3D CBCT McNamara's cephalometric analysis in an adult southern Chinese population.

Preliminary results were determined for a database on 3-dimensional (3D) cephalometrics using McNamara's analysis in an adult southern Chinese population based on cone-beam computerized tomography (CBCT). 3D dentoskeletal morphology was assessed from CBCTs from 80 (39 males; 41 females; 21-30 years) consecutive adult southern Chinese without gross craniofacial deformity or asymmetry, adopting 16 variables from McNamara's cephalometric method. For variables in relation to maxilla to cranial base, mandible to cranial base and dentition, there were no significant differences between males and females. For variables in relation to mandible to maxilla, 8 of 11 showed significant differences between males and females: Cd(L)-Gn (♂: 127.65 mm; ♀: 119.56 mm, P<0.01), Cd(R)-Gn (♂: 127.85 mm; ♀: 119.94 mm, P<0.01), Cd(L)-A (♂: 99.38 mm; ♀: 94.18 mm, P<0.01), Cd(R)-A (♂: 93.93 mm; ♀: 94.99 mm, P<0.01), MxMD-DF(L) (♂: 28.26 mm; ♀: 25.40 mm, P<0.05), MxMD-DF(R) (♂: 27.74 mm; ♀: 24.02 mm, P<0.05), ANS-Me (♂: 71.09 mm; ♀: 65.84 mm, P<0.01), and MD-P(L) (♂: 22.85°; ♀: 25.25°, P<0.05). The method errors did not exceed 0.5 mm for any variables. A preliminary CBCT cephalometric database of the population was created. The significant sexual differences in the 3D McNamara's analysis indicate that gender specific data should be made available. The sample size should be increased to create a more representative database.

Antimicrobial activity of Chinese medicine herbs against common bacteria in oral biofilm. A pilot study.

Twenty traditional Chinese medicines (TCM) were evaluated for their antimicrobial activity against four common oral bacteria. TCMs were tested for sensitivity against Streptococcus mitis, Streptococcus sanguis, Streptococcus mutans and Porphyromonas gingivalis. Aliquots of suspension of each bacterial species were inoculated onto a horse blood agar plate with TCMs soaked separately on 6mm paper disks. The plates were incubated for 48h anaerobically and the mean diameters of growth inhibition of three different areas obtained. 0.2% (w/v) chlorhexidine was used as a positive control. Broth microdilution assay was used to determine minimum inhibitory concentration and minimum bactericidal concentration. Fructus armeniaca mume was effective against all four bacteria. Thirteen TCMs demonstrated antimicrobial activity against Porphyromonas gingivalis, including Cortex magnoliae officinalis, Cortex phellodendri, Flos caryophylli, Flos lonicerae japonicae, Fructus armeniaca mume, Fructus forsythiae suspensae, Herba cum radice violae yedoensitis, Herba menthae haplocalycis, Pericarpium granati, Radix et rhizoma rhei, Radix gentianae, Ramulus cinnamomi cassia and Rhizoma cimicifugae. Cortex phellodendri showed antimicrobial activity against Streptococcus mutans, while Radix et rhizoma rhei was effective against Streptococcus mitis and Streptococcus sanguis. Fructus armeniaca mume had inhibitory effects against Streptococcus mitis, Streptococcus sanguis, Streptococcus mutans and Porphyromonas gingivalis in vitro.

Virtual model analysis as an alternative approach to plaster model analysis: reliability and validity.

The objective of this study was to assess the feasibility of virtual models as an alternative to orthodontic plaster models. Virtual dental models (obtained from OrthoCAD) and corresponding plaster models of 80 patients in the permanent dentition were randomly selected from patients seeking orthodontic care. Inter-examiner error was assessed by measuring tooth width, overjet, overbite, intermolar width, intercanine width, and midline discrepancy. Criterion validity of virtual model analysis was determined by the agreement between the measurements from virtual and plaster models. Test-retest reliability was determined by remeasuring 10 virtual models 1 week later. Comparison analysis was assessed by calculating the mean directional differences and standardized directional differences. Correlation analysis was determined by calculating the intraclass correlation coefficients (ICCs). Both intra- and inter-examiner reliability and test-retest reliability of virtual model analysis were acceptable in measuring intercanine, intermolar, overjet, overbite, midline discrepancy, space analysis, and tooth width (ICC > 0.7). Good criterion validity was indicated by agreement between the results from the plaster and virtual models (ICC > 0.8). There were substantial agreements for canine and molar relationship classifications (κ > 0.70). The results suggest that analysis performed on virtual models is as valid as traditional plaster models for intra- and inter-arch relationship.

The effects of Rhodiola rosea extract on 5-HT level, cell proliferation and quantity of neurons at cerebral hippocampus of depressive rats.

The purpose of this study was to investigate the effects of Rhodiola rosea extract and depression on the serotonin (5-HT) level, cell proliferation and quantity of neurons at cerebral hippocampus of depressive rats induced by Chronic Mild Stress (CMS). Seventy male Sprague-Dawley rats were divided into seven groups (10 per group): normal control group, untreated depressive rat model group, negative control group, positive control group, low dosage Rhodiola rosea extract (1.5g/kg) group, medium dosage Rhodiola rosea extract (3g/kg) group and high dosage Rhodiola rosea extract (6g/kg) group. After the depressive rats induced by CMS had received Rhodiola rosea extract for 3 weeks, the 5-HT levels at cerebral hippocampus were detected by high performance liquid chromatography. Bromodeoxyuridine (BrdU) was injected in vivo to label the proliferating cells at hippocampus, and morphometry was used to count the hippocampal neurons. The results showed that the 5-HT level of the three experimental groups had recovered to normal status. The immunohistochemistry of hippocampus BrdU positive cells had returned to the normal level in the group of depressive rats with low dosage Rhodiola rosea extract. In conclusion the results demonstrated that Rhodiola rosea extract could improve 5-HT level in hippocampus in depressive rats, and low dosage Rhodiola rosea could induce neural stem cell proliferation at hippocampus to return to normal level, repairing the injured neurons at hippocampus.

Orthodontic treatment need and oral health-related quality among children.

OBJECTIVES: To determine the association between the impact of oral health on quality of life (OHQoL) among children and their need for orthodontic treatment. METHODS: Children (217) were screened for orthodontic treatment need using a number of professionally derived indices: Index of Orthodontic Treatment Need (IOTN)--Aesthetic Component (AC) and Dental Health Component (DHC); Index of Complexity, Outcome and Need (ICON) and the Dental Aesthetic Index (DAI). In addition, all children self-completed the 37-item Child Perception Questionnaire (CPQ), a measure of OHQoL, to assess Oral Symptoms (OS) experienced, Functional Limitation (FL), Emotional Well Being (EWB) and Social Well Being (SWB). RESULTS: Different prevalence of orthodontic treatment need was observed depending on occlusal indices used (ranged from 31.6% to 85.9%). However, there were significant correlations between the different occlusal indices (p < 0.01). Significant differences in overall CPQ scores existed between those with and without an orthodontic treatment need irrespective of occlusal indices used to categorize treatment need (p < 0.05); Effect sizes ranged from 0.24 to 0.51. However no single index's categorization of treatment need could identify variations in all of CPQ domain scores (OS, FL, EWB and SWB). CONCLUSION: Different occlusal indices (AC, DHC, ICON and DAI) prescribe a different prevalence of orthodontic treatment need. Those categorized as having an orthodontic treatment need by AC, DHC, ICON and DAI criteria had poorer overall OHQoL compared to those ascribed as not having a treatment need. None of the occlusal indices could comprehensively differentiate poorer OHQoL across all its domains.

A survey on the preference for continuing professional dental education amongst general dental practitioners who attended the 26th Asia Pacific Dental Congress.

AIMS: To identify the subjects of interest and to examine the modes as well as means of study for continuing professional dental education amongst general dental practitioners who attended the 26th Asia Pacific Dental Congress, 28 May-1 June 2004, Hong Kong. METHODS: A total of 381 general dental practitioners as the registered conference delegates from Hong Kong, Mainland China and other Asia-Pacific regions were randomly selected for the present survey. The survey was conducted through face-to-face interviews by a group of practising dentists in Hong Kong. RESULTS: Overall, orthodontics and prosthodontics were the most popular subjects for clinical degree programmes, whilst oral implantology and cosmetic dentistry were the highly preferred subjects for continuing education courses. Concerning the preferred mode of study for degree programmes, the part-time study mode was chosen by 68.3% of the participating dentists. A didactic teaching approach was preferred by most of the participants (81.7%) for postgraduate study. The majority of the interviewees (76.5%) were interested in a proposed clinical degree programme to be offered jointly by The University of Hong Kong and a leading university in the Mainland. Overall, there was no marked difference in the preference for continuing dental education amongst the respondents from Hong Kong, Mainland China and other Asia-Pacific regions. CONCLUSIONS: The present survey shows the currently preferred specialty areas and subjects for continuing professional dental education amongst the general dental practitioners who attended the 26th Asia Pacific Dental Congress, with didactic teaching as the most preferred mode of study on a part-time basis.

The impact of malocclusion and its treatment on quality of life: a literature review.

AIM: The aim of this paper is to review the literature relating to the impact of malocclusion, and the treatment of malocclusion, on physical, social and psychological health (i.e. quality of life, QoL). DESIGN: English-language papers, including cross-sectional studies, retrospective and prospective longitudinal studies, randomized controlled trials, and reviews and meta-analyses were reviewed to determine the impact of malocclusion and its treatment on QoL. RESULTS: Malocclusion and its treatment can affect physical health in terms of pain (e.g. temporomandibular disorders, and dental and gingival trauma), speech and mastication. In terms of psychological health, malocclusion and its treatment is reported to affect self-concept. Socially, malocclusion and its treatment can affect perceived attractiveness by others, social acceptance and perceived intelligence. However, the evidence is conflicting owing to differences in study designs, population's studied and methods of assessment of psychical, social and psychological health. CONCLUSION: Much controversy exists about the impact of malocclusion and its treatment on QoL. There is a need for a more comprehensive and rigorous assessment of the impact of malocclusion and its treatment on QoL, employing standardized, valid and reliable data collection instruments.

The Gold Medal of the Conjoint M. Orth. Examination of the Royal College of Surgeons of Edinburgh and the College of Dental Surgeons of Hong Kong, surgical orthodontic cases.

The Conjoint Gold Medal was awarded to the candidate who scored the highest overall mark in Part II of the Membership of Orthodontics examination held by the Royal college of Surgeons of Edinburgh and the College of Dental Surgeons of Hong Kong. It is the intermediate examination for the orthodontic specialty training pathway in Hong Kong. Part of this examination involved the presentation of a fully documented fixed appliance case and a multidisciplinary case, and three other cases with condensed case histories. This article described two surgical orthodontic cases presented during the 1999 and 2002 examinations by the award winners.

Long-term dentofacial changes in Chinese obstructive sleep apnea patients after treatment with a mandibular advancement device.

The objective of this study was to evaluate long-term dentofacial changes in Chinese obstructive sleep apnea (OSA) patients treated with a mandibular advancement device (MAD). Lateral cephalograms in natural head posture were obtained from 67 consecutive OSA patients (mean age = 46.9 +/- 8.9 years) treated with an MAD. The cephalograms were obtained at start of treatment (T0), after 1 year (T1), 2 years (T2), and 3 years (T3) of treatment. The lateral cephalograms were digitized twice, and the average of two readings was used for statistical analyses. Small, but statistically significant changes occurred in some dentofacial variables. The lower anterior facial height steadily increased during the observation period, and this increase was significant for the T0-T1 and T1-T2 periods and marginally significant for the T2-T3 period. A significant increase in the mandibular plane angle was observed during the T0-T1 and T2-T3 periods only. Significant reductions in the overjet and overbite were observed for the T0-T1 period but not thereafter. Statistically significant dentofacial changes were observed in this study, but they were of small magnitude. The overjet and overbite changes observed mainly occurred at the initial stage of treatment.

Repeated mechanical loading enhances the expression of Indian hedgehog in condylar cartilage.

Indian hedgehog (Ihh) acts as a mechanotransduction mediator that converts mechanical strain into cellular proliferation and cartilage formation in mandibular condylar cartilage. The aim of this study was to examine the effect of repeated mechanical strain on the level of expression of Ihh and type II collagen mRNA in condylar growth. Two hundred and eighty 35 days old Sprague-Dawley rats were divided into 10 experimental and 10 control groups. Repeated mechanical loading was applied by advancing the mandible in a stepwise manner by fitting a stepwise bite jumping appliance. Animals were sacrificed together with their matched controls on 10 different time points. Total RNA was extracted from condylar cartilage immediately after dissection. Ihh and type II collagen mRNA was quantified using real-time PCR. In the experimental group, Ihh mRNA increased significantly on experimental day 7. Upon the second advancement, another peak was elicited 7 days later. Type II collagen showed a significant increase on days 21 and 44 of advancement. This indicated that mechanical loading in a repeated manner, triggers the expression of Ihh which in turn increases the number of replicating mesenchymal cells as well as the amount of the cartilage formed. Taken together these events increase condylar growth.

Identification of temporal pattern of mandibular condylar growth: a molecular and biochemical experiment.

OBJECTIVES: Based on the phenomenon that expression of type X collagen and capillary endothelium correlates with endochondral ossification, the prime aim of this study was to establish the temporal pattern of condylar growth in Sprague-Dawley rats by biochemically identifying the expression of these two factors. DESIGN: Sprague-Dawley rats were divided into five groups representing five different stages during somatic pubertal growth. In situ hybridization and immunoperoxidase were performed to examine expression of type X collagen in hypertrophic zone and capillary endothelium in erosive zone of condylar cartilage. Computer-assisted imaging analyses were conducted to allow for a quantitative assessment of the expression of these two factors, from which the temporal pattern of condylar growth was inferred. RESULTS: (1) Synthesis of type X collagen and emergence of capillary endothelium were critical factors during the transition of condylar cartilage from chondrogenesis into osteogenesis, a biological pathway that leads to endochondral bone formation, the mode through which the condyle grows. (2) Quantitative analyses revealed the temporal pattern of the expression of these two factors, indicating that the thrust of natural growth of the condyle in the rats occurred in concomitance with somatic pubertal growth, featured by an acceleration starting from day 38, a maximum growth rate on day 56, followed by a decrease afterwards. CONCLUSION: It is suggested that the biochemical examination of growth markers, such as type X collagen, might be a new approach to accurately depict temporal pattern of condylar growth which is too delicate to be reflected by gross measurement not only in Sprague-Dawley rats but potentially also in other species.

Skeletal effects of bite jumping therapy on the mandible - removable vs. fixed functional appliances.

UNLABELLED: AUTHORS: Shen G, Hagg U, Darendeliler MA. OBJECTIVE: Based on an extensive review of the literature, the aim of this study was to explore the mainstream consensus on the controversial topic of whether the bite jumping treatment could enhance mandibular growth. DESIGN: The data for removable and fixed functional appliances were respectively comprehended and analyzed with regard to their attributes in mandibular growth modification. Furthermore, numerous reported findings were assessed by relating them to some important factors influencing the effects of bite jumping, such as treatment timing, treatment duration and post-treatment follow-up, to allow for a more objective and accurate evaluation. RESULTS: The key differences between removable and fixed appliances are working hours (intermittent vs. continuous), length of treatment time (long vs. short), optimal treatment timing (before puberty growth vs. at or after puberty spurt), and mode of bite-jumping (considerable vertical opening vs. limited vertical opening). These different features lead to different treatment effects on mandibular and TMJ growth, such as the intensity of possibly increased growth (clinically less significant vs. significant), the direction of enhanced growth (vertical vs. horizontal), and the stability of treatment changes (unstable vs. stable). The short-term or long-term post-treatment relapse mainly relates to the rebound of dental position. CONCLUSION: The immediate effects of bite jumping functional appliances on the mandibular growth enhancement are convincing during actual treatment. This extra gain of growth might be sustainable during the short-term and long-term post-treatment period.

Alternative gene therapy strategies for the repair of craniofacial bone defects.

Craniofacial anomalies, bone defects and cartilage lesions pose a difficult and challenging problem for both the doctor and for patients and their families. Conventional therapies focus on orthopaedic surgery, grafting with autogenous bone, allogenic bone grafts, or distraction osteogenesis. However, the efficacy of these techniques is limited by high cost, donor morbidity, scarcity of tissue resources, and alterations in volume [Marx & Morales, 1988]. On the basis of recent insights into the development, growth, and adaptation of bone, together with the significant advances in recombinant DNA technology, gene therapy is increasingly becoming recognised as an alternative technique for augmenting and promoting bone regeneration in vivo. It can be applied in craniofacial skeletal tissues by transferring genes encoding for specific growth factors such as BMPs in osteoblasts, chondrocytes or progenitor cells for the purpose of enhancing protein production [Scaduto & Lieberman, 1999]. It can be performed by either direct administration of gene delivery vectors, or by transplantation of genetically modified cells. This review will focus on recent advances in molecular mechanisms of bone formation, and development in various viral and non-viral vectors for direct in vivo therapeutic gene transfer and genetically engineered cells ex vivo therapy.

An update on the aetiology of orofacial clefts.

OBJECTIVE: To review recent data on the aetiology of cleft lip and palate. DATA SOURCES: MEDLINE literature search (1986-2003). STUDY SELECTION: Literature and data on aetiology of cleft lip and palate using the following key words: 'cleft lip', 'cleft palate', 'aetiology', and 'genetics'. DATA EXTRACTION: Relevant information and data were reviewed by the authors. DATA SYNTHESIS: Cleft lip and palate is one of the most common types of congenital malformation. The aetiology seems complex, but genetics plays a major role. Recently several genes causing syndromic cleft lip and palate have been discovered. Three of them--namely T-box transcription factor-22 (TBX22), poliovirus receptor like-1 (PVRL1), and interferon regulatory factor-6 (IRF6)--are responsible for causing X-linked cleft palate, cleft lip/palate-ectodermal dysplasia syndrome, and Van der Woude's and popliteal pterygium syndromes, respectively; they are also implied in non-syndromic cleft lip and palate. The nature and function of these genes vary widely, illustrating high vulnerability within the craniofacial developmental pathways. The aetiological complexity of non-syndromic cleft lip and palate is also exemplified by the large number of candidate genes and loci. CONCLUSIONS: The aetiology of non-syndromic cleft lip and palate is still largely unknown, but mutations in candidate genes have already been identified in a small proportion of cases of non-syndromic cleft lip and palate. Determining the relative risk of cleft lip and palate, on the basis of genetic background and environmental influence, including smoking, alcohol use, and dietary factors, will aid in genetic counselling and the development of future preventive measures.

Forward mandibular positioning enhances condylar adaptation in adult rats.

The aim of this investigation was to assess quantitatively the adaptive changes in the condyles of adult rats to forward mandibular positioning. The level of types II and X collagen expressed in the condyles of adult rats was compared with that formed in response to forward mandibular positioning and the levels of expression were correlated to the amount of bone formed in response to mandibular advancement. Seventy-eight 120-day-old female Sprague-Dawley rats were included in this study. The rats were randomly allocated to six groups. Each group consisted of nine rats with bite-jumping devices and four untreated controls. The animals in each group were sacrificed on days 3, 7, 14, 21, 30, and 60. Immunostaining was used for the detection of types II and X collagen, while Alcian blue-PAS was used to observe the extracellular matrix and new bone formation. The results showed that new cartilage was formed in the posterior condyle. The highest level of expression of types II and X collagen were present on day 21, the amount of increase was 247.99 and 540.08 per cent, respectively. The highest level of new bone formation was measured at day 30 of advancement when the amount of increase in new bone formation was 318.91 per cent. These findings indicate that forward mandibular positioning causes changes in the biophysical environment of the temporomandibular joint (TMJ) of adult rats that leads to condylar adaptation.

Neovascularization and bone formation in the condyle during stepwise mandibular advancement.

The aims of this investigation were to identify the temporal expression of vascular endothelial growth factor (VEGF) in the mandibular condyle and to correlate it with the pattern of new bone formation during stepwise mandibular advancement. Two hundred and fifty female, 35-day-old Sprague-Dawley rats were randomly divided into 10 groups, with 10 rats allocated to the single-step bite-jumping subgroup, 10 rats to the stepwise advancement subgroup and five rats to the control subgroup. In the experimental groups, the mandibles were kept in a continuous forward position. The initial stepwise advancement commenced on day 35, whereas the second advancement started on day 65. The rats were sacrificed on experimental days 3, 7, 14, 21, 30, 33, 37, 44, 51 and 60. Sections (7 microm) were cut through the condyle in the parasagittal plane and stained with anti-VEGF antibody. Each section was counter-stained with haematoxylin for observation of the cellular response. The sections were digitized and quantitatively analysed with a computer-assisted image analysing system. The results showed that the initial advancement in the stepwise group led to significantly less expression of VEGF when compared with single advancement. However, the second advancement on day 30 resulted in a significant increase in VEGF expression when compared with the one-step group and the natural growth control group. Thus, it was concluded that changes in the amplitude of mechanical loading, produced by stepwise advancement, have a significant effect on the production of VEGF by the chondrocytes. During the later stages of advancement, more VEGF and more condylar bone was produced.

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.

The effect of fixed orthodontic appliances on the oral carriage of Candida species and Enterobacteriaceae.

The aim of this investigation was to evaluate the prevalence of Candida and Enterobacteriaceae in a group of adolescents during fixed orthodontic appliance (FOA) therapy. The experimental group was recruited from a larger sample of orthodontic patients who were clinically examined once to obtain baseline data before active treatment. The group comprised 27 subjects; 13 males, 14 females (mean age 15.5 +/- 2.3 years). Thereafter, the experimental group was examined three times during a 3 month follow-up period after insertion of the FOA. The whole mouth plaque score was obtained, and the oral cavity was then sampled for Candida species and Enterobacteriaceae using three different microbiological culture techniques, namely the oral rinse, pooled plaque and the imprint culture.A significant increase in candidal numbers was observed after FOA insertion when the imprint technique was used (P < 0.001), although the overall candidal prevalence rates obtained using the oral rinse and pooled plaque techniques did not demonstrate such a change. The predominant Candida species isolated was C. albicans and the number of coliform carriers significantly increased after the insertion of a FOA, as detected by the oral rinse (P < 0.05) and the pooled plaque (P < 0.05) techniques. In total, eight coliform species were isolated following FOA therapy compared with the three species isolated before insertion of the appliance. The results also revealed a significant increase in plaque index due to the introduction of a FOA. Taken together, these data imply that insertion of a FOA is likely to promote oral carriage of Candida and coliform species. Furthermore, it appears that routine oral hygiene instruction and information on appliance hygiene given to these patients may not necessarily reduce plaque accumulation and possible attendant effects. Further work with a larger cohort is required to confirm these findings.

[An immunohistochemical study on neovascularization in TMJ during mandibular advancement].

OBJECTIVE: Neovascularization is proved to be closely correlated with ossification. This study was designed to determine the biochemical path through which the new bone formation is enhanced in TMJ during mandibular protrusion. METHODS: SD Rats were fitted with bite-jumping appliances to allow for an adequate advancement of the mandible. The animals were sacrificed 3, 7, 14, 21 and 30 days, respectively, after placement of the appliances. Slides with TMJ tissue were prepared for biochemical procedure. Immunohistochemical approaches were adopted to examine neovascularization in TMJ by immuno-localizing the newly formed endothelial cells. Computer-assisted image analysis system was applied to quantify the positive immunoreaction. RESULTS: Neovascularization in connective tissue close to the condyle was 200% higher in the experimental groups than that in the control, and, within the bony tissue of the condyle, neovascularization in experimental animals was found to be 103% higher than that of the control. CONCLUSION: Increased neovascularization triggered by mandibular protrusion might intensify new bone formation in condyle and glenoid fossa and finally lead to a growth adaptation of TMJ to bite-jumping therapy.

PTHrP regulates chondrocyte maturation in condylar cartilage.

PTHrP is a key factor regulating the pace of endochondral ossification during skeletal development. Mandibular advancement solicits a cascade of molecular responses in condylar cartilage. However, the pace of cellular maturation and its effects on condylar growth are still unknown. The purpose of this study was to evaluate the pattern of expression of PTHrP and correlate it to cellular dynamics of chondrocytes in condylar cartilage during natural growth and mandibular advancement. We fitted 35-day-old Sprague-Dawley rats with functional appliances. Experimental animals with matched controls were labeled with bromodeoxyuridine 3 days before their death, so that mesenchymal cell differentiation could be traced. Mandibular advancement increased the number of differentiated chondroblasts and subsequently increased the cartilage volume. Higher levels of PTHrP expression in experimental animals coincided with the slowing of chondrocyte hypertrophy. Thus, mandibular advancement promoted mesenchymal cell differentiation and triggered PTHrP expression, which retarded their further maturation to allow for more growth.