Biomechanical finite-element investigation of the position of the centre of resistance of the upper incisors

The position of the centre of resistance (CR) is an essential parameter regarding the planning of orthodontic tooth movements. In the present investigation, the combined CR of the upper four incisors was determined numerically using the finite-element (FE) method. Based on a commercially available three-dimensional data set of a maxilla, including all 16 teeth, as well as known and earlier determined material parameters, FE models of the upper incisors and their surrounding tooth-supporting structures were generated. In the FE system, the model of the anterior segment was loaded with torques of 10 Nmm each at the lateral incisors. The FE model indicated that the individual incisors moved independently, although they were blocked with a steel wire of dimension 0.46 x 0.65 mm(2). The individual CRs were located at 5 mm distal and 9 and 12 mm apical to the centre of the lateral brackets. Thus, the classical view of a combined CR for the anterior segment was disproved and the planning of orthodontic tooth movements of the upper incisors should no longer be based on that concept.

Parathyroid hormone modifies human periodontal ligament cell proliferation and survival in vitro

BACKGROUND AND OBJECTIVE

Periodontal ligament (PDL) cells show traits that are typical of osteoblasts, such as osteoblastic marker gene expression and the ability to respond to parathyroid hormone (PTH) stimulation in an osteoblast-like manner with respect to differentiation and local factor production. In the present study, we hypothesized that human PDL cells might respond to PTH stimulation with changes in proliferation and cell survival and thereby provide another mechanism by which PTH might affect the reparative potential of PDL cells. We speculated that the maturation state of the cells and the mode of PTH(1-34) administration would have an impact on the cellular response.

MATERIAL AND METHODS

PDL cells were challenged with PTH(1-34) intermittently or continuously at different maturation states. Cell number, 5-bromo-2-deoxyuridine (BrdU) incorporation, DNA fragmentation, nitric oxide production and the duration of the PTH(1-34) effect were determined.

RESULTS

Intermittent PTH(1-34) treatment of preconfluent cells caused a significant increase in proliferation and DNA fragmentation, whereas in more mature cells, proliferation was less enhanced while apoptosis was more pronounced than in immature cells. Continuous PTH(1-34) exposure did not alter proliferation in any maturation state but increased DNA fragmentation in preconfluent cells. PTH(1-34) prevented etoposide-induced apoptosis after 6 h but no longer after 24 h. Nitric oxide production was unaffected.

CONCLUSION

These results indicate that human PDL cells respond to PTH(1-34) with changes in proliferative and apoptotic signaling in a maturation-state-dependent manner. Besides changes in local factor production, these findings provide a further possible mechanism to support the idea that PDL cells possess the potential to be involved in the regulation of dental hard tissue repair.

Computer-aided analysis of the biomechanics of tooth movements

Orthodontic biomechanics started in the early 1960s with the work of Burstone and later Nikolai. Experimental and theoretical studies using finite element methods (FEM) focused on the determination of the position of the center of resistance of single and multi-rooted teeth. Due to the complex structure of the system tooth/periodontal ligament/alveolar bone and because of the limited power of computers, the first numerical models were quite simple. Improved FE software, sophisticated programs for model generation and the explosion of computer power in the last decade resulted in more complex tooth-periodontium models and model assumptions. This paper describes the application of finite element methods in orthodontic biomechanics with the help of several typical examples. The examples cover aspects from basic orthodontic biomechanics to possible future applications in treatment planning using bone remodelling theories: determination of the mechanical properties of the periodontal ligament in a combined numerical and experimental study, calculation of the centers of resistance of different teeth, and simulation of orthodontic tooth movements. The examples show that nowadays finite element methods are a useful and easy-to-handle tool for the solution of a larger number of structure-mechanical and biomechanical problems. Nevertheless, in spite of the enormous technical progress in the last decade, many problems in orthodontic biomechanics remain to be solved.

Parathyroid hormone(1-34) mediates proliferative and apoptotic signaling in human periodontal ligament cells in vitro via protein kinase C-dependent and protein kinase A-dependent pathways

Periodontal ligament (PDL) cells exhibit several osteoblastic traits and are parathyroid hormone (PTH)-responsive providing evidence for a role of these cells in dental hard-tissue repair. To examine the hypothesis that PDL cells respond to PTH stimulation with changes in proliferation and apoptotic signaling through independent but convergent signaling pathways, PDL cells were cultured from human bicuspids obtained from six patients. PDL cells at different states of maturation were challenged with PTH(1-34) intermittently for 0, 1, or 24 h/cycle or exposed continuously. Specific inhibitors to protein kinases A and C (PKA, PKC) and the mitogen-activated protein kinase cascade (MAPK) were employed. At harvest, the cell number, BrdU incorporation, and DNA fragmentation were determined by means of cell counting and immunoassays. Intermittent PTH(1-34) caused a significant increase in cell number in confluent cells as opposed to a reduction in pre-confluent cells. In confluent cells, the effect resulted from a significant increase in proliferation, whereas DNA fragmentation was reduced when PTH(1-34) was administered for 1 h/cycle but increased after PTH(1-34) for 24 h/cycle. Inhibition of PKC inhibited PTH(1-34)-induced proliferation but enhanced apoptosis. Inhibition of PKA enhanced proliferation and DNA fragmentation. Similar results were obtained in less mature cells, although, in the presence of the PKA inhibitor, the PTH(1-34)-induced changes were more pronounced than in confluent cells. In the presence of the MAPK inhibitor, all of the parameters examined were reduced significantly in both maturation states. Thus, PTH(1-34) mediates proliferative and apoptotic signaling in human PDL cells in a maturation-state-dependent manner via PKC-dependent and PKA-dependent pathways.

Maturation-state dependent response of human periodontal ligament cells to an intermittent parathyroid hormone exposure in vitro

BACKGROUND AND OBJECTIVES

Parathyroid hormone (parathyroid hormone) has been shown to be capable of exerting anabolic effects on bone when administered intermittently. We hypothesized that parathyroid hormone will modulate the response of periodontal ligament cells in terms of anabolic effects with respect to proliferation, differentiation and the production of key regulatory factors of bone remodeling such as osteoprotegerin and receptor activator of nuclear factor kappaB ligand (RANKL) in a maturation-state dependent manner.

METHODS

Periodontal ligament cells were cultured from human bicuspids obtained from six patients. Following characterization, confluent and preconfluent periodontal ligament cells were challenged with parathyroid hormone (1-34) for 0, 1, 3, 6 or 24 h within three incubation cycles of 48 h each. At harvest, the cell number, alkaline phosphatase specific activity and osteocalcin, osteoprotegerin and RANKL production were determined by means of semiquantitative polymerase chain reaction (PCR) and immunoassays. Dermal fibroblasts and MG63 osteoblast-like cells served as a reference.

RESULTS

Intermittent parathyroid hormone treatment of confluent periodontal ligament cells caused a significant increase in proliferation (+32% maximum) whereas alkaline phosphatase activity, osteocalcin and osteoprotegerin decreased at the transcriptional and translational level (-59.7% maximum). In preconfluent periodontal ligament cells, parathyroid hormone induced a decrease in proliferation (-66.3% maximum) but an increase in differentiation and osteoprotegerin production (+49.2% maximum). RANKL was hardly detectable and unaffected by parathyroid hormone treatment. Similar results were obtained in MG63 cells, whereas parathyroid hormone stimulation did not alter any of the parameters examined in dermal fibroblasts.

CONCLUSION

These results indicate that human periodontal ligament cells respond to an intermittent parathyroid hormone exposure with changes in proliferation, differentiation and osteoprotegerin production in a maturation-state dependent manner and therefore might be regulatorily involved in periodontal regeneration.

[Axial load in case of press-fit fixation of the ACL graft--a fundamental study]

AIM

The aim of this study was the determination of the axial fixation load resting on smooth press-fit dowels needed for fixation of the patellar tendon graft (BTB) in order to reach the same fixation properties compared to the interference screw on anterior cruciate ligament (ACL) plasty.

METHOD

Bovine test specimens with 27 BTB grafts fixed in tibial drill holes were used and divided in 3 groups: interference screw, and press-fit cylinder (Ø 7 mm) with 150 N and 100 N axial loads. Prior to fixation, impactation of the transplant into bone was carried out. Failure testing was done in a tensiometer at a cross-head speed of 50 mm/min. Determinations of peak load and stiffness were also made.

RESULTS

Similar peak loads and stiffness were reached on introducing a press-fit dowel (slashed circle 7 mm) with 100 N and 150 N axial load compared to interference screw fixation of the BTB graft. Peak load: 988.1 N +/- 365.1 (screw) versus 1 210.4 N +/- 292.4 (dowel 150 N) and 1 109.8 N +/- 505.4 (dowel 100 N). Stiffness: 86.4 N/mm +/- 20.5 (screw) versus 102.4 N/mm +/- 15.2 (dowel 150 N) and 77.1 N/mm +/- 11.0 (dowel 100 N). There was no significant difference.

CONCLUSION

When introducing a press-fit dowel (slashed circle 7 mm) with 100 N axial load into a preformed bone bed, the same fixation properties are reached as in the case of an interference screw on BTB-ACL plasty.

[MR-based 3D-analysis of the pathomechanics of traumatic and atraumatic shoulder instability]

AIM

Until now it is unknown to what extent malpositioning of the scapula is a relevant factor in shoulder instability that should be considered in therapy. The objective was to analyse 3D-scapular kinematics and humeral head (de-)centering in patients with atraumatic and/or traumatic shoulder instability and to investigate the correlation between the two factors.

METHOD

The shoulders of 28 healthy volunteers and of 14 patients each with atraumatic or traumatic instability were examined in various arm positions - with and without muscle activity - using open MR imaging. After 3D reconstruction, analyses of scapular kinematics and glenohumeral translation were performed.

RESULTS

In atraumatic unstable shoulders, the scapular position [30 degrees of abduction: scapulo-humeral rhythm: 3.5 +/- 2.6 : 1 vs. healthy 2.4 +/- 1.3 : 1; internal rotation: 59 +/- 9 degrees vs. healthy 49 +/- 3 degrees (p < 0.05)] and humeral head position was significantly decentered in both planes (p < 0.05). While the correlation between the two factors was high during passive elevation (r = 0.60-0.87), it was low during muscular activity (r = 0.25-0.62). In patients with traumatic instability no alterations of the scapula kinematics were observed. Significant humeral head decentering (p < 0.05) occurred only during abduction and external rotation.

CONCLUSIONS

Patients with atraumatic instability demonstrated significant alterations of scapular kinematics and decentering of the humeral head. In traumatic instability a decentering occurred only in specific arm positions with no changes in scapula position. Because of the high correlation between the two factors, physiotherapeutic strategies for the scapula-stabilising muscles should be adapted to the direction of instability.

Numerical simulation of the biomechanical behaviour of multi-rooted teeth

The elastic properties of the periodontal ligament (PDL) in eight multi-rooted teeth were examined in a combined experimental and numerical study in six minipigs. The initial tooth movement of the mandibular primary molars surrounded by the periodontium was registered three-dimensionally (3D) in an optomechanical measuring system. The dissections were then embedded in resin and cut in transverse sections. Based on these sections, 3D finite element (FE) models were constructed and numerically loaded with the same force systems as used in the experiment. The material behaviour of the PDL registered in the experiment was non-linear and could be approximated with a bilinear parameter set consisting of two Young's moduli, E1 and E2, and one ultimate strain, epsilon12, separating both elastic regimes. When a deficient congruence existed between the experimental and numerical force/deflection curves the material parameters were varied to obtain a satisfactory congruence. The material behaviour determined for these specimens delivered mean values of E1 = 0.05 MPa, E2 = 0.18 MPa and epsilon12 = 6.4 per cent for the elastic behaviour of the multi-rooted minipig teeth. There was no significant difference in the material parameters determined for specimens with two, four or six roots. The results were in close agreement with the material parameters of the PDL, determined in previous investigations of single-rooted human and pig teeth.

Distribution of components of the insulin-like growth factor system in the temporomandibular joint of the aging mouse

The temporomandibular joint (TMJ) is a exceptional joint involved in growth as well as mastication. In adult mice, it provides a model for age related natural osteoarthritis (OA). The insulin-like growth factor (IGF-) system plays was tested because it plays important roles in cartilage biology and OA pathogenesis. Decalcified and paraffin embedded TMJs of 48 NMRI mice sacrificed in groups of three male and females each at the ages of 3, 4, 5, 7, 9, 10, 12, and 18 months were prepared for histopathology and immunohistochemistry for IGF-I and -II, IGF1 receptor and IGF binding proteins -1, -2, -3, -4, -5, and -6. Histopathological signs of OA were obvious in the TMJ of all animals older than 5 months, but did not show a clear age-related staging. Immunoreactivity for all IGF components was found in unchanged anterior and posterior regions of the condyle and in regions of advanced OA lesions. Receptor immunostaining was obvious in all ages. Most IGFBPs showed immunostaining patterns similar to IGFs. While the anterior and posterior zones of the condylar cartilage appear to be specialized judging by structure and IGF immunostaining pattern, probably due to metabolic or biomechanical peculiarities, the central portion undergoes early degeneration. In advanced OA stages, the IGF system seems to be upregulated to induce repair processes. According to their mainly inhibiting functions, IGFBPs may suppress anabolic IGF activities.

Applications of surface-surface matching algorithms for determination of orthodontic tooth movements

Orthodontic tooth movements are described as the differences between initial and final tooth positions. A computer based method for determination of tooth movements for different treatment methods was developed. A total of 20 casts of the upper jaw of patients treated with tooth positioners or fixed appliances were used as a basis for this study. Tooth movement was analysed on casts before (Ci) and after treatment (Cf). The casts were digitized either with a COMT or 3D laser scanning systems. After digitization, the models were superimposed in the palate by using a surface-surface matching algorithm. Tooth surfaces of the orthodontically moved teeth were segmented and determination of tooth movement was accomplished by matching the moved teeth from Ci to Cf. The resulting transformations delivered three dimensional information on translations and rotations. An accuracy of 0.2 mm in translations and 1 degree in rotations could be demonstrated, showing the different efficiency of treatment schemes.

Pin-Refixation der lateralen Femurkondyle bei traumatischer osteochondraler Fraktur nach Patellaerstluxation: Case Management und Follow-up beim Jugendlichen

AIM

Intraarticular osteochondral fractures resulting from traumatic patellar dislocation in children are reported most frequently between 13 and 15 years of age. Fracture localization concerns, apart from loose intraarticular bodies, the inferiomedial patellar facet and the lateral femoral condyle. Osteochondral fractures of the lateral femoral condyle with more than 50 % of its surface are extremely rare and reported infrequently.

METHOD

We report a traumatic patellar dislocation in a 14 year old patient that let to an osteochondral fracture of the lateral femoral condyle. MRI-scan demonstrated an extensive fracture size concerning more than 50 % of the condylar surface with intraarticular dislocation. Initially arthroscopic surgery followed an open reduction and internal refixation of the osteochondral fragment with resorbable, poly-p-dioxanon pins.

RESULTS

Follow-up MRI-scan revealed 7 weeks after surgery an adequate repositioning of the fragment with correct pin placement. Second-look arthroscopy demonstrated an osteochondral reintegration of the fragment within a period of 7 months after prior surgery.

CONCLUSION

Resorbable poly-p-dioxanon pins as a mean for refixation of an osteochondral, intraarticular fracture in an adolescent, with an arthroscopic confirmed acceptable result, seem to be a considerable therapy option.

Experimental and numerical determination of initial tooth mobility and material properties of the periodontal ligament in rat molar specimens

The mechanical parameters of the periodontal ligament (PDL) in rat specimens were investigated in a combined experimental and numerical approach. Tooth mobility of the rat mandibular first molar was measured in vitro using a high precision experimental set-up. Finite element models (FEM) were developed, based on histological sections of the measured specimens, to simulate tooth mobility numerically under the same force systems as used in the experiment. Force/deflection curves from the measurements showed a significant non-linear behaviour of elastic stiffness of the PDL. A bilinear material parameter set was assumed to simulate tooth deflections. The numerical force/deflection curves were fitted to the experimental curves by repeatedly calculating theoretical tooth deflections and varying the parameters describing the non-linearity. Mean values of E1 = 0.15 MPa, E2 = 0.60 MPa and an ultimate strain of epsilon12 = 6.3 per cent were derived for the elastic behaviour of the rat PDL. Comparing fresh specimens and those frozen in a 0.9 per cent saline solution, differences between the measurements were significant. Using the agent, Periston, for freezing significantly reduced the deviation. The results indicated that strains in the PDL with a maximum of 14 per cent at the furcation were 10(4) times higher than strains in the bone, while the variability of stress values in both PDL and bone was not significant.

[Numerical study of tension and strain distribution around rat molars]

A knowledge of the mechanical processes triggered in the bone and periodontal ligament (PDL) by orthodontic forces applied to a tooth is of decisive importance for an understanding of the subsequent remodelling around the tooth. To investigate these mechanical relationships, three-dimensional finite element (FE) models of the first lower molar in the rat were established. On the basis of digitized serial histological sections, these FE models were generated semi-automatically. Using various simplified geometrical variations, an appropriate FE model for the analysis of the stress and strain distributions was established. The numerical analyses were carried out under a mesially directed force of 0.1 N. Stress distributions in the bone and PDL showed a similar pattern, while strains in the bone were lower than in the PDL by a factor of 10-5. The data confirm the assumption that strain patterns in the PDL may be the key stimulus of bone remodelling.

[Ten year follow-up after single incision anterior cruciate ligament reconstruction using patellar tendon autograft]

AIM

We evaluated 74 patients 10 years after arthroscopically assisted ACL reconstruction using the central third of the patellar tendon as autograft.

METHOD

IKDC, Tegner and Lysholm scores were used for clinical evaluation. Ligament stability was tested using the Rolimeter instrument. For statistics we used the Chi square test.

RESULTS

At follow-up the Tegner activity level was 5.2, the Lysholm score was 93.6 points. Subjective assessment for function was rated normal or nearly normal in 83.7 %, for stability in 71.6 %. The side-to-side difference measured with the Rolimeter was normal in 87.8% and nearly normal in 12.2 %. Pivot shift was proven to be negative in 94.6 %. 29.7 % of patients showed degenerative changes in X-rays at follow-up. There was a significant correlation between time interval from injury to surgery and the grade of degenerative changes. Arthrosis significantly correlates with the rate of meniscus injury. Acute operative treatment increases the rate of arthrofibrosis significantly.

CONCLUSION

To avoid osteoarthrosis we recommend an early (subacute) ACL reconstruction and meniscus refixation in the case of meniscus injury.

[Comparison of mechanical properties of orthodontic nickel-titanium wires]

Two packages each, containing 10 wires per package, of different batches of 25 different types of orthodontic archwires made of super-elastic nickel-titanium alloys measuring 0.41 x 0.56 mm2, were investigated. The wires were characterized by obtaining the following measurements at an ambient temperature of 37 degrees: a three-point bending test with the supporting points spaced 10 mm apart, and determination of the torque/bending angle curves using a pure bending test. The force/deflection curves provided the parameters characterizing the super-elastic unloading plateau: average force, slope and endpoint. From the torque/bending angle curves, the parameters average torque, plateau endpoint and the elasticity parameters were determined. Average force (0.8-4.5 N), endpoint (0.2-0.9 mm) and the slope of the unloading plateau (0.2-2.1 N/mm) of the three-point bending test clearly differed for individual wires. Significant differences were also seen for average torque (1.5-11.5 Nmm), unloading plateau endpoint (2.7-20.0 degrees) and elasticity parameters epsilon 4, E4, E5 and E6 in the pure bending test. Individual batches showed only minor differences. The results permit the conclusion to be drawn that super-elasticity is applicable to only a small portion of the wires examined. Although other wires showed super-elastic behaviour, the unloading plateaus has a force level of up to 6 N, and cannot be recommended for orthodontic application. The super-elastic plateau is often of use only for deflections greater than 1.5 mm. The use of super-elastic archwires made of nickel-titanium alloys makes sense only when the elastic properties of the respective wires are known. This makes the provision by the manufacturer of relevant data on the elastic properties of wires a necessity.

Localization of IL-1alpha, IL-1 RI, TNF, TNF-RI and TNF-RII during physiological drift of rat molar teeth--an immunohistochemical and in situ hybridization study

Proinflammatory cytokines such as IL-1 and TNF play a crucial role in the initiation of an inflammatory response to bacterial irritants and subsequent periodontal tissue destruction. The object of the present investigation was to examine the possible role of these cytokines in the periodontal tissues under physiological conditions. To this end we studied the expression of IL-1alpha and TNF both at the transcription and protein level by means of in situ hybridization and immunohistochemistry and investigated the distribution of IL-1RI, TNF-RI and TNF-RII immunohistochemically in 10 jaw specimens taken from male Wistar rats. We found IL-1alpha and TNF mRNA to be focally transcribed in bone marrow cells of the monocyte/macrophage lineage, in gingival epithelium as well as in single osteoblasts and osteoclasts. Additionally, IL-1alpha mRNA was detected in PDL-fibroblasts and epithelial remnants of Malassez. The IL-1alpha immunohistochemistry observations were corroborated by the in situ hybridization results. TNF and its receptors were not detected at the protein level. These data suggest that IL-1alpha and its receptor are of some importance in the maintenance of tissue homeostasis and remodeling events accompanied by physiological tooth movement.

[Is meniscal repair an adequate procedure to prevent early osteoarthritis in athletes with chronic anterior knee instabilitity?]

We retrospectively evaluated the clinical outcome of arthroscopic assisted meniscal suture repair in athletes on different competitive sports levels with stable joint function and persisting anterior knee instability. Return to former sports levels and early osteoarthrotic changes were especially focussed. Examination included 50 athletes (32 men, 18 women) who underwent meniscal repair in inside-out technique during the period of 1989 to 1998. 23 patients had isolated full-thickness meniscal tears, 27 an associated rupture of the anterior cruciate ligament which was reconstructed in 13 cases with a patellar-tendon autograft. 3 study groups were formed referring to the athletes preoperative sports level evaluated with Tegner's score. Reexamination included Lysholm score, IKDC score and Fairbank's score. With a mean age of 32.1 years (range 13-53 years) and an average follow-up of 6.3 years 72 % of the patients (n = 36) showed a stable joint function on reexamination. With no persisting anterior knee instability 86 % of the professional athletes returned to former full sports activities on competitive levels. Non competitive athletes returned in all cases (100 %) to their former level. Fairbank's score increased by 0.1 observing minimal osteoarthitic signs. However, persisting anterior knee instability showed on reexamination poor results. Only one third of all athletes were able to return to former activity levels. Osteoarthritic changes were observed in all patients. Professional athletes had the most severe osteoarthritic changes with a significant (p = 0.03) increase of 0.8 in Fairbank's score. The results demonstrate that complete recovery on sports activities after meniscal repair is not possible without reconstruction of the anterior cruciate ligament. Isolated meniscal repair shows poor results in persisting anterior knee instability and does not prevent increasing osteoarthritic changes in athletes.

[Replacement of the anterior cruciate ligament with a patellar tendon transplant]

The bone-patellar tendon-bone graft (BTPB) was the most commonly used graft for many years. The scientific database is more complete than for every other graft option. This review article presents the surgical techniques of ACL reconstruction with the BPTB graft, aspects of rehabilitation, clinical results, and postoperative problems with special emphasis on donor site morbidity.

[History of surgery of the anterior cruciate ligament]

Early comments on the anterior cruciate ligament were found in ancient literature, and the first scientific reports were published in the nineteenth century. The first surgical treatment of a ruptured anterior cruciate ligament was carried out in 1895 by Robson performing a primary suture of the torn ligament. In 1903 F. Lange suggested a complete replacement of the injured ligament using silk ligaments and in 1914 Grekow was probably the first who recommended autogenous transplants by using a fascia lata strip. In 1917 Hey-Groves presented his surgical technique that was the fundament for reconstruction surgery in the following years. Today, the autogenous transplant is accepted to be the golden standard for replacement of the injured anterior cruciate ligament. The bone-tendon-bone transplant of the patellar ligament and the semitendinosus or gracilis tendon are recommended by most surgeons. In the history of anterior cruciate ligament surgery, the surgical technique of the operative procedures has also changed. The evolution started with open arthrotomy followed by mini-arthrotomy and led to arthroscopically assisted replacement of the anterior cruciate ligament.

Immunohistochemical localization of receptor activator of nuclear factor kappaB (RANK) and its ligand (RANKL) in human deciduous teeth

Osteoblasts and osteoclasts are involved in bone formation and resorption. RANK and RANKL [receptor activator of nuclear factor kappaB (ligand)], two cytokine-like proteins of the tumor necrosis factor superfamily, are localized on these bone cells and are crucial for the regulation of osteoclastic cell differentiation from hematopoietic precursors and also for the upregulation of mature osteoclasts mediated by cell-to-cell contact and a subsequent cascade of diverse intracellular signaling processes in the osteoclasts. It was the aim of this study to examine the sites of expression of RANKL and RANK in the corresponding cells of human dental hard and periodontal tissues using immunohistochemical light microscopical methods on tissue sections of 15 paraffin-embedded human deciduous teeth undergoing root resorption. We detected granular cytoplasmic RANKL-immunoreactivity in odontoblasts, pulp fibroblasts, periodontal ligament fibroblasts, and in single odontoclasts, the latter finding suggesting an autocrine/paracrine role. RANK-positive cells were identified as multinucleated odontoclasts localized near the dentine surface in resorption lacunae or as mononucleated precursors. These findings indicate that human dental cells express key mediators of hard tissue resorption and, though the RANK/RANKL-system may not be the sole regulator of tooth root resorption, these factors could at least contribute to this complex process under both physiological and pathological conditions.

Immunohistochemical localization of components of the insulin-like growth factor-system in human deciduous teeth

To investigate the occurrence of components of the insulin-like growth factor (IGF) system during the resorption process of shedding human deciduous teeth, we investigated sections of 13 decalcified and paraffin-embedded deciduous teeth immunohistochemically with antibodies against IGF-I and -II, six IGF binding proteins (IGFBPs 1-6) and the IGF receptors IGF1R and IGF2R. The teeth were in different stages of resorption and all showed reparative cementum formation. It was found that acellular extrinsic fiber cementum, reversal lines and reparative cellular intrinsic fiber cementum were immunoreactive for both IGFs and various IGFBPs. Therefore, in human deciduous teeth, all subgroups of cementum, but not dentine, may represent sources of components of the IGF system. Odontoclasts did not carry IGFs or the IGF1R, but IGFBPs and the IGF2R. Therefore, these cells, in contrast to osteoclasts, may not respond to IGFs, but may be involved in the release and sequestration of IGFs from cementum during the resorption process. In contrast to odontoclasts, cementoblasts and periodontal ligament (PDL) fibroblasts carried IGF1R. The influence of the IGF system on the function of these cells with respect to periodontal matrix turnover and cementogenesis is discussed. On the behalf of the IGFBP immunoreactivities found, the PDL extracellular matrix can be considered to be a reservoir for IGF system components, where binding proteins may regulate IGF distribution and activity.