Transcrestal sinus elevation in extremely atrophic bone (2-3mm of residual bone height) using PRFG-endoret as grafting material. A retrospective case series.
Corresponding author: Eduardo Anitua DDS, MD, PhD1,2,3
1Private practice in oral implantology, Eduardo Anitua Institute, Vitoria, Spain.
2Clinical researcher, Eduardo Anitua Foundation, Vitoria, Spain.
3University Institute for Regenerative Medicine and Oral Implantology – UIRMI (UPV/EHU-Fundación Eduardo Anitua), Vitoria, Spain. Dr. Eduardo Anitua, Eduardo Anitua Foundation; C/Jose Maria Cagigal 19, 01007 Vitoria, Spain; Phone: +34 945160653, e-mail: eduardo@fundacioneduardoanitua.org.
ABSTRACT
Introduction
Rehabilitation of the posterior maxilla with dental implants remains challenging in patients with severe vertical bone atrophy caused by sinus pneumatisation and post-extraction alveolar resorption. Transcrestal sinus floor elevation has progressively emerged as a minimally invasive alternative to the lateral approach, particularly when combined with short or extra-short implants and biologically driven regenerative protocols. The aim of this retrospective study was to evaluate the longterm clinical outcomes of transcrestal sinus elevation performed in severely atrophic posterior maxillae using PRGF-Endoret® as the sole grafting material.
Materials and Methods
A retrospective case series was conducted including patients treated between January 2010 and June 2015 with 5.5- and 6.5-mm implants placed in posterior maxillary sites with residual bone height ≤5 mm using transcrestal sinus elevation and exclusive use of PRGF-Endoret®. Only implants with a minimum of 10 years of follow-up after loading were included. Implant placement was performed by a single surgeon using a biologically guided low-speed drilling protocol with a frontal cutting drill for controlled sinus floor access. Primary outcome was vertical apical bone gain. Secondary outcomes included implant survival, peri-implant marginal bone loss, and complications.
Results
Thirty-five patients receiving 47 implants fulfilled the inclusion criteria. Mean residual bone height increased from 3.94 ± 0.82 mm to 7.15 ± 0.63 mm after treatment, resulting in a mean vertical gain of 3.21 ± 0.99 mm (p < 0.001). Mean insertion torque was 23.08 ± 3.36 Ncm. Implant and prosthetic survival reached 100% after a mean follow-up of 133.63 ± 16.29 months. Mean mesial and distal marginal bone loss was 0.51 ± 0.56 mm and 0.52 ± 0.50 mm, respectively. Minor complications included screw loosening and one provisional resin fracture.
Conclusions
Transcrestal sinus elevation combined with extra-short implants and PRGF-Endoret® appears to be a predictable long-term treatment option for severe posterior maxillary atrophy, achieving stable bone regeneration and excellent implant survival with minimal morbidity.
Introduction
Rehabilitation of the posterior maxilla with dental implants continues to represent one of the greatest challenges in oral implantology, especially in patients with advanced loss of vertical bone volume secondary to progressive maxillary sinus pneumatisation and physiological resorption of the alveolar process following tooth loss1-3. These anatomical alterations frequently result in insufficient residual bone height for the placement of conventional implants, requiring the clinician to resort to reconstructive procedures aimed at restoring adequate bone volume for functional rehabilitation of the posterior maxillary sector1,4,5.
For decades, sinus elevation through the lateral window approach was considered the reference procedure for the treatment of these atrophic situations, especially in cases with reduced residual bone heights (residual bone height less than or equal to 5 mm)6-8. However, the advancement of contemporary implantology toward less invasive protocols, together with the evolution of implant design and a better understanding of biomechanics and the biological processes associated with osseointegration, has progressively modified this therapeutic paradigm4, 9–12. Currently, transcrestal sinus elevation techniques have gained increasing relevance by allowing a significant reduction in surgical morbidity, operative time and complications associated with the lateral approach, while maintaining high implant survival rates and peri-implant bone stability13–17.
Since the original description by Dr. Robert B Summers, transcrestal techniques have undergone multiple modifications aimed at improving procedural safety and expanding their clinical indications. Initially, these techniques were reserved for situations with relatively favourable residual bone heights; however, the introduction of new surgical protocols and biomaterials has progressively extended their use to cases with more severe atrophy. In parallel, the development of short and extra-short implants has contributed decisively to this conceptual change14,15,18–22.
The combination of transcrestal sinus elevation and extra-short implants has become established as an alternative for the rehabilitation of the atrophic posterior maxilla23–25. With the aim of optimising this procedure, our group developed a technique based on biologically guided drilling using a frontal cutting drill as the final part of the protocol, designed to perform controlled and atraumatic access to the sinus floor26. This protocol allows progressive preparation of the implant bed, promotes preservation of the sinus membrane, and facilitates placement of extra-short implants with adequate insertion torque.
Additionally, the use of PRGF-Endoret as a biological grafting material in transcrestal sinus elevation procedures represents an alternative based on stimulation of the body’s own regenerative mechanisms, avoiding the need to use large volumes of biomaterials or heterologous grafts26–30. The autologous fibrin matrix generated through this technology acts as a biological scaffold rich in growth factors, promoting angiogenesis, cell migration, and new bone formation within the subantral space29,31,32. Different clinical and experimental studies have shown that the use of PRGF-Endoret may promote stable and predictable bone regeneration in sinus augmentation procedures, with adequate tissue maturation and high biocompatibility, while also reducing surgical manipulation and morbidity associated with the use of other grafting materials28,32–35.
The aim of the present retrospective study is to analyse the clinical behaviour of 5.5- and 6.5-mm implants placed in posterior maxillary sectors with reduced residual bone heights (up to 5 mm) by means of transcrestal sinus elevation using the frontal drilling protocol described by our study group, associated with the use of PRGF-Endoret as a biological grafting material. The evaluated outcomes include implant survival, peri-implant bone stability, vertical bone gain after the procedure, and possible complications during long-term clinical follow-up, with a mean follow-up exceeding 11 years, providing clinically relevant information on this minimally invasive approach in situations of severe maxillary atrophy.
Materials and Methods
Patients who underwent placement of 5.5- and 6.5-mm-long dental implants in residual bone crests with up to 5 mm of bone height, associated with transcrestal sinus elevation using PRGF-Endoret exclusively as grafting material, between January 2010 and June 2015, were retrospectively recruited. As a requirement to establish long-term follow-up, implants were required to have at least 10 years of follow-up after loading and patients had to maintain follow-up until the present with periodic radiographic controls.
All patients were evaluated before implant placement by means of diagnostic casts, intraoral examination, and dental CT (cone-beam) subsequently analysed using dedicated software (BTI-Scan III). Before implant placement, antibiotic premedication consisting of oral amoxicillin 2 g one hour before surgery and oral paracetamol 1 g (as analgesic) was administered. Subsequently, patients continued treatment with oral amoxicillin 500–750 mg every 8 hours (according to body weight) for 5 days.
Implant placement was performed by a single surgeon using the biologically guided drilling technique, at low rotational speed and without irrigation [36–38]. Final drilling of the sinus cortical plate was carried out using the frontal cutting drill (designed for this technique), allowing removal of the maxillary sinus floor without damaging the Schneiderian membrane39–42. Once the membrane became accessible and was elevated through the crestal perforation, the graft (PRGF-Endoret) was placed and the implant inserted using a surgical motor set at 25 Ncm and 25 rpm, completing implant insertion with a torque wrench.
At the end of surgery, a panoramic radiograph was obtained following a standardized positioning protocol. To ensure image reproducibility during follow-up, fixed references were used for patient positioning, including simultaneous support at the glabella and chin, as well as floor positioning references for proper body alignment. At all subsequent follow-up visits, new panoramic radiographs were obtained using the same technical protocol, allowing reliable comparison of longitudinal implant evolution and peri-implant bone level changes.
After implant placement, a waiting period of approximately four to five months was established for osseointegration before proceeding with the second surgical phase, depending on bone density and final insertion torque. At this stage, multi-im transepithelial abutments were placed, designed to support multiple screw-retained rehabilitations.
Radiographic evaluation of marginal bone loss was performed on the last orthopantomography obtained under these standardised conditions. Digital images were calibrated using dedicated radiographic analysis software (Digora for Windows, SOREDEX Digital Imaging Systems), using a known implant dimension as reference. After entering this calibration value, the software automatically corrected the magnification inherent to panoramic imaging, allowing accurate linear measurements.
Crestal bone loss was independently recorded on the mesial and distal surfaces of each implant. Marginal bone loss was evaluated by measuring the distance from the implant shoulder to the first visible contact point between bone and implant surface. Apical bone gain, in contrast, was quantified by a perpendicular measurement from the implant apex to the newly formed sinus cortical wall, forming a right angle (90°) relative to the longitudinal axis of the implant on the cone-beam acquired before implant loading.
Statistical analysis
For descriptive analysis, the implant was considered the unit of analysis for all variables related to location, dimensions, and radiographic parameters. Demographic variables and medical history were analysed considering the patient as the statistical unit. Distribution of quantitative data was assessed using the Shapiro–Wilk normality test.
Qualitative variables were expressed as absolute frequencies and percentages, whereas quantitative variables were described as mean and standard deviation.
Cumulative implant survival was calculated using the Kaplan–Meier method. The primary outcome of the study was vertical bone growth induced in the apical region following the transcrestal elevation technique. Secondary outcomes included implant survival rate and mesial and distal marginal bone loss. Statistical processing and data analysis were performed using SPSS v15.0 for Windows (SPSS Inc., Chicago, IL, USA).
Results
Thirty-five patients, in whom 47 implants were placed, fulfilled the inclusion criteria. All implants were inserted using transcrestal sinus elevation with progressive drilling and PRGF-Endoret as the sole grafting material. Implant placement was performed in the first and second maxillary molar regions, with the exception of one implant placed in position 15 (Figure 1). The most frequent position was tooth 26, accounting for 31.9% of cases.
[Figure 1
Caption: Implant locations included in the study]
Implant length was 5.5 mm in 17% of cases and 6.5 mm in the remaining 83%. Implant diameters ranged from 4.25 to 6.25 mm. Implant diameters and lengths are shown in Figure 2.
[Figure 2
Caption: Diameters and lengths of the implants included in the study]
Mean baseline bone height was 3.94 mm (± 0.82), while mean bone height after implant placement and consolidation was 7.15 mm (± 0.63). This represented a mean bone gain of 3.21 ± 0.99 mm compared with baseline conditions. Statistical analysis using paired sample comparison demonstrated statistically significant differences between both measurements (p < 0.001), confirming the ability of the procedure to predictably increase subantral bone volume in cases with reduced residual bone height (Figure 3).
Implant insertion torque ranged from 10 Ncm to 30 Ncm, with 25 Ncm being the most frequent value (57.4%) and a mean insertion torque of 23.08 (± 3.36).
[Figure 3
Caption: Initial and final bone height, showing the length of the implant inserted in each case]
All implants were restored with screw-retained prostheses placed on transepithelial abutments. Three cases were restored with single crowns (Unit – single transepithelial abutment), while the remaining cases received multiple restorations. Among the multiple prostheses, 12.8% corresponded to full-arch rehabilitations and 78.7% to fixed bridges.
Initially, restorations were fabricated in resin using prefabricated bar structures as progressive loading prostheses between 4 and 6 months after implant placement, with a mean loading time of 5.2 months (± 0.80). Definitive restorations in metal-ceramic were subsequently delivered within a period ranging from 5 to 7 months (mean: 5.6 months ± 2.3).
During the follow-up period, no implant failures were recorded, corresponding to an implant survival rate of 100%. Likewise, no prosthetic failures were observed. Reported complications included screw loosening in five cases and fracture of the resin component of the progressive loading prosthesis in one case.
Mean follow-up time was 133.63 months (± 16.29; range: 100–148 months). At the end of follow-up, mean mesial bone loss was 0.51 mm (± 0.56), while mean distal bone loss was 0.52 mm (± 0.50).
Figures 4–16 show two of the cases included in the study.
[Figures 4-16]
[Figures 4 and 5
Caption: Follow-up cone-beam images of the first case, showing a residual bone height of 3.2 mm, as observed, and planning of the implant to be placed using the transcrestal elevation technique]
Figure 6
Caption: Placement of PRGF-Endoret after preparation of the neo-alveoli and before implant insertion.
Figure 7
Caption: Postoperative radiograph showing the implant placed in position following transcrestal elevation.
Figure 8
Caption: Bone gain achieved with the procedure after implant integration.
Figure 9
Caption: Initial loading of the implant with the progressive loading prosthesis six months after implant placement.
Figure 10
Caption: Radiograph after placement of the definitive prosthesis.
Figure 11
Caption: Radiographic image at 10 years after loading.
Figure 12
Caption: Planning section of the second case, showing the residual bone height and the implant to be placed in the area.
Figure 13
Caption: Postoperative radiograph.
Figure 14
Caption: Cone-beam image before loading showing the vertical bone gain achieved in the area.
Figure 15
Caption: Radiograph of the implant during progressive loading.
Figure 16
Caption: Follow-up image with the definitive prosthesis at eight years.
Discussion
The findings of the present study confirm the effectiveness and predictability of the transcrestal sinus elevation technique using PRGF-Endoret® exclusively as grafting material for rehabilitation of the atrophic posterior maxilla. This surgical strategy not only allowed significant vertical bone gain after the intervention but also maintained high long-term peri-implant stability, with reduced marginal bone loss and a cumulative implant survival rate of 100% during follow-up. Overall, these results reinforce the validity of this minimally invasive and biologically optimised protocol for the treatment of severe maxillary atrophy.
The high predictability observed is probably related to the combination of different biological and mechanical factors integrated within the surgical protocol. The use of biologically guided drilling at low rotational speed, progressively adapted to the recipient site and finalised using a frontal cutting drill specifically designed to minimise the risk of Schneiderian membrane perforation, allows controlled and atraumatic access to the maxillary sinus15,26,43. Thanks to this approach, even in borderline situations characterized by limited residual bone volume or low bone density, it was possible to achieve adequate primary implant stability and subsequent successful osseointegration. Although a residual bone height greater than 5–6 mm has classically been considered necessary to indicate transcrestal techniques13,14,25,44, more recent evidence demonstrates that, through controlled surgical protocols and highly osteoconductive implant surfaces, favourable outcomes can also be achieved in heights below 4 mm [45,46]. Our results support this trend, showing 100% implant survival and absence of intraoperative surgical complications, which is especially relevant considering that sinus membrane perforation remains the most frequent complication of these procedures, with reported incidences ranging from 4% to 12%4,5,47–50.
Another notable aspect of this study was the high peri-implant bone stability observed after more than one decade of functional follow-up. Recorded marginal bone loss was 0.51 ± 0.56 mm mesially and 0.52 ± 0.50 mm distally, values that are particularly favorable compared with other published series on sinus elevation in the atrophic posterior maxilla. These results fall within the lowest range reported for transcrestal elevation procedures. In a recent prospective study with a mean follow-up close to 8 years, Jiménez-Guerra et al. [51] reported a mean vertical gain of 4.3 ± 0.4 mm, implant survival of 97.2%, and biological complications below 10%, although peri-implantitis was observed in 9.3% of implants. Likewise, in a systematic review focused on transcrestal sinus elevation with simultaneous implant placement, Lin et al. [25] reported mean marginal bone loss values of 0.16 ± 0.62 mm for short implants versus 0.33 ± 0.71 mm for conventional implants, suggesting that the combination of transcrestal approaches and reduced-length implants may be associated with limited crestal remodeling and clinically stable long-term outcomes.
Precisely, one of the distinguishing features of the present study is the exclusive use of PRGF-Endoret® as regenerative material. Unlike most publications on transcrestal sinus elevation, which are based on heterologous biomaterials or graft mixtures, subantral regeneration in this series was performed exclusively using an autologous matrix rich in fibrin and growth factors. Studies specifically published on PRGF-Endoret® have shown that this technology promotes early angiogenesis, cellular migration, and tissue maturation, while improving biological clot stability within the elevated space26,27,32,52–54.
Our study group has experimentally demonstrated that PRGF-Endoret® stimulates proliferation and activity of primary human osteoblasts, promoting bone regeneration phenomena through autocrine and paracrine mechanisms [31,32,54]. Subsequently, Solakoglu et al. [30], in a review focused exclusively on the use of PRGF-Endoret® in guided bone regeneration and sinus elevation, described favourable histological and radiographic outcomes, with adequate tissue integration and high biocompatibility of the material.
Another relevant aspect is that the exclusive use of PRGF-Endoret® eliminates the need to introduce slowly resorbing biomaterials into the sinus cavity. Although xenogeneic grafts have demonstrated good clinical results, different histological studies have shown prolonged persistence of residual particles even years after surgery [55–57]. In contrast, the use of an autologous matrix allows regeneration based fundamentally on newly formed bone and vital tissue, while also reducing surgical manipulation and morbidity associated with harvesting additional grafts [58–60]. This concept becomes particularly relevant in minimally invasive transcrestal procedures, where surgical simplicity and initial biological stability constitute key factors for treatment success and long-term predictability.
Conclusions
The results obtained suggest that the combination of transcrestal sinus elevation, extra-short implants, and PRGF-Endoret may constitute a valid alternative even in situations traditionally considered borderline for this type of approach. Beyond the implant survival recorded, the bone stability observed after more than 11 years of follow-up provides particularly relevant clinical information regarding the capacity of this protocol to maintain stable functional and biological outcomes over the long term in patients with severe posterior maxillary atrophy.
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