Nilza Pereira da Costa

Preload and torque removal evaluation of three different abutment screws for single standing implant restorations

Several authors still consider the mechanical problems of fracture and component loosening as the main causes of failure of implant-supported restorations. The purpose of this in vitro study was to compare the preload of three types of screw for transmucosal abutment attachment used in single implant-supported prosthesis through strain gauge and removal torque measurements. Three external hex fixtures were used, and each received a transmucosal abutment (Cera One®), which was fixed to the implant with its respective screw: Group A- gold screw, Group B- titanium screw and Group C- surface-treated titanium screw (Ti-Tite®). Ten screws of each type were attached applying a 30.07±0.28 Ncm torque force and maintained in position for 5 minutes. After this, the preload values were measured using strain gauges and a measurement cell. Gold screws presented higher preload values (131.72±8.98 N), followed by surface-treated titanium screws (97.78±4.68 N) and titanium screws (37.03±5.69 N). ANOVA (p<0.05) and Tukeys test (p<0.05) were applied. Statistically significant differences were found among the groups for both preload and removal torque values. In conclusion, gold screws may be indicated to achieve superior longevity of the abutment-implant connection and, consequently, prosthetic restoration due to greater preload values yielded.

Evaluation of mandibular implant sites: correlation between panoramic and linear tomography

The reliability of the linear tomography and panoramic radiography made with X-ray equipment was evaluated (Vera View Scope X-600; Morita). The sample was composed of 20 dry human hemimandibles, in which the area selected for analysis was 1.5 cm distal from the limit set before the mental foramen. Four measurements were made. The images obtained were drawn on acetate paper and the hemimandibles cut at the demarcated area. The measurements were made using a digital electronic pachymeter. The values found for the radiographic images were compared to those obtained in the mandibular specimens and submitted to statistical evaluation by the Wilcoxon test. It was concluded that both techniques were reliable for the accomplishment of vertical linear measurements in the selected area. However, a 2.0 mm safety margin is recommended.

Influence of soft tissues on mandibular gray scale levels

The purpose of this study was to analyze the gray levels, expressed in pixels, of the mandibular retromolar region, with regard to the influence of muscular and fat soft tissues near this region. Fifteen dry mandibles were X-rayed with the presence of soft tissue simulators. The radiographs were digitized and evaluated by Digora software. A one cm thick layer of wax was used as a simulator of the muscular soft tissue. Animal fat samples of different thicknesses - 0.5, 1.0, 1.5 and 2.0 cm - were used as a simulator of the fat soft tissue. Results showed that the fat soft tissue simulator influenced the gray level values in pixels of the mandibular retromolar region when analyzed in different thicknesses using the Digora digitized image software.

Optical density and chemical composition of microfilled and microhybrid composite resins

This study evaluated the optical density of two microfilled and two microhybrid resins, as well as the composition of these materials with regard to their optical density. Cavities prepared in 12 2-mm- or 4-mm-thick acrylic plastic plates were filled with Z250 (3M-ESPE), A110 (3M-ESPE), Charisma (Heraeus-Kulzer) and DurafillVS (Heraeus-Kulzer). The resin increments (2-mm-thick) were light-cured for 40 s. Three 0.12-s radiographic exposures were made of each #2 acrylic plastic plate. DenOptix system optical plates were used to obtain the digital images. Three readings of the composite resin surface were made in each radiograph, totalizing 216 readings. The mean of highest and lowest grey-scale values was obtained. Two specimens of each composite resin were prepared for SEM analysis of the chemical elements related to optical density, using energy dispersive x-ray analysis (EDX). The results were subjected to Shapiro-Wilks test, ANOVA, Tukeys test at 1% level of significance and Pearsons correlation. The mean grey-scale values at 2 mm and 4 mm were: Z250 = 154.27a and 185.33w; A110 = 46.77b and 63.05y; Charisma = 163.40c and 200.46z; DurafillVS = 43.92b and 58.99x, respectively. Pearsons test did not show any positive correlation between optical density and percentage weight of optical density chemical elements. It was concluded that the microhybrid resins had higher optical density means than the microfilled resins; among the evaluated resins, Charisma had the highest optical density means.

Accuracy of linear measurements before and after digitizing periapical and panoramic radiography images

The aim of this study was to evaluate the accuracy of linear measurements made on conventional and digitized periapical and panoramic radiographic images of dry human hemi-mandibles. Images from the posterior region of 22 dry human hemi-mandibles were obtained by conventional panoramic and periapical radiography technique. Using a digital caliper, 3 vertical measurements were marked directly on the dry hemi-mandibles (reference measurements) as well as on the tracing from the conventional radiographic images of the specimens made onto acetate paper sheet: Distance 1: between the upper limit of the alveolar ridge and the lower limit at the mandible base; Distance 2: between the upper limit of the alveolar ridge and the upper limit of the mandibular canal; Distance 3: between the lower limit of the mandibular canal and the lower limit of the mandible base. Next, the radiographs were digitized and the three measurements were made on the digital images using UTHSCSA Image Tool software. Data were analyzed statistically by one-way ANOVA (α=0.05). There was no statistically significant differences (p>0.05) between periapical and panoramic radiographs or between the measurements recorded using the digital caliper and UTHSCSA software compared with dry mandible specimens for Distances 1 (p=0.783), 2 (p=0.986) and 3 (p=0.129). In conclusion, the radiographic techniques evaluated in this study are reliable for vertical bone measurements on selected areas and the UTHSCA Image Tool software is an appropriate measurement method.

Accuracy of periapical radiography, panoramic radiography and computed tomography for examining the mental foramen region

Purpose: To determine the accuracy of different radiographic methods for bone height estimation at the mental foramen area. Methods: Twenty dry human hemimandibles were examed by using periapical and panoramic radiography, and computed tomography. An electronic digital caliper was used to measure the tracings obtained from the radiographies in three different times (groups A1, A2 and A3) and in the cross-sectioned hemimandibles (group B). Measurements consisted of: Measure 1 - from the upper limit of the alveolar ridge to the upper limit of the mental foramen; Measure 2 - from the upper limit of the mental foramen to the inferior limit of the cortical bone of the base of the jaw; Measure 3 - from the upper limit of the alveolar ridge to the inferior limit of the cortical bone of the base of the jaw. Data were analyzed with Student-t and Friedman tests. Results: The average difference values in Measure 1 were 0.33 mm, 0.35 mm and 0.85 mm for the periapical radiography, computed tomography and panoramic radiography, respectively (confidence intervals of 0.17 mm to 0.49 mm, 0.18 mm to 0.53 mm and 0.38 mm to 1.32 mm, respectively). Panoramic radiographies showed the greatest differences in Measures 2 and 3, with average values of 1.05 mm and 1.93 mm, respectively. Conclusion: Periapical radiography and computed tomography showed the best accuracy. A safety margin for surgical purposes has been suggested.

A Comparison between Panoramic Digital and Digitized Images to Detect Simulated Periapical Lesions Using Radiographic Subtraction

This study compared digital and digitized panoramic radiographs to detect incipient periapical lesions using the digital subtraction radiography (DSR) technique. Bone defects were created in 77 apical sites of dried human mandibles through the application of 70% perchloric acid. Conventional and digital radiographs were obtained twice at time zero and 2, 4, and 6 hours after application of the acid solution. Conventional radiographs were digitized by using the same attributes than direct digital radiographs. The baseline images were subtracted of the negative control and experimental groups and assessed by an experienced and blinded observer who assigned score 0 (normal) or 1 (mineral loss) to each image. The sensitivity of both modalities was statistically different in relation to experimental times. The percentage of correct responses significantly increased regarding experimental times. The specificity was high both for digitized and digital images. DSR of panoramic images, both digitized and digital, allows for the diagnosis of incipient-simulated periapical lesions with no differences in their performance.

Evaluation of the quality of different endodontic obturation techniques by digital radiography

ObjectivesThis study was aimed to evaluate different endodontic obturation techniques (Thermafil, lateral condensation, and Tagger’s hybrid technique) regarding the homogeneity of the obturation radiopacity.Materials and methodsSeventy roots of human upper central incisors were filled using the Thermafil system, lateral condensation. and Tagger’s hybrid technique. Radiopacity of the filling was evaluated based on mean of grey levels, and its homogeneity was assessed by the coefficient of variation (CV), analyzing the histograms obtained of digitized and digital radiographs.ResultsThe increase in mean grey levels (p < 0.001) and reduction in the CV (p < 0.05) were higher for Tagger’s hybrid technique compared with other methods.ConclusionsTagger’s hybrid technique provided better homogeneity of the obturation radiopacity and better apical sealing compared with lateral condensation technique.Clinical relevanceThe results suggest that Tagger’s hybrid technique provided the best compaction of the root canal filling material, an important factor for the sealing of obturations and, consequently, for the effectiveness of treatment.

Seqüela após redução de fratura zigomática empregando fio de Kirschner: relato de caso.

In this study we present and discuss a case of a patient in which a Kirschner wire was used for fixation of a fractured zygomatic bone. The Kirschner wire was not removed after four weeks as recommended in the literature but only after behaving as foreign body.

Effects of radio-opacifier addition in dental impression material.

OBJECTIVE The aim of this in vitro study was to determine the effects of barium sulfate addition in two dental impression materials previously proved as radiolucent. MATERIALS AND METHODS An irreversible hydrocolloid (IH) and polyether (PE) were tested for optical density, linear dimension stability and detail reproduction. STATISTICAL ANALYSIS USED The optical density data were submitted to Kolmogorov-Smirnov normality test and compared with two-way ANOVA and Tukey (alpha=0.05). RESULTS The results of optical density (pixel) were: IH control 45.24 f (+/-7.6), PE control 54.93 e (+/-4.45), PE 5Wt% 60.43 d (+/-6.27), IH 1Wt% 61.54 cd (+/-5.3), PE 1Wt% 66.9 bc (+/-5.05), IH 5Wt% 67.17 b (+/-6.01), PE 10Wt% 84.55 a (+/-5.14), IH 10Wt% 85.33 a (+/-5.53). On detail reproduction, polyether control was able to copy the 6 microm line. Adding 1 or 5Wt% of barium sulfate have not change this characteristic. For the irreversible hydrocolloid, the control group was able to copy a line with 14 microm, however, adding 1Wt% barium sulfate, the capability decreased to 22 microm. Adding barium sulfate in the polyether promoted an increase in between the copied lines, for the control, the average distance was 931.6 microm, 936 microm to 1Wt% and 954.5 microm to 5 Wt%. For the IH, the control presented 975 microm in comparison to 987.25 microm for 1 Wt% samples. CONCLUSION The addition of barium sulfate was capable of increasing significantly the optical density of tested material, have changed the linear dimension stability, however, have not interfered in detail reproduction only for PE.