Implant supported maxillary overdentures in the augmented maxilla: 4 versus 6 implants

Implant supported overdentures in the edentulous maxilla are common in The
Netherlands. In case of a severe atrophic maxilla, the implant procedure is
only possible after a bone grafting procedure is performed prior to the implant
placement.
The augmentation of the maxilla is mostly done with the use of autogenous bone
from the anterior iliac crest.
After a four-month healing period, usually four to six implants are placed to
support an overdenture. In literature, there is no evidence whether four or six
implants should be placed in the augmented maxilla for the support of an
overdenture. In the systematic review of Slot et. al. (#1), it is stated that
the survival rate of both four and six implants is above 95 percent (98.2 vs.
96.3%) if the prosthetic procedure is done with bar anchorage.
In another study of Slot et. al. (#2), a comparison is made between the use of
four versus six implants in the non-augmented maxilla only. The success rate
for both groups is very high, almost 100 percent. In this group, strict patient
selection criteria and a strict protocol for the procedure was followed. This
strict protocol cannot be compared with the normal practice, because patients
who don*t meet the selection criteria also receive implants and those implants
are not always placed in a academic setting with one implantologist and one
prosthodontist. Secondly, the majority of patients need an augmentation of the
maxilla. Only the group with limited resorption allows the placement of
implants in the pre-existing bone of the maxilla.
In a third study of Slot et. al. (#3), a comparison between four and six
implants in the augmented maxilla was made. In this study the augmentation
procedure was a sinus elevation procedure only to augment the maxilla. Although
success rates in this study are very high, a sinus elevation procedure alone is
not sufficient enough to place implants in the severe atrophic maxilla.
Together with the sinus elevation procedure, it is also necessary to perform a
buccal plating procedure in order to to gain enough width in the maxilla to be
able to place implants.
The goal of this study is to investigate the change in functional outcome of
implant surgery in the severe atrophic maxilla after augmentation (sinuslifting
and buccal plating) in a setting that comes closer to the normal daily practice
than done in the studies of Slot et. al.
Since implant supported overdentures for the maxilla seem to be highly
successful (Raghoebar et. al #4), this study is carried out to investigate the
change in functional outcome of four versus six implants in the augmented
maxilla.
Also cost effectiveness, change in bone level on x-rays, clinical parameters
(pocket depth, bleeding score and plaque score), change in facial appearance,
necessity of replacement of implants, VAS-scores, time of inability to work/to
join social activities will be investigated.
The cost of the procedures are high and if there can be made a reduction of
costs (four versus six implants, shorter operating time and shorter time of the
prosthetic procedures and aftercare), it will help to reduce the total budget
of health care costs.

1. A systematic review of implant-supported maxillary overdentures after a mean
observation period of at least 1 year. Slot W, Raghoebar GM, Vissink A,
Huddleston Slater JJ, Meijer HJ. J Clin Periodontol. 2010 Jan;37(1):98-110.
doi: 10.1111/j.1600-051X.2009.01493.x. Epub 2009 Dec 7.

2. Maxillary overdentures aupported by four or six implants in the anterior
region; 1-year results from a randomized clinical trial. Slot W, Raghoebar GM,
Vissink A, Meijer HJ.
J Clin Periodontol. 2013;40 303-310.

3. A comparison between 4 and 6 implants in the maxillary posterior region to
support an overdenture; 1-year results from a randomized controlled trial.
Slot W, Raghoebar GM, Vissink A, Meijer HJ.
Clin Oral Implants Res. 2013 Feb 13. doi: 10.1111/clr.12118. [Epub ahead of
print]

4. Maxillary bone grafting for insertion of endosseous implants: results after
12-124 months.
Raghoebar GM, Timmenga NM, Reintsema H, Stegenga B, Vissink A.
Clin Oral Implants Res. 2001 Jun;12(3):279-86.

Primary Objective: The objective of this study is to asses whether or not the
use of four implants in the augmented maxilla is as effective on the
improvement of the patient*s oral functioning measured with the MFIQ as the use
of six implants
Secondary Objective(s): Comparison of cost effectiveness of the procedures,
comparison of the clinical parameters (pocket depth, bleeding score and plaque
score), change in bone level, experienced pain measured with VAS-scores, time
of inability to work/to join social activities and evaluation of the change in
facial aesthetics and the difference in the facial aesthetics between the two
study groups will be investigated.

This study will be a randomized controlled trial (RCT) in a non-inferiority
design. The intention of this
research project is to determine if both therapies are comparable. Main reason
for the study is the disparity in costs of the two treatments. There will be
allocation concealment through central randomization with a computer, web-based
program in Oracle. The doctor and patient are not blinded for the number of
implants (not applicable for this study). When the patient meets the inclusion
criteria,
the patient will be asked to participate in this research. Patients will be
asked to sign the informed consent in case they want to participate. Patients
can be added to the research at any moment in time until the maximum of 32
patients in each therapy group is reached.
This study will be a randomized clinical trial.
The time of the study will be at least 1,5 years after the placement of the
implants.
The augmentation procedure and implant placement will take place in the Amphia
Hospital in Breda, The Netherlands.
After the patient selection with the inclusion criteria: 2 groups of patients
will be made.
One group for the procedure with four implants and one group with six implants.
Photographs will be taken of all patients in the two study groups.
All patients will be asked to fill out the questionnaires (see attachments).
At the beginning of the study (T0) patients will fill out page 1 of the
questionnaire and the MFIQ on page 2.

T1
The augmentation procedure will be performed at the Amphia Hospital in Breda,
The Netherlands. At this time of the study patients will be asked to fill out
page 3 and 4 of the questionnaire.

T2
Two weeks after the augmention procedure patients will visit the outpatient
clinic of the maxillofacial surgery department of the Amphia Hospital for a
check up. If necessary stitches will be removed. The referring dentist can
alter the prosthesis and the prosthesis can be used again.

T3
Six weeks after the augmention procedure patients will visit the outpatient
clinic of the maxillofacial surgery department of the Amphia Hospital for a
check up and panoramic X-ray. The placement of the implants (4 months post
augmentation) will be scheduled at this visit.

T4
After a four-month period, the implants will be placed at the Amphia Hospital
in Breda, The Netherlands. Implants used are from Bego Implants, Germany. They
will be placed according to the manufacturers protocol.
Direct postoperatively, a panoramic X-ray will be made. At this time of the
study patients will be asked to fill out page 5 and 6 of the questionnaire. The
referring dentist can alter the prosthesis and the prosthesis can be used again.

T5
Two weeks after the implant placement the patients will have a check up at the
dental hygienist in The Amphia Hospital for instructions of dental hygiene.

T6
Six weeks after the implant placement, clinical parameters (presence of plaque,
bleeding and pocket depth) will be measured by the dental hygienist. (Mombelli
1987 #5).
Stability of the implants will be evaluated by percussion.
In case sufficient stability is found, the prosthetic procedure can be started
ten weeks after the implant procedure.
A bar supported overdenture will be made at the practice of the referring
dentist or at the Centre for Special Dentistry in the Amphia Hospital, Breda.

T7
Six months after the implant procedure the patients will visit the Amphia
Hospital for a check up and panoramic X-ray to check the fit of the bar on the
implants and the clinical parameters will be scored by the dental hygienist.
The dental hygienist will also perform cleaning of the implants and will
provide the patient with cleaning instructions.

T8
Every three months the patient will visit the dental hygienist for measurement
of the clinical parameters. The dental hygienist will also perform cleaning of
the implants and will provide the patient with cleaning instructions.

T9
One year after the placement of the implants, a panoramic x-ray and photographs
will be taken.
One observer will measure bone levels in the x-rays. This will be done at three
different times to lower the risk of intraobserver differences.
Implant and overdenture survival will be measured. Loss of implants will be
noted at any time of loss of the implant. Remake and adjustments of the
overdenture will be noted and time of repair/replacement will be scored.
Patients will be asked to fill out page 7 and 8 of the questionnaire.
Patient function and satisfaction will be evaluated with the MFIQ and the
questionnaire involving questions about satisfaction of the procedure and final
prosthetic result and change in facial appearance(including VAS-scores).

5. Oral Microbiol Immunol. 1987 Dec;2(4):145-51.
The microbiota associated with successful or failing osseointegrated titanium
implants.
Mombelli A, van Oosten MA, Schurch E Jr, Land NP.

There is no difference in the number of visits for the two groups.
The difference rests in the number of implants placed. Knowing that the minimum
number of implants required in order to support a denture is four implants, the
outstanding risk is that of implant loss. Should such loss occur, it will have
more impact on patients in the group with four implants, because, provided that
only one implant is lost, the patient in question will only have three implants
left. On the other hand, should an implant be lost by a patient receiving six
implants, there will still be five implants left. As such, for the group
receiving four implants, a second operation for implant replacement will be
necessary.
Benefits for the group with four implants are the probable lower time of
surgical and prosthetic procedures, less discomfort, easier dental hygiene and
lower costs, since there will 2 implants less be placed, resulting in lower
costs for the implant and prosthetic procedures.