Distribution of bone thickness in the human mandibular ramus - a CBCT-based study

Background

The bone thickness of the human mandibular ramus is an important parameter in mandibular surgeries. The aim of this study was to systematically measure the bicortical bone thickness, the ramus dimensions and the position of the lingula. The measurements were tested on significant correlations to the patients’ parameters.

Methods

Based on CBCT scans 150 rami were reconstructed as 3D polygon surfaces. An anatomical grid was adapted to the ramus surface to mark the bone thickness measurement points and to achieve comparability between the measurements on different mandibles. The bone thickness, ramus height, ramus width and the gonion angle were measured. A cluster analysis was performed with these parameters to identify clinically relevant groups with anatomical similarities.

Results

The median distribution of the bone thickness was calculated and visualized in a pseudo-colour map. The mean ramus height was 44.78 mm, the mean width was 31.31 mm and the mean gonion angle was 124.8°. The average distance from the lingula to the dorsal tangent was 53% of the total width and its distance to the caudal tangent was 65% of the total height. Significant correlations between the bone thickness and the ramus proportions could be identified. Age and sex had no significant influence on the mean bone thickness. The measured rami could be divided into two groups by cluster analysis.

Conclusion

The dimensions of the human mandibular ramus can be determined from 3D reconstructed surface models from CBCT scans. Measurements could be made comparable by applying an anatomically oriented grid. A cluster analysis allowed the differentiation of two groups with different bone thickness distributions and geometries, which can be used for the optimization of osteosynthesis systems and their precision of adaptation to different ramus morphologies.

3D printed simulation models based on real patient situations for hands-on practice

During the last few years, the curriculum of many dentistry schools in Germany has been reorganised. Two key aspects of the applied changes are the integration of up-to-date teaching methods and the promotion of interdisciplinarity. To support these efforts, an approach to fabricating individualised simulation models for hands-on courses employing 3D printing is presented. The models are based on real patients, thus providing students a more realistic preparation for real clinical situations. As a wide variety of dental procedures can be implemented, the simulation models can also contribute to a more interdisciplinary dental education. The data used for the construction of the models were acquired by 3D surface scanning. The data were further processed with 3D modelling software. Afterwards, the models were fabricated by 3D printing with the PolyJet technique. Three models serve as examples: a prosthodontic model for training veneer preparation, a conservative model for practicing dental bonding and an interdisciplinary model featuring carious teeth and an insufficient crown. The third model was evaluated in a hands-on course with 22 fourth-year dental students. The students answered a questionnaire and gave their personal opinion. Whilst the concept of the model received very positive feedback, some aspects of the implementation were criticised. We discuss these observations and suggest ways for further improvement.

A prospective comparison of octyl-2-cyanoacrylate and suture in standardized facial wounds

Regarding the cosmetic results of wound closure using tissue adhesives as opposed to sutured wounds, most published studies are performed on children and with non-standardized lacerations, which makes it difficult to transfer the results to facial incisional wounds in adults. There are also conflicting conclusions about the cosmetic results. The purpose of this randomized prospective study was to compare the cosmetic outcomes of wound closure with sutures and octyl-2-cyanoacrylate in standardized facial wounds in adults. To compare very similar facial wounds, the infraorbital cut (lower eyelid incision) was used in 45 patients. The assessment was performed by patients and surgeons blind to the data. Phase-shifting profilometry was used to measure the profile of the scars. No early complications were observed in any group. The wound depth in the tissue adhesive group was significantly greater than in the suture group. There were no differences in the overall cosmetic results among all patients in the two groups. Interestingly, in the younger patients the result of the sutured wounds was superior to that of the adhesive-treated patients. The Dermabond skin adhesive provides a means of closure of facial surgical wounds without early complications, but adjustment of the edges of the wound and the cosmetic result in younger patients are less successful than with thin sutures.

Möglichkeiten zur objektiven Beurteilung von Narben

AIM OF THE STUDY

Cosmetic outcome of surgical treatment in the facial region is influenced by the appearance of the scar. The purpose of this investigation was to evaluate the objectivity and validity of various methods for the assessment of scars.

MATERIAL AND METHODS

45 patients undergoing facial surgery were examined three months after surgery. Three maxillofacial surgeons evaluated the wounds in a blinded manner using a visual analog scale (VAS). The patients also used the VAS for evaluation of their own scar. The surface of the scars was also measured by optical profilometry. Finally, the colour of the scars was analysed using both the RGB colour model and the HSV colour model.

RESULTS

Interestingly, there was no significant correlation between the values of R (red) as assessed by the three surgeons. However, there was a very strong correlation between the values of H (hue) as assessed by the three raters. The appearance of the surface was more important in the patients' evaluation than in the raters' assessment.

CONCLUSION

The hue of a scar as measured in terms of the H value in the HSV colour model is an objective and reliable measure for assessing the cosmetic outcome of facial surgery.

[Investigation of influencing variables on the computer-aided simulation of contacts in dynamic occlusion based on optically digitized plaster casts]

In dentistry, mechanical articulators with which mandibular movements can be reproduced in dentals casts play a major role. Commonly used semiadjustable articulators, however, have major limitations: On the one hand, the movement of the mandible is not reproduced exactly, on the other, they do not provide time-related information on jaw movement. Both problems can be solved by replacing the mechanical articulator by a digital simulation ("virtual articulator") based on digitized plaster casts and electronically recorded masticatory movements. We present a system for the 3D measurement of plaster casts in a skull-related, anatomical coordinate system using the fringe projection technique, and electronically recorded condylar movements. Using numerical algorithms, the contacts between upper and low jaw, and the angle of rotation of the temporomandibular joint can be computed for each movement in dynamic occlusion. Taking the data recorded from a patient as an example, the influence of the accuracy of the digitization of plaster casts on the computation of the rotation of the temporomandibular joint is discussed in relation to the anatomy of the masticatory apparatus.

[Computer-assisted development of epitheses after optical recording of facial defects]

A major drawback of conventional impression techniques used for customizing facial prostheses is the fact that pressure applied deforms soft tissue, thus reducing accuracy and causing patient discomfort. A possible solution is the use of optical 3-D coordinate measuring techniques, such as the fringe projection technique, which enables precise and contact-free recording of facial surfaces. The application of this method is demonstrated on a patient who lost his left eye and part of the jaw bone during surgery for cancer. 3-D CAD software that supports the construction of a facial prosthesis from the data obtained has been developed. For this purpose, spline functions are used to define border curves, and the intact half of the face is used as a model for the prosthetic surface. The resulting digital data are used to construct first a model made of synthetic resin, and then a final wax model with the aid of rapid prototyping techniques.

The influence of maxillary central incisor position in complete dentures on /s/ sound production

STATEMENT OF PROBLEM

The insertion of prosthodontic restorations often leads to speech defects, most of which are transient but nevertheless a source of concern to the patient. For the dental practitioner, there are few guidelines on designing a prosthetic restoration with maximum phonetic success.

PURPOSE

This study investigated the effect of different maxillary central incisor positions on phonetic patterns.

MATERIAL AND METHODS

The inclination angle of central incisor blocks in duplicate complete maxillary dentures was changed in a range of -30 degrees to +30 degrees from the original position (0 degrees). Test words and sentences were acoustically analyzed. Spectral parameters such as first peak, noise band (defined by upper and lower limits of the most intensively blackened frequency area), Fast Fourier Transformation power spectrum, energy spectrum, and time were investigated. Influences of oral stereognosis, hearing, and age as cofactors on /s/ articulation were also taken into account.

RESULTS

The change of incisor block angle in both directions usually caused a poorer execution of the /s/ sound. The labial angulation seemed to have a greater effect than the palatal angulation. The most significant changes were those in the noise band and energy spectrum.

CONCLUSION

Immediate phonetic adaptation of prosthetic restorations in the maxillary incisor region can be achieved only if the original position of the natural teeth is transferred to the denture. Although these misarticulations are, in most cases, likely to disappear within a few weeks, they may persist and even lead to psychosocial problems. A better understanding of the causes of misarticulation and the limits of adaptation according to certain morphologic parameters of dentures is important.

A pivoting appliance for intracavitary brachytherapy in patients with reduced mouth opening

PURPOSE

The risks of radiotherapy to normal tissues are well known. In many cases, a tumor patient suffering a relapse cannot undergo radiotherapy a second time. One exception may be the local application of brachytherapy. Afterloading devices allow the position of radiating materials near the site for treatment exactly according to three-dimensional treatment planning. This report shows the technical procedure for the fabrication of an intracavitary afterloading radiation device.

MATERIALS AND METHODS

A 48-year-old woman who had received neutron radiotherapy and tumor surgery for adenoid cystic carcinoma had to be treated for relapse. The mouth opening was limited to 15 mm. The mixing tip of a silicone impression system was used as an axis for a pivoting appliance.

RESULTS

Two years after reradiation, the patient was free of relapse symptoms, although an increased limitation of mouth opening was recorded.

CONCLUSION

Even if the mouth opening is severely limited after tumor surgery and/or radiation, intracavitary brachytherapy still can be performed in edentulous patients using a pivoting device.

Three-dimensional quantification of color-marked occlusal paths on anatomically oriented casts

STATEMENT OF PROBLEM

The analysis of occlusal contacts on mounted diagnostic casts is an important task in prosthetic diagnostics. However, it is still restricted mainly to qualitative aspects because existing measuring techniques fail to provide 3-dimensional data for more than a few single points in acceptable time.

PURPOSE

The aim of this study was to develop a method for quantifying occlusal contacts and paths by using anatomically oriented diagnostic casts and to design the method to allow fast acquisition of digital 3-dimensional coordinates.

MATERIAL AND METHODS

Plaster casts with color-marked contacts were digitized optically with a profilometric system based on the fringe projection technique. Digital camera images taken simultaneously were used to define the contact areas by marking them either manually or automatically with the help of image-processing routines. Three-dimensional coordinates were determined by finding the corresponding points within the profilometric data set.

RESULTS

Color-marked contact areas on diagnostic casts were successfully digitized with a computer-controlled, automatic setup in approximately 30 seconds. The accuracy of the acquired 3-dimensional data was estimated to be better than 60 microm in lateral and 30 microm in height resolution. The data set was visualized and evaluated in a skull related coordinate system.

SUMMARY

This study verified the use of a new tool to quantify color-marked occlusal contacts on diagnostic casts in terms of spatial coordinates. The resulting digital data may be stored easily and analyzed numerically as well as visualized 3-dimensionally with computer graphic equipment. Because the anatomic orientation of the casts is maintained throughout the measurement process, it is possible to compare the data with electronically registered condyle paths and therefore to investigate, for example, their relation to the corresponding guidance paths of the frontal teeth and the canines in dynamic occlusion.

Endoscopic double-pulse electronic-speckle-pattern interferometer for technical and medical intracavity inspection

An endoscope electronic-speckle-pattern interferometer (ESPI) camera system is presented that can be applied to examinations of technical objects as well as for in vitro and in vivo minimal invasive medical diagnostics. Integration of optical fibers for the guidance of a cw-laser beam and an endoscopic imaging system yield a compact ESPI system that opens up new possibilities for highly sensitive interferometric intracavity inspection under handheld conditions. A CCD camera in combination with a fast frame-grabber system allows dynamic image subtractions at a frequency rate of as much as 25 Hz with high fringe contrast. Results from investigations of technical objects and biological objects in vitro and in vivo are obtained. In endoscopic minimal invasive therapy this method could substitute for the missing operator's tactile contact with the treated tissue by replacing it with visual information (endoscopic taction).

Clinical anatomy and palpability of the inferior lateral pterygoid muscle

STATEMENT OF PROBLEM

The intraoral palpation technique of the inferior belly of the inferior lateral pterygoid (ILP) muscle is a standard diagnostic examination method for temporomandibular joint dysfunction syndrome, although different studies have revealed inconsistent results.

PURPOSE

This study assessed the feasibility of the ILP muscle palpation by a simulated clinical setting.

MATERIAL AND METHODS

Three dentists performed a bilateral palpation of the ILP muscle in 53 fresh and unfixed human cadavers and decided whether the muscle was palpable or unpalpable. In a second step, it was observed through the dissected infratemporal fossa, whether the examiner's finger did or did not touch the ILP muscle by simulating the performed palpation. Palpatory findings were supplemented by 1-dimensional measurements for determination of topographic relations of the ILP muscle within the infratemporal fossa. For statistical analysis, sensitivity, specificity, and negative and positive predictive values of the palpation technique were calculated. Interexaminer agreement was estimated with the kappa value.

RESULTS

In 86 of 106 dissected specimens, a superficial fascicle of the medial pterygoid muscle was found in direct proximity to the ILP muscle. In these cases, a residual distance of 7.8 +/- 3.2 mm remained between the ILP muscle and buccinator fascia indented by the tip of the examiner's finger. In 10 of 20 specimens with an absent superficial fascicle, the finger was able to reach the ILP muscle.

CONCLUSION

It is recommended that the ILP muscle palpation technique should no longer be considered as a standard clinical procedure because it is nearly impossible to palpate the ILP muscle anatomically and because the risk of false-positive findings (by palpation of the medial pterygoid muscle) is high.

Three-dimensional visualization and quantification of the mandibular articular surface by optical profilometry

The aim of this study was to introduce a nondestructive optical technique for the quantitative assessment of natural biological surfaces as demonstrated with the example of the articular surface of the human temporomandibular joint. The computer-assisted quantitative evaluation of the surface is realized by the acquisition of three-dimensional images via the optical technique of phase measuring profilometry. After mathematical processing of the data set the resulting image can be visualized as three-dimensional object surface reconstructions or as grid surfaces from which arbitrary sections may easily be extracted. From such single sections we can calculate a value that represents the degree of height deviations of the section profile and can be regarded as a parameter for the surface roughness. Further quantitative information about the surface topography is provided by the Fourier transform analysis of the profiles. The Fourier spectrum contains information about the spatial distribution of roughness-causing protuberances along the overall surface. As an example one healthy condyle and one remodeled condyle from macerated cadaver mandibles were investigated. For the two samples evaluated we calculated a mean surface roughness of the entire articular surface with a value of 0.03 +/- 0.005 mm for the healthy condyle with its smooth surface and a value of 0.14 +/- 0.009 mm for the remodeled condyle. We recommend optical profilometry as a sophisticated technique for a more objective and quantitative pathological classification of articular surfaces and similar objects.

Three-dimensional acquisition and visualization of dental arch features from optically digitized models

A method for the acquisition and evaluation of 3D coordinates from anatomically oriented plaster casts is presented, which is based on optical phase shifting profilometry (a fringe projection technique). With the computer-controlled setup, measurements from different views can be combined to obtain a complete three dimensional reconstruction of the model surface. To allow faster evaluation, the result is converted into a range image. From this digital data set the characteristic features like cusp tips can be identified and located semi-automatically. Based on these marks, quantitative values for differences between situation models like local displacements, e.g. during orthodontic treatment, can be determined. The results are visualized as interactively controllable 3D computer graphics, which helps to make spatial relations clearer.