Ming-Lun Hsu

Failure Analysis: Enamel Fracture after Debonding Orthodontic Brackets

OBJECTIVE To determine the location and size of enamel fracture (EF) when debonding a bracket. MATERIALS AND METHODS Tests on actual EF situations were conducted in different debonding load modes (tension, shear, and torsion) via mechanical testing, finite element model (FEM) analysis, and scanning electronic microscopy (SEM). Through these simultaneous analyses of the relationships among debonding load modes, value/distribution of stress, and actual enamel fracture location/size, an investigation was undertaken to explore the complex failure mode during enamel fracture after debonding of an orthodontic bracket. RESULTS The EF usually was located in the area where the force was exerted during various loading modes. The tensile, shear, and torsion debonding modes produce EF sizes and incidences with no significant differences. Findings on FEM matched the mechanical testing and SEM results. CONCLUSIONS The EF locations coincided with the areas where the tensile, shear, or torsion force was exerted. Therefore, the dentist should give extra care and attention to these specific areas of enamel after debonding. The sizes and incidences of EF produced by these three debonding modes showed no significant difference. Thus, clinically, when the sizes and incidences of produced EF are considered, it should not matter which of these three exerting forces is used to debond a bracket.

Pain Catastrophizing is Associated with Dental Pain in a Stressful Context

Pain is associated with anxiety in a dental setting. It has remained unclear how cognitive-affective factors modulate pain and anxiety in a stressful context, such as receiving dental procedures. We hypothesized that both the situational factor (unpredictability about painful stimuli) and the trait factor (pain catastrophizing, i.e., the tendency to interpret pain in negative orientation) account for dental pain. Fifteen healthy participants were recruited to perform an associative learning task. They were asked to learn the pairing between visual cues and the intensity of incoming painful stimuli delivered at the right upper central incisor. Brain activation associated with pain was recorded by functional magnetic resonance imaging (fMRI). The participants reported increased anxiety and pain in the stressful context, where stimuli intensity was not predicted by the preceding cue. The score of the Pain Catastrophizing Scale was positively correlated with the increased pain modulated by unpredictability. Brain activation at the right posterior hippocampus, a region critically related to associative learning of aversive stimuli and context, was correlated with the individual catastrophizing level. Our findings suggest that both the situational factor (unpredictability) and the trait factor (catastrophizing) influence dental pain, highlighting the role of cognitive-affective factors in pain control of dental patients.

The effect of hyperbaric oxygen and air on cartilage tissue engineering.

AbstractThere is an urgent need to develop tissue-engineered cartilage for patients experiencing joint malfunction due to insufficient self-repairing capacity of articular cartilage. The aim of this research was to explore the effect of hyperbaric oxygen and air on tissue-engineered cartilage formation from human adipose-derived stem cells seeding on the gelatin/polycaprolactone biocomposites. The results of histological analyses indicate that under hyperbaric oxygen and air stimulation, the cell number of chondrocytes in cartilage matrix was not significantly increased, but the 1,9-dimethylmethylene blue assay showed that the glycosaminoglycans syntheses markedly increased compared to the control group. In quantification real-time polymerase chain reaction results, the chondrogenic-specific gene expression of SOX9, aggrecan, and COL2A1 were compared respectively. Within the limitation of this study, it was concluded that 2.5 atmosphere absolute oxygen and air may provide a stress environment to help cartilage tissue engineering development.

Meta-analysis on Brain Representation of Experimental Dental Pain

Functional magnetic resonance imaging (fMRI) has been widely used for investigating the brain representation associated with dental pain evoked by pulpal electrical stimulation. However, because of the heterogeneity of experimental designs and the small sample size of individual studies, the common brain representation regarding dental pain has remained elusive. We used imaging meta-analysis to investigate six dental pain-related fMRI studies (n = 87) and tested 3 hypotheses: (1) Dental pain is associated with the ‘core’ pain-related network; (2) pain-related brain activation is somatotopically organized in the somatosensory cortex; and (3) dental pain is associated with the cognitive-affective network related to pain. Qualitative and quantitative meta-analyses revealed: (1) common activation of the core pain-related network, including the somatosensory cortex, the insula, and the cingulate cortex; (2) inconsistency in somatotopically organized activation of the primary somatosensory cortex; and (3) common activation in the dorsolateral prefrontal cortex, suggesting a role of re-appraisal and coping in the experience of dental pain. In conclusion, fMRI combined with pulpal stimulation can effectively evoke activity in the pain-related network. The dental pain-related brain representation disclosed the mechanisms of how sensory and cognitive-affective factors shape dental pain, which will help in the development of more effective customized methods for central pain control.

Response of the temporomandibular joint tissue of rats to rheumatoid arthritis induction methods

Background/purpose The pathogenesis of rheumatoid arthritis (RA)-related temporomandibular joint (TMJ) disorder remains unclear. Studies have reported the change of the TMJ after complete Freunds adjuvant (CFA) injection, which is consistent with osteoarthritis. However, few studies have reported that the tissue response of the TMJ in collagen-induced arthritis (CIA) can mimic RA. The present study was aimed to investigate the TMJ response in rat models by CFA-induced arthritis and CIA to verify the proper RA-related TMJ arthritis rat model. Materials and methods In total, 24 rats were randomly divided into four groups: (1) control group; (2) type I collagen injection group; (3) CFA-induced arthritis group; and (4) CIA group. Drugs were injected on Day 0, and the rats were sacrificed on Days 7 and 35. Next, TMJ tissue was collected for hematoxylin and eosin staining, and inflammatory gene (IL-1β and MMP3) expression was investigated. Results Compared with the control group, the type I collagen injection group confirmed the negative inflammatory response through hematoxylin and eosin staining and IL-1βand MMP3 expression. Although CFA-induced arthritis and CIA groups showed inflammatory response (P < 0.05) compared with the control group, histological changes were different. The 7-day CFA-induced arthritis group showed adaptive changes and partly recovered after 35 days of induction. In contrast, 7- and 35-day CIA groups underwent a degenerative process. Conclusion Considering the study limitations, the CIA method is a proper method to study the mechanism of RA-related TMJ arthritis.

Osteogenic prospective of deriving human dental stem cells in collagen matrix boost

Stem cells derived from oral tissue represent a highly attractive alternative source for clinical bone regeneration because they can be collected by non-invasive or minimally invasive procedures. Herein, we describe the human dental stem cells (DSCs) deriving from buccal fat pads (BFP), dental pulp (DP) of impacted teeth, and periodontal ligaments (PDL) to obtain BFPSCs, DPSCs, and PDLSCs, respectively. Cells were purified with selected medium and expanded through passages in stem cell culture medium. Purified cells were characterized for stemness by their growth rate, immunostaining, and multilineage differentiation ability. They showed plastic adherence, expression of stemness-specific markers, and multilineage differentiation potential. Immunocytochemistry analysis confirmed that DPSCs had more osteogenic potential than BFSCs and PDLSCs. Calcium-rich deposits, evaluated by von Kossa and Alizarin red staining, showed greater mineralization when DPSCs were cultured on collagen type I matrix than without collagen. Furthermore, DPSC-seeded collagen type I matrix maintained consistent osteogenesis and boosted mineral formation by 1–2 weeks over that in DPSCs cultured without collagen. Radiographic analysis of DPSC-seeded collagen type I matrix transplanted into rat cranial defects showed significant bone regeneration after 8 weeks. These results suggested that the redundant oral tissue can be used as a source of adult multipotent stem cells for clinical bone regeneration.Graphical abstractTriple overlay images with biomarkers (red), nuclei (blue) and bright field morphology of DPSCs. The specifically osteo-differentiation shown by osteocalcin (left) expression and lack of sox9 (right) expressed in the images below which were cultured with collagen matrix, contrast with no collagen matrix group above.

Transneuronal Degeneration of Thalamic Nuclei following Middle Cerebral Artery Occlusion in Rats

Objective. Postinfarction transneuronal degeneration refers to secondary neuronal death that occurs within a few days to weeks following the disruption of input or output to synapsed neurons sustaining ischemic insults. The thalamus receives its blood supply from the posterior circulation; however, infarctions of the middle cerebral arterial may cause secondary transneuronal degeneration in the thalamus. In this study, we presented the areas of ischemia and associated transneuronal degeneration following MCAo in a rat model. Materials and Methods. Eighteen 12-week-old male Sprague-Dawley rats were randomly assigned to receive middle cerebral artery occlusion surgery for 1, 7, and 14 days. Cerebral atrophy was assessed by 2,3,5-triphenyltetrazolium hydrochloride staining. Postural reflex and open field tests were performed prior to animal sacrifice to assess the effects of occlusion on behavior. Results. Myelin loss was observed at the lesion site following ischemia. Gliosis was also observed in thalamic regions 14 days following occlusion. Differential degrees of increased vascular endothelial growth factor expression were observed at each stage of infarction. Increases in myelin basic protein levels were also observed in the 14-day group. Conclusion. The present rat model of ischemia provides evidence of transneuronal degeneration within the first 14 days of occlusion. The observed changes in protein expression may be associated with self-repair mechanisms in the damaged brain.

The Potential Risk of Conical Implant-Abutment Connections: The Antirotational Ability of Cowell Implant System.

BACKGROUND Conical implant-abutment connections are popular because of good antibending performance. However, the cross section is round, and the antirotational ability is questionable because restorations in the oral cavity also have to bear torsional moments resulting from chewing patterns. PURPOSE The purpose of this study was to investigate the antirotational ability of conical implant-abutment connections with and without an index. MATERIALS AND METHODS Conical connection implant system (Cowell Medi, Busan, South Korea) was selected. Two kinds of cyclic loading, a bending moment with (C) and without (L) a torsional moment, were respectively applied to two kinds of abutments, pure cone (N-Octa) and cone with an octagonal index (Octa). The number of cycles to fatigue and the failure modes was recorded. Morphologies of the abutments were examined with scanning electron microscopy. RESULTS Only group C(N-Octa) passed the fatigue test, whereas the other three groups failed because of different failure modes. In group L(N-Octa), all abutments generated rotation within 150 cycles. In groups C(Octa) and L(Octa), all abutments fractured but in different areas. CONCLUSIONS In Cowell implant system (taper angle = 7°), there was no antirotational ability in purely conical connections. Adding an octagonal index could provide an antirotational function but could compromise the antibending strength of the abutment.

Functional disorders of the temporomandibular joints: Internal derangement of the temporomandibular joint

Temporomandibular joint (TMJ) is one of the most complex joints of the human body. Due to its unique movement, in terms of combination of rotation and translator movement, disc of the joint plays an important role to maintain its normal function. In order to sustain the normal function of the TMJ, disc must be kept in proper position as well as maintain normal shape in all circumstances. Once the disc is not any more in its normal position during function of the joint, disturbance of the joint can be occurred which will lead to subsequent distortion of the disc. Shape of the disc can be influenced by many factors i.e.: abnormal function or composition of the disc itself. Etiology of the internal derangement of the disc remains controversial. Multifactorial theory has been postulated in most of previous manuscripts. Disc is composed of mainly extracellular matrix. Abnormal proportion of collagen type I & III may also leads to joint hypermobility which may be also a predisposing factor of this disorder. Thus it can be recognized as local manifestation of a systemic disorder. Different treatment modalities with from conservative treatment to surgical intervention distinct success rate have been reported. Recently treatment with extracellular matrix injection becomes more and more popular to strengthen the joint itself. Since multifactorial in character, the best solution of the treatment modalities should be aimed to resolve possible etiology from different aspects. Team work may be indication to reach satisfied results.

Correction to: Osteogenic prospective of deriving human dental stem cells in collagen matrix boost

The original version of this article unfortunately contained a mistake. The country was incorrect in the authors affiliations. It should read as “ROC”. The corrected affiliations are given below.