Aaron Yu-Jen Wu

Effects of the 3D bone-to-implant contact and bone stiffness on the initial stability of a dental implant: micro-CT and resonance frequency analyses

This study investigated the effects of bone stiffness (elastic modulus) and three-dimensional (3D) bone-to-implant contact ratio (BIC%) on the primary stabilities of dental implants using micro-computed tomography (micro-CT) and resonance frequency analyses. Artificial sawbone models with five values of elastic modulus (137, 123, 47.5, 22, and 12.4 MPa) comprising two types of trabecular structure (solid-rigid and cellular-rigid) were investigated for initial implant stability quotient (ISQ), measured using the wireless Osstell resonance frequency analyzer. Bone specimens were attached to 2 mm fibre-filled epoxy sheets mimicking the cortical shell. ISQ was measured after placing a dental implant into the bone specimen. Each bone specimen with an implant was subjected to micro-CT scanning to calculate the 3D BIC% values. The similarity of the cellular type of artificial bone to the trabecular structure might make it more appropriate for obtaining accurate values of primary implant stability than solid-bone blocks. For the cellular-rigid bone models, the ISQ increased with the elastic modulus of cancellous bone. The regression correlation coefficient was 0.96 for correlations of the ISQ with the elasticity of cancellous bone and with the 3D BIC%. The initial implant stability was moderately positively correlated with the elasticity of cancellous bone and with the 3D BIC%.

Relation between initial implant stability quotient and bone-implant contact percentage: an in vitro model study.

OBJECTIVE This study evaluated the correlation between the initial stability of a dental implant, quantified as the implant stability quotient (ISQ), and the bone-implant contact percentage ( BIC%). STUDY DESIGN Dental implants were inserted into specimens comprising an artificial cortical shell representing cortical bone and foam bone representing cancellous bone with 4 elastic moduli. Each specimen with an implant was subjected to microcomputed tomography (micro-CT) scanning, from which the 2D and 3D BIC% values were calculated. The values of the Spearman correlation coefficient (r) were calculated between the ISQ and the 2D and 3D BIC% values. RESULTS Increasing the elasticity of the specimen enhanced the ISQ. There was statistically significant correlation between the ISQ and 3D BIC% values (r = 0.85, P < .0001). However, the correlation between ISQ and 2D BIC% values was not statistically significance (r = 0.42, P = .062). CONCLUSIONS The initial implant stability was strongly positively correlated with the 3D BIC%.

An in vitro biomechanical evaluation of a new commercial titanium-zirconium alloy dental implant: a pilot study.

Background: The study compared the implant mobility and surrounding bone strain between the titanium-zirconium (Ti-Zr) alloy and the commercial pure (CP) Ti implants. Methods: The mobility—quantified as the implant stability quotient (ISQ) and Periotest value (PTV)—of implants constructed from Ti-Zr alloy and CP Ti placed into artificial type-2 jawbone models were measured. Specimens were tested by applying 190 N vertically or at 30 degrees laterally. Peak values of the principal strains of bone were recorded by rosette strain gauges with a data acquisition system and were analyzed statistically using Wilcoxon rank-sum test. Results: PTV and ISQ values did not differ significantly between the Ti-Zr and CP Ti implants (P > 0.01). Under vertical loading, the peak bone strains did not differ significantly between the Ti-Zr and CP Ti specimens (P > 0.006). However, the peak strains were 52% lower around the Ti-Zr implant than around the Ti implant on the buccal side of bone under lateral loading (P < 0.001). Conclusions: The implant material (Ti-Zr alloy vs CP Ti) had no effect on the mobility of small-diameter dental implants. However, using Ti-Zr alloy as an implant material decreased the periimplant bone strain under lateral loading in this pilot study.

Analyses of Antibacterial Activity and Cell Compatibility of Titanium Coated with a Zr–C–N Film

Objective The purpose of this study was to verify the antibacterial performance and cell proliferation activity of zirconium (Zr)–carbon (C)–nitride (N) coatings on commercially pure titanium (Ti) with different C contents. Materials and Methods Reactive nitrogen gas (N2) with and without acetylene (C2H2) was activated by Zr plasma in a cathodic-arc evaporation system to deposit either a zirconium nitride (ZrN) or a Zr–C–N coating onto Ti plates. The bacterial activity of the coatings was evaluated against Staphylococcus aureus with the aid of SYTO9 nucleic acid staining and scanning electron microscopy (SEM). Cell compatibility, mRNA expression, and morphology related to human gingival fibroblasts (HGFs) on the coated samples were also determined by using the MTT assay, reverse transcriptase–polymerase chain reaction, and SEM. Results The Zr–C–N coating with the highest C content (21.7 at%) exhibited the lowest bacterial preservation (P<0.001). Biological responses including proliferation, gene expression, and attachment of HGF cells to ZrN and Zr–C–N coatings were comparable to those of the uncoated Ti plate. Conclusions High-C-content Zr–C–N coatings not only provide short-term antibacterial activity against S. aureus but are also biocompatible with HGF cells.

Biomechanical investigations of the expanded platform-switching concept in immediately loaded small diameter implants

STATEMENT OF PROBLEM Use of a small diameter implant may increase the stress on bone around the implant neck; however, an expanded platform design may mitigate these stress concentrations. To date, no study has compared the biomechanical effect of regular platform and extended platform designs on an implant. PURPOSE The purpose of this in vitro study was to evaluate the biomechanical effects of an expanded platform-switching design for immediately loaded small diameter implants on bone strains. MATERIAL AND METHODS Three groups of artificial jawbone models were prepared for small diameter (3.25-mm) and standard diameter (4.0-mm) implants with expanded or regular platform designs. Platform-switching implant design was implemented by assembling implants with a smaller connected abutment. Specimens were tested under both vertical and lateral static loads at 190 N. Peak values of the principal microstrain of bone were recorded and analyzed statistically with Kruskal-Wallis test and multiple comparisons Bonferroni test (α=.05). The initial stability of each implant was also measured for 3 types of implant. RESULTS Under vertical loading, the bone strain was lowest for the regular type of immediately loaded small diameter implant. Under lateral loading, peak bone strain around the expanded platform small diameter implant with platform switched abutment was up to 74.9% lower than that of the regular type of small diameter implant. Increasing the implant diameter from 3.25 mm to 4.0 mm on the expanded platform implants reduced the bone strain by approximately 10% and 30% under lateral and vertical loading, respectively. The initial implant stability did not vary significantly among the implants tested. CONCLUSIONS Using the expanded platform small diameter implant with a platform-switched abutment may decrease the marginal bone strains around immediately loaded small-diameter implants under lateral loading.

A modified one-step putty-wash impression technique

aClinical Instructor, Chang Gung Memorial Hospital, Chang Gung University College of Medicine. bProfessor, School of Dentistry, University of North Carolina. (J Prosthet Dent 2007;98:245-246) Although the literature demonstrates that optimum accuracy can be achieved with custom trays and stock trays,1-4 the putty-wash impression technique using an elastomeric impression material is a popular method. Two variations of the putty-wash impression technique are commonly used, the 2-step and 1-step.5 With the 2-step technique, a preliminary preoperative putty impression is made and, subsequently, “washed” with low viscosity material after tooth preparation. In terms of the 2-step puttywash impression technique, several methods are described for control of the bulk of the wash material,6-8 which is essential for fabricating accurate stone dies. With the 1-step procedure, low viscosity impression material is injected around the prepared tooth or teeth, and then the putty impression material is immediately placed intraorally and the materials polymerize simultaneously. Accuracy of impressions resulting from the 1-step putty-wash technique is controversial. Some authors found that there was no difference in accuracy between techniques,5,9-11 while others criticized several potential disadvantages with this approach. These disadvantages include lack of control of the bulk of wash material and the high risk of capturing portions of the prepared margin in putty material rather than lower viscosity material.12 Most putty viscosity materials have inadequate fine detail reproduction for this purpose. This article describes a modified 1-step putty-wash technique using vacuum-formed resin sheets as spacers to control the wash bulk and minimize the chance of unfavorable impression results. Using this technique, the limitations of using 1-step putty-wash impression can be eliminated.

All-on-4 concept implantation for mandibular rehabilitation of an edentulous patient with Parkinson disease: A clinical report

Parkinson disease (PD) is a progressive neurologic disorder. Compromised voluntary and involuntary muscle control of the orofacial-pharyngeal muscles of patients with PD may lead to difficulty in mastication, dysphagia, and tremor of the mouth and chin. All of these problems represent major challenges for the clinician with respect to the oral rehabilitation. This clinical report describes the use of the All-on-4 concept implantation for mandibular rehabilitation with a fixed detachable dental prosthesis in an edentulous patient with PD. The treatment steps, outcome, and limitations are discussed.

Engaging the physiological posterior palatal seal with the framework of a maxillary complete overdenture

This article describes the concept of engaging the physiological PPS with the framework of a maxillary complete overdenture. The clinical indications must be carefully evaluated, and this technique should be only considered when the supporting structures are limited and the patient has experienced wearing a traditional complete denture or overdenture.

A method of fabricating an accurate repositioning device for relocating multiple multiunit abutments

A screw-retained restoration may provide the most definitive and rigid splinting for multiple implants. Multiunit abutments (MUAs) allow great variability in the angles between splinted implants, which facilitates prosthetic reconstructions. The complete-arch, screwretained, immediate-loading, implant-supported prosthesis using MUAs is easily retrievable for future maintenance. Angled MUAs accompanied by metal collars of uneven heights allow changes in the direction of abutments. However, they are also associated with esthetic limitations in that the metal collar may show through the gingival tissue, especially in the anterior region. This may make it necessary to fabricate a cement-retained definitive prosthesis after immediate loading. Clinically the angled MUA can be changed to a straight one by using the lowest metal collar to order for a better esthetic outcome. One method of reducing clinical chair time and facilitating the exchange of multiple MUAs is to replace the new abutments with an interim prosthesis after the healing period. However, this may lead to a poor esthetic outcome for the interim prosthesis, especially in the maxillary anterior area. Another method is to change the new MUAs at each step in the fabrication of the definitive prosthesis and then change back to the original abutments for the interim prosthesis. However, the MUAs can be positioned in 12 different orientations on a hexagonal implant, so the number of different possible orientations increases exponentially when more than 1 implant abutment is being replaced. This can be inconvenient and time consuming for the clinician, who must fabricate a precise acrylic resin repositioning device for simply and rapidly relocating the original multiple MUAs.

The use of vacuum-formed plastic sheets to create reservoir space for fluoride trays.

aResident. bAssistant Professor. (J Prosthet Dent 2009;101:144-145) Daily supplemental fluoride is indicated for patients at high risk of caries due to xerostomia or other factors. Fluoride plays an important role in cariostatic activity: when the pH of the oral environment drops, calcium fluoride acts as a pH-dependent reservoir and releases fluoride; then, the Ca2+ and PO4 3that were originally lost from the surface are reprecipitated as fluorhydroxyapatite.1 A number of factors are critical to achieve optimal cariostatic activity using fluoride treatment, the most important being exposure time and the fluoride concentration in the applied solution.1 Reservoirs maintain a solution in contact with tooth structure, and several studies demonstrate their use for bleaching trays.2–5 Although there is no clinical difference in tooth whitening whether or not a reservoir is present, 2,3 reservoirs maintain the gel at a higher concentration and act as a continual supply4; they can also prevent the bleaching gel from overflowing and can reduce the amount of gel ingested.5 In the absence of a reservoir, the use of a custom-fitted tray results in the highest gross oral-retained fluoride dose, because of the intimate contact between tray and teeth.6 The cariostatic effect may be enhanced by using reservoirs because of their provision of a continual supply of fluoride of an adequate concentration. Flowable composite resins have been used to create the localized space required for bleaching trays7; however, factors such as difficulty in controlling the flow of resin and placing the resin accurately result in a relatively time-consuming procedure. A simple technique for providing the generalized space necessary for reservoirs for fluoride trays is described below.