[Three-dimensional analysis of the early correction of anterior crossbite using eruption guidance appliance].

OBJECTIVE: To investigate the clinical effect of eruption guidance appliance in the treatment of anterior cross bite in mixed-dentition children. METHODS: In the study,10 mixed-dentition children with anterior cross bite, totally 12 incisors, were selected. Alginate was used to take upper and lower dentition impression and make a hard plaster model,which served as the eruption guidance appliance for treatment. The pre- and post-operative dental casts were digitized with SmartOptics Activity 880 scanner,and the three-dimensional overlapping models were obtained by reverse engineering software,Geomagic Studio 2012,then the three-dimensional movements of the upper and lower incisors were analyzed using Imageware 13.2 software. The overbite and overjet were analyzed using the same methods. Measurement with copper wire was used to analyze the upper and lower arch length. Space analysis was the result by the sum of crown width minus the arch length. The crown width of unerupted permanent teeth was according to X-ray method to predict. The SPSS 17.0 software was used to analyze the pre- and post-operative measurements of the same child. The normality test of the measured data showed that it conformed to the normal distribution. Therefore,the t test and double side test were used,and the significance level was 0.05. RESULTS: The course of treatment was (5.6±2.7) months. During orthodontic treatment, the upper incisors moved mainly labially (P<0.001) in three-dimensional displacement, and the lower incisors moved mainly the same direction (P=0.025). During the treatment of eruption guidance appliance,the average overbite decreased (1.01±0.9) mm (t=-3.531, P=0.006), and the difference was statistically significant. There was no statistically significant difference between the pre- and post-operative average overjet (t=0.771, P=0.460). The severity of crowding in upper arch decreased (1.9±0.99) mm (t=-6.042, P<0.001),and that in lower arch decreased (1.9±0.74) mm (t=-8.143, P<0.001), both of the differences were statistically significant. CONCLUSION: The anterior cross bite in mixed dentition could be corrected by eruption guidance appliance, and at the same time, the normal overjet and overbite were established, and the teeth were aligned.

Effect of Removal of Enamel on Rebonding Strength of Resin Composite to Enamel.

Objective. To examine the effect of removing the surface layer of enamel on the rebonding strength of resin composite. Methods. Teeth in four groups (n = 10) were etched, a small amount of resin composite was bonded and debonded, then specimens in three groups were ground for different lengths of time (10 s, 20 s, 30 s) to remove an increasing amount of enamel, one group was left untouched. The teeth were bonded again and the bond strengths of 1st and 2nd bonding were compared and analysed against the amount of enamel loss in different groups (7 µm (±2); 12 µm (±1); 16 µm (±3)). Specimens were examined with SEM and by noncontacting optical profilometer. Results. Although results indicated higher rebonding strength with increasing enamel removal ANOVA showed low statistical differences between the groups (p > 0.05). However, values between first bonding and rebonding strengths differed significantly (p < 0.05) in the group that was not ground. SEM revealed that enamel-surfaces that were ground after debonding etched well, compared to the surfaces that still contained adhesive remnants. Conclusions. Removal of small amount of enamel refreshed the surface for rebonding. Rebonding strengths without grinding the surface before bonding were lower than bond strength to intact enamel.

Transmission of Curing Light through Moist, Air-Dried, and EDTA Treated Dentine and Enamel.

Objective. This study measured light transmission through enamel and dentin and the effect of exposed dentinal tubules to light propagation. Methods. Light attenuation through enamel and dentin layers of various thicknesses (1 mm, 2 mm, 3 mm, and 4 mm) was measured using specimens that were (1) moist and (2) air-dried (n = 5). Measurements were repeated after the specimens were treated with EDTA. Specimens were transilluminated with a light curing unit (maximum power output 1869 mW/cm(2)), and the mean irradiance power of transmitting light was measured. The transmission of light through teeth was studied using 10 extracted intact human incisors and premolars. Results. Transmitted light irradiance through 1 mm thick moist discs was 500 mW/cm(2) for enamel and 398 mW/cm(2) for dentin (p < 0.05). The increase of the specimen thickness decreased light transmission in all groups (p < 0.005), and moist specimens attenuated light less than air-dried specimens in all thicknesses (p < 0.05). EDTA treatment increased light transmission from 398 mW/cm(2) to 439 mW/cm(2) (1 mm dentin specimen thickness) (p < 0.05). Light transmission through intact premolar was 6.2 mW/cm(2) (average thickness 8.2 mm) and through incisor was 37.6 mW/cm(2) (average thickness 5.6 mm). Conclusion. Light transmission through enamel is greater than that through dentin, probably reflecting differences in refractive indices and extinction coefficients. Light transmission through enamel, dentin, and extracted teeth seemed to follow Beer-Lambert's law.

Comparison of treatment costs and outcome in public orthodontic services in Finland.

The objectives of the study were to compare the costs and outcome of orthodontic treatment in eight municipal health centres in Finland. A random sample of the age groups of 16- and 18-year-olds (n = 1109) living in these municipalities was clinically examined by two calibrated orthodontists. The acceptability of the morphology and function of the occlusion were assessed with the Occlusal Morphology and Function Index (OMFI). The data concerning previous orthodontic treatment were collected from the patient records of all subjects (n = 608) who reported previous or ongoing orthodontic treatment or who could not recall if they had received orthodontic treatment. The health centres were grouped into an early and a late timing group according to the mean age of starting the treatment. The mean age for starting orthodontic treatment was 8.0 years (SD 1.9) in the early group and 10.7 years (SD 2.3) in the late group. The visit costs and the costs of orthodontic appliances without overheads comprised the operating costs. The cost-effectiveness of orthodontic services was measured by estimating how much each health centre had to have paid for one per cent unit of acceptable morphology and acceptable function of occlusion. The mean appliance costs were higher in the late timing group and the mean visit costs higher in the early timing group. The mean operating costs per case were €720 in the early and €649 in the late timing group. However, there was a great variation within both groups. The cost of one per cent unit of acceptable morphology was the same in the two timing groups, while the cost of one per cent unit of acceptable function was lower in the early timing group. The low operating costs as such did not totally explain the better cost-effectiveness of orthodontic care. Furthermore, the cost-effectiveness was not directly connected with the timing of treatment.

Orthodontic treatment practices in Finnish municipal health centres with differing timing of treatment.

The aim of this study was to compare orthodontic practices in eight Finnish municipal health centres selected on the basis of an earlier survey to represent early and late timing of treatment. The health centres were grouped according to the mean age of starting treatment; earlier versus later than 9 years of age. A random sample of 16 and 18 year olds (n = 2325) living in these municipalities were invited for a clinical examination, and 1109 adolescents participated. The participants reported on their previous or ongoing orthodontic treatment by means of a questionnaire. Data on orthodontic treatment received were collected from the dental files of the adolescents who reported a treatment history and for those who did not recall exactly whether or not they had received orthodontic treatment. Analysis of the non-respondents was made on the basis of their dental files. Differences between the features of orthodontic treatment in the early and late starting health centres were analysed using a two-tailed t-test. In the early group, 70 per cent, and in the late group 42 per cent, of adolescents had a history of orthodontic treatment. General dentists carried out 90 per cent of the treatment in the early group and specialists every third treatment in the late group. An early start resulted in more frequent visits (P = 0.004) and a longer treatment duration (P < 0.001), while later timing resulted in an increase in the number of appliances (P < 0.001).

Morphological, functional and aesthetic criteria of acceptable mature occlusion.

At present, there are no generally accepted criteria that could easily be applied to the evaluation of occlusal acceptability in clinical examinations at population level. The present study analyses the opinions of Finnish orthodontists and general practitioners on the characteristics required for acceptable occlusion in the full permanent dentition. A questionnaire was sent to all 37 health centres where at least one orthodontist was employed, 31 regionally comparable health centres without an orthodontist, 12 private orthodontists, and 13 orthodontists working at university dental clinics. Seventy-four orthodontists returned the questionnaire giving a response rate of 80 per cent. They were asked to give their views on the importance of morphology, function, long-term stability, and dental appearance as elements of acceptable occlusion. They were also encouraged to indicate other significant characteristics and requested to assess the relative significance of these features. In general, the respondents expressed the need to assess morphological, functional and aesthetic aspects of occlusion as a whole. Good function, rather than morphology, was considered to be the most important feature of an acceptable occlusion, with a relative significance of 40 per cent (range 20-90 per cent). According to the respondents, the acceptability of occlusion is determined not only by morphological features, but also by the functional status and long-term stability, as well as by the patient's opinion of the dental appearance.

Outlining the morphological characteristics of acceptable occlusion.

OBJECTIVES: The aim of this study was to outline the definitions of a morphologically acceptable occlusion in young adults that could be applied to assess the outcome and effectiveness of orthodontic treatment. The opinions of Finnish orthodontists and general practitioners were investigated for this purpose. METHODS: A semi-structured questionnaire was sent to all health centres where at least one orthodontist was employed (n=37), to health centres without any orthodontist (n=31), to private orthodontists working as consultants (n=12) and to orthodontists working at university dental clinics (n = 13). The criteria for moderate and little orthodontic treatment need in the Need of Orthodontic Treatment Index (NOTI) and the Index of Orthodontic Treatment Need (IOTN) were chosen to describe the basic characteristics of occlusal acceptability. RESULTS: The questionnaire was returned by 76 subjects (82%). The respondents' views on an acceptable occlusion in young adults were not totally in line with the chosen definitions. Only 16% of the respondents accepted the definitions of both indices as such; the criteria in NOTI were accepted by 25% and those in IOTN by 21% of the respondents. Functional considerations of the occlusion were the main reasons for the desire for further details in the description of an acceptable occlusion. Crossbites with a discrepancy between retruded contact position and intercuspal position were the least accepted anomalies. The opinions were statistically significantly associated with the level of the respondents' orthodontic education and their type of employment. CONCLUSIONS: We conclude that the selected definitions of NOTI and IOTN can serve as a basis for the characteristics of a morphologically acceptable occlusion in young Finnish adults, but measures of the functional aspects of occlusion must be added for studies on the outcome of orthodontic services.

Cost and productivity analysis of orthodontic care in Finland.

The aim of the study was to investigate the costs of orthodontic care provided for children and adolescents up to the age of 18 by municipal health centers in Finland, and to study the productivity of these services. The data were gathered by a questionnaire sent to all health centers; 96% responded. The majority of respondents estimated the share of orthodontic care as 10% of the total gross costs of dental care, given that 14% of all dental visits were for orthodontic reasons. To study the productivity in individual health centers, the output was measured by the estimated number of completely treated patients. The cost of orthodontic treatment per completely treated patient was, on average, FIM 7358, ranging from FIM 1299 to FIM 24751. The strongest explanatory factor for the average total costs of orthodontic clinics was the number of general dentists with little experience in providing orthodontic treatment. Other explanatory factors were the number of orthodontists or experienced dentists, the percentage of orthodontic tasks performed by auxiliary personnel, and the timing of treatment. Savings might be obtained by devolving treatment to orthodontists or experienced dentists instead of to dentists with little orthodontic experience, and by starting treatment early. The estimated optimal size for an orthodontic clinic was found to be a unit with 830 completely treated patients per year, but most of the orthodontic clinics were in fact much smaller with, on average, 133 completely treated patients per year.

Early developmental traits in class II malocclusion.

The occlusal traits of Class II occlusion in the deciduous dentition include distal terminal plane of the second deciduous molars, distal canine relation, large overjet, and large overbite. Other findings are narrow upper dental arch and maxillary base and poor anterior spacing. Skeletally, Class II children differ less from normal children. The cranial base, including the base flexure, and the maxilla are normal. The mandibular corpus and lower facial height are short, the gonial angle is large, and the dentoalveolar position of the mandible is retruded. The height of the ramus is normal, as is the skeletal position of the mandible, with the exception of the chin, which becomes slightly retruded after 5 years of age. As most skeletal traits of Class II occlusion develop later than the occlusal characteristics, it is suggested that no evidence can be found for a skeletal Class II growth pattern in the deciduous dentition. The deficient transversal growth of the maxilla and the sagittal growth of the mandible seem to cause the typical Class II occlusion. Further skeletal changes are likely to develop as secondary adaptations.

The medial axis branch point in the human mandible.

The medial axis method was applied to radio-cephalometric images of the mandible in 20 adults and 18 children and to panoramic X-ray images of these children, and also directly to 50 halves of dry mandibles. It was found that the location of the posterior branch point coincided almost invariably with the mandibular foramen/lingula. The foramen may be regarded as the posterior limit of the mandibular body, from which the condylar and coronoid processes branch off. The medial axis appears to reflect the developmental and functional anatomy of the human mandible.

Extent and provision of orthodontic services for children and adolescents in Finland.

Orthodontic services for Finnish children and adolescents up to the age of 18 in 1992 were monitored by a questionnaire sent to all municipal health centres responsible for children's dental care in Finland, and 96% responded. All health centres provided some orthodontic treatment, but the percentage of 0 18-year-old children receiving treatment ranged from 1% to 19%. One-quarter of all dental visits of the 0 18-year-olds were in connection with orthodontics. The timing of treatment was early, the average age for starting was 9.5 years. In statistical analyses, the number of children receiving treatment was associated with the timing of treatment. At the age of 7, the most frequently used appliances were quad helix, removable appliance and orthopaedic headgear and, at the age of 13, fixed appliance and activator. Most treatments were provided by nonspecialists. The specialist expertise needed was usually purchased from an outside orthodontist by means of consultation contracts. Every fifth health centre, usually the largest, had employed one or more specialist orthodontists. The regional distribution of orthodontists was uneven, emphasizing regional variation in the delivery of orthodontic services.

The occlusal theory further complicated.

This paper reviews the critique presented against the occlusal theory of the temporomandibular disorders (TMD) and presents a new hypothesis. Although no empirical evidence has been found to refute the role of occlusion in the etiology of TMD, we argue that the occlusal theory in its present form is biased in that it is based on the findings in adults and assumes that the causal chain proceeds from structure to function. However, the close developmental relationship between function and structure and the recent changes in the functional environment of the stomatognathic organ indicate that the causal influences take place in both directions. We suggest that the occlusal theory should be reformulated in such a way that it includes mutual interactions between function and structure during growth. We assume that the structural adaptations taking place in the growing child in response to functional stimuli may play an important role in the etiology of TMD. Testing of our hypothesis requires longitudinal studies which focus on both functional and structural development.

Torus mandibularis in 45,X females (Turner syndrome).

Ninety-three Finnish females with a 45,X chromosome constitution, 78 first-degree female, and 37 first-degree male relatives were examined to determine the frequency and expression of torus mandibularis. The results indicate that among adults the frequency of the trait was significantly lower and the expression weaker in the 45,X females than in male control relatives. A similar trend was observed in comparison to normal females. In juveniles the trend was reversed. Our findings suggest that the sex chromosomes may have an influence on the occurrence, expression, and timing of development of the mandibular torus. Sexual dimorphism in the manifestation of torus mandibularis may result particularly from the effect of the Y chromosome on growth.

Effect of 45,X/46,XX mosaicism on root morphology of mandibular premolars.

The effect of X chromosome mosaicism on root morphology of mandibular premolars was studied in 14 females with 45,X/46,XX chromosome constitution. Occurrences of two-rooted premolars and the morphology of the roots were examined from orthopantomograms. Six (43%) of the 45,X/46,XX mosaics had two-rooted mandibular premolars. Two-rooted first premolars were found in four (29%) and second premolars in three (21%); in one, all four mandibular premolars were two-rooted. The results indicate that the frequency of two-rooted mandibular premolars was similar in 45,X/46,XX mosaics and in 45,X females, and in both groups significantly higher than in normal 46,XX females. Compared with 45,X females, the 45,X/46,XX mosaics showed a slight tendency toward more simplified root morphology in the first premolars. The findings suggest that the presence of normal 46,XX cells among the defective 45,X cells does not affect the development of the mandibular premolar roots. Furthermore, the results do not support the earlier proposal that the presence of normal 46,XX cells in 45,X/46,XX mosaic individuals would be reflected in gradual normalization of dental development.

Dimensional variation of craniofacial structures in relation to changing masticatory-functional demands.

A reduction in masticatory stress has been an important factor in the evolution of the human skull. Similarly, the recent increase in the occlusal variation has been related to a change in masticatory activity. The present study investigates short-term variation in craniofacial dimensions by examining cephalometrically two Finnish samples, one exposed to a hard and the other to a soft diet. The samples comprised 32 skulls, derived from the 16th and 17th centuries, and 50 living individuals. Out of 18 dimensions measured, 12 showed only non-significant differences between the samples. In the present-day sample, the cranial length and the anterior cranial base were significantly longer, and the upper incisors segment significantly higher. In the skull sample, the posterior facial height, the height of the mandibular ramus, and the antero-posterior width of the pharynx were significantly larger. The results suggest that hard diet, which requires more chewing force and time, promotes vertical growth of the ramus and anterior translocation of the maxilla. The greater posterior face height and greater height of ramus are in accordance with the earlier finding that the mandible shows more anterior growth rotation in an attritive environment. These findings support the hypothesis that the growth of the craniofacial skeleton is regulated by masticatory stress. It is suggested that both the dimensional changes and the lack of dental attrition may have contributed to the higher occlusal variation of modern individuals.

Dental studies of a Finnish skeletal material: a paleopathologic approach.

This paper reviews a series of paleo-pathologic studies made to investigate associations between dietary factors and development of occlusion, periodontal diseases and caries. The findings indicate that the change from hard to soft food, which has taken place during the last few hundred years, influences occlusion, craniofacial structures and oral health in several ways. Comparative studies show that the frequency of malocclusion has increased substantially. In the same time, a number of alterations have taken place in the morphology of the craniofacial skeleton. The results support the hypothesis that masticatory stress is a regulative factor in craniofacial growth and occlusal development. With soft food and low masticatory activity, jaw growth is not adequate for optimal occlusal development. Approximal wear itself, caused by the attritive diet, seems to be only a minor adjustive factor. Because of the occlusal wear, the crown height decreased with age and the teeth continued to erupt. As a result, root surfaces were exposed. This process has been equated with bone loss but the lack of inflammatory changes on the bone surface indicates that the alveolar bone was not affected by periodontal diseases. This suggests that the alveolar height was maintained at a constant level throughout life and no growth nor resorption took normally place at the crest. Only the exposure of the furcations increased the occurrence of periodontitis. The caries frequency was decreased by mechanical cleaning effect of attritive food but increased by exposure of the root surfaces. Furthermore, the oral microflora may have been modified by factors related to the chemical and physical properties of the diet.

Taurodontism and the presence of an extra Y chromosome: study of 47,XYY males and analytical review.

A sample of 47,XYY males was examined for taurodontism to provide further information on the effects of chromosome aneuploidies on the trait. The etiology of taurodontism is reviewed in light of recent findings. Two models have been put forward to explain the association of taurodontism with chromosome abnormalities: (1) Taurodontism results from a generalized disruption of developmental homeostasis, and (2) the development of taurodontism reflects a more specific action of the genes. The recent findings in 45,X females indicate that this chromosome aneuploidy does not have any effect on the development of taurodontism, in contrast to the findings of increased frequency of the trait in individuals with extra X chromosomes. The present results in 47,XYY males suggest that the presence of an extra Y chromosome does not cause an increase in the expression of taurodontism. It is concluded that the observed variation in the occurrence of taurodontism in individuals with sex chromosomes aneuploidies does not corroborate the hypothesis of disrupted homeostasis. Instead, the findings indicate that more specific action of gene(s) on the X chromosome is involved. We suggest that the effect of the Y chromosome on growth of both enamel and dentin, possibly in a regulative way, could be involved in the balanced growth of dental structures in 47,XYY males.

Genetic and epigenetic regulation of craniofacial development.

This paper reviews a series of odontometric, anthropometric and cephalometric investigations of genetic and epigenetic regulation of dental, occlusal and craniofacial development. The results show that genes encoded with the X and Y chromosomes regulate the development of tooth crowns and roots. The Y chromosome seems to affect general somatic growth by regulating both cell function and mitotic activity. The effects of the X chromosome seem to be more restricted and include influences on the growth of cartilaginous structures and dental enamel. The findings also indicate that high masticatory stress promotes jaw growth and decreases occlusal variation, supporting the hypothesis that masticatory activity regulates occlusal and craniofacial development. In addition, the findings suggest that nerve growth may affect bone growth in the craniofacial skeleton.

Occurrence of malocclusion in attritive environment: a study of a skull sample from southwest Finland.

Occlusal variation and occurrence of malocclusion were examined in a Finnish skull sample derived from the 15th and 16th centuries. The material consisted of 207 adult individuals; 141 maxillas and 159 mandibles, including 93 pairs, were in observable condition. In the skull sample, only dental anomalies were observed; no skeletal malocclusions were found. The frequency of an Angle Class I lateral relationship was 97.7%. The mean values for overjet and overbite were 1.6 and 1.4 mm, respectively. A comparison with present-day Finns revealed that the skull sample showed less variation in all occlusal variables studied. An Angle Class II type occlusion, deep bite, crowding, spacing, and lateral crossbite occurred with significantly lower frequencies in the skull sample than in the present-day Finns. Advanced dental wear in the skull sample shows that a hard and attritive diet was eaten at that time. It is suggested that a dietary transition from hard to soft food is the most probable cause of the increased occlusal variation and high frequency of malocclusion in present-day Finns.