H θεραπεία των καταγμάτων της γωνίας της κάτω γνάθου είναι αμφιλεγόμενη και παραμένει ένα θέμα διαρκούς αντιπαράθεσης στη διεθνή βιβλιογραφία. Οι τρισδιάστατες μίνι πλάκες (3D) είναι σχετικά καινούργιες και υποστηρίζεται ότι εμφανίζουν βελτιωμένη μηχανική συμπεριφορά, χωρίς όμως να υπάρχουν βιβλιογραφικά δεδομένα ή κλινικές έρευνες που να υποστηρίζουν τη χρήση τους. Σκοπός της μελέτης αυτής είναι να αξιολογηθούν δύο τρισδιάστατα μίνι συστήματα οστεοσύνθεσης και να συγκριθούν με αντίστοιχα κλασικά συστήματα μίνι πλακών που χρησιμοποιόυνται ευρέως στην κλινική πράξη. Υλικό-Μέθοδος: Συνθετικές κάτω γνάθοι χρησιμοποιήθηκαν για την αξιολόγηση των τρισδιάστατων συστημάτων οστεοσύνθεσης, σε σύγκριση με τέσσερα ακόμα συστήματα. Οι ομάδες μελέτης ήταν οι εξής: Ομάδα 1 Mία 3D μίνι πλάκα2x2 οπές, τετράγωνη 2.0mm Ομάδα 2 Mία 3D μίνι πλάκα4x2 οπές, ορθογώνια, 2.0mm Ομάδα 3 Σύστημα δύο πλακών, 4 οπές, ευθείες, 2.0mm & 1.6mm Ομάδα 4 Mια μίνι πλάκα, 4 οπές, ευθεία με διάστημα, 2.0mm Ομάδα 5 Σύστημα δύο πλακών, 4 οπές, ευθείες, 2.0mm & 1.6mm Ομάδα 6 Μια πλάκα κατάγματος (fracture plate) 6 οπές, γωνία 140ο, 2.0mm Κάθε ομάδα υποβλήθηκε σε φόρτιση στην πρόσθια τομική περιοχή και στην σύστοιχη με το κάταγμα γομφιακή περιοχή, μέσω ενός μηχανήματος εφαρμογής τάσης (Monsanto Tensometer 20). Έγινε μέτρηση και καταγραφή του κενού στο άνω όριο του κατάγματος καθώς επίσης και μετρήσεις τιμών ακαμψίας (stiffness) για κάθε τύπο φόρτισης ξεχωριστά. Υπολογίστικαν οι μέσες τιμές και οι σταθερές αποκλίσεις των παραπάνω τιμών και ακολούθως έγινε στατιστική ανάλυση των αποτελεσμάτων με χρήση του απλού t-test. Στατιστικά σημαντικά θεωρήθηκαν αποτελέσματα με p< 0,05 %. Αποτελέσματα: Κατά τη φόρτιση της ομόπλευρης προς το κάταγμα γομφιακής περιοχής η στατιστική ανάλυση ανέδειξε στατιστικά σημαντικές διαφορές μεταξύ των ομάδων. Κατά τη φόρτιση της πρόσθιας τομικής περιοχής δεν αναδείχθηκαν στατιστικά σημαντικές διαφορές. Το κενό στο άνω χείλος του κατάγματος ήταν οριακό σε τέσσερα από τα συστήματα που εξετάστηκαν. Συμπεράσματα: Με βάση το πειραματικό μοντέλο που χρησιμοποιήθηκε η ομάδα 1 (τετράγωνη 3D) εμφάνισε την καλύτερη εμβιομηχανική συμπεριφορά. / Therapy of mandibular angle fractures is controversial and is still a subject of continuous interest in international literature. Three dimensional (3D) mini plates are relatively new, with no biomechanical or clinical studies to support their use. The aim of this study is to comparatively evaluate the use of two 3D mini plating systems for the treatment of mandibular angle fractures, with mini plates used in ordinary clinical practice. Materials and Methods: Synthetic mandible replicas were used to evaluate the effectiveness of the 3D plates along with four other mandibular angle plating techniques. The plating techniques consisted of: 1. A 3D miniplate (2x2 holes, square, 2mm) 2. A 3D miniplate (6x2 holes, curved, 2mm) 3. Two plate system (four hole, straight, 2mm,placed at the lateral oblique ridge and 1,6mm) 4. One single miniplate (four hole, straight, 2mm) 5. Two plate system (four hole, straight, 2mm,placed in the buccal aspect of the lateral oblique ridge and 1,6mm) 6. A fracture plate (six hole, curved). Each group was subjected to incisal and homolateral molar region loading by a tensile materials testing machine (Monsanto Tensometer 20). Load stiffness values and peak measurements of the fracture gap distraction at the superior aspect of the mandible were measured. The mean values (± standard deviation) were derived and compared using students t-test, with statistical significance set at p<0.05. Results: For homolateral molar loading, statistically significant differences existed within groups (P<0, 05). For incisal edge loading, no statistically significant differences were found for stiffness among the fixation methods tested. Gap distraction at the superior aspect of the mandible was limited for four of the groups tested. Conclusion: Under the conditions tested the 3D square plate system provided the most favourable mechanical behaviour.

There is no evidence in the literature of biomechanical stability characteristics comparing conventional rectangular screw placement with that of an angled mono-cortical screw plating system where standard 2mm diameter screws are applied at angles more acute than conventional 90° screws, through plate holes machined (cut) for a definite specific screw angle placement P. Angled screws will have an obvious clinical advantage of direct line of vision insertion, through an intra-oral route without the disadvantage of trans-buccal (cutaneous) approach required for conventional 90° rectangular screw application. Angled screw application will result in the prevention of possible, less post-operative swelling, nerve fall out (motor and/or sensory), haematoma, false aneurysm and scarring as unwanted clinical complications associated with trans-buccal extra-oral surgical technique. Intra-oral angled screw application will result in definitive cost saving due to less operating time required. Post-treatment removal of angled screws is uncomplicated, requiring only intra-oral surgical approach, without trochar use or skin incisions for screwdriver application. By determining angle displacement values at certain clinical relevant force values for both compression/tension and torsion, preference can be established for ideal angle(s) of screw application in a plating system. An own unique, designed and manufactured, jig and inclined screw insertion (ISI) plates were implemented during the biomechanical evaluation of stability at different screw angle applications in a Zwick machine. For the purpose of this biomechanical comparative investigation an inclined screw insertion (ISI) plate was manufactured with 90°, 75°, 60° and 45° angled plate holes orientated in line with the long-axis (quadrant 3) of the distal section of the plates and diagonal across (quadrant 1) in the proximal section of the plates. Screws with an ISI angle of 30° in any quadrant application resulted in lifting the plate from the bone surface and caused cortical bone destruction during pilot drilling. The results for mono-cortical 7mm screw placement proved superior in biomechanical stability during tension/compression - forces for screw insertion angles of 60° and 45°, when compared to conventional 90° rectangular screw placement. Screws inserted at an angle of 75° demonstrated no improvement in compression/tension stability when compared with 90°.Torsion force stability for all of the 75°, 60° and 45° inclined screw insertion (ISI) systems proved more stable compared to conventional 90° screw angle plates. It is concluded that angled monocortical screw placement between angles 60° and 45° has clinical significance as far as stability, intra-oral surgical technique and time-cost factor is concerned. The results of this biomechanical behaviour investigation of ISI, evolved new terminology such as screw-tip shifting, screw-tip travel, lag potential and clinical significance for the range of screw angle placement. Angled orientation to the plate design and plate geometry is also defined in terms of tension line distribution in the anatomical region for application in the mandible. An unique quadrant description for ISI is described for future communication. An international patent, based on the ISI principle, has been registered for monocortical six-hole plates of firstly different geometric designs to conform to specific anatomical topographic sites in the mandible and secondly specific screw plate-holes angled at 60° in different orientation to the plate (Patent:PCT/EP 2006/006365), (Addendum 6). A specific L-shaped, mandibular angle plate with screw holes at a 60° angle where orientation shifts from in-line with the long-axis of the plate in the distal three plate holes to diagonal orientation in the proximal section of the plate, is designed and manufactured by Stryker/Leibinger as an example of such a patent plate. It is recommended that a smart-lock plate with plate holes at 55° angles be manufactured to allow screw angle placements of 65° - 45° in different angle orientations. Pilot hole drilling and ISI can be performed without the use of a drill-guide. / Thesis (PhD)--University of Pretoria, 2009. / Maxillo-Facial and Oral Surgery / unrestricted

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