The International Journal of Prosthodontics, 02/2003

Purpose: This study evaluated the marginal discrepancies and leakage of all-ceramic crowns cemented with different luting agents after fatigue tests. Materials and Methods: Forty-eight all-ceramic crowns were cemented onto natural molars. Zinc-phosphate cement, compomer cement, and an adhesive composite resin luting system were used in 16 specimens each. Sixteen metal-ceramic crowns were cemented with zinc-phosphate cement as a control. Half of the specimens in each group were fatigued in a chewing simulator for 600,000 loading cycles with 3,500 thermocycles. The others received the 3,500 thermocycles only. An impression-replica technique and SEM were used for evaluation of the marginal discrepancies. Leakage of the specimens was microscopically assessed. Results: There were no significant differences between marginal discrepancies of the groups, with the exception of porcelain shoulder margins in the metal-ceramic group, which had significantly larger discrepancies ( P .01). There was no significant effect of the fatigue tests on marginal discrepancies. However, significant differences of leakage were found between the groups cemented with the different luting agents after both fatigue tests. The adhesive composite resin luting system demonstrated the least leakage. The compomer cement showed an intermediate level of leakage, and the zincphosphate cement showed severe leakage that extended through the dentinal tubules to the pulp chambers. No significantly different effect of the two fatigue tests on the leakage was found. Conclusion: The adhesive composite resin luting system showed clinically acceptable marginal discrepancies and an excellent ability to minimize leakage of allceramic crowns.

Purpose: The aim of this randomized clinical trial was to compare the relative efficacy of mandibular overdentures retained by only two implants and a bar attachment with conventional dentures. Materials and Methods: Edentulous adults, aged 35 to 65 years, were randomly assigned to two groups that received either a mandibular conventional denture (n = 48) or an overdenture supported by two endosseous implants with a connecting bar (n = 54). All subjects rated their general satisfaction and other features of their original dentures and their new prostheses (comfort, stability, ability to chew, speech, esthetics, and cleaning ability) on 100-mm visual analogue scales prior to treatment and 2 months postdelivery. Oral health-related quality of life was also evaluated pre- and posttreatment. Results: Multiple regression analysis revealed that the mean general satisfaction was significantly higher in the overdenture group than in the conventional denture group ( P= .0001). Age, gender, marital status, and income were not significantly associated with ratings of general satisfaction. Furthermore, the implant group gave significantly higher ratings on three additional measures of the prostheses (comfort, stability, and ease of chewing; P .05). Conclusion: A mandibular two-implant overdenture opposed by a maxillary conventional denture is a more satisfactory treatment than conventional dentures for edentulous middle-aged adults.

Purpose: The objective was to make an inventory of systematic reviews in the field of prosthodontics and to assess the strength of evidence yielded by these studies. Materials and Methods: The literature was searched using MEDLINE (keywords "dental" in subset combined with "meta-analysis" in publication type, and "dental" in subset combined with "systematic review"). Reviews related to prosthodontics were selected by hand. Analogies between the reviewing processes were assessed, and the quality was described. Results: There were 138 articles qualifying as either systematic reviews or meta-analyses. Of these, 13 reported pooled data on prosthodontic subjects. Two pairs of reviews were identified as dealing with comparable items; the others described all different subjects. In one pair, the studies reviewed the survival of conventional fixed partial dentures (FPD); the other pair was on single-tooth implants. The pooled results within each pair were almost equal. For the FPD reviews, 65% of the unity of studies was included in both reviews. For the single-tooth implants, 29% of the potentially useful studies were included in both reviews. The data pooling processes showed the same pattern. One large study included in both reviews explained a large part of the similarity of the combined survivals of FPDs. For the single-tooth implant reviews, the largest common study explained 20% of the similarity. Conclusion: Although there were methodologic differences between the paired reviews, they produced similar results. The outcomes of the evaluated reviews may be used as prognostic data; however, they cannot be used for direct comparison of treatments.

Purpose: When implants are used to support a removable overdenture, the optimal stress distribution to minimize both forces on the implants and denture movement is desirable. This study compared the stress patterns generated around implants and denture movement among three retention systems. Materials and Methods: Two root-form implants were anchored in a mandibular model made of resin, and a removable overdenture on which all experiments were performed was fabricated. The surface of the model was covered with a layer of impression material to simulate oral mucosa. Ball/ O-ring, bar/clip, and magnetic attachments were used. A vertical force was applied to the left first molar and gradually increased from 0 to 50 N in 5-N steps. The resultant stress distribution and denture movement were evaluated. Results: The ball/O-ring attachment transferred the least stress to both implants and produced less bending moment than the bar/clip attachment. Vertical force applied to the bar/clip attachment created immediate stress patterns of greater magnitude and concentration on both implants. Conclusion: This in vitro study suggested that the use of the ball/O-ring attachment could be advantageous for implant-supported overdentures with regard to optimizing stress and minimizing denture movement.

Purpose: The objective of this study was to test the hypothesis that there is no significant difference between the fracture toughness (KIC) of an experimental hot-pressed core ceramic measured by fractographic analysis of failed ceramic prostheses and the values determined by other standard methods. Materials and Methods: Four groups were subjected to one of four test methods: group 1 = indentation strength technique (standard numerical calculation); group 2 = indentation strength technique (fractographic analysis); group 3 = flexure test of precracked specimens (fractographic analysis); and group 4 = fractographic analysis of failed three-unit fixed partial dentures (FPD). For groups 1 to 3, 20 ceramic bar specimens were subjected to three-point flexure at a cross-head speed of 0.5 mm/min until fracture occurred. For group 4, 10 failed FPDs were collected from a previous study. Stress values at failure were calculated from either a flexure stress equation (groups 1 to 3) or from finite element analyses (group 4). KIC values were calculated from an equation and fractographic measurement data. Results: Mean fracture toughness ranged from 3.1 MPa·m1/2 (SD 0.2) (group 1) to 3.4 MPa·m1/2 (SD 0.2) (group 4). The mean KIC value for group 1 was significantly different from that of group 4; however, no significant differences were found between groups 1, 2, and 3, or between groups 2, 3, and 4. Conclusion: Fracture toughness for an experimental hot-pressed core ceramic measured by fractographic analysis in combination with finite element analysis was comparable with the values determined with other standard fractographic methods.

Purpose: The purpose of this study was to determine the effects of incorporating antimicrobial silver-zeolite on the in vitro cytotoxicities of five tissue conditioners against the living dermal model, which consisted of normal human dermal fibroblasts in a collagen lattice. Materials and Methods: Samples of each tissue conditioner containing silver-zeolite (2 wt% and 5 wt%) were prepared; samples without silver-zeolite were used as a control. Cytotoxicity of each sample against the living dermal model was evaluated by cell viability with MTT assay. Results: Cell viabilities for Visco-Gel, GC Soft-Liner, FITT, and SR-Ivoseal decreased with increasing silver-zeolite content. Cell viability for Shofu Tissue Conditioner showed no significant difference with degree of silver-zeolite incorporation and had higher values than other tissue conditioners. Conclusion: Individual compounds eluted from tissue conditioners and silver ions released from silver-zeolite might cause such cytotoxicity. The results suggest that Shofu Tissue Conditioner is a possible candidate for a novel antimicrobial tissue conditioner containing silver-zeolite because it showed the highest cell viability and the smallest influence of incorporating silver-zeolite.

Purpose: The objective of this study was to verify the influence of resin cement polymerization mode and early cyclic loading on the bond strength of porcelain-dentin specimens. Materials and Methods: Two cementation systems, Choice/One-Step and RelyX ARC/Single Bond, were tested. Porcelain truncated cones were bonded into cavities prepared in sections of bovine root dentin. Each system was tested with the resin cement in dual-cure and self-cure mode (with and without photoactivation, respectively). Half of the specimens were load cycled 15 minutes after cement mixing (60 N, 20 times). The other half were not submitted to mechanical loading (control). After 24-hour storage in distilled water (37°C), the extrusion shear test was performed. Data were analyzed by three-way ANOVA. Results: With both systems, some specimens built with the cement in self-cure mode debonded during cyclic loading (RelyX ARC/Single Bond 47%; Choice/One-Step 13%). No significant system effects were detected. Mean bond strength under the dual-cure mode (13.4 MPa, SD 3.6) was significantly higher than the corresponding mean for the selfcured specimens (5.7 MPa, SD 2.6). No reduction in bond strength was observed for the specimens that survived the early cyclic loading. Conclusion: Resin cements in dual-cure mode presented higher bond strengths than self-cured materials. Early load cycling caused debonding of some self-cured specimens. However, the bond strength of the survivor specimens was not affected by load cycling.

Purpose: The purpose of this study was to evaluate the long-term outcome of In-Ceram Alumina fixed partial dentures (FPD) performed in a general dental practice from 1992 to 1996. Materials and Methods: The study was conducted as a retrospective assessment of up to 9 years of patient records and a clinical follow-up examination of patients treated with In-Ceram Alumina FPDs. In 37 patients, 42 FPDs had been inserted during the selected period. After randomized selection, 16 patients with 18 FPDs were examined clinically. The most common restorations comprised two and three units. Cantilever extensions were present on 64% of the FPDs. Sixty-two percent of the FPDs extended into the posterior region. Results: The mean time in function for the 42 FPDs was 76 months (range 2 to 110 months), with 86% being followed for > 5 years. No adverse effects to either periodontal or pulpal tissues were recorded. The technical quality was very good, and patient satisfaction very high. Five FPDs fractured during the observation period, resulting in a total failure rate of 12%. Two of these FPDs fractured as a consequence of external trauma. Excluding these, the total survival rate during the observation period was 93%. Cumulative survival rate according to life table analysis was 93% after 5 years and 83% after 10 years. Conclusion: The results suggest that the In-Ceram Alumina short-span FPD is a viable prosthetic alternative.

Purpose: This study evaluated the pulmonary risk caused by possible respirable dust of Al2O3 and SiOx resulting from chairside tribochemical sandblasting procedures in a dental office. Materials and Methods: Dust was collected using a trap near the working field, and quantitative morphologic determination and identification were performed with SEM and EDAX. Forty blasting processes (total time 20 minutes) were aimed at a dummy to obtain maximum pollution of the workplace. Respirable dust fraction was measured using personal air samplers with an 8-µm cellulose-nitrate filter and a volume flow rate of 2 L/min. Mass of the respirable dust fraction was determined, and respirable free crystalline silica was identified with the help of infrared spectroscopy. Results: Blasting of metal or ceramic surfaces with tribochemical agents produces respirable and potentially harmful SiOx and Al2O3 particles with a diameter of less than 5 µm, showing a total concentration in the air of less than 0.3 mg/m3. With and without dental suction, the concentration of the respirable free crystalline silica was smaller than 0.02 mg/m3. Conclusion: Concern regarding the risk of chairside tribochemical methods and possible impairment of health of patients and dental staff is unfounded, even under extreme conditions or without protective measures, since the concentrations of SiOx found in the air of the workplace were far below the current threshold value of 0.15 mg/m3.

Purpose: The flexural strength of two commercially available dental fiber-reinforced composites (FRC) (glass fiber-reinforced composite material), one unidirectional and the other bidirectional, were investigated. Materials and Methods: Ten uniform beams of core materials and ten beams of laminated core materials were fabricated for FibreKor and Vectris Frame. The specimens were subjected to a three-point bending test. Flexural strength for both FRC materials was determined with and without their composite laminations. The strength data were analyzed using the Weibull method. Modes of failure for both systems were determined using SEM. Results: The strength of FibreKor was significantly greater than that of Vectris Frame when comparing the core materials with and without their respective composite laminations. Mode of failure of FibreKor was predominantly debonding with fiber fracture. Vectris Frame did not exhibit debonding failure. Mode of failure for Vectris Frame was fiber fracture with delamination and matrix microfracture. Conclusion: FibreKor, a unidirectional FRC, demonstrated higher flexural strength than Vectris Frame, a bidirectional FRC. Debonding of fibers from the matrix possibly contributed to toughening mechanisms such as crack deflection, fiber pullout, and fiber bridging in FibreKor.

Purpose: The purpose of this study was to evaluate the fracture strength and mode of failure of five different single-tooth abutment-implant combinations before and after cyclic loading in the artificial mouth. Materials and Methods: Eighty standardized maxillary central incisor crowns were fabricated for five test groups with 16 specimens each (group 1: Steri- Oss/Novostil; group 2: Steri-Oss/Anatomic abutment; group 3: Steri-Oss/straight HL; group 4: IMZ Twin +/Esthetic abutment; group 5: Osseotite/gold UCLA). Specimens were adhesively luted using Panavia 21, and half were artificially aged via chewing simulation and thermocycling. All nonaged and the surviving aged specimens were tested for fracture strength resistance using compressive load on the palatal surfaces of the crowns. Results: After exposure to the artificial oral environment, survival was as follows: six in group 1; eight in groups 2, 3, and 5; and seven in group 4. Median fracture strengths before and after loading in the artificial mouth were 537 N, 817 N, 893 N, 473 N, and 743 N for groups 1 to 5, respectively. There were no statistically significant differences in fracture strength before and after exposure to the artificial mouth. There were significant differences between the implant systems in both stages of the experiment. In all five groups, abutment-screw bending and abutment fractures (except group 1) were present after static loading, and all implant necks in group 4 showed distortions. Conclusion: The artificial mouth is a useful tool to check the implant-abutment-screw interface stability. The physical properties of screws and screw joints of groups 1 and 4 have to be improved. Groups 2, 3, and 5 have the potential to withstand physiologic biting forces.

Purpose: The purpose of this retrospective study was to present treatment outcome and patient reactions to rehabilitation with implant-supported fixed partial prostheses. Materials and Methods: Eighty-three patients were consecutively treated with implantsupported fixed partial prostheses (Brånemark system) from 1986 to 1995. Seventy-six of these 83 patients were examined (66 maxillary and 31 mandibular prostheses). The mean observation time was 53.9 months. In total, 285 implants were placed. Eleven implants were lost before loading. The first 41 prostheses were removed and the implants examined regarding the criteria for "success" and tightness of the screw joints. Only one implant had lost integration. Results: The survival rate before and after loading was 96%, which included implants placed in augmented bone. All prostheses were stable at the time of examination. In prostheses with cantilevers (98 implants), 12% of the gold screws and 17% of the abutment screws showed a "not acceptable" loosening, compared to none in the prostheses without cantilevers (17 implants). The difference was not statistically significant. The mean marginal bone loss was 0.4 mm for the first year after prosthesis insertion and less than 0.1 mm per year in the following years. The most frequent prosthesis design was one pontic supported by two implants. Prostheses made in gold acrylic and titanium acrylic had more complications and showed a higher need for repair than metal-ceramic restorations. Patients reacted very positively to the esthetic results and comfort with eating, and were overall satisfied with their prostheses. Conclusion: Implant-supported fixed partial prostheses seem to have a very good prognosis and are well-accepted by patients.

Purpose: This study reported on the modes of failure and the influence of various clinical characteristics 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: Fifty-three percent of maxillary and 84% of mandibular FPDs involved one or more nonrigid abutment-pontic connections. Patients were recalled in 1993 (review 1) and 1998 (review 2) and clinically examined by the author. The modes of failure and influence of clinical characteristics, including abutment-pontic connection, post design in nonvital abutments, and regularity of professional maintenance, were evaluated. Results: At review 2, 80% of the FPDs were still in function, while 9% required retreatment. Tooth fracture accounted for 38%, caries for 11%, loss of retention for 13%, and periodontal breakdown for 27% of retreatments. Nonrigid abutment-pontic connection in posterior FPDs and regular professional maintenance were associated with significantly reduced failure rates. Except in posterior molars, there was no difference in failure rates between parallel-sided preformed stainless steel serrated posts and cast-gold alloy posts. Conclusion: Tooth fracture was the most common reason for retreatment of the FPDs, although the rate of periodontal breakdown and caries increased significantly with time. Nonrigid abutment-pontic connection and regular professional maintenance were associated with significantly reduced failure rates. Post design and composition were not related to outcome.

Purpose: Forceful clenching in the intercuspal position has the potential to cause significant mandibular displacement. Such a displacement can be expected to be exaggerated in patients without molar support. The appropriate clenching level for intercuspal position registration or evaluation in these patients has never been clarified. The aim of this study was to clarify the effect of clenching level and absence of posterior occlusal support on mandibular displacement. Materials and Methods: Thirteen women with a unilateral edentulous area posterior to the first premolar were enrolled in this study. They were asked to perform intercuspal clenching at various occlusal force levels, and 3-D mandibular displacements were measured by an optoelectronic method. The effects of ¡°clenching force level¡± and ¡°side of molar tooth loss¡± on the displacements of the condylar and second molar points were analyzed. Results: The mandible was elevated without substantial horizontal displacements during each clenching task. The effect of clenching level on vertical mandibular displacement was significant, with a clenching level >= 50% of maximal voluntary contraction causing significantly greater elevations (P .05). Clenching >= 50% of maximal voluntary contraction caused consistent tipping of the mandible, with greater elevation on the edentulous side (P .05). Conclusion: The clenching level should not surpass 50% of maximal voluntary contraction for registration or evaluation of intercuspal position in Kennedy Class II patients.

Purpose: This in vitro study investigated the (1)retention and microleakage of provisional crowns cemented with temporary cements to which stannous fluoride (SnF2) was added, and (2)solubility of these cements. Materials and Methods: Provisional crowns were constructed of acrylic resin with shoulder preparations for 12 molars. The crowns were luted with Tempbond, Tempbond NE, and Freegenol temporary cements, and also with SnF2 added to these cements. Specimens were thermocycled 100 times, stored for 6 days, and immersed in 0.5% basic fuschin. Seven days after cementation, crown removal (retention) tests were conducted. Marginal leakage was assessed using a five-level scale to score dye penetration. Solubility in water of the cements with and without SnF2 was assessed using cement disks. Results: Freegenol was more retentive than the other cements. The incorporation of SnF2 significantly increased the retention capacity of Freegenol and Tempbond NE but had no effect on Tempbond. Tempbond showed significantly higher dye penetration than Freegenol. The addition of SnF2 did not alter the dye penetration of the cements. There were no significant differences in the solubility of the cements. However, the incorporation of SnF2 increased the solubility of Freegenol and Tempbond NE ( P .001) and Tempbond ( P .01). Conclusion: The addition of SnF2 increased the retention of temporary crowns cemented with Tempbond NE and Freegenol but did not affect the retention of those cemented with Tempbond. The marginal leakage of crowns cemented with the tested temporary cements with and without the incorporation of SnF2 was similar. However, the addition of SnF2 increased the solubility of the cements.

Purpose: The purpose of this study was to investigate and compare the precision of fabrication in repeatedly produced computer numeric controlled (CNC)-milled frameworks with conventional castings, and to analyze the distortion from application of different veneering materials. Materials and Methods: Twenty identical titanium frameworks were fabricated by means of a CNC milling technique for the same master model. Five conventional frameworks were cast as a control group to the same model. The frames were measured with regard to fit in a coordinate measuring machine linked to a computer. Measurements were made during different stages of handling of the titanium framework, and after veneering materials had been applied. Results: The CNC frameworks showed a statistically better fit and precision of fabrication compared to conventional castings ( P .05). The application of veneering material did not statistically affect the fit of the titanium frameworks ( P> .05). Conclusion: It is possible to fabricate implant-supported frameworks by means of the present CNC technique with a very high precision and repeatability.

Purpose: The aim was to retrospectively evaluate the frequencies of different complications, as well as the number of visits to dentists because of such complications, after treatment with implant-supported fixed prostheses. Materials and Methods: The study group comprised 75 patients who had been treated with implant-supported fixed prostheses 3 years earlier. All case records were scrutinized, and notes of complications in association with implants and superstructures were registered. Results: The most common intervention made was occlusal adjustment/selective grinding of the prostheses. Complications in association with both implants and superstructures were fairly common. The most frequent complication was fractures of the acrylic resin matrix, including artificial acrylic resin teeth. Consultations because of periimplant mucosal inflammation were much more common among women compared to men, while complications that could be attributed to heavy loading tended to be more common in men. Conclusion: Complications with both implants and superstructures are fairly common after treatment with implant-supported fixed prostheses. Regular follow-ups to maintain optimal function in these patients are thus mandatory.