Winston W.L. Chee

Development of implant soft tissue emergence profile: a technique.

Despite successful osseointegration of dental implants, patients can be dissatisfied with the definitive restoration because of a poor esthetic result. An esthetic implant restoration depends on correct implant placement and a well-designed and fabricated prosthesis that includes the prosthetic teeth and the surrounding whether it is acrylic resin or soft tissue. This article describes a technique to help predict, develop, and evaluate implant prostheses and their soft tissue contours at the provisional restoration stage. This technique records the planned and subsequently proven contours, which are then used to guide fabrication of the final prosthesis and produce a predictable esthetic result.

A review of powder modifications in conventional glass-ionomer dental cements

Glass-ionomer dental cements (GICs) have proven to be useful in several areas of dentistry such as restorative dentistry. Glass-ionomers are aqueous cements formed by the reaction of an acidic polymer and a basic glass in the presence of water. The oral environment presents many challenges to the longevity of restorative materials. Glass-ionomer cements have many properties that are clinically useful and promote longevity. Importantly, GICs adhere to moist tooth structure without any pretreatment, and provide a prolonged period of fluoride release, which inhibits recurrent tooth decay (caries). These properties together with acceptable aesthetics and biocompatibility make these materials popular and desirable for medical and dental applications. However, glass-ionomer dental cements have limitations that prevent broader clinical adaptation such as poor mechanical properties and moisture sensitivity. Many significant changes and modifications to the chemistry of the acidic polymers and basic glasses and to the formulation of the cements have been made to address these limitations. In this review, advances in the development of the basic glasses and other reinforcing agents will be discussed. An overview of the chemistry of glass-ionomer cements will be discussed followed by an in-depth discussion of the chemistry of novel basic glasses and reinforcing additives.

Encapsulated dental-derived mesenchymal stem cells in an injectable and biodegradable scaffold for applications in bone tissue engineering

Bone grafts are currently the major family of treatment options in modern reconstructive dentistry. As an alternative, stem cell-scaffold constructs seem to hold promise for bone tissue engineering. However, the feasibility of encapsulating dental-derived mesenchymal stem cells in scaffold biomaterials such as alginate hydrogel remains to be tested. The objectives of this study were, therefore, to: (1) develop an injectable scaffold based on oxidized alginate microbeads encapsulating periodontal ligament stem cells (PDLSCs) and gingival mesenchymal stem cells (GMSCs); and (2) investigate the cell viability and osteogenic differentiation of the stem cells in the microbeads both in vitro and in vivo. Microbeads with diameters of 1 ± 0.1 mm were fabricated with 2 × 10(6) stem cells/mL of alginate. Microbeads containing PDLSCs, GMSCs, and human bone marrow mesenchymal stem cells as a positive control were implanted subcutaneously and ectopic bone formation was analyzed by micro CT and histological analysis at 8-weeks postimplantation. The encapsulated stem cells remained viable after 4 weeks of culturing in osteo-differentiating induction medium. Scanning electron microscopy and X-ray diffraction results confirmed that apatitic mineral was deposited by the stem cells. In vivo, ectopic mineralization was observed inside and around the implanted microbeads containing the immobilized stem cells. These findings demonstrate for the first time that immobilization of PDLSCs and GMSCs in alginate microbeads provides a promising strategy for bone tissue engineering.

Evaluation of the amount of excess cement around the margins of cement- retained dental implant restorations: The effect of the cement application method

STATEMENT OF PROBLEM Complete removal of excess cement from subgingival margins after cementation of implant-supported restorations has been shown to be unpredictable. Remaining cement has been shown to be associated with periimplant inflammation and bleeding. PURPOSE The purpose of this study was to investigate and compare the amount of excess cement after cementation with 4 different methods of cement application for cement-retained implant-supported restorations. MATERIAL AND METHODS Ten implant replicas/abutments (3i) were embedded in acrylic resin blocks. Forty complete veneer crowns (CVCs) were fabricated by waxing onto the corresponding plastic waxing sleeves. The wax patterns were cast and the crowns were cemented to the implant replicas with either an interim (Temp Bond) or a definitive luting agent (FujiCEM). Four methods of cement application were used for cementation: Group IM-Cement applied on the internal marginal area of the crown only; Group AH-Cement applied on the apical half of the axial walls of the crown; Group AA-Cement applied to all axial walls of the interior surface of the crown, excluding the occlusal surface; and Group PI-Crown filled with cement then seated on a putty index formed to the internal configuration of the restoration (cementation device) (n=10). Cement on the external surfaces was removed before seating the restoration. Cement layers were applied on each crown, after which the crown was seated under constant load (80 N) for 10 minutes. The excess cement from each specimen was collected and measured. One operator performed all the procedures. Results for the groups were compared, with 1 and 2-way ANOVA and the Tukey multiple range test (α=.05). RESULTS No significant difference in the amount of excess/used cement was observed between the 2 different types of cements (P=.1). Group PI showed the least amount of excess cement in comparison to other test groups (P=.031). No significant difference was found in the amount of excess cement among groups MI, AH, and AA. Group AA showed the highest amount of excess cement. The volume of cement used for group PI specimens was significantly higher than for those in the other groups (P=.001). With respect to the volume of cement loaded into the test crowns no statistically significant difference was observed among other test groups (groups IM, AH, and AA). Group MI used the least amount of cement, followed by group AH and AA. No correlation between the amount of used cement and the amount of excess cement was found in any of the tested groups. CONCLUSIONS Within the limitations of this in vitro study, the least amount of excess cement was present when a cementation device was used to displace the excess cement before seating the crown on the abutment (Group PI). With this technique a uniform layer of the luting agent is distributed over the internal surface of the crown leaving minimal excess cement when the restoration is seated.

Failures in implant dentistry

This article describes the many failures and complications that can occur when using implants to support restorations. Most of these failures can be prevented with proper patient selection and treatment planning. Implant failures can be largely classified into four main categories: 1) loss of integration, 2) positional failures 3) soft tissue defects, and 4) biomechanical failures. Each of these will be discussed with examples to illustrate the problem.

Inhibition of polymerization of polyvinyl siloxanes by medicaments used on gingival retraction cords.

Inhibition of polymerization of polyvinyl siloxane materials by latex products is well documented. It is thought to be caused by contamination of the chloroplatinic acid catalyst by sulfur compounds. Many medicaments, such as aluminum sulfate and ferric sulfate, used on gingival retraction cords have been accused of causing inhibition of set of polyvinyl siloxane materials. Several of these medicaments were tested with two polyvinyl siloxanes and found not to cause any inhibition of set.

Bacterial Colonization of Oral Implants from Nondental Sources

Implants showing signs of peri-implantitis harbor a microbiota similar to that of periodontitis-affected teeth. This case report describes the subgingival microbiota of a 45-year-old female with advanced periodontitis before and after complete edentulation and reconstruction with dental implants. A 3-month healing period post extraction passed before implants were placed using a two-stage submerged implant protocol. At 4- to 6-month recall visits after definitive prosthetic reconstruction, some implant sites showed bleeding on probing and localized mucositis. Microbiological culture of three inflamed peri-implant sites showed an almost identical spectrum of pathogens, including Porphyromonas gingivalis, Tannerella forsythia, and other major pathogenic bacteria characteristic of aggressive periodontitis. As natural teeth were absent for 8 months, this case report suggests that periodontal pathogens can be retained for a prolonged period of time in nondental sites, from where they can later colonize and compromise the health of dental implants. The therapeutic implications of this finding are discussed.

Tooth-to-implant connection: a systematic review of the literature and a case report utilizing a new connection design.

BACKGROUND In the treatment of partially edentulous patients, implants have often been connected to natural teeth. Numerous studies have reported significant complications and problems, while others have demonstrated favorable outcomes. PURPOSE The purpose of this article was to systematically review the literature regarding the splinting of implants and teeth. The difference in the biomechanical behavior between osseointegrated implants and teeth and the efficacy of the different modes of connection that have been employed are explored. MATERIALS AND METHODS A MEDLINE search between 1966 and October 2006 was performed to retrieve relevant articles. A further manual search from the bibliographies of the former articles was performed to include as many references as possible. Prospective and retrospective clinical studies, as well as laboratory and computer-generated research, were included. RESULTS A pronounced difference in the biomechanics of teeth and implants has been revealed in theoretical models. This disparity has also been supported by the majority of the experimental work published. As a result, principal complications, such as intrusion of teeth and higher risk of overload and greater marginal bone loss around the implants have been reported. Among the several types of connections utilized, the rigid connection showed fewer complications but unfortunately did not eliminate them. CONCLUSION Totally implant-supported prostheses should be the treatment of choice. However, there are cases where combining teeth and implants is inevitable. The authors propose a rationale design of connecting implants and teeth. This design minimizes the biologic and technical complications.

Tensile bond strength of polyvinyl siloxane impressions bonded to a custom tray as a function of drying time: Part I

Time-dependent bond strength studies of two polyvinyl siloxane impression materials to acrylic resin disks with their respective adhesives were studied to determine the optimal time for maximum bond strength. Six groups were tested with varying adhesive dry times of 0, 7, 15, and 60 minutes and 8 and 24 hours before testing. The results indicated that the bond strength of the adhesive increased at least twofold from time zero to 7 minutes adhesive dry time and peaked at 60 minutes for one of the materials and at 8 hours for the other. Bond strengths increased rapidly to the 15-minute test interval and then seemed to plateau. Both materials exhibited decreased adhesive bond strengths at 24 hours.

A technique for retrieving fractured implant screws

The use of dental implants as a source of support and retention for fixed restorations is common. This report describes the use of a fragment removal instrument together with the use of ultrasonic instrumentation to retrieve a screw fragment.