Functional Cusp Research Articles

Analysis of occlusal clearance of crown preparations in a predoctoral clinical setting.

This study sought to assess the presence and location of inadequate tooth preparation performed by predoctoral dental students by scanning mounted casts submitted for monolithic zirconia crown fabrication METHODS: An intraoral scanner capable of volumetric measurements of crown preparations was used to analyze 56 crown preparations on mounted stone casts before submission to a lab for crown fabrication. The mounted casts were scanned individually and then a buccal bite was scanned to stitch the models together into virtual occlusion. The distance between the crown preparations and opposing dentition was displayed volumetrically, and the minimum clearance of each preparation was recorded for both the functional and non-functional cusps. Preparations were evaluated for adequate interocclusal clearance and comparisons were made using a Chi-square test with α=0.05 with respect to tooth location, functional versus nonfunctional cusp, and or single versus multi-unit preparation. Over 47% of mounted casts with crown preparations analyzed for the study exhibited a lack of occlusal clearance in at least one area. Functional cusps were more often under-reduced than non-functional (p<0.001). No other comparisons were statistically significant. The present study demonstrates a high percentage of under-reduced crown preparations in a predoctoral clinic and emphasizes the utility of quality control and analysis via digital scanning of crown preparations prior to crown fabrication.

Assessment of physiological posterior-tooth displacement under habitual occlusal force by intraoral scanning using implant-supported crowns as the reference

Statement of problemStudies that have used digital methods to quantitatively evaluate physiological tooth displacement under occlusal force are sparse. PurposeThe purpose of this clinical study was to measure physiological posterior tooth displacement under occlusal force by intraoral scanning and reverse engineering technology by using implants as the reference. Material and methodsA total of 14 participants received 15 implant-supported single mandibular first molar crowns. The surface data of maxillary and mandibular posterior teeth (U1 and L1) and the buccal occlusal data in the maximum intercuspal position (MIP) with habitual occlusal force were obtained by using an intraoral scanner (TRIOS 3, v20.1.2). The U1 and L1 data were segmented into single teeth, which were then aligned to the buccal occlusal data by using the “best-fit alignment” command to build the data under occlusal force (U2 and L2). U1 and L1 data were compared with U2 and L2 data to calculate the centroid and functional cusp vertex displacements and the long axis deflections of the second premolars and second molars, taking the first molar as the reference. The medians, and first quartile (Q1), third quartile (Q3) of the above data were reported, and the Shapiro-Wilk and Wilcoxon tests were used to analyze the differences (α=.05). ResultsUnder occlusal force, the median (Q1, Q3) centroid displacements of posterior teeth ranged from 61 (52, 101) μm to 146 (80, 186) μm; the functional cusp vertex displacements ranged from 82 (62, 117) μm to 146 (98, 189) μm, and the long axis deflections ranged from 0.45 (0.25, 0.87) degrees to 1.03 (0.52, 1.41) degrees. Mandibular second premolars displaced lingually, mesially, and apically; mandibular second molars displaced distally and apically; and maxillary second premolars and second molars displaced lingually and apically. ConclusionsA digital method taking implant-supported single crowns as the reference was used to demonstrate physiological posterior-tooth displacement under habitual occlusal force.

Effect of the CAD-CAM and lost-wax framework fabrication techniques on the fracture strength of porcelain in metal-ceramic restorations.

Ceramic fracture is a common problem in metal-ceramic restorations (MCRs). The advent of computer-aided design and computer-aided manufacturing (CAD-CAM) technology eliminated the lost-wax technique, which was responsible for many of the problems associated with framework fabrication. However, the role of the CAD-CAM technology in decreasing porcelain fracture is not yet known. The aim of the present in vitro study was to compare the fracture strength of porcelain in MCRs with metal frameworks fabricated with the use of the lost-wax and CAD-CAM techniques. Twenty metal dies were prepared with a deep chamfer finish line, with a depth of 1.2 mm and the occlusal taper of the walls of 8°, a 2-millimeter occlusal reduction of the functional cusp, a 1.5-millimeter occlusal reduction of the nonfunctional cusp, and the functional cusp bevel. Ten frameworks were fabricated using the CAD-CAM system and 10 with the lost-wax technique. After porcelain veneering, the specimens underwent thermocycling and cyclic loading to simulate the aging process. The load test was then performed. The fracture strength of porcelain was compared between the 2 groups, and the mode of failure was also determined using a stereomicroscope. Two specimens were excluded from the CAD-CAM group. Thus, 18 specimens were statistically analyzed. The results revealed no significant difference in fracture strength between the 2 groups (p > 0.05). The mode of failure was mixed in all specimens from both groups. Our results indicated that the fracture strength of porcelain and the mode of failure did not depend on the metal framework fabrication technique (lost-wax or CAD-CAM).

The clinical effect of the digital guide in the early implant restoration of second molars.

In the absence of contraindications to implants, implant repair is the preferred method to treat mandibular second molar loss. To compare the clinical effects of a traditional implant guide and digital implant guide in the early implant restoration of second molars. The study included 35 patients with second molar loss randomly divided into two groups. Eighteen patients in the experimental group had an implant procedure using a computer-aided design/computer-assisted manufacturing (CAD/CAM) digital implant guide, and 17 patients in the control group had the procedure using a traditional film pressing implantation guide. Then, the surgical procedure was completed using the two different implant guides. At 3 months after surgery, four parameters including screw hole exit position, coronal deviation of the implant site, disease improvement rate, and clinical effects, which included marginal adaptation, anatomic form, marginal discoloration, postoperative sensitivity, surface roughness, and secondary caries of the upper prosthesis were compared between the two groups. The screw hole exit position in the experimental group was directed to the functional cusp of the opposite jaw, and there was a statistically significant difference between the two groups. There was no statistically significant difference in the rate of disease improvement and the clinical effect of the upper prosthesis between the two groups. There was no statistically significant difference in the bilateral coronal deviation and deviation direction of implants in the two groups. The bilateral coronal deviation of the experimental group was smaller than that of the control group. The digital implant guide can effectively reduce the deviation of the screw hole and the upper prosthesis in the restoration of the second molar. The prosthesis used in the experimental group had a good clinical outcome, which provides a theoretical basis for the restoration of the posterior molar.

Hunter-Schreger Band configuration in human molars reveals more decussation in the lateral enamel of ‘functional’ cusps than ‘guiding’ cusps

ObjectivesEnamel prism decussation, which manifests as Hunter-Schreger Bands (HSB), is considered a mechanism to mitigate crack propagation. During the chewing cycle, the ‘functional’ cusps that are involved in Phase II crushing and grinding experience more complex patterns of stress than do those that ‘guide’ the molars into occlusion (Phase I). This study examines HSB configuration in the lateral enamel of human molars to identify potential differences between these cusps as predicted from their functional distinctions. DesignMeasurements were recorded from scanning electron micrographs of sections through the mesial cusps of unworn permanent molars. For each section, HSB packing density and the relative thickness of decussated enamel were quantified in the cuspal and middle segments of lateral enamel over the guiding and functional cusps. ResultsNo clear trend from first to third molars in HSB configuration was found in either jaw. In maxillary molars, the functional cusp displays higher HSB packing density in the cuspal and middle segments, and relatively thicker decussated enamel in the cuspal segment than does the guiding cusp. In mandibular molars, the functional cusp displays higher HSB packing density in the middle segment than does the guiding cusp, but no difference in relative thickness was found between them. Enamel of mandibular molars shows weaker decussation than maxillary molars. ConclusionsThe results suggest that guiding cusps are intrinsically more susceptible to crack propagation than functional cusps in human permanent molars. Structural factors such as enamel decussation should be considered when interpreting enamel chipping patterns in dietary contexts.

FRACTURE RESISTANCE UNDER CYCLIC LOADING OF LITHIUM DISILICATE VONLAYS VERSUS ROSETTA VONLAYS RESTORING PREMOLARS (IN VITRO STUDY)

The aim of the study was to assess fracture resistance under cyclic loading of Rosetta®SM CAD vs. IPS e.max CAD (control) vonlays restoring maxillary premolars. According to the sample size calculation, a total of 20 samples will be selected and then divided into two equal groups; 10 sample each based on the material type: Group (A): Ten vonlays (n=10) manufactured from IPS e. max CAD blocks (control). Group ( B): Ten vonlays (n=10) manufactured from Rosetta®SM CAD blocks (intervention). A natural tooth presenting an upper first premolar was prepared in accordance with the ceramic onlay restorations preparation guidelines with an occlusal box with half of the bucco-lingual distance and a 2 mm depth from the cusp tip to pulpal floor, gingival seat with 1 mm depth from pulpal floor, occlusal reduction of 2 mm of the functional cusp with extending the preparation at the palatal surface by 2 mm in the cervical direction, occlusal reduction of 1.5 mm of non-functional cusp and 12º divergence angle. The preparation was then extended to the labial surface, with a 0.5 mm chamfer finish line. All line angles were finally rounded, and all margins were finished. For duplication of the natural tooth; the epoxy dies were constructed. Base and catalyst of the epoxy resin material were mixed as instructed by the manufacturer at a rate of 200r/min and then was poured into the silicon mould under vibration to eliminate any air voids, then was allowed to set completely following the manufacturer instructions for 24 hours, this procedure was repeated 20 times for creating 20 epoxy resin dies which replicating the prepared natural tooth. The die was then scanned by optical scanning using Medit i500 oral scanner. Milling of Vonlays was achieved using Sirona MCX5 milling machine using IPS e. max CAD blocks and Rosetta SM CAD blocks: 10 IPS e.max CAD blocks with block size C14 and 10 Rosetta®SM CAD blocks with block size C14 were used. Vonlays were then seated on their corresponding dies and cemented with dual cured self-adhesive resin cement (Variolink, Ivoclar Vivadent). Cementation procedures were performed by keeping each sample under a constant pressure of 5Kg using a custom designed cementation device for standardization the applied load during cementation process. All samples were mechanically aged (cyclic loading) to simulate 6 months of clinical use. Following that, all samples were subjected to fracture resistance testing under a compressive load to the center of their long axis using computer controlled universal testing machine with a load cell of 5 Kilo newton (K N) with a computer software used for data recording (Instron® Bluehill Lite Software). The mean values ± SDs values for e.max group were (502.39 ±102.89 N) with minimum value (338.16 N) and maximum value (721.29 N). The mean values ± SDs values. Rosetta group were (468.76 ± 67.54 N) with minimum value (367.11 N) and maximum value (648.48 N). Failure modes were determined under stereomicroscope and classified into repairable and catastrophic in both groups and showed that 60% of e.max group exhibited repairable failure while 40% of specimens showed catastrophic failure while in Rosetta group, 90% of the specimens exhibited repairable failure. Only 10% displayed catastrophic failure. Then a fractured part within each group was examined under scanning electron microscope (SEM) to reveal and compare their microstructure.

Functional or Nonfunctional Cusps Preservation for Molars Restored with Indirect Composite or Glass-Ceramic Onlays: 3D FEA Study.

Evidence regarding the effect of the onlay preparation design for different CAD/CAM restorative materials considering the preservation of cusps is lacking. Molars were 3D-modeled in four preparation designs for onlay restoration: traditional design with functional cusp coverage (TFC), non-retentive design with functional cusp coverage (NFC), traditional design with non-functional cusp coverage (TNFC) and non-retentive design with non-functional cusp coverage (NNFC). The restorations were simulated with two CAD/CAM restorative materials: LD—lithium disilicate (IPS e.max CAD) and RC—resin composite (GrandioBloc). A 100 N axial load was applied to the occlusal surface, simulating the centric contact point. Von Mises (VM) and maximum principal (Pmax) stress were evaluated for restorations, cement layer and dental substrate. The non-retentive preparation design reduced the stress concentration in the tooth structure in comparison to the conventional retentive design. For LD onlays, the stress distribution on the restoration intaglio surface showed that the preparation design, as well as the prepared cusp, influenced the stress magnitude. The non-retentive preparation design provided better load distribution in both restorative materials and more advantageous for molar structure. The resin composite restoration on thenon-functional cusp is recommended when the functional cusp is preserved in order to associate conservative dentistry and low-stress magnitude.

The Effect of Ceramic Material and Preparation Design on the Fracture Resistance of Onlay Restorations

Objectives: Evaluating the fracture resistance and failure mode of human maxillary premolars restored with two ceramic onlay materials prepared with two preparation designs. Materials and methods: A total of 40 extracted, human maxillary premolars were selected and divided into two groups according to preparation design; Group A: MOD cavity with anatomical reduction of functional cusp and Group F: MOD cavity with flat reduction of the functional cusp. Each group was divided into two subgroups according to the material of construction; Subgroup S: restored using zirconia-reinforced glass-ceramic and Subgroup E: restored using hybrid ceramic. The finished onlay restorations were luted to prepared teeth using self-adhesive resin cement. Specimens were exposed to thermocycling for 5000 cycles. Fracture resistance was assessed using a Universal testing machine. Failure mode was evaluated using a stereomicroscope. Two-way ANOVA was used to assess the effect of different tested variables and their interaction. Intergroup comparison was done using one-way ANOVA followed by Tukey’s post hoc test. The significance level was set at p≤0.05 within all tests. Results: Two-Way ANOVA showed that ceramic material had no significant effect on the fracture resistance of restored teeth. While the preparation design had a statistically significant effect. The interactions between the independent variables, ceramic materials, and preparation designs had a significant effect on the fracture resistance of teeth. Conclusion: Both preparation designs and materials showed clinically acceptable fracture resistance of onlay restorations. All subgroups showed high fracture resistance and favorable failure modes except VITA SUPRINITY with anatomical reduction of the functional cusp.

Monolithic Zirconia Partial Coverage Restorations: An In Vitro Mastication Simulation Study.

To evaluate the survival rate (fatigue resistance), bonding efficiency and marginal integrity of monolithic zirconia partial and full coverage single restorations adhesively bonded to the tooth structure using air-particle abrasion, a primer with 10-methacryloyloxydecyl dihydrogen phosphate and a composite-resin cement (APC) protocol. Extracted human premolars (N = 32) were randomly divided into four groups of eight specimens each. Premolars were prepared for the following restorations: full crown (group 1, control), mesial-occlusal-distal-facial onlay (MODF, group 2) preserving 2 mm facio-lingual functional cusp width, mesial-occlusal-distal-lingual onlay (MODL, group 3) preserving 2 mm facio-lingual nonfunctional cusp width, mesial-occlusal-distal-buccal-lingual onlay (MODBL, group 4), overlay preparation. All restorations were milled from monolithic 3 mol% yttria (3Y) zirconia blocks (ZirCad, A1 LT, Ivoclar Vivadent) with CAD/CAM software presets at minimum occlusal and axial thicknesses of 1 mm. The intaglio surface of the restorations was air-particle abraded (50 µm Al2 O3 , 2-Bar pressure, 15 s, 10 mm distance) and primed. An adhesive cement system was used to bond the restorations. Each group was subjected to thermomechanical loading for 1.2 million cycles (force = 70 N, 1.4 Hz) with simultaneous thermocycling (5-55°C, 30 s dwell time) using a mastication simulator. All specimens were examined under scanning electron microscope (SEM) analysis (30, 100, and 150×) to evaluate cracks and marginal defects. Fracture of restoration and/or fracture within tooth structure, and debonding were considered modes of failure. One specimen from group 2 debonded at 632,000 cycles. None of the specimens failed due to fracture. SEM analysis at 30× indicated marginal integrity issue of the remaining seven intact specimens of group 2 in the area of antagonist contact. No specimens from group 1, 3, and 4 demonstrated marginal integrity issue at 30×. None of the specimens demonstrated any microcrack at 100× and150×. Due to its fatigue resistance, 3Y-zirconia is a viable option for partial and full coverage single restorations. Following a strict bonding protocol, zirconia demonstrated durable adhesion to the tooth structure. Occlusal contact on restoration margins should be avoided.

Shape-preserving erosion controlled by the graded microarchitecture of shark tooth enameloid

The teeth of all vertebrates predominantly comprise the same materials, but their lifespans vary widely: in stark contrast to mammals, shark teeth are functional only for weeks, rather than decades, making lifelong durability largely irrelevant. However, their diets are diverse and often mechanically demanding, and as such, their teeth should maintain a functional morphology, even in the face of extremely high and potentially damaging contact stresses. Here, we reconcile the dilemma between the need for an operative tooth geometry and the unavoidable damage inherent to feeding on hard foods, demonstrating that the tooth cusps of Port Jackson sharks, hard-shelled prey specialists, possess unusual microarchitecture that controls tooth erosion in a way that maintains functional cusp shape. The graded architecture in the enameloid provokes a location-specific damage response, combining chipping of outer enameloid and smooth wear of inner enameloid to preserve an efficient shape for grasping hard prey. Our discovery provides experimental support for the dominant theory that multi-layered tooth enameloid facilitated evolutionary diversification of shark ecologies.

Investigation of posterior teeth displacement under normal bite force by an intraoral scanner

Objective: To quantitatively evaluate the change of the long axis angle and the relative displacement of the crown feature points of the posterior teeth under normal bite force utilizing an intraoral scanner, and to provide clinical reference. Methods: From May to December 2019, fifteen graduate volunteers (5 males and 10 females, aged from 22 to 30, with an average age of 25.7 years) from Peking University School and Hospital of Stomatology were recruited to participate in the study. The surface data (U1, L1) of the maxillary and mandibular posterior teeth were scanned by an intraoral scanner i500, and saved as original data. The volunteers were guided to bite in the intercuspal position with normal bite force. The buccal bite data of the posterior teeth were scanned as the basis for registration. The digital casts were imported into Geomagic studio 2013 software and the boundary lines along the gingival margin and mesial and distal contact area of posterior teeth of data (U1, L1) were determined. Long axis of the crown, crown centroid and mesial functional cusp vertex were establishd. The data (U1, L1) were segmented into single tooth. Single tooth was aligned to buccal bite data separately using best-fit alignment command based on the buccal common area of the crown and new casts data (U2, L2) were obtained as the data under bite force. The long axis angle and centroid distance between adjacent teeth (second premolar and first molar, second molar and first molar) were measured and the deviation between data obtained at mouth-open state and that at biting state was calculated. Negative value meant centroid distance became shorter under bite force. The first molar was set as the common area and registrate the U1, L1 to U2, L2. The angle of long axes, and displacement of centroid and of functional cusp vertex between second premolar of two casts were calculated, as well as between second molar of two casts. Wilcoxon signed rank test was used to analyze the differences of teeth displacement between second premolar and second molar, and between maxillary and mandibular jaws with SPSS 26.0 statistical software. Results: The result of second premolar and second molar in the same jaw had no statistical difference (P>0.05). The centroid distance deviation of mandibular second premolar-first molar [-0.022(0.046) mm] was larger than that of maxilla [-0.006 (0.040) mm] (P<0.05). The long axis angle of second premolar itself [0.913°(0.647°)] and centroid distance of second molar itself [0.102 (0.106) mm] on the mandibular jaw were different from that on the maxillary jaw, which were 0.590°(0.550°) and 0.074(0.060) mm respectively (P<0.05). Conclusions: Under bite force, displacement of the second premolar and second molar was present, including the displacement of centroids and deflection of long axes. The mandibular posterior teeth have larger displacement than the maxillary teeth.

MANAGEMENT OF FRACTURED FUNCTIONAL CUSP OF MAXILLARY FIRST MOLAR: A CASE REPORT

18Feb 2020 MANAGEMENT OF FRACTURED FUNCTIONAL CUSP OF MAXILLARY FIRST MOLAR: A CASE REPORT Anwetakshmi Ray , Karthik Shetty , Anirudh Garg and Priyanka Kenkare Post Graduate Student, Department of Conservative Dentistry and Endodontics, Manipal College of Dental Sciences, Opposite Josallukas Showroom, Light House Hill Road, Hampankatta, Mangalore- 575001, Karnataka (India). Professor and Head of Department, Department of Conservative Dentistry and Endodontics, Manipal College of Dental Sciences, Opposite Josallukas Showroom, Light House Hill Road, Hampankatta, Mangalore- 575001, Karnataka (India).

MANAGEMENT OF FRACTURED FUNCTIONAL CUSP OF MAXILLARY FIRST MOLAR: A CASE REPORT

11Feb 2020 MANAGEMENT OF FRACTURED FUNCTIONAL CUSP OF MAXILLARY FIRST MOLAR: A CASE REPORT Anwetakshmi Ray , Karthik Shetty , Anirudh Garg and Sreelakshmi Pradeep

Effect of tooth preparation design on marginal adaptation of composite resin CAD-CAM onlays

Statement of problemAlthough different preparation designs have been proposed for onlays fabricated by computer-aided design and computer-aided manufacturing (CAD-CAM), their effect on marginal adaptation is unclear. PurposeThe purpose of this in vitro study was to investigate the effect of tooth preparation designs on the marginal and internal adaptation of ceramic-reinforced composite resin CAD-CAM onlays. Material and methodsA traditional preparation with a heavy chamfer on the functional cusp and a contrabevel on the nonfunctional cusp and a shoulder preparation with equal reduction on all cusps were used for mesial-occlusal-distal (MOD) onlay preparations. Ceramic-reinforced composite resin onlays were designed and milled based on the scanned prepared teeth. A digital silicone replica technique was used to determine marginal discrepancies between preparations and onlay restorations. A total of 100 numeric distances (representations of the fit in each region) were measured in 3 distinct regions: the buccal margin, lingual margin, and internal area. Independent Student t tests were used to determine significant differences (α=.05). ResultsTraditional preparation designs resulted in significantly smaller overall discrepancies (50.9 ±0.5 μm and 139.1 ±5.4 μm, P<.001) and smaller marginal discrepancies in the buccal (49.7 ±1.4 μm and 135.8 ±2.2 μm, P<.001) and lingual areas (47.1 ±1.0 μm and 133.4 ±1.1 μm, P<.001). ConclusionsThe marginal adaptation of ceramic-reinforced composite resin CAD-CAM onlays was affected by the preparation design. The traditional preparation design offered better marginal adaptation; therefore, it is recommended in clinical practice.

Influence of Restoration Height and Masticatory Load Orientation on Ceramic Endocrowns

Endocrown restorations are an alternative to restore end-odontically treated teeth. Due to the fact that in the literature it is recommended a remnant of 1.5 mm, different heights of endocrown were elaborated and analyzed, obtaining possible faults and their location. This study aimed to evaluate the mechanism of stress distribution in the tooth/restoration set, varying two factors: "restoration height"-three levels, and load application-two levels (oblique or axial), totaling six groups. For finite element analysis (FEA), a maxillary premolar was modeled with an endodontic treatment. Then, this template was triplicated and each copy received an endocrown restoration of different heights: G6 (4.5 mm), G7 (5.5 mm), and G8 (6.5 mm). The models were exported in STEP format to analysis software (ANSYS 17.2, ANSYS Inc.). During preprocessing, the solids were considered isotropic, linearly elastic, and homogeneous. Initially, a load (300 N) was axially applied in the central fossa region. For a second evaluation, an oblique load (300 N) was applied on the grinding slope of functional cusp. System fixation occurred at the base of poly-urethane cylinder. Results were evaluated through maximum principal stress (MPS). For axial load, lower stress values were generated in all groups. For oblique load, G8 showed a higher stress concentration in the cement layer and root dentin. When an endocrown restoration is performed, there is a tendency of failure in the cement line and in the root directly proportional to its size. However, regardless of the size of the element to be reconstituted, the axial direction of the masticatory loads tends to decrease stress concentration. When performing an endocrown restoration, care must be taken with its high regardless the tooth remnant high, altering even the anatomical angulations of the occlusal face, when necessary, to avoid stress concentration in thick areas.

Biomechanical Behavior of All-Ceramic Crowns with Variable Thicknesses of Zirconia Frameworks

Zirconia is an extremely successful material for prosthetic restorations, offering attractive mechanical and optical properties. It offers several advantages for posterior restorations because it can withstand physiological posterior forces. The aim of the study was to achieve the influence of zirconia framework thickness on the mechanical behavior of all-ceramic crowns using numerical simulation. For the study a premolar was chosen in order to simulate the mechanical behavior in the components of all-ceramic crowns and teeth structures regarding to the zirconia framework thickness. Maximal Von Mises equivalent stress values were recorded in teeth and restorations. Due to the registered maximal stress values it can be concluded that it is indicated to achieve frameworks of at least 0.5 mm thickness in the premolar area. Regarding stress distribution concentration were observed in the veneer around the contact areas with the antagonists, in the framework under the functional cusp and in the oral part overall and in dentin around and under the marginal line, also oral. The biomechanical behavior of all ceramic crowns under static loads can be investigated by the finite element method.

Effect of Stiffness of Single Implant Supported Crowns on the Resultant Stresses : A Finite Element Analysis

Objective: In the present study, the 3D finite element method was used to investigate the effect of crown material on stress distribution in the bone surrounding immediately loaded single dental. Materials & Methods: A 3D Finite Element model of mandibular first premolar was constructed to evaluate the performance of seven crown materials with different degree of stiffness (Porcelain, zirconium, Porcelain fused to gold, pure titanium, titanium alloy, Poly methyl methacrylate, and Polyether ether ketone PEEK). The model was constructed using Solid Works version 2010 software. The model simulated also a cement layer between the implant abutment and the crown (Virolink II, Vivadent). An axial static occlusal force of 200 N was applied to eight points in each functional cusp. The three-dimensional (3D) FE model was analyzed by ABAQUS/CAE version 6.10 software. Results: The results of this study indicated that among all crown materials the maximum von Mises stress values was observed in porcelain crown design (345.390 MPa).The highest von Mises stresses were found in the abutments for all models. In implants, the greatest stress was concentrated on the cervical region. PMMA and PEEK crown designs transferred less stress to abutment and screw. In all models, von Mises stresses increased in the coronal third of cortical bone in which the maximum von Mises stresses observed in the implant – cortical interface. Conclusions: Using more rigid material for the superstructure of an implant supports prosthesis did not have any effect on the stress values and stress distribution at the bone tissue surrounding implant. However, in the abutment, cement and crown structure, stress distributions and localizations were affected by the material’s rigidity. More clinical studies are needed to evaluate the survival rate of these materials.

The quality assessment of teeth prepared by fresh graduates for ceramo-metal full coverage crowns

Abstract Among the most important principles of tooth preparation are adequate tooth reduction and appropriate occlusal clearance for prosthetic restorations. A self-administered questionnaire was distributed to know the opinion of Intern Dentists of King Khalid University, College of Dentistry regarding the difficulties of preparing teeth for ceramo-metal crowns (CMC). The study also included the audit of dental casts of prepared teeth for CMC by the same Intern Dentists. The die and antimere teeth were evaluated for buccolingual (BL) and mesiodistal (MD) dimensions using a digital caliper. The presence of planar occlusal reduction, rounded angles and functional cusp bevel was also recorded. The average BL and MD reductions of the prepared teeth were 2.05 mm (±0.84) and 2.33 mm (±0.79) respectively. Comparison of BL reduction and MD reduction with hypothetically calculated ideal reduction between premolars and molars revealed a statistically insignificant difference ( p > 0.05, unpaired t -test). However, statistical comparison of BL reduction between maxillary and mandibular dies revealed a significant difference ( p t -test). Only one third of the dies had adequate planar occlusal reduction, 60.71% dies showed proper functional cusp bevel and 64% of the dies had rounded cusp angles. In the response to the questionnaire, facial and lingual reductions were considered easy by the respondents, while occlusal surface reduction and maxillary teeth preparation were considered difficult. The amount of tooth reduction performed by the Intern dentists for ceramo-metal crowns was within normal range. Teaching strategies regarding maxillary teeth reduction and planar occlusal reduction may require reconsideration.

Assessment of Porcelain Fused to Metal Crown Preparations by General Practitioners in Saudi Arabia

Background: Principles for fabricating prosthetic restorations include sufficient axial preparation and adequate occlusal clearance of the prepared teeth. This study measured the convergence angles in the prepared teeth for porcelain fused to metal (PFM) crowns done b y general practitioners in different regions of Saudi Arabia. In addition, the presence of planar occlusal reductions, functional cusp bevels and rounded angles in prepared casts were evaluated. Original Research Article

Effect of type of luting agents on stress distribution in the bone surrounding implants supporting a three-unit fixed dental prosthesis: 3D finite element analysis.

Osseointegration of dental implants is influenced by many biomechanical factors that may be related to stress distribution. The aim of this study was to evaluate the effect of type of luting agent on stress distribution in the bone surrounding implants, which support a three-unit fixed dental prosthesis (FDP) using finite element (FE) analysis. A 3D FE model of a three-unit FDP was designed replacing the maxillary first molar with maxillary second premolar and second molar as the abutments using CATIA V5R18 software and analyzed with ABAQUS/CAE 6.6 version. The model was consisted of 465108 nodes and 86296 elements and the luting agent thickness was considered 25 μm. Three load conditions were applied on eight points in each functional cusp in horizontal (57.0 N), vertical (200.0 N) and oblique (400.0 N, θ = 120°) directions. Five different luting agents were evaluated. All materials were assumed to be linear elastic, homogeneous, time independent and isotropic. For all luting agent types, the stress distribution pattern in the cortical bone, connectors, implant and abutment regions was almost uniform among the three loads. Furthermore, the maximum von Mises stress of the cortical bone was at the palatal side of second premolar. Likewise, the maximum von Mises stress in the connector region was in the top and bottom of this part. Luting agents transfer the load to cortical bone and different types of luting agents do not affect the pattern of load transfer.