Crown Thickness Research Articles

Comparison of Fracture Strength of Milled and 3D-Printed Crown Materials According to Occlusal Thickness.

This study aimed to measure the fracture strengths and hardness of final restorative milled and 3D-printed materials and evaluate the appropriate crown thickness for their clinical use for permanent prosthesis. One type of milled material (group M) and two types of 3D-printed materials (groups P1 and P2) were used. Their crown thickness was set to 0.5, 1.0, and 1.5 mm for each group, and the fracture strength was measured. Vickers hardness was measured and analyzed to confirm the hardness of each material. Scanning electron microscopy was taken to observe the surface changes of the 3D-printed materials under loads of 900 and 1500 N. With increased thickness, the fracture strength significantly increased for group M but significantly decreased for group P1. For group P2, the fracture strengths for the thicknesses of 0.5 mm and 1.5 mm significantly differed, but that for 1.0 mm did not differ from those for other thicknesses. The hardness of group M was significantly higher than that of groups P1 and P2. For all thicknesses, the fracture strength was higher than the average occlusal force for all materials; however, an appropriate crown thickness is required depending on the material and component.

Roughness analysis on porcelain sectional surface of porcelain fused to Co-Cr alloy endocrowns

This study aims to compare the roughness between the central and edge points on the porcelain sectional surface of porcelain fused to Co-Cr alloy endocrowns. Utilizing anatomical data from average molar dimensions, a simplified model for the endocrowns was created. Eight porcelain fused to Co-Cr alloy endocrowns were fabricated with an edge thickness of 0.3 mm. Following casting, firing, cutting, and polishing procedures, the roughness on porcelain sectional surface at both the central and edge points of the inner crown was assessed using an atomic force microscope (AFM). The roughness measurement (Sq value) for the central point on porcelain sectional surface was (10.46 ± 3.37 nm), and for the edge point, it was (10.50 ± 1.99 nm). There was no statistically significant distinction between the central and edge points in terms of roughness. Despite the uneven thickness of the inner crown in porcelain fused to Co-Cr alloy endocrowns, it was observed that this disparity had negligible impact on the internal microstructure of the porcelain. Therefore, its application in dental clinical settings could be deemed viable.

Effects of dental tissue substructure and size on fracture strengths of lithium disilicate and zirconia ceramics

We aimed to assess the effects of standard resin preparation models with five different thicknesses of occlusal surface on the fracture strengths of zirconia (ZrO2) and lithium disilicate glass ceramics. The specimens of 10 first maxillary molars collected between January 2019 and January 2020 were selected. Standard mathematical models were formed after scanning the resin matrices using software. The full crowns with five different thicknesses of occlusal surface were established, among which the molar specimens prepared by ZrO2 glass ceramic composites alone were assigned into ZrO2 group (n=5, 40 specimens) while those prepared using ZrO2-lithium disilicate glass ceramic composites were allocated into ZTCLDC group (n=5, 40 specimens). When the thickness of glass-ceramic full crowns was 0.5, 0.8, 1.0, 1.2 and 1.5 mm, the fracture load of the specimens in ZTCLDC group was not significantly different from that in ZrO2 group, and there was no significant difference in the three-point flexural strength between ZTCLDC group and ZrO2 group (P>0.05). The fracture toughness was not significantly different between the two groups in the case of the thickness of glass-ceramic full crown at 0.5, 0.8, 1.0, 1.2 and 1.5 mm (P>0.05). The thickness was positively correlated with fracture load, three-point flexural strength and fracture toughness (P<0.05). The fracture strength of lithium disilicate and ZrO2 ceramics is directly proportional to the thickness of ZrO2 and ZTCLDC crowns.

Fracture characteristics and translucency of multilayer monolithic zirconia crowns of various thicknesses

ObjectivesMultilayer monolithic zirconia (M-Zr) crowns can be engineered to achieve gradational translucency and color intensity. However, this modification may compromise the mechanical strength, raising concerns regarding the ability of M-Zr crowns to withstand occlusal stresses. The effects of M-Zr crown thickness on translucency and ability to endure occlusal forces were investigated at different tooth positions (incisors, premolars, and molars). The objective was to determine the minimal thickness of M-Zr crowns used in tooth preparation to meet aesthetic and functional demands. MethodsM-Zr samples (Vita A1) with four thicknesses (0.5, 1.0, 1.5, and 2.0 mm) were prepared and subjected to translucency testing using a digital colorimeter by 3-third and 9-square division methods. Crown-shaped M-Zr samples with three thicknesses (1.0, 1.5, and 2.0 mm) and three tooth positions (incisor, premolar, and molar) were digitally designed, and 2.0 mm metal abutments were fabricated. The samples were bonded to the abutments; their fracture characteristics were evaluated using a universal testing machine, and their fracture surfaces examined using an optical microscope. Statistical analyses included the Shapiro-Wilk test, Pearson correlation, and one-way and two-way ANOVA with a post hoc Tukey HSD test (α = 0.05). ResultsColor analysis results revealed a significant negative correlation between thickness and translucency (r < −0.96, P < 0.01), with the highest values in the incisal region. Cross-sectional profiles confirmed the uniform thickness and morphology of the digitally designed M-Zr crowns. The results of fracture strength analysis showed position-dependent variability, a strong positive correlation with thickness (r > 0.96, P < 0.01), and fracture strengths consistently exceeding 1200 N across all tooth positions. Fracture patterns indicated that thinner crowns at the incisors and molars were more prone to cracking, whereas those at the premolars demonstrated significantly higher strength (4872.51 N, P < 0.05), only with crack or even no fracture occurring at 2.0 mm. ConclusionsThickness significantly influenced both the translucency and fracture strength of M-Zr, with the tooth position playing an additional role, albeit to a lesser extent. Although thinner crowns exhibited lower strength at each tooth position, even at a thickness of 1.0 mm, fracture strength exceeding 1200 N was maintained, surpassing the typical occlusal forces. Thus, it can be asserted that M-Zr crowns with a minimum thickness of 1.0 mm can meet both aesthetic and functional requirements.

Prolonged post-washing in ethanol decreases bond strength of additively manufactured crown materials

ObjectivesThis study aimed to investigate the effect of post-washing duration and crown thickness on the bond strength between additively manufactured crown materials and dental cement in vitro. MethodsRectangular-shaped specimens of two thicknesses (1.5 and 2.0 mm) were additively manufactured from permanent VarseoSmile Crown (VC) and long-term temporary NextDent (ND) materials. The specimens were post-washed (n = 160) in ethanol for 5 min, 10 min, 1 h, and 8 h then cemented with dual-cure resin cement. Twenty PMMA (TC) were milled as a control. A chevron-notch test was performed to measure the maximum load until failure (N). Interfacial bond strength (J/m2) was calculated and statistically analysed. The mode of failure was analysed by scanning electron microscopy (SEM). ResultsThere was a significant difference in the bond strength between all groups (p < 0.01). VC at 1.5mm thickness post-washed for 10 min showed the highest mean bond strength (1.77 ±0.96 J/m2) while VC at 2.0mm thickness post-washed for 8 h showed the lowest (0.22 ±0.10 J/m2). Exposure to ethanol for 8 h resulted in lower bond strength. Within the type of material, there were no differences in bond strength between the thicknesses when post-washed for the same duration. ConclusionsProlonged post-washing of AM crown materials can significantly decrease the bond strength to resin cement. There were no differences between the permanent and long-term temporary AM materials. When post-washed for 5 min, AM materials observed comparable or higher bond strength values compared to PMMA. Clinical significanceThe output of this research serves as a guide for dental practitioners, emphasising the importance of adhering to correct post-washing procedures for optimal bond strength of additively manufactured crown materials.

Fatigue behavior of three thin CAD/CAM all-ceramic crown materials

ABSTRACT The purpose of this study was to study the effect of crown thickness on the fatigue life of CAD/CAM ceramic materials. CAD/CAM ceramic materials for the crown were virtually designed with three thickness designs of (a) ultra-thin occlusal crown average 0.7 mm thick (group A), (b) thin occlusal crown 1.1 mm average thick (group B), (c) thick occlusal crown 1.5 mm thick. The materials are: zirconia Cercon ZC and IPS e.max CAD (LD). Finite Element Analysis (FEA) simulations were carried out to estimate the fatigue lives of restorative materials. The lives for groups B and C under fatigue load were not significantly different from each other for Zirconia. The predicted lives for group A zirconia crowns, under fatigue load 50 N, 100 N, 120 N is 24 years, 4.3 years, 1.9 years, respectively. Results for crowns made of LD can be summarized as follows: under load 50 N, all groups have survived longer than 5 respectively, while under the load of 100 N, only group C survived longer than 5 years. 0.7 mm thick full contour Zirconia crowns possessed adequate endurance strength to survive under physiologic conditions. On the other hand, the crown made of LD should have at least 1.5 mm thickness to survive longer than 5 years.

Influence of Different Thicknesses of Monolithic Crowns Made from Different Resin-Bonded Glass Ceramic on Their Load-bearing Capacity (An in vitro Comparative Study)

Objective: To investigate the load-bearing capacity of the full-coverage crowns made from lithium disilicate glass-ceramic LDGC (IPS e.max®, Ivoclar Vivadent) and 10% zirconia reinforced lithium silicate glass ceramic ZLS (Dentsply DeTrey) with different thicknesses.&#x0D; Methods: Forty resin dies with supporting bases were duplicated from two prepared typodont teeth for all-ceramic crowns as a maxillary first molar. Forty crowns corresponding to each die were prepared and then they were divided into four groups: Group I (n 10) made from ZLS with a restoration thickness of (1.0 mm occlusally and 1.0 mm radially) and Group II (n 10) made from LDGC with a restoration thickness of (1.0 mm occlusally and 1.0 mm radially), and Group III (n 10) made from ZLS (1.5 mm occlusally and 1.5mm radially) and Group IV (n 10) made from LDGC (1.5 mm occlusally and 1.5 radially). All crowns were fabricated by chair side CEREC CAD/CAM and crystallized with Speed fire Dentsply Furness. The virolink resin cement (VariolinkII, Ivoclar Vivadent) was used to bond the crowns to the corresponding dies. All samples were thermo-cycled (10000 cycles between 5c and 55c) and tested for fracture resistance using a Universal testing machine at 0.5 mm/minute speed until failure. ANOVA and Tukey HSD test were used to compare the fracture resistance between groups.&#x0D; Results: The result demonstrates that the fracture resistance means and SD of ZLS with different thicknesses ranged from 572 N ± 122.002 to 1171±217.432 N, and those of LDGC with different thicknesses ranged from 625 N ±151.676 N to 845 N ±388.222 N.&#x0D; Conclusions: The fracture resistance increased with increasing crown thickness using different glass-ceramic materials.

Effect of abutment design on fracture resistance of resin-matrix ceramic crowns for dental implant restoration: an in vitro study

BackgroundThe purpose of this study is to investigate the performance and fracture resistance of different resin-matrix ceramic materials for use in implant-supported single crowns with respect to the abutment design (crown thickness: 1 mm, 2 and 3 mm).MethodsForty-eight abutments and crowns were fabricated on implants in the right lower first molar. Two resin-matrix ceramic materials for dental crowns were selected for study: (1) a glass-ceramic in a resin interpenetrating matrix (Vita Enamic, Vita, Germany) and (2) a resin-based composite with nanoparticle ceramic filler (Lava Ultimate, 3 M ESPE, USA). Three types of abutments were designed: 1 mm thick crown + custom titanium abutment, 2 mm thick crown + custom titanium abutment and 3 mm thick crown + prefabricated titanium abutment. The experiment was divided into 6 groups (n = 8) according to the crown materials and abutment designs. After 10,000 thermocycles, fracture resistance was measured using a universal testing machine. The statistical significance of differences between various groups were analysed with ANOVA followed by a post hoc Tukey’s honestly significant difference test. The surfaces of the fractured specimens were examined with scanning electron microscopy (SEM).ResultsTwo-way ANOVA revealed that the abutment design (F = 28.44, P = 1.52 × 10− 8<0.001) and the crown materials (F = 4.37, P = 0.043 < 0.05) had a significant effect on the fracture resistance of implant crown restoration. The Lava Ultimate-2 mm group showed the highest fracture resistance of 2222.74 ± 320.36 N, and the Vita Enamic-3 mm group showed the lowest fracture resistance of 1204.96 ± 130.50 N. Most of the 1 and 2 mm groups had partial crown fractures that could be repaired directly with resin, while the 3 mm group had longitudinal fracture of the crown, and the crowns were detached from the abutments.ConclusionBased on the in vitro data of this study, the fracture resistance of the 2 mm thick resin-matrix ceramic crown design was higher than that of the 1 and 3 mm groups. The 2 mm thick resin-matrix ceramic crown and personalized abutment are an option to replace zirconia for implant crown restoration.

Enamel thickness per masticatory phases (ETMP): A new approach to assess the relationship between macrowear and enamel thickness in the human lower first molar

Many anthropological studies have examined the functional implications of enamel thickness in human dental crowns. Despite limitations, Enamel thickness (ET) values are still used to infer taxonomic attribution in the genus Homo, and to identify mechanisms of functional adaptation against macrowear. However, only a few studies have tried to describe the possible relationship between ET and dental wear patterns in permanent lower first molars (M1) aiming to observe whether an adaptive response to the environmental and cultural context is detectable. The present work aims to investigate a possible signal of ET adaptive response in M1 (wear stage 3; Molnar, 1971) belonging to individuals who lived between the Neolithic (early 6th millennium BCE) and the Bronze Age (second half of the 2nd millennium BCE) in Croatia to identify any signal of change in dental tissue proportions based on archaeologically documented shifts in population structure and subsistence strategies. In order to do so, we explored 3D Average Enamel Thickness (AET) of the entire crown and wear pattern distribution among individuals and across chronological groups. We then described a new method called “Enamel Thickness per Masticatory Phases” (ETMP) involving the creation of virtual sections cutting enamel and coronal dentine in three parts based on masticatory phases, and explored the distribution of 3D AET accordingly. Finally, we performed geometric morphometric analysis on dental crown to ascertain possible morphological differences between Neolithic, Eneolithic, and Bronze Age groups. Results show that Bronze Age individuals differ from previous groups due to 1) higher values of ET in both the entire crown and specifically in the buccal area, 2) to an extensive wear pattern localized on the buccal side, and 3) to the distal extension of the hypoconid together with an extended mesio-distal shape of the crown. These patterns may represent an adaptive response of dental tissue to varying functional demands (e.g. archaeologically documented dietary shift). The study of ETMP therefore offers a more nuanced method, in addition to morphology and macrowear analysis, to document biocultural processes of change over time in archaeological populations through dental tissues.

Understanding the cooling capacity and its potential drivers in urban forests at the single tree and cluster scales

Urban forests can mitigate the urban heat island effect by serving as cooling islands. However, urban forest cooling potentials and their influencing factors at the single tree and cluster scales remain unclear. In our study, unmanned aerial vehicle image with very high resolution (5 cm) was used to classify tree species, assess the cooling intensities of different tree species, and ascertain their drivers at single tree and cluster scales. Our results indicate that, unmanned aerial vehicle images can be used well for tree species classification with the accuracy of approximately 87%. We found the different cooling intensities for different tree species, ranging from 5.05 °C to 16.12 °C, with an average value of 11.2 °C. Trees have 1.35 °C higher cooling intensity than shrubs. At single tree scale, the main factors for affecting the cooling intensity were tree height and crown thickness. When tree height increased by 1.82 m or crown thickness increased by 1.3 m, the cooling intensity increased by 0.5 °C. At cluster scale, we found that the cooling intensity does not increase more with increasing tree canopy coverage when the canopy coverage was larger than 40%. In addition, we found that urban forest cooling intensity was positively correlated with the connectivity and contagion of trees at the cluster scale, and the relationship of cooling intensity with diversity conformed to a V-shaped curve. This study could be helpful for the construction and planning of urban forests to handle urban heat waves.

Canine morphometrics as a tool for distinguishing species, sex, and age class in Southern Ocean fur seals.

Carcasses resulting from natural mortalities are invaluable for use in scientific studies, provided species, sex, and age class are known. When such data are unavailable, identifying skeletal remains is necessary if one is to use the information contained within samples. Teeth are amongst the best preserved skeletal remains owing to the durability of enamel and dentine. Here, we tested whether external measurements of canines could be used to distinguish two partially sympatric species of Southern Ocean fur seals, the Antarctic Arctocephalus gazella and Sub-Antarctic A. tropicalis fur seals. We also investigated whether the external measurements of canines could be used to determine the age, sex, as well as island of origin of the animals. Eight morphological variables (crown length, root length, crown width, root width, crown thickness, root thickness, total canine length, and count of external surface annular ridges) were recorded from canines of 340 individuals of known species, sex, and island of origin. The count of external annular ridges provided a good estimate of age, which was confirmed by counting the growth layer groups of sectioned teeth, especially for older animals (> 9 years old). External canine measurements proved useful in distinguishing species, as well as sex within and between species, particularly in adult animals. Species were more difficult to distinguish in females than in males. The islands of origin could only be inferred in male Antarctic fur seals. This study indicates that fur seal teeth of unknown provenance, found either in breeding colonies or as vagrants, provide evidence on species, sex, and age of the animal, which increases the value of associated samples. It further highlights the importance of external measurements of skeletal remains such as canine teeth in separating closely related species.

An in vitro trial on the effect of arch form on connector size requirements in long span anterior zirconia fixed dental prostheses.

To test the fracture resistance of maxillary canine to canine fixed partial denture with four missing incisors, with increasing anterior-cantilevers of the pontics and varying connector sizes. Two 3D-printed titanium alloy (Ti6Al4V) models mimicking a maxillary canine to canine fixed partial denture (FPD) with four pontics replacing the incisors were used as master models. Zirconia FPDs were digitally designed and milled with two different connector sizes (9 and 12 mm2 ) each with three different anterior cantilevers (7, 10, and 13mm) accounting for 6 test groups. Seven samples were milled for each group generating a total of 42 samples. The zirconia FPDs were cemented on the titanium model using resin modified glass ionomer cement and the model fixated to a variable angle vice. A sinusoidal cyclic waveform load from 50 to 280N was applied using a universal testing machine at a frequency of 30 cycles per second and a total of 5 million cycles. The results of Fisher's exact tests showed that the difference in the proportion of fractured versus nonfractured fixed partial dentures was not statistically significant when comparing the 9 with the 12 mm2 connector size (p = 1.00), as well as when comparing the six test groups (p = 0.2338); on the other hand, it proved to be statistically significant when comparing the 7mm cantilever with the 10 and 13mm cantilevers combined (p = 0.0407) indicating that a 7mm anterior spread of the pontics showed a significantly greater proportion of fixed partial dentures that fractured. Fracture susceptibility was not a function of cantilever length in this testing configuration for anterior FPDs. Retainer crown thickness seems to be a more important parameter than connector size thickness. Based on the results, a smaller connector size (9 mm2 ) can be used to improve the esthetics of pontics in long span anterior FPDs.

Symmetrical comparison of crown size, morphology and gingival shape in maxillary incisors

Background: Maxillary anterior tooth proportion has special value in dental aesthetics. Restorative dentistry often involves correcting tooth size discrepancies. Therefore, dental biometrics should play an important role in the planning of an aesthetic restoration. Objectives: To assess and compare clinical crown dimensions and classify crown shape and gingival shape of the maxillary incisors in order to collect anatomical data on the anterior teeth of young population visiting the tertiary centre. Methods: This descriptive cross-sectional study conducted in department of Prosthodontics in November 2021 after getting ethical approval among dental students and patients attending the hospital, with permanent healthy dentitions. Impression of maxillary and mandibular arches were made with alginate and poured in dental stone. Measurement of maxillary central incisors was done for length and thickness with the digital vernier calliper. Convenience sampling was done. Data were recorded and analysis done with SPSS v.20. Results: The mean value of crown length, crown thickness, mesiodistal width of left central incisor was greater compared to the right side (Left vs Right: 9.01 ± 1.14 mm vs 9 ± 1.14 mm , 7.04 ± 0.67 mm vs 6.96 ± 0.61 mm, 8.25 ± 0.59 mm vs 8.20 ± 0.51 mm). Conclusion: Crown length and crown width of maxillary left central incisor were greater compared to maxillary right central incisor. Shape of maxillary incisors determines the shape of the gingiva. The average values of length and widths of the central incisors derived from this study can be a valuable template for prosthodontic and aesthetic planning.

Evaluation of maxillary canine index and Inter canine width to establish Sexual Dimorphism among two different populations

BACKGROUND: Teeth are most useful tools for identification of victims in living as well as in dead in field of Forensic Odontology. Canines being the most stable in oral cavity because of labio-lingual thickness of crown and root anchorage in alveolar process of jaws, have been reported to survive in mass disasters, hence used when facial recognition is inconclusive. AIM OF THE STUDY:The present pilot study was conducted to evaluate effectiveness of canine in sex determination among two different populations (Uttar Pradesh and West Bengal). MATERIALS AND METHODS:The present study comprises of 40 subjects from Uttar Pradesh and West Bengal population.Evaluation of canine index and labio-lingual dimension of maxillary canine was done to establish gender dimorphism among these populations. RESULT&amp; CONCLUSION:The findings revealed that due to smaller sample size, not much difference was seen incanine index amongboth the groups but labio-lingual dimensions showed variations. However, maxillarycanine index and labio-lingual dimensionscan be effectivein sex determination. KEYWORDS: Canine index, Gender dimorphism, Labio-lingual dimension, Sex determination

INFLUENCE OF pH ON THE SPECTRAL-LUMINESCENT CHARACTERISTICS OF THE SOFT PROTEIN CROWN OF SILVER NANOPARTICLES

The spectral and fluorescent characteristics of bovine serum albumin (BSA) molecules in the soft crown of silver nanoparticles (AgNP) were studied at different pH values. The formation of BSA + AgNP complexes was established. The coupling constants of the complex (Kass) and the biomolecular rate constants of the BSA fluorescence quenching (Kq) were determined for different pH values. The dependences of Kass and Kq on pH are nonmonotonic with maxima at pH 6.0. The number of binding sites (Hill coefficient (n)) and the thickness of the BSA soft crown (d) are also maximal at pH 6.0. At higher and lower pH values (relative&#x0D; to pH 6.0), these parameters decrease. Variations in the parameters of interaction between BSA and AgNP are due to changes in the conformational modifications of the protein (content of the а-helix) and the microenvironment of Tyr and Trp protein residues in the soft crown (hydrophobicity of the protein).

Investigation of stress distribution within an endodontically treated tooth restored with different restorations

Background/purposeRecently, metal-free restoration has become the standard in prosthetic treatment. However, it is still unclear which combination is most effective in preventing root fracture and secondary caries. The purpose of this study was to evaluate the influence of different post systems, crown materials, crown thickness and luting agents on the stress distribution around the crown margins, cervical dentin and the tip of the post.Materials and methodsNinety-six mandibular first premolar models were developed and analyzed using finite element analysis (FEA). Two designs of crowns, six kinds of crown materials, four types of post and core systems and two kinds of luting agents were included and evaluated for the stress distribution within the abutment teeth. The Von Mises stress magnitudes were compared among all models.ResultsThe stress at the tip of the post decreased as the young's modulus of luting agent decreased; The stress concentrated more at the cervical area (dentin and crown), as the physical properties of the crown material increased.ConclusionCrowns fabricated using polyetheretherketone (PEEK) can reduce the stress concentration at the cervical area, so it may be possible to reduce the amount of tooth reduction during abutment tooth preparation. The stress distribution around the post tip is affected by the post and core systems and luting agent, regardless of crown materials and thickness. When inserting a post of the higher Young's modulus such as zirconia post, methyl methacrylate luting cement can reduce the stress concentration at the tip of the post.

Influence of inner crown thickness on the bonding strength of porcelain fused to Co-Cr alloy endocrown

The purpose of this study was to investigate the influence of inner crown thickness on the bonding strength of porcelain fused to Co-Cr alloy endocrown by shear strength test. According to the molar average anatomical data to obtain a simplified model for endocrowns, porcelain fused to Co-Cr alloy endocrowns were fabricated with four inner crown thicknesses: 0.3 mm, 0.5 mm, 0.8 mm, and 1.0 mm group, eight specimens were fabricated for each thickness group. Shear bond strength test was used to observe the metal-porcelain bonding strength, scanning electron microscope (SEM) and energy dispersive spectrometer (EDS) analysis were performed after the test to evaluate the interface of metal-porcelain. The shear bond strength means (in MPa) were: 10.50 ± 2.55 (0.3 mm), 13.21 ± 2.27 (0.5 mm), 14.47 ± 1.46 (0.8 mm), and 15.78 ± 2.81 (1.0 mm), one-way ANOVA showed that there was a statistically significant difference among the thicknesses (P < 0.05). The SEM observation showed tight bonding, and the EDS analysis showed element diffusion phenomenon at the metal-porcelain interface. The bonding strength of porcelain fused to Co-Cr alloy endocrown varied according to the different thickness of inner crown and the thinner inner crown was recommended for tooth defects with limited prosthodontic space.

Four-year clinical evaluation of CAD/CAM indirect resin composite premolar crowns using 3D digital data: Discovering the causes of debonding.

To analyze the causes of debonding of computer-aided design/computer-aided manufacturing (CAD/CAM) indirect resin composite premolar crowns with a focus on the morphological factors of the crown and abutment teeth. The clinical courses of 109 CAD/CAM indirect resin composite crowns were observed, and the patients' background characteristics, crown locations, luting methods, types of abutments, distal-most/non-distal-most molars, and types of resin blocks were confirmed. To investigate the influence of the morphology of the crown and abutment teeth, the 1) vertical dimension of the abutment teeth, 2) taper, and 3) thickness of the crown occlusal surface during events were measured from the three-dimensional digital data. The Kaplan-Meier method and multivariable Cox proportional hazard model were used for the statistical analyses. The nonlinearity of the effect of each comparison factor was included in the model. Complications included 21 debonding cases, two crown fractures, five root fractures, and two core debondings. The cumulative no-debonding and no-crown-fracture rate over 1423 days (3 years and 11 months) was 77.4%. The multivariable Cox regression analysis revealed that the abutment teeth type of tooth (first or second premolar) (P = 0.02) and luting materials (P < 0.01) significantly influenced the debonding frequency. All morphological factors (1-3) significantly influenced the debonding. The hazard ratios and nonlinear graph indicated that the crown thickness was less effective than the vertical dimension and taper. The combination analysis of clinical outcomes and 3D digital data revealed that preparation of the abutment is important for avoiding crown debonding.

Fracture strength of secondary crown with different taper and thickness in zirconia double crown attachments.

The objective of this study was to clarify the influences of zirconia materials, one-half taper angle, and thickness of the secondary crown on the fracture strength of the secondary crown. For the primary and secondary crowns, Y-TZP and Ce-TZP/Al2O3 were used, respectively. Samples were prepared at one-half taper angles of 2° and 4°, and a secondary crown thickness of 0.5 and 1.0 mm (n=8). Regarding the fracture strength, the secondary crown was restored on the primary crown, all specimens were loaded until fracture using a universal testing machine. The load value added at the time of secondary crown fracture was regarded as fracture strength. Based on the analysis of variance, the fracture strength of Ce-TZP/Al2O3 was significantly higher than that of Y-TZP with regard to the material and that at 1.0-mm thickness was significantly higher than that at 0.5-mm thickness, but the taper angle had no influence.

The Relation among Teeth and Maxillary Dental Arch Dimensions with Anterior Teeth Angulation and Inclination.

Objectives This study aimed at finding out whether anterior teeth angulation and inclination have a relationship with the maxillary teeth and dental arch dimensions. Methods Fifty study models with normal occlusion were selected from the archive of the Department of Orthodontics at Baghdad Dental Faculty. Maxillary dental arch width and length at different points were determined in addition to measuring anterior teeth angulation, inclination, crown thickness, overjet, overbite, and Bolton's ratios. The unpaired t-test and Pearson's correlation coefficient test were used for data analysis. Results No statistical gender differences were reported in all measurements except the dental arch widths and length where males had significantly higher mean values. Only the maxillary incisor's inclination showed a direct weak significant correlation with the total arch length. Conclusions The inclination of upper incisors had a minimal effect on increasing dental arch length.