Alveolar Ridge Preservation and Augmentation for Optimal Implant Placement
Course Number: 626
Course Contents
Additive Techniques
These involve addition of bone outside the existing native bone envelope. Common examples of additive techniques include:
Guided Bone Regeneration (GBR)
GBR with Particulate Graft
Block Bone Grafts
GBR involves the incorporation of barrier membranes in the treatment of alveolar ridge defects. The membrane separates the bone defect from the overlying soft tissue. This allows the defect space to be repopulated with new blood vessels and osteogenic cells, which differentiate to form osteoblasts and are responsible for forming new bone. Desirable properties of membranes include biocompatibility, cell-occlusion properties, space-maintaining capability, ease of manipulation, and minimal susceptibility to complications.26
Table 2 details the various types of membranes available as well as their advantages and disadvantages.
Table 2.
| Non Resorbable | Resorbable | ||
|---|---|---|---|
| Natural | Synthetic | ||
| e-PTFE (Expanded polytetrafluorethylene) d-PTFE (Dense polytetrafluorethylene) Titanium Foil Micro titanium mesh | Native collagen Cross-linked collagen Freeze-dried fascia lata Freeze-dried dura mater | Polyglactin Polyurethane Polyactic acid Polyglycolic acid Polyactic acid/Polyglycolic acid copolymers Polyethylene | |
| Advantages | • Good mechanical stability • Excellent biocompatibility • Rigidity is suitable for space maintenance, wound stability, and successful bone regeneration • Plasticity, allows for bending, contouring and adaptation to any defect morphology | • Decreased patient morbidity • No need for second surgery to remove membrane • Lower rate of exposure • Simplified surgical procedure • Has hydrophilic properties which allows it to adhere to bone well once saturated with blood | |
| Disadvantages | • Increase risk of exposure • Increased risk of infection after exposure • Increased risk of soft tissue ingrowth • Fixation screws/tacks necessary to hold membrane in place • Second surgery necessary for removal • Technique-sensitive | • Uncontrolled duration of barrier function • Need for tenting screws to avoid collapse • Micromovement of membrane leads to movement of graft material and disruption of blood clot | |
Both resorbable and non-resorbable membranes have shown to facilitate adequate bone gain in minimal to moderate sized horizontal defects. However, the rigidity of non-resorbable membranes becomes beneficial when one desires vertical augmentation or when significant horizontal gain is needed in non-contained edentulous ridges. Animal 29 and human30 studies have shown an average vertical gain of 1.82 mm and 2.2 mm, respectively, with the sole use of non-resorbable e-PTFE membrane. The supplemental use of bone grafting materials along with membranes, can significantly increase the amount of bone gained following augmentation.31
GBR with Particulate Graft involves addition of particulate grafting material to assist with bone formation in GBR procedures. These grafts serve as space maintainers to prevent the membrane from collapsing or act as a scaffold, and/or stimulate bone growth. Based on their functional properties, they can be classified as osteogenic, osteoconductive or osteoinductive in nature.32 Osteogenic grafts allow formation of new bone from living cells that are transplanted within the graft. Osteoconductive grafts assist in the formation of a 3D scaffold which allows cells to migrate for ingrowth of blood vessels and osteoprogenitor cells. Osteoinductive grafts help recruitment of osteoprogenitor cells which are the precursors to osteoblasts, thus resulting in de-novo bone formation.
The origin, examples, and properties of the particulate grafts are detailed in the Table 3.
Table 3.
| Type of Graft | Origin | Example | Properties |
|---|---|---|---|
| Autograft | Patient's own tissue | Intra-orally harvested from jaw, or extra-orally from iliac crest, tibia, calvaria, fibula | Osteogenic Osteoinductive Osteoconductive |
| Allograft | Tissues from individuals of same species | Fresh-frozen bone, freeze-dried bone, demineralized freeze-dried bone from cadaver | May have osteoinductive potential Osteoconductive |
| Xenograft | Tissue from another species | Bovine, porcine, equine bone mineral | Osteoconductive |
| Alloplast | Synthetically produced | Tricalcium phosphate, hydroxyapatite, calcium phosphate cement, calcium bioactive glass, polymers | Osteoconductive |
Adapted from Benic et al, Periodontology; 2000.26
GBR with particulate graft can be used to graft horizontal defects or vertical defects or combination defects requiring bone gain in multiple dimensions. Systematic review and meta-analysis by Sanz et al,33 showed superior bone width gain of 5.68 mm with a combination of particulate xenograft, particulate autogenous graft and bio-absorbable membrane.33 A vertical bone height gain of as high as 8 mm has been documented when e-PTFE membranes when used with particulate grafts.31 These combination techniques can be used not only during staged approaches but also simultaneously during implant placement when there are Class I, II, III defects (as explained in Table 1). The fact that this technique can be used in multiple case scenarios and is, unlike autogenous grafts, not limited by donor site anatomy, makes it fairly popular among clinicians.
Figure 2.
A. Defect after debridement of edentulous #10.
B. GBR with collagen membrane and xenograft.
C. Re-entry after 6 months for staged implant surgery.
Figure 2.
Autogenous Block Bone Grafts are surgically harvested from another site within the same patient. Autogenous block bone grafts are indicated when a staged approach for implant placement is being used in Class 4 defects (Table 1). Autogenous grafts have remained the gold standard for several years and have proven to increase bone volume and quality prior to implant placement.34 However, disadvantages include higher morbidity, inadequate bone volume attainable depending on the defect size and the donor site anatomy. Extra oral donor sites for block bone grafts include iliac crest, tibia or calvaria. More commonly the blocks are harvested intra-orally from the mandibular ramus or the symphysis (the chin).34
When harvesting, it is important to be wary of the nerves and vessels that span this area to avoid alteration of neural sensation and life-threatening hemorrhagic complications.34 Once harvested, the blocks are fixated to the underlying native bone, in the edentulous recipient site, using screws ensuring intimate contact.32,34 A healing period of 4-6 months is necessary for the graft to integrate before one proceeds with implant placement. Though average bone gain with the autogenous graft is dictated by the anatomy of the donor site, a weighted mean gain of 4.25 mm was shown in a meta-analysis by Sanz et al.33
Figure 3.
A. Class 4 defect in #12,13 site.
B. Recipient site - after flap elevation.
C. Donor site - mandibular ramus.
D. Ramus block graft harvested.
Figure 3.
E. Autogenous block graft fixated to the recipient bed with screws.
F. Re-entry at 5 months, screws removed, implant osteotomy done.
Allogenic and xenogenic block grafts have been proposed as an alternative to autogenous block grafts to reduce patient morbidity. Compared to autogenous block grafts, allogenic block grafts result in less vital bone, more graft resorption, and greater peri-implant marginal bone loss following 1-2 years of loading.35 Although allogenic block grafts have demonstrated a horizontal gain ranging from 3-6mm, longer-term studies and studies that are more robust are necessary to determine if it is a comparable or superior option.36 Scientific evidence for block xenografts is limited and caution should be used when considering this as a treatment option.36