Comparison of median and paramedian regions for planning palatal mini-implants: a study in vivo using cone beam computed tomography

Abstract

The purpose of this study was to compare the bone height at the median and paramedian sites of the hard palate using cone beam computed tomography (CBCT). CBCT images of 110 subjects were selected and the palatal bone height measured in the coronal view of multiplanar reconstruction (MPR) images at the midsagittal site and at paramedian sites, 3 mm and 6 mm bilaterally, in the region of the upper first premolars; NemoCeph 3D software was used. Intra-observer and inter-observer agreement was assessed using the intra-class correlation coefficient. Differences between the median site and paramedian sites were calculated with the Friedman test. No significant differences were found among the sites evaluated ( P > 0.05). Paramedian sites at 3 mm and 6 mm bilaterally from the palatal suture showed comparable height to the central site. The observed comparable bone height might be helpful in increasing the choice of host sites for palatal implants. The alternative placement of implants in the paramedian regions is not indicated as a viable treatment option for patients with insufficient bone height, but represents a feasible alternative for mini-implant insertion in patients in whom the middle region should be avoided.

Orthodontic anchorage has been a concern to orthodontists since the introduction of this specialty. With the advent of implants, a new anchorage technique was created, namely skeletal anchorage. This type of treatment uses specific temporary implants, with smaller dimensions than dental implants used for prosthetic rehabilitation, during orthodontic treatment. Skeletal anchorage has now become more favoured than tooth anchoring systems due to its many advantages, including no negative interference in tooth position, maximizing the desired effects, eliminating the use of extraoral devices, and greater acceptance by the patient.

Palatal mini-implants are indicated for anchorage in the maxilla, presenting a low failure rate estimated at 10.5%. The median sagittal portion of the palate is a good site for insertion of these temporary anchorage devices. However, limitations in this anatomical region, such as incomplete ossification of the palatal suture, can contraindicate surgery procedures. The development of the midpalatal suture was evaluated by Revelo and Fishman, and it was demonstrated that this is not fully closed until late adolescence, the process beginning with the posterior portion of the palate, followed by the anterior portion.

Several studies have evaluated alternative regions for the insertion of mini-implants in patients in whom the palatal suture should be avoided. The paramedian area of the palate has been identified as a viable and stable alternative for the placement of temporary implants for orthodontic anchorage. This lateral region, starting from 3 mm, provides stability, adequate bone volume, enough bone height, and little practical tooth interference, and is at a safe distance from the incisive foramen. Distances of 4–9.0 mm posterior to the foramen have also been indicated for this purpose.

Although the literature indicates that the paramedian regions may be suitable for palatal mini-implant insertion, there are no quantitative evaluations available comparing the bone heights at these sites with that of the midpalatal region. The aim of the present study was to compare median and paramedian bone heights in the region of the upper first premolars, using cone beam computed tomography (CBCT).

Materials and methods

This project was approved by the university ethics committee. The sample consisted of CBCT scans of 110 patients from an archive. The CBCT examinations had been required for different treatment purposes unrelated to this study. The images selected were from patients aged 18–35 years with no evident facial or dental asymmetries or anomalies in the head and neck region. Patients with torus palatinus were excluded from the study. CBCT images were obtained with an i-CAT unit (Imaging Sciences International, Inc., Hatfield, PA, USA) set to the following parameters: voxel size 0.3 mm, 120 kVp, 8 mA, field of view (FOV) 23 cm × 17 cm, and a 40-s scan time.

The measurements were done by three evaluators in the region of the anterior hard palate at the level of the upper first premolars, as described by Jung et al., with NemoCeph 3D software (Nemotec, S.L., Madrid, Spain). Using the planar lines of multiplanar reconstructions (MPR) of the CBCT images in NemoCeph 3D software, the midsagittal plane and the upper first premolar region based on its long axis, through the root canal, were defined ( Fig. 1 ). The measurement corresponding to the central site was superimposed on the orientation line of the sagittal plane of the patient, in the coronal window, between the outer cortical layer of the nasal floor and the outer cortical layer of the oral hard palate. Subsequently, the palatal bone height in the paramedian region was measured, in the same coronal view, 3 mm to the right and left and 6 mm to the right and left, using the same parameters ( Fig. 2 ).

Fig. 1
Positioning of the planar lines of multiplanar reconstructions (MPR) in the midsagittal plane and the upper first premolar region of the patient.

Fig. 2
Measurements of the relevant dimensions between the outer cortical layer of the caudal nasal floor and the outer cortical layer of the oral hard palate in the central site and paramedian sites, 3 mm and 6 mm bilaterally, on CBCT coronal view.

After an interval of 1 week, the same evaluation was repeated with 25% of the sample to determine intra-observer reliability. Intra-observer and inter-observer agreement were evaluated through the intra-class correlation coefficient (ICC) using SPSS version 17.0 for Windows (SPSS Inc., Chicago, IL, USA).

The means of the measurements obtained by the three evaluators were calculated. The Friedman test was performed to analyze the differences between the median site and paramedian sites, with a significance level of 5%, using BioEstat statistical package version 5.0 for Windows.

Results

The ICC values for the correlation of intra-observer agreement were close to 1 for all three examiners. With regard to inter-observer agreement, the ICCs ranged from 0.63 to 0.95 with a confidence interval of 95%.

In the comparison of bone height on coronal view at the level of the first premolars, the Friedman test showed no statistically significant difference in the values found at the paramedian sites, 3 mm and 6 mm to the right and left, compared to the central site ( P > 0.05) ( Table 1 ). The normality of distribution of the values had been verified previously, and this non-parametric statistical test was chosen based on the results.

Table 1
Measurements at the palatal sites evaluated: median, minimum, maximum, mean, standard deviation (SD), and confidence intervals (95% CI), expressed in millimetres (mm).
Median Minimum Maximum Mean SD 95% CI
Central site 6.72 2.32 14.05 6.70 2.39 6.25; 7.15
Paramedian site 3 mm right 6.82 1.34 13.47 6.76 2.43 6.30; 7.22
Paramedian site 3 mm left 6.75 2.00 13.96 6.85 2.65 6.35; 7.35
Paramedian site 6 mm right 7.39 1.87 14.25 7.38 2.70 6.87; 7.89
Paramedian site 6 mm left 6.94 1.77 15.26 7.29 2.86 6.75; 7.83
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Jan 19, 2018 | Posted by in Oral and Maxillofacial Surgery | Comments Off on Comparison of median and paramedian regions for planning palatal mini-implants: a study in vivo using cone beam computed tomography
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