Full Crown Research Articles

Comparison of Overall Fit of Milled and Laser-Sintered CAD/CAM Crown Copings.

Background and Aims The aim of this study was to investigate the effect of computer-aided design/computer-aided manufacturing (CAD/CAM) procedures on the overall fit of metal copings. Materials and Methods A standardized die was made in die stone of an upper right molar prepared for a full crown. The die was digitalized by an Identica Blue Light Scanner, and the coping substructure was designed using CAD software. Ten milled specimens and ten laser-sintered specimens were manufactured by Renishaw plc based on the generated file by the software. All twenty copings were digitized by the Identica scanner, and the data were superimposed with the original premanufacturing data file of the prepared full crown. Using the Geometric Modelling Library (GML) package, the fit discrepancies were displayed as colour maps showing discrepancies in three dimensions. Each map was made up of thousands of data points carrying numerical error values allowing detailed analyses. Results The milled group displayed a mean of fit discrepancies of 42.20 μm (SD 3.04 μm), while the laser-sintered group showed a mean of 42.24 μm fit discrepancies (SD 2.94 μm). Thus, a small difference of 0.04 μm between the two groups was detected. Conclusions The evaluated manufacturing systems can be used in dental practice as a small and insignificant discrepancy of fit between the two manufacturing methods was detected.

All-Ceramic inlays and onlays for posterior teeth

The increasing requirement for aesthetic restorations has been matched by the continuing improvements in dental materials and fabrication techniques. These factors have resulted in the development of newer ways of making tooth-coloured restorations for posterior teeth. The value of preserving tooth tissue is widely appreciated and the use of partial coverage restorations can assist this aim. The use of porcelain inlays and onlays etched with hydrofluoric acid together with improved composite resin-luting agents offers the dentist and patient the option of a conservative and aesthetic restoration for more extensively damaged posterior teeth. The paper describes the indications and clinical procedures for the use of these restorations. CPD/Clinical Relevance: Porcelain inlays and onlays offer a predictable alternative to full coverage crowns and should be part of the clinician's armamentarium.

Effect of occlusal-convergence and resin cement on retention of cubic-zirconia based crowns

Purpose. The purpose of this study was to evaluate the retention of cubic zirconia crowns with two occlusal convergence preparations and cementation with two resin cements. Materials and methods. 28 dies were divided according to the convergence angles into two main groups. Group (1): 20° (n=14) Group (2): 12° (n=14) Each group was subdivided according to resin cement used into two subgroups. Subgroup A: RelyX Unicem (3M/ESPE, USA) (n=7) Subgroup B: Panavia v5 with clearfil primer plus (Kurary, Japan) (n=7) Two stainless steel master dies were prepared by a milling machine to simulate all ceramic full coverage crown preparation of a maxillary premolar. Each Steel die was machined with height 5.5 mm and two planes occlusal reduction with palatal cusp bevel. The external diameter of the cylinder was 7.5 mm. one die was prepared with 12˚ and the other with 20˚ occlusal convergence angle. Impressions of the main master dies were taken and poured using a non-shrink epoxy resin material. The crowns were cemented. Instron universal testing machine was used to test the retention. The cemented crowns were pulled off along the path of insertion with a crosshead speed of 0.5 mm/minute. The forces required for dislodgment of the crowns were recorded in N. Data were statistically analyzed using one-way ANOVA and many comparisons were made using .Tukey’s test at pResults. Retention of the zirconia crowns was significantly affected by the occlusal convergence and by the type of resin cement. Self-etching resin cement showed a higher significant result in comparison to self-adhesive. Retention values with occlusal convergence 12° was highly significant with both cementsConclusions. The Retention of cubic zirconia ceramics varied significantly depending on the type of resin cement and degree of occlusal convergence of the preparation.

Casted post and core and full coverage crown restoration over endodontically treated tooth, Case Report

Casted post and core and full coverage crown restoration over endodontically treated tooth, Case Report

Fracture Resistance of Monolithic Zirconia Crowns in Implant Prostheses in Patients with Bruxism.

The aim of this study is to determine the minimum required thickness of a monolithic zirconia crown in the mandibular posterior area for patients with bruxism. Forty-nine full zirconia crowns, with seven different occlusal thicknesses of 0.4, 0.5, 0.6, 0.7, 0.8, 0.9, and 1.0 mm, were made by using a computer-aided design/computer-aided manufacturing system (CAD/CAM). Seven crowns in each group were subjected to cyclic loading at 800 N and 5 Hz in a servohydraulic testing machine until fracture or completion of 100,000 cycles. Seven finite element models comprising seven different occlusal thicknesses of 0.4, 0.5, 0.6, 0.7, 0.8, 0.9, and 1.0 mm were simulated using three different loads of vertical 800 N, oblique 10 degrees 800 N, and vertical 800 N + x N torque (x = 10, 50, and 100). The results of cyclic loading tests showed that the fracture resistance of the crown was positively associated with thickness. Specimen breakage differed significantly according to the different thicknesses of the prostheses (p < 0.01). Lowest von Mises stress values were determined for prostheses with a minimal thickness of 1.0 mm in different loading directions and with different forces. Zirconia specimens of 1.0 mm thickness had the lowest stress values and high fracture resistance and under 800 N of loading.

Use of cone-beam computed tomography as a diagnostic aid in nonsurgical endodontic management of furcation perforations: Two case reports

Iatrogenic furcation perforation is undesirable communication between the pulpal floor and the periodontium. This study reports nonsurgical endodontic management of iatrogenic furcation perforation in mandibular molars in two cases. Cone-beam computed tomography (CBCT) was used as an advanced diagnostic aid to accurately determine the location and extent of the perforation. The perforation was sealed with mineral trioxide aggregate, and the teeth were treated endodontically. Since the pulpal floor was weakened due to perforations, attempt was made to reinforce the coronal tooth structure using composite resin. Full crowns were placed as a definitive restoration. Two-year postoperative follow-up showed the absence of pain or swelling clinically, and radiographic examination revealed complete healing of furcation lesion. The use of CBCT in this report was a valuable diagnostic aid, which helped in better treatment planning and improved treatment outcome for the patient.

Effect of zirconia substructure thickness on the mechanical properties and adhesion of veneering porcelain

Aim: This study investigated the influence of yttrium-stabilized tetragonal zirconia polycrystals (Y-TZP) thickness on fracture load of porcelain-veneered crowns (FL), fracture toughness of porcelain (FT), and the shear bond strength zirconia/porcelain (SBS). Methods: Artificial first molar was prepared for full crown (N=45) with different occlusal reduction. Y-TZP cores were made with different thickness at the occlusal face (1mm, 2mm and 3mm) (n=15). The cores were veneered with VM9 – Vita porcelain with 1.0 mm layer. For FL testing, axial load was applied to the mesiolingual cusp of the crowns. For FT testing, flat Y-TZP plates (5X5 mm) with 1, 2 or 3 mm thickness were veneered with 1.0 mm porcelain layer (n=10). FT by indentation fracture technique was measured close to the interface and at the top surface. For SBS by knife-edge shearing rod, cylindrical porcelain with 5 mm in diameter and 3 mm was applied on flat Y-TZP plates (1, 2 and 3 mm thickness) (n = 10). Results: Data analyzed by 1-Way ANOVA for FL of crowns and SBS between Y-TZP and porcelain were not significant. Two-way ANOVA for FT was significant for zirconia thickness and measurement area. The post-hoc test showed higher values for the groups with 2 and 3mm, and higher values at the interface, irrespectively of Y-TZP thickness. Conclusion: The zirconia thickness did not affect the FL of veneered crowns and the SBS between the ceramics, but FT of porcelain was lower in thinner zirconia substructure and close to the interface Y-TZP/Porcelain.

Retrospective Study of 18 Titanium Alloy Crowns Produced by Computer-Aided Design and Manufacturing in Dogs.

Computer-aided design (CAD) and computer-aided manufacturing (CAM) technology is routinely used in various fields of human dentistry, particularly prosthodontics. Reverse engineering and additive manufacturing allow the technician to create an easier, faster and more accurate restoration, with a natural design and adequate strength. Eighteen titanium alloy full crowns were produced for canine teeth of 7 working dogs using CAD/CAM technology (3D BioCare, Nobel Biocare). Reasons for crown therapy included abrasion, enamel infraction, and crown fracture. Crown preparation was routinely performed, and impressions were delivered to the laboratory where digital impressions were performed with a lab scanner. Using 3D dental design software, the metal crown was designed and sent for manufacture. Each prosthodontic crown was then carved from a solid titanium alloy block to obtain the final crown. All prosthodontic crowns were an adequate fit, and cementation was routinely performed. Crowns were lost from 2 canine teeth during the dogs' normal working activity, in one case, for 2 times. In all cases, replicas were requested. In the first case, the second cementation was successful. In the second case, the second crown was again lost and only the third cementation was successful. Follow up of all cases range from 12 to 62 months. Mean survival time for the crowns was 58.0 months. Here, CAD/CAM technology is shown to be a useful tool for manufacturing accurate prosthodontic crowns for veterinary patients. Moreover, CAD/CAM enables the production of prosthodontic crown replicas in a very short time and at relatively low cost compared to traditional methods, consequently eliminating the need for at least one anesthetic procedure in the incidence of crown cementation failure.

Prosthodontics: preparation and cementation of a full-coverage metal crown on a fractured maxillary canine tooth

Prosthodontics in veterinary medicine is a discipline in veterinary dentistry in which prosthetic dental appliances are applied in order to maintain and/or restore the function and integrity of the teeth....

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

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

Accuracy of crowns based on digital intraoral scanning compared to conventional impression—a split-mouth randomised clinical study

The aim of this prospective in vivo study was to evaluate the accuracy of the marginal and internal fit of crowns based on conventional impression (CI) or intraoral scan (IOS) in a randomised, split-mouth set-up. Nineteen patients needing full coverage crowns, fitting a split-mouth design, were provided with two lithium disilicate crowns: one based on a CI and one based on an IOS. The marginal and internal accuracy of the crowns were assessed with the replica technique and clinically using a modified California Dental Association (CDA) quality evaluation system. At the preparation margin, the median gap was 60μm for IOS and 78μm for CI. For the other points, the median gap ranged from 91 to 159μm for IOS and 109 to 181μm for CI. The accuracy of the IOS was statistically significantly better at all point except at the cusp tip. All crowns where rated R or S at both the 6- and 12-month follow-up appointments. The results for the clinical evaluation with CDA for marginal integrity showed no statistically significant difference between the two impression methods at both the 6- and 12-month evaluations. Crowns based on IOS show statistically significantly better marginal and internal adaptation before cementation compared to conventional impression. However, the clinical evaluation showed similar marginal adaptation. Crowns based on a fully digital workflow can provide clinically acceptable marginal adaptation, comparable to crowns based on CI.

Adequately Prepared? A Study Using an Innovative Computer Application to Measure Clinical Crown Convergence Angles Achieved by Students at a UK Dental School.

This study examined the total occlusal convergence angles created for full coverage crown preparations by students at a UK dental school. Working casts of 82 clinical crown preparations were scanned using a 3D scanner. Stereolithographic files were uploaded to Preppr, a crown preparation analysis application. Mean bucco-lingual convergence angle were 19.6° (+/-11.7) and mesial-distally 17.8° (+/-11.1). Smallest bucco-lingual convergence angles were achieved for canine teeth with the largest on molar teeth. The smallest mesio-distal values were on canine teeth with the largest on molar teeth. Ideal total convergence angles (4-14°) were achieved in 23% of bucco-lingual preparations and 33% of mesio-distal preparation. Results for clinically acceptable angles (10-20°) were 30% and 40% respectively. There were no statistically significant differences between tooth types for mean bucco-lingual values. (p=0.623), mesio-distal mean values were statistically different by tooth type (p=0.003). Mean values for mandibular molars were significantly higher than for maxillary incisors (p=0.001) and mandibular molars had significantly higher values than maxillary canines (p=0.045). Results in this study were comparable to those of other students and qualified clinicians, with a minority of preparation achieving ideal values.

Internal Bleaching of Endodontically Treated Teeth: A Dental Practitioner\'s Perspective from Kingdom of Saudi Arabia

To determine the knowledge and attitude of dental practitioners (DPs) for internal bleaching technique (IBT) in Kingdom of Saudi Arabia. A cross-sectional study was developed based on a convenient sampling of dental practitioners and specialists working in Kingdom of Saudi Arabia. DPs responded to a structured, self-administered questionnaire for evaluation of their knowledge and attitude toward IBT. The questionnaire had two components: (i) the characteristics of the study participants; and (ii) the items related to the internal bleaching technique (IBT). Data analysis was conducted using SPSS (version 25.0), with descriptive statistics and a bivariate analysis. A total of 532 dental practitioners (61.3% males and 38.7% females) participated in this study. The response rate of participation was estimated at 92.5%. Almost 37% participants considered the sodium perborate as the most commonly used dental material for internal bleaching. Almost 70% participants reported that superficial enamel discoloration was a contraindication for internal bleaching in endodontically treated teeth. DPs have good knowledge and attitude on use of IBT for discolored teeth. In general, there is a need to improve knowledge and attitude of dental professionals about the IBT by attending continuing dental educational programs. Saving of the remaining tooth structure is a main principle of the different types of dental treatments. So the IBT should be known for all dental practitioners to use it before going to more aggressive dental treatment options such as full crowns. How to cite this article: Doumani M, Alotaibi AN, Al Hussain F, et al. Internal Bleaching of Endodontically Treated Teeth: A Dental Practitioner's Perspective from Kingdom of Saudi Arabia. J Contemp Dent Pract 2019;20(10):1141-1145.

Comparative evaluation of fracture resistance of self-adapting PFS and elastic FRC post and core systems –An in vitrostudy

Background: Endodontically treated teeth (ETT) with extensive coronal destruction are more prone to fracture, so restoring these teeth with techniques that will not compromise the integrity of remaining tooth structure with the use of Post and core systems to retain full and final crown restorations seems mandatory. Anatomic posts have been introduced which have better adaptability to the canal anatomy and conserve more amount of tooth structure. Aim: This study was done to compare the fracture resistance of ETT restored with two anatomic post systems elastic FRC post (everStick) and self adapting PFS (Spirapost). Materials and Methods: Twenty single rooted maxillary central incisors were selected for the study. All the samples were endodontically treated and randomly divided into 2 groups (n=10) according to the post system used (PFS post – Group I, FRC– Group II). In all the samples, post space preparation was done and the posts were luted using dual cure resin cement (Para core, Coltene, Mumbai, India).The remaining core was built using composite resin (Filtek, 3M, ESPE, USA). The samples were stored in saline for one week. All the samples were thermocycled for 500 cycles from 5 to 55 0 c ±5 0 c with a dwelling time of 30 seconds in each bath and a transfer time of five seconds. Fracture resistance of the samples was measured using universal testing machine. The obtained data was statistically analyzed by using independent t test. Results: There was no statistically siginificant difference between fracture resistance values of FRC and PFS groups. 30% and 70% of the samples of PFS and FRC showed favourable fractures respectively. Conclusion: In this study it was concluded that fracture resistance of PFS was comparable to that of FRC post. However FRC group showed predominantly more number of favourable fractures.

Influence of Varying Ferrule Heights and Configurations on the Fracture Resistance of Endodontically Treated Mandibular First Molars-An in Vitro Study

Purpose: To evaluate the influence of varying ferrule heights and configurations on the fracture resistance of endodontically treated teeth restored with custom cast post and cores and full metal crowns. Method: Fifty extracted human mandibular first premolars were randomly divided into 5 groups: I, no root canal treatment (RCT), crown; II, no post and core, crown; III, 2-mm ferrule, cast post and core and crown; IV, non-uniform ferrule (2 mm buccal and lingual, 0.5 mm proximal), cast post and core and crown; and V, no ferrule, cast post and core and crown. Samples were subjected to a static load on the buccal cusp, 150° to the long axis of the tooth, and failure load was recorded. Statistical analysis was carried out with a 1-way analysis of variance and the Bonferroni pairwise comparison. The mode of fracture was noted by visual inspection. Results: Absence of ferrule resulted in significantly lower fracture resistance (V: 308.27 +/- 75.567 N) as compared to all other groups. Group I: 714.69 +/- 89.37 N, and Group II: 656.90 +/- 133.15 N were significantly more resistant as compared to Group IV: 471.98 +/- 115.99 N (p < 0.01). However, there was no significant difference between non-uniform ferrule and the uniform 2-mm vertical ferrule. Conclusion: The premolars with a ferrule were more fracture resistant as compared to the teeth with no ferrule preparation.

A Conservative Approach to Treatment of Dental Erosion: Case Report

Tooth surface loss is a common condition with nearly three-quarter of the population in Trinidad & Tobago exhibiting signs and about one-fifth of those persons have moderate or severe wear. These patients become difficult to treat due mainly to loss of clinical crown height and also loss of occlusal vertical dimension. This case depicts the use of a conservative approach to treating a patient with moderate tooth surface loss, as assessed via the tooth wear index, with aetiology of acid erosion. The poor appearance of the dentition was the patient’s chief presenting complaint. With the use of 3M Filtek™ Z 250 Universal Restorative Composite (St Paul, MN, USA), temporary posterior build-ups were placed to increase the patient’s Occlusal Vertical Dimension (OVD) and were subsequently replaced with metal onlays. Anterior composite veneers were placed to achieve an aesthetically pleasing result at the increased OVD. The combined use of composite and metal onlays allowed for an economical and more conservative treatment modality for dental erosion rather than full coverage posterior and anterior crowns.

Influence of substrate design for in vitro mechanical testing.

BackgroundThe goal of this study was to evaluate the influence of dental substrate simulator material, and the presence of root and periodontal ligament on the stress distribution in an adhesively-cemented monolithic crown.Material and MethodsFive (5) 3D models according to the substrate simulator material and shape were modeled with CAD software for conducting non-linear finite element analysis (FEA): Tooth with and without periodontal ligament - subgroup “pl” (groups Tooth+pl and Tooth-pl), machined tooth in epoxy-resin with and without pulp chamber - subgroup “pc” (ER+pc and ER-pc) and simplified epoxy-resin substrate without pulp chamber and roots (SiER). Next, adhesively-cemented monolithic crowns in zirconia reinforced lithium silicate were modeled over each substrate. The solids were then imported in STEP format to the analysis software and the contact between teeth and cylinder was considered perfectly bonded; whereas, the contacts involving the resin cement were considered as non-separated. The materials were considered isotropic, linearly elastic, and homogeneous. An axial load (600 N) was applied to the occlusal surface and results of maximum principal stress (MPa) on the restoration were required.ResultsFEA revealed that all evaluated subtracts showed the crown intaglio surface as the most stressed region. The average stress and stress peaks were similar for restorations cemented onto Tooth+pl, Tooth-pl and ER+pc substrates, but, 13% higher in comparison to ER-pc and SiER substrates.ConclusionsSimplified substrates can be used to evaluate posterior full crown behavior without periodontal ligaments and roots, since the rigidity of the specimen is taken into account. Key words:Finite element analysis, axial loading, computed assisted numerical analisys, monolithic crowns,methodological study.

Effectiveness of Two Desensitizer Materials, Potassium Nitrate and Fluoride Varnish in Relieving Hypersensitivity After Crown Preparation

The aim of this clinical investigation was to compare the efficacy of fluoride varnish and potassium nitrate on the reduction of hypersensitivity of prepared teeth both pre and post cementation. In this randomized clinical trial, patients who needed at least three single crowns fixed partial prosthesis were included. Two desensitizing agents including fluoride varnish and potassium nitrate were used in this study and compared to the control group (sterile saline). In each patient, each prepared tooth was randomly assigned to one group. The desensitizing agent was applied on prepared teeth immediately after tooth preparation. The sensitivity of the teeth was measured by means of an air sensitivity test based on the visual analog scale at five different time points: baseline (2 hours after preparation), 7 days after preparation, before cementation, after cementation and one-week post cementation. Data were analyzed by Kruskal-Wallis and Friedman tests with a significant level of 0.05. Overall 300 vital abutment teeth needed full crown coverage in 100 patients were included. Both desensitizers' agents decreased the sensitivity of vital abutment teeth compared to the control group at every time intervals except at baseline (p = 0.089). There was no significant difference between fluoride varnish and potassium nitrate in the reduction of pre-cementation sensitivity while one week after cementation, sensitivity was more relieved by potassium nitrate compared to fluoride varnish (p = 0.023). The application of both desensitizers is effective in sensitivity reduction of vital abutment teeth. Potassium nitrate, however, is more eligible one week after cementation compared to fluoride varnish. Both potassium nitrate and fluoride varnish are capable of desensitizing prepared tooth for the fixed partial denture.

Simple technique to fabricate a crown for abutment of an existing cast partial removable denture

The requirement of full crown restoration for abutments of existing Cast partial removable denture is common. Retrofitting a crown to existing cast partial denture (CPD) clasps and guiding planes is a challenging task. Literature describes various direct, indirect, and direct-indirect techniques to overcome this dilemma. All these involve elaborate steps, necessitating refabrication of CPD or extended clinical adjustment time for ensuring a proper fit that is elusive in most cases and also patient has to do without CPD during laboratory procedure. The recent use of computer-aided design-computer-aided manufacture technology for this purpose is proving to be a promising but expensive option. A simple technique is presented here to generate a blueprint of required final contours to facilitate a fully contoured metal crown to fit under an existing CPD.

A Comparative Analysis on the Accuracy of Special and Prefabricated Impression Trays Using Additional Silicone in a Laboratory Model

Introduction: Impression technique plays a pivotal role in fixed prosthodontic treatments; one of the main steps of impression is selection and preparation of an appropriate tray. Impression technique with insufficient accuracy causes distortions and complications that consequently result in treatment failure. The present study compares the impression accuracy of special and prefabricated trays in a laboratory model. This article compares the accuracy of special and prefabricated impression trays for achieving better impression and finally better crowns with good adaptation. Materials and Methods: In this study, a laboratory-fabricated resin model, resembling a mandibular first molar, was used on a dental arch and prepared by standard method for full crown restorations with a finish line of 1-mm depth and 3° to 4° convergence angle. Impression was made from a laboratory-fabricated resin model, 40 times with monophase medium-body polyvinyl siloxane in special trays and 40 times with putty and light-body polyvinyl siloxane using double-mix impression technique without spacer in prefabricated trays. To measure marginal gap, distance between the restoration margin and preparation finish line was vertically determined on each die in the mesial, distal, buccal, and lingual regions. Statistical analysis was performed and data were analyzed by SPSS 20 software using independent samples t-test. The data were significantly different at P 0.05). However, a significant difference was reported between the techniques in the lingual and distal regions.Conclusion: The present study indicated a higher accuracy for the special tray impression than prefabricated tray impression.