Camouflage orthodontic treatment combined with genioplasty distraction osteogenesis for skeletal class II relationship secondary to osteosarcoma excision surgery.

OBJECTIVE: The treatment of orthodontic patients who survive head and neck tumors is challenging because of dentoskeletal deformities and other unexpected dental and facial complications. This case report describes the case of a 26-year-old woman who presented with mandibular retrognathia after survival from osteosarcoma. CLINICAL CONSIDERATIONS: Camouflage orthodontic treatment was chosen instead of combined orthodontic-orthognathic surgery after primary reconstructive surgery with an iliac bone graft. Genioplasty distraction osteogenesis (DO) was performed to achieve an optimal facial profile. Although unexpected condyle dislocation and epithelial hyperplasia occurred during treatment, a favorable facial profile and optimal skeletal and dental relationships were accomplished after 32 months of treatment. CONCLUSIONS: The patient underwent genioplasty DO and experienced unexpected left condyle dislocation. However, the treatment achieved esthetic goals after intermaxillary elastics were applied.

A cone-beam computed tomographic study evaluating the efficacy of incisor movement with clear aligners: Assessment of incisor pure tipping, controlled tipping, translation, and torque.

INTRODUCTION: This retrospective clinical study aimed to evaluate the efficacy of different types of incisor movements with clear aligners in the sagittal plane. METHODS: Pretreatment and posttreatment cone-beam computed tomography (CBCT) scans were collected from 69 patients who underwent nonextraction treatment with clear aligners (Invisalign; Align Technology, San Jose, Calif). Integrated 3-dimensional models of the virtual incisor position (ClinCheck; Align Technology) and the posttreatment incisor position (from posttreatment CBCT scans) were superimposed over the pretreatment position (from pretreatment CBCT scans) using Mimics software (Materialise, Leuven, Belgium). On the basis of the location of the rotation center, incisors showing pure tipping (>10°), controlled tipping (>10°), translation (>1 mm), or torque (>10°) movements were selected. Efficacy was determined by comparing the predicted and achieved incisor movement, and differences with efficacy were analyzed using Kruskal-Wallis and Shapiro-Wilk tests (α = 0.05). RESULTS: In measurements for 231 incisors, the mean efficacy of incisor movements in the sagittal plane was 55.58%. The most and least predictable movements were pure tipping (72.48%) and torque (35.21%), respectively. Labial root movement was significantly more predictable than lingual root movement, and labial movement of the mandibular incisors was significantly easier than that of the maxillary incisors. The type of tooth movement achieved was different from the type designed. CONCLUSIONS: The efficacy of incisor movement in the sagittal plane using clear aligners varies with designed movement type, and labial root movement appears to be more accurate than the lingual root movement. The biomechanics of clear aligners remains to be further elucidated to achieve more predictable treatment results.

[The impact of personality traits on adolescents' adaptation and compliance to clear retainers].

PURPOSE: The aim of this study was to evaluate the adolescents' adaptation and compliance to clear retainers, and to investigate their associations with personality traits. METHODS: Fifty adolescents at the end of fixed orthodontic treatment were consecutively recruited. After debonding the fixed orthodontic appliances, clear retainers were used. Participants were asked to fill questionnaires 2 months after wearing the clear retainers. A questionnaire was designed to evaluate their adaptation and compliance for clear retianers. Eysenck personality questionnaire was used to assess the personality traits. Spearman rank correlation was used to analyze the associations between personality traits with the adaptation and compliance to clear retainers using SAS8.0 software package. RESULTS: Forty-two of 50 adolescents accomplished the questionnaires. 76% felt no mucous irritation, 95% felt no influence on socializing. However, 75% showed oral constraint, 71% felt impaired speech. Moreover, 40% adolescents wore the retainers less than 18 hours per day. 31% patients had their aligner lost. 83% patients did not brush their teeth after each meal. Neuroticism was positively associated with the effect of impaired chewing (r=0.32). Psychoticism was positively associated with the oral constraint (r=0.31) and facial muscular soreness (r=0.35), but negatively associated with the influence on emotion (r=-0.34). Extraversion was positively associated with the retainers' damage (r=0.31). CONCLUSIONS: Adolescents showed good adaptation for clear retainers, but unsatisfactory compliance. There are associations between adolescents' adaptation and compliance for clear retainers and personality traits. These results suggest that clinicians should pay more attention to the compliance of adolescents when using clear retainer. Personality traits could be a useful prediction to assess the compliance for clear aligners.

[Clinical effect of premolar extraction with high torque self-locking appliances].

PURPOSE: To analyze the clinical effect of extraction correction of patients with maxillary protrusion by using Damon high torque appliances. METHODS: Forty patients with extraction of four first premolars due to orthodontic treatment were selected. They had protrusion of maxilla and were randomly divided into two groups. Both arches of Damon group were treated with Damon high torque appliances and MBT group were corrected with traditional MBT straight wire appliance; patients in two groups received sliding mechanics for adduction of upper anterior teeth. Cephalometric radiophotographs were analyzed before（T0）and after adduction of upper anterior teeth（T1）. The difference between the two groups was analyzed with SPSS15.0 software package. RESULTS: The upper incisors showed a more retruded position in the two groups at T1,although they showed a similar amount in both groups. The backward movement of upper lip was 2.31mm in Damon group, which was significantly less than that of 2.81mm in MBT group(P<0.05). No significant difference in the first molar mesialization was detected between Damon group(2.33 mm) and MBT group(2.36mm) (P>0.05). For anterior teeth retraction, nasolabial angle (NLA) in MBT and Damon group were 107.44°and 106.33°, increase of NLA in MBT group was 9.17°,which was significantly larger than that of 7.22°in Damon group (P<0.05). U1-MxP in MBT and Damon were 110.61°and 114.11°. U1-MxP decreased 12.06°in MBT group, while significant change was deteced in Damon group of 7.61°(P<0.05). CONCLUSIONS: Application of Damon high torque appliances in extraction treatment of maxillary protrusion patients yielded better control of the labial crown torque of anterior teeth, and avoided excessive lingual inclination of anterior teeth compared with MBT in adduction of upper anterior teeth.

The effect of continuous bite-jumping in adult rats: a morphological study.

The aim of this study was to determine the mandibular morphology before, during, and after bite-jumping in nongrowing species. Fifty-two adult female Sprague-Dawley rats were divided into four experimental groups and four control groups. The experimental groups were fitted with fixed bite-jumping devices that protruded the mandible. The animals were sacrificed on days 3, 14, 30, and 60. Right halves of the mandible were harvested and freed of soft tissue. Digital pictures were obtained in a standardized manner. Selected linear and angular measurements were made. There were no morphological differences between the controls and experimental group on days 3 and 14. The length of condylar process increased significantly on day 30 and remained so on day 60 in the experimental group. The angulation of the condylar process was significantly affected because of increased apposition of bone in the middle and especially the posterior parts of the condyle. Thus, bite-jumping of the mandible in adult rats affects the size and angulation of the condylar process because of differential apposition of bone on the condylar head.

[A clinical evaluation on the stability of orthodontic mini-implants using resonance frequency analysis].

PURPOSE: To evaluate the stability of mini-implant by resonance frequency analysis and to determine the optimal loading timing of orthodontic force. METHODS: Fourteen orthodontic patients who had upper first premolars extraction and needed mini-implants to reinforce the anchorage were enrolled in this study. The patients were divided into 2 groups: delay-loading group and selective-loading group. A joined head mini-implant was inserted in the buccal interradicular area on each side of maxilla for each patient and 28 mini-implants in total were used. Osstell resonance frequency device was used to measure the ISQ (implant stability quotients) value. The measurements were performed immediately after the implant insertion and weekly afterwards until week 16. After the ISQ value was stable, orthodontic force of 150g was loaded on the mini-implants in selective-loading group. The same level of force was applied in delay-loading group at week 12. The data was analyzed by one-way ANOVA and t test using SPSS 19.0 software package. RESULTS: Twenty-three mini-implants were stable during the study. Twelve unloading mini-implants in delay-loading group showed maximal ISQ values immediately after insertion and at week 1 (21.48 ± 5.25). The ISQ values decreased gradually from week 2 to week 5 and reached a plateau after week 6 (11.26 ± 3.36). Eleven mini-implants survived in selective-loading group were then loaded at week 6. There were no significant differences of ISQ values in loading and unloading mini-implants after 6 weeks. The remaining 5 mini-implants were loosing during the first 4 weeks, which showed a significant lower initial ISQ values compared to the successful implants. CONCLUSIONS: The stability of mini-implants decreases 1 week after insertion and maintains after 6 weeks. Orthodontic loading after week 6 has no influence on the stability. Lower initial stability is an important factor for the failure of mini-implants.

[Osteoclasts and early bone remodeling after orthodontic micro-implant placement].

PURPOSE: To observe the incidence of osteoclasts during early bone remodeling after orthodontic micro-implant placement. METHODS: Twenty New Zealand rabbits were randomly allotted into 4 groups. One micro-implant was implanted proximal to the epiphyseal plate of the tibia. Animals were sacrificed on day 3, 7, 14 and 28 (n=5). The sequence of histological changes around the micro-implants were evaluated by hematoxylin and eosin (HE) staining. Osteoclasts were identified by TRAP staining. The differences of the number of the osteoclasts among each time point were analyzed by one way ANOVA with SPSS 19.0 software package. RESULTS: After 3 days of implantation, a large number of erythrocytes, inflammatory cells, mesenchymal cells and bone debris were seen at the implant bone interfaces. Few osteoclasts were observed. On day 7, granular woven bone was formed and some osteoclasts were found in the Howship's lacunae. New bone formation and mineralization were apparent on day 14. Meanwhile, large amounts of osteoclasts were found in the latticed woven bone. On day 28, woven trabeculae with lamellate structures connected to lamellar bone and fewer osteoclasts were identified. Semi-quantitative analysis showed that the number of the osteoclasts was at peak on day 14. There were significant differences among each time point (P<0.01). CONCLUSIONS: Osteoclast activity is closely related to bone formation and remodeling after micro-implant insertion.

[Centrographic analysis in Shanghai adults with normal occlusion].

PURPOSE: To obtain the reference value of centrographic analysis of Shanghai adults with normal occlusion. METHODS: Seventy five subjects of Han nationality at permanent dentition with normal occlusion were selected from Shanghai region (34 males, 41 females, age rang:18-21 years). Centrographic analysis was conducted on the basis of the lateral cephalograms, and the obtained data was compared with that of Caucasian. SAS9.2 software package was used for statistical analysis. RESULTS: The reference value of centrographic analysis in Shanghai adults with normal occlusion was established. The facial centroid was located on the Ba-A plane; the upper centroid was positioned on the centroid plane; the lower centroid was positioned anterior to the centroid plane within 0.92-1.29mm; the long axis of lower incisor was positioned posterior to 1/3 Ba-Gn plane symphysis intersection; the long axis of upper incisor was positioned posterior to orbitale and the upper incisor was positioned in proper occlusion with the lower incisor. The lips were positioned on the outer profile plane. There was no significant difference between male and female adults (P>0.05). CONCLUSIONS: Compared with that of Caucasians, mandibular position of adults in Shanghai was in a relative forward position, the incisor was labially inclined and the soft tissue in the lower 1/3 of the face was convex slightly.

[Clinical evaluation of lingual fixed retainer combined with Hawley retainer and vacuum-formed retainer].

PURPOSE: To evaluate the clinical efficacy of vacuum-formed retainers (VFRs) and lingual fixed retainers combined with Hawley retainers (combined retainers, CRs). METHODS: Forty five patients immediately after orthodontic treatment were randomly allocated to either VFRs (n=25) or CRs (n=20) groups. Overbite, overjet and calculus index scores (CIS) were recorded at pretreatment (T0), debonding (T1), 6 months (T2) and 12 months (T3) after maintenance. The tooth rotation, intercanine and intermolar width, and Little's index of irregularity were recorded on the study models of lower arches. The difference between the two groups was analyzed with SAS 6.12 software package. RESULTS: No significant difference was noted during retention time in VFRs(P>0.05). Likewise, there was no significant difference between VFRs and CRs, except that the change of CIS in CRs was significantly larger than those in VFRs(P<0.05). The incidence of breakage of vacuum-formed retainers was 24<, which was comparable with that of lingual fixed retainers (20<). CONCLUSIONS: Both vacuum-formed retainers and lingual fixed retainers combined with Hawley retainers have good retention during the first 12-month retention period. Considering patients' compliance and retention efficacy, lingual fixed retainer with Hawley retainer at night is a better choice for retention.

[Proliferative responses of osteoblasts in expanding pre-maxillary suture determined using sustained-release bromodeoxyuridine].

PURPOSE: The purpose of this study was to examine the proliferative responses of osteoblasts in expanding pre-maxillary suture using sustained-release bromodeoxyuridine (BrdU). METHODS: Poloxamer thermosensitive BrdU gel was prepared and injected to the rats subcutaneously. Blood samples were collected and subjected to high performance liquid chromatography (HPLC) for quantitative determination of BrdU levels in serum. Blood samples collected from rats received a single intraperitoneal injection of BrdU solution were served as control. Forty male Sprague-Dawley rats, 35 days of age, were randomly allotted into the experimental and control groups. Experimental animals were subjected to pre-maxillary suture expansion by helix spring. Both groups were given either a single intraperitoneal injection of BrdU solution (10mg/100g) or a single subcutateous injection of thermosensitive gel (10mg/100g) after 24 hours. Animals in each group were sacrificed at 48h and 96h (n=5). Proliferative cells were identified by BrdU immunostaining. RESULTS: 6h after subcutaneous injection of BrdU thermosensitive gel, 1.21µg BrdU per mL serum was still identified. BrdU immunostaining also showed labeled proliferating cells in pre-maxillary suture. On the other hand, 3h after intraperitoneal injection of BrdU solution, little trace of BrdU (0.17µg/mL) could be detected. BrdU immunostaining did not show labeled cells in pre-maxillary suture. 48h after inter-premaxillary suture expansion, a plenty of BrdU labeled osteoblasts were present along the suture-bone interface. 96h after expansion, some of these labeled cells were embedded in the newly formed bone matrix. CONCLUSIONS: Sustained-release BrdU thermosensitive gel could be used practically and effectively to label proliferative osteoblasts in vivo. Mechanical stretch stimulates proliferation of osteoprogenitor cells, which then differentiate into osteoblasts and secret bone matrix, leading to new bone formation in the suture.

[Morphological and histological adaptation after mandibular functional positioning only in vertical dimension].

PURPOSE: To elucidate the role of mandibular vertical functional positioning in condylar adaptive remodeling. METHODS: Forty female Sprague-Dawley rats at the age of 5 weeks were randomly divided into 4 control and experimental groups. All the animals were sacrificed on day 3, 6, 9 and 12 (n=5). Bite plates on upper posterior teeth were fitted on the experimental animals to induce functional repositioning of the mandible. Morphological and histological analysis was carried out to quantitatively analyze the amount of the adaptive changes of condylar cartilage. Independent-samples t test and One-Way ANOVA using SPSS11.0 software package were performed. RESULTS: Twelve days after mandibular vertical functional positioning the condylar height increased. Nine days after mandibular vertical functional positioning the thickness of prechondroblast layer and chondroblast layer increased significantly compared with control groups. However the thickness of hypertrophic layer decreased significantly after 6 days' mandibular repositioning. No change was found in the thickness of mesenchymal layer during the experimental period. CONCLUSIONS: Mandibular vertical functional positioning could enhance the growth of condyle. The resulted adaptive remodeling in condylar cartilage plays an important role in the treatment mechanism of mandibular deficiency via functional appliances.

[Biological approaches to modification of craniofacial sutures].

The new bone deposition along the craniofacial sutures contributes to the overall growth of the craniofacial complex. The osteogenesis in suture is also regulated by the surrounding mechanical stress, which is the basis that orthodontic or orthopedic forces could therapeutically correct craniofacial growth abnormalities. Applying different kinds of mechanical forces, such as stretching/compression force, light/heavy force, continuous/intermittent force, could modulate the process of new bone formation in suture, by regulating the expression of a contain of growth factors. Recent researches indicated that additional biological manipulation, like physical stimulation and local administration of growth factors, could further assist the growth modification of suture upon mechanical forces. Understanding the tissue and molecular events of bone regeneration in suture upon different biological approaches could have important implications for the clinical management of craniofacial development and growth.

[Identification of cell apoptosis during premaxillary suture expansion in rat].

PURPOSE: To identify the incidence of cell apoptosis during premaxillary suture expansion. METHODS: Forty SD rats were randomly allotted into experimental and control groups. The experimental animals were subjected to premaxillary suture expansion by a helix spring with (200+/-10)g initial force. They were sacrificed on day 1, 2, 3 and 5(n=5). The sequence of histological changes and osteoblast proliferation in the premaxillary suture were evaluated by hematoxylin and eosin(HE) and toluidine blue staining. Cellular apoptosis was identified by ssDNA immunostaining. The difference between experimental and control groups was analyzed by Student's t test with SPSS 15.0 software package. RESULTS: The width of premaxillary suture was enlarged 1 day after expansion and osteoblasts were accumulated along the suture. After 2 days of stretching, the number of the osteoblasts increased to the peak. New bone deposition was identified on day 3 and projection of suture with bone trabeculae was apparent on day 5. ssDNA immunostaining showed few apoptotic cells in premaxillary suture during natural growth. Upon expansion, cell apoptosis was identified in osteoblasts along the suture and the osteocytes embedded in premaxillary bone, especially on day 2 and day 3(P<0.01). CONCLUSION: Apoptotic cell death might regulate the growth modification of premaxillary suture upon mechanical stretching.

[A comparison of rapid palatal expansion and Damon appliance on non-extraction correction of dental crowding].

PURPOSE: To compare the effect of rapid palatal expansion (RPE) and Damon technique on the correction of dental crowding with non-extraction approach. METHODS: 19 adolescent patients with non-extraction orthodontic treatment were reviewed. They had Class I skeletal pattern and moderate crowding. Nine subjects were treated with RPE followed by straight wire appliance, and 10 subjects were treated with Damon appliance only. The dental casts and cephalometric radiophotographs were measured before and after the treatment. The difference between two groups was analyzed for Student's t test with SPSS15.0 software package. RESULTS: Upper and lower inter-canine width increased 2.9mm and 1.3mm respectively in RPE group (P<0.05), while there was no significant change in Damon group. A significant posterior expansion of upper and lower arch width was noted in both RPE and Damon groups (P<0.05). The increase in upper inter-bicuspid width and lower inter-molar width was comparable in two groups. The upper inter-molar width in RPE group expanded 5.3mm, which was significantly larger than that of 3.1mm in Damon group(P<0.05). The increase in lower inter-bicuspid width in Damon group, on the other hand, was larger than that of RPE group (4.5mm vs. 1.5mm). (P<0.05) Both groups showed buccal tipping of bicuspids and molars, with more extend of bicuspid tipping in Damon group (P<0.05). The maxillary base width increased 2.1mm in RPE group, which was significantly larger than that of 0.6mm in Damon group (P<0.05). The upper and lower incisors in Damon group were tipped forward by 9.2 degrees and 7.5 degrees respectively, while the change in RPE group was not significant (P<0.05). CONCLUSION: Both RPE and Damon technique can successfully increase the arch width and correct moderate dental crowding with non-extraction approach. Damon appliance protrudes the upper and lower incisors and expands the dental arch by buccal tipping of bicuspids and molars. RPE expands the maxillary base along with the whole upper dental arch and could maintain the incisors in upright position.

[Arch perimeter changes on non-extraction correction of dental crowding with Damon appliance].

PURPOSE: To clarify the arch perimeter changes and the mechanism of Damon technique on the correction of dental crowding with non-extraction approach in different dental stages. METHODS: 24 patients with non-extraction Damon appliance treatment were reviewed. They had Class I skeletal pattern and upper arch crowding more than 5mm. They were divided into 2 groups according to the eruption of upper second molars, with 9 subjects in group G1 (second molar unerupted) and 15 subjects in group G2 (second molar erupted). The dental casts and cephalometric radiophotographs were analyzed before and after the upper arch crowding correction. The difference between the two groups was analyzed with SPSS15.0 software package. RESULTS: Significant increase in upper arch length and arch width were noted after the correction of crowding, with no significantly difference between the two groups. Stepwise regression analysis indicated that the increase in arch length (X1) and inter-bicuspid arch width (X2) were predictive of the increase in arch perimeter (Y), with the equation of Y=1.35X1+0.63X2+1.77. Both molar distalization and incisor protrusion contributed to the increase in arch length, which were 2.4mm and 1.2mm in G1 group, and 0.9mm and 2.5mm in G2 group. The difference between two groups was statistically significant (P<0.05). CONCLUSIONS: During the correction of upper arch crowding with non-extraction Damon technique, arch perimeter is gained by the increase in both arch length and inter-bicuspid arch width. In addition to the labial movement of incisors, space can be provided by the distal movement of the first molars before the eruption of second molars.

[Indications for non-extraction treatment of dental crowding with Damon appliance].

PURPOSE: To analyze the indications for successful non-extraction correction of dental crowding with Damon appliance. METHODSú 19 patients with non-extraction orthodontic treatment were reviewed. They had Class I skeletal pattern and both arches were treated with Damon 3 or Damon MX appliances. According to the initial diagnosis before treatment (T1), 7 cases needed extraction, but they rejected it. After correction of crowding (T2), they were allotted into either successful group or unsuccessful group. The successful group contained those subjects in whom the Z angle at T2 was no less than 70 degrees or that of T1. Others were allotted into the unsuccessful group. The dental casts and cephalometric radiophotographs were analyzed at T1 and T2. The difference between the two groups was analyzed with SPSS15.0 software package for Student's t test. RESULTS: There were 11 cases in successful group. All the 7 cases rejecting extraction were finally allotted into the unsuccessful group. No significant difference in upper arch perimeter and arch width was detected between the two groups at both T1 and T2. The upper and lower incisors and upper lip showed a more retruded position in successful group at T1, although they showed a similar amount of protrusion from T1 to T2 in both groups. The forward movement of lower lip was 3.4mm in the unsuccessful group, which was significantly larger than that of 1.6mm in successful group(P<0.05). Z angle decreased 10.7 degrees in the unsuccessful group, while no significant change was detected in the successful group. The Holdaway upper lip strain was comparable in two groups, but the successful group showed significantly less soft chin strain than unsuccessful group (P<0.05). CONCLUSIONS: Damon appliance can not rescue extraction cases. Straight soft tissue profile and upright incisor position are prerequisite for non-extraction treatment. And a harmonious chin and lip position is the key leading to the successful non-extraction treatment with Damon appliance.

[Study on perception of Shanghai population with labial profile].

OBJECTIVE: To investigate the perception of Shanghai population with labial profile and evaluate its effect on orthodontic treatment. METHODS: Four facial profiles with different labial convexity were drawn with computer aid on the basis of the pretty Chinese female cephalometric measurements. 650 panelists were selected from Shanghai area including 250 youth with normal profile and 200 adolescents under orthodontic treatment and their parents. Subjects were asked to rank the four facial profiles in descending order of attractiveness. RESULTS: The ranking was as follows: slightly straight style, standard style, straight style and slightly convex style. The normal male youth preferred more convex style than female. Patients with Class profile preferred standard style while Class and patients and the parents were fond of slightly straight style. CONCLUSION: People in Shanghai area tended to prefer straight profile. The perception with labial profile has sex and age difference. It also has difference between non-orthodontic and orthodontic patients and was influenced by the profiles themselves. It was suggested that consultation between orthodontist and patient was essential and more attention should be made on the patient's perception with labial profile.

[A Study On Dental and Craniofacial Structure of Normal Shanghai Adults Occlusion-III The Analysis of Dental Capacity and Craniofacial Structure]

OBJECTIVE:To examine the relationships between dental capacity and cranioficial structures.METHODS:Models, posterioanterior and lateral cephalometric films of 90 adults with normal occlusion in Shanghai area were measured and analyzed.RESULTS:The canine width of lower arch extended an important influence on the upper and lower arch. The dental capacity was highly correlated not only with the width and depth of cranioficial structure but with the height as well. The database of Coben analysis for normal Shanghai adults occlusion was established.CONCLUSION:The growth between dental and cranioficial structure was harmonized in three dimensions.

[Agenesis and the morphology and site of other teeth in the permanent dentition].

OBJECTIVE: To Investigate the relationship among anodontia, anomalously shaped teeth and reduction of teeth crown. METHODS: The position and the number of congenitally absent teeth of 79 patients were analysed, as well as the abnormal morphology of other teeth. The width of the remained teeth was measured and compared with that of normal on base of patients being divided into four groups by the number and the position of agenesis. RESULTS: (1)Most of the congenitally absent teeth were upper lateral incisors and lower central incisors. (2) The congenitally absent teeth of upper central incisors, upper and lower first molars were rare. While in several cases, the central incisors were lightly pet-shaped. (3) There was no significant difference in teeth size between mild hypodontia groups and normal. As the incremental degree of hypodontia, anterior teeth tended to reduce, while the size of posterior teeth was relatively stable. Upper lateral incisors, lower canines, upper second premolars, upper and lower second molars accounted most in the anomalously shaped teeth which could be often found in patients with hypodontia. CONCLUSION: (1) number during evolution. (2) The developmental anomaly of teeth size, teeth morphology and teeth number might be a procedure of continuous variation and it might be different manifestation of the same mechanism.

[A cephalometric study of natural head posture and spinal position in malocclusions].

OBJECTIVE: The purpose of this cephalometric study was to compare the difference of NHP (natural head posture) and spinal position among malocclusions with different skeletal patterns. METHODS: 79 malocclusions aged from 12 to 16 were divided to several groups according ANB and NSL-MP. The features of head posture and spinal position were examined by comparing the groups and the statistical significant correlation among NHP, spinal position and craniofacial morphology was sought. RESULTS: NHP and spinal position was not the same in malocclusions with different NSL-MP, while was identical in malocclusions with different ANB. CONCLUSION: It is believed that there was correlation among NHP, spinal position and vertical, sagittal development of face rather than anteroposterior relationship between maxilla and mandible.