Functional states of mandibular movements and synovial pumps of the temporomandibular joint. Is it possible to provide a biomechanically correct replacement for the TMJ?

Due to its complexity, there is currently an incomplete understanding of temporomandibular joint (TMJ) function, especially in relation to the morphological interplay of the condyle and the disc as well as the disc, the Os temporale and the lateral pterygoid muscle. This also holds true for synovial flow and synovial pumps, the existence of which we postulate and for which we present a theory of their mechanism. In view of the complexity of mandibular movements and the morphology and function of the TMJ, we need to know how precisely a reconstruction of the TMJ, if necessary, must be adapted to nature. An analysis of the morphology of the functional states of the mandible, as well as the synovial pump system, should at least provide a basis for moulding reconstructions.

Biomechanics of the mandible and growth extension.

BACKGROUND AND OBJECTIVE: One way of determining the direction of growth of the mandible is to consider the temporomandibular joint and movement of the mandible as a four-joint gear system, regarding growth then as an extension of the gear system. Our aim was to examine any correlations between the type of biomechanical growth extension and change in the maxilomandibular relation after Class II therapy. SUBJECTS AND METHODS: A total of 130 lateral cephalograms-before and after orthodontic treatment-were available from 65 adolescent class II patients with open bite or deep bite. The two lateral cephalograms from each patient were superimposed on the occlusal plane. Cephalometric values and the vertical base point deviation were determined from biomechanical analyses, together with three distances and three angles. RESULTS: No correlation between the cephalometric data and distances or angles were observed. Although there were no significant differences in the distances, we did note significant differences in all three angles (p < 0.05). CONCLUSION: If gear system extension during growth is considered, this can be interpreted as meaning that the occlusal plane of those patients with an initially open bite dropped during treatment, but that it rose in patients with an initially deep bite.

Changes in insulin like growth factors, myostatin and vascular endothelial growth factor in rat musculus latissimus dorsi by poly-3-hydroxybutyrate implants.

The present study aimed at researching the synergistic effect between an ectopic bone substitute and surrounding muscle tissue. To describe this effect, changes of insulin like growth factors (IGF1, IGF2), myostatin (GDF8) and vascular endothelial growth factor (VEGF) mRNA content of 12 Wistar-King rats musculus latissimus dorsi with implanted poly-3-hydroxybutyrate (PHB) scaffold were examined after 6 and 12 weeks. At each time interval six rats were killed and implants and surrounding tissues prepared for genetic evaluation. Eight rats without any implants served as controls. RNA was extracted from homogenized muscle tissue and reverse transcribed. Changes in mRNA content were measured by Real-Time PCR using specific primers for IGF1, IGF2, GDF8 and VEGF. Comparing the level of VEGF mRNA in muscle after 6 and 12 weeks to the controls, we could assess a significant increase of VEGF gene expression (p<0.05) whereas the level of mRNA expression was higher after 6 than after 12 weeks of treatment. Expression of IGF1 gene was also significantly increased as compared to the controls over the observed period of time (p<0.05). In the case of the IGF2 gene, the expression was significantly elevated after 6 weeks (p<0.05), but not significantly increased after 12 weeks (p>0.05). We observed a significantly decreased GDF8 gene expression (p<0.05) both after retrieval of implants after 6 as well as after 12 weeks. Moreover, mRNA level of GDF8 after 6 and 12 weeks were comparable the same. Our results show that PHB implants in rat musculus latissimus dorsi interact with the surrounding muscle tissue. This interaction works itself on growth potential of the muscle.

How do spinal segments move?

PURPOSE: To study and clarify the kinematics of spinal segments following cyclic torques causing axial rotation (T(z) (t)), lateral-flexion (T(x) (t)), flexion/extension (T(y) (t)). METHODS: A 6D--Measurement of location, alignment, and migration of the instantaneous helical axis (IHA) as a function of rotational angle in cervical, thoracic, and lumbar segments subjected to axially directed preloads. RESULTS: IHA retained an almost constant alignment, but migrated along distinct centrodes. THORACIC SEGMENTS: IHA was almost parallel to T(z) (t), T(x) (t), or T(y) (t), stationary for T(x) (t) or T(y) (t), and migrating for T(z) (t) along dorsally opened bows. IHA locations hardly depended on the position or size of axial preload. LUMBAR SEGMENTS: IHA was also almost parallel to T(z) (t), T(x) (t), or T(y) (t). In axial rotation IHA-migration along wide, ventrally or dorsally bent bows depending on segmental flexional/extensional status. Distances covered: 20-60mm. In lateral-flexion: IHA-migration to the left/right joint and vice versa. In flexion/extension IHA-migration from the facets to the centre of the disc. CERVICAL SEGMENTS: In flexion/flexion IHA was almost stationary for and parallel to T(y) (t). In axial rotation or lateral-flexion IHA intersected T(z) (t)/T(x) (t) under approximately -30 degrees /+30 degrees. CONCLUSIONS: Generally joints alternate in guidance. Lumbar segments: in axial rotation and lateral-flexion parametrical control of IHA-position and IHA-migration by axial preload position. Cervical segments: kinematical coupling between axial rotation and lateral-flexion. The IHA-migration guided by the joints should be taken into account in the design of non-fusion implants. FE-calculations of spinal mechanics and kinematics should be based on detailed data of curvature morphology of the articulating surfaces of the joint facets.

[A novel knee endoprosthesis with a physiological joint shape. Part 1: Biomechanical basics and tribological studies]. / Eine neuartige Knieendoprothese mit physiologischer Gelenkform. Teil 1: Biomechanische Grundlagen und tribologische Untersuchungen.

The natural tibiofemoral joint (TFJ) functions according to a roll-glide mechanism. In the stance phase (0-20 degrees flexion), the femur rolls backwards over the tibia plateau, while further flexion causes increased gliding. This kinematics is based on the principle of a quadruple joint. The four morphological axes of rotation are the midpoints of the curvatures of the medial and lateral femoral condyles and the medial and lateral tibia plateau. In addition, the medial and lateral compartments are shifted a few millimetres in a sagittal direction, the medial tibia plateau being concave and the lateral plateau convex. In most knee arthroplasties, these factors are not taken into account; instead they are equipped with symmetrical medial and lateral joint surfaces. Thereby, the midpoints of the curvatures of the sagittal contours of the lateral and medial joint surfaces, on the femoral as well as on the tibial sides, create a common axis of rotation which does not allow a physiological roll-glide mechanism. The goal of this study was therefore to report on the biomechanical basis of the natural knee and to describe the development of a novel knee endoprosthesis based on a mathematical model. The design of the structurally new knee joint endoprosthesis has, on the lateral side, a convex shape of the tibial joint surface in a sagittal cross section. Furthermore, from a mathematical point of view, this knee endoprosthesis possesses essential kinematic and static properties similar to those of a physiological TFJ. Within the framework of the authorization tests, the endoprosthesis was examined according to ISO/WC 14243 in a knee simulator. The abrasion rates were, thereby, lower than or at least as good as those for conventional endoprostheses. The presented data demonstrate a novel concept in knee arthroplasty, which still has to be clinically confirmed by long term results.

Axial rotation in the lumbar spine following axial force wrench.

The report presents measurements of axial rotation of lumbar motion segments (L1/L2, L3/L4, L4/L5), particularly with small angles of rotation (in the range of +/-1 degrees) following axial force wrenches. The investigation focussed on determining the influence of geometrically varying configurations in axial wrench (consisting of axial torque and axial force) applied on the kinematics (as defined by the migrating instantaneous helical axis, IHA) of lumbar motion segments under constant resulting axial force, and relating IHA-migration to anatomical structures. In all segments, IHA migrated over several centimetres (up to 6 cm). The main portion of IHA-migration was linked to the angle of rotation interval of +/-1 degrees. 3. The shape of the IHA-migration was greatly dependent upon the position of the force line F(z). The-force-wrench-dependent wide IHA-migration found for the rotational angle interval of +/-1 degrees suggests that joint guidance predominates in segment kinematics. The segment kinematics can be adjusted by means of the geometrical configuration of the force wrenches. The design of non-fusion spine implants and FE calculations have to take into consideration joint guidance and muscular force distributions with small intervals of axial rotation.

Knee motion analysis of the non-loaded and loaded knee: a re-look at rolling and sliding.

Many studies of knee motion have been reported in the literature over more than 100 years. Of particular interest to the analysis presented here is the work of the Freeman group, who elegantly measured tibio-femoral kinematics in studies made on cadavers and the knees of living individuals using MRI, anatomical dissection and RSA. We examined and re-evaluated the data collected by Freeman's group and suggest that their conclusion should be considered to be incorrect, since their methods of evaluation were oversimplified from the mathematical and physical perspectives. By applying appropriate methods, however, it is possible to show that the same data yield important insights into physiological knee kinematics and reveal that the rolling-sliding relationship depends on the degree of flexion and on joint load in the medial and lateral compartment, as well. In the initial range of flexion, a considerable amount of rolling was found to occur. Based on this analysis, it is possible to gain useful insights of value for the design of total knee replacements.

Different bone sesitivity to malformations induced by procarbazine in fetal rats.

The study aimed at to induce cleft-lip-alveolus-palate (CLAP) applying procarbazine in rat fetuses at the 14(th) day of pregnancy, to supply thiocyanate and/or folic acid sufficient for preventive treatment and subsequently to investigate cleft extent in the palatal area as well as bone maturity. In this animal model, female primiparous inbred rats (LEW.1A) were used. The gravid animals were separated into treatment groups: group K (control), group P (procarbazine), group TP (thiocyanate and procarbazine) and group FTP (folic acid, thiocyanate, procarbazine). The results reveal that procarbazine may induce clefts in the palate area. Clefts occurred most frequently in group TP and mainly comprised subtotal clefts of the posterior secondary palate. As for palatal length, group FTP displayed the longest palate which was significantly different only from group K. A different picture was shown for the secondary palate with group TP displaying the shortest values which were significantly different from those in groups K, P, and FTP. Thus, group TP showed the most marked negative changes both for cleft frequency and palatal length as compared to group K and the other groups. The preventive application of either thiocyanate (TP) or thiocaynate and folic acid combined (group FTP) failed to completely prevent cleft formation in the palate area. In conclusion, a preventive effect on palatal clefts and growth inhibition could not be proved for the vitaminoid thiocyanate.

Physiological functions of the human finger.

Using morphological data describing the physiological curvature morphology of the corresponding articulating surfaces in each finger joint, it is shown that a) the flexion of each finger joint is described by two angles of flexion; b) in each finger joint, a "pump mechanism" for synovial fluid is present whose function is to lubricate and nourish the joint cartilage and c) finger posture has six kinematic degrees of freedom (DOF). Since six muscle forces control finger posture, the relationship between the muscle forces and finger posture is unambiguously described. The states of flexion of the interphalangeal joints restrict possible flexions in the metacarpophalangeal joint. Since the muscle forces act simultaneously on all three finger joints, the interdependence of the flexional states in the three finger joints can be attributed to the alignment of the lines of force and their sites of insertion, as a function of the corresponding flexion in the joints.

Mandible, maxilla and cervical spine--a functional unit?

The motion patterns of mandibular points were recorded in vivo in closed, free movements of the mandible parallel to the sagittal-vertical plane. The points ran along loops which were valued by their area and length. All points whose loops included the same area under regarding the sense of circulation formed a straight line. Lines belonging to different areas were parallel. When the absolute areas of the oops were plotted for particular points a hollow depression with two minima resulted. The point that showed the lowest minimum in the depression corresponded to the position of the neuromuscular mandibular axis of rotation. The points running along equal loop lengths formed elliptical lines with a minimum below the condyle. The lines of constant loop area and loop length were overlaid with lateral radiographs, to match the patterns of motion with anatomical structures. The mandibular axis of rotation lay mostly cranial anterior of the condyle whereas the point with the shortest path lay mainly below this axis point, inside the bony structures. The row of teeth in the maxilla was found to be located below the line of minimal loop lengths. The cervical spine was arranged along the depression of the minimal absolute areas.

Soft tissue integration in the neck area of titanium implants--an animal trial.

Dental implant materials are required to enable good apposition of bone and soft tissues. They must show sufficient resistance to chemical, physical and biological stress in the oral cavity to achieve good long-term outcomes. A critical issue is the apposition of the soft tissues, as they have provided a quasi-physiological closure of oral cavity. The present experiment was performed to study the peri-implant tissue response to non-submerged (1-stage) implant installation procedures. Two different implants types (NobelBiocare, NobelReplace Tapered Groovy 4.3 x 10 mm and Replace Select Tapered TiU RP 4.3 x 10mm) were inserted into the right and left sides of 8 domestic pigs (Sus scrofa domestica) mandibles, between canines and premolars and immediately provided with a ceramic crown. Primary implant stability was determined using ressonance frequency analysis. Soft tissue parameters were assessed: sulcus depth (SDI) and junctional epithelium (JE). Following 70 days of healing, jaw sections were processed for histology and histomorphometric examination. Undecalcified histological sections demonstrated osseointegration with direct bone contact. The soft tissue parameters revealed no significant differences between the two implant types. The peri-implant soft tissues appear to behave similarly in both implant types.

Cathepsin C gene variants in aggressive periodontitis.

Cathepsin C (CTSC) mutations are known to cause Papillon-Lefèvre syndrome. The aim of this study was to examine the association of CTSC genotype with susceptibility to non-syndromic aggressive periodontitis. The CTSC gene was analyzed in 110 persons with generalized aggressive periodontitis in comparison with 78 control individuals, after identifying different variants in a cohort of 100 persons. Five out of 19 discovered variants were included in this association study, representing 5 single-nucleotide polymorphism groups in tight linkage disequilibrium. The relevance of genotypes on enzyme function was examined. The carrier frequency of the missense variant p.I453V was significantly increased in persons with disease compared with healthy control individuals (17.3% vs. 6.4%, p < 0.05). CTSC activity in leukocytes from individuals harboring this variant was significantly reduced (119.8 Delta OD/min*10(5) cells, 95% confidence interval 17.4-174.9, p = 0.018). No influence of promoter variants was found on mRNA expression. The results support the hypothesis that CTSC gene variants contribute to increased susceptibility in generalized aggressive periodontitis.

Effect of bone conditioning on primary stability of FRIALIT-2 implants.

BACKGROUND: Primary stability is crucial to implants used for orthodontic anchorage. Bone condensing to enhance primary stability is controversial. MATERIAL AND METHODS: Fourteen Frialit-2-stepped screw and cylinder implants were placed in the median palatine sutures of 22 cadaveric human heads. In half of both types, the implant bed was prepared using a Frialit Bone Condenser. Primary implant stability was evaluated using non-invasive resonance frequency analysis. Moreover, the bone-implant contact area was examined histomorphometrically and radiographically. RESULTS: Bone condensing yielded a slightly, yet not significantly increased implant stability quotient compared with a conventional technique. In spongy bone, a significant histomorphometric increase of bone-implant contact (P<0.0001) and a significant increase of radiographic density was revealed for both implant types, while no significant changes were observed within the compact area. CONCLUSION: The study shows that bone condensing yields an improved histologic implant-bone contact only in spongy bone, which was paralleled by radiographic-densitometric findings.

Ritually induced growth disturbances and deformities of the orofacial system--a contribution to cranial morphogenesis.

Numerous ritual acts involving the skull result in orofacial changes. The present study focuses on ritual acts of Brazilian Zoé Indians. A distinct deformation effect of the ritual act (wearing a lip-plug) on the morphology of the orofacial system is demonstrated and documented using jaw models. The studies show that the lip-plug significantly influences tooth position and jaw growth. While the maxilla displays palatal displacement of the lateral incisors and elevation of the palate, retraction occurs in the mandible depending upon plug size. Additionally, both the plug and the nutritional habits of the Indians induce marked abrasion of all teeth. Moreover, it is shown that the duration of lip-plug wear is an essential determinant of sustained orofacial changes.

Histological and fluorescence microscopic examination of the bone/implant interface in orthodontic miniscrews (Mondeal).

The temporary nature of orthodontic implants demands optimisation of size and design in order to minimise damage and risk to the patient. Slender and shorter miniscrews offer the advantage over conventional implants of easier and more ubiquitous positioning with minimised risk of injury to neighbouring anatomical structures such as tooth roots, nerves or vessels. The question is raised, however, as to what extent these advantages are gained at the price of diminished stability or a more unfavourable bone interface. In order to evaluate the screw/bone interface, 14 orthodontic miniscrews (Mondeal Medical Systems, diameter: 1.5 mm, length: 9 mm) were inserted into the right and left mandibles of 7 pigs (Sus scrofa domestica). Bone fluorochromes were administered in a defined order for polychrome sequencing. The samples gathered after 70 days were analysed using histological techniques and fluorescence microscopy. The lower part of the self-tapping thread displayed undisturbed bone apposition. Fluorescence microscopy revealed remodelling and bone apposition within the thread grooves.

The use of ceramic drills on a zirconium oxide basis in bone preparation.

The favourable mechanical properties and high biocompatibility of the newly developed mixed ceramics composed of zirconium oxide and aluminium oxide have continuously extended the scope of their application. Rotating instruments on a zirconium oxide basis are regarded as superior to metal burs in dentoalveolar surgery in terms of favourable temperature effects on the surrounding bone tissue and the economic advantage that they wear slowly, enabling them to be used repeatedly. In this study ten round burs made of zirconium oxide and aluminium oxide mixed ceramics were used for typical dental-alveolar preparation types on an explanted pig jaw. Prior to the first and following the tenth application a scanning electron microscopic (SEM) analysis of possible wear signs was conducted. However, this revealed no evidence of wear or resulting loss of sharpness.

Bacterial colonisation of interior implant threads with and without sealing.

Premature loss of dental implants is due, apart from mechanical factors, to germrelated inflammation. Gaps and hollow spaces within the implant system, for example the gap between implant and abutment in the two-part implant system, may provide a bacterial reservoir causing or maintaining inflammation. The bacterial spectrum involved is similar to that found in periodontitis. This in vitro study aimed to scrutinise the capability of Porphyromonas gingivalis (DSM 20709), the bacterium blamed for inducing peri-implantitis, to pass the implant/abutment gap in titanium implant systems used for orthodontic anchorage and to remain vital in the interior. Additionally, the in vitro effectiveness of gutta percha for gap sealing was examined. Twelve titanium implants (Straumann, diameter: 3.3 mm, length 5.5 mm) were provided with abutments at a defined torque (20 Ncm), six of which were sealed with gutta percha before screwing in the abutment. Subsequently the implants were placed in a nutrient solution (thioglycolate boullion with haemin-menadione solution) that contained Porphyromonas gingivalis. Microbiological specimens were sampled from the implant interiors after 24 and 72 hours and analysed using culture methods. There was evidence that penetration of the periodontal pathogen Porphyromonas gingivalis to the implant interior may occur as early as after 24 hours. Microbes were also detected in the interior of implants sealed with gutta percha. The abutment/implant interface in vitro provides a microbiological leakage for the prospective peri-implantitis-inducing bacterium Porphyromonas gingivalis. Survival of the bacterium is possible in the interior, so that development of a bacterial reservoir is assumed. This in vitro trial produced no evidence that sealing with gutta percha is an effective means to prevent secondary bacterial colonisation in the implant interior.

The survival and proliferation of fibroblasts on orthodontic miniscrews with different surface treatment: an in vitro study.

It is of fundamental importance for prosthodontic and orthodontic applications that there is a short osseointegration time of dental implants without inflammation of the surrounding tissue. In addition to the chemical properties of the implant material, the surface morphology is an equally critical parameter. The objective of this work was to study the effect of two simple surface treatments on the survival and proliferation of fibroblasts. Three groups of orthodontic miniscrews (Mondeal) were used. One group was given an airflow (EMS, Schweiz) treatment, the second was sand-blasted in the area of the threading and a third group served as a control. After preparation sterilised screws were cultured in vitro with fibroblasts (L-929). The metabolic cell activity on the implant surface was determined after 24, 48 and 120 hours using the alamarBlue assay and a count of DAPI labelled fibroblasts was performed with a fluorescence microscope. After 24 hours, but not at 48 hours and 120 hours, the metabolic activity of the fibroblasts was slightly decreased for the airflow screw group. Generally, no significant difference was found regarding metabolic activity and proliferation of fibroblasts within the different groups.

The application of bone graft substitutes for alveolar ridge preservation after orthodontic extractions and for augmentation of residual cleft defects.

The use of bone substitute materials in orthodontics is to be considered prior to orthodontic space closure after tooth extraction during the treatment of marked crowding as well as for treatment of residual defects in cleft-lip-and-palate children. In both cases the common objective is structure preservation or augmentation of the alveolar ridge. The demands to be made on the synthetic bone graft substitute comprise not just complication-free and safe use but also the chance of early tooth movement into the treated defect area with sufficient stability of the new tooth position.

Wound management after the application of bone grafting substitutes in the orofacial region.

Surgical dressing after the application of bone grafting material depends on the type and size of the defect. A complete and tension-free wound closure has proved to be successful. In this context the infection problem needs special attention. Bone graft substitutes with an adequate surface structure, porosity and chemical properties, in combination with sufficient blood circulation, hold osteoconductive potential. They serve as a guide rail for the osteoblast-induced formation of new bone tissue, which at best may lead to complete replacement of the grafting material.