Accuracy of the intaglio surface of 3D-printed hybrid resin-ceramic crowns, veneers and table-tops: An in vitro study

OBJECTIVES

The present study aims to examine the influence of the build angle on the accuracy (trueness and precision) of 3D printed crowns, table-tops and veneers with a hybrid resin-ceramic material.

METHODS

One crown, on table-top and one veneer were printed in five different build angles (0°, 30°, 45°, 60°, 90°) (n = 50) with the digital light processing (DLP) system (Varseo XS, Bego) using hybrid resin (Varseo Smile Crownplus A3, Bego). All printed restorations were scanned using the laboratory scanner (D2000, 3Shape) and matched onto the initial reference design in metrology software (Geomagic Control X, 3D Systems). The root mean square error (RMSE) was calculated between the scanned and reference data. The data was statistically analyzed using the Tukey multiple comparison test and Wilcoxon multiple comparison test.

RESULTS

The crown group showed higher trueness at 30° (0.021 ± 0.002) and 45° (0.020 ± 0.002), and table-tops at 0° (0.015 ± 0.001) and 30° (0.014 ± 0.001) (p < 0.0001). Veneers demonstrated higher trueness at 30° (0.016 ± 0.002) (p < 0.0001). All three restoration types demonstrated the lowest trueness at a 90° build angle and portrayed deviations along the z axis. The veneer and table-top groups showed the lowest precision at 90° (veneers: 0.021 ± 0.008; table-tops: 0.013 ± 0.003). The crown group portrayed the lowest precision at 45° (0.017 ± 0.005) (p < 0.0001).

CONCLUSION

The build angle of DLP-printed hybrid resin-ceramic restorations influences their accuracy.

CLINICAL SIGNIFICANCE

Considering the build angle is important to achieve a better accuracy of 3D-printed resin-ceramic hybrid restorations. This may help predict or avoid the interference points between a restoration and a die and minimize the clinical adjustments.

Crown-Assisted CsCu2I3 Growth and Trap Passivation for Perovskite Light-Emitting Diodes

Copper (Cu)-based perovskites are promising for lead-free perovskite light-emitting diodes (PeLEDs). However, it remains a significant challenge to achieve high performance devices due to the nonradiative loss caused by the disordered crystallization and lack of passivation. Crown ethers are known to form host-guest complexes by the interaction between C-O-C groups and certain cations, and 18-crown-6 (18C6) with an appropriate complementary size can interact with Cs+ and Cu+ cations. Herein, we studied the interaction between CsCu2I3 and two crowns with the same cyclic size, 18C6 and dibenzo-18-crown-6 (D18C6). Particularly, D18C6 can reduce the nonradiative recombination rate of CsCu2I3 film by passivating the defects and optimizing the film morphology effectively. The room mean square (RMS) decreased from 5.06 to 2.95 nm, and the PLQY was promoted from 4.71% to 19.9%. Besides, D18C6 can also decrease the barrier of hole injection. The PeLEDs based on D18C6-modified CsCu2I3 realized noticeable improvement with a maximum luminance and EQE of 583 cd/m2 and 0.662%, respectively.

The influence of different cement spaces on the marginal gap of lithium disilicate crowns constructed by two scanner and milling unit combinations

BACKGROUND

This study compared the marginal gaps of CAD/CAM lithium disilicate (LDS) crowns constructed using a contemporary and older scanner/milling unit combination at three different cement spaces.

METHODS

Twenty-four undergraduate students prepared a Columbia model lower left first molar for an LDS crown in a simulated environment. From each crown preparation, one LDS crown was constructed using an E4D scanner/E4D milling unit (E4DS/E4DM) and TRIOS 3 scanner/Sirona inLab MC X5 milling unit (TRIO/MCX5) at cement space settings of 50, 100 and 200 μm. Each LDS crown was positioned onto the original crown preparation, and then a stereomicroscope was used to make three vertical marginal gap measurements at four locations (mid-buccal, mid-lingual, mid-mesial and mid-distal). The mean marginal gap (MMG) was calculated for each crown and each individual tooth surface.

RESULTS

The MMGs of CAD/CAM LDS crowns constructed by TRIO/MCX5 were 72.31 at 50, 63.73 at 100 μm and 46.23 μm at 200 μm, which were smaller than E4DS/E4DM at each cement space.

CONCLUSIONS

Increasing the cement space decreased the MMG in both scanner/milling unit combinations. The smallest MMG was found using the newer scanner/milling unit at the 200 μm cement space. © 2024 Australian Dental Association.

Metal Marvels: Revolutionizing Endodontic Restoration With a Novel Endocrown Approach

This case report explores the innovative application of the endocrown technique for restoring a severely damaged mandibular molar (tooth #46) in a 28-year-old male patient. With a recent root canal treatment history, the patient presented with a dislodged prosthesis. Due to financial constraints, a base metal alloy was chosen for the endocrown restoration. The unique preparation process involved reducing the occlusal surface by 2 mm, creating a shoulder cervical margin, and preserving enamel walls. The endocrown, crafted from a base metal alloy, demonstrated a semi-conservative approach, providing cost-effectiveness and minimal tooth preparation. The case adheres to the 2013 CAse REport (CARE) guidelines. The discussion highlights the biomechanical benefits of the endocrown, emphasizing stress resistance, stability, and superior performance compared to traditional treatments. Materials like ceramic, resin nanoceramic, and polyetheretherketone are briefly discussed, focusing on the promising success rates of endocrowns, mainly through computer-aided designing/computer-aided manufacturing systems. The report provides valuable insights for clinicians considering this endocrown technique in reconstructing severely damaged molars and premolars.

Long-Term Clinical Outcomes of Single Crowns or Short Fixed Partial Dentures Supported by Short (≤6 mm) Dental Implants: A Systematic Review

Long-term clinical outcomes of short dental implants (≤6 mm) supporting single crowns or short fixed partial dentures have been reported differently in different studies and need more clarification. This systematic study evaluated the rate of bone loss (BL), the durability of implants equal to or shorter than 6 mm supporting single crowns or short fixed partial dentures, and prosthetic-related side effects during 5 years of follow-up. Five databases (PubMed, MEDLINE, Scopus, Google Scholar, and Cochrane) were electronically and manually searched for longitudinal studies with a follow-up period of 5 years or more until January 2023. The study question was, "Does the implant equal to or shorter than 6 mm affect BL and survival rate of the implant-supported prosthesis after 5 years of follow-up?". From 752 identified articles, nine studies were selected for further evaluation. After 5 years of follow-up, most studies had more than 90% survival rate and the maximum BL was 0.54 mm. Still, in internal and external connections, these changes were not substantial. For example, screw loosening was the most common problem with implanted prostheses. Implants of 6 mm or shorter are a suitable treatment option in atrophic ridges with good durability and fewer side effects during a follow-up period of more than 5 years.

Survival of pre-formed zirconia crowns in primary teeth: a prospective practice-based cohort study

BACKGROUND

This study aimed to investigate the (1) survival probabilities of prefabricated zirconia crowns (PZCs) placed on primary teeth and (2) identify demographic and tooth-related factors that might affect survival probability.

METHODS

This study prospectively followed children treated under general anaesthesia by a single practitioner between 2012 and 2020. Demographic variables including the age at treatment, gender and tooth-related variables including FDI tooth number, crown size used and any procedural complications at postoperative reviews were collected.

RESULTS

A total of 155 children involving 319 teeth with PZCs were followed up between 12 and 78 months postoperatively with a mean of 38 months. Of the 319 crowns followed, five failures were observed in three patients requiring extraction. Other procedural complications noted included fracture (n = 3), overhangs (n = 3), internal resorption (n = 5) and 24% of crowns showed signs of radiographic changes on postoperative radiographs when these were taken. Age at treatment, tooth type and need for pulp therapy were not statistically associated with clinical success (P > 0.1).

CONCLUSIONS

PZCs provide an aesthetic and durable solution in the management of children with early childhood caries. This study shows very good clinical success and survival extending up to 78 months for PZCs placed on primary teeth under general anaesthesia.

Do onlays and crowns offer similar outcomes to posterior teeth with mesial-occlusal-distal preparations? A systematic review

OBJECTIVE

Teeth prepared for mesial-occlusal-distal (MOD) restorations have a significant risk of cusp fracture. Crowns and onlays can provide cusp coverage to reinforce posterior teeth at risk. Onlays are often more conservative of tooth structure which may be an advantage for teeth with large MOD preparations. It remains uncertain how onlays and crowns compare for posterior teeth with MOD tooth structure loss. The purpose of this systematic review was to compare the resistance to fracture, success rate, survival rate, and failure rate of teeth with MOD preparations restored with onlays or crowns.

MATERIALS AND METHODS

An electronic search queried Medline (PubMed), Embase (Ovid), Scopus, the Cochrane Library, and grey literature (OpenGrey) from database inception through April 29, 2023.

RESULTS

After eliminating duplicates and irrelevant records, 32 manuscripts were assessed. Only three publications met the criteria for inclusion. Most exclusions were due to poor reporting of restorative design and the amount of tooth structure remaining, or due to combining various restorative designs. Due to the limited sample size and high heterogeneity, no meta-analysis was conducted. One study observed a better outcome for onlays and two observed no difference. All three studies reported the mode of failure for crowns as more catastrophic whereas teeth with onlays could be salvaged.

CONCLUSIONS

Onlays may be an advantageous alternative to crowns for teeth with MOD preparations, but the level of evidence is insufficient to draw meaningful conclusions.

CLINICAL SIGNIFICANCE

Current evidence is insufficient to determine whether onlays or crowns are providing a different outcome when used to restore posterior teeth with MOD tooth structure loss. However, the fracture of teeth with MOD tooth structure loss restored with onlays appears to be less catastrophic than when restored with crowns.

FEA Comparison of the Mechanical Behavior of Three Dental Crown Materials: Enamel, Ceramic, and Zirconia

The restoration of endodontically treated teeth is one of the main challenges of restorative dentistry. The structure of the tooth is a complex assembly in which the materials that make it up, enamel and dentin, have very different mechanical behaviors. Therefore, finding alternative replacement materials for dental crowns in the area of restorative care isa highly significant challenge, since materials such as ceramic and zirconia have very different stress load resistance values. The aim of this study is to assess which material, either ceramic or zirconia, optimizes the behavior of a restored tooth under various typical clinical conditions and the masticatory load. A finite element analysis (FEA) framework is developed for this purpose. The 3D model of the restored tooth is input into the FEA software (Ansys Workbench R23)and meshed into tetrahedral elements. The presence of masticatory forces is considered: in particular, vertical, 45° inclined, and horizontal resultant forces of 280 N are applied on five contact points of the occlusal surface. The numerical results show that the maximum stress developed in the restored tooth including a ceramic crown and subject to axial load is about 39.381 MPa, which is rather close to the 62.32 MPa stress computed for the natural tooth; stresses of about 18 MPa are localized at the roots of both crown materials. In the case of the zirconia crown, the stresses are much higher than those in the ceramic crown, except for the 45° load direction, while, for the horizontal loads, the stress peak in the zirconia crown is almost three times as large as its counterpart in the ceramic crown (i.e., 163.24 MPa vs. 56.114 MPa, respectively). Therefore, the zirconia crown exhibits higher stresses than enamel and ceramic that could increase in the case of parafunctions, such as bruxism. The clinician's choice between the two materials should be evaluated based on the patient's medical condition.

Quality of Fixed Dental Prostheses and Patient Satisfaction in a Sample From Saudi Arabia

BACKGROUND

The objective of the study was to retrospectively assess the clinical performance of dental prostheses, single crowns, and three-unit bridges to identify clinical biological and mechanical complications in the Ha'il province of Saudi Arabia.

METHODS

The study was conducted between March 2021 to October 2021 and included 421 patients who underwent crown and tooth-supported fixed partial denture (FPD) procedures at the Dental Polyclinics Center in the Ha'il region of Saudi Arabia from 2010-2020. The planned sampling approach was applied. Patients who underwent crown and FPD placements at the dental center within the scheduled period were identified through clinical assessments. The inclusion criteria were met by patients with three-unit FPDs and a single crown containing a natural contralateral tooth or teeth. A total of six general dentists conducted clinical exams. Patient satisfaction and technical and biological issues were the evaluation criteria for crowns and FPDs. The frequency and percentage of the various characteristics employed in the current investigation were ascertained using cross-tabulation. The Chi-square test was employed to assess the associations between categorical variables, with p-values ≤ 0.05 considered significant.  Results: Marginal integrity was recorded in 332 participants (78.9%), which was satisfactory for the majority of the restoration. The acceptance morphology was present in 252 (59.9%) restorations. The highest rate of the restorations 274 (66.2%) had satisfactory color. In 86 cases (20.4%), there was visible periodontal depth of at least 5 mm. Three hundred and six (72.7%) of the fixed restorations had gingival bleeding connected to them, and 96 (22.8%) teeth had periapical lesions. A total of 311 patients (73.9%) reported they were satisfied with their fixed restorations.

CONCLUSIONS

The technical and biological complications noted in the current study were not higher compared with other studies of crowns and fixed dental prostheses. The majority of patients were satisfied with the restoration.

A Comparison of Failure Loads for Polycrystalline Zirconia Ceramics with Varying Amounts of Yttria, Glass-Ceramics and Polymers in Two Different Test Conditions

It is unclear how zirconia dental crowns with different yttria compositions will perform clinically, and how they will compare with crowns made of glass-ceramics and polymers. The present objective was to determine failure loads of crowns and discs made of glass ceramics or polymers as compared to yttria-partially stabilized zirconia (Y-PSZ) crowns and discs with varying yttria concentrations. Crowns of zirconia (Cercon XT, Katana UTML, BruxZir Anterior), glass ceramic (Celtra press, IPS e.max press, Lisi press), and polymeric materials (Trilor, Juvora, Pekkton) were fabricated and cemented to epoxy abutments. The total number of specimens was 135 for crowns and 135 for discs (n = 15 specimens per material type and design). A universal testing machine was used to perform compressive loading of crowns/discs to failure with a steel piston along the longitudinal axis of the abutments. Energy dispersive spectroscopy (EDS) was used to identify the yttria concentration for each zirconia brand. The data were analyzed using generalized linear models and regression analyses. The results revealed significant differences (p < 0.05) in mean failure loads for different crown materials: Trilor (6811 ± 960 N) > Juvora (5215 ± 151 N) > Cercon (4260 ± 520 N) = BruxZir (4186 ± 269 N) = e.max (3981 ± 384 N) > Katana (3195 ± 350 N) = Lisi (3173 ± 234 N) = Pekkton (3105 ± 398 N) > Celtra (2696 ± 393 N). The general linear model revealed significant differences (p < 0.05) in mean failure loads when comparing the different materials for the discs, i.e., Trilor (5456 ± 1748 N) > Juvora (4274 ± 869 N) > Pekkton (3771 ± 294 N) > Katana (2859 ± 527 N) > Cercon (2319 ± 342 N) = BuxZir (2250 ± 515 N) = e.max (2303 ± 721 N) = Lisi (2333 ± 535 N) > Celtra (1965 ± 659 N). EDS showed that the zirconia materials contained yttria at different concentrations (BruxZir = 5Y-PSZ, Cercon = 4Y-PSZ, Katana = 3Y-PSZ). The yttria concentration had a significant effect on the failure load of the Katana (3Y-PSZ) crowns, which revealed lower failure loads than the Cercon (4Y-PSZ) and BruxZir (5Y-PSZ) crowns, whose failure loads were comparable or higher than e.max glass ceramic. The failure load of the trilayer disc specimens did not correlate with the failure load of the respective crown specimens for the zirconia, glass-ceramic and polymeric materials.

Efficacy of eutectic topical anesthesia in stainless steel crown procedures for primary molars: A randomized controlled trial

BACKGROUND

Prior literature highlights the importance of local anesthesia (LA) for stainless steel crown (SSC) preparation and placement. Nevertheless, the effectiveness of a eutectic mixture of local anesthesia (EMLA), a topical anesthesia, for this purpose remains unexplored.

AIM

The study evaluated the effectiveness of two EMLA application methods during SSC preparation and placement.

DESIGN

Eighty-four children between 4 and 8 years of age were randomly allocated to three intervention groups. Group A received EMLA applied supragingivally, Group B received a gingival retraction cord impregnated with EMLA (GRC_EMLA), and Group C (control) received LA. Pain was recorded using Wong-Baker Faces Pain Scale (WBFPS) and Children Hospital Eastern Ontario Pain Scale (CHEOPS) at three time intervals.

RESULTS

Control had highest mean pain scores at the first time interval in both maxillary and mandibular arches, followed by Group B and Group A, with statistically significant p-values (p = .00, p < .05). After preparation and placement, all three groups had low mean pain scores, with no statistically significant differences. Group A had minimal pain scores at all three time intervals, although not statistically significant.

CONCLUSION

EMLA is a potent topical anesthetic and can be used as an alternative to LA for conventional SSC preparation and placement in primary molars.

Relation of Crown Failure Load to Flexural Strength for Three Contemporary Dental Polymers

Polymeric materials show great promise for use in a variety of dental applications. Manufacturers generally provide flexural strength information based on standardized (ISO and ASTM) specimen dimensions and loading conditions. It is not clear, however, if flexural strength data are predictive of the clinical performance of dental crowns. The objectives of this study were, therefore, to determine whether flexural strengths, as measured via three-point bending (3PB), would be predictive of failure loads assessed via crunch-the-crown (CTC) tests. Three brands of polymers (Trilor, Juvora, and Pekkton) were fabricated into rectangular bars and fully contoured crowns (10 specimens of each polymer brand, 30 specimens of each shape). Differential scanning calorimetry (DSC), Fourier transform infrared spectroscopy (FTIR), and burn off tests were used to characterize/confirm the materials. Bars were tested blindly in 3PB to determine flexural strength, and crowns were CTC-tested to determine failure load after luting to resin abutments. The statistical significance of the test results was evaluated via one-way ANOVA (α = 0.05) and Pearson's correlation coefficient, while regression analysis was used to test for a correlation between 3PB and CTC results. The fracture mechanisms and failure surface characteristics were characterized using scanning electron microscopy (SEM). There were significant differences (p < 0.05) in the mean crown failure loads (Trilor (7033 N) > Juvora (5217 N) > Pekkton (3023 N)) and mean flexural strengths of the bars (Trilor (468 MPa) > Juvora (197 MPa) = Pekkton (192 MPa)). The mode of crown fracture was different between the materials and included deformation (Juvora), ductile-to-brittle fracture (Pekkton), and a combination of cracks and deformation (Trilor). Flexural strengths did not correlate with the corresponding crown failure loads for any of the materials tested. These results suggest that dental practitioners should not rely on the flexural strengths reported from three-point bending tests, as advertised by the manufacturer, to predict the performance of polymeric crowns.

Selective adhesive luting: A novel technique for improving adhesion achieved by universal resin cements

OBJECTIVE

We aimed to introduce the concept of "Selective adhesive luting-SAL" which is explained through clinical steps and supported by preliminary laboratory evidence.

CLINICAL CONSIDERATIONS

Cementation with rubber dam is difficult to perform in case of short abutment teeth and/or subgingival crown margins. By means of universal resin cements/universal adhesive systems, which can be employed in self-adhesive as well as adhesive luting procedures, this paper presents a novel technique allowing clinicians to perform reliable cementation where rubber dam isolation is difficult. The SAL technique entails the application of a universal adhesive system only on easily accessible abutment surfaces, enabling simultaneous adhesive and self-adhesive luting in different portions of the abutment. The SAL clinical workflow is explained through prosthodontic rehabilitation of maxillary right central incisor affected by microdontia and restored with a lithium-disilicate crown. Furthermore, our laboratory microshear bond strength study supports the rationale behind SAL application demonstrating higher bond strength even when the adhesive resin is placed only on one portion of the cementation substrate.

CLINICAL SIGNIFICANCE

This article advocates the application of SAL technique in clinical situations where effective adhesive luting is uncertain, since it can improve the adhesion between the tooth and universal resin cements.

Comparing Original and Universal Screwdrivers and How They Affect Friction in the Screw

The present study focused on investigating whether universal screwdriver kits cause less friction between the screwdriver and the abutment screw than original screwdrivers. For this purpose, 2 original screwdrivers (Straumann and BEGO) and a universal screwdriver kit (bredent) were investigated. On 1 implant per screwdriver, 26 abutments were properly attached one after the other with the corresponding abutment screws. After tightening the abutment screw, the force required to pull the screwdriver off the screw head was determined with a spring balance. For both manufacturers, greater pull-off forces were measured when using the original screwdrivers than when using the universal screwdriver. The pull-off force (mean ± SD) required for the Straumann original screwdriver was 3.7 ± 1.4 N, while that required for the universal screwdriver was 0.1 ± 0.1 N (P < .001). The pull-off force was 1.5 ± 1.5 N for the BEGO original screwdriver and 0.7 ± 0.9 N for the universal screwdriver (P = .19). Using original manufacturer-supplied screwdrivers could thus minimize the risk of the screwdriver slipping out of the screw head during dental treatment and being swallowed or aspirated by the patient.

Effect of preparation type on the accuracy of different intraoral scanners: An in vitro study at different levels of accuracy evaluation

OBJECTIVE

Evaluation of the effect of preparation type (inlay, onlay, and crown) on the accuracy of different intraoral scanning (IOS) systems at the preparation and arch segment levels.

MATERIALS AND METHODS

Three molars were prepared for inlay, onlay, and crown. Each preparation was scanned 10 times by CEREC Omnicam, Trios 3 (TS), and Medit i500 scanners. Each image was trimmed twice. The first trimming produced a preparation image (PI), and the second trimming extracted a segment image (SI) that involved the preparation with the adjacent teeth. Trueness and precision were calculated at the PI and SI levels.

RESULTS

At the PI level, all IOS systems had similar trueness pattern for all preparations, where the inlay had the best trueness followed by the crown and onlay. At the SI level, the different preparations showed similar trueness. The precision did not show a clear pattern of superiority for any preparation. The TS was significantly more precise than other IOS systems at the PI and SI levels, for every preparation. The proximal areas suffered from the greatest errors, regardless of preparation type.

CONCLUSIONS

The preparation type influenced PI trueness, and the IOS system affected PI and SI precisions.

CLINICAL SIGNIFICANCE

The smaller and less complex preparations have greater IOS accuracy than larger and more complex preparations. As the proximal areas are more affected regardless of the preparation, a more accessible proximal area for scanning is desirable.

Update on Dental Luting Materials

A dental luting material aids in the retention and stability of indirect restorations on the prepared tooth structure. In dentistry, clinicians are using a wide range of luting materials for the cementation of indirect restorations. Zinc oxide eugenol and non-eugenol cements, zinc phosphate cement, zinc polycarboxylate cement, glass ionomer cement and resin cements are common dental cements used in dentistry. Each luting material or cement possesses unique properties and clinical implications. An ideal luting cement should be biocompatible, insoluble, resistant to thermal and chemical assaults, antibacterial, aesthetic, simple and easy to use. It should have high strength properties under tension, shear and compression to resist stress at the restoration-tooth interface, as well as adequate working and setting times. So far, no luting material possesses all of these properties of an ideal cement. Scientists have been modifying the conventional luting cements to improve the material's clinical performance and developing novel materials for clinical use. To achieve the best clinical outcome, clinicians should update their knowledge and gain a good understanding of the luting materials so that they can make a wise clinical decision on the material selection and obtain an insight into the development of luting cements. Therefore, the objective of this study is to provide a discussion on the physical, chemical, adhesive and aesthetic properties of common luting materials. The clinical indications of these luting materials are suggested based on their properties. In addition, overviews of the modification of the conventional luting materials and the newly developed luting materials are provided.

Present status and future directions: The restoration of root filled teeth

This narrative review will focus on a number of contemporary considerations relating to the restoration of root filled teeth and future directions for research. Clinicians are now more than ever, aware of the interdependence of the endodontic and restorative aspects of managing root filled teeth, and how these aspects of treatment are fundamental to obtaining the best long-term survival. To obtain the optimal outcomes for patients, clinicians carrying out endodontic treatment should have a vested interest in the restorative phase of the treatment process, as well as an appreciation for the structural and biomechanical effects of endodontic-restorative procedures on restoration and tooth longevity. Furthermore, the currently available research, largely lacks appreciation of occlusal factors in the longevity of root filled teeth, despite surrogate outcomes demonstrating the considerable influence this variable has. Controversies regarding the clinical relevance of minimally invasive endodontic and restorative concepts are largely unanswered with respect to clinical data, and it is therefore, all too easy to dismiss these ideas due to the lack of scientific evidence. However, conceptually, minimally invasive endodontic-restorative philosophies appear to be valid, and therefore, in the pursuit of improved clinical outcomes, it is important that the efficacies of these treatment protocols are determined. Alongside an increased awareness of the preservation of tooth structure, developments in adhesive bonding, ceramic materials and the inevitable integration of digital dentistry, there is also a need to evaluate the efficacy of new treatment philosophies and techniques with well-designed prospective clinical studies.

The marginal gaps of sequentially milled lithium disilicate crowns using two different milling units

BACKGROUND

The purpose of this study was to compare the marginal gaps of sequentially milled lithium disilicate (LDS) crowns using two different milling units.

METHODS

One lower left first molar typodont tooth prepared for an LDS crown by an undergraduate student in a simulation clinic was selected. The crown preparation was scanned by a TRIOS 3 scanner and twelve LDS crowns milled by an E4D (E4DM) and a Sirona inLab MC X5 (MCX5) milling unit using identical settings. The crowns were seated onto the original crown preparation and three vertical marginal gap measurements were taken at four locations (mid-buccal, mid-lingual, mid-mesial and mid-distal) using a stereomicroscope. The mean marginal gap (MMG) was calculated for each individual tooth surface and each crown.

RESULTS

The MMG for the E4DM (100.40 μm) was not significantly different to the MCX5 (101.08 μm) milling unit (P = 0.8809). In both units, there was a statistically significant trend of increasing MMG with sequentially milled crowns using the same burs (E4DM P = 0.0133; MCX5 P = 0.0240).

CONCLUSIONS

The E4DM and MCX5 milling units produced LDS crowns with similar MMG's and within a clinically acceptable range but with a trend of increasing MMG when analysed sequentially. © 2022 Australian Dental Association.

Moving from analogue to digital workflows in dentistry: Understanding undermilling and overmilling as detrimental factors in fabricating CAD/CAM crowns

Due to the limitations caused by the specific dimensions of milling burs, milling machines may inaccurately fabricate restorations by either over-reducing or under-reducing restorative material, respectively known as "overmilling" and "undermilling". Overmilling occurs when the bur is unable to accommodate areas smaller than the size of the bur, especially at cusp tips and sharp line angles. This results in excess cement space and a weaker restoration. Undermilling occurs when small concavities are ignored by the larger milling bur, particularly at the margins. This results in inadequate seating of the restoration and open margins due to premature binding, which can lead to restorative failure. To prevent these processing errors, clinicians should ensure that all incisal edges and cusp tips are flattened and rounded, verify that there are no undercuts, and prepare teeth with 1mm thick, smooth finish lines. Furthermore, clinicians may use the preparation check and milling simulation step of computer-aided design/computer-aided manufacturing (CAD/CAM) software to confirm the preparation is adequate and the restorative design does not have potential areas that will lead to overmilling.

In Vitro Study of Laser-Assisted Prefabricated Ceramic Crown Debonding as Compared to Traditional Rotary Instrument Removal

This study compared the laser and rotary removals of prefabricated zirconia crowns in primary anterior and permanent posterior teeth. Sixty-two extracted teeth were prepared for prefabricated zirconia crowns cemented with resin-modified glass-ionomer cement. Specimens underwent crown removals by a rotary handpiece, or erbium, chromium: yttrium-scandium-gallium-garnet (Er,Cr:YSGG) laser. Pulpal temperatures, removal times, and scanning electron microscopy (SEM) examinations were compared. The average crown removal time for rotary and laser methods was 80.9 ± 19.36 s and 353.3 ± 110.6 s, respectively, for anterior primary teeth; and 114.2 ± 32.1 s and 288.5 ± 76.1 s, respectively, for posterior teeth (p < 0.001). The maximum temperature for the rotary and laser groups was 22.2 ± 8.5 °C and 27.7 ± 1.6 °C for anterior teeth, respectively (p < 0.001); and 21.8 ± 0.77 °C and 25.8 ± 0.85 °C for the posterior teeth, respectively (p < 0.001). More open dentinal tubules appeared in the rotary than the laser group. The rotary handpiece removal method may be more efficient than the laser with lower pulpal temperature changes. However, the laser method does not create noticeable tooth or crown structural damage compared to the rotary method.

Mechanical stability of fully personalized, abutment-free zirconia implant crowns on a novel implant-crown interface

OBJECTIVES

To test the failure load and failure mode of a novel implant-crown interface specifically designed for the fabrication of fully personalized, abutment-free monolithic zirconia CAD-CAM crowns compared to conventional implant-abutment interfaces involving prefabricated or centrally manufactured abutments for zirconia CAD-CAM crowns.

METHODS

Implants (N=48) were divided into groups (n=12) according to different implant-abutment interface designs: (1) internal implant connection with personalized, abutment-free CAD-CAM crowns (Abut-Free-Zr), (2) internal conical connection with customized, centrally manufactured zirconia CAD-CAM abutments (Cen-Abut-Zr), (3) prefabricated titanium base abutments from manufacturer 1 (Ti-Base-1), (4) additional prefabricated titanium base abutments from manufacturer 2 (Ti-Base-2). All specimens were restored with a screw-retained monolithic zirconia CAD-CAM molar crown and subjected to thermomechanical aging (1.200.000 cycles, 49 N, 1.67 Hz, 30° angulation, thermocycling 5-50°C). Static load until failure was applied in a universal testing machine. Failure modes were analyzed descriptively under digital microscope. Mean failure load values were statistically analyzed at a significance level of p<0.05.

RESULTS

All specimens survived thermomechanical aging. The mean failure loads varied between 1332 N (Abut-Free-Zr) and 1601 N (Ti-Base-2), difference being significant between these groups (p<0.05). No differences between the other groups were seen. The predominant failure mode per group was crown fracture above implant connection (Abut-Free-Zr, 75%), abutment fracture below implant neck (Cen-Abut-Zr, 83%), crown fracture leaving an intact abutment (Ti-Base-1/Ti-Base-2 100%).

CONCLUSIONS

Implant-crown interface with fully personalized, abutment-free monolithic CAD-CAM zirconia crowns exhibited similar failure loads as conventional implant-abutment interfaces (except group Ti-Base-2) involving CAD-CAM crowns with prefabricated or centrally manufactured abutment.

CLINICAL SIGNIFICANCE

The new implant connection simplifies the digital workflow for all-ceramic implant reconstructions. The specific design of the implant-crown interface allows the fabrication of fully personalized, abutment-free zirconia implant crowns both in-house and in-laboratory without the need of a prefabricated abutment or central manufacturing.

Wear of Polymer-Infiltrated Ceramic Network Materials against Enamel

Polymer-infiltrated ceramic network materials (PICNs) have high mechanical compatibility with human enamel. However, the wear properties of PICN against natural human enamel have not yet been clarified. We investigated the in vitro two-body wear behaviors of PICNs and an enamel antagonist. Two PICNs were used: Experimental PICN (EXP) prepared via the infiltration of methacrylate-based resin into the porous silica ceramic network and commercial Vita Enamic (ENA). Two commercial dental ceramics, lithium disilicate glass (LDS) and zirconia (ZIR), were also characterized, and their wear performance was compared to PICNs. The samples were subjected to Vickers hardness tests and two-body wear tests that involve the samples being cyclically impacted by enamel antagonists underwater at 37 °C. The results reveal that the Vickers hardness of EXP (301 ± 36) was closest to that of enamel (317 ± 17). The volumetric wear losses of EXP and ENA were similar to those of LDS but higher than that of zirconia. The volumetric wear loss of the enamel antagonist impacted against EXP was moderate among the examined samples. These results suggest that EXP has wear behavior similar to that of enamel. Therefore, PICNs are mechanically comparable to enamel in terms of hardness and wear and are excellent tooth-restoration materials.

Visualizing the effect of freezing on the vascular system of wheat in 3 dimensions by in-block imaging of dye-infiltrated plants

Infrared thermography has shown after roots of grasses freeze, ice spreads into the crown and then acropetally into leaves initially through vascular bundles. Leaves freeze singly with the oldest leaves freezing first and the youngest freezing later. Visualising the vascular system in its native 3‐dimensional state will help in the understanding of this freezing process. A 2 cm section of the crown that had been infiltrated with aniline blue was embedded in paraffin and sectioned with a microtome. A photograph of the surface of the tissue in the paraffin block was taken after the microtome blade removed each 20 μm section. Two hundred to 300 images were imported into Adobe After Effects and a 3D volume of the region infiltrated by aniline blue dye was constructed. The reconstruction revealed that roots fed into what is functionally a region inside the crown that could act as a reservoir from which all the leaves are able to draw water. When a single root was fed dye solution, the entire region filled with dye and the vascular bundles of every leaf took up the dye; this indicated that the vascular system of roots was not paired with individual leaves. Fluorescence microscopy suggested the edge of the reservoir might be composed of phenolic compounds. When plants were frozen, the edges of the reservoir became leaky and dye solution spread into the mesophyll outside the reservoir. The significance of this change with regard to freezing tolerance is not known at this time.

Thermal cameras that allow visualisation of water freezing in plants have shown that in crops like wheat, oats and barley, ice forms first at the bottom of the plant and then moves upwards into leaves through water conducting channels. Leaves freeze one at a time with the oldest leaves freezing first and then younger ones further up the stem freeze later. To better understand why plants freeze like this, we reconstructed a 3‐dimensional view of the water conducting channels. After placing the roots of a wheat plant in a blue dye and allowing it to pull the dye upwards into leaves, we took a part of the stem just above the roots and embedded it in paraffin. We used a microtome to slice a thin layer of the paraffin containing the plant and then photographed the surface after each layer was removed. After taking about 300 images, we used Adobe After Effects software to re‐construct the plant with the water conducting system in three dimensions. The 3D reconstruction showed that roots fed into a roughly spherical area at the bottom of the stem that could act as a kind of tank or reservoir from which the leaves pull up water. When we put just one root in dye, the entire reservoir filled up and the water conducting channels in every leaf took up the dye. This indicates that the water channels in roots were not directly connected to specific leaves as we had thought. When plants were frozen, the dye leaked out of the reservoir and spread into cells outside. Research is continuing to understand the significance of this change during freezing. It is possible that information about this effect can be used to help breeders develop more winter‐hardy crop plants.

Masking Ability of Monolithic and Layered Zirconia Crowns on Discolored Substrates

There is scarce information on the colorimetric behavior of monolithic and layered zirconia crowns in combination with various abutment colors. This study evaluated the masking ability on discolored substrates of monolithic and layered zirconia crowns. Anterior crowns were fabricated using 3Y-TZP zirconia and layering ceramic and divided into three groups: monolithic (ML), bi-layer (BL), and tri-layer (TL). The crowns were placed over eleven substrates (ND1-ND9, zirconia, metal), and CIE L*, a*, b*, C*, and h° color coordinates were measured in the cervical, middle, and incisal areas with a spectrophotometer. Masking ability was calculated using the color difference formula, and values were interpreted according to the perceptibility and acceptability thresholds. Data were analyzed statistically (α = 0.001). The L* coordinate was not significantly different between BL and TL crowns, regardless of the measurement area or substrate (p ≥ 0.001). In the middle area, the L* coordinate of the ML group was statistically different from the BL and TL groups only for zirconia and metal substrates, while in the incisal area, only for ND7 and metal substrates. The a* coordinate was significantly different between the ML and layered crowns for all measurement areas and substrates (except zirconia). The b* and C* coordinates differed significantly between the groups only in the cervical area (p < 0.001). The ML crown had better masking ability than the BL and TL crowns. However, the color differences for ML crowns were below the acceptability threshold for ND2, ND3, and ND7 substrates in the cervical and middle areas and below perceptibility threshold only for the incisal area. The lowest masking ability of the crowns was found for ND9 and metal substrates in all measurement areas.

Influence of manufacturing technique on the color of zirconia restorations: Monolithic versus layered crowns

OBJECTIVES

The study aimed to compare the color of monolithic and layered zirconia crowns fabricated using different brands in the cervical, middle, and incisal areas.

MATERIALS AND METHODS

A total of 45 crowns were fabricated from three brands (Katana, Nacera, Cercon) using three methods (monolithic = ML (n=5), cut-back + enamel = BL (n=5), cut-back + dentin + enamel = TL (n=5)). CIE L*, a* b*, C*, h° color coordinates were recorded with a dental spectrophotometer in cervical, middle, and incisal areas. Color differences between manufacturing techniques, tooth areas, and brands were calculated using the CIEDE2000(1:1:1) formula, and the values were compared to the perceptibility (PT₀₀ ) and acceptability thresholds (AT₀₀ ). Comparisons between color coordinates were analyzed statistically (Kruskal-Wallis and Mann-Whitney U tests, p < 0.001).

RESULTS

Significant differences were found between CIE L*, a*, b*, C*, h° coordinates of the zirconia crowns (p < 0.001), generally. The lowest color differences were obtained between BL and TL crowns in cervical and middle areas. Color differences between cervical and middle areas were mostly below PT₀₀ . An acceptable color difference was found between Katana and Cercon crowns.

CONCLUSIONS

The manufacturing technique and the brand influenced the color of zirconia crowns. Also, the color of the crowns varied from cervical to incisal.

CLINICAL SIGNIFICANCE

Reproducing the optical properties of teeth with ceramic crowns might be challenging, given the differences in the internal configuration of the enamel and dentine, as well as their complex behavior when interacting with light. When deciding whether to fabricate a monolithic crown in translucent zirconia or improve its appearance by layering with more translucent glass-ceramic, the clinicians and dental technicians must be aware of these procedures' effect on the final color of the restorations.

Effect of Finish Line Design on the Fit Accuracy of CAD/CAM Monolithic Polymer-Infiltrated Ceramic-Network Fixed Dental Prostheses: An In Vitro Study

A polymer-infiltrated ceramic network (PICN) material has recently been introduced for dental use and evidence is developing regarding the fit accuracy of such crowns with different preparation designs. The aim of this in vitro study was to evaluate the precision of fit of machined monolithic PICN single crowns in comparison to lithium disilicate crowns in terms of marginal gap, internal gap, and absolute marginal discrepancies. A secondary aim was to assess the effect of finish line configuration on the fit accuracy of crowns made from the two materials. Two master metal dies were used to create forty stone dies, with twenty each for the two finish lines, shoulder and chamfer. The stone dies were scanned to produce virtual models, on which ceramic crowns were designed and milled, with ten each for the four material–finish line combinations (n = 10). Marginal gaps and absolute marginal discrepancies were evaluated at six pre-determined margin locations, and the internal gap was measured at 60 designated points using a stereomicroscope-based digital image analysis system. The influence of the material and finish line on the marginal and internal adaptation of crowns was assessed by analyzing the data using two-way analysis of variance (ANOVA), non-parametric, and Bonferroni multiple comparison post-hoc tests (α = 0.05). ANOVA revealed that the differences in the marginal gaps and the absolute marginal discrepancies between the two materials were significant (p < 0.05), but that those the finish line effect and the interaction were not significant (p > 0.05). Using the Mann–Whitney U test, the differences in IG for ‘material’ and ‘finish line’ were not found to be significant (p > 0.05). In conclusion, the finish line configuration did not seem to affect the marginal and internal adaptation of PICN and lithium disilicate crowns. The marginal gap of PICN crowns was below the clinically acceptable threshold of 120 µm.

Effect of occlusal anatomy of CAD/CAM feldspathic posterior crowns in the stress concentration and fracture load

OBJECTIVES

This study evaluated the effect of restoration occlusal design on the maximum fracture load and stress distribution of a feldspathic ceramic crown.

MATERIALS AND METHODS

Twenty dentin analogues were used to simulate a full-crown preparation. Next, 20 feldspathic crowns were milled according to the occlusal design parameter available in the CAD database (Young or Adult). The crowns were cemented with dual cure resin-cement and loaded until fracture at 1 mm/min crosshead speed. Data were analyzed by using one-way ANOVA and Tukey tests (p < 0.05). The same geometry and experimental setup was modeled and exported to the computer aided engineering software and tensile stress concentration was calculated using the finite element method with 300 N occlusal load simulation.

RESULTS

The occlusal anatomy significantly influenced the load-to-fracture (p < 0.05). Adult design showed higher mean values (1149 ± 201 N) than Young design (454 ± 77 N). The maximum principal stress criteria showed similar stress pattern for both designs, however, the highest stress concentration was calculated for Young design (91 MPa) in the occlusal surface.

CONCLUSIONS

An anatomy design with reduced cusp angulation and less evident occlusal sulcus can reduce the stress concentration and increase the fracture load for feldspathic CAD/CAM posterior crowns.

Success of Feather Margin Preparation for Full Metal Prosthodontic Crowns in the Canine Teeth in 84 Pet and Working Dogs (2005-2017)

Medical and dental records of Veterinary Dental Specialties and Oral Surgery were searched to identify dogs that received full metal prosthodontic crowns on canine teeth, using a feather or knife edge preparation between 2005 and 2017. A total of 160 teeth in 84 dogs were included in the study. Current follow-up by telephone, electronic mail, or electronic messaging was conducted, in addition to thorough record review for in-person recheck examinations. Treatment was considered successful if the prosthodontic crown was in place and no further or additional injury to the tooth had occurred at the time of reexamination, owner contact, or patient death. Tooth fracture apical to the prosthodontic crown occurred in 2 (1.25%) cases, bond failure between the tooth and the cement or the cement and the crown occurred in a single case (0.625%), and one metal crown required replacement after 3 years due to wear (0.625%), for an overall failure rate of 2.5%. These results suggest that feather preparation of the margin is at least as, if not more, successful as the more commonly accepted and performed chamfer margin, and thus is a successful, practical and durable option for prosthodontic crown treatment in dog canine teeth.

External gap progression after cyclic fatigue of adhesive overlays and crowns made with high translucency zirconia or lithium silicate

OBJECTIVES

To evaluate three-dimensional external gap progression after chewing simulation of high translucency zirconia (HTZ) and zirconia-reinforced lithium silicate (ZLS) applied on endodontically treated teeth with different preparation designs.

MATERIALS AND METHOD

Endodontically treated molars were prepared with low-retentive (adhesive overlay) and high-retentive (full crown) designs above cementum-enamel junction and restored with HTZ and ZLS. Micro-computed tomography analysis was assessed before and after chewing simulation to evaluate three-dimensionally the external gap progression. Results were statistically analyzed with two-way ANOVA and post-hoc Tukey test.

RESULTS

High-retentive preparation design had a significantly inferior gap progression compared to the overlay preparation (p < 0.01); ZLS exhibited a significant inferior gap progression compared to HTZ (p < 0.01).

CONCLUSIONS

High-retentive preparations restored with ZLS seem to better perform in maintaining the sealing of the external margin after cyclic fatigue.

CLINICAL SIGNIFICANCE

The clinician should pay attention to the proper combination of preparation designs and ceramic material selection for an endodontically treated molar restoration. HTZ seems to perform worse than lithium silicate in terms of marginal sealing, still showing lacks in resistance to cyclic fatigue when adhesive preparations are performed.

Comparative evaluation of marginal and internal fit of endocrowns using lithium disilicate and polyetheretherketone computer-aided design - computer-aided manufacturing (CAD-CAM) materials: An in vitro study

Purpose:

To evaluate the marginal and internal fit of endocrowns with different computer-aided design/computer-aided manufacturing (CAD-CAM) materials by measuring them with a stereomicroscope (μm).

Materials and Methods:

A mandibular first molar typodont tooth was prepared to receive an endocrown. The preparation was scanned using an extra-oral scanner. Endocrowns (n = 20) were fabricated using lithium disilicate (IPS e. max CAD LT block; CEREC Ivoclar Vivadent, Liechtenstein) and polyetheretherketone (PEEK) (breCAM. BioHPP^®; Bredent, UK) using CAD-CAM technique. Marginal gap was evaluated using a stereomicroscope at the midpoint of all four surfaces (mid buccal, mid lingual, mid mesial, mid distal). This was followed by sectioning of the endocrowns in a sagittal plane along with the prepared tooth to evaluate the internal fit at four different points (A, B, C, D) using a stereomicroscope. Statistical analysis was performed using one-way analysis of variance test.

Results:

Mean values of marginal gap of lithium disilicate and PEEK endocrowns are 56.6 ± 6.1 μm and 81.3 ± 10.1 μm, respectively. Mean value internal gaps of lithium disilicate and PEEK endocrowns are 158.2 ± 11.1 μm and 199.1 ± 13 μm, respectively. Results in the present study have shown that the marginal and internal fits of lithium disilicate endocrowns are superior to that of PEEK endocrowns.

Conclusions:

Based on the outcomes of this in vitro study, the marginal and internal fit of lithium disilicate endocrowns is better than PEEK endocrowns. The marginal gap clinically acceptable is <120 μm. The marginal gap values recorded in this study are within the acceptable range for both materials.

Pulpal and Periapical Status of the Vital Teeth Used as Abutment for Fixed Prosthesis-A Systematic Review and Meta-Analysis

PURPOSE

This is a systematic review to identify the incidence of pulp necrosis and/or periapical changes among vital teeth which are used as an abutment for crown and fixed partial dentures (FPDs).

MATERIALS AND METHODS

Two reviewers independently searched two electronic databases, PubMed and Scopus. The search was complemented from references of included studies and published reviews. Studies published in the English language through January 2021 that had assessed and documented the clinical and radiographic failure of crown or FPD in vital permanent teeth due to pulpal or periapical pathology with a follow-up of at least 12 months were selected. Data screening, data collection and extraction of data was performed. Quality of studies involved was analyzed using the Newcastle-Ottawa Quality Assessment Scale for cohort studies. Meta-analysis was done using random effects model. Publication bias was assessed using funnel plots.

RESULTS

Electronic searches provided 10,075 records among which 20 studies were selected for systematic review and 7 studies were selected for meta-analysis. With respect to quality assessment, all the studies involved were considered as high quality as the score in scale ranged between 6 and 9 as per the Newcastle-Ottawa Quality Assessment Scale for cohort studies. The meta-analyses showed that there was no statistically significant difference in the incidence of the loss of pulp vitality or pulp necrosis through clinical and radiographic examination with the follow up period of 5 years: p < 0.001, 95% CI: 0.96-1.00, I² = 77.84%; 10 years: p < 0.001, 95% CI: 0.88-0.95, I² = 93.59%; 15 years: p < 0.001, 95% CI: 0.92-0.96, I² = 94.83%; and 20 years: p < 0.001, 95% CI: 0.94-0.96, I² = 95.01%.

CONCLUSIONS

The meta-analysis revealed clinical and radiographic success rate ranging between 92% to 98% at different follow up periods ranging between 5 years and 20 years. Future high-quality randomized clinical controlled trials with a larger population are required to confirm the evidence as only observational studies were considered in this paper.

Longevity of Polymer-Infiltrated Ceramic Network and Zirconia-Reinforced Lithium Silicate Restorations: A Systematic Review and Meta-Analysis

The purpose of this study was to systematically review the existing literature to assess the clinical survival and success of PICN and ZLS indirect restorations as the clinical evidence for them remains lacking. PubMed, SCOPUS, Embase, Cochrane Library, Web of Science, LILACs, and SciElo databases were searched from 1 January 2000 to 1 February 2021. Clinical trials and cohort studies published in English were included while case studies, case series, and in vitro studies were excluded. Results were analyzed qualitatively and a meta-analysis using a random effects model was performed. A strength of recommendation taxonomy (SORT) analysis was conducted and risk of bias (RoB) was assessed using the Newcastle-Ottawa scale and Cochrane RoB tools. An electronic search through the databases yielded 2454 articles, of which 825 remained after duplicate removal. Five studies investigating PICN and four investigating ZLS indirect restorations remained after assessing for eligibility. The overall survival rate of PICN over 1 year was 99.6% and 99.2% over 2 years. The overall survival rate of ZLS over 1 year was 99%. The main mode of failure for both materials was catastrophic fracture. One study had a high RoB, four had a moderate RoB, and four had a low RoB. Both materials demonstrated moderate strength of recommendation at a level 2 evidence for all studies based on SORT analysis. PICN and ZLS show promising short-term clinical performance as full and partial coverage indirect restorations, but longer follow-up studies are required to confirm their long-term performance.

Comparison of Fracture Load of the Four Translucent Zirconia Crowns

Recently, translucent zirconia has become the most prevalent material used as a restorative material. This study aimed to compare the crown fracture load of the four most common different translucent zirconia brands available in the market at 1.5 mm thickness. Standardized tooth preparations for a full ceramic crown were designed digitally with software (AutoCAD) by placing a 1.0 mm chamfer margin and 1.5 mm occluso-cervical curvature for the crown sample manufacturing. Stylized crowns were chosen to control the thickness of the crown. The axial and occlusal thickness were standardized to 1.5 mm thickness except at the central pit, which was 1.3 mm thick. The STL file for the tooth dies was prepared using software (3Shape TRIOS^® Patient Monitoring, Copenhagen, Denmark). The tooth dies were printed with a resin material (NextDent Model 2.0, Vertex-Dental B.V., Soesterberg, The Netherlands) using a 3D printing software (3D Sprint^® Client Version 3.0.0.2494) from a 3D printer (NextDent™ 5100, Vertex-Dental B.V., Soesterberg, The Netherlands). The printing layer thickness was 50 µm. Then, a total of twenty-eight (N = 28) stylized crowns were milled out of AmannGirrbach (Amann Girrbach GmbH, Pforzheim, Germany) (n = 7), Cercon HT (Dentsply Sirona, Bensheim, Germany) (n = 7), Cercon XT (Dentsply Sirona, Bensheim, Germany) (n = 7), and Vita YZ XT (Zahnfabrik, Bäd Sackingen, Germany) (n = 7). Following sintering the crowns, sandblasting was performed and they were bonded to the tooth dies with the resin cement (RelyX U-200, 3M ESPE, Seefeld, Germany) and permitted to self-cure under finger pressure for 6 min. The crowns were loaded on the occlusal surface in a universal testing machine (MTS Centurion) with a stainless-steel ball indenter (7 mm radius) with a loading rate of 1 mm/min to contact the stylized crowns on each of the four cusps until failure. A rubber sheet (1.5 mm thickness) was positioned between the crown and indenter, which helped with the load distribution. Statistical analysis was done using SPSS version 20 (IBM Company, Chicago, USA). The fracture loads were analyzed using Dunnett’s T3 test, and the number of cracks was analyzed using the Mann–Whitney U test among the groups. The significant level was set at p value = 0.05. The mean fracture loads were 3086.54 ± 441.74 N, 4804.94 ± 70.12 N, 3317.76 ± 199.80 N, and 2921.87 ± 349.67 N for AmannGirrbac, Cercon HT, Cercon XT, and Vita YZ XT, respectively. The mean fracture loads for the surfaces with the greatest number of cracks (excluding the occlusal surfaces) were on the lingual surface for AmannGirrbach and Cercon HT, on the distal and mesial for Cercon XT, and on the buccal for Vita YZ XT. We found that the AmannGirrbach had the most overall cracks. Cercon XT had the greatest number of occlusal cracks and appeared to be the most shattered. Cercon HT had the least number of cracks. In conclusion, Cercon HT presented the best strength properties, the highest fracture load, and no visible cracks. AmannGirrbach presented the lowest strength properties.

European Society of Endodontology position statement: The restoration of root filled teeth

This position statement on the restoration of root filled teeth represents the consensus of an expert committee, convened by the European Society of Endodontology (ESE). Current clinical and scientific evidence, as well as the expertise of the committee, have been used to develop this statement. The aim is to provide clinicians with evidence-based principles for decision-making on the choice of restoration following the completion of root canal treatment. By discussing the evidence in relation to key topics regarding post-endodontic restoration, a series of clinical recommendations are made. The scientific basis of the recommendations made in this paper can be found in a recently published review article (Bhuva et al. 2021, International Endodontic Journal, https://doi.org/10.1111/iej.13438). It is the intention of the committee to update this statement as further evidence emerges.

Minimal intervention treatment of crown-root fracture in a mature permanent tooth by MTA pulpotomy and Fragment Reattachment: A Case Report

Treatment of crown-root fracture can be complicated, time-consuming and expensive. This paper presents a treatment approach that minimises intra-operatory intervention and preserves the biologic tissue. A 15-year-old boy reported for treatment of an oblique crown fracture in the left permanent maxillary central incisor (#21, Fédération Dentaire Internationale) with mature root apices. The treatment presented an endodontic, periodontal and restorative challenge as the crown fracture exposed the pulp and extended subgingivally. The patient also had accompanying generalised enamel hypoplasia due to dental fluorosis (grade 3 Deans Fluorosis index), making the aesthetic rehabilitation difficult. The case was managed by preserving the vital pulp by MTA pulpotomy, followed by the adhesive bonding of autogenous crown fragment. A three-year follow-up revealed healthy vital pulp tissue and retained bonded fragment with acceptable aesthetics and periodontal health.

Comparison of Fracture Resistance for Chairside CAD/CAM Lithium Disilicate Crowns and Overlays with Different Designs

PURPOSE

To determine the fracture resistance of chairside computer-aided design and computer-assisted manufacturing (CAD/CAM) lithium disilicate full coverage crowns and two different designs of overlay restorations for premolars.

MATERIALS AND METHODS

CAD/CAM lithium disilicate (IPS e.max CAD for CEREC/HT A1 C14, Ivoclar Vivadent) restorations (15 specimens/group) with 1.5 mm occlusal thickness and 1.0 mm chamfer were designed and fabricated with a chairside CAD/CAM system (CEREC, Dentsply Sirona). The restorations were prepared in three different designs: (1) full coverage crowns, (2) overlays with the margin located 2 mm above the gingiva, and (3) overlays with the margin located 4 mm above the gingiva. Restorations were cemented using conventional resin luting cement (Multilink, Ivoclar Vivadent) with primer system (Monobond Plus, Ivoclar Vivadent) to resin printed dies, load cycled (2,000,000 load cycles at 1 Hz with 275 N force), and then finally loaded with a steel indenter until failure. Scanning electron microscopy observations of fractured surfaces were also conducted. Group results were analyzed with one-way analysis of variance, and the medians were evaluated independently with Kruskal-Wallis.

RESULTS

The fracture force of CAD/CAM lithium disilicate restorations was significantly different (p < 0.001) depending on the design of the restoration. Full coverage crowns showed significantly higher force to fracture (1018.8 N) than both types of overlays (p = 0.002 for overlay 2.0 mm and p < 0.001 for overlay 4.0 mm above gingiva). Among the two overlays, the restoration with the margin located 2 mm above the gingiva showed significantly higher fracture force (813.8 N) than the overlay with margin at 4 mm above the gingiva (436.1 N; p < 0.001). The fracture appearance of the crowns was much more complex than that of the overlay restorations.

CONCLUSIONS

Full coverage chairside CAD/CAM lithium disilicate premolar crown showed higher fracture resistance than overlay restorations. Overlays with the margin located 2 mm above the margin demonstrated higher resistance than those with the margin located 4 mm above the gingiva.

Tissue-level transcriptomic responses to local and distal chilling reveal potential chilling survival mechanisms in maize

Chilling is a major stress to plants of subtropical and tropical origins including maize (Zea mays L.). To reveal molecular mechanisms underlying chilling tolerance and survival, we investigated transcriptomic responses to chilling stress in differentiated leaves and roots as well as in crowns with meristem activity in maize. Chilling stress on shoots and roots is found to each contributes to seedling lethality in maize. Comparison of maize lines with different chilling tolerance capacities reveals that chilling survival is highly associated with upregulation of abscisic acid biosynthesis and response as well as transcriptional regulators in leaves and crowns. It is also associated with the downregulation of translation in leaves and heat response in crowns. Chilling treatment on whole or part of the plants reveals that response to distal-chilling is very distinct from, and sometimes opposite to, response to local- or whole-plant chilling in both leaves and roots, suggesting a communication between shoots and roots in environmental response. This study thus provides transcriptomic responses in leaves, roots and crowns under differential chilling stresses in maize and reveals potential chilling tolerance and survival mechanisms which lays ground for improving chilling tolerance in crop plants.

Survival of Single-Unit Porcelain-Fused-to-Metal (PFM) and Metal Crowns Placed by Students at an Australian University Dental Clinic over a Five-Year Period

The aim of this retrospective study was to determine the survival rate of single-unit porcelain-fused-to-metal (PFM) and metal crowns placed by dental students at an Australian university undergraduate dental clinic over a five-year period. Complications and the incidences of crown failures were recorded. Clinical records pertaining to single-unit PFM and metal crowns inserted over a five-year period were reviewed, including patient-related, tooth-related, and procedural factors for each crown. Crowns were evaluated as surviving, surviving with complications, or failed. Kaplan–Meier statistical analysis was used to estimate survival rate., This study is based on a sample of 232 (78.4%) PFM crowns and 64 (21.6%) metal crowns inserted between 2014 and 2018. Cumulatively, 224 (75.7%) were surviving, 48 (16.2%) were surviving but previously had complications, and 24 (8.1%) failed. The 5-year cumulative survival rate of all PFM and metal crowns was 83.9% (0.839 ± 0.038, Kaplan–Meier). The average survival time for all crowns was 4.432 ± 0.089 years. Comparatively, PFM crowns had a higher survival rate at 1 year (0.972 ± 0.010) and 2 years (0.919 ± 0.017), compared to metal crowns at 1 year (0.964 ± 0.011) and 2 years (0.894± 0.018). The survival rate of metal crowns remained constant from 2 years to 4 years and thereafter, whereas there was a continued decline in the survival rate of PFM crowns to 83.2% (0.832 ± 0.038) at 4 years and thereafter. Crowns placed on premolars had the highest cumulative survival rate whereas those placed on molars exhibited the lowest survival rate for the duration of the study period. Despite single-unit PFM crowns having a higher 1- and 2-year survival rate compared to metal crowns, metal crowns had a higher survival rate at 4 years and thereafter. Survival rates are comparable to previous studies.

Influence of Non-Thermal Atmospheric Pressure Plasma Treatment on Retentive Strength between Zirconia Crown and Titanium Implant Abutment

The aim of this study is to investigate the effect of non-thermal atmospheric pressure plasma (NTP) on retentive strength (RS) between the zirconia crown and the titanium implant abutment using self-adhesive resin cement. Surface free energy (SFE) was calculated on 24 cube-shaped zirconia blocks, and RS was measured on 120 zirconia crown-titanium abutment assemblies bonded with G-CEM LinkAce. The groups were categorized according to the zirconia surface treatment as follows: Control (no surface treatment), NTP, Si (Silane), NTP + Si, Pr (Z-Prime Plus), and NTP + Pr. Half of the RS test assemblies were aged by thermocycling for 5000 cycles at 5–55 °C. The SFE was calculated using the Owens-Wendt method, and the RS was measured using a universal testing machine at the maximum load until failure. One-way analysis of variance (ANOVA) with post-hoc Tukey honestly significant difference (HSD) was performed to evaluate the effect of surface treatments on the SFE and RS. Independent sample t-test was used to compare the RS according to thermocycling (p < 0.05). For the SFE analysis, the NTP group had a significantly higher SFE value than the Control group (p < 0.05). For the RS test, in non-thermocycling, the NTP group showed a significantly higher RS value than the Control group (p < 0.05). However, in thermocycling, there was no significant difference between the Control and NTP groups (p > 0.05). In non-thermocycling, comparing with the NTP + Si or NTP + Pr group, there was no significant difference from the Si or Pr group, respectively (p > 0.05). Conversely, in thermocycling, the NTP + Si and NTP + Pr group had significantly lower RS than the Si and Pr group, respectively (p < 0.05). These results suggest that NTP single treatment for the zirconia crown increases the initial RS but has little effect on the long-term RS. Applied with Silane or Z-Prime Plus, NTP pre-treatment has no positive effect on the RS.

Seating accuracy of implant immediate provisional prostheses fabricated by digital workflow prior to implant placement by fully guided static computer-assisted implant surgery: An in vitro study

OBJECTIVES

Evaluation of seating accuracy of implant immediate provisional prostheses fabricated prior to fully guided static computer-assisted implant surgery (sCAIS).

MATERIALS AND METHODS

Two maxillary training models were used to plan for single anterior (S-Ant) and single posterior (S-Post) implant prostheses, and a bridge (B) spanning from an anterior implant (B-Ant) to a posterior implant (B-Post). A commercial software was used to plan the implant location, design the surgical guides and design the provisional prostheses. The master models with the provisional prostheses were scanned to generate virtual master models. For each maxillary model, a total of 10 guides and 10 surgical models were produced. Following implant placements in each surgical model, the provisional prostheses were attached to the implants and were scanned to produce virtual surgical models. The virtual master and surgical models were superimposed to measure the vertical error, the proximal contact error and the proximal contact quality.

RESULTS

The vertical error was greatest for the S-Post (0.41 mm), followed by B-Post (0.29 mm), B-Ant (0.26 mm) and S-Ant (0.21 mm). There was no significant difference in vertical errors among the prostheses. For the proximal contact, the S-Ant had significantly greater error (0.45 mm - 0.46 mm) than S-Post (0.15 mm) and B (0.09 mm - 0.15 mm). A similar pattern was observed for proximal contact quality.

CONCLUSIONS

All prostheses were associated with errors vertically and at the proximal contacts. Therefore, the clinicians who plan to use this workflow should be prepared to adjust the prosthesis after implant insertion.

Comparison of the marginal discrepancy of PFM crowns in the CAD/CAM and lost-wax fabrication techniques by triple scanning

BACKGROUND

Computer-aided design/computer-aided manufacturing (CAD/CAM) systems are widely used for the fabrication of porcelain-fused-to-metal (PFM) crowns.

OBJECTIVES

This study was conducted to compare PFM crowns through triple scanning in terms of marginal discrepancy between the CAD/CAM and lost-wax fabrication techniques.

MATERIAL AND METHODS

Twenty uniform resin dies of a prepared maxillary first molar were randomly divided into 2 groups: conventional lost-wax; and milling. Marginal discrepancy was evaluated at the framework and porcelain steps through triple scanning and direct visualization under a stereomicroscope. Then, the crowns were cemented to the related die and the marginal gap was measured with triple scanning, direct visualization under a stereomicroscope and scanning electron microscopy (SEM). The data was analyzed using the independent t test and the one-way analysis of variance (ANOVA). The significance level was set at 0.05.

RESULTS

Differences in the mean marginal gap were measured by the various evaluation methods. Triple scanning and stereomicroscopy identified increasing discrepancy during the fabrication process. According to the results of the independent t test, stereomicroscopy showed no difference after cementation between the CAD/CAM and lost-wax groups (p > 0.05), triple scanning showed higher fitness in the CAD/CAM group (p < 0.05), and SEM showed better adaptation in the lost-wax group (p < 0.05); however, there was a positive correlation between the findings of stereomicroscopy and SEM (p < 0.05).

CONCLUSIONS

The cobalt-chromium crowns had clinically acceptable marginal fitness from both the CAD/CAM and lost-wax techniques; however, the lost-wax group showed lower marginal discrepancy after cementation according to SEM.

The restoration of root filled teeth: a review of the clinical literature

Clinicians often face dilemmas regarding the most appropriate way to restore a tooth following root canal treatment. Whilst there is established consensus on the importance of the ferrule effect on the predictable restoration of root filled teeth, other factors, such as residual tooth volume, tooth location, number of proximal contacts, timing of the definitive restoration and the presence of cracks, have been reported to influence restoration and tooth survival. The continued evolution of dental materials and techniques, combined with a trend towards more conservative endodontic-restorative procedures, prompts re-evaluation of the scientific literature. The aim of this literature review was to provide an updated overview of the existing clinical literature relating to the restoration of root filled teeth. An electronic literature search of the PubMed, Ovid (via EMBASE) and MEDLINE (via EMBASE) databases up to July 2020 was performed to identify articles that related the survival of root filled teeth and/or restoration type. The following and other terms were searched: restoration, crown, onlay, root canal, root filled, post, clinical, survival, success. Wherever possible, only clinical studies were selected for the literature review. Full texts of the identified articles were independently screened by two reviewers according to pre-defined criteria. This review identifies the main clinical factors influencing the survival of teeth and restorations following root canal treatment in vivo and discusses the data related to specific restoration type on clinical survival.

Ultrastructure of cell trafficking pathways and coronavirus: how to recognise the wolf amongst the sheep

The severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) pandemic has resulted in an urgent need to understand the pathophysiology of SARS-CoV-2 infection, to assist in the identification of treatment strategies. Viral tissue tropism is an active area of investigation, one approach to which is identification of virus within tissues by electron microscopy of post-mortem and surgical specimens. Most diagnostic histopathologists have limited understanding of the ultrastructural features of normal cell trafficking pathways, which can resemble intra- and extracellular coronavirus; in addition, viral replication pathways make use of these trafficking pathways. Herein, we review these pathways and their ultrastructural appearances, with emphasis on structures which may be confused with coronavirus. In particular, we draw attention to the fact that, when using routine fixation and processing, the typical 'crown' that characterises a coronavirus is not readily identified on intracellular virions, which are located in membrane-bound vacuoles. In addition, the viral nucleocapsid is seen as black dots within the virion and is more discriminatory in differentiating virions from other cellular structures. The identification of the viral replication organelle, a collection of membranous structures (convoluted membranes) seen at a relatively low scanning power, may help to draw attention to infected cells, which can be sparse. © 2020 The Authors. The Journal of Pathology published by John Wiley & Sons, Ltd. on behalf of The Pathological Society of Great Britain and Ireland.

Surface Roughness of Milled Lithium Disilicate With and Without Reinforcement After Finishing and Polishing: An In Vitro Study

PURPOSE

To determine the efficacy of various finishing and polishing techniques on the surface roughness of two computer-aided design/computer-aided manufacturing (CAD/CAM) materials, lithium disilicate (IPS e.max), lithium disilicate reinforced with lithium aluminosilicate (Straumann^® n!ce™), and a stackable low-fusing nanofluorapatite glass ceramic (Ceram).

MATERIALS AND METHODS

Flat specimens (n = 12) per treatment group were fabricated 2 mm thick, 15 mm in length, and 12mm in width. Samples were either glazed or polished. Glazing was accomplished with either Ivoclar IPS e.max CAD crystall glaze spray or IPS e.max Ceram glaze paste, according to manufacturer instructions. Three different polishing systems were tested: Brasseler Dialite HP, Ivoclar OptraFine, and Komet LD/ZR. Polishing was performed using a Kavo adjustable slow speed electric contra-angle handpiece mounted to an oscillating Toothbrush Dentifrice Assessment Instrument. Surface roughness data was collected using a benchtop stylus profilometer and analyzed for statistical significance using two-way ANOVA (α = 0.05). Representative scanning electron micrograph images were generated for all samples.

RESULTS

Overall there was no significant difference in Ra when comparing types of ceramic (p = 0.9315, F = 0.071). However, there was a statistically significant difference when comparing groups of finishing treatments (p < 0.001, F = 113.5) and also when comparing finishing treatment with ceramic type (p < 0.001, F = 11.13). No significant difference was found with IPS e.max CAD crystall glaze spray on Straumann^® n!ce™ versus IPS e.max Ceram glaze paste on IPS e.max Ceram (p = 0.8745) or IPS e.max CAD crystall glaze spray on IPS e.max versus IPS e.max Ceram glaze paste on IPS e.max Ceram (p = 0.3373). Significant differences in Ra of Straumann^® n!ce™ were found when comparing Brasseler with Ivoclar (p = 0.0014) and Ivoclar with Komet (p = 0.047). No significant difference was observed between Brasseler and Komet (p = 0.8099).

CONCLUSIONS

It appears that the degree of surface roughness depends upon the specific finishing system and ceramic combination used. Straumann^® n!ce™ is more efficiently polished using Brasseler Dialite HP or Komet LD/ZR polishing systems. Ivoclar crystal glaze spray was found to be equally as effective on Straumann^® n!ce™ and IPS e.max as IPS e.max Ceram glaze paste on IPS e.max Ceram.

The color stability and wear resistance of provisional implant restorations: A prospective clinical study

Objectives

The aim of the present clinical study was to determine the stability of color and resistance against abrasion and attrition of provisional single implant restorations.

Material and Methods

A group of 16 patients were treated with provisional crowns made of Telio CAD. Shortly before the insertion the crowns were photographed and scanned using a 3D‐laser scanner. After 8 weeks of clinical usage, the crowns were photographed and scanned again. The vertical occlusal wear and color changes between the restorations were measured.

Results

The occlusal plane of the original crown showed a statistically significant reduction of 0.052 mm ± 0.037 mm 8 weeks after placement (p < .05). For the stability of color, a change in red, green and blue was described. All three scopes (red, green and blue) showed a statistically significant reduction (p < .05).

Conclusions

This prospective clinical study showed that Telio CAD experienced a significant occlusal reduction and color change after an intraoral placement of 8 weeks.

Wear in Antagonist Teeth Produced by Monolithic Zirconia Crowns: A Systematic Review and Meta-Analysis

BACKGROUND

The aim of this systematic review and meta-analysis was to determine the wear sustained in the natural antagonist tooth in cases of full-coverage fixed-base prosthetic restorations or monolithic zirconia tooth-supported crowns, as well as to determine the wear in the restoration itself, both in the short- and medium-term and considering the factors that may influence wear.

MATERIAL AND METHODS

A systematic literature review and meta-analysis, based on Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) recommendations, of clinical studies that evaluated wear in antagonist teeth in relation to fixed-prosthesis monolithic zirconia crowns. A total of 5 databases were consulted in the literature search: Pubmed-Medline, Cochrane, Scopus, Embase and Web of Science (WOS). After eliminating duplicated articles and applying the inclusion criteria, eight articles were selected for the qualitative analysis and four for the quantitative analysis.

RESULTS

Mean maximum wear of the antagonist tooth in relation to monolithic zirconia crowns of magnitude 95.45 µm (CI at 95% 79.57-111.33) was observed. By using a meta-regression model (R2 = 0.92) the significant effect of time in maximum wear rate (p < 0.001) was observed, estimated at 6.13 µm per month (CI at 95% 3.99-8.27). Furthermore, monolithic zirconia crowns are subject to a mean maximum wear of 58.47 µm (CI 95% 45.44-71.50). By using a meta-regression model (R2 = 0.53) the significant effect of time in the maximum wear value was observed (p = 0.053), estimated at 3.40 µm per month (CI al 95% -0.05-6.85).

CONCLUSIONS

Monolithic zirconia crowns lead to a progressive maximum wear of the antagonist tooth over time which is greater than the maximum wear sustained in the crown itself. It is not possible to establish an objective and quantitative objection in relation to natural enamel wear or metal-ceramic crowns.

Modification Tests to Optimize Highway Construction in Crown of Slate Random Embankments with Compaction Quality Control

The compaction control of random fills has developed very little due to the limitations of particle sizes, with methods usually using a simple procedural control. In order to develop new quality control procedures for random slate filling, the necessary field work and laboratory tests were carried out. New test procedures for wheel-tracking or settlement tests have been successfully investigated. A total of 4500 in situ measurements of density and 580 topographic settlements, 960 wheel-tracking trolley tests and more than 130 slab rolling tests have been determined. An analysis of variance (ANOVA) has been carried out, obtaining correlations between tests in order to replace the deductibles. The variables that were used to analyze variance were the average lot density, the average settlement between last and first roller pass, the average wheel impression after test carriage, the first vertical modulus of the plate bearing test (PLT), the second vertical modulus of the PLT and the relation between second and first modulus of the PLT. The research proposes a new procedure for the quality control of the compaction of the randomized slate filling used in the crown area.

A comparison of the marginal gaps of lithium disilicate crowns fabricated by two different intraoral scanners

BACKGROUND

The purpose of this study was to assess marginal gaps of CAD/CAM lithium disilicate crowns constructed using two different intraoral scanners of different generations.

METHODS

Twenty four Columbia model lower left molars were prepared for lithium disilicate crowns in a simulated environment by undergraduate students. The crown preparations were scanned by E4D and Trios 3 intraoral scanners and CAD/CAM lithium disilicate crowns designed and manufactured. The crowns were seated onto the original crown preparations and three vertical marginal gap measurements taken at four locations (mid-buccal, mid-lingual, mid-mesial and mid-distal) using a stereomicroscope. The mean marginal gap (MMG) was calculated for each crown and each individual tooth surface.

RESULTS

The MMG was not statistically significantly different for the Trios 3 and E4D scanners (P = 0.111). There was no statistically significant effect of measurement location on the tooth on the marginal gap (P = 0.1134).

CONCLUSIONS

There was no difference in the MMGs of CAD/CAM lithium disilicate crowns constructed using two different intraoral scanners of different generations. Within the limitations of this study, the advances in scanning technology have produced small and insignificant improvements in the accuracy of crown margins.

Cementation of Tooth-colored Restorations - A Survey among Dentists in Germany

Purpose: To survey dentists in Germany regarding their preferred cementation regimen for fixed dental prostheses (FDPs) fabricated from various restorative materials. Materials and Methods: An online survey was developed for completion by dentists in Germany between 08/2019 and 02/2020. The questionnaire gathered information about the cementation regimen (conventional, including the acid-base cements zinc-oxide phosphate or any glass-ionomer cement; self-adhesive; adhesive; don’t know) that the participant would preferably select for the insertion of single- or multi-unit FDPs fabricated from various restorative materials. Data were also collected on demographic and personal characteristics. Results: A total of 721 dentists completed the survey, and the data from 688 questionnaires were included in the analysis. Conventional cementation was the option of choice for restorations fabricated from alloy/porcelain-fusedto- metal among 91.0% of the participants and for restorations fabricated from polycrystalline ceramics among 42.9% of the participants. Adhesive cementation was preferred for restorations fabricated from feldspathic/leucitereinforced glass ceramics (77.9%), lithium-disilicate glass ceramics (67.5%), zirconia-reinforced lithium-silicate glass ceramics (42.0%), and CAD/CAM resin composites (63.8%). Uncertainties regarding the appropriate cementation protocol for restorations fabricated from CAD/CAM resin composites were reported by 15% of the participants. More than 20% of the participants selected a technique that is less or not at all recommended for the cementation of restorations fabricated from zirconia-reinforced lithium-silicate glass ceramic and CAD/CAM resin composites. Conclusion: The results of the survey suggest that dentists in Germany select the cementation regime depending on the restorative material. Some of the participating dentists selected cementation regimens that are less or not at all recommended for restorations fabricated from zirconia-reinforced lithium-silicate glass ceramic and CAD/CAM resin composites, or were not sure about the appropriate cementation protocol.

Pathologic root migration secondary to vertical root fracture and full-coverage crowns: a report of 3 cases

Occasionally, tooth fractures may demonstrate exaggerated pathologic root migration (PRM), often resulting in tooth loss. The early propagation of the root fracture may not be readily identifiable through clinical inspection and conventional radiographic imaging. Ultimately, increased root separation, isolated deep periodontal probing depth, and characteristic radiolucent changes may facilitate the diagnosis. This article describes 3 patients with unusual presentations of PRM in endodontically treated teeth restored with full-coverage crowns. One case illustrates the use of cone beam computed tomography for restorative assessment following root separation. Although it is efficacious to place crowns on most posterior endodontically treated teeth to maintain structural integrity, patients may remain at risk for catastrophic PRM and tooth loss. Timely extraction of teeth with hopeless PRM may minimize underlying bone resorption and the need for osseous regenerative procedures, ultimately improving the dental implant recipient site.