Thickness of buccal bone in the mandible and its clinical significance in mono-cortical screws placement. A CBCT analysis

The aim of this study was to determine the safest length of monocortical screws that can be inserted for the treatment of mandibular fractures following Champy's technique. Fifty cone-beam computed tomography (CBCT) scans of hemi-mandibles were studied. Linear measurements were taken from the buccal cortical plate to the tooth apex, from the canine to the second premolar, and from the buccal cortical plate to the tooth apex and the inferior alveolar canal in the molar area. The minimum values of the horizontal distances both at the level of the apex and the inferior alveolar canal at the second molar were found to be 4 mm, which is greater than those of the first molar. At the canine, first premolar and second premolars, the minimum values of the horizontal distances at the level of the apex was found to be 2 mm, 2.33 mm and 2 mm, respectively. Stabilizing miniplates using 4 mm screws both at the level of the apex and the inferior alveolar canal is safe in the second molar area, anterior to this, there is a risk of injury to tooth root and inferior alveolar nerve.     

Evaluation of anatomical references for locating the course of the posterior superior alveolar artery for dental implant surgery

This retrospective cohort study aimed to identify the best anatomical reference for predicting the posterior superior alveolar artery (PSAA) location. Computed tomographic images of 90 maxillary sinuses were evaluated. We studied five references, including the alveolar crest, maxillary sinus floor, zygomatoalveolar crest, hard palate and soft palate, and measured the distances between them and the PSAA. Variations in the distance were evaluated by the standard deviation and coefficient of variation (CV). The zygomatoalveolar crest was an unstable reference, owing to its high standard deviation and CV. The smallest CV was for the distance between the alveolar crest and PSAA, although the distance was smaller in edentulous jaws than dentulous jaws. The distance between the sinus floor and PSAA was larger in male and edentulous patients. The PSAA was detected in 40.0%, 44.4%, 54.4% and 56.7% of the sinus walls at the first and second premolar and the first and second molar positions, respectively. At these tooth positions, the respective heights above the hard palate were 11.2 ± 4.9, 8.2 ± 4.9, 6.2 ± 2.8 and 8.1 ± 2.9 mm. The hard palate was the most stable reference for predicting the location of the PSAA, irrespective of sex, age and dentition.     

Calvarial graft resorption index in the reconstruction of the maxillary sinus in patients with atrophic maxillas: a prospective clinical study

The objective of this study was to assess the resorption index of particulate calvarial grafts in maxillary sinuses of patients undergoing total reconstruction of an atrophic maxilla with residual alveolar bone that was less than, or equal to, 3 mm thick. Twenty-one maxillary sinus floor elevations were carried out using particulate calvarial grafts in 11 individuals with totally edentulous maxillas. All patients had computed tomography (CT) before (T0), and 48 hours (T1) and six months after surgery (T2). For each CT scan, linear measurements were taken of sections of the anterior, medial, and posterior regions of the maxillary sinus. There was a significant increase in the height of the maxillary sinus floor when T0 was compared with T1 (p = 0.001). There was a statistically significant reduction in all maxillary sinus measurements when T1 was compared with T2; the mean height reduction being 2.36 mm (16.87%) in the anterior region, 3.53 mm (22.47%) in the medial region, and 2.21 mm (22.78%) in the posterior region (p = 0.001). Mean resorption was 20.7%. Autogenous calvarial bone used alone is an option for graft material in pneumatised maxillary sinuses and in cases where there is limited alveolar bone.     

The prevalence and location of the posterior superior alveolar artery in the maxillary sinus wall: A preliminary computed-cone beam study

The lateral wall of the maxillary sinus is supplied by the posterior superior alveolar artery (PSAA). It may be affected by trauma, pathology, or surgery performed to access or correct any fracture involving the maxillary sinus. This study analysed the prevalence and distance of the PSAA from the floor of the maxillary sinus in selected Southeast Asian patients. Methods: This is a cross sectional study conducted using cone-beam computed tomographic images of 83 dentate patients with a mean age of 38.3 years. Results: One hundred sixty-six maxillary sinuses of 54 males and 29 females were evaluated, with PSAA observed in 91.6 % of sinuses. Of the PSAA identified (n = 152), 64.5 % were intraosseous (n = 98), 25.7 % were beneath the sinus membrane (n = 39), and the remaining 15 (9.9 %) were on the external cortex of the lateral sinus wall. The mean distance between PSAA and the lowest point of the sinus floor was 11.44 mm (SD, 3.36). Sixty-four maxillary sinus walls (38.6 %) presented with 2 PSAA branches. The inferior and superior branches were located 6.42 mm (SD, 2.68) and 8.48 mm (SD, 3.56) from the floor of the maxillary sinus, respectively. The mean difference between these 2 branches was 2.25 mm (SD, 1.90). Conclusion: This study confirms the different locations of the PSAA in relation to the lateral wall of the maxillary sinus with no gender influence. Branching of PSAA occurs, and should be highlighted to surgeons.     

Anatomical characteristics of maxillary sinus antroliths and their influence on sinus membrane thickness: a retrospective cone beam computed tomography analysis

The purpose of this study was to assess the anatomy of antroliths and its influence on the thickness of the maxillary sinus membrane. Cone beam computed tomography (CBCT) was performed on 239 patients (478 sinuses). The prevalence of antroliths per sinus was 8.4%. Regarding their distribution, antroliths were predominantly unilateral (82.5%), single (67.5%), and in a dentate area (60.0%). The antroliths were mainly located in the molar region (95.0%) and in the sinus floor (77.5%). The measured dimensions of the antroliths were as follows: length 5.6 ± 4.4 mm, width 4.1 ± 2.9 mm, height 3.5 ± 2.1 mm. The relationships between the antroliths and the sinus membrane (type 1, 34.1%; type 2, 52.3%; type 3, 13.6%) indicated that sinus membranes tended to encircle antroliths, which resulted in a gradual increase in membrane thickness. The sinus membrane was found to be significantly thicker in the presence of antrolith(s) (P < 0.001). Antroliths which are sufficiently large or are located adjacent to the sinus floor or lateral wall increase the risk of sinus membrane perforation during sinus augmentation procedures. Therefore, a thorough CBCT evaluation is needed to minimize the risk of complications prior to sinus augmentation procedures.     

Arteries of the anterior wall of the maxilla in sinus lift surgery

Knowledge of the anatomical course of the anterior maxillary wall and alveolar process arteries is essential for sinus lift procedures. The aim of this study was to analyse the localization of anastomoses between the infraorbital and posterior superior alveolar artery on 101 computed tomography (CT) scans of maxillary sinuses (patients aged 18–70 years). The distance from the anastomosis to the bone point was measured on CT scans for each tooth location; for edentulous patients measurements were made to the lower edge of the alveolar process, and for dentate patients to the neck of the tooth. Measurements were done independently by two observers. The anastomosis analysed was identified on 50% of CT scans. The distance to the anastomosis was longest above the premolar (20.4 mm from tooth cervical line) and shortest above the first molar (15.9 mm to the edge of the alveolar process). The anastomosis can be localized on a CT scan for exact positioning of the antrotomy in 50% of patients. For the remaining patients, the anatomical information provided in this study can be used to reduce the risk of damage to the anastomosis. This study provides information on the distance from the anastomosis to the neck of preserved teeth in partially edentulous patients, which can be used as a reference point during sinus lift procedures.     

The effect of residual bone height and membrane thickness on sinus membrane perforation in crestal sinus grafting: A prospective clinical study

This study sought to determine the rate of sinus membrane perforation in patients undergoing crestal sinus grafting, as well as the effect of Schneiderian membrane thickness and residual bone height (RBH) on membrane perforation, using cone beam computed tomography. The study included 25 patients undergoing 44 crestal sinus grafting procedures. The sites for crestal sinus grafting were divided into a control group (RBH ≥ 5 mm) and a test group (RBH < 5 mm). All sinus grafting procedures were also categorised based on membrane thickness: group A (<1 mm), group B (1–2 mm), and group C (≥2 mm). The rate of membrane perforation was 18.2%. The median RBH measurement was 5.59 mm. No statistically significant difference in membrane perforation rate was found between the test and control groups (P = 0.262). The median thickness of the Schneiderian membrane was 1.35 mm. There was no statistically significant difference in membrane perforation among the three membrane thickness groups (P = 0.431). No significant correlation between RBH and membrane perforation was observed, although clinical observation indicated that there was a tendency for an increased membrane perforation rate in the presence of a RBH < 5 mm. The perforation rate was found to be at its highest when the membrane was thinner than 1 mm.     

One-step lateral window approach for removal of benign minor sinus pathologies combined with transcrestal sinus floor elevation without bone grafts: a retrospective study

The aim of this study was to evaluate the clinical and radiographic outcomes of a lateral window approach for removal of benign minor sinus pathologies combined with transcrestal sinus floor elevation. From 2014 to 2018, all patients who received sinus pathology removal via a lateral window approach combined with transcrestal sinus floor elevation were screened. The serous exudate or minor sinus pathology was drained or removed via lateral window approach. Subsequently, transcrestal sinus floor elevation without grafting and simultaneous implant placement were performed. Panoramic radiographs and cone-beam computed tomography were taken preoperatively, immediately after surgery, and after prosthesis delivery. Twelve patients were included in this study. The decrease in Schneiderian membrane thickness was statistically significant (P < 0.001). Endo-sinus bone formation was observed on the buccal (1.35 ± 2.31 mm) and palatal (1.61 ± 2.65 mm) sites of the implant. The implant survival rate was 100%. All implants survived for an average of 21.83 ± 11.11 months. Within the limitations of this study, we suggest that the lateral window approach for minor sinus pathology removal combined with transcrestal sinus floor elevation has several advantages including endo-sinus bone gain without bone graft, minimal patient discomfort, reduced postoperative complications and shorter treatment period.     

Controversy about the protective role of volume in the frontal sinus after severe head trauma: larger sinus equates with higher risk of death

The “crumple zone” hypothesis suggests that the paranasal sinuses protect the brain as a zone to distribute and absorb energy after trauma to the head. We investigated the relation between the size of the frontal sinus and mortality in patients with cranial trauma. All patients with head trauma admitted to the ICU between 1 January 2016 and 20 December 2017 were reviewed retrospectively. They were divided into two groups (according to their outcome) : died and survived. The volumes of the frontal sinuses and other trauma-related variables were assessed on computed tomographs (CT) on admission. Admission CT of 33 patients (24 male, and nine female, aged between 18-92 years, mean 43) were obtained. Male patients had significantly larger frontal sinuses than female (10.24 compared with 6.6 cm³). Larger sinuses were significantly associated with a worse outcome (p = 0.005). The size of the frontal sinus correlates with mortality after cranial trauma. Our findings do not confirm the “crumple zone” hypothesis, and suggest that the larger the sinus, the greater the risk of death. To our knowledge this is a new finding that warrants further validation.     

Location of posterior superior alveolar artery and evaluation of maxillary sinus anatomy with computerized tomography: a clinical study

Objectives: Knowledge and evaluation of the maxillary sinus anatomy before sinus augmentation are essential for avoiding surgical complications. Posterior superior alveolar artery (PSAA) is the branch of maxillary artery that supplies lateral sinus wall and overlying membrane. The aims of this study were to examine the prevalence, diameter, and location of the PSAA and its relationship to the alveolar ridge and to study the prevalence of the sinus pathology and septum using computerized tomography (CT) scans. Materials and methods: One hundred and twenty‐one CT scans (242 sinuses) from patients undergoing sinus augmentation procedure and/or implant therapy were included. Lower border of the artery to the alveolar crest, bone height below the sinus floor to the ridge crest, distance of the artery to the medial sinus wall, diameter of the artery, and position of the artery were measured; presence of septa and pathology were recorded from CT sections. Results: Prevalence of sinus septa and sinus pathology was 16.1% and 24.8%, respectively. Artery was seen in 64.5% of all sinuses and was mostly intraosseous (68.2%). Mean diameter of PSAA was found 1.3 ± 0.5 mm. No significant correlation between the diameter of the artery and age was observed. Conclusions: The results from this study suggested that CT scan is a valuable tool in evaluating presence of sinus pathology, septa, and arteries before maxillary sinus surgery. Although variations exist in every patient, the findings from this study suggest limiting the superior border of the lateral window up to 18 mm from the ridge to avoid any potential vascular damage. To cite this article:
Güncü GN, Yildirim YD, Wang H‐L, Tözüm TF. Location of posterior superior alveolar artery and evaluation of maxillary sinus anatomy with computerized tomography: a clinical study.
Clin. Oral Impl. Res. 22 , 2011; 1164–1167.
doi: 10.1111/j.1600‐0501.2010.02071.x     

A cone beam computer tomographic study of the cortical bone thickness in different class II facial patterns

PurposeThe purpose of this study was to determine the difference of cortical bone thickness in different Frankfort to Mandibular plane angle (FMA) and anatomical areas by cone beam CT.Materials and methodsTwenty skeletal class II adult females were included, and divided into three groups by the FMA: the high FMA group, average FMA group, and low FMA group. Their cone beam computer tomography data were used for measurements and statistics. The cortical bone thickness was measured in five anatomical areas: (a) the labial alveolar bone located 2.0 mm below the root apex of the mandibular central incisors, (b) the buccal shelf alveolar bone located between the mandibular first and second molars, (c) the labial alveolar bone located 2.0 mm above the root apex of the maxillary central incisors, (d) the buccal alveolar bone located 3.0 mm above the alveolar crest between the maxillary second premolar and the first molar, and (e) the infrazygomatic crest.ResultsThe right and left measurements of cortical bone thickness in five anatomical sites were not significantly different. This study also compared the cortical bone thickness with the patient's age, but no significant differences were observed.The results revealed no significant difference in cortical bone thickness with respect to FMA. The cortical bone thickness in the posterior area was higher than that in the anterior area. Both the anterior area and the posterior area of the mandible were thicker than those of the maxilla, but the bone thickness in the maxillary posterior area and infrazygomatic crest showed no significant difference.ConclusionAlthough the cortical bone thickness did not show a significant difference, such difference was present in different areas. Lower posterior > infrazygomatic crest, upper posterior > lower anterior > upper anterior. The upper posterior area and the infrazygomatic crest area showed no significant difference.     

Dynamics and risk indicators of intrasinus elevation height following transalveolar sinus floor elevation with immediate implant placement: a longitudinal cohort study

Successful intrasinus graft consolidation is essential for the treatment outcome of transalveolar sinus floor elevation (SFE). This study was performed to examine the dynamics and risk indicators related to the elevation height after transalveolar SFE with grafting material and simultaneous implant placement. Fifty-two patients with 55 sites undergoing transalveolar SFE with immediate implant placement were enrolled retrospectively. Cone beam computed tomography (CBCT) images were collected and saved in DICOM format, at the following time-points: pre-surgery (T0), immediately post-surgery (T1), and 6 months post-surgery (T2). Voxel-based CBCT superimposition was performed to measure the sinus width, residual alveolar height, implant protrusion length, total elevation height, and apical graft height. The change in total elevation height from T1 to T2 was defined as the study outcome. Clinical and linear variables were analysed using linear regression. From T1 to T2, the total elevation height showed an average reduction of 1.0 ± 1.1 mm, while 10.9% sites showed an increased elevation height. Univariate regression analysis showed no significant correlation between tested clinical or linear variables and the study outcome. The results suggest that the change in elevation height was not influenced by the alveolar or sinus dimensions, graft materials, implant diameter, implant protrusion length, or the total elevation height at T1.     

Fatigue testing of two porcelain–zirconia all-ceramic crown systems

ObjectiveTo evaluate the mouth-motion step-stress fatigue behavior of two porcelain–zirconia all-ceramic crown systems.MethodsThe average dimensions of a mandibular first molar crown were imported into CAD software; a tooth preparation was modeled by reducing proximal walls by 1.5 mm and occlusal surface by 2.0 mm. The CAD-based tooth preparation was made by rapid prototyping and used as a master die to fabricate all-ceramic crowns with 1.0 mm porcelain veneered on 0.5 mm Y-TZP cores (LAVA veneer + LAVA frame, 3M/ESPE, and Vita veneer + CERCON frame, Dentsply). Crowns were cemented on aged (60 days in water) composite (Z100, 3M/ESPE) reproductions of the die. Three crowns from the LAVA group were subjected to single cycle load to failure for stress profile design; remainder subjected to step-stress mouth-motion fatigue (three step-stress profiles). All mechanical testing was performed by sliding a WC indenter of 6.25 mm diameter 0.7 mm lingually down the mesio-distal cusp. Master Weibull curves and reliability for missions of 50,000 cycles at 200 N load were calculated (Alta Pro 7, Reliasoft).ResultsSingle load to failure showed fractures through the zirconia core. Reliability for a 200 N × 50K cycle mission was not significantly different between systems. In fatigue, failure occurred by formation of large chips within the veneer originating from the contact area without core exposure.ConclusionsLAVA and CERCON ceramic systems present similar fatigue behavior; fatigue loading of both systems reproduces clinically observed failure modes.     

Posterior maxillary alveolar vertical distraction osteogenesis by bi-directional distractor

A patient with severe posterior maxillary hypoplasia was simulated using a 3-dimensional model by rapid prototyping, and segmental vertical distraction osteogenesis was planned to advance the posterior maxillary segment. The bi-directional distractor was adapted to the alveolar ridge and zygomatic buttress. After a 7-day latency period, we started distraction at a rate of 0.35 mm every 12 h. 12 mm of advancement of the posterior maxillary segment was achieved. This distraction osteogenesis using a bi-directional distractor with proper therapeutic planning and good surgical technique will help ensure adequate vector control to predictably regenerate the hard and soft tissues during alveolar distraction.     

Immediate dental implant placement with a horizontal gap more than two millimetres: a randomized clinical trial

The purpose of this study was to evaluate the horizontal dimensional changes in buccal alveolar bone immediately after dental implant placement in the upper premolar area with horizontal gaps >2 mm. A total of 48 patients were enrolled in this randomized clinical trial and were randomly assigned to one of three groups. Group I (flap with graft; n = 16) patients received an immediate implant with bone graft, membrane, and primary flap closure. Group II (flap without graft; n = 16) patients received an immediate implant with primary flap closure only. Group III (flapless without graft; n = 16) patients received an immediate implant without graft, membrane, or primary closure. Cone beam computed tomography (CBCT) scans were obtained preoperatively, immediately after implant placement, and at 6 months postoperative to evaluate horizontal dimensional changes in the buccal alveolar bone. Pain intensity was measured using a numerical rating scale. CBCT examinations revealed that bone had filled the horizontal gap in all three groups. Group II showed the greatest horizontal dimensional changes in the buccal alveolar bone, followed by group I. The least amount of change was recorded for group III. Furthermore, significantly less postoperative pain was recorded in group III when compared to the other groups. Short-term results suggest that the ‘flapless without graft’ technique shows similar results to the ‘flap with graft technique’ for immediate implant placement in the maxillary premolar extraction site with a horizontal gap >2 mm, when the bone plate is intact.     

Maxillary sinus vascular anatomy and its relation to sinus lift surgery

Objectives: To investigate the prevalence, location, size and course of the anastomosis between the dental branch of the posterior superior alveolar artery (PSAA), known as alveolar antral artery (AAA), and the infraorbital artery (IOA). Material and methods: The first part of the study was performed on 30 maxillary sinuses deriving from 15 human cadaver heads. In order to visualize such anastomosis, the vascular network afferent to the sinus was injected with liquid latex mixed with green India ink through the external carotid artery. The second part of the study consisted of 100 CT scans from patients scheduled for sinus lift surgery. Results: An anastomosis between the AAA and the IOA was found by dissection in the context of the sinus anterolateral wall in 100% of cases, while a well‐defined bony canal was detected radiographically in 94 out of 200 sinuses (47% of cases). The mean vertical distance from the lowest point of this bony canal to the alveolar crest was 11.25±2.99 mm (SD) in maxillae examined by CT. The canal diameter was <1 mm in 55.3% of cases, 1–2 mm in 40.4% of cases and 2–3 mm in 4.3% of cases. In 100% of cases, the AAA was found to be partially intra‐osseous, that is between the Schneiderian membrane and the lateral bony wall of the sinus, in the area selected for sinus antrostomy. Conclusions: A sound knowledge of the maxillary sinus vascular anatomy and its careful analysis by CT scan is essential to prevent complications during surgical interventions involving this region. To cite this article:
Rosano G, Taschieri S, Gaudy J‐F, Weinstein T, Del Fabbro M. Maxillary sinus vascular anatomy and its relation to sinus lift surgery.
Clin. Oral Impl. Res. 22 , 2011; 711–715
doi: 10.1111/j.1600‐0501.2010.02045.x     

Three-dimensional assessment of root migration and rotation patterns after coronectomy: bone-embedded roots versus soft tissue-covered roots

In this study, a three-dimensional evaluation was performed to explore differences between bone-embedded and soft tissue-covered roots after mandibular third molar (M3M) coronectomy. Patients were recruited according to the results of cone-beam computed tomography, 6 months after coronectomy. Completely bone-embedded M3Ms were assigned to group B, while completely soft tissue-covered M3Ms were assigned to group S. Data were recorded using digital software. A total of 213 M3Ms in 181 patients were investigated, of which 170 were assigned to the two study groups. Age was the primary factor influencing root migration (P < 0.001). The smaller the degree of angulation of the M3M, the more likely was the root complex to rotate distally (r = ?0.37, P < 0.001). The depth of the impacted M3M contributed to the regeneration of new bone (P ≤ 0.008). The length of the root complex (odds ratio 0.82, P = 0.048) and distance from the root to the alveolar crest (odds ratio 1.23, P = 0.026) were two critical factors influencing whether the root complex was bone-embedded. Ensuring that the length of the root complex is <7.6 mm and the distance between the root and alveolar crest is ≥5 mm were both found to be critical to the remaining root being completely bone-embedded and thus preventing eruption and the need for secondary surgery.     

Effects of Choukroun’s platelet-rich fibrin on bone regeneration in combination with deproteinized bovine bone mineral in maxillary sinus augmentation: A histological and histomorphometric study

PurposeThe potential effect of Choukroun’s platelet-rich fibrin (PRF) in combination with allograft on promoting bone regeneration has been discussed in previous publications. This study aims to evaluate an influence of PRF on bone regeneration in sinus augmentation in combination with a xenograft, deproteinised bovine bone.Materials and methodsEleven sinuses from 10 patients with posterior maxillary bone atrophy were selected for the study. As a test group, six sinus floor elevations were grafted with a Bio-Oss and PRF mixture, and as control group, five sinuses were treated with Bio-Oss alone. Clinical and radiographic examinations were performed pre- and postoperatively. After 6 months of sinus augmentation, bone biopsies were obtained from the grafted posterior maxilla, and un-decalcified ground sections were prepared. Bone characteristics were evaluated using histological observation and histomorphometric analyses.ResultsNo adverse effect was observed in any case within the follow-up period of 6 months after sinus augmentation. Histological observation showed similar morphological characteristics for both the PRF and control groups. The percentage of new bone formation in the PRF group was about 1.4 times of that in control (18.35% ± 5.62% vs. 12.95% ± 5.33%), while the percentage of residual bone substitute in the control group was about 1.5 times higher as that in the PRF group (28.54% ± 12.01% vs. 19.16% ± 6.89%). The percentage of contact length between newly formed bone and bone substitute in the PRF group was 21.45% ± 14.57% vs. 18.57% ± 5.39% in the control. No significant statistical differences between the two groups were found in these observed parameters.ConclusionsOur preliminary result demonstrated neither an advantage nor disadvantage of the application of PRF in combination with deproteinised bovine bone mineral in sinus augmentation after a healing period of 6 months.     

Palatonasal Recess on Medial Wall of the Maxillary Sinus and Clinical Implications for Sinus Augmentation via Lateral Window Approach

Background: Anatomic variations of the maxillary sinus determine the degree of difficulty in performing sinus augmentation. Whereas some variations, e.g., the septum and morphology of the sinus, have been extensively studied, the structure of the medial wall has never been investigated. The aims of this study are to measure the location and angulation of the palatonasal recess (PNR) on the medial wall and identify risk sites that are related to the shape of the PNR. Methods: Cone‐beam computed tomography (CBCT) scans were screened from the University of Michigan School of Dentistry database. Edentulous sites with <10 mm between the floor of the maxillary sinus and the alveolar crest were selected. The residual ridge height (RH), the distance between the PNR and the alveolar crest, and the angulation of the PNR were measured on the selected sagittal planes. The percentage of sites (risk sites) with recesses that were <90°and <15 mm from the alveolar crest was calculated. The PNR location and angulation were compared among premolar and molar edentulous sites. Results: Two hundred seventy‐four sites were studied. The mean ± SE PNR location was 14.2 ± 2.8 mm, 13.1 ± 2.2 mm, and 12.5 ± 2.5 mm for the second premolar, first molar, and second molar sites, respectively, with significant differences between the second premolar and second molar sites. The mean PNR angulation was 109.8° ± 25.3°, 121.6° ± 22.1°, and 144.9° ± 23.1° in the corresponding sites, with significant differences among the site groups. The respective percentages of risk sites were 15%, 8.2%, and 2.4% in the second premolar, first molar, and second molar sites. Conclusions: Maxillary sinuses with acute‐angled PNRs might present a challenge for performing sinus augmentation. Therefore, this anatomic structure should be carefully evaluated.