Phase I

Volume yield from graft depends upon the concentration of viable cells transplanted from the donor through the process of osteogenesis. The autogenous cancellous marrow grafts are known to be the ‘Gold Standard’ for phase I osteogenesis. They are the most useful and predictable grafts because they transfer the viable osteoblast and osteoprogenitor cells to support phase I bone graft healing.

Phase II

Osteoinduction and osteoconduction of osteocompetent cells from the recipient site responsible for graft incorporation, remodelling and replacement according to local stress and strain factors mediated by site specific signalling.

The two-phase theory can be simplified as the autogenous graft transfers the viable osteoblasts and osteoprogenitor cells, which initiate new bone formation at the graft site (phase I osteogenesis), and later on the osteocompetent cells from the recipient site, which get incorporated into the graft, cause remodelling and replacement of the graft with new bone by the process of osteoinduction and osteoconduction (phase II osteogenesis).

Surgical asepsis/absence of infection

Infected sites should never be selected for bone grafting until all the infection has been removed and the site has healed with no sign of any active infection like pain, swelling, and purulent discharge. Bacterial infection reduces the pH level at the infected site, which causes solution-mediated rapid resorption of grafted material. There should be no clinical or radiographic findings of any active infection at the site chosen to graft (recipient site) or harvest (donor site) bone graft material. The grafted site should also be prevented from receiving any infection after the procedure because of poor oral hygiene, suture line opening, or membrane or graft exposure to the oral environment, etc. Antibiotics can be added to alloplastic material and autograft. Although tetracycline is often used in periodontal bone grafting to improve collagen formation, it chelates calcium and arrests the bone formation process. Instead, parenteral penicillin, cephalosporin, or clindamycin should be mixed into the graft material, because these antibiotics do not affect the process of bone regeneration (Fig 13.7A and B). Suture line opening can result in loss of graft, soft tissue ingression, and infection to the graft. To prevent the exposed graft getting contaminated/infected, the site can be irrigated with parenteral antibiotics (e.g. cefazolin or clindamycin) two to three times a day till the site gets healed with secondary intension (Fig 13.8A and B). This provides an increased level of antibiotic concentration at the site, even though vascularization is incomplete.

Fig 13.7 (A) A parenteral form of cefazolin sodium (Reflin) or (B) clindamycin can be mixed with graft material at the time of grafting procedure. These antibiotics can also be added to the graft material when the site has been contaminated and has become infected in the early phase of the healing process. This provides increased level of antibiotic concentration at the site, even though vascularization is incomplete.

Fig 13.8 Suture line opening can result in loss of graft, soft tissue ingression, and infection to the graft. To prevent the exposed graft getting contaminated/infected, the site can be irrigated with parenteral antibiotics (e.g. cefazolin or clindamycin) two to three times a day till the site gets healed with secondary intension (A and B). This provides increased level of antibiotic concentration at the site, even though vascularization is incomplete.

Space maintenance

Space maintenance at the bone graft site is paramount to the bone formation process. The space of the graft site refers to the anatomical site and contour of the desired augmentation, and maintenance refers to the fact that the space must exist long enough for bone to fill the desired region. The barrier membrane which is used to cover the graft often collapses in the grafted space, which leads to the loss/resorption of a partial volume of the graft and results in under contoured new bone formation. The barrier membrane can be prevented from collapsing by using membrane fixation/stabilization screws (‘membrane tacks’) but better contour can be achieved by using a fixation screw which is elevated above the host bone level to the height/width of the desired bone volume to support the barrier membrane from underneath; this screw is called ‘tent screw.’ Tent screws, titanium mesh or titanium-reinforced membrane and graft materials beneath the membrane have been advocated to maintain the desired space during the bone grafting process. The osseous defect, which itself can provide adequate space for new bone regeneration is called ‘favourable osseous defect.’ This kind of defect does not need any tent screw but the walls of the osseous defect itself keep tenting the barrier membrane to maintain the space for new bone regeneration (Fig 13.9A–F). The osseous defect with the missing walls which cannot provide the adequate space by itself for the new bone regeneration is called an ‘unfavourable bone defect’. This kind of osseous defect needs the use of the tent screw to keep tenting up the barrier membrane, to maintain adequate space for bone regeneration (Figs 13.10–13.12).

Fig 13.9 The favourable osseous defect, where implant placement has been possible within the osseous envelope of the defect. (A–F) The walls of the defect have provided adequate space maintenance for the graft by tenting up the membrane from underneath

(Courtesy: Dr Peter Randelzhofer, DDS, private practice, Germany).

Fig 13.10 An unfavourable bone defect is grafted using particulate bone graft covered with barrier membrane. (A and B) The barrier membrane collapsed in the defect, resulting in compromised space for new bone formation of desired volume and contour.

Fig 13.11 Unfavourable osseous defects, where implants could not be placed within the bony envelope. (A–E) Even the defects have been adequately grafted and covered with barrier membrane; the uncovering of the implants shows inadequate amount of bone formation because of inadequate space maintenance and loss of graft.

Fig 13.12 (A) The barrier membrane, which is stabilized using fixation screws (membrane tacks) to prevent the membrane from collapsing. (B) Using a long tent screw, which supports the membrane from underneath, results in better space maintenance for the graft and new bone formation of the desired volume and contour.

CASE REPORT

Lateral and vertical bone augmentation in the posterior mandible using tent screws (Courtesy: Dr Jun Shimada, Japan) (Figs 13.13–13.15).

Fig 13.13 (A) The edentulous posterior mandibular ridge shows vertical as well as horizontal bone deficiency. (B) Two tent screws are fixed to the host site keeping them well emerged out of the bony surface. (C) A particulated allograft mixed with platelet-rich plasma (PRP) is used to augment the deficient area to the desired dimensions and covered with titanium-reinforced nonresorbable TXT membrane, which is supported by the (D) elevated tent screws from underneath.

Fig 13.14 (A) The periosteum is released and sutured to achieve a watertight primary closure. (B) Postgrafting radiograph. (C) The site is uncovered after 4 months of healing period and the TXT membrane is removed. (D) The grafted site shows a remarkable amount of new bone regeneration.

Fig 13.15 (A) The tent screws are removed and (B) implants of adequate sizes are inserted. (C) Clinical view after implants have been restored in function.

Soft tissue closure

The primary closure of the soft tissue is mandatory for the success of the grafting procedure, as it prevents the loss of graft from the site and prevents infection. However, if primary closure is not achieved (e.g. socket grafting), a nonresorbable cytoplast TXT membrane can be used to cover the grafted site to prevent any microbial invasion into the graft or loss of graft material. The primary soft tissue closure ensures healing by primary intension and requires minimal soft tissue collagen formation and soft tissue remodelling. It also minimizes postoperative discomfort to the patient. Often, it becomes difficult to achieve a primary closure over the grafted site because the volume underneath the flap increases after bone grafting. In such cases, primary closure can be achieved by releasing the periosteum of the flap so that it can be advanced to achieve the primary closure. There are two techniques for releasing the flap to achieve primary closure.

Submucosal space technique

This technique, developed by Misch in the early 1980s, is an effective method to expand tissue over larger grafts (greater than 15 × 10 mm in height and width) (Figs 13.16 and 13.17).

Fig 13.16 (A) Grafting of any bone defect increases the volume of the underlying hard tissue at the site, which may result in difficulty in achieving primary closure of the flap. The tension in sutures may result in suture line opening, which may cause the loss of graft and invasion of soft tissue into the defect area. A scalpel is inserted 1–2 mm deep through the periosteum underneath the facial flap and beyond the mucogingival junction. (B and C) Further, a horizontal incision is given parallel to the crestal incision. (D) Then, a soft tissue scissor is pushed into the facial flap for approximately 10 mm with the blades closed, parallel to the surface mucosa. The thickness of the facial flap is approximately 3–5 mm. The tissue scissors are opened, once at the proper depth. (E) This blunt dissection does not sever any blood vessels or nerves to the facial flap but does create a submucosal space or tunnel. (F and G) Once the submucosal space or tunnel has been created over and beyond the vertical release incisions, the facial flap can be advanced over the graft for tension free primary closure of the flap.

Fig 13.17 (A) Bone grafting has increased the volume of the hard tissue under the flap, which results in difficulty in achieving primary closure of the flap without tension in the sutures. (B) Thus a releasing incision is given through the periosteum of the facial flap for the easy coronal advancement of the flap and (C) to achieve primary closure without any tension in the flap.

Advantage: A large degree of flap advancement can be achieved for a tension-free flap closure covering the large grafted sites.

Disadvantage: As the incision is given into the periosteum, the blood supply to the grafted region and overlying soft tissue is affected, which results in longer time taken for soft tissue healing.

Curvilinear-bevelled incision technique

This is another method of flap advancement. The cut back incisions are made at the vestibular ends of the vertical incisions and the flap is coronally advanced and sutured first at the crestal part, followed by suturing of the vertical incisions at the vestibular half by mobilizing mobile vestibular soft tissue together. Only a limited degree of flap advancement is possible with this technique when compared to the submucosal space technique. The advantage of this technique is that it does not hinder the blood supply to the grafted region and overlying soft tissue because no horizontal incisions are made through the periosteum (Fig 13.18A–D).

Fig 13.18 (A) Curvilinear-bevelled incision is given, and (B) extended with two cut back incisions at the vestibular ends. (C) The flap is advanced coronally and (D) sutured first at the crystal part with tension-free primary closure followed by suturing of nonkeratinized mobile vestibular tissue area. This technique can be followed for the smaller grafted regions as the coronal advancement of the flap with this technique is less than that obtained with the submucosal space technique but it has the advantage of not hindering the blood supply of the flap as the underlying periosteum remains intact to the flap.

Graft immobilization/fixation

Graft stabilization is a must to achieve a predictable bone augmentation. If the particulate graft material or the bone block graft is not stable at the host site, it cannot develop the blood supply from the host bone for new bone regeneration. This can further result in the graft becoming encapsulated in fibrous tissue and often sequestrated. For barrier membrane or particulate graft to work effectively, no load should be placed on the soft tissue over the graft, because it may cause movement of the graft. If barrier membrane is used, it should be immobilized to the graft site by using bone tacks. The block bone graft should firmly be immobilized to the host bone using multiple fixation screws to avoid any micromovement during bone remodelling (Fig 13.19A–C).

Fig 13.19 (A) Bone block graft firmly immobilized at the host site by using long fixation screws. (B and C) In another case, the membrane is stabilized using bone tacks to prevent its movement during the graft maturation.

Prevention of soft tissue ingression/barrier membranes

The epithelium and connecting tissue grows much faster than the new bone formation into a grafted area; hence, a barrier membrane is required to cover the bone graft to prevent the infiltration of the soft tissue into the graft site. A thick cortical plate of the block graft may act as a barrier membrane and often, the membrane is not required in the block grafting cases where a cortical block graft is used. If the periosteum of the flap over the grafted site is intact it can also act as natural barrier membrane and prevent epithelium and connective tissue infiltration into the graft.

Types of barrier membranes

There are various kinds of barrier membranes which are used in bone grafting and implant procedures. These membranes can either be the resorbable type (collagen membranes and pericardial membranes), which need to be completely covered by the soft tissue flap and are resorbed with time, or they are the nonresorbable type polytetrafluoroethylene (PTFE) membranes, which can be left exposed to the oral environment and need to be removed after the underlying graft has been consolidated (Fig 13.20A–C).

Fig 13.20 (A) Resorbable collagen membrane, (B) resorbable pericardium membrane from Zimmer Dental, and (C) nonresorbable PTFE Cytoplast TXT membrane.

Resorbable collagen membrane

These membranes are used to cover the graft where the primary closure of the flap is possible. These membranes keep preventing soft tissue ingression into the graft during its resorption and new bone formation. These membranes slowly get resorbed in 6–10 months and do not have to be removed (Fig 13.21A–D).

Fig 13.21 (A–D) The grafted site is covered with resorbable collagen barrier membrane and a primary closure of the soft tissue is achieved to completely cover the membrane.

Resorbable pericardium membrane

It is a biological three-layered membrane, which encases and protects the heart and can be used for guided tissue regeneration. The advantages of these membranes are flexible and adaptable, remodel/are resorbable, tough and resilient, suturable, and space creating.

Nonresorbable high-density PTFE barrier membrane

These are the nonresorbable type of membranes and so need to be removed after graft maturation. These membranes are very useful where soft tissue closure cannot be achieved because being nonresorbable these membranes can be left exposed to the oral environment (Fig 13.22A–F).

Fig 13.22

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