The posterior mandible requires exceptionally careful, reproducible preoperative investigation, for both medical and forensic reasons. The inferior alveolar nerve in particular is at risk from implant placement in the posterior mandible. Damage to this nerve has extremely unpleasant consequences for the patient, as it not only provides sensation to the teeth of the mandible, but also supplies sensory innervation to the lower lip, so that any damage can result in persistent dysesthesia in the latter. Since the functional deficits in the nerve can result from any touch or pressure, most clinicians require a minimum distance of 2 mm to be maintained when placing implants. The vertical position of the nerve canal is normally visible on the panoramic radiograph. However, the latter gives a superimposed view of the anatomical structures, so that an exact, three-dimensional (3D) assessment of the position of the nerve cannot be made on the basis of this radiograph alone. Only standard computed tomography (CT) or cone beam CT (CBCT) allow its 3D position to be assessed precisely.

3D diagnosis and SimPlant planning

3D planning of a single-tooth implant

Clinical examination is followed by extensive diagnostic investigations. Apart from dental cast analysis, radiographic diagnosis is of key importance: it should include at least a panoramic radiograph with measuring template and, best of all, a CBCT or CT scan.

The panoramic image already provides an overview of the anatomical situation (Fig 2-1a). However, 3D diagnosis and planning are far more precise and reliable on the CBCT image. The third dimension, the width of the residual ridge, can be seen on the cross-sectional image (Fig 2-1b).

In such cross sections, the implants can be aligned in the buccolingual direction, while alignment in the mesiodistal direction is generally performed using the panoramic radiograph. Based on the measurements in this case, a wide platform (WP) implant, 13 mm long and 5 mm in diameter, was planned for the replacement of tooth 45. For the provisional loading, a 1-mm high CeraOne (Nobel Biocare) abutment was planned as the connecting component for the provisional crown.

Detailed planning was performed using the SimPlant program (Dentsply). Here, the WP implant was taken from the program library (color code pale blue in this case), virtually placed into the jaw and adjusted in all the planes (Fig 2-1c). The CeraOne abutment (color code pink) was also virtually placed onto the implant. For better visualization of the forces involved, the extension of the implant axis is represented as a yellow bar. If the structures lying behind the implant or in the same plane are to remain visible, the implant can be shown in outline only (Fig 2-1d). The inferior alveolar nerve, as the most important anatomical structure in the mandible, can be marked, allowing its course in relation to the planned implants to be assessed (Fig 2-1e). The marked nerve also appears on the cross-sectional images, so that its position relative to the implants can also be accurately evaluated in this plane (Fig 2-1f).

Moreover, the 3D reconstruction gives a very vivid visual depiction of the positioning of the implants and their relation to the nerve. In this mode, the bone structure can be shown in semi-transparent view (Fig 2-1g) or can even be faded out completely, to visualize the relationship of the implants to the nerve in isolation (Fig 2-1h).

For the treatment course, see page 60.

3D planning of a free-end situation

The free-end situation is one of the most common indications for implant treatment in the mandible. In view of the large number of implants needed in this kind of situation, each individual implant needs to be planned with great care. Apart from the position of the nerve, another factor of key planning significance is the width of the residual ridge. In the case described here, a large mandibular defect had developed following the loss of implants placed at another clinic. The planned treatment included not only the insertion of five implants, but also extensive augmentation. The panoramic radiograph alone clearly showed the extent of the defect (Fig 2-1i). A much more accurate assessment of the situation can be obtained from the CBCT image in the SimPlant planning program (Fig 2-1j). The five planned implants need to be placed in such a way as to use all the available bone (Fig 2-1k). In order to achieve primary stability in the previously damaged, knife-edge jaw after the insertion, the plan was to use narrow platform (NP) implants with a diameter of 3.3 mm. Implants 1 and 3 are only weakly anchored in the bone and need augmentation on the buccal side (Figs 2-1l to 2-1n). The 3D reconstruction provided an insight into the intraoperative situation following insertion of the implants, and showed not only the extent of the defect but also how much bone needed to be augmented (Fig 2-1o).

For the treatment course, see page 70.

Single-tooth gap

In the case of a single-tooth gap, the preoperative diagnostic investigations need to assess not only the location of the nerve, but also the extent of the gap in the mesiodistal direction and the available bone supply in the buccolingual (or labiolingual) dimension. The mesiodistal width of the gap can be determined exactly on the dental cast and approximately on the panoramic radiograph. The buccolingual width of the residual ridge can be determined on the model only in the coronal region, following a determination of mucosal thickness, whereas the panoramic radiograph provides no information on this aspect. Moreover, measuring mucosal thickness in the posterior tooth region is difficult for the dental surgeon, unpleasant for the patient and beset with errors. Thanks to modern 3D imaging techniques, it is now possible to determine the exact width and height of the residual ridge, as well as the position of the nerve, on the CT or CBCT scan images (see page 40).

Either premolars or molars may be replaced in the posterior region. The first molar is a far more common candidate for implantological restoration than the second molar. The first molar is at the center of the masticatory forces, and is thus exposed to a high level of stress. As a result, a single regular platform (RP) implant (diameter 3.75 mm) may become overloaded. Therefore, where sufficient space is available, a WP implant of increased diameter (5 mm) or two RP or even NP implants (diameter 3.3 mm) represent better alternatives. The use of two implants is generally preferable if the residual ridge is inherently narrow and the distance between neighboring teeth is >11 mm, whereas one implant should be the preferred option if the gap is <10 mm and the residual ridge is on the wider side. The considerations involved in replacing the first molar are difficult to reconcile with the rules set out by Dr Tarnow, which state that the distance between two implants should be at least 2 mm, and the distance to the neighboring tooth at least 1.5 mm.

Implant placement

Two Neoss implants were inserted into gap 46 under local anesthesia (Fig 2-2d). The implants were placed at the desired depth and the remaining bone defect was filled with the harvested bone chips. The polyetheretherketone (PEEK) healing abutments were then screwed onto the implants. One of the healing abutments needed shaping on one side due to the limited space and convergence of the implants (Fig 2-2e). To protect the implants from undesirable stresses, it is important that there is neither any contact between the healing abutments and the neighboring teeth, nor any occlusal contact with the dentition in the opposing jaw (Fig 2-2f).

Attention: Where there is good bone quality and adequate primary stability, the implants may be directly fitted with healing abutments and allowed to heal transmucosally. If bone quality is poor, it is advisable to allow the implant to heal submerged and to expose them only after 4 to 6 months.

The postoperative panoramic radiograph shows the position of the implants relative to the neighboring teeth and demonstrates that there is adequate distance to the inferior alveolar nerve (Fig 2-2g). The final photograph shows the transocclusal, screw-retained metal-ceramic crown, which was first cemented onto the customized abutments (Fig 2-2h).

Attention: To assure long-term success following implant loading, it is very important for the implants, the prosthetic crown and the neighboring teeth to be kept clean at all times. For optimal hygiene of the implant-supported restoration, the crown has been fabricated with a cleaning channel to admit interdental brushes (see Fig 2-2h).

Implant placement and mucosal distraction

An arcuate incision was made on the lingual side, to allow the keratinized gingiva to be transplanted in the buccal direction (Fig 2-3c). Since transmucosal healing was planned, the implant was inserted 1 to 2 mm supracrestally (Fig 2-3d). A 5-mm-high PEEK healing abutment was fitted onto the implant (Fig 2-3e) and the harvested bone chips were layered onto the buccal side for the augmentation (Fig 2-3f). For financial reasons, the augmentation was performed without the use of synthetic materials, limiting its volume. The flap was repositioned and stabilized in the interproximal spaces with two 6-0 Mopylen (Resorba) sutures (Fig 2-3g).

Despite transplantation of the keratinized gingiva, the contour of the residual ridge was not optimal, but could be improved slightly with vertical mucosal distraction. A small perforation was made in the plastic of the coronal part of the healing abutment, and the mucoperiosteal flap lifted up and fixed into this position with a suture (Fig 2-3h). The postoperative panoramic radiograph shows the implant in relation to the nerve and the neighboring teeth (Fig 2-3i).

Prosthetic loading

Four months after the implant placement, the soft tissue situation had stabilized; the implant had healed and could be loaded with a crown (Fig 2-3j). While the gingiva had receded somewhat, its contour was still more favorable than directly after implant placement (compare Figs 2-3g and 2-3j). This improvement could be ascribed to the vertical mucosal distraction (Fig 2-3j). The implant and tooth 47 were loaded with metal-ceramic crowns (Fig 2-3k). The patient was very satisfied with both the final result and the lower costs, and the reasonable extent of the treatment.

Implant placement with augmentation

Before implant placement, the right inferior alveolar nerve was numbed using block anesthesia and the provisional partial denture was removed (Fig 2-4e). This made the vertical and horizontal bone defect more clearly apparent. For the planned augmentation and condensation of the gingiva, the incision was made lingually, but still on the residual ridge (Fig 2-4f). Following mobilization of the buccal mucoperiosteal flap (with no releasing incisions), the implant was inserted approximately 2 mm supracrestally, as planned (Fig 2-4g). To spare the patient a second procedure, ie, implant exposure, a 2.7-mm-long PEEK healing abutment was screwed directly onto the implant (Fig 2-4h).

For the augmentation, the cortical bone layer around the implant was perforated in several places to encourage revascularization, and bone chips collected in the filter were layered onto the buccal side of the residual ridge (Fig 2-4i). For larger augmentations, it would also have been possible to use a regenerative bone substitute and a membrane, but this would have meant greater financial cost.

The buccal flap was then repositioned and fixed around the healing abutment with Gore-Tex sutures (W. L. Gore and Associates) (Fig 2-4j). The postoperative panoramic radiograph shows the position of the implant relative to the nerve and the neighboring teeth (Fig 2-4k). The augmentation has had a positive effect not only vertically, but also in the horizontal plane (Fig 2-4l). The improved buccal contour of the residual ridge can be assessed postoperatively once the provisional bridge has been fitted (Fig 2-4 m). If the same provisional restoration is to be reused, sufficient place needs to be made for the protruding healing abutment. The reshaped provisional protects the implant not only from masticatory stresses, but also from possible pressure from the tongue, which can sometimes even be dangerous (Fig 2-4n).

Four months after implant placement, both the implant and the neighboring teeth were fitted with a prosthetic restoration. The final photographs show the clinical situation with apparently healthy gums after 5 years (Fig 2-4o). While the buccal bulge (jugum alveolare) over the implant is smaller than with some teeth, it is still more marked than before implant placement (compare Figs 2-4f and 2-4p). The prosthetic restoration has been harmoniously incorporated into the overall appearance of the mouth (Fig 2-4q). However, the panoramic radiograph after 5 years shows an incidental finding on tooth 47 (Fig 2-4r). According to the radiograph, implant 46 has undergone good osseous integration, but tooth 47 shows a distal zone of radiolucency, probably a periodontal-endodontic lesion, which requires urgent treatment although the patient has no symptoms and has not noticed the inflammation at all.

Attention: The use of a standardized trephine, as small in diameter as possible, minimizes the resultant bone defect. For guidance when using a trephine, it can be helpful to screw an impression post screw onto the implant as a direction indicator. In this case, however, this was no longer possible because the implant thread had fractured completely.

Implant removal and augmentation

Following a buccal incision, the dissected flap was fixed to the premolar in the third quadrant with a single suture to give a clear view of the operation site. The drilling depth was initially determined from the preoperative measurements taken from the radiograph. An intraoperative radiograph with the trephine inserted provided an additional check of the drilling depth (Figs 2-5c and 2-5d). Once the bone around the implant had been fully reamed away, the implant was removed by careful luxation with a lever.

The fractured elements of the implant, with the crown structure screwed on via an abutment, suggest a fatigue fracture of the inadequately sized implant (Fig 2-5e). Based on his experience so far, the patient placed no trust in a single-tooth implant and wanted a restoration loaded on two implants to be on the safe side. However, the resultant bone defect prevented immediate implant placement in this area (Fig 2-5f). Initially, therefore, a single RP implant was inserted mesially of the defect (Fig 2-5g) and the defect augmented with a bone substitute (Bio-Oss; Geistlich).

Delayed implant placement

The radiograph and clinical inspection after 6 months already showed clear reossification in the augmentation area (Fig 2-5h and 2-5i), allowing a second Brånemark System (Nobel Biocare) implant to be inserted (Fig 2-5j). The positioning of the new distal implant relative to the neighboring tooth and the mesial implant is clearly apparent on the radiograph (Fig 2-5k).

Exposure and prosthetic loading

The implants were exposed after a further 6 months (Fig 2-5l). They were then loaded with a prosthesis consisting of an interlocked crown on two customized abutments (Fig 2-5m). The clinical situation 7 years after the restoration was incorporated shows a stable peri-implant situation with no inflammation (Fig 2-5n).

Laboratory technique

In the cast, tooth 85, which needed extracting, was erased and an implant or abutment analog in accordance with the CBCT-based 3D radiologic investigations (see diagnostic investigations, page 40) was inserted into the model (Fig 2-7b). The bone supply and the width of the gap permitted placement of a WP implant 5 mm in diameter. A CeraOne abutment with plastic cap was prepared in the laboratory to take the immediate provisional prosthesis (Fig 2-7c) and a plastic crown was prepared in the form of an eggshell provisional (Fig 2-7d). The provisional crown was to be polymerized onto the plastic cap following insertion of the implant.

Extraction, implant placement and provisional restoration

The primary tooth was extracted immediately before implant placement. After the initial preparation with the 2- and 3-mm drills, the position and alignment of the implant bed were checked using a direction indicator (Fig 2-7e).

The implant bed was then prepared to a further diameter of 4.3 mm. Once the process was completed with a thread cutter, the WP implant (diameter 5 mm) was inserted due to the dense bone structure at the site (Fig 2-7f).

The CeraOne abutment was screwed into place (Fig 2-7g). For the provisional crown, it was important to maintain an adequate occlusal distance (at least 2 mm) to the antagonist tooth (Fig 2-7h). The prepared eggshell provisional was filled with quick-hardening, autopolymerizing plastic and incorporated. After shaping, the provisional crown was cemented into place with TempBond (Kerr) (Fig 2-7i). The final photographs show the clinical situation 5 months after implant placement and 3 years after the incorporation of the definitive prosthetic restoration (Fig 2-7j and 2-7k).

Multi-tooth gap and free-end situation

Patients missing more than one tooth in the posterior mandible present with either a multi-tooth gap between teeth or a free-end situation, the second being far more common. Since treatment for both indications is similar, the focus here will be placed on the free-end situation. In the case of a free-end situation – in contrast to a multi-tooth gap between teeth – the only fixed prosthetic restoration option without the use of implants is a cantilever fixed partial denture. The number of implants depends on the size of the gap, with one implant recommended for each tooth that needs to be replaced. However, a minimum distance of 3 mm needs to be maintained between implants. In a free-end situation, at least two implants, but preferably three or four, are recommended. A superstructure supported on three or more implants shows far fewer complications than one loaded onto only two implants. These include both biologic complications (bone loss if the implants are overloaded) and mechanical complications (loosening or fracture of the retaining screws or even implant fractures).

Diagnosis and planning in the case of a large multi-tooth gap or free-end situation need to proceed with at least as much care as with single-tooth implant placement in the posterior mandible, because each individual implant may lead to damage to the inferior alveolar nerve. Implantology associations recommend a diagnostic measuring radiograph (panoramic image) with a template that contains incorporated measurement devices as the minimum imaging procedure. Its disadvantage is that it does not provide the most important information, namely the width of the residual ridge. A CBCT or CT scan is advisable in most cases not only for forensic but also practical reasons, due to the risk of nerve injury.

Typical treatment course

Two-session approach with augmentation

Baseline situation

A 70-year-old man wished to have a fixed prosthetic restoration on both sides of the mandible. Dental treatment on the right side had already been completed, while tooth 37 remained to be extracted on the left side (Fig 2-8a).

Diagnostic tools

• Clinical examination
• Panoramic radiograph
• CBCT
• SimPlant planning
• Dental cast analysis

Treatment plan

1.Extraction and immediate implant placement or delayed immediate implant placement with augmentation

2.Exposure and definitive prosthetic loading

Fig 2-8a Tooth 37 before the extraction.

Only gold members can continue reading. Log In or Register to continue

Share this:

• Click to share on Twitter (Opens in new window)
• Click to share on Facebook (Opens in new window)

Related

Related posts:

1. The Edentulous Maxilla and Mandible
2. The Posterior Maxilla
3. The Edentulous Maxilla
4. The Anterior Mandible
5. The Anterior Maxilla
6. The Edentulous Mandible

Stay updated, free dental videos. Join our Telegram channel

Join