What Factors Determine the Success of Dental Implants?
Dental implants are long-lasting and the most successful treatment option to restore missing teeth in the oral cavity. The success rate depends on the implant’s primary stability inside the jaw bone or the osseointegration of the implant. For a dental implant to be stable or have primary stability in the jaw bone, the most important criteria are the quality or the density of the bone that needs to be appropriate for the implant site selection, placement, and long-term survival. These parameters or criteria include general health conditions and factors, features and biocompatibility of the patient to the implant, operator sensitivity or approach by the dental implantologist or surgeon, surgical procedure, and most notably on the quality and quantity of bone at the area where the dental implant is to be placed.
How to Find Out Bone Mineral Density (BMD)?
BMD or bone mineral density is the amount of bone tissue in a specific volume of bone. Several methods to measure bone density include DEXA (Dual-energy X-ray Absorptiometry), CT (computed tomography), and CBCT (cone beam computed tomography) scans. OPG is a form of panoramic radiography initially used to visualize the patient’s bone and adjacent tooth structure and nerve in a 2-dimensional form while consulting. However, 2D imaging can be ineffective or error-prone while visualizing the implant selection site and bone quality or density of that site. Densitometric measurements can be appreciated or studied better in three-dimensional imaging like CBCT, which is now the primary modality for preoperative planning of implant placement.
To obtain the anchorage or stability of an implant in a bone that is not dense is not only challenging to the implantologist but also prone to failure considering the long-term survival rate of an implant because the implant will not be osseointegrated correctly or instead osseointegration, it undergoes fibro-osseous integration (integration into connective tissue instead of bone).
How Are Bones Classified Based on Bone Mineral Density?
The architectural integrity of the human face is dependent on the distribution of bone patterns in the maxilla (the upper jaw) and mandible (the lower jaw). The mandibular bone can withstand high stress and impact due to its high bone density. Still, the maxillary bone is associated with delicate vital structures like the maxillary sinus, the maxillary nerve, and its boundaries related to the floor of the nasal cavity and the orbital wall. Maxilla can quickly dissipate forces around but has a low bone density or thin cortical bone than the mandible.
According to the proportion and structure of the compact and trabecular bone tissue, bone quality is mainly categorized or classified into four types by histomorphometric studies, called the Bone Quality Index (BQI). Also, the bone density while implant drilling is comparable to drilling through different consistencies as mentioned below:
D1/Type 1 Bone:
It is a homogenous cortical bone with the densest bone available and is primarily found in the anterior mandible. D1 bone is highly suitable for maintaining an excellent bone-implant contact and exhibits the greatest strength. However, its regenerative capacity is impaired because of poor blood circulation. Drilling an implant through D1 bone is firm and robust and is comparable to drilling through oak wood.
D2/Type 2 Bone:
D2 bone is a thick cortical bone with marrow cavity and has a relatively dense bone found chiefly in the posterior and anterior mandible. D2 bone is also excellent for bone-implant contact and biocompatibility. Drilling an implant through D2 Bone is like Pinewood, comparatively less firm than oak wood, with 75% bone-implant contact.
D3/Type 3 Bone:
D3 bone is a thin cortical bone with good trabecular strength found in the anterior maxillary region. However, the bone-implant contact is less favorable in such bone and is 50% weaker than D2 bone. Drilling an implant through D3 Bone is like drilling through balsam wood, comparatively much softer than pine wood with 60% bone-implant contact.
D4/Type 4 Bone:
D4 bone is a fragile cortical bone with low-density trabeculae of poor strength found in the posterior region of the maxilla. The bone trabeculae are much weaker in this bone, almost ten times less strong than the D1 bone. Drilling an implant through D4 Bone is like drilling through Styrofoam (softest with 25% of bone-implant contact after loading the implant).
Hence, the prognosis of implant survival is reduced in D4 bone, whereas a 99% survivability rate is found in D1, D2, D3 bone at the implant site. Along with this, good systemic and oral health factors play a vital role in osseointegration and favorable bone-implant contact.
What Are the Diagnostic Radiographic Procedures Used in Preoperative Bone Quality Assessment?
Traditionally, after introducing dental implants in the market a few decades ago, conventional methods of assessing the bone quality were only through periapical radiographs and more recently through the introduction of OPG or panoramic radiography. The bone consistency of D1, D2, D3, or D4 bone cannot be solely assessed with the help of radiographs, and the following are used to evaluate bone quality.
Panoramic Radiography:
The overview of maxillofacial structures, maxillary sinus, inferior alveolar nerve, and nasal fossa can be visualized clearly. However, CBCT is now the preferred imaging modality compared to CT scan, which has increased radiation exposure, and panoramic radiography, a 2D imaging technique. That makes panoramic radiography or OPG imaging a popular method for screening and diagnosis.
CBCT (Computed Cone Beam Tomography):
For detailed analysis and accurate preoperative implant site assessment, it is an excellent radiographic technique to provide information to the operator before dental implantation regarding the bone quality, the location of surrounding vital structures like nerves that penetrate the jaw bone, the contour, continuity of the jaw bone, and finally the cortical bone plate analysis. The apparent advantage of CBCT over conventional CT radiography is that the radiation dosage is low. Its advantage over panoramic radiography is that it produces a three-dimensional structure analysis, reduces image distortion, and increases image sharpness or clarity. The resolution of the CBCT image is measured in voxels/individual volume elements. Ease of image acquisition and cross-sectional imaging makes CBCT the most preferred radiographic modality.
Conclusion:
To conclude, diagnostic imaging done preoperatively by panoramic radiograph and CBCT is imperative for the placement of dental implants. Studying and analyzing the implant site by the operator or dental implantologist would be crucial for assessing the implant’s prognosis and long-term survival rate, which is dependent on and directly proportional to the bone quality at the site.
