Implant Surgery
Master the INBDE with Dental Panda: Your go-to resource for expert practice exams and tailored study resources!
BONE GRAFTS
If there is not enough room between the crest of the alveolar bone and the floor of the maxillary sinus, a maxillary sinus graft (sinus lift) may be required. Augmentation of the alveolar crest area is also possible. Patients with uncontrolled diabetes or other systemic disease, smokers, and alcoholics are poor candidates for bone grafting.
Different bone grafting materials can be used, classified according to their source.
Allografts/Homografts/Allogeneic grafts are materials harvested from different individuals of the same species. Allograft bone is taken from cadavers as fresh or fresh-frozen bone, freeze-dried bone allografts (FDBA) or demineralized freeze-dried bone allografts (DFDBA). The extracellular matrix of bone tissue contains bone growth factors, proteins, and other bioactive materials necessary for osteoconduction (not osteogenic or osteoinductive) and successful healing. Fresh bone is rarely used because of the concern of disease transmission.
Autograft/Autogenous bone is taken from the same individual, harvested from non-essential bone (iliac crest, rib, mandibular symphysis, anterior ramus etc) and placed where needed. Rejection is not an issue, but a second surgical site is needed allowing for increased risk of postoperative complications. Autogenous bone grafts are the only grafts that will exhibit osteoinduction, osteoconduction, and osteogenesis.
A free flap graft is an autograft with the periosteum and blood supply still attached.
Isografts/Isogenic grafts/Syngenesioplastic grafts are transplants from a different individual that is genetically identical (twins).
Xenografts/Xenogenic/Heterografts are transplanted from one species to another (e.g bovine), but rarely used in oral surgery.
Alloplastic/Synthetic grafts are inert, man-made synthetic materials that include ceramics such as calcium phosphates (e.g., HA and tricalcium phosphate), bioglass, calcium sulphate, and flexible hydrogel-hydroxyapatite (HA) composite which has a mineral to organic matrix ratio close to human bone.
Growth factors (human growth factors or morphogens) enhance grafts and are produced using recombinant DNA technology. These factors are usually found in the extracellular matrix of bone and include TGF-beta, insulin like growth factors I and II, PDGF, FGF, and BMPs (BMP-2, BMP-4, and BMP-7).
Osteogenesis is the formation of new bone from osteoprogenitor cells (osteoblasts) from within the grafting material.
Osteoconduction is the formation of new bone from host-derived osteoprogenitor cells within a biologic passive framework (scaffolding). There is no inherent ability to produce bone, the scaffolding allows for the conductions of bone-forming cells through the graft.
Osteoinduction refers to the stimulation of new bone formation from the differentiation of osteoprogenitor cells into osteoblasts, producing the new cells needed for bone production. Bone morphogenetic proteins (BMPs) are known for their osteoinductive capabilities.
Guided tissue regeneration uses membranes to inhibit the migration of fibrous connective tissue while supporting the growth of bone.
Alveolar distraction osteogenesis is used in cases of vertical bone atrophy. Bone is formed in the distraction zone, moved 0.5-1mm daily after the gingival incisions are allowed to heal. Final bony infill can take 10-12 weeks.
OSSEOINTEGRATION
A study by Leventhal in the 40’s using titanium optic chambers in rabbits happened on the compatibility of titanium with mammalian tissue. It was found that there was microscopic evidence of direct bony adaptation to the titanium surface.
Osseointegration refers to the direct structural and functional connection between living bone and the surfaces of a load-carrying implant. A direct bone-implant interface is the preferred outcome. Proper osseointegration is linked with long term survival, with the factors most linked to success being the materials used, surface characteristics, quality and quantity of bone, and timing of loading.
A physical evaluation is important, and a radiographic analysis of the quantity and quality of bone needs to be undertaken, most commonly using cone beam CT (3D). Software allows the virtual placement of implants to check space and proximity to vital structures like the inferior alveolar nerve or maxillary sinus floor. The Misch or Lekholm and Zarb classification describes the quality of bone, while the shape of the cross section of the alveolar ridge can be given a letter grading.
Implants are contraindicated in cases with uncontrolled diabetes, immunocompromised patients, poor bone quality or quantity (or not enough room), bisphosphonate therapy, and bruxism.
Tobacco use is a relative contraindication. Failure rates are considerably higher in smokers, nicotine in tobacco has been shown to reduce the blood flow in the mouth. The posterior maxillary area is most known for implant failure (D4 bone). Possible complications including implant failure needs to be explained to the patient to establish informed consent. Implants can be placed immediately after tooth extraction, except in the case of active infections. It is better to wait 8 weeks after the extraction of infected teeth for proper bony healing before placing the implant.
Implant placement is usually guided with a surgical guide stent, ensuring the correct angulation. The vertical placement of the implant is dictated by the alveolar crest position and biological width (~3mm, 1mm for junctional epithelium, 1mm for supracrestal connective tissue, 1mm sulcus depth). Implants should be 0.5-1mm away from adjacent teeth and the buccal plate, 1mm from the lingual plate, maxillary sinus, and nasal cavity, 2mm from the superior aspect of the inferior alveolar canal, and 3mm away from each other.
The anterior loop of the mental nerve is an anatomical structure that should be considered when placing implants near the mental foramen. There is variation on how far this loop extends mesial to the mental foramen. It has been suggested placing implants 1-6mm away to avoid damage to the mental nerve. Cone beam CT will allow the clinician to visualize the anterior loop.
Slow speeds (10-15rpm for the final step) and cooling saline spray avoids heat generation (under 40 degrees C). Implants placement may be a two stage procedure, where the implant is initially submerged and uncovered in a second surgical procedure, or one stage, where a healing abutment is used as the implant stabilizes.
Primary stability is directly linked to implant success. The implant may be buried or a healing abutment fixed to allow for osseointegration, which can take anywhere from 6 weeks to 6 months. Early loading of an implant is linked to failure. Some clinicians will place a crown straight away but leave it in infraocclusion. In the case of the edentulous mandible, 2-5 implants are placed in the anterior region between the mental foramen. A successful dental implant should exhibit an absence of pain, discomfort or infection, be immobile, with no evidence of peri-implant radiolucencies and no more than 0.2mm per year vertical bone loss. Endosseous root form implants are more popular (than blade form, subperiosteal, transosteal, intramucosal, or transosseous). Mobility is the most common clinical sign of failure.
