Mandibular Forward Positioning Research Articles

The Treatment of Growing Class II Malocclusion Patient with Vertical Control

This case report is about a female growing patient with Class II malocclusion, showing 13 mm overjet, hyperdivergent skeletal pattern and mandibular retrusion. Treatment was planned in two stages. In the first stage, cervical headgear and twin block was used for maxillary growth restriction and mandibular forward positioning, followed by the second stage of fixed preadjusted edgewise orthodontic appliance for camouflaging the remaining skeletal and dental discrepancy using orthodontic mini-implant. We achieved satisfying results with harmonious face, Class I molar relationship with proper interdigitation, overbite, overjet, and midline coincidence.

Long-Term Results of Rapid Maxillary Expansion and Facemask: Long-Term of Regular Protraction

ABSTRACT Objective: Evaluation of the long-term skeletal, dental, and soft tissue treatment results of 17 patients who completed their protraction with the facemask. Materials and Method: Twenty-three Class III patients with a mean age of 12, characterized with maxillary retrognathism, who were treated by facemask protraction therapy, were recalled after 6.08 years following protraction. Only 17 patients presented and their records were renewed. Study was carried out on the initial (T0), after protraction (T1), and 6.08 years following protraction (T2) films. Long-term skeletal, dental, and soft tissue changes were measured. Results: After 6.08 years, the profile and dental relationships achieved by protraction were found to be well maintained clinically. The cephalometric examination revealed stable sagittal advancement with a mandibular forward positioning. After protraction (T1) and at 6.08 years of recall (T2), there were no statistically significant changes found in parameters showing sagittal positi...

Forward mandibular positioning enhances the expression of Ang-1 and Ang-2 in rabbit condylar chondrocytes

Functional appliances correct dental malocclusion, partly by exerting an indirect mechanical stimulus on the condylar cartilage, initiating novel bone formation in the condyle. Angiopoietin is involved in the angiogenesis associated with novel bone formation. This study aimed to determine the expression of angiopoietin (Ang)‑1 and ‑2 following forward mandibular positioning (FMP) in the condylar chondrocytes of rabbits. Sixty rabbits (age, 8 weeks) were randomly allocated to the experimental and control groups (n=30 per group). In the experimental group, FMP was induced by a functional appliance. Five rabbits from the experimental group and the control group were sacrificed following 3 days and 1, 2, 4, 8 and 12 weeks, respectively. The right temporomandibular joints (TMJs) were collected and the expression of Ang‑1 and -2 was evaluated by immunohistochemical staining. The expression of Ang-1 increased at day 3 and reached a peak at 2 weeks, whereas Ang‑2 reached maximal expression 4 weeks after FMP. Subsequently, the expression of Ang‑1 and ‑2 gradually decreased. Thus, FMP enhanced the expression of Ang‑1 and Ang‑2 in condylar cartilage, which is related to angiogenesis in the process of endochondral ossification.

Expression of bone histomorphometry parameters in rabbit condyle during mandibular forward positioning

To observe the changes of bone histomorphometry parameters in condyle of rabbits during mandibular forward positioning. Forty rabbits with eight weeks of age were simple randomly divided into the experimental group (n = 24) and control group (n = 16).Mandibles of rabbits in the experimental groups were induced to forward position by a functional appliance.The experimental group and control group were sacrificed after 2 and 4, 8, 12 weeks.The specimens from right tempromandibular joints were processed for undemineralised sections.These sections were used for fluorescent microscopy observation and the measurement of bone histomorphometry. At 8 week bone-volume fraction [(75.83 ± 1.10)%], trabecular thickness [(103.28 ± 2.89) µm], trabecular number [(2.86 ± 0.06) mm(-1)], mineral apposition rate [(2.32 ± 0.02) µm/d] and index of osteoblast [(30.20 ± 0.47) N/mm(2)] in subchondral region of the cartilage in the experimental group were significantly increased compared with the age-matched controls [respectively (64.00 ± 1.54)%, (87.00 ± 1.13) µm, (1.84 ± 0.08) mm(-1), (1.69 ± 0.02) µm/d and (21.07 ± 0.59) N/mm(2)] (P < 0.05). However, trabecular separation [(170.00 ± 2.25) µm] was lower than those in the controls [(241.50 ± 1.57) µm] with significant difference(P < 0.05). There was no significant difference in the bone histomorphometry parameters of the central region between the experimental group and the age-matched control group (P > 0.05). The pattern of bone histomorphometry parameters expression in subchondral region has a high correlation with the adaptive remodeling of the condyle after functional appliance.

Changes in condylar cartilage after anterior mandibular displacement in juvenile pigs

Adaptive remodelling of the mandibular condyle in response to mandibular advancement is the mechanism exploited by orthodontic forward displacement devices. ObjectiveThis work investigated the expression of collagens, matrix metalloproteinases and vascular endothelial growth factor during this process. DesignTwenty juvenile pigs were randomly divided into two experimental groups, where the treatment group was fitted with mandibular advancement splints, and the control group was not. Changes in the mRNA content of condylar cartilage tissue was then were measured by real-time PCR using specific primers after 4weeks of treatment. ResultsThe temporal pattern of the expression of Col1 and MMP13 during condylar adaptation coincided with that during natural condylar growth. The amount of the expression of Col10 during condylar adaptation was significantly lower (p<0.05), whereas the expression of Col2, MMP8 and VEGF was significantly higher compared to natural growth (p<0.05). ConclusionsIt is suggested that condylar adaptation in growing pigs triggered by mandibular forward positioning results not only from passive adaptation of cartilage, but also involves growth affected processes. Our results showed that mechanical strain produced by mandibular advancement induced remodelling and revascularization in the posteriocranial mandibular condyle. These results are mostly consistent with former published histological and histomorphometrical analyses.

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

To clarify the expression of Bcl-2 and Bax following forward mandibular positioning (FMP) in the condylar chondrocytes of rabbits. 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. 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. FMP with functional appliances could change the expression of Bcl-2 and Bax, which is related to apoptosis in condylar chondrocytes.

Expression of BMP/Smads in rabbit condylar cartilage during mandibular forward positioning

To identify the relationship between the expression of BMP/Smads in condylar cartilage and condylar growth modifications in rabbits during mandibular forward positioning. Sixty male rabbits with 8 weeks of age were randomly divided into the experimental group (n=36) and control group (n=24). The mandibles of rabbits in the experimental groups were induced to forward position by a functional appliance. The rabbits in the experimental group and control group were sacrificed after 3 days and 1, 2, 4, 8, 12 weeks, respectively. The expression of BMP-2, Smad1/5, 4 and 6 in condylar cartilage was examined by immunohistochemical staining. The expression of BMP-2, Smad1/5, 4 and 6 was mainly found in the chondrocytes from the transitional zone and hypertrophic zone, and was also found in the chondrocytes and osteoblasts of the mineralized zone. Compared with those of the age-matched controls, the positive signals for BMP-2, Smad1/5, 4 and 6 in the experimental animals were stronger at early stage (P<0.05), coinciding with the remodeling in condylar cartilage after functional appliance. The expression of BMP-2, Smad1/5, 4 and 6 is associated with the adaptive remodeling of the condylar cartilage after functional appliance.

Expression of type X collagen and capillary endothelium in condylar cartilage during osteogenic transition--a comparison between adaptive remodelling and natural growth

Adaptive remodelling of the condylar cartilage in response to mandibular protrusion constitutes the rationale for bite-jumping appliances to solicit growth modification. By investigating the expression of type X collagen and capillary endothelium, this study was designed to evaluate the osteogenic transition of chondrogenesis during adaptive remodelling of condylar cartilage and compare it with that under natural condylar growth. One hundred female Sprague-Dawley rats, 35 days of age, were divided into five experimental groups (n = 15, fitted with bite-jumping appliances) where condylar adaptation was created by forward repositioning of the mandible, and five control groups (n = 5) where the condyles underwent natural growth. The animals were sacrificed at 3, 7, 14, 21 and 30 days and 7 mum serial sections of the condyles were processed for in situ hybridization and immunohistochemical analyses. The expression of type X collagen in the hypertrophic zone and capillary endothelium in the erosive zone of condylar cartilage were examined to evaluate osteogenic transition, a critical programme leading to endochondral ossification. The results showed that (1) The temporal pattern of the expression of type X collagen and capillary endothelium during condylar adaptation coincided with that during natural condylar growth. (2) The amount of the expression of these two factors during condylar adaptation was significantly higher than that during natural growth (P < 0.001). It is suggested that condylar adaptation in growing rats triggered by mandibular forward positioning enhances osteogenic transition which eventually results in increased bone formation.

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.

Mechanical strain leads to condylar growth in adult rats

Mechanical strain produced by forward mandibular positioning was found to enhance mandibular condylar growth in experimental animals and in patients. This study was designed to identify the changes in number and rate of the proliferating mesenchymal cells in mandibular condyles of adult rats and to correlate these changes to the expression of SOX9 and type II collagen under mechanical strain. Seventy-eight 120-day-old female Sprague-Dawley rats were randomly allotted to six groups, nine animals in each experimental group according to different time points. Cell kinetic studies for expression of PCNA were used to identify number and rate of proliferating mesenchymal cells. Immunostaining of SOX9 and in situ hybridization of Col2a1 gene were carried out. Results showed a significant increase in number of replicating mesenchymal cells and proliferation rate. The expression of SOX9 was enhanced and Col2a1 gene transcript was then activated. The proliferative layer became thicker on experimental day 21. The thickness of chondroblast layer and chondrocyte layer showed significant increase from experimental day 14 to day 30. In conclusion, mechanical strain produced by mandibular advancement in adult rats promotes the proliferation of mesenchymal cells. Under control of transcription factor SOX9, these mesenchymal cells are then committed to enter the chondrogenic route leading to condylar growth.

Replicating mesenchymal cells in the condyle and the glenoid fossa during mandibular forward positioning

The purpose of this study was to identify and quantify the temporal sequence of replicating mesenchymal cells during natural growth and mandibular advancement in the condyle and the glenoid fossa. One hundred fifty 35-day-old female Sprague-Dawley rats were randomly divided into 10 experimental groups (10 rats each) and 10 control groups (5 rats each). The experimental groups were fitted with appliances that positioned the mandible forward. One hour before the rats were killed, bromodeoxyuridine (BrdU) was intravenously injected into them. Sections were cut and stained with anti-BrdU antibody to evaluate the number of replicating mesenchymal cells. Cellular uptake of BrdU was quantified with the Leica Qwin (Leica Microsystem Imaging Solutions, Cambridge, United Kingdom) system. The results showed that the numbers of replicating mesenchymal cells during natural growth were highest in the posterior region of the condyle and the anterior region of the glenoid fossa. In the experimental groups, the posterior region had the highest number of replicating cells for both the condyle and the glenoid fossa, with the condyle having 2 to 3 times more replicating cells than the glenoid fossa. The number of replicating mesenchymal cells, which is genetically controlled, influences the growth potential of the condyle and the glenoid fossa. Mandibular protrusion leads to an increase in the number of replicating cells in the temporomandibular joint. Individual variations in the response to growth modification therapy could be a result of the close correlation between mesenchymal cell numbers and growth. (Am J Orthod Dentofacial Orthop 2003;123:49-57)

Functional appliance therapy accelerates and enhances condylar growth

The present study was designed to quantitatively assess the temporal pattern of expression of Sox 9, the regulator of chondrocyte differentiation and type II collagen, the major component of the cartilage matrix during forward mandibular positioning, and compare it with the expression during natural growth. Female Sprague-Dawley rats, 5 weeks old, were used. Results showed that the expression of Sox 9 and type II collagen are accelerated and enhanced when the mandible is positioned forward. Furthermore, we monitored the amount of new bone formation during mandibular advancement and after the removal of bite-jumping appliances. A substantial increase was observed in the amount of newly formed bone when the mandible was positioned forward. No significant difference in new bone formation could be found after the appliance was removed when compared with natural growth. Thus, functional appliance therapy accelerates and enhances condylar growth by accelerating the differentiation of mesenchymal cells into chondrocytes, leading to an earlier formation and increase in amount of cartilage matrix. This enhancement of growth did not result in a subsequent pattern of subnormal growth for most of the growth period; this indicates that functional appliance therapy can truly enhance condylar growth. (Am J Orthod Dentofacial Orthop 2003;123:40-8)

VEGF and bone formation in the glenoid fossa during forward mandibular positioning

This study was designed to identify the relationship between vascularization and bone formation in the glenoid fossa during natural growth and functional appliance therapy. The temporal pattern of vascular endothelial growth factor (VEGF) expression and bone formation in the glenoid fossa during natural growth was identified and compared with that during forward mandibular positioning. We randomly divided 150 female Sprague-Dawley rats, 35 days old, into 10 experimental and 10 control groups. Appliances were fitted to position the mandible forward in the experimental groups. The rats were then killed at different times. Sections were cut and stained with anti-VEGF antibodies to evaluate VEGF expression, and with periodic acid and Schiff's reagent to evaluate new bone formation. Both VEGF expression and newly formed bone were measured by a computer-assisted image analyzing system. The results showed that, during natural growth and forward mandibular positioning, VEGF expression and new bone formation were highest in the posterior region of the glenoid fossa. There were significant increases of VEGF and new bone formation in the experimental groups compared with the controls. The highest amount of VEGF expression occurred before the highest amount of bone formation was reached. Forward mandibular positioning causes significant increases in vascularization and new bone formation in the glenoid fossa. A close correlation exists between vascularization and bone formation. (Am J Orthod Dentofacial Orthop 2002;122:202-9)

Neuromuscular and skeletal adaptations following mandibular forward positioning induced by the Herbst appliance.

The purpose of this study was to examine neuromuscular and skeletal adaptations to changes in sagittal jaw relationships induced by the Herbst appliance. Six patients (age, 9 years and 5 months to 11 years and 2 months) with Angle Class II, division 1 malocclusions were studied longitudinally. The structural changes were determined by analyzing serial lateral cephalograms. Electromyographic recordings of specific masticatory muscles were used to evaluate neuromuscular adaptations. Similar cephalometric changes were observed in all patients. In all patients, lateral pterygoid muscle activity increased immediately after insertion of the appliance, but the activity decreased markedly after 4 to 6 months of treatment. In 4 of the 6 patients studied, however, the condyles were located in a slightly more downward and forward position. These findings indicate that the adaptation of muscular function occurs within a relatively short period and precedes the compensatory morphological changes produced through functional appliance therapy.

Changes in relationship of points A and B during orthodontic treatment

1. 1. The angles SNA and SNB, and especially the difference between them, are a good basis on which to evaluate and plan treatment. 2. 2. Normal face samples show variation in apical base orientation with compensating variations in the positions of the teeth. 3. 3. Treatment objectives should aim at reducing high ANB angles to as near 0 to 2 degrees as possible. 4. 4. Good facial harmony is found in both prognathic and orthognathic persons so long as the apical base orientation does not exceed a range permitting compensating dental adjustments. 5. 5. Patients treated during periods of active growth respond with better apical base changes than do patients treated during nongrowth periods. 6. 6. The nature of the change in relationships of points A and B is influenced materially by the type of treatment followed. 7. 7. The ideal position of the lower incisor (3 mm. anterior to the NB plane) should not be maintained where the apical base dysplasia cannot be reduced to 4 degrees during treatment. Therefore, a flexible scale for incisor orientation is presented in Table 1. 8. 8. The greatest angular changes occur in the SNA angle. 9. 9. The treatment response most desired in most Class II cases is one of forward mandibular positioning due to alteration in the amount and direction of growth, primarily in the growth site at the head of the condyles. 10. 10. The use of Class II elastics of sufficient pull for a long enough period of time to bring about the desired mandibular growth response necessitates the tipping back of mandibular teeth to positions of dynamic anchorage in the first stages of treatment, as described by Tweed. 11. 11. The forward development of the lower third of the face is in harmony with the most common growth changes occurring at this time. 12. 12. Good reductions in the ANB angle have taken place in nearly all cases having higher than a 4-degree ANB angle in which active growth occurred.

The etiology and pathogenesis of angle's “Class two” malocclusion

1.1. The angles SNA and SNB, and especially the difference between them, are a good basis on which to evaluate and plan treatment.2.2. Normal face samples show variation in apical base orientation with compensating variations in the positions of the teeth.3.3. Treatment objectives should aim at reducing high ANB angles to as near 0 to 2 degrees as possible.4.4. Good facial harmony is found in both prognathic and orthognathic persons so long as the apical base orientation does not exceed a range permitting compensating dental adjustments.5.5. Patients treated during periods of active growth respond with better apical base changes than do patients treated during nongrowth periods.6.6. The nature of the change in relationships of points A and B is influenced materially by the type of treatment followed.7.7. The ideal position of the lower incisor (3 mm. anterior to the NB plane) should not be maintained where the apical base dysplasia cannot be reduced to 4 degrees during treatment. Therefore, a flexible scale for incisor orientation is presented in Table 1.8.8. The greatest angular changes occur in the SNA angle.9.9. The treatment response most desired in most Class II cases is one of forward mandibular positioning due to alteration in the amount and direction of growth, primarily in the growth site at the head of the condyles.10.10. The use of Class II elastics of sufficient pull for a long enough period of time to bring about the desired mandibular growth response necessitates the tipping back of mandibular teeth to positions of dynamic anchorage in the first stages of treatment, as described by Tweed.11.11. The forward development of the lower third of the face is in harmony with the most common growth changes occurring at this time.12.12. Good reductions in the ANB angle have taken place in nearly all cases having higher than a 4-degree ANB angle in which active growth occurred.