The objectives were to assess the sinus anatomy and alveolar ridge dimensions and to identify clinical factors and morphological relationships that may predict the characteristics of the sinus anatomy. A total 336 edentulous molar and 168 edentulous premolar regions were analyzed. The mediolateral maxillary sinus (5 mm and 10 mm above alveolar bone), lateral maxillary sinus wall, ostium height, and alveolar ridges were measured. Measurement regions were defined by radiopaque simulation of the restoration goal. Mean molar mediolateral dimensions were >10 mm: first molar, 11.8 mm (range 3.8–21.1 mm); second molar, 12.2 mm (range 7.9–20.1 mm). The extent of the sinus differed significantly between premolars and molars ( P < 0.001). The first molar region had the highest mean value for the lateral sinus wall (2.4 mm, range 0.2–7.9 mm) and the greatest distance between the alveolar crest and simulated restorative goal (8.1 mm, range 1.1–16.3 mm). Septum prevalence was 46% in the molar region and 27% in the premolar region. A lower alveolar ridge height was associated with a wider transverse extent of maxillary sinus and consequently longer distances between the crest and restorative goal. Systematic three-dimensional analysis of the maxillary sinus yields precise preoperative information about sinus configurations. There were significant variations and relationships among characteristics of the maxillary sinus, ridge, and the restorative goal.
Although the success of implant therapy is highly predictable, the surgical placement of dental implants is associated with various complications due to anatomical limitations. Most studies on the anatomy of the jaw within the context of the insertion of dental implants have analyzed the interforaminal or posterior region of the mandible. Comparable studies on the complete anatomy of the maxilla are rare; in most investigations, only single aspects have been considered (e.g., Schneiderian membrane or septa). However, anatomical or surgical findings can necessitate deviations from the standard procedure during maxillary sinus elevation and may lead to complications.
The insertion of dental implants in combination with lateral or transalveolar maxillary sinus floor elevation is a reliable technique with a high implant survival rate and low incidence of surgical complications. The most common intraoperative complication is damage to the Schneiderian membrane. The residual alveolar bone height at the implant recipient site is a key factor in the risk of sinus membrane perforation during crestal sinus elevation. In general, the perforation limit of the sinus membrane after elevation is higher with a greater residual ridge height.
Several studies have found that the sinus floor elevation procedure is hindered by septa. Antral septa are present in approximately 20–35% of maxillary sinuses. A single septum is much more common than multiple septa, and mediolaterally (transversely) oriented septa are more frequent than anteroposteriorly (sagittally) oriented septa. In 2013, Wen et al. classified septa into three categories: easy (E), moderate (M), and difficult (D). These classifications are based on the location, number, orientation, and size of the antral septa. Corresponding treatment approaches were suggested for each category.
Comparisons of cone beam computed tomography (CBCT) imaging with conventional computed tomography (CT) for pre-surgical implant assessments have revealed that CBCT is superior to CT for all investigated anatomical structures. To avoid unnecessary surgical complications, detailed knowledge and timely preoperative identification of the anatomical structures inherent to the maxillary sinus are required. Thus, the aim of this study was to assess the relevant characteristics of the maxillary sinus anatomy (i.e., septa, dimensions of the lateral sinus wall, and the mediolateral dimension of the sinus) and the alveolar ridge dimensions by analyzing a high number of investigation sites. It was also sought to determine whether there are clinical factors and potential morphological relationships that could serve as predictive markers for the occurrence of specific anatomical characteristics of the sinus.
Materials and methods
All images used in this study were obtained from the patient database of the department of oral and maxillofacial plastic surgery between January 2012 and December 2014. No additional radiographic images were taken for this study.
The CBCT examinations (Galileos Comfort; Sirona Dental Systems, Bensheim, Germany) were performed with a scanning template. Dental prostheses were fabricated and duplicated in radiopaque acrylic resin. The volume size of the CBCT was 15 cm × 15 cm × 15 cm. Galaxis software (Sirona Dental Systems) was used for image acquisition and to export the DICOM images. Planning software (coDiagnostiX; Dental Wings Inc., Montreal, Canada) was used to provide real three-dimensional (3D) information for planning implant positions and calculating the morphological shape of the mandibular regions analyzed in this study. 3D planning was conducted on a routine basis to obtain a surgical guide template. In all cases, the template was used during surgery as a drill guide.
The maxillary edentulous first and second molar region and the maxillary edentulous first and second premolar region were investigated. Inclusion criteria for the selection of samples were as follows: (1) unilateral or bilateral loss of one or more of the maxillary teeth in question (first and second molar, first and second premolar); (2) investigated sites with a vertical alveolar bone height of up to 10 mm and sufficient width for an implant of ≥4 mm in diameter; (3) virtual plan of implant positions using CBCT data and surgical guide templates; (4) radiopaque simulation of the fixed partial denture for the relevant region; this enables precisely positioned calculations of morphological shape, which are central to the restorative goal ( Fig. 1 ). In the transverse direction, an alteration of the ideal implant axis (the implant axis is located in the central fissure of the crown) was allowed in order to avoid perforation of the palatal or lateral sinus wall.