This study aims to evaluate the survival rates of onlays placed over posterior endodontically treated teeth restored with zirconia, lithium disilicate and lithium disilicate reinforced with zirconia. Additionally, it seeks to identify and assess the failure modes associated with these types of restorations.
A total of 39 root canal-treated molars were restored with partial coverage onlays. Teeth were divided randomly into three groups: 13 with zirconia, 13 with lithium disilicate and 13 with lithium disilicate reinforced with zirconia. Informed consent was obtained from all patients prior to their participation. A silicon index was used for precise tooth preparation and temporary fabrication. Preparation: Monolithic Zirconia Onlays preparation included a rounded shoulder with the finish line located supragingivally, with a minimum of 1 mm axial reduction and 1.5 to 2 mm occlusal reduction, performed with diamond burs (Komet Dental, Germany). For Lithium Disilicate or Zirconia Reinforced Onlays, teeth were prepared with a rounded shoulder finish line located above the CEJ with axial reductions of 1.5 mm, and occlusal reductions of 2 mm using diamond burs (Komet Dental, Germany) the internal line angles were rounded, and the cavosurface angles achieved to be 90°. Finishing was completed with Al2O3 stones or rubber cups. Impressions were taken using digital scanning technology. Temporary fabrication: The abutment teeth were temporarily restored using Acrytemp (Zhermack, Italy) and temporarily cemented with 3MTM RelyXTM Temp NE Zinc Oxide Non-Eugenol Temporary Cement (3M, Germany). Isolation and Cementation: Teeth were isolated using rubber dam, bleeding was controlled. For ceramic-based onlays, the intaglio surface was treated with 9% hydrofluoric acid, washed and dried followed by application of Ceramic Primer Plus (Clearfil™) and Panavia V5 resin cement (Kuraray Dental-Kurashiki, Okayama, Japan) respectively. Tooth Primer was applied to ensure optimal adhesion. The restorations were seated, excess cement were removed using a tack-curing method, isolation were maintained for 3 minutes or light-cure for translucent onlays. After Isolation were removed, occlusal adjustments were made. For zirconia onlays, the intaglio surface was treated with tribochemical silica-coating using a chairside air-abrasion device. Alumina-coated silica particles 30µm (CoJet Sand, 3M ESPE) were applied to the intaglio surface of the zirconia onlays at a pressure of 2.5 bar, with the nozzle at a 45-degree angle and 10 mm from the surface. The application time for coating was 20 seconds. Afterward, the specimens were air-dried to remove loosely adhered particles. The above procedure has been designed based on the optimized parameters set by Özcan et al. (2013) for the highest silica content and lowest surface damage. Onlays were then treated using Z-Prime Plus, BISCO followed by Ceramic Primer Plus and Panavia V5 resin cement (Kuraray Dental-Kurashiki, Okayama, Japan). Procedures were performed by the same prosthodontist and evaluated by two operators. Restorations were assessed according to modified United States Public Health Service (USPHS) criteria, focusing on: (a) marginal discoloration, (b) secondary caries, (c) marginal integrity, (d) surface texture, (e) restoration fracture, (f) occlusal wear, (g) Color match and (h) Aesthetic anatomic form. Success will be determined based on Alpha and Bravo ratings at 6 months and 1 year intervals.
Study Type
INTERVENTIONAL
Allocation
RANDOMIZED
Purpose
TREATMENT
Masking
DOUBLE
Enrollment
39
Endodontically treated molars restored with adhesive onlays. For the monolithic zirconia, material-specific intaglio surface treatments are applied prior to cementation: zirconia onlays receive tribochemical silica-coating with 30µm alumina-coated silica particles (CoJet Sand) at 2.5 bar for 20 seconds, followed by Z-Prime Plus and Ceramic Primer Plus (Clearfil™). Teeth were isolated using rubber dam and Tooth Primer were applied for dentin/enamel. All restorations are definitively cemented with MDP-based dual-cure resin cement (Panavia V5, Kuraray Dental). Restorations are seated, tack-cured, and isolated for 3 minutes.
Endodontically treated molars restored with adhesive onlays. For the Lithium disilicate (IPS e.max Press), material-specific intaglio surface treatments are applied prior to cementation: Onlays receive 9% hydrofluoric acid etching, washing, drying, and application of Ceramic Primer Plus (Clearfil™). Teeth were isolated using rubber dam and Tooth Primer were applied for dentin/enamel. All restorations are definitively cemented with MDP-based dual-cure resin cement (Panavia V5, Kuraray Dental). Restorations are seated, tack-cured, and isolated for 3 minutes (or light-cured for translucent onlays).
Dental Teaching Clinics at Jordan University of Science and Technology
Irbid, Jordan
Number and Proportion of Successful Onlay Restorations in Posterior Endodontically Treated Teeth Assessed by the Modified United States Public Health Service (USPHS) Criteria
Posterior endodontically treated teeth restored with zirconia, lithium disilicate, or zirconia-reinforced lithium disilicate onlays are evaluated by two independent examiners using modified USPHS criteria across 8 parameters: marginal discoloration, secondary caries, marginal integrity, surface texture, restoration fracture, occlusal wear, color match, and aesthetic anatomic form. Each parameter rated Alpha (clinically ideal), Bravo (minor complication, clinically acceptable), or Charlie (major complication requiring renewal). Failure if Charlie on any single parameter. Data will be analyzed using Kaplan-Meier survival estimation. Outcome reported as absolute count and percentage (%) of successful restorations, stratified by material group. Higher percentage indicates better outcome.
Time frame: 6 months and 12 months post-cementation
Frequency and Distribution of Individual Modified USPHS Parameter Ratings (Failure Mode Analysis) Stratified by Onlay Material
To provide a granular failure-mode analysis to onlays' placed over posterior endodontically treated teeth. This analysis will be stratified by the three onlay material groups (zirconia, lithium disilicate, and zirconia-reinforced lithium disilicate) to identify the most prevalent types of minor complications (Bravo ratings) and failures (Charlie ratings, defined as major complications requiring restoration renewal) associated with each specific material. In this failure-mode analysis, Charlie (C) ratings are explicitly considered failures. Since the USPHS criteria represent an ordinal categorical scale. Data will be aggregated as count distributions and relative frequencies (%) for each rating per parameter, per material group, providing a comprehensive descriptive assessment of failure modes.
Time frame: 6 months and 1 year post-cementation
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Endodontically treated molars restored with adhesive onlays. For the zirconia-reinforced lithium disilicate onlays (Vita Ambria), material-specific intaglio surface treatments are applied prior to cementation: Onlays receive 9% hydrofluoric acid etching, washing, drying, and application of Ceramic Primer Plus (Clearfil™). Teeth were isolated using rubber dam and Tooth Primer were applied for dentin/enamel. All restorations are definitively cemented with MDP-based dual-cure resin cement (Panavia V5, Kuraray Dental). Restorations are seated, tack-cured, and isolated for 3 minutes (or light-cured for translucent onlays).