Guided Bone Regeneration (GBR) technique applied to the restoration of incisor implants 17 January 2017

Guided bone regeneration (GBR) technique applied to the restoration of incisor implants.

The loss of a dental organ normally causes bone resorption— a topic widely discussed in scientific and clinical journals. In order to optimise the results of both the biomechanics and aesthetics of the incisive section, reconstruction of the tissue lost is required. Both hard and soft tissue are involved.

Several techniques have been developed and applied; bone grafts, guided bone regeneration, vertical and horizontal osteotomies, connective tissue grafts to name but a few... with the single objective of getting closer to the initial state of the teeth and obtaining satisfactory, stable and long-lasting results.

In this clinical case, we see the management of a single missing tooth in a section where the aesthetics of the smile are very important.

Case history

Mrs P., a 26 year-old, who does not present with any general contraindications, has a consultation based on aesthetic reasons, as she feels her smile is impaired.

At the age of 7, after an accident, she lost her central incisor (11). After more than two decades, the restorations proposed did not satisfy her. Her priority is the aesthetics.

Can our 3rd millennium technology fully satisfy her request?

Clinical examination

Following the exo-buccal observation which showed a square-shaped face, largely visible massetetic protuberances, and a continuous and regular symmetrical face line, a meticulous analysis of the smile components and topography of the site to be treated will be performed. (Fig.1).

Figure 1: The lip resting position does not allow the central incisive teeth edges to appear. Is this an aesthetic choice made by the patient in order to hide the unsightly appearance of tooth 11?

The patient's spontaneous and discreet smile only allows part of the dental volume to appear at maxillary level. The positioning of the free margin of the upper lip covers the marginal gingiva, to reveal only a few papillary regions. Nevertheless, it is necessary to remain vigilant regarding the amount of pink visible around the maxilla since the gum-tooth gap may be more or less important depending on the circumstances. The square-shaped central incisors are in keeping with the shape of the face; in terms of the position and apparent dissymmetry of the lateral incisors, they do not seem to affect the mesio-distal space available for a future implant-borne prosthesis. (Fig.2).

Figure 2: The apparent dyschromia of tooth 11 underlines a clean aesthetic rupture endured with great difficulty by the patient. Interestingly, the lower smile line leaves some margin for permanent restoration of tooth 11. This margin would be reduced around the mandible if treatment were required at this level

The continuity of the labial frenulum and the interincisal line is important to gain a beautiful final result; it borders a collapsed tissue site whose volume has been modified. (Fig.3).

Figure 3: The transition line between the gum and the oral mucosa is high. Overall, it leaves a strip of keratinized gingiva which is sufficient enough to maintain the stability of the gum tissue. The gingival biotype in this type of toothlessness is preferable for aesthetic reconstruction.

Early loss of tooth 11 has led to the disappearance of the alveolar bone process. The site, restored using a Maryland bridge, has healed with colonised three-dimensional collapsing through a slightly keratinised and unpleasant mucous membrane on the colourmetric aspect. (Fig. 4, 5, 6).

Figures 4, 5 and 6: The concavity marked on the other side of the dental neck of tooth 11 steers us towards the reconstruction of the alveolar bone area. The absence of horizontal and vertical osseous loss in correlation with periodontal disease is observed on the panoramic X-ray.

An examination of the dental occlusion shows canine function with functional anterior guidance and absence of posterior occlusal interferences.

Her oral hygiene is good; some dental restorations without any new carious lesions are observed.

Complementary examinations

In terms of X-rays, the Cone Beam shows a loss of bone tissue (craterisation); the buccopalatal space has decreased. The initial available volume was 16.3mm (height) and 4.6mm (thickness). (Fig.7).

Figure 7: On the CBCT, the coronal section shows a sufficient osseous amount to put in an implant despite the vestibular concavity in place.

Treatment choice

There are several possibilities that can be implemented to restore this type of toothlessness. These include a removable prosthesis—a compound prosthesis—but implant placement is the perfect solution in this case. The patient agrees to it

It is a non-mutilating solution, separate from the other teeth and whose longevity and durability is better than the other proposals in terms of hygiene and regular check-ups.

However, readjustment of the site requires an increase in hard and soft tissue. Bone thickness can be corrected with a extemporaneous bone graft when the implant is put in place. A gum graft with submerged connective tissue will then be applied in a second surgical intervention in order to strengthen the gum tissue and optimise the aesthetic appearance.

The chosen implant is a Nobel Speedy RP (Nobel Biocare), the dimensions of which are 4x13mm.

Third surgical intervention

First stage: implant placement, GBR and temporisation.

After local anaesthesia, a flap is lifted using mesial and distal intrasulcular incisions connected by a crestal incision. Releasing incisions are avoided so as not to produce scar lines or decrease the blood flow in the terminal arterioles. The implant drilling is carried out based on a sequence recommended by the manufacturer and adapted to suit the bone density. The implant is placed in an optimal position, i.e., slightly offset in the palatal aspect and inclined in the mesial aspect to avoid the palatine canal. The emergence axis is thus idealised; it will facilitate the prosthetic design. (Fig.8)

Figure 8: The external hexagon connection-implant is carefully placed in the palate with respect to the incisive cingulum. Its position ensures peripheral bone recovery.

This flaw is fixed by using the guided bone regeneration technique with a non-resorbable titanium membrane (Gore-Tex) fixed in place using titanium studs. The essential function of this membrane is to maintain and protect the xenograft placed on the site, the Bio-Oss (Geistlich) granules and the mucous membrane cell competition. To improve the angiogenesis required for this technique, openings are created at cortical bone level. (Fig. 9, 10).

Figures 9 and 10: The numerous openings created will promote the migration of future osseous cells. The concavity created by the loss of the vestibular table is clearly visible. Full embedding of the head of the implant on the other side of the mesial and distal osseous septums is observed. The presence of the distal osseous septa is required to sustain the papilla, thus preventing the appearance of "black holes".

The horizontal discontinuous matrix stitches allowed us to get closer to the edges without any tension after soft tissue management and periosteul dissection of the vestibular flap. (Fig.11).

Figure 11: The connective tissue co-aptation created by the horizontal discontinuous matrix stitches ensure rapid sealing of the tissue, thus protecting the membrane from any bacterial invasion.

Temporisation in this aesthetic area is created using a Maryland bridge sealed using glass iomer cement on tooth 21. The absence of any compression around the operated area is checked; this could reduce the amount of bone regenerated. (Fig.12).

Figure 12: The bridge is designed so as it does not exert pressure on the operated area. This means the patient must maintain an optimal level of hygiene, avoiding tissue inflammation.

Stage two: Functional loading with the healing abutment and connective tissue graft.

Six months later, during functional loading, the osseointegration of the implant has been attained. The flap (mesial and distal crestal incision) is lifted to remove the membrane. Regeneration has been obtained, the objectives of the bone augmentation have been reached. The spirals are entirely buried in the new bone. Gains are made in terms of thickness (VL) and height. (Fig.13, 14, 15, 16).

Figure 13, 14, 15, 16: On reopening the site to remove the membrane, considerable bone augmentation is observed, replenishing the alveolar bone that had been initially lost. The implant is completely covered in new bone.

A healing abutment (RP 5x3) is used to replace the screws of the cover. A submerged connective tissue graft is made in order to optimise the aesthetic results and strengthen the periodontal tissue. (Fig.17).

Figure 17: A connective tissue graft taken from the palate will help to stabilise the gingival biotype. It contributes to the repositioning of the soft tissue in harmony with the adjacent teeth.

Prosthetic procedure

Two months are needed for the integration and maturation of the graft, a period at the end of which a provisional screw-retained crown is put in place. (Fig. 18). The goal here is to profile the transgingival area, the prosthetic emergence area, in accordance with the data validated at the time.

Figure 18: The morphology of the provisional crown will allow the tissue transition area to be structured in order to get the best possible final aesthetic results. The high vestibular concavity leaves room for thick and stable tissue to heal.

This provisional crown is then recalibrated to refine the profile and make a completely customised crown. (Fig.19).

Figure 19: The vestibular thickness of the gum tissue free from inflammation ensures opacity and an aesthetic emergence profile of the immediate prosthesis. The alveolar structure allowed us to obtain a triangle shape corresponding to the radicular morphology of the central incisors.

The final impression is then taken and the final crown is cemented to a zirconia abutment. (Fig. 20, 21, 22).

Figures 20, 21 and 22: The pickup impression and recording of the gingival bed shape will ensure that the data is sent to the prosthetist for the design of the final prosthesis. Maturation of the tissue guided by the contact point will compel the papilla to fill the embrasures completely.

Regular follow-up on an annual basis was carried out. No complications have been observed to this day. After 6 years, the bone level is stable. (Fig. 23, 24).

Figures 23 and 24: Retroalveolar X-ray image comparison just after the final tooth has been put in place and after 6 years shows satisfactory bone stability.

Discussion

Here is a reminder of the basic principles for Guided bone regeneration (GBR):

Histocompatibility;
Exclusion of mucous membrane cells from cell competition;
Maintaining the width;
Early clot stability;
Osteoconduction.

The principle of excluding mucous membrane cells that have higher kinetics than those of the
osseous cells and maintaining the width are guaranteed by the Gore-Tex membrane. The graft material used is therefore protected. The angiogenesis, the new bone formation and bone mineralisation are not interrupted. The bone regeneration and bone augmentation process may be carried out. The use of this non-resorbable membrane needs a second procedure for its removal. This additional stage may be justified through the guarantee that it contributes to the maintenance of the width and the protection of the clot while present. In terms of the resorbable membranes, the duration of their resorption is variable through their very definition. If this resorption duration is shorted than the time for bone creation, the sought after objective will not be reached. A massive disadvantage of non-resorbable ePTFE membranes is that bacteria can multiply very quickly on them during iatrogenic exposure to an oral environment. The surgical technique must therefore avoid any tension around the flaps, ensure they are embedded and allow for basic hermetic sutures. Regular follow-up is essential.

With regard to graft material, there are two types: materials derived from the bone (living bone or non-living lyophilised bone), and alloplastic biomaterials (organic and inorganic). Bio-Oss is a material derived from non-living lyophilised bone, of a bovine origin. It is a porous bone mineral matrix devoid of all organic bovine bone elements. Thus, its crystalline structure as well as its porosity are close to human hydroxylapatite. It is non resorbable and the risk of viral transmission is very low (the sterilisation process is important). It has osteoconduction properties used as scaffolding for the colonisation of osteoprogenitor cells of the recipient bed, thus encouraging bone onlay and its remodelling. The potential for osteoconduction depends on its chemical composition, surface,
surface properties, the presence of pores and its resorption capacity. Nevertheless, we must note that osteoconduction is different from osteoinduction involving induction of osteoblast differentiation from mesenchymal cells thanks to BMPs and osteogenicity which is bone formation using osteoblastic cells within the both grafts and autologous transplants. Bio-oss is a xenograft widely used in implantology. It has been scientifically and clinically proven. The development of bone regeneration products and surgical techniques has allowed us to move away from using ePFTE membranes nowadays. The use of a titanium framework covered in a resorbable membrane, the appearance of more rigid resorbable membranes that disappear more slowly, the use of treated human bone and the practice of horizontal and vertical osteotomies have reduced the risks involved in non-resorbable membrane exposure and the negative outcomes with soft tissue during their exposure. Nevertheless, the principles of a lack of flap tension and the primary tight cover remain an imperative part of any reconstruction procedure. Furthermore, improving knowledge around the transgingival healing process, implant anatomy modification and extension of the Plate Form Switch concept have made loading and aesthetics possible and even advised during the functional loading when the treatment plan is chosen. This allows the gingival healing process to occur under ideal aesthetic conditions. The final results are improved.

Keywords:

GBR, bone resorption, non-resorbable membrane, incisival sector aesthetics, bone graft, Guided Bone Regenerations, connective tissue grafts, tissue loss reconstruction, Gore-Tex membrane, temporary screw-retained crown, Plate Form Switch

Guided Bone Regeneration (GBR) technique applied to the restoration of incisor implants 17 January 2017