Palatal bone dimensions on cone beam computed tomography. Implications for the palate as autogenous donor site: an observational study

Abstract

This study analyzed cone beam computed tomography (CBCT) records. Radiographic image analysis included: (1) the width and height of the palatal vault, and diameter and location of the incisive foramen; (2) the potential block graft dimensions and their correlation to arch dimensions; (3) the potential graft size and its variation by sex. CBCT scans of 76 patients were included, 42 from female patients and 34 from male patients (mean age 42.3 years). The mean palatal width was 35.2 ± 3.4 mm, while the mean palatal height was 15.2 ± 2.9 mm. The mean diameter of the incisive foramen was 3.1 ± 1.3.mm. The mean potential osteotomy diameter was 7.8 ± 1.5 mm. The mean osteotomy length varied according to site: central incisor region, 5.9 ± 2.0 mm; lateral incisor region, 5.2 ± 2.1 mm; canine region, 4.7 ± 1.9 mm; premolar region, 4.1 ± 1.7 mm. A positive correlation was observed between the osteotomy diameter and the palatal width: a greater osteotomy length was obtained from the more anterior teeth position. Males presented significantly greater osteotomy diameter and length compared to females. The palate represents a potential site for the harvest of autogenous bone block grafts for the reconstruction of ridge defects.

Implant rehabilitation of the aesthetic zone is a challenge due to the atypical anatomy encountered. Correct implant positioning is considered to be essential in order to attain optimum aesthetic results and long-term functional stability. This requires the presence of a sufficient amount of bone at the proposed implant site. However, loss of teeth in the anterior maxilla is inevitably followed by resorption of the alveolar bone. Thus, bone augmentation is often needed to achieve aesthetic implantation. An array of approaches and materials has been utilized to augment the resorbed site. Nevertheless, autogenous bone is still considered the gold standard. Various intraoral sites have been proposed as suitable donor sites, such as the mandibular symphysis/body, the maxillary tuberosity, the zygomatic buttress, and the lateral plate of the mandibular ramus. However, all of these sites are remote from the recipient site and are associated with second surgical site morbidity.

In 2005, Hernandez-Alfaro and Garcia described the palatal vault as a possible donor site that had rarely been used. They stated that the palatal block was ‘rigid’ and that it offered superior mechanical properties when compared to the particulate graft. It was claimed that it was stable and exhibited very little resorption.

The palatal block has several advantages, such as ease of harvesting and low donor site morbidity, and it allows both vertical and horizontal ridge augmentation. Moreover, the palatal block allows the augmentation of the deficient ridge with a block harvested from the palate simultaneous to implant placement. According to Gluckman, the palatal bone block is a simple way to achieve thick and stable buccal bone without having to use a second harvesting site. Moreover, the palatal block harvesting technique exhibits minimal pain and discomfort and very little swelling.

However, due to the anatomical limitations of the palate, the volume of the graft is expected to be smaller than that of grafts obtained from the ramus or the symphysis. There is little information in the literature regarding the quantity of bone that could be harvested from the palatal donor site. The aim of this study was, therefore, to quantify the dimensions of the palatal block that could be harvested.

Materials and methods

The cone beam computed tomography (CBCT) records of 325 patients were examined and those of 76 patients were included in the study. Forty-three of these patients were female and 33 were male, and their mean age was 42.3 years. All available CBCT records were included in the study except those of patients with one or more of the following exclusion criteria: presence of, or a history of, periodontal disease; bone loss related to the upper anterior area or with soft tissue recession. Smokers and patients with respiratory problems, patients with severe crowding, severe spacing, or impacted teeth in the upper anterior region, and patients with missing first molars bilaterally that could affect the readings, as well as patients with a history of orthodontic treatment, were also excluded. Furthermore scattered or distorted images and those showing the presence of restorations, root canal treatment, and dental misalignment were excluded. Additionally, any teeth subjected to any apical surgery and teeth with evident root resorption were excluded. All measurements were taken by one operator. The patients were referred for CBCT examination for various reasons, including implant site analysis, for root fractures, and for various lesions. No patient included in the study had a history of chemotherapy or radiotherapy.

All scans were obtained using a CRANEX 3D unit (Soredex, Tuusula, Finland), with a field of view 61 mm × 9 mm × 41 mm and 1-mm slice thickness. A software program (OnDemand3D, Cybermed Inc.) was used to reconstruct the images and these were used to obtain the measurements.

Radiographic image analysis

The CBCT images were analyzed on a certified monitor. Image analysis was performed using image processing software (OnDemand3D).

The following measurements were obtained in the coronal plane: (1) the horizontal palatal width (PW), represented by the distance between the midpalatal cemento-enamel junction of the left first molar and the right first molar ( Fig. 1 ); (2) the vertical palatal height (PH), represented by the vertical line from the cemento-enamel junction plane (connecting the midpalatal cemento-enamel junction of the left and right first molar) perpendicular to the median line of the palate ( Fig. 1 ).

Fig. 1
Coronal plane section showing the palatal width (PW) and palatal height (PH).

The following measurements were obtained in the transverse plane: (1) the maximum osteotomy diameter. To determine the maximum diameter that could be obtained (maximum diameter of the bone cylinder), a reading was taken from the limiting anatomical structures in the transverse plane extending from the incisive foramen to the apex of the canine. This reading will dictate the maximum width of the trephine bur to be used, thus determining the maximum diameter of the potential bone block ( Fig. 2 ). (2) The size of the incisive foramen ( Fig. 2 ): the size of the incisive foramen was measured at its widest diameter in the transverse plane.

Fig. 2
Transverse plane section showing the potential maximum osteotomy diameter and the incisive foramen readings.

The maximum osteotomy length was measured in the sagittal plane (side) ( Fig. 3 ). The slice orientation was adjusted to pass through the centre of the tooth site examined (central incisor, lateral incisor, canine, or first premolar) perpendicular to the long axis of the tooth. For this measurement, a vertical 12-mm line (V-line; representing the length of an average implant) is drawn from the crest of bone, in the most suitable implant position. The rationale behind the V-line is to simulate a simultaneous implant placement and harvesting of the palatal block graft at the same site without the need for a second surgical site. A second line (P-line) is drawn perpendicular to the V-line, extending buccolingually. A third line (D-line) is drawn following the palatal bone that emerges from the palatal end of the P-line (this represents the maximum trephine diameter). From the middle of the D-line, a final line (H-line) is drawn extending from the middle of the D-line to the anatomical boundary (nasal floor, maxillary sinus, etc.). This line is nearly parallel to the V-line. The H-line represents the maximum length of palatal bone block that can be harvested ( Fig. 3 ). The anatomical boundaries are as follows: incisive canal especially for the upper central incisor; nasal floor and maxillary sinus especially for the first premolar.

Fig. 3
Sagittal plane section showing the potential maximum osteotomy length.

In order to determine whether a correlation exists between the palatal dimensions and the potential graft size, the mean palatal height was divided into three groups: shallow, medium, and deep. This classification was done according to the method proposed by Takanashi et al., who divided maxillary casts into three groups according to the palatal depth : a mean palatal depth group, with a palatal depth within the mean value ±1 standard deviation (SD); a wide palatal group, with values larger than the mean value ±1 SD; and a narrow group, with values smaller than the mean value ±1 SD.

The long axis of the tooth dictated the orientation of the vertical slice (sagittal plane), followed by the measurements. All readings were approximated to the nearest tenth of a millimetre.

The data collected were analyzed in order to obtain the mean and SD and the median and range values, and to determine a possible significant correlation between arch dimensions and osteotomy size. The data were further analyzed to compare the effect of sex on graft dimensions.

Statistical methods

Numerical data were recorded as the mean, SD, median, and range values. Data showed a normal (parametric) distribution, so the Student t -test was used for comparisons between females and males. Pearson’s correlation coefficient was used to determine any significant correlation between arch dimensions and osteotomy size. Qualitative data were recorded as frequencies ( n ) and percentages (%). The χ 2 test was used for comparisons between females and males.

The level of significance was set at P ≤ 0.05. The statistical analysis was performed using IBM SPSS Statistics for Windows, version 20 software (IBM Corp., Armonk, NY, USA).

Results

The sample consisted of 76 patients, 42 females and 34 males, with a mean age of 42.3 (range 24–56) years.

The mean vault height was shallow in 32 cases (42.1%), medium in 12 cases (15.8%), and deep in 32 cases (42.1%). The mean palatal width (PW) was 35.2 ± 3.4 mm when measured at the distance between the midpalatal cemento-enamel junction of the left first molar and right first molar, while the mean palatal height (PH) was 15.2 ± 2.9 mm. The diameter of the incisive foramen was 3.1 ± 1.3 mm. The mean maximum osteotomy diameter was 7.8 ± 1.5 mm, representing the maximum amount of block graft diameter that could be harvested ( Table 1 ).

Table 1
Descriptive statistics of the study variables.
Mean (SD) Median (range)
Palatal width (mm) 35.2 (3.4) 35.0 (29.0–42.0)
Palatal height (mm) 15.2 (2.9) 15.0 (9.7–20.7)
Incisive foramen size (mm) 3.1 (1.3) 3.0 (0.2–8.0)
Osteotomy diameter (mm) 7.8 (1.5) 7.9 (5.0–13.0)
Osteotomy length (mm)
Central incisor 5.9 (2.0) 5.6 (1.6–11.0)
Lateral incisor 5.2 (2.1) 5.0 (2.0–16.0)
Canine 4.7 (1.9) 4.5 (0.9–10.0)
First premolar 4.1 (1.7) 3.9 (1.0–8.5)
SD, standard deviation.

The maximum osteotomy length, representing the maximum length of the graft, which is limited by the anatomical boundaries (nasal floor, maxillary sinus), varied according to the measurement site: in the central incisor region, 5.9 ± 2.0 mm; lateral incisor region, 5.2 ± 2.1 mm; canine area, 4.7 ± 1.9 mm; first premolar area, 4.1 ± 1.7 mm.

Pearson’s correlation coefficient was used to determine significant correlation between arch dimensions and graft size. There was a statistically significant positive (direct) correlation between palatal width and graft diameter, i.e. an increase in palatal width is associated with an increase in graft diameter and vice versa ( Table 2 ). A statistically significant positive (direct) correlation between palatal height and graft length was noted for the lateral incisor area, i.e. an increase in palatal height is associated with an increase in graft length in the lateral incisor area and vice versa ( Table 2 ). There was no statistically significant correlation between other arch dimensions and osteotomy length and osteotomy width.

Table 2
Correlation between arch dimensions and bone osteotomy size.
Correlation coefficient ( r ) P -value
Palatal width and:
Osteotomy diameter 0.327 0.004 *
Osteotomy length (central incisor) 0.009 0.936
Osteotomy length (lateral incisor) 0.207 0.073
Osteotomy length (canine) 0.086 0.458
Osteotomy length (first premolar) 0.103 0.374
Palatal height and:
Osteotomy diameter 0.141 0.223
Osteotomy length (central incisor) −0.020 0.864
Osteotomy length (lateral incisor) 0.236 0.040 *
Osteotomy length (canine) 0.123 0.291
Osteotomy length (first premolar) 0.210 0.068
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Jan 16, 2018 | Posted by in Oral and Maxillofacial Surgery | Comments Off on Palatal bone dimensions on cone beam computed tomography. Implications for the palate as autogenous donor site: an observational study
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