Pulpal regeneration and root development after subcutaneous transplantation of cryopreserved immature teeth in rats.

The purpose of this in vivo study was to investigate revascularization and root growth after autotransplantation of cryopreserved immature teeth. Immature molar teeth were extracted in 4-week-old Wistar rats. In the test group, teeth were cryopreserved for 1 week and transplanted subcutaneously to the abdomen. In the control group, teeth were transplanted subcutaneously immediately after extraction. Material was collected in test and control animals at intervals of 1, 2, 4 and 10 weeks post-transplantation and histological and microradiographical examination was performed. Results showed that during the first weeks after transplantation, pulpal repair was similar in both groups although degenerated pulpal tissue was replaced slower in cryopreserved teeth and some differences in types of hard tissue formation were found between test and control teeth. After 10 weeks, the differences in the regenerated pulpal tissue between cryopreserved and control teeth observed during the first weeks were no longer detectable. No root growth was detected microradiographically 10 weeks after transplantation in any of the transplanted teeth. The presence of dentin-like tissue in the pulp cavity of some autotransplanted cryopreserved teeth, suggests survival of pulpal tissue after cryopreservation.

Apical root resorption of upper incisors during the torquing stage of the tip-edge technique.

The purpose of this study was to investigate whether treatment with the Tip-Edge appliance resulted in more apical root resorption (ARR) of the central and lateral incisors during the torquing (third stage) than the non-torquing phases (first two stages) of orthodontic treatment. The three stages of this orthodontic technique make it possible to examine the amount of root shortening during torque separately from other types of tooth movement. The ARR ratio was calculated in 31 Caucasian patients (20 females, 11 males), after the non-torquing stage of treatment and after the torquing phase, by analysing periapical radiographs taken at the beginning of treatment (T1), before the start of the torquing stage (T2), and at the end of treatment (T3). At T1, the mean age was 13 years 6 months (+/- 3 years 3 months). The mean, standard deviation and range of the ARR ratios were calculated and compared (P < 0.001). T-tests were performed to determine levels of significance, at different stages of treatment, between teeth with and without ARR (ARR ratio = 1). Root shortening at T3 was observed for 70 per cent of the central and 76 per cent of the lateral incisors. At T2, ARR was 48 and 53 per cent, respectively. Compared with T2, 38 per cent of the central incisors and 55 per cent of the lateral incisors showed ARR during the application of torque. At T3, the finding for both was 22 per cent. The mean ARR ratio for the central and lateral incisors was the same after the non-torquing stage of treatment but was significantly different from a tooth with no root resorption. After the torquing stage, the ARR ratio for the central incisors was 0.96 and for lateral incisors 0.92. At the end of treatment, the ratio was 0.89 and 0.85, respectively. This study revealed that both the central and the lateral incisors showed comparable amounts of ARR during the torquing and non-torquing stage of Tip-Edge treatment.

Stability of upper incisor inclination changes in Class II division 2 patients.

The aim of this study was to evaluate the changes in incisor inclination following orthodontic treatment in Class II division 2 patients, and to assess the long-term stability after retention. Dental casts and cephalograms of 61 Class II division 2 patients (31 males and 30 females, mean age 13.4 years) with a closed lip seal were available before (T1), at the end of treatment (T2), and 3.5 years (mean) post-treatment (T3). A method of measuring upper incisor inclination on dental casts was developed for the purpose of the investigation. This involved placing markers on the study casts and then taking radiographs which were measured to establish the upper incisor inclination. Statistical analysis of the data included the calculation of mean values, standard deviation, standard errors, and ranges for each variable. Spearman ranked correlation coefficients were computed for selected model variables and scattergrams plotted. To investigate the influence of the chosen retention therapy, a Mann-Whitney U-test was used. The mean change in incisor inclination during orthodontic treatment was 15.2 degrees. There was a mean relapse of 2.2 degrees between T2 and T3, but this was not considered clinically relevant. The amount of relapse was independent of the type of the retention appliance (Hawley type retainer or lingual retainer). The relationship between long-term stability of the incisor inclination and between the lip line relative to the upper incisors was also investigated, based on cephalometric data. A mean decrease in lip line height of 0.6 mm was seen at T2 and, although the observed change was statistically significant, it would not be clinically relevant.

Osteopontin and bone metabolism in healing cranial defects in rabbits.

Non-collagen proteins such as bone sialoprotein and osteopontin (OPN) form 10% of the extracellular bone matrix. In this study, the influence of OPN on bone repair was investigated. Human OPN (Innogenetics) was produced by a recombinant technique and bonded onto the surface of hydroxyapatite (Interpore 200). Thirty rabbits were divided into six equal groups. A circular defect (10mm) was prepared in each parietal bone. In four rabbits of each group the left and right defects were filled with either OPN-coated hydroxyapatite (OPN-HA) or non-coated hydroxyapatite (HA). One sham animal of each group received no implants. The animals were killed after 1, 2, 6, 12, 18 and 30 weeks. The histological sections were scanned and analysed digitally. There were no statistically significant differences in total bone formation between defects filled with OPN-HA and HA. Bone formation at the borders of the healing area was significantly higher in defects filled with OPN-HA than in those filled with HA. Less bone formation was noted in the OPN-HA and HA groups at the centre of the healing area than at the borders of the healing area and the dural area. Although some animals in the sham group showed a high level of bone formation in the dural area, this was not significantly different to that in the dural area of the other groups. There was no sign of infection or tissue rejection of the graft.

[Orthodontics based on a new scientific method of evaluating results: "evidence-based"]. / L'orthodontie basé sur une nouvelle méthode scientifique d'evaluation des résultats: l'"evidence-based".

In the orthodontic literature, randomized clinical trials are used to establish standards for the comparison of different clinical approaches. The balancing effect produced in a randomized study makes it possible to attribute the differences in results achieved clearly to treatment and not to variations in the biological characteristics of the patients involved. Recently, most randomized studies in orthodontics have been devoted to testing the hypothesis that some orthodontic appliances exert orthopedic effects that modify dento-facial growth. The authors propose definitions of "orthopedic effects" and of "dento-alveolar changes" and discuss the difficulties encountered in measuring them. They also review clinical studies published over the past 10 years on the correction of Class II malocclusions, on the problems of expansion and also report on Class IIl disorders. In addition they assess the problems associated with these clinical studies such as the ethical requirement of assuring that control groups receive treatment as appropriate for their maladies as that delivered to patients under study, the high cost of carrying them out, the relatively long delay before results can be evaluated, the difficulties of measuring all the different parameters involved, and the need to assemble large enough samples. To sum up, one can conclude that, because of all these impediments, randomized clinical studies have not as yet delivered the hope for benefit of collecting enough "evidence based" information for the orthodontic profession to deliver better treatment to its patients.

Digital measurements: a different approach to evaluate bone formation. A technical report.

In this study a digital measurement technique has been proposed to quantify bone formation on histological images. Two standard parietal defects were created in 30 adult rabbits. The animals were divided into six groups. Four animals of each group were randomly chosen as experimental group in which osteopontin-coated hydroxyapatite (OPN-HA) and hydroxyapatite (HA) were inserted alternatively in created defects. To observe the spontaneous healing process of defects, one animal of each group was used as control animal and these created defects did not receive any implants. The animals were sacrificed after 1, 2, 6, 12, 18 and 30 weeks. The histological sections were magnified (x100) and scanned digitally. The newly formed bone surfaces within the healing area were indicated and quantified by means of Adobe Photoshop 7 software. This measuring technique was found to be reliable and reproducible. The results of this study show no significant differences in bone formation between the OPN-HA and non-coated HA defects, although a significant difference in bone formation was measured at the margins of the defects treated with OPN-HA.

Osteopontin and bone metabolism: a histology and scintigraphy study in rats.

Osteopontin (OPN) is one of the major non-collagen proteins in extracellular bone matrix. To elucidate the function of OPN in bone metabolism, a cellular defect was created in parietal bone and tibia of 12 rats. In Group 1, the left defects were filled with OPN-coated hydroxyapatite (OPN-H). In Group 2, the right defects were filled with non-coated hydroxyapatite (N-H). In both groups, the contra lateral defects were used as control defects. In Group 3, OPN-H was inserted in the left defects and N-H in the right defects. Bone metabolism was measured by (45)Ca and technetium-99m methylene diphosphonate scintigraphy for 4 weeks. Scintigraphy did not show any significant differences in bone metabolism between the defects filled with OPN-H and N-H. A higher bone metabolism was measured between the parietal defects filled with OPN-H or N-H in comparison with the parietal control defects. This difference, however, was not significant and was less for tibia defects. Histological observation (7th week) shows less inflammatory cells at the tibia defects filled with OPN-H compared to the tibia defects filled with N-H. This study did not show any acceleration or inhibition of bone metabolism in parietal or tibia bone in rats, but there is some evidence that OPN might influence inflammatory cells in bone matrix.

[Orthodontics: interface between biology and biomechanics]. / Orthodontie: raakvlak tussen biologie en biomechanica.

As far as craniofacial development is concerned, the orthodontist is mainly interested in growth of the jaws, craniofacial growth patterns and physiologic backgrounds of bone remodelling after tooth displacement. In biomechanics, the principle "action is equal to reaction" is one of the most important issues to deal with. The art in orthodontics is to distribute the reaction forces or to use them on purpose in an attempt to achieve one of the treatment goals. Reaction forces can be neutralized intra-orally. In this respect the location of the center of resistance of the tooth or a group of teeth needs to be defined carefully in order to have a good understanding of the biomechanical principles of tooth displacement. The action forces can be neutralized extra-orally. When no reaction forces on other teeth are applied, there will be no side effects of the reaction forces on other teeth. Research on the biomechanical principles of the headgear does offer some clinical information. Recently in orthodontics, the use of implants has been introduced. It can be used to neutralize reaction forces intra-orally. Moreover, the implants can be used primarily as anchorage during orthodontic tooth movement and later on to replace missing teeth. Recent animal studies at our department have shown that non-axial loading of implants with forces higher than 5 Newton can be used.

Anterior tooth morphology and its effect on torque.

This study was undertaken to determine the variation in crown-root angle (CRA) of the upper incisors and canines as well as the variation in their labial contour. In addition, the influence of the variability of the labial contour and of different bracket heights on torque was evaluated. Proximal radiographs were taken of 160 extracted maxillary teeth (81 incisors and 79 canines). They were digitized and analysed with Jasc Paint Shop Pro 7TM and Mathcad 2001 Professional. The incisal edge, the centre of the cemento-enamel junction (CEJ), and the root apex were digitized to define the crown and root long axis. For all teeth the CRA was measured. At several heights of the labial surface a tangent was determined, enabling measurement of the inclination of the labial surface. The CRA had great variability, ranging from 167 to 195 degrees for the canines (mean value 183 degrees) and from 171 to 195 degrees for the incisors (average 184 degrees). The mean inclinations of the labial surfaces for the incisors varied greatly. Between 4 and 4.5 mm from the incisal edge the standard deviations (SD) were the smallest and between 2 and 4.5 mm from the incisal edge the labial surface angle differed by approximately 10 degrees. For the canines the mean inclinations of the buccal surface also varied. This angle differed by around 10 degrees between 2 and 4.5 mm from the incisal edge, but the SD were much larger than for the incisors. It can be concluded that placement of a bracket on a tooth at varying heights, still within a clinically acceptable range, results in important differences in the amount of root torque.

Unicoronal suture immobilization in the fetal rabbit.

Pre-clinical evaluation of surgical procedures aimed to correct craniosynostosis is ideally performed in species of small animals characterized by perinatal brain development, early skeletal maturation, and genuine synostosis in all newborns. It would be nearly impossible to breed such a colony to homozygosity, so most researchers have resorted to artificial postnatal suture immobilization. Our aim was to test the hypothesis that artificial immobilization of a unicoronal suture in the fetal rabbit (25 days of gestation) would result in neurocranial growth alterations similar to those seen in the 9-day postnatally immobilized or congenital synostotic rabbit models. The advantages of prenatal immobilization are that rabbits can undergo the tested corrective procedure at postnatal day 9. This age corresponds to a human age of 6 months and allows the deformity and the effects of its correction to be more readily detected. The heads of 25-day-old fetuses of five time-dated pregnant New Zealand white rabbits were exposed by hysterotomy. The left unicoronal suture of 4 fetuses in each litter was immobilized with a polyglactin suture piercing the frontal and parietal bone plates. The remaining two fetuses were sham-operated. Nine days after spontaneous delivery, all rabbits were marked with four titanium screws close to the sagittal and coronal sutures. Growth was recorded with dorsoventral cephalograms at 9 and 90 days. The group with the immobilized suture showed a small increase in growth across the sagittal sutures. However, the decreases in growth at the unicoronal suture in both the immobilized (5.41-mm difference with sham-treated group) and nonimmobilized (1.17-mm difference with sham-treated group) were significant. Fetal immobilization results in growth alterations similar to those observed after postnatal immobilization.

The effect of changes in tooth position of unerupted canines on cephalograms.

Although many radiographic procedures have been described to localize an impacted canine, they all submit the patient to extra radiation. The purpose of the entire study was to evaluate if the combined interpretation of cephalograms and dental panoramic tomograms (DPTs), which are used in orthodontic practice, can provide adequate information as to the position of impacted canines. In a previous study the radiographic image of impacted canines on DPTs was evaluated. In this investigation, the effect of changes in position and inclination of an impacted canine on cephalograms was studied in an experimental set-up. An upper canine was removed from a human skull and placed in a positioning device to imitate various positions of impaction. Starting from a buccally impacted position, three different displacements were simulated: 10 mm frontally, 10 mm sagittally, and 5 mm vertically. In each of these positions nine different changes in inclination (in the sagittal and the frontal plane) were registered, resulting in 36 different cephalographic exposures. Analysis revealed the following: the degree of vertical and sagittal displacement of the incisal point of the impacted canine, the angulation of the tooth as well as the tooth length, measured on a cephalogram, appeared to give an accurate representation of the experimental set-up. Combining these findings and those from the previous study, it became possible to define a series of points to enable an adequate three-dimensional (3D) estimation of the canine's position. A clinical case of an impacted canine is used as an illustration of this experimental set-up.

[The dry skull model in orthodontics]. / Het droge schedelmodel in de orthodontie.

Orthodontic therapy aims to displace teeth by means of orthodontic appliances. Forces, applied on the teeth, induce remodeling of the alveolar process in upper and lower jaw resulting in a new position of the teeth into both jaws. In this publication an attempt has been made to test a model (dry skull model) which could provide a better understanding of the effect of force application on tooth and bone displacement. Initial tooth displacement (microscopical), right after force application, could give an indication for the longitudinal tooth displacement to be expected. Variables as the point of force application, the amount and direction of the force and the localisation of the centre of resistance are determining factors for the final tooth displacement. This study attempts to forecast the longitudinal tooth displacement by evaluating the initial displacement on the dry skull. Initial tooth displacement has been measured by means of laser measuring techniques (holography, speckle interferometry and laser reflection technique). These techniques are non-invasive (non-destructive testing) and permit the measurement of small tooth and bone displacements varying between 0.5 and 15 microns. According to the results of the animal studies, it became obvious that initial tooth and bone displacements are indicative for the longitudinal effect of the same sort of force application on a short time basis (5 to 8 weeks). The final conclusion is that initial tooth displacement measured on a dry skull has a predictive value for the longitudinal effect of orthodontic force application. Moreover, the creation of a finite element model looks very promising in this respect. More research is needed to test the finite element model further and to make it useful for testing the effect of force application on skull and tooth structures of a patient.

[Tooth transplantation: an extra dimension in orthodontics]. / Tandtransplantaties: een extra-dimensie in de orthodontie.

In the first part of the presentation, the content of orthodontics has been briefly explained by means of some clinical cases. The main part of the presentation consisted of discussing patient treatment by means of autogenous tooth transplantation with special emphasis on its indications and contra-indications. When a tooth transplantation is carried out properly, a success percentage of 90%, even forty years after treatment, can be expected. This high percentage has been reported in a recent study. The success of tooth transplantation is mainly due to the timing of the transplantation and the non-traumatic handling during surgery. According to the literature, the ideal moment for tooth transplantation is when half to three quarters of the root has been formed. One of the indications for tooth transplantation is the transplantation of a tooth in the cleft of a cleft palate patient. Two cleft palate patients have been presented in which tooth transplantation was carried out after bone grafting in the alveolar cleft. Finally some findings of a recent study, carried out at our department, dealing with cryopreservation of teeth before transplantation, has been presented. According to the findings of this study, cryopreservation, after removal of the pulp tissue does not inhibit the normal ingrowth of new pulp tissue after transplantation.

Three-dimensional finite element modelling of a dog skull for the simulation of initial orthopaedic displacements.

From 55 frontal tomograms (CT-scans) using the 'Patran' finite element processor, a three-dimensional finite element model (FEM) of a dog skull was constructed. The model was used to calculate bone displacements under orthopaedic loads. This required good representation of the complex anatomy of the skull. Five different entities were distinguished: cortical and cancellous bone, teeth, acrylic and sutures. The first model consisted of 3007 elements and 5323 nodes, including three sutures, and the second model 3579 elements and 6859 nodes, including 18 sutures. Prior to construction of the FEM, an in vivo study was undertaken using the same dog. The initial orthopaedic displacements of the maxilla were measured using laser speckle interferometry. Under the same loading conditions, using the second FEM, bone displacements of the maxilla were calculated and the results were compared with the in vivo measurements. Compared with the initial displacement measured in vivo, the value of the constructed FEM to simulate the orthopaedic effect of extra-oral force application was high for cervical traction and acceptable for anterior traction.

The clinical significance of error measurement in the interpretation of treatment results.

The aims of this investigation were to determine the errors involved in cephalometric landmark identification and to link these to the interpretation of treatment results. Fifty cephalograms were randomly selected from patient files and the following were determined. (i) Accuracy of the digitizer--single tracing digitized on five occasions on each of 10 different positions on the digitizer by one observer. (ii) Intra- and inter-observer digitizing error--35 landmarks on the same tracing (on a fixed position) digitized on five occasions by each of four judges. (iii) Intra- and inter-observer tracing error--five separate tracings of 10 different cephalograms by four judges. There were no significant differences in the variances of the co-ordinates for each landmark between the different positions on the digitizer (mean variance x-axis 0.07 mm and y-axis 0.08 mm). (ii) One-way ANOVA showed no significant intra- or inter-observer differences in digitation. (iii) Levene's test for homogeneity of variance showed significant differences in the co-ordinates of different landmarks and between the same landmarks on different cephalograms. Two-way ANOVA showed significant differences between observers for the same landmark that were greater than the intra-observer differences. The results indicate that tracing accuracy is a limiting factor in cephalometry. The variance of each landmark is dependent on the quality of the cephalogram. Inter-observer differences were greater than intra-observer effects and these were random, rather than systematic errors. Minimal error estimation calculations enable discrimination between treatment results and measurement errors.

Comparative study of 2 electric and 2 manual toothbrushes in patients with fixed orthodontic appliances.

The objective of this prospective single-blind crossover clinical trial was to evaluate the efficacy of 4 toothbrushes in 33 children undergoing fixed appliance orthodontic therapy. The toothbrushes included in this study were the Braun Oral-B 3D Plaque Remover (Kronberg, Germany), the Philips-Jordan HP 510 (Philips Domestic Appliances, Groningen, The Netherlands), the Lactona orthodontic toothbrush (Bergen op Zoom, The Netherlands), and the Oral-B Advantage Control Grip (Braun); the first 2 are electric, and the last 2 are manual. Every patient tested each type of toothbrush in a randomly designed sequence. Plaque and gingival scores were recorded at baseline and after every 4-week test period. All patients received professional prophylaxis after each clinical evaluation. The data were analyzed with the Friedman test, which showed no significant differences among the 4 brushes for any of the parameters measured. The Wilcoxon signed rank test, comparing the plaque and the gingival scores between the upper and lower jaw for each brush, indicated that plaque removal was more efficient in the lower jaw than in the upper.

Location of the centre of resistance of the upper dentition and the nasomaxillary complex. An experimental study.

The purpose of this study was to investigate the initial displacement of the upper dentition and the nasomaxillary complex as a result of different directions of force application, and to determine the initial centres of resistance for both the upper dentition and the nasomaxillary complex. A macerated human skull with a well-aligned upper arch was used as one experimental model and Araldit 208 as a substitute for the periodontal ligament (PDL). Specifically designed 'antenna-headgear' was developed in an attempt to create different points of force application to simulate high-pull and horizontal traction, and orthopaedic force magnitudes of 8 N were applied to the upper dentition and the nasomaxillary complex. Double exposure holography was used to measure the initial displacement. Reproducibility of the technique was tested and found to be reliable. According to the registered fringe patterns, the force application transmitted by the headgear resulted in complex displacement of facial bones. Pure translation of the maxilla and the upper dentition was observed when the force vector passed by in the area of the key-ridge. No obvious difference was found between the centre of resistance of the upper dentition and the nasomaxillary complex. The location of two different centres of resistance could not be confirmed by measuring initial displacements on this macerated human skull.

Revascularization after cryopreservation and autotransplantation of immature and mature apicoectomized teeth.

Autotransplantation of immature teeth can have a success rate of almost 98% if the tooth is atraumatically transplanted from the donor site to a suitable acceptor site and the extraoral time is kept to a minimum. When the tooth cannot be transplanted immediately, cryopreservation and storage in a tooth bank offer new possibilities for autotransplantation. However, the effect of cryopreservation on the revascularization of transplanted teeth is still unknown. The purpose of this study was to examine revascularization in immature teeth that have an open apex and in mature teeth that have had the apex cut. The study was carried out on 16 teeth in 2 dogs; 8 teeth were removed and immediately transplanted to the contralateral position and 8 teeth were cryopreserved and transplanted 1 week later. The results show that: (1) teeth can revascularize after autotransplantation if the original pulp tissue is removed at the time of extraction, (2) there is no significant difference in the amount of revascularization between teeth stored in a tooth bank for 7 days and those immediately transplanted without freezing, and (3) there is no difference in the ingrowth of new pulpal tissue between mature apicoectomized teeth and immature teeth.

The effect of tooth size discrepancy on occlusion: An experimental study.

The purposes of this experimental study are the following: (1) to compare the anterior and overall tooth size ratios reported by Bolton to values reported in epidemiologic studies, (2) to assess the accuracy of tooth size discrepancy measurements, (3) to investigate to what extent generalized tooth size discrepancy affects occlusion, (4) to investigate the effect of leveling the curve of Spee, and (5) to evaluate the effect of extraction therapy of 4 premolars on occlusion. For the first part of the study, Bolton's mean anterior and overall tooth size ratio (as well as the extraction values) were compared with calculations derived from 4 publications reporting mean mesiodistal tooth width by using the t test (P

[Are removable appliances obsolete?]. / Is uitneembare apparatuur verleden tijd?

Removable orthodontic appliances have some limitations compared to fixed appliances. However, a removable appliance can be used during each period of craniofacial growth and dental development. A number of clinical applications for the removable appliance during the mixed and permanent dentition is explained. The use of functional orthopedic appliances and removable retention appliances are also described. It is concluded that the removable appliance can still play a favorable part in the treatment of malocclusions in each developmental stage.