Chiayi Shen

• University of Florida

Marginal discrepancy of metal ceramic prostheses using cast or milled CP Ti or cast Ti-6Al-7Nb alloy was within the clinically acceptable range of 100 μm. Statement of problem. Titanium is the most biocompatible metal used for dental casting; however, there is concern about its marginal accuracy after porcelain application since this aspect has dir...

Objectives The objective of this study is to test the wear of dual‐cured bulkfill and flowable bulkfill composites. Materials and methods Six dual‐cured bulkfill composites, Cention, Cention‐Exp, Activa, Fill‐up, Hyperfil Injectafill, and two flowable bulkfill composites Tetric Evoflow BulkFill and G‐aenial Universal Flo were tested in this study...

Objectives: To test wear of 10 universal composites. Null hypothesis: there are no differences in the composite and antagonist wear. Materials and Methods: Flat samples, light cured as of manufacturer's instructions and polished were made from Admira Fusion (AF), Filtek Supreme Ultra (FS), G-aenial Sculpt (GS), Harmonize (HR), Herculite Ultra (HU),...

Aim: The study aimed to measure light scattering of a broad spectrum light curing unit (LCU) as influenced by ceramic type, shade and thickness as well as exposure distance and LCU’s position. Methodology: A broad spectrum LED LCU (ASCENT OL5) was mounted above a spectrometer (MARC Resin Calibrator, Blue, Light Analytics) at exposure distances of 1...

Purpose: Evaluate the microshear bond strength (µSBS) of orthodontic resin cement to monolithic zirconium oxide ceramic (MZ) under orthodontic load (OL) and thermocycling (TC) effect. Materials and Methods: Glazed MZ blocks (Zenostar, Ivoclar Vivadent) were tested after air abrasion with 30-µm silica coated aluminum oxide (Al2O3) particles (CoJet,...

Objectives: The aim of this study was to test the hypothesis that there is no difference in wear in vitro among the composites investigated and their respective antagonists. Methods: Cylindrical flat samples (1.5 mm tick, Ø 8 mm) mounted on Al-sample holders filled with Admira Fusion (AF), Filtek Supreme Ultra (FS), G-aenial Sculpt (GS), Harmonize...

Purpose of the Study: Compare occlusal wear of PMMA DCL denture teeth under two different loads in vitro. Materials & Methods: Sixteen mandibular second premolars (SR Orthoplane DCL) with a flat occlusal surface (specimens) were worn by sixteen maxillary second premolar-antagonists (Ortholingual DCL). These teeth were subjected in a chewing simulat...

Introduction: This in vitro study aimed at testing the hypotheses that (1) there is no difference in wear in vitro among 3 bulk-fill composites investigated and their respective antagonists, and (2) the tested bulk-fill wear is not different from enamel. Methodology: X-tra fil (Voco; [X]), Tetric-N-Ceram Bulkfill (Ivoclar Vivadent; [T]), QuiXX (Den...

The effect of restoration depth on the curing time of a conventional and two bulk-fill composite resins by measuring microhardness and the respective radiosity of the bottom surface of the specimen was investigated. 1-, 3- and 5-mm thick washers were filled with Surefil SDR Flow–U (SDR), Tetric EvoCeram Bulk Fill-IVA (TEC) or Esthet-X HD–B1 (EHD),...

Objectives: Evaluate the microshear bond strength (µSBS) of orthodontic resin cement to monolithic zirconium oxide ceramic (MZ) under orthodontic load (OL) and thermo cycling effect(TC). Methods: Glazed MZ (Zenostar, Ivoclar Vivadent) blocks were tested after air abrasion with 30-µm silica coated aluminum oxide (Al2O3) particles (CoJet, 3M Espe). A...

Objectives: Evaluation of firing dimensional changes of Lithium-Disilicate-CAD/CAM crowns (e.max-CAD, Ivoclar Vivadent) with different amounts of firing paste (object fix, OF). Methods: Optical impressions were taken with Cerec Bluecam (Sirona) from tooth # 19 (Ivoclar Vivadent master model #594148) and 45 e.max-CAD crowns (EMC) were milled (Cerec...

Clinical relevance: Independent of the resin used, the incorporation of a grid strengthener increases the strength and modulus, thus the fracture probability of dentures is reduced.

Objectives: To evaluate in vitro the marginal fit of CAD-CAM crowns made from Lithium Disilicate (IPS e.max CAD, Ivoclar Vivadent) and Zirconia (Zenostar, Ivoclar Vivadent) materials as a function of the veneering technique. Methods: One ideally prepared model tooth #46 was duplicated into 64 identical plaster models. From the model a standardized...

Objectives: The aim of this study was to test the hypothesis that there is no difference in wear in vitro among the composites investigated and their respective antagonists. Methods: Tetric-N-Ceram Bulkfil (Ivoclar Vivadent; [T]), and X-tra Fil (Voco; [X]), both composites were with multimodal filler, and QuiX (Dentsply; [Q]) were subjected to wear...

Background: Full dentures show a high rate of fractures under clinical use. Therefore strengthening of the denture base is expected to be beneficial with respect to reducing the fracture risk. Preformed perforated thin metal plates seem to be a simple tool for reinforcement. Objective: To test the strengthening effect of perforated metal plates inc...

This in vitro study investigated the interfacial flexural strength (FS) of amalgam repairs and the optimal combination of repair materials and mechanical retention required for a consistent and durable repair bond. Amalgam bricks were created, each with 1 end roughened to expose a fresh surface before repair. Four groups followed separate repair pr...

Objective: Formulate recommendations for light curing resin-based cements through indirect restorative materials (IRM). Method: Energy delivery of Valo® Cordless (Ultradent, South Jordan, USA) as function of distance was determined (MARC; Resin Calibrator, BlueLight Analytics, Halifax, Canada). 0.5-mm thick of Variolink Veneer (Ivoclar-Vivade...

Objective: To investigate the effect of thickness, translucency and surface finish of prosthetic materials on the transmission of curing-light irradiance. Methods: Slabs of material with various thicknesses (t; 0.5~3.0mm) were sliced from one CAD/CAM block of each material with a diamond saw. Blocks of materials included Celtra Duo (Dentsply; HT-...

Objectives: Test the hypothesis that setting-condition before immersion and pH of the storage media influence fluoride release of glass ionomers and compomer. Methods: Disks (10mm diameter and 1mm thick) were prepared from ChemfilRock (CR), KetacMolar (KM), Fuji IX (F9), KetacNano (KN)and DyracteXtra (DX). After preparation, disks were allowed to...

Objective: Cusp deformation of Class II RBC restorations during light-curing is a well-known problem. Because of the curvature of cusps, the use of strain gauges often generates misleading deformation data. The objective of this study was to explore the use of Digital Image Correlation (DIC) to determine cusp-deformations during and after light-cur...

To test the hypothesis that stress distribution is more complex than generally assumed during microtensile testing by determining the stress level in the adhesive region of a virtual dentin-adhesive-composite stick using FEA (finite element analysis). A 3D FEA model simulating a dentin-adhesive-composite stick was analyzed. The length of the compos...

Objective: To test hypothesis that amalgam repair with amalgam bonding agent or composite is as effective as with amalgam only. Methods: Sixteen sets of 8 amalgam bricks each (8x6x3 mm3) were made from Dispersalloy, and stored for 14 d before repair. One side of the 6-by-3 cross-section was roughened with 240 grit paper to expose fresh surface fo...

The international index for dental fluorosis (DF) is used to record enamel changes caused by excessive fluoride exposure during development. Objective: To analyze the relationship between Vickers microhardness (VHN) of newly erupted fluorotic premolars and DF status. Methods: Tooth specimens (n=24) were collected in San Luis Potosi, Mexico. Flu...

Stresses promoted by thermal processing may potentially contribute to premature fracture of dental prostheses. Objective: Test the hypothesis that greater veneer/core thickness ratios increase the fracture risk for Ce-TZP/Al2O3 specimens bonded to a visco-elastic foundation after aging in water (~1yr). Methods: Forty-five, 12mm-dia Ce-TZP/Al2O3 dis...

Objective: Characterize microstructure and properties of two ceramic-veneers and one ceramic-core used in a clinical trial for wear of ceramic and enamel. These properties are required for finite element models for predicting the time-dependent probability of fracture for in vivo prostheses. Methods: Two veneering glass-ceramics, d.Sign(D) and Eris...

Resin-based materials that release either fluoride or chlorhexidine have been formulated for inhibiting caries activity. It is not known if the two agents, when incorporated into one material, would interact and affect their release potential. We hypothesized that the ratio of fluoride to chlorhexidine incorporated into a resin, and the pH of the s...

This study tested the hypothesis that short-term exposure to acidic drinks can reduce enamel surface hardness, and that subsequent brushing with toothpaste can cause detectable loss of enamel. Enamel specimens (three groups per storage medium) were immersed in one of four acidic drinks for five seconds, one minute, or 10 minutes. The pH values of a...

Titanium is the most biocompatible metal used for dental casting; however, there is concern about its marginal accuracy after porcelain application since this aspect has direct influence on marginal fit. The purpose of this study was to determine the effect that metal selection and the porcelain firing procedure have on the marginal accuracy of met...

Digital photography is an integral aspect of clinical prosthetic dentistry for communicating shade information. Objective: Test the agreement of observer visual arrangements for specimens and photographs using CIELAB measurements. Methods: Three values within six hues (white, yellow, red, brown, gray, black) were produced by adding pigments to Sili...

Objective: This study tested the hypothesis that altering mass ratio of fluoride salts within a resin would alter the fluoride release pattern, and investigated their effects on enamel microhardness after pH cycling. Methods: Three experimental resins based on UDMA (54wt%) TEGDMA (23wt%), and fluoride salts (23wt% of CaF2 and ZnF2) were prepared. T...

This study tested the hypothesis that the size of repair sites on amalgam restorations with mechanical undercuts on the repair surface would affect interfacial strength using a 3-point bending test. Six groups of 12 rectangular bars each were fabricated from an admix alloy and a spherical alloy. Each specimen was cut into 2 equal-sized end sections...

This study tested the hypothesis that the oxygen-inhibited layer on a light-cured methacrylate based resin and the pH of the storage medium would increase significantly the initial fluoride release and long-term release rate from fluoride dental sealant. Forty-eight discs (16-mm diameter x 1-mm thick) were made from FluroShield (<5 wt% NaF) and Hel...

Chlorhexidine salts are available in various formulations for dental applications. This study tested the hypothesis that the release of chlorhexidine from a urethane dimethacrylate and triethylene glycol dimethacrylate resin system can be effectively controlled by the chlorhexidine diacetate content and pH. The filler concentrations were 9.1, 23.1,...

Purpose: To investigate the effectiveness of alternative treatments to the replacement of resin-based composite (RBC) restorations through a prospective longitudinal cohort clinical study. Materials and methods: Forty patients aged 27 to 77 years (mean=55) with 88 RBC restorations, with one or more features that deviated from ideal, participated...

Specific contributions of the core and the veneer thickness on the appearance of layered disk specimens are not well characterized. This study examined the effect of varying core and veneer thickness on the color parameters of layered disk specimens made of 2 ceramic systems. Disk specimens 16 mm in diameter with core/veneer thickness (mm) of 0.8/0...

Clinical Relevance The proper technique of condensing amalgam to the surface of an old amalgam is critical to establishing a bond between the new and old amalgams.

Information on the time-dependent release of fluoride from filled resins containing fluoride particles as a function of particle content and solution pH is limited. This study characterized the fluoride ion release from filled resins containing CaF2 particles as a function of filler content and pH. Urethane dimethacrylate and triethylene glycol dim...

Purpose: To evaluate the performance of a universal resin-based restorative material (Beautifil) in combination with a self-etching primer (Fluorobond) for posterior restorations. Methods: 61 restorations, 26 Class I and 35 Class II, were placed by two clinicians in 31 patients under rubber dam isolation. Two other calibrated clinicians evaluate...

The authors conducted an in vitro study to test the hypothesis that undercuts prepared in old composite restorations could improve the strength between the restoration and a flowable composite as repair material. The authors used three composites to fabricate cylinders as repair substrates. The etched-only group was ground, etched, dried and built...

This study was designed to test the hypothesis that the flowable/dentin interface has the weakest bond and highest frequency of failure when a resin-based composite is repaired using a flowable composite. Comparing three specific groups--dentin, flowable composite, and hybrid composite-under the Kruskal-Wallis test showed that the mean bond strengt...

Whereas replacement of failed restorations is the major treatment for adults in dental practice, repair is an important alternative with the potential to save tooth structure and increase the longevity of restorations at a lower cost. This in vitro study recorded the choices of treatment for the same set of teeth with defective Class II amalgam res...

The authors tested the hypothesis that surface-finishing treatments and the type of storage solutions significantly affected the staining of resin-based composites, or RBCs, and unfilled resins, or URs. Fifty-four RBC and 54 UR disks were polymerized through a polyester film strip (Mylar, DuPont, Wilmington, Del.) and polished in one of three group...

The temperature reported for thermally treating silanated ceramics to improve composite-ceramic bonding is often too high for chairside applications. This study investigated whether post-silanization drying with a stream of warm air could enhance the composite/ceramic tensile bond. Thirty-two ceramic blocks (6 x 6 x 9 mm), 16 of each ceramic, were...

The temperature reported for thermally treating silanated ceramics to improve composite-ceramic bonding is often too high for chairside applications.

Statement of problem. The temperature reported for thermally treating silanated ceramics to improve composite-ceramic bonding is often too high for chairside applications. Purpose. This study investigated whether post-silanization drying with a stream of warm air could enhance the composite/ceramic tensile bond. Material and methods. Thirty-two cer...

This study is to test the hypothesis that chemical etching and silane coating of a ceramic surface will influence the work of adhesion (WA) of adhesive resin to dental ceramic. A hot-pressed lithia disilicate-based ceramic was used as a model material to investigate the influence of probing media and surface treatments on WA using a dynamic contact...

Objective: To test the hypothesis that the oxygen-inhibited layer and environmental pH significantly affect the fluoride release rate from dental sealants. Methods: Forty-eight discs (16-mm diameter x 1-mm thick) were made from Fluroshield (FS, < 5 wt% NaF, Dentsply) and Helioseal (HS, < 30 wt% fluorosilicate glass, Ivoclar) sealants. Twenty-four d...

Mechanical retention based on the surface topography is critical for the success of chairside repair of chipped or fractured ceramic prostheses with a composite. The purpose of this study was to investigate whether the tensile bond strength of a composite to 3 dental ceramics was affected by surface roughening procedures on the ceramics. Three cera...

This in vitro study tested the following null hypotheses: (1) surface finishing treatments do not significantly affect the biaxial flexure strength and microhardness of resin-based composites (RBC) and (2) storage media do not significantly affect these physical properties. Discs (81 RBC and 81 UR; 3M/ESPE) were prepared using a circular polyethyle...

Temporal summation of heat pain during repetitive stimulation is dependent on C nociceptor activation of central N-methyl-d-aspartate (NMDA) receptor mechanisms. Moderate temporal summation is produced by sequential triangular ramps of stimulation that control skin temperature between heat pulses but do not elicit distinct first and second pain sen...

Objective: This study tested the hypothesis that surface drying with heat will reduce the contact angle of ceramic surface using fluid resin as probing liquid. Methods: A veneering ceramic, Eris (Ivoclar AG, Schaan, Liechtenstein) and a core ceramic, IPS-Empress (Ivoclar) were used to fabricate rectangular slabs (15x10x1mm) for each of the followi...

Maximum wetting of ceramic by adhesive resin is required to achieve optimal adhesion of the resin to ceramic. It is unknown whether the adhesion of the resin to the ceramic is affected by the surface topography and wetting by water or the adhesive resin. This study was designed to characterize the effect of surface topography on the wetting of cera...

This study examined the changes in mechanical properties of temporary soft liners introduced by the differential loss of alcohol and plasticizer in different storage media. Four brands of temporary soft liners were used to prepare 128 specimens on Lucite LS substrates. Each group of specimens was stored in a different medium (air, 10% ethanol, wate...

The aim of this study was to evaluate the effect of different cavity designs, cavity depths, and shade matching on the dimensions of Class I resin-based composite preparations during replacement of the restoration. Forty Class I cavity preparations were prepared in extracted premolars. The occlusal depths varied from 1.5 to 2.5 mm. In 20 teeth, the...

Ninety-one Icelandic practicing dentists (51% response rate) provided information related to the reasons for placement and replacement of 8,395 restorations and 741 sealants in 5,997 patients. Information included the patient's gender and age, the clinician's gender and experience in years since graduation, the defined criteria for replacement of r...

The authors investigated the fluoride content uniformity of three commercial fluoride varnishes, as well as their fluoride-release behaviors. The authors examined 20 doses from each of two tubes of Duraphat (Colgate-Palmolive Co., New York) and Duraflor (Pharmascience Inc., Montreal), and 20 doses of individually packaged 0.25-milliliter and 0.40-m...

Operative dentistry

The objective of this in vitro study employing the microtensile test was to test the hypothesis that the tensile bond strength of hot-pressed ceramics to composite is controlled by the ceramic microstructure and the ceramic surface treatment. Hot-pressed IPS Empress (E1) and IPS Empress 2 (E2) ceramic blocks were polished with 1-micron alumina abra...

For controlled release of drugs and other uses, the accurate and precise measurement of swelling of polymer microsphere carriers is often crucial. Most currently available techniques were designed to measure high degrees of swelling. We explored the use of digital light microscopy for the high precision measurement of small degrees of swelling of i...

Successful porcelain repair requires conditioning of porcelain surfaces. Conditioning is intended to facilitate wetting by repair materials and improve interfacial bonding. The objective of this investigation was to determine the effects of selected surface treatments upon the wettability of a representative feldspathic porcelain. Dynamic contact a...

We are developing a system for detecting recurrent caries under dental restorations. The controlled release of dyes under conditions of likely demineralization will alert the dentist to potential secondary caries. Production of acidic species is a characteristic of caries activity; hence, the system uses pH-sensitive polymers to release markers whe...

The aim of this study was to establish a stochastic approach for modeling controlled release of a dye as a function of the composition of a group of polymer microspheres in various pH environments. The microspheres were polymers based on styrene, 4-vinylpyridine and divinylbenzene. The composition of the polymers were characterized by the ratio of...

Currently, the proposed test of the International Standardization Organization (ISO) for measuring working and setting times of resin luting agents is based on measurement of times to reach specified stages on the polymerization exotherm. The objective of this study was to use this test to investigate the influence of variations in the mass ratios...

The purpose of this study was to test the hypothesis that hydration during setting enhances the strength of glass ionomer cements. Thirty-four groups of eight disks each were prepared and sealed in nonpermeable bags to age for 30 min to 360 d before biaxial flexure testing. At each time interval, one group was tested immediately, while the second g...

The objective of this study was to test the hypothesis that the apical seal provided by thermoplasticized root canal obturations depends on the film thickness of the sealer used. The root canals of 120 maxillary cuspid teeth were instrumented and divided into six equal groups of 20 teeth. A thermoplasticized gutta-percha root canal obturator was us...

This study investigated the effectiveness of tempering and ion-exchange treatments on crack growth and bi-axial flexural strength of seven feldspathic porcelains. The results showed that tempering treatment was more effective in strengthening porcelain than was the ion-exchange process as measured by the bi-axial flexural strength. However, the res...

The purpose of this study was to test the hypothesis that high-leucite content feldspathic porcelain can be strengthened best by thermal tempering followed by ion exchange, compared with either thermal tempering or ion exchange alone. The results of biaxial flexure testing indicate that thermal tempering was the most effective way of strengthening...

Tempering of dental porcelain by forced convective cooling in air has been shown previously to inhibit the sizes of cracks induced in porcelain surfaces. However, the depth of compressive stress that is produced by tempering of feldspathic porcelain has not been determined. It can be assumed that the potential of tempered specimens to inhibit crack...

The effect of two alkaline glutaraldehyde base disinfectants on a heat-cured denture base resin was evaluated by the flexural strength, the repair flexural strength, and the surface morphology of the material that had been immersed up to 12 hours in the disinfecting solutions. The flexural strength of the material was not significantly affected by...

The time-dependent microleakage behaviour of two types of restorative materials, a microfilled composite resin and a glass ionomer, was studied. A dentine bonding agent was also included. This study was based on a diffusion model of microleakage. It was found that the initial gap sizes of the restorations increased progressively for restorations mi...

The variables affecting the microleakage of a Zn-containing amalgam, a posterior composite, and a microfilled composite in root surface lesions are compared in a laboratory study. A radiotracer is sealed in root samples containing amalgam, posterior composite, and microfill composite restorations. The amalgam restorations are compared regarding moi...

A delivery system of F- in connection with dental restorations was tested. The system utilized the gap space which often exists between the restorative material and the tooth structure. A known quantity of fluoride compound was placed at a site within prepared plastic cavity blocks prior to restoring with composite resins. It was found that each sp...

The creep rates of six alloys for porcelain-fused-to-metal (PFM) restorations were determined as a function of flexural stress and temperature. Although two Pd-Cu alloys demonstrated excellent resistance to creep at low-stress, high-temperature conditions, they were especially susceptible to deformation at high stresses and temperatures near the gl...

Due to their nature and location, root caries restorations involve either no enamel or enamel only on the occlusal cavosurfaces. This study examines the microleakage of several restorative materials on root surfaces in the absence of enamel bonding: 25 freshly extracted teeth were restored, 5 specimens with a glass ionomer cement, 5 with a microfil...

Microleakage is a significant problem in restorative dentistry. A model based on the principle of diffusion was developed to quantify the process of microleakage. The model required a certain quantity of radiotracer to be placed in the cavity and allowed to diffuse through the microgap that existed around the restoration. The rate of the tracer acc...

The effect of lubricating the canal space prior to making a custom acrylic post pattern was studied in regard to the retention of cast posts cemented with zinc phosphate. Ways of removing the lubricant before cementation were also evaluated.

A microleakage model based on the diffusion phenomenon of a radio tracer from the cavity floor of a restoration to the outside medium was discussed and was solved numerically by the finite element method. The simulation results and laboratory data showed that quantitation of microleakage could be achieved and expressed by a new term named Microleak...

Crystal formation obtained from evaporating clear filtrates of dental stone mixed with various solutions were examined with an optical and scanning electron microscope. It was found that when K2SO4 was present in any concentration, a spherulitic structure dissimilar to that of CaSO4. 2H2O and K2SO4 was dominant. It is concluded that syngenite (a co...

The wear behaviour of 22% PTFE-filled polyoxymethylene (Delrin∗∗) rubbing against a metallic annular counterface has been evaluated. Wear tests were carried out on a thrust-washer type wear tester under three different lubricating conditions: dry, in water, and in plasma. Wear resistance is good under dry conditions but is reduced in the presence o...

The possibility of using some high temperature materials in total hip replacement was evaluated, with special attention to the acetabular cup of this joint. Two commercially available materials, Torlon were studied using a thrust-washer type wear tester. The results indicate that the wear resistance of both materials is excellent in dry conditions....

The wear behavior of polyoxymethylene (Delrin 150) has been studied up to surface pressures of 1200 Ib in−2 using a thrust-washer testing machine. Delrin has the advantages of higher hardness and lower creep than the currently widely used material ultrahigh molecular weight polyethylene (UHMWPE). In contrast to UHMWPE, the wear of Delrin depends on...

The wear behaviour of ultrahigh molecular weight polyethylene has been studied using a thrust-washer testing machine. The data are examined in the light of findings of other workers and of clinical results. The wear factor exhibits a maximum at about 500 lb in−2 surface pressure for polyethylene samples tested in water. The use of plasma in place o...

The friction and wear behavior of gamma irradiated very high molecular weight polyethylene has been studied for radiation doses of 20 to 1000 MRad. For tests run at low loads the effect of irradiation is to increase the friction coefficient and the wear factor. As the load is increased the friction coefficient decreases and the wear factor remains...