Comparison of artificial tooth position in dentures fabricated by heat curing and additive manufacturing

BACKGROUND

The purpose of this study was to compare the displacement of tooth arrangement in dentures fabricated by additive manufacturing (AM) and heat curing.

METHODS

Three-dimensional (3D) scanning was performed for edentulous jaw models. After the teeth were arranged, 3D scanning for the wax denture was performed. Heat-cured dentures were fabricated with heat-cure polymer resin. Based on data obtained by subtracting the model data from wax denture data, AM dentures were fabricated from ultraviolet-cured acrylic resin. Accuracy was verified by superimposing heat-cured and AM dentures on the tooth region data from the wax dentures and measuring displacement of the tooth arrangement.

RESULTS

In the maxillary dentures, the amount of tooth displacement for the heat-cured dentures and for the AM dentures ranged from -0.08 to +0.06 mm and from -0.25 to +0.06 mm respectively. A significant difference was observed between two dentures. In the mandibular dentures, the amount of tooth displacement for the heat-cured dentures and for the AM dentures ranged from -0.09 to +0.07 mm and from -0.03 to +0.07 mm respectively. No significant difference was observed between two dentures.

CONCLUSIONS

The artificial teeth of the maxillary dentures fabricated by AM showed a greater displacement compared to those by heat curing.

Brain responses to stimuli mimicking dental treatment among non-phobic individuals: A meta-analysis

Numerous neuroimaging studies have attempted to identify how the brain responds to stimuli mimicking dental treatment in normal non-phobic individuals. However, results were sometimes inconsistent due to small sample sizes and methodological variations. This meta-analysis employs standardized procedures to summarize data from previous studies to identify brain regions that were consistently activated across studies, elicited by stimuli such as pictures, sounds, or audiovisual footage mimicking those encountered during dental treatments. A systematic literature search was carried out using PubMed and Scopus. The meta-analysis analyzed data from 120 healthy subjects from seven neuroimaging studies. We assessed the risk of bias among the included studies with the Risk of Bias Assessment Tool for Nonrandomized Studies. One study appeared to have a high risk of selection bias, whereas the others were considered to have a low risk of bias. Results revealed three clusters of activation with cluster sizes ranging from 768 mm³ to 1,424 mm³ . Stimuli mimicking dental treatment consistently activated the bilateral anterior insula; right dorsal anterior cingulate, putamen, and medial prefrontal cortex; and left claustrum. This study confirmed that audio and/or visual stimuli mimicking dental treatment consistently activated the fear-related brain regions among healthy subjects, mostly consistent with activations from general anxiety but without the involvement of the amygdala.

In vivo Cross-sectional Area of Human Jaw Muscles Varies with Section Location and Jaw Position

Muscle cross-sectional area (CSA) is used as a measure for maximum muscle force. This CSA is commonly determined at one location within the muscle and for one jaw position. The purpose of this study was to establish a method to standardize the analysis of the CSA of the masticatory muscles in vivo, and to compare the CSAs along their entire length for two different jaw positions (opened and closed). The CSAs in the planes perpendicular to the long axes of the masseter, medial, and lateral pterygoid muscles were measured in ten normal young adult subjects by magnetic resonance imaging. Our results showed large differences among the muscles and a non-uniform change in CSA after jaw-opening. The method enables the CSA measurement to be standardized in vivo, and allows for a correct comparison of CSAs in different skull morphologies.

Size and Orientation of Masticatory Muscles in Patients with Mandibular Laterognathism

Size measurements of jaw muscles reflect their force capabilities and correlate with facial morphology. Using MRI, we examined the size and orientation of jaw muscles in patients with mandibular laterognathism in comparison with a control group. We hypothesized that the muscles of the deviated side would be smaller than those of the non-deviated side, and that the muscles of both sides would be smaller than in controls. In patients, a comparison of deviated and non-deviated sides showed, in orientation, differences for masseter and medial pterygoid muscles, but, in size, differences only for the masseter muscle. Nevertheless, muscle sizes in patients were much smaller than in controls. Lateral displacement of the mandible can explain the orientation differences, but not the smaller muscle size, in patients. It is possible that the laterodeviation initiates an adaptive process in the entire jaw system, resulting in extensive atrophy of the jaw muscles.

The combined use of US and MR imaging for the diagnosis of masses in the parotid region

Purpose: To evaluate the usefulness of the combination of the two non-invasive modalities US and MR imaging to diagnose masses in the parotid region.

Material and Methods: The US and MR findings of 21 patients with parotid masses were analyzed retrospectively by two radiologists without any clinical or histopathological information. The specific points evaluated were location, shape, margin, internal architecture, and intensity level on both US and MR, posterior echo enhancement on US, and capsule-like lining of the tumor on MR.

Results: The findings concerning the shape and margin on US and MR were in fairly good agreement. Concerning the findings of the internal architecture, US could reveal the minute structures of the tumor while MR demonstrated differences in the signal intensities of histological tissue types of the various tumors. The posterior echo enhancement on US and the capsule-like lining on MR of the tumors were also useful for the diagnosis.

Conclusion: Our results suggest that the combination of US and MR is useful for examining soft tissue masses in the parotid region to make a more accurate diagnosis, and not just differentiate malignant lesions from those which are benign.

Evaluation of juxta-apical radiolucency in cone beam CT images

OBJECTIVES

The aim of this study was to analyse the position and relationship of juxta-apical radiolucency (JAR) to the mandibular canal and buccal and/or lingual cortical plates using cone beam CT (CBCT).

METHODS

A retrospective study was carried out to analyse the JAR on CBCT for 27 patients. These findings were compared with 27 age- and sex-matched patients without the presence of JAR, which acted as the control group. The CBCT images were analysed according to a checklist, to evaluate the position of the JAR and its relationship to the mandibular canal. Then, any thinning or perforation of either the buccal or lingual cortical plate due to JAR was noted, and a classification to quantify the thinning of cortical plates was proposed. The findings in the two groups were analysed using a paired comparison by McNemar test.

RESULTS

A statistical increased thinning of cortical plates was seen in the JAR group compared with the control group, and most of the cases were in the J3 group. None of the patients in either the JAR or the control group showed perforation of the buccal and/or lingual cortical plate on CBCT images.

CONCLUSIONS

A classification to quantify the thinning of cortical plates was proposed, which may be used for objective evaluation of the thinning of the cortical plates in future studies. The present study gives an insight into the relationship of the juxta-apical area with the mandibular canal and cortical plates in the mandible using CBCT.

Relationship between the unilateral TMJ osteoarthritis/osteoarthrosis, mandibular asymmetry and the EMG activity of the masticatory muscles: a retrospective study

The purpose of this retrospective study was to investigate the relationship between the unilateral temporomandibular joint (TMJ) osteoarthritis/osteoarthrosis (OA), mandibular asymmetry and electromyographic (EMG) activity of the masticatory muscles. Twenty-two Japanese women (aged 23.2 +/- 5.4 years) and 10 Japanese men (aged 22.4 +/- 2.8 years) exhibiting unilateral TMJ OA were included in this study. Two angular and seven linear measurements were obtained for the analysis of the skeletal hard tissues. The cephalometric measurement values (CV) were normalized using the CV ratio for the evaluation of the degree of mandibular asymmetry. The EMG was recorded during maximal voluntary clenching efforts for 10 s in the intercuspal position. The average values of integral EMG (iEMG) of three trials were normalized using the iEMG ratio for the evaluation of the functional balance of the masticatory muscles. The mandibular midline was shifted to the TMJ OA side with a median value of 9.85 mm. The CV ratio of the ramus height of the TMJ OA side was significantly smaller than that of the non-OA side. For the masseter muscle, the iEMG ratio of the TMJ OA side was significantly larger than that of the non-OA side (P < 0.05). These results suggest that unilateral TMJ OA is related to the dentofacial morphology, thus resulting in a mandibular midline shift to the affected side and it is associated with a masticatory muscle imbalance.

Relationship of TMJ osteoarthritis / osteoarthrosis to head posture and dentofacial morphology

OBJECTIVE

The purpose of this study was to test the hypothesis that there is a relationship between the temporomandibular joint (TMJ) osteoarthritis/osteoarthrosis (OA), head posture and dentofacial morphology.

DESIGN

Case-control study.

SUBJECTS AND METHODS

The subjects consisted of 34 Japanese females with TMJ OA (aged 24.7 +/- 6.1 years) and a control group of 25 healthy Japanese females (aged 23.6 +/- 1.3 years). Six cranio-cervical angular measurements were constructed for head posture analysis. Nine angular and three linear measurements were constructed for the skeletal hard tissue analysis. Five angular and one linear measurements were constructed for the dental hard tissue analysis. Unpaired t-tests were used to compare the mean differences of head posture measurements and dentofacial cephalometric measurements between the TMJ OA and the control group.

RESULTS

The TMJ OA group had significantly larger cranio-cervical angles (p < 0.05) and had more posteriorly rotated mandibles (p < 0.0001) than those in the control group. They also had a significantly shorter posterior facial height (p < 0.0001). The TMJ OA group had more retroclined lower incisors (p < 0.05).

CONCLUSION

These results suggest that an association may exist between TMJ OA, head posture and dentofacial morphology.

Correlation between diagnostic accuracy and perceptibility

OBJECTIVES

To correlate diagnostic accuracy for proximal caries with perceptibility of low contrast image details using regression analysis. The other purpose was to determine the attenuation range required for proximal caries diagnosis.

METHODS

The results of the two types of observer performance tests described above were retrieved from previous studies. Recording media included in those studies were the Compuray and the Dixel, direct digital radiographic systems, and Ektaspeed Plus film. The average numbers of perceptibility of image details from five observers were calculated for each step and for every combination of contiguous steps of the aluminium test phantom from the perceptibility test. The average diagnostic accuracy for proximal caries from the same five observers was correlated with the total number of perceptible details from the phantom using regression analysis. Finally, attenuation range required for proximal caries diagnosis was calculated from the attenuation range of the phantom where the maximum correlation coefficient was obtained.

RESULTS

Maximum correlation (r=0.68) was obtained at the combination of five contiguous steps of the aluminium test phantom. Attenuation range required for proximal caries diagnosis corresponded to the 2 mm to 6 mm thickness of aluminium with acrylic block of 12 mm thickness.

CONCLUSIONS

There is a correlation between perceptibility of low contrast image details and diagnostic accuracy for proximal caries. There may be a possibility to simplify observer performance tests for proximal caries diagnosis by using the standardized phantom simulating its attenuation range.

Effects of the automatic exposure compensation on the proximal caries diagnosis

OBJECTIVE

To elucidate the effect of automatic exposure compensation (AEC) on the diagnostic accuracy of proximal caries by comparing several digital intraoral imaging systems with a film.

MATERIALS AND METHODS

Twenty-seven extracted teeth served as proximal caries samples. Three digital radiographic systems; the Compuray, the Dixel, and the Sens-A-Ray without scintillator layer, and Kodak Ekta-speed Plus films were used as recording media. Radiographs of the teeth samples were obtained with each recording medium under seven to eight different exposures including the optimum level. Six oral radiologists evaluated the possibility of proximal caries with the five-grade-confidence-scale. On digital radiographs, image manipulations were allowed after the initial assessment. Receiver operating characteristic (ROC) curves were obtained at each exposure in each recording medium. The area under the ROC curve (Az) was used as the representative value of diagnostic accuracy. Diagnostic accuracy (DA) curves were obtained by plotting averaged Az values from all observers as a function of incident exposure in each system.

RESULTS

The effect of exposure variation on the DA was slight in the film while it was significantly larger in the digital systems without AEC. Among digital systems, the effect of exposure variation was smaller in the system with AEC than those without AEC. There was no significant effect on the diagnostic accuracy even if digital image manipulation was employed.

CONCLUSION

AEC minimizes the decrease of DA due to inadequate exposures. Since it compensates for the narrow exposure range in the digital intraoral sensor systems, the system with AEC may be preferable for the clinical diagnostic tasks.

Volume changes in human masticatory muscles between jaw closing and opening

Most jaw muscles are complex, multipennate with multiple components. The morphologic heterogeneity of masticatory muscles reflects their functions. We hypothesized that the volume of masticatory muscles changes between jaw closing and opening, and that there is a difference in the volume change among the muscles. Magnetic resonance images of the entire head were obtained in ten normal young adult subjects before and after maximum jaw opening. The volume changes of the masseter, medial, and lateral pterygoid muscles were measured. Only slight changes were seen in the masseter and medial pterygoid muscles. The lateral pterygoid muscle, however, significantly decreased its volume during jaw opening. The results provide normative values of muscle volume in living subjects, and suggest that the volume changes differ among jaw muscles.

Lymphoepithelial lesion of the parotid gland

We describe a case of lymphoepithelial lesion of the parotid gland, also known as salivary lymphoepithelial lesion. Lymphoepithelial lesions are usually seen in conjunction with autoimmune disease of the salivary glands and these lesions do not always remain benign. Our case consisted of two masses that had different imaging features. Moreover, we could investigate the changes of the size and internal architecture on imaging due to the postponement of surgical intervention on the masses. At review 6 months later, the size of the masses had increased. The aims of this paper were to: (1) investigate the contribution of gray-scale sonography, power Doppler sonography, magnetic resonance imaging, and computed tomography to the diagnosis; and (2) consider the appropriate imaging modality to follow-up this case to monitor for recurrence or malignant transformation.

Length changes in the human masseter muscle after jaw movement

The human masseter is a multilayered, complex muscle contributing to jaw motion. Because variations in stretch may cause muscle fibers to function over different portions of their length-tension curves, the aim of this study was to determine how parts of the masseter lengthen or shorten during voluntary jaw movements made by living subjects. Magnetic resonance (MR) imaging and optically-based jaw-tracking were used to measure muscle-insertion positions for four parts of the muscle with six degrees of freedom (DOF), before and after maximum-opening, jaw protrusion and laterotrusion in four adult males. Muscle part lengths and intramuscular tendon lengths were calculated, and these data, with fiber-tendon ratios published previously, were used to estimate putative changes in fiber-length. During maximum jaw-opening, the largest increases in muscle length (34-83%) occurred in the medial part of the deep masseter, whereas the smallest changes occurred in the posterior-most, superficial masseter (2-19%). Smaller changes were found during movement to the ipsilateral side, than during protrusion and movement to the contralateral side. On maximum opening, putative fibers in the deep masseter lengthened up to 83%, whereas those of the superficial masseter stretched up to 72%. The masseter muscle does not stretch uniformly for major jaw movement. Jaw motion to the ipsilateral side causes little length change in any part, and the effect of tendon-stretch on estimated fiber lengths is not substantial. The stretch that occurs infers there are task-related changes in the active and passive tensions produced by different muscle regions.

A follow-up of rhabdomyosarcoma of the infratemporal fossa region in adults based on the magnetic resonance imaging findings: case reports

Two adult patients with rhabdomyosarcoma of the infratemporal fossa region were evaluated by computed tomography and magnetic resonance imaging both before and after treatment. Successful treatment accompanied by reduction of the tumor mass as a result of chemotherapy was demonstrated in one patient. In the other patient a subsequent increase in the tumor mass was documented. Information on not only the size but also the internal architecture of the tumor may be useful when tumor response to therapy is being investigated. Magnetic resonance imaging is recommended as a method for outcomes evaluation in adult rhabdomyosarcoma cases.

Functional movements of putative jaw muscle insertions

BACKGROUND

The craniomandibular muscles control jaw position and forces at the teeth and temporomandibular joints, but little is known regarding their biomechanical behaviour during dynamic function. The objective of this study was to determine how jaw muscle insertions alter position during different jaw movements in living subjects.

METHODS

Computer 3D reconstruction of MR images and jaw-tracking were combined to permit the examination of movement with six degrees of freedom. Maximum mandibular opening, protrusive and laterotrusive positions were recorded in four subjects, and the translation and rotation of the putative insertions of masseter, temporal, medial, and lateral pterygoid muscles were measured.

RESULTS

The sizes and shapes of regional attachments varied markedly among subjects, and their displacement patterns were different in specific muscles. For instance, when the jaw closed to the dental intercuspal position from maximum gape, the region near the superior insertion site of the masseter moved backward and upward, whereas the region near the inferior insertion site displaced mainly forward. In three subjects, the jaw's rotational center during this act was approximately 26-34 mm below the mandibular condyles.

CONCLUSIONS

Since the movements of each muscle part differ according to variations in the size and shape of insertion areas, individual musculoskeletal form, and patterns of jaw motion during function, the prediction of motion-related muscle mechanics in any one subject is unlikely to be possible without direct measurement of the motion of visualized muscle parts. The present study shows that this information can be obtained.