Beata Dejak

Three-dimensional finite element analysis of strength and adhesion of composite resin versus ceramic inlays in molars

STATEMENT OF PROBLEM Previous studies on strength of teeth reconstructed with ceramic or composite resin inlays have not resolved which restoration material provides the highest strength and marginal integrity. PURPOSE The purpose of this study was to compare strength of mandibular molars restored with composite resin inlays to those restored with ceramic inlays, according to the Mohr-Coulomb failure criterion, and to analyze contact stresses in cement-tooth adhesive interfaces of these inlays. MATERIAL AND METHODS The investigation used a 3-dimensional (3-D) finite element analysis with the use of contact elements. Seven 3-D models of first molars of the same shape and size were created: IT, intact tooth; UT, unrestored tooth with an MOD cavity preparation; CRIT, tooth restored with composite resin inlays (True Vitality) with an elastic modulus equal to 5.4 GPa; CRIH, tooth restored with composite resin inlays (Herculite XRV) (9.5 GPa); CRIC, tooth restored with composite resin inlays (Charisma) (14.5 GPa); CRIZ, tooth restored with composite resin inlays (Z100) (21 GPa); and CI, tooth restored with a ceramic (IPS Empress) inlay with an elastic modulus equal to 65 GPa. Each model was subjected to a force of 200 N directed to the occlusal surface. The stresses occurring in the tested inlays, composite resin cement layer, and tooth tissues were calculated. To evaluate the strength of materials, the Mohr-Coulomb failure criterion was used. Contact stresses in the cement-tissue adhesive interface were calculated and compared to tensile and shear bond strength of the luting cement to enamel and dentin. RESULTS In the teeth restored with composite resin and ceramic inlays, the values of the Mohr-Coulomb failure criterion were lower than in the unrestored tooth with a preparation (UT), but still 2.5 times higher than in the intact tooth (IT). For the ceramic inlay (CI), the values of the Mohr-Coulomb failure criterion were nearly 3 times higher than in the composite resin inlays. For the luting agent for the ceramic inlay model, these values were 2-4 times lower than for the luting agents for the composite resin inlay models. At the adhesive interface between the cement and tooth around the ceramic inlays, contact tensile and shear stresses were lower than around the composite resin inlays. In the cervical enamel surrounding the proximal surface of the inlays, the stresses exceeded the tissue strength. CONCLUSIONS Adhesively bonded composite resin and ceramic inlays reinforce the structure of prepared teeth, but do not restore their original strength. The proximal enamel surrounding inlays is prone to failure. The value of the Mohr-Coulomb failure criterion for ceramic inlays was higher than for composite resin inlays. With an increase in the elastic modulus of inlay materials, the values of the Mohr-Coulomb failure criterion decrease in the luting cement. Contact tensile and shear stresses on the cement-tissue adhesive interface decrease as well.

Three-dimensional finite element analysis of molars with thin-walled prosthetic crowns made of various materials

OBJECTIVES The aim of the study was to compare the strength of thin-walled molar crowns made of various materials under simulation of mastication. METHODS Five 3D FE models of the first lower molar with the use of contact elements were created: intact tooth; tooth with a zirconia crown; tooth with a porcelain crown; tooth with a gold alloy crown and tooth with a composite crown. The computer simulations of mastication were conducted. For the models, equivalent stresseswere calculated using the modified von Mises failure criterion (mvM). Contact stresses at the adhesive interface between the cement and tooth structure under the crowns were analyzed. RESULTS Equivalent stresses in the crowns, did not exceed the tensile strength of their material. The mvM stresses in resin cement under the zirconia crown were 1.3 MPa, and under the composite crown they increased over 6 times. The tensile and shear contact stressesunder the stiff crowns (ceramics and gold alloy), were several times lower than those under the composite one. The maximum mvM stresses in the tooth structure for the zirconia crown were only 2.8 MPa, whereas for the composite crown were 6.4 MPa. The higher elastic modulus the crown was, the lower the equivalent stresses occurred in the composite luting cement and in the tooth structures. Also contact stresses decreased with the increasing stiffness of the crowns. SIGNIFICANCE Under physiological loads, the thin-walled crowns perfectly luted to molars, made of zirconia ceramic, gold alloys and composite resin are resistant to failure. Prosthetic crowns made of stiff materials are less prone to debonding than those made of composite resin. Prosthetic crowns made of a material with a higher elastic modulus than enamel will strengthen the dental structures of molar teeth.

Finite element analysis of strength and adhesion of cast posts compared to glass fiber-reinforced composite resin posts in anterior teeth

STATEMENT OF PROBLEM Previous studies on the strength of teeth restored with posts have not resolved the controversy as to which post systems provide the greatest strength and longevity. PURPOSE The purpose of this study was to compare the strength of teeth restored using cast posts with those restored using glass fiber-reinforced composite resin posts and to evaluate the bond strength of the posts to dentin. MATERIAL AND METHODS The investigation was conducted by using finite element analysis, combined with the application of contact elements. Three-dimensional (3-D) models of the maxillary central incisors were generated: IT, an intact tooth; CC, a tooth with a ceramic crown; FP, a tooth restored with an FRC (glass fiber-reinforced composite resin) post; CPAu, a tooth restored with a gold alloy cast post; and CPNi, a tooth restored with an NiCr (nickel chromium alloy) cast post. Each model was subjected to vertical and oblique loads with a force of 100 N. To evaluate the strength of the restored tooth, ceramics, and composite resin, the modified von Mises failure criterion was used, the Tsai-Wu criterion for FRC, and the von Mises criterion for gold and NiCr alloy. The equivalent stresses found in the tested models were compared with the tensile strength of the respective materials. Contact stresses in the luting cement-dentin interface were calculated. RESULTS The maximum mvM (modified von Mises failure criterion) stresses in the dentin of the teeth restored with FRC posts were reduced by 21%, and in those restored with cast NiCr posts, stresses were reduced by 25% when compared to the stresses in the intact tooth. The equivalent stresses in metal posts were several times higher than in FRC posts, but did not exceed the tensile strength of the materials. The highest mvM stress in the luting resin cement around the FRC post was 55% higher than in the luting resin cement around the metal post, under an oblique load. In the ceramic crown, which covered the composite resin post and core, the highest mvM stress was 30.7 MPa, whereas with the metal post and core, it was 23 MPa. CONCLUSIONS Cast metal posts resulted in lower stresses in the dentin of the restored teeth than did FRC posts. Irrespective of the material, the equivalent stresses in the posts did not exceed their tensile strength. Lower stresses were present in the luting cement and the cement-dentin interface around cast posts than around FRC posts. In the ceramic crown supported by a metal post and core, the stresses were lower than those observed in the crown supported by a composite resin core foundation.

3D-Finite element analysis of molars restored with endocrowns and posts during masticatory simulation.

OBJECTIVE The objective was to compare equivalent stresses in molars restored with endocrowns as well as posts and cores during masticatory simulation using finite element analysis. METHODS Four three-dimensional models of first mandibular molars were created: A - intact tooth; B - tooth restored by ceramic endocrown; C - tooth with FRC posts, composite core and ceramic crown; D - tooth with cast post and ceramic crown. The study was performed using finite element analysis, with contact elements. The computer simulations of mastication were conducted. The equivalent stresses of modified von Mises failure criterion (mvM) in models were calculated, Tsai-Wu index for FRC post was determinate. Maximal values of the stresses in the ceramic, cement and dentin were compared between models and to strength of the materials. Contact stresses in the cement-tissue adhesive interface around restorations were considered as well. RESULTS During masticatory simulation, the lowest mvM stresses in dentin arisen in molar restored with endocrown (Model B). Maximal mvM stress values in structures of restored molar were 23% lower than in the intact tooth. The mvM stresses in the endocrown did not exceed the tensile strength of ceramic. In the molar with an FRC posts (Model C), equivalent stress values in dentin increased by 42% versus Model B. In ceramic crown of Model C the stresses were 31% higher and in the resin luting cement were 61% higher than in the tooth with endocrown. Tensile contact stresses in the adhesive cement-dentin interface around FRC posts achieved 4 times higher values than under endocrown and shear stresses increased twice. The contact stress values around the appliances were several time smaller than cement-dentin bond strength. SIGNIFICANCE Teeth restored by endocrowns are potentially more resistant to failure than those with FRC posts. Under physiological loads, ceramic endocrowns ideally cemented in molars should not be demaged or debonded.

Strength estimation of different designs of ceramic inlays and onlays in molars based on the Tsai-Wu failure criterion

STATEMENT OF PROBLEM Successful restoration of large molar defects is a serious clinical problem. Studies on the strength of teeth restored with ceramic restorations of various designs have provided conflicting results. PURPOSE The purpose of this study was to determine the shapes of large MOD ceramic restorations in molars most likely to prevent failure and to produce a favorable distribution of contact stresses between the cement and teeth during mastication. MATERIAL AND METHODS The study was performed using a finite element analysis with contact elements. Eight 2-dimensional models of mandibular first molars with the following designs of MOD ceramic restorations were created: an inlay with a butt joint margin, an inlay with a beveled margin, an onlay with a butt joint margin, and an onlay with a rounded shoulder margin. The restorations had 3-mm or 5-mm isthmus widths. Models of opposing maxillary crowns were also developed. Computational simulation of mastication of boluses in the frontal plane was conducted, during which the stresses occurring in the ceramic restorations, cement, and tooth structure were calculated. The Tsai-Wu failure criterion was used to evaluate the strength of the materials. Contact stresses at the adhesive interface between the tooth structure and resin cement around these restorations were analyzed. RESULTS According to the Tsai-Wu failure criterion, the margin of the beveled inlay and the surrounding tissue could be damaged during masticatory simulation. At the junction of the butt joint margin inlay and enamel, contact tensile stresses appeared. The lowest inverse of the Tsai-Wu strength ratio index appeared in the onlay with a rounded shoulder margin. At the adhesive interfaces around margins of large onlays, compressive contact stresses occurred. CONCLUSIONS For the large molar MOD ceramic restorations tested, the lowest values of the inverse of the Tsai-Wu strength ratio index and a favorable distribution of contact stresses between restoration and tissues appeared in the onlay with a rounded shoulder margin.

A comparison of stresses in molar teeth restored with inlays and direct restorations, including polymerization shrinkage of composite resin and tooth loading during mastication

UNLABELLED Polymerization shrinkage of composites is one of the main causes of leakage around dental restorations. Despite the large numbers of studies there is no consensus, what kind of teeth reconstruction--direct or indirect composite restorations are the most beneficial and the most durable. OBJECTIVE The aim was to compare equivalent stresses and contact adhesive stresses in molar teeth with class II MOD cavities, which were restored with inlays and direct restorations (taking into account polymerization shrinkage of composite resin) during simulated mastication. METHOD The study was conducted using the finite elements method with the application of contact elements. Three 3D models of first molars were created: model A was an intact tooth; model B--a tooth with a composite inlay, and model C--a tooth with a direct composite restoration. Polymerization linear shrinkage 0.7% of a direct composite restoration and resin luting cement was simulated (load 1). A computer simulation of mastication was performed (load 2). In these 2 situations, equivalent stresses according to the modified von Mises criterion (mvM) in the materials of mandibular first molar models with different restorations were calculated and compared. Contact stresses in the luting cement-tooth tissue adhesive interface around the restorations were also assessed and analyzed. RESULTS Equivalent stresses in a tooth with a direct composite restoration (the entire volume of which was affected by polymerization shrinkage) were many times higher than in the tooth restored with a composite inlay (where shrinkage was present only in a thin layer of the luting cement). In dentin and enamel the stress values were 8-14 times higher, and were 13 times higher in the direct restoration than in the inlay. Likewise, contact stresses in the adhesive bond around the direct restoration were 6.5-7.7 times higher compared to an extraorally cured restoration. In the masticatory simulation, shear contact stresses in the adhesive bond around the direct composite restoration reached the highest values 32.8 MPa and significantly exceeded the shear strength of the connection between the resin luting cement and the tooth structure. SIGNIFICANCE Equivalent stresses in the tooth structures restored with inlays and in the restoration material itself and contact stresses at the tooth-luting cement adhesive interface are many times lower compared to teeth with direct composite restorations. Teeth with indirect restorations are potentially less susceptible to damage compared to those with direct restorations. Composite inlays also ensure a better seal compared to direct restorations. Polymerization shrinkage determines stress levels in teeth with direct restorations, while its impact on adhesion in indirectly restored teeth is insignificant.

The influence of ferrule effect and length of cast and FRC posts on the stresses in anterior teeth

OBJECTIVES The purpose was to assess the influence of ferrule effect and length of cast post and cores, and FRC posts on the strength of anterior teeth. MATERIALS AND METHODS The investigations were conducted by means of finite element analysis with the application of contact elements. Thirteen 3D models of maxillary first incisors were generated: model 1 was an intact tooth; 2A - a tooth with all-ceramic crown with ferrule effect, 2B-D a teeth restored with, ferrule and FRC posts of various lengths 13mm, 8mm, 4mm, 3A - a tooth with ceramic crown without, ferrule effect, 3B and C teeth without ferrule and 10mm, 5mm length FRC posts, 4B-D teeth with ferrule, restored by cast posts and cores of 13mm, 8mm, 4mm lengths and 5B and C teeth without ferrule, restored with cast posts and cores of 10mm, 5mm lengths. Each model was subject to a load with a total force of 100N uniformly distributed under the lingual cingulum, at an angle of 130°. To evaluate, the strength of tooth tissues, ceramics and composites, the modified von Mises failure criterion was used, for FRC the Tsai-Wu criterion and for cast NiCr alloy the von Mises criterion. Contact stresses were calculated at the luting cement-tissue interface. RESULTS Ferrule effect in teeth reduces mvM stresses in dentin, in posts and in luting cement. The contact tensile stresses around posts in teeth with ferrule effect were 1.7-3.0 times smaller than in, teeth without ferrule. Lower mvM stresses occurred in teeth with cast posts in comparison with FRC posts. The mvM stresses in teeth with posts of various lengths were similar, irrespective of post material. SIGNIFICANCE Ferrule effect in teeth with posts and cores has a critical influence on stress reduction. Using posts and cores made of rigid materials leads to stress reduction in teeth. Post length has a small, effect on stress values in tooth structures.

Strength comparison of anterior teeth restored with ceramic endocrowns vs custom-made post and cores

PURPOSE The aim of the study was to compare strength of the anterior teeth restored with ceramic endocrowns versus custom-made post and core. METHODS The investigation used the finite element analysis. Three 3-D models of maxillary central incisor were created: model A-tooth restored with metal post and core with ceramic crown; model B-tooth with leucite ceramic endocrown; model C-tooth with lithium disilicate ceramic endocrown. Each model was subjected to a 100N force applied at a distance of 5mm from the incisal edge, at the angle of 130° to the long axis of the tooth. The modified von Mises failure criterion was used to evaluate the strength of the dentin, ceramic and resin cement, and Huber-Mises-Hencky failure criterion for cast alloy. Contact stresses in the cement-tissue adhesive interface were calculated. RESULTS The lowest stresses occurred in the anterior tooth restored with custom post and core (model A). The mvM stress of 47.5MPa concentrated in leucite ceramic endocrown (model B) and its value was close to the tensile strength of this material. The maximal mvM stresses in the lithium disilicate ceramic endocrown (model C) were 4 times lower than tensile strength of this material. In all cases contact stresses in the adhesive interface under restorations did not exceed the resin cement bond strength to dentin. CONCLUSIONS Leucite ceramic endocrowns in incisors may fracture during physiological loading. Endocrowns made of lithium disilicate ceramic are resistant to failure. Posts and prosthetic crowns are still recommended for anterior teeth restorations.

Comparison of fracture resistance of monolithic thin-walled and full-contour zirconia crowns

Streszczenie Wstęp. Korony monolityczne, pełnokonturowe z tlenku cyrkonu stają się alternatywą dla koron złożonych, konwencjonalnych opartych na rdzeniu z tlenku cyrkonu w zębach bocznych. Wymagają znacznie mniejszego opracowania tkanek twardych zębów, nie odłamuje się od nich ceramika licująca. Korony te są wykonywane z bardziej przeziernego tlenku cyrkonu, dzięki temu ich estetyka jest akceptowalna. Nie wiadomo jednak, w jaki sposób zmiana struktury tlenku cyrkonu wpływa na jego wytrzymałość. Cel pracy. Celem pracy była ocena odporności na złamanie koron cienkościennych i pełnokonturowych wykonanych z tlenku cyrkonu. Materiał i metoda. Badaniu poddano 40 koron z tlenku cyrkonu podzielonych na 4 grupy po 10 próbek każda: konwencjonalnego tlenku cyrkonu (Ceramill Zi, Amman Girrbach) – CZi cienkościenne (o grubości 0,5 mm) i FZi pełnokonturowe (o grubości 1,5 mm) oraz wykonane z przeziernego tlenku cyrkonu (Ceramill Zolid, Amman Porównanie odporności na złamania koron monolitycznych cienkościennych i pełnokonturowych z ceramik tlenku cyrkonu

Retention of implant-supported crowns using implant luting agents compared to temporary cement

Streszczenie Cel pracy. Celem badań było porównanie siły retencji koron osadzonych na łącznikach implantologicznych z wykorzystaniem cementu tymczasowego i implantologicznych cementów pół-permanentnych. Określono wpływ modyfikacji powierzchni łącznika za pomocą lubrikantu na siłę połączenia. Uszeregowano cementy pod względem rosnącej siły retencji. Materiał. Wykonano 40 rdzeni koron w kształcie walca ze stopu chromowo-kobaltowego w technologii selektywnego topienia laserowego (SLM) dla standardowych, tytanowych łączników Ankylos (Dentsply Implants) o średnicy 4,5 mm i wysokości 6,0 mm. Rdzenie cementowano przy użyciu TempBond NE, Premier Implant® Cement, MIS Crown Set oraz w zmodyfikowanej procedurze po naniesieniu wazeliny na filar, dla cementu Porównanie retencji koron osadzonych na łącznikach implantologicznych za pomocą cementu tymczasowego i cementów implantologicznych*