The patient was a 42-year-old male with aggressive periodontal disease, with no other pathology of interest.
The intervention followed the following sequence:
- Supracrestal incision with posterior and medial discharges to avoid flap tension and to adequately locate the mentonians.
- Intense curettage of post-extraction alveoli if present.
- Identification of mentonians.
- Regularisation of the ridge, trying to ensure that all implants are at the same occlusogingival height.
- Central osteotomy with a 2 mm drill to a depth of 10 mm; confirm with a direction indicator that the osteotomy is perpendicular to the bipupillary line.

- Positioning of the "all-on-4 guide": this is a guide (Nobelbiocare®) which, thanks to its markings and references, allows the insertion of the implants at the right angle (about 30º) while keeping the tongue away from the surgical field.

- Preparation of the distal implant sites with 30º inclination. Note the presence of the right distal molar which was used by the patient to retain the removable prosthesis and which we will remove in the same session.

- Note also the presence on the left side of an unsightly diapneusis in the lower labial commissure which we will subsequently remove by conventional surgical excision.
- We can also see that the preparation bed of the right distal implant is in the vertical of the exit of the mentonian.
- We drill and insert the right distal implant (Nobelbiocare® Brånemark implant, Ti-Unite Groovy 3.75 x 15), of the same dimensions as the other three fixations used in the case.
- Care should be taken not to use an excessive number of drills so that we achieve a minimum insertion torque of 35 N cm.
- We always use countersink drills on the distal implants, so that they are submerged (infraosseous) distally, so that there are no exposed loops mesially, given the inclination of these fixations.
- Once the first distal implant is in place, we insert its corresponding 30º angled multi-unit abutment. As can be seen in figure 4, the 30º inclination of the implant, corrected with an abutment with the same angulation, results in a perpendicular to the ridge and, as we intend, to the bipupillary line.

- We repeat the procedure with the distal left implant/abutment.
- Next, we prepare the beds for the mesial implants, trying to maintain parallelism and equidistance between them and with the distal implants.

- We place straight multi-unit abutments on the mesial implants already inserted.
- Next, we apply the appropriate torque (15 N cm on the posterior implants and 35 on the anterior implants) as these abutments will never be removed again (the provisional and definitive prostheses will be fabricated on them).
- We then screw in the temporary titanium cylinders that will later be embedded in the temporary prosthesis and suture the wound around them with resorbable suture.
- Once the entire incision has been sutured, we unscrew the cylinders and use a circular scalpel around the multi-unit abutments so that the gingiva does not get in the way during intraoperative screwing and unscrewing in the next few minutes.
- We check the passive seating of the prosthesis, lowering it if necessary.
- We reline the prosthesis with dense silicone and have the patient bite down. Once it has set, the marks of the multi-unit abutments on it will mark the points where the prosthesis must be drilled, a manoeuvre which we then carry out.
- We screw the titanium cylinders back in.
- We check the passive seating of the perforated prosthesis and see if the cylinders allow maximum intercuspidation; if not, we trim the cylinders to allow it.
- We place a rubber dam to isolate the surgical field during subsequent manoeuvres.

- We put cotton wools in the chimneys of the cylinders and close the perforations of the prosthesis with soft wax.
- We dry the prosthesis well and we fill it with self-curing resin and have the patient bite into position.

- We remove the wax "plugs" and fill with more resin occlusally, leaving only the access to the screws uncovered.
- We let it set completely, unscrew and check the stability of the cylinders already embedded in the prosthesis.

- Fill the holes (pores) with more resin and cut the cylinders flush with the prosthesis.
- We cut the fins and the distal ends of the prosthesis (in the provisional prosthesis we leave practically no cantilever); we remove the rubber dam.
- We also remove any resin in contact with the flange; for this we use the GC Fit-checker® used as a reline, which shows us the area that exerts pressure on the flange.

- We polish the prosthesis, screw it in definitively at 15 N cm and adjust the occlusion.

- After 15 days, the patient comes for a check-up and we remove the suture to which we have access; the rest, as it is resorbable, is of no concern to us

- At this point we train the patient in the handling of Superfloss® so that hygiene is optimal (it is quite simple as there are only four implants).
- We carry out regular check-ups until after 5-6 months we proceed to manufacture the definitive prosthesis.
During this period it is not necessary to unscrew the provisional prosthesis.

