Strong genetic control of emergence of human primary incisors

Our understanding of tooth eruption in humans remains incomplete. We hypothesized that genetic factors contribute significantly to phenotypic variation in the emergence of primary incisors. We applied model-fitting to data from Australian twins to quantify contributions of genetic and environmental factors to variation in timing of the emergence of human primary incisors. There were no significant differences in incisor emergence times between zygosity groups or sexes. Emergence times of maxillary central incisors and mandibular lateral incisors were less variable than those of maxillary lateral incisors and mandibular central incisors. Maxillary lateral incisors displayed significant directional asymmetry, the left side emerging earlier than the right. Variation in timing of the emergence of the primary incisors was under strong genetic control, with a small but significant contribution from the external environment. Estimates of narrow-sense heritability ranged from 82 to 94% in males and 71 to 96% in females.     

Sexual dimorphism of primary dentition in Spanish children

Aim: To analyse differences in the eruption of primary teeth between both sexes.

Materials and methods: A cross-sectional study was performed in a sample of 1250 children aged between 3 and 42 months. The clinical emergence of teeth was taken to estimate average ages for primary teeth eruption. The t-test was used to analyse gender and arch differences.

Results: Eruption of primary teeth began at the same time in girls as in boys; although the eruptive process was longer in girls. It was observed that almost all deciduous teeth emerged earlier in boys, except for the first molar (upper and lower) and the maxillary central incisors. The differences were statistically significant for almost all the primary teeth except for the central incisors, both upper and lower.

Conclusions: By comparing the timing of the eruption of primary teeth in both sexes, it was found that eruption of almost all primary teeth took place earlier in boys than in girls and that the eruption process was shorter for boys than for girls. Most of the deciduous teeth erupted earlier in the right side in both sexes. No differences were found in the sequence of eruption of primary teeth between genders.     

Bone augmentation and autogenous transplantation of premolar to the site of the fissure in a cleft palate patient

This article presents a case report of autogenous tooth transplantation to the site of the fissure, in addition to bone augmentation with graft of autogenous bone harvested from the iliac crest, performed in a cleft palate patient, who had insufficient bone volume. A non‐syndromic 10‐year‐old girl, with a unilateral cleft lip and palate, incisal transforamen fissures, agenesis of the maxillary left central incisor and both maxillary lateral incisors, was treated with autogenous bone graft in the cleft area. The orthodontic treatment plan was to replace the missing lateral incisors with the maxillary canines and to extract the mandibular first premolars. One of the mandibular premolars was extracted from its site with 2/3 of its root formation completed and transplanted to the maxillary left central incisor area. After orthodontic treatment, the anatomic crowns were characterized with composite resin. Autogenous tooth transplantation can be performed in the area of the fissure in young cleft palate patients, by performing bone graft augmentation before transplantation of the tooth, to gain sufficient recipient alveolar bone volume. A multidisciplinary approach is mandatory for the success of this clinical procedure, especially in cleft palate patients.     

Pattern of tooth loss in a selected population in Greece

The pattern of tooth loss with age for individual teeth was examined in a selected population. The survey covered patients attending the Dental School of Athens University. Tooth loss increased steadily with age and was higher for the periodontitis than the gingivitis group. Mortality of individual teeth was analyzed for each type of tooth within the maxillary pair and within the mandibular pair and no statistical significance was found. The statistically highly significant differences in loss rates within most groups of four teeth were clearly attributable to differences between the maxilla and mandible. For the permanent second molars differences in loss were close to the significance level while for the first molars the difference was statistically highly significant. A statistically significant difference was found between losses of the four second premolars while highly significantly differences were noticed between first premolars. Mortality for canines was low, but differences in losses were highly statistically significant. The two mandibular incisors had the lowest rates of loss in our sample, difference in loss between maxillary and mandibular incisors was statistically highly significant. Central incisors had a similar pattern of loss to that of lateral incisors but differences in loss rates were not statistically significant.     

A survey of approximal root concavities in an ethnic Chinese population

Eight hundred and forty teeth were surveyed, 60 approximal surfaces for each tooth type being studied. Approximal root concavities were completely absent in maxillary central incisors, in contrast with mandibular central incisors of which 73% had concavities on mesial surfaces and 93% on distal surfaces. Similarly, a markedly higher prevalence was found for mandibular lateral incisors and canines. However, mandibular first and second molars had fewer approximal concavities than their maxillary counterparts. In maxillary teeth, concavities were more frequent on distal surfaces, while for mandibular teeth no definite pattern was seen. In both maxillary and mandibular teeth, approximal concavities often started in enamel, extending down to the root surface. There were differences in the approximal root topography of Chinese teeth in comparison with other populations.     

Ectopic eruption of the maxillary central permanent incisors and mandibular first permanent molars: report of an unusual case.

Ectopic eruption is a disturbance in which the tooth does not follow its usual course. Among its more important etiologic factors are macrodontism, shortened arch length, posterior positioning of the maxilla, atypical eruption angle, and genetic factors. This article reports a rare case of ectopic eruption of 4 permanent teeth, maxillary central incisors and mandibular first molars, in a child aged 7 years and 11 months, in which the treatment consisted of extracting the maxillary primary central incisors and making an orthodontic intervention on the mandibular arch. A bilateral fixed appliance containing 2 hooks with loops, 1 buccal and the other lingual, was placed on the mandibular primary first molars. The hooks were activated in a niche made of light-curing resin on the occlusal surface of the mandibular permanent molars, to bring about the distal drift of these teeth. After 6 months, complete eruption of the mandibular permanent molars occurred, and a slight displacement of the maxillary permanent central incisors toward the median line was noted. The importance of early, adequate treatment is discussed.     

Maxillary anterior tooth dimensions and proportions in an Irish young adult population

This study was undertaken in a young Irish population to determine the dimensions and ratios of the six maxillary anterior teeth. One hundred and nine Irish subjects (age 18-25 inclusive) had irreversible hydrocolloid impressions made of their maxillary dentition poured in type V stone. Clinical crown dimensions were measured with a digital calliper. The stone casts were digitally photographed in a standardised manner enabling calculation of various ratios between the maxillary anterior teeth. Sexual dimorphism existed for various tooth dimensions; most notably canine teeth were in the region of 0·8 mm longer and 0·6 mm wider in males. Central and lateral incisors were found to be 0·5 mm wider in males. It is, therefore, recommended that dimensional tooth guidelines should be given for each of the sexes and not on a population basis. With regard to tooth proportion ratios, no significant differences were found between genders or the left and right sides for any of the measurements or ratios measured. The digitally recorded tooth proportions were similar for both sexes, and the Golden Proportion guidelines could only be applied to the lateral incisor/central incisor widths (0·618). Identified width proportions for the canine/central incisor were 0·58 and for canine/lateral incisor 0·89.     

A controlled study of the morphometric changes in the primary dentition of pre-term, very-low-birthweight children

The aim of the present investigation was to compare the dimensions of the primary incisors from pre-term children and full-term controls. One hundred and eleven pre-term children, consisting of 86 very-low-birthweight (< 1,500 g), 25 low-birthweight (from 1,500 to 2,500 g), and 169 full-term, normal-birthweight (> 2,500 g) children, donated a total of 572 maxillary and mandibular primary central and lateral incisors for study. The teeth were measured by means of a digital micrometer. The results showed that there was a dose-response effect of birthweight on tooth size. The very-low-birthweight teeth showed the smallest dimensions, the normal-birthweight controls the largest, and the low-birthweight teeth intermediate dimensions (p < 0.001). In the maxillary primary central and lateral incisors, and the mandibular primary central incisors, very-low-birthweight teeth were from 6 to 11% smaller in both mesiodistal and faciolingual dimensions compared with normal-birthweight teeth (p < 0.001). The largest differences were observed in the maxillary lateral incisors, where mean decreases of 0.58 +/- 0.45 mm in mesiodistal and 0.50 +/- 0.40 mm in faciolingual dimensions (11% reduction in both measurements) were observed. In addition, in the mandibular and maxillary lateral incisors of very-low-birthweight children, the left-sided teeth were significantly smaller than those on the right side in both mesiodistal and faciolingual dimensions (p < 0.03).     

6 712名少年儿童恒牙萌出时间和顺序的调查研究

目的:调查分析西安市少年儿童恒牙萌出的时间、顺序和性别差异,为口腔医师进行咬合诱导等治疗提供理论参考。方法:在西安市8所幼儿园、小学和中学中整群抽取6712名年龄为3～15岁的少年儿童,收集恒牙萌出横断面调查资料,其中男性3604名,女性3108名,对各项数据进行统计分析。结果:左右两侧同名牙同时萌出,除第一、第二前磨牙外,下颌恒牙萌出早于上颌同名牙;大多数恒牙的萌出时间女性早于男性,萌出顺序也有所不同。结论:结果与以前国内其他地区的调查结果有一定不同。     

Eruption time of primary teeth in Iraqi children

Abstract The mean times and order of eruption of primary teeth were determined cross-sectionally from 1017 Iraqi nursery schoolchildren, ranging in age from 1 to 40 months. No statistical differences were found in the mean ages of eruption between corresponding right and left primary teeth in both sexes. The order of eruption for the maxilla and the mandible was the same in both sexes. In boys teeth erupted earlier than girls except for the maxillary central incisors and the mandible second molars.     

Diversity of supernumerary tooth formation in siblings with cleidocranial dysplasia having identical mutation in RUNX2 : possible involvement of non-genetic or epigenetic regulation

INTRODUCTION: Cleidocranial dysplasia (CCD, MIM #119600) is an autosomal-dominant disorder characterized by hypoplasia or aplasia of clavicles, patent fontanelles and short stature. The responsible gene has been identified as RUNX2. CCD is also accompanied by characteristic dental abnormalities, e.g. supernumerary teeth, delayed eruption and impaction of permanent teeth. Intrafamilial variations of skeletal abnormalities are reported but those of dental abnormalities are obscure. To clarify this point, a precise examination of the dental features of CCD siblings having identical mutation was performed. DESIGN: Gene mutational analysis of three Japanese CCD siblings and their father was performed. Skeletal and dental characteristics were examined by the inquiry and radiographs. RESULTS: Three siblings uniformly showed patent fontanelles and short stature. They and their father had a novel missense mutation in the RUNT-domain (P210S) of RUNX2. The siblings were completely discordant for the dental characteristics with the position and number of supernumerary teeth being completely different. The youngest, a 12-year-old boy, had six supernumerary teeth, which appeared symmetrically around the maxillary canines and mandibular premolars. The second, a 15-year-old girl, had four supernumerary teeth which appeared around the mandibular incisors. The oldest, a 17-year-old boy, had 11 supernumerary teeth, which were symmetrically around the mandibular lateral dentition and asymmetrically around the maxillary incisors and premolars. CONCLUSION: The present study suggests the involvement of non-genetic or epigenetic regulation in supernumerary tooth formation in CCD.     

Bilateral maxillary fused primary incisors accompanied by succedaneous supernumerary teeth: report of a case

Summary. A rare case of fusion between maxillary primary central incisors and supplemental teeth occurring bilaterally, accompanied by succedaneous supernumerary teeth, is presented. The patient was an 8·5-year-old Japanese boy. Intraoral examination revealed fusion of left and right maxillary primary central incisors to supplemental teeth, which had labial and lingual grooves. The maxillary primary lateral incisors were present. Radiographs showed that the fused teeth had separate roots, pulp chambers and root canals. There were two impacted supernumerary teeth and eruption of the permanent maxillary central incisors was delayed. Treatment was performed and the fused primary teeth and the impacted supernumerary teeth were extracted. After 6 months observation, surgical exposure of the two crowns of the permanent maxillary central incisors was performed. The teeth began to erupt and have since been kept under observation.     

Management of the malposition tooth that was caused by dentigerous cyst associated with impacted supernumerary tooth by using an obturator

This report presents a case of eruption guidance for an upper right central incisor with a dentigerous cyst associated with an impacted supernumerary tooth in a 5-year-9-month-old boy. A swelling was seen in the region of an upper right central incisor. Radiographic examinations showed that a well-defined cystic lesion, containing an impacted supernumerary tooth crown in it, was located between the root of the primary upper right central incisor and a permanent upper central incisor germ. Under general anesthesia, the dentigerous cyst was removed at extraction of the upper impacted supernumerary tooth. And then, a socket was kept open wound. A histopathological examination confirmed the diagnosis of a dentigerous cyst associated with a supernumerary tooth. By using an obturator, we guided eruption of an upper right central incisor with malposition that was caused by the dentigerous cyst, and observed the way of the tooth eruption for two years and seven months. The obturator was inserted in the socket directly for three months until it was closed. After that, the obturator was used as only a removable space maintainer. Eight months after the operation, the obturator was removed because the upper left central incisor began to erupt. Two years and seven months after the operation, both upper central and lateral incisors had erupted completely. In this case, the obturator was used for expectation of natural eruption of permanent incisors, space maintenance and aesthetic recovery. The permanent incisors had been able to be guided to almost correct position without traction.     

A longitudinal study on growth and development of dental arches of primary, mixed and permanent dentitions

In dental clinic for children, criteria for growth and developmental changes related to increases in the width and length of the dental arch at the primary, mixed, and permanent dentition stages are essential. This study was carried out to measure the width and the length of normal dental arch and to make detailed observations of growth and developmental processes in the dental arch at each dentition stage. Materials were serial study casts of the maxilla and the mandible taken every 2 month from 127 children (74 boys and 54 girls). The casts were made from 6 months after birth until the age of 15. Measurements of the width of the dental arch were made between bilateral teeth of the same tooth type, both deciduous and permanent. The length of the dental arch was measured on the basis of the perpendicular distance from the contact point of mesial surfaces of central incisors to a line between bilateral teeth of the same tooth type. Measured values were categorized according to either chronological age or tooth age on the basis of the eruption of the central permanent incisors. The indices of the dental arch with relation to the width and the length at each dentition stage were calculated for the sake of partial and total observations of alterations in dental arch form. The results were as follows: 1) In terms of chronological age, until 1 year before the eruption of permanent replacements, the width of the dental arch gradually decreased in both the maxilla and the mandible in the regions of the deciduous central and lateral incisors. Increasing slightly from about the age of 6 years and the period of mixed dentition, the width of the dental arch remained stable until the permanent dentition stage. From the primary dentition stage, the width of the dental arch in the region of the maxillary and mandibular canines and first and second molars gradually increased. Therefore it remained stable until the eruption of permanent dentition. The width in the region of the permanent maxillary and mandibular first molars gradually increased and attained a stable condition at about 12 years of age. In males, the width in the area of the maxillary secondary molars decreased slightly and tended to decrease in the mandible. In females, on the other hand, the width showed a tendency to increase with advancing ages. With the exception of the second permanent molars, the width between the distance of bilateral teeth were consistently larger in males than in females.(ABSTRACT TRUNCATED AT 400 WORDS)     

Relationship between alignment conditions of teeth in anterior segments and incisal wear

This report describes the alignment condition and incisal wear of the anterior teeth in individuals 16–19 years of age. Tooth alignment and incisal wear were assessed on casts in accordance with two index systems NONAT (non-aligned tooth) and IwI (incisal wear index). Tests of the methods showed that the reproducibility of the assessments of tooth alignment and incisal wear were satisfactory. The results of the study of tooth irregularity demonstrated that the prevalence of non-alignment of one or more of the anterior teeth were much the same (∼50%) for the maxillary and mandibular jaws. The highest frequency was found for the maxillary lateral incisors and the mandibular central incisors (∼45%). A relationship between the alignment conditions and incisal wear of the anterior teeth was established. It appeared that non-alignment of one or more teeth in one or both jaws was associated with less severe incisal wear of the anterior teeth. This was most pronounced for non-aligned maxillary central incisors and non-aligned mandibular central incisors.     

Apical root displacement is a critical risk factor for apical root resorption after orthodontic treatment

Objectives:To identify risk factors for apical root resorption (ARR) of maxillary and mandibular incisors using mathematical quantification of apical root displacement (ARD) and multiple linear mixed-effects modeling.Materials and Methods:Periapical radiographs of maxillary and mandibular incisors and lateral cephalograms of 135 adults were taken before and after orthodontic treatment. ARR was measured on the periapical radiographs, and movement of central incisors was evaluated on the superimposed pre- and posttreatment lateral cephalograms. ARD was mathematically calculated from pretreatment tooth length, inclination change, and movement of the incisal edge. Linear mixed-effects model analysis was performed to identify risk factors for ARR, and standardized coefficients (SCs) were calculated to investigate the relative contribution of the risk factors to ARR.Results:Vertical ARD showed the highest SCs for both maxillary and mandibular incisors. Horizontal ARD showed the second highest SC for mandibular incisors but was not significantly correlated with the ARR of maxillary incisors. When horizontal and vertical ARDs were included in the mixed-effects model, the use of self-ligating brackets was significantly correlated with increased ARR of mandibular incisors.Conclusions:ARD is a critical factor for ARR after orthodontic treatment. Careful monitoring of ARR is recommended for patients requiring significant ARD of incisors.     

Delayed eruption of mandibular primary central incisors in a child with severe lingual inclination and their spontaneous movement to appropriate positions

We previously reported a quite uncommon case of delayed eruption of primary mandibular bilateral incisors with severe lingual inclination identified in a Japanese girl aged 2 years 8 months. An intraoral examination demonstrated the tooth crown morphology of the primary mandibular incisors in the lingual submucosal area, while radiographic examinations of the affected teeth revealed what appeared to be a standard root morphology and the permanent successors located close to the affected teeth. We decided to perform periodical examinations at least until the roots of the permanent successors were sufficiently formed and here report recent findings in this case. At 2Y10M, the edge of the tooth crown of the primary mandibular left central incisor had emerged into the oral cavity and one-third of the tooth crown was identified at 2Y11M. Thereafter, the tooth crown of the primary mandibular right central incisor was identified under the mucosa at 3Y1M. A periapical radiograph taken at 3Y7M demonstrated formation of the permanent successors under development. At 3Y10M, nearly the entire part of the tooth crowns of both affected teeth had emerged and then they started to move gradually in a labial direction. At 4Y2M, the crowns of the affected were nearly within the dental arch, while periapical radiograph images showed straight roots for the affected teeth and the developing permanent successors. We intend to continue to perform periodical examinations to follow the development of the permanent successors until eruption.     

Tooth anomalies associated with failure of eruption of first and second permanent molars

The occurrence of tooth anomalies in association with failure of the first and second molars to erupt was assessed in a sample of 1520 nonsyndromic subjects with uncrowded dental arches (mean age, 14 years 4 months) and compared with the prevalence rate calculated in a matched control group of 1000 subjects. The tooth anomalies examined included infraocclusion of deciduous molars, palatal displacement of maxillary canines, rotation of maxillary lateral incisors, aplasia of second premolars, and small size of maxillary lateral incisors. Associations among arrested eruption of first and second permanent molars and anomalies in tooth eruption and position (infraoccluded deciduous molars, palatally displaced canines, rotated maxillary lateral incisors) were highly significant (P <. 001). No significant association was found among the occurrence of molar eruption disturbances, aplasia of premolars, and small-sized laterals. These findings point to a common biologic cause for the appearance of failure of eruption of molar teeth and other disturbances in tooth eruption and position, most likely under genetic influence.     

Macrodontia in association with a contrasting character microdontia

The dental, genetic, radiological and dermatoglyphic findings of a 19-year-old girl showing macrodontia of maxillary permanent central incisors in association with a contrasting character, microdontia of maxillary permanent lateral and mandibular primary central incisors and bilateral absence of maxillary first premolars and missing of the right mandibular second premolar and peg-shaped mandibular primary lateral incisors and canines were presented.     

Changes in the gingival thickness and keratinized gingival width of maxillary and mandibular anterior teeth after orthodontic treatment

ObjectivesTo evaluate changes in the gingival thickness (GT) and keratinized gingival width (KGW) of the maxillary and mandibular central and lateral incisors and canines after fixed orthodontic treatment and their association with sagittal tooth movement (STM).Materials and MethodsIn this study of both arches, 60 periodontally healthy subjects who had completed fixed orthodontic treatment were included. Using pretreatment and posttreatment lateral cephalograms, STM of the maxillary (1-NA angle and distance, and 1-SN angle) and mandibular (1-NB angle and distance, and IMPA angle) incisors were evaluated to divide the subjects into protrusion and retrusion groups. Pretreatment and posttreatment GT was identified via transgingival probing, and KGW was calculated from the free gingival margin to the mucogingival junction.ResultsThe intragroup pretreatment and posttreatment comparison results showed a significant decrease in the GT of the maxillary and mandibular anterior teeth in the protrusion and retrusion groups and a decrease in the KGW of the maxillary lateral incisors in the protrusion group. Pearson correlation coefficient analyses for maxillary and mandibular anterior teeth revealed that the GT changes were not significantly associated with STM. However, a positive correlation existed between the KGW of tooth numbers 13 and 41 and STM.ConclusionsSTM was not significantly associated with decreased GT of the maxillary and mandibular anterior teeth, but it was positively correlated with the KGW of tooth numbers 13 and 41.