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The effect of different micro-implant-assisted rapid palatal expanders designed digitally: a three-dimensional finite
Yixin Liu1, Yusong Zhang1, Peiying Lin1
1Department of Orthodontics, School and Hospital of Stomatology, Cheeloo College of Medicine, Shandong University & Shandong Key Laboratory of Oral Tissue Regeneration & Shandong Engineering Research Center of Dental Materials and Oral Tissue Regeneration & Shandong Provincial Clinical Research Center for Oral Diseases, No.44-1 Wenhua Road West, Jinan, Shandong, 250012, China.
Background:
This study aimed to use finite element analysis to compare the effects of different micro-implant-assisted rapid palatal expanders with varying support methods, different numbers and positions of micro-implants designed digitally, to provide a reference for the improved design and clinical application of expanders.
Methods:
The models of the craniomaxillary complex, micro-implants, and maxillary skeletal expander were constructed by modeling softwares. The positions of micro-implants were digitally designed via the registration of CBCT and intraoral scans, and the models of the new expanders were built accordingly. The expanders were classified into tooth-bone-borne (Type-1) and bone-borne (Type-2) based on their support methods; into 4-micro-implant (Type-A), linear-6-micro-implant (Type-B), and C-6-micro-implant (Type-C) based on the number and position of micro-implants. Assemble to form six groups of models: A1, A2, B1, B2, C1, and C2. The expanders were activated in two stages: 0.4 mm along the X-axis before the separation of the two halves of the maxilla (Stage 1) and 4 mm after they were separated (Stage 2). The differences in the stresses and displacements were evaluated.
Results:
Type-C had the widest VMS distribution range of the craniomaxillary complex. In the same implantation position, the VMS of micro-implants and the cortical bone around them showed Type-B < Type-C < Type-A, Type-1 < Type-2. The tipping of the first molar showed Type-1 > Type-2 in Stage 1, while they were equal in Stage 2. In Stage 2, Type-A achieved parallel expansion (the parallelism of expansion in A1 and A2 were 98.3% and 96.5%, respectively), while Type-B and Type-C exhibit a front-wide, back-narrow "V"-shaped expansion. The efficiency of expansion demonstrated Type-B surpassing Type-C and Type-A, and Type-1 equaling Type-2.
Conclusions:
The expansion effect of the 6-micro-implant-type was superior to those of the 4-micro-implant-type. Among the 6-micro-implant-type, the C-type had a wider stress distribution range, the linear-type had higher expansion efficiency and better stability of the micro-implants. In clinical practice, it is necessary to design the expanders individually via a digital approach to enhance the efficacy and safety of the expansion and achieve the treatment goals more precisely.
