tip, and mid-palatal wall (p ≤ 0.05) in the lithium disilicate group cemented with Panavia SA at 25 °C and 54 °C, as well as the mid-palatal chamfer finish line and palatal margin in the LinkForce group cemented with Panavia SA at 25 °C and 54 °C. At the other measurement points, however, there was no significant difference (p > 0.05). Conclusions: The type of resin cement affects the internal and marginal fit of lithium disilicate crowns. At most measuring points, the cement preheating does not improve the internal and marginal fit of all lithium disilicate crowns.

Lithium disilicate and peek implant-retained single crowns - a randomized, prospective clinical study

Introduction/Objective. Comparing two materials under the same conditions is the best way to define differences between them. PEEK is a polymer that has many possible uses in dentistry as already well-known lithium disilicate ceramics. The aim of this study was to compare peri-implant soft tissue healing and evaluate patient satisfaction with esthetics in different observation periods, as well as the success and survival rate of both types of crowns. Methods. The study was conducted as a clinical, prospective, randomized split-mouth study on 17 patients with bilaterally missing upper teeth of the same type, replaced with dental implants. Study outcomes have been analyzed with subjective (VAS scale) and objective parameters (MBI, MPI and PPD) baseline, six and twelve months after fixing crowns onto the implants. Results. Comparison of the results between PEEK and lithium disilicate crowns showed no statistical differences in terms of MPI, MBI and PPD in the observed periods. Analyzing MPI during observation periods in the PEEK group of crowns, statistical significance was registered between baseline values and after 6 months. Also, statistical significance was noticed in terms of PPD during the observation time both in the study and control group of crowns. Results for VAS for the esthetics showed no statistically significant difference between the groups, while VAS for restoration satisfaction showed a statistically significant difference. Conclusion. This study showed that scores of the applied subjective and objective parameters can be a reliable tool to rate the clinical outcome of implant-retained single crowns over time.

MODERN TECHNOLOGIES FOR THE MANUFACTURE OF GLASS-CERAMIC DENTAL PROSTHESES

The relevance of the problem of improving the quality of life and protecting human health in the context of the successful development of the modern society was presented. A literary review of well-known modern technologies for the design and manufacture of dental prostheses was carried out, as well as the leading domestic and foreign companies that were engaged in this were given. The history of the development of materials for obtaining clinical restorations (crowns, inlays, onlays, etc.) was considered and the main directions of the development of innovative ceramic materials for dental prosthetics were outlined. Based on the analysis of the properties of various types of materials for dental prosthetics, the prospects of using glass-ceramic materials in the development of dental prostheses have been substantiated. The chemical compositions of lithium silicate glasses for the synthesis of the glass matrix have been developed and the technological parameters for the production of glass-ceramic dental prostheses have been selected (Тgl. melting = 1350–1400 °С, Тheat treatment = 600–650 °С). Preliminary heat treatment before the formation of products ensures the formation of the required number of the nucleus of crystalline phase and the prerequisites for creating a volume crystallized structure under conditions of short-term heat treatment. The glass-ceramic prosthesis with a formed interpenetrating sitallized structure was obtained by the method of hot pressing with a short exposure (18-20 min). It was found that the obtained glass-ceramic material containing lithium disilicate as a crystalline phase in an amount of 40-60 vol. %, had high values of bending strength (σ = 400 MPa) and fracture toughness. The indicated mechanical properties of the developed materials, along with the approximate values of their modulus of elasticity to natural teeth, will significantly extend the service life of products under conditions of significant alternating loads that arise during the chewing cycle. A comparative assessment of the competitiveness of the developed dental prostheses based on lithium disilicate with world analogues was carried out, in particular the products of Ivoclar Vivadent and Vita Zahnfabrik, in terms of the main operational parameters. The positive effect of the introduction of domestic developed glass-ceramic dental prostheses to reduce import dependence has been determined.