The International Journal of Prosthodontics, 04/2000

Purpose: To determine if the typical mechanical resistance of one-piece castings can be maintained with an elevated level of marginal precision, the authors evaluated 10 consecutive castings obtained using their normal laboratory techniques for one-piece castings. Materials and Methods: For the evaluation of the marginal precision of the castings, a new method that uses a scanning electronic microscope (SEM) integrated with a computerized measuring system was developed. This method proved to be precise and reliable. A total of 3,564 measurements at 3003 was made of the vertical marginal openings of 10 castings structured with 3 abutments and 2 pontics (casting length 43 mm, mean weight 10.4 g). Results: The mean of such measurements of the marginal openings was 22 µm, although if 2 castings that were judged to be clinically unsuitable when produced are excluded, the abovementioned average is 16 µm. Conclusion: The proposed casting technique can offer one-piece castings of higher quality, with a level of precision that introduces a new reference standard in the marginal accuracy of these castings in fixed prostheses.

Purpose: The purpose of this prospective multicenter study was to evaluate and compare the clinical performance of laser-welded titanium fixed partial implant-supported prostheses with conventional cast frameworks. Materials and Methods: Forty-two partially edentulous patients were provided with Brånemark system implants and arranged into 2 groups. Group A was provided with a conventional cast framework with porcelain veneers in one side of the jaw and a laser-welded titanium framework with low-fusing porcelain on the other side. The patients in group B had an old implant prosthesis replaced by a titanium framework prosthesis. The patients were followed for 3 years after prosthesis placement. Clinical and radiographic data were collected and analyzed. Results: Only one implant was lost, and all prostheses were still in function after 3 years. The 2 framework designs showed similar clinical performance with few clinical complications. Only one abutment screw (1%) and 9 porcelain tooth units (5%) fractured. Four prostheses experienced loose gold screws (6%). In group A, marginal bone loss was similar for both designs of prostheses, with a mean of 1.0 mm and 0.3 mm in the maxilla and mandible, respectively. No bone loss was observed on average in group B. No significant relationship (P > 0.05) was observed between marginal bone loss and placement of prosthesis margin or prosthesis design. Conclusion: The use of laserwelded titanium frameworks seems to present similar clinical performance to conventional cast frameworks in partial implant situations after 3 years.

Purpose: Previous studies have shown that molar teeth pulsate at rest and displace linguoapically during clenching at maximal intercuspation. The aim of this study was to investigate interproximal contact during clenching by means of a charge coupled device (CCD) microscope. Materials and Methods: Two male subjects aged 28 years with normal dentition and occlusions were selected for in vivo research. Optimum contact tightness was observed at contact points that were defined by some resistance to the insertion of a 50-µm-thick stainless steel strip, with no resistance to the insertion of a 110- µm strip. Spaces between the teeth were detected using a CCD microscope on the buccal side by light bands emitted from the lingual side. During static observation, the chosen distance between the microscope and light guide was maintained using a special device. For dynamic observation, a palatal and lingual plate with a light source was fitted to each subject. Subjects were directed to clench with habitual occlusal force. To compare with in vivo observations, the relation between the width of the light band and the interproximal distance was estimated in vitro using 2 extracted teeth. Light bands were analyzed using software. Results: In the 2 subjects studied, there was a 3- to 21-µm distance between adjacent teeth at rest, which disappeared during clenching. Conclusion: The results of the study sample examined indicate that teeth do not make contact with adjacent teeth at rest, but do so during clenching.

Purpose: The aim of this study was to examine the long-term periimplant bone loss in patients treated with implant-supported fixed prostheses in both jaws. Materials and Methods: The participants comprised 44 edentulous patients who have been followed for a 15-year period after treatment with a fixed implant-supported prosthesis in the mandible. Thirteen of them also received an implant-supported fixed prosthesis in the maxilla, on average 4.5 years after the mandibular treatment. The periimplant bone level was measured on intraoral radiographs. Results: The long-term results of the implant treatment were successful, and only 1% (3/273) of the implants were lost in the mandible and 7% (5/75) in the maxilla. All but one of the failures occurred before the connection of the prostheses. The mean marginal bone loss around the implants was small (less than 1 mm for a 10-year period after implant placement), and was of similar magnitude in both jaws. However, the individual variation was relatively great. There was no significant difference in marginal bone loss between those who had a maxillary complete denture during the entire observation period and those who had received a fixed implantsupported maxillary prosthesis. Smokers lost more periimplant bone than did the nonsmokers; the difference was significant in the mandible but small and nonsignificant in the maxilla. Conclusion: The long-term periimplant bone loss was small and of similar magnitude in the mandible and the maxilla in subjects who had received implantsupported fixed prostheses in both jaws. The prosthetic status in the maxilla, ie, complete denture or fixed implant-supported prosthesis, had no significant influence on the mandibular periimplant bone loss.

Purpose: Functional relationships between occlusal errors and articulator settings have been the subject of numerous investigations. It is, however, not known how frequently errors of a certain size occur under practical conditions. This study attempted to estimate the frequency of occlusal errors that can be expected with the different levels of registration and articulator adjustment that are currently used. Materials and Methods: In 57 asymptomatic subjects, individual articulation parameters, including the condylar and Bennett angles, the spatial relation of dental arches, and the intercondylar distance, were determined experimentally. Tooth-guided lateral movements of the subjects' casts were simulated in a virtual articulator that was programmed to the individual parameters of each person. With respect to this reference setting, occlusal errors that would emerge with different modes of semiindividual adjustment were calculated. The intercondylar distance thereby remained fixed at 110 mm. Results: With complete mean value setting, occlusal errors would exceed 200 µm at the second molar in 16% of the subjects and 300 µm in 6% of the subjects. Individual facebow registration of condylar angles and spatial relations would reduce these rates to 13% (200 µm) and 3% (300 µm). With additional setting of Bennett angles, occlusal errors would exceed the mentioned limits in no more than 1.6% and 0.1% of cases, respectively. This extensive mode of adjustment became, however, increasingly ineffective with higher demands for occlusal accuracy. Conclusion: Complete mean value setting is associated with a relatively low risk of occlusal errors exceeding tolerance limits that are widely accepted in practice. Compared to mean value setting, facebow registration of condylar angle and relations yields no profitable improvement of occlusal accuracy.

Purpose: The objective of this study was to examine the cytotoxic effect of methyl methacrylate (MMA) monomer on 4 mammalian fibroblasts. Materials and Methods: Four cells-C3H10T1/2, L929, Balb/3T3 clone A31, and MC3T3-E1-were incubated for 6 days in 24-well microplates filled with 1 mL of Dulbecco's Modified Eagle medium containing MMA monomer that ranged from 0 to 200 mM/L. Cytotoxicity was evaluated by direct cell number count. Results: L929 possessed the largest TC50 value (the amount of MMA that caused 50% cell death) (34 mM/L), and Balb/3T3 clone A31 had the least value (1 mM/L); C3H10T1/2 and MC3T3-E1 had intermediate values (25 mM/L and 16 mM/L, respectively). Conclusion: This study showed that the MMA monomer had dosedependent cytotoxicity, which varied among the cells tested.

Purpose: Over the last decade, oral implantology has become a major treatment modality to aid the restoration of reduced dentitions. The present study monitored and quantified changes within a 5-year interval (1989-1991 [denoted as 1990*] to 1995) in the provision of different types of implant-supported superstructures and characteristics of recipient patients at the Academic Centre for Dentistry Amsterdam (ACTA). Materials and Methods: All patients who received oral implants in 1990* and in 1995 were selected, and their files (95 and 105, respectively) were consulted. Data of interest were retrieved retrospectively, compared, and statistically analyzed using Chi-squared tests. Results: A number of statistically significant differences was apparent between these 2 periods. By 1995 there was a threefold increase in both the number of patients and the number of implants placed per year. The patient group of ! 40 years of age had significantly increased, from 7% to 23%. Also, in 1995 more maxillae were implanted than in 1990* (44% vs 26%). Whereas the majority of implanted patients was edentulous in 1990* (64%), the majority in 1995 was partially edentulous (60%). By 1995, the new technique of guided bone regeneration (GBR) using membranes was evidenced (no GBR in 1990* vs 33% of all patients in 1995 receiving some form of local GBR therapy). With respect to the type of superstructures, there was a strong increase in the number of single-tooth replacements (from 4% to 23%). In the edentulous group, the majority of superstructures in 1990 was fixed prostheses (64%), whereas in 1995 the majority was overdentures (71%). Conclusion: Major changes in oral implantology treatments were noticed between the 1990* and 1995 periods at ACTA. There is a trend toward implanting younger patients for partial implant-supported reconstructions using more regenerative procedures and with a more equal distribution in the maxilla and mandible.

Purpose: Fatigue behavior of luting cement film between model fixed partial dentures (FPD) and their dies was investigated to gain a better understanding of the mechanical properties of zinc-phosphate cement. Materials and Methods: Fifty-six brass dies were made, half of them with grooves and half without grooves. A cantilever FPD for each die was cast in Au-Pd-Ag alloy. Four linear strain gauges were attached to the marginal portions of each retainer. The FPDs were cemented to the dies using zinc-phosphate cement. A fatigue test machine was used to cyclically load the specimens with 50 or 100 N for 5.5 3 105 cycles (1 Hz) in 37°C water. During the fatigue test, strain measurements were made after every 0.5 3 105 load cycles to discover if strain response was altered. After completion of the fatigue test, ultimate tensile strength of each specimen was measured and statistically analyzed by 2-way analysis of variance. Results: With or without grooves, strain responses were the same at every periodic strain measurement throughout the 50-N fatigue test. For the 100-N fatigue test, strain responses for the specimens without grooves were different before and after cyclic testing, but there was no difference for the specimens with grooves. There were no significant differences in tensile strength among the specimens after the fatigue tests. Conclusion: No fatigue fracture was observed in zinc-phosphate cement film after repetitive loading. Repetitive loading may improve stress transmission within the zinc-phosphate cement film.

Purpose: This study aimed to determine whether patients with long-standing nocturnal bruxing behavior present different body movement activity during sleep compared with healthy subjects. Materials and Methods: Eleven bruxers and 8 nonbruxers were studied in the sleep laboratory, and motor activity was detected with sensor pads placed under the mattress. Movements simultaneously recorded on videotapes were classified according to their duration and grouped in different types according to their characteristics. Results: Subjects with bruxism had significantly more movements during sleep compared with controls; the difference was especially obvious for movements of short duration ( 5 seconds). The differences became significant from the fourth hour of sleep. These short movements were twitches, jerks, or any sudden, brusque movements of the extremities, but without the periodicity encountered in, for example, periodic limb movements during sleep. No significant relationship was found between the occurrence of masseter activity and movements. Conclusion: The findings suggest that subjects with nocturnal bruxism have movement disorders that are expressed not only as grinding or clenching of the teeth, but also as an increase of short-duration body movements during sleep. This reinforces the hypothesis of a central etiology common to both bruxism and short movements during sleep.

Purpose: The aim of this study was to determine the effect of long-term water immersion on the flexural properties of fiber-reinforced composite. Materials and Methods: Continuous, woven, silanized E-glass fibers and woven silica fibers were used to reinforce heat-cured and autopolymerized denture base polymers. Fibers were oriented at a 45- degree angle to the long axis of the test specimens. Control specimens were unreinforced. Dry test specimens and those stored in water for up to 180 weeks were tested with a 3- point loading apparatus. Results: Ultimate transverse strength and flexural modulus of unreinforced and fiber-reinforced composite test specimens decreased during water storage (P 0.001, analysis of variance). Post hoc analysis revealed that after the storage of 4 weeks no statistically significant reduction occurred. Conclusion: The results of this study suggest that the ultimate transverse strength of the fiber-reinforced composite made from E-glass fibers is reduced by approximately 27% compared to the dry fiber-reinforced composite. The majority of the reduction occurred during 4 weeks of storage in water and remained approximately at that level for 180 weeks.

Purpose: This long-term follow-up study aimed to compare the outcome of fixed prostheses supported by teeth and implants and by freestanding implants only. Materials and Methods: From prosthesis insertion up to 14 years (mean 6.5 y), 18 patients were followed. Implant-supported prostheses with and without tooth connection were compared within the same jaw. The tooth-implant prostheses were supported by 30 implants and 30 teeth, and the freestanding prostheses were supported by 48 implants. Implant outcome, marginal bone stability, and mechanical complications were recorded. Results: Neither implant mobility nor fractures of any component of the implants were observed. No prosthesis complications were observed, and the same applied for crown cement failure and intrusion of teeth. Only one periapical lesion was detected at the first follow up. The annual change of the marginal bone level around connected and freestanding implants did not differ significantly. The mean marginal bone loss (over the 2 groups) for the first 6 months amounted to 1.08 mm. After the first 6 months, an annual marginal bone loss of 0.015 mm was observed. There was no difference between the 3 connection types (single implant connected to single tooth, multiple implants and/or multiple teeth connected with single connector, and multiple connectors) for the first 6 months or thereafter. The marginal bone loss (over the 3 groups) for the first 6 months was 1.15 mm. After the first 6 months, the annual bone loss (over the 3 groups) amounted to 0.015 mm. Conclusion: Based on the results of this study, splinting teeth with implants for implant-supported fixed prostheses did not affect the long-term outcome in comparison to freestanding implants.