Krekmanov et al.26 and Aparicio et al.27 presented the first papers in which a combination of tilted and axial implants was used in patients with severely reabsorbed posterior maxillae. The results indicate that the use of tilted implants is an effective and safe alternative to maxillary sinus floor augmentation or bone grafts procedures.
Peñarrocha-Oltra et al.28 in 2013 wrote that tilted implants, both used alone and combined with axially placed implants and rehabilitated with different prosthetic options have high success rates, minimal complications and high patient satisfaction.
Additionally, Balleri et al.29 presented a very good outcome with 20 fixed partial dentures supported by two implants, one tilted and one axial, in the retro-canine bone triangle. In a recent finite element study for two splinted implants, it appeared that tilting of the distal fixture does not stress the peri-implant bone as compared with the mesial axial fixture30. It was also demonstrated that tilted posterior implants were mechanically more advantageous than distal cantilever units31. Finally, the study of Barnea32 demonstrates no effect of implant angulation on peri-implant bone loss in the posterior maxilla. Nunes et al.33 Analyzed the width and the height of bone volume of the edentulous posterior maxilla using CBCT scans from 122 patients. They found that a high percentage (54%) of molar edentulous sites exhibited a reduced bone height (less than 5mm) and do require a sinus floor elevation procedure if implant therapy is chosen as a treatment option. However Nunes et al. did not take in consideration the possibility of tilted implants placement. On the contrary, Tolstunov et al.34 measured the average bone volume of the edentulous maxilla with cone-beam computerized tomography scans from 30 patients and determined its suitability for implant treatment without additional bone grafting. The results indicated that in many maxillary edentulous cases the existing bone volume can be often enough for a full-arch maxillary implant treatment with also tilted implants, without an additional trauma or expense associated with bone grafting or sinus lift.
Candel Marti et al.35 Evaluated soft tissue conditions and bone loss around palatal positioned implants supporting fixed full-arch prostheses to rehabilitate edentulous atrophied maxillae and compare them with conventional well-centered implants placed in non-atrophic maxillae after a minimum follow-up of 5 years. The results suggested that palatal positioned implants may be a good treatment alternative for patients with severe horizontal maxillary alveolar bone atrophy.
Owing to mechanical and anatomic difficulties, implant treatment in the atrophic maxilla represents a challenge.
The short and ultra-short implants in the posterior areas could be an alternative, but the trabecular compartment of the canine/premolar region offered higher quality when compared with the posterior maxilla. In addition, the basal bone showed a higher density than the alveolar bone. Corroborating the statement, Gonda et al.36 showed that premolar areas offer the most favourable scope in terms of bone height, width, angulation and quality.
In this paper the examiners were able to find enough bone to adequately distribute the virtual tilted implants in all cases except two. This study presents some limitation such as the retrospective nature of the present analysis and the virtual placement of the implants. Nevertheless, the statistical analysis demonstrates that an implant could be longer if its angulation is more accentuated. Hence, tilting implants would allow inserting the fixture apex in a high bone density area. Longer iuxtameatal implants in the mid-maxilla area consent more implant stability and, eventually, an immediate prosthetic load37–38.
Benefitting from the virtual plan previously developed, the implants will unlikely exceed the cortical lamina of the nasal lateral wall. In the eventuality that it happens, the associated risks may be epistaxis, implant displacement in the nasal cavity and rhinitis. Nonetheless, this statement has to be confirmed through future clinical studies.
These tilted implants do not compromise implant placement in the anterior maxilla because they have a marked angulation in the palatal sense. But in the ortho-panoramic radiography the correct vestibular-palatal angulation of the implants cannot be planned: only CBCT scans can suggest the ideal angulation with extremely high precision. With this paper, clinicians could become aware of the importance of the 3D anatomical view to evaluate the amount of cortical bone around the nasal cavity and could learn the importance of simulation software to virtually insert implants also in severely atrophic maxillae.
Among CBCT scans gray-scales vary widely due to different factors, such as the lack of grey level uniformity, the presence of artifacts, the effects of scatter and beam hardening39. On the other hand, different studies demonstrated how grey levels of CBCT can be used to derive Hounsfield units40–41. The gray-scale outcomes reported in this study could suggest that the peri-implant bone density was greater than the average density of the cancellous bone. It indicates that the apex of the iuxtameatal fixtures is effectively inserted in the cortical bone of the walls of the nasal meatus.
No studies were found measuring the atrophic maxilla bone volume related to tilted implant treatment. The absence of similar studies in the scientiﬁc literature limits the founding of comparisons with other study.