Significance of Implant Distribution on a Screw-retained Implant-Supported Mandibular Hybrid Restoration of PEEK framework with Immediately Loaded Implants applying All-On-Six Protocol: A Two Years Clinical Study
Mostafa Helmy Mostafa Ahmed1, Henri Diederich2* and Enas Anter Abd El Ghaffar3
1Lecturer of Removable Prosthodontics, Cairo University, Egypt
2Dental surgeon, Dental Clinic Henri Diederich, Luxembourg
3Lecturer of Radiology, Cairo University, Egypt
Submission: May 08, 2018; Published: May 23, 2018
*Corresponding author:Henri Diederich, Dental surgeon, Dental Clinic Henri Diederich, 51 av Pasteur, L-2311Luxembourg, Europe,
Tel: 00352621144664; Email: [email protected]
How to cite this article:Mostafa H M A, Henri D, Enas A A E G. Significance of Implant Distribution on a Screw-retained Implant-Supported Mandibular Hybrid
Restoration of PEEK framework with Immediately Loaded Implants applying All-On-Six Protocol: A Two Years Clinical Study. Adv Dent & Oral Health. 2018; 9(1):
555751. DOI: 10.19080/ADOH.2018.09.555751
Objectives: The aim of this study was to compare the effect of the distribution of implants on a Screw-retained Implant-Supported Mandibular Full Arch Prosthesis with Immediately Loaded Implants utilizing All-On-Six Protocol, both clinically & radiographically. In addition to Patients’ satisfaction over two years of clinical investigation.
Materials & methods:For the purpose of this clinical study, fourteen patients with completely edentulous mandibular ridges with satisfactory bone quantity and quality were carefully selected to receive the screw-retained full arch mandibular prosthesis according to specific criteria. Patients were instinctively divided into two groups; First group (of seven patients) obtained an Implant-supported, fully-splinted screw-retained full arch mandibular prosthesis with immediate functional loading protocol utilizing 6 implants (placed in central incisors, canines & first molars regions Bilaterally), while Second group (of seven patients) obtained an Implant-supported, fully-splinted screw-retained full arch mandibular prosthesis with immediate functional loading protocol utilizing 6 implants (placed in first premolar, second premolar & first molars regions Bilaterally). The clinical & the radiographic outcomes of the Implants supporting the screw-retained full arch superstructure had been measured at time of implants insertion, 6 months and 12 months, 18 months & two years respectively. In addition, patients’ satisfaction was also measured utilizing a customized chart of question (A four-point scale).
Results:Regarding parametric data; repeated measures ANOVA test was used to study the changes by time within each group as well as to compare between the two groups. Bonferroni’s post-hoc test was used for pair-wise comparisons when ANOVA test is significant. Student’s t-test was used to compare between amounts of bone loss or gain in the two groups. Whereas for non-parametric data; Mann-Whitney U test was utilized to compare between the two groups. All data showed normal (parametric) distribution except for satisfaction scores data which showed non-normal (non-parametric) distribution.
Conclusion:Regarding this study, it may be concluded that proper distribution of immediately loaded implants used for supporting mandibular screw-retained implant-supported full arch restoration, through proper implant placement pattern results in favorable response in terms of clinical, radiographic outcomes as well as patients’ satisfaction. In addition, Both modalities presented a feasible treatment option for supporting a screw-retained mandibular prosthesis with better outcomes in first distribution pattern. Furthermore, the Bio-Hpp material used in implant supported prostheses had several benefits for the implant restorations such as lower chipping rate, reduces stress shielding, metal free, easily monitoring implant-abutment connection fit.
Treatment of the edentulous mandible has always been one of the most challenging matters in dentistry [1-5]. Traditional full denture is the most common treatment modality for these cases.
However, owing to lowered stability when compared with natural teeth or fixed partial dentures, patients often complain of struggle adapting to a removable prosthesis.
The introduction of osseointegrated implants has infinitely
improved treatment consequences in patients with complete
edentulism. Increased stability and retention of prostheses can
be achieved by one of two means, either an implant-retained
removable overdenture or an implant-supported fixed prosthesis
Implant-retained dental restorations have verified to be a
good solution for the rehabilitation of edentulous patients. The
literature indicates that the implant-supported screw-retained
prosthesis provides liable results with enhanced stability, function
and a high degree of patient satisfaction compared to conventional
removable dentures [12,13].
The oral rehabilitation of an edentulous patient treated
through a fixed implant-supported prosthesis using appropriate
biomechanical and prosthetic basics has been a target in oral
implant research for the last years . With the fixed implantsupported
restoration, a satisfactory distribution of stress is
highly significant to decrease implant and prosthetic failures .
Moreover, these failures can also be predisposed by several factors,
including prosthetic design, implant number, implant distribution
& occlusal scheme .
A common treatment strategy for an edentulous mandible
is the placement of implants in the inter-foraminal region and a
full arch fixed implant-supported prosthesis with distal cantilever
[17-19]. However, this form of prosthesis can endorse a high level
of stress that can be damaging to the implant and the surrounding
bone because of the unfavorable lever arms . For this reason,
it has been recommended that the use of multiple implants in the
anterior and posterior mandible could enhance the distribution
of stress with more favorable implant support, avoiding lengthy
Completely edentulous patients with abundant bone height
and width can be successfully restored with fixed implantsupported
prostheses. The edentulous mandible can be restored
successfully with an immediately-loaded implant-supported fixed
Immediate loading of dental implants permits immediate
restoration of esthetics and functions with reduced morbidity
of a second surgical intervention, and facilitates functional
rehabilitation, consequently increasing patient acceptance and
satisfaction. Furthermore, it eliminates the need for multiple and
lengthy appointments that might affect the practitioner’s time for
adjustment of provisional prostheses delivered to the patients
during the healing period of delayed loaded implants [23-35].
An ideal stress profile is mandatory to preserve a strong
and healthy jawbone: a stress that is too high might produce
permanent injury to the jawbone; one that is too low may fail
to stimulate the bone sufficiently for satisfactory healing of the
wound and hence, for osseointegration. Moreover, the primary
stability is especially crucial because the bone is still in a state of
remodeling and dictates that the applied stresses to enhance bone
Biomechanical considerations correlated to the stress
transferred to the peri-implant bone and during function of the
prosthesis might necessitate implants placement more distally, at
premolar or molar regions, or to combine one anterior implant
and the other posterior contralaterally .
Prosthetic management with a fixed, screw-retained
restoration on four or six implants is a feasible concept as
proposed by several authors . Those techniques - frequently
mentioned as all-on-four and all-on six - diminish or eliminate
cantilever length by introducing implants in the distal regions.
Following theses modalities, the entire dental arch could be
Most of the studies examining all-on-four and all-on-six were
performed using cylindrical implants. However, our knowledge
regarding the increasingly popular tapered dental implants is
pretty limited in this respect. Mostly, tapered implants appear
to be superior to cylindrical implants for immediate loading
as insertion torque has been proved to be the most rational
prognostic factor for the Osseointegration of immediately loaded
splinted implants .
Implant distribution in any dental arch can aid to reduce the
stress applied separately on the implants. this could be achieved
by bearing in mind the importance of the anteroposterior distance
(A/P). The A/P spread measurement is a formula utilized to
calculate the maximum specified cantilever length off the most
posterior implant in a fixed restoration [33-35].
Undue force distribution pattern in peri-implant bone might
trigger implant loss or mechanical failures in the prosthetic
structure when the produced stresses and strains exceed
the physiologic tolerance thresholds of the alveolar bone,
consequently, certain studies have declared that the stresses
beyond this threshold might cause marginal bone loss or complete
loss of osseointegration .
Large cantilevers, parafunctional habits, improper occlusal
designs and premature contacts may cause excessive loads which
adversely affect the survival rate of the implants. Therefore,
optimal occlusion within physiologic limits is an important factor
to ensure the long-term implant success .
There is also a lack of randomized controlled trials (RCTs) to
compare the outcome of specific enquiries related to the optimum
distribution of implants used for screw-retained implantsupported
Conventional metallic frameworks are the most commonly
used modalities for implant-supported restorations. But the
dark metal framework endures the natural esthetics. Recently, a
paradigm shift in the replacement of all-ceramic framework for
Because of its mechanical advantages and high biocompatibility.
The PEEK (Biohpp) framework material used in
implant restorations develops many Advantages; the modulus of
elasticity is close to that of bone that means during loading the
bone related rotation can be reduced. Additional advantages are
shock-absorbing, metal free restoration, low plaque accretion as
well as no corrosion .
Polymer-based frameworks utilizing poly-ether-ether-ketone
(PEEK) material has become an alternative predictable technique
in screw-retained implant-supported full arch restorations.
Moreover, use of prefabricated composite veneers for the
restoration of full arch cases permits an aesthetic outcome similar
to that for individual ceramic veneering .
The aim of this clinical study was to evaluate and compare
the effect of two implant distribution patterns of mandibular
implant-supported screw-retained restorations in terms of
clinical and radiographic outcomes. The first pattern utilized
six implants (placed in central incisors, canines & first molars
regions bilaterally), while the second pattern utilized six implants
(placed in first premolar, second premolar & first molars regions
The null hypothesis was that there will be no significant
difference in outcomes between the two implant distribution
patterns, over the whole investigation period.
Fourteen patients were carefully selected from the outpatient
clinic of the Removable department, Faculty of Oral and Dental
Medicine, Cairo University. Where, patient selection was
accomplished according to the following criteria:
a) Age ranged between 35-50 years.
b) Patients with completely edentulous mandible (Figure
c) Patients with good oral hygiene.
d) Patients free from bad oral habits.
e) Patients free from any systemic or debilitating diseases
such as diabetes mellitus, bone diseases, blood discrasis or
other diseases that affect bone healing around the implants.
f) Absence of any medical disorder that might obscure the
surgical phase or disturb osseointegration.
g) Patients with Angle’s class І maxillo-mandibular
relationship with normal occlusion.
h) Uncooperative patients were omitted & only cooperative
patients were included in the study
The patients were asked for their approval to the conduction
of the research & being recalled for follow-up appointments.
All details were written & signed by the patients in consent
forms. The study was conducted according to principles stated
in Helsinki Declaration & being approved by the Faculty ethical
committee. After taking full patient’s personal, medical and dental
history, each patient received a thorough clinical and radiographic
Upper and lower primary impressions were made utilizing
alginate impression material1 according to the manufacturer’s
instructions and poured into stone plaster2 to attain diagnostic
casts over which acrylic resin3 special trays were fabricated.
a) For every patient, the casts were mounted on a simple
hinge articulator aided by a Tentative inter-occlusal wax
record. Afterwards, the occlusal relation between the upper
and lower teeth was thoroughly examined.
1Cavex alginate, dust free, high consistency, Holland
2Type III dental stone Lascod SP, sestofino, Italy
3Moldano. Bayer Leverkusen, pekatray, Germany
b) Final mandibular impressions were made by twostep
rubber base impression material4 according to the
c) Master casts were obtained, Occlusion blocks were
constructed centric jaw relation was recorded using the
traditional wax-wafer method.
d) Master casts were mounted on semi-adjustable
articulator, where, the upper cast was mounted according to
a face bow record & the lower cast was mounted by the aid of
the recorded centric jaw relation record.
e) Setting-up of mandibular teeth then, Try-in stage was
carried out in the usual manner
It is worth to clarify that all laboratory steps were made by the
same dental technician in the same laboratory.
a) Duplication of the mandibular trial denture was
encountered utilizing a radio-opaque material to construct
radiographic stents for every patient.
b) Patients were imaged using cone beam computed
tomography scans (CBCT scans) through a cone beam CT
machine (CBCT, i-CAT Vision)5. Each patient was instructed to
bite on a piece of cotton to achieve adequate jaw separation.
Finally, the resultant image was obtained as a DICOM file.
c) The images were processed using specialized image
processing software (Blue Sky implant software)6.
Surgical guide fabrication
For Group [I]: Virtual implants were placed in the position
of lower central incisors, canines & first molar teeth (bilaterally),
A solid block was modeled & guiding holes denoting the implant
direction were opened into the block & positioning sleeves were
For Group [II]: Virtual implants were placed in the position of
first premolar, second premolar & first molars teeth (bilaterally).
A solid block was modeled & guiding holes denoting the implant
direction were opened into the block & positioning sleeves were
a) The sterile box of the implant12 was unwrapped, and
then the inner vial was also opened & the implant osteotomy
was washed thoroughly using sterile saline solution
b) The sterile implant was introduced into its site (according
to the selected group), by screwing it using moderate finger
pressure [self-tapping] Once resistance was felt, the abutment
was unscrewed from the implant fixture & the ratchet wrench
was adapted to the implant and the screwing process was
c) The screwing process was stopped when the implant
becomes flushed with the crest of the bone or preferably
0.5mm below the crestal bone level.
Then, utilizing the Osstell device13, four readings (buccal,
lingual, mesial & distal) were obtained for each implant those
readings represented the first clinical readings.
Finally, a Panoramic as well as CBCT radiographic pictures
were obtained for the implants to ensure proper positioning.
Whereas other separate radiographs were taken to be read out by
the Digora computerized system to calculate the first radiographic
readings (Figure 7).
10Listerine mouthwash, USA.
11Listerine mouthwash, USA.
12ROOTT Two-piece Dental Implant, TRATE AG, Switzerland.
Directly following implant placement surgery, gingival formers
were screwed onto corresponding implants, to ensure the need for
any suturing required.
The gingival formers are then unscrewed from the implants
and transfer copings with long screws were screwed into
corresponding implants to start preparation of a single step Opentray
impression (Implant level impression).
Windows were opened in a plastic stock tray (appropriate
to the patient arch) opposite the transfers and widened mesiodistally,
and then a single-step impression (utilizing Putty and
light addition silicon rubber base impression)14 was made, as
follows: Rapid dryness of the surgical field was accomplished
using pieces of gauze. Then, a light-body impression material
was injected around the implants necks and the transfer mounts,
followed by insertion of the stock tray loaded by a putty rubber
base impression material in the patient’s mouth. The tray was
secured in place and detected for complete seating and finally, the
open-tray impression making was completed by manipulating the
oral tissues in the usual manner. Following complete setting of
the impression material, the screw driver was utilized to unscrew
those mounts from the implant fixtures. The tray was then removed
from the patient’s mouth and the impression was cleaned, dried
and checked for its accuracy in addition to enclosing the transfer
mounts accurately in their places.
The gingival formers were placed onto the implants &
secured in place & the patient was given important postoperative
The patients were immediately given after surgery Diclofenac
Sodium non-steroidal anti-inflammatory analgesic tablets
(Voltaren 75mg)15. It was prescribed as one tablet three times
daily for three days to reduce pain and swelling and were advised
to follow the antibiotic regimen previously prescribed (Augmentin
1g) for 5-7 days. Patients were given the following instructions:
a) To apply ice packs for 10 minutes with 10 minutes
intervals along a period of 3-4 hours immediately following
b) To follow strict oral hygiene protocol.
c) Asked for some recall appointments within the next days
to complete the restorative procedures.
The implant analogues were fitted accurately into their
corresponding mounts in the impression, using the screw driver.
In the laboratory, a small cotton pellet was utilized to varnish
the impression surfaces surrounding the analogues with Vaseline.
Then, a gingival mimic was created around the analogues using
a plastic impression syringe loaded with a special gingival mimic
material16 was performed, then impression was poured utilizing
extra-hard stone to obtain a cast that enclosed the implant
analogue part with attached abutment analogue were apparent
from the cast.
A custom tray, occlusion blocks and a segmented implant
verification jig (IVJ) were fabricated. In the patient’s mouth,
Evaluate the VDO, CR, esthetics, occlusion, phonetics and midline
for a correct bite registration record utilizing the occlusion blocks,
then, unscrew the gingival former in order to seat the verification
jig in place
An implant verification jig (IVJ) that has been sectioned and
numbered on a working model. Each acrylic section contains a titanium cylinder. This procedure should be followed to ensure an
accurate final impression.
Seat each section of the jig onto the appropriate implant and
tighten the guide pin. The sections should not be in contact. If
necessary, remove one section, minimally trim it with a disc, and
reseat it. Each section should have a gap about the thickness of
a credit card. Visually verify gaps before luting. Then, lute the
sections together with a suitable material17.
Allow the material to flow through and completely around
the gaps. Ensure the material is completely cured. In addition,
the clinician can test the passivity of the jig with a one-screw test.
Tighten a single guide pin into one of the distal cylinders. No lifting
of the jig should occur.
Check for a passive fit by visibly inspecting completely
around each cylinder for complete seating. If any cylinder is not
completely seated, the jig must be sectioned in that area, re-luted
and rechecked until a passive fit is obtained.
Check the custom impression tray for proper fit (no contact
with the jig or cylinders). Using a putty & light body VPS material,
take the final impression with an open-tray technique in a single
step, Inject light body VPS impression material under and around
the jig to capture the ridge and all anatomical landmarks as for a
full denture including full vestibular extensions (Figure 12).
Completely fill the impression tray with putty VPS impression
material. Seat the filled impression tray, ensuring the heads of
the guide pins are exposed through the tray (Figure 13). Once
the material has set, remove guide pins and then remove the
impression; Ensuring that, the verification jig is picked up in the
impression. Then, inspect the impression for the required details.
And finally, replace the healing abutments again.
The final implant-supported prosthesis framework was
made using a precision-made custom CAD/CAM PEEK (BIOHPP)
When receiving the PEEK framework from the Laboratory,
remove the healing abutments, then check for the Passive fit of
the PEEK framework which is critical for the long-term success
of the case; this could be done by utilizing The single screw test,
as follows; Tighten one screw and verify a passive fit on all of the
implants (no lifting of the framework from any side). Remove
the screw and repeat the process for each implant. Remove the
framework & replace the healing abutments. Return the case to
the Laboratory for setting up of teeth.
When receiving the PEEK framework with Visio-lign veneered
teeth from the Laboratory, remove the healing abutments, and
then check for the Passive fit (as previously done). Then, Verify the
VDO, CR, occlusion, esthetics, shade, tooth arrangement, phonetics
and midline (Figure 15). An articulating paper was utilized to
detect any pressure areas, which were removed (if present) by
When accurate verification was assured, replace the healing
abutments & return back the final try-in to the laboratory for
processing into final restoration.
Remove the healing abutments, seat the final denture on the
implants & hand tighten the prosthetic screws, alternating from
one side to the other. Tighten the screws to the appropriate torque
per manufacturer instructions. Wait approximately 5 minutes
and retorque the screws. The occlusion was confirmed & any
necessary adjustments were made. Then, place small amount of
cotton in the screw access holes and fill with light cure composite
prevent bacteria build-up. Final finishing and polishing of the light
cured composite was then made.
Final adjustments & follow-up: After denture insertion and
training the patient on easy insertion & removal of the denture;
patients were instructed to follow strict oral hygiene measures
and asked for a recall appointment every week in the first two
months for any required denture adjustments &/or refinement of
This included the following:
Osstell measurements: A specially designed measuring
tool termed “Smart Peg”19 was inserted with a special plastic
cap (to measure the Implant Stability Quaint, ISQ), screwed into
the internal surface of the implant. Then, utilizing the frequency
transducer device “Osstell”20, four readings (buccal, lingual, mesial
& distal) were obtained for each implant. Mean of the 4 readings
will represent the ISO of that implant.
The procedure was repeated in other implants and finally,
the mean of all implants ISQ was utilized to represent the mean
Osstell reading in that stage. Measurements were made at time
of implants insertion, 6 months, 12 months, 18 months and 24
Radiographic evaluation: Direct digital radiography utilizing
the Digora computerized system21 was applied for making intraoral
digital radiographic images to assess the following:
a) Changes in the mesial and distal marginal bone height
around the implants
b) Changes in bone density around the implants.
The imaging plate was introduced into a protective bag which
was sealed by the Digora system. The stored images of every single
patient were interpreted at the end of the follow up period. Digital
images were made for the implants, immediately following their
insertion, six months later and then every passing six months of
the successive two years.
Implant measurements were made as follow: The distance
from the shoulder of the implant to the crest of the alveolar ridge,
where a line was drawn tangential to the implant and parallel to
its long axis. The mean value of both mesial and distal readings
was taken, tabulated and statistically analyzed.
The procedure was repeated in other implants and finally, the
mean of all implants measurements was utilized to represent the
mean bone height reading in that stage.
The increase in the marginal bone height measurements denotes
The Digora system software was utilized for assessment
of the changes in bone density mesial & distal to each implant.
The measurements were as follows: Two lines were drawn; the
first line extended mesial to the implant from the shoulder of
the implant to the apex of the implant and parallel to its long
axis, while the second line extended distal to the implant from
the implant shoulder to its apex. Bone density alongside each of
the two lines was documented and then the mean value of both
readings was calculated for further assessment.
The procedure was repeated in other implants and finally,
the mean of all implants measurements was utilized to represent
the mean bone density measurement in that stage. Patients’
satisfaction was also measured (the day following prosthesis
placement) utilizing a customized chart of question, where;
Patients answered a series of questions to evaluate the IMPLANTSUPPORTED
PROETHESIS in Both Groups (4 POINTS SCALE) in
terms of; masticatory function, pain sensation, presence of any
discomfort, muscle fatigue during function.
Finally, each patient had to give a number representing his
General satisfaction (90-100%= Excellent, 80-89%= very good,
70-79%= good, 60-69%= fair, 50-59%= working, BELOW 50%=
not satisfied) Regarding the previous questions.
a) Patients of both groups were asked for recall
appointments every six months, following overdenture
insertion till 2 years of implants insertion for measuring the
clinical and radiographic outcomes.
b) All the results were calculated, tabulated and then
Numerical data were explored for normality by checking the
data distribution and using Kolmogorov-Smirnov and Shapiro-
Wilk tests. All data showed normal (parametric) distribution
except for satisfaction scores data which showed non-normal
For parametric data, repeated measures ANOVA test was
used to study the changes by time within each group as well as to
compare between the two groups. Bonferroni’s post-hoc test was
used for pair-wise comparisons when ANOVA test is significant.
Student’s t-test was used to compare between amounts of bone
loss or gain in the two groups. For non-parametric data, Mann-
Whitney U test was used to compare between the two groups.
The significance level was set at P ≤ 0.05. Statistical analysis
was performed with IBM® SPSS® Statistics Version 20 for
Comparison between the two groups: It revealed that at
base line there was no statistically significant difference between
the two groups. After 6, 12, 18 and 24 months; Group I showed
statistically significantly higher mean Osstell values than Group II.
As regards the changes by time within each group: Both
groups showed a statistically significant decrease in mean Osstell
values after 6 months. From 6 months to 12 months, there was a
statistically significant increase in mean Osstell values. From 12
months to 18 months as well as from 18 to 24 months, there was
no statistically significant change in mean Osstell values. However,
the mean Osstell value after 12 months showed statistically
significantly higher values than base line measurement (Table 1
& Figure 20).
*: Significant at P ≤ 0.05, Different superscripts in the same column are statistically significantly different.
As regards Group I: A non-statistically significant increase
in mean bone height measurements was detected after 6 months.
From 6 months to 12 months; there was a statistically significant
decrease in mean bone height measurements. From 12 months
to 18 months as well as from 18 months to 24 months; a nonstatistically
significant change in mean values was detected.
While in Group II: A statistically significant increase in mean
bone height values was observed after 6 months. From 6 months to
12 months; there was non-statistically significant decrease in the
mean bone height measurements. From 12 months to 18 months
as well as from 18 months to 24 months; there was a statistically
significant increase in the mean values.
Comparison between amounts of bone loss or gain in
the two groups: It revealed that after 6 months; Group I showed
statistically significantly lower amount of bone loss than Group
II. From 6 months to 12 months; Group I showed statistically
significantly higher mean bone gain than Group II. From 12 to
18 as well as from 18 to 24 months; Group II showed statistically
significantly higher mean amount of bone loss than Group I (which
showed bone gain) (Table 2 & Figure 21).
*: Significant at P ≤ 0.05, Different superscripts in the same column are statistically significantly different.
Comparison between the two groups revealed that at base
line as well as after 6 months; there was no statistically significant
difference between the two groups. After 12, 18 as well as 24
months; Group I showed statistically significantly higher mean
bone density than Group II.
As regards the changes by time within Group I: There
was a statistically significant decrease in mean bone density
measurements after 6 months. From 6 months to 12 months,
there was a statistically significant increase in mean bone density
measurements. From 12 months to 18 months; there was no
statistically significant change in mean values. From 18 months
to 24 months; there was a statistically significant increase in
mean bone density. The mean bone density after 24 months
showed statistically significantly higher mean value than base line
While in Group II: There was a statistically significant
decrease in mean bone density measurements after 6 months.
From 6 months to 12 months, 12 months to 18 months as well
as 18 months to 24 months; there was no statistically significant
change in mean bone density measurements. However, the mean
bone density after 24 months showed statistically significantly
lower value than base line measurement (Table 3 & Figure 22).
*: Significant at P ≤ 0.05, Different superscripts in the same column are statistically significantly different.
In this study, all factors that could affect the osseointegration
of implants were carefully considered during patient selection
and later after restoration. These factors may be biological or
mechanical or both; The biological factors could be related to the
patient’s selection, to the steps of implant installation and to the
level of oral hygiene measures followed .
Fourteen healthy patients of edentulous mandibles of age
ranging from 35-50 years old were included in this study to avoid
any fluctuation in bone changes that might affect the obtained
results. Maintenance of good oral hygiene has a great influence on
the success of this study to the extent that it has a great impact
on the osseointegration process. The oral hygiene of each patient
was, therefore, evaluated at the beginning of the study and then
throughout the whole investigation period.
Patients with superior general health were only selected, to
avoid the reflection of any systemic disorder on the bone condition,
and hence, osseointegration . Only cases with normal maxillamandibular
relation were included in the study to avoid the effect
of transmission of abnormal forces to the implants.
Uncooperative patients were excluded, where only cooperative
patients were included in the study to ensure their commitment to
the oral hygiene measures and the regular follow up visit.
Bone quality and quantity were evaluated radiographically to
ensure primary stability of the implant at the time of its placement.
In addition, patients with sufficient bucco-lingual width at sites
of implants placement were only selected to ensure at least one
mm. thickness of bone remaining buccal and lingual to the implant
after its placement .
Construction of a computer-guided surgical stent was
carried out, to ensure accuracy of implant placement in the three
dimensions as well as decreasing the human interfering factors
that might affect the adjustment of implants angulation .
All implants used were Two-piece, threaded, self-tapping,
root form implants, 12mm length and 3.8mm width. This implant
design was used to ensure primary stability during the initial
healing period, as well as, increasing the contact area between
the implant and the surrounding bone for better osseointegration
Panoramic radiograph was the imaging modality of choice
in evaluating implants osseointegration, to avoid the metallic
artifacts that accompany CBCT (due to presence of multiple
implants)  In addition, post-operative CBCT was performed
also to ensure accurate duplication of pre-operative planning
The cases were followed up for Two years to ensure proper
evaluation of clinical & radiographic parameters as well as
patients’ satisfaction throughout a suitable period of time.
An implant supported, screw-retained hybrid prosthesis that
consists of minimalized framework enclosed in a bulk of PEEK
material and artificial teeth in order to prevent overloading of the
implants and to ensure a more acceptable esthetics. Obviously,
the distribution of the load applied to the superstructure (i.e.
the prosthesis) is more favorable when the superstructure is
supported by well distributed six implants (in Group I), than in
Biomechanical implant complications have been related
to several factors such as the bone quality, implant surface
characteristics, presence of parafunctional habits and prosthetic
design as well as implant number and distribution.
In implant-supported fixed prostheses, an ideal biomechanical
distribution of stresses at the prosthetic superstructure and
implant infrastructure is of dominant importance, being affected
by several factors such as correct prosthetic design and occlusal
scheme. Furthermore, attaining less stress in an implantsupported
restorative system is one of the main goals of implant
Oral rehabilitation with implant-supported hybrid restoration
in completely edentulous mandibles offers a wide range of
treatment modalities based on the varying number & distribution
of implants utilized, as well as the loading behaviors approached
Criteria for the successful immediate loading of dental implants
were strictly followed in this study according to the guidelines
advocated by several authors [45,46] Clinical assessment of
primary implant stability was ensured by the insertion torque at
the moment of implant placement, which was no less than 30N.
cm in almost all cases. This torque is considered by some authors
[47-50] as the minimum torque necessary for osseointegration in
cases of immediately loaded implants.
Tapered implants used in this study possess a progressive
thread design, which is grit blasted to produce a sharp edge and a
rough surface, ensuring fast cellular adhesion and osseointegration,
high primary mechanical stability in bone immediately after their
placement, and increased total surface contact with surrounding
In the present work, properly distributed implants in Group
(I) presented better clinical & radiographic outcomes, which might
be attributed to better antero-posterior distance (AB distance)
than present in Group (II).
A study of stress analysis has shown that frameworks
constructed with a precise and passive fit induce significantly
smaller amounts of stress on the implant  and this could be
achieved by use of Verification jigs
Immobilization of the implants in the early healing phase
was particularly important (early healing phase), where it acts
as a splint by remaining firmly placed on the implants. Moreover,
functional load was minimized by a soft diet in the first month of
prosthesis insertion .
In the current study, the installation of posterior implants in
both groups was used to decrease the lever arm, allowing greater
posterior extension and increased occlusion scheme in the
mandibular fixed implant-supported prosthesis, which provided a
better distribution of occlusal forces and increased the prosthesis
The statistically significant decrease in the mean Osstell
measurements from base line to six months might be attributed
to the inflammatory, resorptive and remodeling activities during
the healing process.
These findings were in line with those studies which concluded
that; although new implant surface and chemistry designs have
shortened and improved osseointegration, the initial implant
stability drop is still present and remains a challenge for future
research and development .
Moreover, the mechanism behind the decrease of
measurements during the first six months might be related to the
changes of bone-implant interface as well as the properties of the
surrounding bone (i.e. the interfacial stiffness). Firstly, the tapered
implant creates a lateral compression of the bone tissue during
insertion and it is likely that the relaxation of the inbuilt stresses
between the implant and bone occurred after implant placement,
which can be considered as a decrease in scores. Secondly, it can
be speculated that loading might induce microfractures in the
surrounding bone. These were in line with many similar studies
The statistically significant increase in the mean Osstell
readings from six months to twelve months of prosthesis insertion,
indicating greater implant osseointegration . The statistically
significant increase in the mean Osstell readings from base line to
twelve months matched the time frames of bone formation and
maturation around the dental implants .
The significant increase in the mean bone height measurements
in both groups, indicating increased crestal bone resorption in
the first six months compared to those measurements from six
to twelve months, which might be explained by the continuous
remodeling process of bone surrounding the implant resulting in
bone resorption, followed by bone deposition .
The crestal bone resorption around implants is a well-known
phenomenon occurring mostly in the initial phase of functional
implant loading and considered as an immediate bone response
after insertion of the implant supported prosthesis. The mean
marginal bone loss in the present study from base line to twelve
months is considered within accepted permissible limits occurring
with most dental implants .
Concerning changes of bone density around the implant, it
was evident that there was a significant decrease of mean values
of bone density at the first six months in both groups. This was
mainly attributed to the surgical trauma during implant surgery.
In addition to, the precautions given to the patient to maintain soft
diet during the initial phase of treatment .
Peri-implant bone density measurements were our concern
in this study as an evaluation of the overall bone response to the
selected treatment protocols regarding distribution of immediately
loaded implants supporting mandibular overdentures. The
immediate loading protocol was preferred to the traditional
delayed loading protocol according to the encouraging results of
Barone et al.  who found that bone was significantly denser
around immediately loaded than unloaded oral implants.
The statistically significant increase in the bone density
measurements in periods from six to twelvemonths, indicating
favorable bone reaction to the applied forces that were within
the physiologic limit tolerated by the bone and hence, favorable
progress of the osseointegration process.
During the recall periods of all patients, there were no
complaints from the installed implant and all the patients followed
the oral hygiene instructions to avoid any harmful effect which
might influence the results of this study . Several studies
declared that, the patients’ quality of life had been improved by
the increased retention and stability of their implant-supported
fixed prostheses .
The statistically significant difference in patients’ satisfaction
between the two groups throughout the whole study period
showed that implant distribution would affect the efficiency
of the used prosthesis . The results of the present clinical
investigation were in contradiction of the null hypothesis
Within the limits of this clinical research study, concerning the
relatively small sample size, it could be conservatively determined
a) This study was conducted to compare the effect
implant distribution on screw-retained, immediately-loaded
mandibular hybrid prosthesis with immediate functional
b) The clinical & the radiographic outcomes of the Implants
supporting the screw-retained full arch super structure had
been calibrated at time of implants insertion, 6 months and
12 months, 18 months & two years respectively. In addition,
patients’ satisfaction was also measured utilizing a customized
chart of question (A four-point scale).
From the results of this study, the following conclusions could
a) Within the limitations of this study, it may be concluded
that proper distribution of immediately loaded implants used
for supporting mandibular screw-retained implant-supported
full arch restoration, through proper implant placement
pattern results in favorable response in terms of clinical,
radiographic outcomes as well as patients’ satisfaction.
b) Both modalities presented a feasible treatment option
for supporting a screw-retained mandibular prosthesis with
better outcomes in first distribution pattern.
c) The Bio-Hpp material used in implant supported
prostheses had several benefits for the implant restorations
such as lower chipping rate, reduces stress shielding, metal
free, easily monitoring implant-abutment connection fit.
d) The use of composite veneering material allows a high
aesthetic acceptance with a reduced complication rate.
e) Use of the combination of a PEEK- framework with resin
veneering showed a good alternative modality in implantsupported
full arch restorations.
f) Enhanced clinical investigations with larger sample
sizes and over longer periods of time, are still needed.