Preoperative Cone Beam Computed Tomography Assessment of Intraoral Autogenous Bone Graft Volumes Linked to Sex and Tooth Condition

Introduction

Implant treatment has a very important place in the rehabilitation of the toothless area after tooth extraction. However, there is not always sufficient alveolar bone height and width for implant treatment. Alveolar bone loss occurs rapidly as a result of dental trauma, tumor surgery, periodontal pathologies, and tooth extractions. In a systemic analysis study conducted in 2012, it was stated that in the first 6 months after tooth extraction, vertical alveolar bone lost 11–22% and horizontal alveolar bone lost 29–63% [1]. Rapid bone resorption occurs in the first 6 months and occurs mostly in the vestibular cortical bone [2]. In addition, bone destruction can increase further, depending on anatomical, functional, and prosthetic factors [3,4].

In cases of very severe bone loss, difficulties may be experienced in dental implant applications. Especially when the amount of bone loss is high in the anterior regions, long crown-implant ratios can cause aesthetic and functional disorders. In cases of excessive bone loss that causes such problems, bone augmentation methods are preferred before dental implants. Dental implants can be placed more easily after bone augmentation using autogenous particle or block grafts, allografts, xenografts, or alloplastic grafts [5,6]. Autogenous bone grafts are still considered one of the most widely preferred graft types [7,8]. Allografts have osteogenic, osteoinductive, and osteoconductive properties, but also cause minimal immunogenic reactions [7]. Autogenous grafts can be obtained extraorally and intraorally. Generally, extraoral grafts are preferred for alveolar crests with extensive bone loss, and intra-oral grafts are preferred for crests with less bone loss. Intra-oral grafts have advantages such as being close to the recipient area, not often requiring general anesthesia, shorter operation time, less local anesthetic solution required, and causing less morbidity [7,9,10]. Despite all these benefits, its major disadvantage is that it causes morbidity in the donor area [11]. Intraorally, the mandibular ramus, symphysis, and maxillary tuber regions are most frequently preferred. Extraorally, it can be taken from the iliac crest, tibia, costa, and calvarial bone [12,13].

CBCT is the criterion standard for imaging the skeletal anatomy of the maxillofacial region [14]. CBCT has become more popular in three-dimensional volumetric analysis due to its higher resolution and lower radiation compared to computed tomography (CT) [15]. In addition, the semi-automatic segmentation performed with CBCT has been reported to be effective in previous studies [16].

There are not yet enough studies in the literature comparing the volumes of intra-oral areas from which autogenous grafts were taken [17,18]. Additionally, there is no study evaluating the graft volume that can be taken from the donor site due to missing teeth and the presence of an impacted third molar.

The null hypothesis (H0) of the present study was that sex and tooth deficiency have no effect on autogenous bone graft volumes. The clinical importance of this study is that in case of bone deficiency in the jaws, the maxillofacial surgeon can predict the amount of graft that can be taken intraorally and guide the decision on which intra-oral area to take the graft from. Therefore, this study used CBCT to evaluate preoperative donor site graft volume according to sex, donor site, and tooth impaction in 100 patients.

Material and Methods

INCLUSION AND EXCLUSION CRITERIA:

Exclusion criteria wereystemic diseases involving bone, presence of lesions in the areas to be measured, impacted teeth in the symphysis region, individuals with crown-bridge restorations, individuals with total edentulism, and under age 18. Inclusion criteria were not having any artifacts in the images, wanted to have an implant due to partial edentulism or a single missing tooth, and age 18 and over.

IMAGE ACQUISITION AND EVALUATION:

CBCT images were obtained using the Castellini X Radius Trio Plus (Imola, Italy) tomography device as a routine preoperative procedure from patients undergoing implant treatment or surgery for various reasons between 2022 and 2023 at the Department of Oral and Maxillofacial Radiology, Faculty of Dentistry, Harran University. All images were created by the specialist physician in a standard way using 90 kVp, 16 mAs, 13×10 cm FOV, and 0.3 mm³ voxel. Ramus, symphysis, and tuber regions, which are the areas where intra-oral graft can be taken, were left a safe distance from the right and left anatomical formations and tooth roots, the relevant area was marked semi-automatically, and the volume was calculated with IRYS 15.1 (Imola, Italy) software program. This software program automatically measures the marked area. All measurements were performed by a dentomaxillofacial radiologist (MED) with 5 years of experience. The patients’ sex, age, edentulous status, and presence of impacted third molar were recorded. Tooth deficiency condition was grouped according to the jaws as single tooth deficiency, partial tooth deficiency, and total tooth deficiency. The bilateral presence of an impacted third molar was considered as the presence of an impacted third molar. Impacted third molar tooth status was grouped as presence in the maxilla, presence in the mandible, presence in both the maxilla and mandible, and absence.

RAMUS: The reference points for ramus measurement was the plane drawn from the point at which a 2-mm distance was left in the sagittal section to form a right angle with the mandibular canal. Above, the superior point was determined by leaving a 2-mm distance to the plane passing inferiorly from the coronoid and ramus junction. Below, in the presence of an impacted tooth, a 2-mm distance was left between the tooth and the point to be measured, creating a reference plane. In cases without an impacted tooth, the corner of the ramus and corpus mandible junction was determined as the reference point. The segmentation process was performed by examining the marked points in other sections (Figure 1).

SYMPHYSIS: The symphysis was measured by dividing it into right and left parts in the midline. In the axial section, a 5-mm distance was left on the lateral side with the mental foramen, considering the possibility of a loop. The midline and lingual cortex were used as a reference in the medial side. A horizontal plane was drawn by leaving a 3-mm distance to the incisor roots in the superior side. The most anterior and extreme points of the mandible (pogonion) were used as a reference in the inferior side (Figure 2).

TUBER: Anteriorly, a reference point was determined by leaving a distance of 1.5 mm distal of the tooth, depending on the presence of the 2nd or 3rd molar. Superiorly, the maxillary sinus floor was accepted as the border. Posteriorly, the junction of the maxilla with the pterygoid bone was used as a guide for segmentation. In this way, the measurements were standardized (Figure 3).

STATISTICAL ANALYSIS:

SPSS 25 (Armonk, NY, IBM) was used to examine and analyze the data. Descriptive statistics were used to obtain values such as numbers, percentages, averages, minimum, and maximum. The distribution of data was analyzed using the Kolmogrov-Smirnov normality test. ANOVA was used in the analysis of normally distributed data, the Kruskal-Wallis test was used for group comparisons that were not normally distributed, Tukey’s test was used for homogeneously distributed variances, and Tamhane’s T2 test was used for non-homogeneous variances. The level of statistical significance was accepted as P<0.05. Measurements were repeated in 20 patients and intraclass correlation coefficient (ICC) test analysis was applied for intraobserver agreement. G power 3.1 software was used for power analysis.

Results

In this study, a total of 100 individuals, 51 (51%) males and 49 (49%) females, with a minimum age of 18 and a maximum age of 71, mean age of 37.06±14.29, were included. Intraobserver agreement correlation coefficients were excellent (0.90). Maximum potential graft volume was highest at the right symphysis (2.46 cm3) and lowest at the left maxillary tuber (1.35 cm3). The distribution of the maximum graft volume that can be taken by region is shown in Table 1.

When comparing right and left sides, the average volume of graft obtained from the left tuber (0.43±0.44 cm3) was significantly higher than the right tuber (0.34±0.40 cm3). The average of the right ramus was higher than the left ramus. Likewise, a statistically significant difference was detected between the right and left symphysis and tuber (P<0.05). The average graft volume that can be taken from donor sites according to sex is shown in Table 2. A statistically significant difference was found in the right and left symphysis region according to sex (P<0.05). The average of autogenous grafts obtained from the right symphysis region in males was 1.64 cm3. The average of autogenous grafts obtained from the left symphysis region in males was 1.66 cm3. The average of autogenous grafts obtained from the right symphysis region in females was 1.41 cm3. The average of autogenous grafts obtained from the left symphysis region in females was 1.39 cm3. The average amount of grafts that could be obtained from both the right and left symphysis was greater in males than in females. No significant difference was detected in the ramus and tuber (P>0.05). In the presence of an impacted tooth, the amount of graft in the tuber and symphysis regions showed a statistically significant difference (P<0.05). The amount of graft taken from the right and left tubers was lower in the presence of impacted third molars in the maxilla and on both sides compared to when there was no impacted tooth.

The graft volume 1.60 cm3 obtained from the right and left symphysis regions was significantly higher in the absence of an impacted third molar tooth. The relationship between the impacted third molar tooth and donor site graft volumes is shown in Table 3. When compared according to tooth deficiency status, no statistically significant difference was found in graft volume between the regions (P>0.05).

Discussion

Autogenous grafts used for bone augmentation in jaws that do not have sufficient bone height for implant treatment are still considered the criterion standard [8]. Autogenous bone grafts can be taken from extraoral regions (eg, calvaria, iliac, ribs) and intra-oral regions (eg, ramus, symphysis, tuber) [12,13,19]. Obtaining the desired quality and quantity of bone and high healing potential in the postoperative period are important parameters in selection of the donor area. Studies have reported that bone collection in extraoral donor areas is associated with longer hospital stay, increased cost, and high morbidity [12]. It is frequently preferred in intra-oral donor sites due to its advantages such as low morbidity risk and outpatient treatment [20]. Intra-oral ramus, symphysis, and tuber block grafts are frequently preferred in bone augmentation procedures [8]. Measuring and estimating the graft volume that can be taken from the regions before surgery play an important role in selecting the most appropriate region as the donor site. Thus, unnecessary or additional surgical procedures are prevented. Therefore, this study is clinically important.

Grafts taken from the maxillary tuber region have advantages such as ease of access and fewer complications compared to grafts taken from the mandibular region [21,22]. However, grafts taken from the tuber region have disadvantages such as having more spongy and thin cortical bone [23]. Although grafts taken from the mandible have a higher risk of complications compared to the maxilla, autogenous grafts taken from the mandible are denser and have better bone quality [24].

Data on intra-oral autogenous bone volumes can be obtained through radiological examinations. Studies have shown CBCT segmentation reliability but have not specified a reference model for comparison [25]. Maximum potential graft volume was highest at the right symphysis and lowest at the right maxillary tuber. When the average maximum graft volumes that could be taken were compared, it was calculated as right symphysis 1.53±0.33 cm3, left symphysis 1.53±0.32 cm3, right ramus 1.46±0.37 cm3, left ramus 1.41±0.34 cm3, left tuber 0.43±0.44 cm3, and right tuber 0.34±0.40 cm3. In agreement with our study, previous studies found that the symphysis has a larger autogenous graft volume than the ramus.

Verdugo et al calculated the volumes of symphysis and ramus block grafts as 1.4±0.5 mL and 0.8±0.2 mL, respectively [26]. In another study, using 60 CBCT images, Zeltner et al evaluated the symphysis and retromolar regions. As a result of CBCT scans, they calculated maximum potential bone volumes of 3.5±1.3 mL and 1.8±1.1 mL for the symphysis and ramus, respectively [27].

In the 50 CBCT evaluations performed by Ataman-Duruel et al, the highest volume was calculated for the symphysis and the lowest volume was calculated for the maxillary tuber. They calculated the symphysis and tuberosity as 3.14±1.05 cm3 and 0.53±0.34 cm3, respectively [17]. However, contrary to our study, there are also studies stating that the ramus has more autogenous graft volume. A study of 59 cadavers by Yates et al found the volume of the symphysis was 1.15 ml and the ramus was 2.02 ml [19]. These differences in values among studies may be due to the anatomical point selection used for measurements and the different volume calculation methods used. In our study, when comparing right and left, the average volume of graft obtained from the left tuber was significantly higher than the right one, and the average of the right ramus was higher than the left ramus. Likewise, a statistically significant difference was detected between the right and left symphysis. This situation has been reported in a previous study to be due to skeletal growth direction and mandibular deviation [28]. One of the reasons why teeth remain impacted is that the jaws are not developed enough and cannot find a place for themselves in the arch. A decrease in the graft volume that can be obtained in the presence of an impacted third molar was observed. This may be due to inadequate development of the jaws.

A statistically significant difference was found in the right and left symphysis region according to sex. The average of autogenous grafts obtained from the symphysis region on both the right and left was higher in men, possibly because men’s jaw tips and outer lines are coarser than women’s. No significant difference was detected in the ramus and tuber. In their studies on the bone volume of intra-oral donor sites, Brockmeyer et al stated that there was no sex-specific difference in terms of bone volumes of autogenous bone collection sites, but the interforaminal distance in the chin region of males was significantly higher [18]. One reason why the third molar tooth remains impacted is that the jaw development is not sufficient and it cannot reach sufficient dimensions. For this reason, graft volume may have been measured higher in jaws without impacted third molars.

One of the reasons for regional differences in graft volume was that it was limited by the mandibular canal in the ramus, by the mental foramen, tooth roots and lingual canal in the symphysis, and by posterior anatomical formations and adjacent tooth roots in the tuber.

The limitation of this study was that since the study was a retrospective study, so it was not known how long the tooth extractions and tooth loss had been going on.

Conclusions

In case of need for bone grafting, it is possible to estimate the bone volume that can be taken from the donor site with CBCT taken before the operation. Pre-measurement of donor site intra-oral graft volume prevents unnecessary surgical procedures. More autogenous grafts can be obtained from the symphysis region in men than in women. In the presence of an impacted third molar in the maxilla, the graft volume obtained from the tuber decreases. Missing teeth in the mandible did not significantly affect the amount of graft to be obtained. In clinical applications, when a graft is needed, the symphysis region is recommended in men in need of more grafts. If there is an impacted tooth in the upper jaw, the tuber should not be the first choice. It was determined that partial or single tooth deficiency did not cause a significant difference in graft volume between regions. Further research is needed to examine racial differences by conducting more comprehensive studies with different races, and studies should either evaluate age groups separately or narrow the age range. It is also recommended to perform a comparative study using all impacted or all non-impacted teeth.