The International Journal of Prosthodontics, 06/2001

Purpose: The purpose of this study was to develop a method to integrate three dimensional data of dentition and facial morphology measured by a high-speed laser scanner, and visualize them by computer graphics. The accuracy of integration was also examined. Materials and Methods: The 3-D shapes of upper and lower dental casts and the face of a subject were measured by a high-speed laser scanner with zoom lens facility. As an interface to integrate the coordinates between dentition and face, an extraoral marker plate attached to the occlusal record plate was devised. It was applied between the upper and lower dental casts, and with the subject, and measured. Integration was attempted by coinciding the data of the interface. The accuracy of integration was examined using the conditions of the marker plate such as surface shape and attachment angle. Results: Integration of the data of dentition and face was accomplished. The 3-D relationship between them could be visualized in any direction or section by computer graphics. For optimal accuracy of integration, the marker plate with a mixed shape of flat and sinusoidal wave attached at 45 degrees to the occlusal record plate showed the most appropriate results. Conclusion: An original method to integrate the 3-D data of dentition and face measured by 3-D laser scanner was developed and shown to have acceptable accuracy.

Purpose: This is a report on Procera AllCeram crowns in a prospective multicenter study. The aim of the study was to evaluate AllCeram crowns in dental practice over a 5- to 10.5- year period. Some of the AllCeram crowns were among the very first that were placed. Materials and Methods: The crowns were placed between 1989 and 1995. Twelve clinicians at nine clinics placed 87 crowns in 50 patients. The California Dental Association quality evaluation system was used for assessment of marginal integrity and esthetics. Results: After 5 and 10 years a cumulative survival rate of 97.7% and 93.5%, respectively, and a cumulative success rate of 97.7% and 92.2%, respectively, was recorded. Six crowns (7%) were recorded as failures; five of these crowns (6%) had to be remade. The marginal integrity was considered excellent or acceptable for 92% of the crowns. Bleeding was somewhat more often recorded at teeth with AllCeram crowns (39%) than at contralateral teeth (27%). Endodontic treatment was performed for a low number (2%) of the AllCeram crowns. The patients found the esthetics to be excellent. Conclusion: The results of this study demonstrate about the same clinical outcome as has been reported by similar studies on all-ceramic crowns built on a core of alumina. The outcome is also in agreement with that reported for metal-ceramic crowns. The results indicate a good prognosis for Procera AllCeram crowns also for posterior teeth.

Purpose: The purpose of this study was to investigate the vibration characteristics of three different designs of mandibular major connectors in vitro by observing modal animation, decay rate, and maximum amplitude. Materials and Methods: Three removable partial denture frameworks-lingual bar, Kennedy bar, and lingual plate-were studied. They were excited by a shaker, and the frequency response functions were recorded on a Fast Fourier Transformational analyzer to identify their modal shapes. Natural frequency and animation of motion at each natural mode of vibration of the three frameworks were observed. In addition, transient response simulations were recorded, and decay rates and maximum amplitude of the resultant transient response waves were computed. Results: The mean decay rate calculated from all the measurement points of the lingual bar, Kennedy bar, and lingual plate was 3.10 s-1 (standard deviation [SD] 0.07), 2.42 s-1 (SD 0.04), and 2.01 s-1 SD 0.03), respectively. Significant differences in decay rate were found among all pairs (P.001). Maximum amplitude of the direct and indirect retainers at the nonimpacted side also differed (P =.008). Conclusion: All three designs demonstrated no elastic deformation at each natural mode of vibration. In terms of vibration analysis, the lingual bar demonstrated the maximum decay rate and the minimum maximum amplitude of the direct and indirect retainers, both on impacted and nonimpacted sides, indicating that the lingual bar will dissipate the energy through vibration faster than the other designs. Hence, the possibility of creating harmful effects to the oral tissue is lesser.

Purpose: The aim of this clinical study was to evaluate if an arbitrary facebow registration and transfer provides significant advantages for the fabrication of an occlusal appliance in comparison with the omission of such a procedure. Materials and Methods: For 20 fully dentate adult patients diagnosed with bruxism, two Michigan occlusal splints were constructed. One of the two upper dental casts was transferred to the articulator with an arbitrary earpiece facebow; the other maxillary cast was mounted arbitrarily using a flat occlusal plane indicator. Upon splint delivery, the number of intraoral occlusal contacts and the time needed for chairside occlusal adjustment were recorded. Results: The number of occlusal contacts on the appliance fabricated with or without facebow was similar in most cases both in the articulator and in the mouth. The one-sided Wilcoxon rank sum test showed with high probability that the use of an arbitrary facebow does not yield a clinically relevant improvement with regard to the number of occlusal contacts or the chairside adjustment time. Conclusion: From this pilot study, it appears that for the fabrication of an occlusal appliance, registration and transfer with an arbitrary earpiece facebow does not yield clinically relevant benefits. Of course, this conclusion cannot be transferred to other facebows and is restricted to the levels of clinical relevance defined in the study.

Purpose: The purposes of this study were to develop a technique to measure the angulation between two implants and between each implant and reference planes, to analyze the relationship between the maintenance (adjustments and repairs) of ball-attachment mandibular implant overdentures and implant angulation, and to see if there is any correlation between surgeon experience and implant orientation. Materials and Methods: Final casts of 41 patients who had received two-implant ball-attachment mandibular overdentures were used to measure implant angulations using digital photographs and plane geometry. The measured angles were compared with the number of adjustments and repairs of the prostheses and analyzed by surgeon experience for any trends. Results: No significant relationships were found between number of adjustments and repairs and the interimplant angles. However, there was a significantly higher number of repairs when the lingual inclination of an implant was >= 6.0 degrees (P =.033) or if the facial inclination was 6.5 degrees (P = .036). Less experienced surgeons had a significantly greater tendency to place implants that diverged from each other in the frontal plane (P =.045) and with a facial or lingual inclination in the sagittal plane (P =.035). Conclusion: While interimplant angulation did not appear to affect prosthesismaintenance, individual implants with a lingual inclination >= 6 degrees and a facial inclination 6.5 degrees were associated with significantly more prosthesis repairs. There was a tendency for implants placed by less experienced surgeons to demonstrate greater inclination.

Purpose: This study reports the effect of five surface treatments on the bond strength established between three denture reline materials and a denture base resin. Materials and Methods: Cylindric columns of denture reline materials were bonded to columns of denture base resins that received one of the surface treatments: application of dichloromethane, the monomer of the denture base resin, the recommended bonding agent or the monomer of the denture reline material, polishing with 240-grit silicone carbide paper, and air abrasion. A control group without surface treatment was included for each material. Specimens were immersed in water for 1 day and then thermocycled. The strength at which the bond failed under shear was recorded. Results: None of the surface treatments significantly improved the bond strength of Kooliner. Triad bonding agent and denture base monomer applications most significantly improved the bond strengths of Triad and GC reline, respectively. Conclusion: Triad bonding agent and denture base monomer should be used in conjunction with Triad and GC reline, respectively, when relining a denture base resin.

Purpose: The aim of this 5-year longitudinal study was to investigate the influence of the retention mechanism for overdenture fixation on the periimplant parameters of mandibular implants. Materials and Methods: Ninety edentulous patients, each with two interforaminal implants supporting an overdenture, participated in the study. They had received either a straight or slightly bent round clip bar, a U-shaped rigid bar with or without distal extensions, or single-ball anchors. Anatomic-morphologic and prosthetic variables were assessed related to the implant position and the type of overdenture retention. The degree of mandibular atrophy was determined using cephalometric radiographs. The angle ß between the virtual axis connecting both implants and the mandibular hinge axis was measured on mounted casts. A supporting surface was identified between bent clip bars and U-shaped extension bars. Clinical periimplant parameters were recorded, and changes of the probing attachment level after 5 years were analyzed in 70 patients with respect to the retention device and anatomic-morphologic and prosthetic variables. Results: A significant increase of the Plaque Index was observed after 5 years. The mean clinical attachment loss after 5 years was about 0.2 mm. In more than 50%, ß was small, ie, = 5 degrees. For these implants, loss of clinical attachment was significantly lower. The correlation between attachment loss and ß was weak, while no significant correlation was found with regard to the degree of atrophy and surface. Conclusion: In view of the long observation period, it was concluded that the position and retention mechanism of mandibular implants supporting an overdenture have little influence on the long-term stability of the clinical parameters.

Purpose: The aim of this study was to evaluate the efficacy of a new bonding-luting system in resin tag, adhesive lateral branch, and hybrid layer formation when used in combination with an experimental fiber post. Materials and Methods: Thirty anterior teeth extracted for periodontal reasons were selected for this study. They were endodontically treated and randomly divided into three groups of 10 samples each: group 1 = Excite light-cured bonding agent in combination with Variolink II resin cement; group 2 = Excite dual-cured bonding agent self-activated by an experimental microbrush in combination with MultiLink resin cement; and group 3 = one-step bonding system in combination with Dual Link resin cement. In groups 1 and 3, the primer-adhesive solution was light cured before placing the resin cement and the post, whereas in group 2 the adhesive/luting materials were not light cured. Twenty FRC Postec translucent posts (groups 1 and 2) and 10 EndoAesthetic translucent fiber posts (group 3) were used. One week later, the root samples were processed for scanning electron microscopic (SEM) observations. Results: Microscopic examinations of restored interfaces from group 2 revealed a resin-dentin interdiffusion zone higher than that seen in samples from groups 1 and 3 (P .05). At the apical and middle thirds, the samples from group 2 showed significantly more resin tags than the other two groups. Conclusion: The dual-cure self-activating system showed a more uniform resin tag and resin-dentin interdiffusion zone formation along root canal walls than light-curing systems.

Purpose: This study was undertaken to investigate the relationship between occlusal variables and clinical and radiologic findings as well as patient response to treatment outcome in patients with mandibular implant-supported fixed prostheses opposing maxillary complete dentures. Materials and Methods: The study group consisted of 109 consecutive patients attending for annual control. They had received their mandibular implant-supported prostheses according to the Brånemark system on average 8 years previously (range 1 to 27 years). All patients were interviewed with standardized questions by one examiner, who also performed the clinical examination. The questions focused on the patients' opinion on masticatory and prosthetic function and problems. The clinical examination comprised occlusal and prosthetic factors and the health of the oral mucosa. Results: The great majority of the patients were very satisfied with their present dental situation and masticatory function. Two thirds reported no problems with their maxillary complete dentures at all. Balanced occlusion was found bilaterally in 61%, and a further 4% had balanced function on one side. More than one third thus lacked balanced occlusion. Only about 60% had optimal occlusion, and 8% had poor occlusion according to common prosthodontic criteria. This was interpreted as a continuing impairment of the occlusion with time. The mean bone loss was 0.5 mm, according to available radiographs, for a mean observation period of 54 months. There were no or only weak correlations between the variables examined. Conclusion: The occlusal factors registered were of limited importance for patient satisfaction and treatment outcome recorded clinically and radiographically at follow-up examination of the actual prosthodontic rehabilitation.

Purpose: The purpose of this study was to evaluate the ability of newer fluoride-releasing restorative materials to protect the root surface from acid attack. Materials and Methods: The materials used were glass-ionomer cement (GIC), resin-modified glass-ionomer cement (RM-GIC), and a compomer (Comp). A composite resin (CR) was used as the control. The restored teeth were stored in deionized, distilled water for 14 days and subjected to 300 thermocycles (55°C and 5°C). The teeth were cycled in a demineralizing solution (pH 5.0 or 4.0) for 6 hours and in a remineralizing solution (pH 7.0) for 17 hours for 10 days. The depths of lesions created by acid challenge were measured at the interface of the tooth and the restorative material and then at a distance of 50, 100, and 300 µm from the tooth-restoration margin using polarized light microscopy and contact microradiography. Results: At pH 4.0, there was significant difference in the depth at the interface between the tooth and the restorative material (P .001). The GIC and RM-GIC were protective, and the lesion depths were significantly shallower than for Comp or CR. The protective effect varied depending on the distance from the interface of the tooth and the restorative material. At pH 5.0, the GIC and RM-GIC had no lesions at the interface, while the Comp and the CR had lesions (P .001). Conclusion: Fluoride-releasing glassionomer cement seems to be an appropriate material to seal the root canals of overdenture abutments, because it has an inhibiting effect on demineralization at the cavity wall in vitro.

Purpose: Previous studies proposed to estimate masticatory forces from electromyograms (EMG) by substituting chewing activities of a particular muscle into bite force-activity relations obtained from isometric clenching. For biomechanical reasons, this method requires that ratios between muscle forces in chewing be the same as in clenching. The purpose of this study was to investigate whether this assumption is valid. Materials and Methods: In 32 asymptomatic subjects, EMGs of bilateral temporal and masseter muscles were registered in unilateral clenching on a bite fork and in chewing. Ratios of peak activities of different muscles were compared between the two biting tasks. Results: In clenching, the working:balancing ratio of the masseters amounted to 0.92, while in chewing this ratio increased to 1.9. The working:balancing ratio of the temporalis was 1.8 in clenching and dropped to 1.3 in chewing. The temporalis:masseter ratio on the balancing side increased from 0.65 in clenching to 1.1 in chewing. Conclusion: The finding that ratios of muscle activities in chewing differed from corresponding ratios in clenching implies different combinations of muscle forces and/or different bite force-activity relations in the two biting tasks. In any of these cases, prediction of chewing force from the EMG of a particular muscle could lead to indefinite overestimations.

Purpose: The aim of this article is to describe a technique that attempts to solve titaniumrelated problems while affording passive fit. Materials and Methods: The method basically involves the manufacture of a cast titanium framework fitted onto titanium machined abutments. After verifying the passive fit of the framework presoldered to the abutments, Nd-YAG laser welding is completed in the laboratory. Results: The aim of the technique is to secure the following clinical benefits: (1) use of titanium, as it is the best-suited material; (2) use of high-precision machined abutments; (3) laser welding and its advantages; and (4) achievement of passive fit. Conclusion: The technique described is adequate to achieve passive fit in implant prostheses using titanium and laser welding.

Purpose: The purpose of this study was to evaluate clinical treatment outcome of fixed prostheses in different sizes and with combinations of different numbers of teeth and implants as abutments. Materials and Methods: A total of 115 implants were placed in 36 patients, 75 (65%) in the maxilla and 40 (35%) in the mandible. The implants were connected to 85 abutment teeth, 50 in the maxilla and 35 in the mandible. Of the prosthetic restorations, 19 were gold ceramic, 17 were gold acrylic, three were titanium acrylic, one was titanium ceramic, and one was titanium composite. The observation period ranged from 14 months to 8.9 years. The treatments comprised both fixed partial dentures supported by one tooth and one implant as well as complete-arch fixed prostheses supported by a number of teeth and implants. Results: A total of nine implants were lost, three during healing and six after loading. The postloading cumulative implant survival rate was 89.8% after 5 years. Five abutment teeth were lost, and of the 41 prostheses included in the study, only two (5%) were lost during the observation period. Marginal bone loss was registered around 46 implants at the 1-year follow-up examination. During the following observation period, only slight changes in the marginal bone level adjacent to the implants and teeth were registered. The magnitude of technical complications was low. Conclusion: This investigation confirms the findings in similar studies that treatments with periodontally healthy teeth and implants splinted together in rigid one-piece superstructures show excellent long-term follow-up results.