Background: All-on-four concept is widely applied in dental clinics, which comprises only four implants placed in the anterior
region and requires two phases in its treatment plan; the provisional and definitive prosthesis. For the provisional, the patient's
denture is altered and screwed to implants for immediate loading and used in the osseointegration period for nearly four month
then replaced with the hybrid definitive prosthesis.
Objective: The purpose of the current study was to assess and correlate the short-term changes in occlusal contacts distribution
and masseter muscle activity in patients rehabilitated with mandibular All-on-Four fixed-detachable and to compare between
provisional acrylic versus definitive porcelain fused to metal prosthesis.
Material and method: For this within-subject crossover clinical study; seven completely edentulous patients were selected
following certain criteria to receive mandibular hybrid prosthesis based on All-on-Four concept using guided surgical procedures
following flapless approach. Patient's new lower denture were modified and screwed to act as “provisional prosthesis" and
after three month of using the prosthesis, the occlusal contacts were assessed using T scan and masseter muscle activity were
evaluated with Surface Electromyography. After one month washout period, the “definitive hybrid prosthesis" was constructed
using porcelain fused to metal and screwed on the multiunit abutments. Patients were allowed to wear it for 3 month after which
the same records were obtained. The collected data were statistically analyzed and correlated.
Results:The EMG records analysis showed; On comparison between soft and hard food using Independent t-test revealed that
hard food was significantly higher than soft in both groups. While comparing provisional and definitive groups the data showed
that the provisional group was significantly higher than the definitive group. Regarding the T scan records analysis showed
on comparison between provisional and definitive groups that the former was significantly higher than last one at right side,
while provisional group was significant lower at left side. Correlation between EMG and T-scan revealed positive insignificant
correlation in soft food provisional group. While in hard food, provisional group revealed negative significant correlation. On
the other hand both types of food in definitive group revealed positive insignificant correlation.
Conclusions: The T scan and EMG outcomes in the current study revealed that both provisional and definitive All-on-Four
fixed detachable prostheses can be considered a functionally efficient treatment option for edentulous mandible as detected by
the favorable masseter muscle activity. However the definitive prosthesis better maintain the occlusal equilibrium. Based on
these findings frequent occlusal adjustments are required for the provisional prosthesis whenever long-term use of it is planned.