The International Journal of Prosthodontics, 05/2010

Purpose: The aim of this study was to compare the core survival rates (CSRs) of cast metal versus resin core restorations luted with adhesive resin cement, as well as to determine the risk factors for core failure. Materials and Methods: Nine hundred ninety-one patients (2,124 cores) who received either cast metal or resin cores luted with adhesive resin cement at the Fixed Prosthodontic Clinic of Okayama University Dental Hospital between April 1988 and December 1991 and whose structured clinical core record was filled appropriately comprised the study subjects. The clinical core record included information regarding patient age, sex, core restoration type, tooth location, tooth type, remaining coronal dentin, and root canal form. CSRs, as well as causes for failure, were analyzed 15 years postinsertion. Since 381 patients lacked data regarding predictors for core failure, a subsample of 610 patients (1,053 cores) was used for the subsequent risk factor analysis. Results: The cumulative CSR of resin cores (78.7%) was significantly higher than that of cast metal cores (55.4%; log-rank test, P < .0001). The Cox proportional hazards test revealed that sex (male, P < .0001), absence of remaining coronal dentin (P = .0057), core restoration type (cast metal, P = .0186), and higher age at core insertion (P = .0380) were significant predictors for core failure. The incidence of complications, such as core loosening (P = .0016) and tooth extraction (P < .0001), was significantly higher in cast metal cores. Conclusions: Cast metal cores were associated with a significantly lower CSR than resin cores, and significant risk factors for core failure were sex (male), absence of remaining coronal dentin, core restoration type (cast metal), and higher age at core insertion.

This study compared the effects of various surface treatments and techniques on the marginal leakage of full-coverage crowns using a quasi-three-dimensional evaluation. Crowns were cast using a gold-silver-palladium alloy by means of the lost-wax technique. Twenty-eight recently extracted human molars were divided randomly into four groups according to surface treatment before crown cementation: (1) no pretreatment (negative control), (2) primer (positive control), (3) resin coating and primer, and (4) phosphoric acid, sodium hypochlorite, and primer. All specimens were cemented with composite cement. The lowest marginal leakage was observed in group 4. Variation in marginal leakage between specimens originating from the same tooth was observed.

Purpose: Denture survival, or the time between the date of a denture's insertion and the date of its renewal for any clinical reason, was assessed in this retrospective study on 353 complete dentures. The procedures required to prolong the useful time of the study sample-relines, repair of denture base fractures, or replacement of lost artificial teeth-were also evaluated. Materials and Methods: All dentures were examined by the authors and were constructed according to a standardized protocol by full-time staff members of the Department of Prosthodontics, Regensburg University Medical Center, between 1984 and 2009. Two subgroups were assigned: 94 patients had one complete denture in each arch (group 1), while 165 patients had one complete denture in either the mandible or the maxilla (group 2). Results: In group 1, the median (75th, 90th percentile) survival time of dentures was 15.8 years in the mandible (15.7, 7.0; 95% confidence interval [CI]: 15.5 to 16.1) and 19.4 years in the maxilla (15.8, 8.7; 95% CI: 14.0 to 24.7). Reline procedures were required most frequently in the maxilla, while 5-year event-free rates were 69.7% for the maxilla and 80.5% for the mandible. Denture base fractures were reported in 5.8% of patients in group 1 and tended to occur more frequently (median: 15.2%) if patients had only one denture (group 2, n = 25 [maxilla: n = 23, mandible: n = 2]). Loss of artificial teeth was a rare complication and found in only 5.8% of patients in group 1 and 10.9% of patients in group 2. During the first 5 years of service, more than 95% of patients in group 1 and 90% of patients in group 2 were "event free" with regard to loss of artificial teeth. Conclusions: Long-term functional service of complete dentures requires a high number of maintenance procedures, and there is a greater need for interventions in patients wearing only one complete denture (group 2).

This case report describes the effect of complete denture abstention and subsequent rehabilitation with mandibular implant-supported overdentures (IOD) on masseter muscle thickness (MMT) in a 97-year-old patient. MMT was measured bilaterally using an ultrasound scanner during 1 year of wearing a conventional denture, after 101 days of voluntary denture abstention, and 3, 6, and 12 months after delivery of the IOD. MMT decreased by 17% during denture abstention following repeated implant surgery, and returned to 100% during the 12 months with the mandibular IOD. This case suggests that muscle bulk may be related to denture function.

Purpose: The effect of impaired oral functions is best described by the patient, and a shift toward a patient-oriented decision-making process in oral rehabilitation is evident. The Oral Health Impact Profile-49 (OHIP-49) questionnaire has been the most commonly used method to measure oral health-related quality of life (OHRQoL) in dentistry. An individualized method, the Schedule for the Evaluation of Individual Quality of Life-Direct Weighing (SEIQoL-DW), has proven to fulfill most of the criteria for a method to assist in the decision-making process. The purpose of this study was to compare the ability of the OHIP-49 questionnaire and the SEIQoL-DW method in measuring OHRQoL and generating useful information for decision making in oral rehabilitation. Materials and Methods: Sixty participants in need of oral rehabilitation were enrolled in the study. Patients received a clinical examination, were interviewed using the SEIQoL-DW, filled out the OHIP-49 questionnaire, and answered two global oral health-rating questions. Results: The SEIQoL-DW generated additional information compared to the OHIP-49. The information was more oral- and treatment-specific, including consultation issues and the patient-practitioner relationship. The overall SEIQoL-DW and OHIP-49 scores were significantly correlated. The OHIP-49 and SEIQoL-DW scores were related to oral health subjectively. Conclusions: The SEIQoL-DW method proved a useful aid in clinical decision making for oral rehabilitation. The SEIQoL-DW was more appropriate for generating information useful for decision making than measuring OHRQoL; the OHIP-49 was more appropriate for measuring OHRQoL than generating information.

Thirty-two patients who had been treated with 71 computer-aided design/computer-assisted manufacture-fabricated Cercon crowns were followed to assess clinical performance by time-to-event analysis. Clinical examinations consisted of a complete dental and oral hygiene examination and a quality assessment by modified California Dental Association criteria. Four patients (6 crowns) were lost to follow-up; another 11 crowns had to be excluded from evaluation for comparability reasons. Six of 54 evaluated crowns experienced complications (PC = 11.1%) throughout a mean observation time of 21 months. Survival was estimated at 0.98 over 24 months. The good overall clinical performance was affected predominantly by technical complications of the veneering ceramic (PTC = 9.3%).

Purpose: The aim of this research was to evaluate the fatigue behavior and reliability of monolithic computer-aided design/computer-assisted manufacture (CAD/CAM) lithium disilicate and hand-layer-veneered zirconia all-ceramic crowns. Materials and Methods: A CAD-based mandibular molar crown preparation, fabricated using rapid prototyping, served as the master die. Fully anatomically shaped monolithic lithium disilicate crowns (IPS e.max CAD, n = 19) and hand-layer-veneered zirconia-based crowns (IPS e.max ZirCAD/Ceram, n = 21) were designed and milled using a CAD/CAM system. Crowns were cemented on aged dentinlike composite dies with resin cement. Crowns were exposed to mouth-motion fatigue by sliding a WC-indenter (r = 3.18 mm) 0.7 mm lingually down the distobuccal cusp using three different step-stress profiles until failure occurred. Failure was designated as a large chip or fracture through the crown. If no failures occurred at high loads (> 900 N), the test method was changed to staircase r ratio fatigue. Stress level probability curves and reliability were calculated. Results: Hand-layer-veneered zirconia crowns revealed veneer chipping and had a reliability of < 0.01 (0.03 to 0.00, two-sided 90% confidence bounds) for a mission of 100,000 cycles and a 200-N load. None of the fully anatomically shaped CAD/CAM-fabricated monolithic lithium disilicate crowns failed during step-stress mouth-motion fatigue (180,000 cycles, 900 N). CAD/CAM lithium disilicate crowns also survived r ratio fatigue (1,000,000 cycles, 100 to 1,000 N). There appears to be a threshold for damage/bulk fracture for the lithium disilicate ceramic in the range of 1,100 to 1,200 N. Conclusion: Based on present fatigue findings, the application of CAD/CAM lithium disilicate ceramic in a monolithic/fully anatomical configuration resulted in fatigue-resistant crowns, whereas hand-layer-veneered zirconia crowns revealed a high susceptibility to mouth-motion cyclic loading with early veneer failures.

The aim of this study was to analyze the influence of melting and casting procedures and the cervical finish line design on the marginal fit of nickel-chromium-titanium alloy crowns. Sixty standardized specimens were prepared to receive metal-ceramic crowns and were divided into two groups according to the cervical finish line: chamfer or rounded shoulder. Three melting and casting procedures were analyzed: (1) induction-centrifuge (IC), (2) gas oxygen torch-centrifuge (TC), and (3) induction-vacuum/pressure (IP). The marginal fit was measured with an image analysis system. Significant differences (P = .005) were observed among the groups, with TC showing the lowest discrepancies (45.87 µm). No significant differences were observed between the two finish lines. The accuracy of fit achieved for the groups analyzed may be regarded as within the range of clinical acceptance.

This clinically simulated study examined the accuracy of full-arch impression materials using successive casts reproduced from single impressions. Materials tested included a polyether polyvinyl siloxane, medium viscosity material, and putty wash. Maxillary full-arch Dentoform models were created with four abutments prepared for complete crowns. Six impressions of each material produced successive first and second generation casts. Individual cast copings were then fabricated and assembled into full-arch fixed dental prostheses. Marginal discrepancies were measured on both the casts and Dentoform. Data analysis suggests insignificant differences between successive casts. However, among second generation casts, clinically similar marginal discrepancies were exhibited. Outcomes demonstrated that second generation casts enabled fabrication and assembly of full-arch restorations that were clinically equivalent to first generation casts obtained.

To evaluate the short-term efficacy of oral positioning stents in minimizing the adverse oral effects of external beam radiation therapy in patients suffering from lingual carcinoma, 48 subjects were selected for this study. Half of the patients (n = 24) were given positioning stents while the other half (n = 24) formed the control group. Subjects were evaluated for oral radiation toxicity effects using the Radiation Therapy Oncology Group's 045 head and neck cancer adverse events grading tool from the National Cancer Institute's Common Toxicity Criteria for Adverse Events over a period of 60 days. The control group showed a significant increase in palatal mucositis, xerostomia, and salivary changes compared to the study group.

The phenomenon of sleep bruxism (SB) has been recognized and described for centuries, including literary references to the gnashing of teeth. Early etiologic explanations were generally focused on mechanistic factors, but later, attention was focused on psychologic issues such as stress and anxiety; by the end of the 20th century, most opinions combined these two ideas. However, recently, the study of the SB phenomena has occurred primarily in sleep laboratories in which patients could be observed and monitored over several nights. Various other physiologic systems were also studied in sleep laboratories, including brain activity, muscle activity, cardiac function, and breathing. As a result of these studies, most authorities now consider SB to be a primarily sleep-related movement disorder, and specific diagnostic criteria have been established for the formal diagnosis of that condition. All of these changes in the understanding of the SB phenomena have led to a corresponding change in thinking about how oral appliances (OAs) might be used in the management of SB. Originally, they were thought to be a temporary measure that could help dentists analyze improper dental relationships. Unfortunately, this often led to dental procedures to "improve" these relationships, including equilibrations, orthodontics, bite opening, or even major restorative dentistry. However, it is now understood that the proper role for OAs is to protect the teeth and hopefully to diminish muscle activity during sleep. This paper reviews these evolutionary changes in the understanding of SB and how this affects concepts of designing and using OAs.

Purpose: Reconstructive surgery in oral cancer patients uses thick flaps, which may render the placement of miniscrews for stabilizing radiosurgical templates difficult. The realization of noninvasive systems for the repositioning of surgical templates has been proposed. The present study aimed to assess the clinical usefulness of these noninvasive repositioning systems. Materials and Methods: Two noninvasive (ie, without osseous anchorage) repositioning systems (one intraoral, one intra- and extraoral) were tested. They were coupled with a computer-aided system for oral implantation. The criteria for evaluation were: accuracy, cost, time for placement and removal, and six additional subjective criteria (ease of use and production, bulk of the device, patient comfort, stability during surgery, and ergonomics). Results: Nine edentulous patients undergoing surgery to the oral cavity, oropharynx, or pharynx; external radiotherapy of the mandible; or microvascular flap reconstruction were included. Twenty-seven implants were placed in the mandibles of seven patients. For the extraoral system, the angular deviation between planned and achieved position was 6.04 degrees, with differences of 2.14 mm at the tip and 2.16 mm at the base. For the intraoral system, deviations were 5.05 degrees, 1.13 mm, and 1.82 mm, respectively. Subjective criteria were consistent with expected values, especially ease of use, comfort, and ergonomics. Conclusions: Noninvasive systems remain less accurate than templates stabilized by miniscrews and should be reserved for treating arches in which miniscrews cannot be placed. These methods may be unacceptable in areas where vital structures may be damaged by a misguided implant, and further studies are required. More satisfactory results should be obtained in partially edentulous patients.

The aim of this study was to investigate the effect of different resin cement film thicknesses on the shear bond strength of resin core materials to lithium disilicate ceramics. Forty IPS Empress 2 ceramic disks were bonded to the core materials (Bis-core and Smile) with resin cement film thicknesses of 50 or 100 µm. Shear bond strength was measured using a universal testing machine. Data were analyzed using two-way analysis of variance and independent t tests. The core material used and resin cement film thickness had a significant effect on shear bond strength values (P < .001). Greater resin cement film thickness resulted in decreased bond strength of the core materials to lithium disilicate ceramics.

An index was developed to estimate the residual periodontal ligament support for individual teeth during treatment planning for partially edentulous patients. The Residual Periodontal Ligament Index (rPLI) was derived from a formula that calculates the remaining area of periodontal attachment and the Normal Periodontal Ligament Index (nPLI). To illustrate the applicability of the rPLI, the total nPLI scores of the remaining teeth corresponding to Eichner subclasses of partial edentulism were charted by assessing the average occlusal support numerically. The rPLI is proposed to be a possible suitable tool for epidemiologic research on the progression of tooth loss and the survival rate of prostheses.