Combined Symphyseal and Condylar Fractures: Considerations for Treatment in Growing Pediatric Patients.

BACKGROUND: Combined symphyseal-condylar mandible fractures are relatively common but difficult to manage in children. This study investigated the cause and management of symphyseal-condylar fractures in pediatric patients. METHODS: This study presents a retrospective review and expert opinion of pediatric symphyseal-condylar mandibular fracture management at the authors' institution between 1990 and 2019. National data from the Healthcare Cost and Utilization Project Kids' Inpatient Database (2000 to 2016) were used to determine whether institutional data had national applicability. RESULTS: Twenty-one patients at the authors' institution met inclusion criteria. Of these patients, 26.7 percent of deciduous dentition patients underwent open reduction and internal fixation, 40 percent underwent closed treatment (maxillomandibular fixation), and 33.3 percent received a soft diet. All mixed dentition patients underwent open reduction and internal fixation or closed treatment; all permanent dentition patients underwent open reduction and internal fixation. The national database (n = 1708) demonstrated similar treatment patterns: most permanent dentition patients (88.7 percent) underwent open reduction and internal fixation, most mixed dentition patients (79.2 percent) underwent closed treatment, and among deciduous dentition patients, 53.5 percent patients received a soft diet; 38 percent received closed treatment. In this study, the overall posttreatment complication rate was 62.5 percent among open reduction and internal fixation patients, 14.3 percent among closed treatment patients, and 16.7 percent among patients treated with a soft diet. CONCLUSIONS: Symphyseal-condylar mandibular fractures were associated with substantial morbidity in children. The authors created a treatment algorithm to maximize outcomes in children who suffer from this challenging fracture pattern. CLINICAL QUESTION/LEVEL OF EVIDENCE: Therapeutic, III.

ADAMTS5 is required for normal trabeculated bone development in the mandibular condyle.

OBJECTIVE: Determine the role of the extracellular matrix protease ADAMTS5 in development of the trabeculated bone of the mandibular condyle. METHODS: The mandibular condyles of wild type and mice deficient in the protease ADAMTS5 were examined for histopathology with Safranin O staining. Microcomputed tomography was performed to analyze the developing bone of the mandibular condyle. RNAscope and immunohistochemistry were utilized to investigate cell type and extracellular matrix expression. RESULTS: Mice deficient in Adamts5, (Adamts5tm1Dgen/J) exhibit an increase in trabecular separation (n = 37 wild type; n = 27: P < 0.0001) and reduction of trabecular thickness P = 0.0116 and bone volume fraction P = 0.0869 in the mandibular condylar head compared to wild type littermates. The altered bone parameters were more pronounced in male Adamts5-/- mice compared to female Adamts5-/- mice (TbSp; P = 0.03). Adamts5 was co-expressed with versican and Gli1 in mesenchymal, stem-like cells in the transition zone where the trabeculated bone is adjacent to mature hypertrophic chondrocytes. Loss of Adamts5 caused a reduction of Bglap expressing osteoblasts throughout mandibular condylar development and in young adult mice. The protease Mmp13, that is involved in mineralization and is expressed by hypertrophic chondrocytes and osteoblasts, was reduced in the mandibular condyle of Adamts5 deficient mice. CONCLUSION: This is the first report of a novel and critical role for Adamts5 in bone formation within the mandibular condyle of the temporomandibular joint. These data indicate Adamts5 may be required in the transdifferentiation of hypertrophic chondrocytes to osteoblasts during trabecular bone formation in development of the mandibular condyle.

Mandibular ramus height and condyle distance asymmetries in individuals with different facial growth patterns: a cone-beam computed tomography study.

PURPOSE: This study aimed to quantify mandibular ramus height and condylar distances asymmetry indexes in adult patients with different vertical facial growth pattern using Cone Beam computed tomography (CBCT). METHODS: An observational cross-sectional study was conducted by using CBCT of 159 patients (mean age 26.36 ± 5.32 years). Vistadent 3D® software was used to determine the facial pattern in 3 groups (N = 53): hypodivergent, normodivergent and hyperdivergent-by Ricketts VERT index. Mandibular ramus height and the condylar linear distance in relation to the median sagittal plane were evaluated. The asymmetry index was calculated considering the right and left sides. Data were analyzed by generalized linear models and Tukey post-hoc test (α = 0.05). RESULTS: Significantly lower values were found for the left and right mandibular ramus height in the hyperdivergent skeletal pattern (P < 0.05). There was no statistically significant difference for condylar and intercondylar distances among the facial groups (P > 0.05). Asymmetry indexes (mandibular ramus height and condylar distance) were similar, and no statistically significant differences were found among the skeletal patterns. In most subjects, the severity of mandibular ramus height asymmetry varied from light to not clinically significant independently of the facial type. CONCLUSION: The findings suggest that vertical facial growth pattern not affected the asymmetry index of mandibular ramus height and the intercondylar distance. The results also demonstrated significantly shorter mandibular ramus height for the hyperdivergent skeletal pattern individuals.

Assessment of mandibular characteristics in patients affected with ß-thalassaemia major: A retrospective case-control study.

OBJECTIVE: Thalassemia is the most common hereditary blood disorder across the world. This study aimed to identify some mandibular features of thalassaemic patients and compare them with unaffected counterparts. MATERIAL AND METHODS: This retrospective case-control study was carried out on lateral cephalograms of 60 subjects (26 males, 34 females) with class II malocclusion and age range of 11 to 15 years. The control group consisted of 60 non-thalassaemic subjects with class II malocclusion and similar chronological age, gender and vertical facial dimension. Based on the Jarabak index, the case and control subjects were classified into hyperdivergent, normodivergent and hypodivergent growth patterns. Four linear (ramus height, ramus width, mandibular depth, and antegonial notch depth) and 3 angular (symphyseal angle, gonial angle, and mandibular arc angle) cephalometric parameters were measured to represent mandibular morphology. The data were analysed using Chi-square test and Student's t-test. RESULTS: No significant difference was found in linear measurements between thalassaemic patients and controls. The symphysis angle was significantly greater and the mandibular arc angle was significantly smaller in the total thalassaemic sample than the control individuals (P<0.001 and P=0.004, respectively). The difference in symphysis angle was significant in both hyperdivergent and normodivergent subjects (P=0.004 and P=0.002, respectively), whereas the difference in mandibular arc angle was only significant in the normodivergent subgroup P=0.001). CONCLUSIONS: The smaller mandibular arc angle in the thalassaemic sample suggests a more superior than posterior growth direction of condyles compared with healthy individuals. The difference in symphyseal angle represents inherent differences in chin morphology between thalassaemic subjects and controls.

[Advances in research of microRNA in the growth and development of mandibular condyle cartilage].

MicroRNA (miRNA) are a class of small non-coding single-stranded RNA that exert their biological effects by binding to target messenger RNA (mRNA). There is new evidence that miRNA may play an important role in regulating the growth and development of mandibular condylar cartilage. In this paper, the production and mechanism of miRNA are reviewed, and the progress of studies on the growth and development of mandibular condylar cartilage, which is helpful to further study the growth and development of mandibular condylar cartilage.

Effects of occlusion modification on the remodelling of degenerative mandibular condylar processes.

OBJECTIVE: The temporomandibular joint (TMJ) displays a high remodelling capability in response to occlusion changes. The purpose of the current study was to investigate the responses of TMJ condyles of growing mice to the installation of a unilateral anterior crossbite (UAC) prosthesis and the replacement of the UAC prothesis with a bilateral anterior elevation (BAE) prosthesis. MATERIALS AND METHODS: C57BL/6J mice were randomly assigned to the blank control and experimental groups. In mice in the experimental groups, UAC was created, while in others, BAE was created after the creation of UAC or removal of UAC. Changes in TMJ condylar cartilage and subchondral bone were assessed. RESULTS: The degradation of condylar cartilage induced by UAC was reversed by BAE, as evaluated by cartilage histochemical changes, collagen II-positive area, collagen X-positive chondrocytes and expression levels of Adamts-5, Mmp13, Tnf-α and Il-1ß. Subchondral bone was assessed based on the subchondral bone volume, the number of TRAP-positive cells and the Opg/Rankl ratio. CONCLUSION: The growing mouse TMJ condyle displays a high remodelling capability, which can be degenerative or rehabilitative in response to the creation of UAC and the replacement of UAC with BAE. Early correction of occlusion is beneficial for the recovery of degenerative condyles.

Photobiomodulation and Mandibular Advancement Modulates Cartilage Thickness and Matrix Deposition in the Mandibular Condyle.

Objective: We evaluated the effects of photobiomodulation (PBM), mandibular advancement (MA), and the combination of both treatments (PBM+MA) on condylar growth, by the analysis of cartilage and bone formation, fibrillar collagen deposition, proteoglycan content, cell proliferation, and clastic cell index (CCI). Methods: Forty male Wistar rats were randomly assigned to CONTROL, PBM, positive control-MA, and PBM+MA groups. The appliance was worn 10 h/day. Laser was irradiated bilaterally on mandibular condyles in 8 alternate days (1 irradiation point per condyle) using the following parameters: 780 nm, 10 J/cm2, 40 mW, 1 W/cm2, 10 sec/point, 0.4 J/point, and cumulative dose per point: 3.2 J. PBM+MA received both treatments simultaneously. After 15 days, the animals were euthanized and the condyles dissected and embedded in paraffin. Histological sections from the intermediate portion of the condyle were used for morphometric analysis. The relative frequency (%) of fibrillar collagens was determined in sections stained with picrosirius red-hematoxylin under polarized light or Gömöri's method for reticular fibers. Proteoglycan content was evaluated by computerized photocolorimetric analysis. CCI was determined by tartrate-resistant acid phosphatase (TRAP), and proliferating cell nuclear antigen (PCNA) was detected by immunohistochemistry. Results: PBM and MA influenced condylar cartilage thickeness and matrix deposition, but none of the treatments affected significantly the area of the condyle. CCI were not influenced by the treatments, but clastic cells distribution was influenced by MA and PBM+MA treatments. There was no significant difference in proliferating cells among the groups. Conclusions: This study demonstrated that PBM and MA stimulates matrix deposition and cartilage thickening in the mandibular condyle, but was not able to demonstrate a synergistic effect between the treatments. Additional studies should be conducted to evaluate the possible synergistic effect between PBM and MA.

Relationship between mandibular condyle and articular eminence cortication with mandibular cortical index on cone-beam CT.

PURPOSE: Mandibular condyle development can be evaluated with radiographic evaluation of subchondral cortical bone. The aim of this study is to investigate mandibular condyle cortication (MCC), articular eminence cortication (AEC) and mandibular cortical index (MCI) according to age and gender on CBCT, and relationship between each other. METHODS: CBCT scans of 520 patients (312 male and 208 female, age range 7-84) were retrospectively investigated to evaluate MCC, AEC and MCI. MCC and AEC were examined in sagittal section and MCI in panoramic reformatted image. MCC and AEC were classified as Type I, Type II and Type III according to density difference between the cortical bone enclosing condyle and articular eminence. Categorical variables were tested by Chi square. RESULTS: When MCC, AEC and MCI were compared, a significant relationship was detected (p < 0.05). According to age, there was a significant difference between MCC, MCI and AEC types with each other (p < 0.05). No significant discrepancy was found between gender and MCC, AEC and MCI (p > 0.05). CONCLUSIONS: This study evaluated the distribution of MCC, AEC, MCI according to age and gender and detected that these cortications were correlated. This result may be caused by anatomical proximity bone components and functional stimuli. Knowledge of these cortications can be important for accurate diagnosis of TMJ disorders and may also be helpful for prediction of osteoporotic changes.

Differential growth of craniofacial and tibial bones to sympathetic hyperactivity-related hypertension in rats.

OBJECTIVE: To evaluate the effect of sympathetic nervous system hyperactivity on craniofacial skeletal growth in growing spontaneously hypertensive rats (SHRs). DESIGN: Craniofacial skeletal growth was compared between male SHR and Wistar-Kyoto rats (WKR) using linear measurements on lateral and transverse cephalometric radiographs at the age of 12 weeks. Tibia length was measured as an index of whole body growth. Body weight　and blood pressure were measured from 3 to 12 weeks of age. Bone microstructure in the mandibular condyle and tibia between the two groups was compared at the age of 12 weeks using microcomputed tomography. RESULTS: The SHRs had a significantly lower body weight than WKRs from 7 weeks of age, and tibial length was significantly smaller in the SHRs than in the WKR at 12 weeks of age. In all SHRs, blood pressure was significantly higher than in WKRs from 3 to 12 weeks of age. Cephalometric analyses revealed decreased measurements of the neurocranium, viscerocranium, and mandible in SHRs, and mandibular growth was most negatively affected in this group. Lastly, in SHRs, microcomputed tomography analyses revealed decreased bone mineral density and bone volume/tissue volume in the mandibular condyle but not in the tibia. CONCLUSION: In growing SHRs, hypertension related to the hyperactivity of the sympathetic nervous system reduced craniofacial skeletal growth more than the growth of the tibia.

Nutritional supplementation with myo-inositol in growing mice specifically augments mandibular endochondral growth.

INTRODUCTION: The purpose of this study was to examine growth-promoting effects of myo-inositol nutritional supplementation on the mandible in experimental animals. METHODS: Mice were fed on diets that contained various concentration of myo-inositol for 3 to 12 weeks. The length of the mandible, maxilla, and femur were measured on µCT images. The mandible and tibia were examined histologically and immunohistochemically. The effects of myo-inositol on cell proliferation and chondrocytic differentiation were examined using ATDC5 cells. RESULTS: Myo-inositol supplementation had no effects on body weight, length, and maxilla and femur lengths. However, the length of mandible and the thickness of the mandibular condylar cartilage (MCC) were increased by myo-inositol supplement. Microarray analysis revealed that Pik3cd was highly expressed in MCC as compared to that in the cartilage of the tibial growth plate, which was confirmed by real-time RT-PCR and immunohistochemistry. ATDC5 cells also highly expressed Pik3CD. Myoinositol induced increases in cell proliferation and chondrocytic differentiation in ATDC5 cells. The addition of a PIK3CD inhibitor blocked the induction of cell proliferation by myo-inositol in ATDC5 cells. CONCLUSIONS: Nutritional supplementation with myo-inositol in growing mice augmented mandibular endochondral growth without any systemic effects. The specific promotion of mandibular growth by myoinositol is primarily dependent on the specific intensive expression of PIK3CD in the MCC.

Effect of Rapid Maxillary Expansion on Condyle-fossa Relationship in Growing Patients.

AIM: This study tests whether rapid maxillary expansion (RME) exerts long term effects on interglenoid fossa distance and condyle fossa relationship. MATERIALS AND METHODS: Consecutive growing patients aged 8 to 13 years were allocated either to the RME group or control group. Cone-beam computed tomography was performed at baseline and at 6 months. Specific software was used to determine fixed landmarks. Multivariate Analysis of Covariance (MANCOVA) models were used, with time by group interaction, using age as a covariate. RESULTS: Twenty-seven patients with a mean age of 11.4 ± 1.5 years were included. There was an overall significant group by time interaction (p = 0.012, effect size 0.59). Change in the lateral position of the glenoid fossa, the primary outcome, was reached (p = 0.008, effect size 0.258). Change in the laterolateral position of the center of the condyle, and the co-primary outcome was also significant (p = 0.011, effect size = 0.24). Nasal cavity width increased (p = 0.065, effect size = 0.14). There was an initial asymmetry in the horizontal position of the condyles that was carried on with no effect of RME. CONCLUSION: Rapid maxillary expansion (RME) produces a significant increase in the interglenoid fossa distance and displacement of the mandibular condyles at 6 months in growing patients compared to a control group. CLINICAL SIGNIFICANCE: The current study shows that RME is effective during growth, widening the interglenoid fossa distance and the lateral positions of the condyles and eventually enlarging the nasal cavity, without causing asymmetry.

The effects of elevated fibroblast growth factor 23 on mandibular growth in rats.

OBJECTIVE: The aim of this study is to elucidate the local effects of fibroblast growth factor 23 (FGF23) in on mandibular condylar growth in growing rats. DESIGN: Growing Sprague-Dawley rats received intra-temporomandibular joint injections of phosphate buffer solution (PBS), adenovirus-mediated green fluorescent protein (Ad-GFP) or adenovirus-mediated fibroblast growth factor 23 (Ad-FGF23), which were marked as groups A, B, and C, respectively. In vitro, we treated rat mandibular cartilage chondrocytes with PBS, Ad-GFP, and Ad-FGF23. RESULTS: The mandibular condyles in group C grew smaller sizes than those in the other control groups due to significant differences among the experimental and control groups with the value of C-D, Q-R (P ≤ 0.05), accompanied by diminished bone mass of sub-cartilage condyles via micro CT analysis. Histologically, the length of the hypertrophic zone was diminished and was associated with decreasing chondrocyte proliferation in group C. Quantitative real-time PCR indicated significant decreases in the expression of chondrogenesis marker genes, including Type X collagen (Col X) and SRY-type box 9 (Sox 9). Moreover, elevated Ad-FGF23 suppressed chondrocyte proliferation and the expression of the chondrogenic differentiation markers Col X and Sox 9 of in vitro. CONCLUSIONS: Local injection of FGF23 suppressed the development and decreased the bone mass of condyles through the decreasing the formation of condylar cartilage, specifically by regulating condylar cartilage cell viability and chondrogenesis expression.

[Facial symmetry after conservative treatment of unilateral condylar fracture in children: a three-dimensional study].

Objective: To investigate the influence of condylar fractures on the growth of condylars after conservative treatments by three-dimensional measurement. Methods: Twenty three children with unilateral condylar fracture followed-up for at least 1 year in Shanghai Ninth People's Hospital were included from June 2016 to March 2017. CT scans were performed for each patient. Three-dimensional virtual skulls were reconstructed and measuring points were defined with Simplant 11.04 software. The depth of glenoid fossa, height of articular eminence, width, height and depth of condylar, deviation of pogonion were measured. Statistical analyses were conducted to assess difference between the bifid group and the normal group. Results: No difference was observed in the vertical position of crest of the articular eminence between two groups (P=0.110). The vertical position of roof of the glenoid fossa in bifid side was significantly superior than the one in normal side (P=0.010). Bifid side had a shorter (P=0.002) and wider(P=0.002) condylar than normal side did. No difference was observed in the depth of condylar between two groups (P=0.071). The average deviation of pogonion was (0.69±1.75) mm (P=0.072) from sagittal plan. Conclusions: This short-termed study indicates that children's growth potential of condylar is under average after conservative treatments. Because the bone hyperosteogeny of glenoid fossa compensates the hypotrophy of condylar, no deviation of pogonion is detected.

The impact of dietary consistency on structural craniofacial components: Temporomandibular joint/condyle, condylar cartilage, alveolar bone and periodontal ligament. A systematic review and meta-analysis in experimental in vivo research.

OBJECTIVE: The aim of this systematic review was to provide a comprehensive synthesis of available evidence evaluating the effect of dietary loading on temporomandibular joint/condyle, condylar cartilage, alveolar bone of the mandible and the periodontal ligament in healthy mice and rats. DESIGN: Medline via PubMed, EMBASE and Open Grey databases were searched for published and unpublished literature. Search terms included "mandiblular condyle", "alveolar bone", "temporomandibular joint", "condylar cartilage", "periodontal ligament", "rat", "mice". After data extraction, risk of bias (SYRCLE) and reporting quality (ARRIVE) were assessed. Random effects meta-analyses were performed for the outcomes of interest where applicable. RESULTS: A total of 33 relevant articles were considered in the systematic review, while only 6 studies were included in the quantitative synthesis. Risk of Bias in all studies was judged to be unclear to high overall, while reporting quality was suboptimal. Comparing soft to hard diet animals, significantly reduced anteroposterior condylar length (4 studies, weighted mean difference: -0.40 mm; 95% CI: -0.47, -0.32; p < 0.001) and width (4 studies, weighted mean difference: -0.043 mm; 95% CI: -0.51, -0.36; p < 0.001) were found in rats. Decreased anteroposterior condylar dimensions were detected for mice as well (2 studies, weighted mean difference: -0.049; 95% CI: -0.56, -0.43; p < 0.001). CONCLUSIONS: Overall, there was strong evidence to suggest a significant effect of soft diet on reduced condylar dimensions in rodents; however, there is need for further high quality experimental studies to inform current knowledge on condylar cartilage, alveolar bone and periodontal ligament related outcomes.

Mandibular Condylar Aplasia Treated with a Functional Appliance: A Five years Follow Up.

This report presents a follow up of a clinical case published five years ago by the same authors. In the previous report, the authors showed a young girl treated with a myofunctional appliance due to a mandibular condylar agenesia. After a traditional graft had failed, the patient successfully responded to the functional treatment by forming a mandibular condyle. In this new report, the authors are showing how the mandibular condyle has continued developing within normal limits and, the mandibular ramus has continued positively remodeling. The bone biology embedded in the biological process reported here is discussed by the authors.

Developmental characteristics of secondary cartilage in the mandibular condyle and sphenoid bone in mice.

OBJECTIVE: Secondary cartilage develops from osteochondral progenitor cells. Hypertrophic chondrocytes in secondary cartilage increase within a very short time and then ossify rapidly. In the present study, we investigated the sequential development process of osteochondral progenitor cells, and the morphology and size of hypertrophic chondrocytes in secondary cartilage. DESIGN: ICR mice at embryonic days (E) 14.5-17.5 were used. The mandibular condyle and the medial pterygoid process of the sphenoid bone were observed as secondary cartilage, and the cranial base and the lateral pterygoid process of the sphenoid bone, which is primary cartilage, were observed as a control. Thin sections were subjected to immunostaining and alkaline phosphatase (ALP) staining. Using a confocal laser microscope, 3D stereoscopic reconstruction of hypertrophic cells was performed. To evaluate the size of hypertrophic chondrocytes objectively, the cell size was measured in each cartilage. RESULTS: Hypertrophic chondrocytes of secondary cartilage first expressed type X collagen (Col X) at E15.5. SRY-box 9 (Sox 9) and ALP were co-expressed in the fibroblastic/polymorphic tissue layer of secondary cartilage. This layer was very thick at E15.5, and then rapidly became thin. Hypertrophic cells in secondary cartilage were markedly smaller than those in primary cartilage. CONCLUSIONS: The small hypertrophic cells present in secondary cartilage may have been a characteristic acquired in order for the cartilage to smoothly promote a marked increase in hypertrophic cells and rapid calcification.

Evaluation of the relationship between mandibular condyle cortication and chronologic age with cone beam computed tomography.

PURPOSE: The aim of the present study is to evaluate the relationship between mandibular condyle cortication and chronologic age and gender via cone-beam computed tomography (CBCT) and to investigate the effectiveness of using the condylar cortication as a new method of age estimation. METHODS: CBCT images from 433 subjects aged 8 to 31 years were included in this study. The right and left condyle cortication were assessed on the sagittal plane separately for each individual by the same investigator via a new method that describes the cortication of the condyle. Type I: There is no cortication on the condyle. Type II: The bone that is on the superior surface of the condyle is seen less density than the structures around the condyle. Type III: The surface of the condyle is seen similar or higher density than the surrounding cortical areas. RESULTS: The type of the condyle cortication in the right and left mandible was similar for almost each subject and there was no statistically significant different between them (p = 0.375). When we evaluated the results without including these patients for male, Type I cortication of the condyle was seen at 14.14 ±â€¯2.3 years, Type II cortication of the condyle was seen at 16.11 ±â€¯3.18 years and Type III cortication of the condyle was seen at 19.39 ±â€¯3.96 years. For the female, Type I cortication of the condyle was seen at 13.01 ±â€¯2.16 years, Type II cortication of the condyle was seen at 15.52 ±â€¯2.71 years and Type III cortication of the condyle was seen at 17.95 ±â€¯3.13 years. The minimum age of Type III cortication was 11 and 15 years old for male and female, respectively. However, there are subjects, who are 30 year old man and 31 year old female, have no cortication as much as similar or higher than the surrounding the cortical areas. CONCLUSION: This study is the first investigation of the relationship between condyle cortication and chronologic age with CBCT in the Turkish population. The type of cortication in the right and left condyle may be different for the same individual. Chronologic age increased as the stages of the cortication process from Type I to Type III in male and female individuals, and all the stages of the cortication in the mandibular condyle of male occur later time according to female.

Effect of different masticatory functional demands on the 3D mandibular condyle morphology of growing rats using posterior bite-blocks.

Background and objectives: Apart from the primary effect of bite-blocks on tooth position, they may also influence the mandibular condylar growth. Our aim was to investigate their influence on the condylar morphology, with variable masticatory forces. Material and methods: Fifty-two 4-week old male rats were divided into hard and soft diet groups in order to create individuals with different masticatory muscle capacity. Two weeks later, they were equally divided into bite-block and control groups. After a total of 6 weeks experimental time, the animals were sacrificed. The mandibles were scanned with high-resolution micro-CT and 3D analysis was performed on the condylar neck and head of the condyle. The volume and the length of the condylar process were measured. Statistical analysis was done with a one-way analysis of variance. Results: The use of bite-blocks decreased the length of the condylar process (P = 0.001) as well as the volume of the condylar neck (P = 0.001) and head (P = 0.006). The soft diet decreased the volume of the condylar neck (P < 0.001) and head (P < 0.001) two to three times more than the bite-blocks but did not affect the condylar process length. The interaction between the two variables was not statistically significant. Conclusions: Both the bite-block appliance and weak masticatory muscle function reduced the volume at all regions of the condylar process, although the functional factor had a substantially greater effect. However, only the bite-block appliance affected the condylar process length. In the presence of both factors, an additive effect was found but no interaction detected.

Mechanical stress promotes matrix synthesis of mandibular condylar cartilage via the RKIP-ERK pathway.

Mandibular hypoplasia is a common jaw deformity that affects breathing, occlusal function and facial aesthetics. Stimulating mandibular condylar growing with functional appliances is an ordinary but controversial treatment method in orthodontics. Therefore, it is vital to clarify how functional appliances affect condylar growing. Raf-1 kinase inhibitor protein (RKIP), as an endogenous inhibitory molecule of the ERK signaling, is postulated to involve in stress-induced response to articular cartilage. This study was to reveal the role of RKIP in regulating cartilage matrix synthesis with functional appliance treatment. Here, position rat mandibular forward simulating functional appliance effect to examine the stress-induced modification of mandibular condylar in vivo, meanwhile rat mandibular condylar chondrocytes (Mccs) were subjected to cyclic tensile stress (CTS, 16%, 1 HZ). The results showed that mandibular forward therapy enhanced condylar cartilage growth. The thicknesses of all layers of condylar cartilage were increased significantly. RKIP expression was also increased in the mature cartilage layer. In addition, CTS could enhance extracellular matrix formation and cartilage marker expression (aggrecan and collagen II), which shared a similar expression pattern with RKIP in Mccs. However, CTS induced up-regulation of collagen II and aggrecan was blocked by RKIP knockdown. Nuclear p-ERK, targeting downstream of RKIP, showed a decrease after CTS,which was disappeared in RKIP-knockdown Mccs. Taken together, physiological mechanical stimulation promotes cartilage growth modification by up-regulating RKIP through inhibiting ERK signaling pathway.