Fig 22.1 Flaps are elevated to expose the bony ridge, and the mental foramina are located. An osteotomy of approximately 10 mm depth in the midline is prepared using a ϕ 2 mm twist drill and the All-on-4 guide is correctly placed in this midline osteotomy. The posterior osteotomies are prepared to the appropriate depth and tilted distally to the maximum angle of 45°. (A) The posterior osteotomies are prepared in such a manner that the posteriorily tilted implants are placed minimum 2 mm anterior to the inferior alveolar nerve. The osteotomies for the anterior implants are prepared in the usual manner. (B and C) After placing all the four implants, the straight or 17° multiunit abutments are placed on top of the anterior implants whereas the 30° multiunit abutments are inserted over the posterior tilted implants. Multiunit abutments of appropriate collar height should be selected for each implant and should be tightened to 15 Ncm using torque ratchet. (D and E) Immediate provisional and later on definitive hybrid prosthesis are fixed over these implants using fixation screws.
(Courtesy: Nobel Biocare, India).
Step by step diagrammatic presentation of All-on-4™ in the maxilla is shown in < ?xml:namespace prefix = "mbp" />
Fig 22.2 Flap is elevated to expose the bony ridge as well as lateral wall of the maxillary sinus. A small opening on the lateral wall of the sinus is prepared where the anterior wall of the sinus is expected. Further, the anterior wall of the maxillary sinus is explored by using a probe through this opening. (A) The lateral window is extended if necessary and position of the anterior wall is marked using a sterile pencil. An osteotomy approximately 10 mm depth is prepared in the midline using a ϕ 2 mm twist drill and the All-on-4™ guide is correctly placed in the midline osteotomy. (B) The osteotomies for the posterior implants should be started as posterior as possible to minimize the cantilever and allowing approximately 4 mm distance from the sinus. The posterior osteotomies are prepared to the appropriate depth and tilted to the maximum angle to the 45°, so that the posteriorly tilted implants are placed a minimum 2 mm anterior to the anterior wall of the sinus. Two implants at the most-anterior position are placed in the usual manner. (C) The 17° or straight multiunit abutments are placed on the anterior implants whereas the 30° multiunit abutments are placed on the posterior implants. (D) Immediate provisional and later on definitive hybrid prosthesis are fixed over the implants using fixation screws.
(Courtesy: Nobel Biocare, India)
Because of graftless implant placement and immediate loading, the All-on-4™ technique is very successfully being performed by many dentists and has gained high popularity among implant dentists as well as patients. The only limitation with this technique is that prosthesis with only limited number of teeth (10–12 units) can be fixed over these four implants. Further, the loss of any one implant reverts the entire procedure to the initial stage.
To avoid such problems and also for the patients who express the desire for a 14-unit prosthesis, two more implants can be inserted posterior to the posterior wall of the sinus in the maxillary tuberosity and tilted anteriorly at 45° to minimize the length of the unsupported bridge framework between two distal implants. The severely resorbed posterior maxilla with a large volume of posterior expansion of the sinus often does not leave enough bone volume in the tuberosity region to place an implant of an adequate size. In such cases, the implant is inserted in the tuberosity with the apex of the implant at the junction of the pyramidal process of the palatine bone and the pterygoid process of the sphenoid bone. The implant placed would then engage all three bone segments that constitute this region. The implant placement in the tuberosity with its apex engaging the medial pterygoid process of sphenoid bone is the most preferred option because it allows the multicortical engagement of the implant to achieve adequate initial stability for the implant.
To perform the All-on-6 procedure in the mandible, the two straight implants should be inserted usually at the first or second molar site but if inadequate ridge height above the mandibular canal does not allow placement of implants in the molar region, then the short and wide implant can be inserted at the angle of the mandible (into the buccal shelf area) tilted anteriorly at 30–45°.
With the few advantages, there are also several disadvantages with All-on-6 procedures such as increased cost, need of a highly skilled approach to correctly place implants in pterygoid process, difficult approach for the insertion and restoration of posterior implants, need of a skilled technician to fabricate the prosthesis, and problems in oral hygiene maintenance in the back region.
|COMPARATIVE FEATURE||TRADITIONAL APPROACH FOR RESTORING FULL-ARCH||ALL-ON-4™/ALL-ON-6 APPROACH|
|Sinus grafting||May be required||Not required|
|Only grafting||May be required||Not required|
|No. of implants||More no. of implants are inserted||Less no. of implants are needed|
|Immediate fixed restoration in function||May not be possible||Possible|
|Surgery||More invasive||Less invasive|
|Surgical steps||May require multiple surgical steps like grafting procedures, implants insertion, uncovery, etc.||Only one surgical step, i.e. implant insertion|
|Time span needed to deliver the final prosthesis||May take 6 months to 1 year||Can be completed in a few weeks|
|Sinus pathology contraindicating the grafting and implant placement||May not be possible||Possible|
|CT guided implant placement||Possible in selective cases||Possible in most cases|
6. Long tilted distal implant can be maximally stabilized by utilizing high-density bone of the anterior region. Placement of longer implants, enhancement of the area of interaction between bone and implant, and also primary anchorage.
4. With the All-on-4™, only the 10- to 12-unit prosthesis is delivered over the four implants, and often patients request the addition of more posterior teeth to maximize chewing efficiency and improve the overall maxillofacial prosthesis.
2. Anterior wall of the sinus is located far anterior to the usual position, contraindicating tilting of the posterior implants to reach the second premolar or first molar position (
6. Sequential radiographs with the drill into the osteotomy during initial osteotomy preparation for posterior implants, to evaluate the direction of the drilling in respect to vital structures such as the sinus wall and the mandibular canal.
7. Placement of the implants with minimum diameter of 3.3mm at the anterior positions and 3.75–4.2mm for the posterior positions to avoid problems such as connection screw loosening and implant body fracture.
8. Adequate vertical ridge reduction before implant placement to avoid the display of the unaesthetic transition line of prosthesis and ridge tissue when the patient smiles (
Fig 22.4 (A) Unaesthetic gingival line with the old prosthesis is visible during the smile. A planned vertical ridge reduction before the implant placement results in nonvisibility of the transition line of the final All-on-4™ implant prosthesis, when the patient smiles. (B–D) This gives a natural appearance to the All-on-4™ prosthesis.
(Courtesy: Saad Zemmouri, Morocco).
2. Perforation through the inferior or anterior wall of the sinus. It can be avoided by proper exploration of the anterior wall of the sinus. Pilot drilling should begin a minimum of 4 mm anterior to the sinus, evaluated with a radiograph. If the pilot drill has perforated the sinus cavity, it should be evaluated with a radiograph and the osteotomy preparation should be redirected to the planned direction, avoiding the enlargement of the perforation. The path of the anterior wall of the sinus should be marked on the facial wall using a sterile pencil, so that it can be visualized when drilling for implants.
Fig 22.5 (A) Edentulous maxilla. (B) The panoramic radiograph shows adequate bone for All-on-4™ (C) as well as All-on-6 procedure. (D) The dental CT scan shows sinus membrane thickening, contraindicating sinus grafting procedure. Adequate amount of bone is luckily present bilaterally posterior to the sinus to insert adequate size implants, but needs to be laterally condensed to achieve adequate stability for the inserted implants.
Fig 22.6 (A) Mucoperiosteal flaps are elevated to expose the bone ridge as well as the facial wall of the ridge and (B and C) planned amount of vertical ridge reduction is done using a bone rongeur to achieve the wide ridge crest to place implants with adequate diameters as well as to shift the transition line of the future prosthesis and ridge tissue apical to the high smile line of the patient.
Fig 22.7 (A) A small opening at the lateral wall of the right sinus is prepared using a round carbide bur. (B) The anterior wall of the sinus is explored using a probe. (C) The opening is extended to appropriately explore (D) the complete path of the anterior wall of the sinus. (E) The anterior wall of the left sinus is also explored in the same way and (F) it is marked using a sterile HB pencil.
Fig 22.8 (A) An osteotomy is prepared using 2.0 mm pilot drill in the midline and (B) the All-on-4™ guide (Nobel Biocare, India) is placed. (C and D) The osteotomies are prepared for the posterior implants angled at the 45° and just anterior to the anterior wall of the sinus.