The thickness of the facial bone wall in the anterior maxilla may have the highest impact when choosing the proper implant treatment approach (1). The existence of a buccal bone plate of sufficient vertical height and width is important for the long-standing stability of acceptable mucosal margins around implant restorations (2, 3). In the anterior maxilla, the facial bone wall is often thin or lacking, due to the facial position of anterior teeth, (4) and undergoes substantial resorption following tooth extraction (5, 6). More so than the rate of implant survival, severe tissue alteration can result in an inadequate esthetic result that may range from soft tissue asymmetry, labial tissue discoloration to marked tissue dehiscence and the abutment or implant exposure (7). Thus, when the buccal bone wall is thin, cause the bone fenestration and dehiscence and soft tissue recession following immediate implant placement (8).Fenestration and dehiscence (9) occur approximately in 20% of teeth that are mostly on the buccal surface of anterior teeth and often occurs bilaterally (10). Since few maxillary anterior teeth may have greater than 1mm of the facial alveolar bone thickness, the consequence of the implant therapy must also be examined in relation to the tissue biotypes and the dental implant outcomes (11). However, the minimal required facial thickness of the vertical crestal bone needed to prevent resorption has yet to be determined (12). Whenever this least necessity is no present, bone augmentation techniques is recommended; since the thickness of the labial bone walls in the anterior maxilla is often reduced, it is suggested that bone augmentation is implemented in most implant sites in the esthetic region (13). The minimum initial thickness of the facial bone plate required to reduce the chance of facial bone loss was around 2mm (12). However, the thickness of the buccal bone is more than 2 mm in only 2.6% of teeth in the premaxillary area (13). Vera (11) found that the median distance from the CEJ to the labial alveolar bone crest was 2.79 mm, and measurements were similar among other teeth studied. The median facial alveolar bone thickness 1mm apical to the alveolar bone crest was 0.83mm, the median facial alveolar bone thickness at the mid – root was 0.70mm and the median width of the facial plate at 1mm from the tooth apex was 0.88mm for all maxillary anterior teeth. Nowzari et al. Used CBCT to measure the maxillary labial bone thickness that is overlying intact teeth of 101 patients which were randomly selected. The overall average thickness of the bone was 1.05mm for left and right central incisors and revealed that study evidenced prevalence of a thin facial alveolar bone (dehiscence, and soft tissue recession after immediate implant therapy (8). Another study, which used CBCT scans by January et al. reported the width of the facial bone wall in the anterior maxillary area. In this study, the mean buccal bone thickness of the canine at 1, 3, and 5mm apical to the bone crest was reported to be Ghassemian et al. described that the average bone thickness at 3mm from the CEJ for the maxillary right central incisor was 1.41mm and for the maxillary left central incisor was 1.45mm. To the maxillary right and left lateral incisors, the crestal bone width averaged 1.73 and 1.59mm and for the maxillary right and left canines, the crestal bone thickness averaged 1.47 and 1.60mm, respectively (16). Botticelli et al. measured the facial bone wall (1mm apical to the bone crest) with a caliper immediately after 21 extractions. The study included both maxillary anterior teeth and premolars, and a mean bone width of 1.4 – 0.04mm was reported (17).
The main purpose of this study was to investigate the bone thickness on the facial aspect of the anterior maxillary teeth using CBCT. Furthermore, to investigate the variability between left and right-side measurements and between males and females. The effects of systemic diseases, smoking habits and occlusal relationship to the bone thickness of maxillary in the anterior section.

Method and material:
A cross-sectional study was conducted using a sample of 132 with healthy periodontium, (67 males and 65 females; aged 18 to 80 years) of the intact anterior maxilla was randomly designated and assessed by two calibrated and independent reviewers; the patients had been referred to the Department of Periodontology, at Islamic Azad University of Tehran, Dental Branch, for implant placement with at least 4 intact teeth in the anterior maxilla, were randomly selected. All CBCT scans were performed with 1mm slice thickness and Informed consent was obtained from all participating patients. This study was accepted by the Research Committee. Exclusion criteria were: 1) chemotherapy, 2) immunosuppressive disease, 3) pregnant or breastfeeding, 4) the presence of restorations, root canal treatments, apical root surgery, periapical lesion in the area, 5) tooth malposition, 6) traumatic history in the anterior area, 7) orthodontic therapy, 8) medications affecting gingival tissue and bone, 9) decayed teeth, 10) periodontal procedures performed in the last 6 months, 11) prosthetic crowns, 12) crowding of the anterior teeth, 14) facial asymmetry, 15) an abnormal overbite and overjet, 16) lack of consent to participate in the study. A software program was used to reconstruct the images and perform the measurements. Three observers were calibrated using 12 randomly selected scans. Each of the three observers measured 132 scans independently at the exact alike slice and magnification. Measurements were taken of the six maxillary anterior teeth at the crest to 8mm from the facial bone crest .The dimensions were averaged to calculate final measurements for each scan The following determination was achieved: 1) length from the CEJ to the bone crest, and 2) the diameter of labial alveolar bone overlying intact maxillary anterior teeth (Figure1). Demographic and general data was collected for any patient scan. Subcategories were designed to study the effect of systemic diseases, sex, age, and smoking habits on the bone thickness and CEJ–bone crest distance.

Statistical methods:
Data for the study was compiled in Excel software and SPSS (version 20.0) is transmitted measurements were analyzed using the software. Descriptive statistics and frequent analyses were performed. Paired-Sample T-Tests were used to compare the numeric values between the right and left side and for testing the variability of the investigators. Independent T-Test was used for comparison between genders, smoking habits, systemic disorders. One-way ANOVA was used for the remaining analysis, In other words, the ANOVA test was used to compare parameters evaluated. Differences between frequencies for fenestrations and dehiscence were assessed using x2 and Fisher exact tests; a linear regression model was used to define any possible correlation among CEJ, thickness of the facial plate, and coronal margin of the facial plate for each tooth at each millimeter. In all statistical tests a statistical significance level (P-value) was set at α = 0.05.

Result:
In this study, we surveyed 132 patients, which were 65 (49.3%) females and 67 (50.7%) males, aged from 18 to 80 years old, and 13.6% were smokers and 36.4% had a systemic disease. for the maxillary right and left central incisors, the CEJ– bone crest distance was (2.4 ± 2.14 mm) and (2.3± 2.17mm), respectively (Table 1), but was noted the apparent differences between males and females. The CEJ distance to crest in all teeth except tooth right lateral incisor was more in men, while in women, the bone thickness at 2 and 5 mm on tooth #13, #12, #11, and #23 was more (Table 2), but no significant difference was observed in the measurement of the distance from the CEJ to the crestal bone of smokers, however, the distance from C.E.J to the crestal bone increases with age and systemic diseases (Table 3); in addition, table (8-14) represents the number of teeth with facial bone buccal bone thickness and the occlusal relationship, no significant effect was observed (Table 4), although in the patients with class II, class III occlusal relationships, as well as more frequent of fenestrations and higher prevalence of dehiscence, was detected (Table 5). A high number of teeth presented with fenestration (0% to 3.2%) and dehiscence (1.8% to 6.06%). No statistically significant difference was found between the teeth regarding the distribution of fenestrations; while the highest fenestrations were in the right lateral incisors and left canines of the maxillary, and also, Fenestration was mostly detected at 5 mm from the bone crest; therefore other interesting findings on the fenestration and dehiscence at the right and left lateral incisor and canine teeth left, most were observed (Table 6). Over 132 patients only 31% of them had fenestration and dehiscence and from these, 31% only 2.27% of them were diabetics, 7.5% smokers (Table 7).

Discussion:
Former studies have established that there is a thin facial bone thickness covering maxillary anterior teeth (8, 16). The current study confirms the high occurrence of thin buccal bone covering the six maxillary anterior teeth. The means of the facial bone width at 2mm from the CEJ for the maxillary right central incisor was 0.63± 0.69 mm (0 to 2.3mm) and for the maxillary left central incisor it was 0.59± 0.71mm (0 to 1.9mm). Additionally at 5mm from CEJ for both central and lateral incisor, it was 0.62±0.66mm (0 to 2.2 mm) and 0.61± 0.7 mm (0 to 2.1mm) respectively. The present study showed that the distance of CEJ to bone crest increases with systemic disease and increasing age; although, various studies (18-20) have outlined the importance of age as a risk factor for periodontal pathology, but some studies analyzed the effect of age on the biologic width (21,22). Another interesting finding was an increase in CEJ–bone crest distance between individuals who were 50 years or older, Zekry reported that there was no significant difference between the values of right and left sides, or between genders. Moreover, statistically significant variations were observed between age groups at all levels, also mentioned that the distance from the CEJ to crestal bone is variable, and the overall inclination to increase with age (23). (23). Asgarpour in 2013 (24), compared CBCT of 60 patients in which result of this study shows more thickness of the facial bone in the lateral incisor teeth. The occurrence of a thicker bone (≥2 mm) was the greatest for the maxillary right (28.8%) and the maxillary left (21.2%) lateral incisors at 5mm from the crest. We measured a thicker facial bone at maxillary incisor locations. Buccal bone thickness plays a major role in the outcome of implant treatment. However, when a site is compromised by infection or a thin labial bone plate is present with the presence of thin, high scalloped periodontal biotype, immediate implant placement would take a serious esthetic risk (25-28), and may result in gingival recession (29); moreover, Tomasi in 2010 (28) revealed that the position of the implant opposite in buccolingual dimension is influenced the amount of buccal plate resorption; However, this investigation has revealed that the width of the buccal bony wall may have a significant influence in determining its resorption pattern.In accordance with the results of the present study, Zekry described that the mean width of the facial alveolar bone wall at the anterior teeth was 0.9mm and increased towards posterior regions. Infrequently, a width of 2mm was yielded. At a 5mm distance from the bone crest, minimal widths of facial alveolar bone were identified for the anterior teeth (23). Braut et al. (1) described that CBCT measurements of the labial bone wall for teeth in the anterior maxilla have been rarely more than 1mm, only in approximately 10% of the teeth. Less bone was presented in central incisors (4%-8%). Our findings for bone thickness were similar to Ghassemian et al. (16) and Nowzari (8), mentioned that an anterior maxillary bone thickness was about 1 mm, which has a thickness similar that obtained in the present study (8). In 2011 another study by Eber et al. (30) on 125 CBCT, found that facial bone thickness was less than 1 mm in most sites. In a similar study by Fuentes et al. mentioned the average of the facial wall widths in the central incisors, lateral incisors and canines were 1.14±0.65 mm, 0.95±0.67 mm and 1.15±0.68 mm, respectively; Also on the left side were significant differences in some examination of labial bone thickness observed according to age and gender (31). Lee et al. (32) surveyed CBCT scans from 20 objects, identifying the mean facial wall diameter at 3 mm from the CEJ of 0.68 mm, 0.76 mm and 1.07 mm, for the central incisors, lateral incisors, and canines, respectively. Januário et al. (33) analyzed some CBCT scans, described the average of the facial plate, which ranged from 0.5 to 0.7 mm. Another significant finding included frequency of teeth with fenestration and dehiscence. In the present study, fenestrations were mostly detected at 5 mm from the crestal bone, which was in accordance to study carried out by Nowzari et al (8) , revealed that the frequency of dehiscence ranged from 9.9% to 51.6% for anterior . Chen and Buser described that 59 sites (69.4%) of labial socket walls were intact and 15 sites (17.6%) of facial bone exhibited dehiscence (7). In our study, the frequency of fenestrations and dehiscence was considered related to the class of occlusion. Class II malocclusion patients had a greater prevalence of fenestrations and class III malocclusion a higher prevalence of dehiscence. Another study reported (34) that dehiscence was associated with 51.09% of all teeth, and fenestration with 36.51%. Class I malocclusion patients had a higher prevalence of dehiscence of 35%, which was higher than those with Class II Division 1 malocclusion (P <0.01) even though, there was no statistically significant difference between the facial types. Due to the small number of fenestrations and dehiscence found in this study, the results may not be statistically significant. Conclusion The present study shows the maximum thickness of bone is in anterior right maxillary teeth and particularly the canine, though generally; the thin labial alveolar bone wall was usually being in the monitored area. For buccal bone thickness, at a distance of at 8mm, no systemic factor had influenced the thickness of the bone. Therefore, for most patients, adjunctive bone augmentation may be needed when installing implants in areas of esthetic concern.