The International Journal of Prosthodontics, 05/2002

Purpose: The effect of major connector design on deflection in maxillary removable partial denture (RPD) frameworks under simulated occlusal loading was analyzed by means of three-dimensional finite element models. Materials and Methods: Thirteen maxillary major connectors were produced for a Kennedy Class II case. Eleven frameworks consisted of posterior palatal straps with different anteroposterior widths at the midline. Anteroposterior and horseshoe bars were also constructed for comparison. In each framework, the occlusal rest on the abutment adjacent to the edentulous ridge was fixed in a vertical direction, and the rest on the contralateral side was fixed in all directions. A biting force of 20 N was vertically distributed simultaneously on each of the three missing posterior teeth locations. Results: For the posterior palatal straps, the maximum vertical displacement at the saddle and the buccal displacement at both the saddle and the rest adjacent to the saddle decreased as their connector width increased from 6 to 29 mm, whereas maximum distal displacements were insensitive to the connector width. The posterior straps with anteroposterior widths of more than 18 mm revealed comparable rigidity to the anteroposterior bar. The horseshoe bar and the posterior straps with smaller widths demonstrated greater displacements than the other frameworks. Conclusion: The rigid connectors proved to be the most effective in transmitting applied occlusal forces to the contralateral side of the framework.

Purpose: This study reports on the outcome of 515 metal-ceramic fixed partial dentures (FPD) involving 1,209 abutments and 885 pontics placed by one operator in a specialist prosthodontic practice between January 1984 and December 1997. Materials and Methods: Clinical and laboratory protocol was kept constant as much as was practical. Each FPD and abutment was given a subjective prognostic rating at the time of cementation. Patients were recalled in 1993 (review 1) and 1998 (review 2). Clinical examination by the author covered 85% of 342 FPDs at review 1 and 82% of 515 FPDs at review 2. At review 2, 37% had been in clinical service for 5 to 10 years (group b), and 34% had been in service for 10 to 15 years (group c). An objective classification protocol was used to assess outcome. Results: At review 2, the FPDs had failure rates of 2%, 7%, and 11% in groups a, b, and c, respectively. There was a significant increase in the failure rate of group c at review 2 (11%) compared with review 1 (5%). Cumulative survival analysis indicated that FPDs have an expected survival rate of 96%, 87%, and 85% at 5, 10, and 15 years, respectively. The applied prognostic rating proved more accurate as clinical service time increased. Outcome was not related to number of units. Cantilevered FPDs, nonvital abutments, and anterior abutments had significantly greater failure rates. Of initially vital abutments, 2% were subsequently endodontically treated. Conclusion: Tooth-supported FPDs have an expected survival rate of 85% at 15 years when the described clinical and laboratory protocol is applied.

Purpose: The aim of this study was to develop a shortened version of the Oral Health Impact Profile (OHIP) appropriate for use in edentulous patients and to evaluate its measurement properties. Materials and Methods: Data were collected from the Ontario Study of Older Adults and a longitudinal clinical trial of implant-retained prostheses undertaken in Newcastle Dental Hospital, UK. All subjects completed an OHIP at baseline, and UK subjects also completed an OHIP posttreatment. Using an item impact reduction method, a shortened version of the OHIP (called OHIP-EDENT) was derived from both datasets. Discriminant validity and responsiveness properties of this modified version were compared with OHIP-14 and OHIP-49. Results: Using an item impact method of reducing the 49 OHIP items produced very similar subsets in both Canadian and British populations; the modified version had little overlap with the current short version (OHIP-14). Discriminant validity properties of OHIP-EDENT were similar to OHIP-14 and OHIP-49. Using effect sizes to assess sensitivity to change, OHIP-EDENT exhibited less susceptibility to floor effects than OHIP-14 and appeared to measure change as effectively as OHIP-49. Conclusion: The modified shortened version of the OHIP derived in this study has measurement properties comparable with the full 49-item version. This modified shortened version may be more appropriate for use in edentulous patients than the current short version (OHIP-14).

Purpose: This study evaluated the clinical performance of posterior CAD/CAM-generated In-Ceram Alumina and In-Ceram Spinell core crowns. Materials and Methods: Nineteen In- Ceram Spinell core crowns (four premolars and 15 molars) and 24 In-Ceram Alumina core crowns (two premolars and 22 molars) in 21 patients were examined using modified USPHS criteria at baseline and after a mean service time of 39 ± 11 months. The crown copings were machined from Vitablocs In-Ceram Alumina and Vitablocs In-Ceram Spinell using the Cerec 2 CAD/CAM system. Results: Two molar In-Ceram Alumina core crowns fractured after respective service times of 14 and 17 months in the same patient. The Kaplan-Meier survival rate regarding fracture of the ceramic was 92% for In-Ceram Alumina and 100% for In-Ceram Spinell. At the follow-up examination, 80% alpha ratings and 18% beta ratings for In-Ceram Alumina core crowns and 84% alpha ratings and 15% beta ratings for In-Ceram Spinell core crowns were recorded. Conclusion: Despite the two fractures, the clinical quality of CAD/CAM-generated In-Ceram Alumina and In-Ceram Spinell posterior crowns was excellent. Within the limitations of this study, both types of crowns appeared to be feasible.

Purpose: The purpose of this study was to evaluate the effect of crowns with different emergence profiles on marginal plaque formation. Materials and Methods: Seven crown preparations were performed on premolar teeth in six patients. Four titanium crowns for each tooth-with different marginal emergence angles-were manufactured according to the Procera technique. The three experimental crowns and the final permanent tooth were cemented with phosphate permanent cement. Plaque samples were collected from the marginal area after 1 week with normal oral hygiene, and again after refraining from oral hygiene for 2 days. The contralateral tooth served as a control. The quantity and quality of plaque were registered. The restoration was removed, the next crown version cemented, and the protocol repeated. Results: All experimental crowns, irrespective of emergence profile, showed a significantly lower (P = .01) plaque quantity than controls. No intraindividual differences were found regarding the accumulation of mutans streptococci at the different experimental emergence profiles. No differences in quality between experimental and control sides were found. Conclusion: Within the limitations of this study, it was found that titanium crowns with emergence profiles of up to 40 degrees formed less plaque than healthy controls. There was no higher accumulation of mutans streptococci in relation to increasing emergence profiles.

Purpose: This study assessed multiple pain conditions and their association with psychosocial functioning, psychologic distress, and somatization in patients with temporomandibular disorders (TMD) based on RDC/TMD Axis II findings. Nonspecific pain items examined included headaches, heart/chest pain, lower back pain, nausea/abdominal pain, and muscle pain. Materials and Methods: In this study, 202 TMD patients (58 men and 144 women) referred to two TMD clinics participated. The mean age of the predominantly Chinese patient population (82%) was 32.6 years (range 13 to 65). The RDC/TMD history questionnaire was input directly into computers by patients. Graded chronic pain and SCL-90 scales were generated online and automatically archived for statistical analysis. Data were subjected to Spearman's rank-order correlation and Kruskal- Wallis and Mann-Whitney tests at a significance level of .05. Results: Of the patients, 43% were moderately to extremely distressed by headaches. The percentage of patients who were distressed by heart/chest pain (7%), lower back pain (26%), nausea/abdominal pain (17%), and soreness of muscles (22%) was lower. Of the TMD patients, 16% experienced more than three pain items. Significant and positive correlations were observed between number of pain items experienced and graded chronic pain severity, depression, and somatization. Correlation coefficients ranged from .27 to .65 for graded chronic pain scales and somatization (without pain items) scores, respectively. Conclusion: Results suggest that the number of nonspecific pain conditions reported may be a predictor of psychosocial dysfunction, depression, and somatization.

Purpose: This in vitro study investigated the marginal adaptation and fracture resistance of three-unit fiber-reinforced composite fixed partial dentures (FPD) luted with two different resin-modified glass-ionomers. Materials and Methods: A total of 48 FPDs were constructed from the glass fiber-reinforced materials FibreKor/Sculpture, Vectris/Targis, or the polyethylene fiber system BelleGlass/Connect (n = 16 for each brand). The reconstructions were conventionally luted on human molars using resin-modified ProTecCEM or Fuji Plus and then exposed to thermocycling and mechanical loading. Results: During thermocycling and mechanical loading, cementation failed in seven of eight FibreKor or BelleGlass FPDs and in one of eight Vectris/Targis FPDs luted with ProTecCEM. All Fuji Plus-cemented FPDs showed no signs of damage or cementation loss. The fracture resistance of the remaining FPDs was as follows: Vectris/Targis-ProTecCem 1,361 ± 360 N, Vectis/Targis-Fuji Plus 923 ± 207 N, BelleGlass/Connect 940 ± 155 N, and FibreKor/Sculpture 524 ± 202 N. The marginal adaptation of the cement-tooth interface deteriorated by 13% to 21% for all reconstructions after stress application, which was not statistically significant. The crown-cement interface had a significantly greater marginal gap only with the combination of FibreKor and Fuji Plus after stress simulation (change 33%). Conclusion: Conventional cementation of fiber-reinforced FPDs can lead to cementation loss. The marginal adaptation and fracture resistance deteriorated in comparison to adhesively cemented reconstructions.

Purpose: This in vitro study investigated the element release from seven commercially available dental casting alloys and tested their cytotoxic effects. Materials and Methods: The casting alloys tested were one high-noble alloy (Bioherador N) and six base-metal alloys, including four Ni-Cr alloys (Remanium CS, Heranium NA, Wiron 99, CB Soft), one Co-Cr alloy (Wirobond C), and one Cu-based alloy (Thermobond). Ten specimens from each alloy were prepared in the form of disks, and each of the seven dental casting alloys (10 disks per group) were conditioned in distilled water at 37°C for either 72 or 168 hours. The conditioning media were analyzed for element release, and the cytotoxic effects were assessed on Balb C fibroblasts using MTT assay. Results: Element release was greater at 168 hours of conditioning than at 72 hours. The extract from the high-noble alloy showed the least amount of element release (only Zn), with no cytotoxic effects. The greatest amount of element release was detected in the Cu-based alloy Thermobond and the Ni-Cr alloy CB Soft; their extracts were significantly more toxic than all the other alloy extracts. The cytotoxic effects of the other Ni-Cr alloy extracts were not statistically significantly different from the high-noble alloy extract. However, the Co-Cr alloy (Wirobond C) extract was significantly more cytotoxic than the high-noble alloy extract. Conclusion: Element release from casting alloys is proportional to the conditioning time. The content of Cr and Mo in the alloy protects the alloy from dissolution, while the Cu content makes it more susceptible to corrosion and dissolution, rendering it more cytotoxic.

Purpose: The sealing of provisional filling material in overdenture tooth abutments during provisional rehabilitation is of primary importance to the long-term success of roots bearing gold casting copies. The aim of this in vivo study was to evaluate the microleakage of four different provisional filling materials after a period of 1 week. Materials and Methods: Five patients needing treatment with overdenture prostheses and scheduled for the extraction of at least four teeth were chosen. After performing endodontic treatment on the roots to be extracted, a standardized cavity preparation 3 mm in depth was made using a diamond bur. Each cavity was filled with one of the four provisional materials selected for the evaluation (Cavit-W, IRM Caps, Guttapercha, Fermit-N), and the interim prostheses were delivered to the patients. After 1 week, the roots were extracted and stored for 24 hours in 0.5% basic fuchsin at 37 ± 1°C for 24 hours. Subsequently, the roots were severed and observed under a stereomicroscope for microleakage evaluation. Results: The materials showed different degrees of microleakage, but none allowed dye penetration to the bottom of the cavity. IRM Caps showed the lowest mean value of dye penetration (168 µm), while Fermit-N showed the highest (1,475 µm). All materials differed from each other (P .05). Conclusion: Within a period of 1 week, the materials provided acceptable to good sealing properties. All of the materials may be considered suitable for provisional fillings if they do not remain in the oral cavity for more than 1 week. IRM Caps gave the best results.

Purpose: Because of abrasion by toothbrushing, dental materials in the oral cavity are subjected to substance loss to a different extent depending on the hardness of the material. This study investigated the color-change effect of substance loss and change of roughness resulting from toothbrushing of internally and externally stained metal ceramic. Materials and Methods: Metal-ceramic specimens 15 mm in diameter and 2 mm thick were made. Blue colorant suspension was applied over the enamel porcelain (enamel-stained), in the body porcelain (dentin-stained), and over the opaque porcelain (opaque-stained). One group was not stained. Each group was made up of seven samples. All specimens were brushed in an experimental device. Material loss, roughness measurements, and spectrophotometric evaluations were made before and after brushing. Overall color change, chroma change, and value change were calculated with the use of the CIE-LAB uniform color scale. Results: Significant substance loss as a result of brushing was observed. No significant differences between chroma changes, between value changes of different groups, or between overall color changes of dentin- and enamel-stained groups were found. The difference between overall color changes of opaque-dentin and opaqueenamel stained groups was statistically significant. Conclusion: Staining should be done as deeply as possible to obtain durable color appearance.

Purpose: This article reviews the development of esthetic implant abutments and illustrates the use of aluminum oxide implant abutments in two cases. Materials and Methods: Two patients were restored with single-tooth implants for the replacement of anterior teeth. One patient received a prefabricated aluminum oxide abutment, which was customized by the dental technician. A second patient received a custom aluminum oxide abutment, which was designed and fabricated using CAD/CAM technology. Both cases were restored with all-ceramic crowns. Results: Satisfactory functional and esthetic results were achieved in both cases. The CAD/CAM abutment required no further customization in the dental laboratory. Conclusion: The use of aluminum oxide ceramic abutments improves dental and mucogingival esthetics in single-implant restorations. The use of CAD/CAM technology simplifies the design and customization process. Clinical studies are required to confirm the long-term performance of this type of restoration.

Purpose: The purpose of this study was to examine changes in translucency and color of particulate filler composite resins that can be fabricated into metal-free crowns. Materials and Methods: Eight types of materials were used in this study. The particulate filler composite resins were represented by Artglass, BelleGlass, Estenia, Gradia, and Targis. Herculite XRV and Solidex were the conventional composite resins for crowns and fixed partial denture facings, and Empress was the ceramic material. Disks with a thickness of 1.0 mm were fabricated from each material and subjected to an accelerated test by immersion in 60°C distilled water for up to 8 weeks. Color measurements were made before and after water immersion. Changes in translucency were evaluated by determining the contrast ratio, and changes in color were evaluated by determining color difference. Results: After water immersion, Targis and Solidex demonstrated a significant increase in contrast ratio (6% to 7%) and a decrease in translucency. A color difference of more than 2.0, a visually perceptible value, was found for Targis, Gradia, and Solidex. However, the maximum color difference for these was 3.0, a value that would be considered clinically acceptable. Conclusion: Within the limitations of this study, the particulate filler composite resins were stable in both translucency and color.