The International Journal of Prosthodontics, 06/1997

An in vitro nondestructive fatigue test was applied to adhesive posts and cores made on endodontically treated human teeth. Five post-and-core systems were evaluated: one zi rcon oxide post, two titanium osts (with resinous or ceramic coating), and two resin-fiber posts. Each test specimen was intermittently loaded and thermocycled. The scanning electron microscope observation of sample sections showed that only the interfaces between restorative materials and dentin exhibited substantial deficiencies. The Komet ER (Brasseler) exhibited the greatest percentages of continuity at the coronal (83.88%) or the radicular (78.12%) dentin levels, while the Zircon experimental post presented insufficient adaptation to the radicular (21.25% continuity) and to the coronal (53.25% continuity) dentin. Seven of eight samples in the Komet group showed root fractures. The carbon-fiber post (Composipost) behaved satisfactorily (67.38% radicular continuity), in spite of the use of an older bonding agent formulation.

This study evaluated the resistance to plastic deformation under a flexural load (PLf) of a denture base material relined with four different types of denture reline materials. A heat-processed poly(methyl methacrylate) denture base was relined with varying thicknesses of denture reline materials and subjected to a flexural load. The flexural load at the proportion limit (PLf) was recorded. The PLf of the bulk denture base and denture reline materials were also measured for comparison. All relined denture bases showed significantly lower PLf than the bulk denture base. Generally, the PLf of the reline-denture base composite progressively decreased with an increasing proportional thickness of the reline material

This study obtained information on the long-term efficiency of prosthetic rehabilitation with fixed partial dentures performed by undergraduate students. From a list of discharged patients treated from 1975 to 1976 by undergraduate students at a dental school, 101 were recalled for free clinical examinations after 6, 11, and 18 years. A total of 163 fixed partial dentures were inserted. The majority (85%) of the fixed partial dentures were acrylic resin veneer-gold restorations; 15% were metal ceramic restorations. During this study period, 14 individuals died, leaving 138 fixed partial dentures to be examined. Of these, 35 (25%) were removed after a mean of 11 eyars in function, which left 75% in place and functioning after 18 years. The main causes for removal included caries, periodontitis, root fracture, and endodontic complications. Fewer metal ceramic restorations than acrylic resin veneer-gold restorations were removed. The removal rate for abutments with cast posts and cores was higher than the removal rate of total abutments. There was no difference in removal frequency between fixed partial dentures with moderate cantilever extensions and thsoe with end-supported extensions.

This investigation evaluated the shear rebond strength of Rexillium III to enamel using various resin composite luting systems (Panavia, Imperva Dual, ABC Enhanced, C & B Met abond, Optibond, and Comspan). Cast Rexillium III cylinders (3.9% x 6.0 mm) were bonded to human molar buccal enamel surfaces (n = 8) with each cement type after etching with 37% phosphoric acid for 30 seconds. Bonded specimens were stored in distilled water for 7 days at 37 degrees C ± 2 degrees C and thermocycled (1,500 cycles) in 5 degrees C and 55 degrees C water baths (1 minute dwell time). Specimens were randomly tested in shear mode on an Instron Testing Machine at a crosshead speed of 0.5 mm per minute. Debonded specimens were then rebonded after appropriate metal conditioning and re-etching the enamel surface for 30 seconds. Analysis of variance (P < 0.001) and the Ryan-Einot-Gabriel-Welsh multiple range test showed significant differences between several of the resin cements (P < 0.05). Panavia exhibited significantly higher shear rebond strength than any of the other cements tested. Only Imperva Dual exhibited a significantly lower shear rebond strength compared to its initial shear bond strength.

Replication of desirable design features of an existing implant prosthesis is often appropriate in the construction of a replacement that produces the same spatial relationship to the supporting dental implants. An adaptation of a laboratory copy technique used in conventional complete denture prosthodontics is described. A silicone putty mold that enables the creation of the corresponding fit surface, polished surface, and archform is s ued for making a transitional or a definitive complete or partial fixed implant prosthesis. Variations using a basic replication technique are appropriate in clinical practice for refabricating a prosthesis of a preferred design. The procedure is suitable for both acrylic resin-metal or metal ceramic restorations.

In Part I of this two-part study, the authors investigated heat production during osteotomy drilling at three different speeds, and determined that high-speed drilling produced the least heat when using 700 XL carbide burs. Part II of the study histologically examines the rate and quality of healing after drilling osteotomies at the three speeds in the mandible. Osteotomies were histologically examined 2, 4, and 6 weeks postoperatively. Histologic findings suggested that in the initial 6 weeks, the rate ofhealing and quality of new bone formation were higher after high-speed drilling than after low-or intermediate-speed drilling. These results, when considered wi th the results reported in Part I in which a 4.3 degrees C difference in heat production was observed between the speeds, seem to imply a relationship between heat production and healing for osteotomy drilling.

This study evaluated the Digitizing Computer System (DCS Production) for computer-controlled fabrication of titanium copings. The three-dimensional shape of the crown preparations was acquired through micropalpation with a contact digitizer on the master cast. In this in vitro study t he marginal fit of computer-machined titanium frameworks for veneered crowns was assessed using scanning electron microscopy. Measurement of the marginal gap between the framework and the tooth was performed along the entire length of the finish line. The evaluation was based on 1,475 individual measurements on 10 test specimens. The mean values of marginal fit for the individual crowns ranged from 21.2 ± 14.6 um to 81.6 ± 25.1 Um. The mean value for all crowns was 47.0 ± 31.5 um.

In this study fatigue resistance of experimentally prepared titanium-nickel (50.8% nickel and 49.2% titanium) cast clasps was evaluated in a simulated clinical situation. The change in force required to remove the titanium-nickel clasps was recorded under a repeated placement-and-removal test on steel model abutment teeth. Commercially-pure titanium, cobalt-chromium alloy, and gold-silver-palladium-copper alloy clasps were also tested for comparison. The tips of the clasps were located in the 0.25- and 0.50-mm undercut areas of the abutments. No signific ant changes in the retentive force were found in titanium-nickel clasps in the 1,010 repeated cycles, whereas the other three types of clasp revealed a significant decrease in the force required for removal during the test procedures (repeated alaysis of variance P < 0.001). The results suggest that the cast titanium-nickel clasp may be suitable in removable prosthodontic constructions because of its significantly less permanent deformation during service. This report also discusses clinical applicability and some current problems with this new application.

This study describes salivary fluoride levels after topical fluoride gel application on overdenture abutments. Fluoride levels were evaluated separately for the subjects with normal unstimulated salivary flow rate (n = 16) and for those with a low flow rate (n= 8). One drop of fluoride gel (Karigel-N, Lorvic) was placed in two abutment depressions of the duplicated overdenture, after which unstimulated whole saliva was collected for 30 minutes. Samples for fluroide analysis were taken at 5-minute intervals. Two additional samples were taken at 45 and 60 minutes. Fluoride concentration at the abutment-denture interface (remaining fluoride concentration) was measured at the end of the study. Salivary fluoride concentrations decreased gradually in both groups of subjects, but after 1 hour they remained at a higher level in subjects with low flow rates. Subjects' salivary flow rates correlated negatively with remaining fluoride concentration at the denture-tissue interface. Consequently, mean remaining fluoride concentration was significantly higher in subjects with low flow rate than in their normal counterparts.

Thirty-five implant torque wrenches were tested for torque delivery accuracy. Seven of these drivers had a 10-Ncm value, 12 had a 20-Ncm value, 10 had a 30-Ncm value, and six had a 35-Ncm value. All of the wrenches had been in clinical service for a minimum of 1 month or a maximum of 3 years and were assumed by the clinicians to be fully effective in delivering the required torque values. Torque delivery accuracy was determined using a Tohnichi torque wrench calibrated to ± 1% of the scale value. All torque wrenches had been subjected to steam sterilization following clinical use. Data collected on all wrenches included (1) age since purchase, (2) number of sterilization cycles to which each wrench had been subjected during the use period, and (3) 10 sequential torque readings using the Tohnichi wrench as the torque reading device. The results of this study showed that there was no significant correlation of delivered torque with (1) age or (2) number of sterilization cycles. Furthermor e, in each torque category there wre torques botha bove and below the control values. For the 10-Ncm torque wrenches, the largest value was 455.0% greater than the control, the largest values were 41.6% greater for 20-Ncm wrenches, 17.0% greater for the 30-Ncm torque wrenches, and 58.6% greater for the 35-Ncm wrenches. Corrosion of the spring in the handle of the torque wrench was found to be the reason for the 455.0% value.