Richard G. Stevenson

Effects of Bioactive Compounds on Odontogenic Differentiation and Mineralization

Direct pulp capping involves the placement of dental materials directly onto vital pulp tissues after deep caries removal to stimulate the regeneration of reparative dentin. This physical barrier will serve as a “biological seal” between these materials and the pulp tissue. Although numerous direct pulp capping materials are available, the use of small bioactive compounds that can potently stimulate and expedite reparative dentin formation is still underexplored. Here, the authors compared and evaluated the pro-osteogenic and pro-odontogenic effects of 4 small bioactive compounds— phenamil (Phen), purmorphamine (Pur), genistein (Gen), and metformin (Met). The authors found that these compounds at noncytotoxic concentrations induced differentiation and mineralization of preosteoblastic MC3T3-E1 cells and preodontoblastic dental pulp stem cells (DPSCs) in a dose-dependent manner. Among them, Phen consistently and potently induced differentiation and mineralization in vitro. A single treatment with Phen was sufficient to enhance the mineralization potential of DPSCs in vitro. More importantly, Phen-treated DPSCs showed enhanced odontogenic differentiation and mineralization in vivo. Our study suggests that these small bioactive compounds merit further study for their potential clinical use as pulp capping materials.

Conservative and Esthetic Cast Gold Fixed Partial Dentures—Inlay, Onlay, and Partial Veneer Retainers, Custom Composite Pontics, and Stress-breakers: Part I: Fundamental Design Principles

Although in todays dental world implant restorations are considered the standard of care in the replacement of missing teeth, clinical contraindications and patient nonacceptance of implant placement can be encountered. Several scenarios are discussed here in which a single missing tooth can be restored with conservative fixed partial dentures (FPD) that employ cast gold retainers; each with a customized design in order to preserve tooth structure, maintain esthetics, and provide a long-term prognosis. The abutment teeth are prepared for conservative partial coverage restorations by using Brasseler burs (Brasseler USA, Savannah, GA, USA). Impressions are taken of the preparations, along with any retentive features, utilizing either the Vented Pin Channel technique or the Shooshan Plastic Pin technique. The latter technique utilizes Kodex twist drills and corresponding impression pins (Coltene Whaledent Inc., Mahwah, NJ, USA). The conservative FPD with non-rigid connectors is fabricated by using type III gold alloy. The pontic cage portion is chemically prepared utilizing the Panavia F2.0 cement kit (Kuraray America Inc., Houston, TX, USA) or other dual-polymerizing resin cement and restored with any type of direct composite resin material. A palette of opaquers and tints are used for chairside characterization of the esthetic pontic facing. The final polish of the pontic is completed by using FlexiDisc and FlexiBuff discs (Cosmedent Inc., Chicago, IL, USA). CLINICAL SIGNIFICANCE In cases where an implant restoration is contraindicated for replacement of a single tooth, a semi-precision FPD is a conservative, functional, and esthetic alternative.

Covering the implant prosthesis screw access hole: A biological approach to material selection and technique.

W ith implant treatment in the esthetic zone, it is a constant endeavor to maintain and increase the volume of peri-implant tissues. Many recent developments in implant and abutment design have this as the primary goal. Thus we have seen the evolution and creation of ‘‘platform switch’’ abutments, narrowed abutment diameters, and conical implant connections—all in an effort to maximize the volume of the peri-implant bone and soft tissues. The conical connection in particular was developed with the aim of maximizing the integrity of the abutment– implant connection and thus reducing movement, decreasing peri-implant bone stress, and minimizing leakage of the contents inside the abutment into the delicate zone where bone, connective tissue, implant, and abutment all merge (Figure 1). This concept is sound and it does appear to reduce leakage into the peri-implant tissues, but it does not eliminate leakage. This is a problem that worsens over time with repeated loading. The ‘‘platform switch’’ design has mostly (but not entirely), proven to better maintain bone levels than abutments that flare directly from the head of the implant. Multiple finite element analyses have shown that the conical connection may serve to significantly reduce the stresses on the peri-implant crestal bone. It appears that the mechanical integrity of the conical connection provides a biologic benefit even outside the implant itself. The reason for the success seen with platform switch implants appears to be twofold: First, the nonintegrating abutment components are more narrow and thus further away from the bone allowing more space for the necessary biologic width. When nonintegrating components encroach upon this space, the bone remodels laterally and apically to create the necessary biologic space. Secondly, the platform switch design moves the implant–abutment junction (IAJ) away from the bone, and thus moves the inflammatory cell infiltrate coming from inside the implant / abutment and exiting at the IAJ further away from the crestal bone. Much histological study has been made into the biologic environment adjacent to the IAJ, and it has been well established that bone is maintained at a more coronal position when leakage is minimized by use of conical connections, and when the leakage that does occur is moved further away from the bone by use of platform switch abutments. Recent short-term data suggest that the conical connection and minimizing leakage at the IAJ is the more important factor in limiting bone loss. Based on these concepts, it is evident that the contents inside the implant/ abutment directly, and negatively, affect the peri-implant bone position. Leakage from the IAJ cannot be eliminated, but efforts should be made by the clinician to minimize it. It is clear that the contents of the implant/abutment negatively affect the peri-implant bone, and that they will leak from the IAJ. Thus, what is put into the abutment to cover the screw can have a significant effect. According to a 2008 survey, 59% of prosthodontic residency directors and 77% of restorative department chairpersons in the United States use cotton pellets to cover the screw access opening under the definitive restoration. The use of cotton is an adaptation of the method used to temporarily fill the access for endodontically treated teeth, though it appears to be falling out of vogue for this purpose as well. It should be noted that cotton was never intended for use under a definitive restoration. The problem with the use of cotton is that the internal aspect of most implants and implant abutments are hollow, whereas the connection at the IAJ between them is prone to leakage. This creates a 358C, mostly oxygen-free, hollow tube filled with saliva, oral flora, and nutrients—an environment ripe for the proliferation of anaerobic bacteria. As the patient functions on the implant, the IAJ continues to flex and wear, pumping saliva, nutrients and oral flora into the implant chamber from the peri-implant area (not the screw access hole). As the anaerobic bacteria proliferate and the IAJ continues to flex and leak, the anaerobic byproducts are pumped out of the implant at the IAJ and directly into the peri-implant tissues. Covering the screw with cotton, in particular, appears to be problematic because it is an open, organic, scaffold-like structure (Figure 2). These properties provide pathogenic oral flora an ideal substrate upon which to flourish and which likely increases the volume and potency of the inflammatory cell infiltrate. Additionally, cotton has been shown to allow the most leakage into the implant, when compared in vitro to gutta-percha, silicone plugs, and polyvinyl siloxane (PVS) impression materials. The seal created by polytetrafluoroethylene (PTFE) tape has been shown to be effective in sealing endodontically treated teeth and in implant abutments when compared with cotton. Ultimately, it appears that the 1 Section of Restorative Dentistry, University of California-Los Angeles School of Dentistry, Los Angeles, CA, USA. 2 Department of Restorative Dentistry, Loma Linda University School of Dentistry, Loma Linda, CA, USA. 3 Private practice limited to prosthodontics, Bellevue, WA, USA. * Corresponding author, e-mail: tschoenbaum@dentistry.ucla.edu DOI: 10.1563/aaid-joi-D-16-00119

Systematic reviews in oral health: A quality imperative.

Systematic reviews must be conducted responsibly, eliminating any scope for error and bias. The reporting quality of a systematic review should follow and conform to the PRISMA (Preferred Reporting Items for Systematic Reviews and Meta‐Analyses) guidelines. AMSTAR (Assessment of Multiple Systematic Reviews) is an assessment tool, which has been developed specifically to assess the quality of the process used in conducting the review. There has been a significant increase in the number of systematic reviews in oral health and several reports have been published stating low AMSTAR ratings of systematic reviews in dentistry. Systematic reviews answer key clinical questions objectively, and are often used to underpin clinical guidelines in oral health. If the quality of these reviews is compromised, this can result in inadequate or inappropriate clinical guidelines. Consequently, ensuring consistent high quality is a key imperative for systematic reviews in oral health.

Measuring Luxation of Dental Implants In Vitro

Loading of dental implants immediately after placement is an important attribute for the patients receiving the implants, but may induce a failure in the osseointegration of the implant. Even though the loading required to induce such failures is currently unknown, it is estimated that the osseointegration may fail if an implant is luxated in bone by more than 50 μm. Therefore, the ability to measure this loading can provide the practicing dentist with critical information in estimating the functional life of a newly placed implant. This paper discusses the design and fabrication of a cost-effective test setup for measuring the amount of horizontal force required to displace a nonosseointegrated implant, and presents the results of our pilot in vitro load measurements for dental implants mounted in a bovine mandible. Although the sample size of our measurements is not statistically significant, the initial data show that the amount of horizontal force required to displace a 4.3 X 13 mm implant by 50 μm is in the order of 150 N, and therefore the implant may fail to osseointegrate for biting forces that are as low as 440 N, which is about half of the typical biting force of an adult in the molar area. One implication of our study is that implants having smaller diameters may move and fail to osseointegrate for even lower biting forces. Furthermore, our work represents the first steps in developing appropriate metrics to correlate the measured biting force generated by a patient with his or her candidacy for immediate functional implant loading.

The hemi-engaging fixed dental implant prosthesis: A technique for improved stability and handling

Clinicians commonly contend that the screw-retained, implant-supported fixed dental prosthesis (FDP) should be fabricated with all nonengaging abutments to allow for the inherent nonparallelism of the implants and the inability of the abutment connections to draw together during insertion and removal. The problem with a fully nonengaging FDP is difficulty in handling and more strain on the abutment screws, ultimately leading to increased rates of breakage and loosening. The hemi-engaging FDP design regains much of the advantage afforded by the internal connection and improves prosthetic handing both clinically and in the laboratory. The benefits of this technique are best seen for short-span (fewer than 5 units), screw-retained, implant-supported FDPs.

Screw Access Mark for Cemented Implant Crowns: A Universal Technique to Simplify Retrievability

The use of cemented implant prostheses for partially edentulous patients continues to increase in clinical practice. One of the primary complications of the cemented implant crown is difficulty in retrieval, should the need arise. Drilling through most prosthetic materials is of little difficulty for most clinicians, but the complication lies in determining where exactly the access hole needs to be drilled. During fabrication, the location of the screw access channel is marked with a strong contrasting color stain on the surface of the prosthesis. The technique proposed here marks the location of the screw access directly on the prosthesis, thus improving the ease and predictability of future retrieval.

Conservative and Esthetic Cast Gold Fixed Partial Dentures—Inlay, Onlay, and Partial Veneer Retainers, Custom Composite Pontics, and Stress Breakers: Part II: Utilization of Additional Retentive Features and Fabrication of Custom Pontic Facings

Although in todays dental world implant restorations are considered the standard of care in the replacement of missing teeth, clinical contraindications and patient nonacceptance of implant placement can be encountered. Several scenarios are discussed here in which a single missing tooth can be restored with conservative fixed partial dentures (FPD) that employ cast gold retainers; each with a customized design in order to preserve tooth structure, maintain esthetics, and provide a long-term prognosis. The abutment teeth are prepared for conservative partial coverage restorations by using Brasseler burs (Brasseler USA, Savannah, GA, USA). Impressions are taken of the preparations, along with any retentive features, utilizing either the Vented Pin Channel technique or the Shooshan Plastic Pin technique. The latter technique utilizes Kodex twist drills and corresponding impression pins (Coltene Whaledent Inc., Mahwah, NJ, USA). The conservative FPD with non-rigid connectors is fabricated by using type III gold alloy. The pontic cage portion is chemically prepared utilizing the Panavia F2.0 cement kit (Kuraray America Inc., Houston, TX, USA) or other dual-polymerizing resin cement and restored with any type of direct composite resin material. A palette of opaquers and tints are used for chairside characterization of the esthetic pontic facing. The final polish of the pontic is completed by using FlexiDisc and FlexiBuff discs (Cosmedent Inc., Chicago, IL, USA). CLINICAL SIGNIFICANCE In cases where an implant restoration is contraindicated for replacement of a single tooth, a semi-precision FPD is a conservative, functional, and esthetic alternative.