Although a number of approaches to implant-supported restoration of severely atrophic maxillae and mandibles have been developed, most of these treatments are costly and protracted. An exception is the All-on-Four concept, which uses only 4 implants to support an acrylic, screw-retained provisional prosthesis delivered on the day of implant placement, followed by a definitive prosthesis approximately 4 months later. After the introduction of a new implant design in 2008, a new protocol was developed for provisionally treating patients with severely atrophic jaws using the All-on-Four concept and 3.5-mm-diameter implants. This article describes that protocol and reports on the results of 227 implants after 1 to 3 years of follow-up. The cumulative survival rate was 98.7% at the end of 3 years, with a 100% prosthetic survival rate. Combining the 3.5-mm-diameter NobelActive implants with the All-on-Four concept promises to become a new standard of care for severely compromised patients.
One of the greatest challenges in implant dentistry is the treatment of patients with severely atrophic jaws (Figure 1a through c). Such atrophy can be horizontal or vertical or both; even if sufficient vertical bone is present, lack of ridge width can still preclude treatment with implants that are 4 mm in diameter or wider. Over the years, many techniques, procedures, and materials have been introduced to solve the complex problems associated with treatment of atrophic jaws. One early approach in the posterior maxilla was to augment the sinus in conjunction with the simultaneous placement of blade-vent implants.1–3 To increase bone volume for reconstruction of both function and esthetics, the use of autogenous bone blocks harvested from the mandibular symphysis and/or posterior horizontal mandibular ramus was documented early on by Collins and colleagues,4 Collins,5 Khoury,6,7 and Khoury and colleagues,8 and later by Pikos.9,10 More substantial defects requiring larger volumes of bone have been reconstructed with autogenous bone harvested from the tibia, iliac crest, calvaria, and ribs.11,12 Graft material choices have also expanded to include xenografts, allografts, and alloplasts, and as they have expanded, the recipes for their use have also evolved.13 Clinicians have reported positive results from combining various forms of bone with autogenous bone marrow, harvested from the iliac crest.14 Platelet-rich plasma has also been used to enhance the quality and quantity of the augmentation materials.15
The high cost and the protracted treatment time required for such approaches have limited their application. A parallel development has been the All-on-Four implant treatment concept. Introduced by Maló et al in 2003, this concept for immediate function involves the use of 4 implants, including 2 distally tilted ones in areas where bone height; nerve proximity; or the proximity of the sinus, inferior alveolar canal, and/or mental foramen have precluded the placement of axially oriented implants. In addition to preserving the relevant anatomic structures, the distal tilting allows for placement of longer implants with good cortical anchorage in optimal positions for prosthetic support. It also increases the interimplant spaces, reduces cantilever length, and reduces the need for bone augmentation. Published studies on the All-on-Four concept have shown cumulative survival rates to range between 92.2% and 100%.17–24
One limitation of the application of the All-on-Four concept to patients with severely resorbed maxillae and mandibles is that an implant diameter of at least 4.0 mm, especially for the 2 distal tilted implants, has been thought necessary to ensure adequate anchorage.18,21,25 Use of 3.5-mm-diameter implants has not been common.18,21,24
In 2008, the introduction of a new implant design (NobelActive, Nobel Biocare AB, Gothenburg, Sweden) led the authors to question whether it might be possible to use immediately loaded 3.5-mm-diameter NobelActive implants in extremely atrophic mandibular and maxillary full arches, thus expanding the pool of patients who could safely be treated with an All-on-Four approach. A protocol for treating patients with severely resorbed maxillae and mandibles was developed. This report analyses results achieved using this approach.
Materials and Methods
All patients presenting at the treatment center were examined, and the volume and quality of their alveolar bone was assessed using a cone-beam computerized tomography (CBCT) scan (I-CAT cone-beam CT scan, Imaging Science Corp, Hatfield, Pa). Whenever analysis of the scan revealed severe horizontal atrophy, the patient was presented with the option of undergoing an exploratory surgical procedure. Severe horizontal atrophy was defined as being significant enough to exclude the possibility of using an implant of 4 mm or greater, as has heretofore been the standard of care.
Patients were informed that despite the sophistication of current diagnostic imaging technology, the likelihood of successful implant rehabilitation was still best determined by an experienced surgeon working directly at the placement site. The exploratory procedure would entail the following possibilities:
After extracting the remaining teeth (if any) and reflecting the mucoperiosteal tissues in the now edentulous jaw, the surgeon would attempt to place 4 implants (NobelActive, Nobel Biocare, Yorba Linda, Calif) and torque them to at least 35 Ncm. If that torque value could be achieved for most of the implants, the patient would be placed into function with an acrylic provisional fixed implant prosthesis on the same day. A final prosthesis would be delivered 4 to 6 months later.
If the torque values for 3 or more of the newly placed implants were below 35 Ncm, a 2-stage technique would be used instead. This would entail the placement of healing screws into the implants, followed by soft-tissue closure. The patient would be fitted with a removable complete denture prosthesis to be worn for a healing period of approximately 3 months. After osseointegration of the implants, they would be uncovered, and the multiunit abutments would be connected. The removable complete denture would be converted to a fixed acrylic provisional implant bridge according to the All-on-Four protocol.
If the degree of bone atrophy proved to be too severe and the placement of any implant was impossible, the mucoperiosteal flaps would be closed and sutured, and the patient would be given a removable complete denture to wear while the soft tissues healed. Three to four months later, a custom final complete denture prosthesis would be fabricated and delivered to the patient.
Patients were included if they were medically able to undergo the procedure, had acceptable oral hygiene, and signed an informed consent form. Smoking was not an exclusion criterion, although patients who smoked were informed about the increased risk of implant failure and urged to enroll in a smoking cessation program. Exclusion criteria included alcohol or drug abuse, severe bruxism, psychiatric disease, compromised medical history that would affect implant survival (eg, treatment with intravenous bisphosphonates or chemotherapy), and the need for bone augmentation to enable ideal implant positioning.
The minimum length required for all implants placed was 10 mm. In order to be included in the retrospective analysis, at least 3 of the 4 implants placed with this protocol (in the maxilla or the mandible) had to have diameters of 3.5 mm. Analysis of the CBCT scans was used to select the optimal implant diameter and length, as well as the location for each placement site. No surgical guides were used. In all patients, local anesthesia (Septocaine, articaine 4% with 1:100,000 epinephrine, Septodont, Louisville, Colo) was administered before surgery. Other details of the surgery and prosthetic reconstruction followed the protocol previously described.17,26
The following 3 cases illustrate treatment with this protocol.
Case no. 1
The patient, a 70-year-old white woman who had been edentulous in her maxilla and mandible for more than 2 years, was highly dissatisfied with the function and esthetics of her existing maxillary and mandibular complete removable dentures. Her CBCT scan revealed severe advanced maxillary and mandibular horizontal atrophy (Figures 2a through 3b). Her medical history was very complicated and included a pacemaker that had been installed several years earlier. She smoked 1 pack of cigarettes per day and was taking cardiac medication that consisted of metoprolol and aspirin. For hypertension, she was taking hydrochlorothiazide. She also had gastroesophogeal reflux disease; early chronic obstructive pulmonary disease, which was being treated with Advair (GlaxoSmithKline, Philadelphia, Pa); and arthritis, which was being treated with prednisone, tramadol, and methotrexate (2.5 mg, 7 tablets for 1 week).
After a medical evaluation by her physician, the patient was cleared for the procedure to be carried out under general anesthesia at a local surgical center, where she would be treated as an ambulatory patient. Because of the possibility of her bisphosphonate usage complicating oral surgery and potentially causing osteonecrosis of the jaw, a C-terminal telopeptide blood test was suggested. However, the patient refused; she understood the potential risk and still wanted to move forward with the procedure.
On May 18, 2010, general nasotracheal anesthesia was administered to the patient at the surgery center, and the maxillary and mandibular All-on-Four procedures were carried out to reconstruct her with 3.5-mm implants (Figures 4 through 6b). The patient tolerated the procedure well, and later that day, maxillary and mandibular fixed provisional restorations were installed.
The patient was discharged without complications and followed over the next several months (Figure 7). She was reconstructed with definitive fixed maxillary and mandibular prosthetic appliances (Figures 8 and 9). After several years, she remains asymptomatic, nonpathological, and fully functional, greatly enjoying the security of the fixed appliances in addition to the function and esthetics that were created for her.
Case no. 2
The patient was a 76-year-old white woman who described continuing problems with tooth decay and breakage. To end the cycle of continuous filling and repair, she wanted to replace her terminal dentition with implant-supported restorations.
Her medical history was positive for mitral valve prolapse with regurgitation and arthritis, for which she was taking several anti-inflammatory medications. Her previous surgical history included bilateral hip replacements, a right knee replacement, and cosmetic surgery. She smoked 1 pack of cigarettes per day but stated that she would attempt a cessation program before surgery.
She underwent the standard workup for maxillary and mandibular All-on-Four reconstruction. Her CBCT scan revealed adequate maxillary bone quality and quantity for the standard All-on-Four protocol. However, her mandible exhibited severe advanced horizontal atrophy (Figure 10), so she consented to the alternative approach offered to her using the exploratory protocol.
On March 2, 2010, under general anesthesia, the patient's remaining teeth were extracted. Four NobelActive implants were placed in the maxilla following the All-on-Four treatment concept, and a torque of 70 Ncm was achieved on all. Four implants were also placed in the mandible. The 2 anterior mandibular implants were torqued to 50 Ncm, and the 2 distal angled implants were torqued to 70 Ncm. All-acrylic temporary screw-retained prostheses were positioned in both the maxilla and mandible later that day. The patient was discharged with postoperative analgesic medication, and her postoperative course was uneventful. Fabrication of the definitive prosthesis was initiated 3 months after implant placement. Figure 11a demonstrates the bone levels 4 months postoperatively, before the definitive prosthesis was placed. After delivery of the definitive prosthesis (at 25 months' follow-up), note the constant bone level (Figure 11b).
Case no. 3
The patient was a 94-year-old African-American woman who was edentulous in the maxilla and had only 6 mandibular teeth remaining. Although happy with her maxillary denture, her chief complaint was having insufficient teeth for adequate mastication; she also expressed a desire for “a pretty smile” (Figure 12a and b).
The patient's medical history revealed that she had atrial fibrillation treated with coumadin therapy. She was also under treatment for hypertension, gastroesophageal reflux disease, muscle spasm of the back, and osteoporosis. Her CBCT scan revealed that the width of the mandibular bone was severely diminished in quality and quantity (Figure 13). The patient understood the exploratory procedure and the possibility of replacing her hopeless mandibular teeth with an All-on-Four fixed prosthesis, and she reiterated her strong desire to be able to eat steak.
On June 23, 2009, the patient was admitted to an ambulatory surgery center for the day, as recommended by her primary care physician. Under general nasotracheal anesthesia, her remaining 6 nonrestorable teeth were surgically excised, and 4 NobelActive implants were placed in the usual All-on-Four configuration in the mandible. After all 4 implants were torqued to 70 Ncm, an acrylic temporary screw-retained prosthesis was prepared and positioned later that day. The patient was discharged with postoperative analgesic medication, and her postoperative course was uneventful. Four months later, fabrication of the final prosthesis was initiated (Figures 14 through 16).
Between August 27, 2008, and June 7, 2011, 54 patients were identified as having severe atrophy in 1 or both jaws. These patients were presented with the option of being treated with the previously described protocol. All 54 consented to treatment. In the course of exploratory surgery, 1 of the patients was excluded from any implant placement because of inadequate bone. This resulted in 53 patients treated with the All-on-Four concept (11 men and 42 women), with an average age of 62 years (SD = 9.85).
Three patients required reconstruction of both jaws, bringing the total number of jaws treated to 56 (29 maxillae and 27 mandibles). A total of 227 implants were placed in the 56 jaws, 117 in the maxilla and 110 in the mandible (Table 1). Four implants were placed using the All-on-Four concept in 50 of the jaws; 5 patients received 5 implants because softer bone and/or lower torque values were noted during surgery. One patient who had 2 preexisting implants received 2 additional implants, and the 4 implants were treated using the All-on-Four concept (Table 2).
Of the 227 implants placed, 211 were 3.5 mm in diameter, 13 were 4.3 mm in diameter, and 3 were 5.0 mm. Table 3 provides additional information about the lengths of the implants. Torque values recorded while placing the 227 implants are represented in Table 4.
Of the 219 immediately restored implants, 2 implants in 2 patients failed due to lack of osseointegration (one after 5 months and one after 7 months) and had to be removed. One of the 2 was replaced immediately. One was not replaced, but instead the defect was grafted and a decision was made not to attempt reimplantation. This patient had 5 implants to begin with, and the 4 remaining implants were judged to be sufficient to enable long-term survival of the prosthesis. Of the 8 implants placed in a 2-stage procedure, 1 implant also failed at 5 months due to lack of osseointegration and was replaced immediately. The cumulative survival rate for all the study implants was 98.7% (Table 5).
Follow-up ranged from 12 to 36 months: all patients completed the 12-month follow-up, 27 patients completed the 13- to 24-month follow-up, and 10 patients were followed from 25 to 36 months. Throughout the follow-up period, no total arch or prosthetic failures occurred, resulting in a prosthetic cumulative survival rate of 100%.
Use of narrow-diameter implants to treat horizontally atrophic ridges has been successful when 6 to 8 or more implants have been placed to support full-arch reconstructions.27–29 Until recently, however, it has not been possible to deliver All-on-Four treatment with narrow-body (3.5 mm) posterior (angled) implants. For one thing, the necessary components were not commercially available. Moreover, there was uncertainty about whether such narrow implants would adequately support an immediately loaded restoration supported by only 4 implants.
Several aspects of the NobelActive implant's design suggested that a narrow-diameter version of the implant would perform well. This variable thread tapered implant has an extensive self-drilling capacity and an inward tapered collar designed to maintain marginal bone and stability of the peri-implant soft tissues. Placement results in axial and radial bone compression and can be achieved in narrower osteotomies than those required by standard implants. Because of the implant's bone-compression effect, bone quality can often be actively improved, and very high torque values (35–70 Ncm) can typically be achieved, resulting in very high initial stability.26 Examining the initial stability of 140 NobelActive implants placed in different types of bone, either as delayed or immediate implants into fresh extraction sockets, Irinakis and Wiebe30 found a mean torque value of 50.8 Ncm. Even when placed into soft bone, the implants achieved an average torque of 47.9 Ncm, significantly more than the 10 to 35 Ncm torque values typically found for straight-walled and tapered implants.
In a retrospective chart analysis of primary implant failures in 285 consecutively treated maxillae using the All-on-Four concept, Parel and Phillips31 found that a diagnosis of soft bone (based on CBCT scan Hounsfield unit values) was a significant finding. Failed implants were also found to have lower insertion torque values than those found in adjacent integrated maxillary sites. For that reason, Parel and Phillips recommended planning for additional (ie, >4) implants for immediate-load situations in certain selected cases. In the present study, a finding of softer bone or lower torque values in 5 patients led to placement of 1 additional implant in each of those patients. Only one of those patients experienced an implant failure. It was not necessary to replace that single failed implant, however, because the patient already had 4 functional implants.
Because the previous standard of care was to use only 4-mm-diameter (or wider) implants with delivery of immediately loaded All on Four implant treatment, patients with horizontally atrophic jaws were formerly excluded from such treatment. The availability of the 3.5-mm NobelActive implant allows for such treatment to be extended to a wider range of patients, and the results of the present study are an initial demonstration that immediate restorations supported by 4 narrow implants can produce high success rates.
Previous attempts to treat the severely resorbed maxilla and mandible have had limited success, but placement of 3.5-mm-diameter NobelActive implants using the All-on-Four protocol promises to become a new standard of care for severely compromised patients.
This investigator-sponsored study was supported by Nobel Biocare Services AG, grant 2011-1106.