Predictability of bone density at posterior mandibular implant sites using cone-beam computed tomography intensity values

Jawbone quality classification in dental implant planning and placement studies. A scoping review

Aim

Cone beam computed tomography has become an attractive method for implant planning. However, in most cases, not all the information is taken advantage of and often the radiographic evaluation of bone quality is based on subjective assessment by the individual clinician. Therefore, the aim of this study was to examine classifications of bone tissue characteristics and methods for assessing them in dental implant planning and placement studies.

Materials and Methods

Three databases (Pubmed, Scopus, Web of Science) were searched using specific index terms: "Bone quality, bone quantity, bone density, cone-beam CT and cone-beam computed tomography". Three reviewers selected titles and analyzed abstracts according to inclusion and exclusion criteria. Some descriptions of bone tissue characteristics (bone quality, density, and quantity) used before or during dental implant placement were selected and categorized.

Results

The search yielded 442 titles. A total of 32 articles were selected and read in full text. Seventeen articles were considered relevant. Different classification systems were found to evaluate bone tissue characteristics as well as different examination protocols. Thirteen publications included in this review reported on bone quality and quantity using the Lekholm and Zarb classification. However, only four studies implemented and/or proposed modifications of the Lekholm and Zarb system. Four other publications described bone quality according to different classification systems such as Misch, University of California Los Angeles (UCLA), or Trisi and Rao. The assessment methods were often briefly described (or not described at all in one publication). Of the articles analyzed, five presented observer performance, whereas three presented diagnostic accuracy of the assessment method.

Conclusion

Currently, there are different classification systems applied to dental implant planning and placement, particularly regarding whether bone quality or quantity affects treatment outcomes. However, most authors have not validated the diagnostic accuracy and reproducibility of the classification used. Therefore, it is necessary to develop a classification system consistent with characteristics of bone tissue, taking into consideration an adequate description of bone tissue assessment methods, their diagnostic accuracy, and observer performance.

Role of CBCT in Prediction of Oro-antral Communication Post Third Molar Extraction: A Retrospective Study

OBJECTIVE

 Oro-antral communication (OAC) is one of the most frequently encountered complications during third molar extraction. Various radiographic factors, like excessive maxillary sinus pneumatization, long periods of edentulism, periapical lesions, etc., have been considered high-risk factors for OAC. However, a panoramic radiograph has not proven to be accurate in predicting the chances of OAC. Through this retrospective study, we evaluated the efficacy of a CBCT in predicting the incidence of OAC after maxillary third molar extraction.

MATERIALS AND METHODS

 We conducted a retrospective study in our department, which included the patients who had undergone extraction of a maxillary third molar over five years with the presence of panoramic X-rays and/or CBCT scans prior to extraction. Primary outcomes assessed from the case files were intra-operative complications like OAC, root fracture, tuberosity fracture, pterygoid plate fracture, etc. The incidence of these complications was correlated with the presence or absence of CBCT before extraction.

RESULTS

 Out of 920 extracted maxillary third molar, only 148 teeth (16.1%) had a CBCT record before extraction. The most commonly encountered complication was broken inaccessible root piece/s (4.9%), followed by OAC (3.5%). An inter-group comparison showed that a significantly higher percentage of patients (p < 0.001) with CBCT records had an incidence of OAC (11.5%) as against the group of patients with no CBCT record (1.9%).

CONCLUSION

 A CBCT scan prior to cases with high-risk factors for OAC can be a valuable tool in accurately predicting the chances of OAC after maxillary third molar extraction.

Reliability of Grayscale Value for Bone Density Determination in Oral Rehabilitation using Dental Implants

Introduction

Quality and quantity of jaw bones have been previously classified in literature using different methods. Imaging modalities such as computed tomography (CT), successfully determine bone density of jaws. This study aims to establish the role of cone-beam CT (CBCT) in determining the density of cortical and cancellous bones at different jaw sites.

Materials and Methods

Eighty-three possible implant sites in healthy patients were evaluated using NewTomGiano CBCT machine. Cross-sections were obtained and cortical and cancellous bone densities on different aspects of the virtual implant in terms of Hounsfield unit (HU) were determined using New Net Technologies software version 6.1 and were classified according to software from D1 to D4. Data were entered into SPSS software (version 19.0) and were statistically analyzed.

Results

The mean HU showed the highest value for cortical and cancellous in the anterior mandible (mean HU 1874.01 and 1131.73, respectively) followed by the posterior mandible (mean HU 1789.20 and 872.95, respectively) and least in posterior maxilla (mean HU 1068.26 and 830.04, respectively). Maximum D1 bone type was found in cortical bone and D2 bone type was noted in cancellous bone area. Males showed very highly significant cortical bone thickness (P < 0.001) whereas females showed more cancellous bone thickness but the results were nonsignificant.

Conclusion

A high degree of concordance between different regions of jaw bones with a strong correlation between the four bone types was obtained. Bone density plays a pivotal role in determining the prognosis of the implant. CBCT has proven to be beneficial in bone density analysis.

New classification for bone type at dental implant sites: a dental computed tomography study

OBJECTIVE

This study proposed a new classification method of bone quantity and quality at the dental implant site using cone-beam computed tomography (CBCT) image analysis, classifying cortical and cancellous bones separately and using CBCT for quantitative analysis.

METHODS

Preoperative CBCT images were obtained from 128 implant patients (315 sites). First, measure the crestal cortical bone thickness (in mm) and the cancellous bone density [in grayscale values (GV) and bone mineral density (g/cm³)] at the implant sites. The new classification for bone quality at the implant site proposed in this study is a "nine-square division" bone classification system, where the cortical bone thickness is classified into A: > 1.1 mm, B:0.7-1.1 mm, and C: < 0.7 mm, and the cancellous bone density is classified into 1: > 600 GV (= 420 g/cm³), 2:300-600 GV (= 160 g/cm³-420 g/cm³), and 3: < 300 GV (= 160 g/cm³).

RESULTS

The results of the nine bone type proportions based on the new jawbone classification were as follows: A1 (8.57%,27/315), A2 (13.02%), A3 (4.13%), B1 (17.78%), B2 (20.63%), B3 (8.57%) C1 (4.44%), C2 (14.29%), and C3 (8.57%).

CONCLUSIONS

The proposed classification can complement the parts overlooked in previous bone classification methods (bone types A3 and C1).

TRIAL REGISTRATION

The retrospective registration of this study was approved by the Institutional Review Board of China Medical University Hospital, No. CMUH 108-REC2-181.

Removal of a Horizontally Displaced Dental Implant below the Mandibular Canal

A clinical case of a horizontally displaced dental implant, which moved below the level of the mandibular canal during surgery is presented together with a brief review of the comparable published cases. The bone mineral density and the morphology of the alveolar ridge were analyzed at the site of osteotomy, and the low bone density of $265.32\pm 86.41$ Hounsfield Units was found in the area. The factors related to implant displacement were: the anatomical features of bone structure, and the applied mechanical pressure during the implant insertion. The displacement of the dental implant below the level of the mandibular canal during implantation can be a severe complication. Its removal requires the safest surgical approach to avoid damaging the inferior alveolar nerve. The description of one clinical case does not provide grounds for drawing definite conclusions. To avoid similar incidents, detailed radiographic assessment before implantation is necessary; it is also important to follow the surgical protocols of implant placement into soft bone and to create conditions for a good visibility and sufficient control of bleeding during surgery.

Image Segmentation Technology Based on Attention Mechanism and ENet

With the development of today's society, medical technology is becoming more and more important in people's daily diagnosis and treatment and the number of computed tomography (CT) images and MRI images is also increasing. It is difficult to meet today's needs for segmentation and recognition of medical images by manpower alone. Therefore, the use of computer technology for automatic segmentation has received extensive attention from researchers. We design a tooth CT image segmentation method combining attention mechanism and ENet. First, dilated convolution is used with the spatial information path, with a small downsampling factor to preserve the resolution of the image. Second, an attention mechanism is added to the segmentation network based on CT image features to improve the accuracy of segmentation. Then, the designed feature fusion module obtains the segmentation result of the tooth CT image. It was verified on tooth CT image dataset published by West China Hospital, and the average intersection ratio and accuracy were used as the metric. The results show that, on the dataset of West China Hospital, Mean Intersection over Union (MIOU) and accuracy are 83.47% and 95.28%, respectively, which are 3.3% and 8.09% higher than the traditional model. Compared with the multiple watershed algorithm, the Chan-Vese segmentation algorithm, and the graph cut segmentation algorithm, our algorithm increases the calculation time by 56.52%, 91.52%, and 62.96%, respectively. It can be seen that our algorithm has obvious advantages in MIOU, accuracy, and calculation time.

Three-dimensional descriptive study of the pterygomaxillary region related to pterygoid implants: A retrospective study

The objective of this study was to analyze three-dimensionally the morphological characteristics of the pterygomaxillary region related to pterygoid implants. Volume, height, width and bone density were studied in relation to age, sex and dental status. This retrospective observational study analyzed the CBCT of 52 hemi-maxillas three-dimensionally (females n = 28, males n = 24; dentate = 31, edentulous = 21). Patients were exposed between September 2009 and October 2014, and data collection was performed between November 2015 and May 2016. Bone density, volume, height and width were analyzed in various locations of the maxilla and pterygoid process, and the variables age, gender and dental status patients were compared. The results show that the mean width of the pterygomaxillary joint was 7.5 mm (SD 1.00 mm), mean height was 12.51 mm (SD 1,82 mm) and mean volume was 321.7 mm³ (SD 142.02 mm³). Statistically significant differences between dentate and edentulous patients were found, showing a higher osseous density in dentate patients in the pterygoid process (758.2, SD 106.8, 95% CI 729.2 to 787.3 GSD - Gray Scale Density - compared to 689.9, SD 107.3, 95% CI 660.8 to 719.1 GSD; P = 0.022). In the maxilla, density was statistically significant lower in female subjects (571.0, SD 74.1, 95% CI 594.9 to 645.4 GSD) than in male subjects (620.2, SD 93.8, 95% CI 594.4 to 645.4 GSD, P = 0.047). In conclusion, due to the significant variation in the morphological characteristics of the pterygomaxillary region among subjects, personalized pre-surgical radiological assessment should always be performed. Gender, age and dental status are critical factors as they significantly affect bone density in this region.