Maxillary Sinus Lateral Wall Thickness and Their Morphologic Patterns in the Atrophic Posterior Maxilla

Abstract

Purpose: The aim of the present study was to examine the sinus lateral wall thickness of atrophic posterior maxilla (< 10 mm) of complete and partial edentulous patients and determine the influence of the residual ridge height (RH), gender and age upon maxillary lateral wall thickness (LWT). Material and methods: Four hundred fourteen measures were taken from 140 consecutive patients that met the inclusion criteria. On the selected sagittal section, a built-in digital caliper recorded in millimeters the following measurements: residual ridge and lateral wall thickness [a perpendicular line at 3, 5, 7, 10, 13 and 15 mm from the lowest point of the sinus floor]. The edentulous spans were further classified as complete edentulous atrophic maxilla (CEM) and partial edentulous atrophic maxilla (PEM). The mixed linear model was used to test the effects of "gender", "type of edentulism", "edentulous span", and "residual height" on the measurement of the LWT of the sinus Results: Mean LWT for PEM was 1.71 ± 0.12 mm, while for CEM was 1.57 ± 0.07 mm (p=0.01). The mixed model yielded significant effect of "edentulous span" (p=0.048), and the interactions between "type of edentulism" and "edentulous span" (p<0.001), and "edentulous span" by RH (p<0.01). "Age" and RH were positively associated to LWT, however they do not interact with RH, "gender" or "type of edentulism". RH has been shown to correlate with "edentulous span" (p<0.001) and "type of edentulism" (p=0.01). The longer the "edentulous span", the thinner the LWT. Similarly, RH was larger for PEM (6.85, SE=0.34) than CEM (5.69, SE=0.26). Conclusions: The maxillary sinus lateral wall tends to increase in thickness from the second premolar to the second molar; and from 5mm up to 15 mm. In addition, residual ridge height, presence of teeth adjacent to the edentulous atrophic ridge, and age have all been shown to influence maxillary sinus lateral wall thickness. KEY WORDS (MESH 2013): Maxillary sinus, maxillary sinus floor augmentation, Morphology, Maxillofacial procedures, Bone regeneration Oral rehabilitation in the posterior maxilla often presents a challenge to the clinician due to ridge resorption after tooth extraction and subsequent sinus pneumatization. 1, 2 Several techniques have been used to overcome this challenge: bone augmentation, 3 short implants 4 or tilted implants; 5, 6 however, shorter and tilted implants may not have long-term stability due to strong occlusal forces exerted in this area. 10 Two main approaches for sinus augmentation have been proposed: lateral window approach 11 and crestal approach using primarily osteotomies. 12 Both have shown acceptable results; 10 however, the lateral window approach is still considered more predictable in terms of outcomes and safety, especially for cases with minimal bone height. 13 Despite this predictability, complications do occur, most related to sinus anatomy. 14 Extensive bleeding, implant migration and sinus infection should be considered when performing sinus augmentation. Hence, clinicians should learn how to prevent and manage these problems. 14 The presence of septum, sinus shape/morphology, and a sharp angulation between the lateral and medial wall have all been shown to increase the chance of membrane perforation and indirectly leads to sinus complications 17 Hence, knowledge of the sinus anatomy, including lateral wall thickness, is key to minimize these potential complications. Cone-beam computed tomography (CBCT) offers a 3-dimensional reliable diagnostic image for detecting anatomical variations of the maxillofacial region and enables us to report more precise data. Presently, only two studies have evaluated sinus lateral wall thickness by radiographic assessment, MATERIALS AND METHODS This research study used a retrospective clinical database that included patients who were previously treated as part of routine periodontal care using accepted therapy for each patient's specific clinical needs. Since the current research involved a retrospective analysis of pre-existing data and current data do not include any identifiable private information, this research did not require approval by an institutional ethics board. Patient Selection Overall, 414 measures were taken from 140 consecutive Caucasians patients fulfilling the inclusion criteria, of which 270 were female and 144 were males (2:1 female: male ratio) with a mean age of 67.2 ± 18.8 years. Image Acquisition The scans used in the present study were selected from the CBCT database. All images were obtained with a CBCT machine ‡ ‡ ‡ in the Center of Implantology, Oral and Maxillofacial Surgery (CICOM), Badajoz, Spain by an experience radiologist (VC) between 2010 and 2013. The imaging parameters were set at 120kVp, 18.66mAs, scan time 20 seconds, resolution 0.4 mm, and a field of view (FOV) which varied based on the scanned region. The CBCT scans of each individual were transferred to a desktop computer equipped with an implant planning software program § § § .Data were saved in the Digital Imaging and Communications in Medicine (DICOM) format. Inclusion and Exclusion Criteria One examiner (AM) conducted the image screening using the following inclusion/exclusion criteria. -Images were included if: 1. Maxillary sinuses located between premolars and molars as a result of missing single or multiple teeth 2. The residual ridge height (RH) was < 10 mm. 3. Presence of teeth adjacent to or opposing the edentulous area so the location of the edentulous ridges corresponding to the tooth site could be identified 4. The maxillary sinus to be measured was visible from its floor to at least 15 mm from the alveolar crest of the edentulous ridge. -Images were excluded if: 1. Images were unclear or incomplete due to scattering or other reasons 2. Edentulous ridge height was more than 10 mm 3. The location of the edentulous ridge cannot be determined 4. Presence of sinus pathology that made the measurement impossible 5. The outline of the edentulous ridge cannot be identified, e.g. extraction sockets 6. The sinus had been grafted or in which implants had been placed Image Analysis On the selected sagittal section, a built-in digital caliper made the following measurements in millimeters: residual ridge height (RH) [the distance from the alveolar crest up to the lowest point of the sinus floor] and lateral wall thickness (LWT) [a perpendicular line at 3, 5, 7, 10, 13 and 15 mm from the lowest point of the sinus floor] Statistic Analysis The mixed linear model as implemented in SPSS v17.0 was used to test the effects of "gender", "type of edentulism", "edentulous span" (within patients: 1M, 2M, 2PM), and RH of the measurement (within patients: 3, 5, 7, 10, 13 and 15 mm) on the LWT of the sinus. The RH and patient age served as covariates for the analysis. The mixed model was also used to test the effects of "gender", " type of edentulism", and "edentulous span" on RH, with patient age serving as a covariate. The type of covariance matrix was selected using the Schwarz Bayesian criterion. A p-level of 0.05 was setup for significance level. When needed, the Sidak correction for post-hoc comparison was used. RESULTS The average thickness in millimeters (mm) and the 95% confidence intervals for the LWT as a function of edentulous span and height of the measurement are presented in Using a compound symmetry covariance matrix, the mixed model yielded main effect of "edentulous span" Regarding the influence of RH upon LWT, the mixed model yielded only main effect of "type of edentulous", F (1,141)=6.82, p=0.01, and "edentulous span", F (2,213)=9.56, p<0.001. RH was larger for PEM (6.85, SE=0.34) than CEM (5.69, SE=0.26). In addition, RH was found to be smaller for 1M and 2M (5.96, SE=0.23, 5.89, SE=0.30) than for 2PM (6.96, SE=0.27) edentulous spans. DISCUSSION Maxillary sinus augmentation via lateral approach presents complexity for dissection and elevation of sinus membrane, often due to the irregular anatomy associated with the sinus. The management of the lateral wall during sinus augmentation via lateral approach has been emphasized due to the fact that its thickness may influence the integrity of the Schneiderian membrane. 24 On the other hand, Neiva et al. showed, in Caucasian skulls, that mean LWT was thinner than the one found in the present study (0.91 ± 0.43 mm). Again, instruments used to record the data might be the cause of this disparaty. Regarding the vertical height where LWT were measured, significant differences were found at 10 mm from the sinus floor of the edentulous region between the first molar and second premolar and between the second molar and second premolar, as well as at 15 mm between the first and second molar. Our results showed similarities to previous studies In addition, previous studies have assessed the influence of gender and age on the maxillary sinus anatomy; Results from our study implies that the less RH, the thinner the lateral maxillary sinus wall. As reported by Monje et al. who showed that bone density in maxillary sinus region is influenced by the remaining bone height, a thinner LWT suggests a lower bone 5 Journal of Periodontology; Copyright 2013 DOI: 10.1902/jop.2013 density CONCLUSION The maxillary sinus lateral wall tends to increase in thickness from the second premolar to the second molar and from 5mm up to 15 mm. In addition, residual ridge height, presence of teeth to adjacent the edentulous atrophic ridge, and age all have been shown to influence maxillary sinus lateral wall thickness. Nonetheless, each case must be individualized in order to foresee possible complications due to the anatomic variations. ACKNOWLEDGEMENT