Comparação entre as propriedades físicas e mecânicas de alinhadores ortodônticos confeccionados por termoformagem e por impressão tridimensional direta (3d): uma revisão sistemática e metanálise

Abstract

Aesthetic orthodontic aligners are removable polymer-based devices widely used for the correction of dental malocclusions. These aligners can be fabricated using thermoforming (AOCT) or direct three-dimensional printing (AOCID). The different manufacturing techniques impart distinct characteristics to the devices, which may influence their clinical performance. This systematic review aimed to compare the physical and mechanical properties of AOCT and AOCID. A comprehensive search was performed in six electronic databases (May/2025), including in vitro laboratory studies that directly compared AOCT and AOCID. Study selection, data extraction, and risk of bias assessment were independently conducted by two reviewers. When feasible, data were synthesized through meta-analyses. A total of 23 studies met the inclusion criteria, of which 4 were eligible for meta-analysis. AOCID demonstrated superior performance across multiple parameters. AOCT showed a significant reduction in thickness (−39.76%, SD=14.09), whereas AOCID exhibited an increase (+11.02%, SD=21.43; p<0.001). Geometric accuracy favored AOCID (p<0.001), which also presented a lower glass transition temperature (42.3 °C), greater shape recovery (p<0.001), higher vertical tensile forces (p<0.005), improved marginal adaptation, and reduced bacterial adhesion (p<0.005). Conversely, AOCT demonstrated greater storage modulus stability (p<0.005), higher microhardness (p<0.005), greater flexural strength (p<0.05), and better stability under cyclic compression. Regarding surface roughness, AOCID exhibited higher Sa values (SMD=2.73; 95%CI: 2.14–3.31; p<0.00001) and Sz after use (SMD=1.70; 95%CI: 0.67–2.74; p=0.001), while AOCT showed higher Sv (SMD=−1.19; 95%CI: −2.29 to −0.08; p=0.04) and lower Sa after use (SMD=−1.07; 95%CI: −2.12 to −0.02; p=0.04). No significant difference was observed between planned and actual thickness (SMD=1.48; 95%CI: −7.26 to 4.30; p=0.62). Methodological heterogeneity among the included studies limited additional analyses. AOCID presented physical, mechanical, and behavioral advantages over AOCT. However, methodological variability and the lack of clinical validation weaken the strength of current evidence, highlighting the need for standardized experimental protocols and future clinical investigations to guide evidence-based orthodontic practice.