Over the past 17 years, the All-on-4 treatment concept has been a reliable and predictable modality to rehabilitate edentulous jaws with immediate function as full-arch prostheses. This article highlights clinically relevant data compiled by numerous All-on-4 investigators including complications and their remedies, occlusion and cantilever trends, implant size utilization, and controversial topics. We provide insights for navigating the complexities of medically diverse populations, faced by our daily practice, with a focus on patient avoidance, risk factors for implant and prosthetic failures, in hopes to minimize complications so clinicians would choose this treatment with confidence.
Key points
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Using the All-on-4 concept is biomechanically sound with implant survival rates for the maxilla ranging from 93.9% to 100% with up to 13 years of follow-up. The cumulative survival rate for the mandible is 91.7% to 100% with up to 18 years of follow-up.
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Immediate loading provisional prosthesis survive well when implants are torqued between 30 to 50 Ncm ideally with no cantilever and with a one tooth cantilever maximum if necessary. If possible, use metal reinforced acrylic prosthesis to decrease incident of fracture.
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Final cantilever length to Anterior-Posterior spread (CL/AP ratio <1) should not exceed ratio <0.9 to minimize prosthetic fracture.
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Final restoration can have 10 to 12 teeth for proper esthetics and function. Final prosthesis survival rates using the “All-on-4” concept range from 97.06% to 100.0% in the maxilla with up to 13 years of follow-up and between 98.8% and 100% with up to 18 years in the mandible.
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Patient satisfaction was 95.6% surveyed by questionnaire.
Introduction
For the past 17 years, the All-on-4 concept has been used to rehabilitate the edentulous jaws with a full fixed arch prosthesis and immediate function. The intent of this article is to highlight some of the current data, contraindications/exclusion criteria, complications and remedies, occlusion and cantilever trends, implant size, and controversial topics. Conforming to the amount of material allowable to be written for this publication, please refer to the “Contemporary All-on-4 Concept” article for more descriptive surgical indications, and detailed stepwise procedures for surgery and prosthesis ( Fig. 1 ).
Implant survival rate
Data revealing implant survival within the All-on-4 concept are demonstrable by multiple investigators with continuous positive outcomes. Studies reported on maxillary implant survival ranges from 93.9% to 100% (up to 40 months to 13 years), whereas the mandible registered between 91.7% and 100% (up 3 years to 18 years) , , , , of follow-up. It is noteworthy, the lowest survival rate has been associated with the longest follow-up period for both arches. ,
The lack of standardization used for implant success and survival criteria by numerous investigators makes interpreting data heterogeneous. Furthermore, most investigators choose to use survival rate’s metrics over success primarily for the ability of these implants to ultimately support the prosthesis as the end goal resulting in better overall percentages commonly known as cumulative survival rate. In addition, the definition for survival is broader and generally refers to an implant remaining in the jaw; whereas, success has a defined set of subjective and objective parameters. Nevertheless, some investigators reference Albrektsson’s criteria as the gold standard ( Box 1 ). , , , In the future, Papaspyridakos and colleagues suggest a more uniform set of success criteria evaluating implant-prosthetic complex as a unit rather as a separate entity.
| 1 | Absence of pain, paresthesia or Infection | Success |
| 2 | Absence of peri-implant radiolucency | Success |
| 3 | Absence of mobility | Success |
| 4 | Vertical bone loss must be less than 0.2 mm annually after first year of function | Success |
| 5 | Implant success rate of 85% at end of 5 years and 80% at end of 10 year period | Success |
Contraindications and/or exclusion for All-on-4 concept
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Insufficient bone volume ,
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Poor oral hygiene , , , ,
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Patients noncompliant to follow-up , , , ,
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Parafunctional habits
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That is, bruxers, clinchers, or oromandibular dystonia , , , , , ,
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Acute infection at prospective implant site , , , , ,
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Smoking
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Risk factor , ,
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>10 cigarettes/d =
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>20 cigarettes/d =
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Drug abuse ,
Systemic conditions may not be amenable to implant placement
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Recent cardiovascular incident
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Myocardial infarction <6 months is contraindicated
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Peri-implantitis risk , ,
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Diabetes
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Peri-implantitis risk , , ,
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Uncontrolled diabetes as exclusion criteria for All-on-4 implant placement , , , ,
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Autoimmune disease
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that is, rheumatoid arthritis, and other low-grade inflammatory disease
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Metabolic bone disease
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Antiresorptive (AR) Therapy
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General exclusion criteria from longitudinal studies ,
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Oral bisphosphonate (BP) is a risk factor for implant loss ,
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High dose/intravenous contraindicated ,
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Disease of immune system , ,
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Chemotherapy or head and neck radiation
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Previous chemotherapy and radiation therapy ,
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Active chemotherapy and radiation therapy
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Radiation within 1 year
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Radiation within 5 years ,
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Chemotherapy or radiation therapy within 1 years , ,
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Chemotherapy or radiation therapy within 5 years
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Coagulopathy , , ,
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Hematological disease , ,
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Pregnancy or lactation , ,
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Psychiatric illness ,
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American Society of Anesthesiologist (ASA III and IV)
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Steroid Therapy ,
What are some risk factors reported for ailing or implant failures?
In general, implant failures can be categorized into 2 groups: early and late. Early failures are attributed to lack of osseointegration. Although some failures are universally accepted within the range of surgical failure, it is only natural to speculate what these factors are. Some postulate post-extractive sites (extraction with immediate implant placement) with presence of periapical infection as a contributing factor. Another suggested inexperienced clinicians with fewer than 50 cases have more failures than experienced ones. A recent prospective randomized control trial investigated high insertion torque (>50 Ncm) implants had approximately 50% more peri-implant bone remodeling and approximately 2 times the buccal soft tissue recession than implants inserted with regular torque (<50 Ncm) at 12 months.
Numerous investigators have documented peri-implantitis as a late complication for implant failures. Many have attributed poor oral hygiene as the primary etiologic factor for development of mucositis (gingival redness and swelling without bone loss) to eventual peri-implantitis (peri-implant soft tissue inflammation with evidence of persistent bone loss). , Derks and colleagues showed early peri-implantitis (66%) can be seen on radiographs at 3 years with greater than 0.5 mm bone loss in 81% of patients and will cause continuous bone loss over time. They reported the progression to moderate/severe peri-implantitis with an average marginal bone loss to be 3.5 ± 1.5 mm with mean follow-up of 8.6 ± 0.7 years. Clinicians should have a regular maintenance recall schedule to intercept the disease at the earliest signs to prevent disease progression.
Parafunctional Habits
Excessive and constant jaw motion have many investigators report an overall negative impact to this full-arch prosthesis design. Multiple investigators recommend avoidance of patients with severe parafunctional habits (ie, bruxing, clenching, and/or oromandibular dystonia) to prevent future prosthetic and implant-related complications. , , , , , , , Additionally, Lopes and colleagues have found 7.2% of patients with bruxism leading to peri-implantitis resulting in failures.
Smokers
Smoking is controversial with some investigators reporting a direct correlation to marginal bone loss, peri-implantitis, and/or implant failure for All-on-4 cases, , , , , while others did not find any difference with implant survival rates above 98.6%. , , Although there is an intuitive cause-and-effect relationship of the negative effects of smoking, more control studies are need to quantify the number of cigarettes (ie, fewer than or more than 10 cigarettes/d), length of smoking history, and a larger sample size with long follow-up period to get a better assessment for this All-on-4 design. Peri-implantitis requires lifelong maintenance to salvage some ailing cases.
Cardiovascular
In 2019, Maló and colleagues revealed 80% of cardiovascular patients are at risk to develop peri-implantitis but warned not to draw these conclusions given the small sample size and lack of experimental control. However, a comprehensive systematic review performed by Ting and colleagues concluded cardiovascular and uncontrolled diabetics were at high risk of developing peri-implantitis. Dhadse and colleagues also reported cardiovascular patients were at a higher risk of developing peri-implantitis and 3 times more likely to be associated with Epstein-Barr virus.
Diabetes
Generally, people with diabetes are at higher risk for peri-implantitis. It has been shown poorly controlled group has greater probing depths and peri-implant bone loss than control group. , In addition, the longitudinal All-on-4 study of Malo and colleagues found diabetic individuals with more biological complications (ie, abscess, infection, and peri-implantitis) leading to implant failure. Numerous investigators listed uncontrolled diabetes as an exclusion criteria for All-on-4 implant placement. , , , ,
Antiresorptive therapy
Antiresorptives (AR) are widely used to treat osteoporosis and cancer with 2 common classes encountered by clinicians: Bisphosphonate (BP) and Denosumab (Receptor Activator of Nuclear factor-KB ligand [RANKL] inhibitor). Although both medications prevent bone resorption, they work on different pathways. BP binds to the lattice structure of the hydroxyapatite found on bony surfaces. When osteoclast ingests bone saturated with BP, the ability for osteoclast to bind to bone has been nullified resulting its ability to resorb bone. On the other hand, RANKL inhibitor is a humanized monoclonal antibody that exerts its antiresorptive effects by blocking RANKL to RANK essential to initiate osteoclast differentiation. Unlike BP that binds to bone directly, RANKL inhibitors work on osteoclast “precursors” ultimately disabling production of mature osteoclasts. The disruption of osteoclast’s function with these medications could in theory cause more implant failures, increased marginal bone loss, and medication-related osteonecrosis of the jaw (MRONJ). It is also theoretically possible to discontinue denosumab (6 months) before implant placement because the mechanism of action does not affect bone directly but needs to await for new production of osteoclasts after the drug’s biological inactivity. Cumulative dosages and relative drug potency are more important than the mode of administration with low dose typically prescribed for osteoporosis and high for malignancies ( Table 1 ). , ,
| Name | Class | Relative Potency to Etidronate = 1 | Route of Administration and Dosage | Indication |
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| Alendronate (Fosamax) | BP | 500 | 70 mg po weekly (low dose) | Osteoporosis |
| Denosumab (Prolia) | Denosumab | ? | 60 mg sc 6 mo (low dose) | Osteoporosis |
| Denosumab (Xgeva) | Denosumab | ? | 120 mg sc 4 wk (high dose) | Cancer |
| Ibandronate (Boniva) | BP | 1000 | 150 mg po monthly (low dose) | Osteoporosis |
| Ibandronate (Boniva) | BP | 1000 | 50 mg po qd or 1500 mg monthly total (high dose) | Cancer |
A recent review by Stavropoulos and colleagues investigated the outcome and complication rate of implant therapy with and without antiresorptive drug treatment. They concluded low-dose oral BP for osteoporosis treatment does not increase the rate of implant failures, marginal bone loss, peri-implantitis, and MRONJ when compared with the non-medication group. However, minimal clinical data are available to effectively assess patients on high-dose BP or denosumab but only to categorize this high-risk group for those who are on oral BP for a prolonged period with concurrent comorbidities or high-dose AR used for malignancies.
Controversially, in another recent systematic review, Chappuis and colleagues also found no increased risk of implant failure with oral BP but emphasize the absolute contraindication with intravenous BP. Interestingly, the investigators did find an association between proton pump inhibitors (PPIs) and serotonin reuptake inhibitors (SSRIs) with an increased risk for implant failures. PPIs impair calcium absorption from the intestine and therefore disrupt bone formation. SSRIs disrupt osteoclasts activation and differentiation thus having a negative influence on osseointegration.
A more nuanced view taken by De-Freitas and colleagues mirrors the American Association of Oral and Maxillofacial Surgeons recommendations by highlighting the importance of taking patient’s concomitant risks into consideration. Ingesting oral BP for less than 4 years with no other risk factors can proceed with implant placement with specific informed consent explaining possible long-term implant failure and a low risk of osteonecrosis of the jaws. However, if patients have taken oral BP for less than 4 years, but have also been taking corticosteroids or antiangiogenic medications or if patients who have taken oral BP for more than 4 years, a drug holiday for at least 2 months before implant placement is suggested. This recommendation is based on the drug’s half-life and urinary excretion to render the medication biologically as inactive suggested by Damm and Jones. If possible, BP should be held until osseointegration is achieved.
Furthermore, a prospective cohort study by Tallarico and colleagues on patients taking alendronate (Fosamax) 35 to 70 mg weekly for at least 3 years with a 6-month drug holiday reported implant success rate of 98% with a marginal bone loss of 1.35 ± 0.21 mm. Conversely, 2 All-on-4 longitudinal studies have correlated implant failure with oral BP as a risk factor without a drug holiday. ,
Many investigators listed BP therapy as an exclusion criteria. , , Although oral BP still lacks general consensus, the IV version is widely regarded as an absolute contraindication for dental implant placement. , ,
Chemotherapy and radiation therapy
In a longitudinal study, Niedermaier and colleagues revealed a patient with a history of chemotherapy as a risk factor for the All-on-4 design without achieving osseointegration. The investigators mentioned interpreting these results with caution because 2 other studies reported successful outcomes and further investigation is needed in particular with immediate load. Currently, there is no clear consensus on the exclusion criteria for patients with past treatments with various investigators listed within 1 to 5 years. , , , , , , , , ,
Steroid therapy
The use of corticosteroids have been documented to cause impaired cellular healing, hyperglycemia, increased rate of infection with overall negative effects on osseointegration. , Osteoporosis is a known consequence of chronic glucocorticoids therapy. Bone formation is thought to be disrupted by altering the Wingless-related integration site (Wnt) signaling through upregulating the Wnt antagonists, specifically sclerostin (SOST), and dickkopfrelated protein 1 (Dkk1). These Wnt antagonists decrease the production of osteoblasts resulting in less bone formation and increased osteoclastic activity with bone resorption creating an osteoporotic milieu.
Generally, chronic steroids are listed as an exclusion criteria. , This, however, does not preclude use of short course of steroids (ie, medrol-dose pack) for nonsteroid users to help decrease postsurgical edema.
Prosthetic survival rate
Similar to the implant survival criteria, prosthetic survival does not have a universally accepted standard, but most clinicians adopt the ability to fabricate a final prosthesis on existing osseointegrated implants. According to Malo and colleagues, prosthetic survival is based on function, with the necessity of replacing the prosthesis classified as failure.
Nevertheless, final prosthesis survival rate also yields a successful outcome with the maxilla ranging from 97.06% to 100.0% (up to 36 months to 13 years), whereas the mandible registers between 98.8% and 100% with (up to 3 years to 18 years) , , , , of follow-up by multiple investigators.
Marginal bone loss
Marginal bone loss data are based on radiographic bone measurements on the mesial and distal site for each implant. Specifically, the difference is calculated between the implant/abutment interface and existing bone level for pre and post loading. ,
Adell and colleagues first reported an average crestal bone loss for loaded implants to be 1.2 mm during the first year and 0.1 mm annually with these parameters during the implant’s life expectancy. This finding was consistent with Niedermayer and colleagues, who reported 1-mm bone loss with 0.2 mm annually.
Recent studies with short-term (up to 3 years), medium-term (between 3 and 7 years), and long-term (beyond 7 years) marginal bone loss range from 0.14 mm ± 0.59 to 1.19 mm ± 0.33 (mean ± SD/mm), 0.39 mm ± 0.18 to 1.9 mm ± 1.1, and 1.30 mm ± 0.63 SD to 2.30 mm for short-term, medium-term, and long-term, respectively, with 15-year follow-up. , ,
While comparing among different size diameter implants, Babbush and colleagues demonstrated narrow (3.5 mm) diameter implants had statistically more bone loss but emphasized that the results were not clinically relevant up to 3 years of follow-up.
Maló and colleagues reported 3 risk factors associated with advanced bone loss (>3 mm) at 10 years particularly with biological complication, previous implant failure, and smokers. In addition, through the binary logistic regression model, Malo and colleagues found male gender, smoking, biological complication, and age to play a role for greater than 2.8 mm bone loss at 5 years. Simply put, the likelihood of the amount of bone loss observed in a given period will occur with the preceding variables when compared with the absence of exposure.
Another often overlooked reason for marginal bone loss has been documented by Durkan and colleagues. They described improper occlusion, implant, or prosthetic design will often burden the rest of the healthy implants with undue stress resulting in crestal bone loss.
What are the technical complications associated with All-on-4?
Technical complications are defined as the complications related to prosthetic components ( Table 2 ). Acrylic prosthesis fracture is the most common complication followed by provisional screw loosening (abutment and/or prosthetic) for the provisional period. Bruxers are responsible for a good majority of the cases while opposing implant-supported bridge are attributed by the non-bruxer group. , Prosthetic repair, occlusal adjustment, and nightguard fabrication along with decrease in occlusal load (ie, softer diet) remedied the fracture situation while retightening the screw corrected the latter. , , , To counter acrylic resin fractures, Tallarico and colleagues suggested metal reinforced provisional prosthesis.
