Retention force of removable partial dentures with different double crowns.

OBJECTIVES: The aim of the study was to compare the retentive behaviors of double crowns with different designs and material compositions before and after artificial aging. MATERIALS AND METHODS: Six pairs of double crowns were fabricated: telescopic crowns 0° made of high-noble metal (group A) or non-precious metal (group B), telescopic zirconia copings with secondary crowns made of electroplated gold 2° (group C), crowns with friction pins 2° made of non-precious metal (group D) or zirconia (group E), and conical crowns 6° made of high-noble metal (group F). Retention forces were assessed before and after artificial aging, and after axial and non-axial loading. RESULTS: Initially, specimens in group D (13.9 N), B (12.5 N), and E (12.2 N) exhibited the highest retention forces. Retention forces in groups A (9.6 N), C (7.4 N), and F (6.0 N) were statistically significantly lower than those of the other groups (p < 0.05). After artificial aging, double crowns with additional retention elements exhibited the highest retention forces. The largest retention force losses were evident in groups A (70%), B (64%), C (39%), and F (47%). CONCLUSIONS: Double crowns with different designs and made of different materials exhibited different retention forces and different long-term retentive behavior. The highest retention force losses were evident in double crowns with more extended surface contact, such as telescopic crowns. CLINICAL SIGNIFICANCE: Telescopic crowns with additional retention elements were more resistant to wearing than double crowns without additional retention elements. An additional clinical benefit might be the quick and easy possibility of enhancing retention.

Accuracy of CAD-CAM-fabricated removable partial dentures.

STATEMENT OF PROBLEM: The conventional fabrication of removable partial dentures (RPDs) is a complex, error-prone, time-consuming, and expensive process. The use of computer-aided design and computer-aided manufacturing (CAD-CAM) techniques, especially rapid prototyping, promises a more effective method for fabricating RPD frameworks. PURPOSE: The purpose of this in vitro study was to evaluate the fit of RPD clasps fabricated by means of 4 different CAD-CAM-systems and to compare those fittings with that of the conventional lost-wax casting technique (LWT). MATERIAL AND METHODS: A master model of a partially edentulous maxilla with the canines and second molars as the remaining teeth was fabricated. After the model was optically scanned, we designed a quadrangularly supported RPD with 4 clasps and a palatal strap major connector. A standard tessellation language data set was used to fabricate 12 identical RPDs by using 4 different CAD-CAM techniques: indirect rapid prototyping (wax inject printing combined with LWT), direct rapid prototyping (selective laser melting), indirect milling (wax milling with LWT), and direct milling (resin milling [polyetheretherketone]). Three conventionally cast RPDs (LWT) served as the control group. The fit accuracy of the clasps (n=12 for each group) was determined in both the horizontal and vertical dimensions by using light microscopy. RESULTS: Indirectly milled RPDs (117 ±34 µm horizontal and 45 ±21 µm vertical) and directly milled RPDs (43 ±23 µm horizontal, and 38 ±21 µm vertical) showed significantly better (P<.05) fit than did conventionally fabricated LWT RPDs (133 ±59 µm horizontal; 73 ±25 µm vertical). The worst fit was found for RPDs fabricated using indirect rapid prototyping (323 ±188 µm horizontal and 112 ±60 µm vertical) or direct rapid prototyping (365 ±205 µm horizontal and 363 ±133 µm vertical), which were unstable on the master model, making them unsuitable for clinical use. Most RPDs exhibited smaller vertical measuring distances. CONCLUSIONS: Compared with the LWT, milling techniques enabled fabrication of RPDs with comparable or better fit. However, RPDs fabricated with rapid prototyping techniques showed distinct fitting irregularities.

The repeatability of digital shade measurement--a clinical study.

OBJECTIVES: The intraoral VITA Easyshade spectrophotometer is a shade measurement system that provides for objective determination of the shade of natural teeth and of dental materials. Over a period of 2.5 years, this clinical study assessed the repeatability of VITA Easyshade measurement, using metal ceramic restorations and based on L*a*b* parameters. MATERIALS AND METHODS: Shade tests of 25 metal ceramic crowns were carried out objectively in 19 patients using VITA Easyshade and subjectively by a dentist. The measurements were taken using a separate positioning device at the time of insertion, after 14 days (baseline), after 6 months, after 1.5 years and after 2.5 years. RESULTS: ∆E was calculated from ∆L*, ∆a*, ∆b* data as a measure of the differences in shade. The average values during the follow-up controls were ∆E 2 = 2.2 (6 months), ∆E 3 = 2.3 (1.5 years) and ∆E 4 = 2.0 (2.5 years). Subjective shade analysis during the follow-up controls did not reveal any changes in the ceramic veneer. CONCLUSIONS: The average of ∆E = 2.1 represented the difference in color. The examiner could not detect any difference in color over the evaluation period of 2.5 years. CLINICAL RELEVANCE: Good results in terms of the repeatability and accuracy of VITA Easyshade measurements were reported in previous in vitro studies. Objective assessment under clinical conditions is required in order to evaluate the shade stability of tooth-colored restorative materials in the oral cavity. For this purpose, the quality and handling of VITA Easyshade must be verified from a clinical perspective.

Frictional telescopic crowns in severely reduced dentitions: a 5-year clinical outcome study.

Clinical outcomes for frictional telescopic crowns supporting removable prostheses in patients with severely reduced dentitions with one to three remaining teeth per arch have been inadequately documented. Seventy-four patients with severely reduced dentitions received 82 telescopic removable partial dentures that were supported by 173 frictional telescopic crowns. The recorded individual telescopic abutment survival rate over a 60-month period was 80.6%. This observation was significantly influenced by sex and tooth vitality and mobility (Kaplan-Meier). The risk of loss of telescopic crowns was significantly influenced by sex, arch, vitality, and abutment tooth distribution (Cox regression). Telescopic removable partial dentures were proven to be a favorable treatment concept for severely reduced dentitions in the selected group of patients.

Longevity of frictional telescopic crowns in the severely reduced dentition: 3-year results of a longitudinal prospective clinical study.

OBJECTIVES: The longevity of frictional telescopic crowns (FTC) in severely reduced dentitions with 1 to 3 remaining teeth per jaw has not yet been studied prospectively and exclusively. Aims of this study were to estimate risks of telescope loss and abutment tooth loss and to determine abutment tooth mobility over time. METHOD AND MATERIALS: A total of 74 patients with severely reduced dentitions received 82 telescopic removable partial dentures (TRPDs) retained with 173 FTCs. Dentures were reexamined after 1 week and 3, 6, 12, 18, 24, 30, and 36 months. Tooth mobility was monitored with Periotest values. Adjuvant therapies were carried out if necessary. Survival probabilities of telescopes and abutment teeth as well as the influence of clinical factors (age, sex, jaw, vitality, opposing dentition, axis inclination, end Periotest value, crown length, crown margin quality, wearing mode, tooth types, abutment distribution, number of telescopes) were calculated with Kaplan-Meier estimators. The relative risks for telescope loss were calculated with Cox regression. RESULTS: The survival rate was 93.9% for abutment teeth and 87.5% for telescopes. Number of telescopes, abutment distribution, vitality, and gender as factors influenced the survival rates (Kaplan-Meier). In combination with the jaw as a factor, these affected the risk for telescope loss (Cox regression). Periotest values (mean of abutment teeth per examination) decreased significantly (P < .0001). Altogether, 11% of teeth fractured and 4.6% of teeth were extracted. Patients were mostly very satisfied. CONCLUSION: TRPDs proved to be a favorable treatment concept for severely reduced dentitions. FTCs can be considered as elements with a good benefit-maintenance relation. A general increase of abutment tooth mobility could not be verified.

Prospective observation of CAD/CAM titanium ceramic single crowns: a three-year follow up.

STATEMENT OF PROBLEM: Computer-aided design/computer-aided manufacturing (CAD/CAM) titanium ceramic restorations were developed with the potential for replacing expensive, high noble metal ceramic restorations. However, there is a lack of information about the clinical performance of CAD/CAM titanium ceramic single crowns. PURPOSE: The purpose of this study was to evaluate CAD/CAM titanium ceramic single crowns after 3 years in function. MATERIAL AND METHODS: A total of 41 crowns were fabricated for 21 patients. The titanium copings were CAD/CAM milled (Everest CAD/CAM system) with an even thickness of 0.5 mm, and low-fusing veneering porcelain (Vita Titanium Porcelain) was added incrementally. The crowns were cemented using zinc phosphate cement after confirming that there were no mechanical and biological complications. The patients were recalled at 12, 24, and 36 months after cementation to examine the presence of any complications and measure periodontal parameters such as probing depth (PD), bleeding on probing (BOP), and plaque index (PI). The success and survival rates were estimated using the Kaplan-Meier analysis. RESULTS: The success rate of CAD/CAM titanium ceramic crowns with regard to mechanical complications was 82.3% (95% confidence interval: 71.2% to 95.1%). The cumulative survival rate of the crowns was 94.9% (95% confidence interval: 88.3% to 100%) after 3 years. No biological complications were observed. At the end of the follow up, PD was 2.93 mm, percentile of surface with BOP was 29.2, and PI was 0.31. CONCLUSIONS: The clinical performances of the CAD/CAM titanium ceramic crowns for 3 years were acceptable, with no biologic complications and a high cumulative survival rate.

The significance of marginal gap and overextension measurement in the evaluation of the fit of complete crowns.

INTRODUCTION: An important criterion for the success of a crown is marginal fit. However, in the patient's mouth fit can only be evaluated by subjective methods. This study describes the correlation between objective marginal fit and its subjective evaluation by dentists and dental technicians. MATERIALS AND METHODS: Thirty human premolars and molars were randomly divided into six groups and prepared with a shoulder. For each of the six groups, complete crowns were made of different alloys and technologies (casting: AuAgCu, AuPdPt, PdAgAu, CoCrMo, and Ti; milling: Ti). The crowns were cemented with provisional cement. Ten dentists and 10 technicians were asked to evaluate the fit of the crowns with a new dental explorer. The crowns were then cleaned and cemented with a zinc-oxide-phosphate-cement. The marginal gap and a possible overextended margin of the crowns were examined under a special 4x light microscope with a magnification level of 560 X. The means of the gaps and the overextended margins were calculated for each group. Significances were detected by analysis of variance (ANOVA) and the post-hoc-test (Bonferroni, p<0.05). Correlations between objective measuring and subjective evaluation were evaluated using the Pearson test. The influence of the measured values on the subjective evaluation was determined by regression analyses. RESULTS: Crowns made from different alloys and technologies showed partly significantly (p<0.05) different marginal gaps (mean ranging from 35 microm to 92 microm) and significantly (p<0.05) different overextended margins (mean ranging from 40 microm to 149 microm). There were significant correlations (p<0.05) between subjective findings and objective data. Significant correlations (p<0.01) were also found between the subjective findings of dentists and technicians. Compared to the marginal gap, only the overextended margin had a significant influence (p=0.00) on the subjective evaluations of the clinicians. CONCLUSION: Crowns from different alloys and technologies showed differences in marginal fit. Marginal gap and the overextension of the crowns significantly correlated with the subjective evaluation of their fit by dentists and dental technicians. For the decision of the clinicians, whether a crown is acceptable, overextension was more important than marginal gap.

Problems reported by patients before and after prosthodontic treatment.

PURPOSE: This study sought to investigate problems reported by patients before and after prosthodontic treatment. MATERIALS AND METHODS: Patient-reported problems were studied using the item list contained in the German version of the Oral Health Impact Profile in a convenience sample of 107 prosthodontic patients before (T0), 1 month after (T1), and 6 to 12 months after treatment (T2). "Frequently reported" problems were defined as impacts experienced fairly often or very often. The prevalence of frequently reported problems was compared among treatment groups and across appointments. RESULTS: At baseline, the most prevalent frequently reported problems were "difficulty chewing" (31%), "take longer to complete a meal" (28%), "food catching" (26%), "uncomfortable to eat" (24%), and "unable to eat (because of dentures)" (23%). At T2, the most prevalent frequently reported problems were "sore spots" (5%), "painful gums" (4%), "discomfort (because of dentures)" (3%), and "sore jaw" (2%). The number of reported problems decreased from 18.0 (T0) to 7.5 (T1), and further to 4.5 (T2). The decrease was the fastest in fixed partial denture wearers and the slowest in removable partial denture wearers. Some problems emerged during or after prosthodontic treatment. The kind of pre- and posttreatment problems differed substantially. CONCLUSION: The number of problems decreased substantially after prosthodontic treatment. Fixed partial dentures more effectively influenced the problems reported before treatment than did removable partial or complete dentures.

Oral health-related quality of life in patients treated with fixed, removable, and complete dentures 1 month and 6 to 12 months after treatment.

PURPOSE: This study described oral health-related quality of life (OHRQoL) before and after treatment in patients with fixed, removable, and complete dentures. MATERIALS AND METHODS: OHRQoL was measured using the German version of the Oral Health Impact Profile (OHIP-G) in a convenience sample of 107 prosthodontic patients at baseline and 1 and 6 to 12 months after treatment. The sum of OHIP-G item responses (OHIP-G49, range 0 to 196) characterized OHRQoL impairment in 42 patients treated with fixed prosthodontics, 31 patients treated with removable dentures, and 34 patients treated with complete dentures. OHIP-G49 medians were compared with the OHRQoL level in a general population sample (n = 2,026). A multivariable binomial regression analysis, controlling for the effects of baseline OHRQoL and follow-up wave, was used to compare the level of impaired OHRQoL in different prosthodontic treatment groups at follow-ups. RESULTS: OHRQoL improved in 96% of the subjects. OHIP-G49 medians reached the level of OHRQoL in the general population 1 month after treatment (fixed prosthodontics patients 6 OHIP-G units; general population subjects 5 units; removable denture patients 23 units, 15 units in general population subjects; complete denture patients 13 units, 23 units in general population subjects). OHIP-G49 medians were below population norms 6 to 12 months after treatment. In patients treated with removable/complete dentures, the expected posttreatment OHIP-G49 problem rate was 1.9 times the problem rate in patients treated with fixed prosthodontics, holding baseline OHIP-G49 and follow-up wave constant. CONCLUSION: OHRQoL changed substantially comparing pretreatment scores with 1 and 6 to 12 months of follow-up in patients treated with fixed, removable, and complete dentures.