Evaluation of palatal support tissues for placement of orthodontic mini-implants in mouth breathers with high-narrow palates versus nose breathers with normal palates: a retrospective study

The aim of this study was to compare the palatal total support tissues (TSTs) and bone support tissues (BSTs) at 5-mm paramedian section to the midsagittal suture between mouth breathers with high-narrow palates and nose breathers with normal palates and confirm the practicability and limitation on superimposition of lateral cephalograms and plaster models for orthodontic mini-implant (OMI) implantation in these patients.

The sample consisted of 27 mouth breathers with high-narrow palates (study group (SG)) and 27 nose breathers with normal palates (control group (CG)). Upper digital dental models were superimposed with corresponding cone beam computed tomography (CBCT) images; then, TSTs and BSTs vertical to the curvature of the palatal mucosa were measured on the 5-mm paramedian section to the midsagittal suture. The measuring sites were the third ruga (R) and the sites anterior and posterior to R at 2-mm interval (A₂, A₄, A₆, and A₈; P₂, P₄, P₆, and P₈) along the palatal mucosa outline. TSTs and BSTs were also measured on the superimposition of lateral cephalograms and plaster models, and the site with the largest TST value in each patient was recorded. Descriptive statistics, independent-samples t test, and hierarchical clustering heat map were used for statistical analysis.

The greatest average values of TSTs and BSTs in SG were 12.24 ± 2.63 mm and 9.59 ± 2.36 mm at P₂ site, and those in CG were 12.96 ± 2.39 mm and 10.56 ± 2.38 mm at R site, respectively. The average values of both TSTs and BSTs in SG were less than those in CG at all insertion sites. Significant differences (P < 0.05) were found at A₄, A₆, and R for TSTs and at R and P₄ for BSTs. P₂ and R were clustered together for both TSTs and BSTs by the cluster analysis on heat map in both SG and CG. In both groups, only one patient from SG was found to have the insertion site with the largest TST value on 2D superimposition located in the blue area on the heat map, where the measurement values of TSTs were less than 8.5 mm and those of BSTs were less than 5 mm.

Mouth breathers with high-narrow palates may have less palatal support tissues than nose breathers with normal palates at 5-mm paramedian section to the midsagittal suture of palate. The site a little posterior to R is more suitable for OMI implantation in mouth breathers. Two-dimensional superimposition of lateral cephalograms and plaster models can provide relatively effective assessment for the site choice of OMI implantation in both mouth breathers with high-narrow palates and nose breathers with normal palates.

Three-dimensional superimposition of CBCT data and digital dental model can provide accurate information for palatal OMI implantation. Meanwhile, 2D superimposition of lateral cephalograms and plaster models can be used for assessing the implantation sites at 5-mm paramedian section to the midsagittal suture of palates in mouth breathers under most conditions even those who have less palatal support tissues.