The International Journal of Prosthodontics, 03/2002

Purpose: The purpose of this in vitro study was to evaluate the influence of the framework design on the fracture strength of all-ceramic resin-bonded fixed partial dentures (RBFPD) in the mandibular incisor region. Materials and Methods: Twenty-four aluminum oxide ceramic frameworks were copy milled with the Celay system, glass infiltrated, and veneered with feldspathic porcelain to replace a mandibular incisor. Forty-eight extracted human incisors were used as abutments by embedding them in a polyester resin. The master casts were fabricated according to a typical clinical case. The sandblasted restorations were bonded to the acid-etched abutment teeth with a composite resin. Twelve RBFPDs had a conventional two-retainer design, and 12 had a cantilevered single-retainer design. Subgroups of eight specimens were subjected to a quasistatic load in the direction of the long axis of the abutment teeth in a universal testing machine. Additional subgroups of four specimens were subjected under 0 degrees to dynamic loading of 25 N in a dual-axis chewing simulator. Results: The mean fracture strengths under quasistatic loading were 313 N (SD 42) for the two-retainer design and 291 N (SD 100) for the single-retainer design. The mean cycles sustained by specimens subjected to dynamic loading at 25 N were 50,081 (SD 42,705) for the two-retainer design and 297,099 (SD 508,439) for the single-retainer design. There was no statistically significant influence of the framework design on the fracture strength of the restorations under quasistatic or dynamic loading. Conclusion: The clinical application of cantilevered all-ceramic RBFPDs in the mandible may be an alternative to all-ceramic RBFPDs with two retainers.

Purpose: This article evaluates the reporting of randomized controlled trials (RCT) in prosthodontics, excluding endosseous implant-based prosthetics. Materials and Methods: Reports of RCTs published to the end of 2000 in any language were identified using a multilayered search strategy. The Cochrane Oral Health Group specialized register, Medline, and personal libraries were searched. Three researchers appraised the articles independently using guidelines following Jadad and CONSORT, complemented with an evaluation of the appropriateness of the reported statistics. Results: Ninety-two reports of RCTs were evaluated, covering a wide spectrum of study hypotheses, topics, and issues within various prosthodontic domains. The interrater agreements on appraisal criteria were relatively high, with median kappa values ranging between 0.65 and 0.79. The reports were in general of poor methodologic quality. Randomization and procedures for concealment allocation were not described in 70% of the articles. The methods used to generate the random allocation sequence were not mentioned in 82%. The methods used to implement the random allocation sequence, clarifying whether it was concealed until all interventions were assigned, was not mentioned in 94%. Reporting who generated allocation sequence, who enrolled patients, and who assigned participants to groups was not reported in 7%. Reasons for withdrawals were not given in 23% of the reports. No attempt at blinding was reported in 72%. Statistical analysis was not described in 6% of the papers, while these analyses were assessed as appropriate for 75%, unclear in 12%, and inappropriate in 7%. Conclusion: Few RCTs in prosthodontics are reported in accordance with contemporary guidelines for adequate reporting of trials.

Purpose: Composite resin teeth are more widely used than porcelain or acrylic resin teeth in the fabrication of removable dentures because of their high fracture toughness and high abrasion resistance. The purpose of this study was to evaluate the shock absorbability of commercially available artificial posterior teeth by the free drop-ball test with an accelerometer and to evaluate the Vickers hardness at the surface. Materials and Methods: The tested artificial teeth included seven composite resin teeth, one acrylic resin tooth, and one porcelain tooth. Specimens were tested 50 hours after immersion in distilled water at 37°C. The impact value and Vickers hardness were measured. A one-way analysis of variance was used to analyzed the data (P = .05). Results: The composite resin teeth showed an intermediate impact value between that of the acrylic resin tooth and the porcelain tooth. Among the artificial teeth investigated, the porcelain tooth showed the highest impact value. A significant difference in the impact value was observed between the porcelain tooth and the composite resin and acrylic resin teeth. However, no significant difference was observed among the composite resin teeth tested. A significant correlation was found between the impact values and the Vickers hardness of the artificial teeth. Conclusion: The present findings suggest that composite resin teeth and acrylic resin teeth have a higher shock absorbability than porcelain teeth.

Purpose: The objective of this study was to test the following hypotheses: (1) hydrofluoric acid (HF)-treated ceramic surfaces produce the highest tensile bond strength to resin cements, independent of the ceramic microstructure and composition; and (2) the tensile bond strength test is appropriate for analysis of interfacial adhesion for ceramic-bonded-toresin systems. Materials and Methods: Ceramic specimens were polished with 1-µm alumina abrasive and divided into four groups of 10 specimens for each of seven ceramic types. One of the following surface treatments was applied: (1) 10% ammonium bifluoride (ABF) for 1 minute; (2) 9.6% HF for 2 minutes; (3) 4% acidulated phosphate fluoride (APF) for 2 minutes; and (4) a silane coupling agent. The surface-treated areas were coated with an adhesive resin and bonded to a resin cement. Specimens were loaded to failure in tension using a testing machine. Tensile bond strength data were statistically analyzed, and fracture surfaces were examined to determine the mode of failure. Results: Silane-treated surfaces showed statistically higher mean tensile bond strength values than surfaces treated with any etchant (HF, ABF, APF). HF produced statistically higher mean tensile bond strengths than ABF and APF. All failures occurred in the adhesion zone. Conclusion: The tensile bond strength test is adequate for analysis of the adhesive zone of resin-ceramic systems. The chemical adhesion produced by silane promoted higher mean bond strength values than the micromechanical retention produced by any etchant for the resin-ceramic systems used in this study.

Purpose: The aim of the study was to measure the influence of the maxillary central incisors free from adaptation phenomena using spectral analysis. Materials and Methods: The maxillary dentures of 18 subjects were duplicated. The central incisors were fixed in a pivoting appliance so that their position could be changed from labial to palatal direction. A mechanical push/pull cable enabled the incisor section to be handled extraorally. Connected to the control was a sound generator producing a sinus wave whose frequency was related to the central incisor angulation. This acoustic signal was recorded on one channel of a digital tape recorder. After calibration of the unit, the denture duplicate was inserted into the subject's mouth, and the signal of the /s/ sounds subsequently produced by the subject was recorded on the second channel during alteration of the inclination angle simultaneously with the generator signal. Spectral analysis was performed using a Kay Speech-Lab 4300B. Results: Labial displacement in particular produced significant changes in spectral characteristics, with the lower boundary frequency of the /s/ sound being raised and the upper boundary frequency being reduced. Conclusion: Maxillary incisor position influences /s/ sound production. Displacement of the maxillary incisors must be considered a cause of immediate changes in /s/ sound distortion. Therefore, denture teeth should be placed in the original tooth position as accurately as possible. Our results also indicate that neuromuscular reactions are more important for initial speech sound distortions than are aerodynamic changes in the anterior speech sound-producing areas.

Purpose: This prospective study evaluated the prosthodontic maintenance requirements during the first year of service of mandibular overdentures supported by two unsplinted implants using three different implant systems. Materials and Methods: Seventy-two patients randomly allocated to three equal groups were each provided with a conventional complete maxillary denture and a mandibular overdenture supported by two unsplinted implants. A different implant system was used for each group (Steri-Oss, ITI, or Southern Implants), and their prosthodontic maintenance requirements were compared, primarily for the patrix and matrix. Additional maintenance categories recorded included any type of overdenture fracture, reline or remake of the overdenture, and maintenance of the maxillary denture. Results: Sixty-eight percent of the patients, regardless of implant system, required prosthodontic maintenance in the first year, most commonly for the matrices. The Southern Implants matrices required less maintenance than those of Steri-Oss or ITI (P .05). Additional overdenture maintenance was required by 28% of patients, irrespective of implant system. When all categories of prosthodontic maintenance were combined, there were no differences between implant groups. Evaluation of overall prosthodontic success using six-field tables revealed statistically significant differences between the three implant systems, with more ITI and Steri-Oss patients than Southern Implants patients requiring overdenture retreatment (repair). Conclusion: During the first year of service, the matrix maintenance requirements of Southern Implants were significantly lower than those of the ITI or Steri-Oss groups; this was reflected in the number of retreatment (repair) categories recorded. Although the three systems did not differ significantly for overall prosthodontic maintenance, both the Steri-Oss and the ITI titanium matrices showed problems of clinical significance.

Purpose: The purpose of this study was to evaluate the influence of different storage conditions on the bond strength of adhesive bonding systems to yttria-partially stabilized zirconia ceramic. Materials and Methods: Acrylic glass tubes filled with composite resin were bonded to ceramic disks. After sandblasting and ultrasonic cleansing of the ceramic samples, they were bonded using five bonding methods. Samples were tested for tensile bond strength following five different storage conditions: 3 days in distilled water at 37°C, 31 days in distilled water at 37°C, 37,500 thermocycles between 5 and 55°C within 31 days, 150 days in distilled water at 37°C, and 150 days in distilled water with 37,500 thermocycles performed at intervals. Results: Mean resin bond strength values ranged from 7.7 to 41.9 MPa. There were statistically significant differences among groups, as revealed by the Kruskal-Wallis test. Some storage conditions influenced the resin bond strength statistically significantly, as revealed by the Wilcoxon rank sum test modified by Bonferroni-Holm. Conclusion: Thermocycling had a much higher impact on the durability of the resin bond strength to zirconia ceramic than did water storage at a constant temperature.

Purpose: This study was undertaken to compare the facial appearance of patients from six racial groups (African American, Caucasian, Chinese, Hispanic, Japanese, and Korean) for interracial and/or gender differences and to determine if orms existed. Materials and Methods: A total of 253 subjects (144 men and 109 women) ranging in age from 18 to 41 years (mean age 26.5 years) were evaluated using a standardized protocol. The data were collected and analyzed to establish reference ranges for seven frontal and six profile extraoral parameters. Mean scores were compared by race and gender using a one-way analysis of variance, followed by the Tukey- Kramer test for honestly significant difference when statistically significant differences were found (P .05). Results: There were no significant differences for any of the seven frontal or six profile extraoral parameters between men and women. No significant differences were found between racial groups for five of the seven frontal and one of the six profile extraoral parameters. Conclusion: Most of the frontal facial parameters and one profile extraoral parameter might be considered norms for male and female patients of different ethnic origins. Additional research with larger patient populations would be needed to confirm or refute these trends.

Purpose: This article compares interracial or gender differences of six intraoral dental parameters among six racial groups (African American, Caucasian, Chinese, Hispanic, Japanese, and Korean). Materials and Methods: The same 253 patients participating in part 1 were included in this portion of the study to evaluate six intraoral parameters. The data were collected and analyzed using a one-way analysis of variance, followed by the Tukey-Kramer test for honestly significant difference when statistically significant differences were found (P .05). Results: Women displayed significantly more gingival tissue in four of the six races, and African Americans displayed significantly more gingival tissue than any other race. Women had significantly more missing teeth than men in three of the six races studied. Japanese subjects had significantly fewer missing teeth and smaller maxillary central incisors than all other groups except Caucasians. Women had significantly narrower maxillary central incisors in three of the races. There was a significantly higher prevalence of Angle Class III relationships in Chinese subjects. The Japanese had significantly more Class II molar relationships than other races. Conclusion: Racial and gender differences were found in gingival tissue display, the number of missing teeth, maxillary right central incisor crown width, and Angle molar classification, but not in the amount of vertical or horizontal overlap of the anterior teeth.

Purpose: The purpose of this study was to develop an easy-to-use procedure for individual registration and to test its accuracy. Unlike common principles, the method should be based on a transfer of the articulator geometry to the patient. Materials and Methods: The system consists of an articulator holding a bite plate in a standard position. The bite plate connects to an electronic recording system, which transfers the articulator's condylar points virtually to the patient's mandible by a centric relation record. The trajectories of the transferred points are recorded during mandibular protrusions and laterotrusions. From the trajectories, sagittal condylar and Bennett angles are measured and are adjusted at the articulator after mounting of the casts via the bite plate. Using a mechanical testing device, the accuracy of the measured angles was examined by comparison with preset values varying from 10 to 60 degrees (condylar angle) and from 0 to 40 degrees (Bennett angle) in 10-degree increments. Results: The mean deviations of measured condylar angles from preset values ranged between 1.5 and 0 degrees. The mean deviations of the Bennett angles ranged from -0.5 to -1.3 degrees. Conclusion: The transfer of articulator geometry to the patient reduces the number of individual parameters necessary to imitate jaw motion to the condylar and Bennett angles. This leads to a significant simplification in registration and cast transfer. Since the required parameters are recorded with high accuracy, the method could be an alternative to traditional sophisticated instrumental registration.

Purpose: The purpose of this study was to investigate the influence of mandibular residual ridge shape on masticatory efficiency in complete denture wearers. Materials and Methods: Twenty-eight complete denture wearers (mean age 75.6 years, SD 4.8) who received their complete denture treatment by one of the authors and had no troubles in daily use were selected. The mandibular residual ridge was evaluated by using a replica of the ridge obtained with heavy-body silicone impression material. The basal area of the replica was measured by a digitizer. The volume and the height of the replica were calculated. Masticatory efficiency in each subject was measured by the sieving method. Results: There was a significant correlation between the masticatory efficiency and basal area, volume, and height of the residual ridge. The basal area showed the strongest correlation. Conclusion: The basal area of the denture foundation greatly influenced the masticatory efficiency, suggesting that the masticatory efficiency in complete denture wearers was limited by their own residual ridges and that clinicians should inform their patients about the limitation of the recovery of masticatory ability before the beginning of denture treatment.

Purpose: A recently introduced technique, the CoJet system, using SiOx (Al2O3 coated with silisic acid), provides ultrafine mechanical retention by sandblasting, as well as a chemicophysical bond between the metal/ceramic and the composite resin. This study determined the reasons for and locations of failures of metal-ceramic restorations and evaluated the survival of the intraoral silica-coating system used for the repair of failed restorations. Materials and Methods: A total of 153 patients possessing 289 fractured crowns were involved in this study; 255 of these fractures were on fixed partial dentures, whereas 34 were on single crowns. The mean observation period was 34.6 months. The materials used for the repair process were ESPE-Sil for silane; Visiogem, Sinfony, and Dentacolor as opaquers; and Pertac II Aplitip, Sinfony, and Charisma as repairing composite resins. Results: The majority of the failures (65%) occurred in the anterior region. Sixty percent of the failures were observed at the labial, 27% at the buccal, 5% at the incisal, and 8% at the occlusal regions. The fractures were mainly in the maxilla (75%), predominantly at the labial surface. The overall cumulative survival rates of the repairs (89%) showed that the first failures happened mostly from 1 week to 3 months after the repair, without any difference between the composite resins. Conclusion: The original failures happened mainly during chewing function or because of accidents, iatrogenic factors, and surgical operations, whereas secondary failures after repair using intraoral silica coating and composite resin were due to trauma, chewing function, or lack of rubber dam application.

Purpose: This article describes a new procedure for immediate implant-supported oral rehabilitation using a photocurable resin skull model and a laser-welding apparatus. Materials and Methods: Preoperatively, the framework was fabricated on a photocurable resin skull model produced from a CT scan and individually designed guide template. The implants were immediately placed using the guide template; laser welding connected the components of framework. Results: Despite the custom-made prosthesis, the total treatment from implant placement to superstructure placement can be completed within only 1 day. Conclusion: This procedure for immediate implant-supported oral rehabilitation using a photocurable resin skull model and a laser-welding apparatus may be useful for any implant system and patient.