Systematic evaluation of the features influencing the accuracy of third order measurements

The aims of this study were to evaluate the relationship of third order measurements on dental casts with those on lateral radiographs, and to identify those incisor features on radiographs which can best explain third order measurements on dental casts. Lateral cephalograms and corresponding dental casts were obtained from 39 untreated Caucasians (12 males, 27 females; mean age 19.5 years; standard deviation 3.7 years) with occlusal relationships considered to be ‘normal'. The upper (U1) and lower (L1) incisors were assessed with reference to the occlusal plane perpendicular which was established on the lateral radiographs, including third order angles (U1TR, L1TR) which were also derived from direct dental cast measurements (U1TA, L1TA). Both single regression and multiple linear regression analysis with stepwise variable selection were performed using third order measurements on casts as the dependent variable and crown axis (U1C, L1C), root axis (U1R, L1R), tip-apex connecting line (U1E, L1E), and radiographic third order measurements as independent variables. Single regression analysis indicated an overall difference of 0.02 degrees between radiographic third order inclination and cast assessment in the maxilla (mandible: −2.83 degrees). A change of 1 degree in radiographic third order inclination would produce a change of 0.65 degrees for U1TA and 0.86 degrees for L1TA assessments. Third order measurements on dental casts can best be explained by a linear combination of U1TR and U1E (maxilla) and of L1TR and L1C (mandible) measurements. This study demonstrates the functional enmeshment between two different third order assessments and the most common incisor features on lateral radiographs. Both methods of third order evaluation show sufficient reliability and are appropriate for routine orthodontic practic

The third-order angle and the maxillary incisor's inclination to the NA line

Objective: To evaluate the relationship between the angular measurement data (incisor's long axis to NA line) and the third-order angle (TA) according to Andrews' description. Materials and Methods: The materials in the study included the lateral radiographs and corresponding dental casts of 32 males and 35 females between 10 and 25 years of age, regardless of their skeletal and dental relationships. All subjects were white and none had undergone orthodontic therapy. Using lateral radiographs, upper and lower incisor angulations were assessed in reference to the NA line. These data were compared with third-order angles derived from direct dental cast measurements, which were performed using an incisor inclination recording appliance. Results: The third-order angle measurements recorded from the dental casts were a mean of 16.2 degrees (SD = 5.3 degrees) smaller than the axial inclination according to the NA line. In this sample, there was a range of 42.7 degrees for the TA variable (mean = 5.6 degrees, SD = 9.73 degrees) and 47 degrees for the 1 NA/deg variable (mean = 21.7 degrees, SD = 8.67 degrees). A highly significant correlation existed (r = 0.84) between Andrews' angle and the inclination estimated in reference to the NA line. Conclusion: Incisor inclination can be better estimated by recognizing the relationship between the torque angle and the axial inclination referred to the NA line. Third-order measurements using dental casts can offer a simple way to get an objective and rapid vision of the incisor's inclination

Effects of mechanical and bacterial stressors on cytokine and growth-factor expression in periodontal ligament cells

The goal of the study was to examine the effects of a mechanical (orthodontic force simulation by static compressive loading) and a bacterial (endotoxins from a heat-inactivated gram-negative periodontal pathogen) stressor on the expression patterns of factors that are key to regulating osteoclastogenesis and bone remodeling. Three experimental groups were formed with fifth-passage periodontal ligament (PDL) fibroblasts treated by the static application of compressive force (2 g/cm(2)), heat-inactivated aggregatibacter actinomycetemcomitans (1 x 10(7) cells), or both of these stressors combined. Real-time polymerase chain reaction (RT-PCR) was used to study gene expression of IL-6, IL-8, COX-2, IGF-1, VEGF, and MMP-13 in the 3 groups. Protein levels of COX-2, prostaglandin E2 (PGE(2)), and IL-8 production were quantified using immunoblotting and enzyme-linked immunosorbent assay (ELISA). The mechanical stressor upregulated the genes of COX-2, IL-8, IGF-1, and MMP-13 in PDL fibroblasts and the bacterial stressor upregulated IL-6, IL-8, COX-2 and MMP-13. Both stressors in combination upregulated VEGF and caused COX-2 gene expression to increase further; the latter effect was also detected at the protein level and indirectly via the enhanced production of PGE(2). We noted that the posttranscriptional regulation of IL-8 was induced by the mechanical stressor and influenced by PGE(2). While mechanical-stressor application increased the gene expression of COX-2, IL-8, and VEGF in the presence of the bacterial stressor, IL-8 production was posttranscriptionally regulated by the mechanical stressor, whereas COX-2 expression correlated with enhanced production of the inflammatory tissue hormone PGE(2), which exerted a suppressive effect on endotoxin-induced IL-8 production

Elongated styloid process in patients with temporomandibular disorders — Is there a link?

Background: Elongated styloid processes may display clinical signs that can easily be confused with symptoms associated with temporomandibular disorders (TMD). Thus, the present study aimed to investigate alterations of the styloid process in patients with TMD. Methods: Temporomandibular joint (TMJ) X-ray images of 192 patients with RDC/TMD diagnoses were examined retrospectively. On each side, the styloid process and mandibular ramus were evaluated regarding length as well as sagittal angulation. Data were statistically analyzed using two-way ANOVA, Pearson's r and Kruskal-Wallis test. In order to confirm the accuracy of the obtained X-ray measurements, the available cone-beam-computed tomographies (CBCT) of the subjects were also examined as reference standard and compared with the X-ray TMJ data by using Bland-Altman analysis. Results: In a group of TMD patients we assessed a mean styloid length of 40.8 mm over both genders. In female subjects the means of length and angulation of the styloid process were 40.4 mm and 54.9 degrees, male subjects showed means of 42.1 mm and 63.4 degrees. The mean height of the mandibular ramus in males was significantly higher than the same measurement in females (66.8 mm vs 59.7 mm). Styloid length in relation to ramus height (relative styloid length) was significantly larger in females. No significant correlations between RDC/TMD diagnoses and process length as well as process angle were found. A Bland-Altman analysis revealed conformity of CBCT and digital X-ray results. Conclusion: The mean styloid length measured in a group of TMD patients is referred to as elongated, whereas females showed longer styloid in relation to body height. However, it appears that alterations of the styloid are not related to TMD diagnoses. (C) 2018 Elsevier GmbH. All rights reserved

Dimeric link chain and instantaneous centers of rotation of the mandible

The primary aim of the study was to reveal whether the free opening movement of the mandible can be determined by only 2 rotational axes as suggested in recent literature. For this purpose, the free opening movement of the mandible was registered in 20 asymptomatic patients using an ultrasonic measuring system. Subsequently, the locations of the instantaneous centers of rotation (ICR) were determined directly from the raw data. In a second approach, the same data were used to construct a mandibular and maxillar rotational axis according to the dimeric link chain (DLC) concept. On the basis of the angular velocities around these 2 axes, the positions of the ICR were calculated in the sagittal-verticat plane. Calculating the ICR by the DLC method provides similar results to that of the conventional approaches. It can be concluded that the DLC method is a valid approach and that considering the planar mandibular movement as a movement with 2 degrees of freedom is justified. (C) 2007 Elsevier GmbH. All rights reserved

The mandibularly fixed hinge axis - investigation of patients with sound and pathological jaws

In former works, we had proved that test persons with sound temporomandibular joints (TMJs) used a mandibularly fixed hinge axis (MFHA) and were able to pilot the mandible by solely two kinematical degrees of freedom. We wondered if we could evaluate the MFHA the same way for patients who had problems with their TMJs. Actually, the MFHA could be determined likewise. The results could provide information on the reason for the distortion of the movement of the TMJs, which cannot be yielded by X-ray radiographs. (C) 2007 Elsevier GrnbH. All rights reserved

Effects of centric relation prematurities of the frontal teeth

Centric relation prematurities of frontal teeth are frequently found with patients who have severe orthodontic anomalies or received extensive restorative treatment. They can cause a range of symptoms ranging from Loosening of the teeth to temporomandibular disorders (TMD). The objective of this work has been to derive a mathematical description of the mandibular and periodontal forces generated by anterior prematurities for different incisor relations. In order to quantify the effect of contact area (location and inclination) and the tooth inclination, a two-dimensional mathematical approach was used. Vectorisation of the forces and bending moments makes it possible to predict under which conditions the load increase mainly affecting the anterior teeth can and may cause localized pain and eventually Loosening and flaring/crowding of the upper/lower incisors and under which conditions the temporomandibular joint wilt suffer a large increase in retrusive force, which potentially Leads to TMD. For 10 patients with anterior prematurities, analysis of the incisor relation was carried out. For all cases the conclusions drawn from the mathematical model were in full agreement with the reported symptoms, which could be successfully treated. (C) 2007 Elsevier GmbH. All rights reserved