The alveolar bone is part of the periodontal tissue, and its anatomy is different in different patients. It is affected by the location, angulation, and tilt of the teeth as well as by occlusal forces. The anatomy of the alveolar bone is of great clinical importance because of the presence of dentoalveolar lesions such as fenestration and dehiscence. Fenestration is the condition, in which the bony coverage of the root surface is lost, and the root surface is only covered by the periosteum and gingiva. In such lesions, marginal bone is intact. When this bone defect spreads toward the marginal bone, it is called dehiscence. ¹

Fenestration and dehiscence bone defects are observed more in the facial than lingual root surfaces and also more in anterior than in posterior teeth. ¹

Curved and protruding root form, labial tooth protrusion, occlusal trauma, bruxism, and tooth movement along with the thin cortical bone plate are some of the predisposing factors for these bone defects. ²

Therefore, dentists should have adequate knowledge of the anatomy of normal bone to achieve satisfactory results, to improve esthetic outcomes and to prevent complications of periodontal, endodontic, and orthodontic treatments. It is recommended that dentists determine the alveolar bone morphology through imaging before treatment. ³

The diagnosis of fenestration and dehiscence is not easy clinically because although clinical findings derived from the gingival probing and conventional radiographic modalities can provide the guidelines for evaluating the alveolar bone defects, not fenestrations. ⁴

Two-dimensional modalities include bitewing; periapical and panoramic radiographs are used to help in periodontal examinations. These modalities have limitations such as overlapping of anatomical structures, difficulty in standardization and determination of the dimension, and the presence of bone defects. ⁵ , ⁶

Braun et al. showed that using cone-beam computed tomography (CBCT), the precise analysis of periodontal defects becomes possible due to the third dimension. Thus, bone defects could be detected significantly more accurate. ⁷

CBCT is a novel method in dentistry with proven superiority in the maxillofacial area over computed tomography (CT) scan. CBCT exposes the patient to less radiation than does CT. ⁸ CBCT has suitable capability in assessing the alveolar bone because of its high resolution. In this technique, the evaluation of small defects of the alveolar bone and their locations is possible because of the lack of superimposition of adjacent structures. ⁸

There are several studies ⁵ , ⁷ , ⁹ , ¹⁰ , ¹¹ , ¹² and reviews, ¹³ , ¹⁴ , ¹⁵ on different aspects of using CBCT in the analysis of periodontal bone defects and soft-tissue structures. Mengel et al. ¹¹ and Leung et al. ¹⁶ didin vitro studies on the accuracy and reliability of CBCT in the detection of periodontal bone defects.

Several studies have determined the frequency of bony defects such as fenestration and dehiscence in the alveolar processes on dry human skulls through autopsy in several countries. ¹⁷ , ¹⁸ In addition, the major studies on human populations have compared the frequency of these lesions on different classes of facial skeletal deformities. ¹⁹ , ²⁰

To the best of our knowledge, no epidemiological survey has been conducted on an Iranian population on alveolar bone defect. These epidemiological studies help to plan proper treatment strategies, particularly in orthodontic treatment. These findings could be helpful how to be applied orthodontic force on the teeth having this kind of alveolar bone defects.

With the possibility of using the CBCT imaging archive and considering the current lack of sufficient information about this population, this study was designed to assess the incidence of fenestration and dehiscence and the locations of these lesions on the root surfaces of maxillary and mandibular anterior teeth by CBCT images.

In this cross-sectional study, all CBCT images of patients who had been referred to a Private Maxillofacial Radiology Center and School of Dentistry in Rasht during 2016 were reviewed. This study was confirmed by the Ethics Committee of Guilan University of Medical Sciences (IR.GUMS.REC.1396.48). After evaluating all available CBCT images, those of CBCT images of the patients with normal dentoalveolar structures of anterior maxillary and mandibular teeth are included in this study.

However, generalized bone loss secondary to periodontal disease or a systemic condition, positive history of trauma, orthodontic treatment, and the presence of apical lesion as well as root canal therapy on anterior maxillary or mandibular teeth were considered as exclusion criteria. Poor quality CBCT images were also excluded from this study.

CBCT images were obtained with a Vatech CBCT device (Gyeonggi-do, Korea) (voxel size: 0.2 mm, FOV: 8 cm × 8 cm for maxilla or mandible mode and 12 cm × 9 cm for maxilla and mandible mode) from the faculty of dentistry in Rasht, Iran, and with a New Tom VG (Verona, Italy) (voxel size: 0.2–0.24 mm, FOV: 10 cm × 10 cm for standard zoom mode and 22.5 cm × 22.5 cm for full zoom mode) from a private maxillofacial radiology clinic.

After the reconstruction of volumetric data, cross-sectional images with 1-mm thickness and distance in buccolingual or buccopalatal dimensions were provided. Two maxillofacial radiologists independently evaluated cross-sectional and axial images for the presence or absence of fenestration and dehiscence. Figure 1and Figure 2illustrate fenestration and dehiscence in cross-sectional views of anterior maxillary teeth. In addition, the locations and extension of the bony lesions were designated according to the cervical, middle, and apical third of buccal or lingual (palatal) surfaces. Figure 1

Fenestration bone defect at the apical third of the right maxillary canine in cross-sectional view (a) and lingual aspect of mandibular central incisors in axial view (b) and in cross-sectional view of left mandibular central incisor (c).

In this cross-sectional study, 216 image samples were reviewed to determine the presence of fenestration and dehiscence. A total of 67.6% of the images (146 cases) were from females and 32.4% (70 cases) from males. Most of the samples (72.2%) were from individuals between the ages of 30 and 60 years.

The frequency of fenestration in 216 CBCT images was 17.6% (13%–23.1%, with 95% confidence interval). Dehiscence was observed in 9.3% (5.9%–13.7%, 95% confidence interval) of cases. Table 1illustrates that there was a statistically significant difference between the maxilla and mandible (P = 0.0001) in the frequency of fenestration, but there was no statistically significant difference (P = 0.82) in the frequency of dehiscence between the jaws.{Table 1}

The frequency of fenestration and dehiscence in the 1189 teeth was 5.55% and 2.52%, respectively. Table 2details the frequencies of these bone defects based on tooth number (type).{Table 2}

The frequency of fenestration and dehiscence in this study was much higher in females than in males, and these differences were statistically significant (P = 0.016 for fenestration and P = 0.032 for dehiscence). Meanwhile, the frequency of fenestration and dehiscence did not show any significant difference between age groups Table 3.{Table 3}

In this study, 85.9% of fenestration lesions were detected in apical thirds, 12.6% in middle thirds, and 1.4% in cervical thirds. It should be noted that the number of cases of fenestration increased from 66 to 71 because the lesions can spread out to more than one level. Because dehiscence spreads from the alveolar bone crest, 100% of the lesions were found in the cervical third, 30% of cases spread up to the middle third, and only 6.6% of cases spread up to the apical third level Table 4.{Table 4}

A total of 92.5% of fenestration and 80% of dehiscence lesions were observed on the buccal aspect of root surfaces Table 5.{Table 5}

To evaluate the frequency of fenestration and dehiscence lesions, different methods are used, such as imaging and anthropology. In several studies, human dried skulls were used to evaluate fenestration and dehiscence lesions, ³ , ¹⁷ , ¹⁸ , ²¹ , ²² whereas other studies ¹⁹ , ²⁰ , ²³ , ²⁴ , ²⁵ used CBCT images for this evaluation.

Assessing fenestration and dehiscence lesions using human dried skulls not only reduces the risk of non-recognition of these lesions but also eliminates the ability to observe the presence of these lesions clinically. Therefore, the use of CBCT images could be helpful in making appropriate treatment plans because of their ability to detect periodontal lesions and alveolar bone defects. ²⁴

In Mengel et al.'s study, CBCT, in comparison with the histologic specimens, revealed a mean deviation of 0.19 ± 0.11 mm in the measurement of the alveolar bone defect. ¹¹ In Leung et al. study, alveolar bone height can be measured to an accuracy of about 0.6 mm using a voxel size of 0.38 mm in CBCT. They presented that root fenestrations can be defined with greater accuracy than dehiscences. ¹⁶

In the present study, the frequencies of fenestration and dehiscence in the studied sample were 17.6% and 9.3%, respectively, which is very low compared to the Nimigean et al.'s study, which found 89.58% for both lesions. ³ This difference can be explained by the Pan et al. theory. ²⁴ In dry skulls, the structures of the tooth and alveolar bone are different; therefore, when they are exposed to the air and the soil (especially at labial levels), the alveolar bone is destroyed faster than the teeth, thus causing bone lesions. ²⁴ In Nimigean et al.'s ³ study, they studied on dry skulls.

In our study, the prevalence of root fenestration based on the available anterior surface of the teeth was 5.5%, which is consistent with the results obtained from other studies. ³ , ¹⁷ , ¹⁸ , ²¹ , ²² , ²⁴

The prevalence of dehiscence in the current study is 9.3% (2.52% of total teeth), which is much lower than what was reported by Yang et al. ²⁵ (75% of participants, 8.8% of total teeth), Nimigean et al. ³ (53.6% of participants, 4.25% of total teeth), and Rupprecht et al. ²¹ (40.4% of participants, 4.1% of total teeth). The significant difference in the prevalence of dehiscence in the present study is likely because we only evaluated the anterior teeth, whereas other studies evaluated all teeth. ³ , ¹⁷ , ¹⁸ , ²¹ , ²² , ²⁵

On the other hand, differences in the prevalence of fenestration and dehiscence in various studies may be due to different measurement methods, racial variety, and how to interpret lesions in dried skulls or CBCT images. ²⁴ Rupprecht et al. ²¹ also noted that different diagnostic criteria in different studies can influence the outcomes, and hence that the definition of dehiscence varies from an alveolar bone defect in the absence of a cortical bone plate to an exposed root surface. The degree of dehiscence bone defect varies from 1 mm to 4 mm from the alveolar bone crest; this can, therefore, affect the results. ²⁴

In the current study, a higher incidence of fenestration was observed in the maxilla than in the mandible (16.2% vs. 1.4%), followed by canine, lateral, and central teeth. Most previous studies ¹⁷ , ¹⁹ , ²⁰ , ²¹ , ²² , ²⁴ reported similar results with a higher frequency of fenestration bone lesions in the maxilla than in the mandible.

Rupprecht et al. ²¹ and Nimigean et al. ³ reported the prevalence of fenestration based on the tooth number in the first molar, maxillary molar, mandibular molar, maxillary canines, mandibular canine, and lateral mandibular incisor. In Tal et al.'s study, ¹⁸ as in our study, the highest frequency of fenestration was observed in canine teeth. Pan et al. ²⁴ reported that the prevalence of fenestration was higher in the maxillary first premolars, lateral incisors and canines, and mandibular molars. They believed that this difference in the prevalence of fenestration in teeth remains unknown in different populations.

While in the present study, the frequency of dehiscence in the maxilla and mandible was not significantly different, nearly all previous studies ¹⁸ , ¹⁹ , ²⁰ , ²¹ , ²² reported a higher prevalence of dehiscence in the mandible, followed by the mandibular premolar and canine teeth.

In our study, the prevalence of bone defects was reported more on the buccal surface (92.5% of fenestration bone defect and 80% of dehiscence bone defect) than on the lingual or palatal surfaces. This finding is similar to the report of Rupprecht et al. (94.5%). ²¹ Nimigean et al. ³ and Tal ¹⁸ did not report any lesions at the lingual or palatal surfaces. Most previous studies reported the same results regarding the location of bone lesions on the buccal, palatal, and lingual surfaces. ¹⁹ , ²¹ , ²² , ²⁴ , ²⁵

In this study, the highest frequency of fenestration was observed in the apical third (85.9%). In other studies, ³ , ²¹ , ²² , ²⁴ the frequency of fenestration was reported to range from 54.73%–92.57%. However, due to the nature of dehiscence lesions, 100% of the lesions were observed in the cervical area, while in 30% of cases, they extended up to the middle third and only in 6.6% of cases did they spread to the apical portion. The results of the present study were consistent with the Yang et al. study. ²⁵

In the present study, the prevalence of fenestration and dehiscence lesions was significantly higher in females than in males. There were no significant differences in the prevalence of bone defects between female and male groups in some studies, ¹⁸ , ²⁴ while a much higher incidence of these lesions was reported in females than in males in other studies. ²¹ , ²⁵ The reason for this difference is believed to be the thinness of the alveolar bone in females.

There was no significant difference among the age groups in terms of the frequency of fenestration and dehiscence. This result is consistent with Yang et al.'s study. ²⁵ However, some researchers ³ , ²¹ , ²⁴ reported that the prevalence of fenestration and dehiscence decreases with age. The logical reasoning for this concept is that aging increases the chance of periodontal disease, and hence, the deterioration of these bony defects is intensified, and the teeth are lost. Therefore, the prevalence of the bone defects of dehiscence and fenestration are lower in the remaining available teeth. ²⁴

In general, the position of teeth in the dental arch seems to be one of the most important determinants of alveolar bone thickness and contour. ³ After mucogingival flap surgery, the marginal bone naturally remodels to repair. If the alveolar bone is thin, sufficient bone healing does not occur after the surgery, and the risk of bone loss increases. Such conditions convert existing fenestration lesions to dehiscence and small dehiscence lesions to a widespread problem. ²¹ , ²⁵

Kim and Kratchman noted that marginal bone defects have a significant effect on the prognosis of endodontic surgeries. If the thickness of the buccal bone is >3 mm, then desirable results will be obtained. ²⁶ Spray et al. concluded that if the thickness of the alveolar bone is >2 mm, the long-term results of implant placement would be satisfactory. ²⁷ Merheb et al. also reported that dehiscence affects implant stability. It is recommended that bone augmentation before implant surgery be performed in patients with thin alveolar bones. ²⁸

Furthermore, the alveolar bone must be examined before orthodontic treatment to detect the presence of fenestration and dehiscence in the bone. These bony defects are present on the alveolar bone coverage of the prominent and buccally-protruded roots. These teeth are more likely to exhibit fenestration and dehiscence. Thus, rapid orthodontic movements can aggravate alveolar bone lesions and spread bone loss. In such situations, gingival augmentation is recommended before beginning orthodontic treatment. ²¹

One clinically important factor is that fenestration and dehiscence are not detectable by conventional radiographs. These lesions are usually detected by exposure of the alveolar bone during periodontal surgeries. The presence of fenestration and dehiscence lesions can interact with the process of wound healing. ³

Further studies of the effects of fenestration and dehiscence on the extent and pattern of alveolar bone loss as well as on repair following surgical treatments are needed. It is also important to conduct more studies to determine the frequency of fenestration and dehiscence lesions on all tooth numbers in the Iranian population, and hence that high-risk areas will become more apparent during the planning for periodontal surgeries and orthodontic treatments.

The prevalence of fenestration in this study was consistent with the results of previous studies. The prevalence of dehiscence in this study was lower than the results of previous studies. The frequency of fenestration was higher in the maxilla, especially on labial surfaces. The maxillary canines were the most common sites of fenestration. Fenestration was detected most often in the apical third. Dehiscence extension was observed more in the cervical 3 ^rd, followed by the middle thirds. The prevalence of alveolar bone defects was higher in females than in males.

Acknowledgment

We appreciate Dr. Ehsan Kazemnejad for his help with the statistical analysis of the data. We would like to thank Dr Ali Moshajari, Department of orthodontics, Guilan University of Medical Sciences for his scientific suggestions in this research.

Financial support and sponsorship

Nil.

Conflicts of interest

The authors of this manuscript declare that they have no conflicts of interest, real or perceived, financial or nonfinancial in this article.