Luting Cements for Prefabricated Zirconia Crown Retention in Primary Anterior Teeth in Children

This prospective, parallel-group, three-arm, randomized controlled trial evaluates the long-term clinical performance of three commercially available luting cements when used to bond prefabricated zirconia crowns (PZCs) on primary anterior teeth in pediatric patients. Although PZCs are increasingly preferred over stainless steel crowns for anterior restorations due to their superior esthetics and biocompatibility, their retention relies entirely on the luting cement because of their passive fit and conservative preparation design. Comparative clinical evidence on cement performance in this specific anatomical and functional context remains limited.

Trial Design:

The trial is conducted at the Pediatric Dental Clinic of Qassim University, Riyadh, Saudi Arabia. Eligible children aged 2 to 7 years requiring full-coverage restoration of one or more primary incisors are randomized in a 1:1:1 ratio to one of three cement groups using a computer-generated randomization sequence. Allocation labels are reshuffled after each assignment to preserve equal group sizes. An independent outcome assessor is blinded to group allocation throughout the trial, and standardized cheek retractors are used to mask cement margins during evaluations. Operators cannot be blinded due to material-specific application protocols.

Intervention Protocols:

Tooth preparation follows standardized anterior-specific minimal reduction principles (1.0-1.5 mm incisal, 0.5-0.8 mm uniform labial, feather-edge proximal margins) under rubber dam isolation. NuSmile® prefabricated zirconia crowns are used for all participants. Cement application follows manufacturer instructions for each group:

Group 1 (GIC): Fuji IX GP Extra (GC America) - tooth conditioned with 20% polyacrylic acid for 20 seconds, rinsed, gently air-dried; cement hand-mixed, loaded into crown, seated under finger pressure for 3 minutes.

Group 2 (BioCem™): BioCem™ Universal BioActive Cement (NuSmile®) - tooth cleaned with pumice and water, rinsed, dried; cement auto-mixed into crown, seated, briefly light-cured (2-3 s) for excess removal, then fully light-cured 20 s per surface.

Group 3 (SARC): RelyX™ Universal Resin Cement (3M) - tooth cleaned with pumice and water, rinsed, dried; cement loaded, crown seated, tack-cured 2-3 s, excess removed, full light-curing 20 s per surface.

All crowns are placed by a single calibrated pediatric dentist. Post-cementation periapical radiographs verify marginal integrity. Parents receive standardized oral hygiene instructions and a 7-day course of 0.12% chlorhexidine mouthwash.

Follow-Up and Safety:

Clinical evaluations occur at baseline, 12, 24, and 36 months. Retention is assessed by visual/tactile examination with a sharp explorer and LED transillumination (DEXIS CariVu®). Failed crowns are recemented and excluded from subsequent analyses. Adverse events including soft-tissue irritation, crown fracture, debonding, and aspiration risk are continuously recorded.

Statistical Methodology:

Sample size was calculated using G\*Power 3.1.9.7 assuming a medium effect size (f = 0.25) for ANOVA, 90% power, and α = 0.05, yielding 28 participants per group; this was inflated to 40 per group (total 120) to accommodate an anticipated 30% attrition over 36 months. The primary retention outcome will be analyzed by Kaplan-Meier survival analysis with between-group comparison using the log-rank test, supplemented by Fisher's exact test for proportional retention and Cox proportional hazards regression for hazard ratios. Gingival Index and Plaque Index will be compared between groups by one-way ANOVA and within groups by repeated-measures ANOVA. Margin discoloration distribution will be compared by chi-square (with Cramér's V as effect size) and within-group transitions by McNemar's test. Significance is set at p \< 0.05. Analyses will follow an intention-to-treat principle, with per-protocol sensitivity analyses.

• Plaque Accumulation Measured by the Silness & Löe Plaque Index (1964) [Time frame: Baseline, 12, 24, and 36 months post-cementation]
• Gingival Health Measured by the Löe Gingival Index (1967) [Time frame: Baseline, 12, 24, and 36 months post-cementation]
• Marginal Discoloration Measured by the Modified United States Public Health Service (USPHS) Criteria [Time frame: Baseline (immediately post-cementation), 12, 24, and 36 months]