Recent advances of ultrasound imaging in dentistry--a review of the literature

Feasibility of A-mode ultrasound based intraoperative registration in computer-aided orthopedic surgery: A simulation and experimental study

PURPOSE

A fast and accurate intraoperative registration method is important for Computer-Aided Orthopedic Surgery (CAOS). A-mode ultrasound (US) is able to acquire bone surface data in a non-invasive manner. To utilize A-mode US in CAOS, a suitable registration algorithm is necessary with a small number of registration points and the presence of measurement errors. Therefore, we investigated the effects of (1) the number of registration points and (2) the Ultrasound Point Localization Error (UPLE) on the overall registration accuracy.

METHODS

We proposed a new registration method (ICP-PS), including the Iterative Closest Points (ICP) algorithm and a Perturbation Search algorithm. This method enables to avoid getting stuck in the local minimum of ICP iterations and to find the adjacent global minimum. This registration method was subsequently validated in a numerical simulation and a cadaveric experiment using a 3D-tracked A-mode US system.

RESULTS

The results showed that ICP-PS outperformed the standard ICP algorithm. The registration accuracy improved with the addition of ultrasound registration points. In the numerical simulation, for 25 sample points with zero UPLE, the averaged registration error of ICP-PS reached 0.25 mm, while 1.71 mm for ICP, decreasing by 85.38%. In the cadaver experiment, using 25 registration points, ICP-PS achieved an RMSE of 2.81 mm relative to 5.84 mm for the ICP, decreasing by 51.88%.

CONCLUSIONS

The simulation approach provided a well-defined framework for estimating the necessary number of ultrasound registration points and acceptable level of UPLE for a given required level of accuracy for intraoperative registration in CAOS. ICP-PS method is suitable for A-mode US based intraoperative registration. This study would facilitate the application of A-mode US probe in registering the point cloud to a known shape model, which also has the potential for accurately estimating bone position and orientation for skeletal motion tracking and surgical navigation.

Updates on ultrasound research in implant dentistry: a systematic review of potential clinical indications

OBJECTIVES

Ultrasonography has shown promising diagnostic value in dental implant imaging research; however, exactly how ultrasound was used and at what stage of implant therapy it can be applied has not been systematically evaluated. Therefore, the aim of this review is to investigate potential indications of ultrasound use in the three implant treatment phases, namely planning, intraoperative and post-operative phase.

METHODS

Eligible manuscripts were searched in major databases with a combination of keywords related to the use of ultrasound imaging in implant therapy. An initial search yielded 414 articles, after further review, 28 articles were finally included for this systematic review.

RESULTS

Ultrasound was found valuable, though at various development stages, for evaluating (1) soft tissues, (2) hard tissues (3) vital structures and (4) implant stability. B-mode, the main function to image anatomical structures of interest, has been evaluated in pre-clinical and clinical studies. Quantitative ultrasound parameters, e.g. sound speed and amplitude, are being developed to evaluate implant-bone stability, mainly in simulation and pre-clinical studies. Ultrasound could be potentially useful in all three treatment phases. In the planning phase, ultrasound could evaluate vital structures, tissue biotype, ridge width/density, and cortical bone thickness. During surgery, it can provide feedback by identifying vital structures and bone boundary. At follow-up visits, it could evaluate marginal bone level and implant stability.

CONCLUSIONS

Understanding the current status of ultrasound imaging research for implant therapy would be extremely beneficial for accelerating translational research and its use in dental clinics.

Correlation of ultrasound microscopy and Vickers hardness measurements of human dentin and enamel - A pilot study

OBJECTIVE

To investigate if Vickers microhardness of dentin and enamel correlated with acoustic velocity c(l) or acoustic reflection from the sample's top (amplitude).

METHODS

Eight transversal sections of a sound human tooth were investigated with scanning acoustic microscopy (SAM) and Vickers microhardness measurements. Longitudinal acoustic velocity c(l), amplitude and microhardness MHV were evaluated and for each c(l) test point corresponding amplitude and MHV were linearly interpolated and graphically analyzed. Spearman rank order correlation (r_S) was calculated (p<0.05).

RESULTS

c(l) was predominantly 6100-7000ms^-1 in enamel and 3800-4600ms^-1 in dentin and correlated significantly with MHV with 27-420 in enamel and 20-90 in dentin (r_s=0,57). Amplitudes significantly correlated with MHV, too, but even better (r_s=0,77).

SIGNIFICANCE

Acoustic velocity and amplitudes were appropriate to detect microhardness differences of dentin and enamel and certain value ranges of both could be assigned to certain MHV ranges. Further research is needed to differentiate more precisely between the different hard tooth tissues.

Utility of Transfacial Dental Ultrasonography in Evaluation of Cystic Jaw Lesions

OBJECTIVES

Plain radiography has been widely used in dentistry. Because of the variability of the quality of equipment, radiographic technique, accuracy of interpretation, and radiation risk to the patients, the field is ripe for the introduction of other newer diagnostic modalities. In this report, we demonstrate the utility of ultrasonography in the diagnostic workup of cystic or cystlike lesions of the jaw.

METHODS

We used a transfacial ultrasonographic scanning approach to examine 32 patients with clinical or radiographic presentation of a jaw cyst. Computed tomography and histopathologic analysis were used as the reference standards to confirm the findings.

RESULTS

Ultrasonography could establish the presence or absence of a lesion, erosion of the buccal cortical plate, and identification of associated soft tissue involvement in all cases (sensitivity and specificity, 100% and 100%, respectively; area under the receiver operating characteristic curve, 1.0; P < .001).

CONCLUSIONS

Our observations revealed the usefulness of ultrasonography and demonstrated its potential value when introduced as a routine office-based imaging method for dentistry.

Integration of ultrasound imaging into pre-clinical dental education

INTRODUCTION

Patients have complex healthcare needs and typically require more than one healthcare discipline to address issues regarding their health. Interprofessional teams of healthcare professionals may be able to address these complex needs and improve patient outcomes by combining resources. To evaluate the feasibility of integrating ultrasound into a dental school curriculum to teach anatomy as part of an interprofessional education experience, the current study surveyed first-year dental students to determine their perceptions of the integration of ultrasound techniques into the curriculum.

MATERIALS AND METHODS

Ultrasound laboratory exercises were developed for first-year dental students as part of their anatomy course. The exercises were focused on head, neck and abdominal anatomy. To assess student perception of the integration of ultrasound into the dental curriculum, a survey was created specifically for the current study.

RESULTS

Between 2013 and 2015, two classes of first-year dental students participated in the ultrasound laboratory exercise and completed the survey (n = 83). Student survey responses suggested ultrasound was a valuable teaching tool because it allowed them to visualise anatomical structures using live imaging. They also agreed that the ultrasound laboratory exercises were an efficient learning tool, but the majority did not believe that they would use ultrasound regularly in their future practice.

CONCLUSIONS

Results of the current study suggested first-year dental students were satisfied with the integration of ultrasound techniques into the dental curriculum. Survey results indicated that the students enjoyed the ultrasound laboratory exercise and felt ultrasound was an effective learning tool.

Ultrasound Assessment of Bone Healing after Root-end Surgery: Echoes Back to Patient's Safety

INTRODUCTION

The aim of this study was to present ultrasound imaging (UI) techniques as promising and safe tools for the follow-up of root-end surgery (RES) in vivo.

METHODS

The study included 8 patients who underwent RES. All were followed up using UI at 1 week, 1 month, 2 months, 3 months, and 6 months (if necessary) after RES. The bony crypt was defined on the ultrasound image, and the following observations were made during follow-up: cortical bone interruption and surface area measurement of the residual echoic bony crypt image.

RESULTS

In all cases, the hypoechoic image became hyperechoic, indicating gradual bone healing of the crypt. Compared with baseline, at 3 months a remaining cortical opening of 51.2% (±12.6%) and a bony crypt surface area of 24.3% (±10.8%) was detected for all patients. For 50% of the patients, the echographic follow-up ended at 3 months because the ultrasound waves could no longer enter the bony crypt. For 4 patients who attended the 6-month recall, a remaining cortical disruption of 43.2% (±9.9%) and a bony crypt surface area of 17.2% (±7%) compared with the baseline was noted.

CONCLUSIONS

UI is a promising follow-up tool for RES. It helps clinicians understand the initial stages of bone healing, allows close healing monitoring, and is radiation free.

Alternative methods to visual and radiographic examinations for approximal caries detection

A shift in caries prevalence from occlusal surfaces to approximal surfaces has been demonstrated by epidemiological studies. Two recent meta-analyses evaluated the performance of visual examination and radiography for carious lesion detection, and reported low sensitivity but high specificity for early approximal caries detection. This suggests that the conventional methods have a higher risk of failing to detect approximal lesions. Consequently, in caries susceptible populations, there is a risk of progression of non-cavitated lesions to irreversible tooth destruction before the lesions are detected. This paper aims to review the performance of unconventional and novel methods for approximal caries detection. In vitro and in vivo studies identified through a MEDLINE search using keywords such as caries detection, approximal caries detection, light fluorescence and dental caries, and transillumination and dental caries were reviewed. The unconventional methods known to be used for approximal caries detection and included in this review are: cone beam computed tomography, fiber-optic trans-illumination, digital imaging fiber optic trans-illumination, near-infrared digital imaging transillumination, optical coherence tomography, laser fluorescence, ultrasound, and LED reflection and refraction.

Ultrasound evaluation of intra-osseous cavity: A preliminary study in pig mandibles

AIMS

To assess the role of ultrasonography as a possible tool for diagnosis of intra-osseous lesions.

METHODS

Our sample comprised five macerated pig jaws. The regions of bony crypts of third molars were examined on both sides, totaling 10 examinations. The degrees of difficulty for both ultrasound image visualization and bone translucency were rated by two groups of evaluators (i.e. dental radiologists and physician ultrasonographers).

RESULTS

Our results showed that it is possible to detect images of the intra-osseous cavity at a low-degree difficulty by using both radiographic and ultrasonic techniques (46.6% and 43.3%, respectively). However, the crypts were not fully detected by both groups (16.6% and 13.3%, respectively).

CONCLUSIONS

We concluded that ultrasonography is a useful method for evaluation of intra-osseous lesions in jaws, provided that the cortical bone is thin enough to allow ultrasound waves to pass through.

Evaluation of the effects of the low-level laser therapy on swelling, pain, and trismus after removal of impacted lower third molar

BACKGROUND

In current study we aimed to examine the effect of a low-level laser therapy on the pain, mouth opening and swelling of patients whose impacted 3rd molar tooth was extracted in addition measurement volumetrically to the edema with 3dMD face system.

METHODS

It was surveyed 15 patients who had bilateral symmetric lower 3rd molars. Surgical sides of patients were randomly separated into two groups: the study group and the control group. It was applied extra oral low-level laser therapy (LLLT, 0.3 W, 40 s, 4 J/cm(2)) to the study group (n = 15) after the surgical operation and on the 2nd day. Only routine postoperative recommendation (ice application) was made in the control (n = 15) group. The maximum mouth opening, pain level and facial swelling evaluated. 3dMD Face® (3dMD, Atlanta, GA) Photogrammetric System was used to evaluate volumetric changes of the swelling.

RESULTS

There was no statistically significant difference in the edema and interincisal opening between the groups and the pain level in the laser group was significantly lower than in the control group on the 7(th) postoperative day.

CONCLUSIONS

Although there were decreasing trismus, swelling, and pain level, with this LLLT, there was significant difference only in the 7th day pain level in the laser group compared with the control group.

Ultrasonography in the diagnosis of bone lesions of the jaws: a systematic review

The diagnostic use of ultrasonography in dentistry and maxillofacial surgery has previously been described in the literature. Considering that ultrasonography may be useful for the diagnosis of bone lesions of the jaws, a systematic review was carried out to examine the evidence. This review determined that ultrasonography has been used effectively for the diagnosis of infective and/or inflammatory lesions, cysts, nonodontogenic tumors, odontogenic tumors, and arteriovenous malformations and for the differential diagnosis of lesions of endodontic origin, compared with the gold standard of histologic analysis. Ultrasonography may be a viable adjunct to other special tests for the diagnosis of intraosseous lesions of the jaws, as it is noninvasive and does not involve ionizing radiation exposure of the patient.

Assessment of cortical bone thickness using ultrasound

PURPOSE

The aim of the study was to analyze the accuracy of measuring the cortical bone thickness using a combination of low- and high-frequency ultrasound (US) compared with cone-beam computed tomography (CBCT) and using stereomicroscopy as reference method.

MATERIAL AND METHODS

Ten jawbone models were prepared using bovine ribs and porcine gingiva. A dental implant was placed in each model. All models were investigated by US, CBCT, and stereomicroscopy. The cortical bone thickness was measured directly above and 4 mm beside the implant with each method in different slices.

RESULTS

The median deviation of US measurements compared to the reference method was 0.23 mm. The CBCT method was slightly more accurate (median percent deviation of 9.2%) than the US method (10.3%). However, US measurements directly above the implant were more accurate than CBCT measurements with a median percent deviation of 10.5% for US vs. 11.8% for CBCT.

CONCLUSION

Ultrasound showed a high potential to supplement CBCT for measurements of the cortical bone thickness.

The use of intraoral ultrasound in the characterization of minor salivary gland malignancy: report of two cases

It is generally accepted that ultrasound is now the first line of imaging of palpable lumps of the neck. Standardized protocols exist for the evaluation of thyroid, salivary gland and nodal disease, and sonography is increasingly being used in the characterization of intraoral soft tissue lesions. Here, we present two cases where intraoral sonography was invaluable in the early detection of oral malignancy.

Review on the applications of ultrasonography in dentomaxillofacial region

Use of ultrasonography (US) in dentomaxillofacial region became popular in recent years owing to increasing radiation dose concerns and economic limitations. It helps to visualize fine detail of the surface structure of the oral and maxillofacial tissues without ionizing radiation. In diagnostic ultrasound, high frequency sound waves are transmitted into the body by a transducer and echoes from tissue interface are detected and displayed on a screen. Sound waves are emitted via piezoelectric crystals from the ultrasound transducer. US technique can be used in dentomaxillofacial region for the examination of bone and superficial soft tissue, detection of major salivary gland lesions, temporomandibular joint imaging, assessment of fractures and vascular lesions, lymph node examination, measurement of the thickness of muscles and visualization of vessels of the neck. It has the potential to be used in the evaluation of periapical lesions and follow up of periapical bone healing. Also, it may be used for the evaluation of periodontal pocket depth and for the determination of gingival thickness before dental implantology.

Oral and Maxillofacial Imaging

This article provides the reader with the knowledge and skills of identification and diagnostic interpretative skills using planar images, tomographic images, CBCT, MDCT, pertinent MR images, as well as bone scans and PET images. The goal is to provide sufficient in-depth knowledge of the technique, anatomy, and radiographic identifiers for the diagnosis of local and systemic pathoses. The information will train the reader to be an advocate of selection criteria as well as a follower of the "Image Gently" campaign and philosophy supported by the organized dentistry in the United States, especially in Diagnostic Radiology.

Ultrasonographic pilot study of mental foramen size, with and without postoperative neurosensory dysfunction

OBJECTIVES

To evaluate the ability of a portable ultrasound system to visualize the mental foramen in patients with unilateral neurosensory dysfunction after third molar removal.

STUDY DESIGN

In 20 patients, an ultrasound scanner (13 MHz linear-array transducer) was used to measure the mental foramen. The anteroposterior diameter was calculated on both sides, and differences between injured and contralateral sides were tested. Intrarater and interrater reliability were calculated using Intraclass Correlation Coefficient (ICC).

RESULTS

We found a relatively high reliability on interindividual observations (ICC ≥0.89) and intraindividual observations (ICC ≥0.76). The average diameter on the injured sides was significantly smaller than the control sides. Subjective sensibility was not significantly correlated to the dimension of the mental foramen.

CONCLUSION

The results indicate a reduced size of the mental foramen, as determined by ultrasonography, in patients with permanent neurosensory dysfunction. These findings have to be verified in a larger number of patients.

A computer-aided automated methodology for the detection and classification of occlusal caries from photographic color images

The aim of this work is to present a computer-aided automated methodology for the assessment of carious lesions, according to the International Caries Detection and Assessment System (ICDAS II), which are located on the occlusal surfaces of posterior permanent teeth from photographic color tooth images. The proposed methodology consists of two stages: (a) the detection of regions of interest and (b) the classification of the detected regions according to ICDAS ΙΙ. In the first stage, pre-processing, segmentation and post-processing mechanisms were employed. For each pixel of the detected regions, a 15×15 neighborhood is used and a set of intensity-based and texture-based features were extracted. A correlation based technique was applied to select a subset of 36 features which were given as input into the classification stage, where five classifiers (J48, Random Tree, Random Forests, Support Vector Machines and Naïve Bayes) were compared to conclude to the best one, in our case, to Random Forests. The methodology was evaluated on a set of 103 digital color images where 425 regions of interest from occlusal surfaces of extracted permanent teeth were manually segmented and classified, based on visual assessments by two experts. The methodology correctly detected 337 out of 340 regions in the detection stage with accuracy of detection 80%. For the classification stage an overall accuracy 83% is achieved. The proposed methodology provides an objective and fully automated caries diagnostic system for occlusal carious lesions with similar or better performance of a trained dentist taking into consideration the available medical knowledge.

High-frequency ultrasound as an option for scanning of prepared teeth: an in vitro study

Because of its ability to non-invasively capture hard structures behind soft tissue, high-frequency ultrasound (HFUS)-assisted microscanning could be a patient-friendly and promising alternative for digitization of prepared teeth. However, intra-oral HFUS microscanners for taking digital impressions of prepared teeth are still not available in the clinical setting. Because working range, scanner size, scanning time, surface reconstruction accuracy and costs are major factors in such a system, our overall objective is to minimize hardware efforts and costs while maintaining the accuracy of the surface-reconstructed tooth model in the range 50 μm. In the work described here, we investigated the accuracy of tooth impression taking using a single-element HFUS microscanner with only three translational degrees of freedom under the restriction that only one occlusal scan is performed per tooth. As in favor of time and scanning efforts the data density is expected to be low, the surface reconstruction process is linked to a model-based surface reconstruction approach using a thin spline robust point matching algorithm to fill data gaps. A priori knowledge for the model is generated based on the original HFUS measurement data. Three artificial teeth and one human molar were prepared and scanned using an extra-oral HFUS laboratory microscanner that was built to test and evaluate different scanning setups. A scanner with three translational degrees of freedom was used to scan the teeth from an occlusal direction. After application of the proposed thin-spline robust point matching algorithm-based reconstruction approach, reconstruction accuracy was assessed by comparing the casts with a control group scanned with an extra-oral laser-scanning system. The mean difference between the reconstructed casts and the optical control group was in the range 14-53 μm. The standard deviation was between 21 and 52 μm. This let us assume that the suggested approach can help to decrease hardware efforts while maintaining the robustness of the 3-D surface reconstruction process for future HFUS-based intra-oral scanners.

Advances in diagnostic imaging for pathologic conditions of the jaws

Advances in dental and maxillofacial imaging are delineated along with the advantages and disadvantages of each imaging modality. The imaging modalities that are included are intraoral radiography, panoramic radiography, cone-beam computed tomography, multidetector computed tomography, magnetic resonance imaging, nuclear medicine, and ultrasound.

Visibility of dental pulp spaces in dental ultrasound

The purpose of this study was to assess the feasibility of dental ultrasound with conventional sonographic equipment. The teeth of three adult volunteers who had cone beam CT examinations performed previously with clinical indications and one extracted tooth were examined using linear and compact (hockey stick) sonographic probes. The sonographic images were compared with cone beam CT images reconstructed accordingly. Dental pulp spaces were demonstrated in all teeth not covered with prosthetic crowns. The dentin and pulp were best visualized at the level of the neck of the teeth. The dentin was hypoechoic, and the superficial layer comprising the cementum and the pulp spaces were hyperechoic. Dental ultrasound is feasible with general purpose sonographic machines. The buccal surfaces of all teeth are accessible with a compact (hockey stick) probe. Visualization and differentiation of dental pulp spaces, dentin and the superficial layer comprising cementum is possible in the portions of teeth not covered by the alveolar bone or prosthetic crowns. The dental pulp spaces are best seen at the level of the tooth neck. Pulp and endodontic fillings can be distinguished on ultrasound.

Quantitative diagnosis of salivary gland tumors with contrast-enhanced ultrasound--a preliminary study

OBJECTIVE

To quantitatively analyze the value of qualitative diagnosis of salivary gland masses with contrast-enhanced ultrasound (CEUS).

STUDY DESIGN

The enhanced sonographic features of 68 salivary gland masses were analyzed to differentiate them. The final diagnoses were confirmed by biopsy pathology.

RESULTS

We observed from the perfusion kinetics of CEUS that most pleomorphic adenomas manifested lower enhancement and well-defined margins; most Warthin tumors presented with higher enhancement and well-defined margins; and most malignant tumors had higher enhancement and poorly defined margins. Their time-intensity curves showed pleomorphic adenomas were hypovascularized with a poor perfusion, whereas Warthin tumors and malignant tumors were hypervascularized with a rich perfusion. Additionally, malignant tumors showed significantly shortened time to peak and richer maximum signal intensity compared with Warthin tumors.

CONCLUSIONS

The features of salivary gland masses identified with CEUS were helpful in the differential diagnosis of salivary gland masses.