F.P.G.M. van der Linden

Evaluation of a technique for standardized periapical radiographs

A paralleling instrument with an orientation bite-block was designed to provide standardized projections on periapical radiographs with the extension cone paralleling technique. The reproducibility of root images on these radiographs and the relocation of the orientation bite-block in relation to root structures were tested in five patients. Three radiographs were subsequently made of each patient and compared. The projection error proved to be negligible.

The role of interdigitation in sagittal growth of the maxillomandibular complex in Macaca fascicularis

The role of the interdigitation of posterior teeth in maxillomandibular growth and development was studied longitudinally in Macaca fascicularis monkeys. Fourteen monkeys were divided into a control group (n = 7) and an experimental group (n = 7). At the start of the study, the mean age of the animals was 29 weeks. At that stage the interdigitation in the experimental group was eliminated by grinding the cusps of the molars and canines. The animals were followed until 143 weeks of age and studied with the aid of tantalum implants and lateral radiographs. The findings indicated that elimination of the interdigitation resulted in a deviating anteroposterior relationship between the jaws and a significant inhibition of the vertical growth of the maxilla in the second half of the experimental period, while total face height was not noticeably affected. As a result, a more prognathic mandible and a more mesial occlusion developed. It can be concluded that the interdigitation plays a role in the regulation of vertical and anteroposterior facial growth and constitutes an important factor in the jaw relation in Macaca fascicularis monkeys.

4D-computerized visualisation of human craniofacial skeletal growth and of the development of the dentition

The understanding of growth and developmental changes can be improved when shapes and changes in size, proportion, and relationships are visualized in 3 dimensions and at different stages. This applies particularly to craniofacial skeletal growth and the development of the dentition. For that purpose 3D-data were collected from prenatal human heads ranging from 18 up to 275 mm CRL and from a collection of macerated fetal and postnatal skulls. Computer-aided graphical reconstructions were obtained from histological serial sections of embryonic and early fetal specimens. Proportional changes in the growing skull were recorded by means of radiological and cephalometric evaluation. In addition, computed tomography was applied to fetal and postnatal skulls. Furthermore, the prenatal and postnatal development of the dentition was digitized. To that end 3D-polygone sets of these data were read into a workstation computer and animated by means of the software Soft Image (Microsoft). This comprehensive 4D insight into growth facilitates the understanding and teaching of normal and abnormal development.

Compensation of differences in density of radiographs by densitometry

Radiographs were made of a dried human mandible with variations in kilovolt peak, exposure time, soft-tissue thickness substitutes, and developing time. The densitometric measurements of the image of dental and bony structures were transformed into millimeters of aluminum equivalents by means of densitometric measurements on the penetrometer. Variations in kilovolt peak, exposure time, soft-tissue thickness substitutes, and developing time do not affect the densitometric measurements after transformation, except when radiographs are very dark.

The role of intercuspation in the regulation of transverse maxillary development in Macaca fascicularis

The role of intercuspation of the teeth in transverse maxillary growth and dental arch development was investigated radiographically with the aid of implants in Macaca fascicularis monkeys. Fourteen animals were randomly allocated to a control group (n = 7) and an experimental group (n = 7) and were followed from 29 to 100 weeks of age. Intercuspation was eliminated in the experimental group by grinding the canines and molar cusps in both dental arches as soon as possible after emergence. Maxillary occlusal radiographs were taken at regular intervals. Linear and angular analyses of skeletal changes revealed that midpalatal sutural growth seems to be independent of intercuspation. The developing dental arch, however, showed a significantly greater increase in width in certain areas in the experimental group than in the control group. Most findings support the hypothesis that the width of the maxillary dental arch is guided by the width of the mandible through the intercuspation of the posterior teeth.