| Background:Malocclusion as a consequence of hereditary factors or acquired factors which included disease,oral bad habits and abnormal dentition,was defined as the deformity of tooth,jaw and craniofacial region in the process of children’s growth and development.The irregular alignment of teeth,abnormal occlusal relationship between upper and lower dental arch and abnormal size,shape or position of jaw were considered as the main manifestations of it.Malocclusion,tooth decay and periodontal disease have been seen as the three common diseases in oral cavity.And there is a high prevalence rate of malocclusion in our country.Because malocclusion will not only damage the function and health of oral cavity and affect the appearance of human,may also serve as the lesions that can cause systemic disease.Therefore,more and more adolescents or adults began to pay attention to the correction of malocclusion.Dentists exert orthodontic force on teeth and maintain sufficient strength and time using brackets,buccal tubes,arch wires and draw hooks in the process of orthodontic correction.Osteoclast in pressure side of alveolar bone was activated to make bone be absorbed,while osteoblast in expanded side of alveolar bone was activated to make bone be formed.At the same time alveolar bone and periodontal tissue around the root remodeling,tooth would move to a new location following the external force.However,it was founded in preliminary study that the base bone determined the shape of dental arch,in other words,the tooth moving range was limited by basal arch,so base bone was the key to maintain the long-term stability of dental arch form.Building a dental arch which was compatible with basal arch was one of the main goals in orthodontic treatment,because the shape and size of dental arch affected the available space of oral cavity,the stability of dentition and the aesthetics of teeth.Studying dental and basal arch form and the discrepancy and relevance between the two has important clinical significance for making a more stable individual arch form and doing a delicate adjustment to dental arch form according to the corresponding base bone.In the meantime of studying dental and basal arch form,morphological differentiation of length and width indicators and buccolingual position diversity,which might be related to the compensatory mechanism of teeth,have been found between dental arch and basal arch in different types of malocclusion.Whether base bone was poorly developed or overdeveloped,compensatory inclination would be happened on teeth just for maintaining the cutting bit function and building a good intercuspal occlusal relationship with contralateral teeth.Studying tooth compensatory characteristics and its relevant factors have a significant guideline value for early prevention treatments and orthodontic treatments before orthognathic surgical procedures.Some scholars founded that the adverse growth factors of malocclusion may be related to the compensating mechanism for hypodevelopment,hyperevolutism or improper position of mandible.Moreover,the mandible still maintains a rapid growth within two years after maxillary growth rate slowed down.Obviously,the vegetative form of upper and lower jaws has mainly depended on the development of mandible,and so the studies on arch form were mostly based on mandibular dental arch and base bone.Therefore,combining with cone-beam computed tomography(CBCT)and medical digital technology and regarding normal occlusion as the control group,our study was to investigate the morphological characteristics and compensatory inclination characteristics of mandibular dental and basal arch in skeletal Class Ⅰ,Ⅱ,Ⅲ malocclusion.The purposes of this study were to realize the individuation of dental arch shape in orthodontic treatment,and to achieve the blocking correction and preoperative guidance by predicting the development of base bone according to the tooth inclination and guiding the dental decompensation by orthodontic methods before orthognathic treatment.The paper includes the following three parts:The first part Measurement and correlation analysis of mandibular dental and basal arch in skeletal Class Ⅰ,Ⅱ,Ⅲ malocclusion and normal occlusionObjective:The purposes of this study were to analyze length and width differences of mandibular dental and basal arch form in skeletal Class Ⅰ,Ⅱ,Ⅲ malocclusion and normal occlusion,and to investigate whether dental arch form was related to basal arch form,so as to design the future trend of dental arch according to the patients’basal arch form in clinical treatment.Methods:1.For our study,27 Class Ⅰ,30 Class Ⅱ,20 Class Ⅲ malocclusions and 27 normal occlusions were selected for the CBCT scanning before orthodontic treatment.The CT data,exported in Dicom format,were imported into the Mimics 15.0 software to reconstruct 3D mandibular models.2.Locating dental arch reference points(FA points)and basal arch reference points(AP points)on 3D mandibular models,then establishing coordinate system:The midpoint of four reference points of bilateral mandibular incisors became the origin of the 3D coordinate system;the line through the origin and the midpoint of four reference points of bilateral mandibular first molars was adopted as the y-axis;the xy plane was taken to be the plane through the origin and parallel to the occlusal plane.3.The FA and AP points were redrafted from the left to right mandibular second molars in new 3D coordinate system,named FA37→FA47 and AP37→AP47.4.Measuring the width variables of dental and basal arch:width between canine facial-axis points,width between first molar facial-axis points,width between canine alveolar process points and width between first molar alveolar process points;Measuring the length variables of dental and basal arch:anterior dental length,whole dental length,anterior basal length and whole basal length.5.Independent-samples T test were used to compare the differences of length and width indicators between skeletal Class Ⅰ,Ⅱ,Ⅲ malocclusion and normal occlusion.The relevance between dental and basal arch width(and length)was evaluated by Pearson correlation.Besides,fitting the curves of dental and basal arch forms.Results:1.The widths between bilateral canine and first molar facial-axis points were significantly greater in skeletal Class Ⅲ malocclusion group(30.13±2.40mm and 54.09±2.34mm)than in skeletal Class Ⅱ malocclusion group(28.72±1.80mm and 52.76±2.02mm).The width between canine alveolar process points in skeletal Class Ⅲ malocclusion group(30.60±2.90mm)was significantly greater than skeletal Class Ⅰ,Ⅱ malocclusion and control groups(28.91 ±1.97mm,27.85±2.44 mm and 29.04±2.22mm).While there was no difference in width between first molar alveolar process points of the four groups.2.Anterior dental length in skeletal Class Ⅱ malocclusion group(5.17±0.78mm)was significantly greater than skeletal Class Ⅰ,Ⅲ malocclusion and control groups(4.37±0.72mm,4.42±0.82mm and 4.64±0.85mm),whole dental lengths in skeletal Class Ⅲ malocclusion and control groups(36.99±2.07mm and 36.52±1.79mm)were significantly greater than skeletal Class Ⅰ malocclusion group(35.39±1.87mm),anterior and whole basal lengths in skeletal Class Ⅲmalocclusion group(4.52±0.83mm and 38.04±1.94mm)was significantly greater than skeletal Class Ⅰ,Ⅱ malocclusion and control groups(3.77±0.80mm and 34.64±2.02mm,3.65±0.95mm and 34.75±2.14mm,3.73±0.89 mm and 35.42±1.82mm).3.Significant high correlation was found between dental and basal arch widths in canine region,dental and basal arch widths in molar region,whole dental and basal lengths(relative coefficients were 0.818,0.836 and 0.818 respectively),while anterior dental length was low related to anterior basal length(relative coefficient was 0.395).All relative coefficients were statistically significant.4.The curves of dental arch showed that skeletal Class Ⅰ,Ⅱ malocclusion groups coincided with control group in anterior teeth region,while skeletal Class Ⅲmalocclusion group was located the lingual side of other three groups.The curves of basal arch showed that skeletal Class Ⅰ malocclusion group closely coincided with control group,while skeletal Class Ⅱ malocclusion group was located the lingual side of control group and skeletal Class Ⅲ malocclusion group was located the buccal side of control group.Conclusion:1.The mandibular dental and basal arch of skeletal Class Ⅲ malocclusion was transversely overdeveloped,while this of skeletal Class Ⅱ malocclusion was poorly developed.2.The mandibular basal arch of skeletal Class Ⅲ malocclusion was sagittally overdeveloped.The basal arch in anterior tooth region of skeletal Class Ⅱmalocclusion was poorly developed,however,the dental arch length in anterior tooth region was the largest because of the compensatory labial inclination of mandibular anterior teeth.3.Even if there is a slight irregular arrangement of teeth,it is possible to affect the shape of the dental arch.4.The initial formation of dental arch form is based on the shape of the underlying bone,the two are highly correlated.The second part Comparison and relationships of sagittal inclination,dental and basal arch lengths of mandibular anterior teeth in skeletal Class Ⅰ,Ⅱ,Ⅲ malocclusion and normal occlusionObjective:The aim of this study was to measure and evaluate the discrepancy and relevance between sagittal inclination,dental and basal arch lengths of mandibular anterior teeth in skeletal Class Ⅰ,Ⅱ,Ⅲ malocclusion and normal occlusion,and to analyze the compensatory mechanism of mandibular anterior teeth with different dental arch forms.Methods:1.For our study,27 Class Ⅰ,30 Class Ⅱ,20 Class Ⅲ malocclusions and 27 normal occlusions were selected for the CBCT scanning before orthodontic treatment.The CT data,exported in Dicom format,were imported into the Mimics 15.0 software to reconstruct 3D mandibular models.2.Locating dental arch reference points(FA points)and basal arch reference points(AP points)on 3D mandibular models,then establishing coordinate system:The midpoint of four reference points of bilateral mandibular incisors became the origin of the 3D coordinate system;the line through the origin and the midpoint of four reference points of bilateral mandibular first molars was adopted as the y-axis;the xy plane was taken to be the plane through the origin and parallel to the occlusal plane.3.The FA and AP points were redrafted and named from the left to right mandibular canine and bilateral second molars.4.Measuring variables:central incisor dental arch length,lateral incisor dental arch length and canine dental arch length;central incisor basal arch length,lateral incisor basal arch length and canine basal arch length;the sagittal inclination of bilateral central incisor,the sagittal inclination of bilateral lateral incisor and the sagittal inclination of bilateral canine.5.One-way classification ANOVA and LSD-t test were used to compare the sagittal inclination,dental and basal arch lengths of mandibular anterior teeth between skeletal Class Ⅰ,Ⅱ,Ⅲ malocclusion and normal occlusion.The relevance between sagittal inclination and dental,basal arch length was evaluated by Pearson correlation.Results:1.The inclination of mandibular anterior teeth between skeletal Class Ⅰ,Ⅱ,Ⅲmalocclusion and normal occlusion was presented as being statistically significant.The inclination of bilateral anterior teeth was found to be significantly less in skeletal Class Ⅲ malocclusion group than in skeletal Class Ⅰ,Ⅱ malocclusion and normal occlusion groups.The inclination of bilateral incisors was found to be significantly greater in skeletal Class Ⅱ malocclusion group than in skeletal Class Ⅰ,Ⅲ malocclusion and normal occlusion groups.2.Although all length variables between the four groups showed statistical difference,the difference of the basal arch length was more significant than dental arch length.The dental arch length of skeletal Class Ⅰ malocclusion group(35.39±1.87mm)was significantly less than skeletal Class Ⅲ malocclusion and normal occlusion groups(36.99±2.07mm and 36.52±1.79mm)in the incisor regions.For skeletal Class Ⅲ malocclusion group(33.00±1.82mm),the dental arch length was significantly greater than skeletal Class Ⅰ and Class Ⅱmalocclusion groups(31.41±1.82mm and 31.41 ± 1.67mm)in the canine region.The basal arch length of skeletal Class III malocclusion group was significantly much greater than other three groups in all anterior regions.3.The mean sagittal inclination of mandibular anterior teeth was moderately negatively correlated with basal arch length in corresponding region(relative coefficients from central incisor to canine regions were-0.557,-0.554 and-0.489 respectively),but not with dental arch length.Conclusion:1.Compared with skeletal Class Ⅰ,Ⅱ malocclusion and normal occlusion,the mandibular anterior teeth of skeletal Class Ⅲ malocclusion was tilted more lingually,while skeletal Class Ⅱ malocclusion was noted to be tilted more labially than skeletal Class Ⅰ,Ⅲ malocclusion and normal occlusion just in incisor regions.2.The dental arch of skeletal Class I malocclusion was shorter than skeletal ClassⅢ malocclusion and normal occlusion in incisor regions,this of skeletal ClassⅢ malocclusion was longer than skeletal Class Ⅰ,Ⅱ malocclusion in canine region.The basal arch of skeletal Class Ⅲ malocclusion was overdeveloped in sagittal direction.3.The inclination of mandibular anterior teeth was negatively related to basal arch length to a medium extent,but not related to dental arch length.4.We can evaluate the sagittal development of base bone according to anterior tooth inclination.The three partComparison and relationships of coronal inclination,dental and basal arch widths of mandibular posterior teeth in skeletal Class Ⅰ,Ⅱ,Ⅲ malocclusion and normal occlusionObjective:The aim of this study was to measure and evaluate the discrepancy and relevance between coronal inclination,dental and basal arch widths of mandibular posterior teeth in skeletal Class Ⅰ,Ⅱ,Ⅲ malocclusion and normal occlusion,and to analyze the compensatory mechanism of mandibular posterior teeth with different dental arch forms.Methods:1.For our study,27 Class Ⅰ,30 Class Ⅱ,20 Class Ⅲ malocclusions and 27 normal occlusions were selected for the CBCT scanning before orthodontic treatment.The CT data,exported in Dicom format,were imported into the Mimics 15.0 software to reconstruct 3D mandibular models.2.Locating dental arch reference points(FA points)and basal arch reference points(AP points)on 3D mandibular models,then establishing coordinate system:The midpoint of four reference points of bilateral mandibular incisors became the origin of the 3D coordinate system;the line through the origin and the midpoint of four reference points of bilateral mandibular first molars was adopted as the y-axis;the xy plane was taken to be the plane through the origin and parallel to the occlusal plane.3.The FA and AP points were redrafted and named from bilateral first premolars to second molars.4.Measuring variables:widths between first premolar facial-axis points and alveolar process points,widths between second premolar facial-axis points and alveolar process points,widths between first molar facial-axis points and alveolar process points and widths between second molar facial-axis points and alveolar process points;the coronal inclination of bilateral first premolars,the coronal inclination of bilateral second premolars,the coronal inclination of bilateral first molars and the coronal inclination of bilateral second molars.5.One-way classification ANOVA and LSD-t test were used to compare the coronal inclination,dental and basal arch widths of mandibular posterior teeth between skeletal Class Ⅰ,Ⅱ,Ⅲ malocclusion and normal occlusion.The relevance between coronal inclination and dental,basal arch width was evaluated by Pearson correlation.Results:1.The inclination of mandibular premolars between skeletal Class Ⅰ,Ⅱ,Ⅲmalocclusion and normal occlusion was presented as being statistically significant,while the inclination of mandibular molars between four groups had no significant difference.The inclination of mandibular premolars in skeletal Class Ⅲ malocclusion group was significantly less than skeletal Class Ⅰ,Ⅱmalocclusion and normal occlusion groups.2.The width difference in posterior mandibular exist only in basal arch widths of first and second premolar regions,while there was no difference in dental arch widths of all posterior teeth regions and basal arch widths of molar regions.Based on the multiple comparisons of basal arch widths in premolar regions,the basal arch widths in first and second premolar regions were significantly greater in skeletal Class Ⅲ malocclusion group(40.97±2.96mm and 49.09±2.86mm)than in skeletal Class Ⅰ,Ⅱ malocclusion and normal occlusion groups(39.03±2.28mm and 47.49±2.27mm,38.15±2.01mm and 46.99±2.03mm,39.22±1.96mm and 47.90±2.24mm).3.Low to moderate negative correlations was found between coronal inclination and basal arch width(relative coefficients from first premolar to first molar regions were-0.557,-0.254 and-0.208 respectively),while there was low correlation between coronal inclination and dental arch width(relative coefficients from second premolar to second molar regions were 0.384,0.324 and 0.487 respectively).Conclusion:1.Because the tooth inclination and basal arch width in mandibular premolar regions were more unstable than molar regions of skeletal Class Ⅰ,Ⅱ,Ⅲmalocclusion and normal occlusion,so former transverse development would be strongly affected by external forces.2.The mandibular premolars of skeletal Class Ⅲ malocclusion,of which the basal arch was transversely overdeveloped,were tilted more lingually than skeletal Class Ⅰ,Ⅱ malocclusion and normal occlusion.3.Low correlation was found between coronal inclination and dental(or basal)arch width in mandibular posterior teeth regions.The more distal tooth locates,the stronger relationship was found between posterior tooth inclination and dental arch width,but the weaker relationship was found between posterior tooth inclination and basal arch width. |
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