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Although clinicians routinely aim to provide a prosthesis with an accurate fit on implants, a degree of prosthesis misfit is inevitable. This exploratory pilot animal study evaluated the effects of framework vertical misfit and the timing of implant loading on implant position and screw loosening. Four implants were placed in healed ridges of each side of mandibles of 3 sheep. On the right side, 2 immediate frameworks were placed after 2 days. One framework was fitting, and the other one had a vertical gap of 0.5 mm on the distal implant. After 8 weeks (first review), the left side received 2 conventional frameworks with similar fit conditions to the right side. All animals were euthanized after 8 weeks (second review). At the first and second reviews, implant-level impressions were taken to measure the vertical displacement of distal implants, and the loosening torque values of the retaining screws were measured. The loosening torque values for the immediate fitting frameworks were considerably greater than the immediate misfitting frameworks. This was noticeable at the first review. At the second review, the loosening torque values were comparable to the immediate fitting and misfitting frameworks. Vertical implant displacement was observed for all misfitting frameworks. However, much greater implant displacement occurred under the immediate frameworks. Therefore, implant frameworks with vertical misfit in the present study were associated with less screw stability and more implant displacement. Retightening the retaining screws during the maturation of bone seemed to maintain the torque values.
Subject(s)
Dental Implants , Dental Prosthesis, Implant-Supported , Animals , Bone Screws , Mandible , Sheep , TorqueABSTRACT
INTRODUCTION: A dental impression is a negative imprint of an oral structure that can be used to produce a positive cast of a patient's teeth as a permanent record. The accuracy of the impression affects the accuracy of the cast, and a precise impression is needed in order to create prosthesis with optimal fitting. Minimization of misfit is an important aim in prosthesis science and dental implants. The aim of this study was to evaluate the effects of the materials and techniques used to take an impression on the vertical misfit of implant-supported, screw-retained, three-unit bridges. MATERIALS AND METHODS: The principal model used was an acrylic block with two ITI implants. A 1.5-mm abutment was attached to fixtures with torque of 25 N.cm. A base-metal framework was built on the abutment in the acrylic block. The abutments of the acrylic model were unscrewed and fixture-level impressions were made. The impression techniques included open/closed-tray techniques and the impression materials were polyether and polyvinyl siloxane. Forty acrylic custom trays were built for each impression. The marginal gap in the framework at three points (buccal, lingual, and distal) was measured using an optical microscope with ×250. RESULTS: It is demonstrated that in all 360 evaluated samples, the mean vertical misfit in polyether samples of molar and premolar teeth was significantly lower than in polyvinyl siloxane (P < 0.001 and P = 0.017, respectively) in all three locations of the molar and lingual premolar examined (buccal, lingual, and distal), the mean vertical misfit of the polyether samples was significantly lower than those of polyvinyl siloxane (P < 0.01). On the other hand, although the mean vertical misfit using the open-tray technique in the molar teeth was significantly lower than with the closed-tray method (P = 0.002), no statistical difference was seen between the open-tray and closed-tray technique in general (P = 0.87). CONCLUSION: Within the limitations of this study, the following conclusions can be drawn: The impression method had no effect on marginal discrepancy of 3-unit screw retained fixed partial dentures. A higher marginal accuracy was obtained using polyether impression material compared to polyvinyl siloxane.
ABSTRACT
BACKGROUND/AIMS: This study evaluated the teeth movement in maxillary dentures and mandibular implantsupported prostheses processed by microwave flasks. METHODS: A model mounted on articulator was used to manufacture Co-Cr frameworks. Pins were placed for measurements on the incisal edge of upper and lower central incisors (I), buccal cusp of first upper and lower premolars (PM), and mesiobuccal cusps of upper and lower second molars (M). Distances I-I (incisor to incisor), PM-PM (premolar to premolar), M-M (molar to molar), RI-RM (right incisor to right molar), and LI-LM (left incisor to left molar) were measured before and after processing using a microscope (0.0005 mm). Vertical misfit between abutment and implant platform was evaluated for regions A (left distal implant), B (left median implant), C (medial implant), D (right median implant), and E (right distal implant) in predetermined labial and lingual sites. Prostheses were divided into groups G1 - conventional flask, and G2 - experimental HH flask. Acrylic resin was microwaved at 1400 W (30% for 3 min, 0% for 3 min, and 60% for 3 min). Horizontal teeth displacement and vertical misfit between abutment and implant platform were considered before and after procedures. Data were submitted to three-way ANOVA and Tukey's test (α = 0.05). RESULTS: Except for M-M distance, the teeth showed displacements without statistical difference for prosthesis and flask factors. There was no significant difference for vertical misfit values for both flasks. CONCLUSION: Diferente flasks did not cause significant changes in the teeth displacement, except for M-M. Vertical misfit values were not influenced by the flasks.
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Aim: To evaluate vertical misfit and cement line quality of onlays cemented with resin luting cements using two different methods for removal of excess cement. Materials & Methods: Lithium di-silicate restorations were fabricated and cemented at 24 human molars that received onlay type preparations. The specimens were randomly divided in two groups (n = 12): Group 1 (G1) where cement excess was removed at pre-gel stage and Group 2 (G2) with cement excess was removed after polymerization. Vertical misfits measurements at cement line were performed twice, before and after cementation. Epoxy resin replicas were obtained from the specimens and cement line quality was analyzed with a scanning electron microscope before and after the finishing and polishing procedures. The replicas were also classified according to their condition in unsatisfactory, acceptable or good. Vertical misfits values were submitted to Student test (p < 0.05) and the quality line data were analyzed with Mann-Whitney for independent samples (p < 0.05) and Wilcoxon test for paired specimens (p < 0.05). Results: Vertical misfit and cement line quality presented no difference values to G1 (26.60 ± 8.0) and G2 (24.10 ± 8.0). However, finishing and polishing procedures affect positively the cement line quality in both groups (p = 0.59). Conclusion: The cement excess removal methods had no influence on vertical misfit and cement line quality for restorations. Finishing and polishing procedures improved the cement line quality in both groups.
Objetivo: Avaliar adaptação marginal e a influência do polimento sobre a linha de cimentação de restaurações cerâmicas cimentadas com cimento resinoso utilizando duas formas dois métodos de remoção do excesso do cimento. Métodos: Foram fabricadas restaurações em cerâmica reforçada por dissilicato de Lítio e cimentadas à vinte e quatro molares humanos que receberam preparos protéticos tipo onlay. Os corpos de prova foram divididos aleatoriamente em dois grupos (n = 12): Grupo 1 (G1) em que o excesso de cimento foi removido no estágio pré-gel e Grupo 2 (G2) em que o excesso de cimento foi removido após a polimerização. A mensuração da desadaptação marginal foi realizadas em dois momentos, antes e depois da cimentação. Réplicas em resina epóxi de todos os corpos de prova foram confeccionadas para avaliação da qualidade da linha de cimentação utilizando um microscópio eletrônico de varredura antes de depois dos procedimentos de acabamento e polimento e classificado como insatisfatório, aceitável e boas condições. Os valores de desadaptação foram submetidos ao teste t de Student (p < 0,05) e os dados de qualidade da linha de cimentação foram analisados pelo teste de Mann-Whitney para amostras independentes (p < 0,05) e pelo teste de Wilcoxon para amostras pareadas (p < 0,05). Resultados: A desadaptação marginal e a qualidade da linha de cimentação não apresentaram diferença significativa G1 (26,60 ± 8,0) e G2 (24,10 ± 8,0). Entretanto, os procedimentos de acabamento e polimento influenciaram positivamente a qualidade da linha de cimentação em ambos grupos (p = 0,59). Conclusão: O método de remoção do excesso de cimento não influenciou a adaptação ou a qualidade da linha de cimentação das restaurações cerâmicas. Os procedimentos de acabamento e polimento melhoraram a qualidade da linha de cimento nos dois grupo
Subject(s)
Dental Marginal Adaptation , Denture, Partial, FixedABSTRACT
OBJECTIVES: This study evaluated the influence of prosthetic screw material on joint stability in implantsupported dentures at two levels of fit. METHODS: Ten mandibular implant-supported dentures were fabricated. Twenty cast models were fabricated using these dentures. Four groups (n=10) were tested, according to the vertical fit of the dentures [passive and non-passive] and prosthetic screw materials [titanium (Ti) or gold (Au) alloy]. The one-screw test was performed to quantify the vertical misfits using an optic microscope. The loosening torque for the prosthetic screws was measured 24 hours after the tightening torque (10 Ncm) using a digital torque meter. Data were analyzed by two-way ANOVA and Tukey's test (alpha=0.05). RESULTS: Overall, dentures with passive fit and Ti screws resulted in significantly higher loosening torque of the prosthetic screws (p<0.05). No significant interaction was found between fit level and screw material (p=0.199). The prosthetic screw material and fit of implant-supported dentures have an influence on screw joint stability. Ti screws presented higher joint stability than Au screws and minimum of misfit should be found clinically to improve the mechanical behavior of the screw joint.
