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

Short-term report of an ongoing prospective cohort studyevaluating the outcome of full-arch implant-supported fixedhybrid polyetheretherketone-acrylic resin prostheses and theAll-on-Four concept

Paulo Maló DDS, PhD1 | Miguel de Araújo Nobre RDH, MSc Epi2 |

Carlos Moura Guedes DDS3 | Ricardo Almeida DDS3 | António Silva CDT4 |

Nuno Sereno PhD5 | João Legatheaux CDT4

1Department of Oral Surgery, Maló Clinic,

Lisbon, Portugal

2Research and Development Department,

Maló Clinic, Lisbon, Portugal

3Department of Prosthodontics, Maló Clinic,

Lisbon, Portugal

4Malo Clinic Ceramics, Lisbon, Portugal

5Invibio Biomaterial Solutions & JUVORA,

Global Technology Center, Hillhouse

International, Thornton Cleveleys, United

Kingdom

Correspondence

Miguel de Araújo Nobre, Maló Clinic, Avenida

dos Combatentes, 43, 11th floor, Edificio

Green Park, 1600-042 Lisbon, Portugal.

Email: mnobre@maloclinics.com

Funding information

Juvora, Grant/Award Number: 1/2013

AbstractBackground: More research is needed on the study of new materials for fixed prosthetic

implant-supported rehabilitations.

Purpose: The purpose of this study was to report the short-term outcome of full-arch implant-

supported fixed hybrid polyetheretherketone (PEEK)-acrylic resin prostheses and the all-on-four

concept.

Materials and Methods: This prospective cohort clinical study included 37 patients (29 women,

eight men) with an average age of 60 years (range: 38-78 years) with 49 full-arch hybrid PEEK-

acrylic resin prosthesis supported by implants through the all-on-four concept. Primary outcome

measures were prosthetic survival.

Results: Two patients with two maxillary prostheses were lost to follow-up. One patient with a

double full-arch rehabilitation fractured the mandibular PEEK framework, rendering a 98% pros-

thetic survival rate. No implants were lost. The average (SD) marginal bone remodeling after

1 year of follow-up was 0.37 mm (0.58 mm). Technical complications concerning the veneer

adhesion occurred in six patients and were resolved in all patients (with exception of the patient

with prosthetic failure) through the creation of mechanical retentions and changing the bonding

primer. Mechanical complications occurred in three patients and five prostheses consisting in

prosthetic screw loosening (n = 2 patients) and fracture of the acrylic resin teeth (the patient

with a prosthetic failure).

Conclusions: Within the limitations of this study, the results suggest that hybrid polymer

(PEEK)-acrylic resin prostheses supported by implants for full-arch rehabilitation may represent

a valid treatment option, still requiring longer-term validation.

KEYWORDS

all-on-four, immediate implants, polyetheretherketone, prostheses and implants

1 | INTRODUCTION

The rehabilitation of edentulous jaws through fixed implant-supported

prosthesis with immediate function protocols allows the restoration

of aesthetics, phonetics, and mastication,1 providing a psychological

benefit for the patient.2-4 The all-on-four concept (Nobel Biocare AB,

Göteborg, Sweden) is one of such immediate function protocols

involving the insertion of four implants for full-arch rehabilitation of

edentulous jaws with a minimum bone volume and avoiding bone aug-

mentation procedures.5 Provided the implants are placed

strategically—two posterior implants tilted up to 45� and two anterior

axial implants—and they are well anchored (achieving a high primary

Received: 13 November 2017 Revised: 5 March 2018 Accepted: 12 July 2018

DOI: 10.1111/cid.12662

Clin Implant Dent Relat Res. 2018;1–11. wileyonlinelibrary.com/journal/cid © 2018 Wiley Periodicals, Inc. 1

stability of at least 30 Ncm), the treatment success rate is high (98%

for the maxilla and 98.1% for the mandible after 5-10 years of follow-

up).6,7 Under these specific principles in implant arrangement, a large

anterior/posterior spread between implants can be obtained consis-

tently, aiming for prosthodontic stability.7

Full-arch fixed implant hybrid prostheses, in function for over

40 years, require frameworks to splint the implants together for sup-

port, an assemble considered as one of the keys to long-term clinical

success.8,9 The historical perspective of framework materials includes

the evolution from cast noble (gold, silver, etc) or base metal alloys

(nickel and chromium) to the modern milled titanium and zirconium

frameworks, the latter providing high biocompatibility, corrosion resis-

tance, and the possibility of computer assisted-design/computed

assisted-manufacture (CAD/CAM), an important improvement to

achieve a better fit between framework and dental implants.8,10,11

Nevertheless, the high stiffness of these frameworks measured by the

flexural strength (titanium: 434 MPa; zirconia: 900-1100 MPa) can be

considered a potential disadvantage in shock absorption behavior of

the prosthesis.12,13

Polyetheretherketone (PEEK) consists in a high-performance

polymer from the polyaryletherketone (PAEK) family. PEEK is a ther-

moplastic polymer that is typically used as a metal replacement, owing

to its strength to weight ratio and corrosion resistance.14

PEEK was originally developed in the United Kingdom in 1978

(ICI—now as Victrex plc) and requires a particular polymerization pro-

cess, which enables the control of the length of the resulting polymer

chains.15,16 This polymer versatility allows the offering of a range of

processing options and an array of formulations, ranging from unfilled

grades with varying molecular weights, to image contrast, colored and

carbon fiber-reinforced grades.17,18

Implantable PEEK polymer displays a number of properties includ-

ing biocompatibility, biostability, and compatibility with medical diag-

nostic imaging.19 In addition, PEEK provides superior chemical

stability, mechanical behavior, creep, and wear resistance and is there-

fore well suited to the demanding environment encountered by medi-

cal devices.16

Over the last decades, PEEK has seen extensive use in highly

demanding industrial (aerospace, automotive, oil and gas, electronic)16

and medical applications including implantable medical devices such

as orthopedic,20 spinal,20,21 and cranial implants.22 PEEK (Thornton

Cleveleys, United Kingdom: PEEK-OPTIMA Invibio Ltd.) has been

used clinically for more than 15 years and in over 5 000 000

implanted devices across a wide range of medical applications, includ-

ing spinal fusion, where it has become an industry standard implant

material.17,23 Specifically in the field of dentistry, PEEK has been used

over the last decade in healing caps and temporary abutments.24-29

Due to its proven biocompatible nature and its shock absorbing

characteristics,12,13,30 while maintaining the possibility of CAD/CAM

manufacture, such a material could be interesting for use in full-arch

restorations as a nonmetal alternative. Nevertheless, proof on its

long-term outcome in implant-supported fixed rehabilitations is lack-

ing, making it necessary to evaluate the outcome of implant-

supported fixed prosthetic rehabilitations using PEEK material.

The aim of this ongoing prospective study was to report on the

short-term outcome (1 year) of full-arch rehabilitations using the

all-on-four concept (Nobel Biocare AB) and a full-arch hybrid PEEK-

acrylic resin prosthesis (PEEK infrastructure and acrylic resin artificial

gingiva and acrylic resin teeth).

2 | MATERIALS AND METHODS

This prospective cohort clinical study was performed in a private prac-

tice (Lisbon, Portugal) and is estimated to last for 5 years. The present

report concerns the 1-year evaluation (short-term outcome). The

patients were rehabilitated between May 2015 and October 2016.

This study was approved by an independent ethical committee

(Ethical Committee for Health, authorization no. 008/2013). All

patients signed a written informed consent to participate in the pre-

sent study. Thirty-seven full-arch edentulous patients (29 females and

8 males) with an average age (SD) of 59.8 years (10.6 years) and

49 edentulous arches (double full-arch: 12 patients; single full-arch

maxillae: 12 patients; single full-arch mandible: 13 patients) were

included and treated in a private practice (Maló Clinic, Lisbon, Portu-

gal). The patients who met the inclusion criteria were identified at the

treatment planning phase.

2.1 | Inclusion and exclusion criteria

Inclusion criteria were patients submitted to full-arch fixed prosthetic

rehabilitation supported by implants in immediate function inserted

through the all-on-four concept (Nobel Biocare AB). Patients were

excluded from this study if they presented the following criteria:

insufficient bone volume, active radiotherapy or active chemotherapy,

or hindrance to provide written informed consent.

2.2 | Surgical protocol

The surgical and prosthetic procedures are described in a previous

published manuscript.31,32

In brief, surgery was performed with the patient under local anes-

thesia using articaine clorhidrate (72 mg/1.8 ml) with epinephrine

(0.018 mg/1.8 ml) 1:100.000 (Artinibsa 2%; Inibsa Laboratory, Barce-

lona, Spain). Prior to the surgical procedure the patients were adminis-

tered with diazepam (Valium 10 mg, Roche, Amadora, Portugal). The

administration of antibiotics was performed 1 hour before surgery

and thereafter on a daily basis for 6 days (amoxicillin 875 mg and cla-

vulanic acid 125 mg; Labesfal, Campo de Besteiros, Portugal). Cortico-

steroids were given daily in a regression mode (15 mg on the day of

surgery to 5 mg on the fourth day) (prednisone 5 mg [Meticorten

Schering-Plow Farma, Lda, Agualva-Cacém, Portugal]). Anti-

inflammatories (ibuprofen, 600 mg; Ratiopharm, Lda, Carnaxide, Por-

tugal) were given for 4 days postoperatively starting on the fourth

day. Analgesic medication [clonixine (300 mg, Clonix, Janssen-Cilag

Farmaceutica, Lda, Barcarena, Portugal)] was administered to the

patients on the day of surgery and only used postoperatively in case

of experiencing pain. Antacid medication (omeprazole, 20 mg; Lisboa,

Portugal) were administered to the patients on the day of surgery and

from thereafter on a daily basis for 6 days.

2 MALÓ ET AL.

Implant insertion (Nobelspeedy; Nobel Biocare AB) followed stan-

dard procedures33 with the exception of the use of under-preparation,

employed to guarantee a final torque of over 32 N/cm before the

final implant seating. Implant length ranged between 10 and 18 mm.

The two most anterior implants were inserted following the direc-

tion determined by anatomy of the jaw. The two posterior implants

were inserted (one implant on each quadrant) anterior to the mental

foramina (in the mandible) and the anterior wall of the maxillary sinus

(in the maxilla) with a distal tilting between 30� and 45� relative to the

occlusal plane, aiming for good implant anchorage, large inter-implant

distance and short cantilevers.3,31,32

The implants were positioned at bone level. Whenever possible,

bicortical anchorage was established. Soft tissue was readapted and

sutured back into position on each patient using 3-0 nonresorbable

sutures (Silkam, B. Braun Surgical SA, Rubi, Spain). The abutment

choice was made based on the use of straight multiunit abutments

(Nobel Biocare AB) for the anterior implants and 30� angulated abut-

ments for the posterior implants. Whenever was needed a further

compensation of the angulation in the anterior implants due to jaw

anatomy, 17� abutments were used. The specific choice of abutments

was made with the objectives of allowing the prosthesis to have pas-

sive fit, maintaining the prosthesis with an acceptable thickness, and

having the prosthetic screw-access holes emerging on the occlusal or

lingual aspects of the prosthesis.

Patients were informed that the surgical area should be kept cool

and under minimal pressure for the first 48 hours after the surgery;

only soft and cold foods were to be ingested during that period.

2.3 | Immediate provisional prosthetic protocol

High-density acrylic resin (PalaXpress Ultra; Heraeus Kulzer GmbH)

prostheses with titanium cylinders (Nobel Biocare AB) were manufac-

tured at the dental laboratory and inserted on the same day (n = 49).

The occlusion scheme adopted in the provisional prosthesis privileged

anterior occlusal contacts and canine guidance during lateral move-

ments. On the provisional prostheses, the emergence positions of the

screw-access holes were normally at the second premolar level for the

posterior implants. The prostheses exhibited a minimum of 10 teeth.

2.4 | Pilot study

The CAD/CAM guidelines as related to cross-sectional material

dimensions below which fabrication are not advised were a minimum

occlusocervical height of 4 mm, a buccolingual width of minimum

3 mm and a maximum of one cantilever unit according to the manu-

facturer (Figure 1). A pilot study was performed with four patients and

five full-arch prostheses in the period between May 2014 and May

2015. The results of the pilot study determined that a titanium sleeve

had to be inserted within the PEEK infrastructure at the CAM phase

in order to avoid PEEK strangulation provoked by the titanium pros-

thetic screws' torque tightening (Figures 2 and 3). The special reten-

tion mechanism was not necessary for the titanium sleeves that were

inserted on the PEEK infrastructure in its coronal aspect, surrounded

by PEEK and acrylic-resin.

Considering the results of the pilot study, the adopted CAD/CAM

guidelines as related to the cross-sectional material dimensions were a

framework design using an “I” shape, with a minimum occlusocervical

height of 5 mm, a minimum anterior buccolingual width of 4 mm, the

increase of width in the areas of the titanium sleeve for a minimum of

6 mm buccolingual width (Figure 4), and a minimum of 1-2 mm of

acrylic resin to increase the adhesion while considering the previously

mentioned dimensions.

2.5 | Definitive prosthetic protocol

The final full-arch hybrid prostheses were assembled of polymeric-

acrylic resin implant-supported fixed prostheses with a PEEK sub-

structure, reinforcing titanium sleeves, acrylic resin prosthetic teeth

and pink acrylic resin gingiva (patent pending; United Kingdom Patent

Application No. GB1711004.0). The final full-arch hybrid prostheses

determination was based on the all-on-four concept (Nobel Biocare

AB), aiming to achieve the area of the first molar in a prosthesis with

12 functional teeth,34 which is based on the exploratory nature of the

present study implied the inclusion of more than one cantilever unit in

nine patients and nine prostheses.

The dental laboratory used the tooth arrangement on the interim

implant-supported fixed prostheses as a starting point to manufacture

the definitive prostheses.

FIGURE 1 Prestudy CAD/CAM guidelines as related to minimum cross-

sectional material dimensions below which fabrication is not advisedwere a minimum occlusocervical height of 4 mm, a buccolingual width ofminimum 3mm, and a maximum of one cantilever unit

FIGURE 2 PEEK strangulation at the cylinder due to compression of

the titanium prosthetic screw after torque tightening

MALÓ ET AL. 3

A silicone mask index (Zetalabor; Heraeus Kulzer GmbH, Hanau,

Germany) was made with the maxillary and/or mandibular interim

prostheses removed from the patient and screwed onto the master

casts to serve as a guide for the final restoration. The setup (wax pat-

tern and acrylic teeth) was assembled and a try-in was performed in

mouth with the patient. A new silicone mask index (Zetalabor ) was

made over the try-in. The try-in and the stone model were scanned

and CAD designed (DentalCAD software, version 6.0.0.446; Cara DS

Scan scanner, version 3.2.1A 360). A screw-retained framework was

manufactured from a PEEK disk (Juvora Ltd, Lancashire, United King-

dom) after CAM processing adapting to the multiunit abutments. The

reinforcing titanium sleeves comprising a generally tubular wall and an

annular shoulder portion were introduced at the CAM processing step

and shaped to receive the terminal end of the multiunit abutments.

The PEEK substructure (Juvora, Ltd, Lancashire, United Kingdom)

surface was prepared according to the following protocol: the frame-

work was uniformly sand-blasted with silica (Rocatec plus, 3 M;

Maplewood, Minnesota) at a 3 bar pressure and a distance of 1 cm in

a 45� angle. The primer (metal-bond 1 and 2 on all cases; Signum Con-

nector on the cases identified with veneer adhesion issues; Heraeus

Kulzer GmbH) was applied over the framework, followed by a light-

curing pink opaque (Opaque F, Heraeus Kulzer GmbH). The prosthetic

teeth (anterior teeth: Premium; posterior teeth: Mondial; Heraeus Kul-

zer GmbH) were sand-blasted with aluminum oxide (Corundum, Her-

aeus Kulzer GmbH) at a 3 bar pressure-1 cm distance and placed on

the silicon mask from the try-in. The pink acrylic resin was poured on

the framework (PalaXpress Ultra, Heraeus Kulzer GmbH) and poly-

merized using a pressure pot (Palamat, Heraeus Kulzer GmbH) for

25 minutes at 55�C.

The final full-arch hybrid prostheses was a polymer-acrylic resin

implant-supported fixed prostheses with a PEEK framework (Juvora,

Ltd ), reinforcing titanium sleeves, acrylic resin prosthetic teeth

(Premium and Mondial crowns, Heraeus Kulzer GmbH), and pink

acrylic resin gingiva (PalaXpress Ultra, Heraeus Kulzer GmbH). The

average time manufacture process until the connection of the final

prostheses was 6 months.

The occlusion for the final prosthesis was adjusted to a mutually

protected occlusion scheme respecting the patients' centric relations.

Figures 5–14 illustrate the definitive prosthetic protocols of a full-arch

mandibular rehabilitation through the all-on-four concept (Nobel Bio-

care AB) with a polymer-acrylic resin hybrid prosthesis.

2.6 | Postoperative and maintenance protocols

The patients were instructed to have a soft food diet for the first

4 months postsurgery. Ten days after surgery, the sutures were

removed, and hygiene and implant stability (clinical mobility and sup-

puration by finger pressure) were checked. The occlusion was

rechecked according to the initial protocol, a procedure that was

repeated after 2 and 4 months. Usually, at around 4 months, the pros-

theses were again removed, jet-cleaned (using Air-Flow Powder, EMS,

Nyon, Switzerland), and disinfected (using 0.2% chlorhexidine; Elugel,

Pierre Fabre Dermo-Cosmetique), and the implants were checked for

anchorage (clinical mobility), suppuration, and pain.

The connection of the definitive prosthesis was considered the

baseline for clinical and radiographic evaluations. After the connection

of the full-arch definitive prostheses, the patients were evaluated

after 6-months (clinically) and 1 year of function (clinical and

radiographically).

2.7 | Primary outcome measure

Primary outcome measure was prosthetic survival (need to be

replaced) including fracture of framework.

2.8 | Secondary outcome measures

Secondary outcome measures were implant survival, marginal bone

remodeling, modified plaque index, modified bleeding index, technical

FIGURE 4 Study CAD/CAM guidelines as related to the cross-

sectional material dimensions with minimum occlusocervical height of5 mm, a minimum anterior buccolingual width of 4 mm, the increaseof width in the areas of the titanium sleeve for a minimum of 6 mmbuccolingual width

FIGURE 5 Pretreatment orthopantomographyFIGURE 3 Titanium reinforcing sleeves placed on the cylinders

4 MALÓ ET AL.

evaluation concerning manufacture issues, the incidence of mechani-

cal complications, the incidence of biological complications, and

patient subjective evaluation.

Implant survival was evaluated based on function and using the

patient as unit of analysis (first implant failure in a patient considered

as censoring event irrespective of the remaining implants maintaining

function).3

Marginal bone remodeling was evaluated using a conventional

radiographic holder (super-bite; Hawe Neos, Bioggio, Switzerland)

was used, and its position was manually adjusted for an estimated

orthognatic position of the digital film. An outcome assessor examined

all implant radiographs. The marginal bone remodeling was assessed

with image analysis software (rayMage, version 2.3; MyRay, Imola,

Italy). The reference point for the reading was the implant platform

(the horizontal interface between the implant and the abutment), and

the marginal bone level was assessed and defined as the most apical

contact between bone and implant. The difference in marginal bone

level between the 1-year and baseline assessments was defined as

the marginal bone remodeling. The measurements were performed on

FIGURE 6 Intra-oral frontal view at the treatment planning phase

FIGURE 7 Intra-oral frontal view of the double full-arch immediate

provisional acrylic-resin prostheses supported by implants inimmediate function through the all-on-four concept (NobelBiocare AB)

FIGURE 8 Photograph illustrating the silicone mask index

FIGURE 9 Frontal view of the maxillary full-arch setup (wax try-in

and acrylic teeth)

FIGURE 10 Digital image illustrating the CAD

FIGURE 11 PEEK substructure after CAM

FIGURE 12 Intra-oral frontal view of the double full-arch PEEK-

acrylic resin hybrid prostheses final

MALÓ ET AL. 5

the mesial and distal sites, and average values were calculated. The

radiographs were accepted or rejected for evaluation based on the

clarity of the implant threads; a clear thread guaranteed both sharp-

ness and an orthogonal direction of the radiographic beam toward the

implant axis. The radiographs were calibrated using the implant

threads.

Modified plaque index (mPLI),35 evaluated by inserting a peri-

odontal plastic probe 1 mm into the peri-implant sulcus, running a cir-

cular movement all around the implant and measured in a scale

between 0 and 3 (0: no detection of plaque; 1: plaque only recognized

by running a probe across the smooth marginal surface of the implant;

2: plaque can be seen by the naked eye; and 3: abundance of soft

matter).

Modified bleeding index (mBI)35 evaluated on the same moment

as mPLI and measured in a scale between 0 and 3 (0: no bleeding

when a periodontal probe is passed along the mucosal margin adja-

cent to the implant; 1: isolated bleeding spots visible; 2: blood forms a

confluent red line on mucosal margin; and 3: heavy or profuse

bleeding);

The technical evaluation of concerning manufacture issues was

evaluated comprising the infrastructure manufacture issues (presence

or absence), framework integrity issues (present/absent), and veneer

adhesion issues (present or absent).

Biological complications assessed were as follows: probing pocket

depth > 4 mm, evaluated using a plastic periodontal probe calibrated

to 0.25 N; abscess (presence or absence); fistulae formation (presence

or absence); suppuration (presence or absence); and patient adverse

soft tissue reaction (presence or absence).

Mechanical complications assessed were loosening or fracture of

prosthetic screws, abutments, or prosthesis.

The patients' evaluation comprised the “in mouth comfort”, defined

as the comfort felt by the patient with the prosthesis in function regard-

ing an overall fulfillment of expectations, measured in a visual analogue

scale between 0 (poor) and 10 (excellent) and “overall chewing feeling”,

defined as the patients' feeling when chewing food in their daily food

intake routines related to the ability to chew any type of food and mea-

sured in a visual analogue scale between 0 (poor) and 10 (excellent).

2.9 | Statistical analysis

Survival was estimated using life table analysis (actuarial method) and

using the implant and prosthesis as unit of analysis. Descriptive statistics

(average with 95% confidence intervals, SD) were computed for the var-

iables of interest: age, marginal bone loss, and the patient evaluation

variables “in mouth comfort” and “overall chewing feeling”; the mode

was computed for the variables mPLI and mBI; and frequencies were

computed for the technical evaluation concerning manufacturing issues

and for the incidence of biological and mechanical complications. Infer-

ential analysis was computed for the evaluation of the correlation

between mPLI and mBI through the Spearman’s correlation coefficient.

The significance level was set at 5%. The data were analyzed using the

software SPSS for Windows version 17 (IBM SPSS, New York).

3 | RESULTS

3.1 | Sample

A total of 37 patients were rehabilitated with 49 full-arch prostheses.

The average cantilever length in a prosthesis was 0.7 units (SD:

0.6 units; range: 0-2 units). Two patients (5.4%) with two single full-

arch maxillary prostheses (4.1%) were lost to follow-up during the first

6 months of follow-up, becoming unreachable.

3.2 | Primary outcome measure

One patient (male, 55 years of age, heavy bruxer) with a double full-

arch rehabilitation needed to replace the mandibular prosthesis due to

fracture of the PEEK framework, rendering 98% prosthesis survival

rate (Table 1).

FIGURE 14 Patient smiling with double full-arch PEEK-acrylic resin

hybrid prostheses

TABLE 1 Cumulative Prosthetic Survival Rate for Patients Rehabilitated Through the all-on-four Treatment Concept and a Hybrid PEEK-acrylic

resin prostheses

TimeTotal numberof patients

Prostheses

Total numberof prostheses

Prostheticfailures

Lost tofollow-up

Survivalrate

Prosthesis connection—1 year 37 49 1 2a 98.0

PEEK, polyetheretherketone.a Two prostheses in two patients.

FIGURE 13 Orthopantomography with double full-arch PEEK-acrylic

resin hybrid prostheses

6 MALÓ ET AL.

3.3 | Secondary outcome measures

A total of 196 implants were inserted for rehabilitation of 49 edentu-

lous arches. No implant failures were registered, rendering a 100%

implant survival rate after 1 year.

The average (SD) marginal bone remodeling after 1 ear of follow-

up was 0.37 mm (0.58 mm), with 0.33 mm (0.52 mm) for maxillary

implants and 0.40 (0.63 mm) for mandibular implants. The marginal

bone remodeling distribution considering the type of rehabilitation

per patient is illustrated in Figure 15, with a nonsignificant lower aver-

age registered for double full-arch rehabilitated patients compared to

single full-arch rehabilitations evaluating the significant overlap in the

95% confidence intervals.

The mode for the mPLI was two (plaque visible by the naked eye)

at 1 year of follow-up. The mode for the mBI was one (one isolated

bleeding spot visible when tested) at 1 year. The correlation between

mPLI and mBI was a nonsignificant, weak positive linear relationship

(R = 0.321; P = 0.068; Spearman’s correlation coefficient).

Concerning the technical evaluation, no issues were registered

during the manufacture phase of the prosthesis in both infrastructure

manufacture and integrity. The incidence of veneer adhesion issues

with avulsion of the acrylic resin from the PEEK infrastructure was

15.8% (n = 6 patients) at patient level and 14.3% (n = 7 prostheses) at

prosthesis level: One male patient with mandibular full-arch rehabilita-

tion occluding with a mucosal-retained full-arch prosthesis after

2 months of follow-up in position #35 (last cylinder); one female

patient with mandibular full-arch rehabilitation occluding with natural

teeth and implant-supported prosthesis after 4 months of follow-up in

position #46 (last cylinder); one female patient with mandibular full-

arch rehabilitation occluding with a mucosal-retained full-arch pros-

thesis after 10 months of follow-up in position #35 (last cylinder); one

female patient with mandibular full-arch rehabilitation occluding with

a mucosal-retained full-arch prosthesis after 12 months of follow-up

in position #35 (last cylinder); one female patient with a double full-

arch rehabilitation after 12 months in positions #15 and #22. The

issues with veneer adhesion were resolved in five patients and five

prostheses by increasing the amount of exposed PEEK in the cylinder

areas to increase flexion resistance, creating retentions in the PEEK

infrastructure with a tungsten bur to increase mechanical retention,

and changing the bonding primer used to improve the tensile bond

strength (Figures 16–20). In one male patient (55 years of age, heavy

bruxer) with a double full-arch rehabilitation with the avulsion occur-

ring after 5 months in positions #12, #22, #25, and #35, the issue was

not resolved as the patient accumulated this event with a fracture of

the acrylic teeth in both restorations and fracture of the PEEK infra-

structure in the lower restoration (position #35), forcing the manufac-

ture of a new prostheses (considered a failure).

During the follow-up of the study, no biological complications

were registered, with absence of peri-implant pockets >4 mm,

abscess, fistulae, formation, suppuration, or soft tissue adverse reac-

tions. Mechanical complications occurred in three patients (7.9%) and

five prostheses (10.2%) consisting of fractures of the acrylic resin

teeth and PEEK framework in one patient (2.6%) and two prostheses

(4.1%) and loosening of prosthetic screws in two patients (5.3%) and

three prostheses (6.1%). Prosthetic screw loosening occurred in one

female patient with PEEK-acrylic resin maxillary rehabilitation occlud-

ing with a full-arch acrylic resin implant-supported prosthesis after

4 months of follow-up and one female patient with double full-arch

PEEK-acrylic resin rehabilitation after 8 months of follow-up.

The prosthetic screw loosening events were resolved by torque

controlled retightening the prosthetic screws and adjusting the occlu-

sion. No further mechanical complications occurred.

Concerning the patients' evaluation, the registered averages

(SD) were 88% (16%) satisfaction for “in mouth comfort”, and 84%

(19%) satisfaction for “overall chewing feeling”.

FIGURE 15 Error bar chart illustrating the marginal bone loss

distribution according to the type of rehabilitation. Note theoverlapping 95% confidence intervals (bars) of the average (circles)indicating a non-significant difference between single full-arch anddouble full-arch rehabilitations

FIGURE 16 Veneer adhesion issue of crown #46

FIGURE 17 Creating villus for increase of mechanical retention

MALÓ ET AL. 7

4 | DISCUSSION

This study reports the short-term follow-up of a new proposal for full-

arch fixed prosthetic rehabilitations using an implant-supported hybrid

polymer-acrylic resin prosthesis. Considering the outcomes of pros-

thetic survival, implant survival, marginal bone loss, complications and

patients' subjective evaluation, this new proposal for full-arch

implant-supported rehabilitation may be a viable treatment option but

still requiring further follow-up evaluation to validate its use in implant

dentistry.

PEEK, a thermoplastic polymer with excellent thermal and chemi-

cal stability, especially used in a wide range of applications for auto-

motive and aerospace industries36 was proposed as a metal

replacement.14 The PEEK properties include biostability, biocompati-

bility, and shock-absorbing characteristics19,30: Rosentritt et al.30

made an in vitro study to investigate the force absorption capacity of

implant-supported molar crowns made of polymethyl methacrylate,

PEEK, composite, lithium disilicate, titanium and zirconia, and con-

nected to abutments with different luting agents registered that mate-

rials with a higher moduli of elasticity (ceramics and titanium)

exhibited lower shock-absorbing capacity than resin-based materials.

In a study, Sarot et al.29 compared carbon fiber-reinforced PEEK com-

ponents (implants and abutments) with titanium using finite element

analysis, registered a higher stress, and higher load concentration in

the cervical portion and on the cortical bone for carbon fiber-

reinforced PEEK implants when submitted to load, whereas the car-

bon fiber-reinforced PEEK abutment exhibited a similar performance

to the titanium abutments. This increase in stress was attributed to

the higher displacement capacity of the carbon fiber-reinforced PEEK.

Nevertheless, the stress distribution of carbon fiber-reinforced PEEK

abutments was similar to titanium when connected to a titanium

implant. In a study, Stawarczyk et al.24 evaluated the surface proper-

ties and fracture load of three-unit PEEK fixed dental prosthesis

determined the cut-off point of 1200 N for plastic deformation and

1383 N for mean fracture load, concluded that PEEK might be a suit-

able material for fixed dental prosthesis, especially in load-bearing

areas. Therefore, PEEK was chosen for further investigation in this

study, as part of a full-arch hybrid prosthesis supported by dental

implants.

The prosthetic survival registered in this study was 98% due to

one prosthetic failure in a double full-arch rehabilitated heavy bruxer,

presenting a line of fracture on the mandibular PEEK framework sug-

gesting occlusal overload. According to a systematic review, occlusal

overload, associated with parafunctional habits such as bruxism, was

considered the primary etiologic factor in biomechanical implant treat-

ment complications.37 The association of maximum bite force with

bruxing/clenching habits can impact significantly on the outcome of

prosthetic materials. Previous studies investigated the influence of

gender and bruxism on the human maximum bite force registered

peaks between 978-1000 N of bite force in a heavy bruxer males.38,39

Forces of this magnitude or stronger, constantly applied to prosthetic

materials through daily use will impact negatively the prosthetic out-

come even in a material with a deformation point module at 1200 N

of force.24

The present study recommends the following CAD/CAM guide-

lines for a clinically successful framework as related to cross-sectional

material dimensions: a minimum occlusocervical height of 5 mm and

an anterior buccolingual width of 4 mm. The fact that PEEK material is

less stiff and flexes more implied the increase of width in the areas of

the titanium sleeve for a minimum of 6 mm buccolingual width to

compensate flexion as it represented a weak point. Moreover, a

1-2 mm acrylic resin to increase the adhesion while considering the

previously mentioned dimensions together with a maximum of one

cantilever unit (following the manufacturer's instructions) are also

recommended.

The inclusion of cantilevers in the full-arch prostheses is directly

related to the degree of maxillary or mandibular crest resorption when

considering the all-on-the concept given the need of a minimum

12 functional teeth. A previous study evaluating the outcome of all-

on-four concept rehabilitations and proposing an edentulism classifi-

cation reported different implant distributions according to available

bone in volume and density.34 The presence of bone available up to

FIGURE 18 Applying the bonding primer

FIGURE 19 Prosthesis vestibular view after resolving veneer

adhesion issue

FIGURE 20 Prosthesis lingual view after resolving veneer adhesion

issue. Note the increased amount of exposed PEEK in the cylinder

area to increase flexion resistance

8 MALÓ ET AL.

second premolar determined the anterior implant exits in the canine

area and the posterior tilted implants exits on the molar without

including cantilevers; the presence of bone available up to the first

premolar determined the anterior implant exits in the lateral incisor

area and the posterior tilted implants exits on the second premolar

with inclusion of a one unit cantilever; the presence of bone available

up to the canine determined the anterior implant exits in the central

incisor area and the posterior tilted implants exits on the first premo-

lar with inclusion of a two units cantilever. Significant differences

were reported with the absence of cantilever units in the prosthesis

as a protective effect (odds ratio = 0.22) and bruxism (odds ratio =

60.95) as a risk factor for the occurrence of mechanical complications

in a logistic regression model. A similar result was reported in this

study, with bruxism significantly influencing the occurrence of

mechanical complications (framework and prosthetic fracture in one

patient). Given the exploratory nature of this study, nine patients with

nine prosthesis with more than a one unit cantilever were included. In

this study, the use of cantilever units did not imply neither a decrease

in implant or prosthetic survival nor an increase in mechanical compli-

cations (three prosthetic screw loosening events in one prosthesis

with one cantilever unit and two prosthesis without cantilever units)

but was reflected on the technical complications (the veneer adhesion

issues) with an increased trend for prosthesis with longer cantilever

lengths implying the flexing of the distal cantilever are of the PEEK

framework as potential cause. Nevertheless, it is important to rein-

force that the veneer adhesion issues were resolved for all patients

independently of the prosthesis cantilever length, suggesting that the

correct bonding agent between acrylic resin and PEEK could be of

increased importance.

Considering implant survival, the 100% survival rate registered in

this study compares favorably with previous investigations. A study

evaluating the short-term outcome of All-on-4 (Nobel Biocare AB)

full-arch rehabilitations using the same implant design as the present

study registered a cumulative survival rate of 98.9% at 1 year of

follow-up.40 Patzelt et al.41 in a systematic review to evaluate the all-

on-four treatment concept registered a mean (SD) combined cumula-

tive survival rate of 98.6% (1.3%) at 1 year of follow-up and another

systematic review42 on the same topic reported a 99.8% survival rate

for rehabilitations with 2 years or more of follow-up.

The average marginal bone remodeling after 1 year of function

was low and within the accepted standards,43 comparing favorably

with previous reported short-term ranges for full-arch restorations. In

a systematic review44 comparing marginal bone remodeling around

axially versus tilted implants supporting fixed prosthetic reconstruc-

tions of partially and fully edentulous jaws after 1 year of function,

the authors registered a range between 0.51-1.13 mm and

0.43-1.14 mm for axial and tilted implants of full-arch restorations,

respectively.

The mode for mPLI was high, with patients scoring a level 2 of

the mPLI scale (the second worst level of the scale with plaque visible

by the naked eye) corresponding to low levels of oral hygiene habits.

The mBI level was mild (corresponding to the second best level with

only one isolated bleeding spot visible around the implant). The causal

relation between plaque and mucositis was previously explored: Pon-

toriero et al.45 explored the conditions of an experimental gingivitis

model in their study of 20 partially edentulous patients who were

treated with implants and subsequently refrained from oral hygiene

for a period of 3 weeks. The authors observed an increase in mucosi-

tis severity, including inflammation of the soft tissues and an increase

of �1 mm in peri-implant pockets. Salvi et al.46 used the same 3-week

period of undisturbed plaque accumulation followed by a period of

optimal plaque control to monitor clinical, microbiological, and host-

derived alterations on experimental mucositis/gingivitis models of

15 patients. The authors registered median mPLI scores of 1.17, 1.33,

and 1.33 and mBI scores of 1.33, 1.33, and 1.5 after 1-, 2-, and

3-weeks, respectively, suggesting a positive linear relationship; while

after resuming optimal plaque control, the median values for weeks

6, 7, and 8 were always 0 for mPLI and 0.75, 0.5, and 0.5 for mBI, sug-

gesting a negative linear relationship. These findings confirmed the

causal relation between plaque accumulation and peri-implant health.

However, in this study, the correlation between mPLI and mBI was

characterized by a nonsignificant, weak positive linear relationship.

This result, together with the absence of biological complications sug-

gests from an epidemiological point of view that peri-implant pathol-

ogy can be caused by more than one causal mechanism from a

biological and/or biomechanical component (each needing the joint

action of several risk factors) as previously proposed47,48 using the

component cause model,49 rather than a disease process purely driven

by a biofilm-mediated infection.

In this study, the issues with veneer adhesion occurred were

related to the mechanical and chemical retentions used between

PEEK and acrylic resin. After applying the remedies to the complica-

tions, no re-incidences occurred with the exception of the patient that

fractured the PEEK infrastructure. The change of bonding primer in

the present study was supported by previous investigations: Both Sta-

warczyk et al. and Keul et al.24,50 made an investigations using an

in vitro model with 9624 and 68050 specimens to evaluate the tensile

bond strength of veneering resins to PEEK, reported a higher tensile

bond strength of the bonding primer used to resolve the complica-

tions in this study. Furthermore, the increased amount of exposed

PEEK in the cylinder area was performed to reinforce the structure to

have an area of less flexion and also avoid a direct transition line

between acrylic-resin and PEEK as it represented a point of rupture

and infiltration.

Concerning the mechanical complications, the 7.9% and 10% inci-

dence of mechanical complications at the patient and prosthetic level,

respectively. The mechanical complications occurred in double full-

arch rehabilitated patients (two patients with PEEK-acrylic resin pros-

theses and one patient with acrylic resin implant-supported prosthesis

as opposing dentition). This tendency was previously described in a

study investigating the 5-years outcome of double full-arch versus

single full-arch all-on-four (Nobel Biocare AB) implant-supported reha-

bilitations, with the authors reporting an increased incidence rate of

mechanical complications (statistically significant) for double full-arch

when compared to single arch.51

The patients' evaluation of the restorations were high in both “in

mouth comfort” (88%) and “overall chewing feeling” (84%) reflecting

the overall satisfaction in important subjects to be evaluated at the

first year of follow-up. Similar evaluations were reported by Kennedy

et al.52 for metal-acrylic resin mandibular full-arch implant-supported

MALÓ ET AL. 9

fixed prostheses with the patients evaluating at a 79% satisfaction

both the improvement in the ability to chew and that the fulfillment

of expectations.

The limitations of this study were related with a single center, the

short sample, the short follow-up, and the lack of a control group. The

strengths of this study were related with the low dropout rate,

accounting for increased internal validity and the prospective design.

Future research should focus on the outcome at 3 years of follow-up

and in the evaluation of a routine group.

5 | CONCLUSIONS

Within the limitations of this study and considering the high pros-

thetic/implant survival and patient satisfaction, the low marginal bone

loss and the low incidence of biological and mechanical complications,

it is possible to conclude that full-arch hybrid PEEK-acrylic resin

implant-supported prostheses may be a valid treatment option, never-

theless, requiring a longer follow-up to fully attest its validity in

implant dentistry.

ACKNOWLEDGMENTS

The authors would like to acknowledge Dr. André Rodrigues, Dr. José

Figueiredo, Mr. Sandro Catarino, and Mr. Luís Gomes for all the help

provided in this research.

This study was supported by Juvora, grant no. 1/2013.

CONFLICT OF INTEREST

The authors declare that they have no conflicts of interest with

the contents of this article. Doctor Moura Guedes, Mister Miguel de

Araujo Nobre and Mister António Silva received previous educational

fees from Juvora.

ORCID

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

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

Guedes C, et al. Short-term report of an ongoing prospective

cohort study evaluating the outcome of full-arch implant-

supported fixed hybrid polyetheretherketone-acrylic resin

prostheses and the All-on-Four concept. Clin Implant Dent

Relat Res. 2018;1–11. hiips://doi.org/10.1111/cid.12662

MALÓ ET AL. 11