Evaluation of bone thickness around the mental foramen for potential fixation of a bone-borne functional appliance: a computer tomography scan study.

AIM: A mandible bone-borne Herbst appliance (MBBHA) would avoid the proclination of the lower incisors that occurs with any teeth-borne functional appliance. But mapping of the bone characteristics at potential fixation areas around the mental foramen has not been carried out so far. The aim of this computer tomographic (CT) study was to evaluate bone thickness at specific positions around the mental foramen. MATERIAL AND METHODS: CT scans of 60 randomly chosen adult Hong Kong Chinese subjects (mean age 28 ± 6.3 years) were used to measure the bi-cortical bone thickness in the mandible in the mental foramen area. The thickness of buccal and lingual cortical and cancellous bone was assessed at the following locations: 10 mm (A10 mm) and 5 mm (A5 mm) anterior, 10 mm (P10 mm) and 5 mm (P5 mm) posterior, and 5 mm (Inf5 mm) below the mental foramen. RESULTS: The amount of buccal cortical bone thickness ranged between 1.89 mm, 10 mm anterior of the mental foramen, and 2.16 mm, 10 mm posterior to its location. At the A10 mm level, cortical thickness showed a marginal statistically significant difference between A5 and A10 mm. The total amount of bone thickness ranged from 10.19 to 12.06 mm. CONCLUSION: At the locations studied around the mental foramen, a mean bicortical bone thickness of 10-12 mm was measured. No large variation in the thickness was found between bicortical bone thicknesses in the measured locations around the mental foramen. Thorough evaluation on a case-by-case basis is advisable.

The assessment of cell cycle genes in the rat mandibular condyle.

OBJECTIVES: We aimed to investigate the expression profile of cell cycle genes in the mandibular condyle on mechanical strain and natural growth, and quantify their expression intensity. METHODS: Three hundred and fifty 35 days old Sprague-Dawley rats were randomly divided into experimental groups fitted with bite-jumping appliances and control groups. Groups were sacrificed at days 1, 3, 7, 9, 14, 30, and 33. Then, condyles were dissected and total RNA was extracted for microarray analysis. RESULTS: Thirty-nine known cell cycle genes were present in the condyle, where Cyclin D1, PCNA, and Wnt5a were differentially expressed. Reverse transcriptase-PCR confirmed that Wnt5a showed a 2-fold increase on experimental day 1, Cyclin D1 showed a 2-fold increase on experimental day 1 and a 3-fold increase on experimental day 14, while PCNA shows 2.2-fold increase both on experimental days 9 and 30. PCNA, Cyclin D1, and Wnt5a were all expressed by cells in both the proliferative layer and erosive zone. CONCLUSION: Mandibular advancement leads to the expression of Cyclin D1 that accelerates entry to the S phase. The increased level of PCNA indicates increased DNA replication of MSC. Then, elevated level of Wnt5a indicates the commitment of MSC to the chondrogenic lineage.

Pain intensity during the first 7 days following the application of light and heavy continuous forces.

The purpose of the present study was to determine whether a force of 20 cN can be biologically active for tooth movement and to examine the pain intensity during the application of light (20 cN) or heavy (200 cN) continuous forces for 7 days. In the first experiment, a force of 20 cN was applied to eight canines in five volunteers. The mean tooth movement during 10 weeks was 2.4 mm. In the second experiment, two forces of 20 or 200 cN were applied to maxillary premolars in 12 male subjects (aged 24-31 years) to measure pain intensity for 7 days. Spontaneous and biting pain were recorded every 2-4 hours on a 100 mm visual analogue scale (VAS). Wilcoxon signed-rank test was used for statistical analysis. Comparing the VAS score at force initiation with the other time points, there was no significant difference in spontaneous pain for either group, or in biting pain for the light-force group. However, biting pain in the heavy-force group during the time period from 6 to 156 hours was significantly (P < 0.05) greater than that at force initiation. Comparing the VAS scores between the light- and heavy-force group, VAS scores for biting pain in the heavy-force group during the time period from 8 to 100 hours was significantly (P < 0.05) greater than that in the light-force group. A force of 20 cN can move teeth, but pain intensity while biting may be greater approximately 8 hours to 5 days following the application of heavy continuous force compared with light force.

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.

Relationship between anteroposterior cranial vault deformation and mandibular morphology in a pre-Columbian population.

INTRODUCTION: An externally applied force to the cranial vault has been reported to affect the growth of the facial skeleton. However, the effect on the mandible is unclear. The purpose of this study was to investigate the relationship between anteroposterior cranial vault deformation and mandibular morphology. METHODS: The study sample included 44 women's crania with intact faces and bases that were excavated from archaeological sites in the Azapa Valley in northern Chile. The crania were divided into anteroposterior deformation (AP) and undeformed (U) groups according to frontal, parietal, and occipital curvatures. The sizes of the cranial vault, middle face, and mandible were measured with calipers. Lateral cephalograms were taken and analyzed according to a conventional method. RESULTS: Cranial base angle, bizygomatic breadth and upper facial height, bicondylar breadth, anterior breadth, and mandibular body length were significantly larger, and the mandibular angle was significantly smaller, in the AP group than in the U group. CONCLUSIONS: The anteroposteriorly shorter and wider cranial deformation caused by externally applied forces in infancy might affect the bone-remodeling process of the mandibular angle, leading to a smaller mandibular angle in adulthood.