Retrospective CBCT-based analysis of anatomical and demographic factors in implant planning for the maxillary first molar region

Abstract

Background

Implant placement in the posterior maxilla is often complicated by anatomical limitations such as reduced alveolar bone volume, sinus pneumatization, sinus septa, and variations in ridge morphology. Accurate radiographic evaluation of these structures is therefore essential for predictable implant planning in the maxillary first molar region (MFMR). The aim of this study was to investigate the relationships between alveolar bone height (ABH), bucco-palatal crest thickness (CT), buccal concavity, sinus septa (SS), sinus pathology (SP), and demographic factors (age and gender), as well as jaw side and tooth presence in the MFMR, and to evaluate their relevance for implant planning.

Materials and methods

A total of 798 cone-beam computed tomography (CBCT) images from 399 individuals were retrospectively analyzed. ABH and CT were measured from the alveolar crest to a point 2 mm coronal to the maxillary sinus membrane. The presence of concavity, SS, and SP was recorded using a binary (present/absent) classification.

Results

ABH and CT were significantly greater in dentate sites compared to edentulous sites (p < 0.05). Age was significantly associated with CT, buccal concavity, SS, and SP (p < 0.05). Tooth presence was significantly associated with concavity and SP, gender with SP, and jaw side with SS (p < 0.05).

Conclusion

Anatomical variations in the MFMR are significantly influenced by demographic and site-related factors. Comprehensive CBCT-based evaluation of alveolar bone dimensions and sinus-related structures is essential for individualized and risk-aware implant planning in this region.

Introduction

Osseointegrated dental implants have become a standard modality in contemporary clinical dentistry. While treatment planning is predominantly driven by restorative, functional, and technical considerations, it is frequently constrained by anatomical limitations. Therefore, to ensure a predictable and satisfactory aesthetic and functional outcome, the selection and precise placement of the implant must be performed with meticulous attention to the anatomical structures specific to the intended site [1].

The first permanent molars are typically the earliest to erupt and are frequently subjected to early loss due to dental caries. The preferred treatment modality for their replacement is currently dental implant therapy, either with immediate or conventional loading protocols [2]. However, implant placement in the posterior maxilla is associated with several anatomical and clinical challenges. These include poor bone quality and low bone density, the presence of the maxillary sinus, occasional buccal concavities, anatomical limitations that restrict surgical access, and difficulties in achieving and maintaining adequate oral hygiene. Furthermore, this region is exposed to higher occlusal forces compared to other areas of the oral cavity, which can negatively impact implant survival rates [3, 4].

Researchers have improved implant surface characteristics and designs using various techniques to enhance osseointegration, particularly in cases of poor bone quality. One of the most common challenges encountered in the posterior edentulous maxilla is insufficient bone height, which significantly complicates implant placement in this region. To address this issue, sinus lifting procedures are frequently employed. Additionally, zygomatic and short implants have emerged as viable alternatives to overcome limitations in vertical bone height [5].

Understanding and effectively applying implant systems developed to address the anatomical and structural challenges of the posterior maxilla is critical for successful treatment outcomes. For a successful implant surgery, it is essential that clinicians possess a comprehensive understanding of the various factors that influence treatment parameters and surgical decision-making. Neglecting these anatomical considerations and failing to plan appropriately may result in complications such as hemorrhage, damage to adjacent teeth, sinus perforation, implant displacement into the sinus, bone perforation, inadequate primary stability, and ultimately, implant failure [6].

Cone-beam computerized tomography (CBCT) is the most commonly used imaging modality for implant planning, as it allows precise three-dimensional (3D) measurements of the bone area where implants will be placed and accurate analysis of anatomical structures [7]. CBCT examination of the anatomy of the maxilla is frequently requested to assess the need for surgical sinus lift for implant placement in the posterior maxilla or to detect the presence of any septa. or pathologic conditions within the sinus (sinusitis, mucosal thickening, mucosal retention cysts, partial or complete opacification) [8, 9].

It is well-established that demographic characteristics (such as age and gender) and jaw region (right/left) influence alveolar bone volume and density, as well as various anatomical features [10]. The aim of this study is to provide guidance on the maxillary first molar region (MFMR) in dental implant planning by analyzing the associations between parameters, including alveolar bone height (ABH), crest thickness (CT), sinus septa (SS), sinus pathology (SP), the presence of buccal concavities, and demographic factors, the presence of teeth, and the side of the jaw. Previous CBCT-based studies have evaluated posterior maxillary ridge dimensions and sinus anatomy with respect to residual bone height, crest width, and sinus morphology parameters, which are key in implant treatment planning [11, 12]. However, few specifically focus on multifactorial anatomical variations in the MFMR with a large sample size, as in this study.

Materials and methods

Ethics committee approval was obtained from the Batman University Non-Interventional Clinical Research Ethics Committee (Decision no: 2024/02–27). The CBCT images analyzed in this study were retrospectively selected from 1272 scans obtained between 2020 and 2023 for various clinical indications (implant treatment, orthodontic treatment, trauma, etc.) from the picture archiving and communication system of a private imaging center in Diyarbakır province. Informed consent was waived due to the retrospective design. All procedures were conducted in accordance with the Declaration of Helsinki.

A total of 798 MFMR, including both dentate and edentulous sites, from 399 individuals aged 18 years and older with adequate image quality were included. Images were excluded if they presented artifacts impairing anatomical evaluation, previous implant placement in the MFMR, prior surgical or regenerative procedures in the region, or if the individual was younger than 18 years. All CBCT images were obtained using an i-CAT device (Imaging Science International, Hatfield, PA, USA) with the following parameters: 120 kVp, 5 mA, 9 s exposure time, and 0.3 mm voxel size. Although this voxel size is considered appropriate for anatomical assessment, minor measurement inaccuracies related to image resolution cannot be completely excluded. All CBCT images were evaluated under standardized viewing conditions using the manufacturer’s default software settings for density, contrast, and sharpness. No manual adjustments were performed during image evaluation in order to maintain consistency across all measurements. Cross-sectional reconstructions were performed with a slice thickness corresponding to the original voxel size (0.3 mm) to ensure measurement consistency and reproducibility.

Radiographic measurements were performed by a single examiner (GGT) and independently re-evaluated by a second examiner (RFGU). Intra- and inter-rater reliability were assessed using Kappa and Weighted Kappa coefficients, demonstrating high agreement (0.86–0.92 and 0.83–0.90, respectively).

The right and left MFMR of the same individual were evaluated as independent anatomical sites, as regional anatomical variations may differ within the same patient. Age was stratified into three groups (18–38, 39–53, and 54–81 years) to reflect early, middle, and older adulthood and to maintain a relatively balanced distribution of participants (n = 262, n = 262, and n = 274, respectively). In addition, this stratification was based on a tertile distribution and interpreted in accordance with biologically relevant stages, consistent with previous CBCT-based studies. The upper age limit corresponded to the maximum age available in the dataset. Gender was included as a categorical variable (female/male). Jaw side was categorized as right and left, and dental status as dentate or edentulous.

For ABH assessment, a standardized cross-sectional CBCT image centered on the MFMR was selected. The most coronal point of the alveolar crest was identified as the coronal reference. The inferior border of the maxillary sinus membrane was then determined, and ABH was measured vertically to a point located 2 mm coronal to this border. This reference point was chosen to account for the Schneiderian membrane thickness and to avoid overestimation of clinically usable bone height during implant planning. In edentulous sites, bucco-palatal CT was measured 2 mm apical to the crest level (Fig. 1). In dentate sites, bucco-palatal CT was measured (Fig. 2). The presence of buccal concavity (Fig. 3), sinus septa (Fig. 4), and sinus pathology (Fig. 5) was recorded using a binary (present/absent) classification. Sinus pathology was defined as mucosal thickening ≥ 2 mm, retention cysts, or partial/complete sinus opacification, based on previously established radiological criteria for maxillary sinus evaluation in CBCT imaging [8, 9]. All recorded data were entered and tabulated in Microsoft Excel (version 2013).

Fig. 1.

Representative CBCT cross-sectional image of MFMR illustrating the measurement protocol. ABH (1) in the edentulos site was measured from the alveolar crest to a point 2 mm apical to the Schneiderian membrane to represent the vertical bone height that could be reliably obtained. Buccopalatal CT (2) was measured at the alveolar crest level

Fig. 2.

Representative CBCT cross-sectional image of MFMR illustrating the measurement protocol. ABH (1) in the dentate site was measured from the alveolar crest to a point 2 mm apical to the Schneiderian membrane to represent the vertical bone height that could be reliably obtained. Buccopalatal CT (2) was measured at the alveolar crest level

Fig. 3.

Representative CBCT cross-sectional image of the MFMR illustrating buccal and palatal alveolar bone concavities (arrows), which may increase the risk of cortical perforation during implant placement

Fig. 4.

Representative CBCT image illustrating maxillary sinus septa (arrow), which may complicate sinus floor elevation procedures during implant placement

Fig. 5.

Representative coronal CBCT image showing maxillary sinus pathology. Sinus pathology was defined as mucosal thickening greater than 2 mm, retention cysts, or partial/complete sinus opacification. In this image, bilateral mucosal thickening exceeding 2 mm is observed

Statistical analysis

All statistical analyses were performed using SPSS software (version 21.0; IBM Corp., Armonk, NY, USA). Socio-demographic characteristics were analyzed using frequency analysis and presented as counts and percentages. Continuous variables ABH and CT were expressed as mean ± standard deviation. Differences in ABH and CT according to jaw side (right–left) and the presence of teeth were evaluated using the Paired Samples t-test. Comparisons according to gender were performed using the Independent Samples t-test. Differences among age groups were analyzed using ANOVA. Categorical variables, including the presence of concavity, SS, and SP, were analyzed using the Pearson Chi-square test to assess their association with age, gender, jaw side, and the presence of teeth. A p-value ≤ 0.05 was considered statistically significant. Since bilateral regions (right and left MFMRs) from the same individuals were included, paired analyses were performed when comparing right and left sides. For other comparisons, regions were evaluated according to the defined grouping variables. However, potential intra-individual correlation between bilateral measurements should be considered when interpreting the findings. A p-value ≤ 0.05 was considered statistically significant.

Results

The study was conducted on CBCT images of 399 individuals (230 females, 169 males) aged between 18 and 81 years (mean age: 45.52 ± 15.08 years). A total of 798 MFMR sites, including both dentate and edentulous regions, were evaluated.

Height and thickness

No statistically significant difference in ABH was observed between the right and left regions, whereas CT was significantly greater on the right side (Table 1). Both ABH and CT were significantly higher in dentate sites compared edentulous sites (Table 1). ABH differed significantly according to gender, with higher values in females, while CT did not show a significant gender-related difference (Table 2). Age was not significantly associated with ABH; however, a significant association was identified between age and CT (Table 3).

Table 1.

Analysis of whether ABH and CT have a significant difference according to the side of jaw and the presence of teeth

	Variables	Mean	Sd	t	dd	p
The side of jaw (right-left)	ABH	7.71	4.46	-0.017	397	0.986
		7.72	4.55
The side of jaw (right-left)	CT	8.81	3.37	3.169	397	0.002*
		8.16	3.23
The presence of teeth (dentate/edentulous)	ABH	8.62	3.69	5.341	381	0.000*
		6.99	5.04
The presence of teeth (dentate/edentulous)	CT	11.03	1.99	30.203	381	0.000*
		6.10	2.41

* correlation is significant at the 0.05 level

Table 2.

Analysis of whether ABH and CT have a significant difference according to gender

	Variables	Group	n	Mean	Sd	t	dd	p
Gender	ABH	Female	460	8.102	4.140	2.849	650.8	0.005*
		Male	338	7.164	4.908
	CT	Female	460	8.668	3.388	1.856	746.913	0.065
		Male	338	8.231	3.211
		Toothless	416	6.140	2.455

* correlation is significant at the 0.05 level

Table 3.

Analysis of whether ABH and CT have a significant difference according to age variable

Variables	Group	n	Mean	Sd	F	p	Source of Difference
ABH	1- 18-38	262	8.224	4.052	2.630	0.073
	2- 39-53	262	7.495	4.548
	3- 54-81	274	7.409	4.829
CT	1- 18-38	262	10,490	2.691	115.086	0.00*	1–2; 1–3; 2–3
	2- 39-53	262	8,385	3.079
	3- 54-81	274	6,657	2.992

* correlation is significant at the 0.05 level

Buccal concavity

A statistically significant association was found between age and the presence of buccal concavity. Concavity was also significantly more frequent in dentate sites compared to edentulous sites. No significant association was observed between concavity and gender or jaw side (Table 4).

Table 4.

Relationship between age, gender, the side of jaw and the presence of teeth variables and concavity, SS and SP

Gruplar	Total	Age			Ki-kare	sd	p	Gender		Ki-kare	sd	p	The side of jaw		Ki-kare	sd	p	The Presence of teeth		Ki-kare	sd	p
		18–38	39–53	54–81				Female	Male				Right	Left				Dentate	Edentulous
-Presence of	122	58	34	30	14.555	2	0.001*	77	45	1.765	1	0.184	63	59	0.132	1	0.716	82	40	21.594	1	0*
Concavity -Absence of Concavity	676	204	228	244				383	293				337	339				300	376
-Presence of SS	322	113	118	91	9.034	2	0.011*	185	137	0.008	1	0.929	182	140	8.835	1	0.003*	162	160	1.289	1	0.256
-Absence of SS	476	149	144	183				275	201				218	258				220	256
Presence of SP	302	83	103	116	6.823	2	0.033*	145	157	18.458	1	0	154	148	0.146	1	0.702	117	185	16.223	1	0*
Absence of SP	496	179	159	158				315	181				246	250				265	231

Level of signifcance set at p ≤ 0.05 marked as bold

Septa

The presence of SS was significantly associated with age and jaw side. However, no significant relationship was found between SS and gender or the presence of teeth (Table 4).

Pathology

A statistically significant association was observed between age and the presence of SP. SP was also significantly more frequent in males and in edentulous sites. No significant association was found between SP and jaw side (Table 4).

Discussion

Evaluation of alveolar bone morphology and the identification of vital anatomical structures in relation to the planned implant site are fundamental components of implant treatment planning [7]. The MFMR presents particular anatomical challenges, including reduced bone volume and density and the proximity of the maxillary sinus, all of which may limit available bone height for implant placement [4]. In this study, a detailed CBCT-based analysis of the MFMR was performed to support implant surgical planning by evaluating anatomical parameters in relation to age, gender, the presence of teeth, and jaw side. Both ABH and CT were significantly greater in dentate sites compared to edentulous sites. In dentate sites, measurements reflect socket-related anatomy, whereas in edentulous sites they represent residual ridge morphology. Therefore, inherent structural differences related to tooth presence should be considered when interpreting dimensional comparisons. This finding is consistent with the well-documented effects of tooth loss, which leads to reduced functional stimulation of the alveolar bone, progressive vertical and horizontal bone resorption, and sinus pneumatization in the posterior maxilla [13, 14]. Regarding gender differences, females demonstrated significantly higher ABH values than males, whereas no significant difference was observed in CT. Although several previous studies have reported lower bone height in females [14–16], the discrepancy may be explained not only by methodological differences but also by biological factors. Volumetric studies have demonstrated that males generally exhibit larger maxillary sinus volumes, which may predispose to greater sinus pneumatization and consequently reduced residual alveolar bone height following tooth loss [17, 18]. However, these findings may also be influenced by inter-individual variability in sinus anatomy and pneumatization patterns, and therefore should be interpreted with caution. In line with our findings, Temple et al. [19] also reported no significant association between gender and CT.

Analysis of age-related changes revealed no significant association between age and ABH, while a significant relationship was observed between age and CT. The lack of association between age and ABH may be related to the anatomical constraint imposed by the maxillary sinus floor, which limits vertical bone availability irrespective of age once pneumatization has occurred [20]. In contrast, CT may be more susceptible to age-related remodeling and progressive horizontal resorption, particularly in partially or completely edentulous areas. Maxillary bone resorption following tooth loss occurs in a centripetal and apical direction, resulting in progressive narrowing of the alveolar ridge [21]. The increase in edentulism with age, together with the observed reduction in CT, supports this pattern. From a clinical perspective, these findings underscore the importance of site-specific anatomical evaluation, particularly in immediate implant placement, where sufficient residual bone height and thickness are essential for achieving primary stability [22].

Buccal alveolar bone concavities, although more commonly discussed in the anterior maxilla, may also be present in the posterior maxillary region and increase the risk of cortical plate perforation during implant placement [23]. Such concavities are often overlooked in two-dimensional imaging modalities, emphasizing the value of CBCT in preoperative assessment. Consistent with cadaveric findings reported by Uchida et al. [24], our study demonstrated a higher prevalence of concavities in dentate sites compared to edentulous sites.

The presence of SS is a clinically relevant finding, as septa may increase the risk of Schneiderian membrane perforation during sinus floor elevation procedures [24]. In the present study, SS were detected in 40.4% of cases, a prevalence consistent with previous CBCT-based investigations [25–28]. Similar to earlier reports, no significant association was found between SS and gender or the presence of teeth [29–33]. However, a significantly higher prevalence of SS was observed on the right side, in agreement with findings reported by Zahrani et al. [34]. The association between age and SS observed in this study points toward a potential age-related trend in sinus morphology. Although differences in age group categorization across studies may account for variations in reported prevalence rates, it can be hypothesized that sinus anatomy may exhibit variations over the lifespan. Septa may be classified as primary or secondary; the latter is potentially associated with irregular sinus pneumatization following tooth loss and alveolar bone resorption. Our findings support the hypothesis that secondary septa may develop as a consequence of post-extraction sinus expansion, suggesting a relationship between long-term edentulism and septa formation [25].

SP was identified in 37.8% of cases, a prevalence lower than that reported in some previous CBCT studies [10, 35–37]. This discrepancy may be related to variations in diagnostic criteria and imaging parameters. For example, some studies classified any mucosal thickening or radiopaque change as sinus pathology [10], whereas others differentiated specific entities such as retention cysts, mucosal thickening beyond a defined threshold, or partial/total opacification [35–37]. Differences in voxel size and the inclusion of symptomatic versus asymptomatic populations may also have influenced reported prevalence rates. A significant association was found between age and SP, with higher prevalence in older individuals, consistent with findings reported by Ritter et al. [34]. In contrast, other studies have reported no age-related association [4, 38], which may reflect differences in age stratification, study design, or sample characteristics. In line with several previous reports [9, 36, 37, 39], SP was more frequently observed in males than in females in the present study. This difference may be associated with behavioral or environmental factors; however, due to the absence of smoking data, such interpretations should be considered speculative.

From a clinical perspective, the findings emphasize the importance of individualized CBCT-based assessment in the MFMR, particularly in elderly and edentulous patients where reduced bone dimensions and sinus-related anatomical variations may complicate implant placement. Reduced alveolar bone height may indicate the need for sinus floor elevation or the selection of shorter implants, whereas decreased crest thickness may necessitate narrower implant selection or additional bone augmentation to achieve adequate primary stability. Identification of buccal concavities is essential to minimize the risk of cortical perforation and to guide implant angulation. The presence of sinus septa should be carefully evaluated prior to sinus lift procedures due to the increased risk of Schneiderian membrane perforation. Likewise, the detection of sinus pathology may require further clinical or otorhinolaryngological evaluation before implant surgery. The present study provides a comprehensive CBCT-based evaluation of the MFMR by integrating alveolar bone dimensions, sinus anatomy, and pathological findings within a single analytical framework. The relatively large sample size and multifactorial assessment enhance the robustness of the findings and contribute to a clearer understanding of anatomical variability in this clinically demanding region. These findings should also be interpreted considering the tertile-based age stratification, which reflects biologically relevant stages and is consistent with previous CBCT-based studies.

Nevertheless, certain limitations should be acknowledged. The retrospective design and the absence of clinical data regarding periodontal status, systemic health conditions, smoking habits, and long-term implant outcomes limit causal interpretation. As a retrospective radiographic study, clinical variables such as periodontal status, duration of edentulism, systemic conditions, and smoking habits could not be controlled and may have influenced bone morphology [40]. Bilateral MFMR sites from the same individual were analyzed as independent units; therefore, potential intra-individual clustering effects cannot be completely excluded and should be considered when interpreting the results [41]. CT measurements obtained from dentate and edentulous sites represent inherently different anatomical conditions (socket width versus residual ridge thickness) [42], which may introduce structural heterogeneity and limit direct dimensional comparability. Although a voxel size of 0.3 mm is considered appropriate for anatomical assessment, minor measurement inaccuracies related to image resolution cannot be completely excluded [43]. In addition, exact numerical values for display parameters (e.g., contrast and density) were not available due to the use of default software settings, which may limit full reproducibility. Finally, the binary classification of concavity, SS, and SP (present/absent) may not fully capture their morphological variability or severity [44]. Future prospective studies incorporating clinical correlations, longitudinal follow-up, and refined morphological classification systems may further clarify anatomical risk patterns and optimize implant planning strategies in the MFMR.

Authors’ contributions

GGT and RFGU designed the study. Designed, created/collected and analyzed data. GGT was involved in writing the manuscript and interpreting the results. RFGU checked every step. All authors read and approved the final manuscript.

Funding

Not applicable.

Data availability

The datasets used and/or analysed during the current study available from the corresponding author on reasonable request.

Declarations

Ethics approval and consent to participate

Ethics committee approval was obtained from the Batman University Non-Interventional Clinical Research Ethics Committee (Decision no: 2024/02–27). This study involved retrospective analysis of anonymized CBCT images. The requirement for informed consent was waived by the ethics committee due to the retrospective nature of the study. All procedures were performed in accordance with the Declaration of Helsinki.

Consent for publication

Not applicable.

Competing interests

The authors declare no competing interests.