Article Type : Review Article
Authors : Shah K and Kulshrestha R
Keywords : Implants; Full mouth rehabilitation; Prosthesis
Generally, a complete edentulous arch requires
5-7 implants. This is not possible always because of biologic or economic
factors. Such scenario pivots the need for treatment by All-on-4 concept.
Though, biological, and mechanical complications can arise due to reduce
implant support, but the success rates are quite satisfactory. This article
describes the All-on-4 concept in general. This concept is mainly indicated to
maximize the use of available alveolar bone and to allow for immediate
function. It greatly increases patient’s satisfaction.
The “All on four” treatment concept
is used for full mouth rehabilitation in complete edentulous arch with either a
denture or bridge supported by four implants [1]. In the early concept by Branemark,
it was stated that use six implants in a mandible with sufficient ridge and 4
implants in severely deficient alveolar ridge [2]. The two anterior
implants are placed axially and remaining two posteriors are angled and placed
distally to minimize cantilever and aid in mastication. In addition, the
posterior angulation also prevents implant’s interference with mandibular nerve
in lower arch and maxillary sinus in upper arch [3]. Nobel Biocare
was amongst the first company to identify the evolution of All-on-four
technique for full mouth rehabilitation.
The ill-fitting complete denture can result in soreness and
atrophy of the jaws which is a discomfort to the patients [13]. The all-on-four concept offers
comfortable solution for patients with atrophic jaws. The immediate
implant-support restoration provides patient greater satisfaction. The outcome
is better quality of patient’s life [14]. In the study of Lopes et al.,
difficulty in doing surgery was classified based on a score- low (residual
ridge of > 5mm), moderate (irregular residual ridge of 4-5mm) and high
(irregular residual ridge of < 4mm) [15]. The under drilling of implant site
does enhance the insertion torque by preventing counter sinking to maximize
stability of the implant. Biologically, this approach is justified because
mechanical stimulation around a newly placed implant modulates the release of
bone mediators [16]. Indiscriminately and immediately loading of dental implants
is not always favourable because of unfavourable stress distribution and
non-favourable cellular response during initial healing phase in un-splinted
implants like in over dentures or partial fixed dental prosthesis [17]. Furthermore,
high torque during insertion of implant at an under drilled site which is
commonly used for immediate loading can reduce crestal bone-to-implant contact
during initial healing phase [18]. To reduce the chance of patient’s morbidity,
flapless surgery with the use of prefabricated customized guides are used. This
makes the surgery more accurate and avoids interference with anatomical
structures [19]. Primary stability is extremely important for
osseointegration which can be achieved by greater insertion torque. For this
splinting is recommended during a full arch restoration with immediate loading [20]. On contrary,
extra high insertion torque can lead to wearing on the implant surface and
cause a foreign body reaction because of titanium debris and ions that are
emitted from the implant surface [21].
The all-on-four treatment concept had overall great success
rate of more than 98% at 24 months follow up. The window technique to locate
anatomic structures allows adequate implant insertion and safeguards sinus and
nerve. To attain primary stability and to prevent countersinking of implant in
cortical bone the implant bed was under-prepared. It is recommended to use
guided surgery to ensure proper positioning and inclination of distal implants.
Acrylic fracture and peri-implantitis are the complication of all-in-four
implant treatment. Furthermore, there is a need for more follow-up studies to
determine the effectiveness of all-on-4 implant concept.