Osteogenesis in the glenoid fossa in response to mandibular advancement

Differential impact of chronic intermittent hypoxia and stress changes on condylar development

OBJECTIVES

This study aimed to determine the effects of chronic intermittent hypoxia (CIH) and stress change (SC) on the development of the condyle in mouth breathing rats.

DESIGN

A total of 120 4-week-old rats were randomly assigned to one of five groups. The control (Ctrl) group was the blank control and the intermittent nasal obstruction (INO) group was the positive control. Mild CIH (mCIH) and severe CIH (sCIH) groups were developed by adjusting environmental oxygen concentration and monitoring real-time blood oxygen saturation (SpO2). The SC group was developed using INO, increased environmental oxygen concentration, and real-time SpO2 monitoring. Six rats from each group were sacrificed for analysis at 0, 1, 2, or 4 weeks.

RESULTS

Similar to the INO group, condyle and mandibular body development in the sCIH group, but not in the mCIH group, was significantly inhibited compared with the Ctrl group. The SC group had inhibited development of the condyle, especially of the posterior zone, but had minimal impact on the growth of the mandible.

CONCLUSION

The inhibitory effects of CIH on the development of the condyle and mandibular body were SpO2-dose-dependent. When SC occurred, inhibited development was observed in the posterior zone of condyle but not the whole mandible. These findings provide important insights for targeted interventions that address the consequences of mouth breathing in children.

Influence on the temporomandibular joint induced by mandibular malpositioning caused by vertical dimension elevation and occlusal loss in adult rats: An imaging, histological and immunohistochemical study

BACKGROUND

Mandibular malpositioning may result in an abnormal concentration of stresses within the temporomandibular joint (TMJ) in adult rats, which may further lead to a series of pathological changes, such as articular cartilage wear, subchondral bone sclerosis and osteophyte formation. However, the pathological and adaptive changes in condylar cartilage caused by different stress distributions are still controversial.

OBJECTIVE

The aim of this study was to observe the effect of sagittal changes in mandibular position on condylar cartilage by changing the occlusal vertical dimension (OVD) in adult rats.

METHODS

Fifteen-week-old female rats were divided into three groups: control (CON), increased OVD (iOVD) and loss of occlusion (LO) groups. An occlusal plate and tooth extraction were used to establish the animal model. TMJ samples of the experimental and CON groups were observed and investigated by bone morphological, histomorphological and immunohistochemical staining analyses at 3 days, 1 week, 2 weeks, 4 weeks and 8 weeks. Weight curves were plotted.

RESULTS

Micro-computed tomography showed that, compared with the CON group, cartilage destruction followed by repair occurred in both experimental groups, which was similar to the trend observed in haematoxylin-eosin staining. All experimental results for the iOVD group showed an approximately similar time trend. Compared with the iOVD group, the toluidine blue and immunohistochemical staining results in the LO group showed no obvious change trend over time.

CONCLUSION

Compared with occlusal loss, an increase in OVD caused faster and more severe damage to condylar cartilage, and subchondral bone repair occurred later.

Comparison of Skeletal Changes in the Temporomandibular Joint between the Twin Block Appliance and Fixed Functional Appliance: A Longitudinal Follow-up Study

Aim

This current study evaluated and compared the skeletal changes in the head of the condyle, glenoid fossa, and articular space between the twin block appliance and PowerScope™ a fixed functional appliance.

Materials and methods

This study was a pilot, randomized, single-blinded, assessing the skeletal changes in the components of the temporomandibular joint (TMJ) using cone-beam computed tomography (CBCT). The study was conducted in 20 subjects in the age range of 11-14 years with class II division 1 malocclusion. These subjects were distributed randomly between two groups with an allocation ratio of 1:1 (group I-twin block and group I-PowerScope™). Follow-ups of both groups were done till desirable skeletal correction was attained (clinical edge-to-edge incisor relation).

Results

Condylar parameters such as position, height, and length were evaluated bilaterally in the CBCT scans. After using both devices, there was an increase in all condylar qualities; however, the twin block appliance showed a more noticeable difference, which has been determined to be statistically significant. In the twin block group, there was an average decrease of 0.56 mm in the anterior articular space and an increase of 1.2 and 2.64 mm in the middle and posterior articular spaces, respectively. In the PowerScope™ group, there was an average decrease of 0.23 mm in the anterior articular space and an increase of 2.55 and 1.85 mm in the middle and posterior articular spaces, respectively. In the case of the twin block device, the change in glenoid fossa angle was observed to be 6.1 mm on both sides and a mean difference of 1.25 mm on the right-side and 1.75 mm on the left-side was observed in the case of PowerScope™. The difference was established to be significant with a p < 0.05 in all cases.

Conclusion

Condylar attributes increased after the application of both devices but the difference was more pronounced in the case of twin block appliances. The difference in articular space (middle and posterior) between the twin block group and PowerScope™ group, was not significant statistically. In the present study, the remodeling in the glenoid fossa was greater in the twin block group compared to the PowerScope™ group.

How to cite this article

Halapanavar B, MN P, Deshmukh S, et al. Comparison of Skeletal Changes in the Temporomandibular Joint between the Twin Block Appliance and Fixed Functional Appliance: A Longitudinal Follow-up Study. Int J Clin Pediatr Dent 2024;17(1):7-14.

Stress distribution of the modified clear twin-block aligner on the temporomandibular joint, alveolar bone and teeth: A finite element analysis

OBJECTIVE

The modified clear twin-block aligner (CTBA) was developed to provide a mandibular advancement appliance for the treatment of mandibular retrognathia. The objective of this study was to analyse the stress distribution changes of CTBA with 45°, 60° and 70° bite blocks.

MATERIAL AND METHODS

A three-dimensional model of the craniomaxillofacial bones and teeth was generated from a spiral computed tomography (CT) scan. The models of the articular disc, capsule, periodontal ligament and CTBA were constructed mathematically. After assigning the appropriate material properties and the boundary condition using ABAQUS software, we simulated the CTBA with different bite blocks to analyse the mechanical effects.

RESULTS

In the temporomandibular joint (TMJ) region, the posterior aspect of the condyle and glenoid fossa experienced tensile stress that was approximately about 22 times greater at 70° than at 45°. The Von Mises stress distribution on the articular disc tended to be uniform. The strain direction of the condyle was backward. In the maxillary bone, the stress on the labial alveolar bone was about 5.83MPa at 70° and greater than that on the lingual side. The resulting displacement of the dentition revealed a tendency for the upper teeth to shift backward and the lower teeth to move forward by 0.46 to 0.49mm. The foregoing stress and displacement rose as the angle of the bite blocks increased.

CONCLUSIONS

CTBA with 70° bite blocks constituted an advantageous biomechanical setting for the treatment of mandibular retrognathia in teenagers and provided a superior therapeutic effect.

Treatment effects of Herbst appliance in skeletal Class II cases during pre-pubertal and post-pubertal periods: a cone-beam computed tomographic study

In the present study, Thirty-six Class patients II (A condition in which the upper jaw is larger than the lower jaw) were randomly selected and assigned to one of two groups based on their maturation stage: the pre-pubertal group (18 patients, mean age 9.15 ± 1.5 years) and post-pubertal group (18 patients, mean age 16.3 ± 1.0 years). All patients were treated with a metallic splint-supported Herbst IV appliance (An appliance that acts like artificial joint working between the upper and power jaws that keeps the lower jaw in a forward position, thus improving the Class II condition). Pretreatment (T1) and post-Herbst IV treatment (T2) scans were obtained for both groups. Dental and skeletal measurements were made on the scans and statistically analyzed using paired and independent t-tests. The study hypothesis was that; the dentoskeletal changes in Class II malocclusion treatment using Herbst appliance in the Pre-pubertal is more than the Post-pubertal growth stage due to the remaining growth potential for the pre-pubertal patients. The comparison between the two groups revealed statistically significant differences in horizontal skeletal parameters in the lower jaw only, while other readings were similar.

Wnt/β-catenin signaling pathway is activated in the progress of mandibular condylar cartilage degeneration and subchondral bone loss induced by overloaded functional orthopedic force (OFOF)

Objective

To explore the role of Wnt/β-catenin signaling pathway in the pathogenesis and progression of temporomandibular joint osteoarthritis (TMJ OA) caused by overloaded force.

Materials and methods

We generated a rat model of forward mandibular extension device to induce TMJ OA by overloaded force. Condylar cartilage samples were collected at 2wk, 4wk, and 8wk after appliances were installed. Changes of the condylar cartilage and subchondral bone were evaluated by hematoxylin and eosin (HE), Safranin O and Fast Green staining (SO&FG), micro-CT, tartrate resistant acid phosphatase (TRAP) staining. The expression levels of β-catenin, COL-2, MMP3 and sclerostin (SOST) were detected by immunohistochemistry (IHC) and PCR.

Results

HE, SO&FG, micro-CT, OARSI and Mankin scores showed that the condyle cartilage layer was significantly thinner and proteoglycan loss in the overloded group. TRAP staining exhibited that the number of positive osteoclasts increased and OPG level decreased in the overload group. IHC, PCR showed that the expression of COL2 and SOST decreased, while MMP3 and β-catenin increased in the overload group.

Conclusion

Wnt/β-catenin signaling pathway is activated in the progress of mandibular condylar cartilage degeneration and subchondral bone loss induced by overloaded functional orthopedic force (OFOF)

Effects of the advanced mandibular spring on mandibular retrognathia treatment: a three-dimensional finite element study

Background

The Advanced Mandibular Spring (AMS) was newly developed as a dentofacial orthopedic appliance in conjunctive use of clear aligners to treat Class II malocclusion with mandibular retrognathia in adolescents. This study aimed to launch a biomechanical assessment and evaluate whether the stress patterns generated by AMS promote mandibular growth.

Methods

A three-dimensional finite element model was constructed using images of CBCT and spiral CT. The model consisted of craniomaxillofacial bones, articular discs, retrodiscal elastic stratum, masticatory muscle, teeth, periodontal ligament, aligner and AMS. Mechanical effects were analyzed in three types of models: mandibular postural position, mandibular advancement with AMS, and mandibular advancement with only muscular force.

Results

The stress generated by AMS was distributed to all teeth and periodontal ligament, pushing mandibular teeth forward and maxillary teeth backward. In the temporomandibular joint area, the pressure in the superior and posterior aspects of the condyle was reduced, which conformed to the stress pattern promoting condylar and mandibular growth. Stress distribution became even in the anterior aspect of the condyle and the articular disc. Significant tensile stress was generated in the posterior aspect of the glenoid fossa, which conformed to the stress pattern stimulating the remodeling of the fossa.

Conclusions

AMS created a favorable biomechanical environment for treating mandibular retrognathia in adolescents.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12903-022-02308-w.

Three-Dimensional Evaluation of Condyle-Glenoid Fossa Complex Following Treatment with Herbst Appliance

The purpose of the present retrospective observational study was to compare the effects of treatment with Herbst appliance and fixed therapy with elastics on the condyle and glenoid fossa complex. Thirty patients aged between twelve and sixteen years with skeletal Class II malocclusion who met the inclusion criteria were included in the study: fifteen patients treated with Herbst appliance (Group 1), and fifteen patients treated with orthodontic camouflage using MBT prescription (MBT^TM Versatile+ Appliance System) (Group 2). For Group 2, patients had CBCT scans taken before treatment either after Herbst appliance removal or at the end of treatment. CBCT scans were evaluated for changes in condyle-glenoid fossa complex using the In Vivo Dental 5.1 software. Statistical significance was set at p ≤ 0.05. On inter-group comparison, the Herbst group showed statistically significant increases in the condylar height of 1.35 mm (p ≤ 0.001) on the right and 1.21 mm (p ≤ 0.01) on the left side, and a condylar volume of 111.03 mm³ (p ≤ 0.01) on the right and 127.80 mm³ (p ≤ 0.001) on the left side. The Herbst group showed anterior remodelling on the postero-superior aspect of glenoid fossa. Herbst appliance treatment induced growth at the condylar head and anterior remodelling of glenoid fossa, thereby improving the maxilla-mandibular relationship in growing skeletal Class II patients.

Evaluating the effects of functional orthodontic treatment on mandibular osseous structure using fractal dimension analysis of dental panoramic radiographs

OBJECTIVE

To evaluate the effects of functional appliance treatment on mandibular trabecular structure using fractal dimension (FD) analysis of dental panoramic radiographs.

MATERIALS AND METHODS

This study was conducted using digital panoramic radiographs of 45 patients with Class II malocclusion treated with functional appliances (treatment group, mean age: 11.39 ± 0.97 years; 23 girls, 22 boys) acquired before (T0) and after (T1) treatment and the panoramic radiographs of 45 control subjects who had undergone no orthodontic treatment (control group, mean age: 11.31 ± 0.87 years; 23 girls, 22 boys). FD values in the condylar process, mandibular corpus, and mandibular angle were analyzed from the panoramic radiographs of both groups.

RESULTS

Analysis of changes in FD between T0 and T1 revealed significant increases in the FD values of the right and left condylar processes and right mandibular corpus in the treatment group (P < .001) and in the right condylar process in the control group (P < .05). Between-group comparisons demonstrated that the treatment group showed greater changes in the condylar process (right, P < .001; left, P < .05) and right mandibular corpus (P < .05) compared to controls. Correlation analysis between the cephalometric and FD changes in the treatment group showed the right condylar process changes were negatively correlated with GoGn/SN angle (P < .05) and positively correlated with Co-Go (P < .05), although these correlations were weak.

CONCLUSIONS

FD analysis demonstrated significant changes in trabeculation of the condyle and mandibular corpus in the treatment group compared to the control group. Functional appliance treatment may lead to skeletal correction by altering skeletal form and trabeculation of the mandibular bone.

Post-treatment cephalometric changes in adolescent patients with Class II malocclusion treated using two different functional appliance systems for an extended time period: a randomized clinical trial

OBJECTIVES

To assess the post-treatment changes in Class II adolescent patients treated with two different functional appliances for an extended time period.

DESIGN

Randomized clinical trial.

SETTING

One university and one district general hospital in the UK.

PARTICIPANTS

Caucasian adolescent patients with a Class II malocclusion.

METHODS

Pairs of patients of similar age and gender were randomly allocated to one of two functional appliance systems, the Twin Block or Dynamax appliance. The appliances were used for 15 months full time. Changes were measured from lateral cephalograms taken at the start (T1) and at the end of treatment at 15 months (T2) and 30 months (T3).

RESULTS

Hundred patients completed the trial, 52 Twin Block and 48 Dynamax. Mandibular forward movement was 3.5 mm (±2.5) in the Twin Block group and 1.7 mm (±2.1) in the Dynamax group (P < 0.01; T1-T2) and, subsequently, by 0.3 mm (±2.6) and 0.9 mm (±2.5), respectively (P = 0.3; T2-T3). Mandibular length increased by 6.3 mm (±2.7) in the Twin Block group and 4.0 mm (±2.5) in the Dynamax group (P < 0.01; T1-T2) with treatment and, subsequently, by 0.5 mm (±2.3) and 1.5 mm (±3.1; P = 0.05). Anterior face height increased in both groups.

CONCLUSIONS

Treatment resulted in greater mandibular growth with the Twin Block than the Dynamax. In the follow-up period, there was less growth in the Twin Block group compared to the Dynamax.

TRIAL REGISTRATION

This trial was not registered on any major database of clinical trial.

PROTOCOL

The protocol was not published before the commencement of the trial but can be given on request.

Ubiquitin-Regulated Cell Proliferation and Cancer

Ubiquitin ligases (E3) play a crucial role in the regulation of different cellular processes such as proliferation and differentiation via recognition, interaction, and ubiquitination of key cellular proteins in a spatial and temporal regulated manner. The type of ubiquitin chain formed determines the fate of the substrates. The ubiquitinated substrates can be degraded by the proteasome, display altered subcellular localization, or can suffer modifications on their interaction with functional protein complexes. Deregulation of E3 activities is frequently found in various human pathologies, including cancer. The illegitimated or accelerated degradation of oncosuppressive proteins or, inversely, the abnormally high accumulation of oncoproteins, contributes to cell proliferation and transformation. Anomalies in protein abundance may be related to mutations that alter the direct or indirect recognition of proteins by the E3 enzymes or alterations in the level of expression or activity of ubiquitin ligases. Through a few examples, we illustrate here the complexity and diversity of the molecular mechanisms related to protein ubiquitination involved in cell cycle regulation. We will discuss the role of ubiquitin-dependent degradation mediated by the proteasome, the role of non-proteolytic ubiquitination during cell cycle progression, and the consequences of this deregulation on cellular transformation. Finally, we will highlight the novel opportunities that arise from these studies for therapeutic intervention.

Three-dimensional comparison of the skeletal and dentoalveolar effects of the Herbst and Pendulum appliances followed by fixed appliances: A CBCT study

OBJECTIVES

To compare three-dimensional (3D) skeletal and dentoalveolar effects of the Herbst and Pendulum appliances followed by fixed orthodontic treatment in growing patients.

SETTING AND SAMPLE POPULATION

A sample of 35 adolescents with cone-beam computed tomography scans obtained prior to Herbst and Pendulum treatment (T1) and immediately after fixed appliance treatment (T2).

MATERIALS AND METHODS

Patients with Class II malocclusion was assessed retrospectively and divided into two treatment groups: Herbst group (n = 17, age: 12.0 ± 1.6 years) and Pendulum group (n = 18, age: 12.1 ± 1.5 years), with a mean treatment duration of 2.8 ± 0.8 years and 2.5 ± 0.7 years, respectively. Reconstructions of the maxillomandibular and dentoalveolar regions and data in 3D were obtained relative to cranial base, maxillary and mandibular regional superimpositions. Treatment outcomes (T2-T1) were compared between both groups using t tests for independent samples (P<.05).

RESULTS

Significant increase in mandibular length was observed in the Herbst group (7.3 ± 3.5 mm) relative to the Pendulum group (4.6 ± 4.5 mm). Inferior and anterior displacements of Pogonion were 2.2 mm and 1.6 mm greater in the Herbst group, respectively. The mesial displacement of the lower first molars was significantly greater in the Herbst group (1.9 mm). The upper first molars had contrasting results in sagittal displacement, with 0.6 ± 1.7 mm of distal displacement with the Pendulum and 1.4 ± 2.1 mm of mesial displacement with the Herbst. Lower incisor projection and proclination were similar between groups.

CONCLUSIONS

The Herbst and Pendulum appliances followed by comprehensive orthodontic treatment effectively corrected Class II malocclusion in growing patients, but with differing skeletal and dentoalveolar effects.

Expression of lubricin in rat posterior mandibular condylar cartilage following functional mandibular forward repositioning

PURPOSE

The aim of the present study was to investigate the effects of mandibular forward repositioning on expression of lubricin in rat posterior condylar cartilage.

METHODS

In total, fifty 5‑week-old female Sprague Dawley rats were divided randomly into experimental groups and control groups. The animals in the experimental groups were fitted with modified acrylic inclined planes to advance the mandible, whereas rats in the normal control groups were left intact. Rats were sacrificed on days 3, 7, 14, 21, and 30, and temporomandibular joint (TMJ) samples were collected. The expression of lubricin of the posterior mandibular condylar cartilage was evaluated by immunohistochemistry.

RESULTS

In the control groups, higher expression of lubricin was observed in the proliferative zone of the posterior mandibular condylar cartilage compared with the hypertrophic zone during the experimental period. Compared with the control group, the positive signals for lubricin of the posterior mandibular condylar cartilage in the experimental animals were significantly higher on days 7, 14, and 21; however, no statistical difference was found on day 3 or 30.

CONCLUSIONS

Data analyses suggest that the bite jumping appliance temporarily enhanced lubricin expression, providing a good mechanical environment for the physiologic growth of the condyle and mandible, and contributes to TMJ remodeling by the regulation of condylar chondrocyte proliferation.

Are morphologic and topographic alterations of the mandibular fossa after fixed functional treatment detectable on tomograms? Visual classification and morphometric analysis

AIM

The goal was to evaluate if changes in morphology and topography of the mandibular fossa after Functional Mandibular Advancer (FMA) treatment are detectable on tomograms. Furthermore, the suitability of digital tomograms (DT) over magnetic resonance imaging (MRI) for this particular question was investigated.

MATERIALS AND METHODS

In all, 25 patients (14 female, 11 male) with a skeletal class II malocclusion received treatment with a FMA. DTs were available prior to (T1) and after (T2) FMA treatment. A total of 50 temporomandibular joints were investigated. The mandibular fossae were evaluated metrically and visually regarding treatment-induced alterations. A p < 0.05 was set as the level for statistical significance for all tests. Results were compared to the results of a recent MRI study.

RESULTS

Visual inspection of all 50 joints in the DT at T1 and T2 revealed no alterations of the fossa shape in the sagittal plane; 24 patients showed identical morphology of right and left joints. The metrical analysis revealed no significant changes regarding width, depth and ratio thereof between T1 and T2. There also were no bilateral differences. Another 18 different distance measurements between porion, mandibular fossa, articular eminence and pterygoid fossa showed no significant changes. There was no detectable proof of a fossa shift.

CONCLUSIONS

No changes in the sagittal plane, mandibular fossa, the articular tubercle, or a possible fossa shift were found in the DT of class II patients after FMA treatment. DT and MRI measurements and the visual inspection revealed identical findings; thus, DT appears to be a valuable research tool for sagittal analysis of mandibular fossa changes.

Three-dimensional treatment outcomes in Class II patients with different vertical facial patterns treated with the Herbst appliance

INTRODUCTION

The aims of this study were to evaluate, using 3-dimensional superimposition techniques, the skeletal changes in Class II subjects with different vertical facial patterns treated with the Herbst appliance and to compare these skeletal changes to those of Class II controls treated with elastics.

METHODS

Sixteen Herbst patients who met the inclusion criteria were divided into 2 equal groups based on vertical facial pattern as determined by the Frankfort mandibular plane angle (brachyfacial, ≤22°; mesofacial, 23°-29°) and had cone-beam computed tomographs taken before treatment, 8 weeks after Herbst appliance removal, and after subsequent fixed appliance treatment. Eleven Class II control patients treated with fixed appliances and elastics had cone-beam computed tomographs taken before and after treatment. Three-dimensional models were generated from the cone-beam computed tomography images, registered on the anterior cranial bases, and analyzed using color maps and point-to-point measurements.

RESULTS

There were minimal differences in treatment response between the 2 Herbst groups across all skeletal parameters measured. The Herbst subjects showed a greater inferior displacement of anterior nasal spine compared with the Class II controls (Herbst brachyfacial, -1.44 mm; Herbst mesofacial, -1.95 mm) with other maxillary changes being clinically insignificant. The Herbst subjects showed greater inferior displacement of B-point compared with the Class II controls (Herbst brachyfacial, -2.59 mm; Herbst mesofacial, -2.75 mm). There were no statistically significant differences in mean linear mandibular measurements. All groups showed a trend toward posterior displacement of the condyles and glenoid fossae from the start to the end of treatment, with no significant differences across the 3 groups. There were minimal differences in the changes in gonial angle and Frankfort mandibular plane angle across all groups.

CONCLUSION

Approximately 2 years after Herbst treatment, the Herbst subjects with different vertical facial patterns showed similar patterns of skeletal change compared with the Class II controls treated with elastics.

Effects of growth hormone and functional appliance on mandibular growth in an adolescent rat model

OBJECTIVES

To investigate the individual and synergistic effects of growth hormone (GH) and functional appliance (FA) on mandibular growth in an adolescent rat model.

MATERIALS AND METHODS

Forty adolescent (6-week-old) female Wistar rats were randomly divided into four groups (10 rats in each group). The control group received a sham treatment (intra-abdominal injection of phosphate-buffered saline), the GH group received an intra-abdominal injection of recombinant human growth hormone, the FA group was treated with a mandibular advancement device, and the GH+FA group received both the GH and FA treatments. The amount of mandibular growth in each group was measured quantitatively using cone-bean computed tomography. The growth of condylar cartilage and expression of matrix metalloproteinases-1 and -13 (MMP-1 and MMP-13) and type II and X collagen (Col II and Col X) were assessed using histological staining and immunostaining techniques.

RESULTS

After 4 weeks, there was significant mandibular growth in the FA group compared with the control group ( P < .05). The GH+FA group had significantly greater mandibular length, thickness of condylar cartilage, and expression of MMP-1, MMP-13, Col II, and Col X in the cartilage than the other groups ( P < .05). The GH+FA group and GH group had significantly greater weight than the FA and control groups ( P < .05).

CONCLUSIONS

The FA as well as GH+FA stimulated mandibular growth in adolescent rats.

The biological basis of treating jaw discrepancies: An interplay of mechanical forces and skeletal configuration

Jaw discrepancies and malrelations affect a large proportion of the general population and their treatment is of utmost significance for individuals' health and quality of life. The aim of their therapy is the modification of aberrant jaw development mainly by targeting the growth potential of the mandibular condyle through its cartilage, and the architectural shape of alveolar bone through a suture type of structure, the periodontal ligament. This targeted treatment is achieved via external mechanical force application by using a wide variety of intraoral and extraoral appliances. Condylar cartilage and sutures exhibit a remarkable plasticity due to the mechano-responsiveness of the chondrocytes and the multipotent mesenchymal cells of the sutures. The tissues respond biologically and adapt to mechanical force application by a variety of signaling pathways and a final interplay between the proliferative activity and the differentiation status of the cells involved. These targeted therapeutic functional alterations within temporo-mandibular joint ultimately result in the enhancement or restriction of mandibular growth, while within the periodontal ligament lead to bone remodeling and change of its architectural structure. Depending on the form of the malrelation presented, the above treatment approaches, in conjunction or separately, lead to the total correction of jaw discrepancies and the achievement of facial harmony and function. Overall, the treatment of craniofacial and jaw anomalies can be seen as an interplay of mechanical forces and adaptations occurring within temporo-mandibular joint and alveolar bone. The aim of the present review is to present up-to-date knowledge on the mechano-biology behind jaw growth modification and alveolar bone remodeling. Furthermore, future molecular targeted therapeutic strategies are discussed aiming at the improvement of mechanically-driven chondrogenesis and osteogenesis.

Platelet-rich plasma inhibits RANKL-induced osteoclast differentiation through activation of Wnt pathway during bone remodeling

Platelet-rich plasma (PRP) is used in the clinic as an autologous blood product to stimulate bone regeneration and chondrogenesis. Numerous studies have demonstrated that PRP affects bone remodeling by accelerating osteoblast formation. With the research perspective focusing on osteoclasts, the present study established a mouse model of mandibular advancement to examine the effect of PRP on osteoclast differentiation induced by modification of the dynamics of the temporomandibular joint (TMJ). The lower incisors of the mice were trimmed by 1 mm and the resultant change in mandibular position during the process of eating induced condylar adaptation to this change. PRP significantly increased the bone mass and decreased osteoclastic activity, in vitro as well as in vivo. Mechanistically, the reduced expression of receptor activator of nuclear factor-κB ligand (RANKL)-induced differentiation marker genes, including nuclear factor of activated T-cells, cytoplasmic 1, c-fos and tartrate-resistant acid phosphatase, and that of the resorptive activity marker genes such as cathepsin k, carbonic anhydrase 2 and matrix metalloproteinase 9, indicated that PRP suppresses RANKL-induced osteoclast differentiation. A microarray analysis revealed that several genes associated with the Wnt pathway were differentially expressed, which indicated the involvement of this pathway in osteoclast differentiation. Furthermore, the activation of the Wnt pathway was verified by reverse transcription-quantitative polymerase chain reaction and immunoblot analysis of Dickkopf-related protein 1 and β-catenin. The results of the present study indicated that PRP inhibits osteoclast differentiation through activation of the Wnt pathway.

Assessment of condyle position, fossa morphology, and disk displacement in symptomatic patients

OBJECTIVE

The aim of the study was to determine whether there are any associations between the morphology of the glenoid fossa, articular spaces, and disk displacement by evaluating the magnetic resonance imaging (MRI) scans of symptomatic patients. Gender and age were also evaluated for any effect on the parameters.

STUDY DESIGN

MRI scans of 199 temporomandibular joints were assessed for the morphology of the glenoid fossa and articular spaces in both sagittal and coronal views. The presence of disk displacement and its type in closed-mouth and open-mouth positions were also assessed. Analysis of variance (ANOVA), Tukey, and Student t tests or Mann-Whitney rank sum tests were used to investigate the associations among these variables.

RESULTS

A total of 113 joints (56.8%) were presented with disk displacement. The articular spaces observed in sagittal and coronal views were, overall, significantly larger in males than in females in 3 of the 6 spaces (superior, posterior, and central spaces). Larger superior and medial articular spaces were associated with angled glenoid fossae. Higher mean values of the articular space sizes were associated with normal disk position (P < .001), except for the anterior articular space. When displacement was identified, higher values of the articular space sizes were also associated with disk reduction in the open-mouth position (P < .05).

CONCLUSIONS

Condyles in the central position in the coronal view and slightly anteriorly positioned in the sagittal view are less likely to present disk displacement.

Histologic effects of mandibular protrusion splints in antigen-induced TMJ arthritis in rabbits

BACKGROUND

Although it is common clinical practice to treat children with Juvenile Idiopathic Arthritis (JIA) with functional appliances, the scientific evidence for this is limited. The aim of this study was to study the histologic effects of mandibular protrusion splints in temporomandibular joint (TMJ) arthritis in rabbits.

METHODS

Twenty-eight ten-week old New Zealand white rabbits were randomly divided into four groups: AO (TMJ arthritis, no splint), AS (TMJ arthritis, mandibular splint advancement), OS (no arthritis, mandibular splint advancement) and OO (no arthritis, no splint). TMJ arthritis was induced in the groups AO and AS; 1 week later mandibular protrusion splints were placed on the upper incisors of the AS and OS animals. After 60 days the animals were sacrificed and a semiquantitative histologic evaluation of each TMJ was carried out to analyze the amount of inflammation and bone modeling.

RESULTS

AO and AS animals had a higher inflammation score (AO = 1.3; AS = 1.8) than the non-arthritis groups (OO = 0.6; OS = 0.4). Whereas in the untreated control (OO) the amount of apposition and resorption was almost in balance (+1), OS animals displayed significantly more apposition (+9) and AO animals significantly more resorption (-3) than the untreated control. Arthritis animals with protrusion appliances (AS), however, had remarkably more bone apposition (+3) than resorption, indicating a similar bony reaction as in healthy animals, although reduced in extent.

CONCLUSIONS

Mandibular advancement in rabbits with TMJ arthritis is possible without detrimental histologic reactions and appears to partially compensate for the bone loss seen in rabbits with TMJ arthritis but without protrusion splints.

Effect of Increasing Low-Intensity Pulsed Ultrasound and a Functional Appliance on the Mandibular Condyle in Growing Rats

OBJECTIVES

Functional appliances are used for treatment of lower-jaw deficiencies in growing individuals; however, their effectiveness is debatable. Low-intensity pulsed ultrasound (US) is a noninvasive method, which has been shown to stimulate cartilage and bone formation with 20 minutes of application. This study was designed to test the hypothesis that increasing low-intensity pulsed US application from 20 to 40 min/d will enhance mandibular condylar growth in growing rats, especially when combined with a functional appliance.

METHODS

Fifty-four Sprague Dawley rats were divided into 6 groups (n = 9): control, low-intensity pulsed US for 20 minutes, low-intensity pulsed US for 40 minutes, the functional appliance, the functional appliance plus low-intensity pulsed US for 20 minutes, and the functional appliance plus low-intensity pulsed US for 40 minutes. Low-intensity pulsed US was applied for 28 days. All rats were then euthanized, and their mandibles were dissected for morphometric, histomorphometric, and micro-computed tomographic analyses.

RESULTS

Among all study groups, the 20-minute US group showed significant increases in most of the measured variables (P < .05) except for condylar process length (P = .18), whereas the functional appliance-plus-40-min US group showed the least favorable results. The 20-minute US group showed increases in proliferative and hypertrophic cell counts and widths and enhanced microarchitecture of trabecular bone compared with the 40-minute US group. The functional appliance-plus-20-minute US group showed better results compared with the functional appliance-alone and functional appliance-plus-40-minute US groups.

CONCLUSIONS

A daily application of low-intensity pulsed US for 20 minutes in growing rats affects mandibular growth, either alone or in combination with a functional appliance. Further study with a longer observation period is required to study the long-term effects and stability of newly formed bone.

Runx2 Regulates Endochondral Ossification in Condyle during Mandibular Advancement

Runx2 is a transcription factor prerequisite for chondrocyte maturation and osteoblast differentiation. We tested the hypothesis that Runx2 is responsible for signaling chondrocyte maturation and endochondral ossification in the condyle during mandibular advancement. Fifty 35-day-old Sprague-Dawley rats were fitted with functional appliances for 3, 7, 14, 21, and 30 days. Experimental animals with 50 matched controls were labeled with bromodeoxyuridine for evaluation of the invasion of chondroclasts and osteoblasts into condylar cartilage. Mandibular advancement elicited Runx2 expression in condylar cartilage, and subsequently led to an expansion of type X collagen domain in the hypertrophic layer. Stronger Runx2 mRNA signals in subchondral bone corresponded with the increase in the recruitment of osteoblasts and chondroclasts, which preceded the increase of new bone formation in the condyle. Thus, Runx2 mediates chondrocyte terminal maturation and endochondral ossification in the mandibular condyle in response to mandibular advancement.

The Adaptive Remodeling of Condylar Cartilage— A Transition from Chondrogenesis to Osteogenesis

Mandibular condylar cartilage is categorized as articular cartilage but markedly distinguishes itself in many biological aspects, such as its embryonic origin, ontogenetic development, post-natal growth mode, and histological structures. The most marked uniqueness of condylar cartilage lies in its capability of adaptive remodeling in response to external stimuli during or after natural growth. The adaptation of condylar cartilage to mandibular forward positioning constitutes the fundamental rationale for orthodontic functional therapy, which partially contributes to the correction of jaw discrepancies by achieving mandibular growth modification. The adaptive remodeling of condylar cartilage proceeds with the biomolecular pathway initiating from chondrogenesis and finalizing with osteogenesis. During condylar adaptation, chondrogenesis is activated when the external stimuli, e.g., condylar repositioning, generate the differentiation of mesenchymal cells in the articular layer of cartilage into chondrocytes, which proliferate and then progressively mature into hypertrophic cells. The expression of regulatory growth factors, which govern and control phenotypic conversions of chondrocytes during chondrogenesis, increases during adaptive remodeling to enhance the transition from chondrogenesis into osteogenesis, a process in which hypertrophic chondrocytes and matrices degrade and are replaced by bone. The transition is also sustained by increased neovascularization, which brings in osteoblasts that finally result in new bone formation beneath the degraded cartilage.

Indian Hedgehog: A Mechanotransduction Mediator in Condylar Cartilage

Indian hedgehog (Ihh) is a critical mediator transducing mechanical signals to stimulate chondrocyte proliferation. To clarify the cellular signal transduction pathway that senses and converts mechanical signals into tissue growth in mandibular condyle, we evaluated Ihh expression and its relation to the kinetics of replicating mesenchymal cells in condylar cartilage during natural growth and mandibular advancement. Thirty-five-day-old Sprague-Dawley rats were fitted with functional appliances. Experimental animals with matched controls were doubly labeled with iododeoxyuridine and bromodeoxyuridine so that we could evaluate the cycles of the proliferative mesenchymal cells. Mandibular advancement triggered Ihh expression in condylar cartilage. A higher level of Ihh expression coincided with the increase of the replicating mesenchymal cells’ population and the shortening of the turnover time. These findings suggested that Ihh acts as a mediator of mechanotransduction that converts mechanical signals resulting from anterior mandibular displacement to stimulate cellular proliferation in condylar cartilage.

Adjunctive techniques for enhancing mandibular growth in Class II malocclusion

Class II malocclusions are generally characterized by mandible retrusion. For this reason, forward bite jumping appliances, also known as functional appliances were originally designed to enhance mandibular forward projection. However, there is still insufficient evidence to support the effectiveness, predictability and stability of functional appliances in modifying mandibular growth. This article was aimed at presenting evidences and hypotheses that mandibular growth may be enhanced through the use of adjunctive methods in conjunction with functional appliances. In formulating our hypothesis, we considered relevant data, mostly derived from animal studies, concerning alternative methods, such as low-intensity ultrasound and light-emitting diode, as well as their related cellular and molecular mechanisms. According to the evidences covered in this article, we suggest that both methods are potentially effective, and theoretically able to act in synergistic way to enhance functional appliances treatment on mandibular and condylar additional growth. The rationale for the use of these methods as adjunctive therapies for mandibular underdevelopment is attributed to their abilities on stimulating angiogenesis, cell differentiation, proliferation, and hypertrophy, as well as enhancing matrix production and endochondoral bone formation, especially on the condyle of growing animals. This article also proposed a study design which would be able to either prove or refute our hypothesis. If ratified, it would represent a significant scientific accomplishment which provides support for further investigations to be carried out on well-designed clinical trials.

Three-dimensional treatment outcomes in Class II patients treated with the Herbst appliance: a pilot study

INTRODUCTION

The aims of this study were to analyze 3-dimensional skeletal changes in subjects with Class II malocclusion treated with the Herbst appliance and to compare these changes with treated Class II controls using 3-dimensional superimposition techniques.

METHODS

Seven consecutive Herbst patients and 7 Class II controls treated with Class II elastics who met the inclusion criteria had cone-beam computed tomographs taken before treatment, and either after Herbst removal or at posttreatment for the control subjects. Three-dimensional models were generated from the cone-beam computed tomography images, registered on the anterior cranial bases, and analyzed using color maps and point-to-point measurements.

RESULTS

The Herbst patients demonstrated anterior translation of the glenoid fossae and condyles (right anterior fossa, 1.69 ± 0.62 mm; left anterior fossa, 1.43 ± 0.71 mm; right anterior condyle, 1.20 ± 0.41 mm; left anterior condyle, 1.29 ± 0.57 mm), whereas posterior displacement predominated in the controls (right anterior fossa, -1.51 ± 0.68 mm; left anterior fossa, -1.31 ± 0.61 mm; right anterior condyle, -1.20 ± 0.41 mm; left anterior condyle, -1.29 ± 0.57 mm; P <0.001). There was more anterior projection of B-point in the Herbst patients (2.62 ± 1.08 mm vs 1.49 ± 0.79 mm; P <0.05). Anterior displacement of A-point was more predominant in the controls when compared with the Herbst patients (1.20 ± 0.53 mm vs -1.22 ± 0.43 mm; P <0.001).

CONCLUSIONS

Class II patients treated with the Herbst appliance demonstrated anterior displacement of the condyles and glenoid fossae along with maxillary restraint when compared with the treated Class II controls; this might result in more anterior mandibular projection.

Temporomandibular joint changes after activator appliance therapy: a prospective magnetic resonance imaging study

The aim of this prospective clinical and magnetic resonance imaging study was to analyze the effect of 1-year Activator (Yi-fan Dental Co., Shanghai, China) treatment in internal anatomical relationships of the temporomandibular joint (TMJ) complex, including the condyle-disc relationship, condyle-fossa relationship, condylar height change, disc length change, and morphologic change of the glenoid fossa. The study was composed of patients with class II division 1 malocclusion (11 girls and 13 boys) who underwent 1-year Activator treatment. All the patients were in the acceleration or peak phase of the pubertal growth spurt. Magnetic resonance imaging in closed-mouth position and lateral cephalometric radiographs before and after 1 year of Activator treatment were analyzed metrically. Overall, condylar height showed a significant increase (P < 0.001), and the eminence angle decreased (P = 0.037). TMJ disc length has no statistically significant change before and after treatment. A slight advancement (P = 0.041) was found in the sagittal condylar position. A significant backward movement (P = 0.04) was shown in the sagittal disc position. Our results showed that the disc is not impaired by Activator therapy; it seems possible that adaptive remodeling, including a shallower glenoid fossa and increased condylar height, was seen after treatment.

The biology of TMJ growth modification: a review

Several studies have indicated a positive response of the temporomandibular joint (TMJ) to mandibular advancement, while others have reported that TMJ adaptive responses are non-existent and negligible. Controversy continues to grow over the precise nature of skeletal changes that occur during mandibular growth modification, due to an apparent lack of tissue markers required to substantiate the precise mechanism by which this is occurring. However, evidence suggests that orthopedic forces clinically modify the growth of the mandible. To further our knowledge about the effect of orthopedic treatment on the TMJ, it is necessary that we understand the biologic basis behind the various tissues involved in the TMJ's normal growth and maturation. The importance of this knowledge is to consider the potential association between TMJ remodeling and mandibular repositioning under orthopedic loading. Considerable histologic and biochemical research has been performed to provide basic information about the nature of skeletal growth modification in response to mandibular advancement. In this review, the relevant histochemical evidence and various theories regarding TMJ growth modification are discussed. Furthermore, different regulatory growth factors and tissue markers, which are used for cellular and molecular evaluation of the TMJ during its adaptive response to biomechanical forces, are underlined.

The role of vascular endothelial growth factor in ossification

Osteogenesis and angiogenesis are two closely correlated processes during bone growth, development, remodelling and repair.Vascular endothelial growth factor (VEGF) is an essential mediator during the process of angiogenesis. Based on an extensive literature search, which was carried out using the PubMed database and the keywords of osteogenesis, VEGF, endochondral ossification and intramembranous ossification, this manuscript reviews the role of VEGF in ossification, with emphasis on its effect in endochondral and intramembranous ossification. Osteogenesis and angiogenesis are closely correlated processes. VEGF acts as an essential mediator during these processes. It not only functions in bone angiogenesis but also in various aspects of bone development.

The effect of low level laser on condylar growth during mandibular advancement in rabbits

INTRODUCTION

It has been shown that Low Level Laser (LLL) has a positive effect on bone formation. The aim of this study was to evaluate the effect of low level laser on condylar growth during mandibular advancement in rabbits.

MATERIALS AND METHODS

Continuous forward mandibular advancement was performed in fourteen male Albino rabbits with the mean age of 8 weeks and the mean weight of 1.5 ± 0.5 kg, with acrylic inclined planes. The rabbits were randomly assigned into two groups after 4 weeks. LLL (KLO3: wave length 630 nm) was irradiated at 3 points around the TMJ, through the skin in the first group. The exposure was performed for 3 minutes at each point (a total of 9 minutes) once a day for 3 weeks. The control group was not exposed to any irradiation. The rabbits in both groups were sacrificed after two months and the histological evaluation of TMJ was performed to compare fibrous tissue, cartilage, and new bone formation in condylar region in both groups. Disc displacement was also detected in both groups. Student's t-test, Exact Fisher and Chi square tests were used for the statistical analysis.

RESULTS

The formation of fibrous tissue was significantly lower, while bone formation was significantly greater in lased group as compared with control group. The thickness of cartilage did not differ significantly between two groups.

CONCLUSION

Irradiation of LLL (KLO3) during mandibular advancement in rabbits, increases bone formation in condylar region, while neither increase in the cartilage thickness nor fibrous tissues was observed.

Comparison of treatments with the Forsus fatigue resistant device in relation to skeletal maturity: a cephalometric and magnetic resonance imaging study

INTRODUCTION

The aim of this study was to compare the dentoskeletal changes and alterations of mandibular condyle-disc-fossa relationships in subjects at the peak and the end of the pubertal growth period treated with the Forsus fatigue resistant device (3M Unitek, Monrovia, Calif).

METHODS

The sample consisted of 29 subjects with Class II Division 1 malocclusions who were classified according to their hand-wrist radiographs. Fifteen patients were at or just before the peak phase of pubertal growth (peak pubertal group). Fourteen patients were near the end of the pubertal growth period (late pubertal group). The study was conducted by using lateral cephalometric radiographs and magnetic resonance images obtained at the beginning and at the end of the application of the Forsus fatigue resistant device. The treatment period was 9 months.

RESULTS

The Wilcoxon signed rank test was used to evaluate differences within groups. The changes observed in both groups were compared by using the Mann-Whitney U test. There were statistically significant group differences in mandibular length and ramus length, with significant increases of these parameters in the peak pubertal group (P <0.05). No significant differences were observed between the groups concerning dental parameters (P >0.05), with the exception of mandibular molar vertical movements, which were significantly greater in the peak pubertal group (P <0.05). Analysis of the magnetic resonance images showed no positional changes of the mandibular condyle in relation to the glenoid fossa in either group (P >0.05). Although the articular disc was positioned more anteriorly in the peak pubertal group compared with its pretreatment position (P <0.05), the position of the disc was still within the physiologic range. No significant intergroup difference was observed for disc-condyle relationship (P >0.05).

CONCLUSIONS

The Forsus fatigue resistant device did not appear to cause significant increases in mandibular dimensions in subjects in late puberty. According to the magnetic resonance image findings, Forsus treatment is not a risk factor for the development of temporomandibular dysfunction in subjects with no signs and clinical symptoms of dysfunction.

The Herbst appliance updated

The aim of this paper is to analyze the evolution that the Herbst appliance has experienced in the last 30 years. In particular the different designs proposed for the Herbst appliance are examined and the related differences in clinical management, indications, and treatment effects are also illustrated. The two major challenges in the clinical management of the Herbst appliance are represented by the choice of the type of stabilization and by the control of the proclination of the lower incisors. The use of acrylic splints presents a set of relevant advantages: the construction technique is simple, the appliance can be worn easily by the patients, and the height of the splint can be adjusted to the growth pattern. Moreover, the acrylic splint Herbst can be used to reposition the mandible in cases with temporomandibular disorders. As for the proclination of the lower incisors, an accurate assessment of the neuromuscular pattern of the individual patient before treatment can provide the clinician with reliable criteria to evaluate the risk for incisor proclination during Herbst therapy.

A histochemical study on condylar cartilage and glenoid fossa during mandibular advancement

OBJECTIVE

To evaluate cellular hypertrophic activities in the mandibular condylar cartilage (MCC) and the glenoid fossa (GF) during mandibular advancement in the temporomandibular joint (TMJ) of Sprague-Dawley rats, as evidenced by fibroblast growth factor 8 (FGF8).

METHODS AND MATERIALS

Fifty-five female 24-day-old Sprague-Dawley rats were randomly divided into four experimental and control groups, with a mandibular advancement appliance on the experimental rats' lower incisors. The rats were euthanized on days 3, 14, 21, and 30 of the study, and their TMJ was prepared for a immunohistochemical staining procedure to detect FGF8.

RESULTS

FGF8 expression was significantly higher among the experimental rats (P  =  .002). Patterns of ascension and descension of FGF8 expression were similar in experimental and control samples. The results show an overall enhanced osteogenic transition occurring in both the MCC and the GF in experimental rats in comparison with controls. The level of cellular changes in the MCC is remarkably higher than in the GF.

CONCLUSION

In the MCC and the GF, cellular morphologic and hypertrophic differentiations increase significantly during mandibular advancement. It is also concluded that endochondral ossification in the MCC and intramembranous ossification in the GF occur during adaptive remodeling.

Stress distribution in mandible and temporomandibular joint by mandibular distraction: a 3-dimensional finite-element analysis

The effects of mandibular distraction on the mandible and its surrounding tissue remain to be clarified. Here, we used a 3-dimensional finite-element method to investigate the effects of unilateral horizontal lengthening of the mandibular body and vertical lengthening of the mandibular ramus on the mandible and temporomandibular joint (TMJ). With horizontal loading that assumed mandibular body lengthening, tensile and compressive stresses were great near the anterior region of the mandibular angle (the loading area). With vertical loading that assumed mandibular ramus lengthening, tensile and compressive stresses were great at the center of the mandibular ramus (the loading area). Under both loading conditions, stress distribution in the TMJ was greater on the loading side than on the non-loading side. With mandibular body lengthening, the center of the mandible deviated in the direction of the non-lengthened side to widen the mandible in the lateral direction. With mandibular ramus lengthening, the occlusal plane tilted in the inferior direction on the lengthened side. In the TMJ, stress was greatest on the affected side during mandibular ramus lengthening, suggesting the need to consider the mandibular condyle on the affected side during this procedure.

Mandibular condylar cartilage response to moving 2 molars in rats

INTRODUCTION

The purpose of this study was to investigate the responses of mandibular condylar cartilage to moving 2 molars in different combinations.

METHODS

Rats were assigned to male and female control and experimental groups (each, n = 5). Elastic rubber bands were used to move medially the maxillary left and the mandibular right first molars in experimental group I. The same method was used to distally move the maxillary left and the mandibular right third molars, 2 mandibular third molars, and 2 maxillary third molars in experimental groups II, III, and IV, respectively. At the end of the eighth week, all condyles were examined histologically. The areas of histologic change as a percentage of total cartilage area were compared by using the Mann-Whitney U test.

RESULTS

Cartilage degenerative remodeling was observed in experimental groups II, III, and IV. The percentage areas of degenerative remodeling were higher in female experimental groups II and III than in the female control group, and in female experimental group II than in female experimental group IV and male experimental group II (all, P <0.05).

CONCLUSIONS

The mandibular condylar cartilage of female rats responded variously to different combinations of molar movement; the most obvious remodeling was observed in groups in which the maxillary left and mandibular right third molars were moved.

Temporomandibular joint adaptations following two-phase therapy: an MRI study

AIM

To document the alterations within the condyle-glenoid fossa (C-GF) complex and the positional changes of the glenoid fossa in the cranium after removable functional appliance therapy and after the completion of fixed appliance therapy.

SETTING AND SAMPLE

The Department of Orthodontics, Centre for Dental Education and Research, All India Institute of Medical Sciences, New Delhi, India. The study sample consisted of 12 growing children (eight girls and four boys) between 10 and 14 years of age with skeletal Class II division 1 malocclusion selected on well defined criteria.

MATERIALS AND METHODS

All patients were treated with either the Twin Block or the Bionator appliance followed by fixed appliances. Mean total treatment duration was 28 months. The changes in and around the C-GF complex were evaluated using MRI at pre-treatment stage, after functional appliance therapy and at the completion of fixed mechanotherapy.

RESULTS

Forward condylar position within the glenoid fossa and articular disc retrusion with respect to the condylar head were statistically significant after functional appliance therapy. However, the condyles had a relatively concentric position within the glenoid fossa, while the articular disc resumed its pre-treatment position at the end of the treatment. Linear measurements from the centre of the external auditory meatus to the post-glenoid spine revealed a 1.3-mm forward relocation of the post-glenoid spine along the Frankfurt Horizontal plane.

CONCLUSIONS

Forward relocation of the C-GF complex seems to be one of the mechanisms of action of functional appliances, while the internal anatomic arrangement within the temporomandibular joint (TMJ) complex normalizes to its pre-treatment position.

Time Course of Expression of Bcl-2 and Bax in Rabbit Condylar Chondrocytes Following Forward Mandibular Positioning

Objective: To clarify the expression of Bcl-2 and Bax following forward mandibular positioning (FMP) in the condylar chondrocytes of rabbits.

Materials and Methods: Sixty rabbits at 8 weeks of age were randomly allocated to the experimental group (n = 36) and control group (n = 24). Rabbits in the experimental group were induced to FMP by a functional appliance. Six rabbits from the experimental group and four from the control group were sacrificed after 3 days and 1, 2, 4, 8, and 12 weeks, respectively. All the right temporomandibular joints (TMJs) were collected and the expression of Bcl-2 and Bax was evaluated by immunohistochemical staining.

Results: The results showed the expression pattern of Bcl-2 and Bax during 12 weeks after FMP. The expression of Bcl-2 reached the highest level at 1 week, whereas Bax reached its maximal expression after 4 weeks. Subsequently, the expression of Bcl-2 and Bax gradually decreased. The ratio of Bcl-2/Bax began to decrease 3 days after FMP and continued to decline until 12 weeks.

Conclusions: FMP with functional appliances could change the expression of Bcl-2 and Bax, which is related to apoptosis in condylar chondrocytes.

Does the degree of advancement during functional appliance therapy matter?

The aim of this study was to assess the effect of varied degrees of mandibular advancement on condylar growth. Three hundred and thirty five 35-day-old female Sprague-Dawley rats were randomly divided into 10 experimental groups (n = 10) and five control groups (n = 5) for analysis of new bone formation and 10 experimental groups (n = 14) and five control groups (n = 14) for molecular analysis. The experimental animals were fitted with bite-jumping appliance to advance the mandible 2 and 4 mm. The rats were sacrificed on days 3, 7, 14, 21, and 30. A computer-assisted image analysing system was used to assess the quantity of new condylar bone formation. Molecular analysis utilizing real-time reverse transcription-polymerase chain reaction was used to assess the different levels of mRNA expression of different growth markers in the condyle. One-way analysis of variance (ANOVA), with a Bonferroni multiple comparison test, showed significantly more newly formed bone in the 4 mm group compared with the 2 mm and control groups on days 21 and 30 (P < 0.05). Most of the examined growth markers demonstrated a significant increase during the 4 mm advancement (P < 0.05). Indian hedgehog (Ihh) mRNA showed a 7- and 5-fold change, parathyroid hormone-related peptide (PTHrP) a 5.2- and 3-fold change and type II collagen a 9.6- and 3.7-fold change in the 4 and 2 mm advancement groups, respectively. Varied degrees of mandibular advancement result in different quantities of new bone formation and levels of expression of growth members: Ihh, PTHrP, and type II collagen.

Factors Regulating Endochondral Ossification in the Spheno-occipital Synchondrosis

Objectives: To identify the temporal pattern of core-binding factor α1 (Cbfa1) and vascular endothelial growth factor (VEGF) expressions in the spheno-occipital synchondrosis in vitro with and without tensile stress.

Materials and Methods: Sixty male BALB/c mice were randomly divided into an experimental group (with tensile stress) and a control group (without tensile stress) at each of five time points. Animals were sacrificed and the cranial base synchondroses were aseptically removed. In the experimental groups, mechanical stress was applied on the surgical explants with helical springs and incubated as organ culture for 6, 24, 48, 72, and 168 hours. In the control group, the springs were kept at zero stress. Tissue sections were subjected to immunohistochemical staining for quantitative analysis of Cbfa1 and VEGF expression.

Results: Quantitative analysis revealed that Cbfa1 and VEGF expressions reached a peak increase at 24 and 48 hours, respectively. Compared with the control groups, both Cbfa1 and VEGF were expressed consistently higher in the experimental groups at all time points.

Conclusion: Mechanical stress applied to the spheno-occipital synchondrosis elicits Cbfa1 expression and subsequently up-regulates the expression of VEGF. Increased levels of expression of both factors could play a role in the growth of the spheno-occipital synchondrosis.

Glenoid Fossa Responses to Mandibular Lateral Shift in Growing Rats

Objective: To evaluate the morphological and histological responses of the glenoid fossa to mandibular lateral shift in growing rats.

Materials and Methods: A resin plate was placed on the upper incisors of 4-week-old rats in the experimental groups to displace the mandible to the left during closure. The rats were killed after 2, 4, 8, and 12 weeks. The morphometric measurements were performed on dry skulls, and tissue blocks were processed for periodic acid and Schiff's reagent (PAS) staining to examine the new bone formation.

Results: Gross measurements showed asymmetry in both the position and size of the fossae between the two sides after 4 weeks of lateral shift. The glenoid fossa on the ipsilateral side was repositioned relatively backward, outward and upward compared with the contralateral side and control group, whereas the fossa on the contralateral side was relocated relatively forward and downward compared with the control group. The length of the fossa was smaller on the ipsilateral side than on contralateral side and control group. At 2 weeks, the amount of newly formed bone in the posterior region of the fossa was higher in the experimental group than the control group.

Conclusion: It is suggested that the mandibular lateral shift causes asymmetry in the position and size of the glenoid fossa and that this phenomenon can be related to different bilateral directional new bone formation in the posterior region.

Functional Changes of the Temporomandibular Joint Mechanoreceptors Induced by a Lateral Mandibular Shift in Rats

OBJECTIVE

To investigate changes in functional characteristics of the temporomandibular joint (TMJ) mechanoreceptors under mandibular lateral shift.

MATERIALS AND METHODS

Forty 7-week-old male Wistar rats were divided into control and experimental groups. Rats in the experimental group received a modified guiding appliance (MGA) that was designed to shift the mandible to the left side in the occlusal position. Single-unit activities of the TMJ mechanoreceptors were evoked by indirect stimulation of passive jaw movement. Electrophysiologic recordings of TMJ units were obtained 1, 3, 5, 7, and 9 weeks after MGA setting from the gasserian ganglion.

RESULTS

At 1 week after mandibular shift, the firing thresholds were the lowest and the maximum instantaneous frequencies were the highest in TMJ units. At 5 weeks, the firing thresholds in the nonshifted side were significantly lower than those in the shifted side. The maximum instantaneous frequencies in the nonshifted side were significantly higher than those in the shifted side at 1, 5, and 7 weeks.

CONCLUSION

These results suggest that the functional lateral shift of the mandible could alter the response properties of TMJ mechanoreceptors, particularly on the nonshifted side.

Mandibular advancement and morphological changes in the mandibles of female mice of different ages

Mandibular advancement (MA) by means of functional orthopedic techniques is currently used in young patients to stimulate mandibular growth. The aim of this study was to evaluate the morphological changes in the mandibles of 2-, 7-, and 16-month-old female mice after MA. Every 3 days during 1 month, the lower incisors were trimmed by 1mm to induce protrusion when the animal was feeding. The left mandibles of the 30 experimental and 28 control individuals were subsequently dissected and digital images were obtained to analyze nine linear/angular measurements. The condylar microstructure was also analyzed by scanning electron microscopy (SEM). The linear/angular measurements showed a growth response in different mandibular regions in 2- and 16-month-old individuals. SEM showed that, in the 7-month-old mice, the condylar cartilage had regenerated in the treated individuals but not in the controls. The results suggest that MA produces mandibular growth in 2- and 16-month-old female mice. Although there was no mandibular growth in 7-month-old mice, regeneration of the condylar cartilage was detected, thus demonstrating that different responses to the MA stimulus occur in female mice of different ages.