Gender-Based Variation in Alveolar Bone Thickness of Maxillary Incisor Teeth: A CBCT Retrospective Study

Introduction

Orthodontic treatments can result in significant tooth inclinations and are identified as risk factors for developing dehiscence and fenestration. A potential contributing factor to these bone occurrences is reduction in the thickness of the alveolar bone surrounding the roots [1]. Hence, it is imperative to approach orthodontic treatment with caution in patients who have thin soft tissue margins before orthodontic treatment. Labial tooth movement can render the vulnerability of gingival tissue, making it less resilient against plaque accumulation and susceptible to trauma from tooth brushing [1–4].

Also, in terms of alveolar bone thickness, to obtain favorable results in dental implant therapy, it is essential to focus on the morphological characteristics of periodontal tissues, including the thickness of buccal bone and soft tissues [5]. Cicciue et al [6] stated that a buccal bone margin exceeding 2 mm and a palatal margin surpassing 1 mm could effectively inhibit vertical bone loss around implants after surgical procedures. Ensuring a sufficient volume of soft and hard tissue during implant treatment is imperative for achieving optimal results in function and aesthetics [7]. For the best optimal treatment approach, it is crucial to consider the buccolingual angulation of the teeth and the distance between the cementoenamel junction and the alveolar crest.

Having sufficient hard and soft tissue when placing implants is essential for achieving the best functional and aesthetic results. After tooth extraction, the reduction of the alveolar ridge is a significant worry, especially in areas where appearance matters. Changes in soft and hard tissue volume after extraction are linked to histological and morphological changes during socket healing, leading to tissue collapse and insufficient ridge formation. This can result in thinner bone on the buccal and palatal side or the development of fenestration and dehiscence [8].

The standard method for assessing incisor inclination is lateral cephalometric radiographs [5]. In addition, superimpositions affect anatomic structures and teeth identification in 2-dimensional (2D) radiographs [9]. Therefore, 3-dimensional (3D) radiographs have greater accuracy in determining the inclination of incisors and also for measurement of alveolar bone thickness during implant planning [10]. Cone beam computed tomography (CBCT) represents anatomy in 3 dimensions [9], provides more accurate measurements of craniofacial structures, and enables analyzing high-quality diagnostic 3D images at any dimension [11]. It is also possible to measure the thickness of alveolar bone surrounding the roots of the incisors using CBCT images [12–14].

CBCT imaging aids in the preparation of complex dental restoration procedures, encompassing the examination of tooth and bone integrity, analysis of occlusal alignment, and creation of precise surgical guides for placing prosthetics

Savadi et al [15] stated that good periodontal health forms the foundation for any dental restoration work. Given that periodontal disease can cause a reduction in alveolar bone thickness, dental professionals must understand the biological factors related to restorative procedures, grasp fundamental concepts, and be familiar with available clinical treatments. A thorough comprehension of the connection between periodontal tissues and restorative dentistry is crucial to guaranteeing proper form, function, aesthetics, and comfort of the teeth.

Also, factors such as racial disparities of population, sex, age, and side of the tooth can influence the thickness of the buccal alveolar bone. Sex-based studies about buccal and palatal alveolar bone thickness in the Cypriot population have not been conducted. In addition, most of the CBCT studies have been conducted to analyze bone thickness in the buccal region [13,16–19]. Therefore, this retrospective study from a single center in Cyprus aimed to assess labial (buccal) and palatal bone thickness in 6 anterior maxillary teeth of 120 adults using CBCT.

Material and Methods

ETHICS APPROVAL AND SAMPLE SELECTION:

The Ethics Committee of Cyprus International University (protocol number EKK23-24/005/09) reviewed and approved this study. The research was conducted according to the principles of the Declaration of Helsinki (1964) and its later revisions. Informed consent was obtained from all individual participants included in the study.

Results of power analysis showed that, for a power of 80%, a sample of at least 116 patients was necessary. Hence, this study included 120 patients (720 teeth), who were selected randomly.

Inclusion criteria were (1) scans showing the fully erupted 6 maxillary anterior teeth from canine to canine, and (2) participants must be above the age of 18 years. Exclusion criteria were (1) the absence or decay of teeth, (2) presence of prosthetic crowns, (3) crowding exceeding 3 mm or spacing surpassing 1 mm in the maxillary anterior alveolar segment, (4) evident periodontal disease, (5) patients with systemic diseases, and (6) craniofacial dysmorphology.

CBCT scans were chosen from individuals listed in the database of a private radiology clinic in Nicosia, Cyprus. The CBCT scans were conducted for various clinical purposes, such as implant planning, impacted teeth, orthodontic treatment, and surgical purposes.

CBCT IMAGE ACQUISITION:

CBCT scans were obtained by using a Newtom GO 3D/2D (Quantitive Radiology s.r.l., Verona, Italy). Scanning parameters were 90 kvP, 24 s, 4 mA, voxel size 0.3 mm, and field of view of 10×6 cm. The measurements were done by using the machine’s computer software (NNT viewer 4.2, QE Verona, Italy) and were recorded in millimeters.

IMAGE ANALYSIS:

CBCT images were evaluated twice by 2 observers (D.K., M.F.) at a 1-week interval to look for any inter- and intra-observer variability. For assessing the buccal and palatal alveolar bone thickness, all maxillary incisors were categorized into 3 distinct points in terms of point B (buccal) and point P (palatal). Point B1 (buccal) and P1 (palatal) were measured at 4 mm below the cementoenamel junction; points B2 and P2 at the midpoint between the labial and palatal alveolar crest plane extending to the root apex; and points B3 and P3 at the root apex of the tooth. The alveolar bone thickness measurement involved assessing the distance from these points to the labial and palatal alveolar bone (Figures 1, 2).

All images were examined in the same sagittal view on a consistent monitor and under uniform lighting conditions.

STATISTICAL ANALYSIS:

The data obtained from the measurements were transferred to SPSS 24 via Excel. In the analysis of the measurements B1, B2, B3, P1, P2, and P3, descriptive statistical analyses were performed and mean [x_] and standard deviation [σ] values for the groups were calculated. The independent sample t test, one of the hypothesis tests, was used to compare the measurements according to sex, since they met the assumption of homogeneity due to the skewness value being between±2. In addition, Q-Q plot graphs and box plot graphs of the 6 measurements (B1, B2, B3, P1, P2, P3) were examined as a second reference point in deciding on the normal distribution. In the Q-Q plot graphs, we observed that most of the data were distributed on the same line and there were very few outliers far from the line. In the box plot graph, we observed that the median was in the middle and close to the middle of the boxes, the whiskers at both ends of the box were symmetrically distributed, and the extreme values were very few. We observed that the parameters analyzed above converged to the normal distribution. In this context, in the comparisons to be made in terms of patient sex were made with an independent sample t test. The Levene test for equality of variances was examined in terms of deciding the significance of the comparisons made with t tests, and it was decided whether there was a significant difference according to the 2-tailed P value, considering the homogeneity of variance.

Measurements of intra- and inter-observer validation were done. For repeated measures, the Wilcoxon matched-pairs signed-rank test was used to evaluate intra-observer reliability. The intraclass correlation coefficient and the coefficient of variation (CV ¼ [standard deviation/mean] 100%) showed interobserver dependability. The intraclass correlation coefficient has values between 0 and 1. Great dependability is expressed by intraclass correlation coefficient values of more than 0.75, and reproducibility is represented by the precision error’s low coefficient of variation and low coefficient of variation.

Results

DISTRIBUTION OF PATIENTS:

Within the scope of the research, dental measurements were made on a total of 120 patients, 58 of whom were women and 62 of whom were men. The ages of female patients ranged between 18 and 56, with an average age of 37.5 years. Male patients were between the ages of 19 and 63, with an average age of 40.18 years. There was no significant difference between the mean ages of the female and male patients who participated in the study, and it was observed that the groups were equivalent in terms of age distribution.

EVALUATION OF THE PARAMETERS:

Table 1 shows the mean alveolar bone thickness values by buccal and palatal side according to the tooth number. The distribution of the mean values of buccal and palatal bone thickness according to patient sex is shown in Tables 2 and 3.

When the measurements of buccal bone thickness at the B1, B2, and B3 points were compared according to sex, there was no significant difference in all measurements made in teeth 11, 12, 21, 22, and 23 (P>0.05). In tooth 13, there was no significant difference in B1 and B2 points according to sex, but in the results of the B3 measurements of tooth 13, it was observed that the bone thickness of men (mean 1.50 mm) was significantly higher than that of women (mean 1.19 mm, P<0.05; Table 4).

At points P1, P2, and P3 for tooth 11, the palatal bone thickness of men was significantly higher than that of women (P<0.05). At point P1 of tooth 12, palatal bone thickness did not differ according to sex (P>0.05). At points P2 and P3 of tooth 12, palatal bone thickness of men was significantly higher than women (P<0.05). Tooth 13 palatal bone thickness showed a significant difference at points P1, P2, and P3, and male patients had thicker bone thickness (P<0.05; Table 5).

At points P1, P2, and P3 of tooth 21, there was no significant difference in bone thickness according to sex (P>0.05). For tooth 22, there was no significant difference in palatal bone thickness in terms of sex in only point P1 (P>0.05), while in points P2 and P3, men had thicker palatal bone thickness than did women (P<0.05). Bone thickness of tooth 23 showed a significant difference at points P1, P2, and P3, and men had thicker bone on the palatal side than did women (P>0.05; Table 5).

Discussion

The correlation between the thickness of maxillary alveolar bone and factors such as sex and age were examined in this study. CBCT allows studying of alveolar bone morphology, with the advantages of 3D imaging, such as there is no distortion or superimposition of anatomical structures. The prominent advantage of this study was making 3D measurements at 6 different levels.

In the present study, female patients had less buccal alveolar bone thickness than did male patients. When the thickness of the teeth on the buccal side was analyzed, point B3 was the thickest in all tooth numbers. The mean alveolar bone thickness at point B1 was thicker than that of point B2 in all tooth numbers. In this respect, the mean bone thickness at point B2 was lower than that of points B3 and B1 in all tooth numbers. Also, the thickness of the buccal alveolar bone was less than the palatinal alveolar bone thickness at all measured levels at the maxillary anterior region. The thickness of the alveolar bone was decreased from the first level of measurements. The mean highest alveolar thickness in B2 was observed in teeth 11 and 12. The maxillary left lateral incisor had the highest mean bone thickness at level B3. The least buccal alveolar bone thickness was observed in the right maxillary canines at the B2 and B3 levels.

According to the study of Morad et al [16], gingival phenotype, age, and sex influence results. It was reported that patients over 50 years old exhibited a thinner buccal alveolar bone. This result is contrary to our findings. There was no significant difference between the mean ages of this study’s participants. Association between sex and alveolar bone thickness at maxillary incisors and canines was also found in their study [17]. Similarly, in the study of Rojo-Sanchis et al [12], an influence of sex on the thickness of alveolar bone buccally and palatally was found concerning the palatal alveolar bone. Likewise, women had less buccal alveolar bone thickness than did men in the present study. On the contrary, at points P1, P2, and P3 for teeth 11, 13, and 23 and at points P2 and P3 of teeth 12 and 22, the palatal bone thickness of men was significantly higher than that of women. All these results were in contrast to studies [16,19] in which there were no significant differences between female and male participants in alveolar bone thickness.

According to our findings, the mean buccal alveolar thickness at levels B1 and B2 was less than 1 mm. This result is consistent with results of other studies, in which the maxillary anterior buccal alveolar bone thicknesses were measured less than 1 mm [20–23]. One study showed an association between 80% of the extraction cases and alveolar bone thickness less than 1 mm. Furthermore, 71% of cases with alveolar bone resorption after an extraction were related to thin buccal alveolar bone [24–26]. Moreover, applying a dental implant to the anterior region of the maxilla is esthetically challenging, especially for the immediate placement of the implant. It is reported in many studies that placing a dental implant immediately with a buccal alveolar bone thickness of less than 1 mm causes severe buccal plate loss and gingival recession [27–29].

The findings of the present CBCT study revealed that the thickness of buccal alveolar bone was less than that of palatinal alveolar bone thickness at all measured levels at the maxillary anterior region. This result supports that dental implants should be placed palatally in the maxillary anterior region. Our results are consistent with those of Rojo-Sanchis et al and Morad et al [12,16].

The results of the present study were also consistent with those reported by Esfahanizadeh et al [19], who studied the buccal bone thickness of all maxillary incisors and canines at the level of the crest, 2 mm apical to the crest, and 5 mm apical to the crest. In their study, the thickness of buccal alveolar bone decreased from 2 mm below the alveolar bone crest to 5 mm below the crest, and in our study, the thickness of alveolar bone was decreased from the first level of measurements, which is 4 mm apical from the crest, to the second level, which is the midpoint between the crest and root apex. These results may be findings of the convexity of roots, which affects the buccal alveolar bone’s tendency to be thinner.

Among the points in alveolar bones, the B1 and P1 levels may be the most relevant areas with mucosal recession. Crestal bone and surrounding bone support the gingiva, and since any resorption occurs in these areas, mucosal recession can occur and lead to esthetic problems. Gingival recession in the palatal side does not affect esthetics. However, periodontal follow-up can be needed to prohibit severe periodontal tissue loss. In the present study, according to the measurement levels and teeth numbers, the thinnest buccal alveolar bone at levels B1 and B2 were seen in teeth 21 and 13, respectively. Gingival recession in the anterior maxillary region, specifically in central incisors, contributes to esthetic problems [19]. Therefore, alveolar bone thicknesses of teeth should be examined carefully in the anterior region either at the pretreatment or posttreatment sessions.

The mean highest alveolar thickness in B2 was observed in teeth 11 and 12. The maxillary left lateral incisor had the highest mean bone thickness at level B3. The least buccal alveolar bone thickness was observed in the right maxillary canines at the B2 and B3 levels. This result is consistent with the study of Esfahanizadeh et al [19], in which the least buccal bone thickness was seen in the canines. This outcome can be explained by the form and the prominence of canines’ roots. Tooth number 12 was found to be thick in points B1 and B2. This was due to the decreased diameter of the lateral incisors’ roots. These findings are in accordance with those of previous studies [12,25].

Insufficiency of alveolar bone thickness, especially in incisors, is a complicating factor for orthodontic movements. During the orthodontic treatment, dehiscences and fenestrations can occur due to orthodontic force magnitude and direction and also anatomic variations of surrounding alveolar bone and periodontal tissues [1]. In the planning of orthodontic treatment, orthodontists have to consider the thickness of the alveolar bone to prevent dehiscences and fenestrations in the surrounding alveolar bone. The loss of alveolar bone has an impact on esthetics, and severe loss of periodontal support can occur. Therefore, patients with insufficient alveolar bone thickness should undergo a periodontal follow-up after an orthodontic treatment. During the regular appointments of orthodontic patients, check-ups for periodontal tissues and dental biofilm control should be done carefully to prevent alveolar bone and periodontal tissue support loss.

This study had limitations. First, there is a lack of medical and dental histories of patients that might affect alveolar bone thickness. Second, the study had a relatively small sample size.

Conclusions

We found a correlation between alveolar bone thickness and patient sex in the North Cyprus population. In patients undergoing implant treatment for the anterior maxilla and different orthodontic treatment techniques, thickness of the alveolar bone should be considered, to avoid dehiscences and fenestrations. Therefore, using CBCT images is recommended in the presurgical period or before the orthodontic treatment starts.