Equivalence testing with dental clinical trials.

Clinical trials whose purpose are to show equivalence of two or more treatments have traditionally utilized methods for demonstrating superiority, and, if no statistical differences are found, the treatments are assumed to be equivalent. Methods for directly demonstrating equivalence have been developed by the pharmaceutical industry to establish the bioequivalence between drug formulations. This approach should have significant future implications for dental research. It is presently well-characterized in the statistical literature, but is virtually unknown within the dental literature and has had limited documented application with dental clinical trials. The purpose of this paper is to consider equivalence testing with dental clinical trials. Equivalence and superiority testing are contrasted, and comparisons between parallel and crossover designs with equivalence testing are discussed. To exemplify equivalency trial methodology for dental research application, several examples are proposed, including, in detail, an implant overdenture clinical trial to test the equivalence of treatment outcome between a two- and a four-implant overdenture treatment. Sample size calculations for otherwise-identical crossover and parallel equivalence studies are demonstrated. Results show that for a power of 0.90, a sample size of 24 is required for the crossover trial and over 150 subjects for the parallel design. For this dental research application, the equivalence/crossover design methodology is shown to be an efficient and appropriate approach.

In vitro comparison of the fracture resistance and failure mode of fiber, ceramic, and conventional post systems at various stages of restoration.

PURPOSE: This in vitro study evaluated 6 post systems over 4 simulated clinical stages of tooth restoration to (1) determine quantitatively the fracture resistance strength at each stage when a static loading force is applied to cause failure; (2) determine the failure mode for each post system at each simulated clinical stage; and (3) determine the feasibility of removing failed post systems. MATERIALS AND METHODS: Ten post systems made with various materials and designs were tested at the following 4 stages of simulated clinical treatment: stage #1: posts only, loaded using a 3-point loading model to failure, to determine transverse strengths and failure modes for each post system; stage #2: posts alone, bonded into teeth; stage #3: posts bonded into teeth with core build up; stage #4: post and core build up and full veneer restoration. For stages #2 through #4, the coronal portion of 60 mandibular premolars was amputated at the cemento-enamel junction, the canals were treated endodontically, and the specimens were mounted in acrylic blocks. A testing force was applied to the posts at 90 degrees to the long axis of the tooth, 4 mm from the cemento-enamel junction. The O'Brien test for constant variance was performed over the treatment groups. For nonconstant variance, the Welsh analysis of variance was used to test for equalities of treatment means. The Tukey Kramer procedure determined which treatment procedures differed. RESULTS: The failure thresholds for each post system were significantly different at each stage of testing, but the order of test results by post type remained generally consistent from one stage to the next. ParaPosts (Coltene, Whaledent Int, New York, NY) and core build up resulted in significantly higher failure thresholds through all 4 stages of testing. This post system also consistently displayed a high number of nonfavorable tooth fractures. FibreKor post and cores (Jeneric Pentron Inc, Wallingford, CT) resulted in significantly lower failure threshold values in stages #2 through #4. This post system displayed no tooth fractures in stages #2 and #3 and a similar number of nonfavorable tooth fractures in stage #4 when compared with the other systems. C-Post (Bisco Dental Products, Schaumburg, IL), CosmoPost (Ivoclar Vivadent North America Inc, Amherst, NY), and AesthetiPost (Bisco Dental Products) grouped in descending order through stages #2 to #4. These systems displayed intermediate fracture resistance strengths, as well as a moderate number of nonfavorable tooth fractures. CosmoPost exhibited a significant number of brittle post fractures with fragments left in the root canal at all stages. The fracture resistance of the cast metal post varied from stage to stage. No teeth fractured at stage #2. At stage #3, 9 of 10 teeth fractured nonfavorably, and all teeth fractured nonfavorably in stage #4. CONCLUSIONS: The fiber posts evaluated provided an advantage over a conventional post that showed a higher number of irretrievable post and unrestorable root fractures. At the stage of final restoration insertion, there was no difference in force to failure for all but the FibreKor material, which continued to be weaker than all other tested materials. The fiber posts were readily retrievable after failure, whereas the remaining post systems tested were nonretrievable. J Prosthodont 2001;10:26-36.

Mandibular implant overdenture treatment: consensus and controversy.

A literature review of implant overdenture treatment for the edentulous mandible is presented. The report focuses on the knowledge base for this treatment modality, in an effort to distinguish between areas that are well characterized and enjoy a higher level of consensus among practitioners as compared with those that are more controversial and not clearly understood.

Effect of endodontic sealers on dowels luted with resin cement.

PURPOSE: This study evaluated the retention of prefabricated parallel-sided dowels luted with resin cement in extracted teeth that were obturated with gutta percha using a eugenol sealer or a calcium hydroxide sealer. MATERIALS AND METHODS: Extracted maxillary incisor roots (N = 51) were instrumented to simulate conventional root canal therapy and divided into 3 groups (n = 17). One group was not obturated. Second and third groups were obturated with gutta percha using a eugenol-containing or calcium hydroxide-containing sealer. Gutta percha was removed using a heated plugger, and dowel spaces were prepared to a 7 mm depth. Dowel space walls were acid etched and primed, and prefabricated stainless steel dowels were luted using resin cement. After 24 hours, the load required to dislodge each dowel along a path parallel to its long axis was measured and recorded. A one-way analysis of variance (alpha = 0.05) was performed to identify differences in the means among groups. The incidence of failure within the cement or at the dentin-cement interface was also recorded. RESULTS: No statistically significant difference was found among the control (159.9 +/- 96.3 N), eugenol sealer (153.1 +/- 77.3 N), and calcium hydroxide sealer (192.0 +/- 89.3 N) groups. Nearly all specimens displayed adhesive failure at the dentin-resin cement interface. CONCLUSIONS: Conventional endodontic obturation using a eugenol-containing or a calcium hydroxide-containing endodontic sealer did not affect retention of prefabricated stainless steel dowels luted with resin cement.

Prospective clinical evaluation of mandibular implant overdentures: Part I--Retention, stability, and tissue response.

Seventeen subjects with preexisting conventional complete dentures were evaluated in this prospective clinical study. Two implants were placed bilaterally in the anterior mandible. In a crossover experimental design, the conventional dentures were modified, and the retention, stability, and tissue response for conventional dentures were compared with implant overdentures that had O-ring and magnet overdenture attachments for all subjects. The study indicated statistical superiority of the implant overdenture to the conventional denture. The O-ring attachment proved significantly better than the magnet attachment for retention and stability. The soft tissue response showed a slight but significant improvement with implant overdenture therapy.

Prospective clinical evaluation of mandibular implant overdentures: Part II--Patient satisfaction and preference.

In a crossover experimental design, a prospective clinical study was performed with 17 subjects with existing complete dentures. After data collection, two implants were placed bilaterally in the anterior mandible. Conventional dentures were modified into implant overdentures by use of O-ring and magnet attachments. Each attachment was maintained with each subject for 6 months. Subjects responded to patient satisfaction and preference questionnaires about the conventional denture and each attachment. Subjects were satisfied with both attachment overdentures but showed a strong preference for the O-ring. Both attachments resulted in a significant increase in patient satisfaction when compared with the conventional denture.

The construction of crowns for removable partial denture abutment teeth.

The construction of crowns for teeth that will serve as abutment teeth for removable partial dentures is an important and technically demanding procedure. The preparation of the tooth itself must include provision for the components and path of placement of the removable partial denture and at the same time conform to all the parameters associated with proper tooth preparation. Some of the factors unique to surveyed crowns that must be considered include the position of the tooth in relation to the proposed occlusal plane with the removable partial denture, the type of facial and lingual tooth contours desired for the direct retainer, the size and suitability of existing restorations, and the proposed path of placement and removal of the removable partial denture relative to the orientation of the abutment tooth as well as to other adjacent teeth if the abutment also is to be used as a fixed partial denture retainer. The design requirements for the removable partial denture must be determined before treatment is initiated, to account for all of these factors.

Comparison of the retention of endodontic posts after preparation with EDTA.

Significant differences in the retention of preformed endodontic posts for endodontically treated teeth were determined with (1) parallel-sided, passively placed Para-Post dowel versus mechanically engaging, threaded Flexi-Post dowel; (2) irrigation of canals with EDTA; (3) cementation with urethane dimethacrylate resinous or zinc phosphate cement. It was hypothesized that EDTA would substantially increase retention by removing the smear layer on the prepared canal wall and create micromechanical retention in the dentin. Extracted teeth were prepared with endodontic posts and divided in groups representing combinations of variables. The forces for post removal and the locations of the retentive bond failures were recorded. The results indicated that EDTA did not significantly affect retention. The Flexi-Post dowel was significantly more retentive than the Para-Post dowel but also exhibited a greater potential for tooth damage compared with the Para-Post dowel during retentive failure loads.

Three-dimensional numerical modeling of geoacoustic scattering from seafloor topography.

A three-dimensional (3-D), second-order finite-difference method was used to create synthetic seismograms for wave propagation in heterogeneous media in order to investigate the scattering of elastic and acoustic energy due to topography on the seafloor. The method uses a fully staggered grid in Cartesian coordinates as developed by Virieux [Geophysics 51, 889-901 (1986)]. Numerical results were generated for two models: a linear fault scarp on the seafloor, and a flat seafloor containing a rectangular channel. Wave-front snapshots allow the scattering and focusing of different wave modes with direction to be visualized. Compressional and shear wave backscattering from the sides of the features can be seen together with the trapped compressional wave energy propagating inside the channel. The results illustrate the effects of out of the plane scattering due to simple seafloor topographic features.

Stress distribution surrounding endodontic posts.

This study compared the stress distribution during insertion and function of three prefabricated endodontic posts with different designs using the criteria of post length and diameter. Test blocks of photoelastic material were prepared with simulated endodontic canals. Three posts for each design, diameter, and depth were cemented. Each specimen was examined and photographed without load, with 135 Newton (N) compressive force, and with 90 N and/or 135 N oblique force applied at 26 degrees by use of a circular polariscope. Para-Post and Para-Post Plus posts produced similar, evenly distributed patterns of stress using the criteria of diameter, depth, and load. Flexi-Post posts produced asymmetric stress patterns with concentration of stress at each thread. During compressive loading and after cementation alone, Flexi-Post posts displayed significantly higher shoulder stresses and substantially greater stresses along the coronal surface of the post's length than Para-Post and Para-Post Plus posts. Apical stresses were similar for Flexi-Post, Para-Post, and Para-Post Plus posts during compressive loading.

Dimensional stability of acrylic resin materials after microwave sterilization.

Microwave sterilization techniques have previously been discussed in the literature, but there is need for information regarding the stability of acrylic resins subjected to these techniques. The purpose of this investigation was to measure and determine the potential influence of microwave sterilization on the dimensional stability of polymerized acrylic resin denture base materials. Uniform samples of previously heat-polymerized, autopolymerized, and visible-light-polymerized acrylic resins were measured for changes in weight and length before and after microwave exposure. All three acrylic resin materials maintained excellent stability; all materials had shrinkage values in the range of 0.02% to 0.03%. This is clinically insignificant compared to polymerization shrinkage, which averages 0.2%.

A review of attachments for removable partial denture design: Part 2. Treatment planning and attachment selection.

Part 2 follows the initial review of attachment partial dentures presented in Part 1 and considers the analysis of specific treatment requirements to provide a rationale for appropriate attachment selection. The tooth/tissue-supported removable partial denture is carefully reviewed and several treatment philosophies for attachment use in this situation are discussed.

The use of the splint bar in conjunction with removable partial denture treatment.

The use of a bar, joined to lone-standing abutment teeth, that spans an edentulous space is an important treatment option for many partially edentulous situations. The splint bar provides positive vertical support for the removable partial denture while rigidly splinting the abutment teeth. This article defines the situations in which this treatment should be considered and describes the technique to achieve a successful result.

Review of attachments for removable partial denture design: 1. Classification and selection.

An attachment is a mechanical device, other than a clasp assembly, that functions as a direct retainer. Attachments for removable partial denture treatment are reviewed and a method for classifying different types of attachments is provided. Attachments are categorized as precision or semiprecision, depending upon the method of manufacture; internal or external, according to their intracoronal or extracoronal location relative to the abutment tooth; and rigid or resilient, as determined by the amount of movement allowed between the component parts. They are also classified by design. The advantages and disadvantages of attachment use as well as indications and contraindications are considered. Additionally, the conventional clasp-type direct retainer is compared to attachments.

The Transosteal implant in the prosthodontic reconstruction of the edentulous mandible.

It is the purpose of this article to review transosteal implants, specifically the Mandibular Staple Bone Plate and the Transmandibular Implant, in regard to their clinical prosthodontic applications. In addition, those aspects of prosthodontic treatment shared will be highlighted and the differences in the techniques will be reviewed.

Removable partial denture design and fabrication survey of the prosthodontic specialist.

In an effort to better understand and define the present standard of practice for removable partial denture design and fabrication, a questionnaire was prepared and distributed to prosthodontic specialists and graduate students or residents attending the American College of Prosthodontists annual meeting in 1987. The survey was designed to determine the philosophies and techniques used by prosthodontic specialists in treatment involving the removable partial denture. There were 195 questionnaires completed and used in determining the results. The results indicate areas of general agreement. Comparison with other data shows areas of controversy, but prosthodontists tend to follow techniques and philosophies similar to what is taught in most U.S. dental schools and what is recommended by the Academy of Denture Prosthetics.

Template for positioning and angulation of intraosseous implants.

Presurgical planning for submerged implant location and angulation within bone relative to the opposing occlusion is important for the prosthodontist. This information is accurately communicated to the surgeon by using a surgical template. A technique for fabrication of the template is described.

Transfer impression for accurate adjustment of a metal coping insert for the submerged implant.

A technique allowing accurate alignment and interocclusal spacing of the coping insert for submerged implants has been described. Transferring the coping from the mouth to the master cast will provide predictable treatment results and is particularly useful when intraoral visualization is difficult.