Stephan Haney

Precision of fit between implant impression coping and implant replica pairs for three implant systems

STATEMENT OF PROBLEM The fabrication of an accurately fitting implant-supported fixed prosthesis requires multiple steps, the first of which is assembling the impression coping on the implant. An imprecise fit of the impression coping on the implant will cause errors that will be magnified in subsequent steps of prosthesis fabrication. PURPOSE The purpose of this study was to characterize the 3-dimensional (3D) precision of fit between impression coping and implant replica pairs for 3 implant systems. The selected implant systems represent the 3 main joint types used in implant dentistry: external hexagonal, internal trilobe, and internal conical. MATERIAL AND METHODS Ten impression copings and 10 implant replicas from each of the 3 systems, B (Brånemark System), R (NobelReplace Select), and A (NobelActive) were paired. A standardized aluminum test body was luted to each impression coping, and the corresponding implant replica was embedded in a stone base. A coordinate measuring machine was used to quantify the maximum range of displacement in a vertical direction as a function of the tightening force applied to the guide pin. Maximum angular displacement in a horizontal plane was measured as a function of manual clockwise or counterclockwise rotation. Vertical and rotational positioning was analyzed by using 1-way analysis of variance (ANOVA). The Fisher protected least significant difference (PLSD) multiple comparisons test of the means was applied when the F-test in the ANOVA was significant (α=.05). RESULTS The mean and standard deviation for change in the vertical positioning of impression copings was 4.3 ±2.1 μm for implant system B, 2.8 ±4.2 μm for implant system R, and 20.6 ±8.8 μm for implant system A. The mean and standard deviation for rotational positioning was 3.21 ±0.98 degrees for system B, 2.58 ±1.03 degrees for system R, and 5.30 ±0.79 degrees for system A. The P-value for vertical positioning between groups A and B and between groups A and R was <.001. No significant differences were found for vertical positioning between groups B and R. The P-value for rotational positioning between groups A and B and between groups A and R was <.001. No significant differences were found for rotational positioning between groups B and R. CONCLUSIONS The results of the study confirmed that implant systems differ in precision of fit. Vertical precision between paired implant components is a function of joint type and the tightening force applied to the guide pin. The magnitude of vertical displacement with applied torque is greater for conical connections than for butt joint connections. The rotational freedom between paired components is unique to the implant system and is presumably related to the machining tolerances specified by the manufacturer.

Marginal Gap of Milled versus Cast Gold Restorations.

PURPOSE This in vitro study evaluated and compared the vertical marginal gap of cast and milled full coverage gold copings using two margin designs (chamfer and chamfer bevel) before and after fitting adjustments. MATERIALS AND METHODS Ten impressions were made of two metal master dies (one chamfer margin, one chamfer-bevel margin) and poured twice in Type IV stone. The 20 subsequent casts with 40 dies were split into four groups (n = 10); cast gold bevel, cast gold chamfer, milled gold bevel, and milled gold chamfer groups. The cast specimens received approximately 40 μm die relief no closer than 1 mm from the finish line. Cast copings were hand waxed, cast in a high noble gold alloy, chemically divested, and the sprues were removed. For milled gold copings, casts were scanned and copings designed using 3shape D900 scanner and software. Parameters were set to approximate analog fabrication (cement gap = 0.01 mm; extra cement gap = 0.04 mm, drill radius = 0.65 mm). Copings were milled from the same high noble alloy. All copings were seated on their respective master die in a custom scanning jig and measured using a measuring microscope at 90× (60 measurements per specimen, 15 per surface). Following initial measurements, all copings were adjusted on stone dies. The number of adjustment cycles was recorded and post-adjustment measurements were made using the same method. Data were analyzed using independent and paired t-tests. RESULTS Milled gold copings with a beveled margin (11.7 ± 20.4 μm) had a significantly (p < 0.05) smaller marginal gap than cast gold copings with a beveled margin (43.6 ± 46.8 μm) after adjustment. Cast gold copings with a chamfer margin (22.7 ± 24.7 μm) had a significantly (p < 0.05) smaller marginal gap than milled gold copings with a chamfer margin (27.9 ± 31.6 μm) following adjustments. Adjustments significantly decreased marginal gap for both cast groups (p < 0.05) and the milled chamfer bevel group (p < 0.05) but had no significant effect on the milled chamfer group. CONCLUSIONS Within the limitations of this study, results indicate that gold restorations milled with the tested parameters provide a vertical marginal gap that is an acceptable alternative to traditional gold crown casting techniques.

Effect of a temporary cementing agent on the retention of castings for composite resin cores

mass of the castings, oscillations passing through the fixed partial denture, and the light lifting force exerted by the spring under the center of the pontic. It was somewhat surprising that the impacts directed toward the lingual at a 45-degree angle did not result in failure significantly sooner than the vertical impacts. This may be because inclining the line of force toward the lingual plane did not increase the primary leverage arm in a mesiodistal direction. In addition, the vertical component of a 45-degree angle force is only about seven-tenths that of a 90-degree vertical force, and it is the vertical component that produces the most effective tensile force at the distant retainer. It should be noted that impacts angled toward the mesial and distal planes were not tested, nor were angled impacts that fell between the centers of rotation of the two abutment teeth.

Enhancing Fracture and Wear Resistance of Dentures/Overdentures Utilizing Digital Technology: A Case Series Report

Since it was first introduced into the dental world, computer-aided design/computer-aided manufacturing (CAD/CAM) technology has improved dramatically in regards to both data acquisition and fabrication abilities. CAD/CAM is capable of providing well-fitting intra- and extraoral prostheses when sound guidelines are followed. As CAD/CAM technology encompasses both surgical and prosthetic dental applications as well as fixed and removable aspects, it could improve the average quality of dental prostheses compared with the results obtained by conventional manufacturing methods. The purpose of this article is to provide an introduction into the methods in which this technology may be used to enhance the wear and fracture resistance of dentures and overdentures. This article will also showcase two clinical reports in which CAD/CAM technology has been implemented.

Management of Challenging Esthetic Anterior Cases with Limited Restorative Space: A Clinical Report: Challenging Esthetic Cases with Limited Restorative Space

With careful restorative planning and surgical placement, dental implants can be used to support and retain a wide range of esthetic prostheses. When implant planning or surgical executions are less than ideal, however, the resulting restorative space can be a significant obstacle to successful treatment. The aim of this article is to describe the use of a customized anterior bar to support a partial overdenture prosthesis for a youthful patient with a high smile line and a limited restorative space of 6 mm. Details of the treatment and an illustration of the customized design are also presented.

Marginal discrepancy of noble metal–ceramic fixed dental prosthesis frameworks fabricated by conventional and digital technologies

Statement of problem. Studies evaluating the marginal adaptation of available computer‐aided design and computer‐aided manufacturing (CAD‐CAM) noble alloys for metal‐ceramic prostheses are lacking. Purpose. The purpose of this in vitro study was to evaluate the vertical marginal adaptation of cast, milled, and direct metal laser sintered (DMLS) noble metal‐ceramic 3‐unit fixed partial denture (FDP) frameworks before and after fit adjustments. Material and methods. Two typodont teeth were prepared for metal‐ceramic FDP abutments. An acrylic resin pattern of the prepared teeth was fabricated and cast in nickel‐chromium (Ni‐Cr) alloy. Each specimen group (cast, milled, DMLS) was composed of 12 casts made from 12 impressions (n=12). A single design for the FDP substructure was created on a laboratory scanner and used for designing the specimens in the 3 groups. Each specimen was fitted to its corresponding cast by using up to 5 adjustment cycles, and marginal discrepancies were measured on the master Ni‐Cr model before and after laboratory fit adjustments. Results. The milled and DMLS groups had smaller marginal discrepancy measurements than those of the cast group (P<.001). Significant differences were found in the number of adjustments among the groups, with the milled group requiring the minimum number of adjustments, followed by the DMLS and cast groups (F=30.643, P<.001). Conclusions. Metal–ceramic noble alloy frameworks fabricated by using a CAD‐CAM workflow had significantly smaller marginal discrepancies compared with those with a traditional cast workflow, with the milled group demonstrating the best marginal fit among the 3 test groups. Manual refining significantly enhanced the marginal fit of all groups. All 3 groups demonstrated marginal discrepancies within the range of clinical acceptability.