Shih-Hao Huang

The Effect of Rubber Dam Usage on the Survival Rate of Teeth Receiving Initial Root Canal Treatment: A Nationwide Population-based Study

INTRODUCTION It is well-known that the usage of rubber dams during root canal treatment (RCT) improves infection control and treatment efficacy and protects patients. However, the effect of rubber dam usage on endodontic outcomes remain uncertain. The aim of the present study was to investigate whether rubber dam usage affects the survival rate of initial RCT using a nationwide population-based database. METHODS A total of 517,234 teeth that received initial RCT between 2005 and 2011 met the inclusion criteria and were followed until the end of 2011. Univariate and multivariate Cox proportional hazards models were used to estimate the effects of rubber dam usage on the risk of tooth extraction after initial RCT. RESULTS Of the 517,234 teeth, 29,219 were extracted, yielding a survival rate of 94.4%. The survival probability of initial RCT using rubber dams after 3.43 years (the mean observed time) was 90.3%, which was significantly greater than the 88.8% observed without the use of rubber dams (P < .0001). After adjusting for age, sex, tooth type, hospital level, tooth scaling frequency per year after RCT, and systemic diseases, including diabetes and hypertension, the tooth extraction hazard ratio for the RCT with rubber dams was significantly lower than that observed for RCT without rubber dams (hazard ratio = 0.81; 95% confidence interval, 0.79-0.84). CONCLUSIONS The use of a rubber dam during RCT could provide a significantly higher survival rate after initial RCT. This result supports that rubber dam usage improves the outcomes of endodontic treatments.

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 specimens 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 specimens 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 specimens diameter is less than 0.85, and the ratio of the specimens thickness to the specimens 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.

A novel dentin bond strength measurement technique using a composite disk in diametral compression

New methods are needed that can predict the clinical failure of dental restorations that primarily rely on dentin bonding. Existing methods have shortcomings, e.g. severe deviation in the actual stress distribution from theory and a large standard deviation in the measured bond strength. We introduce here a novel test specimen by examining an endodontic model for dentin bonding. Specifically, we evaluated the feasibility of using the modified Brazilian disk test to measure the post-dentin interfacial bond strength. Four groups of resin composite disks which contained a slice of dentin with or without an intracanal post in the center were tested under diametral compression until fracture. Advanced nondestructive examination and imaging techniques in the form of acoustic emission (AE) and digital image correlation (DIC) were used innovatively to capture the fracture process in real time. DIC showed strain concentration first appearing at one of the lateral sides of the post-dentin interface. The appearance of the interfacial strain concentration also coincided with the first AE signal detected. Utilizing both the experimental data and finite-element analysis, the bond/tensile strengths were calculated to be: 11.2 MPa (fiber posts), 12.9 MPa (metal posts), 8.9 MPa (direct resin fillings) and 82.6 MPa for dentin. We have thus established the feasibility of using the composite disk in diametral compression to measure the bond strength between intracanal posts and dentin. The new method has the advantages of simpler specimen preparation, no premature failure, more consistent failure mode and smaller variations in the calculated bond strength.

Diametral compression test with composite disk for dentin bond strength measurement – Finite element analysis

OBJECTIVE A novel technique using a composite disk under diametral compression was presented in a previous study for measuring the bond strength between intracanal posts and dentin. This study deals with the stress distribution within the composite disk to allow the bond strength to be calculated accurately. The effects of changing geometrical and material parameters on the post-dentin interfacial stress are also evaluated. METHODS The finite element method with 3D models is used to analyze the stress distribution and to carry out the sensitivity analysis. Progressive post-dentin interfacial debonding is also simulated to better understand the failure process observed in experiments. RESULTS Material mismatch causes stress concentrations at the interfaces. The results are presented as correction factors to be used in conjunction with the analytical solution for a homogeneous disk. Comparison between the stresses at the post-dentin interface and those in dentin confirms that interfacial debonding will take place prior to fracture in the dentin. SIGNIFICANCE The numerical solutions presented here will facilitate the adoption of the composite disk in diametral compression for bond strength measurement.

A novel dental implant abutment with micro-motion capability—Development and biomechanical evaluations

OBJECTIVE The aim of this study was to develop a novel dental implant abutment with a micro-motion mechanism that imitates the biomechanical behavior of the periodontal ligament, with the goal of increasing the long-term survival rate of dental implants. METHODS Computer-aided design software was used to design a novel dental implant abutment with an internal resilient component with a micro-motion capability. The feasibility of the novel system was investigated via finite element analysis. Then, a prototype of the novel dental implant abutment was fabricated, and the mechanical behavior was evaluated. RESULTS The results of the mechanical tests and finite element analysis confirmed that the novel dental implant abutment possessed the anticipated micro-motion capability. Furthermore, the nonlinear force-displacement behavior apparent in this micro-motion mechanism imitated the movement of a human tooth. The slope of the force-displacement curve of the novel abutment was approximately 38.5 N/mm before the 0.02-mm displacement and approximately 430 N/mm after the 0.03-mm displacement. SIGNIFICANCE The novel dental implant abutment with a micro-motion mechanism actually imitated the biomechanical behavior of a natural tooth and provided resilient function, sealing, a non-separation mechanism, and ease-of-use.

The use of a fiber sleeve to improve fracture strength of pulpless teeth with flared root canals.

OBJECTIVES This study aimed to investigate how use of a fiber sleeve may reduce interfacial debonding and improve fracture strength of pulpless teeth with flared root canals. METHODS Pulpless premolars with flared root canals were restored either with a fiber-reinforced post (FRP) alone or with an FRP wrapped in a hollow tubular fiber sleeve. A normal root restored with an FRP alone served as a control. The integrity of resin-dentin and resin-fiber interfaces in the restored roots was evaluated by a stereoscopic system after penetrating a dye. Four roots were tested for each experimental group. Fracture resistance in pulpless premolars with flared root canals restored with an FRP alone or with an FRP/sleeve combination were investigated under bonded and non-bonded conditions with static fracture testing (n=8), and stress distribution in these restored premolars were tested by finite element analysis (FEA). RESULTS Flared root canals restored with an FRP/sleeve combination demonstrated superior integrity at the cervical resin-dentin interface to root canals with an FRP alone. Premolars with a flared root canal restored with an FRP/sleeve combination showed significantly greater fracture resistance compared with premolars restored with an FRP alone. FEA showed that once interfacial de-bonding extended to the cervical region of the root, stress concentration in the root dentin dramatically increased. SIGNIFICANCE The FRP/sleeve combination was effective in reducing debonding and, hence, improving the fracture strength of pulpless premolars with flared root canals.

Influence of cyclic heating on physical property and biocompatibility of α- and β-form gutta-percha

BACKGROUND/PURPOSE Thermoplasticized techniques with high temperature and repetitive heating in root canal filling may cause degeneration of gutta-percha, producing cytotoxic byproducts and interfering sealing quality. This study was conducted to investigate the influence of cyclic heating on the physical property and biocompatibility of α- and β-form gutta-perchas. METHODS Both α- and β-form gutta-perchas were submitted to two heating processes: continuous heating and cyclic heating. Continuous heating was carried out by heating the samples up to 300°C and 400°C. The samples were then analyzed by differential scanning calorimetry, differential thermal analysis (DTA), and thermogravimetry. For cyclic heating process, samples were heated from 30°C to 200°C for seven cycles and analyzed with DTA and thermogravimetry. For cell adhesion assay, samples were treated (30°C to 200°C, one and seven cycles), submitted to cell culture and examined by scanning electron microscope. RESULTS Differential scanning calorimetry and DTA indicated that α-form gutta-percha presented a major endothermic peak at 50-57°C, while β-form gutta-percha showed two major endothermic peaks at 46-50°C and 60-63°C. Total weight loss of β-form gutta-percha was about 2-fold greater than that of α-form gutta-percha after continuous heating up to 300°C, or cyclic heating for seven times. Scanning electron microscopy showed no obvious difference of cell adhesion on α- and β-form samples, even with seven cyclic heating or one heating cycle. However, the attachment of the cells to the culture plate (the control) is better than to the gutta-percha samples. CONCLUSION The increase of heating cycles for α- and β-form gutta-percha exerts no adverse influence on their biocompatibility. Because the physical property of β-form gutta-percha becomes unstable when it is heated at over 300°C or subjected to cyclic heating, β-form gutta-percha may not be recommended for use in thermoplasticized gutta-percha techniques.