Possibilities of reconstruction and implant-prosthetic rehabilitation following mandible resection

Introduction. Mandible reconstruction is still very challenging for surgeons. Mandible defects could be the consequence of ablative surgery for malignancies, huge jaw cysts, infection and trauma. Segmental resection of the mandible may compromise orofacial function and often lead to patients psychological disorders. Despite very frequent use of microvascular flaps, autogenous bone grafts are still very reliable technique for mandible reconstruction. Comprehensive therapy means not only mandible reconstruction, but prosthodontic rehabilitation supported by dental implants, which can significantly improve patients quality of life. The aim of this paper was to evaluate possible techniques of mandible reconstruction and to present a patient who had been submitted to mandible resection and reconstruction with autogenous iliac bone graft and prosthodontic rehabilitation with fixed denture anchoraged by disc-shaped implants in early loading protocol. Case report. Mandible reconstruction was performed simultaneously with resection. Autogenous iliac bone graft was taken, reshaped and placed in two parts, to the required optimal contour of the mandible. After graft consolidation, decision was made for prosthodontics rehabilitation with fixed dentures supported by implants. In addition to the standard preoperative procedures, planning was done based on a biomodel gained by rapid prototyping after CT scan. It offered a real 3D planning to obtain a proper shape, dimension and the position of implants. Conclusion. If bone dimensions of a reconstructed mandible are insufficient, like in the presented case, the use of basal osseointegrated implants may be a method of choice. Avoiding bone augmentation procedures, as well as early loading protocol for this type of implants, shorten the total rehabilitation time, which is very convenient for patients. Fixed denture supported by dental implants is the best solution for comprehensive rehabilitation after mandible resection. [Projekat Ministarstva nauke Republike Srbije, br. 175075

Napetostno-deformacijska analiza opornega zoba z zapornim sedežem, izdelana s kompozitnim popravilom

Placing a composite restoration on abutments for the removable of partial dentures gives favorable aesthetic results with minimal intervention. The objective of this paper is to analyze the stress distribution of a tooth with occlusal rest-seat preparation in the composite and compare it to the biomechanical behavior of an intact tooth, assuming that the stress and strain distribution throughout the intact tooth provides the control scenario. For this finite-element study two different models were designed. The first model was the three-dimensional (3D) model of an intact tooth, and the other one was a 3D model of a tooth with a composite restoration and an appropriate occlusal rest-seat preparation. Load stimulations were performed when the rest was fully seated on its corresponding rest seat and abutment tooth in order to obtain data about the biomechanical behavior of the abutment tooth compared to the intact toothćs stress-distribution pattern. The results of our analyses are presented and analyzed qualitatively. The occlusal loading effect along the sound tooth exhibits a wider high-stress area, localized in correspondence with the occlusal enamel, than the restored teeth. This is due to the rigidity of the enamel. The reduction in the stress values occurs in the composite restoration, which is less rigid. Its lower rigidity allows larger cusp movements. The stress-distribution pattern of the restored tooth with the rest seat showed that introducing an occlusal restoration does not differ from the intact tooth globally, but locally. Our findings indicate that the composite rest-seat restoration absorbs the loading, so reducing the stresses inside the tooth\u27s structure.Postavitev kompozitnega popravila opore za odstranljive dele zobovja daje dobre estetske rezultate z minimalno intervencijo. Cilj tega članka je analizirati porazdelitev napetosti na zobu z zapornim sedežem s kompozitno zaporo in jo primerjati z biomehanskim vedenjem intaktnega zoba s predpostavko, da odloča razdelitev napetosti in deformacije intaktnemu zobu. Za to študijo sta bila na podlagi končnih elementov razvita dva različna modela. Prvi je tridimenzionalen (D) model intaktnega zoba, drugi pa je 3D-model zoba s kompozitno restoracijo in ustrezno pripravo zapornega sedeža, da bi tako dobili podatke o biomehanskem vedenju mostičnega opornika in o porazdelitvi napetosti v intaktnem zobu. Rezutati so prikazanai in analiziranikvalitativno. Zaporna obremenitev povzroči široko področje visoke napetosti v zdravem zobu zaradi stika s sklenino in ne restoriranega zoba. To je posledica velike togosti sklenine. Manjše so napetosti v manj togi kompozitni restoraciji, kar omogoča večje premik opornega vrha. Porazdelitev napetosti restoriranega zoba z opornim sedežem kaže, da uporaba zaporne restoracije ne vpliva globalno, ampak lokalno. Ugotovitve kažejo, da popravilo zob z oporo absorbira obremenitev, ker zmanjša napetosti v strukturi zoba