Evaluation of Polyetheretherketone and Monolithic Zirconia Versus Conventional Metal Band and Loop Space Maintainers in Children: A Randomized Split-Mouth Clinical Trial

BACKGROUND AND RATIONALE Premature loss of primary first molars can cause space loss, crowding and ectopic eruption of the permanent successors. The conventional stainless-steel band and loop space maintainer is widely used but has limitations, including poor esthetics, plaque retention around the band, possible nickel sensitivity and the need for laboratory soldering. Metal-free CAD/CAM-fabricated appliances made from PEEK and monolithic zirconia (BruxZir) may offer better esthetics and periodontal response. Clinical evidence comparing them with conventional appliances in children is limited.

STUDY DESIGN Randomized clinical trial with two parallel arms and a 1:1 allocation ratio. Within each arm a split-mouth design is used: each child receives the esthetic appliance on one side of the mandible and a conventional stainless-steel band and loop on the contralateral side, so each child serves as his or her own control. PEEK and BruxZir are each compared with the conventional appliance within their own arm; the two esthetic materials are compared indirectly, between arms. The study is reported according to the CONSORT guidelines. It is part of a thesis from which separate papers are being prepared. This record was updated after enrollment had started to describe the full design.

SAMPLE SIZE The sample size was calculated in R for a comparison of clinical performance (alpha 0.05, power 80%, Cohen's omega 0.31 from a published systematic review), adjusted for the split-mouth design using an assumed within-subject correlation of 0.30. This gave 30 pairs per comparison, increased to 35 pairs to allow for dropouts.

RANDOMIZATION AND ALLOCATION CONCEALMENT Sequentially numbered, opaque, sealed envelopes were prepared by an independent investigator who was not involved in recruitment or clinical work. Each child selected one envelope, which determined the side (right or left) on which the esthetic appliance was placed. The conventional appliance was placed on the contralateral side.

PROCEDURES All clinical steps were performed by one calibrated operator. Medical and dental history, clinical examination and bitewing radiographs were obtained before treatment. Mandibular first primary molars that were not already extracted were extracted and a healing period of 1-2 weeks was allowed.

Conventional appliance: a prefabricated stainless-steel molar band was fitted, a polyvinyl siloxane impression was taken, and the appliance was made in the laboratory by silver-soldering a 0.9-1.0 mm stainless-steel wire loop to the band, then polished. It was cemented with self-cure glass ionomer cement (GC Gold Label).

PEEK and BruxZir appliances: digital impressions of both arches and a buccal bite scan were taken with an intraoral scanner and exported as STL files. The appliances were designed in exocad DentalCAD with a two-arm clasp and loop, a minimum thickness of 1.5 mm (PEEK) or 1.0 mm (BruxZir), about 1 mm of soft-tissue clearance and a loop 2-3 mm from the gingival margin. Occlusal clearance was checked digitally. Appliances were milled on a five-axis milling machine (PEEK wet milled, BruxZir dry milled), then polished (PEEK) or sintered and glazed (BruxZir). Fitting surfaces were sandblasted with 50-micrometer aluminum oxide and treated with a primer (CeraBond for PEEK, a zirconia primer for BruxZir). The abutment tooth was etched with 37% phosphoric acid and the appliance was cemented with TheraCem adhesive resin cement.

FOLLOW-UP AND ASSESSMENTS Parents received oral hygiene and appliance-care instructions and were asked to report any loosening, breakage or discomfort. Children were recalled at 3, 6, 9 and 12 months. A debonded appliance was recemented and followed up; a fractured appliance was recorded as a failure and replaced with a conventional appliance. Plaque and gingival status were scored on the abutment tooth with the Loe and Silness indices, and comfort with the Wong-Baker FACES scale.

BIAS CONTROL Blinding of clinicians and patients was not possible because the appliances look different. The statistician analyzed coded data without knowing group allocation. All laboratory and digital steps were performed by one experienced technician.

STATISTICAL ANALYSIS Categorical data are summarized as frequencies and percentages and continuous data as mean (SD) and median (IQR). Clinical performance is analyzed with Firth-penalized logistic regression with cluster-robust covariance to account for the split-mouth design. Non-normal longitudinal outcomes are analyzed with mixed Aligned Rank Transform models, with Holm-adjusted post hoc comparisons. Survival is analyzed with Kaplan-Meier and Cox models. Significance is set at p < 0.05 and analyses are done in R.

CONSENT AND ETHICS Written informed consent was obtained from parents or guardians and oral assent from children aged six and above. The study was approved by the Research Ethics Committee, Faculty of Dentistry, Ain Shams University (FDASU-RecID032109).