OR I G I N A L A R T I C L E

The All-on-4 concept for full-arch rehabilitation of theedentulous maxillae: A longitudinal study with 5-13 yearsof follow-up

Paulo Maló PhD1 | Miguel de Araújo Nobre RDH, MSc2 |

Armando Lopes DDS, MSc1 | Ana Ferro DDS1 | Mariana Nunes DDS1

1Oral Surgery Department, Maló Clinic, Lisbon,

Portugal

2Research and Development Department,

Maló Clinic, Lisbon, Portugal

Correspondence

Miguel de Araújo Nobre, Maló Clinic, Avenida

dos Combatentes, 43, piso 11, 1600-042

Lisboa, Portugal.

Email: mnobre@maloclinics.com

Funding information

Nobel Biocare Services AG, Grant/Award

Number: 2016-1437

Abstract

Background: Full-arch immediate function protocols such as the All-on-4 concept

need long-term validation.

Purpose: To report the 5-13 year outcomes of the All-on-4 treatment concept for

the rehabilitation of the edentulous maxilla.

Materials and Methods: This retrospective case series study involved 1072 patients

(4288 maxillary implants) rehabilitated through the All-on-4 treatment concept. Pri-

mary outcome measures were cumulative prosthetic and implant success (life table

analysis). Secondary outcome measures consisted in marginal bone loss (MBL) at 5 and

10 years, biological and mechanical complications. The estimation of risk indicators

was performed through multivariable analysis for the outcome variables implant failure

(Cox regression to estimate hazard ratios and 95% confidence intervals [95% CI]),

MBL > 2.8 mm at 5 years, MBL > 3.0 mm at 10 years, biological and mechanical com-

plications (binary logistic regression to estimate odds ratios [OR] with 95% CI).

Results: Eighteen patients deceased unrelated to the implant treatment (1.7%) and

219 patients (20.4%) were lost to follow-up. The prosthetic success rate was 99.2%;

Implant cumulative survival and success rate was 94.7% and 93.9%, respectively, with

up to 13 years of follow-up. Male gender (HR = 1.73), smoking (HR = 1.94), and

mechanical complications (HR = 0.59) were significantly associated with implant failure.

Average MBL at 5 and 10 years was 1.18 mm (95% CI: 1.16, 1.21) and 1.67 mm (95%

CI: 1.58, 1.77) with age (OR = 0.97), male gender (OR = 0.58), smoking (OR = 1.73), and

biological complications (OR = 2.1) associated with MBL > 2.8 mm at 5 years. The inci-

dence of biological complications was 7.8% at implant level, with age (OR = 0.98) and

smoking (OR = 1.53) significantly associated. The incidence of mechanical complications

was 58.8% for the provisional prostheses and 7.3% for the definitive prostheses.

Conclusions: The high success rates registered for both implants and prostheses

together with the low MBL confirm the All-on-4 treatment concept is predictable

and safe in the long term outcome.

K E YWORD S

All-on-4, biological complication, edentulous maxilla, immediate function, longer-term

outcome, marginal bone loss, tilted implants

Received: 17 December 2018 Revised: 13 February 2019 Accepted: 15 March 2019

DOI: 10.1111/cid.12771

Clin Implant Dent Relat Res. 2019;1–12. wileyonlinelibrary.com/journal/cid © 2019 Wiley Periodicals, Inc. 1

1 | INTRODUCTION

The “immediate function” concept consists in the insertion of dental

implant(s), abutment(s), and fixed prostheses on the same day for

edentulous rehabilitation.1 From a patient standpoint, the ability to be

provided with a fixed prostheses on the day of surgery through an

immediate function protocol was considered as an important psycho-

logical benefit as registered in previous studies.1,2 Furthermore, the

safety and reliability of immediate function protocols in both short-

term and mid-term follow-up was previously proven to be consistent

and safe.1,3–6 Considering the specific situation of edentulous maxil-

lary rehabilitations, no significant differences in implant success and

peri-implant marginal bone loss (MBL) were registered between

immediately loaded and conventionally loaded implants,7 a result

supported by a previous systematic review.8

The “All-on-4” treatment concept is based on the insertion of four

implants in the anterior region of completely edentulous jaws to sup-

port an immediate implant-supported fixed prosthesis: The two most

anterior implants are placed axially, whereas the two posterior

implants are placed with a distal tilting of up to 45�, allowing the con-

nection of prostheses with up to 12 teeth.9 The “All-on-4” treatment

concept was developed to maximize the use of the available residual

bone in atrophic jaws, allowing immediate function and avoiding

regenerative procedures (such as bone grafting) that increase treat-

ment costs, patient morbidity, and complications inherent to these

procedures.10 The concept benefits from the use of tilted implants

that relate to several surgical and prosthetic advantages previously

described: The possibility of placing longer implants with improve-

ment of bone anchorage by engaging the apex of the implant with the

cortical bone of the anterior wall of the sinus, the reduction of the

need for bone grafting, the possibility of reaching a more posterior

implant position and avoiding long cantilevers, and a good anterior-

posterior spread with the possibility of increasing the distance

between anterior and posterior abutments, resulting in an improve-

ment of the load distribution.5,11–17

The All-on-4 concept was further validated in the short and mid-

term outcomes considering the results of two systematic reviews that

reported high survival rates in the rehabilitation of completely edentu-

lous patients.18,19 Nevertheless, long term evidence of the All-on-4

treatment concept for the rehabilitation of the edentulous maxilla is

lacking.

The aim of this study was to evaluate the long-term outcome

(5-13 years) of the All-on-4 concept in the maxilla.

2 | MATERIALS AND METHODS

This article was written following the STROBE guidelines for observa-

tional studies.20 The retrospective case series was performed at a pri-

vate rehabilitation center (Maló Clinic, Lisbon, Portugal) and approved

by an independent ethics committee (Ethical Committee for Health;

Authorization n� 01/2016). Patients were treated between November

2002 and July 2010. Patients were included provided their need for

fixed prosthetic full-arch maxillary rehabilitations supported by imme-

diate function implants due to edentulism or the presence of hopeless

teeth. The same team performed surgery and prosthetic restoration.

Exclusion criteria were patients who were not followed (only rehabili-

tated) at the private practice.

2.1 | Surgical protocol

The patients' medical chart was reviewed, and clinical examinations

(including information on smoking and smoking cessation instructions to

patients who were smokers) supplemented by an orthopantomography

and computerized tomography scan were performed. The intervention

was performed using local anesthesia with mepivacaine chlorhydrate

with epinephrine 1:100 000 (Scandinibsa 2%, Inibsa Laboratory,

Barcelona, Spain). Prior to surgery, the patients were administered

diazepam (Valium 10 mg, Roche, Amadora, Portugal). Antibiotics (amoxi-

cillin 875 mg + clavulanic acid 125 mg, Labesfal, Campo de Besteiros,

Portugal) were given 1 hour before surgery and daily for 6 days thereaf-

ter. Cortisone medication (prednisone [Meticorten Schering-Plough

Farma Lda, Agualva-Cacém, Portugal], 5 mg) was administered daily in

a regression mode (15-5 mg) between the day of surgery and 4 days

postoperatively. Anti-inflammatory medication (ibuprofen, 600 mg,

Ratiopharm Lda, Carnaxide, Portugal) was given between the 4th and

7th day postoperatively. Analgesics (clonixine [Clonix, Janssen-Cilag

Farmaceutica Lda, Barcarena, Portugal], 300 mg) were given on the day

of surgery and only if needed on the first 3 days postoperatively. Ant-

acid medication (Omeprazole, 20 mg, Lisbon, Portugal) was administered

between the day of surgery the 6th day postoperatively.

A mucoperiosteal flap was raised along the top of the ridge with

relieving incisions on the buccal aspect in the molar area. Implant

insertion was performed according to standard procedures with the

exception of under-preparation that was done aiming to achieve

insertion torques in the range of 30-50 Ncm before the final seating

of the implants. The implant platform was positioned 0.8 mm above

the crest (conforming to the lower corner of the implant neck for Mk

III and Mk IV implants; Brånemark system, Nobel Biocare AB,

Göteborg, Sweden) or flush with the bone level (NobelSpeedy

implants, Nobel Biocare AB). When managing the insertion of tilted

implants, the bone crest was sometimes previously leveled to ensure

the implant platform was positioned at bone crest level and to cor-

rectly position the angulated abutment. Bicortical anchorage was

established whenever needed (when anticipating high occlusal loads

and encountering low density bone to achieve high primary stability in

allowing immediate function).21 To assist the insertion and positioning

of the posterior implants a surgical guide was used (All-on-4 Guide,

Nobel Biocare AB). The implants position was located between the

anterior wall of the maxillary sinus, reaching an angulation of 30-45�

in relation to the occlusal plane. The posterior implants emerged typi-

cally at the second premolar position benefiting from the distal tilting

along the anterior sinus wall. The two anterior implants were inserted

in an axial position with the exception of the presence of severe bone

resorption and/or buccal concavities where they were positioned with

vestibular tilting. Multi-unit abutments (Nobel Biocare AB) were

2 MALÓ ET AL.

connected to the implants: 30� angulated abutments connected to

the two posterior tilted implants and straight (0�) or angulated (17�)

connected to the anterior implants. The flap was closed and sutured

using 3-0 nonresorbable sutures (B Braun Silkam, Aesculap Inc, Center

Valley, Pennsylvania) and the abutments were accessed by means of a

punch (Mechanical soft tissue punch, Nobel Biocare AB).

2.2 | Prosthetic protocol

The provisional prosthesis was connected on the same day of surgery

consisting of high-density acrylic resin (PalaXpress Ultra, Heraeus Kulzer

GmbH, Hanau, Germany) and acrylic resin crowns (Premium teeth,

Heraeus Kulzer GmbH) with Temporary Coping Multi-Unit Titanium

(Nobel Biocare AB). The definitive prostheses were connected at the ear-

liest, 6 months postsurgery. The type of prostheses was manufactured

considering the patients' choice: a titanium framework (Procera, Nobel

Biocare AB) and either all-ceramic Alumina crowns (Procera crowns;

NobelRondo Ceramics, Nobel Biocare AB) or high-density acrylic resin

(PalaXpress Ultra) and acrylic resin crowns (Premium teeth).

2.3 | Follow-up visits and maintenance protocol

The patients were instructed for soft food diet in the first months.

A postoperative maintenance protocol was indicated to each patient

including oral hygiene instructions.22 Follow-up clinical appointments

were performed at 10 days, 2, 4, and 6 months, 1 year and every

6 months thereafter, consisting in the assessment of clinical parame-

ters, prophylaxis, and dental hygiene instructions.

2.4 | Outcome measures

The primary outcome measures were prosthetic and implant success.

Prosthetic success was based on function, with the necessity of

replacing the prosthesis or the necessity of including more than four

implants (either standard or zygomatic implants) classified as failure.

Implant success was based on the Maló Clinic success criteria23:

(a) implant fulfilled its purported function as support for reconstruction

(the potential existence of a sleeping implant was considered a failure);

(b) implant was stable when individually and manually tested; (c) no

signs of persistent infection that could jeopardize the implant outcome;

(d) absence of radiolucency around the implant; (e) the rehabilitation

registered good esthetic outcome (classified as the absence of esthetic

complains from the Prosthodontist or patient); and (f) allowed the man-

ufacture of a fixed prosthesis, which provided the patient with comfort

and maintenance (classified as the absence of comfort and hygiene

complains from the patient). The implants that did not complied with

the success criteria were considered survivals. The removal of the

implants was classified as a failure.

Secondary outcome measures were MBL at the 5- and 10-year

follow-up and the incidence of biological and mechanical complica-

tions. Marginal bone levels were evaluated using periapical radio-

graphs on the day of surgery (baseline measurement), after 5 years

and after 10 years. The radiographs were taken by using a film holder

(Super-bite, Hawe-Neos) to assist in the positioning through the paral-

lel technique. The film holder was positioned manually to obtain an

estimated orthogonal positioning of the film. A calibrated outcome

assessor performed the measurements. The periapical radiograph were

scanned with a resolution of 300 dpi using a digital scanner (HP Scanjet

4890, HP Portugal, Paço de Arcos, Portugal), and the marginal bone

level measurements performed using a software (Image J v. 1.40g,

National Institutes of Health). To perform the reading, the reference

points considered were the implant platform (horizontal interface

between implant and abutment for the axial implants and the orthogo-

nal interface for tilted implants) and the implant-bone first contact. The

calibration of the radiographs was performed digitally by using as refer-

ence the implants' interthread distance. Mesial and distal measure-

ments were performed with calculation of average values per implant.

The marginal bone level at 5 and 10 years were compared with the

measurement at the day of surgery and MBL was calculated. The radio-

graphs were accepted or rejected for evaluation based on the clarity of

the implant threads: a clear thread guarantees both sharpness and an

orthogonal direction of the radiographic beam toward the implant axis.

A radiographic illustration is provided in Figures 1–3.

Biological complications (implant infection occurring in the first

year postoperatively), fistula, abscess or peri-implant disease (peri-

implant pockets over 4 mm with bleeding on probing and MBL with

F IGURE 1 Baseline periapical radiographs (day of surgery) of a patient rehabilitated according to the All-on-4 concept

MALÓ ET AL. 3

or without suppuration after the first year of follow-up); and mechani-

cal complications (loosening or fracture of any prosthetic component)

were assessed throughout the study follow-up and registered as pre-

sent or absent.

2.5 | Statistical analysis

Descriptive statistics were calculated for prosthetic and implant as well

as for MBL. Cumulative implant survival was estimated through life

tables. The Cox proportional hazards regression model was used to

evaluate potential associations with implant failure. Univariable ana-

lyses was used to identify variables associated with implant failure: age

(measured in years of life; scale and ordinal categories: less than

48 years of age; 49-54 years, 55-60 years, and more than 60 years),

gender, systemic condition (absence/presence), smoking status (smoker/

nonsmoker), type of opposing dentition (implant-supported fixed

prosthesis, natural tooth-supported fixed prosthesis, natural teeth,

miscellaneous, removable denture), mechanical complications (pres-

ence/absence), biological complications (presence/absence). Variables

potentially associated with the outcome (P < .20 in univariable ana-

lyses) and with biological plausibility were inserted in a multivariable

Cox proportional hazards regression model; the regression coefficients

and corresponding SEs were estimated.24

For “advanced MBL” (MBL > 2.8 mm at 5 years; MBL > 3 mm at

10 years), “biological complications” and “mechanical complications”

(remaining outcome variables) the odds ratios (ORs) were estimated

together with the corresponding 95% confidence intervals (CI's) using a

binary logistic regression model. Univariable analyses were used to identify

associations between potential predictors (all variables described in the

Cox regression analysis together with the variable “previous failure of a

contiguous implant within the rehabilitation”) and the outcome variables.

Variables potentially associated in the univariable analysis (P < .20) were

entered into a multivariable logistic regression model. A comparison

between patients lost to follow-up and patients followed to the end of the

study was performed on the demographic variables age (Mann-Whitney

U test) and gender (chi-square test), and the variables smoking, systemic

condition, and opposing dentition (chi-square test) to evaluate potential

differences between both groups. Significance was considered for P < .05.

Statistics were performedwith SPSS 17.0 (IBM, Rochester, New York).

3 | RESULTS

3.1 | Patient and implant characteristics

The sample included 1072 patients (men: 442 patients; women: 630

patients; average age 55.8 years, range: 20-88 years) were rehabilitated

F IGURE 2 Five-year of follow-up periapical radiographs of the same patient rehabilitated according to the All-on-4 concept

F IGURE 3 Ten-year of follow-up periapical radiographs of the same patient rehabilitated according to the All-on-4 concept

4 MALÓ ET AL.

with a full-arch restoration in the maxilla supported by four implants in

immediate function placed anterior to the sinus wall with a total of

4288 implants with anodically oxidized surface (Brånemark System Mk

III implants [n = 17], Brånemark System Mk IV implants [n = 92, 7 fail-

ures], NobelSpeedy Groovy implants [n = 4179, 118 failures]) with

3.3-5 mm of width and lengths between 7 and 18 mm.

A total of 555 patients were positive for ICD-11 with 241 patients

who were smokers (22.5%) and 376 patients (35.1%) who had a single

systemic condition with 128 patients with more than one condition

(Table 1). Regarding the opposing dentition, 33 patients had a remov-

able prosthesis, 177 patients presented natural teeth, 3 patients pres-

ented fixed prosthetics over natural teeth, 490 patients presented a

miscellaneous combination of implant-supported fixed prosthesis and

natural teeth, and 369 patients presented implant-supported fixed

prosthesis.

A total of 18 patients deceased due to causes unrelated to the den-

tal treatment (1.7%) and 219 patients (20.4%) became unreachable and

were lost to follow-up (Table 1). The comparison between patients lost

to follow-up and patients followed to the end of the study rendered no

significant differences for the demographic variables age (P = .196,

Mann-Whitney U) and gender (P = .272, chi-square), nor for the

variables smoking (P = .892, chi-square), systemic condition (P = .802,

chi-square), or opposing dentition (P = .802, chi-square).

3.2 | Prosthetic and implant success

Nine patients lost their prostheses due to implant failures: after

3 months (the patient lost three implants supporting the provisional

prosthesis and received zygomatic implants), 4 months (the patient

lost four implants and the provisional fixed prosthesis was changed to

TABLE 1 Overall medical status distribution according to the International Classification of Disease, version 11 (ICD-11); distribution ofpatients deceased and lost to follow-up in the sample

ICD-11classification ICD-11 group description Examples

Number ofpatients

Number ofimplants

1 Certain infectious or parasitic diseases (HIV, hepatitis) 31 124

2 Neoplasms (Cancer) 11 44

3 Diseases of the blood or blood forming organs (Coagulation problems) 3 12

5 Endocrine, nutritional, or metabolic diseases (Diabetes, hypercholesterolemia, hyperthyroidism) 83 332

6 Mental, behavioral, or neurodevelopmental

disorders

(Depression) 3 12

8 Diseases of the nervous system (Alzheimer, epilepsy) 12 24

11 Diseases of the circulatory system (Hypertension, arrhythmia, angina) 213 852

12 Diseases of the respiratory system (Emphysema, asthma) 11 44

13 Diseases of the digestive system (Heavy bruxer) 40 160

14 Diseases of the skin (Epidermolysis bullosa) 1 4

15 Diseases of the musculoskeletal system or

connective tissue

(Osteoporosis) 29 126

16 Diseases of the genitourinary system (Menopausal and perimenopausal disorders,

prostatitis)

12 48

21 Symptoms, signs, findings Hemiplegia, nervous tachycardia 2 8

24 Factors influencing health status or contact with

health services

(Smoking) 241 964

Total 692a 2754

Distribution of the patients deceased and lost to follow-up

First year 1 patient deceased 16 patients unreachable Total of 17 patients

1-2 years 2 patients deceased 31 patients unreachable Total of 33 patients

2-3 years 3 patients deceased 25 patients unreachable Total of 28 patients

3-4 years 1 patient deceased 29 patients unreachable Total of 30 patients

4-5 years 6 patients deceased 20 patients unreachable Total of 26 patients

5-6 years 5 patients deceased 34 patients unreachable Total of 39 patients

6-7 years 5 patients deceased 23 patients unreachable Total of 28 patients

7-8 years 1 patient deceased 24 patients unreachable Total of 25 patients

8-9 years 3 patients deceased 4 patients unreachable Total of 7 patients

9-10 years — 4 patients unreachable Total of 4 patients

aA total of 555 patients presented a single condition, with 128 patients with more than single condition.

MALÓ ET AL. 5

a removable prosthesis), 5 months (the patient lost three implants and

the provisional fixed prosthesis was changed to a removable prosthe-

sis), 6 months (the patient lost three implants supporting the provi-

sional prosthesis and received zygomatic implants), 9 months (the

patient lost four implants and the provisional fixed prosthesis was

changed to a removable prosthesis), 16 months (the patient lost four

implants supporting the definitive prosthesis and received zygomatic

implants), 18 months (the patient lost four implants supporting the

definitive prosthesis and received zygomatic implants), 45 months

(the patient lost three implants supporting the definitive prosthesis

and received zygomatic implants), and 72 months (the patient lost

four implants supporting the definitive prosthesis), rendering a 99.2%

prosthetic success rate.

A total of 125 implants in 75 patients failed and were removed,

rendering a cumulative implant survival rate of 96.7% at 10 years and

94.7% with up to 13 years of follow-up (Table 2). Considering the

evaluation of the implants success criteria, 16 implants in 13 patients

exhibited persistent infections that could potentially threaten the

implant's successful outcome (MBL extending beyond 50% of the

implant length) and were classified as survivals, rendering a cumulative

implant success rate of 95.2% at 10 years and 93.9% with up to

13 years of follow-up (Table 3; Figure 4). Figure 5 illustrates the

TABLE 2 Implant cumulative survival distribution for implants supporting full-arch maxillary rehabilitations according to the All-on-4treatment concept

Time periodTotal numberof implants

Number ofimplants lost Lost to follow-up

Follow-upnot completed

Cumulativesurvival rate

0-1 year 4288 61 70 0 98.6%

1-2 years 4157 19 134 0 98.1%

2-3 years 4004 7 107 0 97.9%

3-4 years 3890 6 119 0 97.8%

4-5 years 3765 2 115 0 97.7%

5-6 years 3648 3 156 100 97.6%

6-7 years 3389 7 112 468 97.4%

7-8 years 2802 4 100 679 97.3%

8-9 years 2019 6 28 652 96.9%

9-10 years 1333 5 16 683 96.4%

10-11 years 629 2 0 286 96.0%

11-12 years 341 3 0 232 94.7%

12-13 years 106 0 0 95 94.7%

13-14 years 11 0 0 11 94.7%

TABLE 3 Implant cumulative success distribution for implants supporting full-arch maxillary rehabilitations according to the All-on-4 concept

Time periodTotal numberof implants

Number ofunsuccessfulimplantsa

Lost tofollow-up

Follow-up notcompleted

Cumulativesuccess rate

0-1 year 4288 61 70 0 98.6%

1-2 years 4157 19 134 0 98.1%

2-3 years 4004 8 107 0 97.9%

3-4 years 3889 6 119 0 97.8%

4-5 years 3764 2 115 0 97.7%

5-6 years 3647 6 156 98 97.5%

6-7 years 3387 11 112 466 97.2%

7-8 years 2798 7 100 677 96.9%

8-9 years 2014 7 28 652 96.5%

9-10 years 1327 9 16 681 95.6%

10-11 years 621 2 0 284 95.2%

11-12 years 335 3 0 229 93.9%

12-13 years 103 0 0 94 93.9%

13-14 years 9 0 0 9 93.9%

aThe sum of implant failures and implant survivals (with marginal bone loss that could jeopardize the successful outcome as defined by the success criteria).

6 MALÓ ET AL.

distribution of survival according to the health status of the patients

(healthy or systemic compromised/smoker).

3.3 | Regression analysis of implant failure—Coxproportional hazards

The univariable Cox proportional hazards regression analysis registered

gender (P = .018), systemic compromised condition (P = .184), smoking

(P = .004), and mechanical complications (P = .022) as potentially

associated with an increased hazard for implant failure. Multivariable

regression model (Cox proportional hazards) disclosed gender (male:

HR = 1.73) and smoker (HR = 1.94) as risk indicators for implant failure

and mechanical complications as a protective effect (HR = 0.59) after

controlling for systemic compromised condition (Table 4).

3.4 | Marginal bone loss

At 5 years of follow-up, 758 of the 920 patients had readable radio-

graphs (82.4%). The average MBL registered was 1.18 mm (95% CI:

1.16, 1.21) (Figure 6). At 10 years of follow-up, 129 of the 155 patients

had readable radiographs (83.2%). The average MBL registered was

1.67 mm (95% CI: 1.58, 1.77) (Figure 6).

3.5 | Binary logistic regression analysis for advancedMBL at 5 and 10 years

There were 89 patients with 120 implants exceeding an MBL of 2.8 mm

at 5 years. The univariable binary logistic regression analysis registered

age (P < .001), gender (P = .023), opposing dentition (P = .109), systemic

compromised condition (P = .118), smoking (P = .002), and biological

complications (P < .001) as potentially associated with MBL > 2.8 mm.

The variables age (OR = 0.97), gender (male: OR = 0.58), smoking

(OR = 1.73), and biological complications (OR = 2.1) remained signif-

icant after adjusting for opposing dentition and systemic com-

promised condition in the multivariable logistic regression model

(Table 5). There were eight patients with implants exceeding MBL of

3 mm after 10 years of follow-up and no risk indicators were associ-

ated (due to lack of statistical power).

3.6 | Incidence and risk indicators of biologicalcomplications

Biological complications occurred at 312 of the implants (7.8%) in

203 patients (18.9%) consisting of abscess/suppuration (n = 12

implants in 8 patients), implant infections occurring during the first year

of follow-up (n = 149 implants in 106 patients resulting in six implant

failures) and peri-implant disease (n = 151 implants in 106 patients

resulting in eight implant failures). Concerning the potential risk indica-

tors, the univariable analysis disclosed age (P = .004) and smoking

(P = .002) as variables significantly associated with the incidence of bio-

logical complications, with smoking (OR = 1.53) remaining significant in

the multivariable analysis after adjusting for age (Table 6).

3.7 | Incidence and risk indicators of mechanicalcomplications

Mechanical complications occurred in the provisional prostheses for

630 patients (58.8%) and in the definitive prostheses for 78 patients

(7.3%), with one patient accumulating complications in both prostheses

F IGURE 4 Cumulative success rate for the implants supportingAll-on-4 maxillary rehabilitations: A 95.2% cumulative success ratewas registered at 10 years of follow-up while a 93.9% cumulativesuccess rate was registered with up to 13 years of follow-up

F IGURE 5 Cumulative success rate for the implants supportingAll-on-4 maxillary rehabilitations. Illustrative comparison of thedistribution of implant success between healthy and systemiccompromised patients at 10 years of follow-up and with up to13 years of follow-up

MALÓ ET AL. 7

(Table 7). There were no significant associations between potential risk

indicators and mechanical complications.

4 | DISCUSSION

The current study evaluated the long-term outcome of the All-on-4

concept in the full-arch maxillary rehabilitation, registering a 99.2%

prosthetic success rate and a 93.9% cumulative implant success rate

with up to 13 years of follow-up. The results of this study comple-

ment the recent systematic reviews validating the All-on-4 con-

cept18,19 as well as previously published follow-up evaluations of up

to 5 years5,25 by including a sample of 1072 patients with a follow-up

beginning at 5 years and registered a cumulative implant survival rate

of 96.7% at 10 years of follow-up and 94.7% in a follow-up with up to

13 years. The implant failure distribution was characterized by an

increased density in the first year of follow-up (n = 61 implants lost)

and a stable low density from the first year onwards until the eleventh

year of follow-up where the last implant failure occurred in the

sample. It is worthwhile underlining the fact that the current results

were achieved in a sample where the majority of patients included

were either smokers or had systemic compromised conditions, leading

to cumulative implant success rate differences of 1.9% at 10 years

and 4.3% up to 13 years favoring healthy patients.

The influence of one of these conditions was particularly

evidenced in the multivariable regression analysis where smoking

habits increased the hazard ratio of implant failure by 94%. The dele-

terious effect of smoking was previously stated by a significant body

of scientific evidence.

Previous investigations reported higher probability for implant fail-

ure in smokers compared to nonsmoking patients26–28 in both early

and late failure. A systematic review26 and meta-analysis of 18 studies

evaluated the impact of smoking on the outcome of implant

supported restorations yielding an increase of 2.83 and 2.25 in the

OR for early and late implant failure, respectively. Another systematic

review and meta-analytic study28 of 51 studies with 40 000 implants

estimated an overall risk ratio of implant failure in smokers of 1.92.

Furthermore, subgroup analysis to investigate differences between

TABLE 4 Multivariable analysis of potential hazard risk indicators associated with implant failure using the Cox proportional hazardsregression model

Variables Hazard ratio univariate P Multivariable ß Multivariable SE P Multivariable hazard ratio (95% CI)

Age 1.01 .233

Gender (male) 1.71 .018 0.551 0.227 .015 1.74 (1.11, 2.71)

Systemic condition 0.71 .184 −0.391 0.256 .128 0.68 (0.41, 1.12)

Opposing dentition 0.98 .792

Smoking 1.95 .004 0.663 0.234 .005 1.94 (1.23, 3.07)

Mechanical complication 0.59 .022

Biological complication 1.22 .461 −0.527 0.229 .021 4.14 (2.07, 8.31)

Abbreviation: CI, confidence interval.

F IGURE 6 Boxplot illustrating the marginal bone loss measured inmillimeters at 5 and 10 years of follow-up. At 5 and 10 years themedian (horizontal black line inside the box) was 1.05 mm and1.50 mm, respectively

TABLE 5 Binary logistic regression to evaluate the potential riskindicators for marginal bone loss >2.8 mm at 5 years

Factor OR (95% CI) P ORa (95% CI) P

Gender (female) 0.57 (0.35, 0.93) .023 0.58 (0.35, 0.94) .029

Age 0.96 (0.94, 0.98) <.001 0.97 (0.94, 0.99) .017

Opposing

dentition

0.86 (0.72, 1.03) .109 0.8-1.91 .486

Previous implant

failure

0.72 (0.22, 2.40) .592

Mechanical

complications

0.79 (0.51, 1.23) .297

Biological

complications

2.45 (1.52, 3.93) <.001 2.10 (1.28, 3.43) .003

Systemic condition 0.68 (0.41, 1.11) .118

Smoking 2.08 (1.30, 3.29) .002 1.73 (1.06, 2.83) .028

Abbreviations: CI, confidence interval; OR, odds ratios.aOR from logistic regression analysis with pervious implant failure,

biological complications, and smoking included given its significance

(P < .20) in the unadjusted model. R2 = .095; Sensitivity = 1.1%;

Specificity = 100%; Accuracy = 88.4%.

8 MALÓ ET AL.

studies included in meta-analysis registered no significant differences

in the outcome when follow-up was analyzed, registering a risk ratio

of 1.98 for studies <5 years and 1.72 for studies ≥5 years. A possible

explanation for these results might rely on the particular effect of

impaired healing29 promoting early implant failure and the setting of a

chronical inflammation state that potentiates biological complications

leading to late implant failure.30

Male gender was also associated with implant failure, with a 73%

increase in the hazard ratio. In our study, male patients also exhibited

more smoking habits (a 4% increase compared to female patients) but

provided an 8% excess of implant failures in the absence of smoking

habits, which combined with the multivariable analysis excluded the

potential confounder effect. Moreover, the result is also supported by

previous publications: A meta-analytic investigation31 of 91 studies

with 52 357 implants registered a 21% increase on the implant failure

rate for male patients while assessing the outcome of dental implant-

supported restorations.

The protective effect of mechanical complications may be related

to a potential confounder effect. This effect may be explained by the

fact that patients with mechanical complications had more visits and

clinical appointments compared to patients without mechanical com-

plications and this way were provided with an overall increase in the

clinical control appointments that influenced positively the implant

survival outcome.

The average MBL at the 5- and 10-year evaluations was character-

ized by a stable condition with an average annual bone loss under

0.1 mm between the 5th and the 10th years of function. Despite being

suggested only as a general yard stick for the evaluation of new implant

systems coming into the market and not as a specific criterion for

implant success evaluation (considering there is no evidence to support

specific levels),32 the Albrektsson success criteria33 is still considered

the gold standard for MBL evaluation. Under this criterion, the MBL

outcome of this study compared favorably both in overall (on average

0.62 mm and 1.13 mm below the threshold of 1.8 mm at 5 years and

2.8 mm at 10 years, respectively) and annual bone loss per year (only

evaluated between 5 and 10 years with under 0.1 mm of annual MBL).

These values are favorable when compared to other longer-term

studies evaluating immediate function implants supporting full-arch

fixed prostheses with 5 and 7 years of follow-up.5,34,35 Maló et al in an

investigation assessing the outcome of the All-on-4 treatment concept5

in the maxillae reported an average MBL of 1.95 mm at 5 years of

follow-up in a smaller sample of only 106 implants (33 patients).

Niedermaier et al registered an average of 1.30 mm of MBL at 5 years

of follow-up using four to six implants in the full-arch rehabilitation of

the severely atrophied edentulous jaw.34 Nevertheless, the direct com-

parison of results across different studies might not be possible due to

lack of differentiation between treatment protocols in mandibular and

maxillary implants. A further illustration relies for example on the fact

that Vervaeke et al disclosed implant placement in the maxilla as a pre-

dictor of peri-implant bone loss36; however, other studies found no

differences.18,37

In about 2.8% of the implants (n = 120) in 89 patients the MBL

exceeded 2.8 mm after 5 years of follow-up. Nevertheless, there was

a low overall number of implants affected and in the large majority of

patients only one of the implants per prosthesis was affected (n = 65

patients, 73%), suggesting a potential low impact on the prosthetic

survival and therefore low clinical significance. Considering the events

of MBL > 2.8 mm and the incidence of mechanical or biological com-

plications in the same implants it may be assumed that the excess

MBL could be partly explained as secondary to biological or mechani-

cal complications. Sixty-five (54%) of the 120 implants were attached

to prostheses that registered mechanical complications and/or were

preceded by episodes of infection, fistulae, or peri-implant disease.

Multivariable analysis registered age, gender, smoking, and previous

biological complication to be significantly associated withMBL > 2.8 mm

at 5 years after controlling for the presence of other potential risk

indicators. Female gender exhibited an increase of 68% in the risk for

advanced MBL. This result was previously reported in several long-

TABLE 7 Incidence of mechanical complications in the provisionaland definitive prostheses

Provisional prostheses (n = 630 patients; 6 patients >1 complication)

Complications Number Percentage

Prosthesis fracture 143 13.3%

Abutment fracture 6 0.6%

Cylinder fracture 73 6.8%

Abutment screw loosening 399 37.2%

Prosthetic screw fracture 3 0.3%

Prosthetic screw loosening 12 1.1%

Definitive prostheses (n = 78 patients; 1 patient >1 complication)

Complications Number Percentage

Ceramic crown fracture 15 1.4%

Acrylic crown fracture 29 2.7%

Crown avulsion 1 0.1%

Cylinder fracture 7 0.7%

Abutment fracture 4 0.4%

Abutment screw loosening 21 2.0%

Prosthetic screw loosening 2 0.1%

TABLE 6 Binary logistic regression to evaluate the potential riskindicators for the incidence of biological complications

Factor OR (95% CI) P ORa (95% CI) P

Gender (male) 1.06 (0.78, 1.45) .706

Age 0.98 (0.96, 0.99) .004 0.98 (0.97, 0.99) .027

Previous implant

failure

— .999

Mechanical

complications

— .996

Systemic condition 1.04 (0.75, 1.44) .807

Smoking 1.69 (1.21, 2.37) .002 1.53 (1.08, 2.17) .016

Abbreviations: CI, confidence interval; OR, odds ratios.aOR from logistic regression analysis with age and smoking included.

R2 = .021; Sensitivity = 0%; Specificity = 100%; Accuracy = 81.5%.

MALÓ ET AL. 9

term follow-up studies where higher MBL was registered compara-

tively to male patients.38–42

Biological complications may have a significant impact on the suc-

cess of implant-supported restorations. This negative impact can be

related to both early failure (infection forcing implant removal) and

late failure (peri-implant disease influencing MBL). A recent systematic

review investigating the prevalence of peri-implant disease, disclosed

a significant association between follow-up time and the prevalence

of peri-implant disease, concluding that the prevalence of peri-implant

diseases tends to increase with follow-up time.43 Nevertheless, when

properly diagnosed and treated, the situation might be resolved or

mitigated while preserving the implant. The biological complications

registered in the present study consisted of implant infections,

mucositis, peri-implant disease, and a scarce number of fistulae or

abscesses. The authors assume that the present study finding has

potentially low clinical relevance considering the following reasons:

(a) the overall low biological complications rate (under 10% of the

implants); (b) peri-implant disease occurred at 3.5% of the implants

and in under 10% of the patients; (c) the majority of biological compli-

cations was responsive to treatment; (d) in a large majority of patients

(65%) there was one single implant exhibiting a biological complica-

tion, bearing a low risk of prosthetic failure considering the patients

were rehabilitated with a full-arch restoration. Nonetheless, it is cru-

cial to identify complications at the earliest stage so to avoid its evolu-

tion into major complications that could jeopardize the survival

outcome. Therefore, an effective recall program is advised.

In both logistic regression models (for the outcome variables

MBL > 2.8 mm at 5 years and for biological complications), it should

be noted that the potential confounder effect the variable age exerted

on both outcomes as: (a) age was independently associated with both

outcome variables in the univariate analysis; (b) age was simulta-

neously associated with smoking in both models (younger patients

had a significantly higher frequency of smoking habits); and (c) age is

not on the causal pathway of advanced MBL for dental implants on

the first 5 years post-treatment nor with biological complications. The

multivariable analysis accounted for that confounder in the smoking

effect in both models.44 Smokers exhibited a 67% and 57% increase

on the risk for MBL > 2.8 mm at 5 years and for biological complica-

tions, respectively, compared to nonsmokers. The impact of smoking

on implant success still lacks consensus, with studies registering both

negative impact35,45 and absence of such impact on MBL or implant

failure.33 Particular difficulties concern the lack of precision in the def-

inition of smoking habit as well as the variability on the impact assess-

ment considering the type of statistical analysis (descriptive,

univariable, or multivariable), making it challenging to retrieve robust

inferences. The present study supports previous results of implant-

rehabilitations in smokers suggested by meta-analytic and review

studies, with high risk for MBL and incidence of biological complica-

tions.28,36 Chrcanovic et al29 in a systematic review and meta-analysis

investigating the outcome of implant treatment in smokers, including

107 investigations with 19 836 implants placed in smokers (n = 1259

failures) and 60 464 implants placed in nonsmokers (n = 1923 fail-

ures). The authors concluded that smoking has a potential deleterious

effect affecting both healing and the outcome of implant treatment.

The same effect was observed in the current study, with the majority

of biological complications occurring in the first year of function prob-

ably due to impaired healing and with smoking significantly associ-

ated. The implications of this result render considering informative

sessions and smoking cessation programs (not only preoperatively but

also postoperatively) tailored for patients who are smokers and reha-

bilitated with dental implants for maximizing the probability of a suc-

cessful outcome.

The interpretation of the results should be made with caution con-

sidering the study limitations: The single center retrospective design;

the lost-to-follow-up patients that could result in an overestimation

of the implant success rate; the 17% of nonreadable radiographs at 5-

and 10-year, represents a potential bias in the estimation of the MBL;

the fact that previous presence of periodontal disease was not

accounted for in the analysis is another limitation that may impact the

impact of the remaining risk indicators for implant failure, MBL, and

biological complications. The large sample size, multivariable statistical

analysis considering several factors simultaneously and the ~20% lost

to follow-up rate reflect strengths of the present study taking into

consideration a long follow-up up to 13 years.

Future research should focus on the very long-term outcome

(15 years +) of full-arch implant supported maxillary rehabilitations

through the All-on-4 concept, in a large sample size and considering

the soft tissue outcome.

5 | CONCLUSION

Considering the prosthetic, implant, MBL, biological, and mechanical

complications outcomes and the follow-up time of up to 13 years, it

can be concluded that the full-arch rehabilitation of the edentulous

maxillae according to the All-on-4 concept is a viable treatment option.

Smoking negatively impacted the implant success, biological complica-

tions, and MBL outcomes when adjusted for other variables of interest.

ACKNOWLEDGMENTS

The authors would like to acknowledge Mr Sandro Catarino concerning

the management of data during the study.

CONFLICT OF INTEREST

This study was supported by Nobel Biocare Services AG, grant

2016-1437. Paulo Maló received previous grants and educational fees

from Nobel Biocare Services AG and is currently a consultant for

Nobel Biocare. Miguel de Araújo Nobre, Armando Lopes and Ana Ferro

received previous grants and educational fees from Nobel Biocare

Services AG. Mariana Nunes declares no conflict of interest.

ORCID

Miguel de Araújo Nobre https://orcid.org/0000-0002-7084-8301

10 MALÓ ET AL.

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How to cite this article: Maló P, de Araújo Nobre M,

Lopes A, Ferro A, Nunes M. The All-on-4 concept for full-arch

rehabilitation of the edentulous maxillae: A longitudinal study

with 5-13 years of follow-up. Clin Implant Dent Relat Res.

2019;1–12. https://doi.org/10.1111/cid.12771

12 MALÓ ET AL.