Correlation Between Bone Density and Instantaneous Torque at Implant Site Preparation: A Validation on Polyurethane Foam Blocks of a Device Assessing Density of Jawbones.

PURPOSE: Bone density at implant placement sites is one of the key factors affecting implant primary stability, which is a determinant for implant osseointegration and rehabilitation success. Site-specific bone density assessment is, therefore, of paramount importance. Recently, an implant micromotor endowed with an instantaneous torque-measuring system has been introduced. The aim of this study was to assess the reliability of this system. MATERIALS AND METHODS: Five blocks with different densities (0.16, 0.26, 0.33, 0.49, and 0.65 g/cm(3)) were used. A single trained operator measured the density of one of them (0.33 g/cm(3)), by means of five different devices (20 measurements/device). The five resulting datasets were analyzed through the analysis of variance (ANOVA) model to investigate interdevice variability. As differences were not significant (P = .41), the five devices were each assigned to a different operator, who collected 20 density measurements for each block, both under irrigation (I) and without irrigation (NI). Measurements were pooled and averaged for each block, and their correlation with the actual block-density values was investigated using linear regression analysis. The possible effect of irrigation on density measurement was additionally assessed. RESULTS: Different devices provided reproducible, homogenous results. No significant interoperator variability was observed. Within the physiologic range of densities (> 0.30 g/cm(3)), the linear regression analysis showed a significant linear correlation between the mean torque measurements and the actual bone densities under both drilling conditions (r = 0.990 [I], r = 0.999 [NI]). Calibration lines were drawn under both conditions. Values collected under irrigation were lower than those collected without irrigation at all densities. The NI/I mean torque ratio was shown to decrease linearly with density (r = 0.998). The mean error introduced by the device-operator system was less than 10% in the range of normal jawbone density. CONCLUSION: Measurements performed with the device were linearly correlated with the blocks' bone densities. The results validate the device as an objective intraoperative tool for bone-density assessment that may contribute to proper jawbone-density evaluation and implant-insertion planning.

Mechanical Reliability Evaluation of an Oral Implant-Abutment System According to UNI EN ISO 14801 Fatigue Test Protocol.

PURPOSE: The aim of this in vitro study was to evaluate the mechanical reliability of a dental implant system by testing its maximum fracture load and mechanical performance under cyclic fatigue stress. METHODS: An experimental study according to the international standards (UNI EN ISO 14801: 2008) was performed using 13 implants (3.80 mm in diameter and 12 mm in length) with straight titanium abutments tightened to 30 N. Five samples were subjected to compression stress at break. Based on the mean fracture load value obtained in this test, the levels of dynamic loading range were set and were carried on at a frequency of 15 Hz for 5 × 10 cycles. RESULTS: The compression stress at break mean value of the tested implants was 430 N (SD ± 35.66 N). In the mechanical fatigue stress test, the fatigue limit for 5 × 10 load cycles was 172 N. CONCLUSIONS: The evaluated implant system proved to withstand considerable mechanical loads under the "worst-case" loading situation performed according to UNI EN ISO 14801 standard. The reliability of this test protocol makes it suitable to be accomplished for understanding and comparing mechanical properties of implant systems.

Evaluation of an endosseous oral implant system according to UNI EN ISO 14801 fatigue test protocol.

PURPOSE: The aim of this in vitro study was to evaluate the maximum fracture load and the mechanical performance to cyclic fatigue stress of a dental implant system. METHODS: An experimental study according to the international standards (UNI EN ISO 14801: 2008) was carried out using 15 implants (3.80 mm of diameter and 13 mm of length) with applied straight titanium abutment tightened to 30 N. Five samples were subjected to compression stress at break. Based on the mean fracture load value obtained in this test, the levels of dynamic loading range were set that were carried on at a frequency of 15 Hz for 5 × 10 cycles. RESULTS: The compression stress at break mean value of the tested implants was 499.40 N (SD ±50.1 N). In the mechanical fatigue stress test, the fatigue limit for 5 × 10 load cycles for all tested samples was 250 N. CONCLUSIONS: The evaluated implant system proved to withstand considerable mechanical loads under the "worst-case" loading situation performed according to UNI EN ISO 14801 standard. The reliability of this test protocol makes it suitable to be accomplished for understanding and comparing mechanical properties of other implant systems.

Limitations of push-out test in bond strength measurement.

INTRODUCTION: The push-out test has been widely performed to measure the bond strength of intracanal materials in dentistry. However, it is difficult to compare equitably the bond strengths from different testing specimens. The aim of this study was to investigate how a specimen's geometric parameters and the elastic moduli of dentin and intracanal filling materials may affect the bond strength measurement. METHODS: Finite element analysis was used to simulate a push-out test. A base model was established, and 3 parameters were modified: the diameter of the pin, the specimen's thickness, and the elastic modulus of the intracanal filler. The analytic stress results and the calculated bond strengths derived from the original formula for the push-out test were compared at the interfaces. RESULTS: Specifically, the following observations were made: the interfacial stress distributions are mostly unaffected when the ratio of the pin diameter to the specimen's diameter is less than 0.85, and the ratio of the specimen's thickness to the specimen's diameter is greater than 0.6. Two correction factors were suggested for fillers with diverse elastic moduli with respect to the dentin modulus. Two modified formulas for the push-out bond strength test for the test specimens using different bonded composite materials were proposed. CONCLUSIONS: The results showed that geometric parameters and materials have certain effects on the push-out bond strength. A more rigorous standard for the push-out test can be established for future applications.

Correlation of clinical performance with 'in vitro tests' of restorative dental materials that use polymer-based matrices.

OBJECTIVE: Review correlations of in vivo clinical performance with in vitro laboratory tests of restorative dental materials involving polymer-based matrices. Identify those factors interfering with the process. MATERIALS AND METHODS: An evidence-based dentistry approach was used to identify clinical trials, critical reviews, and meta-analyses involving correlations. Factors impacting meaningful correlations were reviewed. The limited bona fide correlations were reviewed. RESULTS: In vitro tests include physical, chemical, mechanical, and biological properties. Clinical research measurements routinely include 10-15 categories of clinical observations of performance such as color match, caries resistance, marginal integrity, surface texture, and others, but do not correspond well with laboratory properties. Clinical trials of restorative dental materials represent a small fraction of the total research in this arena (typically <10% of dental materials research over many years). Trials are generally short-term (2-5 years) and are designed primarily to test product "safety and efficacy." A large number of risk factors (operator, design, material, intraoral location, patient) affect clinical outcomes and are not simulated well in laboratories. Little long-term information exists for clinical performance other than on composite wear. Very few meaningful correlations of laboratory tests and clinical results are demonstrated. CONCLUSIONS/RECOMMENDATIONS: New studies should be focused on recovering restorations from service and characterizing them with the same tests as normally conducted in the laboratory. Many more long-term clinical trials that involve 10-20 years of observations are needed. Those trials should include planned restoration recovery to assess changes in laboratory properties of interest.

Implant reconstruction of a large mandibular defect following removal of a nonossifying fibroma.

The fixed implant-supported restoration of this mandibular surgical defect deliberately violated the principles of mandibular flexure, crown-to-implant ratio, and off-axis loading. A custom-made implant-mounted jig revealed no mandibular flexure in this patient, but crown-to-root ratios of up to 39:12 were unavoidable. The restoration has needed no maintenance for 14 years. This apparent success calls into question the blind application of prevailing clinical principles.

Validation of implant stability: a measure of implant permanence.

Implant stability is a requisite characteristic of osseointegration. Without it, long-term success cannot be achieved. Continuous monitoring in a quantitative and objective manner is important to determine the status of implant stability. Measurement of implant stability is a valuable tool for making decisions pertaining to treatment protocol and also improves dentist-patient communication. Owing to the invasive nature of histological analysis, various others methods have been proposed like radiographs, cutting torque resistance, reverse torque, modal analysis, resonance frequency analysis and Implatest® . This review focuses on objectives and various methods to evaluate implant stability.

Spotlight on bond strength testing--unraveling the complexities.

The variability in methods and outcomes of bond strength testing reports is well documented in the dental literature. Many studies lack important information, which impairs the ability to reproduce them as well as to compare them to other studies in the literature. In order to critically discuss the important issues around bond strength testing methods, and to move closer to at least standardizing the reporting of such studies, the Academy of Dental Materials held a conference in 2009 entitled Adhesion in Dentistry-Analyzing Bond Strength Testing Methods, Variables, and Outcomes. Short synopses of the presentations are presented in this article. This article also provides a list of the variables that should be reported in bond strength studies, regardless of testing methods, to be used by authors conducting future studies, as well as journal reviewers and editors. The goal is to provide guidance and a rationale for what should be included in a study so that reporting might be more standardized and to enhance the possibility that more meaningful comparisons and conclusions may be drawn across studies. The table lists detailed descriptions covering all aspects of testing procedures, including variables related to tooth substrate, restorative material, specimen preparation, pre-testing conditions, testing methods, data reporting and analysis.

Measuring bond strength between fiber post and root dentin: a comparison of different tests.

PURPOSE: the aim of this study was to evaluate the ability of bond strength tests to accurately measure the bond strength of fiber posts luted into root canals. MATERIALS AND METHODS: the test methods studied were hourglass microtensile (HM), push-out (PS), modified pushout (MP), and pull-out (PL). The evaluated parameters were: bond strength values, reliability (using Weibull analysis), failure mode (using confocal microscopy), and stress distribution (using finite element analysis). Forty human intact single-rooted and endodontically treated teeth were divided into four groups. Each group was assigned one of the test methods. The samples in the HM and PS groups were 1.0 ± 0.1 mm thick; the HM samples were hourglass shaped and the PS samples were disk shaped. For the PL and MP groups, each 1-mm dentin slice was luted with a fiber post piece. Three-dimensional models of each group were made and stress was analyzed based on Von Mises criteria. RESULTS: PL provided the highest values of bond strength, followed by MP, both of which also had greater amounts of adhesive failures. PS showed the highest frequency of cohesive failures. MP showed a more homogeneous stress distribution and a higher Weibull modulus. CONCLUSION: the specimen design directly influences the biomechanical behavior of bond strength tests.

Evaluation of test protocol variables for dental implant fatigue research.

OBJECTIVES: This work begins to explore the influence of cycling rate and environment on fatigue testing of dental implants according to the ISO protocol 14801. METHODS: Twenty-four Straumann implants (4.1 mm x 12 mm) were tested up to five million cycles per ISO 14801: loaded at either 2 or 30 Hz in room air at 25 degrees C or normal saline at 37 degrees C (n=6 per group). Implant displacements/cycle were captured during all testing. Fracture-surface features were examined using scanning electron microscopy (n=12). Two complimentary methods were developed to estimate fatigue crack growth rates. RESULTS: Failures (bulk fracture) were found to be bi-modally distributed, either <350,000 cycles or >1.5 million cycles at both cycling rates. Following initial crack formation, fatigue crack growth required merely 1100-4200 cycles to failure. Initial crack pop-in was statistically more likely under 2 Hz than 30 Hz (chi(2), p<0.05) but testing in air and normal saline were equivalent in terms of likelihood of fracture versus runout (chi(2), p>0.6). On a microscopic level, fatigue crack growth rates appears to be similar at 2 and 30 Hz, but may be slower in the presence of saline versus dry at 2 Hz. SIGNIFICANCE: Implant failure under fatigue conditions involved "classic" damage mechanisms. Failure appears more likely at 2 Hz than 30 Hz for reasons that remain to be elucidated. Saline may enable chemically assisted crack growth involving grain boundaries during the stage of fatigue crack growth, but did not influence likelihood of failure.

An initial investigation on torsional properties of nickel-titanium instruments produced with a new manufacturing method.

A new manufacturing process involving twisting of a ground blank combined with heat treatment has been recently developed to produce nickel-titanium rotary files for root canal preparation. The aim of this study was to compare torsional resistance of prototype instruments produced using the new manufacturing method versus traditional nickel-titanium instruments produced by the customary grinding process. Twenty prototypes instruments of the same design and dimensions were divided in two groups of 10 each, according to the different manufacturing method. A file-testing apparatus specifically designed to perform torsional testing was used in accordance with the International Organization for Standardization 3630-1. The results indicated that instruments manufactured by the new manufacturing process demonstrated significantly higher average maximum torque levels than those manufactured by the existing grinding process (P < 0.05). Since instruments design and dimensions of the instruments were the same, the different manufacturing process could be the only explanation for this improvement in torsional resistance.

Axial shrinkage-stress depends upon both C-factor and composite mass.

OBJECTIVES: To measure and then mathematically model polymerization stress-dependence upon systematic variations of C-factor (bonded/unbonded area ratio) for the Bioman instrument [1], recording stress by free cantilever-beam deflection; compliance 1.5 microm/MPa. METHODS: A light-cured resin-composite (RZD103; Ivoclar) with 57% (v/v) 450 nm filler was studied. Facing surfaces: glass slab and steel rod-end, constituting the Bioman test chamber, being perpendicular to the measured axial stress-direction, were varied: (a) with rod-diameters (phi), from 1 to 10mm in 1mm increments (with 0.8mm gap height); and then (b) with gap heights (h) in 16 steps from 0.05 to 1.50mm (with phi=10mm). For each h and phi combination, giving C-factors ranging from 0.6 to 100, shrinkage-stress was recorded for 1h from start of 40s irradiation at 600 mW cm(-2) for photo-polymerization at 23 degrees C (n=3). Shrinkage-stress (S(sigma)) was plotted directly as functions of h, phi, and C and also per unit composite mass, (S(sigma)g(-1)). ANOVA and Tukey's statistics were applied. RESULTS: Series A-diameter variation; with C-factor increasing from 0.6 to 6, gave an exact exponential decrease in S(sigma) from 45 to 8 MPa. Series B-height variation; with C-factor increasing from 3 to 100, gave increasing S(sigma) from 1 to 8 MPa. Since composite mass played an equally dominant role, plots of stress-variations per unit composite mass, (S(sigma)g(-1)) separated these effects, confirming progressive off-axial stress-relief with increasing h. SIGNIFICANCE: (i) Values of h=0.8 and phi=10mm, recommended [1] for Bioman use, were confirmed as appropriate. Every lab instrument for measuring S(sigma) necessarily embodies specific C-factors and compliance values in the instrument design. (ii) Configuration (C) factor is recognized as an important parameter affecting manifestation of shrinkage-stress within restorative cavities and luting gaps. However, the restorative mass must equally be considered when translating shrinkage-science into specific clinical recommendations.

Comparison of wire loop and shear blade as the 2 most common methods for testing orthodontic shear bond strength.

INTRODUCTION: The purpose of this study was to compare 2 common methods of measuring orthodontic shear bond strength. METHODS: Brackets were bonded to 40 bovine incisors, and the teeth were mounted in a jig. The teeth were paired for symmetry, and the pairs were divided into 2 groups for debonding. In group 1, the shear force was applied with a rectangular wire under the tie wings. In group 2, a shearing blade applied force to the junction between the bracket base and the adhesive. RESULTS: Debonding with the shear blade produced higher (24.86 +/- 7.44 MPa) and more dispersed (coefficient of variation = 29.91%) bond strengths compared with the wire loop (17.12 +/- 3.16 MPa, coefficient of variation = 18.44%). Adhesive remnant index (ARI) scores showed a tendency for cohesive failure in the enamel in the shear-blade group (ARI = 5) compared with adhesive failure (ARI = 3) in the wire group. CONCLUSIONS: There is a need to standardize bond strength tests. The results of this study favor the wire-loop method, which might have more similarity to clinical loads. The regression formula might make comparison of previous studies easier.

Dimensional stability of distances between posterior teeth in maxillary complete dentures / Estabilidade dimensional de distâncias entre dentes posteriores em prótese total superior

The aim of this study was to assess the displacement of posterior teeth in maxillary complete dentures stored in water at 37°C. Twenty acrylic resin-based maxillary complete dentures were constructed with the anterior teeth arranged in normal overlap and the posterior teeth in Angle class I. Metallic pins were placed on the labial cusp of the first premolars (PM), and on the mesiolabial cusp of the second molars (M). The final acrylic resin pressing was made in a metallic flask with aid of the RS tension system, and polymerized in a moist-hot cycle at 74°C for 9 hours. The dentures were deflasked after cooling in their own polymerizing water or after cooling in polymerizing water plus bench storage for 3 hours, and stored in water at 37°C for periods of 7, 30, and 90 days. Following deflasking and after each storage period tested, the PM-PM (premolar to premolar), M-M (molar to molar), LPM-LM (left premolar to left molar), and RPM-RM (right premolar to right molar) distances were measured with an STM Olympus microscope, with an accuracy of 0.0005 mm. Collected data were submitted to ANOVA and Tukey's test (5 percent). There was no statistically significant difference for the PM-PM, M-M, and LPM-LM distances after all storage periods when the flask cooling methods were considered. With exception of the RPM-RM distance after the 30-days water plus bench storage period, the other distances remained statistically stable.

O propósito deste trabalho foi verificar a movimentação de dentes posteriores em prótese total superior armazenada em água a 37°C. Vinte próteses totais superiores foram confeccionadas com resina acrílica, com os dentes anteriores em transpasse normal e os posteriores em Classe I de Angle. Pinos metálicos foram colocados na cúspide vestibular dos primeiros pré-molares (PM) e cúspide mésio-vestibular dos segundos molares (M). A prensagem final da resina acrílica foi feita em mufla metálica com auxílio do dispositivo RS de contensão e a polimerização em ciclo de água a 74°C durante 9 horas. As próteses foram demufladas após esfriamento em água de polimerização ou em água de polimerização mais armazenagem em bancada por 3 horas e armazenadas em água a 37°C pelos períodos de 7, 30 e 90 dias. Após demuflagem e após cada período de armazenagem em água, as distâncias PM-PM (pré-molar a pré-molar), M-M (molar a molar), PMD-MD (pré-molar direito a molar direito) e PME-ME (pré-molar esquerdo a molar esquerdo) foram medidas com microscópio Olympus STM, com precisão de 0,0005 mm. Os dados coletados foram submetidos à análise de variância e ao teste de Tukey com significância de 5 por cento. Em todos os períodos de armazenagem, as distâncias PM-PM, M-M e PME-ME não apresentaram diferenças estatisticamente significativas quando as muflas foram esfriadas pelos dois métodos. Com exceção da distância PMD-MD no período de 30 dias de armazenagem em água mais bancada, as demais distâncias permaneceram sem diferença estatística significativa.

Effect of changing a test parameter on the shear bond strength of orthodontic brackets.

The purpose of this study was to determine the effect of changing the crosshead speed of the testing machine on the shear bond strength of orthodontic brackets to enamel while standardizing all the other variables. Forty freshly extracted human molars were bonded using the Transbond XT adhesive system (3M Unitek, Monrovia, Calif). The teeth were randomly divided into two groups. In group I, the shear bond strength was measured at a crosshead speed of 5.0 mm/min, and in group II the shear bond strength was measured at a crosshead speed of 0.5 mm/ min. Within half an hour from the initial bonding of each tooth, an occlusogingival load was applied to the bracket, producing a shear force at the bracket-tooth interface. This was accomplished by using the flattened end of a steel rod attached to the crosshead of a Universal Test Machine (Zwick GmbH & Co, Ulm, Germany). The t-test results (t = 2.71) indicated that there was a significant difference (P = .014) in the shear bond strengths between the group tested at a crosshead speed of 5.0 mm/min and the group tested at a crosshead speed of 0.5 mm/min. The mean shear bond strengths for the two groups were 7.0 +/- 4.6 MPa and 12.2 +/- 4.0 MPa, respectively. These findings indicated that it is important to identify the parameters included in shear bond testing in order to enable meaningful comparisons of the performance of different materials.

Method for immediate measurement of in vitro bond strength of bonded direct esthetic restorations.

There are many different ways to measure the bond strength of direct esthetic restorations to various dental substrates. Unfortunately, most methods cannot measure bond strengths immediately after a restoration has been placed. This lack of clinically-relevant information seriously affects the clinician's ability to select and use various bonding agents and procedures. The aim of this article is to provide a very detailed method for immediate measurement of in vitro bond strengths of direct bonded esthetic restorations. It focuses on the steps that should be taken to select and prepare various tooth substrates for bond strength testing, the steps to "restore" various tooth substrates, and to measure the immediate in vitro bond strength. A fundamental understanding of a standardized testing protocol should provide clinicians with a clearer appreciation of bond strengths associated with various bonding procedures.

Stress distribution of abutments and base displacement with precision attachment- and telescopic crown-retained removable partial dentures.

Five types of removable partial dentures (two attachment dentures, two telescopic dentures and one clasp denture) were designed. The two attachment dentures were retained by the rigid-precision attachments with or without a stabilizing arm, and the two telescope dentures were retained with cone telescope crowns with or without cross-arch stabilization. The stresses acting on abutment teeth and denture bases and the movements of denture bases were investigated, and the influences of denture design were clarified. The stress acting on a terminal abutment tooth retained by a rigid-precision attachment or cone telescopic crown was larger than that acting on a terminal abutment tooth retained by a clasp. The attachment dentures tended to concentrate more stress at the terminal abutment tooth than did the telescopic dentures. The stress of denture base of an attachment denture and a telescopic denture was less than that of a clasp denture. There was no difference between the stresses of attachment and telescopic dentures. The displacement of the denture base tended to be less when the denture was designed with a rigid connection for the retainer and with cross-arch stabilization.