Leonardo Flores Luthi

Influence of the casting technique and dynamic loading on screw detorque and misfit of single unit implant-supported prostheses.

Abstract Objective. This study aimed to evaluate the influence of the casting procedure and cyclic loading of prosthetic frameworks on detorque of prosthetic screws and marginal misfit of single unit implant-supported prostheses. Materials and methods. Twenty specimens were obtained, each one consisting of a set of an implant (external hexagon 3.75 × 13 mm – Branemark type), a prosthetic abutment (entirely calcinable or overcasted UCLA) and a prosthetic screw. After the specimens were obtained, the prosthetic screws were tightened with 30 Ncm torque and released 24 h later in order to evaluate initial detorque. The screws were retightened and marginal gaps were assessed. All specimens were submitted to 106 loading cycles, performed with 2 Hz frequency and 130 N load. The specimens were re-evaluated for marginal misfit and detorque after the mechanical loading (final marginal misfit/final detorque). The results were submitted to analysis of variance for repeated measurements, followed by Tukey HSD test (α = 0.05). Results. No statistically significant differences were found on detorque values of the prosthetics screws for all groups and intervals evaluated (p = 0.8922). The entirely calcinable abutments showed higher initial marginal misfit compared to the overcasted ones (p = 0.0438). There was no statistically significant difference on marginal misfit before and after mechanical loading for both groups (p > 0.05). Conclusions. It can be concluded that the overcasted abutments showed lower misfit values when compared to the entirely casted abutments. No difference was observed on detorque values of prosthetic screws. After mechanical loading there was no difference on marginal misfit and detorque between the groups.

An in vitro comparison between two different designs of sagittal split ramus osteotomy.

Objectives To evaluate the influence of the type of osteotomy in the inferior aspect of the mandible on the mechanical performance. Materials and Methods The study was performed on 20 polyurethane hemimandibles. A sagittal split ramus osteotomy (SSRO) was designed in 10 hemimandibles (group 1) with a vertical osteotomy in the buccal side (second molar level) and final osteotomy was performed horizontally on the lingual aspect, while the mandible body osteotomy was finalized as a straight osteotomy in the basilar area, perpendicular to the body. For group 2, the same osteotomy technique was used, but an oblique osteotomy was done in the basilar aspect of the mandibular body, forming continuity with the sagittal cut in the basilar area. Using a surgical guide, osteosynthesis was performed with bicortical screws using an inverted L scheme. In both groups vertical compression tests were performed with a linear load of 1 mm/min on the central fossa of the first molar and tests were done with models made from photoelastic resin. Data were analyzed using Students t-test, establishing a statistical significance when P <0.05. Results A statistical difference was not observed in the maximum displacements obtained in the two osteotomies (P <0.05). In the extensiometric analysis, statistically significant differences were identified only in the middle screw of the fixation. The photoelastic resin models showed force dissipation towards the inferior aspect of the mandible in both SSRO models. Conclusion We found that osteotomy of the inferior aspect did not influence the mechanical performance for osteosynthesis with an inverted L system.

Osteotomía Sagital de Rama Mandibular con Osteosíntesis en L Invertido: Estudio Mecánico con Fotoelasticidad

El objetivo de esta investigacion es identificar las tensiones presentes en tornillos de osteosintesis utilizados en la fijacion de la osteotomia sagital de rama mandibular (OSRM). Se utilizaron dos modelos de OSRM realizados con resina fotoelastica donde el grupo 1 presentaba una osteotomia basilar recta mientras que el grupo 2 presentaba una osteotomia basilar angulada; en ambos se utilizo el sistema de L invertido para la osteosintesis con tornillos 2.0 de 13 mm de longitud. Posteriormente el sistema fue instalado en un pilar sobre la maquina Instrom, donde se aplico una carga vertical de 1 mm/minuto hasta conseguir el desplazamiento de 3 mm; el punto de carga estuvo en la fosa central del primer molar. La distribucion de franjas mostro mayor tension en el tornillo mas proximo de la osteotomia en ambos grupos; en el grupo 2 se produjo una diseminacion de fuerzas levemente hacia la basilar y en el grupo 1 se mantuvo la diseminacion a traves de la linea oblicua. Se puede concluir que ambas osteotomias mandibulares son eficientes en la distribucion de cargas y que no se observan diferencias cualitativas entre tornillos en terminos de cantidad de diseminacion de energia.

Strain gauges's analysis on implant-retained prosthesis' cast accuracy.

INTRODUCTION A proper cast is essential for a successful rehabilitation with implant prostheses, in order to produce better structures and induce less strain on the implants. AIMS The aim of this study was to evaluate the precision of four different mold filling techniques and verify an accurate methodology to evaluate these techniques. MATERIALS AND METHODS A total of 40 casts were obtained from a metallic matrix simulating three unit implant-retained prostheses. The molds were filled using four different techniques in four groups (n = 10): Group 1 - Single-portion filling technique; Group 2 - Two-step filling technique; Group 3 - Latex cylinder technique; Group 4 - Joining the implant analogs previously to the mold filling. A titanium framework was obtained and used as a reference to evaluate the marginal misfit and tension forces in each cast. Vertical misfit was measured with an optical microscope with an increase of 120 times following the single-screw test protocol. Strain was quantified using strain gauges. Data were analyzed using one-way ANOVA (Tukeys test) (α =0.05). The correlation between strain and vertical misfit was evaluated by Pearson test. RESULTS The misfit values did not present statistical difference (P = 0.979), while the strain results showed statistical difference between Groups 3 and 4 (P = 0.027). CONCLUSIONS The splinting technique was considered to be as efficient as the conventional technique. The strain gauge methodology was accurate for strain measurements and cast distortion evaluation. There was no correlation between strain and marginal misfit.

A new portable vibrator for plaster pouring: effect on the marginal fit at cylinder-abutment

Objective The aim of this study was to test a new portable vibrator for plaster pouring (developed for this purpose), comparing the effect of its use on the accuracy of working cast of implant-supported restorations to the conventional vibrator. Material and methods From a master cast with 2 implants, 30 transfer moldings were made randomly and divided into three groups: Group I (GI): pouring performed in an outsourced dental laboratory with conventional plaster vibrator (10 casts), Group II (GII): pouring performed in the laboratory of the Federal University of Santa Catarina (UFSC) with conventional plaster vibrator (10 casts) and Group III (GIII): pouring performed with the portable vibrator fabricated for this study (10 casts). The position of the analogue and marginal adaptation of the infrastructure were verified by testing the single screw on the master model and on the working model. The measurement of misfit was blindly performed with a precision microscope and analyzing unit, Quadra-Check 200. The data were statistically analyzed by analysis of variance (ANOVA) and the Holm-Sidak test (α=0.05). Results Means±standard deviations were as follows: GI: 19.19±4.73 µm; GII: 21.72±5.41 µm; GIII: 13.5±2.39 µm (P<0.05), with GIII significantly lower as compared to the other groups. Conclusion Within the limitations of this study, it was concluded that a greater accuracy of working cast was achieved when a portable vibrator was used for casting molds.

Correlação entre o desajuste marginal e a tensão gerada sobre os implantes

A inducao de tensoes ao implante e ao tecido osseo peri-implantar pode ser responsavel pela reabsorcao tecidual e pela perda do implante. Proteses com o minimo desajuste marginal sao desejadas, acreditando-se na geracao de menores valores de tensao as fixacoes. No entanto, nao se tem certeza desta correlacao, uma vez que a literatura nao apresenta resultados confiaveis que venham a elucidar tal aspecto. Assim, o objetivo deste trabalho foi verificar se existe correlacao entre os valores de desajuste marginal e de tensao gerados as fixacoes pelo parafusamento de infraestruturas implanto-retidas. Foram obtidas dez infraestruturas em titânio fundido, utilizando-se matriz metalica contendo dois implantes conectados a pilares conicos para construcoes multiplas. As infraestruturas foram aleatoriamente avaliadas quanto aos desajustes marginais mediante o teste do parafuso unico e observacao em microscopio otico (120X). As tensoes nas fixacoes foram avaliadas por extensometria. A media de desajuste marginal foi 118,07 (58,61) μm e a media de tensao, 580,06 (253,93) gf. O teste de Pearson foi utilizado, mostrando nao haver correlacao entre desajuste marginal e tensao (-0,072), com p = 0,842. A presenca e a intensidade do desajuste marginal, por si so, nao sao indicadores seguros no prognostico da geracao de tensoes as fixacoes.