Abstract: Trans-sinus implant is a technique for the immediate fixed restoration of the posterior maxilla in patients with reduced bone height and sinus pneumatization. A longer implant can be inserted, with crestal position at the first molar or at the second premolar and with 30°-45° degrees of mesial inclination, through the sinus to have its apical portion anchored in the anterior sinus wall bone, engaging 3 cortical layers: the alveolar crestal bone, floor of the sinus cavity, and anterior sinus wall with its body. The level of primary stability is theoretically higher than conventional implant insertion with simultaneous sinus elevation. Therefore, delivering an immediate restoration is possible, resulting in reduced total treatment time and the prompt reestablishment of function and esthetics for the patient. This approach is suggested in the posterior maxilla atrophy and when an 'L'(or concave) anterior sinus wall anatomy is present. This technique could be considered as the first choice of treatment option when indicated due to some clinical advantages to utilization of zygomatic implants. There is less surgical morbidity and is similar to a standard lateral sinus approach. Potential complications compared to zygomatic implants are reduced as the surgical trauma to the patient during operative period is reduced.

Key words: trans-sinus, implant, atrophic maxilla, maxillary sinus, primary stability