Types Of Crowns Research Articles

Three-dimensional fit of self-glazed zirconia monolithic crowns fabricated by wet deposition.

This study evaluated the 3-dimensional (3D) fit of self-glazed zirconia monolithic crowns fabricated by wet deposition, in comparison with milled zirconia and lithium disilicate monolithic crowns. Dual-scan protocol was used to assess the fit of crowns. Root mean squares (RMS) and uniformity index (UI) were calculated to describe the gap size and uniformity. The self-glazed zirconia crowns had significantly lower RMS values for the gaps at axial wall and transition regions than the milled zirconia crowns, and for the gaps at occlusal region than both milled crowns. All 3 types of crowns had comparable RMS values for the gaps at marginal and chamfer regions and comparable UI values for both marginal and internal gaps. The 3D fit of the self-glazed zirconia monolithic crowns was clinically acceptable and they exhibited better fit at occlusal region than the milled crowns.

Comparative evaluation of the fracture resistance of newly developed prefabricated fibreglass crowns and zirconium crowns.

Prefabricated fibreglass crowns (PFCs) require less tooth structure reduction than prefabricated zirconium crowns (PZCs) for restoring primary molars. Little is known, however, about their mechanical properties. To investigate the fatigue survival and fracture resistance of PZCs and PFCs cemented with two different types of luting cement [glass-ionomer cement (GIC) and resin-modified GIC (RMGIC)]. One hundred and twenty extracted human primary molars were randomly divided into subgroups (n=15) according to the crown type (PFCs/PZCs), the luting cement (GIC/RMGIC) and crowns subjected to the chewing simulation test with thermocycling mechanical loading (CSTTML). The surfaces of the teeth were reduced by approximately 2mm in the PZC group and 1mm in the PFC group. All the samples were subjected to fracture tests. None of the samples subjected to CSTTML exhibited signs of surface damage, fracture or premature debonding. The forces required to fracture PFCs were higher than those required for PZCs in all groups (p=.001). The highest mean fracture resistance values were obtained from the group of PFCs cemented with GIC that were subjected to the CSTTML (2515.8N±619.2N). PFCs presented high fatigue survival and could be used as alternatives to PZCs as they require less tooth structure reduction. Crowns cemented with GIC had a similar fracture resistance value when compared with RMGIC.

Results of a long-term study of introduced apple varieties in the conditions of the Southern Urals

The article presents long-term data on the study of introduced apple varieties. The experiment was carried out on the basis of the Orenburg branch of the Federal Scientific Center for Horticulture. The objects of research were the introduced winter-ripening apple varieties Anis Sverdlovskiy, Blagaya Vest’, VEM YArkij, Krasa Sverdlovska, Otlichnik, Pervoural’skoe, Rumyanka Sverdlovskaya, Samotsvet, Fermer, Ekrannoe, Bratchud (K), Kovrovoe 1, Kovrovoe 3, Bolotovskoe, Kandil’ Orlovskiy, Kulikovskoe. The planting scheme was 3.0x5.0 m. Modern industrial horticulture requires intensive orchards that meet a range of quality requirements: their early fruiting, restrained growth, compact crown type, active increase in yield, high commercial and consumer quality of fruits, reduction care costs compared to gardens on vigorous rootstocks. In this regard, the following features were studied: winter hardiness, tree height, crown diameter, bole circumference, precocity, and yield. After a critical winter, the most winter-hardy varieties turned out to be Blagaya Vesti, Farmer, Screen, Otlichnik, Bratchud (K). The varieties Kovrovoe 1, Kovrovoe 3, Krasa Sverdlovska had the highest reductive capacity. The highest average fruit weight over the years of the study had the Kovrovoe 1 variety (132.0 g), the high-yielding varieties included Kovrovoe 1, Kovrovoe 3, VEM YArkij, Krasa Sverdlovska (from 12.4 to 13.0 t/ha).

Hypo and hyperbaric pressure effect on the fracture resistance of three types of dental crowns: PFM, LD, and Y-TZP

ObjectivesLoss of dental restorative materials can lead to severe problems in some occupations, especially diving and piloting. This study aimed to compare the fracture resistance of three types of materials (PFM, LD, and Y-TZP) under hyper and hypobaric conditions to simulate diving and flight and control conditions for introducing a suitable restorative material for individuals under these conditions. MethodsThree dental crowns related to the upper premolar were prepared. Seven pieces of these materials were subjected to hyperbaric pressure and seven to hypobaric pressure. Cases related to the flight conditions were investigated after exposure to low-pressure conditions equivalent to 0.5 atm, while cases pertaining to diving conditions were exposed to a pressure of 2 atm. After using the pressure cycles, the crowns were subjected to fracture tests with occlusal force. Further, a finite element study on maxillary premolar behavior was performed under the three working conditions. ResultsA significant difference between each crown in flight condition was noted. In the diving condition, no significant difference between LD and Y-TZP was observed, while in the control condition, no significant difference between PFM and Y-TZP was noted. Finite element results showed that PFM exhibited higher principal stresses in all working conditions. ConclusionsThis study shows that PFM has better resistance to failure in diving and flight conditions among other groups, while Y-TZP offers better resistance in control conditions. Further studies on other working conditions and different experimental conditions on dental crowns are needed.

Comparative Microleakage Evaluation through the Interfaces between the Tooth and Cement after Stainless Steel Crown Cementation in Primary Molars: An In Vitro Study.

The longevity of stainless steel crowns is related to perfect adaptation and long-term union between restoration and teeth. In this respect, evaluation of marginal leakage of luting cement is essential. To compare and evaluate the ability of new adhesive cement to prevent microleakage under stainless steel crowns on primary teeth. Forty-five specimens were embedded, standardized preparations were made onto selected extracted primary molars, and stainless steel crowns were adapted. Samples were assigned randomly to cement groups: Glass ionomer (GI), resin-modified glass-ionomer (RMGI), and Adhesive resin (AR) cement, followed by storage in water, artificially aging, staining, sectioning, and the linear dye penetration and proportion of microleakage evaluation. AR showed the lowest microleakage, followed in increasing order by RMGIC and GIC showed the greatest microleakage (p-value < 0.0001). There are many kinds of luting agents that vary considerably from the viewpoint of solubility, strength, and ability to adhere to the tooth structure. Lack of adhesion of the luting cement to the tooth structure is one of the reasons for microleakage related to different types of crowns. Cement breakdown may result in the entrance of fluids and microorganisms along with the tooth restoration interface. In this study, attempts were made to simulate standard clinical procedures, although this is not a substitute for the complex oral environment, the results provide useful information to choosing the best cement materials. Adhesive resin cement can be recommended for cementation of Stainless Steel Crowns because of added advantages over others. Gundewar MS, Saha S, Arora D, et al. Comparative Microleakage Evaluation through the Interfaces between the Tooth and Cement after Stainless Steel Crown Cementation in Primary Molars: An In Vitro Study. Int J Clin Pediatr Dent 2022;15(2):159-163.

Survivability and fracture resistance of monolithic and multi-yttria-layered zirconia crowns as a function of yttria content: A mastication simulation study.

To compare four different types of monolithic zirconia crowns in terms of survival rate and fracture resistance after thermocycling and/or thermo-mechanical loading in a chewing simulator. Partially stabilized zirconia (PSZ) crowns with fiber-reinforced resin die assemblies (n=80) were fabricated using: multi-yttria-layered 5Y-PSZ/3Y-PSZ, multi-yttria-layered 5Y-PSZ/4Y-PSZ, monolithic 4Y-PSZ, and monolithic 3Y-PSZ as control (n=20). Half of the samples in each group were subjected to thermo-mechanical loading under 110N, 1.4Hz, 1.2 million cycles with simultaneous thermocycling (10,000cycles, 5-55°C). The other half were subjected to thermocycling alone. The samples were loaded to failure to measure their fracture resistance. The data were analyzed using by two-way ANOVA and Tukey's HSD post-hoc test (α=0.05). All specimens survived the aging protocols. The yttria content significantly affected the fracture resistance of the crowns (p<0.0001). The mean fracture resistance, from highest to lowest: 3Y-PSZ, 4Y-PSZ, followed by the two multi-yttria-layered systems. The mean difference between the two multi-yttria-layered systems were not statistically significant (p=0.98). The mechanical loading protocol did not affect the mean fracture resistance within each group (p=0.18). Within each group, there was no difference in fracture resistance after thermocycling alone and thermo-mechanical loading. However, increasing the yttria concentration at the occlusal third of the crown decreased its fracture resistance. The term "monolithic zirconia" alone without specifying the actual yttria content is misleading. This term represents different materials with different mechanical properties. The yttria content has an inverse relationship with the fracture resistance of zirconia crowns. The fracture resistance of multi-layer zirconia crowns is determined by the amount of the weaker zirconia phase at the occlusal part of the restoration rather than enforced by the stronger zirconia at the cervical part of the crown.

Review on Preformed Crowns in Pediatric Dentistry—The Composition and Application

The purpose of this review is to compare and contrast the various types of preformed crowns that can be used to restore the primary teeth in children. Historically, preformed crowns have been widely available for the past 50 years. The clinical performance of preformed crowns has evolved to meet higher functional, mechanical, and aesthetic demands. Preformed crowns are available in a range of prefabricated sizes and shapes. Preformed crowns can vary depending on their properties, compounds, methods of preparation, and biocompatibility.

COMPARATIVE ASSESSMENT OF NOVEL 3D PRINTED RESIN CROWNS VERSUS DIRECT CELLULOID CROWNS IN RESTORING PULP TREATED PRIMARY MOLARS.

The primary objective of this randomized controlled trial is to compare the clinical impact of using crowns manufactured by 3D printing and direct composite celluloid crowns as a final restoration for primary molars after pulpotomy procedures. Fifty primary molars selected from the children needing treatment at the Pediatric Dentistry Clinic at Damascus University Faculty of Dentistry were randomized by using SPSS and divided into 2 groups based on fabricating methods: Group A: 3D-printed crowns with the utilization of biocompatible light-curing composite, and Group B: Crowns were made directly using composite carried out by prefabricated celluloid crown. The evaluation team assessed the crowns in each group using the United States Public Health Service (USPHS) criteria for retention, marginal integrity, and gingival health at baseline, followed by 3 follow-up sessions at 3, 6, and 12 months. Chi-Square statistical testing was accomplished using SPSS software to compare crown failure among the experimental group. At the 12-month follow-up, no statistically significant differences were noted between groups (P = .157). For gingival health assessment, the Mann-Whitney test was used. No statistically significant differences were recorded between the 2 groups in the third follow-up month (P = .058); However, a significant difference was noted in the 6th and 12th follow-up months (P = .023, P = .000). For marginal integrity comparison, Mann-Whitney statistical Test was used for the third, sixth, and twelfth-month follow-up sessions. A significant difference was noted in all follow-up periods (3-6-12 months) between the direct and indirect crowns (P = .025, P = .025, P = .002, respectively). The 2 types of experimental crowns (direct composite celluloid crowns and the resin crowns manufactured via 3D printer) were suitable esthetic alternatives for restoring pulp-treated primary molars with a notably higher rate of retention with direct composite crowns. 3D-printed resin crowns, however, portrayed superior gingival health in addition to greater marginal integrity.

Adaptation and uniformity of monolithic zirconia crowns fabricated by additive 3-dimensional gel deposition

Statement of problemA novel monolithic zirconia restoration fabricated by additive 3-dimensional (3D) gel deposition, named as self-glazed zirconia (SGZ), has recently been developed. SGZ crowns exhibit reliable mechanical properties and esthetic appearance, but their adaptation and uniformity are unclear. PurposeThe purpose of this in vitro study was to compare the adaptation and uniformity of monolithic zirconia crowns fabricated by additive 3D gel deposition with that of milled zirconia and lithium disilicate crowns. Material and methodsTen identical resin abutments were made based on the scanning data of an extracted and prepared human mandibular first molar. Three types of monolithic crowns were then fabricated by using 2 different processes: 3D gel deposition zirconia (SGZ), milled zirconia (ZZ), and milled lithium disilicate (EMX) (n=10) through a completely digital workflow. The nondestructive direct-view technique and replica technique were used to measure the marginal and internal discrepancy values individually. The uniformity index was calculated to describe the uniformity of the internal space. The results were analyzed by using 1-way ANOVA and Kruskal-Wallis statistical tests (α=.05). ResultsThe marginal discrepancy of EMX exhibited the highest values among the 3 groups (P=.001). The 2 types of zirconia crowns had comparable marginal discrepancy values (P>.05). The internal discrepancy values of SGZ were significantly lower than those of EMX at the occlusal region and of ZZ at all measured locations (P<.05). All 3 types of monolithic crowns showed comparable good uniformity (P=.056). ConclusionsThe marginal and internal adaptations of novel monolithic zirconia crowns were within clinical requirements. Compared with the zirconia and lithium disilicate crowns fabricated by subtractive milling, monolithic zirconia crowns fabricated by additive 3D gel deposition had comparable uniformity and better internal adaptation.

Assessing the diversity of hidden dental morphology in Hyperodapedontinae rhynchosaurs (Archosauromorpha, Rhynchosauria)

ABSTRACT The Hyperodapedontinae taxa are mainly diagnosed by characters from the maxillomandibular apparatus. Here we report two Hyperodapedon specimens from Brazil with apically serrated teeth crowns, which led to the identification of one new non-conical maxillary tooth morphotype, Sh, and the first records of serrated teeth in Rhynchosauria. The known types of pyramidal crowns are here expanded to three morphotypes (P1, P2, P3). Flutes, only reported for Hyperodapedon huxleyi (India), were identified in Hyperodapedon sp. and Teyumbaita sulcognathus (Brazil). Using qualitative and morphometric geometric approaches, we investigated whether the maxillary crown morphology is taxonomically informative or reflects ontogeny. The qualitative analysis demonstrated that crown morphology is not taxonomically constrained. The geometric morphometric analysis revealed that the maxillary crown shape varies according to the relative size and form of the tooth plate, parameters related to ontogeny. Flutes and serrations are recorded in Carnian hyperodapedontines from Brazil and India, a restrained paleolatitudinal range of Gondwana. The lack of information concerning dental ornamentations in other hyperodapedontines from the same latitudinal belt (e.g. Argentina) should be due to the scarcity of more detailed studies focused on crown morphology. Our results open the possibility for further studies focusing on hidden details of Rhynchosauria dental morphology.

The Comparison of Fracture Resistance between Low Translucent and Ultra-High Translucent Monolithic Zirconia Crown

Abstract Objective From the beginning of its discovery, the monolithic zirconia crown was highlighted for its remarkable strength; therefore, only available in opaque color. During the past decade, the translucent monolithic zirconia crown was manufactured to meet the aesthetic and restoration demand but was thought to be the cause of decreasing its strength. This study aimed to compare the fracture resistance between two types of translucent monolithic zirconia crowns, that is, low translucent monolithic zirconia (LT) and ultra-high translucent monolithic zirconia (UHT). Material and Methods The premolar crown model was prepared using a computer-aided design/computer-aided manufacturing system, producing 1 mm of thickness. Ten crown samples were divided into LT and UHT. Then, each sample was measured for its fracture resistance using Universal Testing Machine until a fracture occurred. The differences in fracture resistance were analyzed using an independent t-test with p &lt; 0.05. Result The LT showed a higher fracture resistance than UHT (p &lt; 0.05). Conclusion The LT monolithic zirconia crown has strength and can be used for posterior crown restoration.

Lithium disilicate and PEEK implant-retained single crowns - a randomized, prospective clinical study

Introduction/Objective. Comparing two materials under the same conditions is the best way to define differences between them. Ceramic-reinforced polyether-etherketone (PEEK) is a polymer that has many possible uses in dentistry as already well-known lithium disilicate ceramics. The aim of this study was to compare peri-implant soft tissue healing and evaluate patient satisfaction with esthetics in different observation periods, as well as the success and survival rate of both types of crowns. Methods. The study was conducted as a clinical, prospective, randomized split-mouth study on 17 patients with bilaterally missing upper teeth of the same type, replaced with dental implants. Study outcomes have been analyzed with subjective (visual analogue scale ? VAS scale) and objective parameters (modified bleeding index ? MBI, modified plaque index ? MPI and peri-implant probing depth ? PPD) baseline, six and twelve months after fixing crowns onto the implants. Results. Comparison of the results between PEEK and lithium disilicate crowns showed no statistical differences in terms of MPI, MBI, and PPD in the observed periods. Analyzing MPI during observation periods in the PEEK group of crowns, statistical significance was registered between baseline values and after six months. Also, statistical significance was noticed in terms of PPD during the observation time both in the study and control group of crowns. Results for VAS for the esthetics showed no statistically significant difference between the groups, while VAS for restoration satisfaction showed a statistically significant difference. Conclusion. This study showed that scores of the applied subjective and objective parameters can be a reliable tool to rate the clinical outcome of implant-retained single crowns over time.

Point of View about Corona Pandemic: An Approach towards Health Perspectives

It's been about a half year since there's been a word that's spread throughout the globe faster than wildfires, and it's not only the most talked-about topic, but also the most feared; yes, it's "crown." Hearing the word itself strikes dread in all individuals around the world. So what is this crown or COVID-19 truly? Coronavirus is an irresistible sickness brought about by the newfound strain of Covid, the SARS-CoV-2. Covid was accounted for from china in late December and early January from the province of Wuhan in China. Covid was found in the absolute most punctual known cases connected to Wuhan’s discount wet food market. The word crown got its fear of India on 30th January 2020 in Kerala. The patient was an understudy, concentrating in the city of source, and had returned to the nation because of the pandemic. Since January, this infection has been spreading and is accounted for everywhere in the world. Crown has become a dread that has not saved anybody from its effect. The everyday existence surprisingly around the globe has been affected since. This infection is a freak type of crown that is novel Covid covid19. Covid pandemic has instructed us that there are different exercises to be scholarly in the current pandemic circumstance. Crown has carried our thoughtfulness regarding how much progress should be around us. An alternate view and viewpoint have become known about our nation's current medical services plan. The establishment of medical care framework with medical services suppliers has come to stake. Ample opportunity has already passed that we investigate the current wellbeing administrations and strengthen them at the center level. Natural selection is one of the oldest adages in clinical research, and it has stayed consistent in situations like this. In the current circumstances, endurance has become an essential component.

Clinical Evaluation of Reduced-Thickness Monolithic Lithium-Disilicate Crowns: One-Year Follow-Up Results

Purpose: The purpose of this in vivo study was to investigate whether the less invasive approach (reduced thickness of the restoration) will result in a comparable risk of failure and similar aesthetic results, compared to conventional layered full porcelain crowns, and can, therefore, be used as a good alternative. Material and Methods: The tested ceramic was lithium-disilicate ceramic (IPS e.max). Forty-four patients with endodontically treated premolars or molars were randomized into two groups and provided with single crowns. One group received conventional all-ceramic crowns made from a lithium-disilicate core and hand-veneered aesthetic ceramic, while another group received full-contoured lithium-disilicate ceramic crowns with reduced wall thickness than manufactures recommendations. The teeth for conventional crowns were prepared with 1 mm rounded shoulder and 2 mm occlusal reduction, while teeth for monolithic crowns were prepared with 0.6 mm wide rounded shoulder and 1 mm occlusal reduction. All crowns were prepared by the same clinician and manufactured in the same laboratory by the same technician. The survival and aesthetics of the crowns were assessed by the independent clinician. Apart from this, patients’ aesthetic satisfaction was evaluated. The assessment was double blind as both the examiner and the patients did not know which type of crown was provided. The observation period was 36 months. Survival of the crowns was assessed using the modified United States Public Health Service (USPHS) criteria and aesthetics and participants’ aesthetic satisfaction with the crowns was evaluated using a visual analogue scale. Results: The one-year survival rate for layered crowns was 100% and for monolithic crowns 95.5%. The median patients’ aesthetic satisfaction with both crowns was 100%. Conclusions: The results indicate similar one-year survival rate of reduced-thickness monolithic lithium-disilicate crowns and conventional veneered crowns. Differences with patients’ satisfaction with the aesthetics of both crowns were not statistically significant and it can be said that the patients’ aesthetic satisfaction was the same for both crowns.

Growth features of apple varieties and forms with natural and compact crown types

This research explores the compactness of apple varieties and forms with different types of crown. Orchards on semi-vigorous rootstocks with density and high density planting systems are cost-effective in modern horticulture. For making such gardens, it is necessary to have trees with special compact crown shape. They ensure the high-quality fruits production, meeting the requirements of world standards. To date the most perspective apple varieties and forms for domestic intensive gardening from the rich gene pool of the Selection and Genetic Center of Federal State Scientific Institution «I. V. Michurin Federal Scientific Center» are identified. Varieties of folk domestic and foreign breeding took part in the creation of new genotypes. Apple varieties and promising forms (more than 160 genotypes), including from near and far abroad selection, were used as materials for crown features studying. We conducted our study by the following indicators: tree height, crown volume, “degree of compactness” and the shoot-forming ability. We found that the genotypes Sholokhovskoye, Zvezda Artemyeva, 25-7(11), 40-9(8), 36-8(21), 40-9(6), 8-7(72), 40-9(7), 36-8(17), 62-5(140) have optimal crown parameters. We recommend their use for industrial horticulture and further breeding to create restrained growth, low-volume crown, and a high degree of compactness varieties.

Digital assessment of marginal accuracy in ceramic crowns fabricated with different marginal finish line configurations.

To digitally evaluate the marginal adaptation of different types of all-ceramic crowns on two different marginal configurations such as Shoulder and Chamfer of the prepared teeth. The marginal fit of the crown specimens on the model of the prepared teeth were assessed using the dual scan replica technique. Two plastic teeth were prepared; one having a Shoulder finishing line (A), while the other with a Chamfer finish line (B). Three types of different all-ceramic crowns, layered zirconia, monolithic zirconia, and pressed lithium disilicate, were fabricated for each prepared tooth (A) and (B). Measurements for assessing the marginal discrepancy were done on four designated points on the mesial, distal, buccal, and palatal surface of the superimposed image. The average marginal gap was the largest in the layered zirconia group, followed by monolithic zirconia, while pressed lithium disilicate crowns showed the least marginal gaps. Crowns with Chamfer finish lines were better fitting (less marginal gap) than the shoulder finish lines across all the groups. Chamfer finish lines produced better fitting restorations, and heat-pressed lithium disilicate crowns showed better adaptation at the margins than both layered zirconia and monolithic zirconia.

Parental satisfaction regarding two types of commercial crowns for restoring pulpotomized primary molars

Background: Restoration of pulpotomized primary molars with esthetic restorations becomes a priority in pediatric dentistry. Aim: The purpose of this study was to assess parental satisfaction towards prefabricated zirconia crowns. Methods A randomized controlled trial included 60 children; pulpotomized mandibular right second primary molars restored with prefabricated zirconia crowns and mandibular left second primary molar restored with stainless steel crowns. On a 5 point-Likert-scale, a questionnaire was used to assess parental satisfaction was evaluated by parents at 12 months. Results Parental satisfaction with the treatment was excellent; however, satisfaction with regard to color received the highest significant rating (100%) for zirconia crowns compared to stainless steel crowns. Parents rated their overall satisfaction in the size, shape and durability after 12 months from baseline. The ratings were (50.8%) for size, shape and durability for both zirconia and stainless steel crowns. Conclusion Zirconia crowns had more esthetic parental satisfaction than stainless steel crowns. Keywords: Pediatric; Esthetic; Crown.

Effect of CAD/CAM Bur Deterioration on the Surface Roughness of Ceramic Crowns.

To evaluate the effect of repetitive milling on the surface roughness of ceramic crowns. Twenty feldspathic ceramic crowns (VITABLOCS Mark II; Vita Zahnfabrik, Bad Säckingen, Germany) milled with hard milling protocol, and 20 zirconia crowns (5Y-TZP, inCoris TZI; Dentsply Sirona, York, PA) milled with soft milling protocol, using a 5-axis milling machine (inLab MC X5; Dentsply Sirona) were investigated. Atomic force microscopy (SPM SmartSPM™-1000) was used for surface roughness measurements (Ra, RMS). Pearson correlation between bur deterioration percentage as provided by the software of the milling machine and surface roughness was performed with an (r) range between 1 and -1. Trend analysis between the 2-half and among the 4-quarter bur lifetime was performed with linear contrast analysis and partial eta squared (η) for estimate of effect size. Analysis of mean variance between the zirconia and feldspathic ceramic groups was performed with a t-test, with α = 0.05. Correlation analysis showed small correlation for Ra, RMS (r = -0.02, -0.16 for the feldspathic ceramic crowns and r = 0.044, 0.034 for the zirconia crowns), and no significant differences for the 2-half and 4-quarter groups (p > 0.05) for both crown types. Estimate of effect size was rated as medium for the 2-half groups (Ra = 0.420, RMS = 0.395) and large for the 4-quarter groups (RA = 0.22, F = 1.48, RMS = 0.19, F = 1.26) for the feldspathic ceramic crowns, and small effect size for the 2-half groups (Ra = 0.18, RMS = 0.20) and the 4-quarter groups (Ra = 0.035, RMS = 0.037) for the zirconia crowns. There was no significant difference (p = 0.178, F = 0.016. p = 0.088, F = 0.002) between the feldspathic ceramic and zirconia crowns with medium and large effect size (0.45, 0.57) for RA and RMS. Milling zirconia and feldspathic ceramic crowns had small correlation between bur deterioration and surface roughness when the burs were used within their recommended lifetime. However, hard milled feldspathic ceramic crowns had higher surface roughness than the soft milled zirconia crowns. Bur deterioration had a larger effect on the surface roughness of the feldspathic ceramic crowns than the zirconia crowns.

ASSESSMENT OF ANGULAR DEVIATIONS OF THE VERTICAL SURFACES OF TEETH STUMPS OBTAINED DURING ODONTOPREPARATION FOR FIXED ORTHOPEDIC STRUCTURES (METAL-CERAMIC AND SOLID CROWNS)

Relevance. Odontoreparation is fundamental to ensure the functional efficiency, high aesthetics and durability of fixed prostheses. At present, with fixed prosthetics of defects in hard tissues of teeth and dentition, various types of artificial crowns are widely used [1][2].Purpose of the study: to determine the angular deviations of the vertical surfaces of molars, prepared by students of the 3rd year. Based on the data obtained, calculate the average value for the group and identify which surfaces of the stump are most prone to errors during odontopreparation.Materials and methods. Frasaco® phantom teeth (mandibular molars) were used as research materials. Preparation for metal-ceramic crowns was carried out according to the traditional method by thirteen third-year students of the Samara State Medical University of the Ministry of Health of Russia. In this work, 6° was taken as the optimal angle of convergence of the vertical walls (3° on each of the two opposite surfaces). During the preparation, a fissure bur d = 1.6 mm was used.Conclusion. The average time spent on preparation is quite long, which indicates an insufficient level of manual skills. The revealed phenomena of wall divergence also indicate that the preparation skills are insufficient. In addition, divergence was found mainly on the distal surface, which is explained by more difficult access and limited visibility of the prepared surface.

ASSESSMENT OF ANGULAR DEVIATIONS OF THE VERTICAL SURFACES OF TEETH STUMPS OBTAINED DURING ODONTOPREPARATION FOR FIXED ORTHOPEDIC STRUCTURES (METAL-CERAMIC AND SOLID CROWNS)

Relevance . Odontoreparation is fundamental to ensure the functional efficiency, high aesthetics and durability of fixed prostheses. At present, with fixed prosthetics of defects in hard tissues of teeth and dentition, various types of artificial crowns are widely used [1, 2]. Purpose of the study : to determine the angular deviations of the vertical surfaces of molars, prepared by students of the 3rd year. Based on the data obtained, calculate the average value for the group and identify which surfaces of the stump are most prone to errors during odontopreparation. Materials and methods. Frasaco ® phantom teeth (mandibular molars) were used as research materials. Preparation for metal-ceramic crowns was carried out according to the traditional method by thirteen third-year students of the Samara State Medical University of the Ministry of Health of Russia. In this work, 6° was taken as the optimal angle of convergence of the vertical walls (3° on each of the two opposite surfaces). During the preparation, a fissure bur d = 1.6 mm was used. Conclusion. The average time spent on preparation is quite long, which indicates an insufficient level of manual skills. The revealed phenomena of wall divergence also indicate that the preparation skills are insufficient. In addition, divergence was found mainly on the distal surface, which is explained by more difficult access and limited visibility of the prepared surface.