Upper and lower reconstruction

Dr Jerome P Sullivan presents an upper and lower full arch dental reconstruction with implant supported over-dentures with a special focus on the rehabilitation of the maxilla using a bilateral ridge-splitting technique with a combined Summers lift technique

In the maxilla, bone atrophy following tooth extraction presents a challenge to the placement of dental implants. Anteriorly, resorption is at the expense of the labial plate.

Posteriorly, pneumatisation of the sinuses combined with alveolar ridge loss, often leaves reduced residual bone height. These bony changes vary in the individual, but are exacerbated by ill-fitting dentures, as was the situation here.

The elastic nature of the maxilla allows manipulation with hand instruments (osteotomes). Implant sites can be prepared while preserving bone, rather than drilling it away.

Where there is enough residual bone height (12mm), alveolar ridge expansion is possible. Where inadequate, elevation of the sinus floor facilitates implant placement. As bone is preserved, density is increased making primary fixation achievable in regions where natural bone density is poor. This has been shown to be a predictable method of achieving implant osseointegrationı.

By increasing width, height and density, bone manipulation reduces the indication for more invasive treatments such as autogenous block grafting and guided bone regeneration (GBR).

GBR is a technique for growing new bone to allow osseointegration, functional support and aesthetic restoration of dental implants2. Using a barrier membrane to isolate a bony defect, preference is given to osteogenic bone marrow cells over epithelial cells, to proliferate within a stabilised blood clot. A bone substitute can be used as a graft material to maintain space and stabilise this blood clot.

However, autogenous bone is still the gold standard, and remains the only graft material that stimulates direct bone apposition. Substitutes just create a framework into which host bone will eventually grow3.

The osteogenic potential of autogenous bone can therefore be exploited by mixing it with other graft materials. The 39-year-old female patient was a non-smoker and non-drinker. She suffered with depression for which she took the serotonin re-uptake inhibitor Cipramil, 20mg, once a day. She was allergic to penicillin.

She presented with a resorbed edentulous maxilla, complicated by pneumatasized maxillary sinuses and a prominent torus palatinus. As a result she was unable to wear her full upper denture without a thick layer of adhesive.

Her jaws displayed a variation on combination syndrome (CS). A pattern of resorption first described by Kelly (1972), CS occurs where a full upper denture opposes a lower partial denture in the presence of only anterior teeth4. Typically, the anterior maxillary ridge is over loaded and becomes resorbed and flabby.

Posteriorly, there is hyperplasia of the tuberosities as a result of poor posterior contacts. In the mandible, over eruption occurs of the remaining anterior teeth with further resorption of the free end saddles. Removable dentures should be renewed regularly. However, they are usually ill-fitting with a posterior open bite present, which exacerbates resorption patterns.

In this case, the resorption of the anterior maxilla was limited and there was no overgrowth of the tuberosities, possibly due to the absence of a lower denture.

The patient’s mandible displayed a CS pattern of resorption, with extruded anteriors and alveolar loss of both free end saddles. The lower right canine was partially erupted, the lower left canine was completely encased in bone. Both were lying vertically. All remaining erupted teeth were grossly carious as a result of a high sugar diet and dry mouth related to her medication.

After extracting her remaining teeth, bony healing was allowed to proceed for six months prior to the taking of a cone beam computerised tomograph (CBCT).

Mandible

The CBCT showed good bone density and volume in the anterior mandible (Fig ı). Four ı4mm long, 3.5mm wide implants (Ankylos CX Aı4), were submerged ı-2mm below the bone crest between the mental foramina. A thread was cut using a bone tap at all four implant sites due to high bone density.

A six-month healing period was allowed before these were restored with a system of four telescopic abutments with female copings (Ankylos SynCone), picked up chair side with cold cure acrylic in the finished cobalt chrome over-denture.

Maxilla

The maxilla was restored in parallel using five ıımm-long, 3.5mm-wide implants (Ankylos C Aıı). Six implants would have given a more balanced distribution. However, this was not possible without sinus grafting, which the patient did not want.

A ridge-splitting technique was used to separate the narrow cortical plates to facilitate implant placement. Where bone height was also limited below the left maxillary sinus, the ridge splitting technique was combined with a Summer’s lift procedure.

In the maxilla, the bone is generally soft type 3 and 4. Cortical bone is either thin or absent, making over preparation with drills and subsequent loss of primary implant stability a real risk. Alveolar bone loss at the sites of missing premolars and molars, combined with expansion of the sinus spaces, further diminishes bone volumes for primary implant fixation. In 1994, a new technique was described by Robert B Summers, as a less invasive alternative to full sinus grafting5. The ‘Summer’s lift’ facilitates the placement of implants which are longer than the available residual bone height.

The initial osteotomy is prepared 1-2mm short of the sinus floor. Where bone is elastic, this can be achieved with osteotomes alone. Where bone is harder, some drilling may be required for site development. A series of blunt ended osteotomes, in widening diameters, are then used with a surgical mallet. A light tapping against the sinus floor is usually enough to in-fracture the bony floor without perforation to the sinus membrane, which is raised by a hydraulic effect of bone displaced apically by the osteotomes.

Implant placement can then proceed as normal, except that the apex of the implant can extend safely some 4mm above the surrounding sinus floor, while the membrane remains intact. Studies have shown this to be a reliable technique where residual bone height exceeds 7mm, allowing new bone to form below the raised sinus floor6.

Following six months bony healing the maxillary implants were exposed and healing abutments attached. These were subsequently replaced by permanent abutments (Ankylos balanced base), linked by a milled titanium bar. The final restoration was a palate-free cobalt/chrome framed over-denture, which attached to the bar with four Locator micro-attachments. (Zest Anchors, Escondido, CA, USA).

Method

Pre-operative clinical photos showed rampant decay in the remaining dentition. The aetiology was a high intake of hard sweets, compounded by a dry month due to the Citalopram (Fig 2).

An atrophic maxillary alveolus, the prominent torus palatinus and at lack of saliva combined to make retention of the patient’s upper denture impossible without denture adhesive (Figs 3 and 4). The remaining teeth were extracted surgically under local anaesthetic. Special care was taken to minimise bone destruction when elevating the impacted lower canines.

At six months, a CBCT was taken of both jaws with the patient wearing radiographic stents copied in clear acrylic from a diagnostic wax up of the final dentures (Figs 5 and 6).

The images were reformatted for SimPlant software (Materialise, Leuven, Belgium) which yielded cross sections to plan the case. Radio-opaque markers were composed of gutta percha (Fig 7).

Five implants were planned in the maxilla in the positions of the missing upper right second premolar and canine; upper left canine, second premolar and first molar. Pre-operative meds were given orally: 8mg dexamethasone taken on morning of surgery, and clindamycin 600mg, one hour pre-operatively.

Studies show that prophylactic antibiotics can decrease the incidence of implant failure by a multiple of two to three7. The bioavailability of the antibiotic given should peak at the onset of surgery, hence the high dose given – which can be two to three times the therapeutic level to ensure adequate tissue perfusion. It should also be effective against the specific bacteria. In the oral cavity, the most likely pathogens are aerobic streptococci as well as anaerobes.

Penicillin is the drug of choice as it is bactericidal and non-toxic. In this case, where allergy was a factor, clindamycin was substituted. However, the patient found this particularly irritated her stomach so it was therefore discontinued. Instead, metronidazole 400mg, three times a day was prescribed for the five days immediately post-operatively. Although only effective against anaerobes, the patient tolerated this without side effects.

In the immediate post-operative period, studies show the use of antibiotics to reduce implant failure rates to be inconclusive8.

Indeed, it is the closure and primary healing of soft tissues that is pivotal in the prevention of postoperative infection9.

Under local anaesthetic and aseptic conditions, bilateral full thickness, remote palatal flaps were raised either side of the midline and extended posteriorly as far as the maxillary first molar region. The alveolar ridge was exposed. Care was taken not to over extend distal palatal incisions to avoid the greater palatine artery. Importantly, the gum was left attached to the buccal plate.

Later on, when the ridge was expanded, the presence of an intact periosteum helped to minimise the propagation of fracture lines through the buccal plate. Also, in the healing phase, an uninterrupted blood supply from the periosteum promoted faster healing with less resorption of the buccal plateı0.

A fine tungsten carbon disc, externally cooled by sterile saline, was used to dissect the crest of the ridge. This was the only time any bone was drilled. Non-cutting

hand instruments were used at all subsequent stages (Fig 8). A combination of osteotomes and bone spreaders were then tapped and manipulated to create the osteotomies (Fig 9).

The absence of drilling allowed the little bone available to be preserved. The use of osteotomes condensed this bone, converting spongy cancellous type 4 and 3 bone into harder type 2 bone. Primary implant stability was, therefore, increased.

At the position of the missing upper left first molar, ridge-splitting was combined with a Summers lift procedure so that a longer implant could be placed. This was possible as residual bone height underneath the left sinus was greater than 5mm. Below, this threshold and primary implant stability may have been insufficient, increasing the risk of failure.

The specification of all maxillary implants was Ankylos C length ıımm, diameter 3.5mm (Fig 10). There was sufficient elasticity in the palatal flaps to facilitate tension-free closure without the need for periosteal releasing incisions. Suturing was interrupted using 30 Vicryl Rapide reverse cutting (Fig 11).

No biomaterials or GBR was required as all implants were submerged between the now split buccal and palatal cortical plates. Instead I relied on a stable blood clot, which was derived from the bone, to provide the osteogenic potential for bony healing (Fig 12).

Immediate post-operative healing was uneventful. Clinical photograph shows soft tissue healing at two weeks. The maxillary alveolus is clearly much wider than its original pre-operative dimensions (Fig 13). At six months, the maxillary implants were exposed and healing abutments attached.

At seven months, soft tissues were mature and ready for impression taking and restorative phases (Figs 14-18).

The patient’s mandible was restored in parallel to the maxilla. Four inter-foraminally placed ı4mm Ankylos CX implants with SynCone 40 abutments, supported a full cobalt chrome-reinforced over-denture (Figs ı9-21). Final fit is shown in Fig 22.

Results

As a single case study, what is described here only demonstrates a technique that, in this instance, has given a successful outcome. Without a comparison group of similar treatments, it has no statistical value. However, taken for what it is, this case study has shown that in the atrophic maxilla, bone can form between separated cortical plates and it is possible for dental implants to osseointegrate within this new bone.

At six months, all implants were integrated and the maxillary

alveolus showed significant expansion in width. The bony healing that occurred can be likened to what happens inside a tooth socket when an implant is placed immediately post extraction. There was no soft tissue invasion between the separated cortical plates. Instead, the stabilised blood clot provided an osteogenic matrix into which new bone was woven, while the implants prevented collapse of the cortical plates.

Discussion

Autogenous bone is the gold standard bone graft material. As well as being ı00 per cent biocompatible, it is the only known osteogenic graft material. While xenograft products such as Bio-Oss provide a framework into which the body eventually grows bone, autogenous bone actually stimulates osteoblasts to lay down bone.

The problem lies in its availability. Continued »

Intra-oral sites are limited to the ramus and the chin. Where a lower wisdom tooth is present, harvesting from the ramus may be prevented. Equally, long lower incisor and canine roots or a shortened lower facial height, may rule out the chin.

Extra-oral donor sites such as the hip (iliac crest), offer plenty of bone, however patients are put off by the need for a general anaesthetic and donor site morbidity.

The most common alternative to the use of autogenous bone is GBR. Patient acceptance for such treatment is higher due to the absence of donor site morbidity. However, histological studies show that bone created by GBR without the additional osteogenesis of autogenous bone, does not mirror lamella boneıı.

The use of biomaterials also increases the biological load and can increase the risk of infection9.

The techniques described were executed without additional biomaterials. The risk of wound breakdown due to post-operative infection was therefore reduced.

Conclusion

In the maxilla, new bone capable of supporting dental implants can form between dissected cortical plates provided a stable blood clot can be protected.

Published: 31 December, 2013 at 13:00