Birte Melsen

The aim of this study was to describe the stress and strain fields around orthodontically loaded dental implants using the finite element method and to evaluate the relationship between the generated strain and the biologic reaction expressed through histomorphometric parameters. Finally, this study aimed to evaluate the interaction between the orthodontic loading and the deformation generated by normal occlusal function. Sixteen titanium dental implants were inserted in extraction sockets after the removal of the second premolars and first molars of 4 adult Macaca fascicularis monkeys. After 17 weeks of healing, the implants were loaded by a pair of Sentalloy springs (50 cN) for 16 weeks. After sacrifice, tissue blocks including the implants and surrounding bone were excised. Five tissue blocks were scanned with a synchrotron radiation-based microtomography (microCT) scanner and sample-specific finite element models were generated. Subsequently all samples were prepared for histomorphometric analysis. All implants were osseointegrated, although the surrounding alveolar bone differed from sample to sample. As a consequence the finite element analyses showed that the stresses and strains in the peri-implant alveolar bone greatly varied among the samples. A high level of remodeling activity was found close to the implants. Individual differences between the receptors (in this case, the monkeys) have a large effect on both the biologic and morphologic parameters. These variations were indeed found to have a substantial impact on the (re)modeling dynamics and the load transfer mechanisms around the implants. By integrating different analysis techniques to evaluate bone (re)modeling around orthodontically loaded implants, this study has demonstrated the complexity and case-specific character of alveolar adaptation to orthodontic loading. Furthermore, stresses generated by combined functional and orthodontic forces should not be neglected.

The risk of developing bony dehiscence and gingival recession may lead clinicians to prefer extraction to expansion in borderline cases. The purpose of this research was to compare changes in clinical crown height that occur at the buccal aspect of the maxillary lateral teeth of adult patients in which the transverse dimension was increased with those occurring if no expansion had been performed. Secondly it was the intention to identify factors increasing the risk of development of gingival recessions. The material comprised the pre- and post-treatment study casts from two groups of 50 adult patients. In one group an average transverse expansion of 3 mm was performed while in the other no change in the arch width was generated during treatment. Clinical crown heights of the two groups before and after treatment were compared with a Student's t-test and correlation analysis was used to determine whether any demographic or treatment-related parameters could be applied to predict an increase in clinical crown height. The increase in transarch width was greater in males (2.4–3.4 mm) than in females (1.8–2.5 mm), and greater at the level of the premolars than at the molars. No significant increase in buccal crown height could be identified. The increase in width was, however, related to buccal tipping as a positive correlation was found between the amount of expansion and tipping (P < 0.01). No detrimental effect of slow maxillary expansion could be demonstrated.

Structured Authors – Dalstra M, Melsen BObjectives – To examine whether the transition temperature of Cu–NiTi archwires has an effect on the tooth movement during the alignment phase of orthodontic treatment.Design – ‘Split mouth’ design in randomly selected patients.Setting and Sample Population – The Department of Orthodontics, School of Dentistry, University of Aarhus. Fifteen randomly selected patients with identical level of irregularity in the alignment phase of their treatment.Experiment Variable – Specially manufactured Cu–NiTi archwires for the upper arch were inserted. These consisted of two separate halves, each with its own transition temperature, respectively 27° and 40°C, and clamped together in the middle.Outcome Measure – The tooth movement, expressed as two translations and a rotation, in the occlusal plane was measured from the patients’ intraoral photographs taken upon insertion of the archwires and again after 1 month.Results – Tooth movements tended to be larger on the 40°C‐side, however only in case of the total translation of the premolars was this difference significant. In general, patients had not noticed any difference between the two sides of the archwire, although one patient stated the 27°C‐side to be more comfortable as the 40°C‐side had bothered her when drinking hot beverages.Conclusion – The transition temperature of Cu–NiTi archwires has indeed an effect on the amount of tooth movement during alignment. However, the differences are so small though that it is the question whether they can be noticed clinically. The study corroborates the trend towards the use of lower forces within orthodontics.