The goal of this clinical trial is to compare the long-term clinical performance of three different luting cements used to bond prefabricated zirconia crowns (PZCs) on primary front teeth in young children. The trial will determine whether any single cement offers superior retention, gum health, or marginal sealing compared to the others over a 3-year period.

Main Questions:

The study aims to answer the following:

Are conventional glass ionomer cement (GIC), bioactive resin-modified glass ionomer cement (BioCem™), and self-adhesive resin cement (SARC) equivalent in retaining prefabricated zirconia crowns on primary incisors over 36 months? Do these cements differ in their effect on gingival health, plaque accumulation, or marginal discoloration around the cemented crown?

Comparison:

Researchers will compare three parallel groups of children whose primary incisors are restored with identical prefabricated zirconia crowns but cemented with one of the three different luting cements.

Participants will: Receive a clinical and radiographic dental examination at screening. Undergo placement of one or more prefabricated zirconia crowns on primary anterior teeth using their randomly assigned cement. Return to the clinic for blinded follow-up evaluations at 12, 24, and 36 months for assessment of crown retention, gingival health, plaque, and marginal staining.

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.

Inclusion Criteria:

1. Healthy children aged 2 to 7 years
2. One or more primary maxillary or mandibular incisors requiring full-coverage restoration due to caries or trauma
3. Adequate remaining tooth structure following preparation, defined as greater than 50% of the clinical crown
4. Parent or legal guardian able and willing to provide written informed consent and to commit to the 36-month follow-up schedule

Exclusion Criteria:

1. Active periodontal disease at the index tooth, defined as a Löe Gingival Index score of 2 or higher
2. Parafunctional habits such as bruxism, severe thumb-sucking, or tongue-thrust documented at screening
3. Known allergy or hypersensitivity to zirconia, resin, glass ionomer, or any component of the assigned cement
4. Inconsistent oral hygiene, defined as less than twice-daily toothbrushing per parental report
5. Systemic disease affecting bone metabolism, tooth development, or wound healing
6. Current participation in another interventional dental clinical trial

The investigators will share de-identified individual participant data underlying the results reported in the final publication. Shared data may include retention status at each time point, time-to-failure, Gingival Index and Plaque Index scores, USPHS marginal discoloration ratings, and adverse event records. The study protocol and statistical analysis plan will also be made available.

Data will be available beginning 6 months and ending 36 months following article publication.

Data will be shared with researchers who provide a methodologically sound proposal and whose intended use has been approved by an independent review committee. Proposals should be directed to the primary investigator. To gain access, requestors must sign a data access agreement.

The outcome assessor performing all post-cementation clinical evaluations is blinded to group allocation. Standardized cheek retractors are used to mask crown margins. The statistical analyst is also blinded to group allocation until after the analysis dataset is locked.