The effect of implant splinting on the load distribution in bone bed around implant-supported fixed prosthesis with different framework materials: A finite element study.

Analysing the influence of implant splinting and its relation to different framework materials is a complex issue. The stiffness of framework materials and the overload of the implant system directly affect the final transferred load of the bone around implants. A finite element model of a long-span cementable implant-supported fixed prosthesis was created. Three materials were analysed for the framework: Titanium, gold alloy, and zirconia. The connection screws were first preloaded with 200 N. Two loading conditions were studied: The implant at the molar region was first loaded without splinting to the framework, and in the second condition, the implant was splinted to the framework. A total force of 500 N and 1000 N in 30° from the long axis of the framework were applied in buccal or distal direction on the implant system. The stresses and strains within the framework materials, implant system, and bone bed around the supporting implants were analysed. Loading the implant distally was associated with high stresses within the implant system in comparison to buccal loading. By splinting the implant, the stress in the implant system was reduced from 5393 MPa to 2942 MPa. Buccal loading of the implant was more critical than the distal loading. In the splinted condition of the implant, the stresses in the cortical bone were reduced from 570 MPa to 275 MPa.

The lateral leeway in the habitual intercuspation: experimental studies and literature review.

The habitual intercuspation is used ubiquitous for manufacturing small dental restorations. However, a little is known on its precision. The aim of the present study was therefore to investigate the unambiguity and accuracy of the habitual occlusion in mounted plaster casts from fully dentate persons. Eighty-one fully dentate volunteers, 36 women and 45 men aged 26.8 +/- 6.2 years (18-55 years), with minor fillings and no signs or symptoms of TMD took part in the experiments. Silicone impressions were taken, poured with stone plaster and the obtained casts mounted into Dentatus ARL(R)- articulators using an individual face bow transfer. Subsequently, the models were transferred to a custom-made measuring articulator where the lateral leeway and the accuracy of the hand-held habitual intercuspation were quantified in the condylar area. Measurements were repeated seven times with the upper cast pushed either to the maximum right or the maximum left intercuspation. The hand-held habitual intercuspation of upper and lower cast proved ambiguous in 57% of pairs of casts. The average lateral leeway of the habitual intercuspation in the condylar area was 0.10 +/- 0.05 mm (0-0.51 mm; median 0.07 mm) between the maximum right and left occlusal positions. The average accuracy of three repeated measurements was 0.22 +/- 0.09 mm (0.02-1.17 mm; median 0.16 mm). Natural occlusal surfaces in a full dentition do not guarantee an unambiguous habitual intercuspation of the plaster casts. The described leeway and technical limits might be possible causes for occlusal adjustments that are sometimes necessary when inserting restorations manufactured in habitual intercuspation.

Accuracy of check-bite registration and centric condylar position.

In a dentate subject a jaw relation can either be determined in maximum intercuspation and is as such given by the occlusal morphology, or the mandibular position can be allocated according to the centric position of the condyles. For comprehensive restorative treatment or analytic measures of the occlusion it is important to record the centric condylar position. Various registration methods have been described in the literature, but there is no consensus on which is the 'best'. The aim of the present study was therefore to assess the accuracy of various registration methods and evaluate a possible influence of the used materials. Four dentists were involved in the clinical part of the study, another was responsible for the measurements. Impressions were taken from 81 fully dentate volunteers. The casts were mounted by face-bow transfer and central-bearing-point (CBP) registration into Dentatus articulators. Subsequently the centric condylar position was determined with six different methods and materials, respectively. Each method was reproduced twice so that a total of 18 registrations was performed per patient. The mandibular positions which resulted from the individual registrations were then repeatedly compared in the condylar area using a computer supported specially modified measuring articulator. The accuracy was found best for the unrefined wax wafer registration (x=0.33 mm) and with an average of 0.44 mm worst when using acrylic wafers. The CBP and frontal jig methods as well as tin-foil and refined wax wafers showed an accuracy in-between these boundaries. The biggest measured mandibular displacement between any two registrations were considerably 2.0 mm. However, the described differences in accuracy between the various methods and materials proved statistically not significant. All investigated jaw registrations showed an accuracy of about 20 times the tactile fine sensibility of natural teeth which has to be taken into account when inserting fixed prosthetic restorations in centric condylar position. Despite meticulous clinical and technical procedures small occlusal adjustments are therefore almost unavoidable.

[Differential diagnosis of electronic TMJ tracings in dysfunction patients]. / Zur Differentialdiagnostik elektronischer Aufzeichnungen der Gelenkbahnen funktionsgestörter Patienten.

Only in a minority of cases do electronic TMJ tracings allow a clear differentiation between arthrogenous dysfunctions. To us, the major application of this recording technique appears to be the diagnosis of dislocations of the articular disk. Because of the great variability of possible dislocation patterns it is mandatory that the interpretation of electronic jaw tracings be standardized to avoid contradictory interpretations and to enhance the validity of this diagnostic tool. In trying to establish reliable, hardware-independent criteria for the evaluation of joint tracings in TMJ dysfunctions, it is the shape of the condylar inclination, the time-correlation of condylar path changes in all three planes and the direction of these changes, that are of utmost diagnostic significance: Repeated recordings of all functional movements are necessary to ensure tracings of high diagnostic value. The diagnostic potential of three-dimensional electronic jaw tracings can be further enhanced by guided jaw movements, e.g. functional compression, which result in characteristic changes of the tracings.

[Bennett movement. A literature review]. / Die Bennettbewegung. Eine Literaturübersicht.

The transversal movement of the human mandible on the balancing side is characterized by a downward, forward and inward movement of the condyle. Projected onto the horizontal plane, an angle between the midsagittal plane and the curve of the non-working condyle can be seen. This angle is called the Bennett angle. The rigid connection established by the body of the mandible results in a simultaneous rotation of the working side condyle. Additionally, there is a lateral shift of the mandible towards the working side called the Bennett movement. A review of the literature demonstrates that there are controversies regarding a physiological or pathological amount of Bennett movement, the direction and pattern, the reaction to occlusal equilibration and to the multitude of influencing factors. Unresolved aspects of the lateral movement of the mandible have been discussed and the direction of valuable investigations has been indicated.

[Studies on the transversal movement capacity of the TMJ]. / Untersuchungen zur transversalen Bewegungskapazität des Kiefergelenkes.

The range of transversal movements of the temporomandibular joint was determined by electronic measurements under different types of mandibular guidance. The results illustrate that there is a certain freedom in transversal movement. The mean transversal movement of the balancing condyle supported by the operator was 0.09 mm with a maximum at 0.4 mm. The results without guidance of the mandible or under tooth guidance were found to be smaller. The mean lateral operator-guided movement of the working condyle was 0.3 mm with a maximum at 0.9 mm whilst applying a horizontally directed pressure to the angle of the mandible. Furthermore after 0.5, 1 mm and 2 mm translation of the balancing condyle, the greatest transversal movements were observed again under operator-assisted guidance. The authors recommend rules for the selection of the adjustment of semiadjustable articulators, a wax-up to provide transversal freedom in movement and a technique to check fixed restaurations for proper occlusion and articulation.

[Anterior guidance compared with curvatures of sagittal TMJ excursions]. / Die Frontzahnführung im Vergleich mit Krümmungen sagittaler Kiefergelenkbewegungen.

The sagittal condylar paths of 17 healthy persons with class I occlusion were recorded by electronic axiography. Based on the radius values established for the geometry of each condylar path these could be compared with the protrusive facets of the incisors and the first premolar teeth. The results are important for our understanding of the movement profiles of the masticatory system. Correlations between the TMJ and the anterior teeth in terms of functional morphology were observed.

[Pre- and post-eruption effects on the functional morphology of the articulating structures]. / Prä- und posteruptive Einflüsse auf die Funktionsmorphologie der artikulierenden Strukturen.

Profile traces of latero- and protrusive facets of subjects with class-I-occlusion showed characteristic regular patterns in curvature and angle to the occlusal plane. There was no significant correlation between the laterotrusive surface profiles and the corresponding transversal movement of the condyle which was recorded electronically in 3 dimensions. Curvature morphology was plotted as a function of tooth eruption, development of the dental hard tissues, and tooth wear. In conclusion the results were applied to comprehensive occlusal restorations.

[Morphology of the laterotrusive paths in dentitions with normal function]. / Die Krümmungsmorphologie der Laterotrusionsbahnen im funktionsgesunden Gebiss.

The occlusal surface of the posterior teeth of 20 subjects with class-I-occlusion were analysed by means of an electronic profilograph in laterotrusion. Each of the curvatures recorded was defined by an approximated radius as well as its angle to the occlusal plane. The software used was specifically developed to suit this particular purpose. The data showed characteristic regularities. The results indicate that the average radius of the canine is longer than that of the molars. An alternating increasing and decreasing tendency of the angles to the occlusal plane was observed. The results suggest that the concept of canine-protected occlusion may be strengthened by the fact that there is a genetic determination of the canine dominance.

[Relationship between transversal joint guidance and buccal curve morphology]. / Beziehung zwischen transversaler Gelenkführung und laterotrusiver Krümmungsmorphologie.

The relationship between the morphology of the curvature of laterotrusion facets and tooth-guided tracings of the mediotrusive condyle path was studied in 20 probands with normal function. The varying inclinations of the dominant laterotrusion facets in cuspid-protected or group-guided occlusion has no bearing on the angle of the mediotrusive paths relative to the horizontal plane. The morphology of the buccal curve allows no predictions as to the direction of the mediotrusive path curvature. Only the movements of the idling condyle were influenced by the type of occlusal guidance. In lateral excursive movements of the mandible with the teeth in contact group-guidance frequently resulted in an upward movement of the laterotrusive condyle and thus to a compression of the intraarticular soft tissues. Although valid conclusions regarding any type of interdependence are impossible unless we are able to measure real tooth and joint movements simultaneously, the results of our study contradict other hypotheses at any rate.

[Adding to the diagnostic possibilities of MR tomography of the TMJ]. / Erweiterungen der diagnostischen Möglichkeiten der MR-Tomographie des Kiefergelenkes.

54 patients with arthrogenous dysfunctions were examined by means of MR tomography. Imaging of the position and shape of the intraarticular soft tissues was achieved in 64 out of the 67 TMJs examined. The results give rise to the expectation that MR tomography can be further developed to provide a reliable diagnostic tool not only for detecting dislocations in the sagittal plane, but also for imaging mediolateral alterations in the disk position, disk perforations and restrictions in the physiologic mobility of the articular disk.

[Comparative studies on the morphology of the curvature of the protrusive paths in anterior and posterior teeth]. / Untersuchungen zur Krümmungsmorphologie der Protrusionsbahnen.

The occlusal surfaces of 20 class I probands were recorded during protrusion with an electronic profilograph. Using a circular template, a definite radius could be attributed to each of the recorded curvatures. The radii and angles determined relative to the occlusal plane showed characteristic regularities. Thus, the radii of the anterior teeth are longer than those of the posterior teeth. The longest radius was generally found for the canines. The same tendency, although less pronounced, was observed with the angles. These phenomena can be explained by the fact that the masticatory system involves both "biting" and "grinding". Evolutionary and embryological theories have also been included in the discussion.

[Effects of projection errors on the pantographic diagnosis of TMJ dysfunction]. / Einfluss von Projektionsfehlern auf die pantographische Diagnostik bei gestörter Kiefergelenkfunktion.

Extraoral recording methods are bound to produce geometric projection errors. Mirror projections of the curvatures on both sides are a particular problem in clicking joints, thus complicating diagnosis. With the aid of magnetic resonance tomography it has been demonstrated in clinical examples that misinterpretations of the recordings can be avoided by means of computer-supported measuring systems providing accurate projection error correction. Furthermore, it is important that diagnosis be based not only on the usual sagittal plane recordings but also on additional information from the horizontal and frontal planes. Magnetic resonance tomography is then used to confirm the eccentric disc luxation established with the aid of the electronic recordings.

[Etiology of eccentric-posterior and centric-anterior displacements of the articular disc]. / Zur Atiologie exzentrisch-posteriorer und zentrisch-anteriorer Verlagerungen des Discus articularis.

40 patients with suspected intraarticular soft tissue displacement have been examined clinically and with the aid of electronic recording methods. The disc position has been verified by means of magnetic resonance tomography. Based on these results and on functional as well as anatomic considerations the development of various forms of articular disc displacement is discussed. Within the pathogenetic considerations particular attention must be paid to the role of dysfunctional excessive mouth opening and the loosening of the posterior cranial attachment of the disc on the base of the skull. This attachment is subjected to individual variations. An intact posterior cranial attachment of the articular disc via the superior stratum of the bilaminar zone at the base of the skull may result in an eccentric posterior displacement under existing dysfunctional loads. On the other hand, lack of repositioning forces due to a weak or loosening attachment may favor the development of centric anterior types of displacement.

[Forms of eccentric posterior displacement of the articular disc]. / Formen exzentrisch-posteriorer Verlagerungen des Discus articularis.

The temporomandibular joints of 40 patients with suspected intraarticular soft tissue displacement have been examined clinically and with the aid of electronic recording methods. The disc position has been verified by means of magnetic resonance tomography. The results demonstrate that Farrar's reciprocal clicking noises, interpreted as an anterior displacement of the articular disc, are not pathognomonic for the presence of a centric anterior displacement, but may also be associated with eccentric posterior disc displacement. Non-invasive imaging procedures show them as posterior displacements of the articular disc in eccentric mandibular positions. Eccentric posterior disc dislocation out of the joint space is associated with reciprocal clicking, i.e. an initial or terminal dislocation click during opening and a terminal repositioning click during closure. Centric anterior dislocation, on the other hand, was not found to be associated with terminal joint clicking during opening.

[Comparison of mechanical and three-dimensional electronic axiography]. / Vergleich der mechanischen und der dreidimensionalen elektronischen Achsiographie.

Three-dimensional electronic recording of the condylar path is a reliable technique for diagnosis of internal TMJ. Since three-dimensional imaging of dislocations or repositioning movements of the TMJ is diagnostically important but complicated to provide, three-dimensional electronic recording systems are superior to simple mechanical recording techniques. In diagnostically complicated cases the working diagnosis should be confirmed either by electronic recording of the functional movements of the lower jaw or by non-invasive imaging techniques. In our opinion this is very important in all those cases, in which an anterior repositioning splint is supposed to establish a physiological disk-condyle relationship. In view of the great variability of eccentric-posterior and centric-anterior dislocations of the disk and the difficulties of available examination techniques, this modified clinical approach should be given priority among all screening techniques for internal derangements of the temporomandibular joint.

[Diagnosis and therapy of myofacial dysfunctions. Study using systematic treatment planning]. / Diagnostik und Therapie bei myofacialen Dysfunktionen. Versuch einer systematischen Planung des Behandlungsablaufes.

A holistic treatment concept is a fundamental condition of the successful therapy of the myofacial-dysfunction-syndrome. Nevertheless the elimination of occlusal disturbances as well as the therapeutic alteration of the Condyle-Discus-Fossa-Relationship following logical principles are placed in the center of the dentists efforts.

[MR tomography of the temporomandibular joint using T1-weighted multislice-gradient echo-sequences]. / MR-Tomographie des Kiefergelenkes unter Anwendung T1-gewichteter Multislice-Gradientenecho-Sequenzen.

31 examinations of temporo-mandibular joints, using T1-weighted multislice gradient echo sequences have been performed. The short scan time of one minute and 50 seconds ensured that there were no movement artefacts in 28 cases. The position of the disc was visible in more than 90% of examinations. Degenerative changes in the cartilage and arthroses of the joint cannot be demonstrated adequately by the rapid sequences.