Comparison of clinical and radiographical outcomes following placement of hybrid and moderate rough implants in the posterior mandible of periodontally compromised patients: a 3-year randomized clinical trial

The first screw type endosseous titanium dental implants placed in the sixties
of the last century by Professor Per-Ingvar Brånemark were machined surface
implants. The orthopedic surgeon from Sweden discovered that titanium implants
were almost impossible to be removed from the tibia and fibula of rabbit
specimens. He called this phenomenon osseointegration. Brånemark and his group
found stable implants supporting bridges in 81% of the maxillary machined
fixtures and 91% of the mandibular machined fixtures after 5-9 years.
Since that time, the industry is continuous looking for the ideal implant
surface roughness to promote osseointegration. Dental implants are roughly
divided into three different types of surface roughness (Sa): machined/minimal
(± 0.5 m), moderate (1.0-2.0 m), and rough (> 2.0 m) by Professor Thomas
Albrektsson and Professor An Wennerberg.
Rougher surface implant types show higher initial clinical survival rates
compared to machined surface implants. On the other hand, a disadvantage of
this increased roughness might be that it facilitates bacterial adhesion at the
implant's surface.
Recently, Albrektsson et al. demonstrates in a meta-analysis of prospective
clinical studies a 10-year survival rate of moderate rough fixtures of 95,14%
at implant level. He also reported a prevalence of peri-implantitis of 5,20% at
patient level.
Peri-implantitis is an inflammatory process in the tissues surrounding a dental
implant characterized by loss of peri-implant bone beyond the physiological
bone resorption. This disease is also often associated with suppuration and
deepened pockets. Bone resorption leads to soft tissue recession and ultimately
to implant loss. The etiology of peri-implantitis is multifactorial. In the
literature peri-implantitis is by some authors described as a biofilm induced
disease, while others manifest an imbalance in the foreign body response.
Because the difficulties to treat the disease, the focus is shifting from
treatment to prevention of peri-implantitis.

Periodontitis is likewise peri-implantitis a multifactorial disease whereby
biofilm and host response play a prominent role. Besides inflammation of the
soft tissue surrounding a tooth also loss of tooth supporting bone is present.
Successfully treated periodontitis patients are generally receiving the same
dental implants as patients without a history of periodontitis. However, these
patients were significantly at a higher risk of implant failure and increased
marginal bone loss compared with periodontally healthy patients. There is some
limited evidence present showing that implants with machined surface were less
prone to bone loss related to peri-implantitis compared with implants with
rougher surfaces.
The question arises why not combining the best of two worlds in periodontitis
susceptible patients using a hybrid implant with an apical moderate rough
surface for optimal osseointegration characteristics and a marginal machined
part less susceptible for peri-implantitis on the long term.
Prospective studies on performance of hybrid dental implant supporting single
restorations in the posterior region of the mandible are lacking. There is no
evidence yet, whether a hybrid surface, leads to higher implant survival rates
or effects marginal bone loss.

Thel aim of this project is to analyse hybrid implants placed in de posterior
mandible of periodontally compromised patients and to compare the treatment
outcome of either moderate rough or hybrid implants.

The study is set up as a multicentre randomized clinical trial. Each patient
will receive two implants with different surface roughness from the Southern
Implants system. The implants are to replace single partially edentulous spaces
in the mandibular premolar and molar region. The implants have an identical
macro-design, but are different in micro-design/surface roughness:
" Group A: hybrid (apically moderate rough surface (1.0-2.0 mircometer) and 3.0
millimeter coronally machined surface (+/- 0,5 micrometer)) implants with 1,8mm
polished neck, external 45-degree bevel top, internal octagon and 8-degree
internal taper
" Group B: moderate rough (1.0-2.0 micrometer) implants with 1,8 mm polished
neck, external 45-degree bevel top, internal octagon and 8-degree internal taper
All surgical interventions and prosthetic procedures are performed by
experienced clinicians.

Surgical procedure:
" All surgeries are performed under local anaesthesia.
" After a crestal incision and intrasulcular incision at the adjacent teeth, a
buccal and lingual full-thickness mucoperiostal flap is reflected. The shape of
the bone is properly judged and sharp ridges are removed. The implant osteotomy
is performed according to the Southern Implant surgical drilling protocol.
Because the macro-design of both implant groups is identical, the osteotomies
are identical. A prefabricated jig is used to control the prosthetic ideal
implant location.

Implant seating:
" The implant is placed both mesial and distal even with the alveolar crest.
Thus, the junction from implant surface threats to implant polished neck is
placed on bone level. If necessary, the bone is flattened.
" With a manual torque wrench the insertion torque is measured. Maximum
insertion torque during implant installation is 60 Ncm, according to Southern
Implants surgical manual. Primary implant stability is assessed by insertion
torque measurement and as the absolute absence of axial or rotational movement
by the removal of the implant mount. If implant stability is not reached, the
patient is excluded from the project and treated regular.
" In case of a small buccal dehiscence, autologous bone particles that are
locally harvested in the area close to the implant site or tuberosity, can be
used. No other grafting materials are allowed.
" All implants are placed non-submerged (one stage). The height of the
screw-retained healing cap depends on local soft tissue thickness.
" Both wounds are tension free closed.
" Immediately after surgery, the pre-made implant position transfer jig
will be used to pick-up an impression coping to register the implant position.
" Clinical photographs are obtained.
" Routine oral hygiene at the implant site is not allowed until sutures are
removed after 7 days. At that time point the healing process is reviewed and
the patient is given oral hygiene instructions to clean carefully the healing
abutment with a soft (surgical) toothbrush. An intra-oral radiograph is
obtained.

Prosthetic work flow:
" Six weeks after implant surgery the oral hygiene is checked by visual
inspection of plaque on the healing caps and the condition of the peri-implant
mucosa. If plaque is noticed, the patient will receive oral hygiene
reinforcement.
" After 3 months (delayed loading protocol), a final full arch open tray
impression using a custom acrylic resin impression tray and polyether
impression material is taken at implant level. The maxilla-mandibular
relationship is recorded. With individualized implant analogues connected to
the impression copings a scan is made of the polyether impression. The final
FPDs are made on the basis of this hybrid method and their fit is checked on
the conventional poured stone model. Everything is done by one experienced
dental laboratory. The final full zirconia FPDs are cemented to standard
titanium-based abutments. All FPD's will be screw retained. The internal
abutment screws are torqued with a torque wrench according to the
manufacturer's guideline. Tightening of the abutment without implant movement
or pain is considered a sign of clinical osseointegration. The passive fit is
checked on a periapical radiograph.

The patient will be affected two to three days post-operative by the performed
implant surgery. Analgetics wil suppress the pain.
The tax in terms of time for the patient will as good as equal to the time
required a regular dental office or refer practice for oral implantology.
The is no increased risk by the procedure, we follow the standard protocol.