Indirect miniscrew anchorage: biomechanical loading of the dental anchorage during mandibular molar protraction-an FEM analysis.

AIMS: While there are many studies in the literature addressing direct miniscrew anchorage, the biomechanical effects of indirect miniscrew anchorage remain unknown. The aim of the present study was to biomechanically analyze the load on the anchor teeth during mandibular molar protraction using different types of anchorage. MATERIALS AND METHODS: Four finite element method (FEM) models of the right mandible were created using the morphological CT data of a 21-year-old male. All models were morphologically identical, but they differed in anchorage type (dental anchorage, direct miniscrew anchorage, indirect miniscrew anchorage with one anchor tooth, indirect miniscrew anchorage with two anchor teeth). To analyze the load on the dental anchorage during mandibular molar protraction, we measured the induced effective strain (µstrain) at specific control points on the alveolar bone. RESULTS: With indirect miniscrew anchorage, we observed that the effective strain at an average of 7.21 µstrain (one anchor tooth) or 6.57 µstrain (two anchor teeth) was almost as high as in pure dental anchorage where no miniscrew was used (mean 8.38 µstrain). In contrast, we noted significantly lower strain values in conjunction with direct miniscrew anchorage. We observed highly significant differences between direct and indirect simulated miniscrew anchorage (p=0.008). CONCLUSION: Our FEM results reveal relatively high loads on the dental anchorage when using indirect miniscrew anchorage. This may carry an increased risk of anchorage loss during mandibular molar protraction; however, further studies are necessary to confirm this.

Orthodontic bracket debonding: risk of enamel fracture.

OBJECTIVES: Until now, it is not clear if various procedures of bracket debonding differ with regard to their risk of enamel fracture. Therefore, the objective of the present study was to compare these procedures biomechanically for assessing the risk of complications. MATERIALS AND METHODS: An anisotropic finite element method (FEM) model of the mandibular bone including periodontal ligament, enamel, dentin, and an orthodontic bracket was created. The morphology based on the CT data of an anatomical specimen. Typical loading conditions were defined for each method of bracket debonding (compression, shearing off, twisting off). Shortly before the adhesive's break, the induced stress in enamel, periodontal ligament, and in the alveolar bone was measured. The statistical analysis of the obtained values was performed in SPSS 19.0. RESULTS: Relatively high stresses occurred in the enamel using frontal torque (max. 44.18 MPa). With shearing off, the stresses were also high (max. 41.96 MPa), and additionally high loads occurred on the alveolar bone as well (max. 11.79 MPa). Moderate maximum values in enamel and alveolar bone appeared during the compression of the bracket wings (max. 37.12 MPa) and during debonding by lateral torque (max. 35.18 MPa). CONCLUSIONS: The present simulation results indicate that the risk of enamel fracture may depend on the individual debonding procedure. Further clinical trials are necessary to confirm that. CLINICAL RELEVANCE: For patients with prior periodontal disease or loosened teeth, a debonding procedure by compression of the bracket wings is recommended, since here the load for the periodontal structures of the tooth is lowest.

Sutural strain in orthopedic headgear therapy: a finite element analysis.

INTRODUCTION: The goal of this study was to analyze the strains induced in the sutures of the midface and the cranial base by headgear therapy involving orthopedic forces. Does the mechanical signal induced in the sutures sufficiently account for a growth-influencing effect? METHODS: A finite element model of the viscerocranium and the neurocranium was used. It consisted of 53,555 tetrahedral elements and 97,550 nodes. The strain induced in the sutures of the cranial base and the midface when applying orthopedic headgear forces of 5 and 10 N was computed and recorded with an interactive measurement tool. RESULTS: The magnitude and the distribution of the measured strains depended on the level and the direction of the acting force. Overall, the strain values measured at the sutures of the midface and the cranial base were moderate. The measured peak values at a load of 5 N per side were usually just below 20 microstrain irrespective of the force direction. A characteristic distribution of strain values appeared on the anatomical structures of the midface and the cranial base for each vector direction. The measurements based on the finite element method provided a good overview of the approximate magnitudes of sutural strains with orthopedic headgear therapy. The signal arriving in the sutures is apparently well below threshold, since the maximum measured strains in most sutures were about 100 fold lower than the minimal effective strain. A skeletal effect of the orthopedic headgear due to a mechanical effect on sutural growth cannot be confirmed from these results. CONCLUSIONS: The good clinical efficacy of headgear therapy with orthopedic forces is apparently based mainly on dentoalveolar effects, whereas the skeletal effect due to inhibition of sutural growth is somewhat questionable.

Biomechanical analysis of maxillary expansion in CLP patients.

OBJECTIVE: To carry out a comparative biomechanical analysis of maxillary low force expansion using the quadhelix appliance in cleft and noncleft patients. We also intended to determine whether a sufficient transverse skeletal effect could be achieved among cleft patients using the quadhelix appliance. MATERIALS AND METHODS: Three finite element models of the viscerocranium and neurocranium were established in which a transverse expansion of the maxilla using a quadhelix (transverse force of 2 N) was simulated. RESULTS: The skeletal effects at the anatomic structures of the midface and the cranial base were far more marked in the simulation models with clefts compared to the morphologically normal state. The highest expansions were measured for bilateral cleft palates. Thus, the expansion measured at the supraorbital margin was 4.7 mustrain with a bilateral cleft, 2.1 mustrain with a unilateral cleft, and only 0.2 mustrain with the morphologically normal state. For bilateral and also for unilateral bone clefts, the skeletal effect of a maxillary low force expansion with a quadhelix on the anatomical structures of the viscerocranium and neurocranium is very much larger than is the case for individuals without clefts. CONCLUSION: In the presence of a continuous cleft in the jaw and palate area, orthodontic forces (quadhelix) are apparently already sufficient to allow a skeletal expansion of the maxilla. Maxillary expansion using the quadhelix appliance represents a reasonable alternative to using conventional rapid maxillary expansion appliances among cleft patients.