Influence of geometric dimensions on early failures of adhesively retained composite resin core build-ups.

OBJECTIVE: To determine the influence of the geometric dimensions of core build-ups on early core build-up failure, that is, loss before definitive prosthesis cementation. MATERIALS AND METHODS: Adhesive core build-ups of exclusively vital teeth in 114 participants were evaluated (n materials: 40 Rebilda DC, 38 Multicore Flow, 36 Clearfil DC Core; n teeth: 8 incisors, 54 premolars, 52 molars). Impressions of the abutment teeth were made (1) after removal of insufficient restorations/caries and (2) after core build-up and preparation for a fixed prosthesis. Digitized model surfaces of both situations were aligned (Geomagic Design X) and core build-up volume (VCBU ), remaining hard tissue volume (VAbut ), and size of the adhesive surface (Aadh ) were assessed. The derived measure dCBU  = VCBU /Aadh can be interpreted as mean arithmetic core build-up thickness. Associations between participant or core build-up design characteristics and the occurrence of early failures were statistically evaluated (SPSS v27, α = 0.05). RESULTS: A total of six (5.3%) core build-up failures were registered. Higher participant age, greater core build-up volume VCBU and greater arithmetic uniform thickness dCBU were associated with a greater incidence of failure in bivariate and univariate, however, not in multivariate statistics. CONCLUSIONS: Core build-up volume and thickness were associated with early success or failure. CLINICAL SIGNIFICANCE: In the case of voluminous/thick core build-ups in relation to the adhesive surface, additional measures, such as the preparation of retentive elements to increase the bonding area, might be considered to reduce the risk of early core build-up failure.

Variability of sleep bruxism-findings from consecutive nights of monitoring.

OBJECTIVES: To determine sleep bruxism (SB) behavior during five consecutive nights and to identify correlations between SB episodes per hour (SB index) and sleep-time masseter-muscle activity (sMMA). MATERIAL AND METHODS: Thirty-one participants were included in the study. Of these, 10 were classified as sleep bruxers (group SB-1) and nine as non-sleep bruxers (group non-SB). The bruxism status of these 19 patients was identified by means of questionnaires, an assessment of clinical symptoms, and electromyographic/electrocardiographic data (Bruxoff® device). The remaining 12 participants were also identified as bruxers, but based exclusively on data from the Bruxoff device (group SB-2). Data analysis included descriptive statistics and Spearman's correlation to assess the relationship between the SB index and sMMA. RESULTS: Participants in group SB-1 showed an overall mean SB index of 3.1 ± 1.6 and a mean total sMMA per night of 62.9 ± 38.3. Participants in group SB-2 had an overall mean SB index of 2.7 ± 1.5 and a mean total sMMA of 56.0 ± 29.3. In the non-SB group, participants showed an overall mean SB index of 0.8 ± 0.5 and a mean total sMMA of 56.8 ± 30.3. Spearman's correlation yielded values of - 0.27 to 0.71 for the correlation between sMMA and SB index. CONCLUSIONS: The data revealed variable SB activity and the absence of a reliable correlation between sMMA and the SB index. CLINICAL RELEVANCE: The high variation in SB activity and lack of correlation between sMMA and the SB index should be considered when diagnosing SB. TRIAL REGISTRATION: Clinical Trials [NIH], clinical trial no. NCT03039985.

Early failures when using three different adhesively retained core build-up materials-a randomized controlled trial.

OBJECTIVES: To compare the failure rates for three different adhesively retained core build-up composites up to the incorporation of a permanent fixed dental prosthesis (FDP), and to identify potential failure risk factors. MATERIAL AND METHODS: A randomized controlled trial of 300 participants in need of a core build-up to restore a vital abutment tooth before prosthetic treatment was conducted. Participants were assigned by stratified block randomization to one of three study groups: Rebilda DC (RDC), Clearfil DC Core (CDC), or Multicore Flow (MF). Test teeth were prepared by use of the respective manufacturer's adhesive system. The total-etch technique was used for RDC and MF, and the self-etch technique for CDC. Participants were treated by dentists (n = 150) or dental students (n = 150). Failure rates of core build-ups before incorporation of FDPs were investigated using univariate and multiple logistic regression. RESULTS: The overall failure rate was 8% (n = 23). Rate differences between the three investigated groups did not reach statistical significance (p > 0.05). The mean time between placement of core build-ups and placement of fixed dental prostheses was 12.2 (SD: 14.2) weeks. Conversely, larger cavities (> 3 surfaces) and treatment by dental students were independently associated with an increased failure risk (p < 0.05). CONCLUSIONS: The main risk factors for early failure seem to be the size of the core build-up and clinical experience of the operator, whereas failure rates of core build-up materials combined with a self-etch approach seem to be similar to the rates of materials combined with the total-etch technique. CLINICAL SIGNIFICANCE: This research article should give clinicians an impression of the short-term performance of different adhesively retained core build-ups using different adhesive techniques/materials. Moreover, predominant influencing factors for the success or failure should be pictured.

Validity of patient self-reports and clinical signs in the assessment of sleep bruxism based on home-recorded electromyographic/electrocardiographic data.

BACKGROUND: Reliable and suitable bruxism assessment would be desirable, but available studies presented heterogeneous results. OBJECTIVE: To determine the agreement of patient self-reports and clinical signs of sleep bruxism (SB) with electromyographic/electrocardiographic data. METHODS: Two hundred individuals from a German dental clinic population (120 women and 80 men) participated in the study. Participants completed different SB questionnaires, had a clinical examination to evaluate bruxism signs and used the Bruxoff® device to record electromyographic/electrocardiographic data for five nights. To investigate interrater reliability for clinical diagnosis of bruxism, 126 of the 200 participants were assessed for clinical signs of bruxism by two independent uncalibrated examiners. Statistical evaluation included calculation of sensitivity, specificity and accuracy and of Cohen's kappa. RESULTS: Based on the Bruxoff® data, 106 participants were identified as bruxers and 94 as non-bruxers. The 106 bruxers were further classified into 47 moderate and 59 intense bruxers. The highest accuracy and sensitivity values were recorded for the overall score for clinical bruxism signs (accuracy: 72.0% and sensitivity: 70.8%). The best specificity (96.8%) was seen for the question regarding tooth grinding in the last two weeks reported by others, but concurrent sensitivity was very low (3.8%). Analysis of interrater reliability revealed a substantial agreement (Cohen's kappa of 0.6). CONCLUSION: The study results indicate that self-report questionnaires and clinical signs have moderate sensitivity, specificity and accuracy for diagnosing bruxism comparing with an ambulatory device for current SB (Bruxoff®). Regarding interrater reliability for clinical signs of SB, substantial agreement was found between the two examiners. CLINICAL TRIAL NO: NCT03039985.

Clinical Performance of Posterior Inlay-Retained and Wing-Retained Monolithic Zirconia Resin-Bonded Fixed Partial Dentures: Stage One Results of a Randomized Controlled Trial.

PURPOSE: To prospectively compare the clinical performance of posterior inlay-retained and wing-retained monolithic zirconia fixed partial dentures (FPDs). MATERIALS AND METHODS: After simple randomization, 30 participants received either one inlay-retained (n = 15; mean age: 56.38 ± 12.70 years; 10 men [66.7%]) or one wing-retained (n = 15; mean age: 45.90 ±13.24 years; 7 men [46.7%]) FPD. The restorations, which predominantly replaced first molars, were fabricated from translucent, 3 mol% yttria-stabilized zirconia and attached with self-etching resin cement. Restorations and abutment teeth were clinically followed up for complications one week and 3, 6, and 12 months after cementation. Plaque and gingival scores, probing pocket depths, and attachment levels were recorded for the abutment and contralateral reference teeth both before treatment and during follow-up examinations. The restorations were also assessed in accordance with FDI World Dental Federation criteria. Statistical analyses were conducted with R (α = 0.05). An adaptive, 2-stage study design based on the incidence of failure-free survival in the groups after 12 months (stage 1) was implemented. Predefined decision rules were used to determine whether further recruitment (stage 2) would enable the detection of a statistically significant difference between the restoration designs with sufficient power. RESULTS: During 12 months, only one wing retainer debonded which required removal of the FPD. Failure-free survival was thus 93.3% for wing-retained and 100% for inlay-retained FPDs (log-rank test, p = 0.317). Moderate aftercare resulted in intervention-free rates of 78.8% and 86.7% for inlay-retained and wing-retained restorations, respectively (log-rank test, p = 0.605). Based on FDI World Dental Federation criteria, all restorations were acceptable at the 12-month follow-up (Fisher-Boschloo test, p = 0.161). Plaque, gingival, and periodontal scores remained practically unchanged from before treatment to the 12-month follow-up. Recruitment was stopped after stage 1 because, based on the small difference in the incidence of failure-free survival in the groups, it was accepted that it would not be possible to recruit the necessary number of participants to show a statistically significant difference between the retainer designs. CONCLUSIONS: Both inlay-retained and wing-retained monolithic zirconia resin-bonded FPDs performed well for the 12-month, short-term follow-up period.

Performance of zirconia ceramic cantilever fixed dental prostheses: 3-year results from a prospective, randomized, controlled pilot study.

STATEMENT OF PROBLEM: Little is known about the clinical performance of ceramic cantilever fixed dental prostheses on natural teeth. PURPOSE: The purpose of this randomized controlled pilot study was to evaluate the clinical performance of ceramic and metal ceramic cantilever fixed dental prostheses (CFDPs) after 3 years of service. MATERIAL AND METHODS: Twenty-one participants were randomly allocated to 2 treatment groups. Participants in the ceramic (ZC) group (n=11) each received 1 CFDP made of yttria-stabilized, tetragonal zirconia polycrystal; the others (n=10) were fitted with a metal ceramic (MC) CFDP. All CFDPs were retained by 2 complete crown abutments and replaced 1 tooth. The clinical target variables were survival, incidence of complications, probing pocket depth (PPD), probing attachment level (PAL), plaque index (PI), gingival index (GI), and esthetic performance as rated by the participants. The United States Public Health Service (USPHS) criteria were used to evaluate chipping, retention, color, marginal integrity, and secondary caries. Descriptive statistics and nonparametric analyses were applied to the target variables in the 2 groups. The esthetic performance of the CFDPs was also visualized by using a pyramid comparison. RESULTS: The overall survival of the CFDPs was 100% in both groups. During the 3-year study, 6 clinically relevant complications requiring aftercare were observed among 5 participants (4 in the ZC group and 2 in the MC group). Changes in the PI, GI, PPD, and PAL of the abutment teeth were similar for both groups (P>.05). The participants regarded the esthetic performance of ZC-CFDPs and MC-CFDPs as satisfactory. CONCLUSIONS: Within the 3-year observation period, the clinical performance of MC-FDPs and ZC-FDPs was acceptable. More extensive research with larger sample sizes is encouraged, however, to confirm the evaluation of the survival of Y-TZP hand-veneered cantilever FPDs.

Comparison of fracture-load values of cantilevered FDPs.

OBJECTIVE: Evaluation of the effect of different framework designs and of fatigue on the fracture-load values of cantilevered fixed dental prostheses (FDPs). The load values were compared with those for lithium disilicate ceramic and metal-ceramic FDPs. MATERIALS AND METHODS: Fifty cantilevered FDPs were manufactured using a zirconia framework veneered with a feldspathic ceramic. Ten FDPs were made from a lithium disilicate ceramic and 10 were designed as metal-ceramic FDPs. All FDPs were anchored by two premolar crowns to replace a missing premolar. Twenty of the 50 zirconia FDPs were regarded as the control groups; these were divided into two groups-with and without fatigue. The other 30 zirconia FDPs were divided into three test groups with different framework designs. The load to fracture was measured and fracture sites were identified. The Kruskal-Wallis test and the Mann-Whitney U-test were used for statistical analysis. RESULTS: Most of the all-ceramic FDPs fractured within the distal wall of the terminal crown abutment. The mean fracture-load ranged between 346-493 N for the FDPs with the 0.7 mm framework. Mean values for the three zirconia test groups ranged from 529-590 N. Reinforcement of the framework resulted in significantly higher fracture-loads than for the control group. Values for lithium disilicate restorations were significantly lower than those for the test groups and the values for the metal-ceramic group were significantly higher than those for the test groups. CONCLUSION: Although reinforcement of the distal crown core might enhance the fracture resistance of all-ceramic cantilever FPDs, they cannot yet be unreservedly recommended for clinical use.

Fracture load of tooth-implant-retained zirconia ceramic fixed dental prostheses: effect of span length and preparation design.

OBJECTIVES: Evaluation of the effect of different span length and preparation designs on the fracture load of tooth-implant-supported fixed dental prostheses (TIFDPs) manufactured from yttrium-stabilized zirconia frameworks. MATERIAL AND METHODS: Forty-eight TIFDPs were manufactured using a CAD/CAM system and veneered with a press ceramic. Rigidly mounted implants (SLA, diameter 4.1 mm, length 10 mm) in the molar region with a titanium abutment were embedded in PMMA bases pairwise with premolars. All premolars were covered with heat-shrink tubing to simulate physiological tooth mobility. Six different test groups were prepared (a) differing in the preparation design of the premolar (inlay [i]; crown [c]), (b) the material of the premolar (metal [m]; natural human [h]) and (c) the length of the TIFDPs (3-unit [3]; 4-unit [4]). All TIFDPs underwent thermomechanical loading (TCML) (10,000 × 6.5°/60°; 6 × 10(5) × 50 N). The load to fracture (N) was measured and fracture sites were evaluated macroscopically. RESULTS: None of the restorations failed during TCML. The mean fracture loads (standard deviations) were 1,522 N (249) for the 3-unit, inlay-retained TIFDPs on a metal abutment tooth (3-im), 1,910 N (165) for the 3-cm group, 1,049 N (183) for group 4-im, 1,274 N (282) for group 4-cm, 1,229 N (174) for group 4-ih and 911 N (205) for group 4-ch. Initial damages within the veneering ceramic occurred before the final failure of the restoration. The corresponding loads were 24-52% lower than the fracture load values. CONCLUSIONS: All restorations tested could withstand the mastication forces expected. Fracture-load values for 3- and 4-unit inlay-crown and crown-crown-retained TIFDPs should spur further clinical investigation.

Factors affecting wear of composite resin denture teeth--24-month results from a clinical study.

The objectives of this study were to measure the occlusal wear of composite resin denture teeth in patients wearing a complete denture and to evaluate factors affecting wear. Fifty participants provided with complete dentures in at least one jaw were included. Gypsum casts were made from preliminary vinyl polysiloxane impressions 4 weeks after insertion, then after 6 (t(1)), 12 (t(2)), and 24 months (t(3)). Three-hundred and three posterior denture teeth were evaluated after 24 months. Wear was measured indirectly, from the casts, by means of a three-dimensional laser scanner device. Sequential images of the occlusal surfaces were digitized and superimposed (occlusal matching). Statistical analysis was performed by the use of mixed regression models, with the patient being a random effect. Mean wear (median, interquartile range; micrometer) of the entire occlusal surface was 8 (19) at t(1), 18 (34) at t(2), and 40 (61) at t(3). Maximum vertical loss (median, interquartile range; micrometer) was 92 (112) at t(1), 146 (148) at t(2), and 226 (184) at t(3). The dental status of the opposing jaw and the nature of the opposing material significantly affected the wear of denture teeth at t (3). Gender, daily wearing time, jaw, and type of tooth had no significant effects on the extent of wear. Clinically relevant vertical loss of composite resin denture teeth occurs after 24 months. Considering the limitations of this study, wear of denture teeth was affected by dental status and opposing material. The results suggest that wear of composite resin denture teeth exceeds that of enamel.

Clinical success rates for polyether crown impressions when mixed dynamically and statically.

The purpose of this study is to compare success rates of dual-viscosity impressions for two types of mixing techniques of the polyether elastomeric impression material. Additionally, influencing parameters on the success rates should be evaluated. The expectation was that there would be no difference between the success rates for the two mixing techniques. Two centres enrolled 290 subjects (727 teeth) into the trial. Patients were randomized for the two types of mixing techniques. One step, dual-viscosity impressions were made with either statically mixed Impregum Soft tray material (SAM) or dynamically mixed Impregum Penta H DuoSoft (DMM). Low viscosity Impregum Garant L DuoSoft was used for both groups. Gingival displacement involved the use of two braided cords. Full-arch trays were used exclusively. Both critical defects and operator errors were assessed for the first impression taken by trained dentists. The primary outcome was impression success. For comparison of the two mixing techniques, the odds ratio for success and the corresponding one-sided 95% confidence interval was calculated by a logistic regression model. To account for the dependence between several teeth within one patient, the method of general estimating equations was used. The overall impression success rate was 35.4%. Both mixing techniques showed equal success rates indicated by an OR of 1.0 and a lower limit of the one-sided 95% confidence interval of 0.71. Using this result to develop the corresponding interval for the difference, it could be shown that the success rate using SAM was at most 8.2% lower than that when using DMM with a probability of 95%. Multivariate logistic regression analysis of other potential influencing factors showed position of finish line (p = 0.008, supra compared to mixed), blood coagulation disorder (p = 0.021) and the level of training of the clinician (student vs dentist, p=0.008) to have an independent influence on the success rate. Dynamic mechanical mixing and the new static mixing of polyether tray material showed nearly equal success rates in the study even though success rates were comparatively low (DMM, 35.3%; SAM, 35.4%).

Effect of gingival ceramic veneer thickness on the fracture strength of zirconia-based fixed dental prostheses.

PURPOSE: To assess the effect of different thicknesses of porcelain at the gingival of pontics, on the fracture load of zirconia-based, all-ceramic fixed dental prostheses (FDPs), anchored by inlays. METHODS: Box inlay cavities were prepared on mandibular molars and premolars. 40 FDPs with yttrium-stabilized zirconia frameworks of identical dimensions were manufactured using a CAD/CAM system and veneered with a press ceramic. The FDPs, replacing a premolar and a molar, were divided into four groups. In Group FR, the framework was all around unveneered. The next three groups received a 1 mm ceramic veneer on the buccal, occlusal and lingual side, but differed in the thickness of the ceramic veneer in the gingival, tensile zone of the pontics. In Group B-0, the gingival veneering was 0 mm, in Group B 1 mm and in Group B-2, 2 mm of gingival porcelain. A group of inlay-retained metal-ceramic FDPs (mc) served as control. All FDPs were subjected to thermal cycling and 600,000 cycles of mechanical load of 50 N. The load to fracture (N) was measured and fracture sites were evaluated macroscopically. A single-factor Analysis of Variance was used to analyze the data. RESULTS: None of the FDPs debonded after thermal cycling or mechanical loading and no signs of fractures or other defects were observed. The mean fracture loads and standard deviations in parentheses were: 647 N (123) for Group B-0, 716 N (102) for Group FR, 812 N (48) for Group B-1, 934 N (129) for Group B-2 and 1005 N (SD 81) for Group MC. Means for Groups B-0 and FR were not shown to differ, and the same for mean fracture strength of Groups B-2 and MC.

Clinical performance of zirconia-ceramic cantilever fixed partial dentures-Longitudinal nine-year results from a prospective, randomized, controlled pilot study.

PURPOSE: The aim of this study was to prospectively compare the clinical performance of veneered zirconia cantilever fixed partial dentures (Z-CFPDs) and metal-ceramic CFPDs (MC-CFPDs) over 9 years of follow-up in terms of survival. METHODS: Twenty-one participants were assigned by simple randomization to receive either 1 Z-CFPD (n=11) or 1 MC-CFPD (n=10). CFPDs were retained by 2 full crowns and replaced a missing premolar or a central or lateral incisor. Modified USPHS (United States Public Health Service) criteria were used to classify material chipping, retention, marginal integrity, secondary caries, and color of the restorations. The satisfaction of the study participants with the esthetics of their restorations was surveyed; pocket probing depths (PPD), plaque index (PI), and gingival index (GI) were also measured. Study groups were compared by use of U tests (continuous variables), or by use of Fisher exact probability tests (categorical variables) with α=0.05. RESULTS: Sixteen participants (n=8 with a Z-CFPD and n=8 with an MC-CFPD) attended the 9-year follow-up examination (response rate: 76.2%). Over the 9-year study period, survival of 50% for Z-CFPDs and 75% for MC-CFPDs was recorded (p=0.608). No framework fractures occurred, and no statistically significant differences were observed between the groups regarding changes in PPD, PI, GI, or participant satisfaction (p>0.05). USPHS criteria revealed statistically significantly poorer marginal quality for Z-CFPDs than for MC-CFPDs (p=0.009). CONCLUSION: Within the limitations of this study, Z and MC-CFPDs demonstrated no statistically significant difference in terms of survival.

The effect of two luting agents, pretreatment of the post, and pretreatment of the canal dentin on the retention of fiber-reinforced composite posts.

OBJECTIVES: The purposes of this study were to evaluate the push-out strength of core-build-up resin used for fiber-post cementation and to test the effects of different post and dentin pretreatment for different regions of the root. METHODS: After endodontic treatment 216 human teeth received a glass-fiber post. The teeth were divided into test groups to simulate the effects of: (I) cementation material (specifically core-build-up resin or conventional luting cement), (II) pretreatment of the root dentin (none, dual-curing bonding, light-curing bonding), (III) pretreatment of the post (none, hydrofluoric acid, tribochemical pretreatment), and (IV) different regions of the root. After thermal cycling all post-cemented roots were sectioned and each specimen was loaded in a universal testing machine until failure occurred. Statistical analysis was performed by use of a mixed-effects regression model. RESULTS: The cementation material (p

All-ceramic inlay-retained fixed partial dentures: preliminary results from a clinical study.

OBJECTIVES: The objective of this study was to evaluate the clinical performance of zirconia-based all-ceramic fixed partial dentures anchored by inlays. METHODS: A total of thirty FPDs, manufactured using a zirconia frame and veneered with press ceramic, were anchored by use of inlay retainers. All FPDs were designed to replace one missing molar and were adhesively luted by use of one of two different resin cements. Documentation included failures and other complications, plaque accumulation, and aesthetic and functional performance. Statistical analysis was performed using a cox-regression model. RESULTS: During the 12 months observation period a total of thirteen clinically relevant complications occurred-four delaminations of the veneer and six decementations. Three FPDs had to be replaced because of a fracture of the framework. The cement chosen, the location, and the design of the retainer had no statistically significant effect on the occurrence of complications. During the observation period, accumulation of plaque on the abutment teeth was not significantly greater than on reference teeth. Postoperative sensitivity did not differ significantly between the different luting cement groups. The aesthetic and functional performance of the FPDs was acceptable. CONCLUSIONS: Improved adhesion between resin cement and inlay retainer is desirable before general recommendation of all-ceramic inlay-retained FPDs. Use of different luting cements seems to have no effect on the occurrence of complications.

Dependence of in vitro fracture strength of adhesive core buildup and crown complexes on preparation design and cementation technique.

PURPOSE: To evaluate the fracture resistance of teeth restored using an adhesive core material placed under artificial crowns without pins or posts and to assess the effect of different preparation designs and cementation techniques (glass ionomer compared with adhesive cementation) used for the crowns. MATERIALS AND METHODS: Eighty-three intact molars were collected. Sixty-seven teeth were decoronated (test groups and one control group), a 2-mm circular ferrule design was prepared, and four different preparation designs (2-mm- or 1-mm-deep cavities and 2-mm- or 1-mm-thick walls) were used. Three control groups were also established. Cores were built up using an adhesive material. After preparation, standardized artificial crowns (cobalt-chromium alloy) were fabricated. Half of the crowns in the test group (n = 32) were cemented using Panavia (P group); glass-ionomer cement was used for the other half (KC group). All teeth were exposed to 10,000 thermal cycles and loaded until fracture. Statistical analysis was performed, including nonparametric tests (Mann-Whitney U-test) and ANOVA. RESULTS: In the P group, the fracture strength was significantly (p = 0.004) higher (591.75 +/- 177.95 N) than in the KC group (430.18 +/- 193.67 N). The effect of the preparation design was more pronounced in the KC group. In all groups simulating the most moderate type of tooth decay (2-mm-deep cavity and a 2-mm-thick wall), the fracture strength was comparable with that of intact teeth. Results from ANOVA showed that the type of cementation of the crowns affected fracture strength. CONCLUSION: Fracture strengths of adhesive core/crown complexes are greater when an adequate cavity for retention (at least 2 mm deep) is prepared and the crown is luted.

Fracture behaviour of zirconia ceramic cantilever fixed dental prostheses in vitro.

OBJECTIVE: Evaluation of the fracture resistance of all-ceramic cantilever fixed dental prostheses (FDPs) manufactured from zirconia frameworks and veneered with a press ceramic. MATERIAL AND METHODS: Two mandibular premolars were prepared either with a box inlay cavity or with a full crown chamfer preparation and then duplicated. 40-three-unit cantilever FDPs replacing one premolar, with a group size of eight for each design, were manufactured. In group i-i the cantilever FDPs were retained by two inlays, in group i-c by an inlay-crown combination, and in group c-c by two crowns. The frameworks in groups i-c-R and c-c-R were reinforced by an additional shoulder on the oral side of the zirconia frameworks. All FDPs were subjected to thermal cycling (TC) and 600,000 cycles of mechanical loading (ML) with 50 N. The load to fracture was measured and fracture sites were evaluated. RESULTS: The mean fracture values ranged from 172 N to 792 N. Fracture-strength values were significantly lower for the i-i retained FDPs than for the i-c and c-c combinations. There was no significant effect of the reinforcing shoulder in groups i-c-R and c-c-R. For FDPs with a crown on the terminal tooth, fractures were usually within the distal wall of the distal crown. CONCLUSIONS: Inlay-inlay retained cantilever FDPs cannot withstand the mastication forces expected. Fracture load values for inlay-crown and crown-crown-retained FDPs encourage further clinical investigation. The mode of fracture indicates that reinforcement of the distal crown wall might enhance fracture resistance.

Optimizing preparation design for metal-free composite resin crowns.

STATEMENT OF PROBLEM: Although composite resin materials are used for posterior crown restorations, the influence of preparation design, material thickness, convergence angle, and method of cementation on fracture resistance remains unclear. PURPOSE: The purpose of this in vitro study was to test the hypothesis that minimal preparation designs provide an acceptable level of fracture resistance for posterior composite resin crowns. MATERIAL AND METHODS: Nonreinforced Artglass composite resin crowns (n=128) were fabricated on human molars in 16 test groups (n=8). Axial tooth preparation included a 1-mm-deep shoulder or a 0.5-mm chamfer preparation, whereas occlusal reduction was either 0.5 mm or 1.3 mm. The total angle of convergence was 4 or 11 degrees and the crowns were cemented either with glass ionomer cement (Ketac Cem) or resin cement (2bond2). After 10,000 thermal cycles, crowns were vertically loaded until failure occurred; load was measured in newtons. Statistical analysis was performed by a 4-way ANOVA (alpha=.05). RESULTS: Statistical analysis revealed significant effects of occlusal thickness (P<.001), cement (P<.001), preparation design (P=.011), and convergence angle (P=.001) on the fracture resistance of the composite crowns. For composite resin crowns with an occlusal thickness of 0.5 mm, the resistance to fracture was lower than for crowns with a 1.3-mm thickness. Fracture resistance was greater when resin cement was used, and greater for the chamfer finish line than for the shoulder finish line. Use of a greater total convergence angle reduced fracture resistance. CONCLUSIONS: Fracture resistance of composite resin crowns was significantly improved by increasing the occlusal thickness of the crowns, by using resin cement, and by reducing the total convergence angle.

Validity of temporomandibular disorder examination procedures for assessment of temporomandibular joint status.

INTRODUCTION: This hypothesis-generating study was performed to determine which items in the Research Diagnostic Criteria for Temporomandibular Disorders (RDC/TMD) and additional diagnostic tests have the best predictive accuracy for joint-related diagnoses. METHODS: One hundred forty-nine TMD patients and 43 symptom-free subjects were examined in clinical examinations and with magnetic resonance imaging (MRI). The importance of each variable of the clinical examination for correct joint-related diagnosis was assessed by using MRI diagnoses. For this purpose, "random forest" statistical software (based on classification trees) was used. RESULTS: Maximum unassisted jaw opening, maximum assisted jaw opening, history of locked jaw, joint sound with and without compression, joint pain, facial pain, pain on palpation of the lateral pterygoid area, and overjet proved suitable for distinguishing between subtypes of joint-related TMD. Measurement of excursion, protrusion, and midline deviation were less important. CONCLUSIONS: The validity of clinical TMD examination procedures can be enhanced by using the 16 variables of greatest importance identified in this study. In addition to other variables, maximum unassisted and assisted opening and a history of locked jaw were important when assessing the status of the TMJ.

Are there associations between sleep bruxism, chronic stress, and sleep quality?

OBJECTIVES: The purpose of this study was to identify associations between definite sleep bruxism, as defined by the American academy of sleep medicine, and chronic stress and sleep quality. METHODS: Sleep bruxism was determined by use of questionnaires, assessment of clinical symptoms, and recording of electromyographic and electrocardiographic data (recorded by the Bruxoff® device). The study included 67 participants. Of these, 38 were identified as bruxers and 29 as non-bruxers. The 38 bruxers were further classified as 17 moderate and 21 intense bruxers. Self-reported stress and self-reported sleep quality were determined by use of the validated questionnaires "Trier Inventory for the Assessment of Chronic Stress" (TICS) and the "Pittsburgh Sleep Quality Index" (PSQI). RESULTS: No statistically significant association was found between sleep bruxism and self-reported stress or sleep quality. However, a significant association between specific items of chronic stress and poor sleep quality was identified. CONCLUSIONS: The results of this study indicate an association between subjective sleep quality and subjective chronic stress, irrespective of the presence or absence of sleep bruxism. CLINICAL SIGNIFICANCE: Chronic stress and sleep quality do not seem to be associated with sleep bruxism. (clinical trial no. NCT03039985).

Clinical wear of posterior metal-free polymer crowns. One-year results from a randomized clinical trial.

OBJECTIVES: The purpose of this randomized clinical trial was to evaluate the clinical wear behavior of posterior, metal-free polymer crowns, with and without a glass-fiber framework, and to compare it with that of metal-ceramic crowns. METHODS: Eighty single crowns manufactured from a newly designed polymer composite were set in posterior teeth. Half of these received a glass-fiber framework (group 1) whereas half were prepared without framework stabilization (group 2). All polymer crowns were adhesively luted with resin cement. As the control group, 40 conventional metal-ceramic crowns were inserted with hybrid cement. Wear was measured, by use of gypsum replicas, at baseline and after 12 months, by use of a 3D laser scanner. Statistical analysis was performed using mixed-effects regression model analyses. RESULTS: The mean total wear of posterior single crowns was -8.1 microm (+/-9.7 microm) in group 1, -7.0 microm (+/-9.1 microm) in group 2, and -3.4 microm (+/-6.3 microm) in the control group. Statistical analysis revealed wear behavior was significantly different from the control group for group 1 (p=0.014) and group 2 (p<0.01). No significant difference was detected between groups 1 and 2. Age, gender, and opposing teeth had no significant effect on wear behavior. CONCLUSIONS: Within a 12-month observation period mean total wear of posterior polymer crowns with and without a glass-fiber framework was significantly greater than for metal-ceramic crowns. The selection of restorative materials should be based on knowledge of clinical wear in order to preserve occlusal stability.