Florian Mack

Accuracy and reliability of methods to measure marginal adaptation of crowns and FDPs: a literature review.

PURPOSEnTo review methods used to investigate marginal adaptation of crowns and fixed dental prostheses (FDPs), and to discuss testing variables employed and their influence on results.nnnMETHODSnOnline libraries including PubMed, Scopus, and Ovid were searched for articles evaluating the marginal adaptation of crowns and FDPs using a combination of the keywords: marginal accuracy, marginal fit, marginal gap, marginal discrepancy, fitting accuracy, crown, and FPD. Peer-reviewed publications in English in the period 1970 to December 2011 were collected, evaluated by their abstract, and included if they met the inclusion criteria. The criteria involved studies evaluating marginal adaptation of crowns and FDPs through clear experimental protocols. Exclusion criteria involved longitudinal prospective and retrospective clinical evaluations, studies using subjective tactile sensation, and other predefined criteria.nnnRESULTSnA total of 277 papers were identified; only 183 met the inclusion criteria. Direct view technique was used by 47.5% of the articles followed by cross-sectioning (23.5%), and impression replica (20.2%) techniques. The marginal gap values reported by these techniques varied among individual crown systems and across different systems because of variations in study type (in vivo vs. in vitro), sample size and measurements per specimen, finish line design, and stage at which the marginal gap was measured.nnnCONCLUSIONnThere was a substantial lack of consensus relating to marginal adaptation of various crown systems due to differences in testing methods and experimental protocols employed. Direct view technique was the most commonly used method of reproducible results. Also, conducting an experimental set-up of testing a minimum of 30 specimens at 50 measurements per specimen should produce reliable results. Additionally, using a combination of two measurement methods can be useful in verification of results.

Lithium Disilicate Restorations Fatigue Testing Parameters: A Systematic Review.

PURPOSEnTo review laboratory studies that investigated fatigue resistance of lithium disilicate (LD) crowns and fixed dental prostheses (FDPs) to elucidate study designs and testing parameters.nnnMETHODSnAn electronic search was performed in PubMed, Scopus, and Ovid to identify in vitro studies that investigated fatigue resistance of LD crowns and FDPs. The search included all studies published in English in peer-reviewed journals in the period from 1998 to June 2014. The search followed a specific strategy that included combination of the following keywords: lithium disilicate, e.max, empress, all-ceramic, all ceramic, glass ceramic, fatigue, cyclic loading, dynamic loading, chewing simulator, fracture resistance, thermocycling, laboratory simulation, aging, crown, FDPs, FPDs, fixed partial denture, fixed dental prosthesis, and bridge. Studies were selected if mechanical and thermal loading parameters were clearly identified. Search results with abstracts were transferred into Endnote reference system, and duplicates were deleted. The remaining studies were then reviewed at three levels (title, abstract, full text) to further refine the articles.nnnRESULTSnThe initial search retrieved 1044 eligible studies. After deduplication, 864 records were examined by titles and then abstracts; 826 were excluded, and 38 were assessed by full-text reading. In total, 19 articles met inclusion criteria and were included in this study.nnnCONCLUSIONnThe studies reviewed showed a level of heterogeneity, as testing parameters were considered through different setups. The current study demonstrated that various setting of the testing parameters and having a lack of testing standardization has likely led to inconsistency in the reported results. The obvious heterogeneity in the setting of testing variables-especially the magnitude of load and number of cycles applied-made it impractical to run direct comparisons between the reviewed studies. Therefore, specific international standardization of fatigue testing of dental restorations is urgently needed to ensure the delivery of consistent, indicative, and comparable data.

The Impact of Core/Veneer Thickness Ratio and Cyclic Loading on Fracture Resistance of Lithium Disilicate Crown.

Purpose n nTo investigate the effect of core/veneer thickness ratio on the fracture strength of lithium disilicate crowns subjected to cyclic loading in a simulated oral environment. n n n nMaterials and Methods n nA typodont molar tooth received a standard complete crown preparation according to the manufacturers instructions. Sixty lithium disilicate crowns were prepared and assigned to three groups with the following core/veneer thickness ratios A: 0.7 (0.6/0.9), B: 1.1 (0.8/0.7), and C: 2 (1.0/0.5). The cores were milled from lithium disilicate e.max CAD blocks and hand-layered using e.max Ceram. Ten specimens from each group acted as control, while the remaining ten specimens were subjected to thermal mechanical loading in a chewing simulator. All specimens were then subjected to the single load to fracture test at 1 mm/min crosshead speed. Data were analyzed using two-way ANOVA, Tukey multiple comparison test, Pearson correlation test, and quadratic regression (p < 0.05). n n n nResults n nAll crowns survived fatigue testing with no signs of fractures or chipping, resulting in a 100% survival rate. The mean fracture load values for control and corresponding fatigued specimens (N) were 1075 and 987 for group A, 1548 and 1482 for group B, and 1455 and 1163 for group C. Increasing the core/veneer thickness ratio from 0.7 to 1.1 significantly increased the fracture load of the crowns; however, a further increase in the ratio up to 2 did not affect the fracture load compared to the 1.1 ratio (p > 0.05). The increase in core thickness significantly positively correlated with the fracture force for control specimens (r = 0.76; p < 0.05). After single load to fracture, crowns predominantly failed by bulk fracture, including the whole thickness of the crowns. Fracture modes were categorized according to fracture path and number of fractured pieces. n n n nConclusions n nCrowns with a 1.1 (0.8/0.7) core/veneer thickness ratio showed the optimum fracture load among control and fatigued groups. Reducing the core thickness from 0.8 mm to 0.6 mm decreased the fracture load significantly, while increasing it to 1.0 mm showed no statistical effect. Cyclic loading in a simulated oral environment did not significantly affect fracture strength of veneered lithium disilicate crowns in any of the tested groups.

Masticatory Loading and Oral Environment Simulation in Testing Lithium Disilicate Restorations: A Structured Review

Objectives: To provide evidence for the need to standardize fatigue testing of restorative materials by reviewing all laboratory studies that tested fatigue resistance of Lithium Disilicate (LD) crowns and Fixed Dental Prostheses (FDPs) to elucidate study designs and testing parameters. Data: A database search on PubMed, Scopus, and Ovid for in vitro (lab-based) studies investigated fatigue resistance of LD crowns and FDPs retrieved 1191 eligible studies. After deduplication, 1054 records were examined by titles and then abstracts; 1016 were excluded and thirty-eight were assessed by full-text reading. In total, nineteen articles met inclusion criteria and were included in this study. Study selection: Studies were selected if they investigated fatigue resistance of LD crowns and/or FDPs in vitro. Mechanical and thermal loading parameters, including magnitude of load and number of cycles, and oral environment simulation, must be clearly identified. Only articles published in peer-reviewed, English-language journals were considered. Conclusion: It is noticeable that simulation of the fatigue phenomenon has become valued, and thus applied more extensively in the last year. However, studies included in this review show level of heterogeneity as testing parameters were considered in different ways through different set-ups. Therefore, standardization of test procedures is required to enable the delivery of consistent, meaningful, and comparable data.

Changes in condylar cartilage after anterior mandibular displacement in juvenile pigs

UNLABELLEDnAdaptive remodelling of the mandibular condyle in response to mandibular advancement is the mechanism exploited by orthodontic forward displacement devices.nnnOBJECTIVEnThis work investigated the expression of collagens, matrix metalloproteinases and vascular endothelial growth factor during this process.nnnDESIGNnTwenty juvenile pigs were randomly divided into two experimental groups, where the treatment group was fitted with mandibular advancement splints, and the control group was not. Changes in the mRNA content of condylar cartilage tissue was then were measured by real-time PCR using specific primers after 4weeks of treatment.nnnRESULTSnThe temporal pattern of the expression of Col1 and MMP13 during condylar adaptation coincided with that during natural condylar growth. The amount of the expression of Col10 during condylar adaptation was significantly lower (p<0.05), whereas the expression of Col2, MMP8 and VEGF was significantly higher compared to natural growth (p<0.05).nnnCONCLUSIONSnIt is suggested that condylar adaptation in growing pigs triggered by mandibular forward positioning results not only from passive adaptation of cartilage, but also involves growth affected processes. Our results showed that mechanical strain produced by mandibular advancement induced remodelling and revascularization in the posteriocranial mandibular condyle. These results are mostly consistent with former published histological and histomorphometrical analyses.

Fracture load and survival of anatomically representative monolithic lithium disilicate crowns with reduced tooth preparation and ceramic thickness

PURPOSE To investigate the effect of reducing tooth preparation and ceramic thickness on fracture resistance of lithium disilicate crowns. MATERIALS AND METHODS Specimen preparation included a standard complete crown preparation of a typodont mandibular left first molar with an occlusal reduction of 2 mm, proximal/axial wall reduction of 1.5 mm, and 1.0 mm deep chamfer (Group A). Another typodont mandibular first molar was prepared with less tooth reduction: 1 mm occlusal and proximal/axial wall reduction and 0.8 mm chamfer (Group B). Twenty crowns were milled from each preparation corresponding to control group (n=5) and conditioned group of simultaneous thermal and mechanical loading in aqueous environment (n=15). All crowns were then loaded until fracture to determine the fracture load. RESULTS The mean (SD) fracture load values (in Newton) for Group A were 2340 (83) and 2149 (649), and for Group B, 1752 (134) and 1054 (249) without and with fatigue, respectively. Reducing tooth preparation thickness significantly decreased fracture load of the crowns at baseline and after fatigue application. After fatigue, the mean fracture load statistically significantly decreased (P<.001) in Group B; however, it was not affected (P>.05) in Group A. CONCLUSION Reducing the amount of tooth preparation by 0.5 mm on the occlusal and proximal/axial wall with a 0.8 mm chamfer significantly reduced fracture load of the restoration. Tooth reduction required for lithium disilicate crowns is a crucial factor for a long-term successful application of this all-ceramic system.