Mechanical loading of orthodontic miniscrews - significance and problems: an experimental study.

Orthodontic miniscrews are exposed to three mechanical loading phases during clinical use: torsional loading upon insertion, flexural loading during anchorage function, and torsional loading upon removal. The aim of this study was to simulate clinical loading conditions for different types of orthodontic miniscrews in vitro to quantify the effects of combined torsional and bending stress. Various orthodontic miniscrew systems (Lomas, Dual-top, Aarhus anchorage, Tomas-pin and T.I.T.A.N.-pin) comprising 10 samples each were subjected to the following loading sequences in vitro: a torsional load corresponding to manual insertion with limited torque; and flexural loading at two different insertion depths. For all screw systems with torsional pre-loading (simulating insertion), subsequent flexural loading (simulating anchorage) yielded permanent deformations of approximately 0.15-0.25 mm, depending on the insertion depth. Since EDX analysis revealed comparable elemental compositions for the different screw systems, the differences in mechanical properties are attributed to screw design. Torsional loading during screw insertion may cause premature mechanical weakening and needs to be minimized. Unless fully inserted, screws show pronounced plastic deformation and hence fracture risk under subsequent flexural loading.

Cranial base features in skeletal Class III patients.

OBJECTIVE: To investigate the cranial base configuration in skeletal Class III patients to clarify the conflicting findings from literature. MATERIALS AND METHODS: Initial lateral radiographs of 54 skeletal Class III patients and 54 matched controls (Class I, II/1, II/2) aged 14 to 24 years were analyzed retrospectively for 21 cephalometric basicranial variables and jaw lengths relative to anterior cranial base length. RESULTS: In contrast to overall cranial base length, the anterior (N-S) and posterior (S-Ba, S-Ar) sections failed to show a significant reduction in Class III patients. The significantly more acute angles Ca-S-Ba and Se-S-Ba reflected increased cranial base flexure. Resulting anterior condylar displacement was shown by significant reduction of Se-S-Cd and Ar-Ca. Relative mandibular length was significantly increased. CONCLUSIONS: Decreased basicranial angulation associated with Class III mandibular protrusion was clearly confirmed for skeletal Class III patients. Overall shortening of the cranial base apparently resulted from various minor alterations. The results are compatible with the deficient orthocephalization hypothesis of Class III morphogenesis. The basicranial-maxillary relationship in skeletal Class III remains unclear.

Study on treatment of condylar process fractures of the mandible.

Treatment of mandibular condylar process fractures may be conservative or surgical. Both treatment approaches aim to reconstruct the articulating joint surfaces in a physiological position to the discoligamentary structures. The study comprised 1812 patients of Wuerzburg University who presented with a fracture of the mandibular condylar process between 1981 and 2001. Besides conservative management options, surgical interventions using mini-plate osteosynthesis and the Wuerzburg lag screw plate were studied for post-treatment changes. Statistical analysis revealed that surgical osteosynthesis is superior to merely conservative therapy in terms of post-treatment dysgnathic severity. Hence, surgical osteosynthesis is advocated especially in patients with high condylar fractures or dislocated fractures in order to ideally achieve 'restitutio ad integrum'.

Primary flap closure combined with Emdogain alone or Emdogain and Cerasorb in the treatment of intra-bony defects.

OBJECTIVES: To compare clinical outcomes of three different modalities of treatment for deep intra-bony defects. MATERIAL AND METHODS: Fifty-six patients were paralleled for clinical parameters and randomly assigned to treatment. They displayed one angular defect each with an intra-bony component > or =3 mm, probing pocket depth (PPD) and probing attachment level (PAL) > or =7 mm, and plaque index (PI) <1. Nineteen defects were treated, respectively, with enamel matrix derivative (EMD)+tricalcium phosphate (TCP) or EMD alone and 18 defects with modified Widman flap (MWF). Primary flap closure was used in all three groups. PI, gingival index, bleeding on probing, PPD, PAL, and recession (REC) were measured before and 12 months after treatment. RESULTS: Treatment with EMD alone yielded a 3.9+/-1.3 mm PPD decrease and a 3.7+/-1.0 mm PAL gain (p<0.001), whereas EMD+beta-TCP produced a 4.1+/-1.2 mm PPD reduction and a 4.0+/-1.0 mm PAL gain (p<0.001). These outcome parameters did not differ between the two groups. REC increased by 0.7+/-1.3 mm. After MWF treatment, attachment gain was 2.1+/-1.4 mm (p<0.001) and PPD reduction was 3.8+/-1.8 mm, whereas REC increased by 1.5+/-0.7 mm (p=0.042 versus EMD). CONCLUSION: Both EMD treatments showed similar clinical effects, with significant PAL gain and a significantly lower REC increase in comparison with MWF treatment.