Adult maxillary expansion: CBCT evaluation of skeletal changes and determining an efficiency factor between force-controlled polycyclic slow activation and continuous rapid activation for mini-screw-assisted palatal expansion - MASPE vs MARPE.

Aim : This consecutive retrospective study compared Mini-implant Assisted Slow Palatal Expansion (MASPE) with rapid palatal expansion (MARPE) using a bone-borne skeletal expander in adults with a narrow maxilla. CBCT scans analyzed transverse changes and potential pterygoid process deformation before (T1) and after expansion (T2). Material and Methods : The Force Controlled PolyCyclic (FCPC) SLOW palatal expansion group (FCPC-MASPE-G) comprised 35 adults aged 18-54 years and received a skeletal expander limiting expansive force only allowing 500 cN at the activation wrench (force control). Discontinuous, polycyclic activations according to the FCPC-protocol were applied. The MARPE-group (n=6) underwent continuous RAPID activation without FCPC until the desired width was reached. CBCT scans were taken pre and post-expansion. Inclusion criteria for both groups were successful outcomes without surgical assistance. Results : The maxilla opened transversally in both groups mildly V-shaped, with a pyramidal shape in the coronal plane, impacting the zygomatic bone. Width measurements at T2 indicated superior mechanical response in FCPC-MASPE-G. Response of zygomaticomaxillary sutures was similar in both groups. Pterygoid process deformations were notably less in FCPC-MASPE-G (0.87 - 1.35 mm) compared to MARPE-G (2.70 - 3.04 mm). Dental measurements were similar, but the ratio “Mid-palatal suture Opening Related to Expander opening” (M.O.R.E.-factor) was better with 84% in FCPC-MASPE-G than with 50% in MARPE-G. Conclusion : Slow expansion with FCPC protocol effectively widens the maxilla in adults, with significant impact on bones and sutures and less pterygoid process deformation compared to rapid expansion. Cranial complications were absent in both groups.