Immediate Rehabilitation of the Severely Atrophic Maxilla Using Trans-Sinus Nasal Protocol and Extended Length Subcrestal Angulated Implants. Case Series With 1-Year Follow-Up

Immediate fixed full-arch rehabilitation of the severely atrophic Cawood and Howe Class IV–VI¹  maxilla is a challenging treatment modality that requires careful planning and execution of advanced surgical and restorative protocols to achieve a successful outcome. Surgical protocol recommendations specifically for immediate rehabilitation are dependent on the volume and location of the remaining residual alveolar ridge²  and, more importantly, the presence of cortical load bearing bone that can mechanically fix an implant adequately.³  The immediate loading site classification developed by Jensen³  recommends the placement of distally angulated trans-sinus implants and zygomatic implants for the most severely atrophic maxillae when the alveolar process is absent and the sinuses project anteriorly to the intercanine region of the anterior maxilla. The five clinical case reports outline immediate rehabilitation of the severely resorbed Cawood and Howe Class V–VI¹  maxilla using extended length subcrestal angulated (ELSA) implants for posterior support.

The recommended inclusion criteria for the use of an ELSA implant in conjunction with a trans-sinus nasal protocol⁴  include: (1) severe atrophy of the posterior maxillary sinuses with pneumatization, (2) extension of the anterior recess of the maxillary sinus in the region of the lateral incisor or canine, (3) residual crestal bone suitable for implant placement limited to the intercanine region, (4) dehiscence or periodontal lesions in the first or second premolar region limiting the placement of implant fixtures, (5) the inability to achieve an adequate anteroposterior spread of at least 12 mm with straight or angled implants with or without simultaneous sinus augmentation, (6) a minimum thickness of 1 mm and minimum buccal-palatal width of 7 mm of crestal bone in the region proposed for the implant fixture head (to ensure there is 2 mm of buccal bone adjacent to the implant fixture head), and (7) when the use of zygomatic or pterygoid implants is contraindicated. The inclusion criteria are an extension of the criteria described Nicoli et al.⁴  For the 5 clinical cases discussed, all patients presented with a severely resorbed Cawood and Howe Class V–VI¹  maxilla and adequate distance between anterior and posterior implants would not be achieved with the graftless All-on-4⁵ protocol.

The ELSA implants are developed by Southern Implants (Irene, South Africa). The case reports outline the use of ELSA implants utilizing a trans nasal sinus technique with simultaneous sinus augmentation for the rehabilitation of the severely resorbed maxilla (Figure 1). The implant specifications include 4.0 mm diameter external hexagonal platform with a 24° subcrestal angulation and 5.0 mm diameter external hexagonal platform with a 36° subcrestal angulation. The implants are fabricated in lengths are 18 mm, 20 mm, 22 mm, 24 mm, and 26 mm (Figure 2).

After a detailed social, medical, and dental history, as well as clinical and radiographic examination, a treatment proposal was formulated that best addresses the concerns and wishes of the patient. Specifically, a detailed diagnostic work up of a 3-dimensional radiographic assessment is critical for treatment planning prior to implant placement and prosthetic rehabilitation. The anatomy of the anterior maxilla, nasal bone, sinus cavity, and posterior residual alveolar ridge in relation to the proposed vector and position of the implant osteotomy should be carefully considered with the goal to maximize the distance between implant fixtures and primary stability for immediate loading.

A full-thickness flap revealing the nasal fossa and lateral sinus wall and extending to the maxillary tuberosity is raised. An alveolectomy is considered to level the residual ridge. The lateral antrostomy window extends medially and superiorly to allow visualization and careful elevation of the Schneiderian membrane (Figure 3). The initial osteotomy position, vector, and depth is determined by anatomical features including the severity of posterior maxilla residual ridge resorption, anatomical contours of the sinus cavity, and the anterior maxilla. A round bur is used to mark the most appropriate position for the commencement of the osteotomy on the crest of the ridge. Due to the limited access and complexity of the procedure, a non-limiting surgical guide is recommended.

Protection of the Schneiderian membrane is required with a periosteal instrument during development of the osteotomy. With copious saline irrigation, the osteotomy is developed in the residual alveolar ridge and into the medial wall of the sinus cavity at an accentuated distal inclination (Figure 4).

The sinus cavity is lined with a resorbable collagen membrane with rigid fixation when required⁶  prior to implant fixture placement. The osteotomy length is confirmed with a surgical measuring tool, and the correctly selected implant length is rotated into the osteotomy (Figure 5). The implant fixture mount is removed and replaced with a straight or angulated multi-unit abutment depending on the prosthetic screw vector.

After placement of the implant fixture, sinus augmentation is completed with a particulate bone graft. A resorbable collagen membrane is fixated over the lateral window (Figure 6). The soft tissues are sutured to achieve primary closure.

In addition, a minimum of 2 anterior implants will likely achieve good insertion torque by engaging into bone at the nasal crest. If the 4-implant scheme has a composite insertion torque of 120 Ncm and vertical stability of all 4 implants is present, immediate function can proceed.⁷ 

For immediate loading, titanium cylinders are attached to the multiunit abutments. Various immediate prosthetic techniques can be utilized to record the position of the implants and deliver an immediate full arch prosthesis. The author favors the same-day implant bridge clinical and laboratory protocol⁸  using a provisional milled polymethylmethacrylate (PMMA) prosthesis to restore the maxillary arch after implant placement.

A 50-year-old patient requested rehabilitation of his terminal dentition to an optimal level of health, functionality, and esthetics. The maxilla was classified as Class D according to the All-on-4 site classification³  (Figure 7). To satisfy the patient's chief requests, the proposed treatment entailed immediate implant-supported fixed prosthetics. The preliminary diagnostic, presurgical, and restorative workup was completed. The remaining maxillary dentitions were removed, followed by bilateral sinus augmentation using a 50:50 mixture of granulated autogenous bone harvested from the posterior mandible and xenograft (Bio-Oss, Geistlich). Three straight implants were placed in the anterior maxilla and 2 ELSA implants were placed posteriorly. The ELSA 4-mm diameter × 26-mm length x 24° implant subcrestal angled implants transversed the grafted sinus and engaged the lateral wall of the nasal bone. Angulated multiunit abutments were placed on the ELSA implant fixtures. The crests of the ELSA implants were situated in the site of the first permanent molar. The implants were restored immediately with a provisional fixed PMMA prosthesis. After biological osseointegration, a definitive all-ceramic prosthesis was inserted (Figures 8 and 9).

A 60-year-old female presented with terminal maxillary dentition, significant resorption of the posterior maxilla, and pneumatization of the sinus (Figure 10). The remaining dentition was removed followed by immediate placement of an ELSA 4-mm diameter × 26-mm length × 24° implant subcrestal angle with a straight multiunit abutment. The crest of the implant fixture was positioned at the upper left first permanent molar site (Figure 11). The sinus graft was completed using a xenograft particulate (Bio-Oss, Geistlich). The implant apical threads engaged the lateral nasal bone. A subcrestal angulated 5-mm diameter × 18-mm length × 36° subcrestal angulation implant was placed using osseodensification drills with a significant distal inclination to engage the anterior maxilla. A 30° angulated multiunit abutment was placed to assist passivity of fit by reducing the divergence of all the abutments to less than 40°.³  Six were placed with favorable distribution to eliminate prosthetic cantilevers (Figure 12). An immediate implant-supported provisional prosthesis was provided followed by delivery of an all-ceramic full-arch prosthesis 12 months after implant fixture placement (Figure 13).

A 70-year-old male presented with a problematic partial maxillary prosthesis, deterioration of the remaining dentition, and a Class D atrophic maxilla³  (Figure 14). The patient requested a fixed restorative solution. The surgical phase sinus augmentation with 50:50 mix autogenous and xenograft (Bio-Oss, Geistlich) followed by simultaneous bilateral placement of ELSA 5-mm diameter × 26-mm length × 24° subcrestal angled implants (Figure 15). Multiunit abutments were used, and passivity of fit achieved. The insertion torque of the implants was 35Ncm and adequate for immediate loading with a fixed full-arch prosthesis. Prosthetic cantilevers were eliminated by the posterior positioning of the implant fixture (Figure 16).

A 50-year-old male presented with a terminal dentition and Class D atrophic maxilla requesting an immediate implant-supported fixed prosthesis (Figure 17). The remaining problematic dentition was removed followed by bilateral sinus augmentation and implant placement using ELSA 4-mm diameter × 28-mm length × 24° subcrestal angulated implants. The implants engaged the lateral nasal wall and transverse the augmented sinus cavity. Six implants were placed in the maxilla with an insertion torque all greater than 35Ncm (Figure 18). The implants were immediately loaded. The crest of the ELSA implants were positioned in the first permanent molar site. The subcrestal angulation change promotes favorable bone adaptation at the crest, which is particularly beneficial when crestal bone thickness is limited to less than 3 mm (Figure 19).

A 70-year-old female presented with an edentulous Class D atrophic maxilla (Figure 20). She requested rehabilitation of the maxilla with a fixed prosthesis. Two straight anterior implants and two distal angulated implants were placed. A 5.0-mm diameter × 15-mm length × 36° implant fixture and an ELSA 5.0-mm diameter × 26-mm length × 36° implants were placed simultaneously with sinus augmentation using 100% xenograft (Bio-Oss, Giestlitch) (Figure 21). The primary stability was favorable for immediate loading with a PMMA prosthesis.

Favorable ELSA implant stabilization for immediate rehabilitation of the severely atrophic Cawood and Howe Class V–VI¹  maxilla is achieved by engaging the anterior maxillary and lateral nasal wall residual cortical bone. The implant transverses a simultaneously augmented sinus and emerges at the region of the first permanent molar. In late-stage atrophy, the paranasal bone is often the only available cortex for the maxilla other than the palate.⁷  The cortical bone regions of the maxilla and nasal bones remain the best aiming point to consistently achieve favorable primary stabilization of the apical portion of the implant fixture, which is necessary for predictable immediate loading. It suggests that the engagement of the maxillary and nasal cortical bone is more critical than the total volume of cancellous bone that encapsulates the body of the implant. A failure to engage cortical bone apically by the ELSA implant is unlikely to achieve favorable and high primary stability to predictably offer immediate loading.

A distal tilted implant and simultaneous sinus graft protocol to support the posterior occlusion for severely atrophic Cawood and Howe Class V–VI¹  or the Class C and D maxilla³  is accepted in the literature. The immediate loading solution offers numerous biological and mechanical advantages with high success rates.^9–11  The novel features of the ELSA implant facilitate immediate loading of the severely atrophic maxilla. The ELSA implant allows the distal tilt to be accentuated up to 60° relative to the residual alveolar ridge to maximize the distance between anterior and posterior implants. The 24° subcrestal angulation, platform switch feature, and use of multiunit abutments promotes passivity of fit of a fixed full-arch prosthesis. The maximum divergence of the multiunit abutments collectively must be less than 40° degrees for passivity of fit of a full-arch abutment level prosthesis.¹²  The subcrestal angulation of the implant maximizes bone-to-implant contact at the critical crestal region and eliminates the necessity of distal bone reduction to fit an angulated multiunit abutment as is usually required with a conventionally straight distal-angulated implant fixture.

ELSA implants may provide an alternative to zygomatic implants for the most severe atrophic maxilla, extending the use of tilted implants to immediately restore the severely resorbed Jensen³ “Class D” maxilla. Although the original design and concept of the ELSA implant was not intended as an alternative to zygomatic implants, the implant appears to be beneficial for posterior occlusal support of a full-arch fixed prosthesis by engaging the anterior maxillary bone. Compared to zygomatic implants, ELSA implants may be associated with a lower morbidity^3,13  and enhanced versatility of the prosthetic screw axis angulation. The ELSA implant is an extension of the biaxial range of dental implants developed by Howes.¹⁴ 

ELSA implants promote favorable biomechanics for the full-arch prosthetic system by maximizing the anteroposterior spread of implants. This effectively reduces the cantilever length of the prosthesis and as a consequence provides better load distribution^5,15,16  and reduction in stress generation.^17,18  Scientific studies on the biomechanics of the multiunit abutments and ELSA implant combined mechanical system in a full-arch rehabilitation is required.

Five case reports documenting successful immediate rehabilitation of a severely atrophic maxilla have been described using ELSA implants and a trans-sinus nasal protocol. The use of ELSA implants improves the biological and prosthetic advantages associated with the use of tilted distal implants in the rehabilitation of a severely atrophic maxilla, and may reduce the necessity of zygomatic implant placement for posterior occlusal support for the most atrophic maxilla rehabilitation.

Cosimo Petrucci for the development of the same day implant bridge protocol and fabrication of the zirconia prostheses.