Anatomical Risk Factors Associated with Immediate Extraction Placement in the Posterior Maxilla: A Human Retrospective Cone-Beam Study

Purpose: The aim of the study was to analyze the spatial relationship between the sinus floor and the alveolar bone of maxillary premolars and molars in order to assess the amount of basal bone available for immediate extraction placement of endosseous implants. Materials and Methods: All the cone-beam computerized tomographic (CBCT) scans taken over a three-year period at four centers were identified. The subsinus bone height (SBH) was evaluated by measuring the distance between the sinus floor and the first and second premolar root apexes. The interradicular septum bone height (ISBH) of all the first and second molars was also measured, and the presence or absence of sinus-floor invagination between the molar roots was recorded. Results: Five hundred twenty-six (526) CBCT scans of fully or partially dentate maxillary arches were examined. The root apex was inside the sinus of 1.8% of all the first premolars. It approximated the sinus floor of 5.3% of them, and the distance between the two points was between 1 and 3mm of 20%, between 3 and 7mm for 34.1%, and more than 7mm for 34.1%. For the second premolars, the findings were 13.5% (inside the sinus), 10.5% (touching the sinus), 32.8% (1-3mm of distance) 28% (3-7 mm), and 15.2% (more than 7mm). Root invagination was noted in 50.2% of the first molars and 43.1% of the second molars, with the ISBHs ranging from 13.4% to 56.9%. Conclusion: Radiological evaluation is essential to determining whether implants should be placed immediately after extraction of maxillary premolars and molars. J o u r n a l D e n t a l a n d O r a l I m p l a n t s ISSN NO: 2473-1005 RESEARCH ARTICLE DOI : 10.14302/issn.2473-1005.jdoi-16-999 Correspondence to: Dr. F. Amato, Viale Alcide de Gasperi, 187, 95127 Catania, Italy. Mail: dr.amatofrancesco@libero.it


Introduction
Although the use of osseointegrated implants to replace missing teeth has become a predictable procedure with high implant survival rates 1,2 , success rates in the posterior maxilla are lower due to the poor quality and inadequate height of bone. 3 Furthermore, after tooth loss, the periosteum of the maxillary sinus can exhibit increased osteoclastic activity, which can cause bone resorption 4 and a resumption of the physiological sinus-floor pneumatization process. 5,6 The result is a progressive reduction of the bone height.
Subsinus alveolar bone height (SBH) has been defined as the distance between the floor of the maxillary sinus and the alveolar crest. 7 A lack of SBH may be treated in different ways depending on the degree of atrophy.
Options include sinus lift augmentation, vertical bone regeneration of the alveolar ridge, interpositional grafting, short implants, or use of alternative sites (tuberal, pterygoid, zygoma, or tilted). 8 Several authors have advocated that one of the main criteria for achieving good primary stability with implants immediately placed in extraction sites is to engage the implant in the bone apical to the root apex. [11][12][13] When taking this approach, however, it is essential   The aim of this retrospective study was to further investigate the relationship between the alveolar bone available for implant insertion and the anatomical structures located apical to it in the maxillary premolar and molar area, including the interradicular bone septum height (IBSH) in the molar area. The goal was to create clinical guidelines so that dentists can better avoid sinus perforation at the time of extraction followed by immediate implant placement in the posterior maxillary area.

Material and Methods
All the cone-beam computerized tomographic (CBCT) scans of patients with fully or partially dentate maxillary arches that were taken over the previous three years were identified at a private dental practice in Catania, Italy, as well as at three different radiology centers. The scans were obtained using several Findings for the premolars were classified into five groups, as follows: • The root apex was located inside the sinus (Group A) • The distance of the root apex from the sinus floor was 0 mm with the root apex, but not penetrating in the sinus (Group B) • The distance was 1 to 3 mm (Group C) • The distance was 3 to 7 mm (Group D) • The distance was more than 7 mm (Group E)   When the atrophic bone is related to the pneumatization of the maxillary sinus, elevation of the sinus floor has been used to enable implant placement. 22 Depending on the amount of residual bone, different bone-augmentation techniques have been proposed, including the lateral window approach described by Boyne and James (1980) and Tatum (1986). 23,24 The crestal approach, in which the Schneiderian membrane is lifted using an osteotome, was first described by Summers (1994). 25 In both techniques, the simultaneous insertion of implants is recommended if the initial bone height is a minimum of 4 to 6 mm. 26 Otherwise a delayed insertion is preferred. 27 While sinus augmentation has been demonstrat-ed to be a predictable technique for increasing bone height in deficient posterior maxillary ridges prior to implant placement, 28  In all the CBCT scans that were analyzed, the distance between root apexes and maxillary sinuses was least for all the second premolars and first molars. This finding was not uniform, however, because of the anatomical variability of sinus growth.
One of the notable anatomical characteristics was the symmetry of the anatomical conditions in either side of each patient's mouth. In the premolar and molar areas, the presence of root invagination inside the sinus was highly symmetrical both in terms of the presence or not of the invagination and in the amount of intrusion inside the antrum. This can probably be explained by the equivalent development of sinus pneumatization on both sides of the mouth and the fact that the premolar and molar roots on each side of any person's mouth tend to be the same shape and length.

Conclusion
The data gathered in this study clearly show a close relationship between the maxillary root apexes and the inferior border of the sinus floor. Whenever CBCT or other radiological examination reveals the tooth apex to be in close proximity to the sinus floor, the use of short