# Crystal Sinus Lift with the Hydrodynamic Technique: Prospective Clinical Study at 3 Years Follow-Up
## 1 Introduction  
Dental implants are currently recognized as a viable therapeutic alternative for replacing missing teeth [1; 2; 3]; however, their placement may be hindered by several issues [4; 5].  
The placement of dental implants in the posterior maxilla is often complicated due to the reduced vertical height of the residual bone ridge, typically resulting from post-extraction bone resorption and subsequent preumatization of the maxillary sinus [6; 7]. Among the various surgical procedures proposed over the years for the implant-prosthetic rehabilitation of the atrophic posterior maxillary sector, sinus elevation with simultaneous graft material placement represents a valid therapeutic solution for restoring correct inter-arch relationships [8; 9].  
In 1980, [PERSON] and [PERSON] introduced the first sinus floor elevation technique, which involves lifting Schneider's membrane by opening a bone window in the lateral sinus wall and filling the subantral space with graft material [10]. In 1986, [PERSON] developed a less invasive surgical approach through the crestal route, which was later refined by [PERSON] in 1994 with the introduction of the osteetome technique [11].  
The Osteotome sinus Floor Elevation (OSFE) procedure reduces treatment morbidity and invasiveness by using bone from the osteotomy site preparation to elevate the sinus floor. Conversely, the Bone-Added Osteotome sinus Floor Elevation (BAOSFE) techniqueachieves the same result using graft material driven into the surgical site through a series of osteotomes. Both techniques are considered more reliable when the residual bone ridge height is at least 5-6 mm [12; 13].  
To avoid greenstick fracture of the sinus floor using osteotomes, [PERSON] and [PERSON] proposed a new surgical procedure involving a specific sequence of drills to perforate the sinus floor [14]. Laceration of the Schneiderian membrane during sinus floor perforation with rotary instruments is less frequent than with sinus floor fracture using osteotomes. The main limitation of transcrestal techniques is the uncertainty of a possible perforation of the sinus membrane. However, an endoscopic study has shown that the sinus floor can be raised up to 5 mm without tearing the membrane [15].  
Crestal sinus elevation promotes simultaneous implant placement in cases where there is sufficient residual bone crest size to achieve primary implant stability. If this is not possible, crestal sinus elevation can be performed with a delayed approach (Future Site Development) to create adequate bone volume for subsequent implant placement [16].  
In 2009, [PERSON] and [PERSON] introduced the gel pressure technique, which involves using injectable grafts in gel form to create controlled pressure capable of lifting the sinus membrane [17]. The biomaterials used for this purpose consist of micronized allogeneic, xenogeneic, or alloplastic graft particles embedded in a collagen matrix or water-based gels, characterized by a pasty consistency and a smooth surface that likely prevents accidental perforation of the Schneiderian membrane during elevation [18].  
This surgical technique utilizes the hydraulic pressure generated during the injection of the gel graft through the crestal antostomy to detach the sinus membrane from the bone walls and simultaneously fill the sub-antral space, significantly reducing surgical time. This allows for increased vertical space available for dental implant placement without needing more invasive surgical techniques [19]. Although graftless sinus lift procedures have been described over the years, using bone substitutes in the transcrestal approach allows greater vertical bone gain and can also be applied in cases with residual bone ridge height \(<\) 5 mm [20].  
The aim of this prospective clinical study was to evaluate the implant survival rate, marginal bone loss, and surgical complications in single dental implants placed in the posterior atrophic maxilla according to the transcrestal sinus lift procedure performed with injectable graft materials in gel.