Wear of primary teeth caused by opposed all-ceramic or stainless steel crowns

Qualitative surface roughness of lithium disilicate endo-crown for pulpotomized primary molars

Rehabilitation of pulpotomized primary molars with an appropriate restoration is essential for recovering function and safeguarding the durability of the treatment. This study aimed to assess and compare the surface roughness of stainless steel (ST) crowns, zirconia (ZR) crowns, fiberglass (FG) crowns, and lithium disilicate (LD) endo-crowns as a restoration for pulpotomized primary molars also, evaluating the surface roughness of their antagonists. Sixty pulpotomized primary mandibular first molars were used for qualitative surface roughness evaluation and divided into four groups (n = 15/group) according to the crown type (group-ST, group-ZR, group-FG, group-LD). While the other sixty sound, unprepared primary maxillary first molars were used for evaluation of their surface roughness against the tested crowns. Specimens' preparation and cementation were carried out according to each crown type and manufacturer's instructions. The surface roughness was done using a two-body wear test. The data were statistically analyzed. All tested crowns showed an increased change in surface roughness, except group-ZR, which had the least change in surface roughness after mechanical wear with no statistically significant difference(P = 0.681). All crown types significantly increased the surface roughness of their antagonists after mechanical wear, except group-ST which showed insignificant affection (p ≥ 0.05). Zirconia crowns and lithium disilicate endo-crowns had the least change in surface roughness compared to other groups while SSCs showed the least tooth loss in the antagonist enamel.

Optimized 3D printed zirconia-reinforced leucite with antibacterial coating for dental applications

OBJECTIVES

This study aims to produce by robocasting leucite/zirconia pieces with suitable mechanical and tribological performance, convenient aesthetics, and antibacterial properties to be used in dental crown replacement.

METHODS

Leucite pastes reinforced with 12.5%, 25%, and 37.5% wt. ZrO2 nanoparticles were prepared and used to print samples that after sintering were characterized in terms of density, shrinkage, morphology, porosity, mechanical and tribological properties and translucency. A coating of silver diamine fluoride (SDF) and potassium iodide (KI) was applied over the most promising material. The material's antibacterial activity and cytotoxicity were assessed.

RESULTS

It was found that the increase of ZrO2 reinforcement up to 25% enhanced both microhardness and fracture toughness of the sintered composite. However, for a superior content of ZrO2, the increase of the porosity negatively affected the mechanical behaviour of the composite. Moreover, the composite with 25% ZrO2 exhibited neglectable wear in chewing simulator tests and induced the lowest wear on the antagonist dental cusps. Although this composite exhibited lower translucency than human teeth, it was three times higher than the ZrO2 glazed material. Coating this composite material with SDF+KI conferred antibacterial properties without inducing cytotoxicity.

SIGNIFICANCE

Robocasting of leucite reinforced with 25% ZrO2 led to best results. The obtained material revealed superior optical properties and tribomechanical behaviour compared to glazed ZrO2 (that is a common option in dental practice). Moreover, the application of SDF+KI coating impaired S. aureus proliferation, which anticipates its potential benefit for preventing pathogenic bacterial complications associated with prosthetic crown placement.

Strength and Surface Characteristics of 3D-Printed Resin Crowns for the Primary Molars

Some resin polymers available for three-dimensional (3D) printing are slightly elastic, which may be advantageous when used for full crown coverage of the primary teeth. This study was performed to evaluate the mechanical properties of two types of 3D-printed resin crowns in terms of strength and surface characteristics. Polymer resins used for temporary crowns (TCs) and temporary flexible dentures (TFDs) were tested. Digitally designed crowns with different thicknesses (0.4 and 0.6 mm) were 3D-printed. Milled zirconia crowns were used as the control. The static and dynamic fracture loads of the crowns were measured. The crown surface was evaluated using scanning electron microscopy. The average strength did not differ between the types of crowns. The differences between the dynamic and static fracture loads were insignificant. In the TC group, thicker crowns showed lower strength both under static and dynamic loads. After thermomechanical loading, microcracks and dropouts of macrofillers were detected on the surface of all types of resin crowns. The deposition of abraded debris occurred more in the TFD group. The 3D-printed resin crowns were thought to endure biting forces in children. However, some limitations of the material itself should be improved for consideration as a new treatment option in pediatric dentistry.

Feasibility study and material selection for powder-bed fusion process in printing of denture clasps

BACKGROUND AND OBJECTIVE

The retention of selective laser melting (SLM)-built denture clasps is inferior to that of cast cobalt-chromium (Co-Cr) clasps engaging 0.01-in undercuts, which are commonly used in clinical practice. Either the clasps engage in excessively deep undercuts or inappropriate printing process parameters are applied. With appropriate undercut engagement and levels of process parameters, the retention of SLM-built clasps (including Co-Cr, commercially pure titanium [CP Ti], and Ti alloy [Ti-6Al-4V] ones) may be comparable to that of cast Co-Cr clasps. Therefore, this feasibility study aimed to evaluate their retention to guide dentists during material selection for the powder-bed fusion process during the printing of denture clasps.

METHODS

We engaged the clasp arm at an appropriate undercut depth (0.01 or 0.02 in), built clasps at the orientation of their longitudinal axes approximately parallel to the build platform, generated square prism support structures at a critical overhang angle of 30°, applied optimized laser parameters (laser power, scan speed, and hatch space), and adopted annealing treatment for Co-Cr, CP Ti, and Ti-6Al-4V clasps. After postprocessing and accuracy measurement, an insertion/removal test of the clasps for 15,000 cycles was performed to simulate 10 years of clinical use, and the retentive force was recorded every 1500 cycles. Permanent deformation of the retentive arms of the clasps was measured. Cast Co-Cr clasps engaging 0.01-in undercuts were designated the control group.

RESULTS

The initial retentive forces of the SLM-built Co-Cr clasps engaging 0.01-in undercuts and CP Ti and Ti-6Al-4V clasps engaging 0.02-in undercuts were comparable to those of the control group. SLM-built Co-Cr clasps engaging 0.01-in undercuts and Ti-6Al-4V clasps engaging 0.02-in undercuts had similar final retentive force and less permanent deformation compared with those of the control group; SLM-built CP Ti clasps engaging 0.02-in undercuts had lower final retentive force and greater permanent deformation.

CONCLUSIONS

Considering the long-term retention and permanent deformation of the retentive arms, Co-Cr and Ti-6Al-4V alloys, except CP Ti, are recommended for printing denture clasps. SLM-built Co-Cr clasps should engage 0.01-in undercuts, and Ti-6Al-4V clasps should engage 0.02-in undercuts.

Expert consensus on clinical management for early childhood caries

Early childhood caries (ECC) is the most prevalent chronic oral disease and one of the worldwide public health problems of great urgency for children. ECC can affect children's teeth, dentition, craniomaxillofacial, and general health and development. Therefore, through dental caries etiologies and caries risk assessment, patient-centered, personalized planning and a combination of prevention and treatment should be implemented in the clinical management for ECC. Periodic and continuous cycle management can only be accomplished with the cooperation of medical staff, children, and their guardians. This expert consensus will expound the clinical management of ECC in the following aspects: caries risk assessment, early clinical prevention, treatment strategies, and postoperative management.

Evaluation of intaglio surface trueness, wear, and fracture resistance of zirconia crown under simulated mastication: a comparative analysis between subtractive and additive manufacturing

PURPOSE

This in-vitro analysis aimed to compare the intaglio trueness, the antagonist's wear volume loss, and fracture load of various single-unit zirconia prostheses fabricated by different manufacturing techniques.

MATERIALS AND METHODS

Zirconia crowns were prepared into four different groups (n = 14 per group) according to the manufacturing techniques and generations of the materials. The intaglio surface trueness (root-mean-square estimates, RMS) of the crown was measured at the marginal, axial, occlusal, and inner surface areas. Half of the specimens were artificially aged in the chewing simulator with 120,000 cycles, and the antagonist's volume loss after aging was calculated. The fracture load for each crown group was measured before and after hydrothermal aging. The intaglio trueness was evaluated with Welch's ANOVA and the antagonist's volume loss was assessed by the Kruskal-Wallis tests. The effects of manufacturing and aging on the fracture resistance of the tested zirconia crowns were determined by two-way ANOVA.

RESULTS

The trueness analysis of the crown intaglio surfaces showed surface deviation (RMS) within 50 µm, regardless of the manufacturing methods (P = .053). After simulated mastication, no significant differences in the volume loss of the antagonists were observed among the zirconia groups (P = .946). The manufacturing methods and simulated chewing had statistically significant effects on the fracture resistance (P < .001).

CONCLUSION

The intaglio surface trueness, fracture resistance, and antagonist's wear volume of the additively manufactured 3Y-TZP crown were clinically acceptable, as compared with those of the 4Y- or 5Y-PSZ crowns produced by subtractive milling.

Clinical Evaluation of Stainless Steel Crown versus Zirconia Crown in Primary Molars: An In Vivo Study

Aim

Materials and methods

Results

Conclusion

Clinical significance

How to cite this article

Wear and marginal quality of aesthetic crowns for primary molars

BACKGROUND

Due to limited aesthetics of stainless-steel crowns, the demand for tooth-coloured crowns has recently risen. Few studies have investigated the marginal integrity and wear behaviour of tooth-coloured primary molar crowns under subcritical load in vitro.

AIM

This in vitro study evaluated the marginal quality and wear of newly introduced resin composite and hybrid ceramic crowns compared with metal and zirconia crowns.

DESIGN

Metal, resin composite, hybrid ceramic (CAD/CAM), and various zirconia crowns were investigated. After thermomechanical loading (2,500 thermocycles/100,000 × 50N), marginal quality of luting gaps and wear of crowns/antagonists were evaluated using replicas under a light or 3D laser scanning microscope. Results were analysed with the Mann-Whitney U test or one-way ANOVA (p < .05).

RESULTS

Marginal quality of the new resin composite and hybrid ceramic crowns performed well in comparison with SSC and zirconia crowns. Adhesive bonding of crowns resulted in superior marginal seal compared with conventional GIC (Mann-Whitney U test, p < .05). Regarding wear, zirconia crowns exhibited significantly worse results than resin composite or hybrid ceramic crowns and SSCs (ANOVA, p < 0.05).

CONCLUSION

The new resin composite and hybrid ceramic crown exhibited good performance in comparison with SSCs and zirconia crowns considering both wear and marginal quality after subcritical loading.

Clinical Evaluation of CAD/CAM Ceramic Endocrown Versus Prefabricated Zirconia Crown in the Restoration of Pulpotomized Primary Molars: A Two-Year Spilt-Mouth Randomized Controlled Trial

Objectives  The current trial aimed to compare lithium disilicate (LS2) endocrowns' clinical performance, gingival health, and parental satisfaction to those of prefabricated zirconia crowns (ZCs) over a 24-month of follow-up.

Materials and Methods  This study designed as a spilt-mouth randomized controlled trial. A total of 88 pulpotomized mandibular second primary molars of 44 children were assigned into two equal groups. Forty-four molars were restored with prefabricated primary ZCs (control group) and the same number were restored with LS2 endocrown (intervention group). Clinical performance and gingival status were evaluated using a modified United States Public Health Service criterion, and plaque and gingival indices. Parental satisfaction was assessed using a 5-point Likert-scale questionnaire.

Statistical Analysis  Paired data were analyzed using McNemar's test, a statistical test used on paired nominal data, and paired t -tests. The significance level was set to 5% at 95% confidence interval.

Results  Both restorations showed comparable gingival health status over the follow-ups. Marginal adaptation of the endocrowns and ZCs at the end of follow-up was 95.5 and 90.9%, respectively ( p  = 0.68). For marginal integrity and discoloration, both restorations showed similar results at the follow-ups. The overall parental satisfaction of both groups was statistically insignificant ( p  = 0.07). However, parents were more satisfied with the endocrown color over that of the ZC ( p  < 0.05).

Conclusion  Endocrowns' clinical performance and gingival health were comparable to those of ZCs. For both restorations, parental satisfaction was nearly similar except for the color that showed an advantage in favor of the endocrowns.

Zirconia crowns for children: A systematic review

BACKGROUND

Preformed metal crowns (PMCs) have been the restoration of choice for paediatric dentistry; however, PMCs have a non-aesthetic appearance, which has become a point of concern. Recently, prefabricated zirconia crowns (PZCs) have been increasingly used as an aesthetic restorative material for primary teeth, as they have pleasing properties.

AIM

This systematic review summarises the clinical results for PZCs in the primary dentition, including wear on the opposing dentition, retention, fracture resistance, parental satisfaction, gingival health, and cementation materials.

MATERIALS AND METHODS

Electronic database searches were conducted using PubMed, Google Scholar, Web of Science, and the Cochrane Library. Clinical trials, observational studies, and case reports/series were included. The quality of the studies was analysed using the Cochrane tool and the domain-based evaluation for non-randomised studies of interventions.

RESULTS

The search retrieved 166 references, of which 14 studies were included for qualitative analyses. The risk of bias varied from low to unclear. The included studies indicated that prefabricated zirconia crowns are retentive and are not associated with accelerated wear on the opposing dentition. They also exhibit a high fracture resistance, satisfy the parents and are compatible with gingival health. There is, however, inconclusive evidence with regard to cementation materials.

CONCLUSION

Prefabricated Zirconia Crowns appear to be a good alternative to preformed metal crowns in term of esthetics, retention, resistance to fracture, parent satisfaction, and gingival health.

Ex Vivo Assessment of Natural Teeth Wear against Zirconia and Novel Glass-Fiber-Reinforced Composite Crowns in Primary Teeth by a Three-Dimensional Assessment Method

Objectives. The main purpose of the study was to assess the material wear, antagonistic natural primary teeth wear, and microhardness of zirconia (ZR), a recently launched novel glass-fiber-reinforced composite crown (GFRC). The research question was, are these aesthetic crowns resulting in antagonistic natural primary tooth wear and the crown material itself? Methods. Forty-five primary canines were divided into three groups (15 per group) and mounted against Zr (Group A), GFRC (Group B), and natural teeth as control (Group C) in the wear test machine. All samples were assessed for surface wear with pre- and post-3-dimensional scanning. In addition, microhardness was assessed for all three groups. Results. The mean microhardness value for the Zr disc was 1157 ± 7 HV; for the GFRC disc, it was 29.35 ± 2 HV; while with natural teeth, it was 105 ± 4 HV. There was a statistically significant difference in teeth wear in the prescan and postscan in the natural tooth ( $p<0.05$ ) group, highly significant difference ( $p<0.001$ ) in the ZR group, and no significant difference in the GFRC group. Conclusion. There is more significant wear loss of glass-fiber-reinforced composite discs as compared to zirconia. In addition, the wear of the antagonistic tooth with zirconia and natural teeth is more remarkable than with GFRC. There is a vast difference of microhardness between natural teeth and zirconia (almost 10 times higher) which suggests further scope of study. Clinical Relevance. Pediatric dentistry deals with the transition of dentition from primary to permanent through mixed dentition. Selection of restorative material needs to be done cautiously when we are dealing with primary teeth and young permanent teeth as antagonistic teeth. Wear of the crown material itself and opposing natural teeth are essential factors that should be considered in selecting crowns in clinical practice. The present study results can be extrapolated to clinical practice, and the practitioner can consider various factors in selecting full-coverage crowns for primary teeth. The vast difference in aesthetic crowns and natural teeth microhardness indicates a further need for research. Additionally, there is no literature published for the recently launched GFRCs.

Can zirconia crowns be the first restorative choice after endodontic treatment of primary teeth?

OBJECTIVE

Early loss of primary teeth due to caries can cause temporary or permanent problems, such as occlusion disorders, aesthetic problems, nutritional problems, abnormal habits, and speech disorders. Although the development of restorative materials has led to significant improvements, failures are still frequent. The purpose of this study was to evaluate the success rates of zirconia crowns compared to other crowns for the restoration of endodontically treated teeth with excessive loss of material.

METHODS

A total of 45 teeth of patients aged under 10 years, including primary molars and anterior teeth, requiring restoration after root canal treatment, were included in this randomized, non-blinded clinical study. Stainless steel (SSC), zirconia (ZC), and strip (SC) crowns were used and compared clinically and radiographically during a six-month follow-up period. Parents were asked to fill out a questionnaire at one week and six months to evaluate the parent and child satisfaction levels. The patients' pain and discomfort levels were assessed using a visual analogue scale. The Mann-Whitney U, Chi-Squared and Friedman and Cochran Q tests were used for statistical comparisons using IBM SPSS Statistics version 23 (IBM, Armonk, NY, USA).

RESULTS

The six-month follow-up evaluations revealed no significant differences in clinical outcomes between the SSC, ZC, and SC groups. There were no significant differences between the groups with respect to parent and child satisfaction.

CONCLUSION

The clinical outcomes of ZCs were comparable to those of the other crowns. ZCs could be a choice for aesthetic purposes, with the disadvantage of a higher cost.

Wear evaluation of CAD-CAM dental ceramic materials by chewing simulation

PURPOSE

To evaluate the wear of computer-aided design/computer-aided manufacturing (CAD-CAM) dental ceramic materials opposed by enamel as a function of increased chewing forces.

MATERIALS AND METHODS

The enamel cusps of healthy human third molar teeth (n = 40) opposed by materials from CAD-CAM dental ceramic groups (n = 10), including Vita Enamic® (ENA), a polymer-infiltrated ceramic network (PICN); GC Cerasmart® (CERA), a resin nanoceramic; Celtra® Duo (DUO), a zirconia-reinforced lithium silicate (ZLS) ceramic; and IPS e.max ZirCAD (ZIR), a polycrystalline zirconia, were exposed to chewing simulation (1,200,000 cycles; 120 N load; 1 Hz frequency; 0.7 mm lateral and 2 mm vertical motion). The wear of both enamel cusps and materials was quantified using a 3D laser scanner, and the wear mechanisms were evaluated by scanning electron microscopy (SEM). The results were analysed using Welch ANOVA and Kruskal Wallis test (α = .05).

RESULTS

ZIR showed lower volume loss (0.02 ± 0.01 mm³) than ENA, CERA and DUO (P = .001, P = .018 and P = .005, respectively). The wear of cusp/DUO [0.59 mm³ (0.50-1.63 mm³)] was higher than cusp/CERA[0.17 mm³ (0.04-0.41 mm³)] (P = .007). ZIR showed completely different wear mechanism in SEM.

CONCLUSION

Composite structured materials such as PICN and ZLS ceramic exhibit more abrasive effect on opposing enamel due to their loss against wear, compared to uniform structured zirconia. The resin nanoceramic causes the lowest enamel wear thanks to its flexible nano-ceramic microstructure. While zirconia appears to be an enamel-friendly material in wear volume loss, it can cause microstructural defects of enamel.

Influence of masticating cycles and chewing patterns on inadvertent enamel wear caused by zirconia brackets

Little information is available about enamel wear caused by zirconia brackets, an inadvertent side effect of orthodontic treatment. The purpose of this study was to examine potential enamel damage induced by contact with zirconia brackets. Sliding and impact wear simulations were performed using bovine enamel specimens positioned at a 25° slant to a zirconium ball to determine wear behaviour. Different chewing patterns, tapping and grinding, were simulated. Specimens were profiled using confocal laser scanning microscopy, and the mean maximum depth and surface roughness were measured. Scanning electron microscopy was also performed. The mean maximum depth of wear values differed according to the number of mastication cycles, with a higher number of cycles producing higher depths of wear. The facet wear depth was significantly greater with the tapping pattern than with the grinding pattern. Scanning electron microscopic observation of the wear facets revealed that surface textures at the edges were rougher than those at the centre of all facets. The results of this study indicated that enamel wear was induced by contact with zirconia brackets during the early period of mastication, and that the patterns and number of cycles of mastication affected the wear progression of enamel.

Management of Amelogenesis Imperfecta in Childhood: Two Case Reports

Amelogenesis imperfecta (AI) is defined as an interruption of enamel formation due to genetic inheritance. To prevent malfunction of the masticatory system and an unaesthetic appearance, various treatment options are described. While restoration with a compomer in the anterior region and stainless steel crowns in the posterior region is recommended for deciduous dentition, the challenges when treating such structural defects in mixed or permanent dentition are changing teeth and growing jaw, allowing only temporary restoration. The purpose of this case report is to demonstrate oral rehabilitation from mixed to permanent dentition. The dentition of a 7-year-old patient with AI type I and a 12-year-old patient with AI type II was restored under general anesthesia to improve their poor aesthetics and increase vertical dimension, which are related to problems with self-confidence and reduced oral health quality of life. These two cases show the complexity of dental care for structural anomalies of genetic origin and the challenges in rehabilitating the different phases of dentition.

Use of Restorative Full Crowns Made with Zirconia in Children: A Systematic Review

Aim and objective

The purpose of this systematic review is to analyze the suitability of the zirconia crowns for restoration of damaged primary teeth in children.

Background

This systematic review has been conducted in line with the preferred reporting items for systematic reviews (which is also called as PRISMA) guidelines. A search for the relevant articles of zirconia crowns in deciduous teeth has been made in electronic database of PubMed and a study design (meta-analysis), i.e., PICOS framework. The words used in the search are “zirconia crowns” and “primary molars,” “zirconia crowns” and “primary incisors,” “zirconia crowns” and “children,” “zirconia crowns” and “primary teeth.”

Review results

The database search showed 44 studies of which 20 articles were excluded as they were irrelevant, duplicates, and data were not available. In the present systematic review, the remaining 24 articles were included.

Conclusion

Zirconia crowns have been proved with better results than other crowns in terms of gingival and periodontal health, esthetics, and crown fractures. However, the quantity of tooth preparation and the wear of antagonist tooth are reported to be more in case of zirconia crowns. Future randomized control studies should be carried out in primary teeth due to less number of randomized studies on this topic.

Clinical significance

Zirconia crowns are now widely used in dentistry and there is an increase in the number of studies, so a systematic review evaluating and comparing results is warranted.

How to cite this article

Ajayakumar LP, Chowdhary N, Reddy VR, et al. Use of Restorative Full Crowns Made with Zirconia in Children: A Systematic Review. Int J Clin Pediatr Dent 2020;13(5):551–558.

Evaluation and comparison two types of prefabricated zirconia crowns in mixed and primary dentition: A randomized clinical trial

Introduction

Prefabricated zirconia crowns are available to treat anterior and posterior primary teeth, which possess high resistance, long durability, and short working time. They are also esthetic and available in various sizes for all primary teeth. However, their high costs can present a clear disadvantage in many communities around the world.

Materials and methods

This random clinical trial study sample included 63 crowns (31 CCZC, 32 NZC) applied to 44 children aged five to nine years with zirconia crowns placed on anterior or posterior primary teeth. Group (1): Locally manufactured crowns were created with different measurements by using CAD/CAM (CCZC) and Group (2): NuSmile® zirconia crowns (NZC). Glass ionomer cement was used to cement all crowns. The children were followed-up at one, three, and six months, using oral hygiene index-simplified (OHI–S), gingival index (GI), plaque index (PI), bleeding on probing (BOP), and crown margin extension. Statistical analyses used: Mann-Whitney U test, Friedman test, and Wilcoxon test.

Results

This study showed that CCZC did not cause gingival changes after crown application in clinical tissue appearance, bleeding, and gingival recession. Reduced plaque accumulation was observed during follow-up periods. Finally, there was no statistically significant difference between CCZC and NZC, according to this study.

Conclusions

CCZCs are a convenient and economical option to achieve esthetic, healthy, and functional aspects during restoring primary teeth.

Zirconia vs. stainless steel pediatric crowns: a literature review

The aim of this review was to assess efficacy and acceptance of aesthetic zirconia crowns (ZCs) compared to the traditionally employed stainless steel crowns (SSCs) for primary teeth restoration. A comprehensive literature search was completed for the relevant keywords in Scopus and Medline databases. Resulting article abstracts and full texts were screened to determine final inclusion. Eighteen articles were included from the initial search. There is still little evidence to support the use of one type of crowns over another for primary teeth, in particularly for ZCs, lately introduced in pediatric restoration. The gold standard for restoring decayed primary teeth is still represented by SSCs, despite the growing importance of the aesthetic issue related to their use. Aesthetic ZCs resulted in having adequate properties to be employed for the treatment of decayed primary teeth, such as mechanical resistance, limited plaque adhesion, wear behavior and natural appearance. There is still a paucity of literature clinically evaluating the efficacy of ZCs for primary teeth restoration, but they can be considered a promising alternative to SSCs. This field of research has to be more deeply explored to improve dental care in children affected by early childhood caries.

Monolithic and Minimally Veneered Zirconia Complications as Implant-Supported Restorative Material: A Retrospective Clinical Study up to 5 Years

Objective

Long-term clinical data on the success and complication rates of monolithic or minimally veneered zirconia implant-supported restorations are lacking. Hence, the purpose of this retrospective clinical study was to analyze the complications of monolithic or partially veneered zirconia implant-supported restorations up to 5 years follow-up. Material and Methods. Single crowns, bridges, and full-arch rehabilitations were included. The selection process was achieved by reviewing data from the prosthetic laboratory and excluding cases in which zirconium and full-ceramic coating restorations were used. A total of 154 restorations were included (82 monolithic and 72 with buccal ceramic stratification). All the complications encountered, and the solutions applied, were explained.

Results

A total of 93 restorative units had a follow-up of between 24 and 60 months, and 61 restoration units had a follow-up of between 12 and 24 months. A total of 7 complications were encountered (14.58% of cases; 95.45% per prosthetic unit). The technical complication rate was 2.08% (one case of minor chipping in one prosthetic unit); regarding the mechanical complications, four decementations (8.33% of the cases) and two screw loosening (4.17% of the cases) were encountered.

Conclusions

Considering the limitations of this study, it can be concluded that monolithic or partially veneered zirconia implant-supported restorations have a good clinical behavior during a follow-up period of up to 5 years.

Tribological performance of the pair human teeth vs 3D printed zirconia: An in vitro chewing simulation study

This study aims to evaluate the tribological performance of the pair human teeth/robocasted zirconia, with a special focus on the enamel wear mechanisms. Zirconia pieces produced by robocasting (RC) and unidirectional compression (UC) were compared in terms of crystalline structure, density, porosity, hardness and toughness. Chewing simulation tests were performed against human dental cusps. The cusps wear was quantified and the wear mechanisms identified. Although most of the properties of UC and RC samples are similar, differences were observed for surface roughness and porosity. Although the samples did not suffer wear, the antagonist cusps worn in a similar way. In conclusion, robocasting seems a promising technique to produce customized zirconia dental pieces, namely in what concerns the overall tribological behaviour.

A State-of-the-Art Review on the Wear of the Occlusal Surfaces of Natural Teeth and Prosthetic Crowns

This review focuses on the wear mechanisms of natural and restorative dental materials, presenting a comprehensive description and analysis of the works published in the last two decades on the wear at the interface of occlusal surfaces. Different groups of tribological pairs were considered: tooth-tooth, tooth-restorative material (tooth-ceramic, tooth-resin-based-materials, and tooth-metal), and restorative-restorative materials. The lack of standardization of the wear tests impairs the direct comparison of the obtained results. However, it was possible to infer about the main wear mechanisms observed on the different classes of dental materials. Concerning ceramics, their toughness and surface finishing determines the wear of antagonist tooth. Abrasion revealed to be the main wear mechanisms at occlusal interface. In the case of resin-based composites, the cohesion of the organic matrix and the nature, shape, and amount of filler particles greatly influences the dental wear. The protruding and detachment of the filler particles are the main causes of abrasion of antagonist enamel. Metallic materials induce lower wear on antagonist enamel than the other classes of materials, because of their low hardness and high ductility. Most of the studies revealed plastic deformation and adhesive wear as the main wear mechanisms. Overall, more research in this area is needed for a better understanding of the mechanisms involved at the occlusal surfaces wear. This would be essential for the development of more suitable restoration materials.

Suitability of 3D printed pieces of nanocrystalline zirconia for dental applications

OBJECTIVES

The main goal of this work is to evaluate the suitability of nanostructured zirconia pieces obtained by robocasting additive manufacturing (AM), for dental applications.

METHODS

The density, crystalline structure, morphology/porosity, surface roughness, hardness, toughness, wettability and biocompatibility of the produced samples were compared with those of samples obtained by conventional subtractive manufacturing (SM) of a similar commercial zirconia material. Chewing simulation studies were carried out against dental human cusps in artificial saliva. The wear of the material was quantified and the wear mechanisms investigated, as well as the influence of glaze coating.

RESULTS

AM samples, that revealed to be biocompatible, are slightly less dense and more porous than SM samples, showing lower hardness, toughness and wettability than SM samples. After chewing tests, no wear was found both on AM and SM samples. However, the dental wear was significantly lower when AM samples were used as counterbody. Concerning the glazed samples, both coated surfaces and dental cusps suffered wear, being the cusps' wear higher than that found for unglazed samples. More, cusps tested against AM coated samples suffered less wear comparatively to those opposed to SM coated samples.

SIGNIFICANCE

Overall, the results presented in this paper show that AM processed nanostructured zirconia can be used in dental restorations, with important advantages from the point of view of processing and tribological performance. Moreover, the option for glaze finishing should be carefully considered both in SM and AM processed specimens.

Comparison of Different Cervical Finish Lines of All-Ceramic Crowns on Primary Molars in Finite Element Analysis

This study aimed to conduct a stress analysis of four types of cervical finish lines in posterior all-ceramic crowns on the primary roots of molar teeth. Four different types of finish lines (shoulder 0.5 mm, feather-edged, chamfer 0.6 mm, and mini chamfer 0.4 mm) and two all-ceramic crown materials (zirconia and lithium disilicate) were used to construct eight finite element primary tooth models with full-coverage crowns. A load of 200 N was applied at two different loading angles (0° and 15°) so as to mimic children’s masticatory force and occlusal tendency. The maximum stress distribution from the three-dimensional finite element models was determined, and the main effect of each factor (loading type, material, and finish line types) was evaluated in terms of the stress values for all of the models. The results indicated that the loading type (90.25%) was the main factor influencing the maximum stress value of the primary root, and that the feather-edged margin showed the highest stress value (p = 0.002). In conclusion, shoulder and chamfer types of finish lines with a 0.4–0.6 mm thickness are recommended for deciduous tooth preparation, according to the biomechanical analysis.

Comparative Evaluation of Physical and Mechanical Properties of Different Brands of Primary Molar Stainless-Steel Crowns: An In Vitro Study

BACKGROUND

There is some cases of perforation and undesirable properties of some primary molars stainless steel crowns.

AIM

The aim of this study was to compare the physical and mechanical properties of different commercial brands of these crowns.

METHODS

In an in vitro study, 10 stainless steel tooth crowns of the second primary mandibular molars size 6 of 4 different commercial brands (a total of 280 crowns) were evaluated. These crowns were included KTR Pre-trimmed and Crimped Nichro Stainless Steel Primary Molar Crowns (KTR, China); 3M Stainless Steel Primary Molar Crowns (ESPE, St paul; USA); NuSmile SSC Pre-contoured (Inc, Houstone, TX; USA) and Kids crown (Shinghung, Seoul; Korea). Corrosion and galvanic corrosion, wear, microhardness, compressive strength, fatigue strength of crowns and weight percent of elements were investigated.

RESULTS

The highest rate of microhardness, compressive and Fatigue strength of the crowns were made by Nu Smile > 3M > Kids Crown > KTR respectively. The highest rate of corrosion potential in corrosion and Galvanic corrosion tests was in KTR > Kids crowns > 3M > Nu smile respectively. The order of crown wear was KTR > Kids Crown > 3M > Nu Smile respectively. The highest amount of nickel element was found in the Nu Smile crown and the highest amount of chrome in the 3M crown with a significant difference with others (p < 0.001). The KTR and Kids crowns lacked molybdenum.

CONCLUSION

The results showed that Nu Smile crown has better physical and mechanical properties than other evaluated crowns in this study.

Monolithic Zirconia: An Update to Current Knowledge. Optical Properties, Wear, and Clinical Performance

The purpose of this paper was to update the knowledge concerning the wear, translucency, as well as clinical performance of monolithic zirconia ceramics, aiming at highlighting their advantages and weaknesses through data presented in recent literature. New ultra-translucent and multicolor monolithic zirconia ceramics present considerably improved aesthetics and translucency, which, according to the literature reviewed, is similar to those of the more translucent lithium disilicate ceramics. A profound advantage is their high strength at thin geometries preserving their mechanical integrity. Based on the reviewed articles, monolithic zirconia ceramics cause minimal wear of antagonists, especially if appropriately polished, although no evidence still exists regarding the ultra-translucent compositions. Concerning the survival of monolithic zirconia restorations, the present review demonstrates the findings of the existing short-term studies, which reveal promising results after evaluating their performance for up to 5 or 7 years. Although a significant increase in translucency has been achieved, new translucent monolithic zirconia ceramics have to be further evaluated both in vitro and in vivo for their long-term potential to preserve their outstanding properties. Due to limited studies evaluating the wear properties of ultra-translucent material, no sound conclusions can be made, whereas well-designed clinical studies are urgently needed to enlighten issues of prognosis and long-term survival.

Wear Characteristics of Dental Ceramic CAD/CAM Materials Opposing Various Dental Composite Resins

The aim of this study was to evaluate the wear properties of opposed dental ceramic restorative CAD/CAM materials and several posterior direct restorative composite resins. Three kinds of dental ceramics CAD/CAM materials (monolithic zirconia, lithium disilicate, leucite) and four dental composite resins—that is, MI Gracefil, Gradia Direct P, Estelite Σ Quick, and Filtek Supreme Ultra—were used in this study. For each of the 12 groups (three ceramics × four composite resins), five each of a canine-shaped ceramic specimen and a cuboidal shape opposing composite resin were prepared. All of the specimens were tested in a thermomechanical loading machine (50 N, 100,000 cycles, 5/55 °C). Wear losses of ceramic specimens and composite resin specimens were evaluated using a three-dimensional profiling system and an electronic scale, respectively. Statistical analyses were performed using the Kruskal–Wallis test and Mann–Whitney U test with Bonferroni’s correction. Zirconia showed significantly less volumetric loss than lithium disilicate or leucite regardless of composite resin type (p > 0.05/3 = 0.017), and that Estelite Σ Quick showed significantly more weight loss than Filtek Supreme Ultra, MI Gracefil, or Gradia Direct P regardless of ceramic type (p > 0.05/6 = 0.083). Zirconia showed less volumetric loss than lithium disilicate or leucite. Some composite resins opposing ceramics showed considerable weight loss.

Comparative study of the wear of the pair human teeth/Vita Enamic® vs commonly used dental ceramics through chewing simulation

Ceramic based prosthetic materials have been used in dental restorations due to their excellent aesthetic and biocompatibility. However, due to concerns related to their mechanical properties and abrasive action against natural teeth, a proper selection of these materials is crucial to preserve the occlusal interactions and prevent abnormal dental wear. The aim of this work is to compare the wear performance of Vita Enamic®, a polymer infiltrated ceramic (PIC), with that of other three commercial ceramic based dental materials - Zirconia, Leucite and Zirconia Veneered - when tested against natural teeth. The crystalline structure, wettability, topography and hardness of the prosthetic materials were characterized before wear testing. Chewing simulator experiments (360,000 cycles, load 49 N) against dental human cusps were carried out using artificial saliva as lubricant. The wear of both teeth and prosthetic materials was quantified and the involved wear mechanisms were analyzed by scanning electron microscopy. The results showed that Zirconia presented the most suitable tribological behavior, since it led to the lowest wear on both occlusal surfaces. The prosthetic material presenting the highest wear was Vita Enamic®. Regarding the cusps' wear, the highest values were found for both Leucite and Zirconia Veneered. Polishing wear was the main wear mechanism in Zirconia system (prosthetic material and opposing enamel), while in the remaining ones was fragile fracture associated with abrasive wear. No direct relation could be established between wettability, initial roughness and hardness of the prosthetic materials and the wear of the tribological systems. Contrarily, microstructure and toughness revealed to be critical parameters.

Guided tooth preparation for a pediatric zirconia crown

BACKGROUND AND OVERVIEW

Unesthetic primary incisors can produce negative self-perceptions in preschool-aged children. In recent years, because of increased esthetic demands, prefabricated zirconia crowns have become increasingly popular. However, zirconia crowns cannot be crimped, and the clinician must prepare the teeth to fit the zirconia crowns. Therefore, extended preparation and fitting times are necessary, especially for inexperienced practitioners. A 1- to 2-millimeter subgingival feather margin also is required. Gingival hemorrhage after subgingival preparation compromises the retention of zirconia crowns.

CASE DESCRIPTION

In this clinical report, the author presents a step-by-step description of the clinical and laboratory procedures for restoring a discolored traumatized incisor with a zirconia crown. The author used a polyvinyl siloxane occlusal registration material as an impression material and made 2 identical casts. The author fabricated 3 reduction guides after prospective tooth preparation on the casts. The author rapidly prepared the discolored incisor with the reduction guides and ultrasonic burs. A zirconia crown provided an optimal esthetic result and gingival health.

CONCLUSIONS AND PRACTICAL IMPLICATIONS

Because the reduction guides provided a visibility intraorally, fast tooth reduction, less trial placement, and passive adaptation of the crown were successful. Because the ultrasonic burs prevented gingival injuries, hemorrhage control was not necessary. The presented technique reduced the patient's discomfort and total chair time. Therefore, this alternative technique is helpful for inexperienced practitioners.

In Vitro Investigation of Wear of CAD/CAM Polymeric Materials Against Primary Teeth

The aim of the study was to evaluate the effects of polymeric computer-aided design/computer-aided manufacturing CAD/CAM materials on antagonistic primary tooth wear. Five CAD/CAM polymeric materials were examined: Vipi Block Monocolor (VBM), Yamahachi polymethylmethacrylate (PMMA) (YAP), Mazic Duro (MZD), Vita Enamic (ENA), and Pekkton (PEK). All of the specimens were tested in a thermomechanical loading machine with the primary canine as the antagonist (50 N, 1.2 × 10⁵ cycles, 1.7 Hz, 5/55 °C). The wear losses of the antagonist tooth and the restorative materials were calculated using reverse modelling software and an electronic scale. VBM and ENA showed significantly higher antagonist tooth wear than PEK (p < 0.05), but there was no significant difference observed among VBM, YAP, MZD, and ENA (p > 0.05). PEK showed the largest value in both material volumetric and weight losses. In terms of material volumetric losses, there was no significant difference between all of the groups (p > 0.05). In terms of material weight losses, PEK was significantly larger than ENA (p < 0.05), but there was no significant difference between VBM, YAP, MZD, and ENA (p > 0.05). Volumetric and weight losses of materials showed similar wear behaviour. However, the wear patterns of antagonists and materials were different, especially in PEK.

Prosthetics in Paediatric Dentistry

Premature loss of teeth in children may lead to both functional and esthetic problems. Missing teeth in both anterior and posterior regions may cause malfunctions in mastication and proper pronunciation. If the missing teeth are not replaced, further complications may occur, including adjacent tooth migration, loss of alveolar bone, and irregular occlusion. Considering the sensitive nature of children, loss of teeth may cause the development of insecurities and low self esteem problems. Due to dynamic nature of growth in children and adolescents, prosthetic appliances must not hinder development of orofacial system, and must meet adequate esthetic and functional standards. Dental prosthetic appliances in paediatrics must be planned with respect to the special conditions that led to tooth loss or damage. Multi-disciplinary approach is needed, under constant supervision of paediatric dentist and orthodontist, as well as regular checkups with clinical and radiographical examinations.