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

Crown Retention (Survival)

The primary outcome is the cumulative retention of prefabricated zirconia crowns over a 36-month follow-up period. Retention is assessed by a single blinded examiner at each scheduled visit using two complementary methods: (a) visual/tactile inspection with a sharp dental explorer applied circumferentially along the crown margin to detect dislodgement, mobility, or marginal gap; and (b) LED transillumination using the DEXIS CariVu® system to detect cracks, debonding, or marginal microleakage. A crown is classified as "failed" (debonded) if any complete loss of cement seal, dislodgement, or detectable marginal gap is observed. Retention is reported as the proportion of crowns surviving at each time point and as the time-to-failure for survival analysis. Higher retention proportions and longer survival times indicate better clinical performance.

Plaque Accumulation Measured by the Silness & Löe Plaque Index (1964)

Plaque accumulation at the gingival margin of each cemented crown is assessed using the Silness \& Löe Plaque Index. The same four sites per tooth (mesial, distal, buccal, lingual) are scored by a blinded examiner on a 4-point ordinal scale: 0 = no plaque; 1 = a film of plaque adhering to the free gingival margin, recognizable only by running a probe across the surface; 2 = moderate accumulation of soft deposits visible to the naked eye; 3 = abundance of soft matter. A mean PI score is calculated per tooth and per participant; the participant-level mean ranges from a minimum of 0 to a maximum of 3, with higher scores indicating greater plaque accumulation.

Gingival Health Measured by the Löe Gingival Index (1967)

Gingival inflammation around each cemented crown is assessed at baseline and at every follow-up visit using the Löe Gingival Index (1967). A single blinded examiner scores four gingival sites per tooth (mesial, distal, buccal, and lingual) on a 4-point ordinal scale: 0 = no clinical inflammation (normal gingiva); 1 = mild inflammation (slight color change, slight edema, no bleeding on probing); 2 = moderate inflammation (redness, edema, glazing, bleeding on probing); 3 = severe inflammation (marked redness and edema, ulceration, tendency to spontaneous bleeding). A mean GI score is calculated per tooth and per participant; the participant-level mean therefore ranges from a minimum of 0 to a maximum of 3, with higher scores indicating worse gingival health.

Marginal Discoloration Measured by the Modified United States Public Health Service (USPHS) Criteria

Discoloration at the crown-tooth interface is evaluated under standardized LED operatory lighting (1,000-1,400 lux) without magnification using the modified USPHS criteria, supplemented by high-resolution intraoral photography with cross-polarized filters. Each crown is assigned one of four ordinal ratings: Alpha (A) = no visible discoloration (best outcome); Bravo (B) = slight discoloration confined to the margin, not penetrating internally; Charlie (C) = obvious discoloration penetrating along the margin; Delta (D) = severe discoloration with secondary caries or restoration failure (worst outcome). The outcome is reported as the proportion of crowns in each category at each time point, with a higher proportion of Alpha ratings indicating better marginal integrity.

Incidence and Severity of Adverse Events

The frequency, type, and severity of all adverse events occurring during the 36-month follow-up will be recorded for each arm. Events of interest include crown debonding, crown fracture, soft-tissue irritation or ulceration adjacent to the crown margin, allergic reaction to cement components, secondary caries, and pulpal complications. Severity will be classified using a three-tier framework adapted from the Common Terminology Criteria for Adverse Events (CTCAE) approach: Mild (Grade 1) - no intervention required; Moderate (Grade 2) - non-urgent intervention required (e.g., recementation at a scheduled visit); Severe (Grade 3) - urgent intervention, crown replacement, or treatment of secondary pathology required. The primary safety endpoint is the incidence rate (events per participant per year of follow-up) in each arm.