Effects of functional mandibular lateral shift on craniofacial growth and development in growing rats.

BACKGROUND: Unilateral posterior crossbite, one of the most frequent malocclusions, is often associated with functional lateral shift of the mandible. Although the effects of functional lateral shift on the mandible and temporomandibular joint have been examined in various animal experiments, cranial and maxillary changes have received less attention. OBJECTIVE: The aim of this study was to investigate the effects of functional lateral shift on the craniofacial complex in growing rats. METHODS: Eighty 5-week-old male Sprague-Dawley rats were randomly divided into an experimental group (n = 40), which received an oblique guide appliance that shifted the mandible to the left during closure, and a control group (n = 40). The rats were scanned by cone-beam computed tomography at 3 days and 1, 2, 4 and 8 weeks. The dimensions of the mandibular bone, condyle, maxilla and cranium were measured. RESULTS: The mandibles of rats in the experimental group were smaller than those of the rats in the control group and were asymmetrical. The condyles of the rats in the experimental group were thinner than those of the control rats. The condylar length on the ipsilateral side was shorter and wider than that on the contralateral side from 4 to 8 weeks. No significant differences in cranial length or height were observed between the experimental and control groups. The height of the upper first molar and alveolar bone on the contralateral side was significantly smaller than that on the ipsilateral side and in the controls from 4 to 8 weeks. CONCLUSION: Functional shift in the mandible produces morphological asymmetries in the mandible and maxillary region and may cause bilateral condylar degenerative changes.

Abnormal eruption of teeth in relation to FGFR1 heterozygote mutation: a rare case of osteoglophonic dysplasia with 4-year follow-up.

BACKGROUND: We report a case and its 4-year follow-up of Osteoglophonic dysplasia (OD), a rare disease that disturbs both skeletal and dental development, which is usually caused by heterozygous FGFR1 mutations. CASE PRESENTATION: This article presents a case where a 6-year-old male patient suffered dysregulation of tooth eruption and was diagnosed with osteogenic dysplasia from a fibroblast growth factor receptor 1 (FGFR1) heterozygote mutation. However, the number of teeth is within the normal range, and their roots are well developed. Several interventions were implemented with varying degrees of results. The details of the 4-year follow-up showed that the signs of OD were more pronounced, including dwarfism, frontal bossing, delayed skeletal maturation, anteverted nares, micrognathia, and prominent ears, but the patient's impacted teeth and edentulous jaws remained unchanged. CONCLUSIONS: FGFR1 heterozygote mutation and OD present significant difficulty for teeth eruption and subsequent intervention. Further measures ought to be taken in recognizing various symptoms presented by the patient. This case supports the significance of careful inquiry, comprehensive physical examination and correct diagnosis as indispensable steps for clinical practice in patients with unerupted teeth. Additionally, the detailed case and its 4-year follow-up length may provide new insights into osteogenic dysplasia and patients with impacted teeth while encouraging further exploration in treatment methods.

Mechanical force system of double key loop with finite element analysis.

BACKGROUND: The mechanics of double key loop (DKL) are not well defined, and this finite element study was designed to explore its force system. METHODS: A simplified 3-dimensional finite element model of single and double key loops with an archwire between the lateral incisor and second premolar was established in Ansys Workbench 17.0. Activation in Type-1 (retraction at the distal end), Type-2 (retraction at the distal key) and Type-3 (Type-2 plus ligation between keys) was simulated. The vertical force, load/deflection ratio and moment/force ratio of stainless-steel and titanium-molybdenum alloy (TMA) loops were calculated and compared. RESULTS: The double key loop generated approximately 40% of the force of a single key loop. Type-2 loading of DKL showed a higher L/D ratio than Type-1 loading with a similar M/F ratio. Type-3 loading of DKL showed the highest M/F ratio with a similar L/D ratio as single key loop. The M/F ratio in Type-3 loading increased with the decreasing of retraction force. The DKL of TMA produced approximately 40% of the force and moment compared with those of SS in all loading types. When activated at equal distances below 1 mm, the M/F ratios of SS and TMA DKL with equal preactivation angles were almost the same. CONCLUSION: The M/F ratio on anterior teeth increases with the preactivation angle and deactivation of DKL. The M/F ratio at a certain distance of activation mainly depends on the preactivation angle instead of the wire material. TMA is recommended as a substitute for SS in DKL for a lower magnitude of force.

Stress overload-induced periodontal remodelling coupled with changes in high mobility group protein B1 during tooth movement: an in-vivo study.

High mobility group protein B1 (HMGB1), a bone-active cytokine and an osteocyte alarmin, might have dual functions in bone metabolism that could benefit bone formation and accelerate osteoclastogenic activity. High mobility group protein B1 was recently shown to be involved in tooth movement. Here, we investigated the expression of HMGB1, which remains poorly elucidated, under stress overload-induced periodontal remodelling conditions in vivo. Thirty-six Sprague-Dawley rats (male, 180-200 g) were randomly divided into three groups: two experimental groups, in which 50 or 100 g of force was applied to the first molars for 7 d to induce movement; and one control group, in which no force was applied. These stresses induced tooth movement over significantly different distances, and marked morphological changes were consistently observed in the periodontal tissues of the experimental rats, as demonstrated by histological staining. A real-time PCR analysis showed upregulation of the receptor activator of nuclear factor-kappaB ligand-to-osteoprotegerin ratio and downregulation of the Hmgb1 gene. Changes in both location and expression of the HMGB1 were observed through immunofluorescence analysis. Our data suggest that HMGB1 expression during orthodontic tooth movement might be regulated in a time- and force-dependent manner that is substantially more complex than anticipated.

The dynamic progression of temporomandibular joint osteoarthritis-like lesions elicited by mandibular shift in a rat model.

BACKGROUND: Temporomandibular joint osteoarthritis (TMJ-OA) presents significant challenges due to its complex etiology, often insidious onset, high incidence, and progressive structural deterioration. While research has explored genetic and molecular factors, treatment outcomes remain suboptimal, emphasizing the need for a deeper understanding of disease progression. OBJECTIVE: This study employs a specific mandibular shift rat model to explore the dynamic progression of TMJ-OA-like lesions and evaluate the potential for self-repair at different stages, aiming to inform early diagnosis and preventative strategies. METHODS: Seventy-two female Sprague-Dawley rats were randomized into three groups: a control group (n=24; average weight: 157.23±1.63 g) receiving sham surgery. an experimental group (n=24; average weight: 157.78±1.88 g) subjected to mandibular shift induction, and a removal group (n=24; average weight: 158.11±2.20 g) experiencing mandibular shift for one, two, or four weeks followed by a one-month recovery period (designated as 1w Removal, 2w Removal and 4w Removal, respectively). Histomorphological and molecular analyses were conducted at designated time points. RESULTS: Rats in the 1-week removal group exhibited substantial recovery in condylar morphology, cartilage thickness, extracellular matrix composition, and expression of OA-related genes. Conversely, the 4-week removal group mirrored the experimental group, indicating limited self-repair capacity at later stages. The 2-week removal group presented with variable outcomes, with some animals showing signs of recovery and others resembling the experimental group, indicating a potential transitional phase in the disease process. CONCLUSION: Recovery from early-stage TMJ-OA involves eliminating provoking factors such as occlusal interference or reducing joint loading. However, advanced stages exhibit diminished self-repair capabilities, necessitating additional therapeutic interventions. These findings emphasize the importance of early diagnosis and intervention in TMJ-OA management.

Mechanical stress reduces secreted frizzled-related protein expression and promotes temporomandibular joint osteoarthritis via Wnt/ß-catenin signaling.

AIMS: Mechanical stress overload in the temporomandibular joint (TMJ) is an important cause of TMJ osteoarthritis (TMJOA). Whether secreted frizzled-related proteins (SFRPs) play important roles in the development of mechanical stress-induced TMJOA remains controversial. In this study, we investigated the roles of the Wnt/ß-catenin signaling and SFRPs in the progression of mechanical stress-induced TMJOA. METHODS: We investigated the progression of mechanical stress-induced TMJOA using an in vivo model via modified increased occlusal vertical dimension (iOVD) malocclusion and an in vitro model in which isolated chondrocytes were subjected to mechanical stress. The effects of inhibition of Wnt/ß-catenin signal on TMJOA induced by mechanical stress were studied by in vitro drug added and in vivo intra-articular injection of XAV-939. TMJOA progression, Wnt/ß-catenin signaling and SFRPs was assessed by Cone beam computed tomography (CBCT) analysis, histochemical and immunohistochemical (IHC) staining, quantitative real-time PCR (qRT-PCR), Western blotting (WB), and immunofluorescence (IF) staining. RESULTS: Our in vivo results showed that iOVD-induced mechanical stress in the TMJ disrupted mandible growth, induced OA-like changes in TMJ cartilage, and increased OA-related cytokine expression. In addition, iOVD activated Wnt/ß-catenin signaling and suppressed Sfrp1, Sfrp3, and Sfrp4 expression in condylar cartilage. Moreover, our in vitro study showed that stress disrupted homeostasis, activated Wnt/ß-catenin signaling and inhibited SFRP3 and SFRP4 expression in chondrocytes. Suppression of Wnt/ß-catenin signaling with XAV-939 promoted SFRP3 and SFRP4 expression and rescued mechanical stress-induced cartilage degeneration in vivo and in vitro. CONCLUSIONS: Our work suggests that mechanical stress reduces SFRPs expression both in vivo and in vitro and promotes TMJOA via Wnt/ß-catenin signaling. Suppression of Wnt/ß-catenin signaling promotes SFRPs expression, especially SFRP3 and SFRP4 expression, and rescues mechanical stress-induced cartilage degeneration. Wnt/ß-catenin signaling and SFRPs may represent potential therapeutic targets for TMJOA.

Experimental functional shift-induced osteoarthritis-like changes at the TMJ and altered integrin expression in a rat model.

Mandibular deviation affects the biomechanical environment of the temporomandibular joint (TMJ) and causes thinning of cartilage on the deviated side. We aimed to evaluate, using a rat model, the effect of mandibular functional deviation on the TMJ in relation to the functional roles of integrin ß family members. The effects of experimental functional deviation on the TMJ of 6-week-old Sprague-Dawley female rats, randomly assigned to control (n = 42) and experimental groups (n = 42), were evaluated at 3 days and 1, 2, 4, and 8 weeks by histological staining, immunofluorescence, real-time quantitative polymerase chain reaction, and micro-computed tomography. The results showed that the experimental functional shift changed the shape of condyles, thinned the cartilage, and increased the proportion of the hypertrophic layer on the deviated sides of condyles. In addition, the extracellular matrix of the condyle cartilage exhibited degradation at 1 week and subchondral trabecular bone was lost at 4 and 8 weeks. Osteoarthritis (OA)-like changes occurred in the left and right condyles of rats in the experimental group and were aggravated over time. Integrin ß family expression, especially integrin ß2 , was altered from week 1, possibly related to the OA-like changes. These data may provide insight into the onset of TMJ OA.

[Study of factors affecting tooth discoloration during fixed orthodontics in vitro].

PURPOSE: To investigate effects of acid etching, adhesives, brackets and debonding process on tooth color during direct bonding technique. METHODS: One hundred freshly extracted premolars were divided into blank control, acid etching, adhesive, acid etching+adhesive and acid etching+adhesive+bracket group. Computerized colorimeter was utilized to evaluate L*, a* and b* of tooth color parameters before treatment, 7 days and 30 days after treatment. SPSS 16.0 software package was utilized for statistical analysis. RESULTS: At 7 day, ΔE** value in all experimental groups were significantly higher than blank control group. ΔE* values of acid etching+adhesive+bracket group, and acid etching group were greater than 3.3, showing that recognizable clinic change was observed, but no significant difference was observed between the 2 groups. At 30 d, for ΔE* value, acid etching+adhesive+bracket group > acid etching group, and acid etching+adhesive group > adhesive group > blank control group. Recognizable clinic change was observed in all experimental groups (ΔE*>3.3). CONCLUSIONS: In fixed orthodontic procedures, acid etching and metal erosion resulting from long time wearing braces are two important factors leading to enamel discoloration, and adhesives removing procedures may also affect tooth discoloration.

[Three-dimensional finite element analysis on En mass intrusion and retraction of maxillary anterior teeth with J-hook headgear].

OBJECTIVE: To investigate the biomechanics of J-hook headgear in En mass intrusion and retraction of maxillary anterior teeth and provide guidance for clinical treatment. METHODS: A three-dimensional finite element model of maxillary teeth, periodontium, straight wire appliance and maxillary bone was established in ANSYS 14.0. En mass retraction of anterior teeth with force of 1.5 N through J-hook headgear was stimulated. Force was applied mesial to lateral incisor in group A and distal to lateral incisor in group B. The force direction was 30° to the sagittal plane and 20° to 60° to the occlusal plane. Force direction to the occlusal plane was changed every 5° and 18 cases were calculated. Displacement of upper anterior teeth and stress distribution in the periodontium were analyzed. RESULTS: As the degrees of force direction to the occlusal plane increased, the moving pattern of upper anterior teeth changed from clockwise rotation (lingual movement with intrusion) to bodily retraction and intrusion, and counter- clockwise rotation (intrusion with labial movement). With the force direction of 35° to occlusal plane applied mesial to lateral incisor or force direction of 45° to the occlusal plane applied distal to lateral incisor, bodily movement of upper anterior teeth without rotation was achieved. CONCLUSIONS: Placement of J-hook mesial to lateral incisor enable orthodontists to maintain better en mass intrusion and retraction of upper anterior teeth. The direction of J-hook should be adjusted according to individual condition and treatment objective.

[3-D finite element analysis on center of resistance of upper anterior teeth].

PURPOSE: To investigate the location of center of resistance(CRe) of six upper anterior teeth. METHODS: A three-dimensional finite element model of premaxillary bone and anterior teeth was established in ANSYS 8.1 software. Anterior teeth were fixed with stainless archwire of 2 mm × 2 mm. A horizontal retraction force of 150 g was applied bilaterally to the segment through hooks of 2 to 14 mm. After loading, solution was done and displacement and maximum principle stress were calculated. RESULTS: Displacement and stress distribution of anterior teeth varied according to the increase of height of horizontal retraction force. Labiolingual displacement of incisors varied from crown lingual tipping to lingual translation and lingual controlling root movement, while canine mainly showed lingual crown tipping. The displacements of teeth increased with the length of hook but their moving tendency remained unchanged. Stress distribution in PDL was in accordance with direction and magnitude of teeth displacement. In all cases, lingual displacement and stress in PDL were most homogeneous when hook was 10 mm long. CONCLUSION: The results of this study suggest that perpendicular location of center of resistance of six upper anterior teeth is about 14 mm gingivally to incisal edge of central incisor.