Instructional multimedia programs for self-directed learning in undergraduate and postgraduate training in orthodontics

OBJECTIVES

The objectives of this study were to develop and evaluate an interactive multimedia courseware package in orthodontics and to provide dental undergraduate and postgraduate students with an interactive means of self-study and self-evaluation.

METHODS

A commercially available software authoring system was used to develop the courseware package. The courseware was presented for evaluation through a questionnaire to four different groups of undergraduate and postgraduate students. Each group consisted of 25 students. The first three groups were third, fourth, and fifth year of dental curriculum at the Katholieke Universiteit Leuven, Belgium. The fourth group comprised postgraduate students. A one-way ANOVA was carried out in order to check for statistical differences, whereas a Scheffe's test was used in order to locate the statistical differences between groups. The p value was set at 0.05.

RESULTS

The majority of undergraduate and postgraduate students in this study were very enthusiastic about this form of educational approach (74/100) because it was experienced as very helpful in understanding the orthodontic curriculum more efficiently (98/100).

CONCLUSIONS

The program provides both undergraduate and postgraduate dental students with a useful interactive means of self-study and self-evaluation.

A split-mouth study on periodontal and microbial parameters in children with complete unilateral cleft lip and palate

BACKGROUND

Complete unilateral cleft lip and palate (UCLP) is a hereditary or multifactorial malformation that can be corrected successfully with a combined orthodontic, surgical and restorative treatment. Such multidisciplinary treatment takes many years and demands a lot of attention to both patients' teeth and periodontium.

OBJECTIVES

This split-mouth study aimed to compare the periodontal health as well as the microbial parameters between cleft and non-cleft region.

MATERIAL AND METHODS

75 patients (52 males, 23 females) between 8 and 20 years with a complete unilateral cleft lip and palate (before (n = 30), during (n = 34) and after (n = 11) the active orthodontic treatment) volunteered for this study. Four regions were defined for the split-mouth comparison: teeth neighbouring cleft (site 1), tooth in cleft (site 2), and the corresponding contra-lateral teeth, respectively, in the unaffected quadrants (sites 3 and 4). At all sites the following periodontal parameters were recorded: plaque and gingivitis indices, pocket depth, attachment loss, bleeding on probing, tooth mobility (visual and Periotest), radiographic bone loss and gingival width. In addition, three pooled subgingival plaque samples were taken (around tooth in cleft, teeth facing the cleft, and contra-lateral teeth of the latter).

RESULTS

The differences between the teeth neighbouring the cleft and the corresponding contra-lateral opponents were of borderline significance (P <or= 0.05) for the plaque index, the approximal probing depths and the attachment loss (teeth facing the cleft always had slightly higher parameters). When the tooth in the cleft was compared to the contra-lateral tooth, differences were only found for both the approximal probing depths, attachment loss and bone loss, which were significantly higher for the tooth in the cleft. The microbial analysis did not reveal differences between the different sites, neither in the proportion of aerobic and anaerobic bacteria (differences < 0.5 log), nor in the detection frequency of periopathogens.

CONCLUSIONS

These data indicate that the periodontium in UCLP patients can cope well with a long-term orthodontic treatment, even in unfavourable conditions (like absence of attached gingiva and poor oral hygiene).

Prevalence of dentofacial characteristics in a belgian orthodontic population

The aim of this retrospective study was to provide quantitative information on the prevalence of dentofacial characteristics to find correlations between them and to determine the orthodontic treatment need in a Belgian orthodontic population. Data were acquired from 1,477 patients who had initial records made at the Department of Orthodontics, Katholieke Universiteit Leuven, Belgium between February 1983 and June 1997. The prevalence of Angle Class I, Class II div. 1, Class II div. 2 and Class III malocclusions was, respectively, 31%, 52%, 11% and 6%. The male-to-female ratio was 4:6. Spacing and trauma to teeth occurred more in males than in females. The prevalence of the following dentofacial characteristics was significantly different between the Angle classes: segmental crossbite; crossbite of one tooth; facial asymmetry; protral and lateral mandibular shift; horizontal and vertical growth patterns, impacted teeth; traumatised teeth; ectopically erupting canines; age at first records. No significant difference in the prevalence of the Angle classes between the sexes was found. Several clinically relevant correlations were found between the examined dentofacial characteristics. This Belgian orthodontic population from the Leuven region seems to be comparable to other orthodontic populations in Europe.

Skeletal and dento-alveolar stability after surgical-orthodontic treatment of anterior open bite: a retrospective study

The aim of this investigation was to assess skeletal and dento-alveolar stability after surgical-orthodontic correction of skeletal anterior open bite treated by maxillary intrusion (group A) versus extrusion (group B). The cephalometric records of 49 adult anterior open bite patients (group A: n = 38, group B: n = 11), treated by the same maxillofacial surgeon, were examined at different timepoints, i.e. at the start of the orthodontic treatment (T1), before surgery (T2), immediately after surgery (T3), early post-operatively (+/- 20 weeks, T4) and one year post-operatively (T5). A bimaxillary operation was performed in 31 of the patients in group A and in six in group B. Rigid internal fixation was standard. If maxillary expansion was necessary, surgically assisted rapid palatal expansion (SRPE) was performed at least 9 months before the Le Fort I osteotomy. Forty-five patients received combined surgical and orthodontic treatment. The surgical open bite reduction (A, mean 3.9 mm; B, mean 7.7 mm) and the increase of overbite (A, mean 2.4 mm; B, mean 2.7 mm), remained stable one year post-operatively. SNA (T2-T3), showed a high tendency for relapse. The clockwise rotation of the palatal plane (1.7 degrees; T2-T3), relapsed completely within the first post-operative year. Anterior facial height reduction (A, mean -5.5 mm; B, mean -0.8 mm) occurred at the time of surgery. It can be concluded that open bite patients, treated by posterior Le Fort I impaction as well as with anterior extrusion, with or without an additional bilateral sagittal split osteotomy (BSSO), one year post-surgery, exhibit relatively good clinical dental and skeletal stability.

Frictional behavior of stainless steel bracket-wire combinations subjected to small oscillating displacements

In orthodontic treatment, sliding is frequently used to cause tooth movement. Inherent to this technique is the generation of a counteracting frictional force. In this pilot study, a fretting test consisting of reciprocating tangential displacements was used to investigate test parameters influencing frictional forces during sliding processes. Tests were run at a normal load of 2 N and a frequency of 1 Hz for tangential displacement strokes of 200 microm. Stainless steel orthodontic wires with cross-sections of .017 x .025 in (W17) and .018 x .025 in (W18), and brackets with slot sizes of .018 in (B18) and .022 in (B22) were used. A specific centered positioning method was developed to achieve a parallel alignment of the wire and the bracket slot. The experimental results indicated the significant role of the centered positioning method on the friction value. Implementation of the centered positioning method resulted in a friction force ranging from 0.89 N to 0.97 N at a 200 microm displacement amplitude and 1 Hz frequency, corresponding to a coefficient of friction ranging from 0.45 to 0.49 for the B18-W17 and the B22-W17 bracket-wire combinations, respectively. When the centered positioning method was not used, significantly higher values for the coefficient of friction were found for both bracket-wire combinations. The slot-filling, bracket-wire combinations (B18-W18 and B22-W22) resulted in an increased coefficient of friction and therefore are not recommended as sliding systems.

A quantitative genetic study of cephalometric variables in twins

This study aimed at determining the relative genetic and environmental impact on a number of well-known cephalometric variables in twins. In order to find a clue in the heritability pattern of some dentofacial characteristics and on the expected limits of the therapeutic impact on the dentofacial subparts they are representing. Cephalograms were collected from 33 monozygotic and 46 dizygotic twins, who did not undergo any orthodontic treatment. Nineteen linear and four angular variables were selected all representing a different definite subpart of the dentofacial complex. The reproducibility of the measurement of most of the linear variables was very high. A genetic analysis using model fitting and path analysis was carried out. First, data were checked on the fulfilment of the conditions for genetic analysis in twins reared together. The results show that the genetic determination is significantly higher for vertical (72%) than for horizontal (61%) variables. As far as the genetic component is concerned, all variables selected seem to be inherited by additive genes, except for mandibular body length, which was determined by dominant alleles. Sex differences in genetic determination were found for the anterior face height, showing a significantly higher genetic component for boys (91%) than for girls (68%). For the angular measurements, no genetic influence was found: only environmental influences common to both members of each pair could be demonstrated.

Hypodontia and tooth formation in groups of children with cleft, siblings without cleft, and nonrelated controls

OBJECTIVE

To compare the occurrence of hypodontia, dental age, and asymmetric dental development in children with cleft with their siblings and a nonsibling control group.

SUBJECTS

The sample consisted of 54 children with cleft (aged 4.2 to 13.1 years), who had at least one sibling available for an orthopantomogram, 63 siblings without cleft (aged 4 to 14.9 years) and 250 controls without cleft (aged between 4 and 14.9 years).

METHOD

Hypodontia, dental age, and asymmetric dental development were assessed on panoramic radiographs of the children with cleft, the siblings without cleft, and the control children without cleft.

RESULTS

Both the cleft (p <.001) and the sibling group (p <.05) showed a significantly higher frequency of hypodontia and a significantly higher occurrence (cleft p <.01 and sibling group p <.001) of asymmetric dental development, compared with the control group. Only a small, but insignificant, delay in dental development could be found in the cleft and the sibling group. CONCLUSIONS; The cleft subjects with siblings showed a significantly higher occurrence of hypodontia and asymmetric dental development than the noncleft control group. This may suggest a genetic component for the occurrence of hypodontia and asymmetric dental development.

Dental age estimation in Belgian children: Demirjian's technique revisited

AIM

The purpose of this study was to evaluate the accuracy of Demirjian's dental age estimation in children in a Belgian Caucasian population and to adapt the scoring system in case of a significant overestimation as frequently reported. We selected 2523 orthopantomograms of 1265 boys and 1258 girls, of which 2116 (1029 boys and 1087 girls) were used for estimating the dental age with the Demirjian's technique. The 407 other orthopantomograms were beyond the original age limit. A second sample of 355 orthopantomograms was used to evaluate the accuracy of the original method and the adapted method. A signed-rank test was performed to search for significant age differences between the obtained dental age and the chronological age. A weighted ANOVA was performed in order to adapt the scoring system for this Belgian population. The overestimation of the chronological age was confirmed. The adapted scoring system resulted in new age scores expressed in years and in a higher accuracy compared to the original method in Belgian Caucasians.

Comparison of modified Teuscher and van Beek functional appliance therapies in high-angle cases

The aim of this study was to investigate the effects of modified Teuscher and van Beek functional appliances on the skeletal and dento-alveolar pattern in high-angle Class II, Division 1 patients. The collective consisted of 32 patients with a high-angle Class II, Division 1 malocclusion. The modified Teuscher activator was applied to a group of twelve patients, and the van Beek activator to a group of ten patients. A control group of ten subjects was used for comparison purposes. The mean chronological ages of the groups were 12, 11.8 and 11.5 years, respectively. 64 cephalograms taken before and after the treatment were evaluated. Intra-group measurement relations were determined by the Wilcoxon test, and inter-group relations by analysis of variance and Duncan tests, using SPSS statistical software. The following results were observed for both treated groups without any change in growth direction: inhibition of maxillary growth, stimulation of mandibular growth, retrusion of upper incisors, distal tipping of upper molars, and reduction of overjet and overbite compared with the control group. The decrease in overbite in the van Beek group was due mainly to intrusion of the incisors, and in the modified Teuscher group to molar extrusion. Both activators were considered preferable in terms of vertical control of the facial height in high-angle cases with deep overbite. However, stimulation of mandibular growth in the modified Teuscher activator group was found to be more significant than in the van Beek activator group.

Treatment and standard evaluation using the Peer Assessment Rating index

The aim of this retrospective study was to determine the outcome of orthodontic treatment carried out on patients by postgraduate students at the Katholieke Universiteit Leuven, Belgium. The treatment outcome of 292 'final examination' patients and of 287 'control' patients was compared by means of the Peer Assessment Rating (PAR) index. The sample consisted of dental casts representing a wide range of malocclusions at the start of treatment and post-treatment. All patients received non-surgical treatment between 1987 and 1996 by one of 18 different postgraduate students. The data were analysed with a variant of the analysis of covariance. A significantly higher (P < 0.001) treatment standard was found for final examination patients compared to the control, indicated by the mean percentage PAR score reduction of 79.1% and 70.7%, respectively. When the results are expressed in terms of treatment outcome, 44.5% of the examination patients and 44.0% of the controls were allocated to the 'Greatly improved' group, while 3.1% of the patients examined and 7.3% of the control patients were classified as 'Worse or no different'.

Delayed dental age in boys with constitutionally delayed puberty

It was the purpose of this study to evaluate dental age in boys with delayed puberty and to compare them with a group of normal, healthy boys. The study group consisted of eight boys with constitutional delay of growth and puberty (CDGP), older than 14 years, and with a testis volume smaller than 4 ml. The control group comprised 38 normal, healthy boys, aged between 12.4 and 14.3 years. Dental age was assessed using the Demirjian method and, on the basis of this evaluation, a dental delay score (i.e. dental age minus chronological age) was calculated in the CDGP and the control group. It was found that Demirjian's dental age assessment is a valid method for scoring dental age in Belgian boys between 12 and 14 years of age, and that CDGP boys showed a significant delay in dental development compared with normal boys (P = 0.0085). This study revealed a significant retardation in dental maturation of boys with CDGP.

[Role of inheritability of tooth form, tooth malformation and tooth position]

A common technique to divide the influence of heredity and environment on certain characteristics, or pathologies is the one that uses twins. There are more or less complex techniques to carry out twin research, from which the most simple procedure consists of determining the amount of concordance of certain characteristics in monozygotic (MZ) and dizygotic (DZ) twins. In individuals who develop from one oocyte, like MZ twins, one would expect a correlation of 1.00 (or 100% concordance) purely from their gene-relation. DZ twins are the result of separate conceptions of the same parents and they thus differ as much from each other as ordinary brothers and sisters. The most recently developed twin-methodologies use path analysis and model fitting for the estimations of the heritabilities and environmental influences on certain characteristics. In this article it is tried to picture the genetic an environmental influence on tooth form, tooth position and occlusal characteristics with different genetic techniques. Generally it can be concluded that our genes are of utmost importance for tooth form and tooth malformations, but the environment has a much bigger impact on tooth position and occlusal parameters.

Effect of low-dose testosterone treatment on craniofacial growth in boys with delayed puberty

Craniofacial growth was investigated in boys treated with low-dose testosterone for delayed puberty (> 14 years old; testicular volume < 4 ml; n = 7) and compared with controls (12-14 years; n = 37). Cephalometric radiographs, statural height and pubertal stage were recorded at the start of the study and after 1 year. Craniofacial growth was assessed by nine linear measurements. At the beginning of the study, statural height, mandibular ramus length, upper anterior face height, and total cranial base length were significantly shorter in the delayed puberty boys than in the controls. After 1 year, the growth rate of the statural height, total mandibular length, ramus length, and upper and total anterior face height was significantly higher in the treated boys than in the untreated height-matched controls (n = 7). The craniofacial measurements were similar in the treated boys as compared with the controls. These results show that statural height and craniofacial dimensions are low in boys with delayed puberty. Low doses of testosterone accelerate statural and craniofacial growth, particularly in the delayed components, thus leading towards a normalization of facial dimensions.

Comparative effects of neonatal and prepubertal castration on craniofacial growth in rats

The role of endogenous testosterone in the craniofacial growth of the young male rat was investigated. First, the effect of neonatal surgical castration was examined in a randomized, cross-sectional study in which male Wistar rats were allocated to be either castrated or sham-operated 4 h after birth. Then, the effect of prepubertal chemical castration was analysed in a second, randomized longitudinal study in which male Wistar rats were randomly allocated either to a control group or to two experimental groups, one injected with triptorelin at day 25 and the other injected on day 25 and on day 45. Every tenth day between 20 and 70 days of age for the first study, and between 30 and 110 days of age for the second, body length and weight were measured, cephalometric X-rays taken, and blood samples obtained. Neonatal and prepubertal castration resulted in decreased plasma concentrations of testosterone and in delayed growth of somatic and craniofacial components. The initiation, duration and magnitude of the effect was dependent on individual bones (cranial base, skull roof) and on the lower incisor, and related to the testosterone concentrations. These results suggest that testosterone effects participate in the process of normal craniofacial growth, particularly during puberty.

A genetic study of anteroposterior and vertical facial proportions using model-fitting

Genetic model-fitting was used to determine the heritability of anteroposterior and vertical facial proportions in twins. Lateral headplates of 33 monozygotic and 46 dizygotic twins, none of whom had undergone orthodontic treatment, were used. Five proportions, based on four vertical and five horizontal measurements, were assessed: lower facial height, anterior- to posterior-facial height, total facial height to face depth, sella-A-point to sella-B-point, and sella-upper incisal edge to sella-lower incisal edge. Reproducibility was high for all variables. Model-fitting indicated that all the facial proportions were controlled by additive genes and the specific environment. The genetic component was 71% for upper-to lower-facial height, 66% for anterior- to posterior-facial height, 62% for total facial height, and 66% for sella-A-point to sella-B-point and sella-upper incisal edge to sella-lower incisal edge.

Craniofacial growth and dental maturation in short children born small for gestational age: effect of growth hormone treatment. Own observations and review of the literature

Short children born small for gestational age (SGA) may be candidates for treatment with growth hormone (GH). We examined craniofacial growth and dental maturation in a cohort of short SGA children. The general growth failure of these children is reflected to a differential extent within the craniofacial complex. As a group, these children have a small retrognathic face with a relatively increased lower anterior face height; in contrast to skeletal maturation, dental age is not delayed. GH treatment in short prepubertal SGA children leads to craniofacial catch-up growth, which is particularly pronounced in regions where interstitial cartilage is involved, the result being that the facial profile becomes less convex; dental maturation does not appear to be influenced by GH treatment. In conclusion, in short SGA children, GH treatment does not only result in an increase of body stature but also in a trend towards normalization of craniofacial growth and this without notable advancement of dental maturation.

Short stature of prenatal origin: craniofacial growth and dental maturation

Recently, children born small for gestational age (SGA) with a catch-up growth failure, have been selected for high dose growth hormone (GH) treatment. In order to gain greater insight concerning dentofacial growth and maturation of these patients, and to evaluate the possible effects of high does GH administration on facial structures, craniofacial growth and dental maturation were evaluated in short SGA persons. Seventy-seven cephalograms and orthopantomograms were available from 48 subjects, aged between 2 and 32 years. Craniofacial growth was assessed by calculating age- and gender-specific standard deviation scores (SDS) for eight linear and five angular measurements. Tooth formation was evaluated by means of a dental delay score (i.e. dental age minus chronological age). The SDS for craniofacial growth measurements for the lateral aspect showed a short anterior cranial base (-1.8 SDS), a small retropositioned mandible (< or = -1.7 SDS) and a small maxilla (-1.5 SDS); a high mandibular plane angle (+1.9 SDS) and a wide cranial base angle (+1 SDS). These findings result in a small retrognathic face with a relatively increased lower anterior face height (+1.7 SDS). In contrast to skeletal maturation, dental age was not delayed. The general growth retardation is, apparently, reflected to a differential extent within the craniofacial complex, while dental maturation appears to be a distinct process tightly linked to chronological age, and independent of general growth and bone age.

Effect of testosterone replacement after neonatal castration on craniofacial growth in rats

Neonatal castration precludes the pubertal increase in serum testosterone and reduces general and craniofacial growth in the male Wistar rat. This study aimed to determine whether exogenous testosterone given at an age beyond the normal pubertal peak restores general and craniofacial growth in male, neonatally castrated rats. The design was a randomized, double-controlled, cross-sectional trial. Male Wistar rats were assigned by weighted randomization to be either castrated early after birth (n = 35) or not (n = 15). On day 57, a 1.5-cm Silastic tube with testosterone was implanted in 18 of the castrated rats. On day 70 and day 110, body length, weight, and craniofacial growth were measured together with the weight of the prostate, and blood samples taken. The exogenous testosterone resulted in a significant increase in serum testosterone and prostate weight. All measures of general and craniofacial growth had higher mean values in the non-castrated control group than in the castrated group, while in the testosterone-implant group the mean values lay between these of the castrated animals and the non-castrated controls. Two-way ANOVA indicated a significant effect of the testosterone administration on lower-incisor growth and the size of the total skull vault.

Cephalometric evaluation of dento-skeletal changes during treatment with the Bionator type 1

Treatment effects of the Bionator functional appliance were studied on the pre- and post-treatment cephalograms of 49 Class II, Division 1 cases. After treatment, a significant more ventral localization of the anterior structures of the mandible was recorded in comparison with the pretreatment situation. The proclination of the maxillary incisors was reduced. No absolute inhibitory effect on maxillary growth was observed. In this study no significant differences in the measured treatment effects on cephalometric radiographs could be demonstrated in cases with a tendency to skeletal open bite from those with a tendency to skeletal deep bite according to the criteria used in this study.

Pain and other cardinal TMJ dysfunction symptoms: a longitudinal survey of Japanese female adolescents

Longitudinal data were obtained for 4 years from 361 Japanese high school girls between the ages of 12 and 16. The data were analysed for the occurrence of pain and its associations with the occurrence of other cardinal TMJ dysfunction symptoms and occlusal states. It was determined that even if pain or noise or jaw-deviation symptoms appeared, those symptoms did not necessarily last thereafter. The symptoms were not persistent but rather appeared and disappeared repetitively. Those who exhibited noise during at least one of the surveys of the 4-year survey period showed a significantly higher prevalence of pain than those who did not exhibit noise at all (P < 0.05). Those who exhibited noise by the age of 13 showed a significantly higher prevalence of pain than those who exhibited noise after age 14 (P < 0.1). The temporal occurrence of pain depended upon the appearance of noise and the age at which noise first appeared. On the other hand, the occurrence of pain symptoms was not necessarily related to specific types of malocclusions, which suggests the significance of multifactorial contributions in understanding the aetiology of pain rather than the occlusal factor.

Craniofacial growth in short children born small for gestational age: two years follow-up after high-dose growth hormone treatment

The craniofacial growth of 17 children born small for gestational age (SGA), who had received high-dose growth hormone (GH) treatment, was studied during the post-treatment phase. The preceding GH treatment consisted of a daily s.c. dose of either 0.2 or 0.3 IU/kg for 2 years. The group consisted of 9 girls and 8 boys with a mean (range) age of 6.9 yr (4-10 years) at the start of the post-treatment period, a mean (SD) bone age of 6.3 (2.1) years, and a mean (SD) height for chronological age of -1.0 (0.6) SDS. During the post-treatment period of 2 years, a catch-down effect was found for all linear craniofacial measurements in both treatment groups, even for the components that had not presented accelerated growth during GH treatment. Major growth vectors, such as the posterior total face height (S-Go) and the overall length of the mandible (Art-Pog), showed a low growth velocity, while minor growth parameters remained almost unchanged during this period. The angular measurements showed no significant changes during this period. It can be concluded that craniofacial growth in short SGA children showed, after a period of GH-induced acceleration, a catch-down period when GH administration is stopped. Despite this low post-treatment growth velocity, the craniofacial linear measurements in lateral aspect, remained larger than in untreated children.

Craniofacial growth in short children born small for gestational age: effect of growth hormone treatment

The effects of growth hormone (GH) therapy in children have yet to be completely catalogued. In the present study, the effect of high-dose GH treatment on craniofacial growth was evaluated once yearly in 21 pre-pubertal, non-GH-deficient children born small for gestational age. These children were randomly allocated to be either untreated or treated with GH at a daily subcutaneous dose of 0.2 or 0.3 IU/kg for 2 yrs. The group consisted of 12 girls and 9 boys with a mean age of 5.1 yr (range, 2 to 8 yr), bone age of 3.4 yr, and height SDS of -3.6. At the start of the study, all children showed an overall delay of craniofacial growth. This cohort of short children born small for gestational age showed a small SNB angle and a large ANB angle; all other angular measurements were within normal range. GH treatment accelerated growth in several craniofacial components, especially the posterior total facial height, the cranial base length, and the overall mandibular length. The increase of the mandibular length increased the SNB angle; no other angular measurements were affected. Age at start of treatment differently influenced the increase in posterior and total cranial base length, the increase in mandibular corpus length, and the position of the mandible in relation to the cranial base. Although GH treatment for 2 yrs led to a craniofacial growth acceleration, the position of the mandible in relation to the cranial base and the craniofacial size in lateral aspect were not normalized in the majority of the GH-treated children. No signs of disproportional growth were evidenced after 2 yrs of high-dose GH treatment. In conclusion, short pre-pubertal SGA children display an overall delay of linear craniofacial growth and a retrognathic mandible. High-dose GH treatment over 2 yrs leads to craniofacial catch-up growth, which is pronounced in regions where interstitial cartilage is involved and results in a less convex face in profile.

The genetic contribution to dental maturation

It has been established in the literature that there is a major genetic impact on tooth size (Potter et al., 1976; Corruccini and Sharma, 1985; Sharma et al., 1985), tooth morphology (Kraus and Furr, 1952; Biggerstaff, 1970), and root formation (Garn et al., 1960; Green and Aszkler, 1970). None of the studies concerning root formation, however, used the more advanced method of path analysis and model fitting to estimate genetic influence. The aim of the present study was to determine the genetic and environmental influence on dental maturation. Dental age scores were determined on panoramic radiographs of 58 pairs of twins--26 monozygotic (MZ) and 32 dizygotic (DZ)--with the method of Demirjian et al. (1973). No mirror-image effect was found between the sides of the same individual or between twin members, so dental maturation seems to be symmetrical for both left and right sides of the mandible. Correlation coefficients were significantly higher in MZ than in DZ twins, which suggests a genetic influence. Model fitting showed that the variation in dental age was best explained by additive genetic influences (A-component) (43%) and by environmental factors common to both twins (C-component) (50%). The specific environment (E-component) added only 8% to the model. The importance of the common environmental factor can be explained by the fact that twins, being raised together, share the same prenatal, natal, and immediate post-natal conditions that are of importance for the formation of the teeth.

The incidence of oral clefts: a review

We have reviewed epidemiological studies on the incidence of oral clefts in several regions of the world, but mainly in Europe. The incidence ranges from 1.0/1000 to 2.21/1000. The highest incidence was in Czechoslovakia (1.81/1000), followed by France (1.75/1000), Finland (1.74/1000), Denmark (1.69/1000), Belgium and the Netherlands (1.47/1000), Italy (1.33/1000), California (1.12/1000) and South America (1.0/1000). The data from Denmark and Finland appeared to be the most reliable. All studies showed a higher incidence of cleft lip and/or palate (CL(P)) compared with cleft palate (CP). There was a predominance of girls in the CP group, while the CL(P) group comprised mainly boys. The left side was affected twice as often as the right side. Black children had a lower incidence than white children. An attempt was made in several reports to clarify the cause of oral clefts, but opinions are contradictory.