Bone Grafting

Insufficient density of the jaw bone can occur due to a variety of factors:

• Chronic gum or periodontal infection: One of the most damaging side effects of chronic gum or periodontal disease is the destruction of jaw bone. Therefore, implants are not placed in patients who have any form of active gingival problems.
• Trauma: Accidental injury to the face or the jaw can also result in the destruction of jaw bone. Implants cannot be placed in such regions of the jaw.
• Prolonged denture wearing: Removable dentures rely on the underlying soft tissues and bone for their retention and support. Prolonged denture wearing results in resorption of the jaw bone due to excessive pressure generated during eating.
• Failure to replace missing teeth: When a tooth is lost or extracted, it should be replaced immediately with an artificial one. Failure to do so results in an accelerate destruction of the jaw bone in the region.

Bone grafting is done in more than one manner:

• Width increase: This procedure is carried out in cases where the bone is knife-edged, and involves lateral expansion of the jaw bone.
• Height increase: In cases where the height of the residual bony ridge is too small, a height increase bone augmentation is performed.
• Sinus lift: Involves raising the floor of the maxillary sinus to create room for placement of a dental implant. This procedure will be discussed in detail below.
• Special procedures: Special, more invasive, and hence more expensive, procedures may have to be followed for larger bone defects.

Other - more invasive - procedures are available for bone defects which are larger. These include:

• Shifting the lower alveolar nerve: this involves bone augmentation in the lower jaw to make space for the fixture.
• Microvascular graft:  along with the graft bone, its blood supply is also transplanted and connected to a local source.

The following steps form part of the alveolar (jaw) bone augmentation:

• Investigations and clinical examination: Before proceeding with the grafting procedure, first your dentist will clinically examine your oral cavity, and prepare a detailed treatment plan for the restoration of your missing teeth. The treatment plan will also include the choice of type and/or location of the donor site for bone graft.
• The surgical procedure: Your grafting surgeon will take a mass of bone from a suitable site in your body, or acquire special grafting material for you, and place it in the planned site.
• Healing period: The surgery is followed by a healing period to allow the growth of enough new and healthy bone which can ensure that the implant will get a good physical support from your jaw. The waiting can be several months and will depend on various factors including your general health. However, in case of minor grafts this wait may not be necessary. Your surgeon will decide this issue for you.
• Implant placement: Once the bone graft has completely healed, the implantologist will place the implant.

• Autograft: Normally, graft material is taken (harvested) from a suitable site of the same patient. This ensures that the body would not reject the graft. This is called an autograft. Harvesting is done preferably at the rear portion of the lower jaw, or sometime, in the pelvic bone. However, this involves two surgical operations: removing the material, and then grafting it.
• Allograft: Graft material may also be obtained from another person (donor). In this case, the donor and you both have to be tested for compatibility of the tissue. This technique is called Allografting (Allo=other).
• Xenograft: a bone graft obtained from another species is known as a xenograft. Examples include bovine or porcine sources.
• Cadaveric: Yet another possibility is to use prepared (cadaveric) bone pieces to act as a scaffold around which natural bone can grow. This technique involves only one surgery. The prepared bone can be purchased from a tissue bank. The bone can be from a human or an animal. It can be:
  - frozen bone
  - frozen-dried bone
  - demineralized frozen-dried bone and could belong to either a human or another species
• Synthetic: Synthetical graft material such as hydroxyapatite may also be used. The advantage of using these materials is that their properties can be easily modified to achieve optimal properties.

This depends on many factors:

• the size and position of the implant planned
• the type of prosthesis it has to support or share with other implants
• the number of implants supporting the same load
• the existing bone condition

As a rule of thumb, a minimum bone height equal to 10 mm, and minimum width equal to 6 mm is desired.

A sinus lift procedure is applicable when an implant is required in the upper jaw and in the region of the rear teeth, ie, premolars and molars, and there is not enough bone height for an implant. This is also a bone grafting procedure for raising the height of the bone.

Again, the grafting procedure must be performed well in advance of the implant surgery so that there is sufficient time gap for good healing. However, the implant expert may not feel the need for a wait in some cases.

Not all patients seeking implants in the rear part of the upper jaw need a sinus lift. The requirement varies from patient to patient. The goal of the sinus lift procedure is to make the floor of maxillary sinus thicker, thus allowing space for insertion of an implant without damaging the sinus.

The exact technique that the dentist follows will vary from dentist to dentist and patient to patient. The traditional procedure for a sinus lift for a dental implant is as follows:

• An incision is made by your dentist in the gum flesh in the relevant region on the cheek side of the upper jaw, ie, the place where an implant has to be placed. This is going to be a place originally occupied by one of your upper molars.
• The dentist lifts back the gum flap so as to expose the jaw bone underneath.
• The next step demands great care. The exposed bone is carefully cut in such a way that a trap with a hinged door is created with the flap downwards.
• The hinge is now carefully pushed (rotated) inwards and upwards so that the hinged flap goes up and pushes up the sinus membrane which is originally attached to it. The sinus thus gets raised creating space below it.
• Bone is then grafted into this vacated space.
• The gum soft flap is sutured back over this and left to heal.
• A healing period of six to nine months may be allowed. The waiting period will vary from case to case, but in some cases the dentist may place the implant immediately.

Sinus lift uses the same materials as the alveolar augmentation processes use. Namely, the dentist can use material from patient himself (or herself), from another donor, prepared bone from a tissue bank or synthetic material like hydroxyapatite.