Lars Hammarström

Tooth ankylosis. Clinical, radiographic and histological assessments.

Ankylosis is a serious condition for the affected teeth as such teeth form part of the remodelling process of the alveolar bone and are therefore progressively resorbed. There are, however, very few clinical studies on tooth ankylosis and the reason for this may be due to the difficulties that are encountered in the diagnosis of minor areas of ankylosis. In the present study, the radiographs, percussion sound and mobility of experimentally extracted and replanted monkey incisors were compared with a morphometric histological study of ankylosis. Ankylotic areas were evident radiographically when the ankylosis was located on the proximal surfaces of the root, but were not evident when the ankylosis occurred on the lingual and labial surfaces. The percussion sound was dull and the mobility normal in all non-ankylotic teeth as well as in those teeth which histologically demonstrated ankylosis on less than 10% of the root surface. When the ankylosis affected 10-20% of the root surface, 2 out of 4 teeth changed their percussion sound from dull to high and these teeth no longer possessed normal mobility. When more than 20% of the root surface was affected with ankylosis, the percussion sound was characteristically high in all teeth and no mobility was present.

Storage of Experimentally Avulsed Teeth in Milk Prior to Replantation

Extracted monkey teeth were endodontically treated, stored in milk or saliva for two or six h, and then replanted. Periodontal conditions were evaluated after eight wk. Teeth that had been stored for two or six h in milk or for two h in saliva showed periodontal healing almost as good as that of immediately replanted teeth. Teeth that had been kept in saliva for six h or bench-dried for one h showed extensive replacement resorption. Milk may thus be recommended as a storage medium for ex-articulated teeth prior to replantation in cases when immediate replantation is not possible.

Emdogain--periodontal regeneration based on biomimicry.

Abstract Biomimicry has been introduced as a term for innovations inspired by nature [1]. Such innovations may appear in almost every part of modern society. This review on the effects of enamel matrix proteins on the formation of cementum and the development of emdogain for regeneration of periodontal tissues lost due to periodontitis shows an example of biomimicry in dentistry. Findings from clinical and laboratory investigations are summarized and the biological basis for enamel matrix-induced periodontal regeneration is discussed.

Tissue responses to natural aragonite (Margaritifera shell) implants in vivo

The purpose of this study was to access tissue reactions to the outer prismatic (prism) and the inner nacreous (nacre) layers of the fresh water Margaritifera shell. The materials, in granule form, were implanted into the back muscles and femurs of rats for 1, 2, 4, 8 and 16 weeks. In the back muscles, a foreign body reaction was observed around the implants, starting from one week after implantation and reaching maximal proportions at two weeks. After four weeks, a thin layer of fibrous tissue encapsulated the implanted particles. The external surface of the material stained strongly with acid fuchsin, indicating degradation of implant. At femoral sites, newly formed bone was directly applied to the implant surfaces. The outer-most parts of the organic sheets in prisms were not degraded until 16 weeks after implantation and were embedded in the newly formed bone. The interface between bone and the implants showed close fusion by scanning electron microscopy (SEM). Energy dispersive X-ray analysis (EDAX) demonstrated a phosphorous-rich zone in the interface between bone and the implants, and no electron-dense layer in the interface was found by transmission electron microscopy (TEM). We conclude that Margaritifera shells are biocompatible, biodegradable and osteoconductive materials. Bonding between this natural aragonite and bone seems to occur via a phosphorous-rich intermediate layer.

Periodontal Healing of Replanted Monkey Teeth Prevented from Drying

Root resorption of replanted teeth is dependent on the duration of the extra-alveolar period and on the storage environment. In the present investigation the significance of preserving the humidity of the periodontal ligament (PDL) during the extra-alveolar period was tested on isolated PDL cells and on replanted monkey teeth. The isolated PDL cells were tested with respect to cell viability (trypan blue exclusion test) and to cell recovery (number of cells after additional cultivation). About 70% of the cells were viable and 44% recovered after 1 h in a humid atmosphere. Practically no cells were viable or recovered after 1 h of drying. Replanted teeth that had been wrapped in plastic foil for 1 h before replantation showed no more resorption than immediately replanted teeth. This is in contrast to teeth dried in air for 1 h before replantation. They showed extensive root resorption on almost all root surfaces. Thus, prevention of evaporation of tissue fluid from the PDL must be considered a primary goal if the tooth cannot be replanted immediately.

RETRACTED: Vulnerability of Glioblastoma Cells to Catastrophic Vacuolization and Death Induced by a Small Molecule

Glioblastoma multiforme (GBM) is the most aggressive form of brain cancer with marginal life expectancy. Based on the assumption that GBM cells gain functions not necessarily involved in the cancerous process, patient-derived glioblastoma cells (GCs) were screened to identify cellular processes amenable for development of targeted treatments. The quinine-derivative NSC13316 reliably and selectively compromised viability. Synthetic chemical expansion reveals delicate structure-activity relationship and analogs with increased potency, termed Vacquinols. Vacquinols stimulate death by membrane ruffling, cell rounding, massive macropinocytic vacuole accumulation, ATP depletion, and cytoplasmic membrane rupture of GCs. The MAP kinase MKK4, identified by a shRNA screen, represents a critical signaling node. Vacquinol-1 displays excellent in vivo pharmacokinetics and brain exposure, attenuates disease progression, and prolongs survival in a GBM animal model. These results identify a vulnerability to massive vacuolization that can be targeted by small molecules and point to the possible exploitation of this process in the design of anticancer therapies.

Osteoclasts: Structure and function

Osteoclasts are multinucleated giant cells showing specialized membrane structures, clear zones and ruffled borders, which are responsible for the process of bone resorption. These cells arrive at the resorption site via the bloodstream as mononuclear cells, derived from haemopoietic precursors in the spleen or bone marrow, which fuse prior to resorption. The osteoclast may share an early progenitor cell, the granulocyte macrophage colony-forming unit (GM-CFU) with monocytes, macrophages and granulocytes, implying that osteoclasts share the pluripotent haemopoietic stem cell with all other haemopoietic cells. In the past, elucidation of the structure of these cells relied upon traditional ultrastructural techniques. Transmission electron microscopic studies revealed details of the unique ultrastructure of these cells and, in combination with stereological techniques, showed the response of cells to various hormonal stimuli. Scanning electron microscopy not only demonstrated the surface appearance of osteoclasts, and their predilection for spreading on various substratum components, but has also been used as an adjunct in resorption assays in which areas of resorption lacunae are measured as indicators of cell activity. Recent advances in fields such as immunocytochemistry and freeze fracture techniques have contributed towards a more detailed delineation of antigenic profile, cytoskeletal structure and localization of enzymatic pathways. The osteoclast is subject to extensive regulatory mechanisms and it has been established that the osteoblast plays a major rôle in mediating the effects of osteotropic hormones and local mediators on these cells. Hence, research aimed at elucidating the coupling mechanisms between these two cells may result in new therapies for bone disease.

Expression patterns of RNAs for amelin and amelogenin in developing rat molars and incisors.

We have recently identified a novel RNA sequence in ameloblasts, coding for amelin (Cerny et al., 1996). In the present paper, its expression has been compared with that of amelogenin in developing incisors and molars of rats, by means of in situ hybridization of paraffin sections. The RNAs for both amelin and amelogenin were highly expressed in secretory ameloblasts. The expression of RNA for amelogenin gradually decreased in the post-secretory ameloblasts. In contrast, the RNA expression for amelin remained high in post-secretory ameloblasts up to the stage of fusion between dental and oral epithelia at the time of tooth eruption. We suggest that amelin might be involved in the mineralization of enamel or in the attachment of ameloblasts to the enamel surface. The whole-mount in situ hybridization procedure is described for the first time in dental research. It proved to be a useful method and confirmed the results of the conventional in situ hybridization.

Orthodontically induced root resorption in rat molars after 1-hydroxyethylidene-1,1-bisphosphonate injection.

A single injection of 1-hydroxyethylidene-1, 1-bisphosphonate inhibits the formation of acellular cementum in rat molars. Instead, an atypical hyperplastic cementum is formed. In this study the resistance of this cementum to resorption was tested by applying an orthodontic force. It was found that roots lacking acellular cementum were readily resorbed. The readiness with which the atypical hyperplastic cementum was resorbed without any increase in multinucleated osteoblasts may offer useful opportunities to study the different phases of hard-tissue resorption.

Tissue responses to nacreous implants in rat femur: an in situ hybridization and histochemical study

The interface of bone and aragonite nacre (Margaritifera, fresh water pearl mussel) was studied by in situ hybridization and a tartrate-resistant acid phosphatase (TRAP) histochemical assay. Columnar implants were inserted into rat femora for 4, 7, 14, 28 and 56 days. In medullary region, a burst of transient bone formation was observed, which propagated from the periphery towards the nacre implant. A fused interface of bone and nacre was observed at 14 days. Later, the new medullary bone was resorbed and bone marrow was re-established while a thin layer of bone tissue remained covering the implant surface. Expressions of collagen alpha1(I), osteocalcin, osteopontin mRNAs and TRAP in the surrounding tissue were monitored. Correlated with the histology events, a strong transient induction of collagen alpha1(I) and osteocalcin mRNAs as well as TRAP expression, exhibiting a peak signal intensity on day 7 and subsequent down-regulation after day 14 was observed. Osteopontin mRNA, in contrast, was expressed continuously. The degrading nacre surface appeared in direct contact with macrophages and multinucleated giant cells at both days 14 and 28. These cells expressed osteopontin mRNA intensively and some TRAP enzyme activity occasionally.