الفهرس 
IntroductionOnly 14 pages are availabe for public view
 |  | from | 140 |  |  |
| | | from | 140 | | |
Abstract
Measurement of bone density is a valuable tool in several clinical applications as surgical reconstruction, preoperative dental implant planning 15, 26, 33, 34. Also, in diagnosing many systemic conditions as hyperparathyroidism, osteomalacia, osteoporosis, osteopetrosis, and blood diseases.3, 6, 29, 30
There are several methods reported in the literature for bone density measurement with variable degrees of accuracy and reliability as DEXA or DXA 45, CT 91, QCT 42, CBCT 103.
Several authors stated that CBCT is accepted as a precise tool for bone density measurements for pre-operative dental implant planning 166. While others as Kei Isoda, Nackaerts, Spin-Neto, and others stated that CBCT voxel density values are unreliable.124, 154, 158, 167 Some authors also stated that CBCT voxel density values are not comparable to predetermined standard values. The main advantage of CBCT over MDCT is reduced machine’s scan dose 168, 169. The measurements of HU using CBCT is susceptible to change due to exposure parameters, FOV, collimation, scattering. pronounced instability of attenuation coefficient is evident. These factors will affect the process of density measurements by CBCT.102, 122-124
The question that needs to be answered by the end of this review: “what are the factors which affect CBCT voxel density values?”
Search was done on PubMed and Cochrane. Search key words used were MeSH terms; “cone-beam computed tomography”, “bone density”, and “cone-beam computed tomography (AND) bone density”. Search was done on April 2016. The search yielded 92264 studies.
Inclusion criteria: relevant papers to CBCT, Studies with clearly defined types and models of the machines were used. Exclusion criteria were: if the machine was not available in the market, if the machine was mounted on radiotherapy unit and non-quantitative studies were excluded.
Screening was done in two levels according to the inclusion and exclusion criteria. The first level was by title and abstract only excluding researches not including CBCT or bone density in either; this yielded a total of 155 studies. All the studies from the first level were downloaded and entered the second level which encompassed a thorough reading and data extraction from the whole paper; this yielded 27 studies that were finally included.
Total 18 factors were found; FOV, mA, Objects position inside the FOV, Objects exo-mass, kVp, time between exposure, number of basis, adjacent air to the ROI, exposure parameters, software, exposure dose, presence of teeth, presence of metallic post in or out the FOV, Machines model, voxel size, objects mass, receptor type, exposure time. The first eight factors were the significant ones. They have an unexpected effect upon voxel density values, and that drove us to conclude the unrepeatability of voxel density values of CBCT.