Stability of edentulous, atrophic mandibles after insertion of different dental implants. A biomechanical study.

OBJECTIVES: Fractures of the atrophic edentulous mandible are a rare complication that can become severe after the insertion of dental implants. This in vitro study investigated the effects of different implant settings varying in number, diameter, and length. and the influence of a fixed bar. MATERIALS AND METHODS: In biomechanical experiments on artificial mandibles, an unmodified reference group, four implant settings with two different implants, and the effect of adding a fixed bar to these settings were tested. All specimens were loaded with incisal biting forces until failure due to fracture. RESULTS: Implants weakened all specimens significantly compared with those in the reference group. Without a fixed bar, four short and thick implants showed the best results, with high significance. With a fixed bar, four long and thin implants withstood the highest loads. The addition of fixed bars reduced the differences between the implant settings. Fixed bars did not show increased stability for all groups; however, these groups showed a higher mean strength. CONCLUSIONS: Four implants with a short and thick design should be the first choice when implants are placed without a fixed bar in an atrophic mandible. With a fixed bar, four long and thin implants should be used.

Which kind of frontal mandibulotomy is the smartest? A biomechanical study.

PURPOSE: Retrospective clinical evaluation and biomechanical tests were performed to compare the primary stability and the rate of pseudarthrosis formation after irradiation for two types of mandibular split osteotomies: the stairstep osteotomy (SSO) and the straight-line osteotomy (SLO). METHODS: The postoperative occurrence of pseudarthrosis was retrospectively analysed in 46 non-consecutive clinical cases of SSO and SLO between 2003 and 2013. Biomechanical tests were performed on 12 standardised synthetic mandibles (Synbone) to compare the SSO and SLO approaches. Two 2.0 mm monocortical miniplates (Medartis) were used for osteosynthesis. The artificial mandible specimens were loaded to 300 N on the Mandibulator test bench while interfragmentary motion was measured using the PONTOS optical measurement device. RESULTS: The retrospective clinical analysis showed a rate of pseudarthrosis of 19% in the SLO group versus only 5% in the SSO group (p = 0.17). In the biomechanical investigation, the average interfragmentary movement was 14.3 ± 7.70 for the SLO group and 4.57 ± 2.33 for the SSO group under a maximum load of 300 N, resulting in a statistically significant difference between the two approaches (p = 0.014). CONCLUSION: To minimise the rate of postoperative pseudarthrosis formation, SSO is superior to SLO for mandibular split procedures, because SSO provides greater resistance to vertical loads and allows less interfragmentary movement. LEVEL OF EVIDENCE: 2C (Outcomes research).

Comminuted fractures of the proximal ulna--Preliminary results with an anatomically preshaped locking compression plate (LCP) system.

INTRODUCTION: The purpose of this investigation was to review the preliminary results and patients outcome following treatment with an anatomically preshaped LCP in patients with comminuted fractures of the proximal ulna. We hypothesized that this fixation system provides equal or superior results in fracture care when compared with other available plating devices, but results in better patient's comfort due to its low-profile design. PATIENTS AND METHODS: Between 2007 and 2009, 15 patients with comminuted fractures of the proximal ulna including three posterior Monteggia fractures were managed with the preshaped LCP olecranon plate. The patients were invited for clinical examination at a mean duration of 16 months, retrospectively. Validated patient-oriented assessment scores involving the Mayo Elbow Performance Index (MEPI) and the shortened Disability of the Arm, Shoulder and Hand (Quick-DASH) score, postoperative range of motion, objective muscle-strengths testing and patient's satisfaction were evaluated. All patients had follow-up radiographs. RESULTS: Fourteen patients were available for evaluation. The mean arc of elbow motion was 129°. The mean MEPI was 97 with good results in two patients and excellent results in 12 patients. The mean Quick-DASH was 13. Thirteen of fourteen patients documented satisfaction with their elbow outcome. There was one patient with symptomatic hardware and one patient complained about deficit of motion. In four patients the hardware was removed including two patients with elective removal. Fourteen fractures healed with ulnohumeral congruity after a mean time to union of 11 weeks. One fracture non-union occurred without mechanical failure or loss of reduction. CONCLUSION: Anatomically preshaped LCP olecranon plating is an effective fixation method for comminuted fractures of the proximal ulna allowing reliable stability for early elbow motion. The functional results are comparable with formerly described plating systems. A low rate of symptomatic hardware removal suggests better patient's compatibility.