Volumetric CBCT analysis of the palatine process of the anterior maxilla: a potential source for bone grafts

Abstract

The aim of this research was to use cone-beam computerized tomography (CBCT) to analyze the available bone volume in the palatine process of the maxilla (PPM), which is a potential source of bone grafts. 20 CBCT scans were evaluated. From the most caudal axial slice of the PPM, the bony surface was calculated cranially up to the nasal floor. The predetermined thickness of each slice was 0.9 mm. A 2 mm safety margin was established considering the incisive canal and teeth 14–24. A ±0.1 mm error deviation was established for all calculations. By connecting these points and those defined at the posterior bone boundary, a surface was obtained. A three-dimensional (3D) image of the delimited zone was constructed and analyzed using 3D imaging software. The study comprised 6 women and 14 men (mean age 39.4 ± 11.5 years). Calculated bone volume averaged 2.41 ± 0.785 cm 3 . The palatine process of the maxilla contains a considerable bone volume (2.41 ± 0.785 cm 3 ). This area should be regarded as a potential donor site for the regeneration of maxillary atrophic bones. Further investigation is required before these findings lead to routine clinical application.

The search for potential bone graft donor sites for use in reconstructing the oral and maxillofacial region has increased steadily during the past years. Although substantial investigation has permitted the incorporation of several allografts, xenografts and alloplastic materials to the routine armamentarium, autologous bone grafting is still considered, in most cases, the gold standard option.

The reconstruction of certain maxillofacial defects requires clinicians to obtain autologous grafts from extraoral sites, such as the iliac crest, tibia and parietal bone. Intraoral donor sites, in the context of an adequate indication, are preferable in order to reduce morbidity, time and costs. However, the intraoral zone often provides a limited source of bone volume. Nevertheless, it is possible that new potential intraoral donor sites can make alternative options available.

Little research has assessed the palatine process of the maxilla (PPM) as a potential intraoral donor site. In one study performed on dry skulls, the authors concluded that the anterior palatal region could be a reliable donor site for routine maxillofacial and oral surgery procedures. Another study provided a correlation between the upper anterior facial height and the hard palate thickness based on craniometric points. In 2005, Hernández-Alfaro et al., provided the first clinical series of patients treated with palatal core grafts for alveolar reconstruction. Based on their successful clinical outcomes, the authors concluded the palatal region provides a practical, reliable source of intraoral bone grafts with minimum added morbidity. Subsequently, Rodríguez-Recio et al. added two more cases to the scientific literature.

Many authors have highlighted the limited volume of intraoral grafts, and the great variability that exists between individuals. Therefore, a precise analysis for each patient is needed.

Standard diagnostic methods, such as clinical examination, orthopantomography, or cephalograms, do not provide precise information regarding the available bone volume. Computerized tomography (CT) used in conjunction with the correct software can provide the most powerful and reliable technique for pre- and postoperative assessment.

New generation CT devices and improved protocols are diminishing the undesirable effects of ionizing radiation based on the ‘as low as reasonably achievable’ (ALARA) principle. Nevertheless, conventional CT scanners are often restricted to hospitals or radiological centres, are costly, unergonomic and emit excessive radiation to the patient’s head and neck region, when often only a small oral area needs to be studied. The advent of cone-beam computerized tomography (CBCT) has provided a very convenient tool for the evaluation of the hard tissues in the dentomaxillofacial area. Its advantages include its wide accessibility, easy handling, and low radiation doses compared to conventional CT.

Based on the senior author’s favourable preliminary clinical results with the palatal core graft, and incorporating the enhanced diagnostic possibilities that CBCT technology and related third-party software provide, the aim of this paper was to assess, in a structured, precise and reproducible way, the available bone volume in the PPM as an alternative source for intraoral grafts.

Material and methods

This study was conducted according to the principles outlined in the Declaration of Helsinki (first adopted in the 18th WMA General Assembly, Helsinki, Finland, June 1964). Ethical approval was obtained from the Ethical Committee of Clinical Research (CEIC) of the Universitat Internacional de Catalunya (study number: B-16-EFP-10 approved on 3/05/2010).

The studied sample comprised the CBCT scans of 20 patients who had been referred for routine dental analysis to the Dental Clinic of the Universitat Internacional de Catalunya (Sant Cugat del Vallés, Barcelona, Spain). These patients were retrospectively selected from the Clinic’s database according to the following inclusion and exclusion criteria. The inclusion criteria were: CBCT scans of the entire maxillary bone; physical growth completed (age ≥ 20 years); and dentate (14–24). Exclusion criteria were: developmental malformations of the maxilla; tumours or cysts of the hard palate; severe periodontitis from 14 to 24; and the presence of impacted teeth in the area of study.

Patient confidentiality was safeguarded in accordance with the Organic Law 15/1999. There was no direct or indirect contact with any of the studied subjects, and their personal information was appropriately separated from the study and filed for any possible audits, inspections or confirmation of information veracity. Accordingly, each patient was assigned a number (consecutive from 1 to 20). Each clinical history contained a signed informed consent form for carrying out a CBCT study.

CBCT scans were obtained with the IS i-CAT ® device version 17–19 (Imaging Sciences International, Hatfield, PA, USA). The radiological parameters used were 120 kV and 5 mA; the axial slice default distance was 0.300 mm and the voxel size was 0.3 mm.

The facial mode with the 23-cm field of view (FOV) was used. Primary images were stored as DICOM (Digital Imaging and Communication in Medicine) files.

In order to create a reproducible measurement system with the SimPlant Pro Crystal ® software (Materialise, Leuven, Belgium), the following steps were followed. The dataset of the patient was opened with SimPlant. The region of interest was defined in a sagittal slice view, eliminating all unnecessary areas. By default, slice thickness was 0.300 mm. In order to obtain a thickness per slice of 0.9 mm, two segments from each slice were omitted. In Segmentation mode, a mask was created marking the starting point of the bone. All irrelevant areas to the study were again eliminated. Then, maximum quality was set for 3D. Once in Planning preparation mode, a panoramic curve was created to facilitate the readings on the different spatial planes. Thereupon the images of the study area in axial view were obtained, working from the base of the hard palate up to the nasal floor (maintaining the latter cortical unspoiled). The next step consisted in establishing a 2 mm safety margin from tooth 14 to 24 with a margin of error of ±0.1 mm for each slice (including teeth 15 and 25 whenever sufficient bone was present). This was done by marking a point in the medial/palatine area of each tooth ( Fig. 1 ). The same procedure was followed for the mesial and distal views wherever an adjacent tooth was not observed (usually in the longest canine roots) ( Fig. 2 ). A 2 mm safety margin was established around the incisive canal. In this case, three peripheral points were marked (one on either side of the paramedials and one on the middle posterior). Similarly, a 2 mm safety margin was also set wherever the maxillary sinus appeared in the most cranial slices ( Fig. 3 ).

Fig. 1
Axial caudal slice.

Fig. 2
Axial middle slice.

Fig. 3
Axial cranial slice, palatal roof.

Once this protocol was implemented, a surface was created by connecting these points plus those created at the posterior bony margin. For the purpose of quantitative volumetric analysis, a three-dimensional (3D) image of the delimited zone was constructed ( Fig. 4 ).

Fig. 4
PPM reconstruction in 3D.

Subsequently, all measurements were submitted for statistical analysis using StatGraphics Plus ® 5.1 (Statistical Graphics, Rockville, MD, USA).

Results

Table 1 displays the individual demographic characteristics and graft volume for each of the 20 patients analyzed. Each patient’s CBCT scan is represented by a consecutive number from 1 to 20. The studied sample comprised 6 women and 14 men with a mean age of 39.4 ± 11.5 years. Mean graft volume of the PPM was 2.41 ± 0.785 cm 3 . Results are expressed in means and standard deviations because the studied sample showed a normal distribution according to the Shapiro–Wilk test ( p > 0.05).

Jan 24, 2018 | Posted by in Oral and Maxillofacial Surgery | Comments Off on Volumetric CBCT analysis of the palatine process of the anterior maxilla: a potential source for bone grafts
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