Premature loss of primary molars can lead to significant space loss and subsequent malocclusions. Fixed space maintainers are used to prevent this, but traditional options like band and loop appliances have drawbacks such as unaesthetic appearance, long assembly time, and potential for caries formation. Removable maintainers are prone to loss. Fiber-reinforced composites offer an aesthetic alternative, but lack sufficient rigidity. Light-cured acrylic resins (LCARs) are widely used in dentistry for applications such as custom trays and temporary crowns, and their potential as space maintainers warrants investigation. This study aims to evaluate the flexural and shear bond strength of a novel LCAR fixed-space maintainer using different bonding systems to determine its suitability as a clinical alternative.

The literature highlights the challenges associated with managing space loss following premature loss of primary molars. While fixed space maintainers offer advantages over removable options in terms of retention, traditional metallic appliances present aesthetic concerns and potential for complications. The use of fiber-reinforced composites as space maintainers has been explored, but limitations in rigidity have been noted. The mechanical properties of various dental materials, including flexural and shear bond strength, are crucial factors determining their clinical success. High bond strength is essential to resist stresses and prevent failure of the restoration, while adequate flexural strength ensures resilience under masticatory forces.

Forty-five extracted lower second primary molars with intact buccal and lingual surfaces, free from decay, cracks, or defects were selected. Teeth were cleaned, examined under a stereomicroscope, and treated with pumice slurry and 0.5% chloramine-T solution. The root portions were removed using a diamond saw. The crown portions were mounted horizontally on cold-cured acrylic resin, exposing the facial surface. Buccal enamel surfaces were superficially prepared. Teeth were randomly divided into three groups (n=15), each using a different bonding system: Group 1 (Transbond XT), Group 2 (Tetric Flow), and Group 3 (Fuji Ortho LC). A standardized enamel preparation protocol involving phosphoric acid etching and a single-bond adhesive was used for all groups before applying the respective bonding agent. Light-cured acrylic resin (Triad VLC) was applied in incremental layers within a Teflon mold, cured, and then further polymerized. Shear bond strength was evaluated using a universal testing machine (LLOYD instruments, LR 5K) at a cross-head speed of 0.5 mm/min. The Adhesive Remnant Index (ARI) was assessed to evaluate the adhesive remaining on the enamel after debonding. For flexural strength testing, ten LCAR bars (16 x 5 x 4 mm) were fabricated using a Teflon split mold, light-cured, and subjected to a three-point bending test using the universal testing machine at a cross-head speed of 1 mm/min. Data were analyzed using SPSS version 23. One-way ANOVA and post hoc Tukey tests were used to compare shear bond strength among groups. The Chi-square test was used to analyze ARI data.

The mean flexural strength of the LCAR was 82.83 ± 5.2 MPa. Shear bond strength varied significantly among the three groups (p<0.05). Transbond XT exhibited the highest mean shear bond strength (18.43 ± 2.93 MPa), significantly higher than Tetric Flow (11.47 ± 2.74 MPa) and Fuji Ortho LC (8.02 ± 1.37 MPa). Post-hoc analysis revealed significant differences between all groups. The ARI scores showed no significant difference between the groups (p>0.05), with the majority of samples exhibiting an ARI score of 0 (no adhesive remaining on the tooth).

The results demonstrate that the LCAR material exhibits acceptable flexural and shear bond strength, particularly when bonded with Transbond XT. The superior performance of Transbond XT is likely attributable to its higher viscosity, enabling better adaptation to the tooth surface compared to the flowable composite (Tetric Flow). The lower bond strength observed with Fuji Ortho LC may be due to the incompatibility of phosphoric acid etching with glass ionomer cements. The absence of a significant difference in ARI scores across groups indicates that the debonding mechanism was not influenced by the type of bonding agent used. The flexural strength of the LCAR exceeded the minimum requirement for polymer-based crown and bridge materials, suggesting its suitability for withstanding masticatory forces. These findings suggest that LCAR has the potential to serve as a viable alternative to existing fixed space maintainers, offering a more aesthetic and potentially less complicated clinical application.

This in vitro study indicates that the light-cured acrylic resin (LCAR) material demonstrates acceptable flexural and shear bond strength, making it a promising candidate for use as a fixed space maintainer. Further in vivo studies are necessary to evaluate its long-term clinical performance, including assessing plaque accumulation and bacterial colonization and to optimize the design for enhanced clinical efficacy.

This study was conducted in vitro, using extracted primary teeth. The results may not fully reflect the complex in vivo environment, and further in vivo studies are needed to evaluate long-term performance and clinical effectiveness. Biological factors such as plaque accumulation and bacterial colonization were not assessed in this study. The bond strength to permanent teeth was also not evaluated.